Since the discovery of the Tahe oilfield,it has been controversial on whether the main source rock is in the Cambrian or Middle-Upper Ordovician strata.In this paper,it is assumed that the crude oil from the Wells YM 2 and TD 2 was derived from the Middle-Upper Ordovician and Cambrian source rocks,respectively.We analyzed the biomarkers of the crude oil,asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions from the Lunnan and Hade areas in the North Uplift of the Tarim Basin.Results show that the ratios of tricyclic terpane C_(21)/C_(23)in the crude oil,asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions are less than 1.0,indicating that they might be from Upper Ordovician source rocks;the ratios of C_(28)/(C_(27)+C_(28)+C_(29))steranes in the saturated hydrocarbon from reservoir bitumen and bitumen inclusions are higher than 25,suggesting that they might come from the Cambrian source rocks,however,the ratios of C_(28)/(C_(27)+C_(28)+C_(29))steranes in oil from the North Uplift are less than 25,suggesting that they might be sourced from the Upper Ordovician source rocks.These findings demonstrate that the sources of crude oil in the Tarim Basin are complicated.The chemical composition and carbon isotopes of Ordovician reservoired oil in the Tarim Basin indicated that the crude oil in the North Uplift(including the Tahe oilfield)and Tazhong Depression was within mixture areas of crude oil from the Wells YM 2 and TD 2 as the end members of the Cambrian and Middle-Upper Ordovician sourced oils,respectively.This observation suggests that the crude oil in the Ordovician strata is a mixture of oils from the Cambrian and Ordovician source rocks,with increasing contribution from the Cambrian source rocks from the southern slope of the North Uplift to northern slope of the Central Uplift of the Tarim Basin.Considering the lithology and sedimentary facies data,the spatial distribution of the Cambrian,Middle-Lower Ordovician and Upper Ordovician source rocks was reconstructed
