Modern Fan Stratigraphy

Abstract On present-day deep-sea fans there are two kinds of stratigraphic information aside from late Pleistocene and Holocene stratigraphy from near-surface piston cores: (1) that from acoustic signatures on seismic profiles, and (2) that from Deep Sea Drilling Project (DSDP) drill holes. The former data set often lacks confirmation of reflector age by drill samples and the latter data set provides no consistent pattern of drill hole stratigraphy on any one fan. Fortunately, some high-resolution seismic stratigraphy can be correlated with near-surface piston cores (Fig. 2-3). Realizing these limitations, this section begins with a general summary of acoustic stratigraphy on fans and associated environments. Following this, the general age, thickness, stratigraphy and sedimentation rates on fans will be discussed. The open continental slope environment normally borders one or more sides of deep-sea fans. Slides or slumps can be mapped acoustically on upper- or mid-slope regions of unstable slope environments (Fig. 5-1) (Field and Edwards 1980; Nardin et al., 1979a). Debris aprons of mass-transport deposits with chaotic acoustic signatures characterize the base-of-slope regions of unstable open slopes (Figs. 5-1 to 5-3). When canyons are present, a complex mosaic of debris aprons and small deep-sea fans can be mapped in restricted basins (Fig. 5-3). Individual slide, slump and debris-flow events in the surface and subsurface of slope and other areas are readily mapped by side-scan sonar (Figs. 4-6 and 4-18), high-resolution echo character (Fig. 2-3), and seismic profiles (Figs. 2-4, 5-1 and 5-2). Grids of seismic profiles exhibiting rotated blocks and incoherent reflectors