Biostratigraphic Application of Shape Analysis and EXTENDED CABFAC-FUZZY QMODEL to Sphaeroidinellopsis Lineage

Anthony C. Gary

The basis for any good biostratigraphy is using unambiguously defined index species. Species that exhibit high morphologic variability within a time slice and lineages that exhibit subtle continuous morphologic change through time (evolutionary) can prove to be less-than-reliable biostratigraphic markers. This lack of reliability, in some cases, may be a function of the descriptive technique traditionally used to define the species rather than a true absence of biostratigraphic information. In this study, a computer-assisted shape acquisition system and Fourier series in closed form are used to quantify morphologic differences in Sphaeroidinellopsis lineage. This approach makes shape description more precise and eliminates the subjectivity inherent to qualitative descript ons. An unmixing algorithm, EXTENDED CABFAC-FUZZY QMODEL, is used to determine objectively the morphologic end members in the biometric data set and the relative proportions of each end member for each sample. Samples are analyzed from five localities in the Caribbean, the Gulf of Mexico, and the eastern equatorial Atlantic for the upper middle Miocene through lower Pliocene. The results indicate that Sphaeroidinellopsis has behaved similarly in the Caribbean and Gulf of Mexico since 10 Ma. Evolutionary innovations seemingly first appear in the Caribbean and, prior to 6 Ma, their migration into the eastern equatorial Atlantic is delayed. This delay, along with the gradual change in test shape, probably contributes to the disagreement in the definition of chronospecies of Sphaeroidinellop is for this time period.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.