Ecologic interpretation of deep-sea trace fossil communities

Abstract

Trace fossil types and their vertical arrangement (tiering) are closely related to the biotope, and hence, can provide information on ecological conditions, especially on oxygenation, benthic food content, sedimentation rate, and substrate consistency. However, to use the full potential of trace fossils for environmental analyses, various ichnologic criteria are necessary in addition to trace fossil taxonomy. Based on a taxonomically oriented, ichnologic evaluation of modern deep-sea environments, six ichnologic aspects to ecologic changes have been found to be of major importance: 1. (1) penetration depth of burrows is influenced by oxygenation, benthic food availability and substrate consistency; 2. (2) the number and vertical extension of tiers varies due to environmental changes. A decrease in the vertical extension of tiers (“telescoping”) indicates a decrease in oxygenation, benthic food content and/or sedimentation rate. If shallow-penetrating traces disappear, oxygen may be depleted, and if the deepest tiers disappear, the benthic food content may be lowered; 3. (3) the size (diameter) of specific trace fossils can indicate oxygen and benthic food availability; 4. (4) degree of bioturbation is related to sedimentation rate and benthic food content, and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation, benthic food content, sedimentation rate and substrate consistency; 5. (5) the type of burrow wall (unlined, mucus-lined, pellet-lined) mainly refers to substrate consistency and — subordinately — to pore water oxygenation; 6. (6) the type of sediment displacement by body appendages used for excavation, ingestion, sideward pressing, or outside pumping is related to substrate consistency and grain size.