A Quantitative Analysis of Calcareous Nannofossils Across a Late Oligocene Paleolatitude Transect of the North Atlantic Ocean

Authors

William Barrett Clark, University of Nebraska-LincolnFollow

First Advisor

David K. Watkins

Date of this Version

8-2018

Document Type

Article

Citation

Clark, W. B., and Watkins, D.K., 2018, A quantitative analysis of calcareous nannofossils across a Late Oligocene paleolatitude transect of the North Atlantic Ocean. [Masters Thesis]:University of Nebraska-Lincoln, 56 p.

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Earth & Atmospheric Sciences, Under the Supervision of Professor David K. Watkins. Lincoln, Nebraska: August 2018

Copyright © 2018 William Barrett Clark

Abstract

Samples from ODP Sites 926, 628, 563, U1406, 647, and 918, 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. Detrended Correspondence Analysis (DCA), a Temperature index (TI), and the Shannon Diversity Index (H), were used to examine the paleoenvironmental gradients which exerted the most control over the distribution of species and their abundances. The temperature index correlates significantly to the first axis of the DCA, suggesting that thermal controls were the most important factor in the distribution of Late Oligocene nannofossils in the North Atlantic. Shannon Diversity and the percent abundance of the taxon Reticulofenestra minuta correlates significantly to DCA 2, suggesting that surface water mass fertility was an important secondary controlling factor during the Late Oligocene. A biochronological analysis utilizing Unitary Associations (UA) divided the assemblage into 6 UAs, correlating with the biostratigraphic scheme of Agnini et al. (2014). UA 3 and UA 4, defined by the base of Sphenolithus calyculus, was not used in the Agnini et al. (2014) biozones, and offers an additional bioevent for the Upper Oligocene. The absence of UA 5 at Hole 926B reveals a disconformity that was not identified previously. The zonation scheme of Bergen et al. (2017) which utilizes S. calyculus, and Agnini et al. (2014) cannot be accurately applied to the North Atlantic Ocean north of 53° latitude. The best biostratigraphic resolution in the Late Oligocene North Atlantic is restricted to the upper mid latitudes Sites 628, 563, and U1406. These latitudes, from 27-40^°, represent the warm gyre center and the temperate gyre perimeter.

Advisor: David K. Watkins