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Ammonoid biodiversity changes across the Cenomanian-Turonian boundary in the Yezo Group, Hokkaido, Japan

100%

Kurihara K., Toshimitsu S., Hirano H.

Acta Palaeontologica Polonica

2012

tom 57

nr 4

Ammonoid biodiversity changes from shallow to offshore environments across the Cenomanian–Turonian (C–T) boundary are reconstructed in the Yezo Group, Hokkaido, Japan. This group was probably deposited at approximately 35–45ºN along a westward subduction margin in the northeastern Asian continent. Temporal changes in species richness in the Yezo Group, which show persistently high values during the middle Cenomanian and then decline stepwise from near the middle–late Cenomanian boundary, resemble those in Europe, but not those in Tunisia and the Western Interior. These differences suggest that the Cenomanian–Turonian “mass extinction” was not a global event for ammonoids but was restricted to mid−palaeolatitudinal regions (Europe and Japan). Sea level and climate changes probably influenced ammonoid faunas in the Yezo Group as well as those in Europe. However, it is unlikely that a single, simple cause led to the C–T boundary “mass extinction” because various abiotic changes in the Cenomanian–Turonian transition have been detected, and biotic and abiotic change are interrelated.

Bivalves from Cretaceous cold-seep deposits on Hokkaido, Japan

80%

Kiel S., Amano K., Jenkins R. G.

Acta Palaeontologica Polonica

2008

tom 53

nr 3

Cretaceous cold−seep deposits of the Yezo Group on Hokkaido, Japan, yield a rich and well−preserved mollusk fauna. The systematics of nine bivalve species previously reported from these deposits can now be reevaluated using newly collected fossils. The fossils include a Cenomanian specimen of Nucinella gigantea with a drill hole possibly made by a naticid, by far the oldest record of a drill hole from a cold seep site. In Japan, Cretaceous seep bivalve assemblages are characterized by (i) the unique occurrence of large specimens of Nucinella (Manzanellidae), (ii) the commonly present nuculid Acila (Truncacila), and (iii) a high diversity of lucinids, possibly as many as four distinct genera. Two new species described are the Albian Acharax mikasaensis(Solemyidae) and the Albian to Campanian Thyasira tanabei (Thyasiridae), of which the former had previously been misidentified as the oldest vesicomyid, the latter as the oldest Conchocele.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Amano K.

1 Hirano H.

1 Jenkins R. G.

1 Kiel S.

1 Kurihara K.

1 Toshimitsu S.

1 2012

1 2008

Wyniki wyszukiwania

Ammonoid biodiversity changes across the Cenomanian-Turonian boundary in the Yezo Group, Hokkaido, Japan

Bivalves from Cretaceous cold-seep deposits on Hokkaido, Japan