GSV Report 87 - Dookie 1:100 000 map geological report
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Product description:Download The downloadable version of this report is supplied in PDF format (20.9MB). Abstract Mapping of the Dookie area has resulted in a 1:100 000 geological sheet accompanied by these updated explanatory notes. The notes describe the physiography, stratigraphy, structure and economic geology. Although the geology is largely masked by Quaternary alluvium, some key exposures are located in the Dookie Hills where Cambrian and Lower Ordovician rocks have been upthrust in the Mt Wellington Fault Zone, one of the major structures cutting across Victoria. The Cambrian rocks are well exposed and consist of basalt, gabbro and, volcanogenic and pelagic marine sedimentary rocks. The basalt and gabbro are of "ocean floor tholeiite" type composition and probably formed in a back-arc setting. Accumulation of marine turbiditic and hemipelagic sediments was more or less continuous from the Late Cambrian through to the Lower Devonian. Lower Ordovician shale and sandstone is exposed in a small area south of the Dookie Hills within the Mt Wellington Fault Zone. Upper Ordovician shale and sandstone, however, outcrop fairly extensively to the east and northeast of the fault zone, on its upthrown side. Siluro-Devonian sandstone, siltstone and mudstone is exposed to the south and west of the fault zone on its downthrown side. The Mt Wellington Fault Zone is a high angle reverse fault which trends northwest-southeast and probably dips to the northeast. The Dookie Hills form an east-west trending belt of Cambrian rocks along which the main fault zone is offset some 10 km with a sinistral sense of displacement. The fault zone formed during the Tabberabberan Orogeny in the Middle to Late Devonian. The Cambrian rocks deformed in a brittle manner by faulting whereas the Ordovician to Devonian sedimentary rocks were folded. During the Late Devonian, granite was intruded into the folded and faulted rocks. Flat lying glacio-marine mudstone of Late Carboniferous-Early Permian age is found in boreholes in the northwest part of the map area. It is only known to outcrop in the Lake Rowan area. The Murray Basin started to form in the Late Mesozoic or Early Tertiary. At that time while sedimentation was taking place in the deeper parts of the basin to the west, the Dookie area was being eroded and a system of palaeovalleys which are ancestral to the present drainage, was formed. Sedimentation began in the Middle Tertiary and continues to the present. Fluviatile processes have dominated, beginning with the carbonaceous sand and clay of the Renmark Group, to the gravel of the Calivil Formation, to the clay and sand of the Shepparton Formation and finally to the silt and sand of the sub-Recent Coonambidgal Formation. The Cambrian rocks contain minor occurrences of sulphide minerals, barite, calcite and talc. There have been reported occurrences of gold and stibnite and geochemical surveys have located anomalous amounts of nickel, chromium, arsenic, copper, manganese and gold in stream sediment and soil samples. Deposits of economic significance have yet to be located. Rock aggregate from various Palaeozoic formations and from the Tertiary basalt at Cosgrove is widely used for roadmaking, as is sand associated with the "prior streams" of the Shepparton Formation. Groundwater is an important resource in the area. Stock and domestic supplies are widely drawn from sand aquifers in the Shepparton Formation, while deeper gravels of the Calivil Formation are a source of irrigation water in the northwestern part of the map area. Bibliographic reference Tickell, S.J., 1989. Dookie 1:100 000 map geological report. Geological Survey of Victoria Report 87. Related products:
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