Australia: The Land Where Time Began

A biography of the Australian continent 

Mullewa Area - Northern Perth Basin

In the Mullewa area, between the Darling Fault and the Urella Fault exposures are dominated by the Nangetty Formation of Carboniferous-Permian age. Along Wenmillia Creek and Wooderarrung River, adjacent to the Darling Fault, there are excellent exposures outcropping of diamictite facies. Along the Irwin River, further to the south, there are diamictites that are similar, also with a matrix of gritty, sandy matrix, that have informally been called 'conglomeratic argillite' (Le Blanc Smith & Mory, 1995). There are common occurrences of crude horizontal stratification, deformed sandstone rafts and conglomerate, though massive facies predominate. Rounded to angular clasts occur, that can be up to several metres in diameter, with no preferred long axis orientation, that are often striated and faceted. Mixtures of extrabasinal and local types are included, mostly of Yilgarn Craton granite, as well as dolomite and quartzite, of Proterozoic age, from the Moora-Watheroo area, 100-150 km to the south (Glover, 1974; Playford et al., 1976; Le Blanc Smith & Mory, 1995), which indicates a flow of ice to the north.

There are many dish and dewatering structures in the highly deformed fine- to medium-grained sandstone that is complexly folded, interbedded with diamictite facies. It is suggested by remnants of the original structures of probable grading, horizontal lamination and rippling. It has been suggested the association of the facies of diamictite-sandstone-mudstone were mostly formed by sediment flows below water, ranging from debris flows, the diamictites, to fine- and coarse-grained turbidites, the sandstone and laminated mudstone (Eyles et al., ). The presence of many striated and faceted clasts are a strong indication that there was a nearby glacial sediment source. It is indicated by the grading and stratification within the diamictite, as well as  by the conglomerate and sandstone rafts, that there was only partial assimilation and homogenisation of the facies of material that was coarser and better drained., during down-slope debris flow (Eyles et al., ).

In the Nangetty Formation in this area, massive, rippled, contorted and pebbly sandstone faces predominate, Mory et al. suggesting they are probably part of the Wicherina Member of Mory & Iasky (1986). Playnomorphs of mid-Late Carboniferous and the Early Permian were recovered by Backhouse from shallow bores to the north of the Greenough River, that proved to be the only known palaeontological evidence that could be used to date the formation.

Near Noondamurra Pool, to the north of Bindoo Spring, is the only other unit of significance in the area. It is a cross-bedded sandstone facies of fluvial origin, assigned to the Tumblagooda Sandstone (Playford et al. 1976). It was later assigned to an unnamed unit from the Devonian (Hocking, 1991). To the west of the Urella Fault there are poor outcrops of Permian and Jurassic age. There are other poor exposures along the fault zone. In Wenmillia Creek and upstream from its junction with the Wooderarrunga River, there are moderately good exposures of the Darling Fault (Locality 14).

Locality 10 - Bindoo Spring, Greenough River.  About 30 km west of Mullewa. Dropstones in fine-grained, glacio-marine Nangetty Formation of ?mid-Carboniferous to Lower Permian age.

Locality 11 - Kockatea Gully. About 25 km west of Mullewa. Along a gully of glacio-marine facies, low, extensive exposures of the Nangetty Formation from the mid-Carboniferous to the Lower Permian, that has many dropstones.

Locality 12 - Badgedong Creek - Wooderarrung River. About 18 km northwest of Mullewa. Coarse-grained channel-fill facies in a long exposure on the river bank, of the mid-Carboniferous to the Lower Permian, Nangetty Formation.

Locallity 13 - Nangerwalla Creek. 23 km north-northwest of Mullewa. Fine-grained glacio-marine facies of the Nangetty Formation from the mid-Carboniferous to the Lower Permian, in a small cliff on the bank.

Locality 14 - Wenmillia Creek - Wooderarrung River. About 7 km northwest of Mullewa. Moderate exposures on the banks of conglomerate, sandstone, and siltstone facies, of glacio-marine origin, of the mid-Carboniferous to the Lower Permian, Nangetty Formation.

Locality 15 - Wootbeeria Pool - Wooderarrung River. About 12 km northwest of Mullewa. Sandstone diamictite and channel-fill facies of the mid-Carboniferous to the Lower Permian, Nangetty Formation, in a good cliff section.

Sources & Further reading

  1. Geology of the Northern Perth Basin, Western Australia - a field guide


Author: M. H. Monroe
Last Updated 21/10/2016


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