川西昌台地区上三叠统勉戈组的双壳类Pergamidia-Halobia群落特征及古环境分析  

CHARACTERISTICS AND PALEOENVIRONMENT OF THE BIVALVE PERGAMIDIA-HALOBIA COMMUNITY FROM MIANGE FORMATION OF UPPER TRIASSIC IN CHANGTAI OF WESTERN SICHUAN

作　　者：庞艳春[1] 付修根[2] 王新利[3] 马叶情[1] 李德亮[1] 

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]中国地质调查局成都地质矿产研究所,成都610082 [3]鑫达金银开发中心,北京100054

出　　处：《古生物学报》2008年第3期341-351,共11页Acta Palaeontologica Sinica

基　　金：国家自然科学基金(No.40472013);成都理工大学青年基金(No.2006QJ26)联合资助

摘　　要：川西昌台地区上三叠统勉戈组上部为一套直接覆盖在流纹质火山岩之上的板岩,该板岩富集双壳类化石。化石保存完整,以食悬浮物质的外栖足丝型双壳类动物为主,根据优势属和常见属可建立一群落,即Pergamidia-Halobia群落。以根隆剖面为例,该群落的发展可分为3个阶段:第一阶段,群落中只出现了Halobia和Parapergamidia两个属,具有个体较小、数量较少的特点;第二阶段,群落中出现了12个属,以底栖双壳类Pergamidia为优势分子,Halobia仍是常见属,该时期群落具有个体较大、数量较多的特点;第三阶段,该时期群落组成分子相对第二阶段发生衰退,只剩下3个属,其中Halobia是常见属。岩石地层特征表明,该化石群落所在层位的沉积环境为火山活动末期的较深水环境。地球化学特征表明化石群落所在层位的岩石具有热水沉积的特点:常量元素的三元投点落入热水区域内及其附近;锰的含量较高;微量元素Si/Ba比值均小于1;铅、锌、钡、铷等金属元素含量明显高于地壳含量。综合分析表明,流纹质火山活动后期的热水活动是导致Pergamidia-Halobia群落发展的外界因素。The Miange Formation of the Upper Triassic is mainly composed of rhyolite in Changtai of Western Sichuan. The rhyolite is covered with slate that has abundant bivalve fossils. The fossils are completely preserved, and their distribution was steady. The fossils from the Miange Formation have a higher concentration and a lower diversity. A fossil community may be established based on its dominant genus and common genus organisms. Take the Genlong profile as an example, the development of Pergerrnidia-Halobia community may be divided into three stages. In the first stage, only the Parapergermidia and Halobia appeared, but they are small and few in number. In the second stage, the community was composed of 12 genera with abundant fossils, predominated by larger Pergerrnidia but with Halobia still as acommon genus. In the third stage, the community was in decline, with only three genera left. The suite of sedimentary rocks which contain the fossils indicates that the environment was deep in the end of volcanic activity. By analyzing the geochemistry characters of the rocks, we conclude that the rocks have some of the same characters as those of the hydrothermal sedimentary rocks. All samples ofthe rocks fell in the hydrothermat area of the Fe Mn （Cu＋Ni＋Co）× 10 diagram;the content of the Mn is higher;the rate of Si/Ba is less than 1;some metal elements are evidently concentrated, for example Pb,Zn,Ba and Rb etc.. Multifactorial analysis shows that the development of the PergamidiaHalobia community was controlled by the hydrothermal activity.

关 键 词：Pergamidia Halobia群落 双壳类 古环境 勉戈组 川西昌台 

分 类 号：Q915[天文地球—古生物学与地层学]