A quantitative analysis of calcareous nannofossils across a late oligocene paleolatitudinal transect of the North Atlantic Ocean

Samples from six ocean drilling sites were analyzed quantitatively across a paleolatitude transect of the North Atlantic Ocean to determine the paleolatitudinal distribution of calcareous nannofossils in the late Oligocene and the effects of that distribution on biostratigraphic resolution. Quantitative methodology utilized a Detrended Correspondence Analysis (DCA), Nannofossil Temperature Index (NTI), and Shannon Index (H) to examine the paleoenvironmental gradients which exerted the most control over the distribution of species and their abundances. The DCA produced two axes which explain 82% of the data matrix. The DCA1 explaining 57% of the variance significantly correlates with the NTI suggesting that thermal controls were the most important factor in the paleoceanographic distribution of nannofossils. The DCA2 explained 25% of the variance and significantly correlates with the percent abundance of the taxon Reticulofenestra minuta as well as the Shannon Index, suggesting that surface water productivity was an important secondary control. The characteristics of the nannofossil assemblage distributions indicate the existence of a well-developed latitudinal diversity gradient in the late Oligocene of the North Atlantic. Based on the loss of biostratigraphic index taxa in higher paleolatitudes the primary limiter on biostratigraphic resolution for the late Oligocene North Atlantic is sea surface temperature, particularly cold-water regimes.