The transition from meandering river delta to braided river delta: Depositional characteristics and controlling factors from the second member of Shanxi Formation to the eighth member of Lower Shihezi Formation in Southeastern Ordos Basin. (2nd August 2020)

• Record Type: Journal Article
• Authors: Min, Wenwei; Deng, Hongwen; Xia, Shiqiang; Ye, Dongqing
• Is Part Of: Geological journal. Volume 55:Number 12(2020)
• Page Start: 8122
• Page End: 8140
• Publication Date: 2020-08-02
• Subjects: controlling factors -- depositional characters -- depositional systems transition -- Lower Shihezi Formation -- Shanxi Formation -- southeastern Ordos Basin; Geology -- Periodicals; 551
• DOI: 10.1002/gj.3933
• Languages: English
• ISSNs: 0072-1050

Abstract

Abstract : The Ordos Basin, as one of the most petroliferous basins in China, hosts 12.9 billion tons of oil reserves and 15.2 trillion cubic meters of natural gas reserves. The extensive hydrocarbon exploration and production shows that the southeastern Ordos Basin contains considerable potential in the Shanxi Formation and Lower Shihezi Formation. In this study, cores, wireline logs, thin sections, and heavy minerals are employed to carry out research on classification of sequence stratigraphy, identification of sedimentary facies, reconstruction of palaeo‐geomorphology, analysis of sediment supply, palaeo‐climate, and accommodation space changes. The results indicate that palaeo‐geomorphology gradient tends to be steep, which results in increasing hydrodynamics and turns to be wide and flat which results in decreasing accommodation space. In addition, heavy mineral distribution reveals the direction of sediment supply which indicates provenance changes. The palaeo‐climate changes commonly cause differences in lithology associations, monsoon and vegetation properties. The differences in temperature and humidity result in different colours of lithology associations which indicate various sedimentary environments. The prevalence of monsoon assists in the preservation of fluvial delta by controlling lateral migration of rivers through affecting vegetation and lithology associations. The accommodation space variations control the development of fluvial delta and result in various depositional characteristics of fluvial delta. All these factors trigger the transition from meandering river delta to braided river delta. The reconstruction of the transition and analysis of controlling factors play an important role on understanding the sedimentary evolution of analogous reservoir successions. Abstract : The article presents a study employing mainly cores, wireline logs, and thin sections to establish sequence stratigraphy and identify sedimentary facies in Shanxi Formation and Lower Shihezi Formation. In addition, the integrated and comprehensive analysis of palaeo‐geomorphology, sediment supply, palaeo‐climate, and accommodation space changes reveal the mechanism for the transition from meandering river delta to braided river delta. The results indicate that palaeo‐geomorphology gradient tends to be steep which results in increasing hydrodynamics and turns to be wide and flat which results in decreasing accommodation space. In addition, heavy mineral distribution reveals the direction of sediment supply which indicates provenance changes. The palaeo‐climate changes commonly cause differences in lithology associations, monsoon and vegetation properties. The differences in temperature and humidity result in different colours of lithology associations which indicate various sedimentary environments. The prevalence of monsoon assists in the preservation of fluvial delta by controlling lateral migration of rivers through affecting vegetation and lithology associations. The accommodation space changes control the development of fluvial delta and result in various depositional characteristics of fluvial delta. These controlling factors together trigger the transition from meandering river delta to braided river delta in southeastern Ordos Basin. The reconstruction of the transition and analysis of controlling factors play an important role on understanding the sedimentary evolution of analogous reservoir successions.