玛湖凹陷风城组碱湖沉积地层水化学特征及成因OA

The Fengcheng Formation in the Mahu Sag is the oldest alkali lake sedimentary stratum in the world,and its stratigraphic water chemistry is significantly different from that of the conventional lake-phase sedimentary stratigraphic water.Meanwhile,alkali lake sedimentary stratigraphic fluids are often conducive to the development of high-quality hydrocarbon source rock,so the study of alkali lake sedimentary stratigraphic water chemistry and genesis is of great significance.In this paper,we collect a large amount of stratigraphic water chemistry data,and analyze the stratigraphic water chemical characteristics of the Fengcheng Formation in the study area and discuss the stratigraphic water genesis by combining the whole-rock major and trace element,carbonate cement carbon and oxygen,strontium isotope,and inclusion hydrogen and oxygen isotope test data.The results show that the stratigraphic water of the Fengcheng Formation in the Mahu Sag is mainly NaHCO3-type water with high mineralization,high HCO3-+CO32-concentration,and high pH value,and it transitions to NaHCO3-type and CaCl2-type water with low mineralization towards the edge of the basin.The original sedimentary water of the Fengcheng Formation in the Mahu Sag was alkali lake water that was jointly controlled by volcanic hydrothermal activity and climatic conditions.The hydrothermal activity during the synorogenic period brought a large amount of Na+and HCO3-+CO32-,while the arid climatic conditions affected the evaporation intensity,both of which jointly influenced the formation and evolution of the alkali lake water during the sedimentary period.Since then,the sedimentary water of the original alkali lake was subjected to differential evaporation and concentration,water-rock reaction,and later hydrothermal fluids,resulting in the present zonal distribution of stratigraphic water from the depression to the basin margin.