Geology
Geologists consider that Kakadu's landscape reflects the geological history of the region. Rocks of different types and ages determine topographical and soil characteristics.
Kakadu's spectacular rock formations have taken millions of years to shape and form.
Landforms
- Kakadu Stone Country
- Kakadu Outliers
- Kakadu Lowlands
- Kakadu Southern Hills and Basins
- Kakadu Floodplains
- Kakadu Estuaries and Tidal Flats
Aboriginal people have probably occupied the Kakadu area for at least 50 000 years, during which time they have had to adapt their lifestyle and technology to survive some major changes in environmental conditions.
Scientists believe that between 120 000 and 6 000 years ago the earth experienced a series of ice ages that caused rises and falls in the sea level as the polar ice caps thawed and froze. The sea level was at its lowest at around 110 000, 90 000, 70 000 and 19 000 years ago. At these times Australia and New Guinea were one continent, separated from the Indonesian chain of islands by only 60-100 kilometres of water (Press et al 1995). It is widely thought that it was during these periods that people using water craft first entered Australia. Incontrovertible evidence to support this theory will probably never be found because the coastline where people would have first landed is now covered by the sea.
Between 9 000 to 7 000 years ago sea-level rises caused flooding of river valleys. In time, the river valleys silted up and huge mangrove swamps were formed over much of northern Kakadu. A completely new range of food resources-such as barramundi, estuarine crocodile, catfish, mullet and shellfish-moved into the region and were used by Aboriginal people. The sea level stabilised and reached its present position about 6000 years ago.
Between about 4 000 and 1 500 years ago estuarine conditions began to be replaced by freshwater conditions. Continued siltation and levee formations restricted the incursion of saltwater tides, and freshwater began to cover areas of mangrove swamps. This process formed the wetlands of Kakadu, which continue to provide Aboriginal people with turtles, file snakes, edible reeds and water lilies, and large numbers of waterbirds.
2,500 million years ago The oldest known rocks of Kakadu formed as granite intrusions in the earth's crust. |
2,000 million years ago Erosion of crust exposes granite. Faulting forms wide shallow depression or "geosyncline". |
1,870-2,000 million years ago The Oxygenated Atmosphere evolves. High areas eroded and deposited as sediments in geosyncline. Faults "sag" and Basin receives 10km thickness of sediments. |
1,860 million years ago Weight of sediments destabilises earth's lower crust and mantle, leading to mountain building - pressure and heat fold and metamorphose sediments to gneiss and schist. New granite intrusions occur. |
1,800-1,860 million years ago Faults open up rift valleys in southern Kakadu and volcanoes fill them with lava. Very rapid erosion occurs by high energy rivers. |
1,800 million years ago Long erosion period in arid climate produces flat desert-like landscapes with scattered low ridges and hills. Rocks are deeply leached. |
1,650 million years ago Large braided reivers spread 1000m thickness of sand during flash floods from unknown source to north west. |
140 million years ago Mesozoic seas spread across the area, eroding older sandstone, into sea cliffs (Arnhem Lands escarpment) and islands (outliers). Fossiliferous sandstone and siltstone deposited over lowlands. |
100 million years ago Mesozoic Seas recede and most of their fossiliferous sediments are eroded away. The major escarpments of today's landscape are now apparent. |
50 million years ago Ancient Faults in southern Kakadu move once more to form local depressions. Swampy sediments with fossil tree palm spores are laid down and preserved. |
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