Carboniferous Brachiopods Communities And Their Environmental Significance Of The Northern Qilian Mountains In Gansu Province

Based on Carboniferous brachiopods fossils from3measured sections and7collected sections of the Northern Qilian Mountains, the distinctiveness and analysisof communities has been conducted in this paper. Combining with sedimentary facies,sedimentary cycle, the research of communities in the horizontal change and verticalreplace and succession has been conducted to discuss the main factors controllingthe growth of communities and the relationship between the replacement and changeof relative sea level.The basic findings are as follows,1．According to on the host position and taphonomy of fossils,38brachiopodabenthic communities, which greatly enriched the files of this area’s brachiopoda fossil,have been found and differentiated from brachiopoda communities in3measuredsections and8collected sections.2．The construction, bottom-dwelling ecological niche, succession of community,their environmental significance have been discussed based on the major components(opportunity molecules, equilibrium species, top molecules of succession), the changeof percentage, ecological analysis. It is believed that the carboniferous brachiopodacommunities in this area are mainly the output of low energy environment. Theirbottom-dwelling ecological niches are between BA1-BA3,and the depths are between0-60m.3．According to the lithology,sedimentary structure and fossil content of sectionfrom Daqinggou in Sunan, Moshigou in Tianzhu, on the basis of section deposition andphase sequence, the research of communities in the horizontal change and verticalreplace and succession has been conducted to discuss the main factors controlling thegrowth of communities and the relationship between the replacement and change ofrelative sea level. and the result shows that, the change of relative eustatic movementrelated palaeobathymetric are the major element, at the meantime, the fundamental base,water cycle and salinity also bear the significance.4．Through the horizontal comparison of different sections, the relationship between horizontal changes of communities, palaeobathymetric and palaeogeographic.There were big horizontal changes of communities in early carboniferous period. Thechange became smaller in the late Carboniferous epoch. The major reason is that apalaeohigh existed in the early carboniferous period in Yongchang area, caused nosedimentation. Water depth grew toward east and west, and not until the lateCarboniferous epoch did the water covered the whole area. The differentiation ofcommunities not only controlled by the palaeogeographic and palaeobathymetric, butalso controlled by the ancient sedimentary facies and microfacies.