Geological Survey of Denmark and Greenland Bulletin 28, 2013, 29-32 29 Geological map of Denmark 1:50 000 – map sheet Mors, NW Denmark Stig A. Schack Pedersen, Peter Roll Jakobsen, Lisbeth Tougaard and Peter Gravesen Danish geological maps of deposits occurring at the terrain surface are published under the name of Geological map of Denmark 1:50  000 and are based on geological field map- ping at 1:25 000. Most of the published maps follow the map sheet division shown in Fig. 1. However, in some instances it is appropriate to publish geological maps covering a regional unit, such as an island. Hence, the geological map of Mors appears as the 1:50 000 map sheet Mors, which covers parts of map sheets 1116 I, 1116 II and 1116 III (Figs 1, 2; Pedersen & Jakobsen 2012). Mors shows spectacular examples of glaciotectonic struc- tures that are beautifully exposed in coastal cliff sections. It also has a unique geological history, which is briefly de- scribed in this paper. Geological features of map sheet Mors The geological map of Mors shows deposits that are present at the terrain surface; they are mainly non-lithified Quater- nary deposits. The mapping was carried out using 1 m long hand augers. The soil and its underlying unit were tested at c. 100 m intervals with the auger, which collects a sample in a groove at its tip. The auger samples are classified in the field and allotted a symbol on a 1:25 000 field map. During more than 100 years of systematic mapping, about 50 symbols have been established which are used by the mapping geologist. The aim of the work is to map the boundaries between vari- ous units shown as polygons on the maps. The testing dis- tance of 100 m provides a semi-statistical documentation of the recognised polygons. Occasional outcrops of pre-Quaternary deposits are clas- sified with letter symbols. On the geological map of Mors, the pre-Quaternary geology is presented as an inset with structural contour lines showing the elevation of the pre- Quaternary surface and the geological units that occur be- low the Quaternary deposits (Figs 2, 3). The map is mainly based on information from the Jupiter well data base, but de- tailed geophysical mapping of Mors (Jørgensen et al. 2005) supported the interpretation of the structural contours. The pre-Quaternary geology The pre-Quaternary geological features on Mors are influ- enced by the Erslev structure, a salt diapir in the central part of the island (Larsen & Baumann 1982), and by glaciotec- tonic deformation (Gry 1940; Pedersen 2000). This is illus- trated by three cross-sections documenting the relationship between the pre-Quaternary and the Quaternary geology (Fig. 2). The diameter of the circular salt diapir is 5–6 km, © 2013 GEUS. Geological Survey of Denmark and Greenland Bulletin 28, 29–32. Open access: www.geus.dk/publications/bull Published map sheets Mapped areas Unmapped areas 1318 I 1318 II1318 III 1217 I 1317 IV 1317 I 1216 II 1316 III 1315 III 1217 II 1315 I1315 IV1215 I 1216 I 1316 IV 1415 IV 1317 II1317 III 1812 III 1812 IV 1417 IV 1416 II 1215 II 1214 I 1514 IV1414 I1314 I 1415 III1315 II 1213 III 1513 IV1413 I1413 IV 1514 II1414 II1314 II1214 II 1314 IV 1214 III 1214 IV 1514 III1414 III1314 III 1213 IV 1215 III 1313 I1313 IV 1212 III 1413 II1413 III1313 II1313 III1213 II 1213 I 1513 III 1412 I1412 IV1312 I1312 IV1212 I1212 IV 1511 III1411 II1411 III1311 II 1511 IV1411 I 1411 IV1311 I1311 IV1211 I 1512 III1412 II1412 III1312 II1312 III1212 II 1211 IV 1112 III 1112 I1112 IV 1112 II 1111 I 1013 II 1113 I1113 IV 1013 I 1113 I1113 IV 1114 II1114 III 1115 II1115 III 1115 IV 1115 I 1215 IV 1116 III 1116 II 1216 III 1116 IV 1216 IV1116 I 1117 III 1114 I1114 IV 1512 I1512 IV 1513 II 1513 IV 1514 I 1217 III1117 II 1511 I 1512 II 1510 IV Mors 10°E 50 km 57°N Jylland Fig. 1. Map of Denmark showing the sheet divisions of the 1:50 000 geo- logical map series. The red frames show map sheets published under the name of Geological map of Denmark 1:50 000. The map sheets are num- bered according to the 1:50  000 topographic maps implemented by the former Danish Geodetic Institute (now the Danish Geodata Agency) in 1953. The map sheet division is based on the UTM system and uses the European Datum 1950. The Survey decided to retain this map sheet divi- sion for the geological mapping, although the National Survey and Cadas- tre (now the Danish Geodata Agency) in 2003 started to use the European Terrestrial Reference System 1989. 3030 and the diapir rises vertically from the base of the Permian salt at a depth of 5–6 km. The top of the salt in the diapir is now found at depths of 600–700 m. A circular dome of chalk caps the salt diapir. Maastrichtian chalk in its centre was for- merly quarried in chalk pits, exposing the Cretaceous–Ter- tiary boundary. The chalk is overlain by bryozoan cherty limestone that forms an aureole around the top of the diapir, and Paleocene clay occurs along the steeply dipping flanks. The uplift of the salt diapir continued in the Paleocene and resulted in an increased thickness of plastic clay away from the diapir centre. In the surrounding marginal depression, Eocene clayey diatomite occurs interbedded with volcanic ash layers. This unit, locally called ‘moler’, crops out in an old clay pit on the northern flank of the diapir (Pedersen 2000). The moler is the most characteristic pre-Quaternary unit in the glaciotectonic complexes that occur on northern Mors. The diatomite is exploited and used for light-weight granulates. On northern Mors, glaciotectonic folds are well exposed in the two largest clay pits. These folds and the sur- rounding hilly terrain were formed by superimposed glacio- tectonic deformation (Pedersen 2000). The most impressive glaciotectonic complex with up-thrust sheets of moler is the Hanklit complex (Figs 4, 5), where a thrust sheet is exposed that was displaced c. 300 m towards the foreland in the south. Parallel ridges trend from Hanklit towards the west, and also here the moler is the target of diatomite exploitation in pits following the crests of the anticlines. Fig. 2. Strongly reduced and modified version of map sheet Mors with three cross-sections: a N–S section (upper), an E–W section (middle) and a NE–SW section of the northern part of Mors (lower). The inset shows the depression on central Mors which coincides with the depression in the top of the chalk covering the salt diapir (Fig. 3). Fig. 4(( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( (( Prækvartæroverfladens geologi / Geology of the pre-Quaternary surface Nedre Miocæn, ler og sand Lower Miocene, clay and sand Oligocæn, ler Oligocene, clay Eocæn, moler (diatomit med askelag) Eocene, clayey diatomite with ash layers Palæocæn, plastisk ler Paleocene, clay Danien, kalk Danian, limestone Øvre Kridt, skrivekridt Upper Cretaceous, chalk Prækvartæroverfladens højdekurver i meter Contours in meters of the pre-Quaternary surface Normalforkastning Normal fault Glacialtektonisk forkastning Glacial tectonic thrust fault 0 5 km 0 1 2 km Kurveinterval: 5 m / Contours interval: 5 m By, anlæg og fyld Town, constructions and dumps Råstofgrav Raw material pit Nedlagt råstofgrav Raw material pit, abandoned Postglaciale aflejringer Postglacial deposits Senglaciale aflejringer Lateglacial deposits Glaciale aflejringer Glacial deposits Ferskvandsler Freshwater clay Ferskvandssand Freshwater sand Ferskvandsgrus Freshwater gravel Ferskvandsgytje Freshwater gyttja Ferskvandstørv Freshwater peat Okker og myremalm Ochre and iron ore Saltvandsler Marine clay Saltvandssand Marine sand Saltvandsgrus Marine gravel Saltvands skalgrus Marine shell gravel Vekslende saltvandsaflejringer Alternating marine deposits Flyvesand Aeolian sand Vekslende tynde saltvandslag, marsk Alternating marsh deposits Smeltevandsler Meltwater clay Smeltevandssand Meltwater sand Smeltevandsgrus Meltwater gravel Moræneler Till, clayey Morænesand Till, sandy Kalkmorænesand Chalky sandy till Vekslende tynde smeltevandslag Alternating thin meltwater deposits Flodslette ler og finsand Outwash clay and fine sand Terrassesand Terrace sand Terrassegrus Terrace gravel 0 -25 -50 -75 E F 6310000 56°55'0 56°50'0 6300000 56°45'0 6290000 56°40'0 6280000 56°55' 6300000 56°50' 6290000 6280000 56°45' 56°40' 8°30' 470000 8°35' 8°40' 480000 8°45' 490000 8°55' Gullerup Stærhøj Mosebjerg Klovbakkerne Sundby Stengrund Hanklit FLADE KLIT Skærbæk Klint Harhøj Ejerslev Lyng Ejerslev havn Ejerslev Klint Nees Øre Holmene Glomstrup Vig Karby Odde Trædemark Odde Ørndrup Hage Stokkær Odde Flejskær Hage Skallerup Hage THISTED BREDNING LIMFJORDEN VISBY BREDNING DRAGSTRUP VIG VI LS UN D KÅS BREDNING SA LL IN G SU ND LIVØ BREDNING Assels Hage Søndervig Lindholm Stenklipperne A G E R Ø Dover Mølle Grund Karby Vig Hage Gudnæs Skyum Øre Å bæ k 5 1 6 5 8 8 8 5 7 5 9 8 5 2 1 3 8 2 25 7 17 16 1 5 7 6 7 1 9 8 4 2 9 18 3 7 1 5 5 11 1 9 5 14 12 11 12 10 11 10 3 18 16 1 1 14 3 1 1 11 1 7 1 1 1 1 Ejerslev Røn Erslev KærGl. Jølby Frøslev Vang Sindbjerg A B E F C D Flade Sejerslev Ejerslev 0 -25 -50 -75 A BSønderby Trehøj VilsCentrum Frøslevvang ErslevErslev Kær Hanklit 0 0 0 0 0 0 0 -25 -25 -25 -25 0 0 -25 -25 -50 -25 -25 -25 -25 -25 -25 -25 -25 -25 -25 -100 -75 -75 -75 -50 -25 -25 -50 -50 -25 -25 -50 +25 -75 -50 -50 -25 -25 +25 +25 0 0 0 0 -25 0 0 0 0 0 -50 -50 -50 -50 -75 -50 0 -25 -50 DC Visby Bredning Damsgård Mollerup Frøslevvang Nykøbing Mors Thisted saltdome Erslev saltdiapir Hannæs Fe gge su nd Sø Bugt Salgerhøj ( (( ( Fig. 4 31 Between the glaciotectonic complexes on northern Mors and the northern flank of the salt diapir, red and green plas- tic clay of the Røsnæs Ler Formation occurs together with dark brown, micaceous, Oligocene to Early Miocene clay. Local outcrops of the Oligocene–Miocene clay (the Brejning and Viborg Formations) are known in the hills along the strait west of Mors. South of the Erslev structure, Miocene heterolithic deposits with mica-rich clay and sand are known from wells and were recognised during the systematic map- ping of southern Mors. The glaciodynamic geology The oldest Quaternary deposits on Mors comprise glacio- lacustrine clay that is referred to the Elsterian Glaciation exposed in coastal cliffs on south-western Mors. On north- ern Mors, alternating beds of till and glaciofluvial sand are exposed along the west coast, and similar Elsterian deposits are known from wells penetrating the buried tunnel valleys. A coastal cliff along the west side of northern Mors exposes 8 m thick sandy till, rich in chalk, which was deposited by a Norwegian ice advance during the Saalian Glaciation (about 300 000 years BP). Characteristic erratic blocks of chalk and flint, originating from erosion of the till, are abundant along the shore (Pedersen et al. 2012). This till and the underlying glaciofluvial sand and gravel are well known from diatoma- ceous clay pits on north-eastern Mors. Glaciolacustrine clay is widespread over large parts of northern and north-western Mors. The clay was deposited during the Middle Weich- selian prior to the Norwegian Ice advance. The depocen- tre was located in the depression between the Thisted salt dome north of Mors and the Erslev salt diapir. Both these areas formed elevated terrains, whereas the remaining part of Mors constituted lowlands characterised by lake-filled depressions with glaciofluvial sand and gravel. In the area around Hanklit, glaciolacustrine clay forms an important element in the glaciotectonic complex (Figs 4, 5). The clay is thrust up into sheets, forming a terrain with E–W-trending parallel ridges. The arc-formed complex was created by the Norwegian Ice advance about 27 000 years BP. A lodgement till rich in indicator boulders such as larvikite and rhombo- hedral porphyries from the Oslo region was deposited during this advance. Fig. 3. Bedrock map of Mors (enlarged version of inset in Fig. 2). The struc- tural contour lines at 25 m intervals show the elevation of the pre-Quater- nary surface. The dome-like structure on central Mors is made of chalk that covers the top of the Erslev salt diapir. The boundaries between gla- ciotectonic complexes and their foreland on northern Mors are also shown. Fig. 4. Part of the map sheet showing the hilly terrain at Flade Klit. The Hanklit glaciotectonic complex is marked by a landscape dominated by elongated hills. The Fur Formation has been thrust-faulted up into paral- lel ridges in the complex. Farther to the south, the thrust sheets mainly consist of glaciolacustrine clay and glaciofluvial sand. Contour interval 5 m. For location see Fig. 2. 26 26 26 581 581 581 26 26 26 581 581 581 581 26 Mosebjerg Klovbakkerne Skærbæk Klint Stokkær Odde Flejskær Hage Skallerup Hage Vilsund Øst Vilsundbroen Under Bakken 8 5 1 3 18 16 1 1 14 3 7 Erslev KærGl. Jølby Gullerup Stærhøj Sundby Stengrund Hanklit FLADE KLIT 1 B E F Salgerhøj 1 km Outwash clay and sand Fur Formation Holocene deposits Late glacial deposits Glacial deposits Tertiary deposits Freshwater clay Freshwater gyttja Peat Marine sand Marine gravel Glaciolacustrine clay Glaciofluvial sand Glaciofluvial gravel Clayey till 56°50´N 8°48´E –50 –50 Normal fault Glaciotectonic thrust fault Contours of the pre-Quaternary surface (m) Thisted salt dome Erslev salt diapir 0 0 0 0 –25 –25 0 –25 –50 –25 –25 –75 –75 +25 –75 0 0 –50 –50 –50 –50 –25 5 km Lower Miocene clay and sand Oligocene clay Eocene diatomite & ash layers Paleocene clay Danian limestone Upper Cretaceous chalk 3232 After the Norwegian Ice melted back, Mors was charac- terised by parallel hills intersected by lake-filled valleys with glaciolacustrine clay deposits as patches scattered over the landscape. A few thousand years later the advancing Swedish Ice remodelled the landscape. On northern Mors, thrusting and folding from the north-east superimposed the architec- ture of the glaciomorphological landscape. When the ice reached south-western Mors it stopped briefly and formed a stationary line, and its meltwater created a cone-shaped outwash plain. At its apex, boulders, stones and gravel were deposited, which are now quarried in gravel pits. The postglacial geology During the late glacial and Holocene periods, Mors was af- fected by three significant events: (1) meltwater erosion dur- ing the deglaciation and formation of a kettle-hole landscape caused by melting of dead ice, (2) marine transgression ac- companied by sedimentation in straits and fjords after the Ice Age, and (3) glacio-isostatic rebound. During the Atlan- tic sea-level highstand, coastal plains formed in front of the fossil coastal cliffs. A number of fossil straits and fjords with marine gyttja and marine sand occur on Mors. The most significant fos- sil fjord is an E–W-trending depression located above the central part of the salt diapir on central Mors. Marine het- erolithic deposits are characterised by shells of Cardium, and mounds of oyster (Ostrea edulis) beds formed where strong currents cut narrow gaps in the former fjord. A number of distinctive fossil coastal cliffs occur, particularly on northern Mors where raised shorelines are found up to c. 5 m above the present sea level. The raised beaches have occasionally dammed coastal lakes. Beach ridges occur along the coastline on southern Mors. Several of these contribute to the closure of small fjords and coastal lakes with peat accumulation. In the past, the coastal plains were larger, but are now subjected to increased erosion along the coastline of Mors. References Gry, H. 1940: De istektoniske Forhold i Moleret. Med Bemærkninger om vore dislocerede Klinters Dannelse og om den negative Askeserie. Med- delelser fra Dansk Geologisk Forening 9, 586–627. Jørgensen, F., Sandersen, P.B.E., Auken, E., Lykke-Andersen, H. & Sø- rensen, K. 2005: Contributions to the geological mapping of Mors, Denmark – a study based on a large-scale TEM survey. Bulletin of the Geological Society of Denmark 52, 53–75. Larsen, G. & Baumann, J. 1982: Træk af Mors salthorstens udvikling. Dansk Geologisk Forening, Årsskrift for 1981, 151–155. Pedersen, G.K et al. 2012: Molerområdets geologi – sedimenter, fossiler, askelag og glacialtektonik. Geologisk Tidsskrift 2011, 41–135. Pedersen, S.A.S. 2000: Superimposed deformation in glaciotectonics. Bulletin of the Geological Society of Denmark 46, 125–144. Pedersen, S.A.S. & Jakobsen, P.R. 2012: Geological map of Denmark, 1:50 000, Mors. Copenhagen: Geological Survey of Denmark and Greenland. Authors’ address Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: sasp@geus.dk Fig. 5. The impressive glaciotectonic thrust sheet exposed in the Hanklit coastal cliff. The thrust sheet is 60 m thick and was displaced for a dis- tance of 300 m towards the foreland to the south. mailto:obe@geus.dk