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Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel's age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less- detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon- Channel may help to understand the evolution of other submarine canyon- channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables. [ABSTRACT FROM AUTHOR]

Compound clinoforms are well‐recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net‐to‐gross, thickness and facies association evaluation show overall coarsening‐upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The subaqueous clinothem records a lower, relatively muddy coarsening‐upward interval, 112 m thick, with net‐to‐gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated subaqueous platform (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near‐bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid‐mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid‐mud carpet. The shoreline clinothem (<8 m thick) has high net‐to‐gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net‐to‐gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop. [ABSTRACT FROM AUTHOR]

The Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southward. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels led to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity. [ABSTRACT FROM AUTHOR]

New Cuyo Group outcrop data complement recently published seismic and well data that detail the progradational character of the Lower‐Middle Jurassic Neuquén Margin (Argentina). The deepwater margin, with shelf topset (Lajas Formation), slope break and deepwater slope to basin‐floor deposits (Los Molles Formation), prograded northward and westward as large‐scale clinoforms (250–500 m high) for 120 km, during 13 My, supplied by sediment mainly from the North Patagonian Massif. The studied Lajas Formation topsets are themselves progradational, with a 500 m‐thick vertical succession of subaqueous delta, shoreface with associated tidal flat, mouth bar, fluvio‐tidal channel and alluvial plain deposits. This pattern is confirmed by facies analysis in five areas of outcrops and well data but is interrupted by frequent marine transgressions that add a short‐term cyclicity to the succession. A new paleogeographic map suggests previous disagreements on process stratigraphy are due to shoreline/paralic strike variability and to increased basinal process impact as the topset/shelf widened. A marked feature of each Lajas topset sequence is a differential partitioning of sand and mud, though not with a simple proximal to distal grain‐size reduction. The sand‐prone outer shelf passes landward to a channelized muddy shoreline environment, and then to a mixed sandy and muddy channelized coastal and alluvial plain. This type of partitioning, important for the characterization and prediction of reservoir quality, can also be recognized on seismic and well log data. [ABSTRACT FROM AUTHOR]

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Arguments for recognizing autogenic vs. allogenic signals in the stratigraphic record are still far from settled, as is the decoding of unsteady allogenic responses to climate vs. tectonic forcing. We offer the case of late Mesozoic Xuanhua basin in the western Yanshan fold‐and‐thrust belt of North China to make these points. The study area is an intramontane basin that has allowed detailed structural, sedimentological, and provenance analyses in a kilometre‐thick succession (the Tuchengzi Formation) of alluvial fan, fluvial, lake‐delta and lacustrine deposits. Extensive geological mapping provided confidence of near‐basinwide later correlation of strata, revealing two large‐scale upward‐coarsening (CU) successions each 80–240 m thick, with prominent vertical changes from lacustrine through deltaic and fluvial to alluvial fan deposits. Two intervals of thrust‐related growth strata identified in the Tuchengzi Fm suggest that the CU successions were the signals of tectonic uplift and accommodation change related to Likouquan and the Mapu thrusting. In the lower CU succession, there is a stacking (30+) of small‐scale (3–16 m thick) upward‐fining cyclothems that are argued to have been generated by alternating wet‐dry climate cycles. The wet half‐cycle is argued to have initiated with high sediment and water discharge of flood‐generated mass flows into the lake and ended with accumulation of lacustrine mudstones as lake level rose. The lake deposits include the maximum flooding during the wet half‐cycle. The dry half‐cycle was characterized by continued lacustrine deposits, but increased evidence of subaerial exposure (rooting, paleosols, and mudcracks) argued to result from falling of the lake level under dry conditions. [ABSTRACT FROM AUTHOR]

We describe and analyze the depositional history and stratigraphic architecture of the Campanian and Maastrichtian succession of the southern greater Green River basin of Wyoming, USA, and surrounding areas to better understand the interplay between tectonic and eustatic drivers that built the stratigraphy. By integrating new measured sections with published outcrop, well-log, and paleogeographic data, two new stratigraphic correlation diagrams, 35 new paleogeographic reconstructions, and six new tectonic diagrams were created for this part of the Western Interior Seaway. From this work, two time-scales of organization are evident: (1) 100--300 k.y.-scale, mainly eustatically driven regressive-transgressive shoreline oscillations that generated repeated sequences of alluvial-coastal plain-shoreline deposits, passing basinward to subaqueous deltas, then capped by transgressive estuarine/barrier lagoon deposits, and (2) 3.0--4.0 m.y.-scale, tectonically driven groups of 10 to 15 of these eustatically driven units stacked in an offset arrangement to form larger clastic units, which are herein referred to as clastic wedges. Four regional clastic wedges are recognized, based on the architectures of these clastic packages. These are the: (1) Adaville, (2) Rock Springs, (3) Iles, and (4) Williams Fork clastic wedges. Pre-Mesaverde deposition in the Wyoming-Utah-Colorado (USA) region during the Middle Cretaceous was characterized by thickening of the clastic wedge close to the thrust-front, driven primarily by retroarc foreland basin (flexural) tectonics. However, a basinward shift in deposition during the Santonian into the early Campanian (Adaville clastic wedge) signaled a change in the dominant stratigraphic drivers in the region. Shoreline advance accelerated in the early to middle Campanian (Rock Springs clastic wedge), as the end of activity in the thrust belt, growing importance of flat-slab subduction, and steady eastward migration of the zone of dynamic subsidence led to loss of the foredeep and forebulge, with the attendant formation of a low-accommodation shelf environment. This "flat-shelf" environment promoted large shoreline advances and retreats during sea-level rise and fall. During the middle to late Campanian (Iles clastic wedge), deep erosion on the crest of the Moxa Arch, thinning on the crests of the Rock Springs and Rawlins uplifts, and subsequent Laramide-driven basin formation occurred as the Laramide blocks began to partition the region. The next clastic package (Williams Fork clastic wedge) pushed the shoreline over 400 km away from the thrust belt during the late Campanian. This was followed by a very large and persistent marine transgression across the region, with the formation of a Laramide-driven deepwater turbidite basin with toe-of-slope fans into the early Maastrichtian. The Mesaverde Group in the Wyoming-Utah-Colorado region is thus characterized by: (1) a succession of four tectonically driven classic wedges, each comprised of a dozen or so eustatically driven packages that preserve large basinward and landward shoreline shifts, (2) broad regional sand and silt dispersal on a low-accommodation marine shelf setting, (3) a progressive, tectonically driven, basinward shift of deposition with offset, basinward stacking of successive clastic wedges, and (4) the gradual formation of various uplifts and sub-basins, the timing and sizes of which were controlled by the movement of deep-seated Laramide blocks. The Mesaverde Group in the Wyoming-Utah-Colorado region provides an outstanding opportunity to study the dynamic interaction among the tectonic control elements of a subducting plate (crustal loading-flexure, dynamic subsidence/uplift, and regional flat-slab basin partitioning), as well as the dynamic interaction of tectonic and eustatic controls. [ABSTRACT FROM AUTHOR]

We propose that a more readily studied, secondary source‐to‐sink (S2S) systems can be formed on direct‐fed margins, in which shelf‐edge deltas are 'sources' and deep‐water fans are terminal depositional 'sinks', with channels working as delivery 'conduits' in between. DionisosFlow stratigraphic‐forward model, coupled to seismic and borehole data from middle Miocene Pearl River margin, are used to explore physical and conceptual linkages of delta‐to‐fan S2S systems, with a focus on the predictability of when and how coarse clastics are delivered from the deltas down to the submarine fans. Middle Miocene Pearl River delta‐to‐fan S2S coupling was stratigraphically enacted in three main ways: (a) deltas that lack downdip fans: high sea level or low sediment supply caused coarse clastics to be stored mainly on inner to outer shelf areas; (b) deltas that are linked downdip to fans: coarse clastics were funneled to submarine fans through slope channels, via direct delta‐to‐fan S2S linkages created by delta overreach at shelf break or channels extending back to shelf‐margin prodeltas; (c) fans that lack updip, coeval deltas: coarse shelf clastics were carried laterally by longshore or other shelf currents, but eventually captured by canyon heads, and then delivered directly to the basin floor. Moreover, our DionisosFlow stratigraphic‐forward models suggest that an oscillation in sea‐level behaviour from slowly falling to rapidly falling would result in a within‐system tract surface occurring within the falling‐stage systems tract. This surface is identified as a significant lower‐order unconformity in its proximal reaches and as a correlative conformity distally. Within‐system tract surfaces are identified by a change in shelf‐edge trajectory regimes from flat to slight falling to moderately falling and in architecture from mixed progradation and degradation to dominant degradation. They are coeval with the onset of the deposition of submarine fans linked updip to deltas or lacking updip deltas, highlighting that sandy deposits can be compartmentalized even within a single systems tract. [ABSTRACT FROM AUTHOR]

The Neogene Orinoco Delta is one of the typical river deltas where both the records of modern and ancient tidal processes can be studied. A ~5 m.y./>10-km-thick succession on the island of Trinidad contains remnants of paleo-Orinoco deltaic deposition preserving both tide- and wave-influenced delta lobes within the same time intervals, just like the modern Orinoco Delta that has both wave-dominated and tidal-dominated lobes. The tide-influenced delta lobes and estuaries preserve some spectacular tidal bedding signals, including tidal rhythmites. The tidal record encoded within the tidal rhythmites is preserved well enough that the primary tidal constituents responsible for the tidal currents that deposited the rhythmic facies can be inferred. Lower to upper Pliocene tidal rhythmites were examined in two main paleo-Orinoco sub-environments: (1) estuarine and delta lobe deposits of Morne L'Enfer Formation at Erin Bay, and (2) abandoned tidal channels associated with tide-influenced deltafront deposits from the Telemaque Sandstone Member of the Manzanilla Formation at Matura Bay. Both wave- and river-current signals are also present in most of the study areas. Tidal constituent analysis of unusually well-preserved paleo-Orinoco tidal rhythmites reveals a hierarchy of tidal signals that include semidiurnal, diurnal, fortnightly (neap--spring), monthly (perigee--apogee), semi-yearly, and possibly seasonal and yearly cycles that span thickness intervals ranging from millimeters to meters. The tidal constituents were dominated by, in decreasing importance, M2, S2, and likely K1 rather than O1. The modern tidal data clearly show that K1 is more important in terms of tide-generating potential than O1, as was likely so in the Pliocene. In both the rock and modern records, N2 is more significant than O1, P1, and K2 in terms of tide-generating potential. The comparison between the constituent analysis of the ancient tidal record and the modern tidal measurements reveals their similarities in tidal patterns and constituent types. From this, we deduce that the tidal constituents responsible for the Pliocene Orinoco Delta tides were mixed semidiurnal tidal cycles similar to those found today in Trinidad (Atlantic type of synodically dominated) rather than the Caribbean (tropically dominated) type. [ABSTRACT FROM AUTHOR]

Marine shelves are a ubiquitous feature of modern Earth, developed across a wide range of scales in many sedimentary basins and representing the flooded portion of basin-margin clinoform topsets. Analysis of 80 clinoforms from 10 basins spanning Cenozoic and Mesozoic icehouse, transitional, and greenhouse climate settings indicates that normalized mean greenhouse marine shelf width is 33% of normalized mean total measured clinoform topset length. The equivalent value for transitional settings is 43%, and 72% for icehouse marine shelves. These values demonstrate that greenhouse marine shelves were substantially narrower than icehouse equivalents, suggesting that narrower shelves with persistent shelf-edge deltas were a consequence of lower rates of accommodation change in greenhouse climate intervals that lacked the large ice sheets required to drive high-amplitude high-frequency glacio-eustasy. Because greenhouse climates have been the dominant mode through Earth history, narrow shelves have probably been the dominant form, and conceptual models based on modern relatively wide shelves may be poor predictors of paleogeography, sediment routing, and sediment partitioning throughout much of Earth history. [ABSTRACT FROM AUTHOR]