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The Early Devonian Coopers Creek Limestone: A deep‐water redeposited limestone in the Melbourne Trough, southeastern Australia

1993; Taylor & Francis; Volume: 40; Issue: 6 Linguagem: Inglês

10.1080/08120099308728105

1440-0952

M. W. Rehfisch, John A. Webb,

Geological and Geophysical Studies

The Coopers Creek Limestone represents an Early Devonian redeposited carbonate accumulation and records the evolution of a carbonate slope in the southeastern portion of the Melbourne Trough. During the earliest Devonian, the underlying Boola Formation was deposited, probably as turbidites, in a moderately deep‐water setting. The presence of chert and greenstone clasts in the top of the formation indicates exposure of an area of Cambrian greenstones in this part of the Melbourne Trough, as a result of uplift associated with the earliest Devonian Bowning Orogeny. This uplift provided ideal conditions for carbonate production along the margin of the exposed landmass. The periodic transportation of carbonate material downslope resulted in the accumulation of the Coopers Creek Limestone. Initially, in the early Pragian, turbidity currents deposited clayey biomicrites and biopelmicrites on a relatively gentle slope. However, the rapid build‐up of carbonate sand banks at the shelf margin steepened the gradient from the shelf into the basin and a bypass margin began to develop. Grainflows deposited pelsparites and biopelsparites and the presence of debris flow breccias indicates erosion of lithified limestone by channelling. Continued carbonate build‐up led to the development of a rimmed reef margin in the earliest Emsian, with a steep fore‐reef gradient. Large blocks of reefal limestone fell or rolled to the base of the slope, to accumulate as reefal megabreccias at the top of the Coopers Creek Limestone. Carbonate production abruptly ceased in the early Emsian, due to the uplift of a quartzo‐micaceous source to the east during the initial stages of the Tabberabberan Orogeny. This uplift supplied abundant terrigenous material into the Melbourne Trough to be deposited as the turbidites of the Walhalla Group, which deeply buried the limestone accumulation.