The structural geology of the Rapid Bay­Second Valley area, Fleurieu Peninsula, South Australia

Abstract

Whilst the geology of the Rapid Bay-Second Valley area is known to be both structurally and stratigraphically complex, previous workers (Daily, 1963; Evans 1987; Drayton, 1963; Campana and Wilson, 1955) have been unable to agree on many aspects of the area. Neoproterozoic and Cambrian aged sediments were first deposited in an extensional basin, which was formed due to lithospheric thinning, and associated subsidence (Jenkins, 1986, 1990). These rocks have then been subjected to at least one phase of deformation, the Cambro-Ordovician Delamerian Orogeny (Offler & Fleming, 1968; Thompson, 1970). Listric extensional faults were formed both before and during sedimentation of the rocks, which has created narrow zones of weakness that the subsequent compressional event has exploited, creating thrust faults (Flottman et al., 1994).

Structural mapping of the area has revealed that it is transected by two thrust faults and is intensely folded in places. Structural data has been collected during eight weeks of field work and has been compiled into a 1:10 000-scale geological map which accurately represents the area. A computer-generated three-dimensional model has been created for the area, based on this map, and cross and profile sections constructed from the data collected. The model was constructed using Vulcan™ software. Strain analysis has also been conducted on many of the folds in the area.