Sedimentary environment shift and organic matter enrichment mechanism in response to volcanic ash influence:A case study of the Permian Lucaogou Formation,Santanghu Basin,NW China  

作　　者：Miao Yu Gang Gao Miao Liu Hui Liang Ji-Lun Kang Xiong-Fei Xu Xin-Ying Zhao 

机构地区：[1]College of Geosciences,China University of Petroleum(Beijing),Bejing 102249,China [2]National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing,102249,China [3]PetroChina Tuha Oilfield Company,Hami,839009,China

出　　处：《Journal of Palaeogeography》2024年第4期793-822,共30页古地理学报（英文版）

基　　金：the financial support provided by Tuha Oilfield Company of Petro China (No.YJYHZC2022)。

摘　　要：The second member of the Lucaogou Formation(P_(2)l_(2))in the Tiaohu and Malang Sags of the Santanghu Basin(study area)underwent periodic volcanic activity and frequent lithological changes.This study comprehensively analyzed the organic geochemistry,mineral composition,organic matter(OM)types,volcanic cycle,and palaeoenvironment of shale in the study area.Techniques such as total organic carbon(TOC),rock pyrolysis(Rock-Eval),organic petrology,scanning electron microscopy(SEM)with energydispersive spectrum(EDS)analysis,X-ray diffraction(XRD),trace elements,and saturated hydrocarbon gas chromatography and mass spectrometry(GC-MS)were employed.The findings suggest that limited terrigenous input during the sedimentary period of the P_(2)l_(2) led to the deposition of a distinctive mixture of volcanic ash(felsic)and carbonate(dolomite and calcite),with a low average clay mineral content of 6%.The P_(2)l_(2) shale emerged as a high-quality source rock,predominantly composed of type I and II kerogens,with moderate OM maturity.The deposition environment was characterized by hot and arid conditions,high salinity,and intensive reducibility,which was favorable for algae development and conducive to OM preservation.Notably,two lamalginite types,labeled as lamalginite“A”and lamalginite“B,”were identified.Lamalginite“B”-rich shales were deposited in a hotter and drier climate compared to lamalginite“A”-rich shales.Lamalginite“B”-rich shale inexhibited high levels of C_(28)regular sterane andβ-carotenes,distinguishing it from lamalginite“A”-rich shale.A comprehensive analysis involving organic petrology,SEM,sedimentary environment,and biomarker characteristics suggests that lamalginite“B”may be a salt-tolerant green alga,while lamalginite“A”may be a cyanobacterium.Finally,an OM enrichment model for the P_(2)l_(2) shale was established.

关 键 词：Volcanic ash Geochemistry PETROLOGY PALAEOENVIRONMENT Lamalginite 

分 类 号：P618.13[天文地球—矿床学]