Storm Deposit Characteristics and Their Environmental Model in the Taiyuan Formation on the Eastern Margin of the Ordos Basin
[Objective]Multiple layer storm deposits are distributed in the Lower Permian Taiyuan Formation car-bonate rocks located at the Gancaoshan zone of Xiangning county on the eastern margin of the Ordos Basin.[Methods]These are primarily distributed in limestone beds L2,L3,and L4.Based on the lithology,sedimentary structure,trace fossils and sedimentary sequence,the main characteristics of the deposit sequence consisting of the eroded basement structure and bioclastic lags,graded bedding,laminated unit,bioturbation structures(trace fossils),and marlstone or calcareous mudstone unit in carbonate rocks are discussed in detail.[Results]From the vertical component features of storm deposits sequence in different limestone beds,five types of tempestite deposit sequences were identified:Type A is comprised of a wavy bottom erosion surface and graded bedding,developing in the near shore zone above the fair weather wave base.Type B is characterized by a wavy bottom erosion surface,graded bedding,and laminated unit(Hummocky-swaley cross-bedding)and is generated in the subtidal zone,name-ly the upper zone between the fair weather and storm wave base.Type C is composed of a wavy bottom erosion sur-face,graded bedding,laminated unit(Hummocky-swaley cross-bedding and gently wavy bedding),and marlstone unit,forming in the lower zone between the fair weather and storm wave base.Type D consists of a wavy bottom ero-sion surface with bioclastic lags,graded bedding,bioturbation structure,and marlstone unit,appearing mainly near the storm wave base.Type E consists of a slight fluctuation bottom erosion surface,thin-bedded graded bedding,ichnofossil-bearing unit,and marlstone unit,occurring in the shallow marine environment near/below the storm wave base.[Conclusion]This result not only provides new understanding of the Lower Permian Taiyuan Formation carbon-ate rocks and their sedimentary environment in the Ordos Basin,but also can provide evidence of sedimentary envi-ronment analysis and palaeogeographic reconstruction for the exploration and development of oil and gas resources in these strata.
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