Tirari formation and contained faunas, Pliocene of the Lake Eyre basin, South Australia

Abstract

First recognized at Lake Palankarinna, south-eastern Lake Eyre Basin, South Australia, the Tirari Formation has subsequently been traced northward to outcrops along the lower Warburton River. Unfossiliferous, red gypsiferous mudstone with interbedded cross-laminated gypsum sand is the most characteristic lithology. A basal streamchannel fill at Lake Palankarinna, the Mampuwordu Member, contains the Palankarinna Fauna, and a widespread nested sequence of channel fills at the top, the Pompapillina Member, produces the Toolapinna and Kanunka faunas. These faunas are dominated by extinct species and contain diprotodontid and macropodid genera not found in Pleistocene or Recent assemblages. They differ from older Tertiary faunas in that their taxa are more closely related to living or Pleistocene clades. The Kanunka and Toolapinna assemblages contain Ewyzygoma Longman, Prionotemnus Stirton, Kurrabi, Protemnodon devisi Bartholomai, and conilurine rodents in common with Pliocene faunas elsewhere in Australia. The presence of conilurine rodents suggests a maximum age of 4.5 Ma for the upper part of the Tirari Formation. Magnetostratigraphic studies indicate that the Tirari Formation is largely reversed in magnetic polarity, but contains normal intervals at and near the base at Lake Kanunka and the lower Warburton. Faunal evidence constrains correlation of the upper part of the Tirari Formation with the youngest reversed normal interval in the Gilbert Chron (3.9 - 3.4 Ma).