Check out this new publication in Nature Geosciences by Mariotti, G., Pruss, S. B., Perron, J. T., & Bosak, T.
Microbial shaping of sedimentary wrinkle structures
Abstract: Wrinkle structures on sandy bed
surfaces were present in some of the earliest sedimentary environments, but are
rare in modern environments. These enigmatic millimetre- to
centimetre-scale ridges or pits are particularly common in sediments that
harbour trace fossils and imprints of early animals, and appeared in the aftermath of some large
mass extinctions. Wrinkle structures have been interpreted as
possible remnants of microbial mats, but the formation mechanism and associated
palaeoenvironmental and palaeoecological implications of these structures
remain debated. Here we show that microbial aggregates can
form wrinkle structures on a bed of bare sand in wave tank experiments. Waves
with a small orbital amplitude at the bed surface do not move sand grains
directly. However, they move millimetre-size, light microbial fragments and
thereby produce linear sand ridges and rounded scour pits at the wavelengths
observed in nature within hours. We conclude that wrinkle structures are
morphological biosignatures that form at the sediment–water interface in
wave-dominated environments, and not beneath microbial mats as previously
thought. During early animal evolution, grazing by
eukaryotic organisms may have temporarily increased the abundance of microbial
fragments and thus the production of wrinkle structures.
