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Evidence of Proterozoic primary CaC03 precipitation from the McArthur Group of northern Australia


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Winefield, PR and McGoldrick, PJ 1998 , 'Evidence of Proterozoic primary CaC03 precipitation from the McArthur Group of northern Australia ', paper presented at the Proceedings of the 9th International Symposium on Water-Rock Interaction, 30 March - 3 April 1998, Taupo, New Zealand.

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ABSTRACT: Radiating fans of acicular 'Coxco needles' are the characteristic feature of the Coxco Dolomite
Member , a subunit of the Teena Dolomite within the Palaeoproterozoic McArthur Group. In the
past, 'Coxco needles' have been variably interpreted as dolomitic pseudomorphs after aragonite, gypsum or
trona. More recently, gypsum and an emergent brine pool depositional setting has been the favoured
interpretation. New work reported here has found that crystal morphology, geochemistry, petrographical and
sedimentological relationships are more consistent with a subaqueously deposited aragonitic precursor. The
widespread occurrence of 'Coxco needles' at a confined stratigraphic interval is thought to be a function of a
subtle change in the HC03 concentration within the water body during deposition of the Teena Dolomite.
Although elevated atmospheric CO2 during the Proterozoic supports increased carbonate precipitation (including
aragonitic fans), it can not satisfactorily explain the apparently synchronous precipitation of Coxco fans.
Therefore, changes in the bathymetry of the McArthur Basin coincident with deposition of a broadly
transgressive sequence is inferred to have triggered the widespread chronostratigraphic precipitation of
carbonate (i.e aragonite tans) within a variety of lithofacies.

Item Type: Conference or Workshop Item (Paper)
Authors/Creators:Winefield, PR and McGoldrick, PJ
Additional Information:

Conference as a result of authors research for PhD thesis. Thesis
title - Sedimentology and diagenesis of late palaeoproterozoic carbonates, Southern McArthur Basin, northern Australia. PhD thesis, University of Tasmania. Held at

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