Cyclicity related to solar activity in lacustrine organic-rich shales and their significance to shale-oil reservoir formation  

作　　者：Miruo Lin Kelai Xi Yingchang Cao Rukai Zhu Xiaobing Niu Honggang Xin Weijiao Ma 

机构地区：[1]Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,China [2]Research Institute of Petroleum Exploration and Development,PetroChina,Beijing 100083,China [3]PetroChina Changqing Oilfield Company,Xi’an 700018,China

出　　处：《Geoscience Frontiers》2023年第5期91-107,共17页地学前缘（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant No.42072161);Innovation Research Group of the Natural Fund Committee(Grant No.41821002)and Fundamental Research Funds for the Central Universities(22CX07008A)。

摘　　要：The formation mechanism of micron-to centimeter-scale sedimentary cycles in lacustrine shales is a hot topic of research,because these small-scale sedimentary cycles significantly influence shale-oil distribution heterogeneity.High-frequency paleoenvironmental evolution is an important controlling factor for the formation of small-scale sedimentary cycles.However,the driving factors of high-frequency paleoenvironmental evolution and the formation process of sedimentary cycles under its constraint remain speculative.In this study,which focuses on lacustrine shales,we find that the alternating deposition of variable thickness of organic-rich lamina(ORL)and silty-grained felsic lamina(SSFL)form sedimentary cycles on the micron to centimeter scale in the Chang 73 sub-member of the Yanchang Formation in the Ordos Basin.Based on detailed petrographic characterization,in-situ geochemical parameter testing,and high-resolution cycle analysis,the formation process of cyclical sedimentary records and related paleoenvironmental evolution are investigated.Three solar activity cycles were identified from the shales,namely the 360–500 yr,81–110 yr,and 30–57 yr cycles(cycles I,II,and III,respectively).Highfrequency paleoenvironmental evolution caused by solar activity induced lake-level fluctuation,which further controlled silty-grained sediment deposition and organic matter preservation in deep lake areas.Cycle I controlled relatively long-term lake-level fluctuation,driving several pairs of SSFL and ORL deposition at the centimeter scale.Cycles II and III were short-term cycles and acted on the millimeter to micrometer scale,further complicating the sedimentary strata forming during the period of lake-level fall induced by cycle I.The cyclic deposition of SSFL and ORL correspond to cycle III.Lake-level fluctuation influenced by cycle II mainly caused SSFL thickness variation in each lamina couplet.During the period of lake-level rise induced by cycle I,periods of lake level rise during cycles II,and III show cyclic varia

关 键 词：Triassic Lacustrine shales Solar activity Lake-level fluctuation Shale-oil exploration 

分 类 号：P534.43[天文地球—古生物学与地层学] P59[天文地球—地质学]