| The Tarim basin is a large-sized superimposed petroliferous basin with multiple sourcerocks. It had experienced multi-stages of tectonic movement, hydrocarbon generation,migration and accumulation, which resulted in complexity in correlation betweenhydrocarbon and source rocks. Previous studies indicated that marine oil and gas of the basinmostly originated from source rocks of Cambrian-Lower Ordovician and Middle-upperOrdovician sequences. Determination of effective source rocks influence upon forecast ofoil-gas resources and select of exploration planning, thus it is very significant to study marinesource rocks in the platform-basin region in detail.Samples were collected from 7 sections including the Kalpin region in the northwest, theBachu region in the west, and the Kruktag region in the northeast, as well as from 8 key wells,such as Zhong 4, Shu2, S115 etc in the basin. By application of advanced technique ofanalysis of organic geochemistry (including carbon isotope,GC-MS of saturated and aromatichydrocarbon,analysis of kerogen and organic petrology,etc),the abundance,types, hydrocarbongeneration potential, maturity of organic matters and characteristics of organic petrology andorganic geochemistry of organic matters which come from Lower Paleozoic source rocks inthe platform-basin region, was described in detail, and general organic geochemical profilesof surface and key wells was set up. It was indicated that:(1)Based on previous many investigations of marine source rock, TOC = 0.4% was takenas lower limit to evaluate marine source rock in the basin. And integrated with analysis ofabundance of organic matters, thickness, lateral distribution of source rocks, it can beconcluded that the Middle-Lower Cambrian was major hydrocarbon source rock, andMiddle-Lower Ordovician was in the second, and the distribution of Upper Ordovician sourcerock was Limited. High quality source rock was developed in abyssal-bathyal basin facies andouter continental shelf basin facies.(2)Mudstone, marlite and gypsiferous argillaceous dolostone are primary effective sourcerock. Studies on carbon isotope, organic elements, SEM of kerogen, feature of organicpetrology, organic geochemical characteristic of soluble organic matter had indicated that thekerogen type of Lower Paleozoic(∈1-2,O1-2,O3) source rocks in the platform-basin region isType I, the oil-prone source rocks.(3)Studies on bitumen reflectance,organic elements analysis and SEM of kerogen,Rock-Eval, organic geochemical characteristic of soluble organic matter had showed thatprimary source rocks of Middle-Lower Cambrian and Middle-Lower Ordovician is in thestage of high mature-supermature in the basin, but primary source rock of Upper Ordovicianis in the range of oil-generating window.(4) Sterane and terpane biomarkers of Lower Paleozoic source rocks in the Tarim basinindicated that there is closer relationship between crude oil and the Cambrian source rocksrather than the Middle-Lower Ordovician source rock, and less relation with UpperOrdovician source rocks.
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