Deep-sea ichnology: Observations in modern sediments to interpret fossil counterparts

Abstract

Extensive areas of the abyss represent a dynamic environment experiencing seasonally strongly fluctuating organic-matter deposition that in turn affects the oxygen content of the pore water. At high organic-matter deposition, oxygenation of the pore water decreases and forces organisms respiring this water to move upward. Thus, times of benthic food richness on the seafloor affect the behaviour of endobenthic organisms; aside from deepdeposit feeding, temporary surface feeding (including unselective bulldozing) represents an additional nutritional strategy. This has been shown for the producers of Nereites and Scolicia as well as Thalassinoides and Zoophycos, the latter two have an open tube. Each of these activities leads to intense sediment mixing and prevents or disturbs the formation of near-surface burrows including graphoglyptids. The distribution of organic matter in the sediments is reflected by the orientation and geometry of Phycosiphon. Quantity and quality of food appear to be related to abundance and size of Scolicia. Food selectivity, the ability of selective feeding and organism mobility all appear to be important factors in benthic ecology, however, they are as yet little known. To use the full potential of uniformitarian studies relying on cores taken in soft sediments, they should be based on X-ray radiographs, contain information about the timing of burrow production and focus on ichnotaxonomically determinable burrows.