燕山西段雾迷山组层序地层格架及古地理演化

Sequence Stratigraphic Framework and Paleographic Environment Evolution of the Mesoproterozoic Wumishan Formation,Western Yanshan Mountains

以野外露头观察和室内详细研究为基础,结合沉积模式和层序地层学基本原理,系统分析了燕山西段雾迷山组的沉积相特征,进行了单剖面的层序地层划分。燕山西段雾迷山组以环潮坪型碳酸盐沉积为主,陆源碎屑贫乏,叠层石非常发育。在延庆千沟剖面可以识别出26个三级层序,并进一步归为6个二级层序(S.1—S.6)。每个三级层序三分性明显,都由海侵体系域(TST)、早期高水位体系域(EHST)和晚期高水位体系域(LHST)组成。通过空间上的大范围追索和对比,建立了燕山西段雾迷山组的层序地层格架,绘制了其中5个主要阶段的栅状图(S.2—S.6),并且根据二级层序所表征的沉积相带空间展布初步恢复了雾迷山组沉积期的古地理环境,编制了相应的古地理图(S.2—S.6)。雾迷山组一、二段沉积期古地理环境表现为缓慢海侵,到三、四段沉积期海域范围达到最大值,随后在五、六段沉积期发生海退作用,沉积相带逐渐向沉降中心收缩,海域范围明显缩小。

Based on field surveying on the outcrop and comprehensive laboratory study,combining with the fundamental principles and methods of sequence stratigraphy,the authors analyze the sedimentary characteristics of the Wumishan Formation occuring in the western Yanshan Mountains, which are mainly composed of tidal flat carbonate rocks and rich in stromatolite.The Qiangou section, the most complete section in study area,can be divided into 26third-order sequences which can be combined into six second-order sequences（S.1-S.6）.Every third-order sequence includes three parts, which are transgressive system tract,early highstand system tract,and late highstand system tract.By correlation of sequences in the study area,the sequence stratigraphic frameworks have been established. According to the distribution of sedimentary facies belts,the paleographic environment has been preliminarily reconstructed.During the deposition period of the Wumishan Formation,the paleographic environment of the First and Second Member was slow transgression.Up to the deposition period of theThird and Fourth Member,the paleo epicontinental sea reached maximum.After then,in the deposition period of Fifth and Sixth Member,the paleo sea regressed to the center of subsidence.