Geology of hill end trough Molong high: Molong anticlinorium succession beneath the narragal limestone

Abstract

The Silurian System of the northern Molong Rise has been re-examined where well displayed between Neurea and Mumbil. The Mumbil Group, forming the upper part of the sequence, comprises the dolomitic Narragal Limestone and the overlying Barnby Hills Shale. The succession beneath the Narragal Limestone can no longer be regarded as an Ordovician to Early Silurian single formation (Oakdale Formation) lacking major breaks. Ordovician and Silurian strata are separated by an Early-Middle Silurian hiatus, possibly marked by slight angular unconformity. The Ordovician sequence is divided into two new formations, the andesitic Cypress Hill Volcanics and the overlying Mona Vale Siltstone, comprising the Oakdale Group. Silurian strata have been excluded from the Oakdale Group and are placed in three new formations. In ascending order these are the Wylinga Formation, which is rich in thinly bedded limestone, the andesitic Warderie Volcanics and the Catombal Park Formation, which contains acid volcanics and calcareous sediments. These three formations make up the Dripstone Group, whose richly fossiliferous members contain a coelenterate fauna which may be of widespread biostratigraphic value within the Lachlan Fold Belt.