The Analysis on the Depositional Environment of Wutong Formation in Northern Chaohu Area, Anhui

Key words: 
• northern Chaohu area /
• Wutong Formation /
• grain size analysis /
• sedimentary environment and its evolution

Abstract: The stratum of Wutong Formation of Devonian is developed widely in Lower Yangtze area. Because it is at the early stage of transgression, there coexists, the continental and marine features which causes the difference in understanding sedimentary environment of this formation. The stratum of Wutong Formation of Devonian in northern Chaohu area of Anhui is a combination of thick sandstone with mudstone, and the depositional characteristics and depositional environment are unclear all the time. So, based on the research results of predecessors and analysis of outcrops, associated with the means of sedimentology, stratigraphy and grain size analysis under the microscope, we analyze the thick sandstone section in detail and find that Wutong Formation is developed in marine environment, that is it has backshore-foreshore of multi-segment pattern that is composed of rolling component and jumping component, foreshore-upper shoreface of bi-segment pattern that is composed of jumping component and suspending component, and mixed flat of siltstone and mudstone of bi-segment pattern that is composed of jumping component and suspending component. Combining with the characteristics of sedimentary sequences and sedimentary characteristics, we can draw a conclusion that the lower part of Guanshan Member in Wutong Formation is gravel beach deposition of backshore-foreshore subfacies, the upper part is sand beach deposition of foreshore-upper shoreface subfacies. The lower part of Leigutai Member in Wutong Formation is siltstone-mudstone deposition of mixed flat subfacies; the middle part is mudstone of bay mudflat subfacies and coastal marsh subfacies with sand beach deposition of foreshore subfacies; the upper part is chalybeate mixed flat deposition of littoral facies. This paper not only has theoretical value, but also has a certain teaching significance.