宁夏牛首山地区中—上泥盆统沉积相组合特征  

Sedimentary facies assemblages of the Middle-Upper Devonian in theNiushoushan area, Ningxia, NW China

作　　者：刘义川 鞠书彬 王洋 王旭日[2] LIU Yichuan;JU Shubin;WANG Yang;WANG Xuri(Graduate School,China University of Geosciences,Beijing 100083,China;Key Laboratory of Stratigraphy and Palaeontology of the Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质大学(北京)研究生院,北京100083 [2]自然资源部地层与古生物重点实验室,中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2023年第3期810-821,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41872018,41672019);中国地质调查局项目(编号DD20190602,DD20221649)联合资助的成果。

摘　　要：在阿拉善和华北陆块南缘结合部位的牛首山地区,出露一套连续的中—上泥盆统陆相沉积组合。该套沉积组合的沉积相和沉积物源区的变化特征,可帮助理解阿拉善和华北陆块及相邻地区晚古生代构造演化。根据野外研究结果,该套沉积组合在牛首山南麓石峡沟地区呈现河流相、湖泊相和小型冲积扇相共同发育的沉积面貌,可分为河道、堤岸、河漫平原、滨湖、浅湖、扇根、扇中和扇端共8个沉积亚相。其中,中泥盆统石峡沟组总体呈现由河流沉积向湖泊沉积过渡,而上泥盆统老君山组则呈现下部为扇根、扇中、扇端亚相与河道亚相的粗碎屑沉积,上部由滨湖沉积向浅湖沉积过渡的沉积组合变化特征。牛首山地区老君山组砾岩层数、厚度及砾石砾径分别呈现向南逐渐减少、减薄和减小的特征。古水流分析结果显示,石峡沟组下部碎屑沉积物来自于北东东—东向物源区,上部沉积物主要来自于南东向物源区,而老君山组沉积物主要来自于北东向物源区。结合前人对老君山组古水流的系统测量、石峡沟组和老君山组砂岩碎屑锆石研究结果以及区域地质资料综合分析,认为中—晚泥盆世时期阿拉善地块东南缘总体具有北高南低的古地理格局,且该时期的沉积物为一套具有向南水体逐渐加深的陆相沉积组合,沉积物源区主要位于其北侧,由晚奥陶世—早志留世、新元古代及古元古代岩石构成。The Middle-Upper Devonian sedimentary assemblages are well exposed in the Niushoushan area at the junction of the Alxa and southern North China blocks.The transitional characteristics of their sedimentary facies and source areas are valuable for understanding the Late Paleozoic tectonic evolution of the Alxa and North China blocks and associated adjacent areas.Based on the field studies,a set of sedimentary assemblages deposited by fluvial,lacustrine and small alluvial fan environments were recognized at the Shixiagou section of the southern margin of Niushoushan area,which includes eight sedimentary subfacies:channel,embankment,river plain,lakeside,shallow lake,inner-fan,mid-fan and out-fan.The Middle Devonian Shixiagou Formation is characterized by the transitional deposition from channel to shallow lacustrine environment.The lower part of the Upper Devonian Laojunshan Formation is mainly composed of relatively coarse-grained detrital depositions,including inner-fan,mid-fan,out-fan and channel sedimentary subfacies.The upper part of the Laojunshan Formation is characterized by transitional deposition from lakeside to shallow lake.The number and thickness of conglomerate layers and gravel diameter of the Laojunshan Formation gradually decrease S-ward.Palaeocurrent data indicate that sedimentary source rocks of the lower and upper parts of the Shixiagou Formation originated mainly from NEE-E and SE source respectively.The sedimentary rocks of the Laojunshan Formation mainly derived from NE source.The published paleocurrent and detrital zircon U-Pb dating data of the Shixiagou and Laojunshan Formations,and regional geology demonstrate that the north of the SSE Alxa block was higher than its south during the Middle-Late Devonian.The associated depositions are composed of a set of nonmarine sedimentary assemblage,indicating water gradually deepening southward.The corresponding sedimentary rocks with a northward source are dominated by the Late Ordovician-Early Silurian,early Neoproterozoic,and Paleoproterozoic rocks

关 键 词：牛首山 石峡沟组 老君山组 沉积环境 沉积物源区 

分 类 号：P618.13[天文地球—矿床学]