GEOLOGY AND SOILS

The geology of the region is characterised by sediments, dominantly of sandstone and siltstone that constitute the southern extension of the coal-bearing, Permo - Triassic age, Sydney Basin. In the Gerringong area the sequence includes localised basaltic lava flows. A detailed description of the geology of the northern area is given by Bowman (1974).

The sediments of the Sydney Basin continue south as far as Durras Lake, south of Ulladulla (McIlveen, 1975).

Soils express the nature of the underlying sandstone, siltstone and shale lithologies and range from sandy loams to clay loams with underlying clays. Local volcanic units generally lead to areas of richer soil.

Detailed descriptions of soils in the region are not commonly available. One of the more recent is by viticulture consultant Richard Smart in a report to the Shoalhaven City Council (Smart 1998).

Smart lists the common soil types occurring in the Nowra area as lithosols on hilltops and upper slopes, brown earths on mid-slopes and red or yellow podzolics on lower slopes and along drainage lines. Litho sols have dark grey brown silty topsoil 20cm thick, overlying brown light medium clay 70cm thick over Berry Siltstone, the dominant rock formation outcropping in the area. Brown earths have 15cm of black silty topsoil over dark brown clay 70cm thick over heavy grey clay with yellow mottles. Red podsolic has 30cm of red-brown light clay over brown medium clay down to 115cm.