A very exciting paper recently came out, which provides the first radiometric dates for 10 of Riversleigh’s 300 fossil sites. Why is this exciting news? Previously, the age of the Riversleigh sites was extrapolated from similarities with other dated sites in Australia, or using the stage of evolution of the animals present in the sites. Basically, previous ages were educated guesses.
Dating the Riversleigh limestones, most of which formed in caves, has been very difficult. The technique used in the paper, Uranium-lead dating, was essentially developed for this purpose. The dates come from flowstone and stalagmites/stalagtites (also known as speleothems) which have been buried at the time that the fossils got deposited in the cave. The caves have since eroded, revealing the fossils.
The dates corroborate previous estimates of the age of the Riversleigh site, all, but one, Rackham’s Roost, which was found to be a lot younger than previously thought.
Woodhead, J., Hand, S., Archer, M., Graham, I., Sniderman, K., Arena, D. A., Black, K. Godthelp, H. Creaser, P., and Price, E., 2014. Developing a radiometrically-dated chronologic sequence for Neogene biotic change in Australia, from the Riversleigh World Heritage Area of Queensland. Gondwana Research. DOI: 10.1016/j.gr.2014.10.004.