Sediment partitioning, continental slopes and base‐of‐slope systems

Abstract

Deciphering the role slope topography plays in partitioning sediment on siliciclastic continental slope and base-of-slope systems helps our understanding of slope depositional processes in significant ways: (1) by validation of large-scale depositional process models for continental margins, (2) by validation of numerical basin-scale stratigraphic forward models used to test and deploy source-tosink (S2S) concepts and (3) by creating models for setting reservoir presence and quality expectations in frontier areas poorly constrained by wells and seismic. A global database consisting of >700 km of drilled stratigraphy provide empirical rock data lacking from most S2S studies. Analysis of calibrated seismic stratigraphic units characterised using the contextual framework laid out in this paper show that both gross depositional environments (GDEs) and sand content occur across slope profiles in systematic ways. The challenge in using these observations to quantify reservoir risk and uncertainty lies with relating the observations to depositional processes that can be used to characterise frontier basins that lack calibration. Depositional process-based understanding encoded in 3D stratigraphic forward models (SFM) can simulate both lithologies and GDEs providing broad predictions for exploration at the scale of an entire basin or slope system. Stratigraphic forward models allow the integration of S2S understanding and provide a framework for testing sediment-partitioning hypotheses in frontier settings. Valid S2S models must balance sediment yield from the source catchments with sinks, and be consistent with basin specific observations. The proportions of GDEs across the slope provide additional validation criteria to ensure the models are plausible.

Disconnected submarine lobes as a record of stepped slope evolution over multiple sea-level cycles

“…1). Topography can include three-dimensional confinement of ponded mini-basins (e.g., Prather et al, 1998Prather et al, , 2012aPrather et al, , 2012bPrather et al, , 2017Badalini et al, 2000;Winker and Booth, 2000;Sinclair and Tomasso, 2002;Shultz and Hubbard, 2005;Sylvester et al, 2015); barriers creating tortuous corridors (e.g., Smith, 2004a;Hay, 2012); and more subtle gradient changes (generally <1° to few degrees) of stepped slope profiles (Figs. 1B and 1C), which create higher gradient ramps linking lower gradient steps (e.g., O'Byrne et al, 2004;Smith, 2004a;Barton, 2012;Deptuck et al, 2012;Hay, 2012).…”

Shelf‐margin clinothem progradation, degradation and readjustment: Tanqua depocentre, Karoo Basin (South Africa)

“…This progressive shallowing pattern is commonly observed in seismic‐reflection examples of either slides or canyons, which are filled by steeper dipping strata until they show a complete healing (e.g. Walsh et al ., ; Ryan et al ., ; Sylvester et al ., ; Prather et al ., ; Gamberi et al ., ) (Figs and ).…”

Clinoform architecture and along‐strike facies variability through an exhumed erosional to accretionary basin margin transition

“…Clinothems building basin margin successions can be subdivided into three physiographic segments: shelf (topset), slope (foreset) and basin floor (bottomset) (Helland‐Hansen & Hampson, ; Prather, O'Byrne, Pirmez, & Sylvester, ; Steel & Olsen, ). These segments are defined according to the geometry and position of two critical sedimentary transition zones: the shelf‐edge rollover (SERZ) and base of slope (BOSZ).…”

“…Two‐dimensional dip‐parallel sections have been widely used in clinoform trajectory analysis (Helland‐Hansen & Hampson, ; Henriksen, Hampson, Helland‐Hansen, Johannessen, & Steel, ; Steel & Olsen, ), to infer changes in relative sea‐level and to predict the timing of coarse‐grained sediment delivery to deep water. Clinoform trajectory analysis, however, tends to underplay the role of dominant process regime and along‐strike variability in basin margin physiography (Dixon et al., ; Jones, Hodgson, & Flint, ), which limits predictability in sediment character and partitioning between the shelf, slope and basin floor segments (Cosgrove, Hodgson, Poyatos‐Moré, Mountney, & McCaffrey, ; Prather et al., ). Modern and subsurface studies demonstrate that along‐strike variability in coastal process regime and shelf morphology commonly results in a laterally variable stratigraphic record (Ainsworth, Vakarelov, & Nanson, ; Jones et al., ; Laugier & Plink‐Björklund, ; Madof, Harris, & Connell, ; Olariu, Carvajal, Olariu, & Steel, ; Sanchez, Fulthorpe, & Steel, ), which can also be a key control on the nature of the SERZ (Pyles & Slatt, ; Olariu & Steel, ; Dixon et al., ; Gomis‐Cartesio et al., ).…”