Contributions From Morphological Analysis in Calcareous Nannofossils to Biostratigraphic Resolution

Abstract

Taxonomy is of paramount importance for sound biostratigraphic interpretation. Biostratigraphy (and biochronology) still largely relies on the ranges of selected taxa. However, as the morphology of species varies through time, evolutionary grades should add detailed information for finer stratigraphic resolution. Recognizing and quantifying these microevolutionary trends and modalities, as well as ecological responses, offer an additional tool to refine uncertainties in biozonation, determine stratigraphic continuity, and the dating of unconformities.

I present several Neogene and Paleogene examples of calcareous nannofossils from the Gulf of Mexico and additional global studies. These examples demonstrate the application of quantitatively detailing morphologic variations for the purpose of increasing stratigraphic resolution. A statistical evaluation to characterize shape and size trends will be presented to illustrate applications of intraspecific and pseudo-cryptic speciation patterns to aid in recognizing stratigraphic intervals, boundaries (i.e. stages and biozones), unconformities, and reworking. Additional examples will demonstrate iterative morphologic themes, along with utilizing variations in morphologic patterns, such as directional and stable speciation patterns in lineages, to show the great potential of morphology as a biostratigraphic tools.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019