中国浙江长兴县煤山二叠－三叠系界线──三叠系底界的全球界线层型剖面点（GSSP）的提案

PERMIAN-TRIASSIC BOUNDARY AT MEISHAN OF CHANGXING COUNTY,ZHEJIANG PROVINCE, CHINA──A PROPOSAL ON THE GLOBAL STRATOTYPE SECTION AND POINT(GSSP)FOR THE BASE OF TRIASSIC

浙江长兴煤山剖面的二叠－三叠系界线层为连续的浮游相沉积没有任何间断，侧向上也是连续的。煤山是长兴阶的层型剖面所在地，长兴阶的上部，界线层和三叠系的下部，每一层都发现有牙形刺，可以逐层追索牙形刺的演化关系。煤山剖面几乎没有任何热力变质（ＣＡＩ＝１—１．５）。煤山剖面的菊石、牙形刺、双壳类、腕足类等多门类化石以及有关事件已得到了很好的研究。绝对年龄和古地磁也已得到深入研究。孢子的存在和易于识别的事件能与陆相地层作很好的对比。煤山剖面交通方便，并得到当地政府的保护。Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ最早出现在界线层２的中部，它由Ｈｉｎｄｅｏｄｕｓｌａｔｉｄｅｎｔａｔｕｓ在连续的单相地层中演化而来，存在两个形态型，形态型１极易识别而且容易与它的先躯分子Ｈ．ｌａｔｉｄｅｎｔａｔｕｓ区分开来。二叠－三叠系的生物地层界线以Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ的首次出现为准。这个界线在煤山非常接近事件地层界线，仅比事件地层界线高１５ｃｍ，比δＣ１３最低值界线高４ｃｍ。Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ在世界各地广泛存在，在集群绝灭事件之后，在由δＣ１３最低值指明的动物群分异度最低值之后，才出现的，并进一步演化出Ｉｓａｒｃｉｃｅｌｌａｉｓ?

Laterally continuous sections at Meishan contain a continuous pelagic sedimentary record across the P/T boundary without stratigraphic gaps.Conodonts are present in every bed of the uppermost Permian Changxingian(Changhsingian)Stage which has its stratotype at Meishan, in every layer of the Boundary Beds and in every bed of the lowermost Triassic.The section is thermally nearly unaltered (CAI=1-1. 5) and its fossil content (ammonoids, conodonts,bivalves,brachiopods)and event succession are well studied.Absolute age and paleomagnetism have been subjected to intensive studies.The presence of sporomorphs and well recognizable events allow correlation with continental beds. The section is well accessible and under protection of the government. Hindeodus parvus made its earliest appearance in the middle part of Boundary Bed 2.It evolved from Hindeodus latidentatus in a phylomorphogenetic continuum in a continuous and monofacies stratum.Both morphotypes of the species are present.Morphotype 1 is especially well recognizable and easily distinguishable from the forerunner species H. latidentatus.The biostratigraphic P/T boundary is defined at the first appearance of H.parvus.This boundary lies at Meishan very close to the event boundary (15 cm above the event boundary and a few centimetres above the minimum in δC13 in the lower Boundary Bed 2). Hindeodus parvus is the first worldwide present species,which evolved after the absolute minimum in the faunal diversity indicated by the minimum in δC13. For the above reasons,Meishan is regarded as the best GSSP for the Permian-Triassic boundary.No other section in the world shows comparably good conditions for defining the P/T boundary in a GSSP.