Interpretation of the Miocene Carl Creek limestone, northwestern Queensland

Abstract

Listen

Translate article

The Miocene Carl Creek Limestone of Riversleigh, northwestern Queensland, is a clastic deposit composed of sediments characteristic of humid alluvial fans and tufas (sensu Pedley 1990). Factors influencing clastic-carbonate yield and processes of carbonate deposition indicate that the calciclastic alluvial outwash comprising the Carl Creek Limestone could only have accumulated under relatively dry, perhaps semi-arid, conditions. This palaeoclimatic interpretation for northern Australia during the Miocene is consistent with interpretations from other data-sets. Other limestone formations of similar age, widely distributed across northern Australia in various sedimentary basins represent different depositional environments, but are here related to the Carl Creek Limestone through a hypothetical hydraulic flow system. Archer et al. (1989) postulated the former presence of rainforest at Riversleigh on the basis of an exceptionally diverse mammal fauna, interpreted by them as being a sympatric assemblage. Under climatic conditions postulated here for the region during the Miocene, any rainforest was probably restricted to the proximity of perennial, springfed streams within the Carl Creek Limestone depositional basin. The high mammal species diversity in the Carl Creek Limestone might result from a combination of a rainforest-adapted proximal community, and mesically-adapted distant communities whose members travelled to permanent water sources during dry periods. Thus, radiation of Australia's marsupial faunas into drier habitats was already well advanced by earliest Carl Creek Limestone times, and Miocene rain forest at Riversleigh represented a refugium for rainforest-adapted taxa.