燕山地区长城纪沉积演化及构造背景

燕山长城纪沉积相特征及环境系统反映出坳拉槽盆地的沉积特点?盆内发育着冲积扇?扇三角洲?浊流沉积?碳酸盐滑塌角砾沉积?颗粒流沉积及火山硅质混合沉积等与同沉积构造活动有关的沉积相型?从早期的大陆内部冲积环境到晚期的环边台地─斜坡─碳酸盐深水盆地,环境系统从较封闭状态向半开放方向演化,其演化过程与盆地构造的扩张活动有着密切关系的?

Environmental Evolutions and Structural Control of Changchengian of the Mid-Proterozoic in the Yanshan Basin,North China

The Ynashan sedimentary basin of Changchengian (1800-1400Ma) of the Mid-Proterozoic is located in North China. Sedimental accumulations of the basin were first one with nature of the covering strata after formation of the crystalline basement of the Archaeozoic-Early Proterozoic.The sedimentary environmental evolutions are described as follows:axial river-fans and braid rivers in alluvial environments,sandy tidal-shallow shoal or bar in marine,mud and carbonate tidal or lagoon in the early Changchengian;and debris-carbonate tidal or shoal with silica from volcanical provenance and fan-dalta,carbonate ringing flatform-slop-basinal facies in the late Changchengian. This shows evolutions of the environmental system from restricted to openning conditions. Alluvial fans, fan-dalta,debris turbidites, carbonate slump breccia,carbonate gravity flow(including grain-flow ), volcanical debris flow and volcanical silica mixed sediments were deposited in the basin. Formation of these facies were controlled by structural action in contemporaneity.Rhythmic shale-micrite carbonates with carbonate dissolution structures and concretion-liked carbonates in the late show the characteristics of deep water carbonate. The sedimentary hydrodynamics of the basin was generally in the condition of mid-low energy due to relatively restricted environments. Framework of the basinal structures consisted of the NE marginal faults and the NW transfer faults. The general longitudal extend and development of the basin were controlled with the Xinglong-Lingyuan fault in the north margin. The vertical of the basin shows a asymmetric shape and main subsidence axis inclines to the north. The basin evolved from narrow half graben to broad downwarp.The facies, environments and structures of the basin were Characteristic of a fail-rift (aulacogen).It showed the process of crust breakup of North China in the early and downwarp subsidence in the late of Changchengian.