Applied Biostratigraphy

Eustatic sea level rises and falls, particularly when driven by the spread or retreat of polar ice caps and/or glaciated areas, can often be linked to changes in climate. Predominantly dry periods are often associated with increases in ice cover which in turn are often associated with lowstand conditions. Features like the tropical coastal mangrove belts are often reduced or absent.

Terrestrial plants are particularly susceptible to changes in climate and palynology can provide valuable data on paleoclimates affecting the hinterland at the time of marine deposition. Among many tell-tale signs, the following have been found to be useful:

• Proportion of mangrove pollen increases during highstand periods as the mangrove belt becomes well established
• Proportion of tropical lowland pollen increases against cooler highland or “montaine” pollen during warmer climates (highstand conditions)
• Abundant freshwater algae usually indicates periods of high rainfall and runoff
• Charred (burnt) grass cuticle originating from grassland fires suggests warm, dry climatic periods associated with lowstand conditions

Summary

Determining detailed paleoenvironments from fossil assemblages can be difficult but a basic knowledge of the main ecological characteristics of fossil groups can yield important information, even for the non-specialist. It is possible to characterise broad paleoenvironmental/depositional settings based on presence/absence of certain fossil groups and an estimation of their approximate proportion within an overall assemblage. Trends in paleoenvironmental change can be important in the determination of systems tract components.