In the early Cretaceous period (95 - 98 million years ago) an inland sea, the Eromanga Sea, covered large parts of Queensland, central Australia, and this very place at least four times. The rivers that fed the sea brought with them sediment which flowed into the sea basin. To bring with them such a huge amount of sediment, the rivers must have been comparable in size to the present day Amazon or Mississippi rivers. As more sediment was brought in, the margins of the inland sea slowly contracted and by around 95 million years ago, the job was completed and the inland sea would never be the same again.
As the sea retreated to the north, western Queensland became a fringe of coastal wetlands and open forest. Huge conifers dominated the landscape amid a wealth of lush vegetation such as cycads, ginkgos, and ferns. Horsetail flourished amongst lakes and swamps; dragonflies flew through the marshes and winged reptiles soared above in search of prey. Heavy rain was common and the climate humid and cool. Rivers meandered northward - north to the inland sea where lungfish, turtles, and crocodiles indulged in their depths.
The rocks that cover large parts of Central Western Queensland are made up of the sediments from the river plains that filled the basin left by the Eromanga Sea. These rocks today tell us fascinating stories about that distant past.
The mesas and knolls of the Lilyvale Hills and in areas to the south are evidence of the erosion caused by the inland sea. These broad, often flat-topped hills are capped with a resistant rock layer. Scientists call this 'dissected residuals' because the sediments laid down by ancient lakes and seas have been carved over the millennia by runoff from countless summer storms. The soils are easily eroded while the hardened cap rocks are more erosion resistant, giving the mesas their distinctive flat tops.
Further information and evidence of the inland sea can be seen at Boulia in the Stone House Museum where fossils of the head and teeth of the Ichthyosaurus are on display. This reptile breathed air but lived a wholly marine life as a fast, agile, underwater hunter whose main method of propulsion was its tail.
Source: outbackway.org.au
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