LATE NEOGENE CLIMATES IN AUSTRALIA - FOSSIL POLLEN-BASED AND SPORE-BASED ESTIMATES IN RETROSPECT AND PROSPECT

Australian sites that are claimed to preserve evidence of fossil spore s and pollen for Late Neogene (Late Miocene, Pliocene) climates, mostl y lack one or both of the prerequisites, i.e. accurate dating and cont inuous 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 vegeta tion successions are ecologically consistent with long-term cooling an d (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-Pl iocene, 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, nor th-eastern Queensland. If these and other estimates are correct, then environments along the northern margin show only gradual (unidirection al?) change or did not fall below biologically critical thresholds dur ing the Late Miocene and Early Pliocene but began to approach modem va lues during Late Pliocene time. Whether the observation implies that m eteorological controls at this time were similar to modern synoptic sc ale systems is unknown. Climates along the southern margin were more l abile. For example, there is unequivocal evidence that Early Pliocene climates in the Bass Strait region were effectively more humid and war mer than at present, possibly resembling conditions now found on the n orthern New South Wales and southern Queensland coast. This phase was preceded (weak evidence) and succeeded (strong evidence) by less tempe rate conditions during the Late Miocene and Late Pliocene respectively . Forcing factors appear to include changes in relative sea level, oro graphic effects and, speculatively, remote events such as the isolatio n and reconnection of the Mediterranean Sea to the world ocean. One pr omising direction for future research is provided by a recently locate d onshore basin in Western Australia which preserves an extraordinaril y long (100 m), detailed sequence of Late Neogene palynofloras.