Abstract:

The Taiyuan Formation of Ordos Basin is a mixed depositional system of coal-bearing paralic facies developed under an epicontinental sea setting. Current inconsistencies in the understanding of its mixed depositional system,as well as unclear mixed characteristics and controlling factors,have constrained the exploration and evaluation of high-quality reservoirs such as tight limestones and tight sandstones. Based on systematic observations of cores,thin sections,and outcrops of the Taiyuan Formation in the eastern basin,combined with well logging and mud logging data,this study conducted an in-depth analysis of the cyclicity,lithofacies,and lithological characteristics of the Taiyuan Formation. Through a systematic examination of multiscale mixed depositional features and patterns,the main controlling factors and formation processes were clarified,and a mixed depositional model was established. The Taiyuan Formation in the study area constitutes a relatively complete third-order sequence,which can be subdivided into five fourth-order sequences,recording a relatively full transgressive-regressive cycle. The fourth-order sequences exhibit a binary structure of transgressive and highstand systems tracts. The transgressive systems tract is dominated by carbonate platform deposits,with local development of deltaic and barrier sandbar sand bodies,while the highstand systems tract is primarily composed of tidal flat and lagoon deposits. The Taiyuan Formation exhibits mixed deposition at three scales: Cyclic mixing at the macro-scale,primarily controlled by high-frequency sea-level fluctuations and their amplitudes,reflects the influence of temporal periodic changes on mixed stacking patterns;Contemporaneous heterotopic facies mixing at the meso-scale,governed by terrigenous clastic supply,carbonate productivity,and depositional topography,highlights the constraints of spatial environmental variations on the distribution of endogenic and exogenic sediments;and Component mixing at the micro-scale,mainly regulated by terrigenous clastic input,hydrodynamic conditions,and physicochemical factors,reflects the control on the distribution of mixed sedimentary components. The mixed deposition in the Taiyuan Formation is characterized by multiscale development,multi-factor synergy,and dynamic evolution of depositional environments.

Key words: mixed sedimentation, mixed sedimentary model, stratigraphic cyclicity, epicontinental sea, Taiyuan Formation, Ordos Basin

摘要：

鄂尔多斯盆地二叠系太原组为陆表海背景下的含煤层海陆交互相混合沉积体系。当前对太原组混合沉积体系认识的不统一,对其混合特征及主控因素的不明确,限制了对致密石灰岩与致密砂岩等优质储集层的勘探与评价。基于对盆地东部太原组岩心、镜下薄片及野外剖面的系统观察,结合测井、录井等数据,深入分析了太原组旋回性、岩相及岩性特征; 通过对多尺度混合沉积特征与样式的系统分析,厘清了其主控因素及主要形成过程,构建了混合沉积模式。研究区太原组为1个相对完整的三级旋回,可细分为5个四级旋回,经历了较完整的海侵—海退过程。四级旋回表现为海侵—高位体系域二元结构。海侵体系域以碳酸盐岩台地沉积为主,局部发育三角洲及障壁沙坝砂体; 高位体系域则以潮坪及潟湖沉积为主。太原组发育3个尺度的混合沉积: 旋回性混合为宏观尺度,主要受高频海平面变化及波动幅度控制,反映时间周期性变化对混合叠置样式的影响; 同期异地相混合为中等尺度,受陆源碎屑供应、碳酸盐产率及沉积地貌等因素控制,反映空间环境差异对内外源沉积物分配的制约; 组分混合为微观尺度,主要反映陆源碎屑供给、沉积水动力及物化条件对内外源沉积物组分分布的调控。太原组混合沉积具有多尺度发育、多因素协同作用、沉积环境动态演化的显著特征。

关键词: 混合沉积, 混合沉积模式, 地层旋回性, 陆表海, 太原组, 鄂尔多斯盆地

CLC Number: 

• P512.2