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With the aid of modern sedimentology, seismic geomorphology, and the comprehensive analysis of geophysical data and core data from more than 10 wells, the Qingshankou Formation has been divided into 3 long-term cycles and further into 6 medium-term cycles in the Qijia area, Songliao Basin. The 3 long-term cycles, SQ1, SQ2 and SQ3 correspond to the members Qing I, Qing II and Qing III of the Qingshankou Formation, spanning 11.5 Ma during the Late Cretaceous. The time scale of the medium-term cycles, which are subunits of the long-term cycles, is approximately 0.5–1.5 Ma with thicknesses ranging from 45 m to 116 m. A shallow-water delta that consists of high-maturity fine-grained sandstone developed in the Qingshankou Formation. The scour surfaces reflect strong flow action, and the parallel bedding and large-scale cross bedding are well developed. Distributary channel sandstones are well developed in the shallow-water delta depositional system, in which a single channel can be several meters thick. The cumulative thickness of the distributary channels can reach tens of meters across a large area, extending tens of kilometers to the center of the lacustrine basin. The development of the subaqueous distributary channel of the shallow-water delta is closely related to base level (lake level) changes. In the early stage of a rising half-cycle and the late stage of a falling half-cycle, the fluviation is significant and the well-developed channel sandstone can extend towards the center of the lacustrine basin more than 50 km, with large cumulative thicknesses of compound sandbodies (17–28 m) and high sandstone-to-strata ratios (78–88%). In the late stage of a rising half-cycle and the early stage of a falling half-cycle, the lake level is high and the fluviation is weak, resulting in a distributary channel extent of less than 30 km, small cumulative thicknesses of compound sandbodies (5–12 m) and low sandstone-to-strata ratios (22–45%). The delta front can be divided into the inner front and the outer front. The subaqueous distributary channels in the inner front have good continuity and extend further, whereas the subaqueous distributary channels in the outer front have poor continuity, and sheet sand is well developed. Therefore, a shallow-water delta generally shows features including (1) sedimentary structures formed by strong currents, (2) stacked fining upward rhythm, (3) subaqueous distributary channels well developed, (4) delta front divided further into an inner and an outer front. There was a relatively good linear relationship between the thickness of the sandbody based on the well data and the maximum amplitude of the seismic trace next to the well. The reddish amplitude of the seismic attribution suggests thicker channel sandbodies (4–9 m), whereas the light amplitude of the seismic attribution indicates thinner channel sandbody (1–4 m). Of the two typical sedimentary models for shallow-water deltas, delta plains develop well in humid climates and delta fronts develop well in arid climates, both of which are found in the Qijia area, Songliao Basin. Stratal slices from seismic geomorphology are applied to display the branchlike sandstone dispersal patterns of the shallow-water delta and the broad distribution characteristics. This study also notes that the delta front distributary channel sandstone, which is near an oil source and faults, would be a favorable exploration target. [ABSTRACT FROM AUTHOR]

The Bohai Bay Basin, a typical intracontinental rift basin, records East Asia's kinematic plate history during the Cenozoic. The rifting process was driven by the counterclockwise rotation in the direction of the Pacific Plate subduction. From the early Eocene to the Oligocene, the rifting process can be divided into three stages: extension initiation, peak extension, and post-extension. The corresponding rifting rate was calculated based on 40Ar-39Ar data. Then, the provenance area evolution of the above three rifting stages was established by combining the detrital zircon U–Pb data and heavy mineral assemblage data (ZTR, GZi, and ATi). According to the results calculated by 40Ar/39Ar analysis, the topography of the sink area in the western Bohai bay basin was characterized by moderately rising subsidence rates (100 m/Ma) during the extension initiation stage (Paleocene-Early Eocene), when surface drainage was restricted to a limited area with steep channel slopes. During this stage, referring to the core description and seismic interpretation results, the fan delta distributes most of the sediment, most of which migrates from the proximal region. Until the peak extension stage, the source-sink system develops as the rate of subsidence increases (200 m/Ma), making the sink area larger, and this period involves multiple types of pathways, including synsedimentary faults and erosional valleys. Sediments from Taihang Massif and Jiaoliao Massif infill the subsidence zone at the distal end. Then, in the post-extension stage, the source-sink systems involve a multi-provenance area (i.e., sourcing from both proximal and distal areas), a large sink area, and a gentle channel gradient due to a decrease in subsidence rate (60–80 m/Ma). Catchment relief, sediment migration distance, and average fault displacement were used, and these parameters were related to the sediment supply (Qs) for the three rifting stages. We find that during extension initiation and peak extension, the source-to-sink systems show a high amount of sand influx (Q sand /) and that the ratio Q sand /Qs total shows a proportional relationship with catchment relief and average fault displacement; this relationship is inversely proportional to the catchment-unit area. Also, according to the types of pathways, we classified the source-to-sink systems during this period into three types, steep eroded pathway (Type-I S2S), gentle slope developed with several boundary faults (Type-II S2S), steep slope with observably eroded valleys or fault-troughs (Type-III S2S). The ratio of Q sand /Qs is only related to the sediment migration distance and average fault displacement in the post-extension stage. Besides the above three types of source-to-sink systems, we found that multi-stage faults developed along the slope (Type-IV S2S) predominated during this stage. • Calculated rifting rate in Bozhong Depression. • Identified the provenance area evolution in Bozhong Depression during Paleogene. • Classified four types of Source-to-sink patterns corresponding to the rifting stage. • Put out the dominated factors to S2S system developed during various rifting stages. [ABSTRACT FROM AUTHOR]

Developed on the North China Craton, the intracratonic Ordos Basin contains a complete Paleozoic-to-Cenozoic sediment record, allowing for long-term paleoenvironmental and climate change investigation. During the Carboniferous–Permian period, convergence between the North China block and the paleo-Yangtze plate to the south resulted in a general marine regression characterized by a series of second-order transgression/regression cycles diachronous along the eastern margin of the Ordos. However, the detailed mechanisms that induced these cycles, as well as the associated paleoecological changes, remain unknown. In this study, we integrate multiple indices, including δ18O and δ13C, rare earth element (REE), paleontological assemblages, and clay content (w (chlorite + kaolinite)/ w ((Illite) ratio) planar distribution, to restore the paleo-water depth distribution. These parameters are then used to reconstruct the paleo-sea level from the Pennsylvanian to the middle Permian. We conclude that the direction of second-order transgression/regression was mainly toward the east during the Pennsylvanian–early Permian and switched clockwise toward the north during the middle Permian. We suggest that the second-order cycles, diachronous in space and time, are mainly linked to local variations in sediment supply and regional uplift. Using detrital zircon U–Pb data and the REE and trace element content and heavy mineral assemblages (HMA), we estimate the sediment provenance area. The sediment volumes deposited in the basin through time are obtained using 2D seismic data. During the Carboniferous, the coarse-grained sediments deposited in the eastern Ordos were derived from the uplifting Helan Mountain (Qiandam–Qilian orogenic belt). By the middle Permian, the detrital material became multi-sourced, thus issuing the Yinshan range to the north and the Qinling range to the south. We then integrate the description of numerous core samples with electric log and 2D seismic data to reconstruct the sediment facies associations across the first-order regression from the Carboniferous tidal flat depositional system to the middle Permian prograding fluvial delta system. According to the transfer of the glacial epoch, the sedimentation rate, and the transgression/regression rate above, we classify the evolution process into three patterns: low-transgression rate and less-sediment supply pattern (the late Carboniferous), high regression rate and mass sediment supply pattern (the north block during the early Permian), and low regression rate and mass sediment supply pattern (the south block during the Sakmarian stage). Lastly, with the quantitative calculation of the source-to-sink (S2S) parameters, including the S2S system volume and the elevated height of regional uplift with the 2D seismic data, we propose the mechanism of transgression/regression in the Ordos Basin, responding to the above three pattern s. The first pattern was controlled by regional uplift, whereas the second pattern was controlled by sediment supply. As to the third one, uplift and sediment supply could affect the transgression/regression process. • Identified provenance area of the eastern margin of the Ordos Basin during the Pennsylvanian to the early Permian. • Reconstructed the clockwise evolution process of the relative sea level in the study area. • Identified different types of source-to-sink systems insight from the sea level and sediment supply. • Proposed an integrated method to determine the dominating factors influencing the relative sea level. [ABSTRACT FROM AUTHOR]

Sedimentary features of a source-to-sink (S2S) system produce distinct responses to diverse bedrock types (i.e., silicate and carbonate rocks) in the catchment; these majorly influence the sediment flux, volume, and grain size in the sink area. By comparing a modern S2S system of Holocene Erhai Lake Basin (ELB) (in southwestern China) and an ancient S2S of Eocene western Offshore Bohai Bay Basin (OBBB) (in eastern China), we investigated the differences and proportional ranges among sandy sediment flux (Q f) and sediment discharge (Q s) from catchment associated with diverse bedrock types in a humid and subtropical lacustrine rift basin by combining with the Google-topographic-map, BQART-model, and seismic-geomorphology analysis. Based on geomorphological and 3D visualization analysis, we identified the differences among multiscale catchment-fluvial segments and their sedimentary responses in S2S systems, and then extracted parameters of catchment-unit area (A), catchment relief (R), and total sediment discharge (Q s , calculated by BQART model). Furthermore, we analyzed sediment-dispersal patterns and sandy sediment fluxes in the nearshore (Q f) using regional geologic data, outcrops and the Google Earth database in the Holocene ELB, and using seismic geomorphology in the Eocene western OBBB. Finally, quantitative analysis of the modern and ancient S2S segments was used to investigate the total sandy sediment flux (Q f), which is supplied by >60% of the entire sediment discharge (Q s) for catchments with silicate bedrocks (e.g., metamorphic rock and granite), while the ratio Q f /Q s corresponding to carbonate bedrocks is less than 30%. Additionally, the ratio Q f /Q s for catchments with mixed silicate carbonate bedrocks ranges between 30% and 60%. These results not only provide a new perspective for investigating sandy sediments in a subtropical lacustrine rift basin, but also yield implications for better understanding of continental S2S system theory for diverse bedrock types. • Divide the modern and ancient source-to-sink (S2S) segments into multi-order catchment units and fan-lobes. • Extract the kernel parameters of sediment discharge from catchments and sediment flux of proximal fans. • Discuss the proportional range between sandy sediment flux and sediment discharge associated with diverse bedrock types. • Establish a flux model of source-to-sink segments with diverse bedrock types in subtropical lacustrine rift basins. [ABSTRACT FROM AUTHOR]

During the Eocene, the western Shaleitian Uplift and its adjacent sags constituted a source-to-sink (S2S) system on an active lacustrine basin margin with a steeply dipping boundary fault. We integrated a range of data types with subsurface observations from the western offshore Bohai Bay Basin (OBBB) that allowed us to quantify the size and classification of catchment-fluvial segments, and analyze the sedimentary architecture and sediment fluxes of the proximal fan-delta system. We then discovered quantitative coupling relationships among the parameters of ancient source-to-sink segments. Results show that in the study area the bedrock of the western Shaleitian Uplift is composed of Proterozoic migmatized granites or granites. On the basis of paleogeomorphology reconstruction, we established classification standards for multi-scale catchment units, divided the provenance into four third-order catchment units, obtained quantitative parameters of the catchment-unit area (A), catchment relief (R), and total sediment discharge (Q s , calculated by BQART model) and then confirmed the scales and distribution (cross-sectional area, S cs) of sediment-transport pathways. Furthermore, we analyzed tectonic subsidence, sediment-dispersal patterns, and sediment fluxes of fan-delta systems (Q f) using seismic sedimentology in the third member of the Eocene Shahejie Formation (Es 3). Finally, we used quantitative, multivariate, statistical analysis of the parameters involved in the source-to-sink segments to (1) show the proportional range between total sediment fluxes of fan delta (Q f) and sediment discharge (Q s) from catchment (largest rate of Q f /Q s in the lower part of Es 3 , smallest rate of Q f /Q s in the middle part of Es 3 , and the range from 30% to 70%) and (2) arrange the mainly controlled parameters in terms of their importance (i.e., rate of tectonic subsidence, catchment area, catchment relief, and cross-sectional area of sediment-transport pathway are listed in order of importance). This study can provide an effective way of quantifying and ordering the parameters important in that controlling a complex ancient source-to-sink system, thus helping to achieve an understanding of the process of tectono-sedimentary evolution on a rifted, lacustrine-basin margin. • Divide the catchment segment into different orders and pick up the main parameters. • Indicate the sediment-dispersal patterns and sediment flux of fan-deltas in an active extensional setting. • Reveal the correlation and ordering of multiple important parameters of ancient source-to-sink in a rift basin margin. [ABSTRACT FROM AUTHOR]

In multi-phase rift basins, the links between fault activities and sequence stratigraphic architectures are still poorly understood compared to single-rift basins. The purpose of this work is to give implications for tectono-stratigraphic signatures in multiphase rifts based on seismic data from the Zhu-3 Depression in the Pearl River Mouth Basin, China. Stratigraphically, three composite sequences (CS1-3) defined by major unconformities in the Paleogene successions of the Zhu-3 Depression are interpreted, with each one subdivided into two or three third-order sequences. Regional unconformities and basin configurations indicate two episodic rift phases, termed rift phase 1 (formed CS1), and rift phase 2 (formed CS2) followed by a lithospheric breakup phase (formed CS3). From rift phase 1 to rift phase 2, the basin evolved from small-sized, independent half-grabens into relatively large-scale grabens and finally a dish-like basin configuration. Fault displacement and stratigraphic stacking patterns revealed three distinctive structural stages of rift phase 1: rift initiation (WC-SQ1), rift development (WC-SQ2), and rift termination (WC-SQ3) stages. However, an immediate decrease in fault activity was recorded in the rift phase 2. Immediate strain localization under rotated extension fields during episodic rift phases led to variabilities in tectono-stratigraphic architectures. In turn, this transition may likely contribute to interpreting the depositional pattern from balanced infill during rift phase 1 to an overfilled pattern during rift phase 2 as well as the breakup stage in response to possible enhanced sediment supply. This work enhanced our understanding of additional hydrocarbon evaluations in the Zhu-3 Depression, South China Sea. • The Eocene-Oligocene sequence framework in the Zhu-3 rift are systematically reported. • Fault pattern, basin geometry and drainages basin in episodic rift phases are illustrated. • Tectono-stratigraphic signatures of three rift cycles in the Zhu-3 rift are proposed. • Controls of boundary fault arrays evolution on two-phase rift development are discussed. [ABSTRACT FROM AUTHOR]

Mudflow gullies are well developed in offshore areas and on the upper deepwater slope. In this paper, we discuss the formation and characteristics of mudflow gullies in a gas field in the Yinggehai Basin along the northwestern South China Sea margin, and address their impacts on sand body distribution, reservoir heterogeneity, and hydrocarbon accumulation. The geological setting and sedimentary characteristics indicate that the sedimentary environment of the study intervals is located in an area between lower shore face and offshore. The gullies are several meters to a few tens of meters wide, and are filled mainly with thick mudstones interbedded with thin siltstones. Gully fills show an overall fining upward depositional trend, and exhibit a high value, low-amplitude linear GR wireline log shape. Mudflow gullies always incise the underlying sand bars or sand sheets, are overlain by offshore shales and are therefore considered to have developed in a transgressive setting. They are of three basic types, i.e., deep-, moderate- and shallow-classes according to the incision depth. The mudflows developed in offshore environment with rapidly varying topography, and deeply cut the underlying sand bars in lower shore face environment. Influenced by diapiric events, plastic mud-rich sediments were apt to slump, yielding the studied gullies. Gullies can converge to generate a lobe at front of them. In particular, during marine transgression, due to the high depositional rate of muddy sediments and tectonic activity, marine transgression offered the most favorable scenario for the development of these gullies. The mudflows also slumped down the slope into the deep water areas of the basin. Because of the incision of mudflow gullies and transgressive wave ravinement from the southeast, the pre-existing sand bars on the lower shore face were reworked by waves and oriented in a NE–SW direction, perpendicular to the east shoreline to Hainan Island. The sand bars were affected by the mudflow gullies and diapir faults, often isolated from each other, resulting in a weak sand connectivity vertically and laterally. The degree of erosion of the sand bodies by mudflows decreases with depth. In addition, diapiric activity not only induces the formation of mudflow, but also causes CO 2 in the deep buried intervals to migrate into gas reservoir attached by faults. The mudflow gullies are important causes of gas reservoir compartmentalization. CO 2 filling process and gully development in the area resulted in more heterogeneity than the areas without them. Therefore, mudflow gullies control not only the reservoir compartments but also the gas content in the reservoir. [ABSTRACT FROM AUTHOR]

Abstract: The South China Sea (SCS) shows favorable conditions for gas hydrate accumulation and exploration prospects. Bottom simulating reflectors (BSRs) are widely distributed in the SCS. Using seismic and sequence stratigraphy, the spatial distribution of BSRs has been determined in three sequences deposited since the Late Miocene. The features of gas hydrate accumulations in northern SCS were systematically analyzed by an integrated analysis of gas source conditions, migration pathways, heat flow values, occurrence characteristics, and depositional conditions (including depositional facies, rates of deposition, sand content, and lithological features) as well as some depositional bodies (structural slopes, slump blocks, and sediment waves). This research shows that particular geological controls are important for the presence of BSRs in the SCS, not so much the basic thermodynamic controls such as temperature, pressure and a gas source. Based on this, a typical depositional accumulation model has been established. This model summarizes the distribution of each depositional system in the continental shelf, continental slope, and continental rise, and also shows the typical elements of gas hydrate accumulations. BSRs appear to commonly occur more in slope-break zones, deep-water gravity flows, and contourites. The gas hydrate-bearing sediments in the Shenhu drilling area mostly contain silt or clay, with a silt content of about 70%. In the continental shelf, BSRs are laterally continuous, and the key to gas hydrate formation and accumulation lies in gas transportation and migration conditions. In the continental slope, a majority of the BSRs are associated with zones of steep and rough relief with long-term alternation of uplift and subsidence. Rapid sediment unloading can provide a favorable sedimentary reservoir for gas hydrates. In the continental rise, BSRs occur in the sediments of submarine fans, turbidity currents. [Copyright &y& Elsevier]