Bulk organic carbon isotope (δ
13C
org) 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. δ
13C
org 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 δ
13C
org 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 δ
13C 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.
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