Western Sichuan Chang Taiwan Late Triassic Biomes Characteristics And Environmental Analysis

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...