Historical distribution patterns of trigonioidids (non-marine Cretaceous bivalves) in Asia and their palaeogeographic significance
The non-marine trigonioidid bivalves show five phases of radiation in the Cretaceous of Pal-Asia: pre-Aptian (?Valanginian/Hauterivian–Barremian), Aptian, Albian, Cenomanian and Turonian–Maastrichtian. Their distribution patterns show two distinct palaeo-river systems feeding trigonioidids. Before the Cenomanian, the river system occupied the southwestern–southern–southeastern Pal-Asian continental margin areas. During the Turonian–Maastrichtian, it extended along the line of southcentral China−eastern China−northeastern China−northern China and Mongolia−northwestern China–eastern Fergana Basin of Kyrgyzstan−western Tajikistan Basin of Tajikistan–Tashkent area of Kazakhstan−central Kyzylkum of northern Uzbekistan–Aral Sea area of Kazakhstan. Furthermore, the general trigonioidid distribution pattern demonstrates that Japan was probably attached to part of eastern China and/or Korea during the ?Valanginian/Hauterivian–Cenomanian stages.
DISTRIBUTION AND DEVELOPMENT OF NONMARINE MESOZOIC BIVALVES AND FORMATIONS IN CHINA
In this paper the author reviews the available materials on the nonmarine Mesozoicbivalves in China and divides these fossils into five faunas and sevoral faunules according totheir geologic ages. Their distributions are briefly summarized. The Early Cretaceous orTPN (Trrgonioides -Plicatounio -Nippononaia ) fauna marks the greatest event and vicissitude inthe developmental history of these faunas. Besides the subdivision and correlation of the nonmarine Mesozoic in China with the aidof these foasil bivalves the stratigraphical development and some phases of the Indosinian andYanshanian tectonic cycles are briefly discussed and chronologically dated. The Early Cre-taceous Mincheian movement is considered to play a more hoportant role than the latest MiddleJurassic Ningchinian movement. The Mincheian with a younger uplift is essentially accordantwith the results recently reached about Mid-Cretaceous events by international geological andpaleontological studies.
Nonmarine molluscan communities and palaeoecology in the Jurassic-Cretaceous Tetori Group, Japan
Abstract In the Tetori Group (Middle Jurassic to mid-Cretaceous) of Japan fossil nonmarine molluscs occur at a number of levels in strata of different sedimentary facies. How far they can be evaluated as chronological indices is discussed on the basis of faunal and sedimentological analyses. Five assemblages in the Group reflect brackish to freshwater environments. Dominant species in the assemblages are interpreted as maintaining space occupation by habitat segregation. These assemblages are also recognized in the Monomiyama Formation, north-east Japan, and the Gyeongsang Group, South Korea. The ecology of bivalves is a vital factor when using nonmarine bivalves as chronological indices.