Australia: The Land Where Time Began

A biography of the Australian continent 

Lake Mungo    Lakes Climate Cycles

Lake Mungo is part of the Willandra Lakes system.

The Murray Basin lakes were full between 55,000 and 30,000 years ago, except for a brief time at about 36,000 year ago. At this time westerly winds and the resulting wave action produced white sand beaches on the eastern side of the lake. During dry summers foreshore dunes were built up by sand blown from the beaches. The Mungo Unit is formed from these dunes. When they reached a height at which they were stable they were colonised by shrubs and trees growing in the soil forming on their surface.

During the dry conditions at 36,000 years ago, lake water salinity increased. In the Mungo Unit are clay zones that indicate times when saline clay pellets were blown onto the dunes. Blowing dust clouds blew salts across the land to the east of the drying lakes. Widespread salination of soils and groundwater occurred at this time.

After the drying episode lake levels again rose, remaining high until about 22,000 year ago. At this time there was a dramatic increase of aridity as the glacial maximum was approached. During this time the Mungo Unit merges progressively into the Zanci Unit of salt-clay-rich sediments.

After all the lakes had completely dried, there was an enormous increase in the volume of saline dust and sand forming clay-rich lunettes that travelled across the land and salt lakes and salt pans dried up and contributed salinity to the dust problem. This time of severe dryness and salt is represented by the Zanci Unit in Lake Mungo.

During the glacial maximum the Murray Basin was a saline wasteland. The salt that was spread widely in the Basin is still present in the groundwater. Deep sumps of very salty groundwater formed under the drying salinas. The mechanism of this process is uncertain.

The formations at Lake Mungo, called the Walls of China, resulted from erosion of the ancient dunes. The former lake bed is a saltbush plain grazed by sheep and kangaroos. The history of the alternating dry and wet times can be read in the layers of the dunes. Layers of clean white beach sand alternate with layers of clay-rich sediment from the lake bed.

Underlying the Mungo Unit is the Gol Gol Unit, representing an earlier phase in the history of the lakes, dunes that formed before the lakes were filled.

Aboriginal Remains

Inland silcretes

The quarry is located on the western edge of the flat lake floor that is now dry, large silcrete blocks and boulders cover a low ridge, silcrete gravel occurring along the edge of the lake. Over the area of the quarry are stone axes, and nearly all the boulders show some signs of human activity (Allen, 1990; Williams, 1991). On the western shores of Lake Chibnalwood and Lake Leaghur there are also silcrete exposures that have been quarried for stone artefacts. There are few stone sources in the area of the Willandra Lakes, the result being that the sources in the area of the quarries have attracted the ancestral Aboriginal groups to the quarries throughout their occupation of the area (Allen, 1998).

In the Willandra Lakes region most of the raw material in archaeological sites is silcrete, together with much smaller amounts of quartzite and sandstone. Both types of silcrete found in the quarries were used to make artefacts, 95 % of the artefacts were made from the medium-grained silcrete and the remainder from fine-grained silcrete (Allen, 1998).

The authors used samples from the quarries for their study reported in Source 2, most of the samples being of a dull yellow orange colour with a thin weathering rind that was grey, with relatively larger inclusions of clay-cemented material that are light grey on the uneven granular fracture surfaces. The medium-grained  Lake Mungo silcrete used for the manufacture of implements consists mostly of a matrix of microcrystalline quartz with quartz clasts that are well-sorted, and sub-angular to sub-round, and mostly medium-sand-sized, and it has a microfabric that is grain-supported (Fig. 2a & Table 1, Source 2).

The Lake Mungo medium-grained silcrete was shown by the mechanical tests of the authors (Table 2, Source 2) to have poor flaking properties, with a high fracture toughness that makes it difficult to knap, the fracture toughness being lowered greatly by the inclusions of clay-cemented material. Fracture propagation of Lake Mungo silcrete lacks directional stability because of a low index of stiffness, resulting in a high frequency of step fracture terminations that are also the result of the defects in microstructure, that are represented by the medium-sand-sized quartz grains. As a result of this the Lake Mungo silcrete is much less suitable for narrow flake detachment and resharpening of the working edges.

The authors suggest the Lake Mungo medium-grained silcrete was often used for the manufacture of steep-stepped flaked artefacts, such as horsehoof cores and steep-edged scrapers (White & O'Connell, 1982; Cottrell & Kamminga, 1987; Allen, 1998), as the mechanical properties have a less deleterious effect for large, wide flake detachment (Cottrell & Kamminga, 1987; Hiscock, 1993). Blocky horsehoof cores and various forms of scraper are common in lithic assemblages from the Late Pleistocene and Holocene in the Willandra Lakes region (Jones & Allen, in Bowler eet al., 1970; Allen, 1998; Hiscock & Allen, 2000).

Links

Australian Pleistocene variation and the sex of Lake Mungo 3 

Mungo National Park

In 1981 Lake Mungo was Australia's first World Heritage site. Its significance is based on the large collection of Aboriginal artefacts as well as the skeletal remains mentioned above. About 45,000 years ago the Mungo area was covered by huge lakes covering an area of 1000 square kilometres, and estimated to have been 10 m deep. The lakes began to dry up 25,000 years ago and over the following 10,000 years formed sand dunes 30 km long along the eastern edge of the lakes. These dunes covered the evidence of human activity around the lake until modern erosion began to uncover them. 

The Mungo area is also of historical significance because it was part of the Gol Gol sheep station from 1860-1979. The Gol Gol wool shed has been preserved for historical value.

For more detailed information and illustrations see Source 1

Sources & Further reading

  1. Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000
  2. Webb, J.A. & Domanski, M, The Relationship Between Lithology, Flaking Properties & Artefact Manufacture for Australian Silcretes, Archaeometry, Oxford University, Archaeometry, 50, 4 (2008) 555-575

 

Author: M. H. Monroe
Email: admin@austhrutime.com
Last updated: 03/07/2015
 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading