Ben Kneller

A Process Model for the Evolution, Morphology, and Architecture of Sinuous Submarine Channels

Although analogies have been drawn between some types of meandering rivers and medium- to high-sinuosity, aggradational, leveed submarine channels, a number of different or additional processes operate in submarine channels. Analysis of several individual submarine channels suggests that they undergo much slower bend growth than alluvial rivers and may reach a planform equilibrium, in contrast to meandering rivers, in which bends progressively migrate downstream. Sinuous leveed submarine channels should therefore aggrade to produce isolated ribbons of thalweg deposits (of predictable 3D geometry), in contrast to the stacked channel belts characteristic of most alluvial meandering rivers. A simple model of the flow structure and flow evolution of turbidity currents traversing submarine channels is proposed, based on theoretical, experimental, and field-derived concepts. It predicts that submarine channel flows are highly stratified, have significant supra-levee thicknesses, and form broad overbank bodies of low-concentration fluid moving along the entire channel length. The interaction between the broad body of overbank fluid and within-channel flow is controlled by the processes of towing and angular shear, whose possible effects on channel sedimentation and planform stability are explored.

Oblique reflection of turbidity currents

Turbidity currents meeting obstacles, for example, the margins of a confined basin, are subject to reflection. The consequent change in flow direction is expressed in the sequence of depositional structures of the resulting bed of sediment. Putative examples of orthogonal reflection have been described, based on 180° opposed current directions. We present field evidence for the more general case of oblique reflection of turbidites, and we report the results of flume experiments indicating a mechanism involving generation of internal solitary waves at an oblique ramp. These propagate normal to the ramp, regardless of the angle of incidence. Flow directions in reflected turbidites may indicate the orientation of reflecting surfaces, such as basin margin slopes, and thus may be of considerable help in paleogeographic and tectonic reconstructions.

Basin-Floor Fans in the North Sea: Sequence Stratigraphic Models vs. Sedimentary Facies: Discussion

Original article : Shanmugan, G., R. B. Bloch, S. M. Mitchell, G. W. J. Beamish, R. J. Hodgkinson, J. E. Damuth, T. Straume, S. E. Syvertsen, and K. E. Shields, 1995, AAPG Bulletin, v. 79, p. 477-512.

A depositional record of deglaciation in a paleofjord (Late Carboniferous [Pennsylvanian] of San Juan Province, Argentina): The role of catastrophic sedimentation

The combination of high sediment supply rates and ample accommodation within fjords provides high-resolution records of deglaciation. Ancient fjord fills provide the potential for three-dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process. We describe the fill (Jejenes Formation) of a well-exposed Late Carboniferous (Pennsylvanian) glacial valley and its tributaries; these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments. The geometry of the valley and its tributaries is controlled by the underlying lower Paleozoic lithologies: a deep valley with steep sides exists where the bedrock is massive limestones, and a broader, shallower valley exists where the bedrock is generally a fine-grained olistostrome. The valleys are locally floored with diamictites, including both in situ tillites and remobilized diamictites. In the trunk valley these are locally overlain by a small, shallow-water delta. The major part of the valley fill consists of a ≤150-m-thick mudstone-dominated succession (probably generated by plumes of glacial outwash) containing numerous dropstones that decrease in abundance down the fjord. The mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys, each of which has a distinctive clast suite related to the local subcrop. The entire succession is overlain by >300 m of sandy turbidites, of which the upper part includes large mass-transport complexes. Intercalated within the succession in the trunk valley are structureless, graded, silty mudstones lacking dropstones but with abundant large wood fragments. Close to the steep western margin of the trunk valley, each of these massive mudstones is underlain by a slump or debris flow, locally containing meter-scale blocks of Ordovician limestone from the valley side. We interpret these as a consequence of rockfalls from the steeper valley sides, triggering debris flows on the subaqueous fjord slopes. We suggest that large solitary waves were generated as the rockfalls entered the water, traveling along the fjord and stripping vegetation from the shoreline. Large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds. These deposits, and other mass-flow deposits within the succession, emphasize the potential importance of catastrophic sedimentation within deglacial successions.

Particulate gravity currents

Preface Introduction Jeff Peakall, Maarten Felix, Bill Mccaffrey And Ben Kneller Theoretical And Numerial Approaches Mechanics And Stimulation Of Snow Avalanches, Pyroclastic Flows And Debris Flows Tamotsu Takahashi An Analysis Of The Debris Flow Disaster In The Harihara River Basin Hajime Nakagawa, Tamotsu Takahashi And Yoshifumi Satofuka Theoretical Study On Breaking Of Waves On Antidunes Yusuke Kubo Nad Miwa Yokokawa Two Dimensional Numerical Model For A Turbidity Current Maarten Felix Granular Flows In The Elastic Limit Charles S. Campbell Bagnold Revisited: Implications For The Rapid Motion Of High-Concentration Sediment Flows Stephen Straub Combined Theoretical/Experimental Approaches Downslope Flows Into Rotating And Stratified Environments Peter G. Baines Two Dimentional And Axisymmetric Models For Compositional And Particle-Driven Gravity Currents In Uniform Ambient Flows Andrew J. Hogg And Herbert E. Huppert Ping-Pong Ball Avalanche Experiments James Mcelwaine And K. Nishimura Dam-Break Induced Debris Flow Herve Capart, Der-Liang Young And Yves Zech Experimental Approaches Mean Flow And Turbulence Structure Of Sediment-Laden Gravity Currents: New Insights Using Ultrasonic Doppler Velocity Profiling Jim Best, Alistair Kirkbride And Jeff Peakall Turbulence Structure In Steady, Solute-Driven Gravity Currents Clare Buckee, Ben Kneller And Jeff Peakall Experimental Evidence For Autosuspension Henry Patin Time- And Space-Resolved Measurements Of Deposition Under Turbidity Currents Frans Derooij And Stuart Dalziel Field-Based Approaches Formation Of Large-Scale Shear Structures During Deposition From High Density Turbidity Currents, Gres dAnnot Formation, SE France Julian D. Clark And David A. Stanbrook Subaerial Liquefied Flow Of Volcaniclastic Sediments, Central Japan Katsuhiro Nakayama Depositional And Eruptive Mechanisms Of Density Current Deposits From A Submarine Vent At The Otago Peninsula, New Zealand U. Martin And James D. L. White Deltaic Density Currents And Turbidity Deposits Related To Maar Crater Rims And Their Importance For Palaeogeographic Reconstruction Of The Bakony-Balaton Highland Volcanic Field (BBHVF), Hungary Karoly Nemeth Synsedimentary Deformation In The Lower Muschelkalk Of The Germanic Basin Katja Fohlisch And Thomas Voigt

Slumps, debris flows and sandy deep-water channel systems: implications for the application of sequence stratigraphy to deep water clastic sediments

The Hecho Group is a classic sedimentary system from which turbidite classifications have been defined. This study of mudstone-rich intervals from this group suggests that published models in which Type 2 and 3 systems develop in response to changes in relative sea level or tectonic activity need to be reassessed. Intervals developed between channel/lobe sandstones comprise mud-matrix supported conglomeratic debris flows and/or slump deposits which blanket the underlying sand-rich channel-fills. They record periods of major disturbance and re-organization of the sedimentary regime. The sandstone bodies are not strongly incised and have high aspect ratios. Previous interpretations of these intervening muddy intervals as overbank wedge/levee deposits, developed during a relative rise in sea level (Type 3) are considered inappropriate for the sections studied.

Silurian turbidite provenance on the northern Avalonian margin

The Windermere Supergroup of NW England was deposited in a foreland basin on the northern margin of Eastern Avalonia and preserves an almost complete Ashgill to Pøídolí sequence. It was ideally positioned to record provenance changes associated with the closure of the Iapetus Ocean. Petrographic, geochemical and Nd isotopic parameters show distinct and concordant temporal trends. The late Ashgill to early Llandovery is characterized by progressive hemipelagic dilution of material derived from the underlying Borrowdale Volcanic Group. From the Llandovery onward, petrographic and geochemical data indicate supply from a recycled orogen source: input from the Scandian orogen may be inferred. No conclusive evidence is recorded of Laurentian input into the basin. By the late Wenlock a unified sedimentary system probably spanned the Iapetus ocean. An abrupt reversal in provenance trends towards the end of the Ludlow records basin inversion, the occlusion of the Iapetus seaway and concomitant cannibalization of older foreland basin sediments. Provenance data derived from upper Wenlock to Pøídolí sediments aid the characterization of marine foreland basins.

ABSTRACT: A Comparative Seismic Architectural Analysis of Shallow Analogue Channel Systems, Focusing on the Einstein Channel, Gulf of Mexico

Submarine channel sands are important hydrocarbon targets for many deepwater plays around the world. Consequently, their architectural geometries and potential as reservoirs are of economic interest to the oil industry. Shallow analogue channel systems show better preservation of depositional geometries than more deeply buried channels and their seismic data has a higher frequency content, which allows for a more detailed understanding of a channel systems internal architectures. A comparative seismic analysis of near-surface deepwater channels into their internal architectures and seismic facies enhances the understanding of channel evolution. Mapping the evolution of channel axis and levee deposits in this way highlights the variability between depositional channel systems. In order to realistically compare channel systems, a channel systems scale and its relative position on the slope must be known. As yet, few comprehensive architectural models have been produced from shallow analogue channel systems.

A Process Model for the Evolution, Morphology, and Architecture of Sinuous Submarine Channels: PERSPECTIVES

ABSTRACT Although analogies have been drawn between some types of meandering rivers and medium- to high-sinuosity, aggradational, leveed submarine channels, a number of different or additional processes operate in submarine channels. Analysis of several individual submarine channels suggests that they undergo much slower bend growth than alluvial rivers and may reach a planform equilibrium, in contrast to meandering rivers, in which bends progressively migrate downstream. Sinuous leveed submarine channels should therefore aggrade to produce isolated ribbons of thalweg deposits (of predictable 3D geometry), in contrast to the stacked channel belts characteristic of most alluvial meandering rivers. A simple model of the flow structure and flow evolution of turbidity currents traversing submarine channels is proposed, based on theoretical, experimental, and field-derived concepts. It predicts that submarine channel flows are highly stratified, have significant supra-levee thicknesses, and form broad overbank bodies of low-concentration fluid moving along the entire channel length. The interaction between the broad body of overbank fluid and within-channel flow is controlled by the processes of towing and angular shear, whose possible effects on channel sedimentation and planform stability are explored.