川西昌台地区晚三叠世生物群落特征及环境分析

【作者】 庞艳春；

【导师】 林丽；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2006， 博士

【摘要】 古热液生物群具有重要的研究意义而成为地球科学前沿领域的热门课题之一。本文以古生物、地层学、古生态学、生态地层学和岩石学为基础，结合现代生态学、地球化学和统计学等相关学科理论，运用对比等手段对川西昌台地区晚三叠世的群落特征及其古环境进行研究，并以此来判断这些化石是否为地质历史期存在的古热液生物群。 研究区内的上三叠统分为根隆组和勉戈组，各组中的化石鉴定结果和剖面资料整理结果表明，根隆组对应的地质年代为卡尼克期，勉戈组对应的地质年代为卡尼克晚期至诺利克期。 通过地层对比可知，本区上三叠统岩性组合复杂，以火山岩为主；邻区上三叠统以沉积岩为主。本区上三叠统产出的化石相对于邻区上三叠统产出的化石类别较单一：本区上三叠统中的化石以双壳动物为主，可见遗迹化石，偶见菊石和海百合碎片；而邻区上三叠统盛产双壳、菊石、珊瑚、腕足和大量腹足类、藻类和牙形石等。 群落特征分析表明，卡尼克时期至诺利克时期的生物群落面貌具有集中程度较高、物种单一、以食悬浮物质外栖足丝型双壳动物为主的特点，优势生物有Halobia、Pergamidia和Modiolus等。纵向上的群落对比具有突变性，横向上的群落对比在优势属上具有一定的差异性。卡尼克中晚期，群落面貌以Halobia为主，代表群落为Halobia pluriradiata—Halobia aff．yunnanensis群落(群落Ⅰ)和Halobia aff．laevia—Halobia cf．ganziensis群落(群落Ⅱ)；诺利克早期，群落面貌以Pergamidia和Modiolus为主，代表群落为Pergamidia cf．eumenea群落(群落Ⅲ)；诺利克早期以后，群落面貌以Halobia为主，代表群落为Halobia cf．ganziensis—H．aff．parallena群落(群落Ⅳ)。根据优势属在区域上的分布差异，群落Ⅲ可细分为两个亚群落，亚群落Ⅲ—1(Pegermidia cf．eumenea—Modiolus qinghaiensis群落)和亚群落Ⅲ—2(Pergamidia cf．eumenea—Halobia superba群落)。根据优势生物的个体生态分析可知，各群落的生活环境相当于下部浅海—半深海—深海的深水海相环境中。根据群落的取代情况可将群落发展分为三个阶段，其中群落发展的第二阶段(群落Ⅲ)水体底部环境的营养物质较第一阶段(群落Ⅰ和Ⅱ)和第三阶段(群落Ⅳ)水体底部环境中的营养物质相对丰富。更多还原

【Abstract】 The fossil hydrothermal community research is an important and hot topic in Earth Science. The paper researches Late Triassic bivalve communities and their environment in Changtai of Western Sichuan and judges whether these bivalve communities are ancient hydrothermal biota.Upper Triassic stratum in Changtai area is divided into Genlong Formation and Miange Formation. The information of the profiles and the results of fossils showed that the Genlong Formation is corresponding to Carnian Period and Miange Formation is corresponding to Late Carnian Period to Norian Period.The bivalve communities feature of Carnian and Norian Period, which lived in the seafloor to eat suspended materials, had a higher concentration and lower diversity. The preponderant genus included Halobia, Pergamidia and Modiolus. There are four communities from Genlong Formation to Miange Formation. From the bottom up, there are Halobia pluriradiata-Halobia aff. yunnanensis community (community Ⅰ) and Halobia aff. laevia—Halobia cf. ganziensis community (community Ⅱ) of Halobia-based in Late Carnian Period, Pergamidia cf. eumenea community (community Ⅲ) of Pergamidia and Modiolus -based in Early Norian, and Halobia cf. ganziensis-H. aff. parallena community of Halobia -based ( community Ⅳ) in Late Norian. Being contrasted in transverse, according to differences in preponderant creature, the community Ⅲ was divided into two sub-communities: sub-community Ⅲ-1 ( Pegermidia cf. eumenea-Modiolus qinghaiensis community ) and the sub-community Ⅲ-2 (Pergamidia cf. eumenea-Halobia superba community). The biological development is divided into three phases according to the communities change. The third phase of development (community Ⅲ) has more nutrients in the bottom environment than the first phase, second and the fourth phase (community Ⅰ, Ⅱ and Ⅳ).Some informations of the profile and rocks indicate that sediment deposited in a sub-abyssal and abyssal environment in the period of the forming Genlong Formation and Miange Formation. The first and the third community developped in the upper volcanic activity period or later stage of volcanic activity, and the second community更多还原