New Evidence on the Sedimentary Framework of the Early Ordovician in Central Tarim and Adjacent Area

Key words: 
• Tazhong area /
• lowermiddle Ordovician /
• trough /
• isolated platform

Abstract: The previous viewpoint considered that,the early Tarim basin was an “unified carbonate platform”, its slope was developed along the GuchengLunnan area.Based on sedimentologic and seismic stratigraphic data from the lowermiddle Ordovician, deepwater slope and basinal facies were recognized along the MJ1TZ29 section, so that the Tazhong and its adjacent areas could have already been isolated from the “unified carbonate platform” and seprated into three platforms of TazhongBachu, Gucheng and Tangnan, which was also faced with TaBei area across a trough. The highenergy reefshore bodies bandingly developed among the edge of each isolated platform as a band, which were mainly composed of midhigh energy grain banks. Inwards, it becomes the deposition of platform,developing the subphases of intraplatform banks, intraplatform depression and interabeach seas and soon. Outwards it becomes deeperwater deposition area of slopetrough. Under this circumstance,the new regional depositional pattern of the Tazhong and adjacent areas has been established.This new pattern has great theoretical and realistic significance for the establishment of new favourable exploration zones.It also greatly increases the strategic position for the petroleum exploration in lower Ordovician of research area.