Growth Patterns of Deep-Sea Fans

TLDR: The La Jolla and San Lucas deep-sea fans with the deep-towed instrument package developed at Marine Physical Laboratory of the Scripps Institution of Oceanography details the fine-scale morphology, structure and internal fill of the fan-valleys and suggests the growth patterns of these fans as mentioned in this paper.

Abstract: The growth pattern of a deep-sea fan relates events in and around the fan-valleys to the structure and morphology of the open fan. The growth pattern cannot be determined without knowledge of the origin and recent history of the fan-valley system. The mapping of La Jolla and San Lucas deep-sea fans with the deep-towed instrument package developed at Marine Physical Laboratory of the Scripps Institution of Oceanography details the fine-scale morphology, structure, and internal fill of the fan-valleys and suggests the growth patterns of these fans. The La Jolla fan, 20 km west of Scripps Institution, has one meandering fan-valley that extends across the entire fan. Except on the toe of the fan, the deeply incised valley has terraced walls with steeper walls on the outside of meanders. Very low-relief levees border the fan-valley in some localities. The present erosional valley bypasses the partly buried remnants of an older distributary system on the lower fan. The San Lucas fan, off the southern tip of the peninsula of Baja California, shows a depositional lobe of sediment, or suprafan, below the short, leveed fan-valley extending from San Jose Canyon. The suprafan appears as a convex-upward bulge on a radial profile of the fan. The surface of the suprafan has a series of discontinuous depressions up to 55 m deep and 1 km wide. The depressions are generally asymmetric in cross section, commonly have terraced walls, and are underlain by coarse sand and gravel. They are interpreted to be channel remnants. A model for deep-sea fan growth, based on this study, predicts that deposition on a fan will be localized in a suprafan at the end of large, leveed valleys commonly found on, and generally confined to, the upper reaches of deep-sea fans. The suprafan normally is on the midfan and is characterized by numerous smaller distributary channels. Rapid aggradation in the suprafan coupled with migration and meandering of the channels produces a surface marked by isolated depressions or channel remnants. Uniform deposition, producing a symmetrical half-cone morphology, results from the shifting through time of fan-valleys across the area of the fan.