Biostratigraphy and paleoenvironmental analysis of the Paleogene sequences of the northern Kyushu by calcareous nannofossil

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The occurrence of calcareous nannofossils and biostratigraphic correlation are studied for the Paleogene marine sequences of five coalfields locating in the northern Kyushu Island. The nannoflora is investigated for the outcrop samples of the Amakusa, Sakito-Matsushima, Karatsu and Chikuho Coalfields as well as for the two offshore wells Drilled in the Ariake Sea (60-Ari-4 well) and off the western coast of the Nishisonogi Peninsula (59Nishi-3 well). A total of 82 taxs and 18 datum events spanning from the early Nfiddle Eocene to early Late Oligocene are recognized, and the studied sequences are correlated with each other by using these datum events.The Paleogene sequence of the Amakusa Coalfield ranges in age between the early Middle Eocene (Subzone CP 1 3a) and the Late Eocene (Zone CP 15). The Yotsuyama Formation of the Make Coalfield recovered in the 60-Ari-4 well corresponds to the upper part of the Amakusa sequence (Zones CP14-15). Though nannofossils are scarce in the outcrop samples of the Sakito-Matsushima Coalfield, core samples taken from the 59-Nishi-3 well are fairly fossiliferous, and the Nakado, Matsushima, Itanoura, Kakinoura. and Ohshima Formations are identifiable to -the uppermost Eocene (Subzone CP15b) through the upper Lower Oligocene (Zone CP17). The Eocene/Oligocene boundary is likely to be situated at very close to the boundary between the Nakado and Matsushima Formations. The Kishima Formation of the Karatsu Coalfield yields nannoflora of the earliest Oligocene (Subzone CP16a) and is correlated to the Matsushima and Itanoura Formations of the Sakito Matsushima Coalfield. The Hatatsu shale member of Karatsu Formation is the upper Lower Oligocene(Zone CP18)with small possibility of being the lower Upper Oligocene(Subzone CP19a). The Sakamizu and Yamaga Formations of the Chikuho Coalfield are the lower Upper Oligocene (Subzone CP19a).