鄂尔多斯盆地西南部下白垩统宜君组砾岩砾组分析及其意义  

Fabric Analysis of Yijun Gravels of Lower Cretaceous in the Southwestern Ordos Basin

作　　者：王建强[1] 贾楠[1] 刘池洋[1] 邱欣卫[1] 赵红格[1] 郭真[1] 

机构地区：[1]大陆动力学国家重点实验室(西北大学)西北大学地质学系,西安710069

出　　处：《沉积学报》2011年第2期226-234,共9页Acta Sedimentologica Sinica

基　　金：国家自然科学基金(重大研究计划)重点项目(批准号:90814005);陕西省教育厅基金项目(批准号:06JK181);西北大学大陆动力学国家重点试验室开放课题基金资助

摘　　要：运用砾组分析方法,结合邻区基岩地层,对鄂尔多斯盆地西南部下白垩统宜君组砾岩的砾性、砾度、砾态及砾向进行了研究,阐述了研究区不同区域砾岩的成分来源、成因、形成的水动力条件及古水流方向。表明宜君组砾岩为早白垩世初期干旱环境下山麓洪积扇—河流相沉积产物,具多物源和快速沉积的特点,砾石分选普遍较差,磨圆呈次棱角—次圆状,风化程度低。其中南部麟游—彬县地区的砾石主要来自北秦岭造山带,西南部陇县—千阳地区主要来自陇山古生界;进而认为今渭北隆起南部及渭河地区在早白垩世仍在接受沉积,渭北隆起的发育时限主要是早白垩世末期以来,早白垩世原始盆地沉积南界可在今渭河地区甚或达秦岭北麓。The study area is located in the southwest of the Ordos Basin,with the tectonic position in the intersection of Ordos Basin and Qinling-Qilian orogenic belt,and the area is adjacent to the western thrust fold belt in the west,and looking at Qinling orogenic belt across Weihe graben in the south.Since the Late Triassic,molasse formations were widely developed because of the neighbouring orogenic belts＇ multi-stage tectonic movements.Among them the Yijun conglomerate at the bottom of the Lower Cretaceous is the typical molasse formation.The study on it has great significance and value to discuss the original basin boundary and basin-mountain evolution in the southwest of the Early Cretaceous basin. Using fabric analysis method to study the composition,particle size,shape and preferred orientations of nine measuring points from west to east in Yijun conglomerate in the southern Early Cretaceous basin can clarify the composition,source and formation environment of these gravels.The composition analysis shows that the component gravels from the west to the east in the study area can be divided into three regions： Longxian-Qianyang area＇s gravels are mainly carbonate rocks,Linyou-Yongping area＇s gravels are dominated by granite and metamorphic rocks,Binxian area＇s gravels are quartzite and metamorphic rocks.Analysis on particle size,shape and preferred orientations indicate that the gravels size show large-small-large-small rule from west to east,generally with poor sorting,subangular to subrounded and low degree weathering,and the material mainly come from the southern of the basin,which can be seen that the Yijun conglomerate is an alluvial fan-fluvial sedimentary gravels with arid environment and rapid accumulation to deposit in the depression at the foot of mountain. Combining with analysis of adjacent areas rock formations and regional geology,we consider that the provenance of Lower Cretaceous should not come from the old strata of southern Weibei uplift or the pre-Cenozoic strata of Weihe garben.Linyou

关 键 词：鄂尔多斯盆地 早白垩世 宜君砾岩 砾组分析 渭北隆起 原盆边界 

分 类 号：P585.2[天文地球—岩石学]