In the Pleistocene Montalbano Jonico composite section (southern Italy) the microhabitat preferences of the benthic foraminifera have been determined by comparison with data on living forms. The stratigraphic distribution of the different living positions seems to be related to the cyclic oxygen fluctuations recorded in the succession. In the high-oxygenated phases, when the oxygenated zone within the sediment column is wide, the assemblages show a distinct vertical microhabitat distribution. In the low-oxygenated phases, when the minor oxygen availability at the bottom–water interface reduces the oxygen penetration within the sediment, infaunal microhabitat is the preferred living depth.
In order to quantify the oxygen fluctuations recorded in the succession, a palaeo-oxygen curve is reconstructed testing Kaiho’s benthic foraminiferal oxygen index (BFOI) in the equation: y=1.686+ 0.033337x. In general, good correlations are observed between the dissolved oxygen regimes and the benthic assemblage composition. The low-oxygenated phases are identified with the low-medium oxic regime and the high-oxygenated phases with the high oxic regime.
In the deeper part of the composite section, oxygen has played an important role on the foraminiferal assemblage composition. In contrast, in the shallower part, a combination of oxygen and sea-level changes regulates the distribution and composition of the assemblages.