In recent years, complex models of bioturbation rates and depths have been
developed, star turns with partial differential equations. Bernard Boudreau, Filip
Meysman, Jack Middleburg, and Karline Soetaert are prominent in this work.
Fig. 14.22 (a) Mixing depths, L, in marine sediments around the world, based on
excess ^210 Pb. There is no trend in L with depth.
(^) (After Boudreau 1998.)
(b) Two examples of sediment compaction curves from the continental slope seaward
of Nova Scotia. Solid volume (1 − φ), where φ is sediment porosity, is plotted vs.
depth in the sediment.
(^) (After Mulsow & Boudreau 1998.)
(^) Filled burrows in sediment can be seen in X-ray photographs of core slices.
Enhanced downward ventilation along burrow walls promotes precipitation of heavy
minerals, manganese, and iron solubilized in reducing sediments. These, plus mineral
and compaction differences between burrow fill and burrow surround, generate a
differential in X-ray absorption, and thus images can be made. There is a definite
layering of burrow sizes: mostly tiny ones in the uppermost few centimeters; a middle
layer several decimeters thick with larger burrows often visible by color differences as
well as X-ray signatures; and a layer of final burial in which burrows fade out (Berger
et al. 1979).
(^) For many oceanographic purposes, the key point about bioturbation is that it occurs;
it must not be forgotten or ignored in stratigraphic work to reconstruct faunal or