Two fundamental forms of hypogenic karst systems (lateral stratiform hypogenic and cross-formational fault-vein hypogenic karst system) are distinguished mainly by differential effects of preexisting faults. In seismic cross sections, hypogenic karst systems are expressed as complex string-beads-like seismic reflections associated with faults. In this study, a new seismic characterization workflow was developed including seismic amplitude thresholding, fault interpretation, pickup, and merge display to enhance the description of the spatial distribution and coupling of hypogenic karst system and faults. The results suggest that the lateral stratiform hypogenic karst systems are predominantly developed at the top of the secondary faults, presenting an overall of “layered distribution and finger-like interaction” features. The cross-formational fault-vein hypogenic karst systems are developed around faults and characterized by dendritic distribution. Furthermore, we infer that the development pattern of hypogenic karst systems has been produced by the interplay of the faults, preexisting epigenic karst systems, and lateral carrier-beds, which together combine the complex hydrothermal migration pathways of fluids with the characteristics of vertical and horizontal combined pathways. In addition, some possible controlling factors (e.g., sequence stratigraphic boundaries, paleogeomorphology, and sedimentary facies) that can influence the development of these hypogenic karst systems have been discussed in detail.

Volcanic effusive facies (VEF) and volcanic conduit facies (VCF) are two important facies units that can be found in a volcanic reservoir or edifice. Because VEF and VCF generally exhibit opposing seismic reflection characteristics, few studies have been applied to simultaneous characterization of the two facies in seismic data. We have developed an integrated 3D seismic data attribute-based characterization technique of VEF and VCF in the BZ34-9 Block, Bohai Bay Basin, eastern China. Our method is based mainly on the 3D visualization of a thresholding display so as to separately describe the strong-amplitude reflection of the VEF with its original amplitude attribute and the weak-amplitude chaotic reflection of the VCF with its variance-cube attribute. The detailed workflow comprises four steps, including seismic facies analysis, characterization of the VEF, characterization of the VCF, and merging a display of the two volcanic-facies units. The resulting 3D image of the different volcanic facies described in the BZ34-9 Block should be able to be viewed from any perspective for a better understanding of the related genesis mechanisms of the first and second members of the Shahejie (Es12) and Dongying Formations (Ed). In total, 28 volcanic edifices have been identified on the basis of the proposed method, among which three volcanic edifices exhibited inherited eruptions, in the Es12 and the Ed. Volcanic edifices in the Es12 are distributed locally in the central part of the BZ34-9 Block, showing a central eruption style, whereas those of the Ed are characterized by a widespread distribution in the southern gentle slope of the BZ34-9 Block, revealing a composite, center-fissure eruption style. The approach should be convenient to operate and would be effective in characterizing different volcanic facies simultaneously. This application can serve as a useful reference for other basins or regions with obvious volcanic influence.

The “source-to-sink” concept originated in the study of global change and atmospheric pollution. In recent years, the concept of a source-to-sink system has been widely applied in continental margin sedimentary analysis. In our research, the idea of source-to-sink is applied to the continental rift basin sedimentary system in the Bohai Sea area. The idea emphasizes that the sedimentation dynamics, including erosion, transportation, and accumulation, are considered as a complete source-to-sink system. The sand-rich region often corresponds to a source-to-sink coupling system in a complex continental rift basin, which includes the effective provenance, high-efficiency routing system, and base-level transition. In addition, (1) the effective provenance can be subdivided into explicit and implicit provenance systems in which the implicit provenance system has been shown to be a significant advancement in reservoir prediction for the Bohai Sea area, (2) the sediment-transport pathways and slope-break zone constitute the routing systems, and (3) the base-level transition is one of the allogenic factors that controls the position of the sandstone distribution in a sequence. Based on a large number of previous studies and different characteristics of sequence-stratigraphic models in the Bohai Sea area, we have evaluated three types of source-to-sink systems, including the fault-steep slope, strike-slip fault slope, and gentle slope pattern. In addition, the fault-steep-slope source-to-sink coupling system can be further subdivided into four types, namely, the corner, relay ramps, fault-throw diminishment-type, and valley-type source-to-sink systems. The source-to-sink system of the gentle slope pattern includes the uplift axis valley-type source-to-sink system and the slope-valley-type source-to-sink system. A small-scale, thick layer of fan delta is formed in the fault-steep-slope zone. A continuous braided river delta is formed in the strike-slip fault slope zone. A large-scale, thin layer of braided river delta is formed in the gentle slope zone. The characteristics of source-to-sink systems in continental rift basins are established for the exploration or prediction of favorable zones in the study area, as well as in similar basins.

The effects of low- to high-angle (>30°) normal faults on sedimentary architectural units in the Eocene Wenchang Formation, Enping Sag, Pearl River Mouth Basin (PRMB), South China Sea were investigated utilising a high-quality 3D seismic data set and restored paleogeomorphology. It has been shown that sequence stratigraphic units and sedimentary architecture are significantly controlled by the low- to high-angle normal faults. The Wenchang Formation, a second-order sequence, can be subdivided into two para-second-sequences (the Lower and Upper Wenchang sequences, E₂W^L and E₂W^U) and seven third-order sequences (from base to top: SQ1∼SQ7). The low-angle fault confined sequence architecture of the Wenchang Formation is mainly characterised by lateral stacking with the ratio of the vertical subsidence (V) to horizontal slip (H) being reduced from 1/2 for E₂W^L to 1/6 for E₂W^U. In contrast, the high-angle fault confined sequence is characterised by vertical stacking with the ratio of V/H close to 1 for sequences SQ1 to SQ7. In the 3D seismic area, the features of sediment-dispersal pattern were interpreted based on an integrated analysis of paleogeomorphology, seismic reflection characteristics, stratal thickness distribution and multiple attribute clustering. The results show that the large-scale fan delta, belt-shape lacustrine deposit and bird-foot braided delta systems mainly developed in the low-angle fault confined sequences, whereas small-scale fan delta, rhombus-shaped lacustrine deposit and lobe-shaped braided delta systems inherited tectono-sedimentary architectures in the high-angle fault confined sequences.

The sedimentary facies, architecture, and depositional mechanism of deltaic systems have been one of the global research hotspots in recent decades; however, the detailed distribution, sedimentary evolution, source rock potential, and major control factors of the coal-bearing shallow-water delta are still unclear. A typical shallow-water braided delta with coal-bearing source rocks developed in the Middle–Late Triassic Mungaroo Formation of the North Carnarvon Basin, which can be a good study area for an analysis of coal-bearing source rocks. In this study, the sedimentary facies, distribution and evolution, and coal-bearing source rock features of the Triassic strata were analyzed based on the integrated study of wireline logs, drilled cores, thin sections, seismic facies and attributes, and geochemical data. A range of shallow-water delta sedimentary facies was identified, including the proximal delta plain channel/interdistributary bay, distal delta plain channel/interdistributary bay, and the delta front. The coal-bearing shallow-water delta system of the Middle–Late Triassic Mungaroo Formation was characterized by the largest scale delta system with relatively broad proximal and distal delta plains and relatively narrow delta front subfacies. The scale of the delta system showed a trend of increasing from the Early Triassic Locker Shale to the Middle–Late Triassic Mungaroo Formation and then decreasing to the Late Triassic Brigadier Formation. The distal delta plain subfacies of the Mungaroo Formation should have the highest potential coal-bearing source rock, and the proximal delta plain also can be a favorable target for source rock evaluation. The major control factors of the coal-bearing source rocks of the Mungaroo shallow-water delta mainly included the Triassic megamonsoon climate, the topographic features, eustatic changes, and provenance supply. The proximal and distal delta plains of the shallow-water delta system with thin coal seams, carbonaceous mudstone, and dark mudstone lithologies’ association could be a favorable source rock exploration facies for the next stage of natural gas field exploration.