A biography of the Australian co

Parts of the Eromanga Basin containing Jurassic and Cretaceous aquifers that form the Great Artesian Basin - GAB. With an area of 1.7 million square km, about 20m % of the continent, underlying parts of Queensland, Northern Territory, New South Wales and South Australia.

The presence of the GAB allowed the introduction of livestock to marginal ands around the desert areas of central Australia. The resulting overgrazing has increased the area of the deserts at the expense of the marginal land.

During the Jurassic and Cretaceous Periods the area of the GAB was covered by forests thought to be similar to the modern day Amazon Basin. Under these conditions large amounts of sand were deposited. During the Cretaceous the sea invaded the basin, the Eromanga Sea. During this marine period more sand was laid down, becoming another layer of sandstone. The multiple layers of sandstone account for the aquifers at different depths.

These layers of sand stone slope down from east to west. This accounts for the pressure of the water. The recharge is mostly at the eastern edge of the basin, along the western slopes of the Great Divide. Along the eastern edge of the basin the layers of sandstone are warped up sufficiently to allow water to seep into it from the rain falling on the western slope of the Great Divide. This edge of the sediments total about 15,000 square km. The recharge rate is highest at places of yellow earth that quickly saturate allowing water to run off to be absorbed by red earths further down the slope.

The travel time for the water is very slow. Water seeping in at the ranges east of Longreach takes 2 million years to arrive at Lake Eyre. When the flow of the water is impeded by impervious rock it can reach the surface where it exits as a spring or mound spring, and can form a salt pan. Te same sedimentary layers can also hold oil deposits where an impervious cap rock lies above the sandstone layers.

Carnarvon Basin

Perth Basin

Great Artesian Basin-GAB

Murray-Darling Basin

Murray Basin

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