北京平原沙河凹陷第四纪磁性地层学研究及其新构造运动的沉积响应

北京地区在古近—新近纪时呈"两隆一凹"的构造格局。由于南口—孙河断裂北段第四纪以来的强烈活动,在上述格局上分化出新的第四纪凹陷盆地——沙河凹陷。本次工作在沙河凹陷内开展了钻孔ZK3的第四纪磁性地层研究,结合14C同位素测年结果获得钻孔剖面早更新世、中更新世、晚更新世和全新世地层底板埋深分别为493.8 m、157.4m、87.7 m和7.2 m,建立了钻孔剖面的第四纪地层序列。通过计算ZK3钻孔剖面第四系沉积速率分别为0.19 mm/a、0.11 mm/a、0.70 mm/a和0.63 mm/a。对比分析控盆断裂南口—孙河断裂的活动规律及北京西山的隆升特点,第四纪以来,受到北京西山隆升的影响,控制沙河凹陷的同生断裂南口—孙河断裂强烈活动,并控制了沙河凹陷的演化形成。钻孔地层平均沉积速率所体现的变化规律与山体隆升速率及断裂活动速率具有较好的响应关系。

Quaternary magnetic stratigraphy and its sedimentary response to new tectonic movement in Shahe depression, plain area of Beijing

The tectonic pattern of Beijing area in Tertiary was"two uplifts and one depression". Due to the strong activity of the north part of Sunhe fault since the Quaternary period, new Quaternary depression basin, i.e., Shahe depression, was separated from the above pattern. The authors conducted research on Quaternary magnetic stratigraphy of drill hole ZK3 in Shahe depression. In combination with the 14C isotopic dating results, the authors obtained the depth of the bottom of the strata in early Pleistocene, Middle Pleistocene, late Pleistocene and Holocene, being 439.8 m, 157.4 m, 87.7 m and 7.2 m respectively. On such a basis, the authors established the Quaternary stratigraphic sequence of drill hole profile. The Quaternary deposition rates were 0.19 mm/a, 0.11 mm/a, 0.70 mm/a and 0.63 mm/a. A comparative analysis of the activity regularity of the basin- controlling fault, i.e., Nankou- Sunhe fault, and characteristics of Beijing Xishan (Western Hills) uplift shows that since the Quaternary period, influenced by Beijing Xishan uplift, the contemporaneous faults that controlled Shahe depression, i.e., Nankou Sunhe faults, activated strongly, and controlled the evolution of Shahe depression. The variation rule of average deposition rate of the strata in the drill hole, the mountain uplift rate and the fault activity rate have a good response relationship.