Basal sedimentary rocks of the western Great Artesian basin record the change from the continental regime in Late Jurassic time to the epicontinental marine environment in the Early Cretaceous. The sequence consists of the Algebuckina Sandstone, the Cadna-owie Formation, and the Mt. Anna Sandstone Member. These units are overlain by the uniform marine Bulldog Shale.

The Algebuckina Sandstone consists of lower, ill-sorted kaolinitic sandstone beds with typical angular current bedding, and well-sorted, concavely current-bedded upper sandstone beds. The Cadna-owie Formation disconformably overlies the Algebuckina Sandstone, and consists of feldspathic sandstone, micaceous and carbonaceous siltstone, Fontainbleu-type and oolitic sandstones, and lenticular boulder beds. The well-sorted Mt. Anna Sandstone Member is in the upper part of the Cadna-owie Formation and is characterized by an abundance of red, porphyritic rhyolite pebbles. The distribution of these units was controlled by topographic features and syngenetic tectonic events.

The lower kaolinitic beds of the Algebuckina Sandstone were deposited on a stable, senile land surface under low-gradient fluviatile conditions with episodic sheet floods. A seasonally arid climate is suggested by the presence of dreikanters. The upper Algebuckina Sandstone is thought to have formed under conditions of depositional regression, and, as indicated by the fossil flora, a moist subtropical climate.

The Cadna-owie Formation represents the sedimentary record of the Early Cretaceous marine transgression. The sediments of this formation, with the exception of those of the Mt. Anna Sandstone Member, were deposited under shallow-water, marginal-marine conditions, and several specialized environments are documented. The boulder beds of the Cadna-owie Formation, previously cited as evidence of Cretaceous glaciation, are the product of sediment creep in the vicinity of "basement highs." The Mt. Anna Sandstone Member was deposited in a fluviatile-deltaic environment. The abundance of red porphyritic rhyolite pebbles within this sedimentary unit is evidence of a major uplift of the porphyry provenance area at the southwestern basin margin in Early Cretaceous time, which resulted in the for ation of the Gawler Range Massif.

Correlation of these basal beds with stratigraphic units recognized in the deeper parts and along the southern and northwestern margins of the Great Artesian basin is discussed.