Palaeobotany illuminates past environments by relating the fossilised species to
the existing geological conditions. This has previously been done with fossilised
leaves and spores but not with fossilised wood.
The recovery of a significant quantity of wood from an area of Tertiary sediments
in New South Wales, enabled the used of fossilised wood as a
palaeoenvironmental tool. Tertiary sedimentary deposits of south eastern
Australia are diverse lithologically, occupy distinct areas and are limited in vertical
and horizontal extent. However, samples in museum collections together with
samples from field work and descriptions of fossil wood from previous researchers
enabled an analysis of the fossil wood.
The geological and palaeontological aspects of the fossil wood were considered
for each specimen. Only specimens with precise information concerning location
and description of the sedimentary deposits in which the specimens were found
were investigated. Lithology, sedimentary structures and the relationship with
surrounding geological units were also considered.
The samples were then classified and identified. It was possible to identify fossil
wood to Family level by comparison with existing taxa. In the majority of cases,
identification to species level was not possible due to the lack of detail in the
specimen and because features such as colour cannot be used with fossilised
specimens. With Australian fossilised wood, a systematic nomenclature based on
structure observed within the palaeotaxa, would be more relevant. Comparisons
of cell structures with previous work on palaeoenvironmental indicators was found
to be possible.
Fossil wood has two uses. Firstly, as a local environmental indicator, usually in
conjunction with sedimentological data, assessing the rate and direction of water
flow, types of depositional environments and localised floral assemblages.
Secondly, as an indicator of regional climate. Within any one particular time
period, comparisons between the cellular structures of wood found in different
parts of south eastern Australia show gross changes in cell size, mean growth ring
size and vessel size, which enabled generalisations about climate for each epoch
in the Tertiary.
Palaeoclimatic indicators from the wood concurred with previous climatic
interpretations based on palynology and sedimentology. Cool conditions during
the Palaeocene were clearly indicated by small cells and small growth rings which
gradually increased throughout the remainder of the Tertiary. Several areas e.g.,
Dargo High Plains, where cold conditions existed in isolation could be clearly
distinguished. This corresponds with the gradual northward movement of the
Australian plate with consequent increasing temperatures on the mainland.
| Identifer | oai:union.ndltd.org:ADTP/219142 |
| Date | January 1999 |
| Creators | O'Brien, Jane, n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Jane O'Brien |
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