Shale of the Tapley Hill Formation.
On the northern fringes of the Flinders Ranges, White Cliff Hill is formed out of gypcrete layers over the older precambrian dolomitic shales and magnesite of the Skillogalee formation.
Coursley crystalline gypsum in the Gypcrete formation.
Outcropping sheets of gypsum. Continue reading “Gypcrete formation: White Cliff Hill”
Weathered red-brown shale, likely Tapley Hill Formation, and quartz in a valley of clay and sand deposits.
The precambrian Copley Quartzite Formation forms the prominent walls in the Aroona Dam.
Quartz outcropping amongst colourful siltstones and claystones in the Lyndhurst area.
In view from Old Warraweena, ascending geological formations from Bunyeroo purple shale in the foreground, slumping dolomitic Wonoka Formation hills in the midground and hard weathering Pound Quartzite in the background.
On the western side of the Blinman diapir in Parachilna Gorge, the ‘Badlands’ are created by rapid erosion of soft rocks.
Published by the Geological Society of Australia, South Australian Division.
One of the best records in the world of sedimentary deposition in the period of geological time between about 800 million and 500 million years ago is exposed in the Flinders Ranges, Mount Lofty Ranges and the Olary region in South Australia. Sandy and silty sediments derived from erosion of older rocks of the Gawler Craton in the hinterland to the west, and island masses of this basement rock rising from an undersea ridge over 200 km to the east, were deposited into an extensive marine basin called the Adelaide Geosyncline in which the seafloor was slowly subsiding along a series of elongated north-south step or graben faults.
During the 300 million years of continuing but intermittent subsidence of the basin floor, a thick pile of sediment accumulated in the geosyncline. This sequence was then compressed and hardened by deep burial and later folded into a high mountain range by a new regime of earth movements.
Subsequent erosion has reduced these highlands to their present form and deposited huge amounts of sediment to the east into younger sedimentary basins formed by later crustal down warping. Continue reading “Brachina Gorge Geological Trail”
An outcrop of blocks of sandstone and beds of crystalline calcite in the vicinity of a copper deposit.
Silicified duricrust formed in low laying outer areas of the Flinders Ranges, likely to have once been saturated by limey waters. Surrounding sediments have eroded leaving these typically rounded, hard wearing silcretes.