The Kalgoorlie Region

Australia: The Land Where Time Began

The Kalgoorlie Region

Kalgoorlie is in the Eastern Goldfields Province of the Yilgarn Craton. The gold mining of the area has had a very large effect on the environment because the surrounding area was scoured for the wood used in the smelting furnaces. It is in the centre of the Roe Palaeodrainage. This drainage system flowed to the east into the Eucla Basin. It is from the Cretaceous to Early Tertiary, that flowed through the present Lake Roe area. It is separated by a palaeodivide from the Rebecca palaeodrainage in the north and the to the south from the Lefroy palaeodrainage system.

A dendritic pattern is formed by the chains of playa lakes occupying the palaeodrainage channels. They drained east and south-east into the Eucla Basin. The basin was a sea during the Eocene and Miocene, before being uplifted to become the Nullarbor Plain. Parts of the palaeodrainage drained south to the Bremer Basin. This basin was a sea during the Eocene.

In some of the valley fill sediments in parts of the palaeodrainage there are plant fossils and spongolite, extending as far as Norseman. The valleys predate the tectonic movements that occurred about 30 Ma in the Mid Tertiary along the Jarrahwood Axis, forming a drainage divide parallel to the south coast.

There is some evidence that the palaeodrainage system predates the separation from Antarctica. If this is the case, the south-trending valleys and their extensions south of the Jarrahwood Axis in the area around Esperence, could be the remnants of palaeoriver valleys flowing from Antarctica to Australia.

The following is a timetable for the formation of the Kalgoorlie section of the Yilgarn Craton.

Permian glaciation 300 million years ago led to the formation of a palaeoplain as the glaciers scoured the land surface, removing much of any pre-existing surface features.
Erosion during the Mesozoic continued, large valleys from at least the Early Tertiary are cut into a very level land surface.
A drainage pattern was established with several kilometres-wide valleys. These ancient valleys are outlined by chains of salt lakes along the palaeochannels. Between the Swan-Avon drainage and the Kalgoorlie area drainage system there was a major divide.
During the Jurassic the separation of Australia from Antarctica occurred, signalling the final break up of Gondwana. The wide valleys of the Avon-Swan catchment used to carry major rivers flowing from Antarctica prior to the rifting. While Australia was still connected to Antarctica it had a warm wet climate, resulting in greater river flows, that were added to by the rivers draining from high Antarctic mountain ranges. In the south-eastern Yilgarn, major south to north trending valley systems, such as the Cowan Palaeodrainage System, are relicts of the connection to Antarctica.
Rivers had cut a system of valleys into the bedrock by the Eocene. Rivers were active between the Late Cretaceous and Early Tertiary because of the warm, wet climate of the time. Valley-fill sediments began to be deposited during the Eocene, indicating that the rivers were flowing less strongly, filling rather than cutting. In sediments from Lake Lefroy, from the Late Eocene a pollen record shows that at least 26 species from 12 genera were present. There were 8 species of PROTEACEAE, 4 species of southern beech (Nothofagus) as well as tree ferns. In other parts of the palaeodrainage system, pollen from a similar age shows the presence of Araucarian and Podocarp conifers. In marginal marine areas Nypa palms and mangroves were present. This mix of pollen types shows that the palaeovalleys were surrounded by riverine rainforest.
During the Middle to Late Eocene, there were 2 marine incursions. The Tortachilla transgression, the first, deposited marine limestones in the Cowan palaeochannel. The Aldinga transgression, during the Late Eocene, extended a long way up the valleys at least as far as 270 km from the present coast. Marine sediments were laid down at Norseman and near Lake Cowan. During the Aldinga incursion, the Princess Royal spogolites were deposited.
The area was uplifted by tectonic activity, in some places by up to 300 m. The southern edge tilted, to form the Jarrahwood Axis. Some palaeorivers from the Eocene crossed this axis, such as the Cowan palaeoriver, near Norseman. The slope of the rivers south of the axis is reversed.
weathering and erosion continued after Eocene sediments filled the valleys. At different times duricrusts formed on surface deposits. As the continent drifted north into different climatic zones Yilgarn rivers were drying up. The flow in the rivers in the palaeovalleys on the east of the main palaeodivide gradually stopped flowing. Now they only carry water at times of heavy rain. It is more than 15 million years since they flowed as normal rivers do in wetter climates.