西藏申扎地区二叠系下拉组中吴家坪期化石的发现及其意义

THE DISCOVERY OF WUCHIAPINGIAN FOSSILS FROM THE XIALA FORMATION IN THE XAINZA AREA(TIBET)AND ITS SIGNIFICANCE

重新研究了西藏申扎木纠错地区下拉组剖面,发现该地区下拉组从空谷晚期到吴家坪期连续,露头出露较好,下与昂杰组泥页岩整合接触,上与木纠错组白云质灰岩整合接触。该剖面根据不同的岩性及生物组合可分为三段,其中前二段亦在申扎县北的下拉地区较为发育,时代为空谷晚期至卡匹敦期;但下拉地区由于受断层和褶皱影响强烈,未完全保存第三段,而该段在木纠错剖面中出露较好,并在其含燧石结核灰岩中发现了牙形类Clarkina liangshanensis(Wang)和类Codonofusiella schubertelloides Sheng,确认其时代为乐平世吴家坪期,首次确认下拉组的上部可以延伸至吴家坪期。

A restudy of the Xiala Formation at the Mujiucuo section in the Xainza area, Tibet （Xizang）, shows that the Xiala Formation at the Mujiucuo section is continuous, with conformable contacts with the underlying shales of the Angjie Formation and dolostones of the overlying Mujiucuo Formation. Its depositional age is from the Kungurian to the Wuchiapingian. Different from stratigraphic sections in the Xiala area, the Xiala Formation at the Mujiucuo section can be divided into three members. The lower and middle members are also recognizable in the Xiala area and ranges from the late Kungurian to the Capitanian, whereas the upper member consisting of thick-bedded nodular limestone only occurs in the Mujiucuo area. The depositional age of the upper member of the Xiala Formation is ascribed to the Wuchiapingian based on the presence of the conodont Clarkina Ziangshanensis （Wang） and the fusulinid Codonofusiella schubertel- loides Sheng. It is the first time to confirm that the Xiala Formation in the Xainza area can range upper into the Wuchiapingian Stage.