Year

2016

Degree Name

BSci Hons

ANZSRC / FoR Code

0403 GEOLOGY, 040311 Stratigraphy (incl. Biostratigraphy and Sequence Stratigraphy)

Department

School of Earth & Environmental Science

Advisor(s)

Brian Jones

Abstract

The first recorded interpretation of the Hawkesbury Sandstone was given by Charles Darwin (1844), with his mention of the prominent cross-bedding. However it wasn’t until Conolly (1969) and Conolly and Ferm (1971) that a solid depositional environment was suggested. This was superseded by the now firmly established fluvial braided river deposition model by Conaghan and Jones (1975), based on interpretations of the cross-bedding within the Hawkesbury Sandstone particularly the large scale cross-beds and confluences (Ashley and Duncan 1977). Given the long-standing assumption that the Sydney Basin’s Hawkesbury Sandstone represents a large braided river system, there is an obvious interest to explore its architecture from an academic view point. The geotechnical need to understand the properties of the main bedrock unit that the city of Sydney is built on, makes this a necessity.

Geological mapping and modelling is a key and intrinsic part of all geological understanding and has evolved throughout the ages. The development of comprehensive 3D modelling and its application is set to revolutionise the geological field. Photogrammetric derived point clouds stand as a midway point for scale application between the small scaled terrestrial laser scanning (TLS) and extremely large scaled light detection and ranging (LiDAR) methods, positioning photogrammetry most ideal suited method for the data capture of a large laterally extensive study site.

The primary aim of this study was to establish a best suited methodology to create a robust representation of a large lateral site which was otherwise inaccessible. The second aim was to produces a series of facie maps highlighting the key internal fluvial features and depositional elements of the Hawkesbury Sandstone braided river system. The application of digital photogrammetric mapping of the inaccessible cliffs between Bundeena and Wattamolla, for the purpose of facies mapping, can be concluded as a resounding success, within the resource limitations of this study. From this study it can also be speculated that a much wider range of channel thickness are present than previously thought within the Hawkesbury Sandstone, eluding to more dynamic braid bars and channels within the braided river depositional system. It would not be recommended to use a similar photogrammetric technique as the sole source of data for interpretations within any study as of yet without field confirmations; however it provides an accuracy of measurements acceptable for interpretive needs.