Paleoceanographic shifts and global events recorded in late Pliocene shallow marine deposits (2.80–2.55 Ma) of the Sea of Japan
Paleoceanographic shifts and global events recorded in late Pliocene shallow marine deposits (2.80–2.55 Ma) of the Sea of Japan
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DOI：
10.1016/j.palaeo.2005.01.006
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发表时间：
2005-05
期刊：
影响因子：
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通讯作者：
K. Yamada;Yuichiro Tanaka;T. Irizuki
中科院分区：
文献类型：
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作者：
K. Yamada;Yuichiro Tanaka;T. Irizuki
研究了日本中部新泻县黑川地区上新世科威特组的介形类化石组合，以了解2.80~2.55 Ma期间日本海由暖气候向冷气候过渡期间的高分辨率古海洋学变化，其年代来自硅藻和纳米化石基准层和磁性地层。所研究的介形类组合不包含现代日本海已知的对马暖核洋流类群，它们大多是嗜冷性和环极性的。已识别的介形类化石组合组合不同于该地区的现代组合，表明浅水区可能比今天更冷。科威特组是在上半深海和下半深海之间的几次水深波动期间沉积的。台内地区在2.70 Ma发生了由上半深海到下半深海的大规模转变，并在4万年(2.70-2.66 Ma)期间迅速转变，这是沉积环境的主导。这种浅化反映了记录在各种证据中的全球变冷引起的变化，例如来自深海岩心的氧同位素数据。详细的古深度波动显示了该地区在2.80-2.55 Ma之间发生的四次浅水事件。2.70 Ma和2.60 Ma时的第三次和第四次浅层都是对全球气候变冷的响应，分别对应于氧同位素阶段G6和/或G4和阶段104，这是由研究断面当代丰富的冷水物种、西北太平洋浅化事件和高纬度海记录的IRD事件推断的。
Fossil ostracod assemblages from the upper Pliocene Kuwae Formation of the Kurokawa area, Niigata Prefecture, central Japan were investigated to discern the high resolution paleoceanographic changes in the Sea of Japan during the transitional interval from a warm to a cold climate in the period from 2.80 to 2.55 Ma, dated previously from diatom and nannofossil datum horizons and magnetostratigraphy. The studied ostracod assemblages did not contain Tsushima Warm Core Current taxa known in the modern Sea of Japan, and most of them are cryophilic and circumpolar. The combinations of recognized fossil ostracod assemblages differ from the modern ones of the region, suggesting that the shallow water area was probably colder than that of today. The Kuwae Formation was deposited during several bathymetric fluctuations between upper bathyal and lower sublittoral zone. A large-scale shift from upper bathyal to lower sublittoral condition, which dominated the depositional setting, occurred at 2.70 Ma in the Tainai area, and occurred rapidly during 40,000 years (2.70–2.66 Ma). This shallowing mirrored the shifts induced by global cooling recorded in various evidence such as oxygen isotope data from deep-sea core. Detailed paleodepth fluctuations show four shallowing events that occurred in this area between 2.80 and 2.55 Ma. The third and fourth shallowings at 2.70 and 2.60 Ma were both responses to global climatic cooling corresponding to the oxygen isotope stages G6 and/or G4, and to stage 104, respectively; deduced from the contemporary abundance of cold water species in the study section, observations of shallowing events in the northwestern Pacific Ocean, and the IRD event recorded in high latitude seas.