克拉通边缘前陆盆地动力层序地层学

DYNAMIC SEQUENCE STRATIGRAPHY OF PERIPHERAL FORELAND BASINS

关键词:  克拉通边缘  边缘前陆盆地  动力层序地层学  前陆挠曲变形体系域(FST)  前陆塑性变形体系域(VST)

Key words:  cratonic margin  peripheral foreland basin  dynamic sequence stratigraphy  flexural deformation systems tract (FST)  viscoelastic deformation systems tract(VST)

摘要:

通过近几年对层序地层学的深入研究,尤其是对上扬子地台西缘中三叠世拉丁期末和晚三叠世卡尼期周缘前陆盆地层序地层学的研究,提出了动力层序地层学。将边缘前陆盆地由盆缘逆冲断块向克拉通稳定边缘分为A区带和B区带(Posamentier等,1993)。在同一视海平面升降旋回周期内,A区带和B区带的视海平面旋回截然不同。A区带构造沉降速率大于全球海平面升或降速率,表现为视海平面的上升旋回,因此,沉积物容纳空间主要由盆缘冲断块的逆冲活动所制约。B区带与被动边缘背景类似。由此,提出了A区带动力层序由前陆挠曲变形体系域(FST)和前陆塑性变形体系域(VST)组成。由FST→VST反映了沉积物容纳空间不断增大的过程,指示了盆山转换系统的发生、发展的历史,反映了盆转山-山控盆的动力层序地层的构成特色。

Abstract:

The general concepts of dynamic sequence stratigraphy are proposed based on the de-tailed studies of sequence stratigrapy of the latest Ladinian(late Middle Triassic)and Car-nian(early Late Triassic)peripheral foreland basins on the western margin of the Upper Yangtze platform.These peripheral foreland basins may be classified into Zones A and B corresponding to those by Posamentier et al.(1993),where there exist distinctive apparent sea-level cycles during a same apparent eustatic period.In Zone A,the rate of subsidence always exceeds the rate of eustatic fall.Consequently,relative sea-level rises continuously during a eustatic cycle,albeit at varying rates.The accommodation spaces are chiefly con-strained by the overthrusting of the peripheral thrust sheets.In Zone B,the rate of eustatic fall periodically exceeds the rate of subsidence,resulting in an interval of relative sea-level fall during a eustatic cycle.It follows that the dynamic sequences in Zone A are made up of the flexural deformation systems tract(FST)and viscoelastic deformation systems tract (VST).The transition from FST to VST reflects the constant increase in the accommoda-tion spaces of the sediments,formation and development of the basin-range transformation systems,and architecture of the dynamic sequence stratigraphy of these transformation systems.The results of research in this paper will assist in the basin-wide basin analysis and allow the rational assessment of the fluid and solid mineral resources.