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Type: Thesis
Title: Aspects of the geology of the Stuart Creek area, north of Lake Torrens, South Australia
Author: Vnuk, M. F.
Issue Date: 1978
School/Discipline: School of Physical Sciences
Abstract: An area to the north of Lake Torrens, encompassing the newly proclaimed Stuart Creek Precious Stones Field, was studied, with particular reference to the opal- bearing Cretaceous sediments. The pre-Mesozoic basement consists of Adelaidean rocks of the Wilpena Group in the east, separated from Lower Cambrian rocks by the Arthur Fault The relatively flat-lying Cretaceous sequence consists of two mappable units. The lower unit, called the "Stuart Creek Beds" in this thesis, is probably a transitional unit marking the transgression of the Lower Cretaceous sea. The early Aptian Marree Formation comprises bioturbated brown montmorillonitic muds with sandy and conglomeratic beds more prominent near the base. Scattered "erratics" occur. The original sediment, deposited in a marginal marine environment was black, pyritic and carbonaceous. It has been affected by a number of weathering events during the Tertiary. The uppermost portion has been very heavily weathered and bleached. Only a thin remnant exists now, due to erosion prior to Tertiary deposition The Tertiary sediments are mostly sands with some clays, silts and limestones. Milky quartz pebbles are a common characteristic. The sediments are non-marine, dominantly fluviatile. Silicification is common but variable. The sequence is correlated with the Mount Sarah Sandstone of Miocene age. Opal, occurring throughout the area, is believed to have formed associated with silicification of the Tertiary. The precious opal is notable in that it occurs within relatively fresh sediments, rather than highly weathered rocks as elsewhere in South Australia. Precious opal is only found on the Field, but all the Cretaceous must be considered potentially opal-bearing until further work is done.
Dissertation Note: Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 1978
Where: Eromanga Basin, northern South Australia
Keywords: Honours; Geology; Cretaceous sediments; Tertiary sediments; weathering; silicification; depositional environments; precious opal
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