LATE EOCENE BIVALVIA FOSSILS FROM THE SHUANGHE FORMATION IN JIANCHUAN BASIN,YUNNAN PROVINCE AND ITS GEOLOGICAL IMPLICATION
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Abstract:
The southeastern Tibetan Plateau is considered as the main region where material escalation caused by the Tibetan Plateau,and it records the sedimentary,tectonic and biological events reflecting the uplift of the plateau.The Jianchuan Basin is one of the pull-apart basins in the southeastern Tibetan Plateau.The Shuanghe Formation is the main sedimentary strata of the Jianchuan Basin.The bivalve fossils from this formation lack detailed study,and only limited reports had been documented.In this paper,nine species and four genera of bivalves are found under systematic specification in the Jianchuan Basin.Four genera are Unio,Acuticosta,Cuneopsis and Anodota,and nine species include Acuticosta huoerguosica, Acuticosta sp., Acuticosta subimmutata,Cuticosta cf.chinensis,Acuticosta cf.cuspidata,Acuticosta cf.semiretiaria,Unio cf.subparallelus,Cuneopsis cf.subceltiformis and Anodontacf.subpiscinalis.All of the species belong to the family Unionidae. The genus Acuticostaand Cuneopsis are modern characteristic genera in eastern Asia,and A.chinensis and C.subceltiformis are present existing species south of the Yangtze River.However,A.chinensis was just reported in Xinjiang before.Based on ages of intrusive veins and standard Ostracoda fossil zones, the Shuanghe Formation could be constrained in late Eocene.Therefore,this paper not only provides new evidence of bivalve fossils in western Yunnan Province, but also reveals a subtropical fresh-water delta-front and prodelta environment of the Jianchuan Basin during the late Eocene.
