云南剑川盆地上始新统双河组双壳类新材料及其地质意义*

青藏高原东南缘一直被认为是高原隆升造成物质逃逸的主要场所,很好地记录了反映高原隆升的沉积、构造和生物演化事件。剑川盆地是青藏高原东南缘的一个拉分盆地。作为剑川盆地最主要的沉积地层,双河组内仅有少量双壳类化石的报道,缺少详细的化石对比研究。本文系统描述双河组最新发现的双壳类共4属9种,分别为Unio,Acuticosta,Cuneopsis和Anodonta 4属,Acuticosta huoerguosica,Acuticosta sp.,Acuticosta subimmutata,Acuticostacf.chinensis,Acuticostacf.cuspidata,Acuticostacf.semiretiaria,Unio cf.subparallelus,Cuneopsis cf.subceltiformis和Anodonta cf.subpiscinalis 9种,均属于古异齿目珠蚌科。其中Acuticosta和Cuneopsis为现代东亚的特征属,Acuticosta chinensis和Cuneopsis subceltiformis为长江以南的现生种,而Acuticosta chinensis以往只在新疆有过化石记录。结合双河组的侵入脉体的年龄和介形虫标准化石的研究确定双河组的时代为晚始新世,故本次研究不仅为相关双壳类的产出时代可以延伸至晚始新世提供了有力的证据和新材料,而且反映出剑川盆地双河组在晚始新世为亚热带的淡水三角洲前缘-前三角洲的沉积环境。

LATE EOCENE BIVALVIA FOSSILS FROM THE SHUANGHE FORMATION IN JIANCHUAN BASIN,YUNNAN PROVINCE AND ITS GEOLOGICAL IMPLICATION

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.