The Cenomanian-Turonian Boundary Event in northern Spain

Abstract

AbstractA sparse but moderately diverse nannoflora is recorded through the Cenomanian-Turonian Boundary Event (CTBE) at Menoyo, Spain and allows recognition of the late CenomanianEiffellithus turriseiffeliiZone and the early TuronianQuadrum gartneriZone, as well as five significant nannofossil bioevents associated with the CTBE. Carbon isotopes record a modest excursion which lasted 250–270 thousand years (ka) in three phases, buildup (105 ka), plateau (126 ka) and recovery (42 ka). Acid insoluble residue values imply that sea level rose through the buildup phase, indicated by a reduction in the accumulation rate of siliciclastic sediment. However, oceanic productivity apparently declined through the CTBE, indicated by reduction in accumulation rates of total carbonate and intact coccoliths to less than a quarter of their initial values. These patterns are very similar to those found through the CTBE at Dover, England and reflect widespread not local effects. A combination of lithological changes, seven key bioevents, and details of the δ13C curve, allows us to suggest a bed-by-bed correlation through the CTBE between Dover and Menoyo, demonstrating the practicality of cyclostratigraphy for international correlation at a precision of ± 10 ka. Graphic correlation produces a straight line fit despite wide fluctuations in sediment accumulation rates at both localities. This can only occur if changes were in phase and of similar magnitudes at both localities, again suggesting widespread, perhaps global, control.