Stratigraphy, Age and Provenance of Madura Shelf Sediments, WA: Implications for the Evolution of the Bight Basin and Australia's Southern Margin

Abstract

The expansive Cenozoic carbonates of the Nullarbor Plain veneer older sediments that preserve an important record of Australia's rifting from Antarctica, and development of the present-day southern passive margin. Importantly, the sediments of the onshore extension of the Bight Basin (Madura Shelf) are far more accessible than those of contemporaneous offshore sub-basins within the Bight, but remain poorly studied despite their relevance to understanding this frontier petroleum province. Stratigraphic logging of newly available boreholes drilled within the WA portion of the Madura Shelf has been combined with pre-existing well-data to enhance 3D stratigraphic modelling within a GIS database. New stratigraphic units have been identified underlying the Mesozoic sequence of the Madura Shelf, which testify to pre-existing depocentres along the southern margin of Australia that may have influenced its later development. Through palynology, it has been possible to resolve the relative timing and environment of deposition of lithostratigraphical units across the Madura Shelf. Localised anomalies in the development of the Madura Shale suggest movement occurred during the Cretaceous along faults that may be correlated into 2D seismic lines offshore. However, by the end of the Cretaceous, the Madura Shale had blanketed all significant pre-existing topography, with the preserved surface showing little evidence for any later disturbance. In-fact, enigmatically, neither the Madura Shale itself, nor its upper surface, evidence the extended periods of time they represent, with little variability/cyclicity or indicators of erosion preserved. Analysis of detrital zircon age-populations recovered from the major stratigraphic units encountered beneath the Eucla Basin, and comparison with sediments from Cenozoic shorelines and the Cretaceous Ceduna Delta indicate: (i) Dominance of Musgrave Province- or Albany-Fraser-sourced sediment. (ii) That these sediment pathways were long-lived. (iii) That a partitioning/disconnection existed between the sediment systems operating in the eastern and western Bight Basin, with little to no sediment from the east being supplied to the west. (iv) That essentially syn-depositional mid-Cretaceous volcanism occurred in the western Bight Basin. This previously unrecognized Cretaceous western volcanic activity may provide important age constraints and correlation opportunities, as well as having implications for the thermal history of the margin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015