4.4 Article

CONTROLS ON DEEP-WATER SAND DELIVERY BEYOND THE SHELF EDGE: ACCOMMODATION, SEDIMENT SUPPLY, AND DELTAIC PROCESS REGIME

Journal

JOURNAL OF SEDIMENTARY RESEARCH
Volume 90, Issue 1, Pages 104-130

Publisher

SEPM-SOC SEDIMENTARY GEOLOGY
DOI: 10.2110/jsr.2020.2

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Funding

  1. Chevron Australia Pty. Ltd.
  2. University of Western Australia
  3. Centre for Energy Geoscience, School of Earth Sciences
  4. American Association of Petroleum Geologists (AAPG)
  5. Australian Society of Exploration Geophysicists (ASEG) Research Foundation
  6. BHP
  7. Chevron
  8. ConocoPhillips
  9. Oil Search
  10. Santos
  11. Shell
  12. TGS
  13. Woodside

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Stratigraphic models typically predict accumulation of deep-water sands where coeval shelf-edge deltas are developed in reduced-accommodation and/or high-sediment-supply settings. On seismic data, these relationships are commonly investigated on a small number of clinothems, with a limited control on their lateral variability. Advanced full-volume seismic interpretation methods now offer the opportunity to identify high-order (i.e., 4th to 5th) seismic sequences (i.e., clinothems) and to evaluate the controls on shelf-to-basin sediment transfer mechanisms and deep-water sand accumulation at these high-frequency scales. This study focuses on the Lower Barrow Group (LBG), a shelf margin that prograded in the Northern Carnarvon Basin (North West Shelf, Australia) during the Early Cretaceous. Thanks to high-resolution 3D seismic data, 30 clinothems (average time span of similar to 47,000 years) from the D. lobispinosum interval (142.3-140.9 Ma) are used to establish quantitative and statistical relationships between the shelf-margin architecture, paleoshoreline processes, and deep-water system types (i.e., quantitative 3D seismic stratigraphy). The results confirm that low values of rate of accommodation/rate of sediment supply (delta A/delta S) conditions on the shelf are associated with sediment bypass, whereas high delta A/delta S conditions are linked to increasing sediment storage on the shelf. However, coastal process regimes at the shelf edge play a more important role in the behavior of deep-water sand delivery. Fluvial-dominated coastlines are typically associated with steep slope gradients and more mature, longer run-out turbidite systems. In contrast, wave-dominated shorelines are linked to gentle slope gradients, with limited development of turbidite systems (except rare sheet sands and mass-transport deposits), where longshore drift currents contributed to shelf-margin accretion through the formation of extensive strandplains. In this context, reduced volumes of sand were transported offshore and mud belts were accumulated locally. This study highlights that variations from fluvial- to wave-dominated systems can result in significant lateral changes in shelf-margin architecture (i.e., slope gradient) and impact the coeval development of deep-water systems (i.e., architectural maturity). By integrating advanced tools in seismic interpretation, quantitative 3D seismic stratigraphy represents a novel approach in assessing at high resolution the controls on deep-water sand delivery, and potentially predicting the type and location of reservoirs in deep water based on the shelf-margin architecture and depositional process regime.

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