Geology of hill end trough Molong high: Silurian environments of the northern Molong Rise

Abstract

For the northern Molong Rise, three Silurian longitudinal palaeogeographic units are postulated: essentially a shallow basin flanked by two acid igneous complexes (Figs. 1, 2). At the time of maximal carbonate development, a central Narragal Lagoon passed westwards onto a shelf edge characterised by non-magnesian carbonate sand and oncoliths, the Molong Shelf Edge. This developed atop earlier acid igneous rocks along the western flank of the Molong Rise. The shallow water areas, either of mud or carbonate sand, may be grouped under the term Narragal Shelf. Late in Silurian time, the entire Molong Rise began to drown, influx of pelagic mud almost everywhere replacing carbonate deposition. Local maintenance of carbonate environments along the shelf edge, as between Molong and Borenore Caves, may have led to bodies of considerable submarine relief.