Geology and Geomorphology of Jenolan Caves and the Surrounding Region

Abstract

Detailed mapping by university students and staff since the 1980s has significantly elucidated previously poorly known stratigraphic and structural relationships in the Jenolan Caves region. Apart from andesite of ?Ordovician age, rocks west of the caves probably correlate with the lower Silurian Campbells Group. That succession is faulted against the Silurian (mid Wenlockian) Jenolan Caves Limestone, in which caves developed during several episodes from the late Palaeozoic. Immediately east of Jenolan Caves, siliciclastic sedimentary and volcaniclastic rocks with interbedded silicic lavas constitute the newly defined Inspiration Point Formation, correlated with the upper Silurian to Lower Devonian Mount Fairy Group. Several prominent marker units are recognised, including limestone previously correlated with the main Jenolan limestone belt. Extensive strike-slip and thrust faulting disrupts the sequence, but in general the entire Silurian succession youngs to the east, so that beds apparently steeply-dipping westerly are actually overturned. Further east, Upper Devonian Lambie Group siliciclastics unconformably overlie the Inspiration Point Formation and both are overlain unconformably by lower Permian conglomeratic facies. Carboniferous intrusions include the Hellgate Granite with associated felsite dykes. The regional geomorphology probably evolved from late Carboniferous–early Permian time, with ‘steps’ in the deep valleys indicating episodic periods of valley formation, possibly including Permian glaciation.