Biomarker classifications of Lower Paleozoic deep source rocks and crude oils from the Tarim Basin and oil sources
To elucidate the provenance of intricate deep crude oils in the Lower Paleozoic strata,in this paper,a systematic geochemical analysis of Lower Paleozoic source rocks and crude oil samples in Tarim Basin has been carried out.The juxtaposition of samples subjected to natural evolutionary processes and thermal simulation ex-periments unveiled that certain aromatic indices exhibit remarkable stability,particularly 1-alkyl-2,3,6-aryl iso-prenoids(2,3,6-AIPs),which demonstrates pronounced resistance to anti-secondary-alteration.A comprehen-sive assessment of the hydrocarbon generation potential of Lower Paleozoic source rocks identified five series of organically enriched strata(Lower Cambrian Yuertus Formation(Є1y),Middle-Lower Ordovician Heituao Formation,Middle Ordovician from the Xihexiu section,Middle-Upper Ordovician Sargan Formation,and Up-per Ordovician Lianglitage Formation).These were categorized into three distinct groups:"low salt-green al-gae","high salt-dinoflagellates",and"photic-zone euxinia(PZE)-green sulfur bacteria(GSB),"predicated on the presence of stable aromatic biomarkers,including 2,3,6-AIPs.And crude oils were categorized into two dis-tinct groups:PZE-green algae oil and PZE-GSB oil.Notably,PZE-GSB source rocks(mainly developed from the Є1y)contained abundant 2,3,6-AIPs,showing similarity to almost all crude oils from the Tazhong and Ta-bei areas,Tarim Basin.Through oil-source correlation and the quantitative deconvolution of mixed crude oils,it was ascertained that the source rock harboring 2,3,6-AIPs likely plays a pivotal role in the substantial contri-butions to the extant deep crude oil reserves in the Tarim Basin.Therefore,finely determining the spatial distri-bution of this source rock developed under the special biological-environmental condition(PZE-GSB),in the next stage,would provide significant reference for the targeted exploration of deep complex crude oil in the Lower Paleozoic from the Tarim Basin and even the world.
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