Controls On Deep-Water Sand Delivery Beyond the Shelf Edge: Accommodation, Sediment Supply, and Deltaic Process Regime

Abstract

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 ∼ 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 (δA/δS) conditions on the shelf are associated with sediment bypass, whereas high δA/δS 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.

Architectural Diversity of Submarine Lobate Deposits

“…Although their proposal is intended to explain morphologically distinct portions within a single lobate deposit, we extrapolate their process-response model and the concept of flow efficiency proposed by Mutti and Normark (1987) to illustrate the relationship between the mud-richness of contributing flows and the relative size and runout distance of lobate deposits (Figure 13). Consistent with this model, the implications of varying mud-richness in fluvial versus littoral drift sediment supply on the size and runout distance of lobate deposits have been documented by Paumard et al (2020). In addition, we propose that mud-poor flows produce poorly channelized lobate deposits whereas mud-rich stratified flows produce lobate deposits with a prominent distributary channel network (Figures 10,11).…”

Clinoforms and clinothems: Fundamental elements of basin infill

“…Po River delta, Trincardi et al, 2019) | 197 EAGE PELLEGRINI Et aL. and 3-4 times shorter than wave-dominated clinothems of similar sandy sediment calibre, with mean gradients of ca 4° and ca 1°, respectively, and mean lengths of 150-230 m and 640-760 m. Similar relationships have been identified in the Early Cretaceous shelf margin of the North West Shelf (Australia) using seismic reflection data (Paumard et al, 2020).…”

“…This topic is further dealt with in the U.S. Western Interior and Spitsbergen outcrops by Plink‐Bjorklund (2019). This author points out that river‐dominated sandstone‐prone clinothems are on average 3–4 times steeper and 3–4 times shorter than wave‐dominated clinothems of similar sandy sediment calibre, with mean gradients of ca 4° and ca 1°, respectively, and mean lengths of 150–230 m and 640–760 m. Similar relationships have been identified in the Early Cretaceous shelf margin of the North West Shelf (Australia) using seismic reflection data (Paumard et al, 2020).…”

Towards a regional high-resolution bathymetry of the North West Shelf of Australia based on Sentinel-2 satellite images, 3D seismic surveys and historical datasets

“…The digital elevation model provides the full picture of modern sedimentary systems, from the source of the sediments (e.g., fluvial and carbonate systems) to their accumulation grounds along the shelf and in the basin. Parts of these modern systems can be used to better understand past sedimentary record (Paumard et al, 2020;Nyberg and Howell, 2016;Ainsworth et al, 2019), the geotechnical properties of marine sediments (Beemer et al, 2019;Beemer et al, 2018;Senders et al, 2013) or the geohazards affecting the area (Lane and Tyler, 2015;Hogan et al, 2017;Scarselli et al, 2019;Hengesh et al, 2013). Therefore, the integration of regional high-resolution bathymetry can constitute a step change and allow researchers to ponder their results with regard to the regional context and hence support the development of more reliable interpretations and models.…”