The Late Paleozoic Brachiopod Communities And Their Environmental Significance In Shanxi Province

Based on the actual measured field sections and materials collected from the papers, the detailed benthic communities of the late Paleozoic have been established. According to the characteristics of the composing structures of the communities and the autecology, combined with the lithologic features of the rocks from which the fossils were collected, each of the benthic niche of the communities has been analyzed in detail. By horizontal correlation, the changes of the ecological niche in time and space have been analyzed. On the basis of the study on lithology and the sedimentary facies, combined with the analysis of the fossil assemblages from the sections, the facies sequence configuration, the division of the sedimentary cycles has been made. Furthermore, by the comparison between benthic ecological niches and the sedimentary cycles, the relationship between brachiopod communities and the relative sea-level changes has been discussed. The main results of the paper are as fallows.(1)Sixty three brachiopod communities have been found after the detailed analysis and study of five measured sections represented by Shuiquangou in Yangquan and Guanjiayu in the east mountain of Taiyuan and five collected sections with Chengjiazhuang in Liulin and Danshuigou in Shuozhou as representatives. (2) It is concluded that brachiopod communities identified were lived in a low energy environment by the analyses of the structures of each community including the characteristics of the dominant species, the typical and the common members as well as autecology of individuals and their environment significance. (3) Based on the community analyses and lithologic features, the benthonic ecological niches of the communities have been discussed and finally proved that they range from BA1 to BA3(BA-Benthic Assemblage), with water-depth between 0 to 60 meters. (4) On the basis of studies on sedimentary facies and brachiopod communities, combined with the analysis of facies system configuration and the sedimentary cycles, it has been found that there are eleven sedimentary cycles from Benxi depositional processes to Shanxi depositional processes, among which, three were in Benxi depositional process, one in Jinci depositional process, four in Taiyuan depositional processes and three in Shanxi depositional processes. Among all these cycles, the one represented Miaogou limestone is the largest scale of marine ingression in the first sedimentary cycle. (5) Based on the lateral comparative studies on benthonic ecological niches of the communities, it has been found that the direction of marine transgression in Benxi depositional processes is from the northeast, and in Taiyuan depositional processes is from southeast. (6) Based on the above investigation, the relationships between the replacement of brachiopod communities and the changes of the relative sea level have been explored and found that the main factors resulted in the replacement are the depth of sea water and water circulation. And global sea level changes affect the changes of relative sea level.