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Lower Cretaceous to Middle Jurassic (Albian to Callovian) deep-sea sediments recovered from DSDP Hole 534A (28°20.6^primeN, 75°22.8^primeW, water depth 4,976 m) in the Blake-Bahama basin represent the oldest oceanic sediments in the northwestern Atlantic Ocean. The presence of radiolarians was recognized by shipboard scientists from cores 46-127 at subbottom depths 950-1,635 m.
The occurrence of radiolarians (all of Early Cretaceous age) was actually limited to the sediments of Blake Bahara Formation, cores 51, and 69 through 82. Judging from the faunal composition, core 51 apparently belongs to the Eucyrtis tenuis Zone of Barremian age, whereas cores 69 through 82 are probably assignable to the Sethocapsa trachyostraca Zone of Valanginian age. Similar radiolarian assemblages have been reported from the submarine deposits of several North Pacific DSDP sites as well as outcrop sections from Japan, suggesting a wide geographic distribution of co-eval marine sediments.
The majority of radiolarian specimens observed during the investigation had their siliceous skeletons replaced by pyrite, which indicates the reducing condition of sediments during the initial diagenesis of the organic remains.
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