Implication of spatiotemporal distribution of black shales deposited during the Cretaceous Oceanic Anoxic Event-2

Abstract

ABSTRACT Oceanic Anoxic Events (OAEs) mark the contemporaneous deposition of organic-rich marine sediments termed “black shales” in the wide areas of the oceans. An anoxic event that occurred at the Cenomanian-Turonian boundary, OAE-2, has been recognized as one of the largest events in the Cretaceous. Carbon isotopic compositions (δ13C) of sedimentary carbonate and organic matter exhibit a positive excursion across the OAE-2, reflecting an enhanced burial rate of 13C-depleted organic carbon during the event. Here we compile a spatiotemporal distribution of black shales on the basis of their onset timings relative to the δ13C excursion as a time-control reference, and discuss the “spreading patterns” of black shale deposition. The patterns suggest that the deposition of black shales started from marginal regions of the southern North Atlantic and the Western Interior Seaway in North America, and spread to the northern North Atlantic and Tethys Sea. Strangely, the black shales whose onset corresponds to th...