Relations between bioturbation features and sedimentologic aspects of abyssal pelagic ooze and clay were investigated in 26 box cores collected in 1,400 to 5,700 m of water in the central and southern Atlantic Ocean. Sediment composition, texture, and core stratigraphy were compared with the occurrences of biogenic structures and other aspects of bioturbation to determine the sedimentologic factors that most affect burrow preservation and biologic mixing of abyssal sediment.

Box core surfaces typically exhibited a heterogeneous microtopography of mounds, lumps, trails, agglutinated tubes, and open holes. Benthic protists (foraminifera and xenophyophorids) and fecal strings of larger organisms were common. Remnants of shallow infaunal tunnel systems sometimes were evident on slightly washed box core surfaces. For example, Paleodictyon occurred in carbonate-rich ooze; Cosmorhaphe occurred in deposits containing 20 to 30% coarse fraction; and Spirorhaphe appeared to be cosmopolitan with respect to sediment type.

Sediments of the mixed layer (upper 5 to 8 cm) and underlying Holocene transition layer were compared with respect to carbonate, organic carbon, and coarse fraction (> 62µm) percentages. Transition layer sediments, which contained the most visible burrows, were much more heterogeneous in terms of carbonate content than mixed layer deposits. However, the heterogeneity of organic carbon and coarse fraction concentrations were roughly equivalent in the two horizons.

Visibility of specific burrows was highest in cores with low carbonate contents (< 30% CaCO₃) and also in cores from the Sierra Leone Rise, where sedimentation patterns appear to have changed following the last glacial stage. Burrow visibility was poorest in cores with high carbonate contents (> 70% CaCO₃) throughout the entire core.

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