Nannofloral extinction and survivorship across the K/T boundary at Caravaca, southeastern Spain

Detailed qualitative and quantitative studies of the calcareous nannofloral assemblages were carried out on 65 cm across the K/T boundary interval of the Caravaca section. Preservation of nannofloral assemblages is moderate to good. Reworking was identified in the lowermost Danian, but did not essentially influence the rest of the section studied. The nannofloral study shows that most of the Cretaceous taxa disappeared in the “fallout” lamina, a bio-event which is synchronous with the mass extinction of the planktonic foraminifera and with significant geochemical anomalies. Beside these events, a rapid decline of the calcareous nannofossils is recorded in the uppermost 12 cm of the Maastrichtian (about 4 ky prior to the K/T boundary). Such decline becomes more pronounced in the transitional layer, just below the K/T boundary, therefore predating the main extinction event. This pattern is in agreement with other evidences of an unstable ecosystem and inputs of cold-water taxa in this area with typical Tethyan upper Maastrichtian nannofossil assemblages. Two successive blooms, of Thoracosphaera spp., followed by that of Braarudosphaera bigelowii, were identified at the base of the Danian. In the upper part of the studied sequence, nannoflora records are already dominated by survivor as well as by incoming taxa, showing an early pioneer calcareous nannofloral ecosystem about 25 ky after the K/T boundary mass extinction event.