BURIAL HISTORY OF THE EASTERN OFFICER BASIN, SOUTH AUSTRALIA

Abstract

The intracratonic Officer Basin of central Australia was formed during the Neoproterozoic, approximately 820 m.y. ago. The eastern third of the Officer Basin is in South Australia and contains nine unconformity-bounded sequence sets (super-sequences), from Neoproterozoic to Tertiary in age. Burial history is interpreted from a series of diagrams generated from well data in structurally diverse settings. These enable comparison between the stable shelf and co-existing deep troughs. During the Neoproterozoic, subsidence in the north (Munyarai Trough) was much higher than in either the south (Giles area) or northeast (Manya Trough). This subsidence was related to tectonic as well as sediment loading. During the Cambrian, subsidence was much higher in the northeast and was probably due to tectonic and sediment loading (carbonates over siliciclastics). During the Early Ordovician, subsidence in the north created more accommodation space for the last marine transgression from the northeast. The high subsidence rate of Late Devonian rocks in the Munyarai Trough was probably related to rapid deposition of fine-grained siliciclastic sediments prior to the Alice Springs Orogeny. Rates of subsidence were very low during the Early Permian and Late Jurassic to Early Cretaceous, probably due to sediment loading rather than tectonic sinking. Potential Neoproterozoic source rocks were buried enough to reach initial maturity at the time of the terminal Proterozoic Petermann Ranges Orogeny. Early Cambrian potential source rocks in the Manya Trough were initially mature prior to the Delamerian Orogeny (Middle Cambrian) and fully mature on the Murnaroo Platform at the culmination of the Alice Springs Orogeny (Devonian).