西藏拉萨地块申扎地区晚二叠世有孔虫动物群及其古生物地理意义

LATE PERMIAN FORAMINIFERS IN THE XAINZA AREA,LHASA BLOCK,TIBET

西藏申扎木纠错地区的上二叠统碳酸盐岩地层是近年来新发现的重要地层,但其中的有孔虫动物缺乏系统研究。本文研究了申扎木纠错剖面下拉组上部灰岩中有孔虫动物群的组成及古生物地理意义。共鉴定出有孔虫类26属52种,其中■类4属7种;有孔虫动物群主要由Reichelina,Codonofusiella,Dunbarula,Colaniella,Pachyphloia,Globivalvulina,Agathammina,Hemigordius,Midiella,Multidiscus等组成,结合同层位中产出的牙形类化石,其时代被限定在晚二叠世吴家坪期。鉴于木纠错组整合于下拉组之上,限定了木纠错组底界的时代至少从吴家坪期最晚期开始。该剖面中发现了结构构造相对简单的Colaniella属原始类型,对研究Colaniellidae的起源演化提供了化石材料。木纠错地区吴家坪期有孔虫动物群呈现的古生物地理面貌和喜马拉雅地区截然不同,说明当时新特提斯洋已有一定的宽度。

The upper Permian carbonates in the Mujiucuo area of Xainza, Tibet has been discovered recently. How-ever, the relevant research on foraminiferal fauna from these strata is lack. In this paper, we studied the foraminiferal fauna from the upper part of the Xiala Formation and discussed their age and paleobiogeography. Totally, 52 species in 26 genera are recognized in the Mujiucuo section, including 7 species and 4 genera of fusulines. The foraminiferal fauna in the upper part of the Xiala Formation mainly consists of Reichelina, Codonofusiella, Dunbarula, Colaniella, Pachyphloia, Globivalvulina, Agathammina, Hemigordius, Midiella and Multidiscus. The conodonts from same strata indicate a Late Wuchiapingian age. In terms of the constraints by fusulines and foraminifers, the lower limit of the Mujiucuo Formation is latest Wuchiapingian. We also found some original types of Colaniella with elementary structure, which may aid in the study of the origin and evolution of Colaniellidae. The presence of Wuchia-pingian warm-water foraminiferal assemblage exhibits contrast paleobiogeographic difference with the contemporaneous faunas from the Tethyan Himalaya region, which suggests a considerable width of the Neotethys Ocean.