Quantifying the Importance of Sediment Supply, Global Eustasy and Fault-Induced Accommodation in Controlling Delta Architecture, Shelf-Margin Growth and Deepwater Sediment Transfer: Insights from Stratigraphic-Forward Modelling in Northern Australia

Bourget, Julien; Salles-Taing, Tristan; Ainsworth, Bruce; Duclaux, Guillaume

Shelf-margin deltaic sediments accumulated at the edge of the 600-km wide Bonaparte continental shelf (NW Australia) during the Late Quaternary. The shelf-margin deltas developed over a fault-controlled topography that resulted from Plio-Quaternary tectonic activity in the context of collision between the Australian plate and the Banda Arc. Along-strike variability in shelf-margin progradation-to-aggradation rates, clinoform geometry, and basinward turbidite system development is clearly observed across the 3200 km2 of 3-D and high-resolution 2-D seismic datasets covering the shelf-margin deltas. Faulting generated localized areas of higher subsidence rates, and promoted shelf-margin aggradation over progradation. However variation in clinoform geometry and basinward sediment transfer (upper slope MTDs and gullies) is also dependant on the distribution of sediment input points at the shelf-margin (delta distributary channels) which varied through time and space.

We have applied a new 3-D parallel geomorphic and stratigraphic modelling code to quantify the relative importance of sediment supply over fault-controlled accommodation space in controlling the along-strike variability in shelf-margin and upper slope architecture. The code is designed to simulate Earth surface dynamics at multiple spatial and temporal scales. The physics for surface processes is primarily based on shallow-water equations solved within a Lagrangian formulation using a particle-in-cell approach. Flow velocity and sediment load are represented at points that move with the fluid. Based on several assumptions on flow motion as well as erosion-deposition rules, the code is designed to compute a variety of fluid and density flows such as rivers, debris flows and turbidity currents. In addition, vertical displacement fields, sea level variations and climatic forcing can be imposed to simulate stratigraphic evolution and assess the impact of both allochthonous and autochthonous controlling parameters on sedimentary architecture at both basin-scale and reservoir-scale.

Here stratigraphic-forward modelling results permit the quantification of the range of (1) sedimentation rates; (2) global shelf-margin subsidence; and (3) local fault-induced subsidence values necessary to reconstruct the three-dimensional, near outcrop-scale architecture of the shelf-margin delta and the Bonaparte Basin, in the context of well constrained Quaternary sea-level fluctuations.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013