High-resolution study of the Cretaceous Oceanic Anoxic events using land-drilling cores in the Pacific and Tethyan region

白垩纪是温室气候的时代，其特点是高纬度地区的海洋表面温度比现在至少高出15℃。在白垩纪变暖的高潮期间，全球海洋的缺氧状况扩大，导致富含有机物质的沉积物堆积，即所谓的黑色页岩。这些事件被命名为海洋缺氧事件(OAEs)，在白垩纪中期至少发生了8次。北海道和北美的OAE事件不同于法国南部和大西洋等特提斯地区的典型OAE事件，因为来自大陆边缘的陆源物质被稀释，因此没有黑色页岩。然而，北海道和北太平洋地区有机碳同位素正漂移2-3‰和总有机碳含量的增加表明存在海洋环境事件。生物扰动在大小和数量上的减少以及稀有宏微化石的出现具有良好的…更多的人认识到有机碳的正向漂移。尤其是在正向漂移附近，粘连的底栖有孔虫很常见，放射虫在漂移的正上方迅速增加。另一方面，沃孔田盆地的海洋环境由石灰岩和泥灰岩中六个主要的黑色页岩夹层组成。这些等级被称为阿普提亚晚期的“Fries”、“Bullot”和“Jacob”等级，以及阿尔比亚时代早期的“Kilian”、“Paquier”和“Leenhardt”等级，按升序排列。根据纹层的发育程度和保存程度，这些岩性单位由强层理、弱层理和块状层位组成，在黑色页岩中是可识别的。高分辨率的沉积学和古生物学研究表明，上Aptian Fries和Bullot层(A型)含有很少的浮游有孔虫和超微有孔虫，但没有巨型化石，而Kilian和Paquier层(B型)的黑色页岩含有丰富的菊石、浮游性有孔虫和超微锥虫

The Cretaceous was a time of greenhouse climates characterized by at least 15 ℃ warmer sea surface temperatures in the high latitudes than the present day. During the climax of Cretaceous warming, anoxic condition in the oceans globally expanded, resulting in accumulations of organic rich sediments, so-called black shales. These events are named as the Oceanic Anoxic Events (OAEs) that occurred at least 8 times during the middle Cretaceous period. The OAE events in Hokkaido and North America differ from the typical OAEs in the Tethyan regions such as the Southern France and Atlantic Ocean in having no balk shales because of dilution of terrigenous materials from the continental margins. However, a positive excursion of 2-3 ‰ in organic carbon isotope and increasing of total organic carbons (TOC) in the sequence of the Hokkaido and north Pacific regions suggest an existence of the OAEs. A decreasing of bioturbation in size and numbers and occurrence of rare macro- and microfossils has b … More een recognized around the positive excursion of organic carbon. In particular, agglutinated benthic foraminifers are common around the positive excursion, and radiolarians rapidly increased just above the excursion.On the other hand, the OAEs in the Vocontian Basin comprise intercalations of six major black shale beds within the limestones and marls. These are called as the "Fries", "Bullot" and "Jacob" levels of the late Aptian age, and the "Kilian", "Paquier" and "Leenhardt" levels of the early Albian age, in ascending order. These lithological units composed of strongly laminated, faintly laminated and massive layers are recognizable within the black shale levels based on the degree of development and preservation of laminations. High-resolution sedimentological and paleontological studies revealed that the upper Aptian Fries and Bullot levels (type A) contain few planktic foraminifera and nannoconids but no megafossils, while the black shales of the Kilian and Paquier levels (type B) bear abundant ammonites, planktic foraminifera and nannoconids Less