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Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary systemanalysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems. The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins. [ABSTRACT FROM AUTHOR]

Enhanced sedimentation at glacial margins can produce submarine megaslides (>10,000 km3). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Slope failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). With accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was triggered by a major sediment influx at the onset of the MPT, when glacial‐interglacial cycles shifted from 41 to 100 Kyr. The absence of repeat megaslides may reflect a changing balance between seismic strengthening and sediment flux, where later sedimentation driven by cross‐shelf ice streams results in thin, fluidized, non‐cohesive slides. Continued accretion of the Surveyor Fan and megaslide also reduces critical wedge taper, further inhibiting major failure. Plain Language Summary: Sediment flux at glacial margins can produce submarine slides >10,000 km3 in size (megaslides). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). Due to accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, but with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was caused by the initial major sediment flux at the onset of the MPT, and that afterward only fluidized, thin, and non‐cohesive slides occurred. This is due to changing balance between seismic strengthening and sediment flux, and accretion of the Surveyor Fan and megaslide which reduces the critical wedge taper inhibiting major failure. Key Points: World's Fifth largest mapped megaslide documented beneath Surveyor Fan Gulf of AlaskaTiming of slope failure linked to onset of mid‐Pleistocene glacial intensificationAbsence of later failures due to changing balance of sediment flux/seismic strengthening and negative feedbacks from critical wedge processes [ABSTRACT FROM AUTHOR]

Investigating the sedimentary architecture and evolution of sand-rich submarine fans is vital for comprehending deep-water sedimentary processes and enhancing the success rate of hydrocarbon resource exploration. Recent drilling activities in the Qiongdongnan Basin, northern South China Sea, have unveiled significant gas hydrate and shallow gas potential. However, exploration in this area faces substantial challenges due to the limited understanding of sandy reservoirs. Leveraging extensive newly acquired extensive 3D seismic data (~9000 km²) and well data, our study reveals five distinct deep-water depositional systems in the Quaternary Ledong Formation, including a submarine fan system, mass transport deposits, deepwater channel-levee systems, slope fans, and hemipelagic sediments. Notably, the targeted sandrich submarine fan lies within the abyssal plain, situated at a water depth of 1300-1700 m. This fan exhibits a unique tongue-shape configuration and a SW-NE flow direction within the plane and spans an expansive area of ~2800 km² with maximum length and width reaching 140 km and 35 km, respectively. Vertically, the fan comprises five stages of distributary channel-lobe complexes, progressing from Unit 1 to Unit 5. Their distribution ranges steadily increase from Unit 1 to Unit 3, followed by a rapid decrease from Unit 4 to Unit 5. Our results suggest that the occurrence and evolution of the submarine fan are primarily controlled by sea level fluctuation, confined geomorphology, and sediment supply. Specifically, sea level fluctuation and sediment supply influenced the occurrence of the submarine fan. Concurrently, the confined geomorphology in the abyssal plain provided accumulation space for sediments and shaped the fan into its distinct tongue-like form. In contrast to the deepwater channels within the deepwater channel-levee systems, the distributary turbidite channels within the submarine fan are marked by lower erosion depth with "U" shapes, greater channel width, and higher ratios of width to depth. The comparative analysis identifies turbidite channels as the focal points for offshore gas hydrate and shallow gas exploration in the Qiongdongnan Basin. Furthermore, the temporal evolution of submarine fan offers valuable insights into Quaternary deep-water sedimentary processes and hydrocarbon exploration within shallow strata of marginal ocean basins. [ABSTRACT FROM AUTHOR]

Deep‐water carbonate deposition is relatively poorly understood but an area of vigorous research in academia and industry, where these deposits are a significant component of many unconventional petroleum reservoirs. Recent studies of modern deep‐water carbonates have highlighted the wide variety of depositional processes, sediment types and resultant geomorphology; however, well‐documented outcrops of ancient systems, their rock types and architecture are relatively sparse. The Mississippian Lake Valley Formation provides world‐class exposures of slope‐basinal carbonate deposits. The Tierra Blanca and Doña Ana members comprise submarine fans that are >14 to 20 km in length, >5 km wide, and exposed in strike and dip view, affording a unique opportunity to constrain the architecture, rock types and sedimentary processes. Tierra Blanca and Doña Ana sedimentation was dominated by crinoids shed from an up‐dip platform and supplemented by sediments sourced locally from Waulsortian mounds. Depositional processes include turbidity flows, debris flows and hybrid sediment‐gravity flows. The Tierra Blanca submarine fan thins towards its lateral flanks and distal fringe, where deposits become more mud‐dominated, gravelly grain‐supported flows are less common, and fewer beds have scoured bases. In proximal settings, bed tracing complemented by measured sections allow mapping of stratal surfaces and identification of stories, elements and complexes. The Tierra Blanca evolved from more unconfined to confined deposition. Point‐sourced deposition of the Tierra Blanca fan required a funnelling mechanism, probably due to bathymetry created by Waulsortian mounds or possibly a platform margin re‐entrant. Outcrop exposures illustrate that younger Doña Ana submarine fan deposits onlap onto, and compensationally stack with, the thickest portions of the antecedent Tierra Blanca fan. These outcrops illustrate both similarities and differences between carbonate and siliciclastic gravity flow deposits. Similarities include comparable deposit types, depositional processes and architecture; differences relate to hydrodynamics of carbonate grains, funnelling mechanisms for point‐sourced deposits and sequence stratigraphic forcing. [ABSTRACT FROM AUTHOR]

We use heat flux measurements colocated with seismic reflection profiles over a buried basement high on the Juan de Fuca plate ∼25 km seaward of the deformation front offshore Oregon to test for the presence of hydrothermal circulation in the oceanic crust. We also revisit heat flux data crossing a buried basement high ∼25 km seaward of the deformation front ∼150 km north, offshore Washington. Seafloor heat flux is inversely correlated with sediment thickness, consistent with vigorous hydrothermal circulation in the basement aquifer homogenizing temperatures at the top of the basement. Heat flux immediately above the summit of the basement highs is greater than expected solely from conduction. Fluid seepage at rates of ∼2.6–5.4 cm yr−1 in a 1–1.5 km‐wide conduit through ∼800–1,300 m thick sediment sections above these basement highs can explain these observations. Observations of thermally significant fluid seepage through sediment >225 m thick on oceanic crust are unprecedented. High sediment permeability, high fluid overpressure in the basement, or a combination of both is required to drive fluid seepage at the observed rates. We infer that rapid seepage occurs because the basement highs rise above the low permeability basal sediment with their tops protruding into the base of high permeability Nitinat or Astoria Fan sediment. Seepage from basement highs penetrating into the submarine fans can affect the thermal state of crust entering the subduction zone. Plain Language Summary: Fluid circulation in the oceanic crust can transport large amounts of heat, influencing the heat content and the distribution of heat within the crust. This fluid circulation primarily occurs in a high permeability aquifer composed of rapidly cooled basalt flows that comprise the upper ∼300 m of oceanic crustal rocks. Most marine sediments that accumulate on the basaltic aquifer have very low permeability and inhibit fluid flow; for sediment covered oceanic crust, fluid recharge/discharge from/to the ocean only occurs at sediment‐free basement outcrops. For most sediment types, ∼40 m of sediment accumulation is sufficient to slow fluid flow rates through them, so that fluid flow is not thermally significant. For sites offshore Oregon and Washington, we document thermally significant fluid seepage through sediment ∼800–1,300 m thick. This seepage occurs over buried basaltic hills that penetrate through low permeability sediment into a thick layer of high permeability sandy sediment that hosts the seepage. The fluid seepage, at ∼2.6–5.4 cm yr−1, is fast enough to remove heat from the underlying crust. This can affect the temperature of the crust entering the subduction zone offshore North America. Key Points: We discovered rapid fluid seepage through 1 km thick sediment on the Juan de Fuca plate 25 km seaward of the Cascadia subduction zoneBuried basement highs penetrating through basal sediments are high permeability conduits to the base of sandy submarine fan sedimentsThis previously unknown thermally significant seepage can affect the thermal state of the crust entering the subduction zone [ABSTRACT FROM AUTHOR]

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The Ledong submarine channel and the Dongfang submarine fan, two remarkable sedimentary systems developed during the late Miocene, are considered promising hydrocarbon reservoirs in the Yinggehai Basin of the South China Sea. A comparative study was conducted to reveal the differences between the source-to-sink characteristics of the two gas-bearing and gravity-driven depositional systems to determine their provenances, formation mechanisms and migration paths as well as their key controlling factors. The heavy mineral assemblages and detrital zircon U-Pb dating results suggest that the Ledong channel was fed by the Hainan provenance from the eastern margin, whereas the Dongfang fan was supplied by northwestern terrigenous sources. The relative sea level transgression and sufficient sediment supply triggered the delivery of deltaic loads toward the continental shelves. Seismic data show that fracture activity had a great impact on the tectono-morphologic features of the margins. During downward flow, the gravity flow along the Yingdong Slope encountered steeply falling faulted slope break belts and formed the Ledong incised channel, and the gravity flow of the Yingxi Slope moved through the gently dipping flexural break slope zone and formed the Dongfang dispersed lobe deposits. Since ca. 30 Ma, the sedimentary center has been migrating from the north to the southeast, which produced a clear control of the southeastward distribution pattern of these two sedimentary systems. Observations of cores and thin sections indicate that the rock structures and their compositions are more mature in the Dongfang channel than in the Ledong fan. This study documents significant differences and similarities by comparing the source-to-sink processes of the two gravity-driven systems that developed in the Yinggehai Basin and provides analogies for understanding similar submarine sedimentary systems that developed under similar geological contexts worldwide. [ABSTRACT FROM AUTHOR]

Sedimentological and petrographic studies of the Haymana Formation sandstones identify a submarine fan in the Haymana Basin. This study is confined to outcrop samples from the submarine-fan sandstones (the L1, L2, and L3 sections) and focuses on documentation of the petrographic characteristics of and depositional controls on reservoir properties of the Haymana Formation sandstones. Analysis of the lithology, texture, sedimentary structure, and petrography of the outcrop samples allows separation of the Haymana Formation sandstones into three distinct lithofacies, A, B, and C. Lithofacies A sandstones exhibit medium-coarse grain sizes (0.4–0.6 mm), moderate-good sorting, and subrounded grains. Lithofacies B sandstones exhibit fine grain sizes (0.2 mm), moderate sorting, and subrounded-subangular grains. Lithofacies C sandstones exhibit very fine grain sizes (0.112 mm) and nonreservoir facies. The main aim of this study is to document the diagenetic history and reservoir quality of the Haymana Formation sandstones. Lithofacies A has the best permeability, ranging from 80 to 120 mD, which can be related to the large grain size, the presence of cross-bedding, small amount of authigenic clays or cements in the pore throats, and enlarged pore apertures. In contrast, Lithofacies B sandstones contain variable yet small pore and pore-throat sizes, which are affected by abundant pore-filling authigenic clays, small grain sizes, and no dissolution. The permeability of the Lithofacies B sandstone ranges from 16 to 35 mD, which is lower than that of the Lithofacies A sandstone. Additionally, the Lithofacies B sandstones have small median pore-throat sizes (mean = 1.52 μm) and low porosities (average 4–6%), and the Lithofacies A sandstones have large pore-throat sizes (mean = 2.06–3 μm) and high porosities (average 20–25%), with most pore throats (50% or more) ranging between 1 and 4 μm. According to these data, the Lithofacies A sandstones show good reservoir characterisation. To date, significant hydrocarbon deposits have not been discovered in the Haymana Formation sandstones, although intensive exploratory work towards this end has been carried out in the Haymana Basin. According to this study, the proximal sandstones of the submarine-fan complex of the Haymana Formation may contain high-potential reservoirs in the Haymana Basin. In the basin, hydrocarbon is sourced from deep zones and may be capped by the proximal part of the Haymana Formation sandstones. According to this study, the Lithofacies B sandstones of the Haymana Formation are not suitable as diagenetic traps for hydrocarbon exploration in the Haymana Basin. However, the Lithofacies A sandstones may be expected to have the highest exploration success. [ABSTRACT FROM AUTHOR]

Submarine channel and fan deposits form the largest sediment accumulations on Earth and host significant reservoirs for hydrocarbons. While many studies of ancient fan deposits describe architectural variability along 2D transects (e.g. axis‐to‐fringe, proximal‐to‐distal), these relationships are often qualitative and are rarely quantified at the event‐bed scale. In order to enable quantitative comparison of the fine‐scale architecture of submarine depositional environments, 56 bed‐scale outcrop correlation panels from five broadly categorized environments (channel, levee, lobe, channel‐lobe transition zone, CLTZ and basin plain) were digitized. Measured architectural parameters (bed thickness, bed thinning rates, lateral correlation distance, net‐to‐gross) provide a large (n = 28,525) and statistically robust framework to compare event‐bed architectures within and between environments. "Thinning rate" data (i.e. the lateral rate of change of bed thickness) clearly differentiate deposits from different submarine depositional environments, helping to quantify generally accepted models for proximal‐to‐distal evolution of stratigraphic architecture. The thinning rates of sandstone beds and mudstone‐dominated intervals vary predictably between environments. For example, the highest sandstone thinning rates occur in channel deposits (0.2–6 cm/m; P10 and P90 values here and below) and decrease to lobe (0.1–1.6 cm/m), CLTZ (0.2–0.9 cm/m), levee (0.0024–0.078 cm/m) and basin‐plain deposits (0.000017–0.0054 cm/m). These quantitative relationships provide valuable insights for downslope flow evolution and the construction of stratigraphic architecture in submarine settings. Due to intra‐environment variability, net‐to‐gross is highly variable and thus (when considered alone) is not a diagnostic indicator of depositional environment. Submarine lobe deposits show the most variability in event bed thickness, thinning rate and net‐to‐gross, likely due to the inherent facies variability and differing boundary conditions. To explore this variability, lobe deposits were sub‐classified based on position (proximal, distal) and effective confinement (unconfined, semiconfined, confined) to provide a more detailed sub‐environment analysis. Unconfined lobe deposits show a proximal‐to‐distal increase in sandstone thickness and decrease in mudstone thickness, supporting conceptual models. Confined lobe deposits have thicker sandstone and mudstone beds and lower net‐to‐gross values as compared to unconfined and semiconfined lobes, supporting a sediment trapping mechanism by confinement. These quantified bed‐scale parameter comparisons enable the recognition of architectural similarities and differences within and between environments, demonstrating the need for more quantitative studies of bed‐scale heterogeneity. The results from this study are immediately applicable to parameterizing forward stratigraphic models, constraining property distribution in reservoir models, and probabilistic determination of depositional environment from outcrop and core descriptions of submarine depositional environments. [ABSTRACT FROM AUTHOR]

The reservoir in the upper Miocene Huangliu Formation, in the Yinggehai Basin, is composed of submarine fan deposits with burial depths from 2600m to 3500m. This paper presents an integrated method in provenance analysis by using data of petrography, heavy mineral assemblages, and geochemical compositions. The analysis produced a number of key results. First, two provenances exist, one in the west and the other in the east. Second, the submarine fan sandstone exhibits low percentages of zircon, tourmaline and garnet, whereas the neritic sandbar rocks exhibit high percentages of zircon, tourmaline and leucoxene, and low percentages of magnetite and garnet. Third, the Chemical Index of Alteration (CIA) values and Rb/Sr ratios of the submarine fan sandstone indicate moderate weathering intensity in the source region. SiO2/Al2O3 ratios indicate moderate sediment maturity. Similar rare earth element patterns of the submarine fan sandstone samples from three wells indicate a common provenance. Th-Sc, Co/Th-La/Sc and REE patterns point to derivation from felsic source rocks. Fourth, the integrated method and comparison of REE patterns of the submarine fan sandstone with that of possible adjacent source rocks indicates that the submarine fan sandstone most probably derived from the western Kuntum uplift. It is concluded that the integration of petrological composition of the sandstone, the heavy mineral assemblage and major and trace elements geochemistry is useful for provenance identification. [ABSTRACT FROM AUTHOR]

Multibeam swath bathymetry survey was carried out in the middle Indus fan region in the eastern Arabian Sea. Using high-resolution bathymetry data, major morphological features such as the Raman seamount and the Laxmi ridge have been mapped. This study also reveals the presence of sinuous channel systems, continuing towards the distal fan. Though there are several reports on the presence of channels in different regions of the Indus fan, we report here the presence of active channels to the east of the Laxmi ridge. The total length of all channels along the channel axis is about 915 km. The individual spreads of the channels vary from 189.8 to 1980.5 m. Most of the channels are shallow with the average depth measuring about 60 m. The longest channel is about 256.3 km long, 702 m wide and about 57 m deep. The channels observed are similar to the land-based fluvial channels. The channels identified are highly sinuous in nature, their meanders and cut-off meanders are similar to the characteristics of fluvial channels. In general, average channel course in the study area is more than twice the straight course. [ABSTRACT FROM AUTHOR]

The Gildirli Formation is the oldest Neogene rock unit in the Adana Basin and was formed prior to the regionally extensive Early Miocene marine transgression. These coarse clastic red-beds provide important evidence about the causes and early phases of filling in this large trough, because the Gildirli Formation sediments fill an irregular palaeotopography carved out of Palaeozoic and Mesozoic basement rocks. Detailed study of the Gildirli Formation reveals the existence of at least two alluvial fans supplied from different source areas. A northeastern fan, exposed around Gildirli Village, was fed by streams draining an area of ophiolitic mélange, Mesozoic and older limestones, and fills an irregular palaeomorphology around and northeast of Gildirli. The southwestern fan, in the Nergizlik area, is dominated by debris flow and sheet flow rudites derived from an area of entirely carbonate bedrock. The lower part of the southwestern fan is characterised by well-bedded carbonate breccias and conglomerates that occupy deep, steep-sided palaeovalleys with approximate E-W trends (parallelling the main basin-margin), whereas higher parts of this fan are muddier and show channelised fluvial and floodplain attributes. The two fans display different provenance characteristics and evidently were fed into an intervening pre-existing depression, probably tectonically controlled. The Lower to Middle Miocene sediments that succeed the Gildirli Formation fan clastics on this basin margin form a mosaic of facies associations, partly contemporaneous and partly diachronous. These include a mixed clastic-carbonate unit (Kaplankaya Formation) of mainly shallow marine character, a reefal to platform carbonate unit (Karaisalı Formation), and a coarse clastic submarine fan system (Cingöz Formation) together with its coeval deep-marine shales (Güvenç Formation). The limestone bodies of the Karaisah Formation in this area display clinoformal geometries that accord with a backstepping pattern and also attest to pre-existing fault control of the steep basin margin. The western part of the partly contemporaneous Cingöz Formation submarine fan system has been supplied through a feeder-channel that now occupies the palaeovalley depression inherited from pre-Gildirli Formation times, The palaeovalley system shows a margin-parallel trend and might have been developed before the deposition of the Gildirli Formation by extensional tectonics. Thus the location, geometry and orientation of this sector of the mid-Miocene submarine fan appears to have been determined by the tectonically mediated pre-Miocene/Early Miocene palaeomorphology. [ABSTRACT FROM AUTHOR]

Submarine canyons play a major role in sediment transfer to the deep sea. When connected with fluvial systems, they can produce large submarine fans, whose sandy bodies have a high potential as petroleum reservoirs. Although canyon-river connections are common on passive margins during lowstands, they are rare during highstands. So far, the only canyon in the Western South Atlantic to have exhibited continuous river connection throughout the Quaternary, regardless of sea level position, is the São Francisco Canyon (SFC) in eastern Brazil. In this study, we used multibeam and 3D seismic records integrated with previously published data to investigate the reasons for the continuous canyon-river connection in the area of the São Francisco River. The SFC comprises two compartments: The Upper and the Mid Canyon. The Upper Canyon indents 15 km of the shelf and acts as an erosive feeder trunk to the São Francisco Submarine Fan. When it emerges on the continental slope (Mid Canyon), depositional processes dominate; the canyon now begins to meander and the thalweg is bordered by numerous terraces and levees. Five stratigraphic units have accumulated in the region of the canyon head since the beginning of the Oligocene. Initially, sedimentation had a uniform aggradational character (Unit 1), which later became more discontinuous in association with the development of reef build-ups (Unit 2) and of a low-lying area around the canyon head. This depression was partially infilled by siliciclastics (Unit 3) and later incised by a precursor of the SFC (Unit 4). The depression still has a morphological expression in the shelf nowadays as a bathymetric low (BL), within which the São Francisco River has built its delta (Unit 5). We hypothesize that the origin and evolution of the SFC is associated with three main factors: (i) breaching by the canyon head of thick carbonates rimming the shelf break; (ii) development of the shelf depression referred above; and (iii) major continental drainage reorganization. Continuous canyon-river connection was ensured by this shelf depression, which helped funnel siliciclastic sediments to the canyon and precluded lateral changes to the lower river trunk. Morphological features, such as axial incision of mass movement deposits is suggestive of some, although very limited, modern canyon activity. This case study contributes to a better understanding of river-basin sediment pathways, particularly on passive margins, which are of great importance for the successful exploration of submarine fan systems. • Shelf morphology controlled canyon-river connection in a narrow passive margin • Distribution of shelf-break reef buildups controlled degree of canyon shelf indentation • A shelf bathymetric depression ensured continuous delta-canyon connection • Morphological features indicate modern, although limited, canyon activity [ABSTRACT FROM AUTHOR]