2000/01/01 by Taldenkova, E.
Earth and Planetary Sciences · #Geological Studies and Exploration #Geology and Paleoclimatology Research #Marine and environmental studies #Science
paper · pdf · doi:10.2312/polarforschung.68.197
openalex publication_date 2000/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/15
The analysis 01' original and published data on the distribution 01' modern and fossil molluscs in the Late Cenozoic deposits 01' the North Pacific and Eastern Arctic allowed to trace variations in the composition 01' fossil assemblages with time and to reconstruct faunistic cxchanges between the two oceans.The first exchange between the Pacific and Atlantic molluscs via the Arctic Ocean probably occurred during the Late Miocene.Recent evidence came from southwestern Alaska showing the strait had opened by ar least the Late Miocene or earliest Pliocene (4.8-5.5.Ma).Detailed analysis 01' the Pliocene formations 01' Kamchatka gives evidence for immigrations 01' species 01' the genera Elliptica (4 Ma), Tridonta, Rictocvma, Nicania and Cyrtodaria (3.5 Ma) frorn the Arctic into the North Pacific.The most abundant migration 01' Pacific species into the Arctic and North Atlantic occurred during the Late Pliocene.Transgressive marine deposits 01' this agc containing molluscs 01' Pacific origin have been found in many localities along the Arctic coast frorn northern Chukotka to the American coast, Greenland.Iceland and even the Pechora Sea.Age detenninations 01' North Arnerican and Canadian shells range from 2.7 to 2.14 Ma, thus suggesting the Bering Strait was opened during this period.Abundance 01' boreal Pacific molluscs throughout the Arctic shelf, together with other paleofaunistic and paleofloristic data, gives evidence for the existence 01' seasonally ice-free coastal areas.However, no arctic species, in a biogeographical sense, have been found in the late Pliocene Beringian and Ust-Limimtevayam assemblages 01' the North Pacific.First traces 01' the arctic cold water species Ponlandia arctica in the North Pacific wcrc found in the Eopleistocene deposits 01' Chukotka (Pinakul beds), Kamchatka (Lower Olkhovaya and Tusatuvayam beds), and Alaska (An vili an anel Middletonian beds).All these mainly boreal assemblages displaya unique coexistence 01' arctic cold water and lower boreal warm water species.Presently such a combination is not observed anywhere.The maximum immigration 01' arctic molluscs into the North Pacific occurred during the Middle Pleistocene, when boreal-arctic and arctic molluscs 01' atlantic origin (Yoldiellafraterna, Y. intermedia, Y. lenticula, Batltyarca glaeialis) appeared in this area for the first time, Latc Pleistocene regression isolated faunas 01' the two oceans for a long time and strongly influenced the modern distribution 01' sublittoral molluscs: recent assemblages 01' the Pacific are warmer than Pleistocene ones (due to the absence 01' arctic species), and the modern high Arctic assernblages are the coldest among Pleistocene ones.