The Analysis Of Sedimentary Environment And Tectonic Significance Of Devonian System In South Tianshan Aierbin Area In Xinjiang

Devonian sedimentary rocks on the south side of Aierbin area in the southern Tianshan Mountains are studied in this paper.On the basis of the field investigation,the following results are obtained through the indoor analysis:The stratum exploded in the studied area are reidentified as three formations,Arpishmebulake Formation(Lower Devonian),Sa'a'erming Formation(Middle Devonian),and Pochengzi Formation(Upper Devonian).These formations are divided into eight lithologic sections.The above exploded area is a large anticline.The Middle Devonian strata,located in the core of the anticline,is in conformable contact with the Upper Devonian strata,located in the the two wings of the anticline.The Lower Devonian strata is in fault contact with the Upper Devonian strata.The stratums exploded in the studied area are divided into one sedimentary facies and five sedimentary subfacies.The first lithologic section of the Lower Devonian is the subfacies of the transition zone of neritic shelf facies,the second one is the subfacies of the offshore shelf of neritic shelf facies,and the third one is the neritic facie.The first lithologic section of the Middle Devonian is the restricted platform facies,the second one is the open platform facies.The first lithology section of the Upper Devonian is the platform margin sand facies,the second one is the open platform facies of carbonate rocks facies,the third one is the restricted platform facies.Based on the sedimentary facies analysis,the following rusults are inferred: the sedimentary environment becomes sable founded by regression(the main sedimentary environment)in Early Devonian and transgression(the only sedimentary environment)in Middle Devonian,while it is complicated founded by regression trend in Late Devonian.Established on the former research achievements and the sedimentary environment characteristics in the studied area,it is concluded that the subduction time of South Tianshan ocean basin would not be earlier than Early Ordovician,norlater than Late Carboniferous.The evolution of Late Paleozoic in South Tianshan is deduced in the paper.