BRALOWER, T. J., S. E. MOCK, J. H. EKDAHL, and L. C. GASKINS, Department of Geology, University of North Carolina, Chapel Hill, NC; and J. M. Blakeney, II, Appalachian State University, Boone, NC

ABSTRACT: Towards Morphometric Biochronology

Morphometrics of several Cenozoic nannofossil lineages have been investigated utilizing an image analysis system connected to a scanning electron microscope (IAS-SEM). This allows rapid measurement of a number of univariate size parameters such as perimeter, length, width and area of a nannofossil and of its components. It also enables measurement of shape parameters such as the angle between Cross bars and ellipticity. Previous morphometric studies of nannofossils, which largely focused on length and width, were performed using a light microscope which provides a resolution of 0.6 micrometers. The IAS-SEM has a resolution of 0.01 micrometers. Because the approach used here allows rapid measurement of multiple features, taxonomic and evolutionary divisions are based on analysis of sim ltaneous changes in several morphometric parameters.

We present detailed morphometric measurements of members of the Paleocene Cruciplacolithus-Chiasmolithus lineage from DSDP/ODP Sites 356, 384, 577 and 690. Taxonomic and evolutionary relationships can be observed in measurements of areas of proximal and distal shields and central area, in ratios of holes to calcite and of the areas of larger to smaller holes. Preliminary results suggest a good statistical basis for most previously-erected species. In separate studies we have analyzed both the small Reticulo fenestra event during the Miocene and the rapid evolution of reticulofenestrids in the Eocene leading to the first occurrence of R. umbilica. In these cases detailed morphometrics suggest that previous taxonomic concepts are less distinct. All groups however show promise for more a tomated approaches to taxonomy and, ultimately, biochronology.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.