Quantification of uplift in the Carnarvon Basin based on interval velocities

Abstract

Sonic velocities in the Toolonga Calcilutite (Upper Cretaceous), the Gearle Siltstone and Haycock Marl (mid-Cretaceous), and the Muderong Shale (Lower Cretaceous) were each used to independently quantify apparent uplift (height above maximum burial depth) in the Carnarvon Basin. Apparent uplift is given by the difference in depth between the present-day velocity–depth trend for a unit in a particular well and the reference trend (unaffected by uplift) of the unit. Apparent uplift results derived from the Toolonga Calcilutite, Gearle Siltstone and Muderong Shale are statistically similar. The consistency of results from carbonate and clastic units suggests that, at the formation and regional scale, overcompaction (i.e. anomalously high interval velocity) in these three units reflects previously greater burial depth, rather than sedimentological and/or diagenetic processes, and validates the use of lithologies other than shale in maximum burial-depth studies. The proposed magnitudes of apparent uplift are greatest along some of the main structural highs of the Carnarvon Basin. Apparent uplift of approximately 800 m was determined along the Legendre Trend, and along the Barrow Arch. In excess of 900 m of apparent uplift was determined on the Bambra Anticline. The consistency of results from units of Early to Late Cretaceous age suggests that uplift must have post-dated the youngest (Late Cretaceous) unit analysed.