Paleobathymetry in the backstripping procedure: Correction for oxygenation effects on depth estimates

This paper aims to provide a straightforward and easily applicable method for estimating the depositional depth evolution of marine basins. Vertical movements of the basin floor can be reconstructed from the sedimentary record, and more accurately constrained when information from the sedimentary history is combined with palaeodepth estimates derived from fauna. To this end we propose to extend an existing method based on the percentage of planktonic foraminifera with respect to the total (planktonic and benthic) foraminiferal association, which is expressed as the percentage planktonics (% P). The ratio between planktonic and benthic foraminifera is related to water depth, and the % P generally increases with increasing distance to shore. However, next to water depth the oxygen level of bottom waters has a profound effect on the abundance of benthic foraminifera, and as such influences the % P. Depending on basin configuration, the oxygen level at the sea floor can vary on Milankovitch time scales and is reflected by the fraction of benthic foraminiferal species that indicate an effect of oxygen stress on the biotic system. These species can be used as stress-markers and their percentage with respect to the total benthic population is here expressed as % S. To assess whether the effect of sea-floor oxygenation impairs depth reconstructions, we studied the percentage of planktonic foraminifera (% P) in five well-dated sedimentary successions from the Lower Pliocene of Crete, Corfu and Milos in Greece. Additionally, we assessed whether different foraminiferal size fractions and counting methods affect the determination of the percentage of planktonic foraminifera. The palaeobathymetric evolution calculated for each basin was confirmed for all successions by an independent check on depth-related occurrences of benthic foraminifera. After correction for bathymetry changes of the basin due to sedimentation, compaction and eustatic sea level variations, the vertical movement history of the basin floor was inferred. We propose a standard methodology for reconstructions of palaeobathymetry of marine sedimentary successions from foraminiferal associations.