沉积学报2025，Vol.43Issue(4)：1178-1198,21.DOI:10.14027/j.issn.1000-0550.2024.077
鄂尔多斯盆地西缘乌拉力克组笔石带划分及对沉积演化的指示
Division of Graptolite Zones in the Wulalike Formation at the Western Margin of the Ordos Basin:Implications for sedimentary evolution
摘要
Abstract
[Objective]A set of black marine graptolitic shales is developed in the Wulalike Formation at the west-ern margin of the Ordos Basin.In recent years,natural gas has continually been discovered in this set of shales and an industrial level of oil flow has been produced,demonstrating that the Wulalike Formation has significant explora-tion potential.This study examines the development of the graptolites and establishes a biostratigraphic framework as a basis for analyzing the sedimentary evolution of the Wulalike Formation.[Methods]The age range of the Wulalike Formation was clarified by analyzing the graptolite content of individual cored wells and comparing the graptolite range.Single-well graptolite zones were identified and biostratigraphic frameworks were constructed on that basis,and the distribution of the graptolite zones is discussed.The spatial evolution of the black shale was analyzed in com-bination with the lithological development.Sea-level variation was also considered based on the response of graptolite morphological complexity to marine transgression.[Results](1)The Wulalike Formation was developed during the Darriwilian-Sandbian stages at the end of the middle-and beginning of the Upper Ordovician.The Wulalike Forma-tion is divided into four graptolite zones from bottom to top:the Pterograptus elegans zone,Jiangxigraptus vagus zone,Nemagraptus gracilis zone and Climacograptus bicornis zone.(2)From a comparative analysis of their develop-ment,it is believed that all four graptolite zones are developed in the northern Wulalike Formation of the study area in the vicinity of well QT9,while the Pterograptus elegans and Jiangxigraptus vagus zones are absent in the southern part of the Formation.(3)Two marine transgression periods are indicated by the Pterograptus elegans and Nemagrap-tus gracilis zones in the Wulalike Formation,transitioning upward into the Climacograptus bicornis zone and then into the Lashizhong Formation,during which time the sea level gradually lowered.[Conclusions]The black graptolitic shale at the bottom of the Wulalike Formation shows strong diachronism from Pterograptus elegans in well QT9 to Ne-magraptus gracilis in well YinT2.Along the western margin of the Ordos Block,the strata are gradually younger to the south,and the deposition center gradually migrates southward.The diachronism is typically manifested as"degra-dational stacking",evident as an upward-shallowing stacking pattern that indicates a forced marine regression inter-face.Alternatively,the diachronism of the black shale may be due to marine transgression deposition and prograda-tion in a highstand systems tract,resulting in the progradation of the black shale towards the south or southwest.Due to the limitations of core sampling,in subsequent studies the causes of the diachronism of the black shale will require determination of the formation ages of the limestone at the top and bottom of the Wulalike Formation,along with veri-fication by seismic data.The establishment of a biostratigraphic framework in this study based on the graptolite zona-tion provides important guidance for understanding the stratigraphic and sedimentary evolution of the Wulalike Forma-tion at the western margin of the Ordos Basin.关键词
笔石带划分/生物地层格架/乌拉力克组/沉积演化Key words
graptolite zone division/biostratigraphic framework/Wulalike Formation/sedimentary evolution分类
天文与地球科学引用本文复制引用
高小洋,王斌,胡勇,王传尚,何文祥,张建伍,封莉,严婧文,万涛,朱建斌,徐鹏程..鄂尔多斯盆地西缘乌拉力克组笔石带划分及对沉积演化的指示[J].沉积学报,2025,43(4):1178-1198,21.基金项目
国家自然科学基金项目(52174019) （52174019）
湖北省教育厅科学研究计划资助项目(D20201302)National Natural Science Founda-tion of China,No.52174019 （D20201302）
Educational Commission of Hubei Province of China,No.D20201302 （）
