Sedimentary Facies Recovered from Amazon Fan during ODP Leg 155: II. Synthesis of Depositional Processes from Core and Wire-Line Log Data

W. R. Normark, J. E. Damuth, C. Pirmez, 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.

The detailed descriptions of cored sequences and the analysis of wire-line logs permit classification of sedimentary facies within the fan and provide insights into the distribution of these facies types throughout the different morphological units and sub-environments of the fan, which have previously been identified on the basis of seismic facies and morphological expression. Distinctive sedimentary facies and structures are present within the levee (overbank), channel (HAR units), base-of-levee (HARP units) and end-of-channel (lobe) deposits of the channel-levee systems, as well as in the large, muddy mass transport deposits, which are interbedded between channel-levee systems. In addition, offset holes provide insights into larger-scale sedimentary structures in levee, channel, lo e and mass-flow deposits.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California