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Geochemical comparisons between asphaltites on the southern Australian margin and source rock analogues of Early Cretaceous age

Created 30/03/2026

Updated 30/03/2026

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Evidence for a mid-Cretaceous source for southern Australian asphaltites is presented, based on geochemical and carbon isotopic comparisons of the asphaltites with onshore source rock analogues from the Albian-Cenomanian Blue Whale Superseguence in the Bight Basin and marine oil shales from the Albian Toolebuc Formation of the Eromanga Basin. The striking similarity between the asphaltites and the Toolebuc organic matter extends across diverse geochemical signatures; from the carbon isotopes being relatively depleted in 13C compared to Anstralian oils through to the similar distribution of age-diagnostic C3o methylsteranes and C26 norsteranes. An unusual feature of the asphaltites compared to all other Australian oils, bnt shared by the Toolebnc Formation, is the presence of metalloporphyrins. These biomarkers typically indicate a relatively deep-water environment with anoxic bottom waters at the time of sonrce rock deposition. In contrast, the dominantly marine organic matter in the sample from Eyre-1 shows a pronounced ten?estrial plant input consistent with a shallow marine depositional environment. This is snpported by the well location near the depositional edge of the Blue Whale Superseguence. Fnrthermore, comparison of the organic matter generated from the artificial pyrolysis of the polar fractions from the asphaltite and the Toolebuc bitumen supports their strong genetic link. Although the mid-Cretaceous is the most likely source for the asphaltites in the sonthern margin, the presence of a similar marine organic facies in the Late Cretaceous Tiger Superseguence cannot be excluded. Obviously, fnrther work on local and global analogues, as well as exploration success in the Great Australian Bight, would help to refine the source rock age and location for the asphaltites.

Article prepared for the Eastern Australian Basins Symposium in 2001.

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Field Value
Title Geochemical comparisons between asphaltites on the southern Australian margin and source rock analogues of Early Cretaceous age
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/4aceeb65-f49b-4a48-a44d-3a7071ab6fcf
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 26/03/2026
Geospatial Coverage Australia
Data Portal Geoscience Australia

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This dataset was originally found on Geoscience Australia "Geochemical comparisons between asphaltites on the southern Australian margin and source rock analogues of Early Cretaceous age". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/geochemical-comparisons-between-asphaltites-on-the-southern-australian-margin-and-source-rock-a1