Publication Name: The Cooper & Eromanga Basins Australia
Authors: G.D. Powis
Date Published: June 1989
Number of Pages: 27
Reference Type: Book Section
Abstract:
In recent years it has become apparent that all of the Triassic-aged strata overlying the Cooper Basin cannotadequately be placed into the only formally defined Triassic formation, the Nappamerri Formation. Not only do these strata not conform lithologically to the siltstone-dominated original type secrion, but many parts of the secrion are Late Triassic in age (i.e. the succession is not restricted to the Early to Middle Triassic as originally defined).
A chronostratigraphic approach is used to formally subdivide and redefine the Triassic strata in an attempt to clarify their age and stratigraphic relationships throughout the Basin and therefore avoid any further
confusion in the stratigraphic nomenclature which has resulted from the numerous informal names currendy used to describe these strata. This study has enabled a broad three-fold subdivision of the strata in South Australia and Queensland. The new stratigraphic section now comprises, from the base, the Early Triassic Arrabury Formation, the Middle Triassic Tinchoo Formation and the Late Triassic Cuddapan Formation. This stratigraphic breakdown not only allows a greater insight into the geological evolution of the Basin, but it allows more accurate delineation of the Triassic stratigraphy using seismic data.
A dramatic change occurs in the overall Basin configuration between the Arrabury and Tinchoo Formations. A tectonic event at the end of Arrabury times terminated deposition which was restricted to within the Permian Cooper Basin sub-crop limits and shifted the Triassic depocentre to the north. This resulted in a depositional phase which was the precursor of the Eromanga Basin depositional regime.