Bedforms and sedimentary processes along the Garrucha and La Linea canyon axis (SW Mediterranean Sea)

Abstract

The combination of high resolution bathymetry, seismic (parametric) and image (hull mounted & AUV multi-beam echo sounders, parametric profilers, ROV) records have allowed to describe the morphological elements and sedimentary processes that characterise the axis of two submarine canyons located in the SW Mediterranean Sea: The Almanzora-Alias-Garrucha canyon (Palomares Margin) and La Linea (Alboran Margin). The statistical analysis of morphometric parameters together with acoustic facies characterization allowed to establish three general types of bedforms in both systems. A) quasi-symmetric, B) upslope asymmetrical and C) downslope asymmetrical. These bedforms are interpreted as cyclic steps, formed by turbidity flows. They would be related to the important rivers/streams discharges favoured by the proximity of the canyon heads to the coast and erosion of canyons margins. The general gradient of the canyons axes and characteristics of the turbidity flow (energy, sedimentary load) seem to exert the main control. The morphological comparison of ¿cyclic steps¿ in both canyons indicates that the downslope asymmetrical forms would be associated with higher energy flows and the upslope asymmetrical forms with lower energy flows. It also points out that their formation would be related to muddy turbidity flows in the Almanzora-Alias-Garrucha canyon and sandy/silty flows in La Linea. The spatial variability of the cyclic step in each canyon could respond to the coexistence of today/subrecent bedforms with deeper relict forms formed during the last period of low sea level