Australia: The Land Where Time Began

A biography of the Australian continent 

Bathurst Island Group

The oldest marine sequences known from Australia in the Upper Cretaceous are in the Bathurst Island Group. These cover the time period between the inland sea in the Early Cretaceous (Aptian-Albian) and its regression from the continent for the last time in the mid-Late Cretaceous (Cenomanian-Turonian). A continuous series of mudstone and glauconitic siltstone/sandstone units comprise the Bathurst Island Group. These units are distributed widely across the Money Platform of northern Australia, especially in the coastal areas around Darwin, such as Casuarina Beach, the Cobourg Peninsula, Bathurst Island and Melville Island. The deposits in the Darwin region, including the Darwin Formation and the Marligar Formation, are mostly from the Lower Cretaceous. The area of Mountnorris Bay, Bathurst Island and Melville Island are the areas where the strata from the Upper Cretaceous are best exposed. Included in these are the conformably overlying Walangarlu Mudstone and the Moonkinu Formation. A regressive event along the northern coastal margin of Australia that was emerging is recorded in these units. Low-energy deep-water environments (the Walangarlu Mudstone) were gradually being replaced by high-energy shallow-water conditions (the Moonkinu Formation).

Molluscs assemblages, mostly comprising ammonites, as well as bivalves, gastropods and scaphopods, have been used to date the Walangarlu Mudstone and the Moonkinu Formation. The age indicated by this method for the Walangarlu Mudstone is uppermost Albian to Cenomanian, though at the base of the unit it may extend into the lower Albian. The overlying Moonkinu Formation is indicated to be from the Cenomanian-Turonian. Along the coast of Western Australia the marine rocks are of a slightly younger Upper Cretaceous age.

Sources & Further reading

  1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.
Author: M. H. Monroe
Last Updated 11/12/2011
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