Structural characteristics and genetic mechanism of Gaoyang low uplift in Jizhong Depression, Bohai Bay Basin

As a secondary structural unit locating in the central Jizhong Depression of the Bohai Bay Basin, the formation and evolution of Gaoyang low uplift is closely related to the development of the adjacent Baoding and Raoyang sags. The understanding for the structural characteristics of the Gaoyang low uplift is valuable for the overall study of the extensional deformation system in the central Jizhong Depression. Based on abundant seismic data, the structural characteristics of the Gaoyang low uplift were determined by using structural analysis method. According to drilling data and regional stratigraphic correlation, the age of syndepositional formation and the time of tectonic activity were determined. By compiling balanced sections and analyzing regional tectonic evolution, the genetic mechanism of the Gaoyang low uplift was discussed in this paper. The Gaoyang low uplift is featured by a gentle anticline which narrows from the south to the north, and the west limb of the anticline is steeper than the east counnterpart. Several NW-SE trending faults with large heave and long plane extension distance developed in the east flank of the Gaoyang low uplift, while only a few small-scale faults were developed in the west flank. The age of the oldest syndepositional strata in the southern part of the studied area is the Late Mesozoic, while that in the north is Paleocene. The Gaoyang low uplift is a compound rollover anticline developed in the common hanging wall of the boundary faults on both sides of the central Jizhong Depression, and its formation was mainly controlled by the extension of the boundary faults. The southern Gaoyang low uplift began to develop earlier than the northern part

Evolution and resource potential of Permian source rocks in the southern depression of the South Yellow Sea Basin

The Permian source rocks in the southern depression of the South Yellow Sea Basin have been proved to be fair-good source rocks. Based on the analysis of recent Paleozoic oil and gas exploration and research results, the thermal evolution and hydrocarbon generation process of Permian source rocks was analyzed by selecting appropriate geological parameters and using TSM basin simulation method, and then the potential of oil and gas resources was evaluated. The research shows that the Permian source rocks distributed in Cenozoic fault depression in the southern depression experienced a two-stage hydrocarbon generation and expulsion process. The first hydrocarbon generation and expulsion occurred from the Late Triassic to the Early-Middle Jurassic and the secondary hydrocarbon generation and expulsion mainly occurred in Paleogene. However, the Permian source rocks distributed in the uplift area only experienced the first hydrocarbon generation and expulsion process. The Permian source rocks have a total resource scale of 20.76×108 t and a resource abundance of 12.2×104 t/km2, reaching a medium abundance level, which can provide a certain material basis for the formation of oil and gas fields. The secondary hydrocarbon generation resources of the Permian source rocks in the whole southern depression account for 30.4% of the total resources, but it can reach 55% in the Cenozoic fault depression. The Cenozoic fault depression with Permian source rocks and Cenozoic source rocks developed is a favorable exploration area

Provenance analysis and geological significance of Paleocene in Lishui Sag, East China Sea Shelf Basin

The provenance evolution of Paleocene is a main factor controlling the sedimentary filling characteristics of the East China Sea Shelf Basin, and is of great significance in the exploration and development of petro-bearing basins. Based on the core samples of the Paleocene of the Lishui Sag, East China Sea Shelf Basin, the systematic analysis of petrological and mineralogical characteristics was carried out. Through the study of the spatial and temporal distribution of sandstone clastic components, light and heavy mineral assemblages and related parameters, the evolution of the Paleocene provenance system in the study area and its significance for the sedimentary filling of the basin were discussed. The Paleocene clastic rocks in the Lishui Sag are mainly lithic feldspar sandstone, feldspar lithic sandstone and lithic sandstone. The sandstone is mainly moderately well-sorted, and the grains are mostly subangular or subrounded, with poor overall rounding, indicating that the structural maturity and compositional maturity are relatively lower. The light mineral assemblages of the Guifeng and Lingfeng formations of Peleocene are obviously different and show zoning features in different parts of the basin. In the central and northern parts of the western subsag, there are mainly parent rock types of cycle orogenic belts, while in the south of the western subsag, there are mainly parent rock types of cycle orogenic belts and magma arc. In the eastern subsag, there are mainly parent rock types of cycle orogenic belts. The characteristics of heavy mineral assemblages in the main horizons of the Paleocene in the study area change little. The Zhejiang-Fujian uplift belt in the west and the Yandang uplift in the east are the most important provenance areas of the Lishui Sag. The Lingfeng low uplift in the center of the basin suffered serious denudation before the deposition of the lower member of the Mingyuefeng Formation, providing local provenance for the basin. The provenance system analysis showed that when the Yueguifeng and Lingfeng formations were deposited, they were in the early and peak stages of fault depression, and the intra-basin provenance area was formed by the intra-basin fault uplift. As the upper member of the Lingfeng Formation was deposited, the basin entered the late stage of fault depression, local intra-basin provenance was no longer developed, and the main provenance system was extra-basin provenance