State University of New York at Stony Brook, United States

Ocean Drilling Program Leg 155 drilled 34 holes at 17 sites on the Amazon deep-sea fan and recovered more than 4000 m of sediment from the various fan sub-environments. Eight sites focused on the sedimentary facies and depositional record of the most recently active channel-levee system from upper to lower fan. Three of these sites recovered continuous sections up to 100 m thick of aggrading sandy channel fills beneath the channel axis, as well as sandy lobe deposits from the lower fan. Seven sites penetrated as deep as 434 m and sampled older buried channel-levee systems and thick, interbedded muddy mass-transport units. Suites of wire-line logs, including FMS, run at eight sites reveal log motifs of various sedimentary facies and provide lithologies for intervals of non-recovery. Sediment facies were described and classified for the various fan sub-environments and morphological units. Of particular interest are the nature and distribution of sandy facies within this mud-rich fan. Muddy levee deposits have laminae and thin to medium beds of graded silt and fine sand, sometimes in fining upward successions. Channel deposits contain turbidites and related mass-flow deposits of fine-to-coarse sand up to several meters thick, which are laterally restricted to beneath the channels axes. More areally extensive, thick sandy deposits occur at the bases of many channel-levee systems containing beds up to several meters thick of fine sand to gravel deposited by turbidity currents and related gravity-controlled mass flows, which spread out from channel mouths. Lower-fan depositional lobes are laterally extensive fine-to-coarse sand beds up to 18 m thick.