Brachina Gorge Geological Trail

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Brachina Gorge Geological Trail: A snapshot of geological time in the Flinders Ranges National Park in South Australia.

Published by the Geological Society of Australia, South Australian Division.

Excerpt:

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”

The Legacy of Time: Story of the Flinders Ranges

Excerpt: The legacy of time

First published by The Royal Geographical Society of South Australia Inc. in 1995.

The Flinders Ranges have been shaped by geological processes that, over hundreds of millions of years, have built the stage upon which the drama of biological interactions is being performed.

The Flinders Ranges form part of a highland chain extending from Kangaroo Island in the south through the Mount Lofty Ranges and Flinders Ranges to Marree and beyond in the north, to Olary in the east, and to Spencer Gulf and Lake Torrens in the west. Like many other mountain chains, they began their history as a subsiding sedimentary basin.

During the late Precambrian era, the Earth’s crust in South Australia consisted of granitic, metamorphic, sedimentary and volcanic rocks formed between 2600 and 1400 million years ago. In the present Flinders, the only rocks from that time are exposed near Arkaroola, including what are now known as the Freeling Heights Quartzite, Terrapinna Granite (Terrapinna Tors Walk) and Mt Neill Granite. Rocks that now constitute the eastern states of Australia were yet to form and the ancestral Pacific Ocean may have had its shores in South Australia. To the south, Australia was still joined to Antarctica.

The main area in South Australia then lay west of an approximate line from Adelaide to Oodnadatta; a smaller one existed in the vicinity of Lake Frome. The intervening area, where the Flinders and Mount Lofty Ranges now stand, became a long-lived basin known as the Adelaide Geosyncline, in which sediments accumulated 800 to 500 million years ago.

Continue reading – download PDF The Flinders Ranges – Legacy of Time