The Amazon-HARP Fan Model: Facies Distributions in Mud-Rich Deep-Sea Fans Based on Systematic Coring of Architectural Elements of Amazon Fan

Although Amazon Fan is one of the largest deep-sea fans in the world, it’s architectural features are typical of "mud-rich" fans developed on passive margins, regardless of their size (c.f. Bouma et al., 1985). Because Amazon Fan is the only modern fan whose architectural elements have been systematically drilled and continuously cored, it is one of the most important modern analogs for understanding “mud-rich” deep-sea fans and their hydrocarbon reservoir potential. Prior to ODP drilling in 1994, architectural elements and the distribution of sedimentary facies within Amazon Fan were inferred from high-resolution seismic, GLORIA side-scan sonar, SeaBeam swath-mapping and pistoncore data (Damuth and Kumar 1975; Damuth and Embley 1981; Damuth et al. 1983a, 1983b, 1988; Damuth and Flood, 1984 and 1985; Manley and Flood 1988; Flood et al. 1991.; Pirmez 1994; Pirmez and Flood 1995) In particular, these studies revealed that distributary channels have highly meandering planforms and are perched on natural levee systems. The aggradational channel-levee system is thus recognized as the basic depositional unit of the fan (Fig. 1). High-amplitude reflections (termed HARs) observed beneath the channel axis were interpreted as coarse-grained channel-fill deposits (Fig. 1). More laterally extensive high-amplitude reflections packets (termed HARPs) at the bases of channel-levee systems were interpreted as coarse sediment deposited either from flows spreading laterally outward from a channel mouth (i.e. depositional lobe), or from flows issuing through a crevasse in a levee during initiation of a channel-avulsion event (i.e. crevasse splays) (Figs. 1, 2). Although only one channel-levee system was active at any given time, repeated channel avulsion developed groups of overlapping, genetically related channel-levee systems, termed channel-levee complexes, across the upper to middle fan surface. In addition, large, regionally extensive mass-transport deposits overlying portions of channel-levee systems were recognized on the modern fan surface (Damuth and Embley 1981) and seismic data showed that older levee complexes buried within the fan are also separated by similar thick, mass-transport deposits at many locations (Manley and Flood 1988) (Fig. 1).