Abstract
Soft-sediment deformation (SSD) structures of the Upper Triassic Yanchang Formation are laterally widespread in the Ordos Basin. In the Huachi-Qingyang (H-Q) area of the Ordos Basin, the Chang6 oil member of the Upper Triassic Yanchang Formation is among the most significant Mesozoic oil-bearing strata. It is characterized by the development of reservoir sand bodies. During the depositional evolution of the Chang6 oil member, SSD structures induced by paleo-seismic events developed in the H-Q area in the middle of the basin. The SSD structures developed in the sand bodies of the Chang6 oil member are mainly ball-and-pillow structures, fold structures, sand dikes, irregular convolute stratifications and synsedimentary faults. The architecture of the sand bodies resulted from paleo-seismic events and gravity slumping and mainly include two types of structures: 1) SSD structures driven by paleo-seismic events with normal sedimentation (delta front sand body) (SN-SSD) and 2) SSD structures driven by paleo-seismic events with turbidites (formed by delta-front slumping and re-distribution due to seismic action) (ST-SSD). As a consequence, genetic models of the sand bodies formed by different sedimentation processes are established.
Highlights
Soft-sediment deformation (SSD) structures and the architecture of sand bodies can provide information on depositional history and reveal aspects of basin evolution
This study aims to identify typical SSD structures in the Chang 6 oil member of the Yanchang Formation of the Southwestern Ordos Basin, based on a large number of research results on the characteristics of seismites, include their identification marks and classification, and analysis of the types and characteristics of the SSD structures and their sedimentary environments (Montenat, 2007)
Mechanism of deformation There are three sand body types were developed during the sedimentary evolution of the Chang 6 oil member in the H-Q area in the central Ordos Basin
Summary
Soft-sediment deformation (SSD) structures and the architecture of sand bodies can provide information on depositional history and reveal aspects of basin evolution. Various SSD structures, related to paleo-seismic events and gravity slumps, are developed in the Chang 6 oil member of the Upper Triassic Yanchang Formation in the H-Q area of Ordos Basin. These SSD structures can be divided into five categories based on morphologic and deformational type: ball-and-pillow structures, fold structures, sand dikes, irregular convolute stratifications, and synsedimentary faults. The SSD structure stratum developed in the Chang 6 oil member of Yanchang Formation in the study area is consistent with the upper and lower non-deformational strata in terms of lithology, rock association and sedimentary environment, which contradicts the SSD structures formed by a landslide.
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