Authors: McLaren, S.¹; Wallace, M. W.¹; Pillans, B. J.²; Gallagher, S. J.¹; Miranda, J. A.¹; Warne, M. T.³

Source: Australian Journal of Earth Sciences, Volume 56, Number 2, March 2009 , pp. 259-270(12)

Publisher: Taylor and Francis Ltd

Abstract:

Paleo Lake Bungunnia covered more than 40 000 km2 of southern Australia during the Plio-Pleistocene, although the age and origin of the lake remain controversial. The Blanchetown Clay is the main depositional unit and outcrop at Nampoo Station in far-western New South Wales provides the most continuous lacustrine section preserved in the basin. Here the Blanchetown Clay represents the maximum lake fill and comprises: (i) a basal well-sorted sand with interbedded clay (Chowilla Sand), representing initial flooding at the time of lake formation; (ii) a thick sequence of green-grey clay comprised dominantly of kaolinite and illite, with the apparently cyclic occurrence of illite interpreted to represent cool and dry glacial climatic intervals; and (iii) a 2.6 m-thick sequence of finely laminated silt and silty clay, here defined as the Nampoo Member of the Blanchetown Clay. New magnetostratigraphic data constrain the age of the oldest lake sediments to be younger than 2.581 Ma (Matuyama-Gauss boundary) and probably as young as 2.4 Ma. This age is significantly younger than the age of 3.2 Ma previously suggested for lake formation. The youngest Blanchetown Clay is older than 0.781 Ma (Brunhes-Matuyama boundary) and probably as old as 1.2 Ma. The Nampoo Station section provides a framework for the construction of a regional Plio-Pleistocene stratigraphy in the Murray Basin.

Keywords: Blanchetown Clay; climate; lacustrine sediments; Lake Bungunnia; magnetostratigraphy; Nampoo Member; Plio-Pleistocene

Document Type: Research article

DOI: http://dx.doi.org/10.1080/08120090802547074

Affiliations: 1: School of Earth Sciences, University of Melbourne, Vic, Australia 2: Research School of Earth Sciences, Australian National University, ACT, Australia 3: School of Life and Environmental Science, Deakin University, Burwood, Vic, Australia

Publication date: 2009-03-01

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