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Palynostratigraphy and age of the Upper Cretaceous Kuji Group, northeast Iwate Prefecture, Northeast Japan

2007; Japanese Association for Petroleum Engineers; Volume: 72; Issue: 2 Linguagem: Inglês

10.3720/japt.72.215

1881-4131

Keita Umetsu, Hiroshi Kurita,

Paleontology and Stratigraphy of Fossils

Palynostratigraphic investigation and age determination based on terrestrial palynomorphs are conducted on the nonmarine to shallow marine deposits of the Upper Cretaceous Kuji Group, Northeast Japan. Four palynostratigraphic assemblages are recognized in the group (assemblages A, B, C, and D, in ascending order). The variation of the assemblages are considered to depend on changes of paleovegetation and depositional environment of host sediments. Especially, the variation of assemblages A to C from marine-influenced deposits suggests a regional paleovegetational change represented by the increase of bisaccate pollen-producing conifers during the deposition of the Tamagawa Formation. The occurrence of angiosperm triprojectate pollen in the Kuji Group shows that the interval from the upper part of the Tamagawa Formation to the Sawayama Formation is confined to Santonian to lower Campanian. This contributes to dating of the potential source rock/reservoir packages within Cretaceous sediments in the Yezo forearc basin.