Re-evaluation of the Mentelle Basin, a polyphase rifted margin basin, offshore southwest Australia: new insights from integrated regional seismic datasets

Abstract

Abstract.Vintage 2-D (two-dimensional) seismic reflection surveys from the sparsely explored Mentelle Basin (western Australian margin) have been reprocessed and integrated with a recent high-quality 2-D seismic survey and stratigraphic borehole data. Interpretation of these data sets allows the internal geometry of the Mentelle Basin fill and depositional history to be reanalysed and new insights into its formation revealed. Basin stratigraphy can be subdivided into several seismically defined megasequences separated by major unconformities related to both breakup between IndiaMadagascar and Australia-Antarctica in the ValanginianLate Hauterivian and tectonically-driven switches in deposition through the Albian.Resting on the Valanginian-Late Hauterivian breakup unconformity are several kilometre-scale mounded structures that formed during Late Jurassic to Early Cretaceous extension. These have previously been interpreted as volcanic edifices although direct evidence of volcanic feeder systems is lacking. An alternative interpretation is that these features may be carbonate build-ups. The latter interpretation carries significant climatic ramifications since carbonate build-ups would have formed at high palaeolatitude, ∼60 • S.Soon after breakup, initial subsidence resulted in a shallow marine environment and deposition of Barremian-Aptian silty-sandy mudstones. As subsidence continued, thick successions of Albian ferruginous black clays were deposited. Internally, seismic megasequences composed of successions of black clays show previously unresolved unconformities, onlapping and downlapping packages, which reflect a com-

Volume 369: Australia Cretaceous Climate and Tectonics

“…The Mentelle Basin is part of a sequence of basins along the western margin of Australia that formed during the breakup with India and separates the Naturaliste Plateau from Australia (Bradshaw et al, 2003). The basin is the southernmost in a series of en echelon basins from a rifting episode that initiated in northwestern Australia in what is now the Argo Abyssal Plain and southward (Maloney et al, 2011) and is separated from the Perth Basin by the basement high of the Leeuwin Block and the Yallingup Shelf ( Figure F2). Despite its water depth (2000-4000 m), the basement under the Mentelle Basin is believed to be continental and to contain Jurassic and possibly older sediments that were deposited in extensional basins.…”

“…Deep Sea Drilling Project (DSDP) Site 258 previously drilled this postrift section on the western margin of the Mentelle Basin but stopped short of the interpreted basalt horizon. Seismic data acquired in 2004 and 2009 by Geoscience Australia (tied to Site 258) provided a regional survey to appraise the stratigraphic, structural, and depositional history of the Mentelle Basin (Maloney et al, 2011;Borissova et al, 2010). Relatively young Neogene carbonate oozes unconformably overlie Paleogene deep marine chalk.…”

Uncertainty analysis of depth predictions from seismic reflection data using Bayesian statistics

“…The stratigraphic features of the MB are not delineated as this area is sparsely drilled. Nevertheless, the results of the borehole site (DSDP 258) in conjunction with newly processed and reprocessed seismic data from GA S280 and S310 surveys, Shell Petrel Development Survey and Geoscience Australia Continental Margins Surveys 18 [Sargent et al, 2011], allowed the division of the stratigraphy of MB into seismically derived tectonostratigraphic megasequences [Maloney et al, 2011].…”

“…4b, 4d). Note, however, that the presence of basalts at around 4.5 seconds TWT [Maloney et al, 2011] attenuates the high frequency content of the seismic energy [Maresh et al, 2006] resulting in a poor reflectivity in the sub-basalt region.…”

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“…The site was expected to sample a series of Cenozoic and possibly Late Cretaceous sedimentary drifts and erosional features that would enable greater insight into the early and later phases of the opening of the Tasman Gateway and restriction of the Indonesian oceanic gateway. The current seabed is composed of Paleogene/Neogene/Quaternary oozes that sit unconformably on the Cretaceous (Maloney et al, 2011).…”