Date of Award

Spring 4-22-1987

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Geology and Geophysics

First Advisor

Sen Gupta, Barun

Second Advisor

Shiebout, Judith

Abstract

The recent benthic foraminifera 1 fauna of the continental margins of Mexico (Gulf of Campeche and Gulf of Tehuantepec) was studied. Surficial sediment samples (lOcc) were collected using a Shipeck dredge and were stained with Sudan Black "B" in order to differentiate the living fauna from the death assemblage. In the 41 samples from the Gulf of Campeche, 279 species were found in the total assemblage in water depths ranging from 9 to 586 m. In the 22 samples in the Gulf of Tehuantepec, 132 species were identified from the total assemblage in water depths of 20 to 180 m. A total of 175 species were found alive in the Gulf of Campeche compared to the 70 found in the Gulf of Tehuantepec. Shannon-Wiener values indicated that the Gulf of Campeche species diversity was higher than that of the Gulf of Tehuantepec. However, living and total faunas in both areas follow the same diversity trends in relation to water depth. Even though the samples from Tehuantepec show lower diversity, the fauna shows a more uniform distribution in terms of evenness (E). The observed diversity trends could be explained by the Time Stability Theory. Based on water depth, the following three assemblages were found in both the Gulf of Campeche and the Gulf of Tehuantepec: Inner neritic (less than 50 m), central and outer neritic (50-150 m), and upper bathyal. Even though assemblages of the two areas are different at the species level, there are similarities at the generic level. The cluster analysis provided a better correlation in both areas between total faunas and water depths. For the living fauna in Campeche, sediment distribution was correlated with faunal distribution. In Tehuantepec, the distribution of the dominant species Hanzawaia nitidula is strongly reflected in the structure of the dendrogram.

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