GRADUAL MASS EXTINCTION, SPECIES SURVIVORSHIP, AND LONG-TERM ENVIRONMENTAL-CHANGES ACROSS THE CRETACEOUS-TERTIARY BOUNDARY IN HIGH-LATITUDES

Stable-isotope and planktic foraminiferal analyses across the Cretaceo us/Tertiary (K/T) boundary transition at Nye Klov indicate long-term o ceanic instability associated with global sea-level fluctuations, a gr adual mass extinction, and decreased magnitude of the deltaC-13 shift in high latitudes. Oceanic instability, which began at least 100 kyr b efore the K/T boundary and continued for about 300 kyr into the Tertia ry, was accompanied by a gradual faunal turnover. The maximum sea-leve l lowstand during latest Maastrichtian is recorded about 75 cm below t he K/T boundary. A sea-level rise first in evidence at 20 cm to 40 cm below the boundary continued into Zone PO (boundary clay). This sea-le vel rise was accompanied by 2-degrees-C of cooling in surface and bott om waters prior to the K/T boundary. DeltaC-13 values remained relativ ely stable up to 10 cm below the K/T boundary. A negative shift of 0.5 to 1.0 per mil occurred in the boundary clay in both planktic and ben thic foraminifera. The surface to deep deltaC-13 gradient remained nea rly unchanged, in contrast to low latitudes, where this gradient is vi rtually eliminated. No sudden mass extinction occurred in this cosmopo litan, high-latitude fauna, and nearly all Cretaceous taxa thrived wel l into the Tertiary, when they gradually disappeared. Shallow seas, do minated by Cretaceous survivor taxa and a well-developed oxygen minimu m zone, prevailed during the earliest Tertiary. Short-term sea-level l owstands are marked by hiatuses at the top of Zones PO and P1a about 5 0 kyr and 230 kyr after the K/T boundary, respectively. Rising sea lev el reestablished normal marine conditions about 300 kyr to 350 kyr aft er the K/T boundary, coincident with the first post-K/T boundary recov ery of the Tertiary fauna and extinction of Cretaceous survivors. Duri ng this time, high-latitude regions temporarily acted as centers of or igin and dispersal for planktic foraminifera. Long-term oceanic instab ility, gradual faunal turnover, absence of a sudden mass extinction, a nd greatly diminished delta-C13 shift in high latitudes suggest that a K/T boundary bolide impact was not the primary cause for the K/T boun dary faunal transition. Moreover, these data strongly imply that the d estructive effects of the bolide impact would have been greatest in lo w latitudes and negligible in high latitudes.