New insights to the lithostratigraphy of the Pedirka Basin, Northern Territory

Abstract

The Pedirka Basin is a Permian to Triassic intra-cratonic sedimentary basin located in the southeast corner of the Northern Territory and extending into South Australia and Queensland. It comprises a stacked succession up to 1.5 km thick of glacial, fluvioglacial, fluvial, lacustrine, coal swamp and continental redbed deposits.

This Record presents a revision of the stratigraphy and depositional environments in the Northern Territory portion of the Pedirka Basin. This revision is based on two main investigative components. Firstly, in-depth logging, comprising detailed observations of HyLoggerTM imagery, visual lithological logging of drill core, and interpretation of wireline logs (where available), which together have enabled updated facies interpretations and refinement of depositional settings of the formations. Secondly, new palynology results have more tightly constrained the ages of the stratigraphic intervals and provided additional information on depositional environments. In addition, recent collaborative work has provided new insights into the correlation of units across the Pedirka Basin and overlying Eromanga Basin boundary.

Outcomes include a sedimentological analysis of the Crown Point Formation that demonstrates interfingering and repetition of facies types, resulting in the use of the term 'Tirrawarra Sandstone equivalent' in the Northern Territory to be abandoned. The internal subdivision of the Purni Formation has been refined and updated; multiple lines of evidence indicate that deposition of the basal part of the Purni Formation occurred in a reducing lacustrine environment or possibly a restricted marine influence. In addition, the study has noted the presence of Late Permian sedimentation in the Pedirka Basin; due to this finding, and from evidence of other workers, the term 'Simpson Basin' should be disbanded and the entire Permo- Triassic stratigraphy be included in the Pedirka Basin

As a result, the lithology and stratigraphy of the Pedirka Basin in the Northern Territory have been updated. This will have direct relevance for the exploration of a range of subsurface resources including energy systems (petroleum, coal, carbon capture and storage, hydrogen, geothermal) and groundwater.

In line with this work, publicly available data was collated into a NTGS digital information package (Doig and Jarrett 2021), and these data have been used to refine the basin history and petroleum prospectivity of the region.