Liaodong Bay Depression is a strike‐slip basin with complex tectonic movement that lead the source‐to‐sink (S2S) systems evolution vary greatly in temporal and spatial characteristics. This study explored the sedimentary characteristics, dispersal patterns, and pathway formation in Liaodong Bay Depression, as well as their controlling factors. We selected more than 10 pathways with north‐west and north‐east directions in Liaoxi Sag in the western part of Liaodong Bay Depression, a typical strike‐slip bet controlled graben, to investigate their S2S system distribution. By combining seismic data, we divided the strike‐slip fault bends into three stress setting parts, namely, a central restraining bend, which is the fault translation part, and two releasing bends in the southern and northern of fault terminals. As the heavy mineral assemblage and clay content in the west side of Liaoxi Sag differs from that in the east side, we put forward an S2S index to show the sediment transport distance according to the data we have obtained. Using this index, we recovered the dispersal pattern and pathway development and speculated on the sedimentary provenance. In the restraining bend, we recognized that the pathways mainly show a symmetrical “V” or “W” shape with unclear erosion boundaries and were dominated by filling processes. Considering the heavy mineral assemblage data, we also found that the sediment provenance area decreased and the sediment provided direction transferred from the two‐side provenance to one. Combining the fast sedimentary rate calculated with clay content data, the S2S systems in this area were steep–wide–deep systems and a wide and shallow system. In the releasing bend, the pathways show an asymmetrical “V” or “W” shape and a clear erosional boundary. As shown by the heavy mineral assemblage data, the sediments from these areas mainly have a west side provenance and were deposited in the proximal area. Thus, the S2S system in this area is a kind of steep–deep system. Then, the investigation by integrated of tectonic movement and S2S geomorphic statistical parameters revealed that the elevation height of the S2S is a key factor in control pattern development. The various evolution patterns within the two different stress settings provide insights into the formation process of the S2S developed in a strike‐slip tectonic belt.
Abstract The Baxian depression is a typical half‐graben located in the Jizhong sub‐basin, north China. Commercial petroleum traps have been discovered in the Jizhong sub‐basin. However, the 3 rd and 4 th members of the Shahejie Formation in this sub‐basin have been poorly explored. These two members, belonging to the Lower Paleogene age, are buried deeply in the depression. Favorable petroleum reservoir conditions exist in such deep intervals of the half‐graben due to the presence of different types and extent of deltas and turbidity fans in various areas. In fact, three types of turbidite fans are developed in the sag below the transitional belt on the eastern gentle slope. This work summarized three stratigraphic trap belts, i.e., the steep slope, gentle slope, and sag. On the steep slope, structural‐stratigraphic traps with small‐scale delta fronts and turbidite sandbodies are well developed. On the gentle slope, hydrocarbons generally accumulate in the large‐scale delta front, onlapping beds and those sandbodies adjacent to unconformities. In the sag, petroleum trap models are typically characterized by pinched‐out turbidite sandbodies. Stratigraphic traps were easily formed in turbidite fans below the eastern transitional belt. The petroleum traps that have already been discovered or predicted in the study area indicate that stratigraphic traps have favorable petroleum exploration potential in deeply buried areas (depth >5000 m) in a half‐graben basin or depression.
Abstract: The Rockcave Member of the Yungang Formation (Middle Jurassic), in the Datong Basin, China, is a multistory sandstone that is interpreted as a sandy braided fluvial deposit based on grain size, lithofacies, and architectural elements. The depositional setting was the mountain front of the Datong Basin, which was tens of kilometers from the shoreline of a lacustrine basin during the Middle Jurassic. The concept of base level is used to analyze the architectural elements of the braided system obtained from photographic mosaics and high-resolution measurement of six outcrop sections from Yungang Rock Cave. Grain size, lithology, and bounding surfaces together with scale and dimension parameters of the sedimentary structures in various architectural elements were used to quantitatively characterize each group of architectural elements and stratigraphic units. Width/thickness values of trough crossbeds were found to be a fundamental component of the hydrodynamic regimes. During base-level rise the braided fluvial system developed large-scale channel units, bar units, and overbank fills. The relatively high proportion of bar units and overbank fills reflect processes operating during positive accommodation. However, during base-level fall there are a high proportion of small-scale channel units that reflect incision-dominated processes such as channels with low W/T values for trough crossbeds and less common overbank fines.
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