Date of Award

Spring 1993

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Geology

Committee Director

Randall S. Spencer

Committee Member

Stephen Culver

Committee Member

Diane Kamola

Call Number for Print

Special Collections LD4331.G4K78

Abstract

This study tested the validity of using intraspecific variation in benthic foraminifera as a means for determining Pleistocene paleobathymetry. Canonical variate analysis was used as a means for determining visually undetectable but statistically significant differences in the morphology of selected species. Two species, Cassidulina subglobosa and Uvigerina peregrina, were collected from Pleistocene well cuttings from the northwest Gulf of Mexico. The canonical analysis involved comparing the intraspecific variation of these Pleistocene species to their counterparts occurring in the modern Gulf of Mexico, where intraspecific variation was previously analyzed and found to be sufficient to allow detection of bathymetric differences of 200 meters or less.

In order to validate this statistical comparison of intraspecific variation between Pleistocene and modern individuals of the same species and their implied bathymetry, a taxonomic analysis of these same Pleistocene samples was conducted in order to construct paleobathymetric estimates. In addition, a Q-mode cluster analysis of species abundances was performed in order to detect any possible paleoenvironmental or paleobathymetric subgroups occurring in the Pleistocene section studied.

The canonical analysis for Cassidulina subglobosa in the top eight samples in the well indicated a paleobathymetric range of 50-100 meters, while that for Uvigerina peregrina indicated a paleobathymetric range of 50-200 meters.

The Q-mode cluster analysis revealed two major groupings and hence changes in biofacies. The first major group contains three samples, the top three samples in the well, and represents a shallow water environment. The second major group contains twenty samples and can be separated into two subgroups, one with fourteen samples, representing deeper water. The other subgroup contains six samples, five of which are immediately below the top three well samples, and represents a transitional environment between the shallower and deeper water groups. These five samples plus the the top three samples in the well are those which were used for canonical analysis.

The species assemblage data indicated a paleobathymetric range of 100-200, and possibly extending to 500 meters, a shallow water environment, for the three samples in the first major cluster group, which correspond to the top three samples in the well. A paleobathymetric range of 100-500, and possibly extending to 1000 meters was indicated for the smaller cluster subgroup with six samples, five of which are immediately below the top three well samples. A paleobathymetric range of 100-1000 meters for the twenty samples in larger cluster subgroup.

Considering the different strategies involved between these two methods of determining paleobathymetry, the results indicate that further investigation of intraspecific variation as it relates to bathymetry is warranted.

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DOI

10.25777/gbr8-sk61

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