A Biometric Analysis of the Calcareous Nannofossil Eiffellithus eximius Species Complex and its Biostratigraphic Implications

Authors

Bradi T. Gaer, University of Nebraska-LincolnFollow

First Advisor

David K. Watkins

Date of this Version

Winter 12-5-2019

Document Type

Article

Citation

Gaer, B T. A Biometric Analysis of the Calcareous Nannofossil Eiffellithus eximius Species Complex and its Biostratigraphic Implications. MS Thesis. University of Nebraska-Lincoln. 2019.

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 and Atmospheric Sciences, Under the Supervision of Professor David K. Watkins. Lincoln, Nebraska: December, 2019

Copyright 2019 Bradi Tennille Gaer

Abstract

The evolution of the calcareous nannofossil E. turriseiffelii – E. eximius lineage in the Turonian from the western tropical Atlantic and Indian Ocean indicates identical eiffellithid forms with morphological change in the rotation of the crossbar, relative to the longitudinal axis, from an “x” (E. turriseiffelii) to a “+” (E. eximius). Within these indistinguishable eiffellithid assemblages, neither the size nor shape show significant change during the morphological transition of the crossbar orientation. The rotation of the crossbar toward an axial alignment results in two shifts in the mean angle values. Prior to the first shift, the mean angles of the eiffellithid assemblage have values between 35^o and 45^o with no forms with crossbar angles of <20^o. The first step occurs at the appearance of specimens with crossbar angles between 20^o and 10^o marking the first appearance datum (FAD) of E. eximius s. Ver. The second shift is a significant change in the mean angle values from 35-45^o to 15-22^o among the Eiffellithus assemblage and the appearance of morphotypes with crossbar angles of <10^o recognized as E. eximius s.s. The results of this biometric study indicate that two forms can be reliably recognized and used to increase the biostratigraphic resolution, with the FAD of E. eximius s. Verbeek near the middle to upper Turonian boundary and E. eximius s.s. near the lower to middle Turonian boundary.

Advisor: David K. Watkins