Winton Formation

The Winton Formation is a Cretaceous formation in central-western Queensland, Australia. It is late Albian to early Turonian in age,[2] so straddles the Cenomanian-Turonian boundary.

Winton Formation Stratigraphic range: Late Albian-Early Turonian ~104–92 Ma PreЄ Є O S D C P T J K Pg N
Type	Geological formation
Unit of	Rolling Downs Group
Underlies	Unconformity with Quaternary Lake Eyre Basin sediments
Overlies	Mackunda Formation,[1] Oodndatta Formation
Thickness	<100 m (330 ft) at the margin 1,200 m (3,900 ft) in the centre
Lithology
Primary	Sandstone, siltstone, claystone
Other	Conglomerate, coal
Location
Region	Queensland
Country	Australia
Extent	Eromanga Basin
Type section
Named for	Winton, Queensland
Named by	Whitehouse
Location	Bores in and around Winton
Year defined	1955
Formation distribution within Australia

The formation is a rock unit that blankets large areas of central-western Queensland. It consists of sedimentary rocks such as sandstone, siltstone and claystone. The sediments that make up these rocks represent the remnants of the river plains that filled the basin left by the Eromanga Sea - an inland sea that covered large parts of Queensland and central Australia at least four times during the Early Cretaceous. Great meandering rivers, forest pools and swamps, creeks, lakes and coastal estuaries all left behind different types of sediment.

In some areas, the Winton Formation is over 400 metres thick. To bring with them such a huge amount of sediment, the rivers that flowed across these plains must have been comparable in size to the present-day Amazon or Mississippi rivers. As more and more sediment was brought in, the margins of the inland sea slowly contracted. By around 95 million years ago, the deposition was complete and the inland sea would never be seen again.

By virtue of its age and the environmental conditions under which the rocks it consists of were deposited, the Winton Formation represents one of the richest sources of dinosaur fossils anywhere in Australia.