辽宁兴城地区前寒武纪地层序列和不整合

辽宁兴城地区位于华北克拉通中、新元古代燕山裂陷槽盆地（燕辽海盆）的东南边缘，地层序列和沉积特征与同属盆地边缘区的河北滦县、北京南口、以及太行山区等地类似。研究区新太古代花岗岩之上沉积了长城系（常州沟组、串岭沟组、团山子组、大红峪组），蓟县系（高于庄组、杨庄组、雾迷山组），以及青白口系（长龙山组、景儿峪组）。与天津蓟县中、新元古界标准剖面相比，本区地层厚度较薄、长城系碳酸盐岩较少、碎屑物粒度较粗、部分层位（铁岭组、洪水庄组、下马岭组？）缺失，几大沉积层序的底界超覆明显，体现了典型的古陆边缘特征。中元古界常州沟组至团山子组为一套局限分布的滨、浅海相海进至海退旋回沉积，常州沟组滨海相砂岩与下伏新太古代花岗岩沉积接触；大红峪组沉积时期广泛海侵，以石英砂岩和粉砂质页岩为主，下部发育复成分角砾岩和石英砂岩质砾岩，与下伏地质体有沉积接触（非整合）、角度不整合、微角度不整合、岩溶不整合等多种接触关系，说明大红峪组沉积之前发生过沉积间断和地层褶皱变形，“兴城运动”所指的不整合并非单纯的海进超覆成因；蓟县系高于庄组下部为一套海侵陆源碎屑岩序列，不整合在大红峪组和新太古代花岗岩之上，中、上部为碳酸盐岩台地沉积；蓟县系杨庄组和雾迷山组总体为碳酸盐岩，仅含少量陆源碎屑成分或薄层；新元古界青白口系长龙山组为又一套陆源碎屑岩海进序列，平行不整合在蓟县系雾迷山组或待建系下马岭组？角砾状含燧石白云质灰岩之上，指示了芹峪上升和蔚县上升影响期间的岩溶平原发育历史；寒武系昌平组角砾状白云质灰岩平行不整合在景儿峪组中、薄层白云质灰岩之上。上述不整合及地层建造特征还说明山海关古陆长期存在并对辽西南部的沉积古地理有明显影响。此外，大红峪组的沉积在区内具有承前启后的意义，自大红峪组沉积开始本区与燕辽海盆完全连通，整个盆地的演化也从强烈断陷向稳定沉降转变。

The Precambrian Stratigraphic Sequence and Unconformities in Xingcheng Area of Liaoning Province,China, with Discussion of the Sedimentary?paleogeographic Evolution of the Southeastern Yanshan Taphrogenic Trough Basin

The Xingcheng area in Liaoning province is located at the southeastern edge of the Meso?Proterozoic Yanshan Taphrogenic Trough Basin in the North China Craton. Its stratigraphic sequences and sedimentary characteristics are similar to other basin?edge areas such as Luanxian of Hebei, Nankou of Beijing and Taihang Mountain areas. In the Xingcheng area, the sedimentary sequences on the Neoarchean granites are the Changchengnian System (Changzhougou, Chuanlinggou, Tuanshanzi and Dahongyu Formations), the Jixianian System (Gaoyuzhuang, Yangzhuang and Wumishan Formations), and the Qingbaikouan System (Changlongshan and Jingeryu Formations). In comparison to the stratotype section of Meso?Neoproterozoic strata in Jixian of Tianjin city, the strata are much thinner, Changchengnian carbonates are rare, the clastics are much coarser, and some beds (the Tieling, Hongshuizhuang and Xiamaling Formations) are absent, and the bottom onlap is significant. These characteristics indicate the setting of the margin as paleo?land. The strata sequences from the Changzhougou Formation to the Tuanshanzi Formation restrict distributed offshore transgression to regression sediments, and the littoral facies sandstone of Changzhougou Formation sedimentary contact to the underlying Neoarchean granite. The transgression was widely developed during the deposition of the Dahongyu Formation, with quartz sandstone and silty shale in the domain, with composite breccia and quartz sandstone component conglomerate in the lower part. The relationship between the Dahongyu Formation and underlying geological units vary, being sedimentary contact (unconformity), angular unconformity, micro-angular unconformity, and karst unconformity, which indicate sedimentary hiatuses and fold deformation of strata occurring before the sedimentation of the Dahongyu Formation. The unconformities indicated by the “Xingcheng Movement” are not purely related to transgression onlap; the lower part of Jixianian Gaoyuzhuang Formation comprises a series of transgressive clastic sequences unconformably overlying the Dahongyu Formation and Neoarchean granite, with the middle and upper parts having been deposited in a carbonate platform setting; the Jixianian Yangzhuang Formation and Wumishan Formation are basically carbonates, with a few being composed of terrigenous clastics or only as thin beds. The Neoproterozoic Qingbaikouan Changlongshan Formation is also a terrigenous clastic transgression sequence parallel?unconformably overlain by the breccia?cherty?dolomitic limestone of the Jixianian Wumishan Formation (or possibly the Xiamaling Formation), which indicates a karst?plain history affected by the Qinyu and Yuxian Uplifts. The Cambrian breccia dolomitic limestone of the Changping Formation parallel?unconformably overlies the medium?to?thinly bedded dolomitic limestone of the Jingeryu Formation. Those unconformities and stratigraphic characteristics further indicate that the Shanhaiguan paleo?uplift continued over a long period and significantly affected the sedimentary paleogeography of southwestern Liaoning. In addition, the sedimentary strata of the Dahongyu Formation are significant since they provide a link in the history of the basin region, where this area is completely connected to the Yanliao Ocean Basin and the evolution of the whole basin transitioned from indistinct rifting to stable depression.