Abstract

The island of Barbados exposes the crest of the Barbados accretionary prism of the Lesser Antilles forearc. The sedimentology of Lower Eocene hemipelagite was studied in three fault-bounded packets near Bissex Hill. Three facies were identified based on coherent stratigraphic successions. Facies 1 hemipelagite strata are well layered to massive and consist of radiolarite layers (T layers), matrix-supported radiolarian mudstone (F layers), layers with an intermediate abundance of radiolarian tests (N layers), mud-rich (M) layers containing less than 20% radiolarian tests, rare quartzose sandstone intervals, mud-chip breccia beds, and wispy, laminated, bioturbated units. Many T and N layers have parallel laminations and sharp basal contacts. Few T and N layers have coarse-tail grading, scour structures, and floating mud clasts. Most T and N layers were deposited by turbidity or bottom-water currents. F layers probably represent waning-flow current or suspended-load deposits. Wispy, laminated units are most likely bioturbated T, N, and F layers. Facies 2 strata are wispy, laminated terrigenous mudstones greater than 10 cm thick. Thorough bioturbation indicates slower rates of deposition relative to facies 1 strata. Facies 3 is mudstone composed of sparse radiolarian tests floating in a terrigenous-mud matrix. Facies 3 deposits are interpreted as extensively bioturbated sediment which, prior to reworking, contained fewer intercalated T layers. Bulk-rock chemistry indicates that the hemipelagites were derived from terrigenous and biogenic sources. Weight-percent Al 2 O 3 correlates with the percentages of clay-sized material in T, N, and F layers. Low total organic carbon (bitumen-free; 0.06-0.83%) and Type III kerogens indicate an oxic depositional environment. The hemipelagic rocks were deposited in abyssal-plain or outer-trench-slope environments.

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