The shelf sand‐plume model: a critique

Abstract

In recent years, a new model for deposition of sand bodies in a shelf environment has appeared. This model, known as the shelf sand‐plume model, is hypothesized to result from storm‐driven currents that are deflected around a deltaic headland, stripping sand from the headland and redepositing it in a downcurrent ‘plume’ on the inner shelf. The modern analogue for this model is considered to be an arcuate shelf sand body located off the Damietta branch of the Nile Delta. However, the distribution of older deltaic and shoreline sands probably controls the arcuate outline of the sand body. The present current system has certainly reworked these sands into ridges and large‐scale bedforms but is not responsible for the overall outline of the sand body. Grain‐size range and distribution of sand on the shelf demonstrate that the source of sand in the Nile shelf sand body is not the modern Damietta headland as postulated by the shelf sandplume model. In our view, the shelf sand‐plume model is presently unsubstantiated and has orginated as a misapplication of the original Nile example. As a geological model, the shelf sand‐plume model lacks a set of observable, consistently applicable criteria. The only common denominator to the model is the ‘plume’ geometry of a sand body located off a deltaic promontory. However, workers postulating the existence of shelf sand‐plumes have neither clearly established a ‘plume’ geometry nor shown the juxtaposition of these bodies with respect to coeval deltaic headlands in their outcrop or subsurface examples. The model does not provide criteria to distinguish a ‘shelf sand‐plume’ from other classes of shelf sand bodies, notably sand ridges and storm‐generated sheet‐like sands. Its application to the rock record should be re‐evaluated.

Wave‐influenced deltas: geomorphological implications for facies reconstruction

“…These models have recently been challenged with the recognition that sea‐level change plays an important role (e.g. Scheihing & Gaynor, 1991; Walker & Plint, 1992; Bergman, 1994). Many of these previously interpreted shelf sandbodies are now interpreted as top‐truncated lowstand shoreface and delta deposits (e.g.…”

Ancient shelf ridges-A potentially significant component of the transgressive systems tract: Case study from offshore northwest Java

“…Consistent with this approach, such shelf sands were suggested to have been transported onto and across the shelf during lowstands of sea level, when much of the shelf would have been subaerially exposed. This mechanism afforded a more elegant mechanism for transportation of relatively coarse-grained sediment across a shelf by nonmarine processes than having sediment transported across a submerged shelf either by traction or suspension (sourced from the shoreline area) (Scheihing and Gaynor, 1991).…”

“…Figure 23 illustrates the stages that characterize the formation of these deposits. The presence of upper fine to medium sand within these interpreted features suggests that it would be unlikely that these sediments were brought out as plumes through the water column (Scheihing and Gaynor, 1991). Instead, these relatively coarse sediments likely were transported onto and across the shelf within fluvial or distributary channels across alluvial and/or coastal plains, en route to deltas and shorelines beyond.…”

3D seismic visualization of shelf ridges: case study from offshore northwest Java

“…Figure 17 illustrates the stages that characterize the formation of these deposits. The presence of upper fine to medium sand within these interpreted features suggests that it would be unlikely that these sediments were brought out as plumes through the water column (Scheihing and Gaynor, 1991).…”

“…Consistent with this approach, such shelf sands were thought to have been transported onto and across the shelf during low stands of sea level when much of the shelf might have been subaerially exposed. This mechanism afforded a more elegant mechanism for transportation of relatively coarse-grained sediment across a shelf than having sediment transported across a submerged shelf either by traction or suspension, sourced from the shoreline area (Scheihing and Gaynor, 1991).…”