Shelf-Margin Architecture and Shoreline Processes at the Shelf-Edge With Controls on Sediment Partitioning and Deep-Water Deposition Style: Insights From 3-D Quantitative Seismic Stratigraphy

Abstract

The Lower Barrow Group (LBG; Latest Tithonian – Early Valanginian) is a shelf-margin that prograded during a late phase of rifting under various subsidence regimes and supply-dominated conditions. A 3D full-volume, semi-automatic seismic interpretation method allows identifying 73 clinothems in which a quantitative analysis of the shelf-margin architecture and processes was conducted.

While fluvial to wave processes can be dominant in all A/S conditions, fluvial-dominated coastlines are associated with high-angle slope clinoforms and short to longer run-out turbidites. Conversely, wave-dominated coastlines are linked to low-angle slope clinoforms and poor turbidite system development (occasional sheet sands and MTDs).

Short and longer run-out turbidite systems present a tripartite architecture (canyon / slope valley; channel; lobes) which mostly appear as short-lived, vertically / laterally stacked elements fed my multiple small rivers forming linear ramp systems. Due to the shallow configuration of the margin (<500 m), the presence of short slopes and overall high sand-to-mud ratio, the turbidite systems are smaller scale (<50 km) and probably shorter lived than most modern turbidite systems (100-1000 km).

Combination of high sediment supply and greenhouse climate during the LBG deposition favored conditions where the shoreline is located at or close to the shelf-edge, allowing an important and stable sediment delivery to deep-water areas (as opposed to icehouse systems where high amplitude eustasy results in sediment storage on the shelf and prolonged periods of basin starvation). We interpret the LBG as a supply-dominated and accommodation-influenced system where sediments are delivered to the shelf-edge by high sediment flux. The presence of fluvial processes at the coastlines is the main driver on the deep-water sand delivery.

This study sheds new lights on the significant role of shelf-margin architecture and processes in predicting the deep-water sediment delivery behavior. This analysis unveiled the high resolution changes in sediment supply and accommodation in time and space in the LBG, and provided new insights on the distribution of shallow and deep marine plays in the basin. The full-volume interpretation workflow constitutes a new step in sequence stratigraphy as it allows interpreters to map sequences in a true 3D environment hence taking into account the full variability of depositional systems in time and space.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018