Trace fossils indicating bottom aeration changes: Folusz Limestone, Oligocene, Outer Carpathians, Poland

Bioturbation sequences in the pelagic Folusz limestone indicate deposition under decreasing bottom aeration, possibly in association with the development of microbial mats. U-shaped burrows Diplocraterion and Arenicolites exclusively were produced in the laminated limestone, and they represent the only colonizers (sessile suspension feeders) of the oxygen-deficient sediment.