DEVELOPING ESR DATING FOR MARSUPIAL TEETH: RECOGNIZING MULTIPLE SEDIMENTATION EVENTS IN THE LAKE EYRE BASIN, AUSTRALIA

In the Lake Eyre Basin, the Katipiri Formation forms the last major fluvial sandsheet in the Pleistocene deposits. The Katipiri has yielded the Malkuni and Kalmurina Faunae, while the underlying Kujitara Formation has yielded Lower Cooper Creek Fauna. In the Pliocene Tirari Formation, the Kanunka, Toolapina, and Palankarinna Faunae occur, while in the underlying Etadunna Formation, the Ngapakaldi Fauna has been found. The Katipiri has yielded fossils from numerous marsupials, flamingoes, and Dromaius (emu), but also comorants, swans, grebes, ducks, herons, turtles, crocodiles, perch, and lungfish. The number of freshwater vertebrates in the Katipiri fauna suggest a fluvial system with long-term low salinity in the major streams. This implies great potential for reworked fossil material. To assess how much of the fauna found in the Katipiri were actually derived from the older units during fluvial reworking episodes, ten diprotodontid teeth from classic Katipiri localities were dated by standard ESR. Most were too small for isochron analyses.

Electron spin resonance (ESR) dating uses radiation-sensitive signals in tooth enamel. It can date tooth enamel from approximately 10 ka to 5 Ma in age, depending on the sedimentary and internal dose rates. U concentrations in the dentine fall into four distinct groups, with minimum values near 7 ppm and maximum values, 124 ppm. U concentrations in the enamel also show significant variation. The ages for the teeth grouped into four distinct groups with respective calculated ages of 80-100±5 ka, 400-500±20-30 ka, 1.1±0.1 Ma, and 2.7±0.2 Ma assuming linear U uptake. These data suggest that a substantial proportion of the teeth in the Katipiri actually have been derived from older units. While it impossible to know the precise age of the reworked teeth without detailed sedimentological of these units or ESR isochron analyses of the teeth, their presence indicates that erosion and redeposition was extremely active during Katipiri times, in late Oxygen Isotope Stage 5.