Search Results (3)

Quaternary climate has been characterized by pronounced glacial–interglacial cycles, with eustatic sea-level fluctuations directly controlling coastal sedimentary environments. The Yellow River Delta, situated on the southwestern coast of Bohai Bay, bears a distinct stratigraphic imprint of marine–terrestrial environmental transitions. However, critical knowledge gaps persist in reconstructing an integrated continental–marine stratigraphic framework. This study focuses on the nearshore core CB2302, integrating sediment lithology, grain size, foraminiferal assemblages, and geochemical proxies to establish a regional stratigraphic chronology since MIS5. Three depositional units (DU1–DU3) and 12 sedimentary subunits (C1–C12) were identified based on grain-size distributions, geochemical signatures, hydrodynamic, and microfossil assemblages. Integration of AMS ¹⁴C dating and sequence stratigraphic analysis establishes a post-MIS 5 stratigraphic framework for the northern Yellow River Delta, revealing sedimentary responses to three transgressive–regressive cycles (MIS 5e, 5c, and 5a) and confirming widespread terrestrial deposition during MIS 4–2, with no detectable marine influence in MIS 3 strata. Furthermore, correlation with representative cores across the Yellow–Bohai Sea coastal system elucidates a unified model of shoreline migration patterns driven by post-MIS5 sea-level oscillations. These findings advance the understanding of Quaternary sediment–landscape interactions in deltaic systems and provide critical stratigraphic benchmarks for petroleum exploration and coastal engineering in active depositional basins. Full article

Laizhou Bay Sag is a typical continental rift lake basin, which is affected by strike–slip activity, salt rock activity, volcanic activity, and paleoclimate change in the Tanlu fault zone, where three major lithologies—volcanic rock, clastic rock, and evaporite—mainly develop. In order to determine the sequence correspondence between the different lithologies in the study area based on drilling, logging data, and seismic data, it is determined that the fourth member of the Shahejie Formation in the southern Laizhou Bay mainly develops three types of sequences: clastic rock type sequences, salt lake type sequences, and volcanic rock/clastic rock type sequences. Two second-order sequence boundaries (SBs₃^L, SBs₄^L) and one third-order sequence boundary (SBs₄^U) were identified, and the principle of three divisions of system tracts (LST, TST, HST) and sedimentary processes in different types of sequences were determined by analyzing the stacking patterns of different sequences. Compared with the previous research results, this study provides a more detailed analysis of the sequence boundary definition of different blocks and different lithologic strata, and it improves the previous general sequence stratigraphic division method. Based on the study of distinct types of sequences, a unified stratigraphic framework is established in the whole zone, and the stratum thickness distribution of the fourth member of Shahejie Formation is smaller in the southwest and larger in the northeast. The study area is generally filled with pyroclastic rocks–evaporite–clastic rocks, changing from fan delta–saline lake filling to braided river delta–freshwater lake–fan delta filling from bottom to top. A sequence stratigraphic model for the comparison of steep slope–gentle slope differences is established to provide guidance for future oil and gas field exploration and development. Full article

Pinch-outs refers to the gradual thinning of the thickness of the sedimentary layer laterally until there is no deposition and are a major topic of modern research on the automated drawing of geological profiles. The rapid development of smart geological systems imposed an urgent need for high-speed, accurate methods to plot pinch-outs. However, because of their complexity, excessive number of branch paths, low rendering speed, and poor reliability in the case of large-scale data, the existing pinch-out drawing methods are inadequate and cannot satisfy the modeling needs of large-scale geological projects. To resolve these problems, based on unified stratigraphic sequences, this paper proposes a unique path method for drawing pinch-out profiles by converting the principle of plotting of pinch-outs into controlling the appearance of stratigraphic boundaries, and a high-speed and reliable method for drawing pinch-out in digital profiles is also proposed. The proposed method is successfully applied to drawing geological profiles for an urban geological project in East China, and greatly reduces the complexity of the method without reducing the drawing accuracy. Compared with those of other methods, the speed and reliability are significantly improved. Therefore, the unique path method for drawing pinch-out profiles based on a unified stratigraphic sequence proposed in the writers’ previous paper effectively avoids the excessive branch paths, slow speed, and insufficient reliability of the existing methods and provides effective and reliable support for the rapid drawing of profiles in smart geological systems. Full article