Patterns of Foraminiferal Distribution, Northwest Gulf of Mexico: ABSTRACT

Within the past 30 years, several investigators have collected material and reported on Recent Foraminifera in the northwest Gulf of Mexico. The investigations include lagoon, delta, shelf, slope, and abyssal environments. Each report, however, includes only a limited area of investigation. This report is an attempt to evaluate and integrate the existing data in the form of geographic-distribution patterns. The species reported in approximately 1,200 samples form the basis of this study; environmental data come from sedimentologic and oceanographic investigations. Marginal marine environments: Faunas reported primarily from Texas bays and lagoons change geographically in composition. On the southwest, the Laguna Madre and lower Corpus Christi and lower Aransas bays are dominated primarily by miliolids and secondarily by species of Elphidium and Streblus. The miliolids are replaced by the Elphidium-Streblus fauna in Aransas, lower San Antonio, Matagorda, and Galveston Bays and in the pass area of Sabine Lake. These areas contain the so-called "Lower Bay" fauna. The landward parts of these same water bodies contain an "Upper Bay" fauna, usually dominated by the arenaceous Ammotium salsum; where streams enter the bays, Eponidella usually is characteristic. Sparse data from Louisiana bays indicate that the "Upper Bay" fauna predominates throughout the coastal area. The southwest-t -northeast changes occur in response to changing climatic zones, increasing stream discharge, and sediment type. Marine environments: The continental shelf extending from the Gulf beach to about 70 fm. contains a variety of geographically bounded faunas. Despite the emphasis on "depth facies," many shelf genera show a pronounced change along strike. For example, the inner shelf from the beach to about 20 fm. generally is dominated by species of Elphidium and Streblus. Offshore from south Texas, a band of Elphidium is dominant nearshore and is succeeded by a band of Streblus in somewhat deeper water; the bands are reversed offshore from southeast Texas and Louisiana. The middle shelf, 20-50 fm. deep, is characterized by a laterally diverse system of dominant taxa. Hanzawaia, Virgulina, and Proteonina occur in elongate and commonly interfingering bands. These dominant forms, however, are replaced in the vicinity of the Mississippi delta by Nonionella, Buliminella, and Epistominella. The outer shelf contains dominant abundances of Cibicides, Uvigerina, and Bigenerina; species of Bolivina occur mainly on the outer shelf off southeastern Louisiana. The continental slope, in contrast to the shelf, is characterized by more uniform lateral distributions of genera. The upper slope from 70 to approximately 500 fm. is strongly dominated by species of Bolivina. This genus is replaced by Bulimina from 500 to 900 fm. and can be considered as indicative of the middle-slope environment. The lower-slope and abyssal environments deeper than 900 fm. are characterized by Pseudoparrella, Eponides, and Glomospira. The number of species per sample increases from a low average of about 10-12 in the bays and nearshore zone to a maximum of more than 55 at or near the shelf-slope break. The faunal diversity decreases again on the slope reaching a minimum of 10-15 species in abyssal samples. Planktonics increase uniformly in abundance from the beach into the Sigsbee Deep. Their increase is related directly to decreasing rates of dilution by sediments and other organisms. End_of_Article - Last_Page 2322------------