OFR 151.pdf - CRC LEME

Haig and Lynch 1993, Erbacher et al. 1999). By the end of the Albian [97 Ma], the sea had
retreated from the southern Eromanga Basin. This allowed extensive freshwater swamps to
form around the margins of the basin although a shallow sea bordered by large deltas and
brackish estuaries remained present in its centre and also in the Gulf of Carpentaria
(Carpentaria Basin) where maximum flooding occurred in the Early Albian (Haig and Lynch
1993, Henderson 1998). Much of the western half of the continent was subaerially exposed
by this time, including part of the continental shelf seaward of the present-day coastline. This
landscape rejuvenation, which is reflected in the marine sedimentary record (Henderson
1998), was broadly contemporary with renewed uplift in eastern and southern Australia. Nott
and Purvis (1995) have recorded a ~100 Ma (Early Albian) basalt outcropping near sea level
in southern New South Wales but its implications for uplift of the Southeastern Highlands
remain controversial (Orr 1996).
5.5.2 Palaeobotany
The mid Cretaceous period was marked by the ecological re-assortment of gymnosperm and
cryptogam communities making up Austral Conifer Forest, and the immigration and
expansion of angiosperms, chiefly at the expense of ferns and fern allies.
Burger (1990) has proposed that, beginning in the Late Barremian/Early Aptian, successive
waves of angiosperms entered palaeo-northeastern Australia (present-day Northern Territory)
from (tropical) East Asia via Indonesia, and, less certain, from Africa via India. The diversity
of angiosperm taxa increased markedly during the Albian. Nevertheless, in palaeo-southern
Australia (present-day New South Wales and Victoria), gymnosperms continued to dominate
the canopy strata into Late Cretaceous-Early Tertiary times. Floristic contrasts between
palaeo-southern and palaeo-northern margins appear to have sharpened and the same may be
true for the Perth and Eromanga Basins. The observations strengthen the case that Austral
Conifer Forest was better developed (more diverse) at higher elevations and palaeolatitudes,
including on the uplands bordering the Eromanga-Surat Seaway, whilst ferns dominated the
coastal lowlands and analogous shoreline habitats.
5.5.3 Palaeoclimates
The relative impact on plant community evolution of marine transgression-regression, and
low light intensities/low temperatures during winter months, are difficult to unravel. Rainfall
may have been unequally distributed throughout the year in many regions but is unlikely to
have limited plant growth during the Aptian-Albian.
Palaeo-northern Australia (~45-60 0 S)
Climates in palaeo-northern Australia (present-day south-west to north-west Western
Australia) were humid, possibly due to the movement of warm water eastwards into the Neo-
Tethys Seaway. Temperatures are presumed to be warm (mesotherm range) and seasonal
contrasts less marked than in inland and southern regions. NLR analysis is unhelpful since
few of the fossil taxa have living relatives, and those that have, provide contradictory results,
e.g. Ruffordiaspora (Anemia).
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