Plate 154

Echinoid traces in section

This is a replica (peel) of a sandy sediment extracted from a shallow sea bottom with a box corer. The sample has been vertically sectioned, and shows a peculiar type of onion-shaped trace produced by the lateral movement of an echinoid (sea urchin). The sense of displacement of the animal was from right to left, and its body left a partial imprint at the end. Similar structures are partly visible near the upper left corner of the picture. They look like horizontal spreiten  (turn the page 90° clockwise and compare with plate 150), and are originated by a similar "stuffing" mechanism.

The visibility of the biogenic structure is enhanced by its contrast with the primary, tractive lamination of the sand, indicating a shallow-water marine environment (above wave base). Echinoids, however, move the same way in resedimented deep-water muds and sands; the degree of preservation of their traces can be weaker there. Being found at various depths, this kind of trace is not a reliable indicator of bathymetry.

Photo: H. E. Reineck 1970.