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

Nicolas Hawie,Jacob A Covault,Zoltán Sylvester

doi:10.3389/feart.2019.00334

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. 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 related to changing boundary conditions, namely changes in the caliber and overall supply of sediment delivery to deep-water basin margins.

Highlights

Submarine fans are deep-water depositional systems that received terrigenous sediment from canyons and channels that extend across continental margins (Piper and Normark, 2001)
We used DionisosFlow forward stratigraphic models to understand the submarine-fan depositional response to changes in diffusion coefficients related to a range of grain sizes and discharges
Finer-grained loads were transported farther across the model domain; coarser loads resulted in the active migration of the depocenter across the model domain. This is consistent with general models of submarine-fan run-out and compensational stacking based on their mud- vs. sandrich sediment supply

Summary

Introduction

Submarine fans are deep-water depositional systems that received terrigenous sediment from canyons and channels that extend across continental margins (Piper and Normark, 2001). Sacchi et al (2016) used a depth-averaged flow in the 2-D horizontal plane, basin-scale stratigraphic-forward model called SimClast (Dalman and Weltje, 2008, 2012) to simulate fluviodeltaic stratigraphic evolution and create a 3-D probability distribution of facies proportions. This probability cube was used as additional input for a geostatistical reservoir model. Falivene et al (2014) improved DionisosFlow basinscale stratigraphic-forward model predictions of stratigraphic trap and reservoir presence by calibrating the models to independent constraints, such as thicknesses from seismicreflection or well data

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Discussion

Conclusion