SEDIMENTARY FEATURES AND HYDROCARBON POTENTIAL IN THE TRIASSIC SYSTEM OF THE TARIM BASIN

The Triassic system of the Tarim Basin mainly consists of the coal-bearing clastic rocks of fluvial-lacustrine facies,intercalated with pan-marine carbonates,sands and mudstones;the thickness of the system ranges 500-1900m,and the distributing area reaches to about 30×10⁴km².In the system the source rocks mainly developed in deep-shallow lake subfacies,delta facies and pan-marine facies,lithologically it is characterized by dark mud,shales,carbonaceous mudstones intercalated with grey carbonate rocks,coals and oil shales.The accumulated thickness is up to 200-800m.The Majiar and Tangguzibasi depressions in the basin are the two major source rock areas totalling to about 13 ×10⁴km².The organics are predominately attributed to types Ⅱ_B~Ⅱ,then to types Ⅱ~Ⅰ,with the R°values ranging 0.6~1.2%,therefore,they have a good hydrocarbon potential.In recent years,the several significant break-throughs of oil/gas exloration have been made in the Triassic system of the Northeast Tarim Basin,suggesting there is an extensive prospect for the petroleum exploration in the Triassic system of the basin.