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The Eucla Basin covers a large area of southwestern South Australia, extending from well into Western Australia to western Eyre Peninsula. The onshore Eucla Basin in South Australia comprises marine limestones (Eucla Group) that pass into shallow marine, coastal and non-marine terrigenous sediments (Immarna Group) towards the basin margin. The onshore limit of the marine limestones largely coincides with the margin of the Bunda Plateau (Nullabor Plain). Tertiary sediments are relatively thin (<150m) on the onshore platform but thicken up to 1500m offshore. Onshore Eucla Basin sediments overlie Mesozoic sediments of the Bight and Polda Basins, Neoproterozoic sediments of the southern Offiocer Basin, and basement rocks of the Gawler Craton.
A large and well-preserved palaeodrainage system extending from western South Australia into Western Australia flowed from the Gawler Craton, Musgrave Block and Yilgarn Block into the Eucla Basin. A unique assemblage of well-preserved Late Eocene coastal aeolian landforms occurs along the inland margin on the Eucla Basin including the 650km long Ooldea Range.
Incision of palaeovalleys in the Gawler Craton and Musgrave Block probably commenced in the Late Cretaceous to Early Eocene shortly after the formation of the Eucla Basin. Sedimentation during this time was only recorded on the continental shelf, while weathering and erosion appear to have been the dominant processes onshore. Two major phases of deposition are present in the eastern basin and adjacent palaeovalleys: Middle Eocene to Late Eocene and Middle Miocene to Early Pliocene, separated by a major sedimentary hiatus.
Prior to the Wilson Bluff marine flooding of late Middle Eocene age, deposition of marine clastics (Hampton Sandstone) was restricted to the central Eucla Basin, while minor deposition of fluvial gravel and coarse sand was probably limited to valley floors. During the Tortachilla and Tuketja transgressions of the latest Middle Eocene to Late Eocene, the basin and channel sediments thickened and were inclined gently in a seaward direction due to tectonic upwarp along the Stuart Range and subsidence of the Eucla Basin. Separated by the Ooldea Range barrier that is mainly composed of Ooldea Sand, Wilson Bluff Limestone was predominantly deposited on the marine carbonate platform, while terrigenous sediments of Pidinga and Khasta Formations were laid down on the coastal and estuarine alluvial plain.
There is little or no evidence for deposition between the Oligocene and Early Miocene in this region because of northerly gentle uplift. During the Middle Miocene to Early Pliocene transgressions marine carbonates of the Nullarbor Limestone were laid down in the Nullarbor Plain region. Marginal marine clastics were deposited in the southern palaeovalley systems (e.g. Kingoonya and Narlaby Palaeochannels), while lacustrine sediments of Garford Formation were predominant in the lakes and fluvial channels (e.g. Tallaringa and Garford Palaeochannels).
