RECENT GEOLOGICAL MAPPING IN THE NORTHERN EROMANGA BASIN, QUEENSLAND

Abstract

The attached map represents the generalised results of five years of systematic regional geological mapping of the northern Eromanga Basin. A new nomenclature based on lithological characteristics now replaces the classic faunal divisions which have been widely used and misused as lithological units.

Gamma-ray logs of many water-bores in the northern Eromanga Basin enable good correlations to be made of the sub-surface Jurassic and Cretaceous sequence over a wide area. lithological and thickness variations indicated by these correlations are inferred to be related to deeper structure.

High radioactivity, associated with three argillaceous units within the Jurassic sequence, possibly indicates marine incursions. Also, the presence of glauconite and acritarchs suggests marine conditions during deposition of the three units.

Correlation of the sub-surface Jurassic units with the exposed sequence is questionable. However, it is evident that only an attenuated sequence is preserved at the present basin margin, and that at the margin periods of non-deposition or erosion were common.