Median grain size and distribution of sand in ODP Hole 108-660A (Fig. 5)

• Main Authors: Sarnthein, Michael, Faugeres, Jean-Claude
• Format: Dataset
• Language: English
• Published: PANGAEA 1993
• Subjects: 108-660A; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Joides Resolution; Leg108; Median; grain size; North Atlantic Ocean; Ocean Drilling Program; ODP; Sample code/label; Size fraction > 0.063 mm; sand; Antarc*; Antarctica; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.763684; https://doi.org/10.1594/PANGAEA.763684

50 m of Middle Eocene pure radiolarian ooze were drilled at ODP Site 660 in the equatorial East Atlantic, 80 km northeast of the Kane Gap. The oozes comprise a 10 m high and 2 km broad mound of seismic reverberations, covered by manganese-rich sediment, and contain trace amounts of sponge spicules and diatoms, negligible organic carbon (0.15%), clay, and variable amounts of pyrite. The yellow to pale brown silty sediments are relatively coarse-grained (30–45% coarser than 6 µm), little bioturbated, and commonly massive or laminated on a cm-scale. The unlithified radiolarian ooze may indicate an interval of high oceanic productivity, probably linked to a palaeoposition of Site 660 close to the equatorial upwelling belt during Middle Eocene time. The absence of organic matter, however, and both the laminated bedding and the mound-like structure of the deposit on the lower slope of a continental rise indicate deposition by relatively intense contour currents of oxygen-rich deep water, which passed through the Kane Gap, winnowed the fine clay fraction, and prevented the preservation of organic carbon. The ooze may be either a contourite-lag deposit, or a contourite accumulation of displaced radiolarians, originating south of the Kane Gap and being deposited in its northern lee, thus documenting the passage of a strong cross-equatorial bottom-water current formed near Antarctica. These Eocene contourites may be an analogue for ancient radiolarites in the Tethyan Ocean.