Abstract
In the northern Itsuki area, western Kyushu, the Lower Jurassic Hirasawatsudani Formation (newly defined) overlying the Upper Triassic Matsukuma Formation was discovered from clastic rocks of the Kurosegawa Terrane. The Matsukuma Formation in the northern Itsuki area, correlated with the Carnian Stage, includes parallel-laminated mudstone with fine sandstone beds and massive mudstone. Lower part of the Hirasawatsudani Formation is composed of thick-bedded coarse sandstone beds with intercalations of conglomerate and turbiditic sandstone beds. Upper part of the Hirasawatsudani Formation is composed of black mudstone with thin sandstone beds. Based on the radiolarian fossils, it is highly possible that the Hirasawatsudani Formation is correlated with the Hettangian Stage. The boundary of the Matsukuma Formation and the Hirasawatsudani Formation is considered to be unconformable, because a certain stratigraphic-gap ranging from the Norian Stage to the Rhaetian Stage is recognized.
