Eocene Gastropods of Western Kamchatka Ð Implications for High-Latitude North Paci®C Biostratigraphy and Biogeography

Palaeogeography, Palaeoclimatology, Palaeoecology 166 (2001) 121±140 www.elsevier.nl/locate/palaeo Eocene gastropods of western Kamchatka Ð implications for high-latitude north paci®c biostratigraphy and biogeography A.E. Oleinik* Department of Geography and Geology, Florida Atlantic University, 777 Glades Road, Physical Sciences Building 336, Boca Raton, FL 33431, USA Received 19 May 1999; accepted for publication 15 September 1999 Abstract Fossiliferous rocks of the Snatolskaya and Kovachinskaya formations comprise a Middle and Late Eocene shallow-marine record of the central part of western Kamchatka. Gastropod assemblages of these formations contain taxa that are conspeci®c with those in Paleogene strata of western North America and Japan, as well as a large percentage of endemic species. Analysis of the latitudinal ranges and worldwide occurrences of gastropod genera from these formations show the presence of three biogeographic components: cosmopolitan, North Paci®c, and endemic. No Tethyan, or circumtropical genera are present in these Kamchatkan Middle and Late Eocene gastropod faunas. Changes in the geographic distribution of North Paci®c gastropod assemblages through the Middle and Late Eocene indicate that only eastern Paci®c Tethyan taxa were subjected to latitudinal range reduction. The distribution of cosmopolitan and North Paci®c elements did not signi®cantly change from the Middle to Late Eocene, which suggests a relatively stable environment and climate stability during that time. High-latitude Eocene gastropod assemblages from western Kamchatka demonstrate a high level of endemism at the species level and a low-level of endemism on the genus level. This pattern is thought to be a result of the unrestricted migration of cosmopolitan taxa northward along the shallow-marine margin of the Paci®c rim. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Eocene; Kamchatka; gastropods; Tethyan; cosmopolitan; endemic; latitudinal ranges; biogeography 1. Introduction climate, and lack of roads resulted in a very incom- plete knowledge of the stratigraphy and paleontology Shallow-marine rocks of Middle and Late Eocene of this area. Specimens studied for the present work age in western Kamchatka contain 86 species of were collected from 1984 to 1989 during extensive gastropods, in 53 genera. This diverse gastropod ®eld studies of the Kamchatka by expeditions of the assemblage remained very poorly studied until recent Soviet Academy of Sciences with participation of the years (Oleinik, 1987, 1988, 1994, Oleinik, 1996; author. Much of this ®eldwork was focused primarily Sinelnikova et al., 1991). Fossil collections made on the stratigraphy and paleontology along the west- prior to the 1980s by Soviet ®eld geologists mainly central coast of the Kamchatka Peninsula (the Tigil contain large and abundant bivalves (Krishtofovich, and Palana regions of local usage), adjacent to the 1947). The combination of a remote location, harsh Gulf of Shelikhov in the Sea of Okhotsk (Fig. 1). This region is characterized by a thick succession of * Fax: 11-561-2972985. Cenozoic sedimentary rocks and is known as the E-mail address: [email protected] (A.E. Oleinik). western Kamchatka Depression (Zinkevich and 0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0031-0182(00)00205-4 122 A.E. Oleinik / Palaeogeography, Palaeoclimatology, Palaeoecology 166 (2001) 121±140 Fig. 1. Geologic map of western Kamchatka with fossil localities. Tsukanov, 1993). Paleogene marine deposits crop out and Kovachinskaya formations suggest that they in the sea cliffs along the coast of the Gulf of Sheli- were deposited at upper subtidal to outer neritic khov for a distance of approximately 500 km, as well depths (10±500 m) in the back of an active volca- as in river bluffs in the inland parts of the western nic arc (Oleinik, 1999). The existence of an active Kamchatka Depression. Middle Eocene to Miocene volcanic arc is evident from the large volume of rocks make up a large transgressive cycle, overlaying Paleogene volcanic rocks, including those of a Late Paleocene±Early Eocene hiatus that can be Middle to Late Eocene age, forming a Western traced throughout western Kamchatka and the Sea Kamchatka Volcanic Belt, also known as the of Okhotsk region (Gladenkov et al., 1990). Middle Koryak±West Kamchatka Volcanic Belt (Zonenshain Eocene strata overlie Paleocene±Lower Eocene rocks et al., 1990). Based on the K±Ar dating of the with angular unconformity and are conformably volcanic rocks, the last episode of Paleogene overlain by the Uppermost Eocene±Lower Oligo- volcanism within the Western Kamchatka Volcanic cene Amaninskaya and Gakhinskaya formations Belt occurred during the uppermost Bartonian± (Gladenkov et al., 1991). The lithology, tectonic lowermost Priabonian (46.5±37.4 my) (Gladenkov et history, and faunal composition of the Snatolskaya al., 1990). A.E. Oleinik / Palaeogeography, Palaeoclimatology, Palaeoecology 166 (2001) 121±140 123 2. Area description, materials and methods: Formation in the Mainach River Section contain stratigraphy, age, and correlation of Middle and Rhizammina indivisa, Bathysiphon nodosariaformis, Upper Eocene rocks of western Kamchatka Silicosigmolinacf. californica, Haplophragmoides glabratus, Asanospira cf. exavata, Asanospira cf. Fossiliferous Eocene shallow-marine rocks crop akkeshiensis, Glomospira corona,andRecurvoides sp. out in sea-cliffs and river bluffs along the western The upper part of the Snatolskaya Formation in the coast of Kamchatka. They are subdivided into the southern ¯ank of the Tochilinskiy Section contains Snatolskaya and Kovachinskaya formations that Trochammina vitrea, Gyroidina kamtschatica, comprise the basal part of a large transgressive Elphidium californicum, Reophax dif¯ugiformis, cycle, and are separated from the older Paleogene Haplopharagmoides snatolensis, Cyclammina ezoensis, rocks by a regional unconformity (Gladenkov et al., Trochammina markini, Cyclammina tani, Dorothia 1991). amakusaensis, Textularia imariensis, Guttulina irregu- The most complete sections of the Snatolskaya and laris, Gyroidina kamtschatica, Elphidium asagiensis, Kovachinskaya formations in the Tigil and Palana Caucasina eocaenica kamtschatica, Globobulimina regions crop out in the sea cliffs along the southeast- paci®ca,andBolivina jacksonensis (Gladenkov et al., ern coast of the Gulf of Shelikhov. This area is char- 1991b). These assemblages strongly imply a Middle acterized by the Tigil and Lesnaya±Palana uplifts of Eocene age for the Snatolskaya Formation (Gladenkov Neogene age, which produced a number of synclines et al., 1991a). Serova (1969), however, noted on the and anticlines of predominantly northeastern strike possible presence of the Upper Eocene rocks within that are incised by a shoreline running generally this formation. The planktonic foraminiferal assem- perpendicular to strike. Poor exposures adjacent to blage is poorly preserved and can be generally assigned the seashore and inland areas necessitated making a to the Globigerina boweri regional zone (Serova, 1969; composite section from numerous outcrops in river Krasheninnikov et al., 1988) and suggests a Lutetian to valleys. Nineteen stratigraphic sections of the Bartonian age for the Snatolskaya Formation. A number Snatolskaya and Kovachinskaya formations, ranging of conspeci®c benthic and planktonic foraminifers in the in thickness from 40 to nearly 800 m, were measured Snatolskaya Formation of western Kamchatka suggest at 16 localities in Tigil and Palana regions of western correlations with the Narizian Stage of California Kamchatka (Fig. 1). (Mallory, 1959), the Middle Eocene (Lutetian± The Snatolskaya Formation is represented mostly Bartonian) Takisawa Formation (Honshu), and the by shallow-marine, medium- to ®ne-grained, laterally lowermost part of the Poronai Formation (Upper continuous sandstones, with abundant lagoonal and Bartonian, Hokkaido) of Japan, which contain both delta front deposits, containing a rich and diverse benthic foraminiferal assemblages and nannoplankton fauna of benthic molluscs. Only its lowermost part (Saito et al., 1984). locally contains alluvial conglomerates and terrestrial The Kovachinskaya Formation conformably over- near-shore deposits, where the Snatolskaya Formation lies the Snatolskaya Formation and consists of marine directly overlay Cretaceous rocks. The thickness of siltstone, claystone, and sandstone. Rocks of the the Snatolskaya Formation in the Tigil and Palana Kovachinskaya Formation contain numerous tuff regions (a continuous and complete section with horizons, which suggest an increase in volcanic activ- observable lower and upper contacts) varies from 10 ity during its deposition. The Kovachinskaya Forma- to 295 m. Rocks of the Snatolskaya Formation tion in the Tigil and Palana regions varies in thickness become thinner and coarser-grained, and change from 30 to 475 m and is conformably overlain by from ®ne-grained sandstones to medium- to coarse- Lower Oligocene rocks of the Amaninskya and grained sandstones and conglomerates, toward the Gakhinskaya formations. areas of exposure of Cretaceous rocks. The Kovachinskaya Formation consists of a ®ne- Benthic foraminifers in the Snatolskaya Formation grained clayey rocks, and reaches its maximum thick- occur at two localities in the Tigil Region: the ness in areas most distant from outcrops of Cretaceous Tochilinskaya Anticline and Mainach River sections rocks. Rocks of this formation become progressively

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