TIMING OF SOURCE ROCK DEPOSITION IN THE GEORGINA BASIN, AUSTRALIA
Naomi Miles, Dept. of Earth and Atmospheric Sciences, University of Alberta
Robert A. Creaser, Dept. of Earth and Atmospheric Sciences, University of Alberta
Chris Boreham, Basin Resources Group, Energy Division, Geoscience Australia
The Georgina Basin is a prospective unconventional oil and gas bearing sedimentary basin in
Australia. The basin had active sedimentation from the Neoproterozoic to Devonian as characterized by
the Central Australian Trilobite Zonation (CATZ). There is limited absolute dating in this basin, or the
surrounding basins. Additionally, there are time gaps in the CATZ. Sedimentary rocks are notoriously
difficult to apply radiometric dating techniques to because the typical mineralogy lacks datable material.
Typically, CATZ biostratigraphy is based on the appearance of characteristic trilobites that can be
correlated globally. In fine-grained sediments and particularly, organic-rich fine-grained sediments, the
depositional environment is anoxic and biodiversity is extremely low, if any fossils are preserved at all.
Many of the major global index fossils cannot survive in these types of environments and another method
of dating these sedimentary rocks is required. This project uses the Re-Os geochronometer to analyze two
organic-rich shales, the Arthur Creek and Hay River Formations (500-508 Ma and 510 Ma respectively),
and expulsed hydrocarbons from these shales in the Georgina Basin.
There are a number of factors that affect the temporal relationships in this basin. Two major
structural features, the Toko Syncline and the Dulcie Syncline, affect the continuity of the Arthur Creek
and the Hay River Formations. Additionally, there is an unconformity between these two formations. We
have used the 187Re - 187Os system to absolute date the both formations in the West Toko Syncline, which
indicates an age younger than the biostratigraphic constaints by ~30 m.y. Isochrons for the Arthur Creek
Formation in the Toko Syncline and the Dulcie Syncline also indicate a younger age, but uncertainty
remains high. Younger ages may signify variable sedimentation rates across the basin. Previous miscorrelations across the basin have been identified, and this data suggests that further re-evaluation of
biostratigraphy is required. We have used XRD, XRF and ICPMS data to look at variations in sediment
type to help understand some of the complexities affecting deposition and radiometric ages.