Date of Award

8-1950

Document Type

Thesis

Abstract

The Lower Mississippi River delta is an area of active sedimentation receiving an estimated two-million tons of material daily via the Mississippi River. This sediment is being deposited in bodies of water which differ in such physical properties as salinity, temperature and depth. Variations in these environmental factors influence or possibly control the distribution of life which in turn determine the nature of the organic remains incorporated with the sediment deposited.

This study of the recent foraminiferal faunules from the environment of the lower delta stemmed from an investigation of the mudlumps at the mouths of the; passes of the Mississippi River conducted for the New Orleans District, Corps of Engineers, U.S. Army. Following the discovery of an unique and prolific foraminiferal assemblage in the sediments of mudlump SP-5 off South pass, an extensive investigation of the foraminiferal genera and species of the present environments in the Lower Mississippi River delta was initiated. The foraminiferal faunule in the clay of mudlump SP-5 was an index to the environment inhabited by the foraminifera when they were living and thus was a clue to the magnitude of vertical displacement of the clay since the time it was originally deposited as mud in the Gulf of Mexico.

Published reports on two previous investigations of the foraminiferal populations in the lower delta did not satisfy the nomenclatural need in conjunction with the study- of SP-5. One report restricted to a study of beach material from the Rio Grande to the Mississippi River described eighteen species and varieties of foraminifera. The other report presented the distribution of the foraminifera in recent sediments as determined from a traverse across the continental shelf with the results of the investigation being presented at the generic level. No species were described.

The major contribution of this study is the taxonomic analysis of foraminifera from the mudlumps and environments in the Lower Mississippi River delta. A total of 258 species and varieties distributed among 104 genera are described and figured of which five genera, thirty-eight species and eleven varieties are reported as new. This detailed analysis has enabled the writer to establish the foraminiferal species indices of the different environments which had not been done by previous investigations and on the basis of these data to establish the original environment of deposition of the mudlump clay.

On the basis of material recovered from environments sampled in the vicinity of Southwest, South and Southeast passes, the littoral environments contributed only negative information in the mudlump study. The species of the near-shore brackish-water assemblages, so distinctively exhibited in the tidal channels and streams and in the inland bays are not represented in the mudlump assemblages. The beaches and distributaries reflect the foraminiferal faunules of the adjacent environments, normally toe environment abutting the beach and into which the distributary discharges.

The environment of the living correlative of some mudlump faunules appears to be the neritic zone. The foraminiferal faunule of SP-5, however, which constitutes over eighty-eight percent of the total number of species described in this report is characterized by an assemblage of foraminiferal genera and species not present in any of the neritic samples taken by the writer. Environmental conditions similar to those occupied by the SP-5 faunule, when living, probably lies beyond the area of active delta growth in deeper water than was sampled. Credence to this assumption can he found in a series of samples taken off the coast of Texas and Florida by other Investigators which the writer has examined. On the basis of these samples it is concluded that the probable original area of deposition of the mud now constituting the clay of SP-5 was in water deeper than 450 feet, and that the probable magnitude of vertical displacement of the cl^ in SP-5 is in excess of 400 feet.

DOI

10.31390/gradschool_disstheses.8358

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