OPCE-STR.vp Acta Bot. Croat. 68 (2), 199–209, 2009 CODEN: ABCRA 25 ISSN 0365–0588 Fossil diatom flora from the marine Paleogene stratigraphic key section of northeast Kamchatka, Russia ANDREY YU. GLADENKOV* Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow 119017, Russia The Oligocene diatom flora from the marine Paleogene stratigraphic key section of north- east Kamchatka is described for the first time. The fossil flora contains a number of taxa of moderate to poor preservation and low abundance. Analysis of stratigraphic occurrence of diatoms throughout the section has been conducted. Two diatom assemblages of different ages are recognized in different parts of the 900 m-thick Alugivayam Formation. The younger assemblage is characterized by the presence of Cavitatus sp. cf. jouseanus and Odontella sawamurae. Co-occurrence of these taxa may indicate the age of enclosing sed- iment not older than ~31 Ma (the early Oligocene). The older assemblage from the basal part of the Alugivayam Formation lacks the mentioned taxa but contains Stephanopyxis species such as St. grunowii and St. marginata. Most likely, its age is at the earliest Oligocene. It is shown that in the studied Paleogene stratigraphic section diatoms appear just above the Eocene/Oligocene boundary. Data obtained on diatoms and diatom bio- markers may indicate increased diatom productivity in the sea basin after the Eocene/ Oligocene transition. The first data on diatom flora from stratigraphically well-controlled samples support the Oligocene age of the Alugivayam Formation in the Il’pinskii Penin- sula section and contribute to regional correlations of the Oligocene strata in Kamchatka. Key words: diatom, biostratigraphy, Paleogene, Oligocene, Pacific, Kamchatka Introduction The stratigraphic section on the Il’pinsky Peninsula, northeast Kamchatka (Fig. 1), is a unique key section for the marine Paleogene of northeast Asia with a practically continuous and complete sequence composed of 2500 m-thick Paleocene through Oligocene sedi- ments. Moreover, it is one of the northernmost known places in the North Pacific region where planktic foraminifera and calcareous nannofossils of the Paleocene and Eocene have been documented from different stratigraphic levels (BENIAMOVSKII et al. 1992, VOLOBUEVA et al. 1994, and others). Numerous mollusk-bearing horizons are also typical of the section. The assemblages of planktic foraminifera and coccolithophorids that are correlative with ACTA BOT. CROAT. 68 (2), 2009 199 * Corresponding e-mail address: agladenkov@ilran.ru U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:11 Color profile: Disabled Composite 150 lpi at 45 degrees their analogues from standard Paleogene zones have been used to subdivide the host sedi- mentary succession and determine the age of established stratigraphic units. However, until recently the two upper formations (the Gailkhavilanvayam and Alugivayam, 1150 m thick in total) have been considered to be barren of both calcareous and siliceous planktic marine microorganisms, including diatoms. The initial data on the first finds of diatom remains from the Alugivayam Formations were reported only two years ago (A. GLADENKOV and Y. GLADENKOV 2007). Meanwhile, fossil diatoms are one of the primary biostratigraphic tools for the dating and correlation of the post-Eocene marine sediments in the middle to high latitudes of the North Pacific (the current North Pacific Oligocene to Quaternary diatom zonation includes more than 20 zones). The Oligocene age and position of its lower bound- ary in the Il’pinsky Peninsula stratigraphic section were determined based on assemblages of benthic foraminifera and mollusks. In general, the Alugivayam Formation was previ- ously attributed to the Oligocene, while the underlying Gailkhavilanvayam Formation was referred to the upper Eocene. The present study of diatoms from the Alugivayam Forma- tion is the first description of Cenozoic diatom flora from the section. Materials and methods In order to collect additional geological and paleontological material, fieldwork in the western part of the Il’pinskii Peninsula was conducted recently by the joint Russian-Japa- nese scientific group. In particular, the work was aimed at collecting samples for diatom analysis from the Gailkhavilanvayam and Alugivayam formations. The Gailkhavilanvayam Formation (~250 m thick) is composed of alternating tuffaceous siltstones, tuffaceous argillites, and tuffstones with thin interbeds of silicic tuffs (Fig. 2). The formation contains abundant concretions of variable sizes and shapes. The base of the formation is corre- sponds to the Laparelam lithologic marker »horizon« 7.5 m thick composed of light-col- ored silicic ash tuff. The overlying Alugivayam Formation (900 m thick) is composed of tuffaceous siltstones and shales with interbeds and lenses of tuffstones. The deposits con- 200 ACTA BOT. CROAT. 68 (2), 2009 GLADENKOV A. YU. Fig. 1. Location of the Il’pinskii Peninsula (shown by black arrow) in Kamchatka U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:14 Color profile: Disabled Composite 150 lpi at 45 degrees tain shape- and size-variable carbonate concretions either isolated or clustered into layers inclusive. Besides, there are glendonites and »floating« pebbles in the rocks. The formation is subdivided into the lower (120 m thick) and upper (approximately 780 m thick) subformations. The Mulatkhan lithologic marker »horizon« (10 m thick) at the base of the Upper Alugivayam Subformation is composed of tuffstones, gravelstones, and tuffaceous siltstones. The contact with the underlying Gailkhavilanvayam Formation is conformable. ACTA BOT. CROAT. 68 (2), 2009 201 OLIGOCENE DIATOMS FROM NORTHEAST KAMCHATKA Fig. 2. Generalized stratigraphic column of the Alugivayam Formation and underlying strata of the Il’pinskii Peninsula stratigraphic section, northeast Kamchatka, with indicated position of diatom-bearing samples, and defined beds with diatoms (modified from A. GLADENKOV and Y. GLADENKOV 2007). 1 – shale, tuffaceous shale; 2 – siltstone, tuffaceous siltstone; 3 – sandstone, tuffstone. 4 – silicic tuffs; 5 – carbonate concretions (a) and glendonites (b); 6 – the Laparelam (L) and Mulatkhan (M) lithologic marker »horizons«; 7 – samples from inte- riors of mollusk shells; 8 – samples from carbonate concretions; FO – the first occurrence. U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:17 Color profile: Disabled Composite 150 lpi at 45 degrees Samples of carbonate concretions and the interiors of fossil mollusk shells were col- lected for diatom analysis during fieldwork. Collection of such material was critical as dia- toms were absent in the enclosing matrix as shown by previous studies. The concretions and interiors of mollusk shells were sampled because in some cases diatoms are present in fine sediment within concretions or shells and are thereby protected from mechanical and chemical abrasion in the course of sedimentation or during fossilization and catagenesis (BARRON and MAHOOD 1993, GLADENKOV 2003, 2007). Due to the induration of the sediments and the low concentration of diatoms, a proce- dure including a treatment by acetic acid and sodium pyrophosphate and subsequent centrifugation with heavy liquid was used to process the samples (GLADENKOV 2003). Strewn slides were prepared on 18 ´18 mm cover glasses and mounted in Naphrax mount- ing medium (index of diffraction = 1.74) on glass slides. The slides were examined in their entirety under a Jeneval (Zeiss) light microscope at 400´, with identifications routinely checked at 1000´. Because of low abundance of diatoms, all valves were encountered on a slide and all of the taxa were tabulated for each strewn slide. The preservation of diatoms is listed as M (moderate), and P (poor) depending on the degree of destruction and dissolution of valves. The relative abundance is evaluated as F (few, more than 100 valves), R (rare, 10–100 valves), and VR (very rare, less than 10 valves). Numerical ages, geological ep- ochs, subepochs and periods are used herein according to the Cenozoic geochronologic and geomagnetic polarity scales (BERGGREN et al. 1995). Results All 10 samples collected from the Gailkhavilanvayam Formation are barren of sili- ceous microfossils. Fossil diatoms (Tab. 1) were found in the 24 examined samples (16 samples are fossil mollusks and 8 are carbonate concretions) from the Alugivayam Forma- tion (Figs. 2, 3, Tab. 1). Overall, diatoms are rare to very rare and moderately to poorly pre- served. The first occurrence of diatoms is in sample GIN 70/44 from the basal part of the Lower Alugivayam Subformation. In particular, the appearance of Stephanopyxis spp., St. grunowii and St. marginata is documented at this level (7 m above the base of the Alugivayam Formation). The stratigraphically lowest sample yielding Cavitatus sp. cf. jouseanus and Odontella sawamurae is sample GIN 70/5 from the Lower Alugivayam Subformation (about 215 m above the base of the Alugivayam Formation). Both these taxa range to the top of the section in sample GIN 70/10 (880 m). Ikebea tenuis occurs from sample GIN 70/19 (260 m) to sample GIN 70/9 (840 m), and Paralia sulcata from sample GIN 70/3 (105 m) to sample GIN 70/9. Chaetoceros spp. spores range from sample GIN 70/4 (145 m) to the top of the section, and Trochosira sp. cf. spinosa from sample GIN 70/18 (300 m) to the top of the section in sample GIN 70/10 (880 m). Samples GIN 70/43 (50 m) and GIN 70/19 (260 m) yield Kisseleviella sp., while sample GIN 70/3 (105 m) con- tains Pyxilla sp. Stellarima microtrias occurs from sample GIN 70/14 (370 m) to sample GIN 70/15 (620 m), while Hemiaulus polymorphus from sample GIN 70/19 (260 m) to sample GIN 70/1 (760 m). The typical diatom flora from the Alugivayam formation is characterized by marine neritic-planktic and sublitoral taxa. Low abundance of diatoms and their poor to moderate preservation may probably indicate abrasion and dissolution of valves during sedimenta- tion and/or diagenesis. 202 ACTA BOT. CROAT. 68 (2), 2009 GLADENKOV A. YU. U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:17 Color profile: Disabled Composite 150 lpi at 45 degrees A C T A B O T .C R O A T .68 (2),2009 203 O L IG O C E N E D IA T O M S F R O M N O R T H E A S T K A M C H A T K A Tab. 1. Stratigraphic occurrence and relative abundance of marine diatoms from the Alugivayam Formation, the Il’pinskii Peninsula stratigraphic section, northeast Kamchatka. Preservation: m – moderate, p – poor. Numbers of valves of diatoms counted in each sample are shown. Relative abundance: F – few; R – rare; VR – very rare. Partial boxes within the Table indicate the first observations of biostratigraphically important taxa in the Alugivayam Formation. Above a base of the Alugivayam formation (m) 7 50 105 145 180 215 260 300 335 370 410 450 490 520 550 585 620 655 695 730 760 795 840 880 Sample #GIN- 70/ 44 43 3 4 42 5 19 18 41 14 40 13 17a 17 16 39 15 6 7 12 11 8 9 10 Relative abundance F VR R VR R R R R R VR R R R R R VR R VR R VR VR R VR VR Preservation p p p p m p p p p p p p p p p p p p Arachnoidiscus sp. 1 Azpeitia sp. 1 Cavitatus sp. cf. jouseanus (Sheshukova) Williams 3 4 3 2 2 2 1 3 4 1 3 1 2 1 2 1 1 Chaetoceros spp. spores 1 2 2 5 3 3 2 3 16 21 11 3 2 9 5 5 3 4 3 3 2 Cocconeis spp. 1 2 1 1 1 1 1 Coscinodiscus argus Ehrenberg 1 C. marginatus Ehrenberg 1 1 Coscinodiscus spp. 1 1 1 3 1 Genus et species indet. 1 1 4 3 3 1 1 1 1 Hemiaulus polymorphus Grunow 2 1 1 2 1 1 Hemiaulus spp. 2 4 1 1 Hyalodiscus sp. 1 Ikebea tenuis (Brun) Akiba 3 1 2 1 3 1 2 1 1 Kisseleviella sp. 1 1 Odontella sawamurae Akiba 2 1 2 8 1 Paralia sulcata (Ehrenberg) Cleve 1 2 1 2 3 1 1 1 1 1 Ploiaria sp. 2 m –p m –p m –p m –p m –p m –p U : \ A C T A B O T A N I C A \ A c t a - B o t a n 2 - 0 9 \ G l a d e n k o v . v p 9 . l i s t o p a d 2 0 0 9 1 3 : 0 6 : 1 7 C o l o r p r o f i l e : D i s a b l e d C o m p o s i t e 1 5 0 l p i a t 4 5 d e g r e e s 204 A C T A B O T .C R O A T .68 (2),2009 G L A D E N K O V A .Y U . Above a base of the Alugivayam formation (m) 7 50 105 145 180 215 260 300 335 370 410 450 490 520 550 585 620 655 695 730 760 795 840 880 Sample #GIN- 70/ 44 43 3 4 42 5 19 18 41 14 40 13 17a 17 16 39 15 6 7 12 11 8 9 10 Relative abundance F VR R VR R R R R R VR R R R R R VR R VR R VR VR R VR VR Preservation p p p p m p p p p p p p p p p p p p Pyxilla sp. 1 Rhabdonema sp. 1 Sceptroneis sp. 1 Stellarima microtrias (Ehrenberg) Hasle et Sims 1 1 1 Stephanopyxis grunowii Grove et Sturt 6 1 1 1 St. marginata Grunow 3 1 1 1 St. spinosissima Grunow 1 St. superba (Greville) Grunow 1 St. turris (Greville et Arnott) Ralfs 2 2 3 1 7 6 1 2 Stephanopyxis spp. 88 3 2 4 19 4 Trochosira sp. cf. spinosa Kitton 2 1 2 1 3 1 1 Xanthiopyxis panduraeformis Pantocsek 1 Xanthiopyxis sp. cf. ovalis Lohman 2 1 1 2 Xanthiopyxis sp. 4 1 1 Tab. 1. – Continued m –p m –p m –p m –p m –p m –p U : \ A C T A B O T A N I C A \ A c t a - B o t a n 2 - 0 9 \ G l a d e n k o v . v p 9 . l i s t o p a d 2 0 0 9 1 3 : 0 6 : 1 7 C o l o r p r o f i l e : D i s a b l e d C o m p o s i t e 1 5 0 l p i a t 4 5 d e g r e e s Discussion Initial analysis of molluscan and diatom assemblages from the Alugivayam Formation made it possible to distinguish the »beds with mollusks« and »beds with diatoms« (A. GLADENKOV and Y. GLADENKOV, 2007). Analysis of diatoms from different stratigraphic levels allows recognition of the beds with Stephanopyxis spp. in the lower part of the Alugivayam ranging approximately from the base of the formation to level of 215 m above this base, and the beds with Cavitatus cf. jouseanus – Odontella sawamurae in the higher stratigraphic interval (Fig. 2). A base of the former beds is characterized by appearance of diatoms in the section, and a base of the latter beds is marked by the first occurrences of Cavitatus cf. jouseanus and Odontella sawamurae. Determining a precise age for the de- fined units has proven difficult owing to the absence of most of age-diagnostic Cenozoic marine taxa. The most biochronologically-important taxa found are Cavitatus cf. jou- seanus and Odontella sawamurae. In particular, their occurrence is of some significance for estimating the lower age limit of the beds characterized by the presence of these taxa. It is known that Cavitatus is the extinct cosmopolitan marine genus including a number of planktonic species. Cavitatus jouseanus is the oldest species within this genus and wide- spread in Oligocene to Miocene sediments. According to available data, in the North Pa- cific region the first representatives of Cavitatus (C. jouseanus) appear in the early Oligocene (AKIBA et al. 1993, GLADENKOV and BARRON 1995, and others). Their first occur- ACTA BOT. CROAT. 68 (2), 2009 205 OLIGOCENE DIATOMS FROM NORTHEAST KAMCHATKA Fig. 3. Diatoms from the Alugivayam Formation. 1, 2 – Cavitatus sp. cf. jouseanus (Sheshukova) Williams; 3–5 – Odontella sawamurae Akiba; 6 – Stephanopyxis marginata Grunow; 7 – St. turris (Greville et Arnott) Ralfs; 8 – St. grunowii Grove et Sturt; 9 – Ikebea tenuis (Brun) Akiba; 10 – Chaetoceros sp. (spore); 11 – Stephanopyxis sp.; 12 – Trochosira sp. cf. spinosa Kitton. Scale bars = 10 mm (A: for 1–2; B: for 3–12). U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:21 Color profile: Disabled Composite 150 lpi at 45 degrees rence is within the early Oligocene Rhizosolenia oligocaenica Zone of the North Pacific di- atom zonation (Fig. 4). The first occurrence of Cavitatus jouseanus marks a base of the Subzone b within the Rhizosolenia oligocaenica Zone at ~31 Ma (GLADENKOV 1998, 1999). A top of the Rhizosolenia oligocaenica Zone defined by the first occurrence of 206 ACTA BOT. CROAT. 68 (2), 2009 GLADENKOV A. YU. Fig. 4. The North Pacific Oligocene through early Miocene diatom zones (after BARRON and GLADENKOV 1995, GLADENKOV and BARRON 1995, GLADENKOV 1998, 1999) correlated to the geochronologic and geomagnetic polarity time scales of BERGGREN et al. (1995). FO – the first occurrence; FCO – the first common occurrence; a–c – subzones; mid. – middle. U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:23 Color profile: Disabled Composite 150 lpi at 45 degrees Rocella vigilans is at the level of 30.2 Ma (GLADENKOV and BARRON 1995, GLADENKOV 1998). Thus, the finds of Cavitatus cf. jouseanus may indicate an age not older than ~31 Ma for diatom flora from the upper part of the Alugivayam Formation. On the other hand, the presence of Odontella sawamurae is also important. This extinct marine species is typical of the northwestern Pacific marginal sediments and is documented from the Oligocene to early Miocene deposits of Japan, Sakhalin, and Kamchatka (MORITA et al. 1996, GLADENKOV at al. 2000, ORESHKINA 2009, and others). Among these localities, the oldest finds of Odontella sawamurae are known from Hokkaido Island and confined to the early Oligo- cene Rocella vigilans Zone (30.2 to 29.6 Ma) (MORITA et al. 1996). However, in sequences from the island slope of the Kuril-Kamchatka Trench Odontella sawamurae ranges from an older interval of the early Oligocene corresponding to the Rhizosolenia oligocaenica Zone (TSOI 2002). These data suggest that the 30.2 to 29.6 Ma age for the first occurrence of Odontella sawamurae from Hokkaido may not apply in more northern regions, such as northeast Kamchatka, where this datum level is maybe older. Thus, the presence of Odontella sawamurae and its co-occurrence with Cavitatus cf. jouseanus do not conflict with a lower possible limit for the early Oligocene enclosing sediments of not more than ~31 Ma. It follows that diatom assemblage from the underlying beds with Stephanopyxis spp. lacking both Cavitatus cf. jouseanus and Odontella sawamurae, and Ikebea tenuis, is older and perhaps its age may be dated as the earliest Oligocene. An early Oligocene age for the diatom assemblages is supported by data obtained on benthic fossil groups. Particularly, a transition from the late Eocene Plectofrondicularia packardi – Caucasina eocaenica kamtschatica benthic foraminifera assemblage to the Oligocene Haplophragmoides laminatus – Melonis chimokiensis assemblage is docu- mented at the boundary between the Gailkhavilanvaym Formation and Alugivayam For- mation (BENIAMOVSKII et al. 1992, VOLOBUEVA et al. 1994). The recent data on magneto- stratigraphy indicate that a base of the normal-polarity Chron 13n (at 33.5 Ma) is located just above a boundary between the Gailkhavilanvaym and Alugivayam formations, and the early Oligocene reverse-polarity Chron 12r is compressed in the Alugivayam Formation (MINYUK and GLADENKOV 2007). The latest data on highly branched isoprenoids (the typical diatom biomarkers) from the Il’pinskii Peninsula section should be especially emphasized. It has revealed that con- centrations of isoprenoids increase drastically just above the boundary between the Gail- khavilanvaym and Alugivayam formations (SHIINE et al. 2008). This means these concen- trations in the lower Oligocene sediments are clearly higher than those from upper Eocene, indicating a higher diatom productivity after the Eocene/Oligocene boundary (SHIINE et al. 2008). Conclusions The Alugivayam Formation of the Il’pinskii Peninsula stratigraphic section, northeast Kamchatka, contains Oligocene marine diatom assemblages of moderate to poor preserva- tion and low abundance. The presence of Cavitatus cf. jouseanus and Odontella sawa- murae in the younger diatom assemblage may indicate the early Oligocene age with a lower possible limit for the enclosing sediments of not more than ~31 Ma. An age of the older assemblage from the underlying strata of the Alugivayam Formation is inferred as the ACTA BOT. CROAT. 68 (2), 2009 207 OLIGOCENE DIATOMS FROM NORTHEAST KAMCHATKA U:\ACTA BOTANICA\Acta-Botan 2-09\Gladenkov.vp 9. listopad 2009 13:06:23 Color profile: Disabled Composite 150 lpi at 45 degrees earliest Oligocene. The data on diatoms from stratigraphically well-controlled samples support and refine the Oligocene age of the Aluginskaya Formation in the Il’pinskii Penin- sula section. Information obtained on the age of diatom-bearing deposits contributes to re- gional correlations of the Oligocene strata in Kamchatka. Data on diatoms together with the latest data on diatom biomarkers from the section indicate increased diatom productiv- ity in the sea basin after the Eocene/Oligocene transition. Acknowledgements I thank the Organizing Committee of the 20th International Diatom Symposium and its Chairman – Prof. Nenad Jasprica from the Institute for Marine and Coastal Research, Uni- versity of Dubrovnik, Croatia, for his invitation to write this paper for Acta Botanica Croatica. 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