Geochronology and provenance of the Late Devonian Canowindra fish bed, Lachlan Orogen

Placoderms, armoured fish, are recognised as the most diverse group of fish in the Devonian period and were found throughout the world in marine and freshwater environments. Fossil records show placoderms occur from Early Silurian to the Late Devonian, and completely disappear from the fossil record at the Devonian to Carboniferous boundary. The Canowindra fish bed of the Mandagery Formation, is a remarkable Lagerstätte of placoderm fish, first discovered in 1956. The timing and cause of death, however, also remains uncertain. This study suggests the Canowindra fish bed was deposited in a shallow marine environment, as opposed to the previously suggested fluviatile environment. Field observations suggest that the fish assemblage lies within the lower rather than the upper part of the Mandagery Formation. Zircon U/Pb radiometric dating presents a maximum depositional age of 363 ± 3.1Ma for the Canowindra fish bed. Finally, using these new findings, a new timescale of the Hervey Group is introduced, as well as a new model for the cause of death of the Canowindra fish fauna. The new model suggests the timing and cause of death may be associated with the Frasnian-Famennian mass-extinction event -- abstract.