Andreas Wetzel
Burrowing animals produce either traces having distinct outlines and characteristic geometry allowing an ichnotaxonomic classification or biodeformational structures, which disturb pre-existing structures considerably by layer-bending, disruption or homogenization. Since biodeformational structures represent structural phenomena, it is proposed to use ‘-textura’ (pl. ‘-texturae’) as a post-modifier. Two major groups of biodeformational structures are distinguished according to size: (1) sub-macroscopic ‘cryptotexturae’ with three informal subtypes [i.st. in the following], and (2) macroscopic ‘deformitexturae’, which are subdivided by structural criteria.(1) Cryptotexturae blur to homogenize the sediment (a) cryptotextura i.st. mixta exists in surface mixed-layer sediments and oxygenated shallow-marine arenitic deposits containing nutritional organic matter, (b) cryptotextura i.st. rubra occurs in oceanic red beds (ORB) that accumulated at low rates under oxygenated conditions and were limited in benthic food resulting – over the long term – in a miniaturization of fauna, and (c) cryptotextura i.st. atra is present in ‘black mud’ formed under oxygen-deficient conditions with small fauna living near-surface.(2) Deformitexturae. (a) Navitexturae with fluidal and soft-sediment deformations occur in soupy substrate wherein burrowing animals need to swim. (b) Turbiditexturae show irregular deformation structures with sharp boundaries resulting from a strong consistency contrast between burrow fill and host sediment. (c) Miscitexturae represent eddy-like disturbances with indistinct boundaries (also ‘mottling’) in sandy to muddy sediment through that animals burrow ‘unspecifically’. (d) ‘Cribritexturae’ (biostratifications) represent a millimeter- to centimeter-thick, but internally poorly organized enrichment of coarser material below heavily bioturbated finer sediment. (e) ‘Fugitexturae’ represent vertically stacked, U- to V-shaped to funnel-like deformations formed by animals rapidly responding to deposition or erosion. (f) Equilibritexturae exhibit concave and/or convex stacked laminae or layers extending vertically for millimetres to centimetres, while animals responded to moderately paced deposition or erosion.