Stratigraphic Division,Correlation and Geologic Significance of Silurian in Tarim Basin

Through survey of Silurian outcrop section in Keping area in western Tarim basin,the Silurian can be divided into Kepingtag,Tataaiertag formations of Lower Silurian,Yimugantawu formation of Middle-Upper Silurian.The Kepingtag can be sub-divided into lower,middle and upper parts,while the Tataaiertag into lower and upper parts.Also,six horizon markers for strata correlation have been identified.The study shows that Tazhong(central Tarim) uplift lacks of the lower and the middle parts of Kepingtag formation,Tabei(northern Tarim) uplift lacks of the lower part in Yingmaili area;the whole Kepingtag formation is found in Manjiaer sag and Tadong(eastern Tarim) area,and Yimugantawu formation is partly found in Tazhong and Tabei areas.Keping and Tabei areas are dominated by shore-neritic facies' clastic deposits,Tazhong area by estuarine-tidal flat deposits and Tadong area by continental river-braided stream delta's coarse fragment deposits.The integrated analysis indicates that before Silurian,Tazhong and Tabei areas were inherited uplifts showing paleo-relief of the higher in east and the lower in west;the transgressive direction was from WN towards ES;the strata were overlapped from WN towards ES.The top stratum denudation of Silurian was caused by the post tectonic uplifting.The unique characteristics of Silurian deposit reveal the paleo-relief feature,source and transgressive directions in Tarim basin.