OFR 151.pdf - CRC LEME

2. Lake Torrens Basin
Abundant leaf impressions are preserved in probable Middle Eocene channel fill deposits
(Willalinchina Sandstone) in the Billa Kalina Basin, north-west of Lake Torrens. These
include the oldest confirmed remains of Eucalyptus in Australia as well as the casts of a reedlike
plant (Callen and Cowley 1995). Probable correlatives of the Willalinchina Sandstone in
the Woomera and Andamooka areas further to the west also preserve silcrete casts, in
particular the moulds of leaves, and fruits (Offler 1969, cited in Callen and Cowley 1995,
Lange 1978b). Fossils provisionally assigned to extant genera include Cupressaceae,
Podocarpaceae (cf. Dacrycarpus, cf Podocarpus), Casuarinaceae, Myrtaceae (Angophora,
Eucalyptus, Callistemon, Calathamnus, Leptospermum and Melaleuca), Proteaceae (cf
.Banksia) and Santalaceae (Santalum).
Inferred Climate
The source vegetation was a mosaic of mesotherm rainforest and sclerophyll communities,
which are presumed to have grown along rivers and across interfluves, respectively
(Christophel 1994, Benbow et al. 1995). Foliar physiognomic analyses (Christophel and
Greenwood 1989, Greenwood 1994, 1996) indicate mean air temperatures were within the
upper mesotherm range (~18-21 0 C) in the southern Eyre Basin and possibly warmer (~21 0 C)
at Poole Creek. Rainfall is seen as being moderate (1000 mm pa) but strongly seasonal
(possibly monsoonal).
3.1.4 South-West Australia
1. Yilgarn Craton
Palaeochannels incised into the south-western margin of the Yilgarn Craton preserve
abundant plant impressions and petrifactions, e.g. the Kojunup, Pallinup and West Dale Floras
(Hill and Merrifield 1993, Scriven et al. 1995, Barnes and Hill 1999b). These have been
assigned a Middle Eocene-Oligocene age range, based on similarities with eastern Australia.
Although the Middle-Late Eocene age is supported by microfloras preserved in other
palaeochannels in the region, it is noted that the minimum age could be as young as mid
Pliocene based on the similarities between the West Dale Flora and the independently-dated
Yallalie flora in the same district (cf. Dodson and Macphail in press).
The West Dale Flora is dominated by Myrtaceae and Proteaceae. Species assigned to extant
families and genera include Agathis, Dacrycarpus, Cunoniaceae, Gymnostoma, Cunoniaceae
(Codia), Lauraceae, Myrtaceae, Nothofagus and Proteaceae (cf. Banksieaephyllum).
Sclerophyll features are present in many leaves but adaptations that minimize water loss
through the stoma are absent (xeromorphic features). This suggests water was readily
available but the parent plants were growing in nutrient-deficient soils.
Inferred Climate
The source vegetation appears to be a form of dry rainforest growing under seasonally wet
(humid) and relatively warm (mesotherm range) conditions. If correct, then the presence of
plicate Nothofagus leaves in the Late Eocene Kojunup flora (N. plicata) is anomalous since
plicate leaves are more typical of deciduous species growing in cool-cold (microtherm range)
climates.
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