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

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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