Late Neogene Climates in Australia: Fossil Pollen- and Spore-based Estimates in Retrospect and Prospect

Abstract

Australian sites that are claimed to preserve evidence of fossil spores and pollen for Late Neogene (Late Miocene, Pliocene) climates, mostly lack one or both of the prerequisites, i.e. accurate dating and continuous preservation of plant microfossils. Nevertheless, the available data confirm that climatic gradients closely parallelled those of the present day in direction although not in strength: broad-scale vegetation successions are ecologically consistent with long-term cooling and (middle to high latitudes) drying trends in global climate. Although it is rarely possible to establish precise meteorological values for the individual sites along these gradients, climatic envelopes can be estimated for many localities. For example, during the Late Miocene–Pliocene, mean annual precipitation along the northern margin appear to range from 600 mm to 1500 mm in the Kimberley region of north-western Western Australia to above 2000–3000 mm on the Atherton Tableland, north-eastern Queensland. If these and other estimates are correct, then environments along the northern margin show only gradual (unidirectional?) change or did not fall below biologically critical thresholds during the Late Miocene and Early Pliocene but began to approach modern values during Late Pliocene time. Whether the observation implies that meteorological controls at this time were similar to modern synoptic scale systems is unknown. Climates along the southern margin were more labile. For example, there is unequivocal evidence that Early Pliocene climates in the Bass Strait region were effectively more humid and warmer than at present, possibly resembling conditions now found on the northern New South Wales and southern Queensland coast. This phase was preceded (weak evidence) and succeeded (strong evidence) by less temperate conditions during the Late Miocene and Late Pliocene respectively. Forcing factors appear to include changes in relative sea level, orographic effects and, speculatively, remote events such as the isolation and reconnection of the Mediterranean Sea to the world ocean. One promising direction for future research is provided by a recently located onshore basin in Western Australia which preserves an extraordinarily long (100 m), detailed sequence of Late Neogene palynofloras.