Australia: The Land Where Time Began

A biography of the Australian continent 

Isa Highlands, Northwest Queensland

The Isa Highlands is an Appalachian style fold mountain belt that involves sediment and metasediments from the Proterozoic, as well as granite intrusions. The orogenesis occurred before the Middle Cambrian, at which time a marine incursion covered the Georgina Basin to the west, that margin of which reached the southern part of the upland of the present. In the Burke River headwater region, the terrain that is low and hilly, that had been buried, has been exhumed. To the east of the highlands, the Carpentaria Basin was downwarped and block faulted, beginning in the Triassic. The uplifted highlands produced an extensive planation surface as a result of erosion, that was mostly low, 50-120 m, though hilly in places. The Late Jurassic sequence is characterised by freshwater deposits, but the oceans had covered the basins and the uplands by the Early Cretaceous. Recurrent upwarping of the Isa Block is indicated by alternating deposits of marine and freshwater origin.

In levels on the quartzite ridge crests the surface from the Late Jurassic-Early Cretaceous is well preserved. In low areas surrounding the ranges there are remnants of the cover from the Cretaceous, though in parts of the higher relief there are also some small remnants. There are remnants in embayments of the uplands, ad in these embayments that are weathered and laterised. Through the Cainozoic the upwarping of the highlands continued, the Selwyn Upwarp being active in the Late Cretaceous.

In the Isa Highlands, the sub-Cretaceous plantation surface that has been exhumed, can be traced into unconformity to the east beneath the Carpentaria Basin, as well as at the edges of the uplands. There are large areas of sediments from the Late Mesozoic where it re-emerges in the Georgetown Inlier, as well as in places where the area that had been covered by the advancing Cretaceous seas has been re-exposed, as occurs in the Isa Highlands, that extended as far as the Newcastle Range to the east.

Sources & Further reading

  1. Twidale, C.R. & Campbell, E.M., 2005, Australian Landforms: Understanding a Low, Flat, Arid, and Old Landscape, Rosenberg Publishing Pty Ltd
Author: M. H. Monroe
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