北西九州の含炭堆積盆地におけるシーケンス層序と堆積過程

抄録

This paper describes the sequence stratigraphy of six sedimentary basins in northwest Kyushu based on offshore seismic, well, and surface geological data. And then regional stratigraphic correlation and sedimentary process are discussed.
The northeastern end of the East China Sea shelf basin extends to the Fukue basin, north of Goto Islands, which mark the northeastern end of the Goto belt. To the south of Goto Islands, there also developed small Paleogene sedimentary basins called the Goto-nada, Nishisonogi, and Karatsu basins. These basins have NW-SE trending rhomboidal frames. On the contrary, NE-SW trending Paleogene sedimentary basins called the Amakusa-nada and Amakusa basins are present to the south of the Goto-nada basin. A single sequence stratigraphic framework is applicable for the strata in these basins, and the strata are subdivided into five Paleogene depositional sequences; DS-P1 to -P5 in ascending order, and three Neogene to Quaternary depositional sequences; DS-N 1 to -N3 in ascending order.
The DS-P1 and -P2 (Middle Eocene) were only deposited in the NE-SW trending sedimentary basins, while the DS-P3 (upper Middle to Upper Eocene) directly overlies the pre-Tertiary basement in the NW-SE trending basins. The first marine incursion to the NW-SE trending basins from the southeast occurred probably during the deposition of DS-P3 of a late Middle to Late Eocene age.
There have been some problems in the previous lithostratigraphic division in onshore northwest Kyushu such as inconsistent definition of a certain group over several basins, as well as mistaking ravinement surfaces for unconformity in some cases. These problems may be resolved with the stratigraphic scheme established here, which is applicable regionally to the Paleogene basins in northwest Kyushu. It will provide a useful tool for identifying regional tectonic events in this region.