Depositional environments and bivalve fossil assemblages of the Lower Cretaceous Arida Formation, southwest Japan.

Abstract

Based on facies analysis, the depositional environments of the lower Cretaceous transgressive Arida Formation are divided into four depositional facies : upper-middle shoreface, lower shoreface, inner shelf, and outer shelf facies. In addition, abundant bivalve fossils are divided into three fossil assemblages : Pterotrigonia pocilliformis (lower shoreface), Nanonavis yokoyamai (inner shelf) and Periploma (?) monobensis (outer shelf). The paleo-ecology of these fossils was previously unknown, but their habitats are inferred from the mode of occurrence, especially autochthonous fossils and articulated valves, and depositional environments.