Three‐dimensional numerical modeling of coarse‐grained clastic deposition in sedimentary basins

Abstract

Abstract. A three-dimensional numerical model of clastic deposition in sedimentary basins is used to investigate the development of coarse-grained deltas in response to relative sea level changes. The model incorporates fully three-dimensional sediment delivery and deposition, together with incised channel formation and slope failure. A combined random-walk/steepestdescent algorithm is used to simulate sediment delivery from a drainage basin outlet to the depositional shoreline, together with a nonlinear three-dimensional diffusion equation for modeling slope-dependent sediment erosion, transport, and deposition. When sediment channels (transport pathways) are out of a specified grade, advective erosion occurs, thereby increasing the total sediment supply delivered to the basin. Multiple sediment sources into a basin can be simulated, together with tectonic subsidence and eustatic sea level changes. The model results presented display many of the key features observed in both modern and ancient coarse-grained deltas. During periods of slowly changing and high relative sea level (highstands), a broad delta front progrades approximately radially away from the sediment source. Conversely, incised channels are developed during rapid falls of relative sea level, leading to localized deposition of deltaic lobes at the mouths of these channels. The incised channels initiate at the exposed delta front and propagate backward toward the sediment source. The rate of growth of incised channels is shown to be an important control on delta morphology, sediment distribution, and lowstand lobe size and location. Lobes are particularly well developed during periods of slowly changing low relative sea level (lowstands). Periods of rapid rise of relative sea level lead to flooding and infilling of incised channel systems and a rapid landward shift in deposition (transgressions). Incised channels and delta lobes are best developed in a model where tectonic subsidence is similar to that expected for hanging-wall-sourced deltas in extensional half-graben settings. In contrast, both channels and lobes are less well developed in a model where tectonic subsidence is similar to that expected for footwall-sourced deltas in such settings. Many of the features developed in the models are, by their nature, three dimensional, and two-dimensional analysis of the model results can lead to erroneous interpretations of the causes of along-strike variability. These aspects of sequence variability have important implications for the application of the sequence stratigraphic methodology to many sedimentary basins.

Normal fault control on bedrock channel incision and sediment supply: Insights from numerical modeling

“…Overall, this leads to radial progradation of the delta over periods of thousands of years but localized progradation over periods of tens to hundreds of years. Further details of the algorithm are given by Hardy and Gawthorpe [1998] and Ritchie et al [1999]. We feel that this algorithm captures much of the complexity of the delivery of sediment from source to shoreline and the radial nature of fan delta progradation.…”

“…The model of coarse‐grained clastic (fan delta) deposition uses a random walk algorithm for three‐dimensional (3‐D) sediment delivery from the drainage basin outlets to the shoreline, together with a nonlinear (threshold) 3‐D diffusion equation for sediment movement on steep delta foresets. The model of clastic deposition has previously been shown to reproduce the morphologies of, and stratigraphic architectures within, small, coarse‐grained deltas [ Hardy and Gawthorpe , 1998; Ritchie et al , 1999]. We feel that the coupled model encapsulates many of the essential elements of the system and may allow a better understanding of the inherent spatial and temporal variability of sediment supply in such settings and its expression in the stratigraphic record.…”

“…In addition, the stratigraphic signature (in basinal sediments) of drainage basin growth, and response to climatic or tectonic forcing, has not been investigated. In parallel with these studies, numerical models of tectonics and sedimentation in two and three dimensions applicable to clastic deposition have been developed and have furthered our understanding of the controls on the preserved stratigraphies in extensional basins and other settings [e.g., Hardy et al , 1994; Hardy and Gawthorpe , 1998; Driscoll and Karner , 1999; Ritchie et al , 1999]. However, these models have treated sediment supply as constant or a known input to the particular numerical model, rather than considering drainage basin evolution and sediment deposition as a coupled system.…”

Prediction of Margin Stratigraphy

“…Mechanistic models apply physical laws to model the important sedimentary processes (Tetzlaff & Harbaugh, 1989;Martinez & Harbaugh, 1993;Haupt & Stattegger, 1999;. Hybrid models combine a variety of approaches and acknowledge that some processes are known well and can employ physical laws while other processes do not yet have accepted physics (Loseth, 1999;Ritchie et al, 1999;. Inverse models simultaneously solve for the values of multiple process parameters using bounded unique solutions constrained by field observations (Cross & Lessenger, 1999).…”

Responses of River Deltas to Sea-Level and Supply Forcing: Autostratigraphic View

“…New insight into the problem has been obtained via experimental research on stratigraphy in general , as well as numerical (Muto & Steel, 1992;Milton & Bertram, 1995;Ritchie et al, 1999;Swenson et al, 2000;Parker et al, 2008a) and experimental research (Paola, 2001;Muto, 2001;Muto & Steel, 2001, 2004) that specifically addresses the question of how river deltas react to steady and unsteady forcing. This work, when combined with site-specific field application (Muto & Steel, 2002a;Parker et al, 2008b), provides a view of the problem that differs rather markedly from the conventional model in three ways.…”