OFR 151.pdf - CRC LEME

Inferred climate
Climates appear to have been very wet (perhumid) but cool (lower mesotherm) relative to
western Tasmania and probably with a stronger seasonal bias.
2.2 Microfloras
Sites preserving Early Eocene microfloras are widely distributed along the southern margin
and extend northwards into central Australia although only rudimentary data were available
for some important sections, e.g. for the Kings Park Shale, Perth. Carbonate facies
accumulating off the northwestern coast rarely preserve plant microfossils other than
dinoflagellates and information for this region is due to fortuitous preservation of miospores
in two offshore exploration wells (M.K. Macphail unpubl. data). Early Eocene sediments are
either absent due to erosion and/or non-deposition, or have not been sampled in wells drilled
in the offshore Bight basins.
Whether or not the Upper Lygistepollenites balmei/Lower Malvacipollis diversus Zone
boundary coincides with the Paleocene-Eocene Thermal Maximum is unproven but the
microfloral data provide reliable evidence that maximum Tertiary warmth occurred during the
Early Eocene in southern Australia.
2.2.1 North-West Australia
1. Bonaparte Basin
Probable late Early Eocene sediments at 582-690 m in Jacaranda-1 preserve diverse
microfloras dominated by Casuarinaceae (Haloragacidites harrisii), Euphorbiaceae
(Malvacipollis diversus) and Restionaceae (Milfordia homeopunctata). These are associated
with frequent Cyperaceae (Cyperaceaepollis neogenicus) and sporadically frequent to
common Myrtaceae (Myrtaceidites parvus-mesonesus), Proteaceae, and unidentified
tricolpate and triporate types (one resembling the warm temperate rainforest tree Celtis).
Gymnosperms are uncommon, with the only genus recorded being Araucaria. Other rare taxa
include aquatic and semi-aquatic freshwater ferns and fern allies (Azolla, Selaginella, Isoetes,
Stenochlaena), Sparganiaceae (Aglaoreidia qualumis), Palmae (Arecipites, Dicolpopollis,
Longapertites, Nypa), Anacolosa (Anacolosidites acutullus), Cunoniaceae, Droseraceae,
Guettarda, Gunnera, Ilex Liliaceae, Poaceae, Polygonum (Glencopollis) and Xylomelum
occidentale-type. Some of these taxa do not appear in the southeastern basins until the Late
Eocene or Early Oligocene and the herbaceous component is unusually prominent relative to
southern Australia as a whole.
2. Browse Basin
Abundant spores of Azolla in possible Early Eocene assemblages in Prudhoe-1 (1010-1274 m)
suggest freshwater swamps fringed the coastline. The only gymnosperm recorded is
Araucaria.
Inferred climate
The combined microfloral data primarily represent freshwater coastal swamp communities
fringed by angiosperm-dominated rainforest. Climates appear to have been hot (megatherm)
and seasonally very wet (perhumid).
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