四川宣汉渡口二叠纪“孤峰组”牙形石序列及其全球对比意义

SUCCESSION OF CONODONT ZONES FROM THE PERMIAN "KUHFENG" FORMATION, XUANHAN, SICHUAN AND ITS IMPLICATION IN GLOBAL CORRELATION

渡口“孤峰组”的牙形石带，自下而上包括Ｍｅｓｏｇｏｎｄｏｌｅｌｌａｓｅｒｒａｔａ带Ｍ．ａｓｅｒｒａｔａ带，Ｍ．ｐｏｓｔｓｅｒｒａｔａ带，Ｍ．ａｌｔｕｄａｅｎｓｉｓ带，Ｍ．ｐｒｅｘｕａｎｈａｎｅｎｓｉｓ带和Ｍ．ｘｕａｎｈａｎｅｎｓｉｓ带。其中前４带可与美国Ｔｅｘａｓ州Ｇｕａｄａｌｕｐｉａｎ统的牙形石带逐个对比。这说明该统Ａｌｔｕｄａ组顶部含Ｍ．ａｌｔｕｄａｅｎｓｉｓ动物群的层位低于吴家坪阶之底：Ｇｕａｄａｌｕｐｉａｎ统和吴家坪阶之间尚存在一个待厘定和命名的新阶。描述了２新种：Ｍ．ｐｒｅｘｕａｎｈａｎｅｎｓｉｓｓｐ．ｎｏｖ．和Ｍ．ｘｕａｎｈａｎｅｎｓｉｓｓｐ．ｎｏｖ．。

Abstract:The Lopingian marine sequence is fully developed in South China and has potential toserve as an international standard for correlation of the Latest Permian. A conventionallower boundary of the Lopingian Series was placed at the base of Clarkinaliangshanensis--C. letteri zone (Wang and Wang, 1979, 1983: Wang, 1990; Ding, 1992) and/or Prototoceras-Anderssonceras zone, which represents the first fossiliferous marine bed in'the shelf sequence. However, information about the precise succession of marine fossilzones from the Latest Maokouan and the Earliest Lopingian based on which the stratigraphic level of Maokouan (Guadalupian)/Lopingian boundary can be selected is still notavailable at present. Such a succession can only be found from the sequences of slope deposits or basin deposits because South China seas had been exclusively affected by a majorregression towards the end of Maokouan. As a result of the regression, a terrigenous formation is sandwiched in between the marine deposits of Maokouan and Lopingian on theshelves. Zhang and others (1990) reported that in the Dukou Section, Xuanhan, Sichuan.the marine sequence from Late Maokouan to Early Lopingian is nearly complete as theyformed in a Maokouan basin. A closer examination shows there still exists a terrigenousbed, though it is much thinner than the equivalents formed in shelf areas. The overlyingWuchiaping Formation produces numerous conodonts that are dealt with in detail in another paper (in print. ). It consists of packstone and wackestone and contains Clarkinaliangshanensis in the middle part and a conodont zone which is temporarily designated asthe Clarkina liangshanensis ? Zone in this paper, in the hasal part.