Legacy product - no abstract available

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These documents have been scanned by the GA Library. Please refer to the document for contents.

Legacy product - no abstract available

Legacy product - no abstract available

Legacy product - no abstract available

A reconnaissance survey of the eastern half of the Canberra 4-mile sheet was made during the period January - February 1952. The area mapped may be arbitrarily divided into two sections: the western section includes the eastern halves of the Canberra, Michelago, and Bredbo 1-mile sheets, and the eastern section comprises four 1-mile sheets - Lake Bathurst, Braidwood, Araluen and Bendethera. Belts of strongly folded Ordovician, Silurian and Devonian strata, with associated elongate masses of granite rocks, were encountered; they trend gradually northwards. Graptolites collected from Ordovician strata provide means to date these rocks accurately, and further study of the corals collected from Silurian limestones will similarly permit precise dating. Three fossil localities were found in the Devonian strata, but the brachiopods collected, although well-preserved and representative of many genera, do not permit precise stratigraphical placing without more intensive examination. Outcrops are generally very good in all parts except the Lake Bathurst area, where an extensive cover of Tertiary and later deposits obscures the Palaeozoic rocks.

The London Bridge Limestone has been traced along its strike from a point five miles south-south-east of Queanbeyan to a point three miles south-east of Bredbo, a distance of forty miles. At London Bridge this formation attains its greatest development and a large-scale geological map of this area has been prepared. Fossil collections have been made from localities along this formation and the fauna has been examined. A description of the coral Pycnostylus ? sp. nov. is given. The stratigraphical position of this formation has been placed within the Wenlock Epoch, possibly within the Lower Wenlock.

The stratigraphy and structure of an area in the Carnarvon sedimentary basin covered by the Williambury and Moogooree one mile sheets, is described. Resting unconformably on a Pre-Cambrian basement of schists gneisses and granites, are Devonian marine sediments 4750 feet thick, followed conformably by Carboniferous approximately 2150 feet thick; these are separated from the overlying Permian more than 8000 feet thick, by a possible hiatus. The Cretaceous System is represented by about 40 feet of siltstone lying unconformably on the Palaeozoic rocks. Marine Tertiary arenaceous deposits are widespread and have a maximum thickness of 80 feet; they are not seen in contact with the Cretaceous rocks. The whole area has been subjected, in Tertiary time, to lateritisation, the most prominent feature of which is the presence of a silicified cap ranging in thickness from a few feet to 30 feet. In one place a post-laterite deposit of 12 feet of probably fresh-water limestone has been observed. An account is given of the structural geology, geological history, and physiography of the region.

The features of the single-point resistance log, obtained in A.A.O. No. 2 Bore, Roma, are described. Single-point resistance, self-potential and geological logs of the lower section of the boreholes are shown. The results indicate that electrical logging can be effectively used for correlation problems and that salt water sands in the reservoir rocks can be detected with reasonable certainty.