Architecture of turbidite channel systems on the continental slope: Patterns and predictions

The diversity of deep-water sinuous channel belts and slope valley-fill complexes

Slope channel sedimentary processes and stratigraphic stacking, Cretaceous Tres Pasos Formation slope system, Chilean Patagonia

Submarine channel flow processes and deposits: A process-product perspective

Mass-Transport Deposits: Combining Outcrop Studies and Seismic Forward Modeling to Understand Lithofacies Distributions, Deformation, and their Seismic Stratigraphic Expression

This study describes for the first time “outer-bank bars,” an intra-channel architectural element that is unique to sinuous submarine channels. The study is based on interpretation of 3D seismic data of sinuous channels in the upper slope of the Amazon Fan, offshore Brazil. Outer-bank bars comprise channel-fill deposits found in tight meander loops at outer corners of bend apices or slightly upstream or downstream of apices. This architectural element can be up to 1.5 km wide and up to 150 m thick with continuous internal reflectors dipping 1–20° towards the inner bend of the meander loop, a direction of dip opposed to that of fluvial point bars or submarine lateral-accretion packages. The angles of outer-bank bar surfaces increased to a maximum at bend apices. Outer-bank bars occur in the final aggradational channel fill in the two separated channel–levee systems in the Amazon data set. They may have been formed as a result of enhanced deposition on the outside of the bend caused by a combination of flow-volume reduction and flow superelevation. Accretion of outer-bank bars may cause the thalweg position to shift towards the inner bends leading to sinuosity reduction. Since this architectural element is likely to be sand prone, its recognition may have significant implications for prediction of hydrocarbon reservoirs.

Outer-Bank Bars: A New Intra-Channel Architectural Element within Sinuous Submarine Slope Channels

Arroyo San Fernando, on the Pacific coast of Baja California, Mexico, provides a superb view of the architecture of a Maastrichtian active margin slope channel system and the record of its evolution through a third-order sea-level cycle. The succession is organized into architectural building blocks (channel-complex sets) consisting of a channel belt with an axial region and a channel-belt margin of terraces and internal levees. The channel belt is confined by an external levee on one side and by an erosion surface into the slope on the other. Each channel-complex set can be subdivided into three stages of evolution: Stage I consists of highly amalgamated coarse-grained channel complexes, Stage II consists of gravelly meander belts with marginal and stratigraphically intervening thin-bedded turbidites, and Stage III consists of mudstones representing abandonment. This succession is associated with repeated and therefore predictable changes in architecture, facies distribution, inferred seafloor morphology, and sedimentary process. We describe variability in the sedimentology, ichnology, palynology, provenance, and inferred sedimentary processes between and within these architectural elements. Channel formation and fill are attributed to erosion, sediment transport, and deposition by turbidity currents and lesser debris flows. Ichnology indicates enhanced oxygenation and supply of organic material, substrate type, and turbidity within the channel belt; the axial region can be differentiated from the terraces by differing response to turbidity-current intensity. Levee environments show ichnological gradients away from the channel towards background slope. Palynology reflects confinement of the supply of terrigenous material to the channel belt, but is also indicative of stratification within the turbidity-currents, as is the distribution of heavy minerals. Provenance is from the extinct part of the continental-margin arc to the east, via high-gradient gravelly streams and across a steep shoreline, with direct supply of coastal material to deep water. Architectural hierarchy bears comparison with other slope channel systems, but in common with them the fill represents only a small fraction of the time that the system was active.

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Philip Thompson

Papers

Mass-Transport Deposits: Combining Outcrop Studies and Seismic Forward Modeling to Understand Lithofacies Distributions, Deformation, and their Seismic Stratigraphic Expression

Outer-Bank Bars: A New Intra-Channel Architectural Element within Sinuous Submarine Slope Channels

Architecture, process, and environmental diversity in a late Cretaceous slope channel system