LIFE BENEATH THE SEA FLOOR: PALEOECOLOGY OF TIERED ICHNOCOENOSES IN MARINE ENVIRONMENTS

The trace fossil record of infaunal tiering reflects a partitioning of the endobenthic habitat by organism communities, and it records the stratification of ecologically vital factors within the substrate, such as sediment consistency (which generally increases downward) and interstitial oxygen content (which generally decreases downward).

Infaunal tiering has changed through time in terms of both complexity (number of tiers) and depth below the water-sediment interface. Tiering complexity is generally related to ethologic diversity but is not necessarily correlated with ichnotaxonomic diversity. Depth of burrowing has different significance for infaunal suspension feeders, sediment ingestors and mobile predators.

The effects of tiered ichnocoenoses on stratigraphic resolution in marine sequences should not be ignored. They include both the upward diffusion effects of vertical conveyor belt mixing of sediment grains (including index microfossils) and the leaking effects of burrow emplacement in older sediment layers.