Detection and Geological Significance of Carotenoid-derived alkanes in the Source Rocks from the well Malu 1 , lucaogou Formation, Santanghu Basin

Key words: 
• Santanghu Basin /
• Malang Sag /
• Lucaogou Formation /
• γ- and β-carotane /
• Carotenoid-derived alkanes

Abstract: [Objective] γ-carotane and β-carotane belong to carotenoid-derived alkanes, which are widely distributed in sediments and crude oil, but carotenoid-derived alkanes with low carbon number are rare in the study of source rocks. The purpose of this study is to explore the sources of γ-carotane，β-carotane and carotenoid-derived alkanes with low carbon number, indicating significance in geological carriers. [Methods] 12 representative source rock samples are from the well Malu1 in the Lucaogou Formation of the Malang Sag,and Santanghu Basin were collected. The geochemical characteristics were demonstrated in detail by Gas Chromatography-Mass Spectrometry, Rock Pyrolysis, Vitrinite Reflectance (Ro) and Total Organic Carbon (TOC) analysis, so as to obtain the biogenic information of the target compound. [Results] The source rocks of Lucaogou Formation from the Well Malu 1 are rich in organic matter, good in type and in 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 and other geochemical parameters, it is considered that 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 also 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 can provide new ideas for the exploration of source rocks.