Documenting the Age of the Bering Strait

阿拉斯加半岛中新世熊湖组中的海洋双壳类软体动物Astarte的存在证明了白令海峡的首次开放。 在新生代，阿施塔特只生活在北大西洋和北冰洋，直到白令海峡的开放允许它迁移到北太平洋。 Astarte以前曾在北太平洋新第三纪动物群中被发现，但没有发现年龄诊断微化石。 Astarte与其他丰富的软体动物群一起出现在熊湖组300米厚、更长的地层剖面中的两个层位。 这两个层位的软体动物壳内的100个硅藻类群代表Neodenticula kamtschatica硅藻带的B亚带。 Neodenticula kamtschatica带的B亚带的年龄范围为480 - 550万年前（Ma），在一个完善的北太平洋硅藻生物年代学中，明显早于研究人员通常引用的白令海峡约3.0-4.0 Ma的年龄。 Astarte在熊湖组剖面中的地层位置并不精确。 该剖面很可能有很大一部分位于Astarte已知矿点之下，因此将含有较老的软体动物和硅藻。Astarte在北太平洋的第一次出现，因此，白令海峡的第一次开放可能是在晚中新世（超过5.32 Ma）。 拟议的研究将基于在阿拉斯加西南部为期一个月的实地考察，随后进行两年的动物区系和微植物区系分析和综合。 本研究的目的是：（1）根据硅藻、磁性地层学和凝灰岩年龄，记录白令海峡首次开放的精确年龄;（2）了解白令海峡开放前后熊湖组软体动物群的组成;（3）将白令海峡开放置于更广泛的地理和古地理背景中。 预计该项目将增进我们对北方海洋和海洋动物群的了解，包括白令海峡的开放。 它还应该提供白令海峡开放后北太平洋，北极和北大西洋海洋无脊椎动物区系的古生态学的见解。

The first opening of Bering Strait is evidenced by the presence of the marine bivalve mollusk, Astarte, in the Miocene Bear Lake Formation on the Alaska Peninsula. Astarte lived only in the North Atlantic and Arctic Oceans in the Cenozoic until the opening of Bering Strait allowed it to migrate into the North Pacific. Astarte has previously been found in North Pacific Neogene faunas, but not with age-diagnostic microfossils. Astarte, with other abundant mollusk fauna, is present at two horizons in a 300-meter-thick, kilometer-long stratigraphic section of the Bear Lake Formation. One hundred diatom taxa from within mollusk shells at these two horizons represent Subzone B of the Neodenticula kamtschatica diatom zone. Subzone B of the Neodenticula kamtschatica zone has an age range of 4.8-5.5 million years ago (Ma) within a well-established North Pacific diatom biochronology and is significantly older than the approximate 3.0-4.0 Ma date for Bering Strait that is commonly cited by researchers. The stratigraphic position of Astarte in the Bear Lake Formation section is imprecisely known. It is likely that a significant portion of the section lies below the known occurrences of Astarte and will therefore contain older mollusks and diatoms. The first occurrence of Astarte in the North Pacific and, therefore, the first opening of Bering Strait was likely to have been in the late Miocene (more than 5.32 Ma). The proposed research is to be based on one month of fieldwork in southwestern Alaska, followed by two years of faunal and microfloral analysis and synthesis. The objectives of the study are to: (1) document a precise age for the first opening of Bering Strait, based on diatoms, magnetostratigraphy, and tuff ages; (2) understand the composition of the Bear Lake Formation molluscan fauna before Bering Strait opened and afterwards; and (3) place the opening of Bering Strait in a broader biogeographic and paleogeographic context. This project is expected to advance our knowledge of the northern oceans and marine faunas, including the opening of the Bering Strait. It should also give insights on the paleoecology of the marine invertebrate faunas of the North Pacific, Arctic, and North Atlantic oceans after Bering Strait opened.