中上扬子克拉通加里东期(寒武-志留纪)沉积层序充填过程与演化模式

Filling process and evolutionary model of sedimentary sequence of Middle-Upper Yangtze craton in Caledonian(Cambrian-Silurian)

以"构造控盆、盆地控相、相控组合"的思路和"过程-响应"原理为指导,即壳-幔耦合、板块活动和构造运动形成盆地,盆地沉积充填形成层序及相带组合的时空展布,而不同级别层序格架中层序结构、体系域叠加样式及相带的时空组合与盆地沉积充填过程密切相关。在前人对中上扬子克拉通盆地取得丰富的研究与勘探成果基础上,加强沉积环境、层序结构与沉积充填过程等方面的研究,对深化研究区认识以及油气资源勘探具有重要意义。因此,通过层序剖面结构、体系域叠加样式和相带组合的沉积响应记录,分析这些记录特征的时空变化规律来有效地揭示盆地沉积充填过程。具体以反映盆地整体特性的构造-层序(二级层序)为基础,以反映盆地充填格架的层序地层(三级层序)为单元,以反映层序沉积充填过程的层序结构、体系域叠置方式(四级以上层序)和相带分布规律为剖析对象"的技术路线,基于中上扬子加里东期克拉通盆地类型与演化阶段的划分,剖析了典型盆地的沉积充填过程,探讨了沉积层序充填特征及其差异性,并分阶段建立沉积演化模式。研究认为,中上扬子克拉通加里东期由克拉通内和克拉通边缘两大沉积域组成,盆地经历了由伸展机制到挤压机制的两个演化阶段,包括由裂谷型、裂陷型和坳陷型盆地构成的3期沉积充填过程。加里东期克拉通盆地在不同演化阶段,以及相同阶段不同类型盆地,具有不同的沉积建造类型、层序结构和体系域叠加样式等沉积响应,反映了个性鲜明的沉积充填特征和差异明显的控制因素。构造-层序充填过程的控制因素复杂多变,包括基底构造特征、构造运动、深大断裂、古隆起、相对海平面变化、气候变化和物源供给等,而多因素相互作用、综合影响,是特定时期特定盆地形成特有层序结构和叠加样式的关键所在。各阶段沉积模式在充填背景、建造类型、相带展布规律、演化过程与控制因素等方面具有继承性和差异性。加里东期中上扬子克拉通以隆坳相间格局为特征,克拉通台地边缘滩体与台地内广泛发育的白云岩滩和膏盐岩对油气的赋存和封盖意义重大。

Guided by the idea of ＂tectonic-controlled basin,basin-controlled sedimentary facies,sedimentary facies-controlled source-reservoir-cap assemblage＂ and the principle of ＂process-response＂,namely that the basin is formed by crust-mantle coupling,plate activation and tectonic movement,and the space-time distribution of the sedimentary sequence and the facies zone association is formed by the sedimentary and filling processes of basin,while the configuration of sedimentary sequence of different orders,the superimposed pattern of system tract and the space-time association of facies zone are closely related with the sedimentary filling process of basin.On the basis of many research and exploration results of the Middle and Upper Yangtze cratonic basin made by previous research findings,it is thought that further study on sedimentary environment,sequence configuration and the filling process of sedimentary and so on,are significantly important to deepening the understanding and oil and gas resources exploration of the researched area.Therefore,relied on the sedimentary response records of the profile configuration of sedimentary sequence,the superimposed pattern of system tract and facies zone association,the sedimentary filling process of basin can be effectively revealed by analyzing the temporal and spatial variation law of these records.Specific technical route is that the tectonic-sequence（second-order sequence） that indicates the overall characteristics of basin is considered as the basis,the sequence stratigraphy（third-order sequence） that indicates the filling framework of basin is taken as the research unit.Meanwhile,the sequence configuration,superimposed modes（above fourth-order sequence） and the distribution pattern of facies belts are taken as the research objects.Based on the division of the type and evolutionary phase of Middle and Upper Yangtze cratonic basin in Caledonian Period,this paper has analyzed the sedimentary filling process of typical basin,discussed the filling characteristics of sedimentary sequence and its difference and established the sedimentary evolution model in stages.It is found by the study that the Middle and Upper Yangtze craton in Caledonian Period is composed of two sedimentary system tracts including intracraton and craton-margin and the basin undergoes two evolutionary phases that change from extension mechanism to compression mechanism,which are composed of three stages of sedimentary filling processes including rift valley type basin,chasmic basin and depression basin.Generally,the Caledonian cratonic basin under different evolutionary phases or the basin of different types under the same evolutionary phase has different sedimentary responses including sedimentary formation type,sequence configuration and superimposed pattern of system tract,which indicates the distinguishable sedimentary filling characteristics and obviously different controlling factors.In a word,the controlling factors for the filling process of tectonic-sequence are complicated and changeable,which are composed of the structural characteristics of basement,tectonic movement,discordogenic fault,paleohigh,the change of relative sea level,climate change,provenance supply and so on,while the mutual effect and comprehensive influence of these factors are the key to form the special sequence configuration and superimposed pattern for the specific basin in specific period.Besides,the sedimentary model of each phase has inheritance and divergence characteristics in some aspects such as filling background,formation type,distribution law of facies zone,evolutionary process and controlling factors.Especially,the Middle and Upper Yangtze craton in Caledonian is characterized by the framework of uplift and depression,in which the platform edge banks,introplatform dolomite beaches and the salt and gypsumis are of great significance to preservation and accumulation of oil and gas.