Oceanic primary productivity and dissolved oxygen levels at the Cretaceous/Tertiary boundary: Their decrease, subsequent warming, and recovery

Thirty-six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous/Tert iary (K/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gr adient between delta(13)C values in fine fraction carbonate and benthic for aminiferal calcite and a decrease in the abundance of phosphorus (a proxy f or organic carbon) and calcium were recorded in sediments 0-0.5 cm above th e WT boundary. These trends imply that an abrupt mass mortality occurred am ong pelagic organisms, leading to a significant reduction in the flux of or ganic carbon to the seafloor. In addition, variations in sulfur isotope rat ios, the hydrocarbon-generating potential of kerogen (measured as the hydro gen index), and foraminiferal indices of dissolved oxygen level all imply t hat a rapid decrease in dissolved oxygen was coincident with the delta(13)C event. Evidence of the low oxygen event has also been recognized in Japan and New Zealand, suggesting that intermediate water oxygen minima were wide ly developed during earliest Danian time. A threefold increase in the kaoli nite/illite ratio and a 1.2 parts per thousand decrease in delta(18)O (carb onate fine fraction) were recorded in the basal 0.1-2 cm of Danian age sedi ments, These trends suggest that atmospheric warming and an increase in sur face water temperature occurred 0-3 kyr after the delta(13)C event. Recover y in the difference between delta(13)C values in the carbonate fine fractio n and in benthic foraminiferal calcite as well as increases in phosphorus a nd calcium contents occur at the base of planktonic foraminiferal Zone Pla, implying that an increase in primary productivity commenced some 13 kyr af ter the K/T boundary.