The presence of life, in its multifarious aspects, has an important bearing on both the origin and the modification of sediments. The ways that life and sediments interact are highly diversified, and the same is true for the morphology and the scale of their products. It is obviously impossible to illustrate them all, and a selection is necessary. Moreover, a sedimentologist cannot describe and understand structures related to life or biological processes (biogenic structures ) without the help of other experts (biologists, ecologists, paleontologists).
In this chapter, some structures are presented that exemplify relatively common categories of biological activity related to sedimentation and, above all, provide useful and often valuable information on sedimentary processes, mechanisms, and environments. Among biogenic structures, in other terms, sedimentological indicators will be emphasized.
I will start with so-called constructive features, which contribute to sediment accumulation in some way or the other. After that, I will examine destructive and biodeformative structures, resulting from organic activities that disturb the sediment and obliterate, in part or entirely, its depositional structures.
Plate 140. Reef-building organisms in living position
Plate 141. Stromatolitic structure
Plate 142. Bacterial mat embedded in gypsum crystals
Plate 143. Microstructure of stromatolites
Plate 144. Organic coatings on grains: rhodoliths
Plate 145. Diffuse bioturbation and mottling
Plate 146. Diffuse bioturbation and burrow traces
Plate 147. Vegetal trace fossils
Plate 148. Birdfoot casts
Plate 149. Vertical structures in shallow water: dwelling traces
Plate 150. Vertical structures in shallow water: escape traces
Plate 151. Callianassa burrows
Plate 152. Crawling (feeding) traces
Plate 153. Crossing trails
Plate 154. Echinoid traces in section
Plate 155. "Problematic" traces: Zoophycos
Plate 156. Horizontal burrows on a bed surface
Plate 157. Helminthoid traces
Plate 158. Problematic traces: Chondrites
Plate 159. Problematic traces: Palaeodictyon
Plate 160. Problematic traces: Neonereites
Plate 161. Traces of boring organisms