Tertiary Lake Bunyan, Northern Monaro, NSW, Part I: Geological setting and landscape history
Titel:
Tertiary Lake Bunyan, Northern Monaro, NSW, Part I: Geological setting and landscape history
Auteur:
Taylor, Graham Walker, P. H.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 33 (1986) nr. 2 pagina's 219-229
Jaar:
1986-06
Inhoud:
The Cainozoic Lake Bunyan Basin occupies part of the Cooma-Canberra corridor, a lowland which is bounded in the W by the Murrumbidgee Fault escarpment and in the E by N-S trending ranges. The Murrumbidgee and Numeralla Rivers are the main streams entering the basin. Lake Bunyan covered an 8 km wide strip of this lowland from near Bredbo to 30 km SE in the vicinity of Cooma. It formed when the Murrumbidgee River became fault-dammed 5 km S of Bredbo, during the late Oligocene or early Miocene, and it was finally breached in the late Miocene. Five sedimentary facies were identified in the Lake Bunyan sequence. A marginal facies of stratified gravels, sands and sandy clays unconformably overlies bedrock or weathered bedrock at the base of the sequence and also overlaps other facies. A lignitic facies is thin and often interbedded with clay. A volcanogenic facies is up to 50 m thick, has strong red colours, and consists of stratified clays and gravels, the latter containing volcanic debris. A 40 m thick clay facies occurs in the upper part of the sequence and is very fine grained. A diatomite facies at the top of the sequence is up to 13 m thick. The sediments of Lake Bunyan generally occur below the present 780 m contour and were deposited over a vertical interval of at least 210 m. The occurrence of Lake Bunyan, when considered with fault-dammed Lake George and scarp-producing movements along the Berridale Wrench Fault, indicates Cainozoic tectonics in the South East Highlands of NSW that were episodic, localized and not synchronous.
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