Abstract
Bulk organic carbon isotope (δ13Corg) analyses across the Cenomanian/Turonian boundary in Hokkaido, Japan, and high-resolution planktic foramiferal biostratigraphy indicate that the timing of the planktic foraminiferal disappearance in the northwestern Pacific was significantly earlier than that in the Atlantic region. δ13Corg shows a prominent ∼2‰ positive excursion, clear trough interval, steady plateau interval, and recovery interval, which can be used as very precise chemo-stratigraphic markers. Planktic foraminiferal biostratigraphy demonstrates a pair of diversity crisis at a horizon below the initial δ13Corg excursion and at the beginning of the plateau interval. This isolated double diversity crisis of planktic foraminifers has also been identified in the Western Interior region and northern Europe. The timings of this double diversity crisis in the Western Interior and Europe show quite good consistency on the basis of the δ13C chemo-stratigraphy. On the other hand, the double crisis in the northwestern Pacific is significantly earlier than those in the Western Interior and Europe. This offset indicates that expansion of the oxygen-depleted water mass in the northwestern Pacific preceded that in the Atlantic region.
