Tegan Smith

Calibrating the middle and late Permian palynostratigraphy of Australia to the geologic time-scale via U–Pb zircon CA-IDTIMS dating

ABSTRACT The advent of chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) has revolutionised U–Pb dating of zircon, and the enhanced precision of eruption ages determined on volcanic layers within basin successions permits an improved calibration of biostratigraphic schemes to the numerical time-scale. The Guadalupian and Lopingian (Permian) successions in the Sydney, Gunnedah, Bowen and Canning basins are mostly non-marine and include numerous airfall tuff units, many of which contain zircon. The eastern Australian palynostratigraphic scheme provides the basis for much of the local correlation, but the present calibration of this scheme against the numerical time-scale depends on a correlation to Western Australia, using rare ammonoids and conodonts in that succession to link to the standard global marine biostratigraphic scheme. High-precision U–Pb zircon dating of tuff layers via CA-IDTIMS allows this tenuous correlation to be circumvented—the resulting direct calibration of the palynostratigraphy to the numerical time-scale highlights significant inaccuracies in the previous indirect correlation. The new data show: the top of the Praecolpatites sinuosus Zone (APP3.2) lies in the early Roadian, not the middle Kungurian; the top of the Microbaculispora villosa Zone (APP3.3) lies in the middle Roadian, not the early Roadian; the top of the Dulhuntyispora granulata Zone (APP4.1) lies in the Wordian, not in the latest Roadian; the top of the Didecitriletes ericianus Zone (APP4.2) lies in the first half of the Wuchiapingian, not the latest Wordian; the Dulhuntyispora dulhuntyi Zone (APP4.3) is exceptionally short and lies within the Wuchiapingian, not the early Capitanian; and the top of the Dulhuntyispora parvithola Zone (APP5) lies at or near the Permo-Triassic boundary, not in the latest Wuchiapingian.

Sponge biodiversity and ecology of the Van Diemen Rise and eastern Joseph Bonaparte Gulf, northern Australia

Australia is increasingly recognised as a global hotspot for sponge biodiversity, but there is a knowledge gap about sponge communities in northern Australia, including those in Commonwealth Marine Reserves. We aim to quantify sponge biodiversity of the eastern Joseph Bonaparte Gulf and adjacent Van Diemen Rise (VDR) and to examine spatial and environmental patterns in community structure. Sponges were collected with a benthic sled from 65 sites encompassing five geomorphic features (bank, terrace, ridge, plain, and valley), study area (as a proxy for distance offshore) and three environmental variables (depth, substrate hardness, and slope). A total of 283 species were collected, representing four classes, 53 families and at least 117 genera. Sponge richness and biomass were related to those of other taxa. Sponge diversity was generally highest further offshore and on raised geomorphic features, particularly banks. Sponge assemblages on the same bank were more similar than those from different banks, although full interpretation of patterns is limited by the relatively low sampling effort. The current study will help facilitate integrated marine management by providing a baseline species inventory, supporting the VDR’s carbonate banks as a key ecological feature, and highlighting the importance of sponges as habitat providers and potential biological surrogates for monitoring.

Recalibrating Australian Triassic Palynostratigraphy to the International Geologic Timescale Using High Resolution CA-IDTIMS Dating

The Triassic is an important interval for Australian petroleum exploration, with Middle to Upper Triassic Mungaroo Formation reservoirs in the Northern Carnarvon Basin, and recent Lower Triassic discoveries in the Roebuck Basin. The chronostratigraphic understanding of Triassic petroleum systems is underpinned by biostratigraphic dating using palynological zonations. The numerical ages of these zones are usually assigned through inference and interpolation, often via tenuous correlations to the international geologic timescale using scattered marine biota, (primarily foraminifera, and rare ammonites, conodonts and/or dinoflagellates). In contrast, we tie Australian biozones to the timescale through Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) dating of interbedded volcanic tuffs. Such ashfalls are reasonably common in Australian basins, and can provide high-precision CA-IDTIMS ages if they contain magmatic zircons. We recently recalibrated Australian middle and late Permian palynozones using this approach and preliminary results suggest that Triassic biozone ages are likewise in need of considerable revision. We have targeted Triassic tuffs across Queensland, (Tarong beds, Brisbane Tuff, Moolayember Formation, Rewan Group), New South Wales (Garie Formation, Coal Cliff Sandstone, Milligan Road Formation), and Tasmania (upper Triassic coal measures) to provide numerical ages for palynozones. Additional dates in New Zealand (Murihiku Supergroup) and Timor-Leste (Wailuli Formation) will allow international correlation of dinocyst and spore-pollen zones. Numerical constraints for Triassic biozone boundaries facilitate correlation of Australian biozones with the international geologic timescale. This can impact burial history models used in petroleum exploration anywhere these biozones are used, often far beyond the basins from which the samples were collected.

The 2017 offshore acreage release areas: petroleum geological overview

In 2017, 21 new offshore petroleum exploration areas have been released. The majority of the areas are located along the North West Shelf spanning the Westralian Superbasin from the Bonaparte Basin in the north-east to the Northern Carnarvon Basin in the south-west. New areas have been released in offshore south-eastern Australia with new opportunities provided in the Otway, Bass and Gippsland basins. Two large areas in the northern Perth Basin, an offshore frontier, complete the 2017 Acreage Release. All Release Areas are supported by industry nominations and one new cash bid area has been offered in the Dampier Sub-basin. Geoscience Australia continues to support industry activities by acquiring, interpreting and integrating pre-competitive datasets that are made freely available as part of the agency’s regional petroleum geological studies. A new regional 2D seismic survey was acquired in the Houtman Sub-basin of the Perth Basin, forming the basis of the latest prospectivity study carried out by Geoscience Australia. The results of the study are presented in the technical program of the 2017 APPEA conference. A wealth of seismic and well data, submitted under the Offshore Petroleum and Greenhouse Gas Storage Act 2006 (OPGSSA) are made available through the National Offshore Petroleum Information Management System (NOPIMS). Additional datasets are accessible through Geoscience Australia’s data repository.