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

Key words: 
• Northern Ordos Basin /
• Jurassic /
• element geochemistry /
• provenance analysis /
• paleoenvironment

Abstract: 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 Ce_anom 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.