Mass transport deposits (MTDs) generate topographic relief on their upper surfaces. The scale and geometry of the topographic features, and the interconnectivity of their sediment fill plays a crucial role in defining the characteristics of associated turbidite reservoirs. Turbidite sands may be ponded in isolated depocenters created by supra-MTD topography. The spacing and maximum thickness of ponded and isolated or tortuously interconnected sands are controlled by the dominant topographic wavelength and amplitude on the surface topography. Once the topography is filled to the saddles (the lowest point between adjacent topographic lows), the sand body forms a continuous sheet peppered with lacunae ('holes') marking the emergent heights ('nunataks'). This is illustrated by confined turbidites over a 200-m thick MTD at Cerro Bola, Western Argentina. Field data differentiate ponded turbidites into a) Underfilled section; an isolated and laterally variable sand interval, confined by short-wavelength (tens to hundreds of meters) topography. Correlation of thicker beds suggests that larger flows were able to over-run at least the saddles in the topography, with only a small portion of the flow being captured in each low. b) Overfilled section; consists of a laterally continuous sand interval that covers the short-wavelength topography while progressively onlapping longer-wavelength (km-scale) features. Depositional facies may help to differentiate the confined/ponded stages, where local topography is still emergent, and thus to indicate the overall connectivity.

Submarine channels are conduits for the transfer of material to deep water by sediment gravity flows. Some channels clearly show meandering patterns in planform that have attracted comparisons with fluvial systems. Many submarine channels, however, are aggradational. Transitions from meandering (at grade) channels to aggradational channels have been described in the subsurface, from seismic data. A field example is presented here in which these meandering and aggradational states may alternate several times during the overall development of a fourth-order sequence before the system is temporarily or permanently abandoned. This implies a change in flow state from one where successive flows behave similarly over extended periods, to one in which the flow parameters are progressively changing. The cause of these cyclic changes is unclear. The generation of sedimentary architectures so strikingly comparable to those of meandering fluvial systems provides strong evidence in favour of stably stratified, essentially two-layer flows, in which the lower high-density part is channel-confined, with a normal (i.e. fluvial-like) secondary circulation, and the upper, low-density part extends onto the overbank regions adjacent to the channel, with minimal mixing and entrainment. Such flows are described as subcritical, in line with published experimental and numerical work, allowing that the critical Froude number in such settings may not be unity. The switch to an aggradational state may be linked to changes in flow criticality, but the ultimate driver for these alternations in flow properties remains unknown. Sinuous deepwater channels may form meander belts or aggrading systems, and may alternate between the two states repeatedly. We invoke two-layer subcritical flow to explain their river-like behaviour, and suggest that a switch from subcritical to supercritical flow may be responsible for the change in behaviour from meandering to aggrading.image

Deep-water megabeds are a particular type of sediment gravity flow deposit that are anomalously thick and often of distinctive composition compared to the deep-water strata within which they are embedded. Pure siliciclastic or carbonate megabeds have been widely reported from deep-marine systems. Less documented are carbonate-rich mixed megabeds with abundant carbonate clasts in a siliciclastic matrix, which are embedded in siliciclastic deep-water systems. Here, such examples are reported from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China, with a focus on the character, processes and implications of these carbonate-rich megabeds. Based on regional geology and characteristics of the encasing siliciclastic turbidites and autochthonous micritic limestones, these megabeds are inferred to have been deposited in a deep marine trough. The megabeds are thick (1 to ca 10 m) compared to surrounding beds (commonly less than 1 m), and are of mixed composition, comprising both siliciclastic grains and shallow-water carbonate clasts. These megabeds are commonly characterised by a distinctive bipartite or tripartite vertical succession of facies. A complete (tripartite) sequence consists of a basal clast-supported conglomeratic division (Division I), an intermediate matrix-supported conglomeratic division (Division II), and an upper normally graded and/or laminated sandy division (Division III). These divisions are interpreted to be deposited from evolving debris flows transitioning to turbidity currents during a single flow event, and are the result of flow deceleration and dilution. The megabeds show variability over very short lateral distances (several tens to a few hundred metres), possibly related to surface relief on the debritic portion of the deposit. A new depositional model is proposed for the mixed deep-water system, with frequent siliciclastic turbidite deposition within this elongate basin from axially flowing turbidity currents, and episodic deposition from laterally-supplied carbonate-rich megaflows that eroded and incorporated the substrate during transport. This article reports an important but rarely documented deep-water sediment gravity flow deposit-the carbonate-rich megabed, from outcrops of the Lower Triassic in the West Qinling orogenic belt, central China. It focusses on the character and processes of these megabeds, explores their implications, and provides a new depositional model for the mixed deep-water system.image

Mass movements are common on the continental slope, affecting not only the subsequent sea floor morphology but often substantially modifying the underlying deposits. Various styles of substrate interaction have been recognised, representing the various degrees of involvement of the underlying material and its incorporation into the mass movement. This work presents a new style of basal interaction not previously described. Based on the morphology of the basal surface of a mass transport deposit, this can be recognised both in seismic data and in an outcrop analogue. A subsurface example, from an ca 100 m thick mass transport deposit located in Santos Basin, offshore Brazil, displays a basal surface with spoon-shaped scours or scoops. These scoops are of the order of tens up to 400 m in maximum dimension, where masses of underlying sediment have been removed and incorporated into the mass movement. Outcrops used for this work are located in La Rioja Province, Western Argentina, where the study involves a well-exposed ca 200 m thick mass transport deposit that crops out continuously over 7 km. Its basal surface is incised irregularly into the underlying sandstones, incorporating the blocks of sandstone into the mass movement. The striking similarities observed between outcrop examples and the northern Santos Basin suggest that they can be effective analogues, facilitating a comprehensive understanding of mass transport deposit dynamics across diverse basin environments. Mass transport deposits outcrop examples from Western Argentina are comparable to seismic deposits of Santos Basin.image

Understanding how subaqueous sediment gravity flows (SSGF) evolve in time and space, and how their deposits vary spatially, is a key research focus for gravity flow sedimentology. This study investigates depositional facies, depositional elements, and sediment transport processes of supercritical flows and hybrid event beds (HEBs) of the Lingshandao Formation in Lingshan Island, Eastern China. Three kinds of depositional elements were recognized: mass transport deposits (MTDs), channel-lobe transition zone (CLTZs), and lobe complexes. MTDs can be sub-divided into proximal and distal deposits. CLTZs are characterized by facies changes from massive coarse-grained pebbly sandstone to backset bedding sandstone in a down-slope direction, which are the deposits of supercritical turbidity currents. HEBs are common in both proximal and distal lobe settings. Tripartite structure in HEBs, which may be caused by up-slope substrate erosion, implies a relatively proximal origin compared with bipartite HEBs, perhaps caused by fluid fractionation in the research area. The succession is formed by a prograding lobe unit, followed by MTDs which are themselves overlain by deposits from a CLTZ. This vertical stacking pattern implies the potential longitudinal facies tract from CLTZ; to lobe complex deposits, is accompanied by emplacement of MTDs at the slope break. The flow types accompanied by sediment transport processes imply that erosion by supercritical turbidity currents associated with a hydraulic jump in the channel-lobe transition zone may be the main reason for mud-clasts and matrix addition to the flow. The large-scale addition of mud-clasts and suspended mud may dampen turbulence in proximal to medial lobe settings, and result in medium-to thick-bedded HEBs with common erosional features and tripartite structures. The remaining suspension flow (with abundant mud) may further transport down-dip and form medium-to thin-bedded HEBs with bipartite structures and rare mud-clasts. These findings may be applicable to other SSGF systems with supercritical flow deposits and hybrid event beds, emphasizing the downdip and lateral variation in depositional elements associated with gravity flow evolution.

We report K–Pg-age deposits in Baja California, Mexico, consisting of terrestrial and shallow-marine materials re-sedimented onto the continental slope, including corals, gastropods, bivalves, shocked quartz grains, an andesitic tuff with a SHRIMP U–Pb age (66.12 ± 0.65 Ma) indistinguishable from that of the K–Pg boundary, and charred tree trunks. The overlying mudstones show an iridium anomaly and fungal and fern spores spikes. We interpret these heterogeneous deposits as a direct result of the Chicxulub impact and a mega-tsunami in response to seismically-induced landsliding. The tsunami backwash carried the megaflora offshore in high-density flows, remobilizing shallow-marine fauna and sediment en route . Charring of the trees at temperatures up to > 1000 °C took place in the interval between impact and arrival of the tsunami, which on the basis of seismic velocities and historic analogues amounted to only tens of minutes at most. This constrains the timing and causes of fires and the minimum distance from the impact site over which fires may be ignited.

Effective exploration, appraisal and development of deep-water reservoirs requires systematic mapping, description and characterization of the depositional systems that host them. Success in these areas requires that there is a firm understanding of hydrocarbon volumes and uncertainties, facies distributions to locate exploration and appraisal wells, and a framework to build reservoir models. We present a practical seismic interpretation workflow methodology which will be applicable in most cases and with most seismic data sets. The workflows are for channels, sheets and mass transport deposits (MTDs). Each step of the workflow is illustrated with subsurface and/or outcrop examples. The channels workflow guides the interpreter through identification of three hierarchical levels of channel architecture and the recognition of six key seismic facies: channel axis; channel margin; basal lags; slumps; thin-bedded facies (internal levees and terraces); and external levees. The sheet sandstone workflow emphasizes a series of steps including: understanding the regional and local context; understanding the evolution of sea-floor topography at basinal and depositional scales; and generating detailed amplitude maps. Mass transport complexes are rarely reservoirs but can have a major impact on reservoir distribution. The workflow encourages enquiries into these impacts which include: potential erosion of underlying reservoirs; ponding on and around the MTD; diversion and deflection of subsequent reservoir-hosting depositional systems; and their potential as sealing facies. The workflows are designed to be efficient and practical, and will provide an appropriate characterization encompassing exploration and appraisal to early development phases.

A continuous Late Cretaceous-Paleocene sedimentary succession within the India-Asia collision suture zone in Xigaze, Tibet contains a c. 80 m thick sand injection complex immediately overlain by a c. 60 m thick mass transport deposit (MTD; the first of several) with the first evidence of Asian provenance, immediately followed by a c. 61 Ma tuff. The youngest in situ strata with unequivocal Indian provenance are probably the source beds of the sand intrusions, separated from the first MTD by c. 50 m of pelagic deposits that potentially represent an interval of several million years; the collision could thus have occurred at any time within this interval. However, the uppermost limit of the sand intrusions closely coinciding with the MTD suggests that they occurred penecontemporaneously, possibly associated with the initial continental collision. This may provide an additional constraint of initial collision onset at c. 61 Ma. The co-occurrence of MTDs and sand injections are possibly good sedimentary indicators of the onset of continental collision and are characteristic of syn-collisional trench basins. Because neither the youngest Indian nor the oldest Asian provenance sediments are in their original stratigraphic position, this study shows that detailed sedimentological work combined with provenance study can better constrain the timing of continental collision.

A new wood type for the Baja California Cretaceous adds to the plant diversity so far known for the area where gymnosperms seem to be dominant. It was collected near El Rosario, Baja California, from rocks of the Rosario Formation, in a sedimentary sequence that comprises ca. 1200 m of non-marine to deep marine sediments from Upper Campanian to Lower Danian age. The wood is characterized by having semiring porous growth rings, predominantly radial multiples of 2-7 with occasional clusters and some solitary vessels, simple perforation plates, alternate intervascular pits, oval to large elliptical vessel element-ray pits with reduced borders, septate thin-walled fibers, 1-4 seriate heterocellular rays, scares paratracheal, vasicentric and marginal parenchyma and oil cells associated with ray parenchyma. All these characters are found in Lauraceae, however, none of the extant taxa of the family have all these characters and even among fossil woods the characters in the Baja California material are better described only among the diverse Laurinoxylon, but vessel grouping, growth ring type, absence of marginal parenchyma, and slightly thicker rays suggest the presence of a new taxon, Rosarioxylon bajacaliforniensis Cevallos-Ferriz, Catharina & Kneller. By the end of the Cretaceous the family formed part of the plant community that represents a western extension of vegetation types more completely described fromareas in themargins of the southern limits of theWestern Interior Sea. The newtaxon is proposed to highlight anatomical differences and geographic isolation fromsimilar taxa and further suggests a large distribution of Lauraceae in what appears to be conifer dominated communities. (C) 2021 Elsevier B.V. All rights reserved.

Late Permian coal deposits are widely distributed throughout southwestern China. This paper describes the petrological composition of the last coal seam in the Longmendong section of the Emeishan area during the latest Changhsingian (Permian) and records important information regarding the evolution of the mass extinction event that occurred at the end of the Permian. The results show that the dominant coal maceral group is vitrinite, followed by liptinite and inertinite macerals, and the coal minerals include quartz, chamosite and pyrite. The pyrofusinite and carbon microparticles occurrence modes could have been formed during wildfires in the adjacent areas. The beta-tridymite occurrence modes and the high proportions and occurrence modes of magmatic quartz indicate that synchronous felsic volcanic activity occurred during the peat mire accumulation period. The chamosite and quartz occurrence modes suggest that they primarily precipitated from Fe-Mg-rich siliceous solutions that was derived from the weathering of nearby Emeishan basalt. The pyritic coal balls occurrence modes in the C1 coal seam are likely the result of coal-forming plants and Fe-Mg-rich siliceous solutions in neutral to weak alkaline conditions during late syngenetic stages or early epigenetic stages within paleomires.

The characterization and predictability of submarine channel-lobe systems on topographically complex slopes have proven challenging, due to the complex responses of such systems to interacting flows and seafloor topography, in terms of their temporal evolution and spatial changes in morphology and architecture. Detailed subsurface studies can reveal important depositional and morphological elements in such settings and help develop predictive models for hydrocarbon exploration. Here, we document a gas-bearing submarine channellobe system on a topographically complex slope, from the Pliocene succession offshore the west Nile Delta where the Giza gas field has been discovered. Based on an integrated analysis of 3D seismic reflection and borehole data, several distinct deep-water depositional elements, including amalgamated channel-fills, aggradational channel-fills, mud-prone channel-fills, lobes, levees and mass-transport deposits are recognized. They are developed on a tectonically influenced continental slope, forming a channel-lobe system that features four main evolutionary phases over a period of ca. 0.26 Myr: 1) Channel belt incision, 2) infill of channel belt by laterally amalgamated channel deposits, 3) development of leveed aggradational channels, with lobes developed within and outside the channel belt, 4) channel avulsion leading to the abandonment of the channel belt, resulting in the formation of a new ponded lobe adjacent to the original channel belt. Spatially, the channel-lobe system shows marked changes in architecture and planform morphology in the areas affected by folds and faults. As the channels cut across a faulted anticlinal structure, they show straightening with some degree of diversion on the upstream limb, while on the downstream limb, channels exhibit increased lateral migration and sinuosity, widespread high-amplitude reflections (interpreted as sand-rich channel-fills), and channel to lobe transitions. In contrast, the last-stage avulsion channel appears to divert along several normal faults at a high angle to the regional slope, and forms a ponded lobe external to the main channel belt. This study shows how the channels and lobes throughout these evolutionary stages respond differently to the presence of folds and faults. It provides a unique analog for submarine channel-lobe systems developed during a third-order sea-level lowstand to transgressive phase with the influence of structurally induced topography and mass transport. The results of this study provide insights into the spatio-temporal development of various types of slope channels and lobes, and may greatly enhance the prediction of associated reservoirs in deep-water systems in tectonically active areas.

Mass-transport processes are notorious for their ability to carry large blocks or megaclasts, to deform sediments, and to interact with the seafloor through deformation and/or erosion of the substrate. These processes, together with their influence on slope sedimentation, are themes we address via direct field observation of three Carboniferous-aged mass-transport deposits (MTDs) (labeled I, II, and III) from Cerro Bola, NW Argentina. Internal deformation can be observed in all three MTDs, although it is best developed in MTD II, a 180 m thick vertically zoned MTD with deformation evolving upward from a simple shear dominated base to a pure shear middle zone and finally back into a simple shear dominated topmost zone. The contact between MTDs I and II and their underlying sandstone substrates are also locally deformed, with plastic deformation affecting up to similar to 20 m of substrate below the MTD base. Conversely, the basal contact between MTD II and the substrate is also in part erosional, marked by scours and grooves that truncate the bedding in the topmost layers of the substrate. Additionally, the presence of large blocks composed of diverse lithologies embedded within the MTDs, together with the sedimentological description of the MTD's matrix and the aforementioned interaction with the seafloor, suggests at least two processes accountable for block generation within MTDs.

The La Pena Canyon section (San Juan Province, western Argentina) provides outstanding examples of different varieties of mass-transport deposits (MTDs) and related sediments, showing a wide range of lithologies (from mud to sand dominated), scales and styles of deformation (from imbricate thrusts comprising the entire thickness of the deposit down to meso- and microscale folding), and mechanical responses (ductile, brittle) according to the rheology of the sediment. Specific observations include (i) the amalgamation of MTDs and the recognition of amalgamation surfaces; (ii) the tendency for MTDs to make up a progressively smaller proportion of the succession as the basin fills; (iii) the progressive disaggregation and homogenization of the protolith, from clear boundaries between a muddy matrix and sandy blocks and slabs up to almost complete mixing generating a "holomictite" (nom, nov.), via intermediate stages of peperite-like lithologies; (iv) slow deformation contemporaneous with deposition of overlying sediments (progressive slumping), suggesting emplacement or post-emplacement modification by creep; and (v) the tendency to find clean, structureless gravel at the sole of some larger MTDs, suggesting a mechanism for MTD sliding involving a layer of gravel with overpressured pore fluid, combining models of hydroplaning and linked cavity systems.

During the Late Palaeozoic, the Gondwana supercontinent formed an extensive Southern Hemisphere landmass that was affected by multiple glacial episodes, known collectively as the Late Palaeozoic Ice Age (LPIA). This resulted in the deposition of glacial, periglacial and deglacial sediments over much of the supercontinent. The Mississippian to early Pennsylvanian phase of glaciation is widely represented along the western margin of Gondwana. This constitutes one of the largest glaciations of the Phanerozoic in terms of its recorded extent and the widespread erosional hiatus it produced in the stratigraphic record. It was this mid Carboniferous glaciation, recorded in the Paganzo Basin of NW Argentina, that carved most of the paleovalleys and paleofjords present there. We report new U-Pb zircon ages from a single glacial succession (Guandacol Formation) of 326 +/- 3 Ma and 320 +/- 5 Ma, that in comparison with neighbouring dated sequences allow for the first time a reliable estimate of the timing and duration of glacial cycles. Palynological studies of these glacial-deglacial events yielded palynoassemblages of the MQ (Late Visean) and DMa (Sepukhovian-Bashkirian) Palynozones. The Carboniferous glacially-related strata and glacial cycles of the Paganzo Basin are compared here with equivalent units of the Parana Basin of SE Brazil, suggesting a similar climate record for most of western Gondwana. We propose a new correlation between these two basins. The new U-Pb zircon ages reported here indicate that a regional glacial peak occurred almost coincident with the Mississippian-Pennsylvanian boundary, suggesting that the ensuing postglacial transgression is the best regional marker to differentiate the Mississippian and Pennsylvanian as it forms an identifiable interbasinal horizon. The biostratigraphic and chronostratigraphic comparison with other LPIA successions from South America reinforces that the First Appearance Datum of monosaccate pollen grains occurs in the late Serpukhovian. Their correlation confirms that similar climate conditions prevailed across most of western Gondwana during this phase of the LPIA.

Summary Our study here deals with the seismic characterization of the stratigraphy of a lacustrine section from the Lagoa Feia Group in the Campos Basin, which extends over an area of 100,000 km2 and in this domain are complex,and heterogeneous which makes accurate reservoir characterization very challenging. . By using an extensive 2D seismic dataset and two deep well logs and core informations, we propose a seismic facies analysis and structural characterization of the Lagoa Feia group in the inner proximal domain of the Campos basin. Inferences from well core and seismic stratigraphy clearly suggest that the all Lagoa Feia group has a syn-rift depositional character. Based on their seismic character, four seismic facies representing the main lithological package in the rift section are recognized: border fault deposits; fine grain-dominated re-sedimented deposits; coarse grain-dominated carbonate rich re-sedimented deposits. Using some simplified kinematic and seismic stratigraphy analysis we show normal faults affecting the lower units of the Lagoa Feia had a long lived intermittent activity during the main passive margin rift history. This work represents an introductory step to a facies classification and structural interpretation applicable in the internal SE Brazil offshore area.

In deep-water settings, the accommodation for sediment transported by turbidity flows relates to the difference between the elevation of the depositional surface and its equilibrium profile. As a consequence, accommodation creation, or disruption, may depend from changes in the physiography of the receiving basin, or changes in the flow properties. In topographically complex slopes, such where salt-withdrawal intra-slope basins occur, three different types of accommodation have been recognized. Among other parameters, the ratio between flow thickness and depth of the intra-slope basin controls the partial, or full, ponding of the sediment in suspension, and consequently, the lithology distribution within the deposit. On a smaller spatial scale, the behavior of bottom-hugging sediment-laden flows can be affected by topographic variations of the sea floor associated with the presence of km-scale bedforms. In this work, we show that ponded lobes accumulate on the convex-up stoss side of pre-existing large-wavelength bedforms (length up to 103, and height up to 102), and that their lithology distribution depends on the flow characteristics respect to the bedform height. In detail, when partial ponding of turbidity currents occurs, flow stripping promotes the accumulation of the coarse-grained fractions on the stoss side of the bedform, while the fine-grained cloud over-spills the lee side, affecting deposition basinward. By introducing the concept of stoss-side accommodation, this work suggests a new mechanism for the formation of ponded coarse-grained facies in slope settings due to the trapping effect large-wavelength bedforms with convex-up stoss sides.

Mass-transport processes are notorious for their ability to carry large blocks or megaclasts, to deform sediments, and to interact with the seafloor through deformation and/or erosion of the substrate. These processes, together with their influence on slope sedimentation, are themes we address via direct field observation of three Carboniferous-aged mass-transport deposits (MTDs) (labeled I, II, and III) from Cerro Bola, NW Argentina. Internal deformation can be observed in all three MTDs, although it is best developed in MTD II, a 180 m thick vertically zoned MTD with deformation evolving upward from a simple shear dominated base to a pure shear middle zone and finally back into a simple shear dominated topmost zone. The contact between MTDs I and II and their underlying sandstone substrates are also locally deformed, with plastic deformation affecting up to ~20 m of substrate below the MTD base. Conversely, the basal contact between MTD II and the substrate is also in part erosional, marked by scours and grooves that truncate the bedding in the topmost layers of the substrate. Additionally, the presence of large blocks composed of diverse lithologies embedded within the MTDs, together with the sedimentological description of the MTD's matrix and the aforementioned interaction with the seafloor, suggests at least two processes accountable for block generation within MTDs.