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土城子组/后城组为广泛分布在中国北方的燕山褶皱冲断带和盆地中晚侏罗世的典型碎屑岩沉积。本文主要是针对目前在燕山地区的通行的有关土城子组/后城组、及其之下的髫髻山组/蓝旗组,和上覆的张家口组/东岭台组火山岩的相关对比方法提出质疑。其他同行近期发表相关的氩-氩法和铀-铅法同位素测年数据指出髫髻山组/蓝旗组年龄为175~147Ma、土城子组/后城组年龄为156~139Ma、张家口组/东岭台组年龄为147~127Ma,显而易见,上述地层组的年龄是相互重叠的。这些测年数据说明以往的地层对比是有问题的,燕山造山带在中、晚侏罗世所发育的火山岩和沉积岩地层是穿时的。因此,传统上用(165±5)Ma和(135±5)Ma之间的区域不整合来作为划分髫髻山组和后城组的层序界限是值得商榷的。尽管一些髫髻山组的火山岩和土城子组/后城组的沉积岩是与向南或向北的冲断作用相伴生的,但在髫髻山组和土城子组/后城组沉积之间的30~35Ma的时间间隔内却是相对的构造平静期。这一结论是基于以往的髫髻山组和土城子组之间为假整合或平行不整合的观点所得出的。新近基于对承德盆地土城子组地层形成研究分析认为承德冲断层的实际位移距离应小于Davis等2001年所提出的位移距离,笔者接受这一观点。但笔者并不同意在承德地区土城子组的沉积主要是受控于承德北部的向南冲断作用。现今承德向形盆地主要是由于向北冲断的承德县冲断层下盘变形的结果,主要是(1)它向北发生倒转;(2)盆地南部的粗碎屑沉积的物源主要是来源于承德县的异地体。土城子组/后城组的沉积没有必要完全受控于构造作用。土城子组/后城组的沉积是紧随着在燕山部分地区发生的,持续了20~25Ma的髫髻山组/蓝旗组火山及岩浆活动。在中、晚侏罗世期间,燕山地区的岩浆活动必定导致地形的起伏,这就为快速剥蚀及粗碎屑的沉积提供了有利条件。最后需要指出的是,从前所提及的有关燕山带的土城子组/后城组和阴山带的大青山组的地层对比的依据并不存在。
The Tuchengzi Formation / Houcheng Formation is a typical clastic sedimentary deposit widely distributed in the Yanshan fold-thrust belt and mid-late Jurassic basin in the north of China. In this paper, we mainly propose the relevant comparative methods for volcanic rocks of the Tucheng Group / Houcheng Formation and the Qiaomishan Formation / Lanqi Formation prevailing in the Yanshan area and the overlying Zhangjiakou / Donglingtai Group volcanic rocks question. Other colleagues recently published relevant argon-argon and uranium-lead isotope dating data show that the Qiaomishan / Lanqi age of 175 ~ 147Ma, Tuchengzi / Houcheng formation age of 156 ~ 139Ma, Zhangjiakou Group / East The Lingtai Formation is 147 ~ 127Ma in age. It is obvious that the above stratigraphic groups overlap each other in age. These dating data indicate that the previous stratigraphic correlation is problematic. The volcanic and sedimentary rock formations developed in the middle and late Jurassic of the Yanshan Orogenic Belt were worn. Therefore, the regional unconformity between (165 ± 5) Ma and (135 ± 5) Ma has been traditionally used as the boundary for the delineation of Jujiashan Formation and Houcheng Formation. Although some volcanic rocks in the Tuojishan Formation and sedimentary rocks in the Tuchengzi Formation and Houcheng Formation are associated with the southward or northward thrusting, there is a significant difference between the deposition of the Tujiashan Formation and the Tuchengzi Formation / Houcheng Formation ~ 35Ma time interval is relatively the construction of quiet period. This conclusion is based on the viewpoint of the past between the Tuoji Mountain Group and the Tuchengzi Group for the purpose of either false integration or parallel integration. Recently, based on the study of the formation of Tuchengzi Formation in Chengde Basin, the actual displacement distance of Chengde thrust fault should be less than the displacement distance proposed by Davis et al. In 2001, and I accept this view. However, I do not agree that the sedimentation of the Tuchengzi Formation in Chengde area is mainly controlled by the southward thrust of the north of Chengde. At present, the Chengde Xiang-shaped basin is mainly due to the deformation of the under-thrust plate of the Chengde thrust belt which is thrust northward, mainly because (1) it is inverted to the north; (2) the source of the coarse clastic sediments in the south of the basin is mainly the source In Chengde County, different body. It is not necessary for Tuchengzi / Houcheng Formation to be completely controlled by tectonics. The deposition of Tuchengzi / Houcheng Formation occurred immediately afterwards in some areas of Yanshan and lasted for 20 ~ 25Ma volcanic and magmatic activities in Qiaomishan Formation / Lanqi Formation. During the Middle and Late Jurassic, the magmatic activity in the Yanshan area must have caused the relief of the terrain, which provided favorable conditions for rapid denudation and coarse crustal deposition. Finally, it should be pointed out that the basis for stratigraphic correlation of the Tuchengzi Formation / Houcheng Formation and the Yinshan Belt in the Yanshan Belt does not exist.