Geochemical characteristics of Neogene mudstone in Guanzhong Basin,recovery of provenance and paleo-sedimentary environment

At present, the geothermal resources developed and utilized in the Guanzhong Basin are mainly Cenozoic sandstone and glutenite pore -fissure geothermal resources, and the development and utilization horizons are mainly Neogene thermal reservoirs. The occurrence characteristics of geothermal resources, the amount of geothermal resources, and the distribution of favorable areas for geothermal resources development are closely related to the provenance and paleo-sedimentary environment. Identifying the characteristics of Neogene mudstone provenance and paleo-sedimentary environment is helpful to indicate the characteristics of sandstone provenance and paleo-sedimentary environment in the same sedimentary period, which is of great influence for the investigation and development and utilization of geothermal resources in the Guanzhong Basin. The geochemical characteristics of elements in sedimentary rocks record important information of provenance and sedimentary environment. Based on the characteristics of major elements, trace elements and rare earth elements of Neogene mudstone core samples in Guanzhong Basin, the provenance and sedimentary environment were comprehensively studied. The results show that the tectonic setting of the source area of the Neogene mudstone in the Guanzhong Basin is mainly the active continental margin, and the source rocks are mainly the Taibai syenogranite and the Huashan biotite monzonitic granite in the northern of the basin, which contain some intermediate-basic igneous rocks. The chemical alteration index (CIA) is between 61.34 and 76.78, with an average of 70.78, reflecting that Neogene mudstone has undergone moderate weathering, indicating that the climate of Gaoling Group and Lantian-Bahe Formation is in a warm and humid climate environment during the sedimentary period, and the climate of Zhangjiapo Formation sedimentary period is transformed from warm and humid climate to cold and dry climate. Geochemical indicators comprehensively reflect that the Neogene mudstone deposition period is mainly in the reducing environment, and the paleosalinity of the water body is generally in a freshwater and brackish water environment. Finding out the provenance and paleo-sedimentary environment features has practical guiding significance for the calculation of resource quantity, the division of geothermal resources sweet spot area and the determination of key strata for development and utilization in Guanzhong Basin.