Cretaceous/Tertiary boundary extinction pattern and faunal

Canudo, J.1., Keller, G. and Molina, E., 1991. Cretaceous/Tertiary boundary extinction pattern and faunal turnover at Agost and Caravaca: S.E. Spain. Mar. Micropaleontol., 17: 319-341. Planktonic foraminiferal extinctions at Caravaca and Agost occurred 'over an extended time period similar to El Kef and Brazos River. Some species disappeared well below the boundary. About 39-45 % of the species, but less than 15 % of the individuals in the population, became extinct at or near the K/T boundary. A second phase of extinction occurred at the top of the boundary clay (PO/Pia) and the remaining Cretaceous species (except G. cretacea) disappeared in Subzone Pia. Species extinctions were selective eliminating geographically restricted large, complex and deeper dwelling forms first and favoring survival of cosmopolitan small, simple surface dwellers. Only surface dwellers survived the K/T boundary event, whereas all deeper dwelling species, as well as some surface dwellers, disappeared at the boundary. We interprete the selective abundance decline during the latest Cretaceous as a result of the seal level regression that reached a maximum just prior to the K/T boundary. The highly selective nature of the two-phased species extinctions at and above the boundary, we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the K/T boundary. A bolide impact however, may have hastened the demise of an already declining Cretaceous fauna