鄂尔多斯盆地北部侏罗系泥岩地球化学特征:物源与古沉积环境恢复

鄂尔多斯盆地北部侏罗系泥岩地球化学特征记录了当时重要的地质信息。通过对该区中侏罗统直罗组及延安组泥岩的X射线荧光常量元素分析以及ICP-MS微量、稀土元素分析对其源区构造背景、源岩属性进行了综合研究。与此同时，根据泥岩典型地球化学参数的垂向变化对其古沉积环境进行了恢复。研究结果表明:盆地北部侏罗系沉积岩与北邻阴山-大青山-乌拉山地区前寒武纪古老基底的片麻岩、麻粒岩、孔兹岩等变质岩系以及各时代侵入岩具有较大的亲缘性，是其主要物源。源区构造背景主要是与大陆岛弧相关的活动大陆边缘。Sr/Cu、Rb/Sr、CIA、Sr/Ba、V/（V+Ni）、Ce_anom等泥岩地球化学指标的垂向变化特征对古沉积环境的反演表明，从延安期→直罗组沉积早期→直罗组沉积晚期，古气候由温湿气候逐渐变得越来越干旱，水体古盐度整体上由微咸水相的淡水环境逐渐向半咸水相的淡水环境转变，古氧化还原环境为水体分层不强的还原环境。

Element Geochemical Characteristics of the Jurassic Mudstones in the Northern Ordos Basin: Implications for tracing sediment sources and paleoenvironment restoration

The geochemical characteristics of Jurassic mudstones in the Northern Ordos Basin Hangjinqi Area recorded important geological information at that time.Based on the method of X-ray fluorescence spectrometry of the major element analysis and ICP-MS trace element and rare earth element analysis,the tectonic setting and provenance attribute of Zhiluo Formation and Yan' an Formation have been comprehensively analyzed.Meanwhile, we restored the evolution of sedimentary setting by the vertical variation characteristics of geochemical parameters.The main conclusions can be drawn as follows:The Jurassic sedimentary rocks in the Northern Ordos Basin have affinities to the Precambrian metamorphotic rocks from old basement,such as gneiss,granulite,khondalite and the intrusive rock which formed in different geological time,so the provenance of the study area mainly came from it.The tectonic setting of source area is the active continental margin associated with the continental island arc.The result of paleoenvironment reconstruction is based on the vertical variation characteristics of mudstone geochemical indexes such as Sr/Cu,Rb/Sr,CIA,Sr/Ba,V/(V+Ni)and Ceanom shows that from Yan' an period to early Zhiluo period and then to late Zhiluo period, the paleoclimate was warm and humid at the beginning and tended to become increasingly dry and hot,the palaeosalinity transformed from the brackish water phase of the fresh water environment to the brackish-water phase of the fresh water environment,the redox condition belong to the reducing environment and the water column stratification is not obvious.