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

对九州岛北部5个煤田古近系海相层序钙质纳米化石产状及生物地层对比进行了研究。研究人员对Amakusa、sakto - matsushima、Karatsu和Chikuho煤田的露头样品以及在Ariake海（60-Ari-4井）和Nishisonogi半岛西海岸（59Nishi-3井）钻探的两口海上井进行了纳米菌群研究。从始新世早期到晚渐新世早期，共识别出82个聚类和18个基准点事件，并利用这些基准点事件对所研究的序列进行了相互关联。天草煤田古近系年龄介于中始新世早期（CP 13a亚带）和晚始新世（CP 15亚带）之间。60-Ari-4井开采的Make煤田Yotsuyama组对应于天草层序上部（CP14-15区）。尽管Sakito-Matsushima煤田的露头样品中缺乏纳米化石，但从59-Nishi-3井采集的岩心样品中，以及中堂、松岛、Itanoura、Kakinoura的岩心样品中，化石含量相当高。从始新统上端（CP15b亚带）到下渐新统上端（CP17带）可识别出大岛组和大岛组。始新统/渐新统界线可能位于离中户组和松岛组界线非常近的位置。卡拉松煤田岸岛组发育早渐新世纳米菌群（CP16a亚带），与松岛煤田松岛组和伊塔努拉组有一定的对应关系。卡拉苏组Hatatsu页岩段为下渐新统上段（CP18带），为上渐新统下段（CP19a亚带）的可能性较小。千湖煤田坂井组和山长组为上渐新统下段（CP19a亚带）。

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).