河北省唐山地区丰台—野鸡坨断裂第四纪活动性——来自14C和磁性地层年代学的证据

丰台—野鸡坨断裂为唐山地区主要断裂之一,西侧为鸦鸿桥凹陷,东侧为唐山凸起,断裂两侧第四系厚度之差巨大。本文依据该断层两侧钻孔对其第四纪以来活动性进行初步的探讨。通过对丰台—野鸡坨断裂上下两盘PZK14和PZK20孔磁性地层学研究,并结合钻孔岩石地层,及浅部光释光和¹⁴C测年结果,建立第四纪地层格架。结果表明：两孔底部“泥包砾”为新近纪沉积;PZK14孔下更新统底界埋深为387 m,中更新统底界埋深为114 m,上更新统底界埋深为71 m,全新统底界埋深为6 m;PZK20孔下更新统底界埋深为155 m,中更新统底界埋深为73 m,上更新统底界为36 m,无全新世地层。丰台—野鸡坨断裂活动在早更新世时表现为逐渐增强的特点,活动速率由早期的5.4 cm/ka增加到13.9 cm/ka。中更新世断裂活动基本处于停滞状态,活动速率为1.0 cm/ka。晚更新世以后,断裂重新活动,且更加剧烈,活动速率达到了54.5 cm/ka。

Quaternary activity of the Fengtai-Yejituo fault in Tangshan, Hebei Province: Evidence from 14C and magnetic stratigraphy

The Fengtai-Yejituo fault is one of the major faults in the Tangshan area. Its west side is Yahongqiao sag, while its east side is Tangshan rise. There is an obvious difference in the thickness of the Quaternary strata between both sides of the fault. Based on the boreholes on both sides of the fault, this paper makes a preliminary study on its activity since the Quaternary period. Combined with drilling information, the composition of rocks, and the results of the optically stimulated luminescence(OSL) and ¹⁴C dating, the Quaternary stratigraphic framework was established according to the magnetic stratigraphy of the boreholes PZK14 and PZK20 which are hanging on the upper and lower plates of the Fengtai-Yejituo fault. The results show that the "boulder-clay layer" at the bottom of the two holes was Neogene sediments. The borehole PZK14 revealed that the buried bottom boundary depth of the Lower Pleistocene, the Middle Pleistocene, the Upper Pleistocene and the Holocene was 387 m, 114 m, 71 m and 6 m, respectively. The borehole PZK20 showed that the buried bottom depth of the Lower Pleistocene, the Middle Pleistocene and the Upper Pleistocene sediments was 155 m, 73 m and 36m respectively, without the Holocene sediments. The activity of Fengtai-Yejituo fault gradually enhanced in the early Pleistocene and its activity rate increased from the early 5.4 cm/ka to 13.9 cm/ka. In the Middle Pleistocene, its activity is basically in a state of stagnation, with an activity rate of 1.0 cm/ka. After the Late Pleistocene, it was reactivated and became more intense active, with activity rate of 54.5 cm/ka.