OFR 151.pdf - CRC LEME

• Pollen are gametes produced by both gymnosperms and angiosperms, and are
functionally equivalent to animal sperm. Dispersal is by wind, animals and/or water,
with some common insect-pollinated species dispersing pollen by two or more
pathways.
The other major classes of plant microfossils are (a) silica cells (phytoliths) produced by many
of the higher plants, and (b) the cysts produced by freshwater and marine algae, e.g. diatoms,
acritarchs and dinoflagellates (dinocysts), and coccoliths (nannofossils). Whilst these can be
common in freshwater or marine sediments, only microfossils with organic (as opposed to
calcareous and siliceous) walls survive the processing techniques used to recover spore-pollen
from sediments or rocks.
Marine algae and microfauna such as planktonic foraminifera (forams) underpin the global
chronostratigraphy (Harland et al. 1990) but are not considered in this review except as
evidence for past sea surface temperatures (SSTs).
Unlike plant macrofossils, miospore assemblages (microfloras, palynofloras) represent distant
plant communities as well as plants growing close to the site of deposition (Macphail et al.
1994). Reasons include their wide dispersal and resistance of the cell walls to physical or
chemical decay.
2.3.1 Taphonomic constraints
Spores, pollen and algal cysts are produced and dispersed in astronomical numbers. The cell
walls, made of sporopollenin, are highly resistant to natural oxidative process and for this
reason, miospores are by far the most commonly found fossils in fine-grained sediments
accumulating in onshore and nearshore sedimentary basins.
The main agencies transporting miospores over long distances are wind (anemophily) and
water. Batten (1984) has proposed that 'lightly sculptured' (psilate-scabrate) pollen grains are
an adaptation to dispersal by wind since anemophily is best developed in open canopied
vegetation types such as savannahs, open woodlands and deciduous forests. Many but not all
of these vegetation types inhabit regions with strongly seasonal climates.
Because of their small size, fossil pollen and spores are subject to the same sorting processes
during transport and deposition as very fine sand and silt particles. For the same reason,
present-day relationships between elevation, basin size, and the area and types of plants
represented by microfossils, are likely to apply to Cretaceous and Tertiary palynofloras
(Dettmann 1994, Macphail et al. 1994, Woo et al. 1998). Empirical and experimental pollen
trapping data indicate:
• The overwhelming majority of plants in Australia are under-represented in that their
miospores are produced in limited numbers or dispersed only short distances (