ABSTRACT

The distribution of benthic foraminifera in surface sediments of the northwest Gulf of Mexico slope is studied in 51 piston core-top samples ranging in depth from 141 to 2,134 m (462 to 7,000 ft). Total faunas (living plus dead specimens) are documented as part of a larger study investigating the relationship of living benthic foraminiferal distributions, their relationship to surface sediment and infaunal environments, and taphonomic processes within these environments that produce fossil assemblages. A total of 161 taxa are recognized in the samples, only 23 of which have population abundances greater than 1%. Quantitative analyses of the data include cluster analysis of samples, principal components analysis (PCA), and detrended reciprocal averaging (DRA). Cluster analysis defines four major biotopes that occupy geographically distinct areas and are oriented parallel to depositional strike. Actual depth ranges of the biotopes overlap, pointing to the gradual nature of faunal change with depth on the slope, as recognized by previous studies in this area. Approximate faunal boundaries are present at 500 m (1,640 ft), 1,100 m (3,610 ft), and possibly 1,500 m (4,920 ft). PCA and DRA identify species relationships that characterize the biotopes. The shallowest biotope (141 to 500 m [462 to 1,640 ft]), within the limits of the weak oxygen minimum in this area (ca. 2.6 ml/l), is characterized by Uvigerina peregrina, Bolivina albatrossi, and Bulimina alazanensis. The next deeper biotope (ca. 500 to 1,600 m [1,640 to 5,250 ft]) is distinguished by Epistominella exigua, Pullenia subsphaerica, and Glomospira charoides. This biotope grades downslope (ca. 1,200 to 2,100 m [3,940 to 6,890 ft]) into one delineated by Eponides turgidus, Bulimina aculeata, Osangularia culteri, and Gyroidina orbicularis. The deepest biotope (ca. 1,500 to 2,134 m [4,920 to 7,000 ft]) is characterized by Alabamina decorata, Hoeglundina elegans, Reophax spp., and Hormosina sp. Downslope transport is evident in several samples.