Ordovician and Silurian lithofacies and base-metal deposits of the Lachlan Fold Belt
Titel:
Ordovician and Silurian lithofacies and base-metal deposits of the Lachlan Fold Belt
Auteur:
Kemezys, K. J.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 25 (1978) nr. 1-2 pagina's 97-107
Jaar:
1978-03
Inhoud:
Two lithofacies maps of the Lachlan Fold Belt, one for the Ordovician and one for the Silurian, are illustrated. Both maps indicate shorelines in western New South Wales, Victoria and Tasmania. The Ordovicoan map suggests open-sea conditions eastwards from the shoreline with one major and two minor andesitic volcanoes (or volcanic centres). The Silurian map suggests segmentation of the Lachlan Fold Belt into the Melbourne Basin, Omeo Land, Newell Basin, and Budawang Land. The Newell Basin displays a nearshore (Louth-Mitta Mitta) coarse clastics facies and an offshore (Wellington-Cooma) platform carbonate facies. Acid volcanism was widespread over the Newell Basin in Silurian time, but did not occur in the Melbourne Basin. The Louth-Mitta Mitta and Wellington-Cooma facies boundary coincides with the position of the Coolac-Honeybugle Serpentine Belt and the outcrop area of the Girilambone Beds, suggesting that these features were already in some way prominent during the Silurian Period: the Serpentine Belt may have been a fault, and the Girilambone Beds may have been land. The origin of base-metal deposits in the Silurian rocks is thought to be somehow related to the heat generated in the subsurface during Silurian time as is indicated by the volcanism and granite intrusion; and also to the fact that the deposits occur in a transgressive sequence which contains the first phase of acid volcanism in the known geological history of the Lachlan Fold Belt.
Tijdschrift beschrijving