HOW FAST DO SUBMARINE FANS GROW? INSIGHTS FROM THE QUATERNARY GOLO FANS, OFFSHORE CORSICA

Deposition rates in terrestrial and shallow-marine environments are well constrained in Quaternary systems with the timescales for the formation of fluvial channel belts or delta lobes known to range from 10³ to 10⁴ yrs. By contrast, timescales required to form key environments within submarine fans are poorly constrained due to the difficulty of measurement in the deep sea and the Holocene sea-level highstand which rendered many submarine fans inactive. Nevertheless, rates of sediment transport and deposition by turbidity currents, and the rates of formation of deep-sea fan elements have been measured in a few instances. Our work on the Golo Fans, Corsica adds important new data and insights into the rates and timing of deep-water deposition.

High-resolution seismic, sedimentological, and geochronological data were used to determine rates and volumes of deposition for submarine fan elements of Quaternary Golo submarine fan system. Data from the Golo submarine fans indicate rates of deposition from 0.1 to 10 m/ka depending on the time scale and the location of the observation. Over 100 kyr glacial-interglacial timescales, vertical and volumetric deposition rates are buffered by changes in global sea level that result in fluvial systems extending across the shelf to connect with submarine canyons and deliver sand to the deep-water basin, or restrict deep-water sediment delivery because the river mouth is located on the inner shelf and far from the canyon head. Over millennial timescales, autogenic river avulsions on the shelf can favor sand transfer through one submarine canyon to its associated lobe complex while, at the same time, the rest of the fan system is draped by mud-rich deposits. On an active fans autogenic avulsion of submarine channels results in lateral shifting of the locus of deposition and construction of a succession of compensationally-stacked lobes and lobe elements. Short-term deposition rates on the fan range from 8.6 m/kyr at proximal portions of submarine fans to 0.4 m/kyr along the distal fringe. Individual submarine fan lobes 5-10 m thick were deposited in as little as 1-13 kyrs.

Our study of the Golo system shows that submarine fans are dynamic environments with deposition of sedimentary bodies 10’s of km across and up to 25 m thick in <20 kyrs, and leveed channels that can extend kilometers in a few thousand years. Rates of deep-water fan deposition and the formation times for submarine fan architectural elements are comparable to those of fluvial and deltaic systems.