Effects of the Oligocene climatic events on the foraminiferal record from Fuente Caldera section (Spain, western Tethys)

An expanded succession of upper Priabonian (upper Eocene) to Chattian (upper Oligocene) hemipelagic marls interbedded with turbiditic sandstone layers is present in the Spanish Fuente Caldera section (Subbetic Zone, western Tethys). We analyzed foraminifera from this section quantitatively, with emphasis on biostratigraphy and paleoecology. Benthic foraminifera indicate an upper to possibly upper–middle bathyal depth of deposition for most of the studied section, with paleobathymetric analysis made difficult because of the common presence of shallow-water taxa, some reworked by turbidites and others epiphytic taxa, which may have been transported by turbidites or by floating plant material. We identified three major biotic and paleoenvironmental events. 1) The major planktonic foraminiferal turnover across the Eocene/Oligocene boundary, which includes several first and last occurrences as well as a decrease in the percentage of surface water-dwellers, possibly linked to global cooling. 2) A dramatic sea-level drop indicated by the presence of a 37-m-thick sequence of calcarenites (lower half of planktonic foraminiferal Zone O2, ~ 31.5 Ma) with abundant trace fossils and allochthonous foraminifera. This sea-level fall, which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin, apparently post-dated the major glacial expansion on the Antarctic continent (Oi1, 33.7 Ma), and predated the later major expansion (Oi2 through Oi2b, 27–30.5 Ma), thus may have been tectonically controlled. 3) A warming event starting in the Chattian (lowermost part of Zone O6, ~ 27.1 Ma), which could be correlated to the globally recognised Late Oligocene Warming Event, but apparently started somewhat earlier (~ 27.1 Ma as compared to 26.5 Ma).