OFR 151.pdf - CRC LEME

wind-pollinated trees and shrubs but only some herbs. Examples are the
Araucariaceae, Cupressaceae and Podocarpaceae (gymnosperms), and Casuarinaceae,
Chenopodiaceae-Amaranthaceae (usually abbreviated to Chenopodiaceae),
Nothofagaceae and Poaceae (angiosperms). A few insect-pollinated angiosperms are
well-represented because of open flowers with numerous anthers or because of their
very wide distribution. Australian examples are wattles (Acacia) and eucalypts
(Eucalyptus). A comparison of macrofossil and microfossil data at the Oligo-
Miocene Pioneer site in northeastern Tasmania shows that that Nothofagus
(Brassospora) spp. are over-represented, and Nothofagus (Lophozonia) spp. are likely
to be under-represented in the Tertiary pollen record (Hill and Macphail 1983).
• Microfloras recovered from sediments accumulating towards the centre of larger
(>200 m diameter) lakes, in estuaries, and marine depositional environments, tend to
be dominated by the pollen of wind-pollinated trees, in particular gymnosperms
(Neves Effect) and/or miospores produced by light-requiring ferns, shrubs and trees
lining waterways (cf. Birks and Birks 1980).
• Microfloras recovered from coals, lignites and other backswamp sediments deposited
in smaller diameter basins tend to be dominated by locally growing (often underrepresented)
plants and often include pollen or spore types not found in sediments
accumulating away from the shoreline in larger basins.
2.3.2 Taxonomic constraints
Miospores are conservative plant organs in terms of evolution. Because of their small size
(10-120 μm), taxonomic characters that might allow one type to be distinguished from
another using scanning electron microscopy, are difficult to resolve using bright field light
microscopy. For this reason, modern pollen, spores and algal cysts should only be identified
to genus or family level unless only one species of parent plant occurs within the pollen
source area. Tasmanian examples are the Huon Pine (Lagarostrobos franklinii) and alpine
creeping pine (Microcachrys tetragona). This can be presumed in the case of Late
Quaternary fossil spores and pollen types but Tertiary examples almost certainly represent
more than one species or ecotype (Macphail et al. 1994).
The further back in time, the less confidently can a spore or pollen be related to a modern
taxon unless the degree of morphological specialisation is exceptional (Truswell and
Marchant 1986, Collison 1990). Accordingly, a very large number of Cretaceous and Tertiary
miospores cannot be assigned to any living genus or family. In many instances, it is
improbable that living descendants exist.
For pragmatic reasons, only the most morphologically distinctive or biostratigraphically
important miospore types are formally described as fossil genera (form genera) or species
(form species). Most fossil species encompass a wide range of morphologies and often are
linked to other fossil species via intermediate morphotypes. This has two important
consequences for the reconstruction of past vegetation and climates. (1) The range of
morphotypes assigned to a given fossil species tends to increase over time. (2) Geographic
variation between microfloras is obscured by broadly defined fossil species.
2.4. Reconstruction of past vegetation and climates
Plant macrofossils and microfossils are direct but partial evidence of past floras only,
although some indication of community dominance and structure is provided by their relative
abundance (Gestaldo and Ferguson 1998). In practice, inferences on palaeohabitat are usually
made by combining palaeoecological with other types of evidence, e.g. lithostratigraphy
(clastic facies analysis).
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