Sedimentary Facies Recovered from Amazon Fan during ODP Leg 155: I. Implications for Depositional Processes and Sand-Body Distribution
W. R. Normark, J. E. Damuth, and R. D. Flood
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 epositional lobes are laterally extensive fine-to-coarse sand beds up to 18 m thick.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California