中国西藏聂拉木色龙西山二叠系—下三叠统牙形刺

PERMIAN-LOWER TRIASSIC CONODONTS FROM SELONG XISHAN OF NYALAM,S.TIBET,CHINA

本文详细描述了西藏聂拉木色龙西山二叠系—下三叠统牙形刺共７属２０种；组建了自下而上的７个牙形刺带：Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ，Ｃｌａｒｋｉｎａｃａｒｉｎａｔａ，Ｎｅｏｓｐａｔｈｏｄｕｓｋｕｍｍｅｌｉ，Ｎ，ｃｒｉｓｔａｇａｌｌｉ，Ｎ．ｐａｋｉｓｔａｎｅｎｓｉｓ，Ｎ．ｗａａｇｅｎｉ，Ｎｅｏｇｏｎｄｏｌｅｌｌａｊｕｂａｔａ－Ｎｅｏｓｐａｔｈｏｄｕｓｔｒｉａｎｇｕｌａｒｉｓ带；发现了这些牙形刺带与菊石带的对比关系。色龙西山剖面缺失二叠系顶部的层位，由于色龙群顶部产Ｍｅｓｏｇｏｎｄｏｌｅｌｌａｉｄａｈｏｅｎｓｉｓ，Ｍ．ｐｈｏｓｐｈｏｒｉｅｎｓｉｓ和Ｍ．ｓｐｐ．等牙形刺，其时代可能为栖霞晚期至茅口早期，考虑到再沉积的可能性，其时代也不会晚于吴家坪期。下三叠统发育较完整，特别是底部，但是由于再沉积或凝缩的原因，在三叠系底部常有二叠系的牙形刺出现或出现混合动物群。本文讨论了二叠－三叠系界线，并把菊石Ｏｔｏｃｅｒａｓｌａｔｉｌｏｂａｔｕｍ带和牙形刺Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ带之底作为三叠系之底界。

The conodonts described here were collected from Selong Xishan of Nyalam,S.Tibet,including 20 species referred to 7 genera.They can be subdivided in ascending order into the Hindeodus parvus, Clarkina carinata,Neospathodus kummeli,N.cristagalli,N.pakistanensis,N.waageni and Neogondolella jubara-Neospathodus triangularis Zones,which are correlated with the ammonoid zones.The strata just below the Otoceras latilobatum Zone contain Mesogondolella idahoensis,M.phosphoriensis and M.spp.,which are referred to Late Chihsian to Early Maokouan.Considering the reworked sedimentation,these strata are not younger than Wuchiapingian in age,indicating a gap between Permian and Lower Triassic in this section.The problem on the Permian-Triassic boundary is discussed in this paper with the base of the ammonoid Otoceras latilobatum and conodont Hindeodus parvus Zones considered as the base of Triassic.