Microfossils Of Cambrian Cherts From Kuluketage Area And Ordovician Cherts From YJ1X Well,Tarim Basin

This thesis researched on Cambrian cherts in Quruqtagh and nodular cherts of Ordovician Yijianfang Formation in YJ1X well both located in the Tarim Basin,Xinjiang.A diverse assemblage of well-preserved organic-walled microfossils have been detected in black cherts of the Xishanblaq Formation at Quruqtagh,including 8 species of 5 genera:Asteridium lanatum,Asteridium tornatum,Heliosphaeridium dissimilare,Heliosphaeridium lubomlense,sponge spicules,Zhijinites Longistriatus and Parazhijinites guizhouensis.The geochemical study of the samples of the Cambrian cherts and carbonate at Quruqtagh area has been carried out in this paper.The geochemical characteristics of the cherts indicate that the Cambrian cherts at Quruqtagh area should be deposited on a pelagic ocean-basin floor in proximity to the mid ocean ridge that provided much interior source,and there was hydrothermal input during the process of deposition.Based on the geochemistry of the carbonate and previous studies about the regional geology,it is considered that the up welling carries the substances formed in the pelagic ocean floor onto continental shelf to deposit,which results in the geochemical characteristics of the bedded cherts retained the characteristics of oceanic basin.The Ordovician Yijianfang Formation of the YJ1X well,contains some laminar and nodular cherts that have been discovered a diverse and well preserved microfossil assemblage in thin sections.The microfossil assemblage of the cherts is dominated by 11 genera,represented by 13 species in all:Aremoricanium sp.,Cheleutochroa oculata,Cymatiogalea sp.,Cymatiosphaera sp.,Dictyotidium microreticulatum,Leiosphaeridia sp.,Polygonium gracile,Pterospermella sp.,Siphonophycus typicum,S.kestron,S.solidum and Oscillatoriopsis longa.All of these filamentous cyanobacterias are first reported in Yijianfang Formation,which greatly increased the composition of the Yijianfang Biota.A large number of broken algae mats and a few acritarchs reflect the process of the sedimentary facies from shallow to deep in this area.