沁水盆地地层剥蚀量研究

摘 要]沁水盆地自晚三叠世以来不断抬升，遭受了多次剥蚀，但其累积剥蚀量一直悬而未决，对盆地模拟和资源评价产生了不良影响。本文在沁水盆地沉积-构造演化史、热演化史研究的基础上，根据野外露头和钻井资料，以镜质体反射率反演方法为主，辅以声波时差法和构造剖面法，较为准确地确定了沁水盆地中新生代以来的累积地层剥蚀量。研究表明，沁水盆地石炭-二叠系煤层在燕山运动时期遭受最高地温，其后回返抬升并伴有地温梯度下降。参照济阳坳陷连续沉积剖面建立了镜质体反射率与深度关系，经地温梯度校正后，计算出了沁水盆地石炭-二叠系最大埋深，从而得到其此后抬升过程中的累积剥蚀量，经与声波时差法、构造剖面法计算结果对比，三者计算结果较为符合。研究结果表明，晚三叠世以来沁水盆地累积地层剥蚀量在1400～3300m之间，其中盆地中部剥蚀量较少，一般小于2500m，盆地边缘剥蚀量较大，可达3000m以上。主要剥蚀时期为晚白垩世至新近纪，地层剥蚀量可达2000m以上；其次为晚三叠世至早侏罗世，地层剥蚀量一般小于1000m。

Strata Erosion Amount of the Qinshui Basin

Abstract: The Qinshui Basin has undergone uplift since the late Triassic Epoch and experienced several erosion phases. The erosion amount of this basin remains unknown, which is unfavorable to the basin simulation and resource evaluation. Based on the history of sedimentation-tectonic evolution and thermal evolution in the Qinshui basin, this work determines accurately the erosion amount in the Mesozoic and Cenozoic using the methods of the vitrinite reflectance, interval transit time and structural section. The results indicate that the Carboniferous-Permian coal beds of the Qinshui basin experienced the highest geotemperature during the Yanshanian movement. Afterwards, the basin began to uplift and the geothermal gradients also declined. According to the successive sedimentation section of the Jiyang depression, the relationship between the vitrinite reflectance and the depth is established. Through the adjustment of geothermal gradient, this relationship is used to calculate the greatest burial depth of the Carboniferous-Permian strata and thus the erosion amount caused by the uplift is determined. Furthermore, the comparison among the three different results suggests that the calculation is accurate and matched relatively. The final results demonstrate that since the late Triassic Epoch, the erosion of the Qinshui basin amounts to 1400 to 3300m and the central part of the basin is eroded slightly with an erosion thickness less than 2500m, while the marginal part of the basin is relatively eroded intensely and causes a denudation more than 3000m. The supreme erosion stage lasted from the late Cretaceous to Neogene period and the second largest erosion stage was the late Triassic Epoch to early Jurassic epoch.