Nullarbor Plain - Geography

Geography

The Nullarbor Plain is a former shallow seabed, as indicated by the presence of bryozoans, foraminifera, echinoids and red algae calcareous skeletal that make up the limestone. The region is also the location of Nullarbor limestone and it has a reputation as a significant karst region with Oligocene and Miocene cave formations.

The sequence within the limestone includes five formations:

• the upper formation is the Nullarbor Limestone which is early middle Miocene in age;
• the Mullamullang member of this formation is a paraconforming member, being separated by 5 million years;
• the third member is the Abrakurrie Limestone that was formed in a central depression of the earlier formation; this is late Oligocene to Early Miocene in age and does not reach the edge of the plain;
• the last two formations are conforming formations; the late Eocene Toolinna Limestone lies on the Wilsons Bluff Limestone which is mid to late Eocene in age; and
• the Toolinna Limestone does not cover the whole Nullarbor and is extant only in the extreme east beside the Abrakurrie formation which lies in a depression.

One theory is that the whole area was uplifted by crustal movements in the Miocene, and since then, erosion by wind and rain has reduced its thickness. The plain has most likely never had any major defining topographic features, resulting in the extremely flat terrain across the plain today.

In areas, the southern ocean blows through many subterranean caves, resulting in blowholes up to several hundred metres from the coast. The Murrawijinie Caves in South Australia are open to the public, but most of the Nullarbor Caves on the Western Australian side can only be visited and viewed with a permit from the Department of Environment and Conservation.

The Nullarbor is known for extensive meteorite deposits, which are extremely well preserved in the arid climate. In particular, many meteorites have been discovered around Mundrabilla, some up to several tonnes in weight.

According to the United States Department of Agriculture, the Nullarbor's soils are considered to be mainly aridisols (see Image:Global soil regions.jpg).

The prevailing climate across the Nullarbor is typical of a desert, characterised by arid to semi-arid conditions, with maximum daytime temperatures of up to 48.5 °C (119.3 °F), although freezing conditions can occur at night. The mean annual rainfall at Cook is 179.7 millimetres (7.07 in).