柴西北上干柴沟组咸化湖盆天文旋回识别及沉积速率分析OA

The Shangganchaigou Formation(N1)in the northwestern Qaidam Basin mainly consists of fine-grained mixed rocks deposited in a saline lake basin,representing an important field for unconventional oil and gas exploration.However,current research on cyclostratigraphy and high-precision astronomical sedimentary response characteristics in this formation remains relatively weak.By comprehensively integrating core and well-logging data,cyclostratigraphic analysis is performed on two drilling wells,identifying Milankovitch cycles including long eccentricity,short eccentricity,obliquity,and precession in the Shangganchaigou Formation,and a floating astronomical time scale is established based on the 405 ka long eccentricity cycle,thereby determining the sedimentation rate and sedimentary characteristics of the Shangganchaigou Formation.It is shown that:(1)Sedimentation time of N1 is approximately 4 Ma,and the average sedimentation rate can reach 20 cm/ka,which is significantly higher than that of other continental lacustrine strata in China.(2)The lithofacies characteristics based on sedimentation rate analysis indicate that lithofacies are significantly controlled by the sedimentation rate.Laminated dolomitic limestone with high organic matter content mainly develops in high-rate segments,while massive argillaceous-silty dolomitic limestone with low organic matter content is dominant in low-rate segments.(3)The continuous orogenic tectonic activity during the Himalayan period control the high sedimentation rate of N1 at a macroscopic scale,and short-term climate alternations shape the oscillatory changes in the sedimentation rate.The identification of astronomical cycles and analysis of sedimentation rates of N1 in the the northwestern Qaidam Basin are helpful for understanding the sedimentary evolution of favorable exploration intervals in salinized lake basins and can provide new ideas for the subsequent efficient exploration and development of shale oil.