摘要： 济阳坳陷始新统沙四上—沙三下亚段页岩岩相类型多样、特征明显,近年来针对该套页岩系统取心10 100余米,为陆相断陷湖盆页岩岩相发育主控因素及分布研究提供了“天然实验室”。综合利用岩心、薄片、XRD、地球化学等资料,以济阳坳陷为研究区,对沙四上—沙三下亚段的页岩岩相类型、发育主控因素和分布规律进行了系统研究。结果表明,济阳坳陷古近系位于北纬亚洲季风气候带,沙四上—沙三下亚段处于强烈裂陷欠补偿期,为典型的闭流咸化湖盆,发育巨厚层纹层发育的富碳酸盐页岩; 受湖盆古水介质(古水深、古盐度和古氧化-还原性)和古物源条件复杂多变控制,发育了多类型页岩,包括碳酸盐页岩、混合页岩、黏土页岩和长英页岩4类,进一步综合岩石组分、沉积构造和有机质丰度细分为富有机质纹层状碳酸盐页岩相、富有机质层状碳酸盐页岩相、富有机质纹层状灰质混合页岩相、富有机质纹层状黏土质混合页岩相、富有机质层状长英质混合页岩相、富有机质纹层状黏土页岩相、富有机质层状黏土页岩相、富有机质纹层状长英质页岩相和含有机质层状长英质页岩相9种; 古气候、古物源和古水介质协同演化,与古地貌共同控制了岩相类型与展布,其中,古气候与盆地构造演化控制了页岩发育的规模,古水介质与古物源控制了页岩岩相类型,古地貌与古物源控制了岩相分区分带差异化展布。建立了济阳坳陷沙四上—沙三下亚段页岩分区分带差异化分布模式,可为陆相断陷盆地页岩油气勘探和相似地质背景下页岩成因研究提供借鉴和参考。

关键词: 济阳坳陷, 始新统, 页岩岩相, 主控因素, 古水介质, 古物源, 古地貌

Abstract: In recent years,over 10 100 meters of cores have been collected to the study of the shale oil and gas system in the Jiyang Depression. These cores provide excellent materials for investigating the main control factors and distribution of shale lithofacies in continental rifted basins. In this study,diverse shale lithofacies in the upper Member 4(Es4S)and lower Member 3(Es3X)of Eocene Shahejie Formation in the Jiyang Depression are identified by utilizing thin section,XRD mineral composition and major element data. The experiment results show the primary development of four types of shale lithofacies in the Jiyang Depression,namely carbonate shale facies,mixed shale facies,clay shale facies,and felsic shale facies. Moreover,these lithofacies are further subdivided into nine subtypes: organic-rich laminated carbonate shale facies,organic-rich layered carbonate shale facies,organic-rich laminated carbonate mixed shale facies,organic-rich laminated clay mixed shale facies,organic-rich layered felsic mixed shale facies,organic-rich laminated clay shale facies,organic-rich layered clay shale facies,organic-rich laminated felsic shale facies and organic-bearing layered felsic shale facies. The Jiyang Depression,located in a northern latitude Asian monsoon climate zone,experienced intense rifting and was underfilled by sediments during the Paleogene. The lacustrine palaeowater medium(palaeo-water depth,palaeo-salinity,and palaeo oxidation-reduction)and palaeo-provenance variations have jointly controlled the types and distribution characteristics of lithofacies. Among these factors,palaeoclimate and basin evolution controlled the large-scale development of organic-rich carbonate laminated shale lithofacies,while the types of shale lithofacies were controlled by the interplay between palaeo-water body and palaeo-provenance. Additionally,the distribution of shale lithofacies was determined by the interaction of palaeogeomorphology and palaeo-provenance. This study has established a belt distribution model of shale in the Es4S and Es3X of the Jiyang depression,which can provide valuable insights for shale oil and gas exploration in continental rifted basins and contributes to the understanding of shale genesis research under similar geological conditions.

Key words: Jiyang Depression, Eocene, shale lithofacies, main control factor, palaeo-water, palaeo-provenance, palaeomorphology

中图分类号: 

• P588.21