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Abstract: Bathymetric Zonation and Relationship to Sea-Bed Environments of Modern Benthic Foraminiferal Biofacies, Northwestern Gulf of Mexico Slope

Martin B. Lagoe, Anthony Gary, Sarah Zellers, Benjamin Sloan, Paula Noble, Ron Johns

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 2134 m. 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 processes within these environments that produce fossil assemblages. One hundred sixty-one taxa are recognized, only 24 of which have population abundances >1%. Quantitative analyses of the data include cluster analysis, principal components analysis (PCA), and detrended reciprocal averaging (DRA). Cluster analysis defines four major biotopes, which occupy geographically nonoverla ping areas and are oriented parallel to depositional strike. Actual depth ranges of the biotopes do 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, 1100 m, and possibly 1500

m. PCA and DRA identify species relationships, which characterize the biotopes. The shallowest biotope (141-500 m), within the limits of the oxygen minimum (ca. 2.6 ml/l), is characterized by Uvigerina peregrina, Bolivina albatrossi, and Bulimina alazanensis. The next biotope (ca. 500-1600 m) is distinguished by Epistominella exigua, Pullenia subsphaerica, and Glomospira charoides. This biotope grades into one delineated by Eponides turgidus, Bulimina aculeata, Osangularia culteri, and Gyroidina orbicularis (ca. 1200-2100 m). The deepest biotope (ca. 1500-2134 m) is characterized by Alabamina decorata, Hoeglundina elegans, Reophax spp. and Hormosina sp. Downslope transport is evident in several instances. The patc y distribution of agglutinated tubes illustrates the problem of generalizing relationships at large scales. Patchiness is a function of both small-scale patchiness in living distributions and the coarse scale of sampling.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994