The Molluscas Fauna And The Environmental Evolution During The Quaternary Of Beijing

Quaternary in Beijing was divided into four parts: Early Pleistocene, Middle Pleistocene, Late Pleistocene and Holocene. We propose to substitute Qp1 for Early Pleistocene, Qp2 for Middle Pleistocene, Qp3 for Late Pleistocene and Qh for Holocene. The deposits from bottom to top are the XiaDian Formation, Zhaili Formation, Tongxian Formation, Xiaojiahe Formation, Yingezhuang Formation and Liubintun Formation.The present paper deals with the Quaternary molluscan fossils from the Beijing Plain. The authors have recognized 14 molluscan assemblages (in ascendant order):(1) Cathaica-Gyraulus assemblage zone (Qp11); (2) Bellamya-Anodontaassemblage zone (Qp21); (3) Gyraulus assemblage zone (Qp31) ;(4)Parafossarulus-Lamprotula assemblage(Qp31); (5) Bithynia-Stenothyra assemblage zone(Q p1 2 ) ; ( 6 ) Galba-Gastrocopta(Sinalbinula) assemblage(Q p 2 ) ; ( 7 ) Radix-Parafossarulus striatulus assemblage zone (Qp22); (8) Galba - Succinea hopeiensis as- semblage (Qp 3); (9 ) Gyraulus-Hippeutis assemblage zone (Qp23); (10) Cathaica-Pupilla-Vertigo assemblage zone (Qp33); (11) Metodontia-Galba truncatula assemblage zone (Q 1h ); (12) Tricula-Bithyniafuchsiana-Segmentina assemblage zone ( Q 2h ) ; ( 13 ) Parafossarlus striatulus-Bithynia fuchsiana assembage zone ( Q 2h ) ; ( 14) Bellamya purificata - Corbicula flumineaassemblage zone (Q3h). The changes of 14 assemblages reflect 11 paleoclimateevolutioinary stages in this area during the Quaternary.In the cold period, the climate was dry and enviroment was deficient of water, therefore, the terrestrial Pulmonata was dominant in the gastropod fauna. In the warm period, the aquatic Bivalvia was well-developed, and the gastropod fauna was obviously prosperous and characteristic by large amount of the aquatic species. The alternative appearance of both cold and the warm mollascan assemblage tpyes reflects the features of the Quaternary climate changes in this area.The Quaternary environmental evolution of the Beijing plain region mainly depends upon the neotectonics and palaeoclimatic changes, which controlled and influenced the distribution, evolution of depositional areas and uplifting erosional areas and changes of sedimentary types, and also the scale and scope of Quaternary transgressions. In early Pleistocene, the ancient Yongding River had not formed a channel crossing the region from west to east. In the middle Pleistocene, there were widespread lakes and swamps. The late Pleitocene was the essential duration for the planation of the region, when the basic frame-work of the present geomorphology of Beijing Plain was constructed. At the end of late pleitocene, influenced by the climateof glacier period, the last great event of the region in the geological time was taken place so that the migration and extinction of organism species were resulted, loess accumulation was generally developed throughout the whole region, In the Holocene, the most important environmental change was fluvial process, which was still influnced by two factors-neotectonics and palaeoclimatic changes.