Can sediment supply variations create sequences? Insights from stratigraphic forward modelling

Abstract

Classic sequence stratigraphy suggests depositional sequences can form due to changes in accommodation and due to changes in sediment supply. Accommodation‐dominated sequences are problematic to define rigorously, but are commonly interpreted from outcrop and subsurface data. In contrast, supply‐dominated sequences are much less commonly identified. We employ numerical stratigraphic forward modelling to compare stratal geometries forced by cyclic changes in relative sea level with stratal geometries forced by sediment discharge and water discharge changes. Our quantitative results suggest that both relative sea‐level oscillations and variations in sediment/water discharge ratio are able to form sequence‐bounding unconformities independently, confirming previous qualitative sequences definitions. In some of the experiments, the two types of sequence share several characteristics, such as an absence of coastal‐plain topset deposits and stratal offlap, something typically interpreted as the result of falling relative sea level. However, the stratal geometries differ when variations in amplitude and frequency of relative sea‐level change, sediment/water discharge ratio, transport diffusion coefficient and initial bathymetry are applied. We propose that the supply‐dominated sequences could be recognised in outcrop or in the subsurface if the observations of stratal offlap and the absence of coastal‐plain topset can be made without any strong evidence of relative sea‐level fall (e.g. descending shoreline trajectory). These quantitative results suggest that both supply‐dominated and accommodation‐dominated sequences are likely to occur in the ancient record, as a consequence of multiple, possibly complex, controls.

Drainage and Sedimentary Responses to Dynamic Topography

“…Those unconformities are diachronous along the margin, as the sediment supply history driven by the laterally migrating dynamic topography is diachronous. This suggests that variations in sediment supply play a significant role (even a dominant role at delta 5) in controlling the formation of unconformities, supporting the supply-dominated sequences (Zhang et al, 2019). Our results can also provide important insights into identifying those supply-dominated sequences in outcrop and in the subsurface.…”

Axial and transverse deep‐water sediment supply to syn‐rift fault terraces: Insights from the West Xylokastro Fault Block, Gulf of Corinth, Greece

“…The representation of stratigraphic surfaces in linked, syn‐rift deep‐water systems may therefore lie in whether the system is accommodation (in‐situ) or supply (Gilbert‐delta) dominated at a given time or location (Burgess & Hovius, ; Carvajal & Steel, ; Zhang, Burgess, Granjeon, & Steel, ; Zhang, Kim, Olariu, & Steel, ). Zhang, Burgess, et al () and Zhang, Kim, et al () infer that this is principally reliant on shelf width and amplitude of base‐level change from numerical models, where high amplitudes of base‐level variation decrease deep‐water sediment export only in large shelf width, supply‐dominated systems. However, Zhang et al () focus on wide, well‐established shelves.…”

Upslope‐climbing shelf‐edge clinoforms and the stepwise evolution of the northern European glaciation (lower Pleistocene Eridanos Delta system, U.K. North Sea): When sediment supply overwhelms accommodation

“…Recent research has identified sediment supply as the main external driver controlling shelf‐margin growth and its architecture (e.g. Carvajal, Steel, & Petter, ; Schlager, ; Zhang, Burgess, Granjeon, & Steel, ). We argue that the very high Eridanos sediment supply in the earliest Calabrian played an important role in the onset of the outbuilding of upslope‐climbing shelf‐edge scale clinoforms in the study area (Figure ).…”