Devonian geological history of the Lachlan Geosyncline

Abstract

The principal Lower Devonian depositional belts of the Lachlan Geosyncline were a western, predominantly non‐volcanic belt, including the Cobar Basin and the Melbourne Trough with its southerly extension into Tasmania, and an eastern, volcanic belt, including the Parkes Platform, Cowra Trough, Molong Rise, Hill End Trough and Capertee Rise. These were separated by a more or less continuous median stabilized block comprising the Girilambone Arch, Wagga Arch and Snowy Mountains Block, which acted as a mildly positive structure during Early Devonian time. The sea regressed from the Cobar Basin and Melbourne Trough in about late Emsian times. Succeeding Devonian deposits in the western belt were entirely of non‐marine type. The Middle Devonian Tabberabberan Orogeny was responsible for the virtual stabilization of the entire geosynclinal tract, for the main uplift, folding and faulting of the Hill End Trough and adjacent rises, and folding in the Melbourne Trough. Non‐marine basin and platform deposits predominated in the Upper Devonian. A short‐lived marine transgression extended on to the eastern flank of the Snowy Mountains Block and across part of the former eastern volcanic belt in Frasnian times. In Central Victoria acid volcanic activity in the Late Devonian was associated with cauldron subsidences.