Grain-Size and Discharge Controls on Submarine-Fan Depositional Patterns From Forward Stratigraphic Models

Abstract

Submarine fans are important components of continental margins; they contain a stratigraphic record of environmental changes and host large accumulations of oil and gas. The grain size and volume of sediment supply to fans is thought to control the heterogeneity of deep-water deposits; predicting spatial variability of sandy and muddy deposits is an important applied challenge in the characterization of fans. Here, we use DionisosFlow stratigraphic-forward models to evaluate the sensitivity of submarine-fan deposition to a range of grain sizes, with corresponding diffusion coefficients ranging from 10 to 100 km2/kyr for coarse sand to silt/clay, and discharges. In general, finer grains are transported farther in our models because they have larger diffusion coefficients. Coarser grains typical of a sand-rich fan tend to pile up and compensationally stack at the mouth of a proximal feeder channel. Finer grains tend to be distributed across the model domain; however, finer load resulted in fewer channel avulsions because finer sediment did not build topography as high as coarser sediment. Increasing sediment-gravity-flow discharge resulted in a thicker depositional system; however, relatively coarse sediment piled up at the mouth of the feeder channel, which created a slope that promoted basinward sediment transport. Our modeling results can be applied to predict the overall geometry, stacking, and grain-size distribution of submarine fans. Improved understanding of grain-size and discharge controls also informs interpretation of the stratigraphic record of submarine fans. For example, outcrop observations of heterogeneity and compensational stacking of depocenters can be quantitatively related to changing boundary conditions, namely changes in the caliber and overall supply of sediment delivery to deep-water basin margins.

Delta‐to‐fan source‐to‐sink coupling as a fundamental control on the delivery of coarse clastics to deepwater: Insights from stratigraphic forward modelling

“…DionisosFlow software is a 4‐D process‐based deterministic multi‐lithology forward stratigraphic model that simulates the first‐order evolution of depositional systems at the spatial scale of 10 2 –10 3 m and temporal resolution of 10 3 –10 5 yr (e.g. Granjeon, 2014; Hawie et al., 2019). For each time step, DionisosFlow is able to numerically calculate three main physical processes, namely the creation of accommodation space (i.e.…”

“…DionisosFlow 3D stratigraphic forward model is widely used to explore the interplay of geological factors related to the volume and architecture of depositional systems (e.g. tectonism, sea level, water and sediment supply) (Harris et al., 2016, 2018, 2020; Hawie et al., 2018, 2019). It has been employed herein to explore physical and conceptual linkages of delta to deep‐water fan systems and their role in the modulation of deep‐water sand delivery beyond the shelf edge.…”

“…The aim of the Dionisos is to simulate the first‐order evolution of large‐scale depositional systems (Harris et al., 2016, 2018, 2020; Hawie et al., 2018, 2019). Sediment transport in DionisosFlow is determined by a nonlinear slope‐ and water‐driven diffusion model (Granjeon, 2014), expressed as follows:where is the sediment discharge (km 3 /Myr); and are, respectively, the gravity‐ and water‐driven diffusion coefficients (km 2 /kyr); is the water discharge (m 3 /s); and are exponents that affect sediment transport capacity related to slope‐ and water‐driven transport, with values ranging from 1 to 2 (Tucker & Slingerland, 1994); h is the topographic elevation (m); is the local topographic gradient or slope (dimensionless) (Harris et al., 2020); and is the dimensionless gradient of the basin (Granjeon, 2014).…”

“…Irrespective of what brings the delivery system to a shelf‐edge position and whether accommodation, supply or shelf‐edge process regime is the more influential, it is by no means guaranteed that shelf‐edge deltaic sands will automatically pass down to toe‐of‐slope submarine fans (e.g. Dixon et al., 2012; Fisher et al., 2021; Hawie et al., 2019; Kim et al., 2013) (Figure 1). There remains significant uncertainty and debate regarding the transport, erosion and deposition of when and how terrestrial sands are delivered into deepwater (e.g.…”

Sedimentary graphic logs: A template for description and a toolkit for digitalization

“…For example, if a hand lens and grain size card are used to estimate a grain size of lower medium sand (250-375 µm), should one plot that point on the line separating fine and medium, or in the center of the lower medium bin? This may seem like a pedantic point, but when digitizing hand-drawn logs, the wrong convention can misrepresent grain size by ½ Ψ or more, which is often the difference between lithofacies and/or subenvironments in clastic systems (Visher, 1969, Hawie et al, 2019. Thus, we propose the following methodology for drawing grain size on the suggested template (Fig.…”