塔河地区寒武纪碳酸盐岩台地沉积演化史与成因机制——来自地层沉积正演模拟的启示

Depositional evolution history and formation mechanism of Cambrian carbonate platforms in Tahe area:insights from stratigraphic forward modelling

综合应用岩心、测井、地震等资料,对塔里木盆地塔河地区寒武系沉积体系的类型、内部结构以及沉积相分布开展了定性分析和地层沉积正演模拟研究,重现了寒武纪碳酸盐岩台地的演化过程,并依据定量表征的各时期沉积相展布规律,结合模拟参数分析,探讨了寒武纪碳酸盐台地的形成与演化机制。研究结果表明,塔河地区经历了发育早寒武世玉尔吐斯组沉积期陆棚、肖尔布拉克组沉积期碳酸盐岩缓坡(初期以发育中缓坡—外缓坡的低能沉积为主,晚期以发育中缓坡的高能丘滩为主)、吾松格尔组沉积期碳酸盐弱镶边台地(台缘发育1期加积-进积型微生物礁滩)、中—晚寒武世大型进积型碳酸盐岩强镶边台地(台缘分别发育3期进积型微生物礁滩)的演化过程。塔河地区沉积体系整体呈现出的多类型、多期次、多级层序结构特征,是全球海平面变化与差异沉降共同控制的物理可容空间,以及碳酸盐沉积物生产(类型、数量、聚集能力、发育位置)和水动力搬运作用耦合的结果。东西分异的沉降作用和初始地形影响着寒武纪碳酸盐岩台地迁移趋势;沉积物类型、水动力搬运作用以及海平面振荡的共同作用导致研究区在肖尔布拉克组沉积期形成碳酸盐岩缓坡并发生阶段分异;物理可容空间和生态可容空间的相互作用是研究区在早寒武世晚期由碳酸盐岩缓坡向弱镶边台地演化以及在中—晚寒武世形成大型进积镶边台地的关键控制因素。

Comprehensively using cores,logging and seismic data,the types,internal structure,and sedimentary facies distribution of the Cambrian depositional system in Tahe area are investigated by qualitative analysis and stratigraphic forward modelling.The formation and evolution process of the Cambrian carbonate platforms in this study area is also reconstructed.Based on quantitatively characterizing the distribution laws of sedimentary facies in each period,in combination with modelling parameter analysis,this paper explores the formation and evolution mechanism of the platforms in Tahe area.The results show that Tahe area experienced five evolution stages during the Cambrian.A continental shelf developed in the Early Cambrian Yuertusi Formation period;a carbonate ramp developed in the Early Cambrian Xiaoerbulake Formation period(dominated by the development of low-energy sediments in middle-outer ramp in the early stage,and that of high-energy mound-shoal complexes in middle ramp in the late stage);a weakly rimmed carbonate platform developed in the Early Cambrian Wusonggeer Formation period,with aggrading and prograding microbial reef-shoal complexes developed in one stage at the platform margin;large-scale prograding strongly-rimmed carbonate platform developed in the Middle to Late Cambrian,with prograding microbial reef-shoal complexes developed in three stages at the platform margin.On the whole,the depositional system is characterized by multiple types,multiple stages and complex stacking patterns,which is the result of the coupling of physical accommodation space(controlled by global sea-level change and differential subsidence),carbonate sediments(types,quantity,accumulation capacity and location of sediments),and hydrodynamic transport.Moreover,migration tendency of the Cambrian carbonate platforms is also driven by the subsidence resulted from east-west differentiation and initial topography of east and west areas.The combined action of sediment types,hydrodynamic transport and high frequency sea-level oscillation leads to the formation of carbonate ramp and staged differentiation in Xiaoerbulake Formation period.The interactions between physical accommodation and ecological accommodation are crucial controlling factors of the transition from carbonate ramp to weakly-rimmed carbonate platform during the Early Cambrian,as well as the growth of large-scale prograding rimmed platform in the Middle to Late Cambrian.