Paleogene and Plio-Pleistocene basin formation around northwestern Kyushu, Japan |
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| Authors: | Yasuto Itoh Kazumi Matsuoka & Keiji Takemura |
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| Institution: | Department of Earth Sciences, College of Integrated Arts and Sciences, Osaka Prefecture University, Gakuencho 1-1, Sakai, Osaka 599-8531, Email: <;>,, Laboratory of Coastal Environmental Sciences, Faculty of Fisheries, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521 and,;Department of Geophysics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan |
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| Abstract: | Cenozoic basin-forming processes in northwestern Kyushu were studied on the basis of geological and geophysical data. Gravity anomaly analysis delineated four sedimentary basins in the study area: Goto-nada, Nishisonogi, Amakusa-nada, and Shimabara. Borehole stratigraphy and reflection seismic interpretation suggest that the Goto-nada Basin was subdivided into the Paleogene and Plio-Pleistocene depocenters (Goto-nada 1 and 2). In the Paleogene, Amakusa-nada Basin was rapidly subsiding together with the Shimabara Basin as part of a large graben. Goto-nada 1 and Nishisonogi basins belonged to another depositional area. After stagnant subsidence stage in the early Miocene, the study area became a site of basaltic activity (since 10 Ma) and vigorous subsidence in the Plio-Pleistocene. Goto-nada 2 Basin is accompanied with numerous east–west active faults, and separated from the Amakusa-nada Basin by a northeast– southwest basement high, Nomo Ridge. Plio-Pleistocene subsidence of the Amakusa-nada Basin is related with low-angle normal faulting on the eastern flank of the Nomo Ridge. Shimabara Basin is a composite volcano-tectonic depression which is studded by east–west faults. Focal mechanism on active faults suggests transtensional stress regime in the study area. |
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| Keywords: | basin formation northwestern Kyushu Paleogene Plio-Pleistocene |
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