OFR 151.pdf - CRC LEME
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OFR 151.pdf - CRC LEME

OFR 151.pdf - CRC LEME OFR 151.pdf - CRC LEME

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• On present indications, Early Cretaceous (Berriasian-Albian) temperatures in palaeosouthern and palaeo-central Australia were cool-cold (microtherm range). Temperatures in palaeo-northern Australia almost certainly were warmer (mesotherm range). • Climates in palaeo-southern Australia remained cool-cold (microtherm range-lower mesotherm) throughout the Late Cretaceous. Elsewhere warming is recorded, with temperatures in palaeo-central and palaeo-northern Australia becoming warm (lower mesotherm) and very warm to hot (upper mesotherm-megatherm), respectively. • Warming during the Paleocene culminated in maximum Tertiary warmth during the Early Eocene when upper mesotherm to megatherm temperature regimes are recorded in northwestern, central, southwestern, central southern and southeastern mainland Australia. The Paleocene-Eocene thermal maximum event (PETM) is reflected in warmer sea surface temperatures within the Australo-Antarctic Seaway but is best represented by the abrupt appearance of a tropical mangrove palm (Nypa) in the Gippsland Basin (palaeolatitude 62 0 S) and Macquarie Harbour (palaeolatitude 66 0 S) during the Paleocene-Eocene transition. Locally high (mesotherm range) temperatures persisted into late Early Eocene time in Macquarie Harbour and the Gippsland Basin, and into Middle-Late Eocene time in the Polda Sub-basin in south-west South Australia. Temperatures in coastal northeastern Queensland appear to have remained cool (lower mesotherm) during the Early Eocene warm period, possibly because of cool ocean currents flowing northwards along the eastern margin. • Very warm to hot (megatherm range) temperatures persisted in northwestern Australia throughout the Middle-Late Eocene and, despite a global cooling, regional temperatures remained high throughout the Late Tertiary due to the rapid northward drift of the continent. Very warm (upper mesotherm) conditions do not appear to have developed in coastal northeastern Australia until Oligo-Miocene time. • Temperatures in central and southern Australia began decreasing to lower mesotherm-upper microtherm values during the Middle Eocene although there is weak evidence for temporary warming in southeastern Australia during the late Late Eocene. This was followed by abrupt cooling, associated with opening of the Tasmanian Gateway and Drake Passage allowing deepwater circulation around Antarctica. Outside of Antarctica, cooling was most severe in Tasmania, where the Eocene-Oligocene transition is marked by transient glaciation (Lemonthyme Glaciation), and in the Gippsland Basin, where the event is reflected in major impoverishment of the rainforest flora. Temperatures in central southern and southwestern Australia remained relatively warm, probably due to warm water gyres within the Great Australian Bight. • Climates in southern Australia appear to have been milder during the Early Miocene than during the Oligocene or the Middle-Late Miocene (microtherm-mesotherm range), and appear to have warmed appreciably (mesotherm range) along the southern margin during the Early Pliocene before continuing to decline during the Late 113

Pliocene. The warm phase correlates with the 'mid' Pliocene warm event recorded elsewhere at middle-high latitudes in the Southern and Northern hemispheres. 8.1.5 Rainfall • Unlike marine microfossils, terrestrial fossil floras provide direct information on one of the major factors (rainfall) promoting chemical weathering. Seaways developing across Australia helped to maintain high humidity in the interior of the continent during the mid Cretaceous. Orographic effects and groundwater discharge helped maintain humid-perhumid microclimates within drying environments during the Late Tertiary. • Apart from the Berriasian-Barremian, when climates may have been subhumid in northwestern Australia, humid to perhumid climates extended across the continent throughout Early Cretaceous time. On present indications, conditions remained wet to very wet (humid-perhumid) in central southern and southeastern Australia during the early Late Cretaceous (Turonian to Early Campanian). • Rainfall appears to have decreased in northwestern Australia from humid-perhumid in the Late Campanian-Maastrichtian to sub-humid-humid in the Paleocene. A similar but less marked decrease is recorded in southwestern Australia. Other regions appear to have become wetter (perhumid). • The Early Eocene thermal maximum is associated with perhumid conditions across the continent, including northwestern and central Australia where rainfall may have been strongly seasonal (possibly monsoonal). Similar conditions persisted into Middle-Late Eocene, except that rainfall in central Australia became more variable (less reliable and more seasonal) and rainfall across basins along the southern margin became more uniformly distributed. • By Oligo-Miocene time, subhumid conditions prevailed in north-west Western Australia although conditions at higher elevations within the Pilbara region remained sufficiently wet during summer months to support temperate rainforest species. There is weak evidence for a decrease in rainfall in central and south-west Australia. Rainfall remained in the perhumid range in the south-east mainland and Tasmania but may have become less reliable or weakly seasonal. • By the Late Pliocene, essentially modern rainfall regimes were in existence across Australia. Conditions on the Southeastern Highlands of New South Wales were effectively wetter during the mid Pliocene than now. The Yallalie site provides unequivocal evidence for three periods of aridification, at 2.9 Ma, 2.59 Ma and 2.56 Ma, in south-west Western Australia during the same interval (Middle Pliocene warm period). The vegetation response is similar to that observed during Quaternary glacial-interglacial cycles and corresponds broadly with the development of continental ice sheets in the Northern Hemisphere. 114

• On present indications, Early Cretaceous (Berriasian-Albian) temperatures in palaeosouthern<br />

and palaeo-central Australia were cool-cold (microtherm range).<br />

Temperatures in palaeo-northern Australia almost certainly were warmer (mesotherm<br />

range).<br />

• Climates in palaeo-southern Australia remained cool-cold (microtherm range-lower<br />

mesotherm) throughout the Late Cretaceous. Elsewhere warming is recorded, with<br />

temperatures in palaeo-central and palaeo-northern Australia becoming warm (lower<br />

mesotherm) and very warm to hot (upper mesotherm-megatherm), respectively.<br />

• Warming during the Paleocene culminated in maximum Tertiary warmth during the<br />

Early Eocene when upper mesotherm to megatherm temperature regimes are recorded<br />

in northwestern, central, southwestern, central southern and southeastern mainland<br />

Australia. The Paleocene-Eocene thermal maximum event (PETM) is reflected in<br />

warmer sea surface temperatures within the Australo-Antarctic Seaway but is best<br />

represented by the abrupt appearance of a tropical mangrove palm (Nypa) in the<br />

Gippsland Basin (palaeolatitude 62 0 S) and Macquarie Harbour (palaeolatitude 66 0 S)<br />

during the Paleocene-Eocene transition.<br />

Locally high (mesotherm range) temperatures persisted into late Early Eocene time in<br />

Macquarie Harbour and the Gippsland Basin, and into Middle-Late Eocene time in<br />

the Polda Sub-basin in south-west South Australia. Temperatures in coastal<br />

northeastern Queensland appear to have remained cool (lower mesotherm) during the<br />

Early Eocene warm period, possibly because of cool ocean currents flowing<br />

northwards along the eastern margin.<br />

• Very warm to hot (megatherm range) temperatures persisted in northwestern<br />

Australia throughout the Middle-Late Eocene and, despite a global cooling, regional<br />

temperatures remained high throughout the Late Tertiary due to the rapid northward<br />

drift of the continent. Very warm (upper mesotherm) conditions do not appear to<br />

have developed in coastal northeastern Australia until Oligo-Miocene time.<br />

• Temperatures in central and southern Australia began decreasing to lower<br />

mesotherm-upper microtherm values during the Middle Eocene although there is<br />

weak evidence for temporary warming in southeastern Australia during the late Late<br />

Eocene. This was followed by abrupt cooling, associated with opening of the<br />

Tasmanian Gateway and Drake Passage allowing deepwater circulation around<br />

Antarctica. Outside of Antarctica, cooling was most severe in Tasmania, where the<br />

Eocene-Oligocene transition is marked by transient glaciation (Lemonthyme<br />

Glaciation), and in the Gippsland Basin, where the event is reflected in major<br />

impoverishment of the rainforest flora. Temperatures in central southern and<br />

southwestern Australia remained relatively warm, probably due to warm water gyres<br />

within the Great Australian Bight.<br />

• Climates in southern Australia appear to have been milder during the Early Miocene<br />

than during the Oligocene or the Middle-Late Miocene (microtherm-mesotherm<br />

range), and appear to have warmed appreciably (mesotherm range) along the southern<br />

margin during the Early Pliocene before continuing to decline during the Late<br />

113

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