The Onshore Southern Carnarvon Basin in Coastal Western Australia during the Quaternary: Tectonic Setting and Facies-Complicated Heterogeneous Stratigraphic Patterns

Abstract

The onshore southern Carnarvon Basin in Western Australia, in existence since the early Palaeozoic, has a history during the Palaeozoic and Tertiary of relatively uniform sedimentary styles with thick laterally-extensive sequences of sediment. Its sedimentary history became more complicated in the Quaternary period with complex tectonics and arrays of sedimentary facies and packages and basin complexity over relatively short distances, with several regions that are sedimentologically and stratigraphically distinct related to the factors of physiographic and geological setting, riverine input, arid climate, migrating climate, tectonism, and degree of protection from open ocean. For the Pleistocene and Holocene epoch, there are distinct north-trending stratigraphic packets, each with their environmentally distinctive shoaling facies sharply juxtaposed against each other or separated by Pleistocene non-marine sediments; in geographic order, from south to north, these are: a limestone aeolianite barrier along western Shark Bay; pocket seagrass bank carbonate complexes of central western Shark Bay that are nestled in the northerly-oriented inter-dune depressions developed as swales of the north-trending parabolic dunes deriving from the limestone aeolianite barrier; an aeolian red sand shoestring of the north-trending Peron Peninsula longitudinally bisecting central Shark Bay; metahaline to hypersaline shoaling carbonate sedimentary packages of south-eastern Shark Bay that fringe Hamelin Pool; the Wooramel delta, a wave-dominated delta composed of quartz sand and locally-generated carbonate sediment; the Wooramel seagrass bank (an extensive shore-parallel wedge of seagrass bank carbonate sequence along the eastern coast, central to northern Shark Bay); metahaline carbonate and quartz sand platforms fringing both sides of the red-sand Peron Peninsula; metahaline to hypersaline carbonate sediments that underlie the deeper-water axially-oriented embayments of Shark Bay; the Boodalia Pleistocene reddened (quartzose) deltaic sediment sequence; the Gascoyne Delta and laterally equivalent beach-ridge complex, the former comprising subtidal quartz-dominated sand capped by tidal sand-and-mud sequences, and the latter comprising subtidal quartz-dominated sand capped by beach-to-beach-ridge deposits; the Lake MacLeod evaporite basin filled with a shoaling sequence of carbonate sediments, halite, and gypsite; Tertiary limestone and Pleistocene aeolian sediments acting as a barrier to Lake McLeod; and the uplifted Tertiary limestone barrier of Cape Range that is fringed by Holocene coral complexes of the Ningaloo Reef. The coastal and onshore near-coastal southern Carnarvon Basin is an example of a complex sedimentary basin, where sedimentary packages can be markedly different over short distances, and illustrates the complexities a geologist would face if analyzing such a basin in the stratigraphic column. This feature of extreme diversity of sedimentary facies and packages within and between separate contemporaneous ‘sedimentary basins’ is the theme of this contribution.