ABSTRACT
This chapter summarizes the formation of Botany Basin. The Basin consists of unconsolidated deposits of Quaternary age which overlie the layered Wianamatta Group Shales or the Hawkesbury Sandstone. The bedrock of the Botany Basin consists both of Hawkesbury Sandstone and Wianamatta Shale; the shale bedrock is most commonly found below the western sector. Particularly useful maps showing the Geology and Basement Contours of Botany Basin have been produced by R. J. Griffin. The surface of the bedrock below the Botany Basin Quaternary deposits is such that it generally slopes towards the centre of Botany Bay. No generalisation as to the subsurface conditions in the Botany Basin can be made because of the variable erosion and deposition history with different emergent levels. The traditional subsurface investigation technique for the Botany Basin area would be by a conventional continuous spiral flight auger rig supplemented by cased or mud stabilised boreholes using wash boring techniques.
