Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 1 of 43 Thermo-tectonic development of the Wandel Sea Basin, North Greenland Peter Japsen*1 , Paul F. Green2 , James A. Chalmers1 1Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark, 2Geotrack International, Brunswick West, Victoria, Australia Abstract The Carboniferous–Palaeogene Wandel Sea Basin of eastern North Greenland (north of 80°N, east of 40°W) is an important piece in the puzzle of Arctic geol- ogy. It is particularly important for understanding how the Paleocene–Eocene convergence between Greenland, the Canadian Arctic and Svalbard relates to the compressional tectonics in the High Arctic, collectively known as the Eurekan Orogeny. In this study, we present apatite fission-track analysis (AFTA) data and review published vitrinite reflectance data combined with observa- tions from the stratigraphic record to place firmer constraints on the timing of key tectonic events. This research study reveals a long history of episodic burial and exhumation since the collapse of the Palaeozoic fold belts in Greenland. Our results define pre-Cenozoic exhumation episodes in early Permian, Late Triassic, Late Jurassic and mid-Cretaceous times, each involving the removal of kilometre-scale sedimentary covers. Mid-Paleocene exhumation defines the timing of compression along the major fault zones during the first stage of the Eurekan Orogeny, after the onset of sea-floor spreading west of Greenland. Regional exhumation that began at the end of the Eocene led to the removal of most of a kilometre-thick cover that had accumulated during Eocene sub- sidence and involved a major reverse movement along the Harder Fjord Fault Zone, northern Peary Land. These events took place after the end of sea-floor spreading west of Greenland, and thus, represent post-Eurekan tectonics. Mid–late Miocene exhumation is most likely a consequence of uplift and inci- sion across most of the Wandel Sea Basin study area. The preserved sedimen- tary sequences of the Wandel Sea Basin represent remnants of thicker strata that likely extended substantially beyond the present-day outline of the basin. We find that the present-day outline of the basin with scattered sedimentary outliers is primarily the result of fault inversion during Eurekan compression followed by deposition and removal of a kilometre-thick overburden. 1 Introduction The Carboniferous–Palaeogene Wandel Sea Basin in eastern North Green- land is an important piece in the larger puzzle of Arctic geology (Figs. 1, 2). The basin records sedimentation along the western margin of Svalbard and the Barents Sea, on the north-western flank of the Danmarkshavn Basin (off- shore North-East Greenland) and south of the Cenozoic sea-floor spreading in the Arctic Ocean. Several aspects of the development of the Wandel Sea Basin remain controversial, in particular, the timing of a major, compres- sional tectonic event that affected the basin in post-Cretaceous times is much debated. Did it happen during a comparatively brief period of time around the *Correspondence: pj@geus.dk Received: 15 May 2019 Accepted: 25 June 2020 Published: 26 April 2021 Keywords: Eurekan Orogeny, uplift, exhumation, Svalbard, Sverdrup Basin Abbreviations: AFTA: apatite fission-track analysis a.s.l.: above sea level CAI: colour alteration index CTB: Central Tertiary Basin EGFZ: East Greenland Fracture Zone HALIP: High Arctic Large Igneous Province HFFZ: Harder Fjord Fault Zone KCTZ: Kap Cannon Thrust Zone TLFZ: Trolle Land Fault Zone VR: vitrinite reflectance GEUS Bulletin is an open access, peer- reviewed journal published by the Geological Survey of Denmark and Greenland (GEUS). This article is distributed under a CC-BY 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. Author(s) retain copyright. Edited by: Catherine Jex (GEUS, Denmark) Reviewed by: Andy Carter (Birkbeck, University of London, UK), Eckart Håkansson (The University of Western Australia, Australia) Funding: See page 41 Competing interests: 41 Additional files: See page 41 RESEARCH ARTICLE https://doi.org/10.34194/geusb.v45.5298 https://orcid.org/0000-0003-1689-7820 https://orcid.org/0000-0001-5478-534X https://orcid.org/0000-0001-6651-2277 mailto:pj@geus.dk Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 2 of 43 www.geusbul let in.org 80°N 70°N 60°N 30°W 30°E 60 °W 120°W 90°W 0° 0 250 500 km 62–55 Ma Sea-floor spreading 55–35 Ma 35 Ma to Present Spreading centres Transform fault Arctic Ocean LR WSB Atlantic Ocean Iceland Svalbard Greenland Labrador Sea Baffin Bay Canadian Arctic Archipelago Fig. 1 Cenozoic sea-floor spreading in the northern North Atlantic area. Sea-floor spreading between North America and Greenland (62–55 Ma) caused the first stage of the Eurekan Orogeny. During this time, Greenland moved together with Europe. Spreading between Europe and Greenland (55–35 Ma) resulted in the sec- ond stage of the Eurekan Orogeny. During this time, North America, Greenland and Europe moved as separate plates. Sea- floor spreading ceased west of Green- land (at c. 35 Ma) after which Greenland moved together with North America and the Eurekan Orogeny ended. The Dan- markshavn Basin is located off North- East Greenland between 76 and 82°N. LR: Lomonosov Ridge. WSB: Wandel Sea Basin. Modified from Brozena et al. (2003), Oakey & Chalmers (2012) and Gaina et al. (2017). Cretaceous–Palaeogene boundary (Håkansson & Peder- sen 1982, 2001, 2015), during the Eocene (von Gosen & Piepjohn 2003), during the late Paleocene–early Eocene (Døssing et al. 2010; Svennevig et al. 2016) or during the Late Cretaceous–Paleocene (Guarnieri 2015)? Insights into the development of the Wandel Sea Basin are thus important for providing a better understanding of the relationship between (1) the mid-Paleocene to Eocene movement of Greenland rel- ative to both North America (Oakey & Chalmers 2012) and Eurasia (Gaina et al. 2017) and (2) the Palaeogene basin formation and compressional tectonics in the Wandel Sea Basin (the Kronprins Christian Land Orog- eny; Håkansson & Pedersen 2001, 2015) and in the neighbouring Carboniferous–Palaeogene basins in Canada (the Eurekan Orogeny; Okulitch & Trettin 1991; Embry & Beauchamp 2019) and on Svalbard (the West Spitsbergen Fold Belt; Steel et al. 1985; Dallmann et al. 1993; Dallmann 2015; Jones et al. 2017). It is widely accepted that these tectonic events, which we refer to collectively as the Eurekan Orogeny, record the Palaeogene convergence between Greenland, the Canadian Arctic and Svalbard (De Paor et al. 1989; Ricketts 1994; Harrison 2008; Oakey & Chalmers 2012; Dallmann 2015; Gion et al. 2017; Jones et al. 2017; Embry & Beauchamp 2019). Others restrict the term Eurekan Orogeny to the time span in the Eocene during which Greenland was part of a separate plate that was able to move independently with respect to both North Amer- ica and Europe (e.g. Piepjohn et al. 2016; Tessensohn & Piepjohn 2000). This definition, however, fails to include the deformations caused by the movement of Green- land during the late Paleocene. The presence of many isolated occurrences of sedi- mentary strata has been suggested to represent at least 20 late Permian to Mesozoic pull-apart basins formed in response to episodes of combined transtension and transpression along the plate boundary between North Greenland and Svalbard (Håkansson & Pedersen 2015). However, the possibility that these sub-basins may have been connected by substantial sedimentary covers that have since been removed by erosion has attracted little attention with some exceptions (Stemmerik et al. 1998; Pedersen et al. 2018). Another unresolved issue is an enigmatic event that affected the north coast of Kro- nprins Christian Land, in which Upper Cretaceous rocks reached extremely high vitrinite reflectance (VR) levels of 7–10% (Håkansson et al. 1994). https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 3 of 43 www.geusbul let in.org In this study, we present new apatite fission-track analysis (AFTA®) data from northern and eastern Green- land, which are focussed on the Wandel Sea Basin. These data shed light on the thermal and tectonic history of the region, both prior to and after the compressional tectonics that affected the Wandel Sea Basin in Palaeogene times. We combine thermal history interpretations from AFTA data in 52 outcrop samples (of which 46 are from north of 79°N) with published VR data (Håkansson et al. 1994; Paech & Estrada 2018; Pedersen et al. 2018) to provide insights into the tectonic development of the region. AFTA data define the timing and magnitude of key palaeother- mal episodes – times at which rocks cooled from higher temperatures compared with present-day values – while VR data provide independent determination of maxi- mum post-depositional palaeotemperatures. We relate the thermal history solutions from AFTA and VR data to former depths of burial and corresponding amounts of exhumation and produce a synthesis of late Palaeozoic to Cenozoic thermo-tectonic events in the region. We inte- grate these results with observations from the geologi- cal record (Håkansson & Pedersen 2015; Svennevig et al. 2016, 2017, 2018; Alsen et al. 2018; Hovikoski et al. 2018; Paech & Estrada 2018; Pedersen et al. 2018; Piasecki et al. 2018; Bjerager et al. 2019). Finally, we compare the results of this study with a companion study of North-East Greenland (Japsen et al. in press) and set the results in a regional context. 2 Geological setting The Wandel Sea Basin occupies a broad, partially sub- merged or ice-covered depression centred around the Wandel Sea (north of 80°N, east of 40°W; Figs. 3 and 4; Dawes & Soper 1973; Dawes 1976; Håkansson & Peder- sen 1982, 2001, 2015; Håkansson & Stemmerik 1989; Stemmerik et al. 1998). The basin is located between the Caledonian Fold Belt along the east coast of Green- land and the Ellesmerian Fold Belt along the north coast (Fig. 1; Higgins et al. 2000). The main deformations took place during the Silurian and the early Carboniferous (Henriksen et al. 2009). The Wandel Sea Basin is the northernmost of a series of fault-bounded late Palaeo- zoic – early Palaeogene basins exposed along the east- ern and northern margin of Greenland (Stemmerik et al. 1998). The basin contains sediments with a cumulative thickness of >15 km, resting unconformably on Precam- brian to Silurian rocks (Fig. 5; Surlyk 1991; Håkansson & Pedersen 2015). Upper Carboniferous – Triassic sedi- ments accumulated in a system of grabens and half-gra- bens referred to as the North Greenland – Svalbard Rift Basin (Håkansson & Stemmerik 1989). The Mesozoic basin evolution has been difficult to assess due to problems associated with correlating scattered outcrops and tectonic overprinting. However, recent studies have made such correlations possible. Hovikoski et al. (2018) provided a Jurassic–Cretaceous Fig. 2 Outline of the High Arctic adjacent to North Greenland. Extent of Kronprins Christian Land Orogeny according to Håkansson & Pedersen (2001) and this study. LR: Lomonosov Ridge. Detail of Fig. 1 with additions from von Gosen & Piepjohn (2003), Oakey & Chalmers (2012) and Piepjohn et al. (2016). Ellesmere Island Greenland Greenland Sea Peary Land Kronprins Christian Land Svalbard Barents Sea Strike-slip fault Thrust zone West Spitsbergen Fold Belt Kronprins Christian Land Orogeny 500 km0 Eurekan Orogeny Fault zone TLFZHFFZ KCTZ 80°N 30°W 30°E 60 °W 90°W 0° Arctic Ocean Fram Strait Fig. 3 LR https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 4 of 43 www.geusbul let in.org lithostratigraphy for Kilen (Kronprins Christian Land), and Bjerager er al. (2019) presented a Triassic (Induan– Norian) lithostratigraphy for the Wandel Sea Basin. Håkansson & Stemmerik (1989) suggested that the Upper Jurassic to Cretaceous sediments accumulated in increasingly smaller sub-basins formed by strike-slip tec- tonics and transtension in what they called the ‘Wandel Hav Strike-Slip Mobile Belt’. According to Håkansson & Pedersen (1982, 2001, 2015), the ‘Wandel Hav Strike- Slip Mobile Belt’ is a north-west to south-east- striking wrench-fault deformation zone that was instrumental in all basin-forming events from the late Permian onwards and includes the following three, major fault systems (Fig. 4): 1. The south-west to north-east-trending Kap Cannon Thrust Zone (KCTZ) is exposed over c. 75 km in north- ernmost Peary Land. Ductile thrusting along the KCTZ took place between 49 and 47 Ma, estimated from the Ar-Ar dating of volcanic rocks of the Campanian to the earliest Paleocene Kap Washington Group (Tegner et al. 2011; Håkansson & Pedersen 2015). 2. The east–west-trending Harder Fjord Fault Zone (HFFZ) is more than 300 km long and traverses Peary K R O N P R I N S C H R I S T I A N L A N D Kap Washington Kap Cannon Kap Rigsdagen Pr. Ingeborg Halvø Pr. Margrethe Ø Pr. Dagmar Ø Pr. Thyra Ø Holm Land Amdrup Land Herluf Trolle Land Depotbugt Hyde Fjord Independence Fjord Frigg FjordHarder Fjord Nakkehoved Station Nord Hovgaard Ø Kilen W a n d e l D a l P E A R Y L A N D W A N D E L S E A 35°W 30°W 25°W 20°W 15°W 40°W 35°W 30°W 25°W 20°W 15°W 10°W 83 °N 82 °N 81 °N 80 °N 83 °N 82 °N 81 °N 80 °N 0 50 100 km 1848 m Sea and lake Ice 300–1500 >1500 Elevation (m a.s.l.) 0–300 Fig. 19 Fig. 3 Elevation and place names of the study area in eastern North Greenland. Pr: Prinsesse. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 5 of 43 www.geusbul let in.org Land within the metasediments of the Palaeozoic Franklinian Basin. Sediments as young as Late Cretaceous (and possibly Palaeogene) occur within the fault zone. 3. The north-west to south-east-trending Trolle Land Fault Z one (TLFZ) is more than 300 km long and 100 km wide and consists of a number of linear faults that cut through sediments as young as Late Cretaceous. According to Piepjohn & von Gosen (2003), the ‘Wan- del Hav Mobile Belt’ (their term) is bordered by the HFFZ in the north and the TLFZ in the south-west. Paech & Estrada (2018) pointed out that the age relations between these fault zones and the Eurekan deformation stages are still unclear. 2.1 Stratigraphic record Throughout this section, we refer the reader to the geo- logical map and stratigraphic column for the Wandel Sea Basin presented in Figs. 4 and 5, respectively. 2.1.1 Palaeozoic strata The fluvial deposits of the lower Carboniferous Sort- ebakker Formation (thickness >1 km) represent the K R O N P R I N S C H R I S T I A N L A N D Ø Hovgaard P E A R Y L A N D 48 10°W 83 °N 82 °N 81 °N 80 °N 15°W20°W25°W30°W35°W 40°W 15°W20°W25°W30°W35°W Nakkehoved Amdrup Land Kilen Holm Land Pr.T.Ø Pr.M.Ø KR DepotbugtFrigg Fjord Herluf Trolle Land Paleocene–Eocene sediments Upper Cretaceous sediments Kap Washington Group Jurassic–Cretaceous sediments Triassic sediments Carboniferous–Permian sediments Cambro–Silurian sediments Precambrian rocks Sea and lake Quaternary Ice Fault Dykes, mostly Upper Cretaceous Sedimentary outlier KCTZ HFFZ TLFZ TLFZ EG FZ 100 km500 Fig. 4 Geology of the Carboniferous–Palaeogene Wandel Sea Basin and surrounding areas. The remnants of the Carboniferous to Palaeogene sediments occur between northern Peary Land and Kronprins Christian Land and thus define the extent of the basin. Kap Washington Group is of Campanian to earliest Palaeogene age (Håkansson & Pedersen 2015). Håkansson & Pedersen (2015) indicated the Trolle Land Fault Zone as one continuous zone from Herluf Trolle Land to Kronprins Christian Land. Here, we indicate one possible correlation between these two areas. Based on Escher & Pulvertaft 1995 with modifications after Croxton et al. 1980; Hovikoski et al. 2018; Piasecki et al. 2018. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.M.Ø: Prinsesse Margrethe Ø. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 6 of 43 www.geusbul let in.org Ma Era Stage/ Age Eocene Oligocene Miocene Pliocene Pleistocene Series/ Epoch Sys- tem/ Period Middle Middle Lower Upper Guadalupian Lopingian Lower Lower Middle Mississippian Upper Mississippian Lower Penns. Middle Penns. Upper Penns. Cisuralian Lower Mississippian Langhian Aquitanian Chattian Rupelian Priabonian Bartonian Lutetian Thanetian Selandian Danian Maastrichtian Campanian Santonian Coniacian Aptian Hauterivian Valanginian Berriasian Tithonian Bathonian Bajocian Aalenian Pliensbachian Sinemurian Hettangian Carnian Ladinian Anisian Olenekian Induan Rhaetian Roadian Wordian Capitanian Wuchiapingian Changhsingian Kungurian Artinskian Asselian Gzhelian Kasimovian Moscovian Bashkirian Serpukhovian Visean Tournaisian Barremian Toarcian Ypresian Burdigalian PA LA EO ZO IC M ES O ZO IC C EN O ZO IC N EO G EN E PA LA EO G EN E C RE TA C EO U S JU RA SS IC TR IA SS IC PE RM IA N C A RB O N IF ER O U S Sakmarian Upper Kimmeridgian Oxfordian Albian Cenomanian Turonian SerravallianSerravallian Tortonian Messinian Upper Norian Paleocene Callovian 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 KW Peary Land K.C. Land Wandel Sea Basin Is ra nd Kap Jungersen PB Sortebakker Mågensfjeld Herlufsholm Strand La de gå rd så en Sølverbæk ? ? Thyra Ø Nakkehoved Channel fills Marine mudstone Marine carbonate Marine sandstone Sedimentary environments Lithological symbols Coal layers Sandstone Siltstone Mudstone/shale Organic rich mudstone/shale Limestone Fluvial, lacustrine Extrusive igneous rocks Volcanics, volcanoclastics Evaporites Conglomerate Foldedal Kim Fjelde Lichenryg Dunken Storekløft Midnatsfjeld G al ad ri el F je ld Legend BF Dd Kl Fig. 5 Wandel Sea Basin stratigraphy and formation names. The representation of the mixed volcanic, volcano-clastic and lacustrine deposits of the Kap Washington Group has been simplified. Some formation names are not shown; the upper Permian Kap Kraka Fm in Peary Land (Håkansson & Pedersen 2015) and the pre-late Bajocian (?) Gletscherport Fm in the Kilen area (Hovikoski et al. 2018). Compiled after Bjerager et al. 2019; Gautier et al. 2011; Håkansson & Pedersen 2015; Hop- per et al. 2014; Hovikoski et al. 2018; Ineson et al. 2020; Piasecki et al. 2018; Stemmerik et al. 1998; Svennevig et al. 2018; Tegner et al. 2011. BF: Birkelund Fjeld. Dd: Dromledome. K.C. Land: Kronprins Christian Land. Kl: Kuglelejet. KW: Kap Washington Group. PB: Parish Bjerg. Penns: Pennsylvanian. oldest unit of the Wandel Sea Basin. It crops out on Holm Land, where it rests directly on the crystalline basement affected by the Caledonian Orogeny (Stemmerik et al. 1998). The upper Carboniferous Kap Jungersen and Foldedal Formations show a marked variation from lat- erally widespread mixed siliciclastic-limestone cycles to dolomitised limestone where they crop out on the east- ern Kronprins Christian Land. The Foldedal Formation is also exposed on Peary Land. Above a lower Permian hiatus, the middle to upper Permian limestones and shales of the Kim Fjelde and the Midnatfjeld Formations are exposed on Herluf Trolle Land and on eastern Kro- nprins Christian Land. The upper Permian, fluvial to lacustrine deposits with syndepositional volcanics of the Kap Kraka For- mation (>1.5 km; not shown) are located in the central part of Hyde Fjord, northern Peary Land, where the deposits are strongly compressed and bounded by the faults of the HFFZ (Håkansson & Pedersen 2015). Unnamed Permian carbonates and deep-marine shales (>2 km) are exposed on Prinsesse Ingeborg Halvø, where they appear as thrust sheets bounded by two of the main faults of the TLFZ (Håkansson & Pedersen 2015). 2.1.2 Mesozoic strata The Wandel Sea Basin contains a nearly complete Trias- sic succession, with an estimated combined thickness https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 7 of 43 www.geusbul let in.org of 700 m (Bjerager et al. 2019). The basal part of the Lower Triassic succession is fluvial, and the remaining Triassic succession is marine, representing a sand-dom- inated basin marginal succession in Peary Land to the west and a marine basinal mudstone succession in Kronprins Christian Land to the east. The succession includes the Lower Triassic Parish Bjerg Formation that crops out in northern Herluf Trolle Land where it rests unconformably on upper Permian sediments. The Tri- assic sediments on Herluf Trolle Land are bounded by two of the main faults of the TLFZ (Håkansson & Pedersen 2015). Alsen et al. (2017) identified mainly the Middle Triassic Isrand Formation in the Kilen area on Kronprins Christian Land. This formation consists of laminated mudstones that accumulated in a slope and basin-floor setting in the eastern and deeper part of the Wandel Sea Basin. These deposits accumulated at the same time as shallow-marine mudstones of the Dunken Formation on Herluf Trolle Land (Alsen et al. 2017). A sedimentary outlier in Amdrup Land is now dated as Early Triassic (Alsen et al. 2017). A minor outcrop of Middle Jurassic (Bajocian) muddy sandstones occurs within a few square kilometres on central Herluf Trolle Land within a dense fault complex in the centre of a broad domal structure (Håkansson & Pedersen 2015). Upper Jurassic – Lower Cretaceous mainly marine sandstones and sandy shales of the Ladegårdsåen For- mation (250 m) crop out on Herluf Trolle Land. The upper Ladegårdsåen Formation is a sandstone-dominated unit deposited in a fluvial through estuarine to fully marine environment, and it rests unconformably on the marine sandstones of the lower Ladegårdsåen Formation (Ine- son et al. 2020). The lower part of the formation rests unconformably on Palaeozoic rocks within several iso- lated, typically fault-bounded occurrences across most of the TLFZ (Håkansson & Pedersen 2015). Piasecki et al. (2018) identified a c. 75 m high sedimentary section exposed at Kap Rigsdagen as part of Ladegårdsåen For- mation, overlain by 5–10 m of the Palaeogene Thyra Ø Formation (see Section 2.1.3). Unnamed Lower Cretaceous (Albian–Aptian), mainly marine mudstones (c. 100 m) bounded by faults, crop out within a few square kilometres on central Herluf Trolle Land (Håkansson & Pedersen 2015). Turonian to Coniacian, fluvial to marginally marine sand-shale series of the Herlufsholm Strand Formation (500 m) crops out on northern Herluf Trolle Land. The sediments are bounded by the northernmost fault of the TLFZ, and they rest unconformably on Palaeozoic sediments (Håkansson & Pedersen 2015). The poorly dated Upper Cretaceous marine sand- stone of the Nakkehoved Formation (>600 m) crops out on the north coast of Kronprins Christian Land, near the northern margin of the TLFZ (Håkansson & Pedersen 2015). The sandstone is gently folded, but intensely cut by a swarm of mono-mineralic quartz veins in the mod- estly deformed sandstone. The vein system is essentially confined to a small semi-nunatak in the ice cap (Håkans- son et al. 1994). Hovikoski et al. (2018) argued that Kilen contains the thickest and stratigraphically most complete Jurassic and Cretaceous sediment succession in North Green- land and presented a new stratigraphic scheme. The Jurassic succession (>500 m) is divided into four for- mations consisting of lagoon and shallow-marine sediments: the poorly dated Gletscherport Formation, the Mågensfjeld and Birkelund Fjeld Formations of Bajocian–Bathonian and Kimmeridgian age, respec- tively, and the Volgian Kuglelejet Formation. The Lower Cretaceous interval (>1500 m) is divided into three for- mations consisting of deep shelf to fluvial and shore- face sediments: the late Ryazanian to Hauterivian Dromledome Formation, the unfossiliferous Lichenryg Formation and the late Aptian to middle Cenomanian Galadriel Fjeld Formation. The Lichenryg Formation and the contemporaneous upper Ladegårdsåen Formation in Peary Land show close stratigraphic and palaeo-environmental parallels: both overlie an Hauterivian – early Barremian, erosional unconformity and show clear transgressive trends from fluvial through estuarine to fully marine (Ineson et al. 2020). Ineson et al. (2020) interpreted the succession to record Hauterivian – early Barremian regional uplift and erosion followed by fluvial sedimentation and subse- quent transgression in the late Barremian – early Aptian. It was suggested that the uplift heralded the onset of the High Arctic Large Igneous Province (HALIP) at about 135 Ma and marked the initiation of the Amerasia Basin (Døssing et al. 2013). The Upper Cretaceous marine succession (650 m) is assigned to the late Cenomanian to Santonian Sølver- bæk Formation dominated by mudstones and sand- stone-mudstones. Intense compressive deformation affected the Mesozoic deposits in Kilen (Håkansson & Pedersen 2001, 2015; Svennevig et al. 2016, 2017). Unnamed, deep-marine, siliciclastic sediments (>400 m) of Santonian age occur in the Frigg Fjord area, bounded by the HFFZ, and their near-vertical orien- tation indicates substantial shortening (Håkansson & Pedersen 2015). The sediments are intruded by doler- itic dikes and sills of similar composition to the basalts of the Kap Washington Group, and these intrusions are affected by deformation along the HFFZ (Paech & Estrada 2018). Further east along the HFFZ, about 500 m of Upper Cretaceous, mainly fluvial sandstone occur in https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 8 of 43 www.geusbul let in.org the Depotbugt area (Håkansson & Pedersen 2015). Their similarity to the Herlufsholm Strand Formation has been used to date these sediments. Volcanics and volcanoclastics interbedded with fluvial and lacustrine deposits of the Campanian to lowermost Palaeogene Kap Washington Group (>5 km) occur on the north coast of Peary Land (Håkansson & Pedersen 2015). Most of the volcanics were emplaced at 71–68 Ma but activity continued into the Paleocene (Tegner et al. 2011). The deposits, which overlie Palaeozoic strata, are bounded on all sides by the thrusts of the KCTZ, interpreted as reactivated normal faults (Håkansson & Pedersen 2015). 2.1.3 Palaeogene strata The fine-grained sandstones, siltstones and coal of the Thyra Ø Formation that crop out on Prinsesse Thyra Ø, Prinsesse Dagmar Ø, Prinsesse Margrethe Ø and Prinsesse Ingeborg Halvø are dated as late Paleocene to possibly earliest Eocene age, with an estimated composite thickness of 50 m (Lyck & Stemmerik 2000). Håkansson et al. (1991) interpreted the depositional environment as dominantly fluviatile; however, Lyck & Stemmerik (2000) documented a marine influenced envi- ronment. In contrast to the folded and thrusted Upper Cretaceous and older deposits within the HFFZ and TLFZ (e.g. in Kilen), the deposits of the Thyra Ø Formation are often reported as undeformed (Håkansson & Pedersen 1982, 2015; Boyd et al. 1994; Lyck & Stemmerik 2000), but some deformational structures are also reported (Pedersen & Håkansson 2001; Piepjohn & von Gosen 2001; Guarnieri 2015). The base of the formation is not known (Lyck & Stemmerik 2000) and on Prinsesse Inge- borg Halvø, the Palaeogene deposits are in contact with late Paleozoic sediments along a wide fault zone (see Section 2.2). Minor outliers of Palaeogene carbonaceous, terres- trial shales occur in the Depotbugt area near the Upper Cretaceous outcrops (Håkansson & Pedersen 2015; Paech & Estrada 2018). Croxton et al. (1980) dated a sparse pollen flora from these deposits as Eocene in age, and Paech & Estrada (2018) noted that they were flat lying. Piasecki et al. (2018) identified the upper 5–10 m of the sedimentary section exposed at Kap Rigsda- gen to be of early to middle Eocene age and to be part of the Thyra Ø Formation, above sediments of Lade- gårdsåen Formation separated by a 65 Myr hiatus. Abundant, reworked Cretaceous dinoflagellate cysts are common in the Thyra Ø Formation (Lyck & Stem- merik 2000; Piasecki et al. 2018). Extensive reworking shows that Cretaceous units were exposed and actively eroded during deposition of the Thyra Ø Formation (Piasecki et al. 2018). 2.2 Structural elements of the Wandel Sea Basin and their relation to the Eurekan Orogeny In this section, we discuss the dominant structural ele- ments of the Wandel Sea Basin and their relation to the Eurekan Orogeny. We use the term Eurekan Orogeny to mean deformation caused by the Palaeogene con- vergence between Greenland, the Canadian Arctic and Svalbard (Figs. 1, 2). We use the development of the sea- floor spreading in the North-East Atlantic to define the following two stages of the Eurekan Orogeny: 1. Sea-floor spreading in the Labrador Sea and Baffin Bay started in the mid-Paleocene (magnetochron C27; c. 62 Ma). The movement of Greenland relative to the Canadian Arctic and Svalbard resulted in the first stage of the Eurekan Orogeny (phase 1 of Gion et al. [2017] and phase 2 of Oakey & Chalmers [2012]). 2. Greenland and Eurasia moved together until the lat- est Paleocene (before C24, c. 55 Ma; Gaina et al. 2017), when the sea-floor spreading started between Greenland and Europe. Subsequently, Greenland moved north relative to the Arctic Islands, which resulted in the second stage of the Eurekan Orogeny (phase 2 of Gion et al. [2017] and phase 3 of Oakey & Chalmers [2012]). Sea-floor spreading between Greenland and North America ceased at the end of the Eocene (C13, c. 35 Ma), when Greenland became attached to North America and the Eurekan Orogeny ended. Phases 1 and 4 of Oakey & Chalmers (2012) consist only of continental extensional movements between Greenland and North America prior to the mid-Paleo- cene and of continued movement of the new Green- land – North America plate relative to Eurasia after the Eocene. None of the movements during these phases are, here, attributed to the Eurekan Orogeny. Initial movement during the Paleocene led to the for- mation of foreland basins, for example, the Central Ter- tiary Basin (CTB) on Svalbard, and to initial transpression on Ellesmere Island, where there was also some com- pression on at least one step-over between strike-slip faults during the first Eurekan stage, defined above. A subsequent change of direction of Greenland relative to North America during the Eocene resulted in compres- sion on Ellesmere Island and transpression on Svalbard during the second Eurekan stage (Steel et al. 1985; Rick- etts 1994; Harrison et al. 1999; Faleide et al. 2008; Oakey & Chalmers 2012; Dallmann 2015; Embry & Beauchamp 2019). The Svalbard margin evolved through strike-slip movements along the plate boundary, the De Geer Line, where Greenland slid past Svalbard (Steel et al. 1985; https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 9 of 43 www.geusbul let in.org Faleide et al. 2008). The Eurekan Orogeny came to an end when the movement ceased between Greenland and North America at the end of the Eocene (Oakey & Chalmers 2012; Piepjohn et al. 2016). Sea-floor spreading between Greenland and Svalbard began in the early Mio- cene (Jokat et al. 2016). Håkansson & Pedersen (2015) observed a 45° off- set in the plate boundary between North Greenland and Svalbard relative to the main trend of rifting and spreading in the North-East Atlantic. As a result, this segment of the plate boundary experienced episodes of combined transtension and transpression, in part con- trolled by the movement of a temporarily independent Greenland Plate. They concluded that the upper Perm- ian – Mesozoic deposits of the Wandel Sea Basin record the plate-boundary history along this offset in a series of disturbed, pull-apart basins. They assigned most of these basins to four tectonic episodes that were finally overprinted by the compressional Kronprins Christian Land Orogeny (Fig. 2). According to these authors, the timing of this orogeny is bracketed by the age of the deformed strata (Upper Cretaceous) and the age of the undeformed cover successions (Thyra Ø Formation), and thus, occurred during a comparatively brief period around the Cretaceous–Palaeogene boundary. The initial formation of the long, linear faults of the TLFZ was related to deformational events in late Palaeo- zoic, Triassic–Jurassic and Late Cretaceous times (von Gosen & Piepjohn 2003). Piepjohn & von Gosen (2001) observed dextral transpressive deformation, coeval with north–south compression at the HFFZ and KCTZ, which they interpreted as Eurekan. von Gosen & Piepjohn (2003) argued that the Eurekan transpressive deformation of the Wandel Sea Basin was younger than the Thyra Ø Forma- tion and thus of post-Paleocene age, probably Eocene. They interpreted a dextral displacement of the Thyra Ø Formation relative to upper Palaeozoic strata within a wide fault zone on Prinsesse Ingeborg Halvø to have occurred in the early Eocene during the deformation of the HFFZ and KCTZ. In contrast, Pedersen & Håkansson (2001) explained the displacement of the Thyra Ø Formation along the fault in terms of post-Paleocene down-faulting after cessation of compression. Håkansson & Pedersen (2001, 2015), therefore, suggested that the compressive tectonics had come to an end before the deposition of the Thyra Ø For- mation. Guarnieri (2015) identified compressive structures and reverse fault planes along the contact on Prinsesse Ingeborg Halvø and interpreted them as a Paleocene thrust fault, offset by strike-slip faults of probable Eocene. To our knowledge, Prinsesse Ingeborg Halvø is the only locality where the sediments of the Thyra Ø Formation are observed in contact with older rocks, and thus, the tim- ing of the end of compressional tectonics remains to be speculative. Svennevig et al. (2016, 2017) interpreted the Cretaceous succession exposed on Kilen as a rift basin, dominated by post-Coniacian extensional faults and overprinted during north–south compression that possibly occurred during the Paleocene–Eocene. Svennevig et al. (2016) also presented a new structural model for the development of the TLFZ based on observations from Kilen. Previous structural models interpreted rhombic-shaped fault pat- terns as evidence for strike-slip tectonics. However, these authors demonstrated the structures to be the result of post-Coniacian, north-east to south-west extension defined by north-west to south-east-trending normal faults, followed later by north–south compression that folded the faults passively. Consequently, the strike-slip faults had only minor status in the resulting basin inver- sion. Svennevig et al. (2016) considered the age of the compressional event on Kilen to be post-Coniacian, since the youngest Cretaceous outcrops are Coniacian in age. Hovikoski et al. (2018) dated these outcrops as Santonian. They also thought that a late Paleocene – early Eocene age for the north–south compression on Kilen was found to be compelling because (1) the Ar-Ar systematics of volcanics of the Kap Washington Group (200 km north- west of Kilen) were partially reset in the early Eocene (Tegner et al. 2011), (2) the West Spitsbergen Fold Belt on the conjugate Barents margin has been dated to be late Paleocene-Eocene in age (Maher et al. 1995) and (3) plate reconstructions showed transpression with 18° conver- gence in the late Paleocene (60 Ma) that culminated in the early Eocene (54–50 Ma; Svennevig et al. (2016) based on Müller et al. 2016). 3 Apatite Fission-Track Analysis A variety of scenarios have been proposed in the litera- ture to explain the complex tectonic development of the Wandel Sea Basin. Studies in the region describe multi- ple episodes of folding and faulting, although the tim- ing remains uncertain. Here, we present AFTA data and thermal history interpretations, with the aim of placing firmer constraints on the timing of key tectonic events. AFTA is a method for determining thermal histories of rocks at temperatures generally less than 130°C. Thermal history constraints derived from AFTA can be converted into information on former depths of burial and amounts of exhumation. In the method, radiation damage features known as ‘fission tracks’ are analysed. Fission tracks form in accessory apatite crystals separated from igneous rocks or in detrital apatite grains obtained from sandstones and other clastic rock types. The number of tracks per unit area of a polished grain surface depends on the uranium content, the time over which tracks have accumulated and the distribution of track lengths in the sample. If all tracks have the same length, then by measuring the https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 10 of 43 www.geusbul let in.org track density and the uranium content, a ‘fission-track age’ can be measured. In the absence of other factors, this age represents the time over which tracks accu- mulated. Once formed, the damage is progressively repaired, and the tracks shorten at a rate dependent on temperature. The probability of intersecting a pol- ished surface depends on the track length, and short- ened tracks produce a lower contribution to the track density than longer tracks, resulting in a reduced fis- sion-track age. As a result, a measured fission-track age does not denote the timing of a specific event and must be assessed together with the distribution of track lengths, referred to as ’confined tracks’. These tracks are totally enclosed within the grains and have been etched because they intersect tracks etched from the surface. The principles of the AFTA method are further described in Japsen et al. (in press), Green & Duddy (2012) and Green et al. (2013). 3.1 New AFTA data from northern and eastern Greenland This research study presents new AFTA data from 52 outcrop samples of basement and sedimentary rocks in northern and eastern Greenland (Fig. 6; Tables 1, 2 and the Supplementary File S1). Of these, 46 are from eastern North Greenland (north of 79°N; east of 40°W) and 6 are from North-East Greenland (between 74 and 79°N). Sixteen further samples were processed but did not yield apatite. As far as we are aware, no apatite fis- sion-track data have yet been reported from Greenland north of 80.5°N. Methods for sample preparation and analysis, basic AFTA data and thermal history interpretations derived from AFTA data for all samples were first reported in Geotrack report GC1113 (Green 2014) – a report pre- pared by Geotrack International, Australia, for the Geo- logical Survey of Denmark and Greenland, as provided in Supplementary File S2. In brief, rock samples are crushed to sand grade and heavy minerals are sepa- rated using standard density and magnetic techniques. Apatite grains are mounted in epoxy on glass slides, polished and etched in dilute nitric acid. The etched grain mounts are then fixed to mica sheets and irradi- ated with thermal neutrons. After irradiation, the mica sheets are detached from the grain mount and etched in hydrofluoric acid. Finally, the etched grain mounts and mica sheets are mounted next to each other on a microscope slide for track counting and length measurement. Ø Hovgaard 48 83 °N 82 °N 81 °N 80 °N 15°W 10°W20°W25°W30°W35°W40°W 15°W20°W25°W30°W35°W A GC1113 samples 100 km500 39 37 43 1544 16 4532 3 30 29 33 34 36 38 6 17 10 64 63 59 65 23 68 67 21 22 5 42 54 1 25 58 8 60 62 18 24 1948 61 7 9 55 3 5 24 1 EG FZK R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ Nakkehoved H E R L U F T R O L L E L A N D KR Pr.T.Ø Kilen TLFZ TLFZ Freuchen Land Land Nansen P. Koch Fjord 45°W 35°W 25°W 15°W 5°W 83 °N 80 °N 77 °N 25°W 4950 51 53 46 52 48 15 0 50 100 km 6 See Fig. 6A B Fig. 6 Location of samples that yielded apatite and division of the study area into six geographical areas with similar thermal his- tories used to define the timing of key episodes in Fig. 10. A: Areas 1–5. B: Area 6. Geology legend in Fig. 4. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 11 of 43 www.geusbul let in.org Table 1 Sample details. A digital version of this table is available in online Supplementary File S1 Sample number GC1113- Stratigraphic age Chronstratigraphic age (Ma) Rock type Latitude Longitude Elevation (m a.s.l.) Location 1 Coniacian 89–85 Conglomerate –14.0866 81.3477 250 KCL, Kilen 3 Cambrian 542–488 Quartzite –40.1618 83.2950 465 Lockwood Ø 5 Cretaceous, L 100–65 Sandstone –21.6885 82.7712 110 HTL, Foldedal 6 Cambrian, E 542–513 Sandstone –31.4713 82.1574 114 Heilprin Land, Glaciologelv 7 Cambrian, E 542–513 Sandstone –20.6893 80.2133 160 Pr. CM Alper 8 Carboniferous, E 360–318 Sandstone –15.1754 80.7875 100 AL, Sommerterrassen 9 Palaeogene, E 66–61 sand/coal –19.2820 81.9368 12 Pr. Thyra Ø 10 Jurassic, L – Cretaceous, E 161–100 Sandstone –21.2511 82.0323 23 Kap Rigsdagen 15 Cambrian 542–488 Psammite –34.8881 83.3972 1341 JVJL, Polkorridoren 16 Cambrian 542–488 Marble? –35.6985 83.5279 320 JVJL, Sands Fjord 17 Neoproterozoic 1600–1000 Sandstone –26.2725 81.9563 275 ICCL, Neergaard Dal 18 Carboniferous, L 318–299 Sandstone –15.7926 80.4417 20 HL, Eskimonæs 19 Carboniferous, E 360–318 Sandstone –17.4994 80.2161 50 HL, Sortebakker 21 Oxfordian–Barremian 161–130 Sandstone –21.4981 82.5801 157 HTL, Kim Fjelde 22 Triassic, E 251–247 Sandstone –21.3657 82.5852 200 HTL, Kim Fjelde 23 Triassic, E 251–247 Sandstone –21.2864 82.6155 190 HTL, Falkefjeld 24 Carboniferous, L 318–299 Sandstone –16.2082 80.3018 37 HL, Hanseeraq Fjord 25 Albian 112–100 Sandstone –12.6921 81.1447 25 KPC, Kilen 29 Cambrian, Ellesm. deform. 542–488 Psammite –30.5000 83.3000 400 JVJL 30 Cambrian, Ellesm. deform. 542–488 - –34.0000 83.5667 340 JVJL 32 Cretaceous, L /Palaeogene 80–50 Rhyolite –39.6667 83.4333 410 JVJL 33 Cambrian, Ellesm. deform. 542–488 Arkose –28.5000 83.2667 825 JVJL 34 Cambrian, Ellesm. deform. 542–488 Psammite –27.0833 83.3000 460 JVJL 36 Cambrian, Ellesm. deform. 542–488 Sandstone –26.1667 83.2833 20 JVJL 37 Cretaceous, L /Palaeogene 80–50 Gabbro –32.7000 83.1833 950 JVJL 38 Silurian 444–416 Greywacke –34.2520 82.2700 775 PL 39 Silurian 444–416 Sandstone, partly –37.6167 83.9333 600 PL 42 Palaeoproterozoic 2500–1600 Sandstone –32.7500 81.7009 720 PL, Vildtland 43 Cambrian, Ellesm. deform. 542–488 Conglomerate –37.1000 83.2333 390 JVJL 44 Cambrian, Ellesm. deform. 542–488 Psammite –36.0000 83.4333 1180 JVJL 45 Cambrian, Ellesm. deform. 542–488 Schist –37.6333 83.5500 80 JVJL 46 Precambrian, Caled. deform. 2500–1600 Metagabbro –19.5000 77.8000 30 Gamma Ø, Nordmarken 48 Precambrian, Caled. deform. 2500–1600 Gabbro –18.4012 79.7217 250 Hovgaard Ø 49 Precambrian, Caled. deform. 2500–1600 Mica schist –25.1697 74.4372 1450 BL 50 Precambrian, Caled. deform. 2500–1600 Mica schist –25.7823 74.4418 1305 BL 51 Precambrian, Caled. deform. 2500–1600 Gneiss –23.6667 78.1000 900 KFVIIIL, Bildsøe Nunatakker 52 Precambrian, Caled. deform. 2500–1600 Banded sequence –23.3167 78.5333 660 KFVIIIL, Grønne Nuuatak 53 Precambrian, Caled. deform. 2500–1600 Gneiss –18.5500 78.5667 10 Franske Øer, Kap Bergendahl 54 Palaeoproterozoic 2500–1600 Siltstone –28.3333 81.4333 251 ICCL 55 Cretaceous, L 100–65 Sandstone –13.1110 81.6990 276 KCL,Nakkehoved 58 Cretaceous, E 145–100 Sandstone –13.9481 81.2638 264 KCL, Dromledome 59 Cretaceous, L 100–65 Sandstone –21.6794 82.7600 130 HTL 60 Mesoproterozoic 1600–1000 Metasediments –15.2836 80.8965 320 AL 61 Archaean >2500 Gneiss –17.1175 80.4068 952 HL 62 Mesoproterozoic 1600–1000 Sandstone –17.7671 80.7579 997 AL, Tobias Gletscher 63 Silurian 444–416 Sandstone –22.8773 82.4813 122 HTL, Vitskøl Elv 64 Oxfordian–Barremian 161–130 Sandstone –22.8718 82.4682 277 HTL, Vitskøl Elv 65 Triassic, M 245–237 Sandstone –21.2546 82.6158 250 HTL, Hjulsporsdalen 67 Triassic, M 245–237 Sandstone –21.0833 82.6703 229 HTL, Dunken 68 Oxfordian–Barremian 161–130 Sandstone –21.1756 82.6753 642 HTL, Dunken AL: Amdrup Land; BL: Bartholin Land; HL: Holm Land; HTL: Herluf Trolle Land; ICCL: IC Christensen Land; JVJL: JV Jensen Land; KCL: Kro- nprins Christian Land; KFVIIIL: Kong Frederik VIII Land; PL: Peary Land; Pr CM Alper: Prinsesse Caroline Matilde Alper; Pr Thyra Ø: Prinsesse Thyra Ø; E: Early; M: Middle; L: Late; Caled.: Caledonian; Ellesm.: Ellesmerian. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 12 of 43 www.geusbul let in.org Table 2 AFTA data. A digital version of this table is available in online Supplementary File S1 Sample number GC1113- Stratigraphic age (Ma) a ρD b (106 tracks/ cm2) ρs b (106 tracks/ cm2) ρi b (106 tracks/ cm2) (Pχ2)c (%) (no of grains) Fission track age d (Ma) Mean track length e (μm) Std. dev. f (μm) 1 89–85 1.209 (1998) 0.343 (138) 2.698 (1085) 38 (20) 29.2 ± 2.8 14.1 ± 0.8 (7) 2.05 3 542–488 1.215 (1998) 0.557 (143) 3.607 (926) <1 (20) 38.8 ± 4.9† 14.2 ± 0.4 (12) 1.51 5 100–65 1.222 (1998) 0.044 (25) 0.258 (148) 37 (20) 39.1 ± 8.5 14.7 ± 0.3 (8) 0.72 6 542–513 1.228 (1998) 1.807 (522) 2.552 (737) <1 (16) 165.9 ± 17.5† 12.7 ± 0.3 (27) 1.58 7 542–513 1.235 (1998) 1.120 (642) 1.950 (1118) 3 (20) 127.1 ± 9.6† 12.8 ± 0.2 (55) 1.64 8 360–318 1.241 (1998) 1.578 (568) 1.842 (663) 47 (20) 199.1 ± 12.6 12.8 ± 0.2 (72) 1.50 9 66–61 1.248 (1998) 0.969 (344) 1.375 (488) 9 (20) 165.6 ± 16.5† 12.8 ± 0.4 (44) 2.35 10 161–100 1.254 (1998) 0.542 (195) 1.036 (373) 3 (19) 127.0 ± 15.8† 11.2 ± 0.5 (15) 1.80 15 542–488 1.260 (1998) 0.334 (176) 2.786 (1469) 6 (20) 28.7 ± 2.4 14.0 ± 0.4 (24) 1.88 16 542–488 1.267 (1998) 0.037 (27) 0.134 (97) 99 (19) 66.7 ± 14.6 14.2 ± 0.5 (2) 0.64 17 1600–1000 1.273 (1998) 1.306 (637) 1.837 (896) 4 (20) 173.1 ± 14.3† 13.0 ± 0.2 (54) 1.37 18 318–299 1.280 (1998) 1.499 (599) 2.275 (909) 4 (18) 153.8 ± 11.8† 11.3 ± 0.3 (21) 1.28 19 360–318 1.292 (1998) 1.130 (833) 1.566 (1154) 68 (20) 175.0 ± 9.2 12.3 ± 0.2 (100) 1.71 21 161–130 1.292 (1998) 0.712 (288) 2.088 (845) <1 (20) 83.4 ± 9.3† 11.9 ± 0.6 (17) 2.28 22 251–247 1.299 (1998) 1.140 (594) 2.140 (1115) <1 (20) 127.0 ± 11.9† 12.1 ± 0.2 (89) 2.06 23 251–247 1.305 (1998) 0.839 (526) 2.699 (1692) <1 (20) 76.3 ± 7.0† 13.3 ± 0.3 (40) 1.91 24 318–299 1.312 (1998) 0.923 (790) 1.249 (1069) 3 (20) 183.8 ± 13.2† 12.8 ± 0.2 (100) 1.60 25 112–100 1.318 (1998) 0.477 (69) 2.701 (391) 53 (12) 44.1 ± 5.9 13.8 ± 0.5 (5) 1.19 29 542–488 1.125 (1885) 0.480 (280) 3.051 (1780) 2 (16) 33.3 ± 3.2† 13.4 ± 0.3 (24) 1.68 30 542–488 1.132 (1885) 0.052 (19) 0.142 (52) 88 (13) 78.2 ± 21.1 - 32 80–50 1.146 (1885) 0.694 (155) 2.551 (570) <1 (11) 65.3 ± 18.6† 12.6 ± 0.6 (6) 1.53 33 542–488 1.153 (1885) 0.953 (413) 4.022 (1744) <1 (20) 49.4 ± 5.0† 14.3 ± 0.2 (52) 1.39 34 542–488 1.160 (1885) 0.296 (36) 3.598 (437) <1 (9) 24.9 ± 6.6† 13.9 ± 1.6 (3) 2.72 36 542–488 1.167 (1885) 1.268 (79) 2.372 (148) <1 (9) 115.9 ± 28.0† 13.9 ± 0.1 (2) 0.16 37 80–50 1.181 (1885) 3.009 (1367) 3.306 (1502) 2 (20) 201.9 ± 11.5† 13.5 ± 0.2 (106) 1.63 38 444–416 1.188 (1885) 2.790 (1415) 2.622 (1330) <1 (20) 237.3 ± 14.7† 13.1 ± 0.2 (100) 1.57 39 444–416 1.195 (1885) 1.282 (426) 1.664 (553) <1 (18) 164.0 ± 18.5† 13.1 ± 0.4 (18) 1.67 42 2500–1600 1.202 (1885) 3.017 (169) 3.357 (188) <1 (4) 174.5 ± 56.5† 14.1 ± 0.9 (5) 1.92 43 542–488 1.209 (1885) 0.818 (478) 4.463 (2609) <1 (20) 45.3 ± 6.0† 13.7 ± 0.2 (53) 1.31 44 542–488 1.216 (1885) 0.093 (8) 0.865 (74) 16 (3) 24.9 ± 9.3 14.2 ± 0.0 (1) 45 542–488 1.223 (1885) 0.877 (302) 1.984 (683) <1 (8) 90.0 ± 32.2† 12.0 ± 0.4 (10) 1.29 46 2500–1600 1.229 (1885) 0.913 (681) 1.163 (867) <1 (20) 163.5 ± 14.5† 13.4 ± 0.1 (100) 1.16 48 2500–1600 1.236 (1885) 1.953 (1563) 1.803 (1443) <1 (20) 251.7 ± 14.8† 13.4 ± 0.1 (101) 1.18 49 2500–1600 1.243 (1885) 0.986 (599) 1.625 (987) <1 (20) 136.1 ± 11.7† 13.2 ± 0.1 (77) 1.28 50 2500–1600 1.250 (1885) 1.982 (1545) 2.450 (1910) 2 (20) 184.7 ± 10.1† 13.4 ± 0.1 (110) 1.50 51 2500–1600 1.257 (1885) 1.479 (1264) 3.773 (3224) <1 (20) 93.9 ± 6.7† 13.4 ± 0.1 (101) 1.15 52 2500–1600 1.264 (1885) 0.759 (603) 1.375 (1092) 1 (20) 129.7 ± 9.8† 12.8 ± 0.2 (61) 1.35 53 2500–1600 1.178 (1924) 0.042 (38) 0.048 (43) 100 (18) 201.4 ± 45.2 13.0 ± 0.5 (15) 1.88 54 2500–1600 1.182 (1924) 1.986 (801) 1.539 (621) 3 (20) 293.7 ± 23.2† 13.1 ± 0.2 (106) 1.64 55 100–65 1.187 (1924) 0.343 (124) 1.838 (665) <1 (19) 48.6 ± 7.5† 11.7 ± 0.9 (10) 3.00 58 145–100 1.191 (1924) 0.552 (323) 2.747 (1606) 15 (20) 47.9 ± 4.1† 13.8 ± 0.2 (113) 1.95 59 100–65 1.195 (1924) 0.169 (118) 0.860 (601) 92 (20) 45.9 ± 4.8 13.6 ± 0.2 (67) 1.69 60 1600–1000 1.199 (1924) 0.478 (430) 0.424 (382) 32 (20) 259.8 ± 19.8 12.8 ± 0.1 (115) 1.40 61 >2500 1.203 (1924) 1.456 (766) 1.363 (717) 38 (20) 247.6 ± 14.8 12.8 ± 0.2 (109) 1.81 62 1600–1000 1.207 (1924) 2.156 (932) 1.855 (802) <1 (20) 258.2 ± 21.8† 13.0 ± 0.1 (116) 1.48 63 444–416 1.211 (1924) 2.129 (939) 1.757 (775) 2 (20) 276.8 ± 19.6† 12.0 ± 0.1 (108) 1.50 64 161–130 1.215 (1924) 2.559 (884) 2.255 (779) <1 (20) 299.1 ± 38.5† 11.8 ± 0.2 (105) 1.97 65 245–237 1.219 (1924) 0.941 (266) 2.297 (649) <1 (15) 80.6 ± 19.9† 13.2 ± 0.5 (22) 2.14 67 245–237 1.223 (1924) 0.979 (364) 4.609 (1714) 13 (20) 50.8 ± 3.3 14.0 ± 0.2 (105) 1.79 68 161–130 1.227 (1924) 0.682 (216) 3.545 (1122) 78 (20) 46.2 ± 3.7 13.5 ± 0.2 (119) 1.76 a All numerical values for stratigraphic ages assigned following Gradstein et al. (2012). b ρs = spontaneous track density; ρi = induced track density; ρD = glass-dosimeter track density. Numbers in parentheses show the number of tracks counted in determining all track densities. c Probability that all single- grain ages belong to a single population (Galbraith 2005). d Central age (Galbraith 2005), used for samples con- taining a significant spread in single-grain ages (Pχ2) < 5%), is denoted with †, otherwise the pooled age is quoted. All ages were calculated using the zeta calibration approach of Hurford & Green (1983), using zeta values for CN5 glass of 380.4 ± 5.7 (samples GC1113-1 to -52); 392.9 ± 7.4 (samples GC1113-53 to 68). All errors quoted at ± 1 σ.  All analytical details are as provided in Supplementary File S1. e Numbers in parentheses show the number of track lengths measured. f Standard deviation of the track-length distribution. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 13 of 43 www.geusbul let in.org The chlorine content exerts a critical influence on fis- sion-track annealing kinetics in apatite. Measuring chlo- rine is essential to obtain both improved accuracy and precision in the timing and magnitude of thermal events. Chlorine compositions were determined by an electron microprobe (see Supplementary File S2) for all individual apatite grains analysed (i.e. all grains in which fission-track ages were determined or lengths were measured). Measured fission-track ages vary between 24.9 ± 6.6 Ma and 299.1 ± 38.5 Ma, with most samples (c. 80%) yielding ages less than 200 Ma (Table 2). Apatite fission-track ages less than 300 Ma in samples of Precambrian basement or early Palaeozoic metasediments show that the samples must have been much hotter than their present-day tem- perature at some time during the last 300 Ma. Youngest apatite fission-track ages (<50 Ma) are gen- erally found in coastal locations, while inland samples give consistently older ages (up to c. 300 Ma; Fig. 7). In addition to the thermal history, measured fission-track ages are sensitive to depositional ages, as well as external factors, such as the composition of apatite within each sample. Thus, regional variation is better described by looking at palaeotemperatures within individual palaeo- thermal episodes, as discussed in Section 4.5. Mean track lengths are generally between 12 and 14 mm, with a small number of samples giving higher values (towards c. 15 µm) and lower values (towards c. 11 µm; Fig. 8A; Table 2). Initial assessment of these data suggests that they are dominated by the late Palaeozoic and later history, and retain little trace of earlier events. The AFTA data define a broadly consistent trend of mean track lengths versus apatite fission-track ages (Fig.  8A), where longest mean track lengths corre- spond to the youngest ages and the mean track length decreases as ages increase. While this trend resembles the classic ‘boomerang’ trend (Green 1986), typical of a suite of samples affected by a single dominant palaeo- thermal episode, the data show much more dispersion, suggesting a more complex history involving a series of discrete cooling episodes. Despite this complexity, the overall trend in Fig. 8A suggests that most sam- ples across the region have undergone a similar style of thermal history involving a series of cooling episodes (Fig.  8A), with the magnitude of individual events varying across the region. Extraction of thermal history informa- tion from the AFTA data and subsequent synthesis has, therefore, been carried out on this basis. As none of the Precambrian samples give fission-track ages in excess of 300 Ma, data from these samples were interpreted by reference to the base of the Phanerozoic at 542 Ma. AFTA data from the Wandel Sea Basin show a simi- lar range to those from North-East Greenland (Japsen et al. in press), in an area immediately south and over- lapping with the study region (Fig. 8B). However, the Wandel Sea Basin samples plot consistently towards longer mean track lengths, particularly at younger ages. Fig. 7 Apatite fission-track ages in out- crop samples from eastern North Green- land (data in Table 2). Youngest ages <60 Ma are focussed along the north coast, while older ages are found in inland samples. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. Geology legend in Fig. 4. Ø Hovgaard 48 83 °N 82 °N 81 °N 80 °N 15°W 10°W20°W25°W30°W35°W40°W 15°W20°W25°W30°W35°W 100 km500 EG FZK R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ TLFZ HFFZ KCTZ Nakkehoved Pr.T.Ø KR Kilen Herluf Trolle Land Fission-track age (Ma) <25 25–45 45–60 60–100 100–200 >200 https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 14 of 43 www.geusbul let in.org This  probably reflects a reduced impact of Neogene cooling in the samples analysed. This is consistent with lower summit heights in the study region, and therefore, less pronounced Neogene uplift and incision. 3.2 Thermal history interpretation based on AFTA data 3.2.1 Principles of thermal history interpretation The techniques of extracting thermal history constraints from AFTA data are discussed in detail elsewhere (Green & Duddy 2012; Green et al. 2013). In brief, fission tracks are formed continuously through time by spontaneous fis- sion of 238U atoms and accumulate at a rate determined by radioactive decay laws. Tracks form within a narrow range of lengths (between c.15 and 17 mm). As an apatite grain is heated, tracks are shortened at a rate that depends on the prevailing temperature. The kinetics of annealing are such that temperature dominates over time. In a sample that has been heated to a maximum palaeotemperature and then cooled, almost all of the tracks formed during the heating phase are shortened to the same length. If the sample remains at lower temperatures, tracks formed after cooling will subsequently undergo less shortening compared with those formed prior to the onset of cooling, resulting in two distinct populations of tracks. The mean length of the shorter population is determined by the maximum palaeotemperature, while the proportion of short vs. long tracks will be determined by the ratio of the time before and after the onset of cooling. If the sample is re-heated to a peak palaeotemperature that is lower than the previous peak, and then cools again, tracks formed prior to the maximum are unaffected but tracks formed after cooling from the earlier maximum will be shortened to a degree determined by the peak palaeotemperature in 9 10 11 12 13 14 15 16 0 50 100 150 200 250 300 350 M ea n tr ac k le ng th (µ m ) Fission-track age (Ma) A 9 10 11 12 13 14 15 16 0 50 100 150 200 250 300 350 M ea n tr ac k le ng th (µ m ) Fission-track age (Ma) This study NE Greenland B Fig. 8 Relationship between the mean track length and fission-track age. A: Outcrop samples from eastern North Greenland (this study). Error bars are shown as ± 2 sigma. B: Results from this study compared with those from North-East Greenland (Japsen et al. in press). Ages span a similar range in both regions. However, data from this study are characterised by higher mean track lengths than those from North- East Greenland, which probably reflects the lower degree of Miocene cooling in samples from this study. Error bars are omitted for clarity. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 15 of 43 www.geusbul let in.org the second heating event. This results in two generations of tracks with different lengths, which allows definition of two episodes of heating and cooling, if the two events are sufficiently separated in temperature and time. In some cases, three episodes might be resolved in a similar fash- ion, while definition of four episodes of cooling may be possible under rare circumstances. As AFTA data are dominated by the maximum palaeotemperature the data preserve no evidence of the history prior to the onset of cooling. For similar rea- sons, the history between successive cooling episodes cannot be resolved. Therefore, it is not possible to con- strain the entire thermal history from the beginning of track retention. Instead, we define the maximum palae- otemperature and subsequent palaeothermal peaks within an overall framework of episodic heating and cooling (Fig.  9), assuming heating and cooling rates of 1°C/Ma and  10°C/Ma, respectively. An order of magni- tude change in heating rate is equivalent to around a 10°C difference in palaeotemperature required to pro- duce a given degree of annealing. As explained in detail elsewhere, the combination of AFTA with geological evidence has provided abundant evidence that thermal histories involving episodic heat- ing and cooling are more realistic than slow, monotonic cooling (Green & Duddy 2012; Green et al. 2013, 2018). This conclusion is based on studies in which AFTA data provide evidence of cooling and exhumation, while times when underlying rocks were at the surface are identified from remnants of the former sedimentary cover. Such situations provide evidence of repeated burial and exhumation, and are generally applicable in a wide variety of settings (Green et al. 2013, 2017). Thermal history solutions are represented by 95% confidence limits on the maximum (or peak) palaeo- temperature and on the time at which cooling from that palaeotemperature began (Fig. 9). The parameters are extracted from data in each sample by comparing mea- sured AFTA parameters (fission-track ages and track lengths) with those predicted from candidate thermal histories, involving up to three episodes of heating and cooling. By varying the magnitude of maximum palaeo- temperature and the onset of cooling in each episode, the range of temperature-time combinations giving predictions consistent with the measured data and within 95% confidence limits can be defined using the likelihood theory based on principles similar to those outlined by Gallagher (1995). Where three episodes are defined, the earliest episode is constrained primarily from the fission-track age data and represents the epi- sode in which samples cool below c. 110°C and began to retain tracks, while the two more recent episodes are defined principally from the distribution of track lengths. 3.2.2 Thermal history interpretation: results Detailed thermal history interpretation of the AFTA data in each sample is provided in Supplementary File S2. As explained therein, AFTA data in almost all samples show clear evidence of higher temperatures after deposition (or in Phanerozoic times for samples of Precambrian basement). Thermal history solutions derived from the AFTA data in each sample, in terms of the maximum palaeotemperature and the timing of cooling in a number of discrete episodes, are sum- marised in Table 3. Fig. 9 Illustration of thermal history solu- tions extracted from AFTA data. Results are presented in terms of up to three palae- othermal episodes, that is, times when a rock sample was hotter than it is today. Note that the palaeotemperature con- straint T1 is a minimum estimate because this is the event in which the apatites begin to retain tracks. In most situations, three events are the most that can be defined from AFTA due to various factors, includ- ing the natural spread in track lengths of a single population of tracks and the rapid decrease in the rate of annealing across the range from c. 110°C to below 60°C. t1, t2 and t3: time intervals during which cooling from the peak palaeotemperature began. T1, T2 and T3: palaeotempera- ture intervals. c.i.: confidence interval. Colours are used to illustrate attribution to regional episodes, although those used here are purely schematic. 100 80 60 40 20 0 120 250 200 50150 100 0 T2: 95% c.i. on maximum temperature T3 t3 T1 t1 t2: 95% c.i. on onset of cooling Te m pe ra tu re (° C ) Time (Ma) Deposition https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 16 of 43 www.geusbul let in.org Ta bl e 3  Th er m al h is to ry s ol ut io ns . A d ig ita l v er si on a va ila bl e in o nl in e Su pp le m en ta ry F ile S 1 Sa m pl e nu m be r G C1 11 3- El ev at io n (m ) St ra tip ra ph ic a ge Ch ro no st ra ti- gr ap hi c ag e (M a) Pa la eo - te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t Pa la eo – te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t Pa la eo – te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t A re a 1                         32 41 0 Cr et ac eo us , L /P al ae og en e 80 –5 0       11 0– 13 0 50 –2 0 En d- Eo ce ne <1 10 20 –0 M io ce ne 37 95 0 Cr et ac eo us , L /P al ae og en e 80 –5 0     85 –5 5 65 –1 0 En d- Eo ce ne     3 46 5 Ca m br ia n 54 2– 48 8     >1 05 45 –2 5 En d- Eo ce ne     15 13 41 Ca m br ia n 54 2– 48 8     >1 10 40 –2 5 En d- Eo ce ne     16 32 0 Ca m br ia n 54 2– 48 8     >1 00 12 0– 10 En d- Eo ce ne     29 40 0 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8 >1 10 75 –3 0 Pa le oc en e 10 5– 12 0 45 –1 5 En d- Eo ce ne 25 –9 5 25 –0 M io ce ne 30 34 0 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8     95 –1 05 10 0– 0 En d- Eo ce ne     33 82 5 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8 >1 15 14 0– 60 Pa le oc en e 11 0– 11 5 55 –3 5 En d- Eo ce ne 20 –5 0 30 –0 M io ce ne 34 46 0 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8 >1 05 >1 0 Pa le oc en e >1 05 >1 0 En d- Eo ce ne <1 20 20 –0 M io ce ne 36 20 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8 ? ? Pa le oc en e 10 0– 12 0 15 0– 20 En d- Eo ce ne <1 00 11 0– 0 M io ce ne 43 39 0 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8     >1 30 55 –4 0† En d- Eo ce ne 40 –6 0 15 –0 M io ce ne 44 11 80 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8     >1 00 70 –5 En d- Eo ce ne     45 80 Ca m br ia n, E lle sm . d ef or m . 54 2– 48 8       >1 15 50 –2 0 En d- Eo ce ne       A re a 2                         5 11 0 Cr et ac eo us , L 10 0– 65 >1 00 70 –2 0 Pa le oc en e             59 13 0 Cr et ac eo us , L 10 0– 65 >1 05 70 –4 0 Pa le oc en e 55 –8 0 35 –1 0 En d- Eo ce ne     10 23 Ju ra ss ic , L – C re ta ce ou s, E 16 1– 10 0 >1 10 19 7– 13 6 L Ju ra ss ic 81 –9 7 19 5– 2 En d- Eo ce ne <7 8 46 –0 M io ce ne 21 15 7 O xf or di an –B ar re m ia n 16 1– 13 0 >1 00 >9 0 L Ju ra ss ic 85 –1 00 55 –1 0 En d- Eo ce ne     68 64 2 O xf or di an –B ar re m ia n 16 1– 13 0 >1 25 60 –4 0 Pa le oc en e 90 –1 10 55 –3 5 En d- Eo ce ne 40 –7 0 25 –5 M io ce ne 64 27 7 O xf or di an –B ar re m ia n 16 1– 13 0     75 –9 0 14 0– 25 En d- Eo ce ne 15 –7 5 35 –0 M io ce ne 22 20 0 Tr ia ss ic , E 25 1– 24 7 >1 15 20 0– 15 0 L Ju ra ss ic 85 –9 5 75 –3 5 En d- Eo ce ne 25 –5 0 20 –0 M io ce ne 23 19 0 Tr ia ss ic , E 25 1– 24 7 10 0– 10 5 90 –6 0 Pa le oc en e 65 –8 5 45 –1 5 En d- Eo ce ne     67 22 9 Tr ia ss ic , M 24 5– 23 7 >1 30 65 –4 5 Pa le oc en e 85 –1 05 55 –3 5 En d- Eo ce ne 30 –6 5 35 –5 M io ce ne 65 25 0 Tr ia ss ic , M 24 5– 23 7 10 0– 10 5 12 5– 30 Pa le oc en e 20 –9 5 60 –0 En d- Eo ce ne     63 12 2 Si lu ri an 44 4– 41 6 95 –1 05 36 0– 23 5 E Pe rm ia n 70 –8 0 35 –0 En d- Eo ce ne       A re a 3                         9 12 Pa la eo ge ne , E 66 –6 1       20 –7 5 45 –0 En d- Eo ce ne       9 pr e- de p 12 >1 25 c 29 2– 18 5c L Tr ia ss ic 91 –1 03 c 17 8– 80 c L Ju ra ss ic 37 –8 0 93 –5 En d- Eo ce ne 1 25 0 Co ni ac ia n 89 –8 5     >1 30 45 –2 5 En d- Eo ce ne     55 27 6 Cr et ac eo us , L 10 0– 65 >1 25 10 1– 48 Pa le oc en e 86 –1 06 56 –1 5 En d- Eo ce ne 36 –8 1 20 –0 M io ce ne 25 46 Al bi an 11 2– 10 0 >1 00 65 –1 0 Pa le oc en e         58 26 4 Cr et ac eo us , E 14 5– 10 0 >1 20 60 –4 5 Pa le oc en e 76 –1 03 48 –2 6 En d- Eo ce ne 25 –7 2 31 –8 M io ce ne Co nt in ue d https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 17 of 43 www.geusbul let in.org Sa m pl e nu m be r G C1 11 3- El ev at io n (m ) St ra tip ra ph ic a ge Ch ro no st ra ti- gr ap hi c ag e (M a) Pa la eo - te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t Pa la eo – te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t Pa la eo – te m pe ra tu re (° C) O ns et o f co ol in g (M a) Ev en t A re a 4                         39 60 0 Si lu ri an 44 4– 41 6 >1 10 >2 00 L Tr ia ss ic 95 –1 10 20 0– –7 5 L Ju ra ss ic 35 –7 0 45 –0 En d- Eo ce ne 38 77 5 Si lu ri an 44 4– 41 6 >1 05 29 5– 24 0 E Pe rm ia n 65 –9 0 24 5– 30 En d- Eo ce ne 20 –6 0 45 –0 M io ce ne 6 11 4 Ca m br ia n, E 54 2– 51 3 >1 15 21 0– 16 0c L Tr ia ss ic 80 –1 05 18 5– 75 L Ju ra ss ic 45 –7 5 65 –0 En d- Eo ce ne 17 27 5 N eo pr ot er oz oi c 16 00 –1 00 0 >1 15 23 0– 17 5 L Tr ia ss ic 70 –9 5 18 0– 45 L Ju ra ss ic 30 –6 5 40 –0 En d- Eo ce ne 42 72 0 Pa la eo pr ot er oz oi c 25 00 –1 60 0 >1 05 35 0– 16 5 E Pe rm ia n         54 25 1 Pa la eo pr ot er oz oi c 25 00 –1 60 0 >1 10 37 5– 29 0   70 –9 0 28 0– 70 L Ju ra ss ic 25 –6 5 85 –0 En d- Eo ce ne A re a 5                         18 20 Ca rb on ife ro us , L 31 8– 29 9 >1 00 25 0– 17 0 L Tr ia ss ic 80 –1 10 b 22 0– 0b L Ju ra ss ic 80 –9 0 45 –0 En d- Eo ce ne 19 50 Ca rb on ife ro us , E 36 0– 31 8 >1 00 >1 75 L Tr ia ss ic 80 –1 00 17 5– 75 L Ju ra ss ic 50 –7 0 35 –0 En d- Eo ce ne 24 25 Ca rb on ife ro us , L 31 8– 29 9 >1 00 25 0– 20 0 L Tr ia ss ic 75 –9 5 20 0– 65 L Ju ra ss ic 30 –7 0 55 –0 En d- Eo ce ne 8 10 0 Ca rb on ife ro us , E 36 0– 31 8 >1 05 27 0– 20 0 L Tr ia ss ic 75 –1 10 b 22 5– 65 b L Ju ra ss ic 45 –7 5 50 –0 En d- Eo ce ne 7 16 0 Ca m br ia n, E 54 2– 51 3 >1 15 17 5– 13 0 Ju ra ss ic 80 –1 05 15 5– 50 M id -C re t. 35 –7 5 60 –0 En d- Eo ce ne 60 32 0 M es op ro te ro zo ic 16 00 –1 00 0 >1 00 35 5– 23 0 E Pe rm ia n 75 –1 05 31 5– 14 5 L Tr ia ss ic 55 –7 5 70 –1 5 En d- Eo ce ne 62 99 7 M es op ro te ro zo ic 16 00 –1 00 0 >1 00 >2 50 E Pe rm ia n 80 –1 05 30 0– 21 0 L Tr ia ss ic 50 –6 5 60 –0 En d- Eo ce ne 48 25 0 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0 >1 05 31 5– 25 5 E Pe rm ia n     55 –7 0 70 –1 0 En d- Eo ce ne 61 95 2 Ar ch ae an >2 50 0 >1 00 >2 50 E Pe rm ia n 85 –1 00 26 0– 16 5 L Tr ia ss ic 55 –7 0 90 –2 0 En d- Eo ce ne A re a 6                         46 30 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0 >1 10 23 0– 18 0 L Tr ia ss ic 60 –9 0 18 5– 35 M id -C re t. 25 –6 0 30 –0 M io ce ne 49 14 50 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0     >1 00 18 0– 12 0 L Ju ra ss ic 50 –6 5 35 –0 M io ce ne 50 13 05 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0 >1 05 22 5– 18 0   60 –7 0 90 –3 0 En d- Eo ce ne     51 90 0 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0     >1 00 11 5– 90 M id -C re t. 50 –6 0 20 –0 M io ce ne 52 66 0 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0 >1 10 >1 65 L Tr ia ss ic 10 0– 11 0 16 5– 10 0 L Ju ra ss ic 55 –7 0 25 –0 M io ce ne 53 10 Pr ec am br ia n, C al ed . d ef or m . 25 00 –1 60 0 >9 5 40 0– 55 L Tr ia ss ic       35 –9 0 21 5– 0 M io ce ne a: O ut ly in g va lu e; b : U nc er ta in c on st ra in ts ; c : P re -d ep os tio na l c on st ra in ts ; E : E ar ly , M : M id dl e, L : L at e; C al ed .: Ca le do ni an ; E lle sm .: El le sm er ia n; C re t.: C re ta ce ou s. Ta bl e 3  Th er m al h is to ry s ol ut io ns . A d ig ita l v er si on a va ila bl e in o nl in e Su pp le m en ta ry F ile S 1 (c on tin ue d) https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 18 of 43 www.geusbul let in.org In most of the samples analysed, the AFTA data require at least three episodes of heating and cooling, while in a small number of samples only two episodes are required to explain the data. Definition of two palaeothermal epi- sodes represents a typical level of resolution that can be achieved from AFTA. Generally, the earlier episode would be defined by the fission-track age data and possibly the shorter track lengths, while the more recent episode would be defined by the shortening of the main mode of the track length distribution. However, where the palaeotemperatures in each episode are sufficiently well separated, three episodes can be resolved. In samples GC1113-19 and -24, the earliest episode produces total annealing of all tracks, a later event leads to shortening of tracks formed after the initial cooling to lengths around 10–11 mm, and another later event then shortens tracks formed after the second episode to lengths around 13 mm. The ability to resolve three episodes often depends on the quality of the data, with 100 track length mea- surements normally required to provide a confident con- clusion. In most samples from this study, this criterion was met. Nevertheless, a random variation in measured parameters can lead to the failure of identifying three episodes in some samples, while nearby samples pro- vide a clear resolution. Thus, in some cases, the quoted thermal history solutions may represent the combined effects of unresolved multiple cooling episodes. This is also particularly important at low temperatures (<70°C), where differences in track length may be insufficient to allow multiple episodes to be resolved. Synthesis of all data, as discussed in Section 3.3, sug- gests that at least seven discrete cooling episodes are required to explain the results from all samples. This emphasises the fact that AFTA data in individual sam- ples, even in the most favourable circumstances, allow resolution of only three discrete episodes. The events that dominate the data in a given sample will be a func- tion of the magnitude of each episode, the quality of the AFTA data and the spread of compositions present. Often, the highest Cl levels may reveal an earlier epi- sode, for which the evidence has been overprinted by later events in the more sensitive, low-Cl apatites. 3.3 Definition of major regional palaeothermal episodes Figure 10 shows timing constraints (95% confidence lim- its) on the onset of discrete cooling episodes in individual samples defined by AFTA (Fig. 9). Thermal history con- straints for all samples are listed in Table 3. Samples are grouped into six geographic regions based on the general uniformity of the data within each of the regions (Areas 1–6; Fig. 6). Based on this uniformity of the data within each region and the evidence for regionally consistent thermal histories, we have sought to define the minimum number of regionally synchronous cooling episodes that can explain the results in all of these samples. Integration of results from all samples requires a total of seven discrete cooling episodes (vertical bars in Fig. 10; see also Table 4). The onset of cooling in each episode ranges from early Permian to middle to late Miocene. These intervals rep- resent the times at which cooling began in each episode, and we do not suggest that cooling was restricted to these intervals. Note that in some cases, the estimated onset of cooling pre-dates the depositional age of the sample. This indicates cooling of the apatite in sediment provenance regions, prior to deposition in the host sample. Pre-Cenozoic episodes are expressed almost exclu- sively at inland locations (Areas 4 and 5 together with locations to the south in Area 6). Three Cenozoic epi- sodes are focussed particularly in northern coastal loca- tions (Areas 1–3). Two constraints shown in Fig. 10 do not conform to the regional synthesis outlined above: (1) AFTA data in sample GC1113-43 (Precambrian) define an initial phase of cooling from >110°C, which began between 55 and 40 Ma. This falls between the two regional events that began at c. 60 Ma and c. 35 Ma. (2) The earliest cooling episode defined in sample GC1113-16 began between 210 and 160 Ma, which is just outside the 225–210 Ma timing derived from the majority of samples. These iso- lated examples most likely represent statistical outliers or may reflect the difficulty in resolving multiple cooling episodes within AFTA data in individual samples. Further sampling in the region may help to resolve these issues. We have allocated the timing constraints for individual samples to specific regional events, such that adjacent samples that show cooling from similar palaeotempera- tures with consistent timing constraints are interpreted as a common episode. We seek to minimise the total number of episodes required. In this way, samples with quite broad constraints can still be allocated to specific regional events. For example, samples GC1113-33 and -34 both cooled from palaeotemperatures >110°C, but while the timing constraint in sample –33 is quite well defined (140–60 Ma), the timing in sample –34 is only defined as >10 Ma. This is probably due to a combina- tion of the low apatite yield (nine ages) and the young age (c. 25 Ma), and as a result, only three track lengths were measured. Given the proximity of both these sam- ples, it seems reasonable to assume that both samples cooled in a common event, in this case the 60 Ma cool- ing episode. This illustrates how data with quite broad constraints can still provide useful conclusions. The results of this study could be interpreted in many different ways, and attempting to explain the data in terms of the smallest number of regionally synchronous cooling episodes may mask a more complex regional variation in thermal history. However, the synthesis https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 19 of 43 www.geusbul let in.org Fig. 10 Timing constraints on the onset of cooling for discrete cooling episodes derived from the AFTA in each outcrop sample. Thermal history solutions for each sample are listed in Table 3. Horizontal-shaded bars represent 95% confidence intervals on the time of cooling onset, as illustrated in Fig. 9. Samples are divided into six areas (Areas 1–6; Fig. 6). Assuming these results represent regionally synchronous cooling episodes, results across the entire region require seven separate episodes, as shown by vertical shaded columns. Constraints for the onset of each episode are listed at the bottom of the figure (see Table 4). Timing constraints for individual samples are assigned to a common regional event when adjacent samples cool from similar palaeotemperatures with consistent timings. In some cases, the estimated onset of cooling pre-dates the depositional age of the sample, indicating cooling of the apatites in sediment provenance regions prior to deposition in the host sample. 225–210295–290Onset of cooling (Ma): c. 35 15–8165–150 115–90 c. 60 GC1113-7 GC1113-1 GC1113-37 GC1113-32 GC1113-3 GC1113-5 GC1113-6 GC1113-9 GC1113-17 GC1113-23 GC1113-67 GC1113-65 GC1113-63 GC1113-24 GC1113-25 GC1113-58 GC1113-39 GC1113-38 GC1113-42 GC1113-54 GC1113-55 GC1113-21 GC1113-68 GC1113-64 GC1113-22 GC1113-10 GC1113-15 GC1113-16 GC1113-18 GC1113-60 GC1113-19 GC1113-29 GC1113-30 GC1113-33 GC1113-34 GC1113-36 GC1113-43 GC1113-44 GC1113-45 GC1113-59 Area 1 Area 2 Area 3 Area 4 Area 5 Area 6 GC1113-48 GC1113-46 GC1113-49 GC1113-50 GC1113-51 GC1113-52 GC1113-53 GC1113-61 GC1113-8 GC1113-62 050100150200250300350400 Time (Ma) Stratigraphic age Outlying value Onset of cooling in indidual sample Uncertain constraints Onset of cooling across the region https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 20 of 43 www.geusbul let in.org presented here provides a consistent framework for interpreting the underlying nature of each episode. As discussed earlier, it is important to remember that AFTA data in individual samples only reveal two or at best three dominant episodes, and in at least some of the samples described here, the results probably represent the unresolved effects of a larger number of episodes. It is also important to realise that AFTA only con- strains cooling from the palaeothermal peaks, and the thermal history in the interval between each cooling episode is not well constrained. A wide range of sce- narios can, therefore, be invoked, involving cooling and reheating to a subsequent palaeothermal peak or pro- longed stability between sequential cooling episodes. For all these reasons, definition of the thermal history in terms of a sequence of cooling episodes should be regarded as a general indication of the overall history, within the context of the cooling episodes defined from AFTA. 3.4 Regional variation in palaeothermal episodes Palaeotemperatures for six of the seven palaeothermal episodes identified are mapped in Fig. 10, excluding sam- ples from Area 6 in Fig. 6 (one episode is recognised only in a single sample from the region shown in Fig. 11). Here, we summarise the variation of palaeotemperatures in each episode and discuss the mechanisms responsible. Early Permian palaeotemperatures around 100°C or above, from which cooling began between 295 and 290 Ma, are identified in samples scattered across most of the study area, but predominantly in the interior away from the major fault zones (Fig. 11A). This is the earliest of the palaeothermal episodes recognised across the region, and as such, it is only recorded in areas where palaeo- temperatures in subsequent episodes have remained sufficiently low as to not overprint it. Locations record- ing this episode, therefore, represent relatively stable areas, which have undergone less post-Permian heating and cooling than the surrounding regions. None of the samples in the region preserve evidence of remaining at temperatures below 100°C prior to the early Permian times, emphasising the magnitude of post-Palaeozoic palaeothermal effects across the entire region. Late Triassic palaeotemperatures, from which cooling began between 225 and 210 Ma, occur predominantly in the centre of the study area and at south-eastern coastal locations (Fig. 11B). Maximum palaeotempera- tures in this episode are in excess of 110°C for two sam- ples in central locations and generally around 100°C or more on the south-eastern coast. As with the early Permian episode, Late Triassic cooling is only recorded in areas where palaeotemperatures in subsequent epi- sodes have remained sufficiently low as to not overprint evidence of this episode. Late Jurassic palaeotemperatures, from which cooling began between 165 and 150 Ma, are more variable than those in earlier events (Fig. 11C). Two samples cooled from >110°C in this episode, which will have removed any evidence of earlier episodes. Other samples cooled from palaeotemperatures generally between 80 and 100°C in this episode. The extent of this episode is simi- lar in broad terms to the early Permian and Late Triassic episodes but differs significantly from the three Ceno- zoic episodes. Only a single sample north of 79°N (Fig. 6) shows definite evidence of mid-Cretaceous cooling, which began between 115 and 90 Ma (GC1113-17, not shown in Fig. 11). However, this episode is also defined in samples to the south (Area 6; Fig. 10). Evidence of cooling at this time is widespread in North-East Green- land (Japsen et al. in press). Paleocene palaeotemperatures, from which cooling began at c. 60 Ma (Fig. 11D), are focussed almost exclu- sively within the HFFZ and the TLFZ, as well as a single sample from Kilen. End-Eocene palaeotemperatures, from which cool- ing began at c. 35 Ma, are recognised across almost the entire study area (Fig. 11E). Highest values (generally Table 4 Intervals defining the onset of episodes of cooling based on AFTA data in all samples and the possible origin of the cooling during each episode Onset of cooling (Ma) Onset of cooling (chronostratigraphy) Mechanism 295–290 Early Permian Regional uplift and erosion 225–210 Late Triassic Regional uplift and erosion 165–150 Late Jurassic Regional uplift and erosion 115–90 Mid-Cretaceous Regional uplift and erosion ~60 Mid-Paleocene Uplift and erosion related to compression in fault zones ~35 End-Eocene Regional uplift and erosion, locally enhanced heating 15–5 Middle to late Miocene Regional uplift and erosion Figure 10 displays the timing of onset of discrete cooling episodes in individual samples. Supplementary File S1 contains digital versions of Table 1 (sample details and additional information), Table 2 (AFTA data) and Table 3 (thermal history solutions). Supplementary File S2 contains Geotrack report with analytical details, basic AFTA data in individual samples and a discussion of thermal history solutions derived from AFTA data in each sample (Green 2014). https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 21 of 43 www.geusbul let in.org >110°C) are recognised not only in Peary Land, north of the HFFZ, but also at coastal locations south of the Wan- del Sea Basin; lower values around 60–70°C are iden- tified across the interior of the region. The dominance of this episode, and to some extent also the Paleocene episode, most likely masked the earlier episodes over much of the coastal region. The Permian and Triassic episodes are only recognised in regions where palaeo- temperatures in Palaeogene events were sufficiently low. On this basis, we suggest it is likely that these ear- lier episodes were also felt across the Wandel Sea Basin, similar to events recognised in North-East Greenland (Japsen et al. in press). Middle to late Miocene palaeotemperatures, from which cooling began between 15 and 5 Ma, are rec- ognised mainly at coastal and near-coastal locations (Fig. 11F), and generally at locations where palaeotem- peratures at 35 Ma were around 100°C or more. In sam- ples that cooled from lower palaeotemperatures at 35 Ma, it is likely that by 10 Ma, these locations had cooled to temperatures too low to be resolved from AFTA data. 4 Thermal history insights from maturity data A number of published studies provide further insights into the thermal history of the region. These are focussed mainly on thermal maturity studies, with some addi- tional information provided by studies of diagenetic and mineralogical properties of rocks. Here, we review these published data in light of the regional thermal history framework derived from AFTA in the previous section. The various datasets combined provide a broadly consistent picture of the thermo-tectonic development of the region. 4.1 Maturity of lower Palaeozoic strata Rasmussen & Smith (2001) sampled conodonts within the lower Palaeozoic rocks across Kronprins Christian Land (79–81°N) at the northernmost limit of the East Greenland Caledonides. They interpreted the conodont colour alteration index (CAI) to provide a measure of maximum burial temperature and, in turn, the thickness of overburden. The data showed a gradual and contin- uous increase across Kronprins Christian Land from CAI 3 (110–200°C) in the west to CAI 5+ (>300°C) in the east (Armstrong et al. 1994). They concluded that the pre- dominant process defining the regional variation was loading by Caledonian thrust sheets. Their modelling of the thickness of the removed overburden, based on a palaeogeothermal gradient of 28°C/km, suggested that it increased from 3.9 km in the west to a maximum of 12.5 km beneath a thrust sheet in the easternmost part of the area. Rasmussen & Håkansson (1996) reported a CAI value of 6 for one sample of Permian limestones from Prinsesse Ingeborg Halvø (360-550°C). The sample may thus have reached these palaeotemperatures at any time since the Permian. Paech & Estrada (2018) reported VR levels of 6.1-8.5% in rocks of probable Ordovician age in the Frigg Fjord and Kap Washington regions (Fig. 12), which indicate maximum palaeotemperatures >300°C. Our AFTA data provide no control on pre-Permian events, so no direct comparison with pre-Permian palaeothermal episodes is possible. However, early Permian cooling from >110°C (Fig. 11A) would be consistent with palaeotemperatures in excess of 110°C in the early Palaeozoic. 4.2 Maturity of Mesozoic–Palaeogene strata Published VR data for the Wandel Sea Basin region are summarised in Fig. 12. The data include (1) a compre- hensive study of the thermal maturity of Mesozoic and Palaeogene sediments from the Wandel Sea Basin, which overlaps with our study area (Paech & Estrada 2018); (2) a review of VR data (Håkansson et al. 1994) and (3) a recently published study of VR data from Kilen ( Pedersen et al. 2018) that were not included in the review by Paech & Estrada (2018). Maximum palaeotemperatures equiv- alent to the VR values in Fig. 12 are calculated based on the algorithm of Burnham & Sweeney (1989). Paech & Estrada (2018) observed that Mesozoic sequences attain high-maturity levels (VR mostly >2%; equivalent to >200°C) within prominent fault zones, including the KCTZ, HFFZ and TLFZ (Fig. 12). These higher maturity levels are typically associated with an increase in deformation intensity evidenced by the occurrence of a weak cleavage. In many cases, sedi- ments as young as Late Cretaceous show evidence of profound tectonism, including steep dips and faulting. Paech & Estrada (2018) also noted that the high VR (up to 5.4%) levels for the Kap Washington Group is asso- ciated with ductile deformation and magmatic activity. The maturity of Jurassic–Cretaceous sediments away from the major fault zones is relatively low, typically around 0.55% (c. 90°C), interpreted as reflecting heat- ing due to regional burial. Relatively flat-lying and undeformed Palaeogene units on, for example, Prinsesse Thyra Ø and in Depot- bugt (Croxton et al. 1980; Håkansson & Pedersen 2015), contrast markedly with nearby, often intensely deformed Upper Cretaceous units that variously show steep dips, folding, faulting and, in some cases, thrust- ing. This contrast is supported by a major difference in maturity levels, with VR values around 0.55% in Palaeo- gene units and 2% or more in Cretaceous units within the major fault zones. Paech & Estrada (2018), there- fore, concluded that the major phase of tectonism that resulted in such high maturity levels occurred around the Cretaceous–Cenozoic boundary. However, the https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 22 of 43 www.geusbul let in.org Ø Hovgaard 48 K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ TLFZ HFFZ KCTZ Holm Land A Palaeotemperature (°C) Ø Hovgaard 48 K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ TLFZ Holm Land B Palaeotemperature (°C) 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N Early Permian (295–290 Ma) Late Triassic (225–210 Ma) Fig. 11 Palaeotemperatures derived from AFTA. A: Early Permian (295–290 Ma). B: Late Triassic (225–210 Ma). C: Late Juras- sic (165–150 Ma). D: Paleocene (c. 60 Ma). E: End-Eocene (c. 35 Ma). F: Middle to late Miocene (15–5 Ma). Palaeotemperature for the mid-Cretaceous episode (115–90 Ma) is not shown as only one sample falls within the map frame. The small arrow in the lower right corner of A, E and F indi- cates sample GC1113-48, which is located just south of the figure frame. Geology legend in Fig. 4. Numbers next to AFTA samples denote sample numbers. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. maturity of the Palaeogene units is very similar to those in Mesozoic units away from the fault zones, and Palaeo- gene units do not occur within the zones of intense tec- tonism. It is, therefore, possible that the regional base level of maturity reflects heating after deposition of the Thyra Ø Formation. Extremely high maturity levels (>7%) were reported in the Upper Cretaceous Nakkehoved Formation exposed on the north coast of Kronprins Christian Land (Håkansson et al. 1994), corresponding to maxi- mum palaeotemperatures well above 250°C (the limit at which palaeotemperatures can be calculated by VR). https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 23 of 43 www.geusbul let in.org Ø Hovgaard 48 K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ TLFZ Holm Land Herluf Trolle Land C Palaeotemperature (°C) Ø Hovgaard 48 K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ Nakkehoved Kilen Herluf Trolle Land TLFZ D Palaeotemperature (°C) 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N Paleocene (c. 60 Ma) Late Jurassic (165–150 Ma) Quartz veins containing fluid inclusions with homo- genisation temperatures of 197–236°C were formed during the thermal event, which was interpreted to have been short-lived and to have occurred at shallow burial depths (Håkansson et al. 1994). Samples of the Nakkehoved Formation showed diagenetic clay assem- blages defining a low-grade greenschist metamorphic fabric, consistent with heating to palaeotemperatures of 200–300°C or above. Palynology studies also indi- cate a high degree of thermal alteration, consistent with such palaeotemperatures. Håkansson et al. (1994) found it unlikely that the thermal influence came from magmatic activity, in part due to the total absence of accessory minerals in the quartz veins. Paech & Estrada Fig. 11 (Continues) Palaeotemperatures derived from AFTA. A: Early Permian (295– 290 Ma). B: Late Triassic (225–210 Ma). C: Late Jurassic (165–150 Ma). D: Paleocene (c. 60 Ma). E: End-Eocene (c. 35 Ma). F: Mid- dle to late Miocene (15–5 Ma). Palaeotem- perature for the mid-Cretaceous episode (115–90 Ma) is not shown as only one sam- ple falls within the map frame. The small arrow in the lower right corner of A, E and F indicates sample GC1113-48, which is located just south of the figure frame. Geology legend in Fig. 4. Numbers next to AFTA samples denote sample numbers. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 24 of 43 www.geusbul let in.org Ø Hovgaard K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ Nakkehoved Kilen KR Herluf Trolle Land Pr.T.Ø TLFZ Holm Land E Palaeotemperature (°C) Ø Hovgaard K R O N P R I N S C H R I S T I A N L A N D P E A R Y L A N D TLFZ HFFZ KCTZ Nakkehoved Kilen Herluf Trolle Land F Palaeotemperature (°C) 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N 10°W15°W20°W25°W30°W35°W40°W 83 °N 82 °N 81 °N 80 °N End-Eocene (c. 35 Ma) Middle to late Miocene (15–5 Ma) (2018) attributed the intense heat to the development of a plate boundary between north-eastern Greenland and Svalbard since the Oligocene. However, why that event should be localised to Nakkehoved is unclear. The profound changes in temperature over a short distance around Nakkehoved are unlikely to be due to differences in heat flow but are more likely to reflect localised heating or differential exhumation (for further discussion, see Section 4.3.1). Håkansson et al. (1994) reported a VR value of c. 2% in a sample of the Thyra Ø Formation from Prinsesse Mar- grethe Ø, which indicates intense heating of this sam- ple after deposition, specifically in post-Paleocene times (Håkansson et al. 1994). This observation, together with Fig. 11 (Continues) Palaeotemperatures derived from AFTA. A: Early Permian (295– 290 Ma). B: Late Triassic (225–210 Ma). C: Late Jurassic (165–150 Ma). D: Paleocene (c. 60 Ma). E: End-Eocene (c. 35 Ma). F: Mid- dle to late Miocene (15–5 Ma). Palaeotem- perature for the mid-Cretaceous episode (115–90 Ma) is not shown as only one sam- ple falls within the map frame. The small arrow in the lower right corner of A, E and F indicates sample GC1113-48, which is located just south of the figure frame. Geology legend in Fig. 4. Numbers next to AFTA samples denote sample numbers. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 25 of 43 www.geusbul let in.org the extreme VR values of Upper Cretaceous sediments around Nakkehoved, led Håkansson & Pedersen (1982, 2001) to argue for a short-lived ‘post-Paleocene thermal event’. However, this VR value was based on only a small number of measurements and was considered to be unreliable (Paech & Estrada 2018). VR values between 0.5 and 1.19% reported by Peder- sen et al. (2018), mainly from the southern part of Kilen, indicate maximum palaeotemperatures of 83–155°C. Just one value lies outside this range (2.57%; 210°C) for Cretaceous formations that have been thrusted and folded in large open folds. These maturity data were inter- preted in terms of large-scale folds with higher palaeo- temperatures in anticlines, lower palaeotemperatures in synclines and an overall warming-northwards trend from the coastal zone of Kilen to inland areas (Pedersen et al. 2018). This suggests that the Mesozoic parts of the Wandel Sea Basin and Kilen represent Late Cretaceous rift basins that subsequently underwent north–south compression (Svennevig et al. 2016). Pedersen et  al. (2018) modelled the pre-folding position of the strata and maturity data along a 9 km long river section, which cuts large-scale folds and thrusts in the southern part of Kilen. This was possible due to the moderate matu- rity along the section (VR between 0.5 and 1.2%) and the consequent limited thermal alteration of, for example, dinocysts, which ensured a good biostratigraphic con- trol. Structural restoration along the section revealed K R O N P C H R I S T I A N L A N D Kilen Ø Hovgaard N D 48 10°W 83 °N 82 °N 81 °N 80 °N 15°W20°W25°W30°W35°W40°W 15°W20°W25°W30°W35°W Pr.T.Ø Pr.M.Ø Pr.D.Ø Depotbugt Nakkehoved KCTZ HFFZ TLFZ TLFZ EG FZKK RRR OOOO N PP CC H R I S T I A N L A N D Kilen NNN DD T.ØPr.T.PPr.T. M.ØMPr.MM Ør.D.ØPr.Dr.D.Ø DepotbugtDepotbuDepotbu Nakkehoved KCTZZZ HFFZHHFFF Z TLFZLFTLFZ TLFZ EGEGEG F G FZFZ EG FFZ Paleocene–Eocene sediments Upper Cretaceous sediments Jurassic–Cretaceous sediments Equivalent palaeotemperature195°C 2.6% 2.6% 2.6% Source of VR dataA, B, C Number of samples(11) VR data Paleocene–Eocene sediments Upper Cretaceous sediments Kap Washington Group Jurassic–Cretaceous sediments Fault Dykes, mostly Upper Cretaceous Sedimentary outlier 3.2% (19) A 230°C 2.1% (7) A 195°C 1.3–2.9% (22) A 150–195°C 0.55% (12) A 90°C 1.6–2.0% (21) A 175–190°C 2.05% (1) C 90°C 0.4% (2) C 66°C 0.45% (1) C 76°C 0.36–0.51% (3) C 59–84°C 0.55% (31) A 90°C 0.5–2.26% (39) B 83–210°C 9.9% (1) C >250°C 7.1% (1) C >250°C 9.4% (1) C >250°C 7.4% (1) C >250°C 2.6–5.4% (3) A >200°C Fig. 13 Fig. 15 Fig. 14 100 km500 Fig. 12 Published vitrinite reflectance (VR) values from Mesozoic and Palaeogene units of the Wandel Sea Basin. Coloured boxes: VR values and corresponding maximum palaeotemperatures (Burnham & Sweeny 1989). Source of VR data indicated by letters A: Paech & Estrada (2018), B: Pedersen et al. (2018), C: Håkansson et al. (1994). When values are available from multiple sources, those from Paech & Estrada (2018) are shown. Pr.D.Ø: Prinsesse Dagmar Ø. Pr.M.Ø: Prinsesse Margrethe Ø. Pr.T.Ø: Prinsesse Thyra Ø. Detail of Kilen in Fig. 15. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 26 of 43 www.geusbul let in.org a deeper pre-deformation burial of the northern area, which Pedersen et al. (2018) interpreted as rift-related maximum burial after the Santonian, which is the age of the youngest sediments on Kilen (Hovikoski et al. 2018). The subsequent folding and thrusting that occurred during basin inversion were assumed by Pedersen et al. (2018) to be of the Paleocene–Eocene age. 4.3 Comparison of AFTA and VR data In this study, we compare thermal history interpreta- tions from AFTA and VR data in Mesozoic and Palaeo- gene units in the region from Herluf Trolle Land to Kronprins Christian Land (Figs. 12–15). This area is cho- sen because variation in VR levels across the region, combined with the thermal history solutions from AFTA, provides key insights into the mechanisms responsible for the observed maturity levels. Thermal history con- straints for Cenozoic palaeothermal episodes derived from AFTA and VR data are shown in Figs. 13–15. These figures do not show the Mesozoic cooling events iden- tified from AFTA, as the VR data are measured in units which post-date these events, and because the AFTA results show that three Cenozoic events dominate the thermal history of this region (Fig. 10). 4.3.1 Northern Peary Land In northern Peary Land, a small number of samples close to the HFFZ cooled below c. 110°C in the Paleocene event (Fig. 12). However, most samples in this region cooled below c.110°C in the end-Eocene event. Given that some samples appear to have cooled in both epi- sodes, it seems likely that samples that cooled below c. 110°C at c. 35 Ma also cooled at 60 Ma, but remained at, or were reheated to palaeotemperatures >110°C until cooling that began at the end of the Eocene. It is possible that cooling from palaeotemperatures of c. 200°C, rep- resented by the higher VR values in the region between the KCFZ and HFFZ, may have begun prior to 60 Ma in a separate event, which cannot be resolved from the AFTA data. However, the simplest interpretation is that cool- ing from c. 200°C in northern Peary Land began in the regional Paleocene episode at c. 60 Ma. 4.3.2 Herluf Trolle Land The mean VR value of 0.55% from Paech & Estrada (2018) in 12 Lower Cretaceous samples from southern Herluf Trolle Land indicates a maximum palaeotemperature of c. 90°C (Fig. 13). Paech & Estrada (2018) considered this level of maturity to be the regional ‘background’ level away from major fault systems and interpreted it to reflect the earlier presence of a considerable overbur- den across the region. AFTA data in samples GC1113-63 and -64, from this area (south-west of fault F in Fig. 13), reveal end-Eocene palaeotemperatures of 75–90°C and 70–80°C, respectively, from which cooling began at c. 35 Ma. Samples GC1113-21 and -22, also south of fault F, define similar end-Eocene palaeotemperatures. These end-Eocene palaeotemperatures from AFTA are broadly consistent with the maximum palaeotempera- tures around 90°C, indicated by the VR data in nearby Upper Jurassic – Lower Cretaceous units (Paech & Estrada 2018). This consistency suggests that VR values reflect maximum paleotemperatures in the end-Eocene episode. We, therefore, interpret maximum palaeotem- peratures of 75–90°C, as defined from AFTA and VR in this region, to primarily reflect deeper burial prior to exhumation, which began at the end of the Eocene. These values are relatively uniform over a wide area. In contrast, VR values up to 3% in the Upper Creta- ceous Herlufsholm Strand Formation from northern Herluf Trolle Land indicate maximum palaeotempera- tures at around 150–200°C within the prominent fault zone (Fig. 13). AFTA data from this region provide consis- tent evidence of palaeotemperatures >100°C from which cooling began in the Paleocene at c. 60 Ma (GC1113-15, -59, -67 and -68). As all tracks were totally annealed prior to cooling that began at c. 60 Ma, AFTA data in these samples define only lower limits to the maximum palae- otemperature, and direct comparison with the VR data is not possible. The most straightforward interpretation is that cooling from a palaeotemperature of c. 200°C, as indicated by the VR data, began at c. 60 Ma. Furthermore, mid-Paleocene palaeotemperatures are strongly con- trolled by the faults of the TLFZ (Fig. 13; Paech & Estrada 2018). Samples to the north-east of fault F cooled at c. 60 Ma (GC1113-15, -23, -59, -67, -68), whereas samples to the south-west of that fault do not show any evidence of this event (GC1113-21, -22, -63, -64). AFTA data from the five samples north-east of fault F also show evidence of cooling beginning at 35 Ma from palaeotemperatures of c. 80–90°C, similar to those defined from AFTA in the four southern samples, and thus, providing further evi- dence that this episode represents relatively uniform regional exhumation. 4.3.3 East of Herluf Trolle Land The mean VR value of 0.55% in 31 Palaeogene samples from Prinsesse Thyra Ø corresponds to a palaeotem- perature of c. 90°C (Fig. 14). VR data in three samples of Palaeogene age from Prinsesse Ingeborg Halvø on Kronprins Christian Land, as well as a Lower Creta- ceous sample from Kap Rigsdagen, define maximum palaeotemperatures of 66–90°C. These are consistent with maximum post-depositional palaeotemperatures of 20–75°C and 80–90°C derived from AFTA data in samples GC1113-9 and -10, respectively. These palaeo- temperatures are again attributed to the end-Eocene palaeothermal episode and are consistent with the https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 27 of 43 www.geusbul let in.org values from Herluf Trolle Land that are also attributed to deeper burial prior to regional exhumation, which began at c. 35 Ma. Along the north coast of Kronprins Christian Land and in parts of Kilen, VR reaches very high values in sam- ples of Cretaceous age: 1. Around Nakkehoved, VR values for Upper Creta- ceous units of 7-10% indicate maximum palaeo- temperatures in excess of 250°C (Fig. 14). AFTA data in sample GC1113-55, also from Nakkehoved, indicate that cooling from >125°C began between 101 and 48 Ma. The simplest interpretation is that these values represent the Paleocene (c. 60 Ma) palaeothermal episode. 2. In 21 samples from inland Kilen, VR values are in the range of 1.6-2% (equivalent to c. 174°C and 200°C, respectively; Fig. 15). AFTA data in sam- ple GC1113-58 from this area also define cooling from >120°C, which began between 60 and 45 Ma, supporting that these elevated maturity lev- els reflect the palaeothermal episode at 60 Ma. However, AFTA data in nearby sample GC1113-1 define cooling from >130°C between 45 and 25 Ma, which we attribute to the cooling episode that began at the end of the Eocene. It could be that this sample initially underwent Paleocene cool- ing from a higher palaeothermal maximum, and then remained at >130°C until further cooling in the end- Eocene episode. In any event, the more recent episode was clearly more pronounced in sample GC1113-1 compared with sample GC1113- 58. The higher end-Eocene palaeotemperature Quaternary cover U. Cretaceous (Herlufsholm Strand Fm) U. Jurassic – L. Cretaceous (Ladegårdsåen Fm) Triassic (Trolle Land Gp) Permian (Midnatsfjeld, Kim Fjelde Fms) Carboniferous (Foldedal Fm) Silurian (Peary Land Gp) Proterozoic rocks Ice Fault Sea and lake Herlufsholm Strand Herlufsholm Strand fs 70–80°C, 35–0 Ma 75–80°C, 140–25 Ma 15–75°C, 35–0 Ma 85–95°C, 75–35 Ma 25–50°C, 20–0 Ma 85–100°C, 55–10 Ma 22 21 63 64 AFTA sample without 60 Ma event >100°C, 70–20 Ma >105°C, 70–40 Ma 55–50°C, 35–10 Ma >130°C, 65–45 Ma 95–105°C, 45–35 Ma 30-65°C, 35–5 Ma >120°C, 60–45 Ma 76–103°C, 48–26 Ma 25–72°C, 31–8 Ma >100–105°C, 125–30 Ma 20–95°C, 60–0 Ma >100–105°C, 90–60 Ma 68–85°C, 45–15 Ma 67 59 5 68 23 65 AFTA sample with 60 Ma event 1.3–2.9% (22) A 150–195°C 0.55% (12) A 90°C Fault F Herluf Trolle Land 20°W 82 °4 5’ N 82 °3 0’ N 21°W22°W23°W 5 km0 Fig. 13 Cenozoic palaeothermal constraints for Herluf Trolle Land. Heating during the Paleocene event (c. 60 Ma) is controlled by the numerous faults belonging to the Trolle Land Fault Zone, as suggested by Paech & Estrada (2018). Only samples north-east of ‘Fault F’ were affected by the Paleocene thermal event. White boxes: Thermal history solutions from AFTA data; colour coding as in Fig. 10. Coloured boxes: VR values and corresponding maximum palaeotemperatures from adjacent samples; see Fig. 12. Source of VR data indicated by letter A: Paech & Estrada (2018). Map location indicated in Fig. 12. Basemap modified from Bjerager et al. (2019). https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 28 of 43 www.geusbul let in.org in sample GC11113-1 emphasises the complex nature of the underlying thermal history and high- lights the need for further studies in this region. 3. In more coastal areas of Kilen, VR values for the Cretaceous sediments are high and quite vari- able across the region (most values between 0.5 and 1.19%, equivalent to 83–155°C; Fig. 15). The variation in VR values was attributed to differing amounts of burial prior to exhumation due to basin inversion of ‘presumed Paleocene–Eocene age’ (Pedersen et al. 2018). The only direct com- parison between AFTA and VR data in this region is sample GC1113-25, which cooled from >100°C between 65 and 10 Ma. We attribute this to the Paleocene palaeothermal episode from which cooling began at c. 60 Ma. This is again consistent with the timing of cooling from extreme palaeo- temperatures, which is indicated by the elevated VR levels further north in Nakkehoved. Given the considerable variation in VR values along the western margin of Kilen and the lack of AFTA data from this region, it is not possible to draw any con- clusions regarding the timing of cooling there. AFTA data in samples GC1113-8 and -60, from Amdrup Land, south of Kilen, define maximum post-Ju- rassic palaeotemperatures of c. 55–75°C (Fig. 14), which is attributed to the end-Eocene (c. 35 Ma) episode. These palaeotemperatures are similar to those derived from AFTA and VR data obtained from areas to the north – away from areas of significant deformation – and pro- vide further evidence of relatively uniform deeper burial across the region prior to the onset of exhumation at the Eocene–Oligocene boundary. 4.4 Synthesis Elevated VR values (1.5–3%; equivalent to 150–225°C) in Mesozoic units within the major fault zones from north- ern Peary Land to Kronprins Christian Land represent a mid-Paleocene palaeothermal maximum from which D Ø Hovgaard P E A R Y L A N D 48 83 °N 82 °N 81 °N 80 °N 15°W20°W 10°W15°W20°W 81 °N 82 °N TLFZ D TLFZ AFTA sample 40 km0 >120°C, 101–48 Ma 86–106°C, 56–15 Ma 36–81°C, 20–0 Ma 55 20–75°C, 45–0 Ma 80–90°C, 60–0 Ma 910 8 60 45–75°C, 50–0 Ma 55–75°C, 70–15 Ma 2.05% (1) C 90°C 0.36–0.51% (3) C 59–84°C Fig. 13 Prinsesse Thyra Ø Kap Rigsdagen Amdrup Land Nakkehoved Fig. 15 0.4% (2) C 66°C 0.55% (31) A 90°C 7.1% (1) C >250°C Fig. 14 Cenozoic palaeothermal con- straints east of Herluf Trolle Land. White boxes: thermal history solutions from AFTA, colour coding as in Fig. 10. Coloured boxes: VR values and corre- sponding maximum palaeotempera- tures from adjacent samples, colour coding as in Fig. 12. Source of VR data indicated by letters A: Paech & Estrada (2018), C: Håkansson et al. (1994). Solid black lines: faults. Map location indi- cated in Fig. 12. Detail of Kilen in Fig. 15. Key to bedrock geology and other abbreviations in Fig. 4. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 29 of 43 www.geusbul let in.org cooling began at c. 60 Ma. In contrast, lower VR values (c. 0.55%, equivalent to c. 90°C), in Mesozoic and Palaeo- gene units located away from zones of major deforma- tion, represent the end-Eocene palaeothermal episode from which cooling began at c. 35 Ma. AFTA data from the zones of deformation also show evidence of cool- ing, which began at this time from palaeotemperatures of c. 80–90°C, thus, emphasising the regional nature of  this episode, although end-Eocene palaeotempera- tures were higher in Peary Land north of the HFFZ (see Section 5.2.2). A major exception to this regional pattern occurs on the north coast of Kronprins Christian Land around Nakkehoved. Extremely high VR values between 7 and 10% in samples of Upper Cretaceous sediments indi- cate maximum palaeotemperatures greater than 250°C. AFTA data in the only sample from this region indicate that cooling from >125°C began in the Paleocene or possibly earlier, since results provide only minimum palaeotemperature estimates. This event may, there- fore, have been synchronous with Paleocene cooling in the fault zones, or may have been earlier and, as the event affected Upper Cretaceous sediments, it must have happened in Late Cretaceous or Paleocene times. AFTA data in sample GC1113-1 from Kilen define cool- ing from >130°C during the end-Eocene cooling episode, suggesting some variation in the magnitude of this epi- sode. The VR value of c. 2% in a sample of Palaeogene age on Prinsesse Margrethe Ø may also reflect the higher end-Eocene palaeotemperature in sample GC1113-1 (note the earlier comments regarding the uncertainty associated with this VR value). We suggest that exhumation that began in the mid-Paleocene represents the inversion of the fault zones, while exhumation that began at the end of the Eocene was regional and primarily represents burial followed by uplift and erosion However, there is also evidence of end-Eocene palaeotemperatures that were 81°10’N 81°05’N 13°W13°30’W Anduin Gåseslette Tågekyst Sølverbæ k K a n g o q R y g Sølverbæk : KR KR KR KR KR KR Sb Q KR Tk? Tk Tk Sb?Sb Sb Sb 5 km Hut and landing strip Iskap Sølverbæk Fm, Quarternary Ice Sea and lake undivided Kangoq Ryg Mb (Galadriel Fjeld Fm) Tågekyst Mb (Galadriel Fjeld Fm) U pp er C re ta ce ou s Sb KR Tk Lo w er C re ta ce ou s AFTA sample >120°C, 60–45 Ma 76–103°C, 48–26 Ma 25–72°C, 31–8 Ma >130°C, 45–25 Ma >100°C, 65–10 Ma 58 25 1 0.66% B 109°C 2.57% B 210°C 0.72% B 118°C 0.92% B 137°C 1.04% B 145°C 0.96–1.05% B 140–145°C 0.78–1.19% B 125–155°C 0.55–0.70% B 91–116°C 0.50–0.60% B 83–99°C 0.58% C 95°C Fig. 15 Palaeothermal constraints for south-east Kilen. The palaeotemperature constraints from VR are consistent with those from AFTA, but the timing constraints on the onset of cooling vary. White boxes: thermal history solutions from AFTA, colour coding as in Fig. 10. Numbers next to AFTA samples denote sample numbers. Blue boxes: VR values and associated maximum palaeotempera- tures for Cretaceous sediments. Source of VR data indicated by letters B: Pedersen et al. (2018) and C: Håkansson et al. (1994). Map location in Fig. 14. Base map modified from Hovikoski et al. (2018, Fig. 4) where further details of the map are explained. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 30 of 43 www.geusbul let in.org higher than the regional, uniform magnitude, for exam- ple, sample GC1113-1 from Kilen and the possibly highly mature Thyra Ø Formation on Prinsesse Margrethe Ø. The extreme palaeotemperatures focussed along the north coast of Kronprins Christian Land were likely reached during the Late Cretaceous or Paleocene times. 5 Geological controls on the cooling episodes identified from AFTA In this section, we compare AFTA and VR results with evidence from the stratigraphic record to investigate the geological processes responsible for the cooling epi- sodes identified in the Wandel Sea Basin (Fig. 16). We also compare these cooling episodes with studies from cen- tral West Greenland and North-East Greenland (Fig. 17; Japsen et al. 2006, in press) and illustrate the heating and cooling (burial and exhumation) history, with examples based on samples that provide stratigraphic constraints on the age of removed sections (Fig. 18). 5.1.Palaeozoic–Mesozoic cooling events 5.1.1 Early Permian episode The early Permian cooling episode (beginning between 295 and 290 Ma) recognised from AFTA data in samples across the study area corresponds to the base-Permian hiatus identified across the basin between the middle– upper Permian Kim Fjelde Formation and the upper Carboniferous Foldedal Formation (Fig. 16; Stemmerik et al. 1998). We, therefore, interpret early Permian cool- ing as reflecting a major phase of exhumation, follow- ing deeper burial. For example, sample GC1113-63, a Silurian sandstone from Herluf Trolle Land, cooled from an early Permian palaeotemperature of c. 100°C, corre- sponding to burial below a cover of Silurian to Carbonif- erous rocks with a thickness of 2.7 km (30°C/km, 20°C at the surface). The timing of this cooling episode is close to that of the late Carboniferous episode identified in North-East Greenland (beginning between 320 and 300 Ma), which also correlates with a regional latest Carbon- iferous to mid-Permian unconformity (Surlyk 1990). It is, therefore, possible that these episodes reflect the same tectonic event (Fig. 17). It is not possible to define any pre-Permian cooling from the AFTA data, and therefore, it is not possible to use AFTA data to discriminate the thermal histories for upper and lower Carboniferous strata on Holm Land based on maturity data, as in Stem- merik et al. (1998). 5.1.2 Late Triassic episode The Late Triassic cooling episode (beginning between 225 and 210 Ma) is identified from AFTA data away from the northern coastal regions. The onset of cooling in this episode could correspond to the older hiatus between the Upper Triassic Sortekløft Formation and the Middle Triassic Dunken Formation, identified on Herluf Trolle Land by Bjerager et al. (2019; Fig. 16). In Kilen, the epi- sode corresponds to the inferred hiatus between the Middle Jurassic Mågensfjeld Formation and the Middle Triassic Isrand Formation (Alsen et al. 2017; Hovikoski et al. 2018; Svennevig et al. 2018). Sample GC1113- 18 of upper Carboniferous Kap Jungersen Formation exposed on Holm Land reached a palaeotemperature above 100°C prior to Late Triassic cooling (Fig. 18A). This palaeotemperature corresponds to burial below a cover of Carboniferous to Triassic sediments, with a thickness exceeding 2.7 km (30°C/km, 20°C at the surface). The Late Triassic episode in the Wandel Sea Basin coincides with the Late Triassic episode in West Greenland, but slightly post-dates a Middle Triassic episode of cooling and exhumation in North-East Greenland (Fig. 17), sug- gesting a possible lag between events in the two areas. 5.1.3 Late Jurassic episode The Late Jurassic cooling episode (beginning between 165 and 150 Ma) is recognised in samples away from the northern coasts and in one sample from Herluf Trolle Land. The onset of cooling in this episode corresponds to the hiatus between the Upper Jurassic – Lower Creta- ceous Ladegårdsåen Formation and the Upper Triassic Sortekløft Formation on Herluf Trolle Land (Håkans- son & Pedersen 2015; Bjerager et al. 2019; Fig. 16). We interpret this cooling episode as exhumation following deeper burial. According to Håkansson & Pedersen (2015), the base of Ladegårdsåen Formation is mid- dle Oxfordian in age (c. 160 Ma), which constrains the onset of Late Jurassic cooling to between 165 and 160 Ma, at the Middle–Late Jurassic transition (Callovian– Oxfordian). This agrees well with the Callovian–Oxford- ian hiatus between the Birkelund Fjeld and Mågensfjeld Formations observed in Kilen (Hovikoski et al. 2018). The temporal overlap between the Late Jurassic epi- sode and the Callovian–Oxfordian hiatus across most of the basin indicates that the cooling episodes involved exhumation. For example, sample GC1113-22 from Her- luf Trolle Land of Lower Triassic sandstone reached a palaeotemperature above 115°C prior to Late Jurassic cooling (Fig. 18B). This corresponds to burial below a cover of Triassic to Middle Jurassic sediments, with a thickness exceeding 3 km (30°C/km, 20°C at the sur- face). The Late Jurassic episode that affected the Wan- del Sea Basin coincides with the Late Jurassic episode that affected West Greenland, but it began after the Early Jurassic episode of cooling and exhumation in North-East Greenland (Fig. 17). As this delay of about 20 Myr is consistent with the delay of the Triassic epi- sode in North-East Greenland compared with western and northern Greenland, it seems likely to represent https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 31 of 43 www.geusbul let in.org Is ra nd Kap JungersenKap Jungersen PB Sortebakker MågensfjeldMågensfjeld Herlufsholm Strand La de gå rd så en Sølverbæk ??? ??? Thyra Ø KW Nakkehoved ld d lFoldedal Kim Fjelde Lichenrygyg enDunken Storekløft elddeMidnatsfje G al ad ri el F je ld BF Dd KlKlKl Peary Land K.C. Land Wandel Sea Basin j Channel fills Marine mudstone Marine carbonate Marine sandstone Sedimentary environments Horizontal shading Lithological symbols Coal layers Sandstone Siltstone Mudstone/shale Organic rich mudstone/shale Limestone Fluvial, lacustrine Extrusive igneous rocks Volcanics, volcanoclastics Evaporites Conglomerate Legend Time interval during which cooling began Ma Era Stage/ Age Eocene Oligocene Miocene Pliocene Pleistocene Series/ Epoch Sys- tem/ Period Middle Middle Lower Upper Guadalupian Lopingian Lower Lower Middle Mississippian Upper Mississippian Lower Penns. Middle Penns. Upper Penns. Cisuralian Lower Mississippian Langhian Aquitanian Chattian Rupelian Priabonian Bartonian Lutetian Thanetian Selandian Danian Maastrichtian Campanian Santonian Coniacian Aptian Hauterivian Valanginian Berriasian Tithonian Bathonian Bajocian Aalenian Pliensbachian Sinemurian Hettangian Carnian Ladinian Anisian Olenekian Induan Rhaetian Roadian Wordian Capitanian Wuchiapingian Changhsingian Kungurian Artinskian Asselian Gzhelian Kasimovian Moscovian Bashkirian Serpukhovian Visean Tournaisian Barremian Toarcian Ypresian Burdigalian PA LA EO ZO IC M ES O ZO IC C EN O ZO IC N EO G EN E PA LA EO G EN E C RE TA C EO U S JU RA SS IC TR IA SS IC PE RM IA N C A RB O N IF ER O U S Sakmarian Upper Kimmeridgian Oxfordian Albian Cenomanian Turonian SerravallianSerravallian Tortonian Messinian Upper Norian Paleocene Callovian 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 Fig. 16 Comparison between the regional cool- ing episodes identified from AFTA (Table 4) and the stratigraphic scheme for the Wandel Sea Basin (Fig. 5). The thickness of the horizon- tal, coloured bars indicates the interval during which the cooling began in each episode. a protracted tectonic development between the two areas. 5.1.4 Mid-Cretaceous episode The mid-Cretaceous cooling episode (beginning between 115 and 90 Ma) is identified in only one sample within the Wandel Sea Basin. The episode corresponds to an Aptian to Turonian hiatus on Herluf Trolle Land between the Upper Cretaceous (Turonian–Coniacian) Herlufsholm Strand Formation and the Upper Juras- sic – Lower Cretaceous (Oxfordian–Barremian) Lade- gårdsåen Formation (Fig. 16) (Håkansson & Pedersen 2015; Piasecki et al. 2018). In Kilen, Hovikoski et al. (2018) marked a possible late Albian to Cenomanian hiatus between the Galadriel Fjeld and Sølverbæk formations in the Kilen Fjelde area. The temporal overlap between this hiatus and the mid-Cretaceous cooling episode suggests that cooling involved exhumation following deeper burial. The mid-Cretaceous episode of uplift and erosion postdates the Barremian unconformity (c. 135 Ma), which resulted from HALIP-related regional uplift and is recorded by stratigraphic and palaeo-environmental changes on Peary Land and on Kilen (Ineson et al. 2020). It is possible that the effects of the Barremian episode overlaps with those of the mid-Cretaceous event as the https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 32 of 43 www.geusbul let in.org Fig. 17 Timing of regional, post-Devonian episodes of uplift and erosion in three regions of Greenland estimated from AFTA. A: Central West Greenland (Japsen et al. 2006, 2009). B: Eastern North Greenland (Table 4; this study). C: North-East Greenland (Japsen et al. in press). Break-up west of Greenland took place in mid-Paleocene (c. 62 Ma), but sea-floor spreading ceased there by the end of the Eocene. In contrast, the opening of the North-East Atlantic, east of Greenland, began at the Paleocene–Eocene tran- sition (c. 56 Ma) and is still ongoing (Chalmers & Pulvertaft 2001; Oakey & Chalmers 2012; Gaina et al. 2017). The Fram Strait between Greenland and Svalbard opened in early Miocene (c. 20 Ma; Jokat et al. 2016). L: Late. E: Early. M: Middle. C: Carboniferous. Pe: Permian. Tr: Triassic. J: Jurassic. Kl: Lower Cretaceous. Ku: Upper Cretaceous. Pal: Paleocene. Eo: Eocene. Oli: Oligocene. Mio: Miocene. Pl: Pliocene. Q: Quaternary. 30 0 20 0 10 0 65 60 40 20 0 30 0 20 0 10 0 65 60 40 20 0 Central West Greenland North-East Greenland 30 0 20 0 10 0 65 60 40 20 0 Eastern North GreenlandA B C M.–L. Miocene (15–5) End–Eocene (c. 35) L. Jurassic (165–150) L. Triassic (225–210) E. Permian (295–290) Paleocene (c. 60) M. Cretaceous (115–90) Break-up Q Pl Mio Oli Eo Pal Ku Kl J Tr Pe C Q Pl Mio Oli Eo Pal Ku Kl J Tr Pe C Q Pl Mio Oli Eo Pal Ku Kl J Tr Pe C Time interval during which cooling began (7–2) Onset of cooling (Ma) from AFTA Ti m e (M a) Eocene–Oligocene (36–30) (Reburial) L. Miocene (11–10) L. Neogene (7–2) Break-up L. Jurassic (160–150) L. Triassic (230–220) E. Pliocene (c. 5) L. Miocene (c. 10) End–Eocene (37–35) Break-up E. Jurassic (c. 180) M. Trassic (c. 240) E. Cretaceous (145–140) M. Cretaceous (95–90) L. Carboniferous (320–300) one sample within the Wandel Sea Basin, which has been assigned to the latter event cooled between 155 and 50 Ma. The onset of cooling in this episode coincides with a mid-Cretaceous episode in North-East Greenland (Fig.  17), which represents an episode of regional exhumation (Japsen et al. in press). We, therefore, suggest that both areas were affected by exhumation at 95–90 Ma. 5.2 Cenozoic cooling episodes 5.2.1 Mid-Paleocene episode The mid-Paleocene cooling episode (beginning c. 60 Ma) recorded in samples from coastal and near-coastal locations corresponds to the hiatus between the upper Paleocene – lower Eocene Thyra Ø Formation and Upper Cretaceous strata (e.g. Santonian Sølverbæk Formation in Kilen; Fig. 16). The study results from the HFFZ and the TLFZ reveal Paleocene cooling from >110°C, which began at c. 60 Ma. We interpret this cooling in terms of exhumation following deeper burial (Fig. 11D). This event is also inferred to have affected northern Peary Land in the region between the KCTZ and HFFZ where high end-Eocene palaeotemperatures dominate. As discussed in Section 4.3.3, AFTA and VR data from Kilen and northern Herluf Trolle Land indicate that cooling from a maximum post-depositional palaeotem- perature of up to 200°C within major fault zones also began during the Paleocene (c. 60 Ma) palaeothermal episode. The results of this study support the inter- pretation of Pedersen et al. (2018), according to which the high maturity of sediments in the southern part of Kilen was reached during the maximum burial prior to post-Coniacian basin inversion in response to a strong compressional event. For example, sample GC1113-58 of Lower Cretaceous Lichenryg Formation exposed in Kilen reached a palaeotemperature of >120°C prior to Paleocene cooling (Fig. 18C). This corresponds to burial beneath more than 3.3 km of Cretaceous to Paleocene sediments. Deep burial of the Cretaceous sediments in Kilen is in good agreement with the occurrence of well-developed stylolites in the lower part of Lichen- ryg Formation in the northern part of Kilen (around Dromledomen; C. Heinberg & H. Dypvik, personal communication 2019). Similar considerations apply to https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 33 of 43 www.geusbul let in.org samples GC1113-5 and -59 of the Upper Cretaceous Herlufsholm Strand Formation (Herluf Trolle Land) that reached palaeotemperatures >100°C prior to Paleo- cene cooling. In summary, we observe a spatial and temporal overlap between the inversion of the major fault zones of the Wandel Sea Basin and the onset of cooling and exhumation that began at c. 60 Ma. We infer that the compression that resulted in inversion of the fault zones began in the mid-Paleocene (i.e. the Kronprins Christian Land Orogeny; Håkansson & Pedersen 1982; Svennevig et al. 2016). This timing is consistent with the late Paleocene age of the lower part of the Thyra Ø Formation, which may represent erosional prod- ucts derived from the inversion of the fault zones. This interpretation is supported by the abundant of reworked Cretaceous dinoflagellate cysts and palyno- morphs in these deposits (Lyck & Stemmerik 2000; Pia- secki et al. 2018). A corresponding episode is not revealed by AFTA data from North-East Greenland or West Greenland (Fig. 17). However, the timing of this episode overlaps with that of a Late Cretaceous – early Cenozoic episode (beginning between 70 and 50 Ma), which affected the southern- most tip of East Greenland (63°–61°N; Green et al. 2014). Dam et al. (1998) reported geological evidence for rapid uplift and fluvial erosion in the mid-Paleocene followed by subsidence contemporaneous with the first volcanic extrusions in both West and East Greenland, and argued that the arrival of the Iceland plume controlled these transient, vertical movements. 5.2.2 End-Eocene episode The cooling episode that began at the end of the Eocene (c. 35 Ma) is recognised in AFTA data in samples across almost the entire study area. The cooling episode affected the Wandel Sea Basin after the deposition of the Thyra Ø Formation and coincides with periods of exhumation in North-East Greenland, as well as West Greenland (Fig. 17). AFTA and VR data define fairly uniform palaeotem- peratures of around 80–90°C away from major fault zones, corresponding to the regional (or background) level of maturity across the region. This is interpreted to represent primarily deeper burial prior to regional, rela- tively uniform exhumation that began at the end of the Eocene. The Palaeogene sediments on Prinsesse Thyra Ø (e.g. GC1113-9) also reached such palaeotempera- tures prior to the end-Eocene episode, implying that the heating there reflects burial below a late Paleocene to Eocene cover. Piasecki et al. (2018) showed that the top 5 m of the section exposed at Kap Rigsdagen are of early–mid Eocene age and are part of the Thyra Ø Formation. The end-Eocene palaeotemperatures (80–90°C) for sample GC1113-10 from Lower Cretaceous sediments overlain by Palaeogene sediments at Kap Rigsdagen must, there- fore, reflect burial below a cover of Eocene sediments of similar thickness to that across Prinsesse Thyra Ø (Fig.  18D). Assuming a palaeogeothermal gradient of 30°C/km and a palaeosurface temperature of 10°C, this range of palaeotemperatures corresponds to burial below 2.3–2.7 km of Eocene sediments. The choice of palaeosurface temperature used here reflects the warm temperate climate that Boyd (1990) estimated based on the Palaeogene flora preserved in the deposits on Prinsesse Thyra Ø. It is thus likely that about 2.5 km of upper Paleocene to Eocene sediments (including the Thyra Ø Formation) covered wide areas across the Wan- del Sea Basin prior to the exhumation that began at the end of the Eocene. This suggests that large parts of the basin subsided during the Eocene. Some samples from north of the HFFZ (e.g. GC1113-15, -43, -45) cooled from much higher palaeotemperatures (>110°C) compared with the majority of samples across the region (see Section 6.3). AFTA data for sample GC1113-1 from the northern part of Kilen also indicate cooling from >130°C between 45 and 25 Ma during the end-Eocene episode. 5.2.3 Mid-late Miocene episode The mid–late Miocene cooling episode (beginning between 15 and 5 Ma) is identified in the AFTA data from samples in coastal and near-coastal locations, and does not correlate with any known strata within the Wan- del Sea Basin. It does, however, correlate with the late Miocene and early Pliocene events of uplift and incision that led to the formation of the present-day landscape in both West and North-East Greenland (Fig. 17; Japsen et al. 2006, in press). As the palaeotemperatures defined for this episode are moderate (c. 50–60°C at sea level), they are unlikely to be related to the early Pliocene cooling observed in North-East Greenland (Japsen et al. in press). We thus suggest that the mid-late Miocene episode identified in this study shares a common origin with the late Miocene episode (c. 10 Ma) in North-East Greenland, reflecting cooling due to uplift and erosion of the continental margin and development of the mod- ern-day topography. AFTA data from Herluf Trolle Land consistently define Miocene palaeotemperatures around 50°C at sea level, corresponding to burial below a 1.5 km thick rock col- umn (30°C/km, 5°C at the surface). Miocene palaeotem- peratures in samples from northern Peary Land and from Kronprins Christian Land are less well constrained but are nonetheless consistent with a similar value. The failure to resolve the Miocene event at locations away from the northern coasts may indicate that Miocene https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 34 of 43 www.geusbul let in.org palaeotemperatures were lower than, for example, on Herluf Trolle Land. Figure 19 shows a three-dimensional elevation model of the region around Independence Fjord and illustrates that Independence Fjord is incised below a low-relief surface at just above 1 km a.s.l., in contrast to the more elevated and dissected alpine relief further north on Peary Land. Incision below that low-relief surface would result in cooling of rocks now near the sea level by <50°C, suggesting that the Miocene palaeotemperatures may reflect cooling due to the inci- sion of the present-day relief following Miocene uplift. This contradicts the suggestion that Neogene uplift and erosion of the Wandel Sea Basin were very limited ( Stemmerik et al. 1998). 6 Discussion The climax of the Eurekan Orogeny is agreed to have occurred in the Eocene (Steel et al. 1985; Piepjohn et al. 2016), but both the onset and the end of the Orogeny have been a matter of debate. Here, we apply AFTA data to place tighter constraints on the timing of these events. We also address the origin of the extreme heat recorded at Nakkehoved on the northern coast of Kro- nprins Christian Land and comment on the likely former extent of the Wandel Sea Basin. 6.1 Mid-Paleocene onset of the Eurekan Orogeny We have demonstrated that cooling and exhumation along the HFFZ and the TLFZ (including Kilen) began Time (Ma) Carboni- ferous Te m pe ra tu re (° C ) Devon EocenePaleoceneCretaceousJurassicTriassicPermian Oligocene Miocene P Q Deposition of Carboniferous sediments A B Present-day exposure ? ? 80–90ºC 80–110ºC >100ºC 0 20 60 80 100 120 40 400 300 20 10 0304050100 606520020 Carboni- ferous Te m pe ra tu re (° C ) Devon EocenePaleoceneCretaceousJurassicTriassicPermian Oligocene Miocene P Q Deposition of Lower Triassic sediments Present-day exposure ? ? 85–95ºC >115ºC 25–50ºC Time (Ma) 0 20 60 80 100 120 40 400 300 20 10 0304050100 6065200 Heating below Triassic to Middle Jurassic sediments Heating below Carboniferous to Triassic sediments Fig. 18 Thermal history diagrams illus- trating the heating and cooling (burial and exhumation) of four samples that provide stratigraphic constraints on the age of removed sections. A: GC1113-18 (20 m a.s.l.) of upper Carboniferous Kap Jungersen Fm exposed on Holm Land. The sample reached a palaeotemperature above 100°C prior to Late Triassic cool- ing. This palaeotemperature corresponds to burial below a cover of Carboniferous to Triassic sediments, with a thickness exceeding 2.7 km. B: GC1113-22 (200 m a.s.l.) of Lower Triassic Parish Bjerg Fm exposed on Herluf Trolle Land. The sam- ple reached a palaeotemperature above 115°C prior to Late Jurassic cooling, corre- sponding to burial below a cover of Triassic to Middle Jurassic sediments with a thick- ness exceeding 3.1 km.The conversion of palaeotecmperatures to burial depths is based on an assumed palaeogeothermal gradient of 30°C/km and palaeosurface temperatures of 10°C for the end-Eocene episode and 20°C for earlier episodes. Red triangles: constraints for conditions at the surface during deposition of sediments or at the present day. Coloured boxes: con- straints from AFTA on palaeotemperature prior to cooling (the width of the boxes is fixed for better overview). Boxes extend below the x-axis of the diagram where only a lower limit of the palaeotempera- ture is known (e.g. >110°C). Sample loca- tions in Fig. 6. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 35 of 43 www.geusbul let in.org during the mid-Paleocene episode (c. 60 Ma), and a sim- ilar timing is likely for the region between the KCFZ and HFFZ, northern Peary Land. This episode, therefore, likely defines the onset of compression along these fault zones. We follow the interpretation of Pedersen et al. (2018) that the high palaeotemperatures in the south- ern part of Kilen were reached during maximum burial, prior to basin inversion, during a strong compressional event that we thus date as mid-Paleocene in age. The Paleocene timing of the compressional event is consis- tent with the assertion of Håkansson & Pedersen (2015 and earlier studies) that the compressional tectonics in the Wandel Sea Basin, the Kronprins Christian Land Orogeny, occurred around the Cretaceous–Palaeogene boundary. The onset of compression in the Wandel Sea Basin coincides with the mid-Paleocene onset of sea-floor spreading in the Labrador Sea and thus with the start of movement of Greenland towards the east-northeast (Oakey & Chalmers 2012). This implies that the mid-Paleocene compression of the Wandel Sea Basin took place during the first stage of the Eurekan Orogeny. The relationship between the undeformed Palaeo- gene strata and the heavily deformed Upper Cretaceous strata in the fault zones in the Wandel Sea Basin is not known from outcrops. It is thus possible that the defor- mation continued in the fault zones during the deposi- tion of the Palaeogene sediments. It has been suggested D C Carboni- ferous Te m pe ra tu re (° C ) Devon EocenePaleoceneCretaceousJurassicTriassicPermian Oligocene Miocene P Q Deposition of Lichenryg Fm Present-day exposure ?? 85–105ºC >120ºC 35–70ºC 6060 Time (Ma) 0 20 60 80 100 120 40 400 300 20 10 0304050100 65200 Carboni- ferous Te m pe ra tu re (° C ) Devon EocenePaleoceneCretaceousJurassicTriassicPermian Oligocene Miocene P Q Deposition of Ladegårdsåen Fm Present-day exposure ? 80–90ºC Thyra Ø Fm resting on Ladegårdsåen Fm Time (Ma) 0 20 60 80 100 120 40 400 300 20 10 0304050100 6065200 Heating below Eocene sediments Heating below Cretaceous to Paleocene sediments Fig. 18 (Continued) C: GC1113-58 (264 m a.s.l.) of Lower Cretaceous Lichenryg Fm exposed in Kilen. The sample reached a palaeotemperature above 120°C prior to Paleocene cooling, corresponding to burial below a cover exceeding a thick- ness of 3.3 km of Cretaceous to Paleocene sediments. D: GC1113-10 (23 m a.s.l.) of Lower Cretaceous sediments of the Lade- gårdsåen Fm exposed at Kap Rigsdagen below a thin cover of the Prinsesse Thyra Ø Formation of early to middle Eocene age (Piasecki et al. 2018). The palaeotempera- ture of 80–90°C for the Lower Cretaceous sediments prior to end-Eocene exhuma- tion reflects heating below a thick cover of Eocene sediments at this location. This range of palaeotemperatures corresponds to burial below 2.3–2.7 km of Eocene sediments. The conversion of palaeotec- mperatures to burial depths is based on an assumed palaeogeothermal gradient of 30°C/km and palaeosurface temperatures of 10°C for the end-Eocene episode and 20°C for earlier episodes. Red triangles: constraints for conditions at the surface during deposition of sediments or at the present day. Coloured boxes: constraints from AFTA on palaeotemperature prior to cooling (the width of the boxes is fixed for better overview). Boxes extend below the x-axis of the diagram where only a lower limit of the palaeotemperature is known (e.g. >110°C). Sample locations in Fig. 6. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 36 of 43 www.geusbul let in.org that deformation at Kap Washington in the western part of the Wandel Sea Basin continued into the Eocene, as the Ar-Ar system of the Kap Washington Group was partially reset in the early Eocene (c. 47 Ma; Tegner et al. 2011). However, the Ar-Ar age spectra do not show well-defined plateaus, and the resulting ages should perhaps be treated with caution. Jones et al. (2017) used U-Pb zircon dates from tephra layers close to the base-Paleocene unconformity of the CTB on the island of Spitsbergen (in the Svalbard archi- pelago) to define the onset of basin formation there as mid-Paleocene, c. 61.8 Ma. Jones et al. (2017) also linked the formation of the CTB to the initiation of compres- sion between eastern North Greenland and Svalbard, and they argued that the cessation of the Kap Wash- ington volcanism around that time was corroborating evidence. Had there been extension between these regions, then the activity would likely have increased (Jones et al. 2017; Fig. 5). Thus, the formation of the CTB on Spitsbergen began at about the same time as the compression in the Wandel Sea Basin, slightly prior to 60 Ma and prior to the deposition of the late Paleocene to earliest Eocene Thyra Ø Formation. Interestingly, the CTB only received sediments from only eastern source areas during the Paleocene, and the basin received sediments only from the west after the earliest Eocene emergence of the West Spitsbergen Fold Belt (Dallmann et al. 2015; Petersen et al. 2016). The mid-Paleocene timing for the onset of the com- pressional event is comparable with the late Paleocene – early Eocene timing suggested by Døssing et al. (2010) and Svennevig et al. (2016) but differs from the Eocene timing suggested by von Gosen & Piepjohn (2003). How- ever, according to von Gosen & Piepjohn (2003) and Svennevig et al. (2016), a late Paleocene or even Eocene north–south compression of the Wandel Sea Basin would agree with a unified timing of Eurekan deforma- tion extending from the Canadian Arctic Archipelago to North Greenland and Svalbard. However, the Eurekan deformation occurred in two stages, as discussed in Section 2.2. During the first (Paleocene) Eurekan stage, the south-south-west to north-north-east movement of Greenland relative to Svalbard gave rise to compression that caused exhumation in the Wandel Sea Basin and subsidence of the CTB during its formation as a foreland basin. During the second (Eocene) Eurekan stage, com- pression continued, but the Greenland Plate changed trajectory resulting in sinistral strike-slip transpression between Greenland and Svalbard. Much of what can be seen today in the field is the final result of north–south transpression during the second Eurekan stage. Independent lines of evidence support a mid-Pa- leocene onset of the Eurekan Orogeny. The Sverdrup Basin in the north-eastern Canadian Arctic Archipelago underwent a drastic change in the earliest Paleocene when the basin began to deform, coincident with the onset of sea-floor spreading west of Greenland (Embry & Beauchamp 2019). Using apatite fission-track data, Arne et al. (2002) reported significant Paleocene cooling in the Sverdrup Basin, and Green & Duddy (2010) reported the onset of extensive cooling in the Paleocene between 60 and 55 Ma in Alaska, Arctic Canada, the northern Bar- ents Sea and Svalbard based on AFTA data. The plate reconstructions published by Müller et al. (2016) showed that transpression with 18° convergence between the Barents margin and North Greenland was initiated in the late Paleocene (60 Ma) and culminated in the early Eocene (54–50 Ma; Svennevig et al. 2016). We conclude that the mid-Paleocene episode of cool- ing and exhumation (c. 60 Ma) along the major fault zones in the Wandel Sea Basin reflects the onset of the Eurekan Orogeny due to the convergence between Greenland and the Barents margin. 6.2 Recent results from Arctic Canada Recent apatite fission-track and apatite (U-Th-Sm)/He data from a suite of samples from the Pearya terrane in northern Ellesmere Island (analogous to Area 1 of this study; Fig. 6) yielded fission-track ages of c. 40–50 Ma over an elevation range of c. 1600 m (Vamvaka et  al. 2019). He-ages in individual grains showed a much wider range, from which the authors selected certain values to derive thermal history constraints. The logic behind this selection is not clear, as the ages show no relation- ship with either equivalent U content or grain size, as required by the models used to interpret these data (see Green & Duddy [2012] for discussion). From the combination of AFTA and He data, they presented a pre- ferred scenario with three periods of cooling, showing a close correspondence with the three episodes defined on independent grounds by Piepjohn et al. (2016). This differs significantly from the preferred thermal history synthesis for Wandel Sea Basin presented here, in which major cooling occurred at c. 60 and 35 Ma. However, we noted from the supplementary information presented by Vamvaka et al. (2019) that their solutions were con- strained to begin cooling from temperatures of 140– 160°C between 60 and 50 Ma, which is consistent with the Paleocene cooling episode defined from AFTA in this study. It, therefore, seems likely that Paleocene cooling in the two areas has a common, tectonic origin, although Vamvaka et al. (2019) considered it to have a non-tectonic origin. On comparing our data with those of Vamvaka, it seems unlikely that their data could independently define three cooling episodes between 55 and 35 Ma. Instead, we believe that a more reasonable interpreta- tion would be two major cooling episodes, which began https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 37 of 43 www.geusbul let in.org about 60 and 35 Ma, as in North Greenland, suggesting a similar tectonic evolution in both North Greenland and Ellesmere Island. 6.3 End-Eocene tectonics in relation to the Eurekan Orogeny There is a clear offset in end-Eocene palaeotempera- tures across the HFFZ (Fig. 11E). Typical palaeotempera- tures correspond to burial below a cover of c. 3.5 km and c. 2.5 km a.s.l. on the northern and the southern side of the fault, respectively (c. 110°C and 85°C at sea level; 30°C/km, 10°C at the surface). This implies that the rocks on the northern side of the fault were more deeply buried by about 1 km, compared with those south of the fault, prior to end-Eocene exhumation. The present-day summit level on both sides of the HFFZ is about 1.8 km a.s.l., corresponding broadly to the thickness of the cover needed to explain Miocene palaeotemperatures of c. 60°C at sea level on both sides of the fault, as defined by AFTA from the high moun- tains north of the fault zone and from Herluf Trolle Land (Section 5.2.3). Based on the landscape devel- opment in North-East Greenland, we suggest that the summit level in this study area of up to 2 km a.s.l. rep- resents a peneplain that was graded to near sea level after end-Eocene exhumation and uplifted to the level of the present-day summits after c. 10 Ma (Bonow & Japsen 2021; Japsen et al. in press). The present-day relief was, therefore, likely shaped by differential uplift and subsequent incision below this peneplain since the late Miocene. The digital elevation model shown in Fig. 19 illustrates the variation of the relief across south-eastern Peary Land to the south of the HFFZ. The constant summit level across the HFFZ implies that there was no significant vertical movement along the fault during the mid–late Miocene tectonic episode, and thus, that the offset of end-Eocene palaeotem- peratures is due to differential vertical movements across the HFFZ that had taken place by the end of the Eocene. North–south compression affected northern Peary Land in post-Santonian times, with reverse faulting at the HFFZ and thrusting along the KCTZ, which Piepjohn & von Gosen (2001) attributed to the Eurekan Orogeny. However, they also argued that compression along the HFFZ was terminated by the change in plate-tectonic configuration at C13 time (c. 35 Ma), when Greenland became part of the North American Plate. Our AFTA data document kilometre-scale, reverse movements along the HFFZ, which is consistent with the north–south reverse and thrust faults observed by Piepjohn & von Gosen (2001). However, the results of this study also show that the inversion of the HFFZ took place in two episodes that began (1) during the mid-Pa- leocene (c. 60 Ma) and (2) at the end of the Eocene (c. 35 Ma). The first episode represents the onset of the Eurekan Orogeny, while the second episode rep- resents post-Eurekan tectonics as the Greenland Plate had become part of the North American Plate. Conse- quently, the Eurekan Orogeny had terminated by the end of the Eocene (as supported by Piepjohn & von Gosen 2001), and the reverse faulting along the HFFZ that occurred at that time is, therefore, unrelated to the Eurekan Orogeny. While the end-Eocene cooling and exhumation began after the termination of spreading in the Labra- dor Sea, and hence after the Eurekan Orogeny, it also coincides with an important phase of plate reorganisa- tion in North-East Atlantic (Gaina et al. 2009, 2017). The episode of uplift and erosion in North Greenland that began at the end of the Eocene is synchronous with epi- sodes of exhumation in East and West Greenland, far from the Eurekan Orogen (Section 5.2.2). Many other observations show that significant tectonic changes affected Greenland and adjacent Arctic regions around the Eocene–Oligocene transition. For example, late Eocene magmatic activity affected the East Greenland margin (Larsen et al. 2014). Uplift of the inner margin of South-East Greenland resulted in a strong flux of coarse clastic turbidites during the late Oligocene on the shelf, above a middle Eocene – upper Oligocene hiatus (Larsen et al. 1994). End-Eocene tectonic uplift led to the formation of regional peneplains on both sides of Greenland during the Oligocene and Miocene time (Japsen et al. in press). End-Eocene exhumation affected Arctic regions beyond Greenland, including the Sverdrup Basin, Canada, as well as the Barents Sea, Svalbard and the north slope of Alaska (Green & Duddy 2010; Embry & Beauchamp 2019). All these observations reveal that a deep-rooted, tectonic process began in the North-East Atlantic at the end of the Eocene after the Eurekan Orogeny. Further studies, including geodynamic modelling, are needed to investigate the origin of these post-Eurekan, tectonic changes. 6.4 The extreme heating recorded at Nakkehoved VR data from around Nakkehoved, on the north coast of Kronprins Christian Land, document an extreme degree of heating of Upper Cretaceous sediments to palaeotem- peratures >250°C within a very limited area (Fig. 12). This extreme heating stands in stark contrast to much lower values (80–90°C) in surrounding areas, and to date, no convincing explanation has been offered for these high temperatures. Nonetheless, they are thought to have occurred post-Paleocene (Håkansson & Pedersen 2001, https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 38 of 43 www.geusbul let in.org 2015; Paech & Estrada 2018). For example, Håkansson & Pedersen (2001) differentiated between (1) the com- pressional tectonics of the Kronprins Christian Land Orogeny that culminated at the Cretaceous– Palaeogene boundary (corresponding to the mid-Paleocene episode of exhumation defined here) and (2) a post-Paleocene thermal event. These authors argued that the latter event was responsible for the elevated VR value of the tectonically undeformed sediments of the Thyra Ø For- mation on Prinsesse Margrethe Ø, as well as for the extreme VR values around Nakkehoved. AFTA data from most samples analysed from around Nakkehoved and Kilen show evidence of Paleocene cool- ing from elevated temperatures. However, whether the palaeotemperatures on Kilen were as high as those responsible for the VR levels of up to 7% or more around Nakkehoved is not certain. The extreme palaeotempera- tures may have been reached before 60 Ma, as AFTA data from Nakkehoved and Kilen provide only minimum palae- otemperature estimates for this time. However, as the event affected Upper Cretaceous sediments, it may thus have happened in Late Cretaceous or Paleocene times. Given the complexity of the region around Nakke- hoved, additional sampling for AFTA and VR, combined with detailed stratigraphic and sedimentological stud- ies is required before the cause of the extreme thermal imprint there can be understood. 6.5 Previous extent of the Wandel Sea Basin Substantial thicknesses of sediments of Carbonifer- ous to Palaeogene age have been present within the present-day outline of the Wandel Sea Basin and out- side the relatively narrow Late Cretaceous rift zones (Fig. 20). The kilometre-scale thickness of these now removed sedimentary covers implies that they must have extended substantial distances beyond the pres- ent-day outline of the Wandel Sea Basin. When we consider the reconstructed geographical positions of Carboniferous–Palaeogene basins in North-East Green- land, Svalbard and the Barents Shelf prior to Cenozoic sea-floor spreading (Gion et al. 2017), it is likely that the Wandel Sea Basin was at times coherent with them. Several authors have highlighted the marked similar- ities among the sedimentary sequences in these three regions (Håkansson & Stemmerik 1989; Mørk et al. 1989; von Gosen & Piepjohn 2003). Håkansson & Stemmerik (1984) presented evidence for a parallel development of the Wandel Sea Basin with Svalbard and the Barents Shelf. They found that the depositional environments of the Wandel Sea Basin in the Carboniferous to Triassic and in the Paleocene compared well with known stra- tigraphy in Svalbard, whereas the late Mesozoic history of the two areas showed major differences. In particu- lar, the presence of thick Upper Cretaceous sequences in North Greenland constitutes the most conspicuous N 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 m Independence Fjord Wandel Dal Fig. 19 3D-elevation model of the region around Independence Fjord (GLOBE 1999; map location in Fig. 3). Note that Independence Fjord and Wandel Dal (valley in Danish) are incised below a low-relief surface at about 1 km a.s.l. This is in contrast to more elevated and dissected, alpine relief north-west of Independence Fjord. The width of the diagram is about 250 km. Illustration: Johan M. Bonow. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 39 of 43 www.geusbul let in.org difference from Svalbard, where sediments of that age are absent (Dallmann et al. 2015). A study of the late Palaeozoic in the North Atlantic found evidence for a change in the overall depositional environment of the North Greenland – Barents Sea area from exten- sive, humid flood plains in the early Carboniferous, to shallow warm seas in the mid-Carboniferous to mid-Permian, and cooler, possibly deeper marine envi- ronments in the late Permian (Stemmerik 2000). In East Greenland, non-marine conditions prevailed during the entire Carboniferous and, following a prolonged, early Permian hiatus, warm-water carbonates were deposited during the late Permian. Stemmerik (2000) concluded that the changes reflect large-scale shifts in palaeoclimatic and subsidence patterns related to the northward drift of the area and ongoing rifting in the region. Stemmerik & Worsley (2005) correlated the late Palaeozoic stratigraphy across North Greenland, Svalbard and the Barents Shelf, and found evidence for regional, mid-late Carboniferous uplift and erosion and local, Permian uplift and erosion. For a long time, it was difficult to correlate the Meso- zoic succession both within the Wandel Sea Basin and with basins in surrounding areas (Dypvik et al. 2002; Håkansson & Pedersen 2015). However, a new Jurassic– Cretaceous lithostratigraphy for Kilen by Hovikoski et al. (2018) showed correlations between Kilen and North- East Greenland, Svalbard and the Barents shelf. A Trias- sic lithostratigraphy for the Wandel Sea Basin presented evidence of a shallow shelf to deep shelf or basin floor transect that forms an outcrop analogue to contempo- raneous intervals in the western Barents Sea basins and the offshore Danmarkshavn Basin (Bjerager et al. 2019). These observations support the suggestion that the now isolated components of the Wandel Sea Basin were once parts of a more extensive depositional system. 7 Conclusions The results of this study reveal a long history of episodic burial and exhumation across the Wandel Sea Basin. The earliest episode recognised is a phase of early Permian uplift and erosion that led to the formation of the basin-wide hiatus between the upper Perm- ian and  upper Carboniferous strata. The exhumation removed 2–3 km of rocks across the basin, including a cover of Silurian to Carboniferous sediments on Herluf Trolle Land. Late Triassic uplift and erosion, which is likely to have affected the entire basin, led to formation of a hiatus between the Upper and Middle Triassic formations on Herluf Trolle Land when kilometre-scale thick covers of sediments were removed, including a cover of more than 2.7 km of upper Carboniferous to Triassic sedi- ments on Holm Land. Late Jurassic uplift and erosion probably affected the entire basin and led to formation of a hiatus between the Upper Jurassic and Upper Triassic strata involv- ing removal of kilometre-thick sedimentary covers, for K R O N P R I N S C H R I S T I A N L A N D Ø Hovgaard P E A R Y L A N D 48 KCTZ HFFZ TLFZ 500 100 km 2.5 km Paleocene– Eocene (GC1113-9, -10) >2.7 km Upper Cretaceous – Paleocene (GC1113-5) Present extent of the Carboniferous–Palaeogene deposits of the Wandel Sea Basin >2.7 km Carboniferous– Triassic (GC1113-18) >3.3 km Cretaceous– Paleocene (GC1113-58) >3 km Triassic – Middle Jurassic (GC1113-22) 40ºW 35ºW 30ºW 25ºW 20ºW 15ºW 10ºW 35ºW 30ºW 25ºW 20ºW 15ºW 80 ºN 82 ºN 81 ºN 83 ºN Fig. 20 Present-day outline of the Car- boniferous–Palaeogene Wandel Sea Basin compared with estimated thick- nesses of removed covers (Fig. 18). Substantial thicknesses of sediments of Mesozoic and Palaeogene age have been present within the present outline of the basin, implying that they extended beyond the present-day outline of the Wandel Sea Basin. The conversion of palaeotemperatures to burial depths is based on an assumed palaeogeother- mal gradient of 30°C/km and palaeo- surface temperatures of 10°C for the end-Eocene episode and 20°C for ear- lier episodes. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. TLFZ: Trolle Land Fault Zone. Geology legend and symbols defined in Fig. 4. https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org Japsen et al. 2021: GEUS Bulletin 45. 5298. https://doi.org/10.34194/geusb.v45.5298 40 of 43 www.geusbul let in.org example, more than 3 km of Triassic to Middle Jurassic sediments on Herluf Trolle Land. Mid-Cretaceous cooling is identified in only one sample within the Wandel Sea Basin, but this epi- sode is contemporaneous with regional exhumation in North-East Greenland. We, therefore, suggest that both areas were affected by exhumation at this time, corresponding to the Aptian to Turonian hiatus on Herluf Trolle Land. Mid-Paleocene cooling and exhumation define the timing of compression along the major fault zones (e.g. the Kronprins Christians Lands Orogeny). A cover of more than 3 km of Upper Cretaceous to Paleocene sediments was present on the north coast of Kronprins Christian Land prior to the Paleocene exhumation. We thus agree with previous interpretations that the high thermal maturities in the southern part of Kilen reflect maximum burial prior to basin inversion. We conclude that the mid-Paleocene inversion of the major fault zones in the Wandel Sea Basin took place during the first stage of the Eurekan Orogeny after the onset of sea-floor spreading west of Greenland. AFTA data from most samples analysed from the northern part of Kronprins Christian Land show evi- dence of Paleocene cooling, including samples from around Nakkehoved where Upper Cretaceous rocks show extreme maturities. Cooling from the extreme heating must have occurred in Late Cretaceous or Paleocene times, as AFTA data define only minimum estimates of the maximum paleotemperature. Given the complexity of the region around Nakkehoved, addi- tional sampling for AFTA and VR combined with strati- graphic and sedimentological studies is required before the cause of the extreme thermal imprint there can be understood. Regional exhumation of the Wandel Sea Basin began at the end of the Eocene and led to removal of most of the kilometre-thick sedimentary cover that had been deposited during Eocene subsidence. Peary Land, north of the HFFZ, was uplifted about 1 km more than the area south of the fault during this episode, suggesting a tec- tonic offset. The regional denudation and reverse fault- ing that began at the end of the Eocene took place after sea-floor spreading west of Greenland had ended and thus post-date the Eurekan Orogeny. The results of this study thus define two distinct epi- sodes of Palaeogene cooling and exhumation across the Wandel Sea Basin: (1) mid-Paleocene cooling iden- tified mainly in inverted fault zones and (2) cooling that began at the end of the Eocene, which affected a wide area and reflects regional exhumation following deeper burial. Mid–late Miocene cooling is identified from AFTA data in near-coastal locations. This episode coincides with a phase of late Miocene uplift and incision that initiated the formation of the present-day landscape in West and North-East Greenland. Miocene palaeotemperatures in the present study area are thus likely to reflect a similar development. The preserved sedimentary sequences of the Wan- del Sea Basin represent remnants of once much thicker strata removed in separate exhumation episodes. The thicknesses of these sedimentary covers imply that they must have extended substantially beyond the pres- ent-day boundary of the basin. The Wandel Sea Basin may, thus, at times have been coherent with the Car- boniferous–Palaeogene basins in North-East Greenland, Svalbard and the Barents Sea. Acknowledgements Many colleagues from the Geological Survey of Denmark and Greenland (GEUS) and from the University of Copenhagen contributed with samples to this study, more than we can list here. Niels Henriksen (Oscar) provided invaluable help in retrieving samples collected in the past few decades from GEUS’ core store. John R. Hopper, Kristian Svennevig and Morten Bjerager kindly provided with comments on the manuscript. Reviewers Andrew Carter and Eckart Håkansson provided constructive comments in the manuscript. Additional information Funding This research work was funded by a consortium of oil companies and GEUS. Competing interests The authors declare no competing interests. Author contributions PJ: Conceptualisation, Funding acquisition, Data curation, Investigation, Writing – review & editing. PFG: Formal analysis, Methodology, Investigation, Writing – review & editing JAC: Investigation, Writing – review & editing. Additional files Two supplementary files are available at https://doi.org/10.22008/FK2/ VLO6NQ References Alsen, P. McRoberts, C., Svennevig, K., Bojesen-Koefoed, J., Hovikoski, J. & Piasecki, S. 2017: The Isrand Formation: a Middle Triassic Daonel- la-bearing, black shale unit in Kilen, North Greenland (with a note on the Triassic in Amdrup Land). 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Tectonics 22, 28. https://doi.org/10.1029/2001TC901040 https://doi.org/10.34194/geusb.v45.5298 http://www.geusbulletin.org https://doi.org/10.2110/pec.85.37.0339 https://doi.org/10.1016/s0031-0182(00)00119-x https://doi.org/10.34194/ggub.v180.5086 https://doi.org/10.1144/GSL.SP.1990.055.01.05 https://doi.org/10.1002/2016TC004152 https://doi.org/10.17850/njg97-1-02 https://doi.org/10.17850/njg97-1-02 https://doi.org/10.34194/geusm.v8.4526 https://doi.org/10.1016/j.epsl.2010.12.047 https://doi.org/10.1029/2019tc005621 https://doi.org/10.1029/2001TC901040 Thermo-tectonic development of the Wandel Sea Basin, North Greenland Abstract 1 Introduction 2 Geological setting 2.1 Stratigraphic record 2.1.1 Palaeozoic strata 2.1.2 Mesozoic strata 2.1.3 Palaeogene strata 2.2 Structural elements of the Wandel Sea Basin and their relation to the Eurekan Orogeny 3 Apatite Fission-Track Analysis 3.1 New AFTA data from northern and eastern Greenland 3.2 Thermal history interpretation based on AFTA data 3.2.1 Principles of thermal history interpretation 3.2.2 Thermal history interpretation: results 3.3 Definition of major regional palaeothermal episodes 3.4 Regional variation in palaeothermal episodes 4 Thermal history insights from maturity data 4.1 Maturity of lower Palaeozoic strata 4.2 Maturity of Mesozoic-Palaeogene strata 4.3 Comparison of AFTA and VR data 4.3.1 Northern Peary Land 4.3.2 Herluf Trolle Land 4.3.3 East of Herluf Trolle Land 4.4 Synthesis 5 Geological controls on the cooling episodes identified from AFTA 5.1.Palaeozoic-Mesozoic cooling events 5.1.1 Early Permian episode 5.1.2 Late Triassic episode 5.1.3 Late Jurassic episode 5.1.4 Mid-Cretaceous episode 5.2 Cenozoic cooling episodes 5.2.1 Mid-Paleocene episode 5.2.2 End-Eocene episode 5.2.3 Mid-late Miocene episode 6 Discussion 6.1 Mid-Paleocene onset of the Eurekan Orogeny 6.2 Recent results from Arctic Canada 6.3 End-Eocene tectonics in relation to the Eurekan Orogeny 6.4 The extreme heating recorded at Nakkehoved 6.5 Previous extent of the Wandel Sea Basin 7 Conclusions Acknowledgements Additional information References Figures Fig. 1 Cenozoic sea-floor spreading in the northern North Atlantic area. Sea-floor spreading between North America and Greenland (62–55 Ma) caused the first stage of the Eurekan Orogeny. During this time, Greenland moved together with Europe. Spreading between Europe and Greenland (55–35 Ma) resulted in the second stage of the Eurekan Orogeny. During this time, North America, Greenland and Europe moved as separate plates. Sea-floor spreading ceased west of Greenland (at c. 35 Ma) after which Greenland moved together with North America and the Eurekan Orogeny ended. The Danmarkshavn Basin is located off North-East Greenland between 76 and 82°N. LR: Lomonosov Ridge. WSB: Wandel Sea Basin. Modified from Brozena et al. (2003), Oakey & Chalmers (2012) and Gaina et al. (2017). Fig. 2 Outline of the High Arctic adjacent to North Greenland. Extent of Kronprins Christian Land Orogeny according to Håkansson & Pedersen (2001) and this study. LR: Lomonosov Ridge. Detail of Fig. 1 with additions from von Gosen & Piepjohn (2003), Oakey & Chalmers (2012) and Piepjohn et al. (2016). Fig. 3 Elevation and place names of the study area in eastern North Greenland. Pr: Prinsesse. Fig. 4 Geology of the Carboniferous–Palaeogene Wandel Sea Basin and surrounding areas. The remnants of the Carboniferous to Palaeogene sediments occur between northern Peary Land and Kronprins Christian Land and thus define the extent of the basin. Kap Washington Group is of Campanian to earliest Palaeogene age (Håkansson & Pedersen 2015). Håkansson & Pedersen (2015) indicated the Trolle Land Fault Zone as one continuous zone from Herluf Trolle Land to Kronprins Christian Land. Here, we indicate one possible correlation between these two areas. Based on Escher & Pulvertaft 1995 with modifications after Croxton et al. 1980; Hovikoski et al. 2018; Piasecki et al. 2018. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.M.Ø: Prinsesse Margrethe Ø. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. Fig. 5 Wandel Sea Basin stratigraphy and formation names. The representation of the mixed volcanic, volcano-clastic and lacustrine deposits of the Kap Washington Group has been simplified. Some formation names are not shown; the upper Permian Kap Kraka Fm in Peary Land (Håkansson & Pedersen 2015) and the pre-late Bajocian (?) Gletscherport Fm in the Kilen area (Hovikoski et al. 2018). Compiled after Bjerager et al. 2019; Gautier et al. 2011; Håkansson & Pedersen 2015; Hopper et al. 2014; Hovikoski et al. 2018; Ineson et al. 2020; Piasecki et al. 2018; Stemmerik et al. 1998; Svennevig et al. 2018; Tegner et al. 2011. BF: Birkelund Fjeld. Dd: Dromledome. K.C. Land: Kronprins Christian Land. Kl: Kuglelejet. KW: Kap Washington Group. PB: Parish Bjerg. Penns: Pennsylvanian. Fig. 6 Location of samples that yielded apatite and division of the study area into six geographical areas with similar thermal histories used to define the timing of key episodes in Fig. 10. A: Areas 1–5. B: Area 6. Geology legend in Fig. 4. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. Fig. 7 Apatite fission-track ages in outcrop samples from eastern North Greenland (data in Table 2). Youngest ages <60 Ma are focussed along the north coast, while older ages are found in inland samples. EGFZ: East Greenland Fracture Zone. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. Geology legend in Fig. 4. Fig. 8 Relationship between the mean track length and fission-track age. A: Outcrop samples from eastern North Greenland (this study). Error bars are shown as ± 2 sigma. B: Results from this study compared with those from North-East Greenland (Japsen et al. in press). Ages span a similar range in both regions. However, data from this study are characterised by higher mean track lengths than those from North-East Greenland, which probably reflects the lower degree of Miocene cooling in samples from this study. Error bars are omitted for clarity. Fig. 9 Illustration of thermal history solutions extracted from AFTA data. Results are presented in terms of up to three palaeothermal episodes, that is, times when a rock sample was hotter than it is today. Note that the palaeotemperature constraint T1 is a minimum estimate because this is the event in which the apatites begin to retain tracks. In most situations, three events are the most that can be defined from AFTA due to various factors, including the natural spread in track lengths of a single population of tracks and the rapid decrease in the rate of annealing across the range from c. 110°C to below 60°C. t1, t2 and t3: time intervals during which cooling from the peak palaeotemperature began. T1, T2 and T3: palaeotemperature intervals. c.i.: confidence interval. Colours are used to illustrate attribution to regional episodes, although those used here are purely schematic. Fig. 10 Timing constraints on the onset of cooling for discrete cooling episodes derived from the AFTA in each outcrop sample. Thermal history solutions for each sample are listed in Table 3. Horizontal-shaded bars represent 95% confidence intervals on the time of cooling onset, as illustrated in Fig. 9. Samples are divided into six areas (Areas 1–6; Fig. 6). Assuming these results represent regionally synchronous cooling episodes, results across the entire region require seven separate episodes, as shown by vertical shaded columns. Constraints for the onset of each episode are listed at the bottom of the figure (see Table 4). Timing constraints for individual samples are assigned to a common regional event when adjacent samples cool from similar palaeotemperatures with consistent timings. In some cases, the estimated onset of cooling pre-dates the depositional age of the sample, indicating cooling of the apatites in sediment provenance regions prior to deposition in the host sample. Fig. 11 Palaeotemperatures derived from AFTA. A: Early Permian (295–290 Ma). B: Late Triassic (225–210 Ma). C: Late Jurassic (165–150 Ma). D: Paleocene (c. 60 Ma). E: End-Eocene (c. 35 Ma). F: Middle to late Miocene (15–5 Ma). Palaeotemperature for the mid-Cretaceous episode (115–90 Ma) is not shown as only one sample falls within the map frame. The small arrow in the lower right corner of A, E and F indicates sample GC1113-48, which is located just south of the figure frame. Geology legend in Fig. 4. Numbers next to AFTA samples denote sample numbers. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. KR: Kap Rigsdagen. Pr.T.Ø: Prinsesse Thyra Ø. TLFZ: Trolle Land Fault Zone. Fig. 12 Published vitrinite reflectance (VR) values from Mesozoic and Palaeogene units of the Wandel Sea Basin. Coloured boxes: VR values and corresponding maximum palaeotemperatures (Burnham & Sweeny 1989). Source of VR data indicated by letters A: Paech & Estrada (2018), B: Pedersen et al. (2018), C: Håkansson et al. (1994). When values are available from multiple sources, those from Paech & Estrada (2018) are shown. Pr.D.Ø: Prinsesse Dagmar Ø. Pr.M.Ø: Prinsesse Margrethe Ø. Pr.T.Ø: Prinsesse Thyra Ø. Detail of Kilen in Fig. 15. Fig. 13 Cenozoic palaeothermal constraints for Herluf Trolle Land. Heating during the Paleocene event (c. 60 Ma) is controlled by the numerous faults belonging to the Trolle Land Fault Zone, as suggested by Paech & Estrada (2018). Only samples north-east of ‘Fault F’ were affected by the Paleocene thermal event. White boxes: Thermal history solutions from AFTA data; colour coding as in Fig. 10. Coloured boxes: VR values and corresponding maximum palaeotemperatures from adjacent samples; see Fig. 12. Source of VR data indicated by letter A: Paech & Estrada (2018). Map location indicated in Fig. 12. Basemap modified from Bjerager et al. (2019). Fig. 14 Cenozoic palaeothermal constraints east of Herluf Trolle Land. White boxes: thermal history solutions from AFTA, colour coding as in Fig. 10. Coloured boxes: VR values and corresponding maximum palaeotemperatures from adjacent samples, colour coding as in Fig. 12. Source of VR data indicated by letters A: Paech & Estrada (2018), C: Håkansson et al. (1994). Solid black lines: faults. Map location indicated in Fig. 12. Detail of Kilen in Fig. 15. Key to bedrock geology and other abbreviations in Fig. 4. Fig. 15 Palaeothermal constraints for south-east Kilen. The palaeotemperature constraints from VR are consistent with those from AFTA, but the timing constraints on the onset of cooling vary. White boxes: thermal history solutions from AFTA, colour coding as in Fig. 10. Numbers next to AFTA samples denote sample numbers. Blue boxes: VR values and associated maximum palaeotemperatures for Cretaceous sediments. Source of VR data indicated by letters B: Pedersen et al. (2018) and C: Håkansson et al. (1994). Map location in Fig. 14. Base map modified from Hovikoski et al. (2018, Fig. 4) where further details of the map are explained. Fig. 16 Comparison between the regional cooling episodes identified from AFTA (Table 4) and the stratigraphic scheme for the Wandel Sea Basin (Fig. 5). The thickness of the horizontal, coloured bars indicates the interval during which the cooling began in each episode. Fig. 17 Timing of regional, post-Devonian episodes of uplift and erosion in three regions of Greenland estimated from AFTA. A: Central West Greenland (Japsen et al. 2006, 2009). B: Eastern North Greenland (Table 4; this study). C: North-East Greenland (Japsen et al. in press). Break-up west of Greenland took place in mid-Paleocene (c. 62 Ma), but sea-floor spreading ceased there by the end of the Eocene. In contrast, the opening of the North-East Atlantic, east of Greenland, began at the Paleocene–Eocene transition (c. 56 Ma) and is still ongoing (Chalmers & Pulvertaft 2001; Oakey & Chalmers 2012; Gaina et al. 2017). The Fram Strait between Greenland and Svalbard opened in early Miocene (c. 20 Ma; Jokat et al. 2016). L: Late. E: Early. M: Middle. C: Carboniferous. Pe: Permian. Tr: Triassic. J: Jurassic. Kl: Lower Cretaceous. Ku: Upper Cretaceous. Pal: Paleocene. Eo: Eocene. Oli: Oligocene. Mio: Miocene. Pl: Pliocene. Q: Quaternary. Fig. 18 Thermal history diagrams illustrating the heating and cooling (burial and exhumation) of four samples that provide stratigraphic constraints on the age of removed sections. A: GC1113-18 (20 m a.s.l.) of upper Carboniferous Kap Jungersen Fm exposed on Holm Land. The sample reached a palaeotemperature above 100°C prior to Late Triassic cooling. This palaeotemperature corresponds to burial below a cover of Carboniferous to Triassic sediments, with a thickness exceeding 2.7 km. B: GC1113-22 (200 m a.s.l.) of Lower Triassic Parish Bjerg Fm exposed on Herluf Trolle Land. The sample reached a palaeotemperature above 115°C prior to Late Jurassic cooling, corresponding to burial below a cover of Triassic to Middle Jurassic sediments with a thickness exceeding 3.1 km.The conversion of palaeotecmperatures to burial depths is based on an assumed palaeogeothermal gradient of 30°C/km and palaeosurface temperatures of 10°C for the end-Eocene episode and 20°C for earlier episodes. Red triangles: constraints for conditions at the surface during deposition of sediments or at the present day. Coloured boxes: constraints from AFTA on palaeotemperature prior to cooling (the width of the boxes is fixed for better overview). Boxes extend below the x-axis of the diagram where only a lower limit of the palaeotemperature is known (e.g. >110°C). Sample locations in Fig. 6. Fig. 19 3D-elevation model of the region around Independence Fjord (GLOBE 1999; map location in Fig. 3). Note that Independence Fjord and Wandel Dal (valley in Danish) are incised below a low-relief surface at about 1 km a.s.l. This is in contrast to more elevated and dissected, alpine relief north-west of Independence Fjord. The width of the diagram is about 250 km. Illustration: Johan M. Bonow. Fig. 20 Present-day outline of the Carboniferous–Palaeogene Wandel Sea Basin compared with estimated thicknesses of removed covers (Fig. 18). Substantial thicknesses of sediments of Mesozoic and Palaeogene age have been present within the present outline of the basin, implying that they extended beyond the present-day outline of the Wandel Sea Basin. The conversion of palaeotemperatures to burial depths is based on an assumed palaeogeothermal gradient of 30°C/km and palaeosurface temperatures of 10°C for the end-Eocene episode and 20°C for earlier episodes. HFFZ: Harder Fjord Fault Zone. KCTZ: Kap Canon Thrust Zone. TLFZ: Trolle Land Fault Zone. Geology legend and symbols defined in Fig. 4. Tables Table 1 Sample details. A digital version of this table is available in online Supplementary File S1 Table 2 AFTA data. A digital version of this table is available in online Supplementary File S1 Table 3 Thermal history solutions. A digital version available in online Supplementary File S1 Table 4 Intervals defining the onset of episodes of cooling based on AFTA data in all samples and the possible origin of the cooling during each episode