Linking Shallow-Marine Process Regime and Slope/Basin Architecture Within the Barrow Group (Northern Carnarvon Basin, Australia): Insights From Quantitative 3-D Seismic Geomorphology

Abstract

The hydrocarbon-bearing Barrow Group constitutes a unique example of a large regressive system developed during a syn-rift to post-rift transition in the Northern Carnarvon Basin, from the latest Tithonian to the Valanginian. It has proven reservoir potential in shallow-marine, slope and basin-floor deposits. This study applies a quantitative seismic geomorphologic analysis of the paleo-coastlines of the Barrow Group where very good quality 3D seismic imaging is available and calibrated by well log and core data. The methodology is based on the application of the WAVE process-based classification, which classifies coastal settings and the depositional elements building them according to the relative proportion of fluvial (F), wave (W) and tidal (T) processes. This workflow is applied to key intervals of the Barrow Group which was deposited under varying accommodation / sediment supply (A/S) ratios. Full volume interpretation of 3D seismic has been used to compute key seismic attributes along regional high-resolution horizon stacks. The key geomorphological features (mapped as geobodies) are assigned to F, W, or T dominant, secondary and tertiary processes. Quantitative analysis of the surface distribution of each depositional elements allows process-classifying individual paleo-coastlines. In the Barrow Group, this approach highlights variations in A/S ratio that were accompanied by different shoreline trajectories and variations in process regime along the paleoshorelines. High-angle clinoforms in low A/S conditions are associated with fluvial (F) or fluvial/tidal (Ft) dominated shorelines which feed extensive turbidite ramp systems. In contrast, low-angle clinoforms in high A/S conditions are associated with wave dominated shorelines (W/Wt) where longshore drift led to accretion of km-scale beach ridges and sand spits. These paleoshorelines were linked to sheet-like turbidites, interpreted from wide areas of higher amplitudes within the slope, and isolated, single channel-fed, lobes. Results show that the balance between subsidence and sediment supply (and resulting shelf margin architecture) is strongly linked with the hydrodynamic processes at the paleoshorelines, which in turn results in important along-margin variations in paralic reservoir architecture and turbidite system development. These variations occur in both time (changes in A/S ratio in individual depocentres) and space (e.g. local changes in A/S ratio along a single paleoshoreline).

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017