Late Maastrichtian paleoclimatology and the paleobiology of Raceguembelina fructicosa, Contusotruncana contusa and Rugoglobigerina rugosa inferred from single specimen delta 13 C and delta18O data.

摘要

Analysis of 944 single individual of three species of late Maastrichtian planktonic foraminifera (Raceguembelina fructicosa, Contusotruncana contusa, and Rugoglobigerina rugosa) from 38 samples that span the last three million of years of the Cretaceous show consistent isotopic trends through time, consistent isotopic differences among taxa, and high isotopic within sample variability throughout. Within sample variability does not seem to change systematically through time for any taxon, but average delta18O values decrease by ∼1.5‰ and average delta13C values diverge up section due largely to a decrease in average delta13C values in C. contusa . In general, delta18O values are similar among the taxa, but delta13C values decrease from R. fructicosa to R. rugosa to C. contusa. Finally, spread of delta13C values is larger for R. fructicosa than for C. contusa, and R. rugosa, consistent with a photosymbiotic habitat for R. fructicosa .; The negative excursion ∼1.5‰ in delta18O would correspond to an increase in temperature of approximately 5°C. For R. rugosa and R. fructicosa there is no obvious size-related trends across the size range analyzed. C. contusa does exhibits lower delta13C and delta18O values as test size increases, but we believe that correlation reflects an increase in C. contusa's size through time rather than ontogenetic trends. The general decrease in delta13C values in C. contusa up section, though, suggests an increasingly stratified water column in the western Atlantic through the late Maastrichtian. The relationship between the long term negative delta18O excursion (warming) and increasing water stratification could reflect a more strongly developed thermocline. Because within sample variability in either delta13 C or delta18O does not change through the section, increased stratification is unlikely to have resulted from a higher seasonal to interannual variability. Thus, we suggest an intensification of the northern hemisphere polar front is a more likely mechanism.