Multivariate analysis of calcareous nannofossils and stable isotopic (δ18O and δ13C) in the upper Campanian — lower Maastrichtian of the Campos Basin, Brazil

Abstract

Qualitative analysis in calcareous nannofossils is a powerful tool for biostratigraphic uses, principally in identification of biozones and determination of relative age. But quantitative studies must be applied for paleoceonographic applications and high–resolution biostratigraphy. In order to better understand the relationships between the different species of nannofossils, new methodologies and non-traditional correlation tools were tested on a 18 m upper Campanian – lower Maastrichtian core from Campos Basin. Multiple regression helped to determine the best counting method. Watznaueria barnesae and Micula decussata dominate the fossil assemblage and have inverse abundances to each other. Both were opportunist species in competition for nutrients. Q mode factorial analysis (57 samples, 19 variables) was applied to the same core and shows that two factors explain 99.2% of the total variance of the microfossil assemblage. The first factor represents 83.6% and the second factor only 15.6% of the total variance. The former is associated with Watznaueria barnesae, Cribrosphaerella ehrenbergii and Stradneria crenulata, which represent the original population of nanoplankton. The latter factor is associated with Micula decussata, which is believed to represent the effect of solution at the sediment-water interface. Both factors were used to develop a dissolution-sea level curve for nannofossils. When combined with oxygen and carbon isotopes, this curve clearly shows that higher dissolution occurred during the late Campanian - early Maastrichtian time when δ18O, δ13C and TOC all had lower values. These correlations indicate a strong link between high sea levels, high temperatures and lower amount of continental organic debris.