Barbados Ridge: Inner Trench Slope Sedimentation

Abstract

ABSTRACT A study of 27 piston cores from the Barbados Ridge shows that Quaternary sediments of this inner trench slope are chiefly foraminiferal-pteropod-nanno oozes that have been reworked and/or emplaced by gravity currents. These oozes are mixed with volcanogenic sediments and minor amounts of material derived from the insular shelf. Irregular topography greatly influences the type and dispersal of bottom sediments, particularly on the east side of the ridge. Reworking occurs on topographic highs where fines are winnowed out and mass wasting and gravity currents are initiated; these processes ultimately result in the leveling of irregular floors of deeper, intervening slope basins. Petrographic analyses of graded intervals from the basin floors and slopes reveal the sands to be mixtures of planktic foraminifers (35%), pteropods (10%), and fresh, angular volcanic detritus (10-90%). Planktic foraminifers are commonly form-segregated on the basis of test shape in the graded intervals. On the east flank of the Barbados Ridge, graded sands of insular-shelf origin are locally important; these sands consist of molluscan, algal, and barnacle fragments (0-25%), quartz (0-30%), and minor metaquartz, K-feldspar, and gneissic fragments. The presence of these terrigenous constituents suggests reworking of sediment from Tertiary land or subsea outcrops; additional evidence in favor of reworking is the occurrence of recrystallized radiolarians (Oceanic Group) and biomicrite gr vels. Volcanogenic sediments are areally widespread and dispersed throughout the upper 6 m of the cores and consist of fresh calcic plagioclase (5-40%), together with tuffaceous and pumaceous fragments. We believe these sediments have experienced reworking and resedimentation by bottom currents, with the initial deposition related to volcanic activity on nearby St. Vincent in the Lesser Antilles.