Search

The shallow-water braided deltas are hot topic in global sedimentology. In China, this depositional environment forms an important reservoir and exploration target within the basins. Therefore, geological and sedimentologic settings of the Jurassic shallow-water braided deltas in the Junggar basin of western China have attracted much attention in recent years based on the comprehensive analysis of geological and geophysical data acquired. These braided deltas deposited in the shallow Junggar lacustrine basins with gentle slope gradients and prograded towards to the central basin from northeast to southwest (more than 10 km). This kind of Jurassic delta was characterized by coarse grain-size (sand to pebble), large cross-beddings, discontinuous fining-upward successions vertically, high percentage of sandstone ratios (up to 70%), very unique distributary channels with few distributary mouth bars, and seismic facies of shingled with a progradational reflections. Based on the detailed research on basin evolution and sedimentary characteristics of deltaic sub-facies, this paper presents the relationship between the shallow-water braided deltaic deposition and lithologic traps predicted to be the favorable and explorable lithological traps in the Junggar Basin. [ABSTRACT FROM AUTHOR]

Majority of the oilfields in the Hongshanzui region are small and complex fault block reservoirs, and the evolution of the sedimentary system under the sequence stratigrapic background has been a controversial topic. Six middle-term base-level cycles were divided, and eight types of lithofacies assemblages were recognized based on the stacking patterns and volumetric partitioning according to the core, well logs, and seismic data correlated with the field investigation of outcrops. Furthermore, the evolution of the sedimentary system under the sequence stratigraphic framework was clarified. Among the six middle-term base-levels, MSC1 belongs to the retrogradational system tract, and the sediment distribution exhibits the characteristics of "large plain and small front." MSC2 belongs to the transgression system tract, and the sediment distribution exhibits has the characteristics of "small plain and large front." In the case of MSC5 and MSC6, the sediment distribution exhibits the characteristics of "dominant channel and repeated channel-switching." Further, the controlling factors of tectonic, base level, climate, and minerals are discussed.This research has been applied to the exploration and development of the Hongshanzui oilfield, and a certain benefit has been achieved. • Sequence-stratigraphic framework is constructed. • Filling and sedimentary models are established. • The base-level were controlled by alicyclic and autocyclic processes. • The controlling factors of the sedimentary evolution of early-middle Jurassic were discussed. [ABSTRACT FROM AUTHOR]

Organic mudstone can be a high-quality source rock in petroleum basins. The accumulation patterns of various types of mudstone can also serve as a useful record of paleogeography. Due to the impact of tectonic movements, the East China Sea Basin (ECSB) saw its deposition setting transform from closed-lacustrine to open marine settings. This provides an opportunity to explore organic matter accumulation patterns within such a transformation setting. This study classified the constituent mudstones according to their differences in composition and sedimentary structure as follows: coaly mudstone or carbonaceous mudstone, calcareous mudstone, clayey mudstone, and siliceous mudstone. Considering the different sedimentary structures, siliceous mudstone can be subdivided into laminated, wavy, and slumped mudstones. Using integrated multiple indices of the paleo-environment, which includes clay mineral content, trace mineral content, and micro-paleontology assemblages, we reconstructed the paleography setting during the Paleocene and inferred that during this time, the ECSB was characterized by sedimentary differentiation. We discerned two different organic mudstone accumulation patterns by combining the results from rock-eval pyrolysis and paleo-environmental indices: 1) A closed-lacustrine mudstone accumulation pattern characterized by abundant sediment supply and dominated by allogenous mudstone formation by the flocculation process. The fresh to slightly salty water environment provided adequate nutrition to microorganisms and an appropriate temperature led to the increased accumulation of type II 1 and II 2 kerogen. 2) An open-marine mudstone accumulation pattern which revealed a sediment-starved setting. The flocculation process and fine-graded turbidities were the main processes leading to mudstone accumulation. More plants were concentrated in shallow water with declining salinity, leading to peat and mass carbon mudstone accumulation. • Classified the mudstone into six types according to its genesis difference. • Build the relationship between the paleo-environment and the abundance/types of organic matters. • Restore the mudstone distribution and the sedimentary facies association evolution process. • Put out the organic matter accumulation pattern in the transition setting. [ABSTRACT FROM AUTHOR]