Rock-magnetic stratigraphy of Leg 108 Sites 658, 659, 661, and 665, eastern tropical Atlantic

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The results are as follows: 1. At Site 658, it is likely that the entire interval was extensively affected by reductive diagenesis, resulting in the loss of fine-grained magnetite. At Sites 659 and 665, a similar diagenetic alteration of fine-grained magnetite probably occurred, but was confined to discrete intervals. At Site 661, the uppermost 60-70 mbsf of the section appears to be relatively unaffected by reductive diagenesis; however, low carbonate content of sediments below were probably affected by oxidative diagenesis/authigenesis, resulting in the production of ultrafine-grained ferrimagnetic material. 2. Preliminary spectral analyses of the uppermost 70 mbsf (i.e., unaltered) rock-magnetic record at Site 661 suggest a decrease in the frequency of magnetite grain-size fluctuations after 2.9 Ma. -after Authors

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Proc., scientific results, ODP, Leg 108, eastern tropical Atlantic

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