Authors / CoAuthors
Tingate, P.R. | Lindsay, J.F. | Marshallsea, S.J.
Abstract
Gosses Bluff, a prominent complex annular structure in central Australia, was produced by hypervelocity impact during the Late Jurassic. The impact occurred in the thick sedimentary succession close to the centre of a major sub-basin within the Amadeus Basin. The structure is well exposed and has good subsurface control as a consequence of earlier unsuccessful hydrocarbon exploration programs. It provides an opportunity to study the effects of impact on a sedimentary succession without basement involvement, and to evaluate the potential of such structures as hydrocarbon plays. Seismic data across the structure show that the original crater was 24 km in diameter, suggesting that originally a major ejecta blanket extended for at least 60 km beyond the rim. The underlying Neoproterozoic and Palaeozoic sedimentary rocks of the Amadeus Basin have been deformed to depths of several kilometres. Uplift at the centre of the Gosses Bluff structure is especially pronounced owing to rebound of the primary shock wave from the upper surface of the evaporites of the Bitter Springs Formation. The thermal effects of impact on outcrop and core samples have been studied from apatite fission-track analysis (AFTA). Samples from the crater floor and remnant crater fill indicate that no significant fission-track annealing has occurred in response to the impact. All samples preserve tracks that were formed before the impact (~140 Ma) and are consistent with the regional thermal history. AFTA data from central uplift samples indicate that the main thermal effect of impact was not heating, but cooling related to exhumation. Results have shown that, whereas shock-related fracturing enhanced porosity and permeability of underlying reservoir units to some extent, quartz cementation associated with impact reduced overall reservoir quality. The only potential hydrocarbon play, as yet untested, is the rim anticline formed beneath the crater rim as a response to post-impact salt migration. Ultimately, the major factor that limits the petroleum potential of the Gosses Bluff structure is the timing of events. The impact occurred too late in basin evolution for an effective seal to be deposited over the structure. Further, the structure formed at about 140 Ma, whereas petroleum was probably generated before 200 Ma. Thus, any hydrocarbons trapped in the structure probably represent migration from pre-impact accumulations. In spite of the limited petroleum potential at Gosses Bluff, it does provide an important analogue for buried impact structures with more favourable thermal histories.
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document
eCat Id
81460
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- GA PublicationJournal
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- NT
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1996-01-01T00:00:00
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geoscientificInformation
Series Information
AGSO Journal of Australian Geology and Geophysics 16:4:529-552
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Extents
[-24.45, -23.3, 131.3, 134.2]
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