Marine ooids commonly are interpreted in the context of hydrodynamic processes, but palustrine ooids are less well understood. Miller and James explore how palustrine ooids are produced in situ and without the necessity of grain movement. Samples from the Nullarbor Plain in Australia reveal a suite of microbially produced structures within degraded minimicrite cortical laminae. These ooids are interpreted to be controlled seasonal wet-dry alternations in the soil which, coupled with microbially mediated mineral precipitation, led to formation of laminae (and ooids) in place.
Autogenic microbial genesis of middle Miocene palustrine ooids; Nullarbor Plain, Australia by Cody R. Miller and Noel P. James