Australia: The Land Where Time Began

A biography of the Australian continent 

Gunnedah Basin

The Gunnedah Basin is northeastern New South Wales, between the Bowen Basin to the north and the Sydney Basin to the south. Marine and non-marine sequences from the Permian and Triassic are present in it, and it contains Permian coal deposits (Tadros, 1993).

In the early Permian, deposition was initiated by basin extension and subsequent subsidence, beginning with the Mauls Creek Formation, a fluvial deposit that contains many coal seams. Marine shelf sediments of the Porcupine Formation and the regressive marine Watermark Formation, overlie unconformably the Mauls Creek Formation. The Black Jack Formation, a coal sequence of deltaic and fluvial origin, was deposited in the Late Permian (Tadros, 1993).

The Permian sequences are overlain unconformably by the sediments from the Triassic. In the Digby Formation there are 2 depositional sequences, the lower stage consisting of a conglomerate unit that was deposited by braided stream systems following uplift of the adjacent New England Fold Belt. When the elevation of the New England source area declined, the system changed from braided to meander streams, sandy sediments of the later stage were deposited. The Digby Formation is capped by a palaeosol that is basin-wide. The upper limit of the Gunnedah sequence is the Napperby depositional sequence, and a regional unconfirmity is situated between the Triassic and the overlying sediments of the Surat Basin, of Jurassic age, north of the Liverpool Ranges (Tadros, 1993).

A number of basic intrusions of rocks from the Mesozoic and Tertiary are included in the Gunnedah Basin sequence, that are associated with the massive extrusion of the Garrawilla Volcanic complex, as well as the Liverpool Ranges, Warrumbungle Ranges and the Nandewar Ranges (Tadros, 1993).

Within the Murray-Darling Basin, the Gunnedah Basin is composed of mountain ranges, to the south, along the edges of the Murray-Darling Basin, and on the low-lying areas of the Liverpool Plains, large areas of alluvium of Quaternary age. Throughout the central and western parts of the basin there are extrusive domes of the Garrawilla Volcanics from the Jurassic, and isolated hills and ridges of outcropping resistant sandstone (Tadros, 1993).

Sources & Further reading

  1. Geology of the Murray-Darling Basin - Simplified Lithostratigraphic Groupings


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                                                                                           Author: M.H.Monroe  Email:     Sources & Further reading