Channel-levee Complexes Research Articles

Tectonic influence on the evolutionary dynamics of deep-water channel systems along the active accretionary prism margin in the Rakhine Basin, Myanmar: A high-resolution 3d seismic analysis

This study reveals the morphological transformations of a deep-water channel system within the Rakhine Basin in the northeastern Bay of Bengal through a comprehensive analysis of high-resolution 3D seismic data integrated with drilling logs. Employing the “source-channel-sink” paradigm, this investigation examined the impact of various factors, including tectonic transformations, sediment influx, slope dynamics, climatic changes, and relative sea-level fluctuations, on the evolutionary trajectory of these channel systems. Applying precise time-slicing techniques integrating root-mean-square amplitude attributes, coherent amplitude attributes, and horizontal amplitudes on seismic profiles, this investigation recognized three distinct stages in the evolution of channel-levee complexes (CLCs): the Middle Miocene erosional deep-water channel-levee complex (CLC-1), the Pliocene erosional-depositional deep-water channel-levee complex (CLC-2), and the Pleistocene depositional deep-water channel-levee complex (CLC-3). Comparative analysis revealed that the CLC-3 exhibits unique characteristics, including shallower channel depth (D), wider channel width (WC), extensive U-shaped cross-sectional area (S), broader natural levee width (WL) and height (H), and the highest tortuosity coefficient (LC/LS) when contrasted with the other two CLCs. Furthermore, this study substantiated how tectonic processes, primarily the collision between the Indo-Eurasian plates, resulting in the Himalayan and Indo-Burma Range orogenies, have shaped the region's geological and climatic framework, thereby influencing monsoon circulation and precipitation patterns, which in turn augmented detrital material influx into the basin. Moreover, this tectonic collision has led to gradual changes in the slope gradient of the Rakhine Basin and its deep-water areas, impacting internal flow velocities and channel curvature, thus governing deep-water channel systems' development and spatial distribution. Also, episodic sea level fluctuations were identified as significant contributors to sediment transport from shelves to deep-water regions and sediment deposit reworking. Overall, this study underscores the role of tectonic changes after the Eocene in driving the evolutionary dynamics of the deep-water channel system within the Rakhine Basin, Myanmar.

Coarse-grained submarine channels: from confined to unconfined flows in the Colombian Caribbean (late Eocene)

Submarine channel mouth settings are hardly preserved in the stratigraphic record. Although they are still poorly known with respect to other segments of turbidite systems, conceptual models are being refined in the light of new discoveries in modern and ancient examples. Still, some questions such as the transition between expansion zones and the traditional Channel-Lobe Transition Zone (CLTZ) remains open in ancient systems. Upper Eocene deposits of the Colombian Caribbean (San Jacinto Fold Belt) are interpreted here as a fan-delta-fed, submarine, coarse-grained channel-lobe system. It displays a well-preserved channel inception stage in the shelf break represented by sigmoidal to lens-shaped gravels, and planar cross-stratified pebbly sandstones (foreset and backset) interpreted as cyclic steps in an expansion zone. In a later stage, a classical channel-levee complex was developed, represented by channel fill elements showing sharp- and erosional-based, fining-upward sequences that are meters thick, having basal massive matrix-supported pebble conglomerates (hard—extrabasinal—clasts, rip-up clasts, coastal bioclasts), vertically evolving to liquefied massive to planar-laminated coarse-grained sandstones with phytodetrital carbonaceous laminae. They are interpreted as concentrated flow deposits (high-density turbidites) coming from continental areas or from coastal systems (i.e., delta reworking). Undifferentiated channel belt thin-bedded turbidites associated with levees and terraces deposits are related to these confined systems. The channel-lobe transition zone is characterized by debrites from cohesionless debris flow in a channel-mouth bar setting, representing bypass processes that developed distally into low-angle, planar cross- and sigmoidally-stratified (upstream antidune) pebble-size to coarse-grained sandstones that fill low-angle scours (cut-and-fill structures) in an antidune field setting with supercritical conditions. When the currents lose channel confinement, the setting is characterized by changes from Froude supercritical to subcritical flow conditions in an inner lobe to lobe off-axis environment. Large seasonal fluctuations in precipitation favor high sediment concentrations, promoting the formation of volumetrically significant fan deltas and coarse-grained submarine channels with high erosive capacity; therefore, their record helps refine interpretations of depositional processes, providing criteria for recognizing areas of the turbiditic systems that are hardly preserved. The particular aggradational conditions for the preservation and stratigraphic characterization of the rare exhumed submarine channel mouth systems make it possible to decipher sediment dispersal patterns and thus connect the models proposed here, from supercritical systems to the traditional models of turbiditic systems.

HELMINTHOPSISANDCYLINDRICHNUSICHNOGUILDS FROM MIOCENE THIN-BEDDED TURBIDITES, TIERRA DEL FUEGO, ARGENTINA

AbstractMiocene thin-bedded turbidites from Tierra del Fuego record scarce graphoglyptids and two unusual ichnoguilds composed of diminutive elite trace fossils. The first, a monoichnospecific Cylindrichnus ichnoguild, consists of crowded, post-depositional burrows formed in surface sediments during the final phase of turbidite deposition. The second, a pre-depositional Helminthopsis ichnoguild, consists of dense aggregates of simple trails, mainly Helminthopsis and Helminthoidichnites, occupying a very shallow tier in organic-rich mud covering the sea floor prior to turbidite deposition. The trace makers of Cylindrichnus were opportunistic suspension/detritus feeding organisms, probably polychaetes, which bloomed during high flux of labile organic matter brought to internal and external levees by turbidity currents. The trace makers of Helminthopsis and Helminthoidichnites were probably nematodes that grazed on organic-rich muddy sediments with abundant disseminated pyrite associated with Kinneyia-like and other problematic wrinkle structures, suggesting sulfur-cycling chemosynthetic microbial communities originated during interturbidite phases. The rhythmical alternation of the Cylindrichnus and Helminthopsis ichnoguilds clearly differentiate the thin-bedded turbidites of the Viamonte Formation from channel-levee complexes elsewhere, stressing the point that ichnoassemblages reflect sets of environmental parameters and not necessarily particular depositional settings.

Direct hydrocarbon indicator analysis to predict reservoir in Deepwater Krishna-Godavari basin: a case study

The amplitude Variations with Offset (AVO) technique is extensively used in hydrocarbon exploration and production for de-risking of the prospect before drilling. The interpretation of AVO results brings more confidence in the presence or absence of hydrocarbon. The AVO and Direct Hydrocarbon Indicator (DHI) analysis have their own inherent limitations. Therefore, to ensure the presence of true AVO in seismic, other attribute supports are crucial. The present prospect in this study was deposited as a channel-levee complex in the shelf-slope of the Krishna-Godavari basin. There is evidence of false AVO within this complex and thus additional attributes were used in this study to support the AVO analysis. The conventional AVO analysis shows the presence of Class-III AVO for a probable reservoir in seismic. However, it is unable to ensure the presence of hydrocarbon in the stacked reservoir unit. The spectral AVO technique was used to check AVO response at low frequencies for laminated and stacked reservoir units. Additionally, seismic attenuation and dispersion attribute studies were incorporated into the de-risking analysis. The drill result showed two distinct reservoir intervals in this prospect, which validated the predrill interpretation. This integrated approach added significant value in de-risking the prospect using AVO and other seismic attributes in complex geologic setups.

Morphology, seismic stratigraphy, and tectonic control of the Yitong submarine canyons – fan apron system in the northern South China Sea

Submarine fans are ubiquitous in modern deep-water environments. Such systems reported in the literature are largely fed by shelf-indented canyons receiving ample fluvial or longshore drift sediment inputs, whereas those nourished by slope-confined canyons far away from terrigenous sediment sources remain poorly understood. Herein, we report such a system, the Yitong submarine canyons – fan apron system (YCFS), from the northern South China Sea. This system was studied using multibeam bathymetric and two-dimensional multichannel seismic data, combined with geological constraints from nearby International Ocean Discovery Program drilling sites. YCFS consists of approximately 12 submarine canyons confined in the lower continental slope of >1200 m water depth, which feed a fan apron in the connecting abyssal plain. The canyons are erosion-dominated, as evidenced by their V-shaped cross-sections with up to 708 m deep incisions. Canyon infillings comprise mass transport deposits and turbidites, and interfluves exhibit features such as landslides, creep-typed sediment waves, and gullies, indicating the canyons and interfluves are dominated by mass transport and turbidity-current processes. The fan apron is generally depositional, in which channels and channel-levee complexes, turbidite lobes, and mass transport deposits comprise the main depositional elements. In the canyon-to-fan transitions, supercritical turbidity current features and bedforms, including plunge pools and connected sediment mounds, cyclic steps, and antidunes, are developed, which are linked to the deceleration and hydraulic-jump effects of the high-velocity turbidity currents shedding off the canyons. Seismic stratigraphic analysis revealed that YCFS was initiated in Late Miocene. The formation and maintenance of YCFS are linked to the long-term existence of an upslope margin-parallel basement high. The latter could have maintained a steep slope condition (up to 6.5°) that favors the development of canyons and supercritical turbidity currents. Because of the blocking effect of the basement high, YCFS receives limited supply of the shallow-water sediments.

Controls on grain-size variability in the Holocene fill of the Indus Submarine Canyon

ABSTRACT What processes control grain size and bed thickness in submarine canyon deposits? Erosive, shelf-cutting canyons contrast with accretionary basin-floor submarine fan accretionary channels because the former tightly constrain turbidity flows in deep channels. This study addresses such a deep-water depositional system in the Indus Submarine Canyon using a series of cores collected along the canyon. Grain-size analysis was conducted for turbidite and hemipelagic sediment deposited in the Holocene Indus Submarine Canyon mostly by diffuse, fine-grained turbidity currents and hemipelagic hypopycnal plumes. We investigate the links between sedimentary grain size, bedding thickness, facies, and canyon morphology. Well-sorted silt in layers mostly < 2 cm thick dominates the canyon. Core sites in the canyon located downstream of knickpoints have coarser, less well sorted sediments because of current acceleration in these areas and then the slowing of flows downslope. Sediments fine with increasing height above the canyon thalweg, implying deposition from a turbulent plume head. The great depth of the canyon, caused by the exceptionally wide shelf and steep slope, prevents channel overspill which controls sedimentation and channel form in submarine fans. Thalweg sediment fines down-canyon into the mid canyon, where sediment bypassing is inferred. The thickest turbidites are found in the sinuous lower canyon where the gradient shallows from ∼ 0.7° to 0.3°. However, canyon gradient has little impact on mean grain size, but does correlate with bed thickness. The active canyon channel, located in a channel belt gradually becomes less steep, more meandering, and narrower farther downstream. Sinuosity is an influence on turbidite bedding thickness but does not control grain size, in contrast to the situation in submarine-fan channel–levee complexes. Compared to the well-known, more proximal Monterey Canyon of California the grain sizes are much finer, although both systems show evidence of > 200 m plume heads.

Architectural complexities and morphological variations of the indus fan and its elements: Understanding of the turbidite system through seismic characterization

The investigations of the processes occurring in submarine fans improve the understanding of intricacies of deepwater turbidity system and their associated developed architectural elements. The seismic patterns and depositional geometries of the channel levee complexes of the Indus fan have been studied using 2D/3D seismic and well data. The Indus fan is the second largest submarine fan in the world, with a horizontal extent of some 1500 km and a thickness of approx. 9 km. The development source of the Indus fan is divided into two units primarily based on their stratigraphic architecture and depositional characteristics. Firstly, the Eocene-Oligocene to Miocene lower unit that is built of channel lobes, and regionally developed large mass-transport deposits including megaturbidites. The other unit is Miocene and the Quaternary upper part that constitute major channel levee complexes with minor intercalations of locally developed mass transport deposits. The former progressively increase in thickness and width upwards the Eocene-Oligocene to Quaternary. This gave rise to symmetrical and asymmetrical growth patterns as a result of multiple phases of erosion and deposition. Such an architecture is present at an extensive scale primarily in the Plio-Pleistocene channels where the vertical to lateral growth ratio is higher than the channels. A single episode of thick MTDs is recognized by seismic reflection geometries suggesting sea level fluctuations that occurred between the Eocene-Oligocene and the Miocene, and from the Pliocene and the Quaternary channels. Regional confinements drastically affected the development of the Indus fan from the Eocene-Oligocene to Miocene, diminishing from the Pliocene-Quaternary. Sediment zonation occurred owing to the presence of structural confinements that controlled the growth of channel levee complexes and in general the entire Indus fan. Our results based on seismic reflection data of channel levee complexes suggest that increasing but alternating sediment supply from Eocene till Plio-Pleistocene, assisted the active channels and levee growth. Continuous increase in turbidity current size and energy along with sedimentation rates modified (i.e., increased the channel aspect ratio) the channel architecture of the Indus Fan.

Sedimentological Analysis of the Turbidite Sequence in the Northern Part of the West Crocker Formation, Northwest Sabah

Gravity-flow deposits form the northern part of the Crocker Formation (Oligocene–Early Miocene), with the most significant interpretation as a sand-rich system in the proximal and a mud-rich system in the distal area of the deep-water turbidite depositional setting. Seven outcrop localities in the northern-part area were selected for mapping and sampling, starting from Kota Kinabalu up to the Telipok area to evaluate the sedimentary sequence. This study used mapping, field observation, and log sketches in the field, as well as extensive analysis and interpretation of sedimentological methods to investigate the sequence of sediment outcrops in the Crocker Formation area of northwest Sabah. During the fieldwork, five main facies were found, namely, massive sandstone facies (f1), graded sandstone facies (f2), laminated sandstone facies (f3), interbedded sandstone and mudstone facies (f4), and mudstone facies (f5). These northern-part outcrops are interpreted as being deposited from the highest to the lowest turbidity currents and the actuality of pelagic mudstone deposition, based on their fining-coarsening-upward pattern. The five geometrical bodies were proposed as laterally contiguous depositional environments, namely, (1) inner fan channel, (2) inner fan channel–levee complex, (3) mid-fan channelized lobes, (4) non-channelized lobes/distal lobes, and (5) basin plains. The facies interpretation shows that the study area consists of lobes, channel–levee complexes, and levees formed in a fan of a deep-water basin setting, with the basinal plain enveloped by thick mudstone deposits. This northern part of the Crocker Formation is interpreted as a multiple-sourced sediment, shelf-fed, Type II, low-efficiency, and sand-rich turbidite depositional system.

Sedimentary–tectonic interaction on the growth sequence architecture within the intraslope basins of deep-water Niger Delta Basin

This paper presents a 3D seismic-based case study from the deep-water Niger Delta Basin to investigate sedimentary–tectonic interaction on growth sequence architecture within the thrust-related intraslope or piggyback basins. Gravitational contraction in the lower continental slope had yielded a series of thrust faults and associated folds in the study area, which formed several piggyback basins. These basins were filled by a suite of growth sequences with varying stratigraphic architecture. Analysis of the 3D seismic data recognized three primary seismic facies types respectively as: convergent, draping and chaotic, which contain seven subtypes. These facies types are combined to form different filling successions for convergent or chaotic growth sequences. The convergent growth sequences mainly occur in the deep section of basin fills during strong gravitational deformation, and always began with convergent-baselapping strata succeeded by convergent-thinning strata, representing pond-to-bypass transition in the ponded-basin accommodation space. The chaotic growth sequences mainly occur in the shallow section of basin fills in response to weak gravitational deformation, and usually began with debris-flow deposits succeeded by channel-levee complexes, reflecting dominant erosion-bypass processes in the slope accommodation space. A dynamic fill-and-spill model considering relationship between episodic sedimentation rate and structural growth rate is proposed to explain the formative mechanisms of growth strata units and associated successions. Interaction between glaciation or deglaciation and sea-level change and gravitational deformation history are suggested to be the factor which resulted in the complex stratal stacking patterns, including progradational or retrogradational stacking patterns within convergent growth sequences, and progradational stacking patterns within chaotic growth sequences.

FACIES ANALYSIS AND DEPOSITIONAL MODEL OF THE MIDDLE-UPPER TRIASSIC SEMANTAN FORMATION, CENTRAL PAHANG, MALAYSIA

This study details the sedimentological analysis of the Middle-Upper Triassic Semantan Formation in the Jerantut-Temerloh-Kemayan region of central Pahang. Seven (F1-7) facies have been identified which are; F1) poorly sorted conglomerate, F2) pebbly sandstone, F3) structureless-to-parallel laminated sandstone, F4) wavy-to-ripple fine-to-medium laminated sandstone, F5) slumped thin-interbeded sandstone and shale , F6) interbedded sandstone and shale, and F7) shale, represent a subordinate part of the Semantan Formation. Examination of the succession of the vertical facies resulted in concession of genetic units (FA1-FA5) which are; FA1) deep channel complex, FA2) distal lobe, FA3) hybrid gravity flow deposit, FA4) channelised lobe and FA5) non-channelised lobe. It is believed that these five genetic units were deposited within four proposed laterally contiguous depositional environments which are; 1) Inner fan – deep channel-levee complex (represent by FA1), 2) Mid fan – channelised lobe (represented by FA5 and FA3), 3) Mid Fan – non-channelised lobe (represented by FA4 and FA3), and 4) Outer fan – distal lobe (represented by FA2). The Semantan Formation deep-water fan is analysed as a sand-rich fan system, based on its sediment types.

Integrated wireline log and seismic attribute analysis for the reservoir evaluation: A case study of the Mount Messenger Formation in Kaimiro Field, Taranaki Basin, New Zealand

The Early Miocene Mount Messenger Formation, which represents a sand turbidite system, is the primary reservoir of the Kaimiro Field in the Taranaki Basin of New Zealand. The present study integrates the available well log and seismic attribute analyses to identify the prospective horizons' petrophysical characteristics and map them to improve understanding the reservoir characteristics. The seismic volume and well log data were imported into the Petrel 2014 software. The subsurface stratigraphic subdivisions are interpreted till 1000 ms (two-way time travel data) with the available wireline log and 3D seismic data. The workflow characterized the reservoir formation with its lithofacies architecture and interpreting its depositional evolution. The findings from the well log analysis are based on a set of charts designed by cross-plotting the various well log data against each other. These charts indicate that the reservoir comprises sandstone with some shale intercalations and also defined the boundaries between the gas sand and shale zones. The petrophysical analysis revealed that Mount Messenger is characterized by fair to good effective porosity (up to 20.5%), shale volume up to 21.4%, and hydrocarbon content up to 61%. The analyses of strata architecture and lithofacies distributions have provided the overall understanding of the subsurface reservoir sand bodies within the studied sequence. Four types of lithofacies, along with their depositional mechanisms, are identified in the study. Seismic attributes like RMS Amplitude, Half Energy and Mean Amplitude helped quantify the reservoir property of interest. The contour maps developed from the RMS, Half Energy and Mean amplitude showed the presence of significant reservoir zones i.e., 16.1%, 15.8% and 4%, within the Mount Messanger Formation. Furthermore, the identification of the Channel-Levee Complex is also established by using seismic geomorphology. The study can be extended to conduct detailed field-scale analysis can be further implied on a global scale.

Morphology and Late Pleistocene–Holocene sedimentation of the Strait of Istanbul (Bosphorus): a review

Abstract The Bosphorus (Istanbul) Strait is a natural strait that connects the Black Sea with the Aegean Sea via the Sea of Marmara and the Dardanelles Strait. It is a 31 km-long and 3.5 km-wide winding channel, with an irregular bottom morphology. It has depressions up to 110 m deep, and two sills with depths of 35 and 58 m in the south and north, respectively. Presently, a two-layer water exchange exists through the strait, with the Mediterranean and Black Sea waters forming the lower and upper layers, respectively. The Bosphorus channel extends as shelf valleys on the Black Sea and Sea of Marmara shelves. However, it operated as a river valley or an estuary during the stadial lowstand periods. The infill sedimentary succession of the Bosphorus channel is up to 100 m thick above the Paleozoic–Cretaceous basement with an irregular topography. The oldest sediments are sandy to muddy fluvial–lacustrine facies of late Pleistocene age, which are preserved only in up to 160 m-deep scoured depressions of the basement. They are overlain by mid–late Holocene estuarine–marine shelly sandy to muddy sediments with patches of bioherms and shelly lag deposits. The Bosphorus outlet areas of the Black Sea and Sea of Marmara are characterized by a submarine fan and a shelf valley, respectively. The fan system in the Black Sea started depositing c. 900 years after the initial vigorous marine water incursion at c. 8.4 14 C ka BP. On the Marmara shelf, extension of the Bosphorus channel is a sinuous shelf valley with a channel–levee complex that was deposited by the Black Sea outflow during 11–10 14 C ka BP. Catastrophic floodings of the Sea of Marmara by torrential Black Sea outflows during the Greenland Interstadial melt-water pulses, as well as the strong Mediterranean current towards the Black Sea during the interglacial periods, were responsible for carving out the Bosphorus channel and the shelf valleys, as well as removing the sediments belonging to the earlier periods.

Diverse gas composition controls the Moby-Dick gas hydrate system in the Gulf of Mexico

AbstractIn marine basins, gas hydrate systems are usually identified by a bottom simulating reflection (BSR) that parallels the seafloor and coincides with the base of the gas hydrate stability zone (GHSZ). We present a newly discovered gas hydrate system, Moby-Dick, located in the Ship Basin in the northern Gulf of Mexico. In the seismic data, we observe a channel-levee complex with a consistent phase reversal and a BSR extending over an area of ∼14.2 km2, strongly suggesting the presence of gas hydrate. In contrast to classical observations, the Moby-Dick BSR abnormally shoals 150 m toward the seafloor from west to east, which contradicts the northward-shallowing seafloor. We argue that the likely cause of the shoaling BSR is a gradually changing gas mix across the basin, with gas containing heavier hydrocarbons in the west transitioning to methane gas in the east. Our study indicates that such abnormal BSRs can be controlled by gradual changes in the gas mix influencing the shape of the GHSZ over kilometers on a basin scale.

The stratigraphic evolution of the Lake Tanganyika Rift, East Africa: Facies distributions and paleo-environmental implications

Active continental rifts are ideal sites for understanding the break-up of continents, and long-lived rift lake environments are known as important reservoirs for endemic communities and biodiversity. The sedimentary fill of the Lake Tanganyika Rift records a long history of continental extension and variable tropical climate, that is unparalleled in its duration and fidelity. Recently acquired, state-of-the-art 2D seismic reflection data, together with reprocessed legacy data, are used to evaluate the evolution and distribution of sedimentary facies over the rift lake. Using seismic stratigraphic analysis, we reconstruct past depositional environments and the paleogeography of the lake and assess how tectonic-driven subsidence and hydroclimate variability modified the lake basin. We identify six syn-rift seismic units that overly the acoustic basement and identify depositional units beneath the syn-rift sequence that suggest episodes of pre-rift sedimentation. Based upon the seismic facies analysis, the earliest seismic stratigraphic unit is interpreted as deposited in an early-stage rift system of low-relief, that was dominated by alluvial, fluvial and shallow lacustrine conditions. Subsequent units exhibit attributes of a lacustrine environment of much greater water depth, enhanced catchment relief and accommodation, consistent with a more mature rift. In Seismic units 2–5, we observe extensive deltaic deposits and deep-water fans, and locally canyons, channels, channel-levee complexes, turbidites, slumps and other mass flow deposits. In the latter part of its history, erosional surfaces and abundant lowstand delta facies are observed, indicating the rift experienced dramatic hydroclimate cycles. We assess the relative timing of key features of the rift, including the emergence of major structures and rift segment boundaries, development of major drainages and linkages to upstream rift lakes. The evolving sedimentary facies of the rift illustrate a shallow- to-deep progression of rift valley environments and the more limited littoral habitats that influenced the evolution of its unique endemic organisms.

Depositional architecture, evolution and controlling factors of the Miocene submarine canyon system in the Pearl River Mouth Basin, northern South China Sea

Submarine canyon system in the Miocene Pearl River Mouth Basin, northern continental margin of the South China Sea, records the process of sediments transported from shelf margin to advanced abyssal plain and comprises important petroleum reservoirs in the basin. Based on integrated analysis of seismic, well logs and core data, the sequence framework, depositional architecture and controlling factors of the submarine canyon system are well documented. As a composite sequence bounded by regional unconformity, the Zhujiang Formation (CS1) can be divided into 5 sequences (CS1-1-CS1-5), and the lower CS1-2 and CS1-3 are the main strata that the submarine canyon system developed. The submarine canyon system can be divided into five segments (A-E) by their distinct geomorphology and depositional architectures. From Segment A to E, the channels in the submarine canyon system transform from “V” shaped single channel, “U” shaped single channel, “gull-wing” shaped channel-levee complex, “W” shaped branch channels to mound shaped distal composite channel and front splay deposits. This is accordantly consistent with sedimentary process of the channels transitional from erosional, erosional-aggradational, aggradational and then lateral migrational. The changing interaction of multi-source sediment supply, differential tectonic subsidence and relative sea level change are considered to be the major control on the development and evolution of the submarine canyon system. The differential tectonic subsidence since the Late Oligocene produced the adequate slope angle, sufficient accommodation and distinct basin geomorphology for the development and segmentation of the submarine canyon system. Slope-gully to slope fan deposits fed by the shelf margin delta systems from the Paleo-Pearl River and the northeastern Dongsha Uplift converged into the submarine canyon system, providing abundant sediments for its development. Relative sea level changes, especially the two regional regressions with abundant sediment supply have made great influence on the evolution of the submarine canyon system.

Stratigraphic evolution of deep-water Dangerous Grounds in the South China Sea, NW Sabah Platform Region, Malaysia

The onshore and shallow marine conventional hydrocarbon resources around the world are mostly at the maturation phase and hence, exploration activity globally, showing increasing interest into progressively deeper water hydrocarbon prospects such as South China Sea basins. However, a comprehensive understanding of basin tectonics, depositional history, and petroleum systems of the basin is required to deduce the exploration prospectivity of these deeper reservoirs. The Sabah Basin is a prolific hydrocarbon province in Southeast Asia and has a significant economic impact on this part. Recent discoveries in the deep-water hydrocarbon prospects in the NW Sabah Trough prompted a comprehensive investigation of the surrounding area, e.g., Dangerous Grounds for hydrocarbon prospectivity. Previous studies in the Dangerous Grounds mainly focused on the sparse 2D seismic and gravity-magnetic data analysis. A systematic review of stratigraphic evolution has not been presented thus far in the published literature. In this paper, recently acquired high-resolution 3D seismic data with the core and cuttings and conventional well log data from the adjacent areas have been combined to characterize the stratigraphic evolution of the Dangerous Grounds in the NW Sabah Platform. Seven horizons interpreted from the 7570 sq. km 3D seismic data, calibrated with the global sea - level curve and geological time scale, to establish the stratigraphic evolution in the study area. Based on distinct structural and seismic characteristics, and calibrated with the adjacent regions well data, two mega-sequences, namely, lower syn-rift and upper post-rift mega-sequences, have been identified and evaluated. The Paleocene to Early Oligocene syn-rift sequence consists of clastic sedimentary fill in grabens and half-grabens is overlain by Late Oligocene to recent post-rift sedimentary successions represented by siliciclastic and carbonates deposits. Major depositional units within these two mega-sequences, including carbonate, channel, mass transport deposits, and turbidites have been identified and evaluated. During Late Oligocene to Middle Miocene, the area has witnessed the deposition of carbonate platform and reefs on top of pre-existing structural highs. Late Oligocene to Middle Miocene channel-levee complexes with convex upward sand filling features is prominent in the seismic data. Mass Transport Deposits and turbidites have also been observed above the Middle Miocene Unconformity with distinct seismic characteristics. The pelagic and hemipelagic nature of the sedimentary succession deposited from Pliocene to recent in a passive margin condition have also been interpreted from their unique seismic features. Paleocene-Early Oligocene syn-rift siliciclastic hydrocarbon play, Late Oligocene-Middle Miocene carbonate play, and Late Miocene turbidite play within the study area have been interpreted.

Upper Cretaceous-Upper Eocene mud-dominated turbidites of the Belaga Formation, Sarawak (Malaysia): 30Ma of paleogeographic, paleoclimate and tectonic stability in Sundaland

The Upper Cretaceous-Upper Eocene Belaga Formation is characterized by thick deep-water sediments that were accumulated as one of the biggest ancient submarine fans covering a time interval of 30 Ma. Although the Belaga Formation is the extensively investigated formation in the Rajang Group, its source and tectonic setting are still arguable. This study utilizes, for the first time, detailed mineralogical and geochemical investigations on sediments from the Belga Formation to examine its origin. The Belaga Formation is subdivided into five members that are made of seven lithofacies dominated by mudstone. Clay fractions from the mudstones of the five members are composed of illite (40–60 wt %), kaolinite (30–45 wt %) and chlorite (5–15 wt %). Al2O3/TiO2 ratios and calculated SiO2 (wt. %) as well as Zr–TiO2, Al2O3–TiO2, SiO2–Al2O3/TiO2 and Cecn-La/Ybcn plots suggested felsic to intermediate igneous source rocks for all members probably the Lower-Upper Cretaceous granites and tonalities of the Schwaner Mountains situated southwest of the studied area. The abundance of kaolinite, Sr/Cu ratios, C-values, Sr/Cu ratios, Sr/Cu versus Ga/Rb plot and high Chemical Index Alteration (CIA) indicate warm and humid paleoclimate throughout the formation of the Belaga Formation. Geochemical proxies from the major oxides (SiO2–K2O/Na2O, K2O/Na2O–SiO2/Al2O3 binary plots and CaO–Na2O–K2O ternary plot), trace elements (Sc/Cr–La/Y discrimination diagram) and uniform REE patterns with distinct Eu negative anomalies propose a mature passive margin tectonic setting for the five members of the Belaga Formation. Facies analysis indicate typical turbidite sequences in all members. Domination of mudstone and the passive margin tectonic setting suggest a channel-levee complex without lobes submarine fan model (Type III) for these turbidites. Stability in source area composition, paleoclimate, palaeogeography and tectonic setting of Sundaland during the Late Cretaceous-Late Eocene (~30 Ma) indicated from sedimentology and geochemical proxies is consistent with the global paleogeographic and paleoclimatic models for this area during this period. Due to their geological and economic importance as potential hydrocarbon source in the region an all over the world, results of this study provide new insights for the architecture and sedimentology of turbidites.

Depositional architecture and evolution of basin-floor fan systems since the Late Miocene in the Northwest Sub-Basin, South China Sea

The sediment budget of the Northwest Sub-basin, South China Sea since the Late Miocene (11.6 Ma, average thickness > 1000 m) accounts for more than two-thirds of the total infill since the initial ocean spreading of the sub-basin (32 Ma). The sediment sources and architectural pattern of these deposits, however, are poorly known. Using high-resolution 2D reflection seismic data with age constraint from IODP boreholes, we have documented two interdigitating basin-floor fan systems that developed since the Late Miocene. These were fed by two of the largest deep-water canyon systems worldwide, from the west (the Central Canyon/Xisha Trough) and the northeast (the Pearl River Canyon), as well as from smaller headless canyons and gullies across the surrounding slopes. Based on careful analysis of seismic facies, their geometry and occurrence, we identify the principal deep-water architectural elements, including the multi-scale channels, channel-levee complexes, lobes, sheets and drapes, mass-transport deposits, volcanic intrusions, turbidity-current sediment-wave fields, and a contourite drift/terrace.Tentative reconstructions show that the development of these Late Miocene-Quaternary basin-floor fan systems was dominated by changes of sediment supply. The Xisha fan reached its largest extent during the Late Miocene, while the Pearl River fan was most active during the Late Miocene to Quaternary. During the Late Miocene, both the conduits of the Central Canyon and the Pearl River Canyon were active with abundant sediment supply, generating the two incipient fan systems. Sediment supply from the west via the Central Canyon persisted throughout the Late Miocene, being coarser-grained than that of the Pearl River fan. With the demise of the Central Canyon during the Pliocene and consequent sharp decrease in sediment supply, the Xisha fan size reduced significantly. By contrast, supply of mud-rich sediments from the Pearl River and northern slope increased through the Pliocene and into the Quaternary, leading to the modern sedimentary pattern of interdigitating basin-floor fans. Insights into the evolution of sediment supply and fan development through time derived in this study contribute to a better understanding of how source to sink systems feed marginal oceanic basins such as the South China Sea.

Sedimentary characteristics and genetic mechanism of a deep-water channel system in the Zhujiang Formation of Baiyun Sag, Pearl River Mouth Basin

The external geometry, internal architecture and sedimentary evolution processes of the deep-water channel system in Zhujiang Formation in the Midwest of Baiyun Sag have been revealed in detail according to the integrated analysis of 3D seismic data and a large number of drilling and logging data sets. In addition, the controlling effect of sediment supply, sea level change, shelf break zone and palaeogeomorphology on the deep-water channel system was discussed. Finally, it is concluded that the development and distribution of the deep-water channel system is controlled by both provenance and landform. The deep-water channel system can be subdivided into different sections: the provenance area, the waterway and the sedimentary area. It presents the features of a ‘three segment channel’ which indicates that the fluid energy of the gravity flow changes from weak to strong and then weak along depositional inclination. Because the processes of internal filling and latter reformation which the channel experienced in different sections during different periods are complex, the inner filling characteristics of the channels are different, mainly high sand-shale ratio superimposed channel (sand-rich deposit) and low sand-shale ratio channel-levee complex (sand-lean deposit). It is clear that the development and spatial distribution characteristics of deep-water channel system in Zhujiang Formation are controlled by the shelf edge delta of Pearl River, forced regression, the shelf break zone and restricted landform collectively. The shelf edge delta at the lower member of Zhujiang Formation in the north of Baiyun Sag provides the large amount of clastic sediments for the development of deep-water channel system. Forced regression drives the continuous transportation of the sediments from shelf edge to deep-water channel system. The shelf break and the fault slope break provide favorable paths and topographic conditions for transportation of the sediments in the deep-water channel system. The fracture systems and the subaqueous low uplifts influenced the spatial distribution of the deep-water channel system together.

Pliocene and Pleistocene stratigraphic evolution of the western Niger Delta intraslope basins: A record of glacio-eustatic sea-level and basin tectonic forcings

Although climate proxy (δ18O) across the world ocean basins reveals that orbital forcing significantly controlled the Pliocene and the Pleistocene sediment deposition, and has been demonstrated in seismic and outcrop studies on the continental shelves of many margins, few or no seismic stratigraphic studies have investigated orbital forcing on deep-water sediment records. In this study, we combined detailed seismic stratigraphy and 3D geomorphological analysis of a high-resolution 3D seismic block in a detailed study of the stratigraphic evolution of the western Niger Delta intraslope basins over the last 5.5 Ma. Two mega seismic units named MSU 1 and MSU 2 were identified. The change in sedimentary architecture from (i) mass flows and turbidite sequences to (ii) hemipelagic and turbidite sequences at the MSU 1/MSU 2 transition coincides with a significant (x3) increase in sedimentation rates and a transition from dominant 400 ka eccentricity cycles (from 5.3 Ma-0.8 Ma) to dominant 100 ka eccentricity cycles, at the Middle Pleistocene Transition (MPT) (circa 0.8‐–0 Ma). The timing of these changes was estimated based on a detailed analysis of seismic facies succession, correlation of seismic markers with high-resolution sea-level and oxygen isotope curves, and estimation of sequence duration. Further changes in the sedimentary record, characterised by turbidite-dominated sequences at the lower part of MSU 1 to mixed mass flows and turbidite sequences at the upper part of MSU 1, were respectively correlated with changes that occurred in the early Pliocene (circa 4.9 Ma) and in the early Pleistocene (circa 2.6 Ma). The depositional sequence on the western Niger Delta intraslope basin is usually characterised by a falling stage erosional surface (FSES) at its base and top (sequence boundary), and by (i) basal MTDs/bypass facies (where preserved), (ii) turbidite feeder channels/aggrading or meandering channel levee complexes and/or MTDs (slides/slumps) and (iii) hemipelagic drapes that successively document the falling stage, lowstand to early transgressive and late transgressive to highstand transits of the shoreline. The Pliocene and Pleistocene sedimentary records of the western Niger Delta intraslope basins were controlled by interplay between allocyclic forcing linked to glacio-eustatic sea-level oscillations and basin tectonics associated with mobile shale movements. .