Differential patterns of benthic foraminiferal extinctions near the Paleocene Eocene boundary in the North Atlantic and the western Tethys

Bathyal benthic foraminifera and stable isotopes from the Caravaca and Zumaya sections of Spain, indicate that the mass extinction near the Paleocene/Eocene (P/E) boundary (upper planktic foraminiferal Zone P6a) was rapid, coinciding with a negative delta(13)C-shift of 2-4 parts per thousand, the onset of dark grey shale deposition and increased carbonate dissolution. Prior to the extinction event, diverse benthic foraminiferal assemblages and high delta(13)C values suggest the presence of a stable intermediate-deep watermass rich in oxygen and saturated in calcium carbonate in both Caravaca and Zumaya sections. After the extinction event, small finely agglutinated (Haplophragmoides, Glomospira) and thin-walled epifaunal taxa (Nuttallides truempyi) dominate in the North Atlantic, Zumaya section. This assemblage indicates sluggish circulation, bottom waters undersaturated in calcium carbonate and dysaerobic conditions. Low oxygen conditions prevailed for the succeeding 400 kyr and are characterized by 1-2 parts per thousand fluctuations in benthic delta(13)C. In the western Tethys, Caravaca section, infaunal taxa (''buliminids'') dominate after the extinction event and prevailed through the succeeding 400 to 450 kyr of decreased delta(13)C values, indicating low oxygen conditions. Despite these common features, benthic foraminiferal assemblages from these two sections exhibit significant differences during the extinction event. At the Zumaya section, the extinction event occurred over less than 50 kyr and resulted in a sudden reduction in species richness after the delta(13)C-shift. In contrast, at the Caravaca section species diversity declined gradually, beginning prior to and in concert with the gradually declining delta(13)C values. This gradual change occurred over a period of 250 kyr and culminated in a 4 parts per thousand delta(13)C-shift. These differences in delta(13)C values and benthic assemblages between Caravaca and Zumaya, suggest that the P-E oceanographic changes that triggered the benthic foraminiferal mass extinction, exhibited its first manifestation in the Tethys region.