Is there a great unconformity between Xiamaling and Longshan formations in the North China Craton?

作     者：Hongwei KUANG Nan PENG Yongqing LIU Yuchong WANG Mingming CUI Xiaoshuai CHEN Dawei QIAO Keining QI Hongwei KUANG;Nan PENG;Yongqing LIU;Yuchong WANG;Mingming CUI;Xiaoshuai CHEN;Dawei QIAO;Keining QI

作者机构：Institute of GeologyChinese Academy of Geological SciencesBeijing100037China School of Earth Science and Mapping EngineeringChina University of Mining and Technology(Beijing)Beijing100083China School of Resource and Environmental EngineeringHefei University of TechnologyHefei230009China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2023年第66卷第5期

页      面：959-984页

核心收录：

学科分类：070904[理学-构造地质学] 070902[理学-地球化学] 070903[理学-古生物学与地层学(含：古人类学)] 0709[理学-地质学] 07[理学] 0705[理学-地理学] 

基　　金：the prospective marine oil and gas exploration project of Sinopec(Grant No.YPH08025) supported by the National Key Research and Development Program of China(Grant Nos.2022YFF0800302,2016YFC0601001) the National Natural Science Foundation of China(Grant No.42072135) the China Geological Survey Program(Grant Nos.DD20221649,DD20190005) the Beijing Science and Technology Project(Grant No.Z201100008320007)。 

主　　题：North China Craton Mesoproterozoic Transition period Unconformity Continuous sedimentation 

摘      要：The existence of a 0.3 Gagreat unconformitybetween the MesoproterozoicUndefined SystemXiamaling Formation and theNeoproterozoicLongshan Formation has long been controversial.In this study,stratigraphy,sedimentology,detrital zircon dating,lithium isotope,and major and trace elements were applied to systematically analyze their relationship.Results demonstrate that coarse to fine sandstone-mudstone normal cycles with different grades and thicknesses exist from the Xiamaling to the Longshan formations.Sedimentary succession formed from a restricted platform with lagoon-shallow marine shelf-tidal flat-beach and tidal shoal developing in ascending order.The pebbly sandstone at the bottom of the Long shan Formation does not have the properties of basal conglomerate with tectonic significance.The youngest detrital zircon is older than 1.6 Ga for the Long shan Formation and overlying Jing eryu Formation sandstones.In addition,no(zircon)provenance has been found from the large igneous province of 1.32-1.2 Ga in Xiamaling Formation.Theδ^(7)Li isotope values exhibit a gradually increasing trend.The Li content and CIA(Chemical index of alteration)gradually decreases from the top of the Xiamaling Formation to the lower part of the Long shan Formation.Simultaneously,as K_(2)O/Al_(2)O_(3)and FeO/Fe_(2)O_(3)decreases,Na_(2)O/Al_(2)O_(3)increases,and Li/Al,V/Cr,and V/(V+Ni)fluctuates slightly.At the boundary,the Ce/Ce^(*)and Eu/Eu^(*)show positive and negative anomalies,respectively.Further,the Rb/Sr and Al/Si values decrease,and U/Th values increase.This indicates that the geochemistry of the weathering crust at the interface of the Xiamaling Formation-Long shan Formation is not characteristic.However,it indicates a weakening of continental weathering intensity from the bottom to the top of the interface.These results do not support the existence of a large unconformity between the Xiamaling and the Longshan formations.Therefore,it is suggested that the Long shan Formation-Jing eryu Formation should be moved to the lower level in the stratigraphic chart,where it should form part of the MesoproterozoicUndefined Systemalong with the Xiamaling Formation.On this basis,the paleogeography of the Xiamaling Formation-Longshan Formation-Jing eryu Formation sedimentary period in the Yanliao area of North China has been reclassified.