Australia: The Land Where Time Began

A biography of the Australian continent 

Kangaroo Island                                                                                                                                      Last updated 21/10/2016

Kangaroo Island is 14.5 km from the South Australian coast. During the later part of the latest glacial phase it was connected to the mainland, a low range of hills on the continental shelf. The Murray River flowed for 70 km across the shelf, in a southwesterly direction, from the present mouth. It passed within 10m km of the eastern end of the present island, entering the sea 20 km to the south.

Kangaroo Island, numerical dating3

The weathered lateritic land surface that dominates the Fleurieu Peninsula or the southern Mt Lofty Ranges and the southern Eyre Peninsula and on Kangaroo Island, though the remnants of this surface on the island have been dissected and stripped (Daily et al., 1974; Daily et al., 1979). Laterite caps the plateau of the upland backbone of Kangaroo Island, having developed on rocks that have been dated to the Precambrian, Cambrian and Permian, indicating that this capping is younger than the Permian rocks, though it is older than a basalt that is above it.

As the basalt has the appearance of being fresh which the led the original mappers in the 1950s to correlate it with the volcanic rocks from the Pleistocene and Holocene that are present in the South East district of South Australia and western Victoria (Sprigg et al., 1954). This appeared to be consistent with the laterite being attributed to the Pliocene, based on long-distance correlation from northern Australia (Northcote, 1946; see also Whitehouse, 1940, though later the laterite in Queensland was adjusted to Miocene). The basalt was found to be old based on (Wellman, 1971; McDougall & Wellman, 1976), based on physical dating by K/Ar ratios. Therefore the laterite, as well as the surface on which it formed, is younger than the Permian and must be older than the Middle Jurassic as it is overlain by basalt that has been dated to 175 Ma.

Laterite is also well developed in the tropics of the present (e.g., Maingnien, 1966). In what is now South Australia such conditions existed in the Triassic 250-210 Ma. At this time the brown coal that has been found at Leigh Creek and other small depositional basins in the Flinders Ranges and elsewhere were formed (Parkin, 1953; Wopfner, 1969; Kwitco, 1995). It has been suggested for 3 reasons that the laterite on Kangaroo Island is a remnant of a Triassic land surface that the author1 says appears to be widely developed in what is now South Australia (Twidale, 2000c) as well as in other parts of Australia.

The upfaulted lateritic surface of the Gulfs Region is indicated by physical dating, in conjunction with its well-established geological relationships,  to be older than was originally believed. Repeated physical analyses have confirmed the Jurassic age of the basalt. A Miocene age for the clays beneath that basalt has been indicated by oxygen isotope ratios (Bird & Chivas, 1988, 18989). Many have questioned the suggested the conclusion of its great age, some suggesting that to the west of Kingscote basalt rests on kaolinised clays that are not related to laterite.

Tim Allen2

The Karten stone industry was concentrated on Kangaroo Island. Near White Lagoon are remnants of linear dunes, the orientation of which are similar to those of the mainland from this time, indicating that this area was also under the influence of the same aeolian conditions during the glacial period. Remnants of lunettes lie beneath the dunes, indicating that prior to the glacial maximum the lake had an area 6 times larger than the maximum size of the present lake.

Sources & Further reading

  1. Flood, Josephine, 2004, Archaeology of the Dreamtime, JB Publications.
  2. Tim Allen, in 1998, Archaeology of Aboriginal Australia, Allen & Unwin.
  3. Twidale, C.R., 2007, Ancient Australian Landscapes, Rosenberg Publishing Pty. Ltd. , NSW
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Last updated 05/08/2013 

 

Glacial Maximum in Australia 

 

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