--> Accommodation, Sediment Supply, Deltaic Process Regime, and Their Controls on Deep-Water Sand Delivery: Insights From High-Resolution 3-D Quantitative Seismic Stratigraphy

2018 AAPG International Conference and Exhibition

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Accommodation, Sediment Supply, Deltaic Process Regime, and Their Controls on Deep-Water Sand Delivery: Insights From High-Resolution 3-D Quantitative Seismic Stratigraphy

Abstract

Traditional stratigraphic models predict that accumulation of deep-water siliciclastic reservoirs occur when falling sea-levels promote basinward migration of rivers and development of shelf-edge deltas. However, recent studies show that the processes redistributing sediments at the shelf-edge seem to have a direct impact on the shelf-to-basin sediment transfer mechanisms and the accumulation of reservoir-grade sands. Here, we present a new approach for the analysis of shelf-margin depositional systems combining full-volume 3D seismic interpretation with a dynamic stratigraphic approach (i.e., 3D quantitative seismic stratigraphy). This study uses the example of the Lower Barrow Group (LBG; Latest Tithonian - Early Valanginian), a shelf-slope-basin system developed during a late phase of rifting on the North West Shelf of Australia. Quantitative analysis was conducted on 30 high-resolution seismic sequences (or clinothems) with an average time span of ~47,000 years. The data collected links together: (1) key shelf-edge geometries (trajectory angle, slope gradient, differential sedimentation between topsets and bottomsets); (2) paleoshoreline processes and architecture of coeval deep-water deposits (both determined through 3D seismic geomorphology). Statistical analysis of these data reveals the genetic linkages between A/S conditions on the shelf, deltaic hydrodynamic regime and slope-to-basin depositional architecture. Results show that low A/S conditions on the shelf were associated with sediment bypass to the slope, whereas high A/S conditions were linked with increasing sediment storage on the shelf. While fluvial to wave processes can be dominant in all A/S conditions, fluvial-dominated coastlines are mostly associated with steep clinoform slope gradients and more mature turbidite systems. Conversely, wave-dominated shorelines are linked to gentle clinoform slope gradients and no to poor turbidite system development (unchannelized sheet sands and MTDs), leaving a starved slope. These variations are observed both through time and along-strike. High-resolution 3D quantitative seismic stratigraphy constitutes a new step in sequence stratigraphy as (1) it allows interpreters to map sequences in a true 3D environment, hence taking into account the full variability of depositional systems through time and space, and (2) it highlights the significant role of shelf-margin architecture and processes in predicting the deep-water sand delivery behavior.