Authors / CoAuthors
Krassay, A.A.
Abstract
Outcrop and core gamma-ray logs have been successfully used to correlate Proterozoic units in northern Australia. This paper highlights the benefits of integrating gamma-ray data and traditional sedimentology for defining large-scale depositional cycles and depositional geometry. Gamma-ray logs of outcrop and cored intervals provide excellent stratigraphic and sedimentological information for areas where conventional down-hole geophysical surveys are lacking. Both total count (scintillometer) gamma-ray profiles and spectral gamma-ray profiles enable recognition of subtle changes in lithology and sedimentary cyclicity that might have been missed during customary section measuring. Lithofacies described from measured sections and core may be characterised by their gamma-ray signatures, and the signatures may then be used as proxies for down-hole gamma-ray logs obtained from the subsurface where direct lithological information is sparse or absent. The integration of traditional lithostratigraphic descriptions with surface and subsurface gamma-ray logs results in a more robust and sophisticated stratigraphic framework than either data set can yield independently. Use of sequence stratigraphic principles enables gamma-ray log trends and their stacking patterns to be interpreted as part of larger sedimentary cycles that reflect changes in sediment supply and relative sea level. Abrupt shifts in gamma-ray values occur at important stratigraphic surfaces that define sedimentary sequences of various scales. Systematic variations in sedimentary thickness and gamma- ray stacking patterns between areas are related to changes in depositional geometry of sequences. Regional mapping of stratigraphic surfaces and sequences by the correlation of vertical gamma-ray profiles and corresponding descriptive logs allows a predictive chronostratigraphic framework to be constructed for a region.
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document
eCat Id
81548
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Keywords
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- GA PublicationJournal
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1998-01-01T00:00:00
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geoscientificInformation
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AGSO Journal of Australian Geology and Geophysics 17:4:285-299
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