Deep-sea sedimentary morphology: Modelling and interpretation of echo-sounding profiles

Wide-beam surface-ship echo-sounding records (3.5 and 12 kHz) are frequently utilized to study the nature and distribution of deep-sea sediments and sedimentary morphology. In particular, sedimentary topography with wavelengths of a few meters to several kilometers may produce distinctive echo patterns on surface-ship profilers. These patterns, which can often be mapped over large areas, indicate important morphological elements which may be controlled by near-bottom processes active in that area. Modelling studies can be used to relate certain types of sedimentary morphology to surface echo pattern. The echo return of a sinusoidal sea-floor profile varies with its water depth, amplitude, and wavelength. Similar echo profiles are observed for sinusoidal waves with the same value of S, where S = 4 × π² × water depth × (amplitude)/(wavelength)². Little distortion occurs for S less than 1, but the wave trough is obscured for S greater than 1. Sedimentary structures constructed from sinusoidal horizons (migrating sediment waves, a filling trough, an undulatory accretionary surface, and growing ridges) show how these features can be obscured in deep water. Hyperbolic echoes can be formed by a number of sea-bed features, and the hyperbola pattern may preserve information on the nature of the topography. Several characteristics of surface echo profiles can aid in the description and understanding of the sea-floor morphology. These include the linearity, orientation, spacing, amplitude, and structure of the sediment surface as well as the regional echo distribution pattern.