Stratigraphy and Sedimentology of a Late Neoproterozoic Shelf-Slope-Basin System, Flinders Ranges, South Australia: An Excellent Outcrop Analogue for Marginal Marine to Deepwater Transitions in the Subsurface

Abstract

The Flinders Ranges in South Australia expose an extensive suite of Late Neoproterozoic clastic sediments deposited in the Adelaide Rift Complex, a major rift-sag basin and passive margin system active from the Proterozoic through the Cambrian. The world-class exposures in this region allow valuable insight into the stratigraphic architecture of analogous basins around the world, which often contain both source rocks and petroleum reservoirs. The Billy Springs Formation in the northern Flinders is the deepwater equivalent of the lower part of the coarser, shallow-marine Pound Subgroup, and provides an opportunity to examine relatively undescribed offshore equivalents of well-studied marginal marine strata to the south. Our investigations consist of several measured stratigraphic sections, which reveal a kilometre-scale sequence of silts and sands containing well-preserved primary sedimentary structures. Detailed sedimentological analysis, including petrography, indicates that deposition was influenced by gravity-driven mass flow processes. Sedimentation patterns differ markedly across the 100+ kilometre-wide study area, likely due to differences in bathymetry related to both larger basin paleogeography and subsidence associated with underlying salt withdrawal. Vertical stratigraphic changes are also present, and reflect the transformation from slump processes to turbidity currents. Ongoing work (2013) will examine additional exposures in Vulkathunha-Gammon Ranges National Park, which will allow offshore deposits of the Billy Springs Formation to be connected in a transect to the type locality over 100 kilometres to the south, where sediments were deposited above wave base. A better understanding of the sedimentary character of this shelf-slope transition, as well as that of salt-withdrawal minibasins, is important for modelling hydrocarbon systems, and for reconstructing the paleogeography of the Neoproterozoic of South Australia. Future work will examine sediment provenance using detrital zircon U/Pb dating, and will expand the investigation of lithologic variability in the Pound Subgroup by focusing on diapir-sediment interaction in other areas.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014