琼东南盆地古近纪幕式裂陷及构造、层序和沉积的综合响应过程

通过对区域性角度不整合、构造沉降阶段性演化以及断裂幕式活动和古构造格架变化等信息的识别与厘定,揭示了琼东南盆地古近纪构造活动的幕式演化过程及其特征。进一步结合层序地层与沉积充填综合分析,系统论述了幕式裂陷作用对沉积层序形成与演化的控制。研究表明:琼东南盆地古近纪经历了3个裂陷阶段,即裂陷Ⅰ幕(S100-S80)、裂陷Ⅱ幕(S80-S70)和裂陷Ⅲ幕(S70-S60),分别对应盆地的初始断陷期、主断陷期和断坳转换期。裂陷活动早期以强烈的差异性块断作用为主导,而晚期逐渐被区域性坳陷作用和少量断裂活动共同控制的均一化沉降作用所取代,整体呈现出弱-强-弱的演化特征。裂陷作用的幕式过程及不同裂陷幕同沉积构造活动的差异性通过对可容纳空间、沉降速率、同沉积断裂活动和古构造格架的深刻影响,进而控制了盆地内层序地层单元与沉积旋回的整体发育、沉积与沉降中心的时空展布以及层序地层格架下沉积体系域的构成样式。

Episodic Rifting and Integrated Response Process of Tectonic, Sequence Stratigraphy and Sedimentary Filling in Paleogene of Qiongdongnan Basin,South China Sea

Based on the recognition and redefinition of regional angular unconformities,staggered evolution of tectonic subsidence,impulsive activities of growth faults and the change of structural framework,the episodic rifting process and its characteristics of Paleogene in Qiongdongnan basin were revealed.Ulteriorly,the controlling of episodic rifting on the generation and evolution of sedimentary sequences was elucidated systematically in association with the comprehensive analysis on sequence stratigraphy and sedimentary filling of Paleogene.The results show that there are three rifting episodes during the rifting period of Paleogene,namely rifting episodeⅠ(S100-S80),rifting episodeⅡ(S80-S70) and rifting episodeⅢ(S70-S60),corresponding to the initial faulted period,the main faulted period and the transition faulted period respectively.The evolutionary trend of rifting activities went from weak to strong and to weak,which is characterized by intense differential subsidence of fault blocks in the early stage of rifting period,while gradually replaced by homogeneous subsidence which was controlled by a combination of regional depression and weak activities of growth faults in the later.Because of the profound influences on accommodation space,tectonic subsidence rate,synsedimentary faulting activity and palaeostructural frameworks,the multistage episodic rifting and differences of tectonic activities among different rifting episodes controlled the development of sequence stratigraphy units and sedimentary cycles at various levels,and the spatial-temporal distribution of depositional and subsidence centers as well as the composition and configuration of depositional system tracts in the sequence stratigraphic frameworks.