Abstract
Lithostratigraphy and geological structure of Mesozoic successions were re-examined in the Kurosegawa Tectonic Belt in the Uminoura area, western Kyushu. The conventional Permian to Cretaceous stratigraphy in the study area is revised, and a new late Early Jurassic to Late Jurassic stratigraphic unit, the Ashikita Group is proposed. The Ashikita Group consists of the Idenohana (newly defined), Kyodomari (newly defined) and Sakamoto (redefined) Formations, which represent discrete fining-upward sequences. The fossils newly found are Late Toarcian ammonite Haugia cf. variabilis and Middle to Late Jurassic radiolarians indicative of the Tricolocapsa plicarum to Pseudodictyomitra primitiva zones. An assessment of the previously reported Pemian and Triassic fossils advocated that these fossils were derived fossils contained in the mass-wasting deposits. Contrary, hemipelagic drape deposits have exclusively yielded Jurassic fossils, although some of which were also suspicious of reworked origin. Furthermore, the newly reported fossil data are concordant with the geological structures characterized by the northwesterly verging overturned to recumbent folds. All facts demonstrated in the present contribution indicate that the previous stratigraphy that had been assigned to the Permian to Cretaceous should be revised.
