Roger Hocking

Vines 1 revisited: are older Neoproterozoic glacial deposits preserved in Western Australia?

The stratigraphy in Vines 1, a 2017.5 m-deep cored stratigraphic hole drilled by the Geological Survey of Western Australia in 2001 near the Western Australian – South Australian border, has been reinterpreted with implications for the Neoproterozoic to Cambrian geological history of the Officer Basin. A previous interpretation considered the intersected succession as a conformable stratigraphic package, the Vines Formation. An assemblage of palynomorphs, found throughout the hole and previously used to infer an age of no older than earliest Cambrian, is now thought to consist of contaminants. An older assemblage, which is considered to be reworked and inherited from underlying rocks, provides a new maximum age constraint of mid-Neoproterozoic. Based on sedimentological interpretations and comparisons with other drillholes in the western Officer Basin, and the succession in the eastern Officer Basin, the Vines 1 succession is reinterpreted as four discrete sedimentary packages, the Pirrilyungka (new name), Wahlgu, Lungkarta and Vines (redefined) Formations, in ascending order. The Pirrilyungka and Wahlgu Formations include glacigenic sediments and may correlate with similar glacial successions in Supersequences 2 and 3 (mid to late Cryogenian) of the Centralian Superbasin, and the Sturt Tillite and Elatina Formation and their equivalents in the Adelaide Rift Complex of South Australia, respectively. The eolian Lungkarta Formation and fluvial Vines Formation are considered, on regional evidence, to be most likely of Ediacaran to earliest Cambrian age.

The answers are blowin' in the wind: Ultra-distal ashfall zircons, indicators of Cretaceous super-eruptions in eastern Gondwana

An Early Cretaceous siliceous large igneous province (SLIP) that developed on the eastern margin of Gondwana produced some of the most voluminous siliceous volcaniclastic deposits known globally. We report U-Pb ages and trace-element and Hf-isotopic signatures of detrital zircons from the Madura Shelf (onshore Bight Basin), Western Australia. These zircons include a geochemically distinct 106 Ma component with age and Hf characteristics that match SLIP volcanics some 2300 km distant in eastern Australia. This young subpopulation shows limited grain abrasion, which contrasts with older detrital components that are stratigraphically persistent. Regional detrital zircon provenance demonstrates that sediment routing systems were disconnected in the eastern and western Bight Basin, negating terrestrial transport mechanisms as a possible vector of the zircons from the SLIP to their recovered position. Palynology indicates that the 106 Ma zircons are syn-depositional, and we interpret them as being significantly transported in an eruption plume. Given the grain size and distance from source, such distal zircon emplacement suggests previously undocumented 106 Ma super-eruptions. The 106 Ma zircons likely reflect Southern Hemisphere winter eruptions when tropospheric polar easterly winds would have been favored across southeastern Australia.

Novel paleoecology of a postextinction reef: Famennian (Late Devonian) of the Canning basin, northwestern Australia: Comment and Reply

[Rachel Wood (2000)][1] discussed changes in the Devonian reef- building biota across the Frasnian-Famennian (F-F) boundary in the Canning basin. This boundary coincides with a major mass extinction of metazoans, yet Wood concluded that the Famennian reef-building community shows “no noteworthy

Keene Basalt, northwest Officer Basin, Western Australia: tectonostratigraphic setting and implications for possible submarine mineralisation

GSWA Lancer 1, drilled in the northwest Officer Basin, intersected 49 m of tholeiitic basalt lava flows between depths of 527 and 576 m. These lavas have been named the Keene Basalt and were erupted during deposition of the shallow-marine Kanpa Formation, a mixed carbonate – siliciclastic succession in the Neoproterozoic Buldya Group. No direct dating of the Keene Basalt has been undertaken. Maximum depositional age constraints for the enclosing Kanpa Formation are provided by youngest concordant detrital zircon ages of 779±6 Ma for sandstone 19 m below the basalt, and 725±11 Ma for sandstone at the top of the Kanpa Formation in another drillhole. Correlation of the Kanpa Formation with the Burra Group of the Adelaide Rift Complex on palaeontological and chemostratigraphic grounds suggests an age older than 700 Ma. Limited geochemical data indicate that the Keene Basalt is of continental origin and shows a close similarity to mafic dykes near Mingary in South Australia. Petrographic and XRD analyses show that the Keene Basalt has been hydrothermally altered by interaction with seawater, and locally contains disseminated sulfides. Massive and disseminated sulfide mineralisation, similar to that of submarine systems, may exist in this tectonostratigraphic setting in the northwest Officer Basin.

Excursions along the Lennard Shelf Devonian carbonates, Canning Basin, Western Australia

ABSTRACT The world-class Middle–Upper Devonian carbonate outcrops of the Lennard Shelf, Canning Basin, Western Australia, offer a unique opportunity to examine reefal carbonate shelf-to-basin evolution in response to multiple coeval extrinsic and intrinsic drivers. Variable styles of carbonate stratigraphic architecture and heterogeneity developed as a function of the interplay between long hierarchical accommodation trends, global biological crises, greenhouse-to-transitional climatic changes, and syndepositional tectonics. The linkage of reservoir-scale, shelf-to-basin carbonate expression to regional, seismic-scale architectures made possible by these pristine exposures allows the generation of conceptual models and predictive relationships that are relevant to steep-sided carbonate hydrocarbon reservoirs and plays. Furthermore, exquisite exposure of syndepositional fracture systems and their association with carbonate facies and position along the depositional profile provide templates for characterization of subsurface nonmatrix flow. In particular, the Lennard Shelf outcrops are excellent analogs for the age-equivalent Canadian Alberta Basin and Carboniferous reservoirs of the Pricaspian Basin in Kazakhstan; however, the breadth of insight contained within the Lennard Shelf outcrop belt is applicable to the greater understanding of reefal carbonate systems in general.