Geological Evolution and Tectonic Controls of the Tertiary Streatham Basin, western Victoria, Australia

Abstract

The stratigraphy and structure of a Tertiary sub- basaltic sedimentary succession near Streatham in western Victoria have been studied as part of a groundwater project linking the geology to the salinity distribution. Using palynological ages, airborne geophysics and an extensive bore log record from exploration and groundwater observation bores, we have modelled the evolution and the extent of this palaeodrainage system. This palaeodrainage/deep lead system covers an area of more than 2000km² and consists of several tributaries which fuse into one central incised valley. It contains up to 140m of fluvial gravel, sand, ligneous clays and coal often with a clear fining upwards trend. Palynological ages conducted on sediments from selected bores within the pallaeovalley indicate that deposition within this complex system took place in at least three major phases ranging from Palaeocene to Late Miocene. Using airborne geophysics (magnetics and gravity) and a digital elevation model we were able to identify the faults affecting the deposition in the Streatham Sub-basin and a comparison with the basement geology map shows that the faults are all reactivated older structures between Palaeozoic units or even tectonic zone boundaries (as in case of the Moyston Fault).