Numerical modelling of depositional sequences in half‐graben rift basins

Abstract

A three-dimensional numerical model of sediment transport and deposition in coarse-grained deltas is used to investigate the controls on depositional sequence variability in marine half-graben extensional basins subject to eustatic sea-level change. Using rates of sea-level change, sediment supply and fault slip reported from active rift basins, the evolution of deltas located in three contrasting structural settings is documented: (1) footwall-sourced deltas in high-subsidence locations near the centre of a fault segment; (2) deltas fed by large drainage catchments at fault tips; and (3) deltas sourced from drainage catchments on the hangingwall dip slope. Differences in the three-dimensional form and internal stratigraphy of the deltas result from variations in tilting of the hangingwall and the impact of border fault slip rates on accommodation development. Because subsidence rates near the centre of fault segments are greater than all but the fastest eustatic falls, footwall-sourced deltas lack sequence boundaries and are characterized by stacked highstand systems tracts. High subsidence and steep bathymetry adjacent to the fault result in limited progradation. In contrast, the lower subsidence rate settings of the fault-tip and hangingwall dip-slope deltas mean that they are subject to relative sea-level fall and associated fluvial incision and forced regression. Low gradients and tectonic tilting of the hangingwall influence the geometry of these deltas, with fault-tip deltas preferentially prograding axially along the fault, creating elongate delta lobes. In contrast, broad, sheet-like delta lobes characterize the hangingwall dip-slope deltas. The model results suggest that different systems tracts may be coeval over length scales of several kilometres and that key stratal surfaces defining and subdividing depositional sequences may only be of local extent. Furthermore, the results highlight pitfalls in sequence-stratigraphic interpretation and problems in interpreting controlling processes from the preserved stratigraphic product.

Sedimentology and microfacies of a mud-rich slope succession: in the Carboniferous Bowland Basin, NW England (UK)

“…3; Waters et al 2007), implying durations for each cycle of the order of c. 4 myr. Shoreline progradation occurs when sediment supply outpaces the rate at which accommodation is generated on the shelf, which may be during relative sea-level stillstand or rising relative sea-level (normal regression) or during relative sea-level fall (forced regression; Mitchum et al 1977;Vail et al 1977;Howell & Flint 1996;Catuneanu 2002;Gawthorpe et al 2003). The duration of these cycles suggests that they represent sequence scale (third order; 1 -2 myr) changes rather than stacked sequences (second order; 9 -10 myr) or parasequence scale (fifth order; 0.01 -0.02 myr; Mitchum & Van Wagoner 1991).…”

The subsurface structure and stratigraphic architecture of rift-related units in the Lishu Depression of the Songliao Basin, China

“…Climatic conditions usually have a significant influence on the sediment source (Ter Voorde et al, 1997;Ravnås and Steel, 1998). Lake level change reveals an important influence on depositional stacking pattern (Lambiase, 1990;Gawthorpe et al, 2003). The main purpose of this paper is to discuss rifting sub-stage's structural and stragiraphic features and analysis the relationship between them.…”

“…Accommodation in marine rift basins is a function of tectonic subsidence, sediment supply rate, sea level change and climatic conditions Ravnås & Steel, 1998;Gawthorpe et al, 2003). Accommodation space in turn controls stratigraphic and sedimentary architectures.…”

“…A single model is typically used to describe the unique tectonic and sedimentary conditions operating during a given stage, even though each stage may consist of several phases of activity. Previous studies addressing the stratigraphic and sedimentary architecture of rift basins have focused on lithofacies properties and sedimentary facies stacking patterns (Rosendahl, 1987;Lambiase, 1990;Frostick & Reid, 1990;Papatheodorou & Fdrenttnos, 1993;Nøttvedt et al, 1995;Ravnås et al, 1997;Leeder, 2011) as well as the effects of tectonism, sea-level change and sediment supply rate on sedimentary architecture (Prosser, 1993;Howell & Flint, 1994;Gawthorpe et al, 1997;Ter Voorde et al, 1997;Ravnås & Steel, 1998;Gupta et al, 1999;Gawthorpe & Leeder, 2000;Yong et al, 2002;Gawthorpe et al, 2003). Few studies have addressed stratal geometry and sedimentary sequence stacking pattern that differentiate each phase of basin rifting.…”

Provenance analysis of the Permo-Carboniferous fluvial sandstones of the southern part of the Boskovice Basin and the Zöbing Area (Czech Republic, Austria): implications for paleogeographical reconstructions of the post-Variscan collapse basins

“…Rivers are often situated in the topographically lowest part of a basin, which again is situated above the zone of the maximum subsidence near the footwall block. The distribution of facies and transport direction in continental, extensional basins are largely controlled by the tilt of the basin floor (Bridge & Leeder 1979;Alexander et al 1994;Mackey & Bridge 1995;Mack & Leeder 1999;Gawthorpe & Leeder 2000;Peakal et al 2000;Gawthorpe et al 2003). This situation may be modified by variables in differential erosion of the rock types in the source areas, headward growth of drainages, fault segregation, or vertical or lateral fault propagation (Leeder & Jackson 1993;Mack & Stout 2005).…”