Detection and Geological Significance of Carotenoid-Derived Alkanes in the Source Rocks:A case of well Malu 1,Lucaogou Formation,Santanghu Basin
[Objective]Both γ-carotane and β-carotane are carotenoid-derived alkanes,which are widely distribut-ed in sediments and crude oil,but carotenoid-derived alkanes with low carbon number are rare in the study of source rocks.This study explored the sources of γ-carotane,β-carotane and carotenoid-derived alkanes with low carbon numbers,indicating their significance in geological carriers.[Methods]Twelve representative source rock samples were collected from well Malu 1 in the Lucaogou Formation of the Malang Sag,Santanghu Basin.The geochemical characteristics were demonstrated in detail by gas chromatography-mass spectrometry,rock pyrolysis,vitrinite reflec-tance(Ro),and total organic carbon(TOC)analysis to obtain the biogenic information of the target compound.[Re-sults and Conclusions]The source rocks of the Lucaogou Formation from well Malu 1 are rich in organic matter,good in type,and in the mature stage.Moreover,the source rocks are rich in γ-and β-carotane with high abundance and have carotenoid-derived alkanes with low carbon number(Carbon number ranges from C13 to C25).Based on the comprehensive analysis of the distribution characteristics of a series of biomarkers such as n-alkanes,terpanes,and steranes,bacteria may be the main biological precursors of γ-and β-carotane.In addition,combining the evidence of thermal evolution of hydrocarbon source rocks,microbial fossils,and volcanic eruptions,the present study proposes that the carotenoid-derived alkanes with low carbon number may be the products of γ-and β-carotane affected by microorganisms or thermal evolution.This study provides new insights the exploration of organic matter source,sedimentary environment and thermal maturation of source rocks.
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