CHANGES IN ORGANIC CARBON STABLE ISOTOPE RATIOS ACROSS THE K/T BOUNDARY: GLOBAL OR LOCAL CONTROL?

Abstract

A global shift in carbonate carbon δ13C-values from heavier values in the Maastrichtian to lighter values in the early Danian indicates recycling of isotopically light organic carbon to inorganic carbon reservoirs during a period of depressed marine productivity. Comparison of organic carbon δ13-values from globally dispersed K/T sections does not show a similar, globally well-developed pattern. Several factors evidently overwhelm the potential impact of an isotopically lighter inorganic carbon source on organic matter isotopic signatures: (1) species changes in biological assemblages may modify the averaged isotopic fractionation of organic matter; and (2) shifts in the proportion of land/marine organic matter contributions to coastal marine locations may overprint the isotopic record. Local phenomena evidently outweigh global change in determining the isotope signature of organic carbon deposited in K/T boundary sections.