Abstract:
Comparison of species extinction and evolution patterns of planktic foraminifera across the K/T boundary in the most complete high and low latitude sections (El Kef, Agost, Caravaca, Mimbral, Nye Klov and ODP Site 738C) reveal major differences in extinction patterns and fundamental similarities in evolution patterns. Evolution patterns are similar across latitudes during the earliest Tertiary (Zones P0 and Pla), although relative species abundance variations reflect local and regional paleoecological conditions. During the later Danian (Zones Plb and Plc), high latitudes are temporary centers of originations and dispersal and act as refugia for Cretaceous survivors. Extinction patterns are very different between high and low latitudes. N significant species extinctions, or major faunal abundance changes coincide with the K/T boundary in high latitudes, and nearly all Cretaceous species survive and thrive well into the earliest Tertiary. In contrast, major species extinctions occurred in low latitudes where 2/3 of the taxa disappeared at or below the K/T boundary. But, only tropical and subtropical, large, complex and ornamented taxa became extinct. Moreover, all of these taxa were already rare and endangered species in the latest Cretaceous ocean comprising only between 5% and 17% of the planktic foraminiferal population. The extinction of these rare taxa could have been caused by relatively minor environmental perturbations in temperature, salinity, oxygen or nutrients. Although it is possible that the extinction of some or most of these taxa was related to the climatic changes associated with a K/T boundary bolide impact, a direct cause-and-effect relationship cannot be demonstrated. Stable isotopic data suggest that the major difference between high and low latitudes across the K/T boundary is in surface productivity. In low latitudes, surface productivity dropped significantly beginning at the K/T boundary and did not recover until about 350-500 kyr later (Zone Plc), whereas in high latitudes surface productivity remained nearly constant. The cause of his high vs. low latitude difference in surface productivity remains an enigma.