Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Barun K. Sen Gupta

Abstract

A study of distribution patterns of benthic foraminifera from the Recent and late Pleistocene northwestern gulf of Mexico revealed a close relationship between assemblages and water masses. Multivariate analyses (cluster and factor) of species-frequency data from 120 core tops (87-1361 m) show that the assemblages are associated with the Surface Mixed Layer, Gulf Water, Oxygen Minimum Water, Subantarctic Intermediate Water, Caribbean Midwater, and the Mississippi River outflow. A similar study of 61 samples (283-1341 m) from the last glacial (15,000 yBP) delineated the boundaries of the late Pleistocene bathyal water masses. These were (in estimated paleodepths) the Subtropical Underwater (100?-350 m), Oxygen Minimum Water (350-570 m), North Atlantic Intermediate Water (570-775 m), and Mediterrenean Outflow Water (775+ m). A delta assemblage was also detected between 91 to 92$\sp{\rm o}$ W. Downcore abundances of species in a core from 726 m depth revealed 3 benthic faunal events, at 13,000, 11,000, and 5,000 yBP, caused by changes in water masses and organic matter content. Factor analysis of presence/absence data of 157 species from 288 core tops (58-1361 m) and the 61 late Pleistocene samples indicated that presence/absence data can be used in paleoceanographic studies; the assemblages could be directly correlated to the water masses, delta outflow, and the carbonate bank environment. A study of downcore variations in 10 box cores was done to determine if abundances of Recent and late Pleistocene benthic foraminifera can be directly compared. Judging by downcore trends produced by taphonomy and living habitat, agglutinated species were dissagregation prone or resistant, while calcareous hyaline species were highly-, moderately-, or poorly-preserved. A preservation index based on these trends shows similar values for the Recent and late Pleistocene samples, indicating that their distributions can be directly compared. Such a comparison demonstrates that distributions of species are affected by water mass properties and organic matter content. Shifts in water-mass boundaries in the last glacial caused concomitant changes in species depth limits.

Pages

509

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