Morphology and ecological significance of Zoophycos in deep-sea sediments off NW Africa

Eighty-six large-diameter (15–50 cm) sediment cores taken off the NW African continental slope have been examined for their bioturbation structures. The Zoophycos “spreiten” — burrows appearing in profile as series of curved arcs — were found to be particularly useful for environmental analysis, because they are (1) widely distributed and numerous in Quaternary sediments, (2) easily identifief due to the characteristic structures in vertical and horizontal core sections, and (3) extraordinarily well preserved. Zoophycos is found off NW Africa in water depths > 2,000 m, in sediments with Corg contents of 0.3–1.8%. It is possible to recognize in the core sections all of the morphological spreiten types of Zoophycos which were described from ancient sediments. All of these spreiten are formed with two modifications classified as “U-type” and “J-type”, according to the shape of the basic tube. The distribution of U- and J-types is significantly related to Corg content and probably depends on the available oxygen content in the respiration water. Morphological analysis leads us to assume that sipunculid animals are the creating organisms. Vertical sediment mixing can be measured by using tracer particles derived from single “event” layers. It is explained by excursions of the creating organism and/or by its active movement of the respiration water. Excellent preservation is a typical feature of Zoophycos, which is evident all over the fossil record. This is due to the considerable depth in the sediment at which the organism producing Zoophycos lives. Core sections with maximum frequency of Zoophycos, indicating optimum living conditions, can be correlated over great distances. For these horizons, it is possible to estimate roughly the maximum population density of Zoophycos-creating organisms, yielding 1 animal/100 m2.