The Winton Formation

The Winton Formation is the name given to a thick sequence of sedimentary rocks which are the uppermost rock sequence in the Great Artesian Basin. The Winton Formation is widely distributed, stretching from just north of Winton in central western Queensland south into New South Wales and South Australia.

Outcrop of the Winton Formation near Diamantina National Park Outcrop of the Winton Formation near
Diamantina National Park

At its northern margins the formation is quite thin, but it is nearly 1200 metres thick in the centre of the Great Artesian Basin near Thargomindah. The rocks present in the Winton Formation are mostly sandstone and siltstone, but there are also thin bands of coal known from drillholes made deep through the rock unit.

The Winton Formation contains a large number of dinosaur and other fossils. These are of Cretaceous age and are between 98-95 Million years old. The three dinosaurs Australovenator, Diamantinasaurus and Wintonititan are from the Winton Formation as are new dinosaurs from the region west of the town of Eromanga. Fossil crocodiles, fishes, lungfish, turtles, insects, freshwater mussels and other dinosaur remains are found in the Winton Formation.

The thickness and extent of the Winton Formation, makes it one of the biggest geological formations on the continent. Much of the sediment which formed the rock unit was derived from far to the east. Looking in detail at the sediment it is clear that it originates from the recycling of volcanically-derived material. During the Early Cretaceous period there were large volcanoes along much of the northeast coast of Queensland. Some of the volcanic rocks are now preserved in the Whitsunday Islands.

Much of the Winton Formation has been deeply weathered creating altered rocks known as laterites and silcretes. In places this alteration has produced opal deposits and mining occurs in several places in western Queensland. Dinosaur fossils are not generally found in the altered rocks. It is only in the less weathered areas that bones have been recovered.

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