Organic petrology and geochemistry of the Upper Ordovician-Lower Silurian Renheqiao Formation shales of the Baoshan Block,western Yunnan,China
Yinlong Wang1
Detian Yan1
Bei Liu2
Haijiao Fu1
Qingling Jiang1
Yin Yuan1
Hui Tian3
1.Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences,Wuhan,Hubei 430074,China;School of Earth Resources,China University of Geosciences,Wuhan,Hubei 430074,China2.Indiana Geological and Water Survey,Indiana University,Bloomington,IN 47405,USA3.State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China
摘要：Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well under-stood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,Rock-Eval pyrolysis,N2 and CO2 adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt％.Rock-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type Ⅳ kerogen,a result of advanced thermal maturation.Graptolite reflectance(GRo)ranges from 1.26％to 1.85％,and equivalent vitrinite reflectance(EqRo)converted from GRo ranges from 1.08％to 1.51％,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqRo based on Rock-Eval Tmax shows large variations,which indicates that Rock-Eval Tmax is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on Tmax when the S2 values are too low.Organic petrographic observations show that OM in these shales is domi-nated by solid bitumen(＞70 vol％of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.
机标关键词：westernorganicchinablockbaoshanformationgeochemistrylower
论文发表日期：2025-08-31
在线出版日期：2026-01-30（本平台首次上网日期，不代表文献的发表时间）
页数：20( 1-20 )
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