Tectonic control of Tertiary deposition in the Streatham Deep-Lead System in western Victoria

Abstract

The mainly sub-basaltic paleodrainage of the Streatham Deep-Lead System covers >2500 km2 between the West Victorian Uplands and the Otway Basin, from which it is separated by a subsurface granite ridge. Five main tributaries flowed southwards into a series of grabens that host up to 140 m of fluvial coal-bearing sediments (Yaloak/Calivil Formation). The grabens were probably initially connected to the ocean (Otway Basin) through a western outlet; in the Eocene, the outlet shifted eastwards. Accumulation of the deep-lead sediments in the central grabens was controlled by synsedimentary subsidence along reactivated north-northwest Paleozoic and east-northeast Cretaceous faults. Fault movement occurred in the mid-Late Paleocene in the western depocentre, and Eocene in the central and eastern depocentres, and correlates well with tectonic activity in the eastern part of the Otway Basin. Following an Early Oligocene hiatus, fluvial sedimentation and syndepositional faulting recommenced from the Late Oligocene to Late Miocene/Pliocene, concomitant with sediment deposition and faulting in deep leads to the north of the divide. A final period of compressional faulting in the latest Miocene – Early Pliocene uplifted some sections of the Streatham Deep-Lead System, before it was almost entirely covered by basalt lavas.