Structurally-controlled deep sea channel courses: examples from the Miocene of southeast Spain and the Alboran Sea, southwest Mediterranean
Authors: Cronin Bryan T. 
Published: April 2008

Two deep water channels, the Tortonian (Upper Miocene) Solitary Channel in the Tabernas Basin in southeast Spain, and Almeria Canyon (Recent) off southeast Spain, are compared and contrasted. Both channels are developed at a similar scale and allow comparison between modern and ancient. Both are sinuous, trunk bypass feeders located in tectonically active, high-gradient turbidite settings, where strike-slip fault patterns appear to deflect channel courses by up to 90°. Sandy turbidites and debris flows dominate the channel-fills, with thick sequences of mudstone deposits outside the channels.

The exhumed Tabernas Solitary Channel is associated with the margin of a Tortonian strike-slip basin in the Betic Cordillera of southeast Spain. It is up to 200 m wide and 40 m thick, and can be mapped almost continuously for 11 km in the field. Half-way along its course the north-south oriented channel is deflected through almost 60° by a strike-slip fault, and from here it meanders southwestwards to terminate abruptly in basin-floor mudstones. The Solitary Channel fill is characterized by four separate fill units which are identified along the length of the channel course, and these are: (1) clinoform surface unit; (2) thin-bedded turbidite unit; (3) massive thick tabular sandstone and debris flow unit; and (4) thin-bedded turbidite unit. The units are inferred to be related to fluctuations in transport processes within the canyon, from large bedform migration to low-density turbidity currents. A conglomeratic thalweg plug is found in the lower channel reaches.

The Almeria Canyon, in the southwest Mediterranean, has a similar planform geometry. The channel is > 24 km long, varies in width from 250–500 m, and varies in depth from 40 to 10 m. The channel is deflected 90° half-way along its length by a fault escarpment. The channel has a variable sinuosity. One meander has a sinuosity value of 3.8, three meanders have sinuosities within the region of 2.0, and elsewhere sinuosity is more commonly in the order of 1.2. The channel is largely, unfilled, though upper reaches contain material which has either slumped into the channel from the walls or been transported down the channel by debris flow. The channel also has a thalweg channel in its lower reaches, which appears braided.

The observations have a number of implications. (1) The planform geometry of the Solitary Channel is very similar to that of the Almeria Canyon, indicating predictable effects of structural control on conduits in tectonically-active settings. (2) The Solitary Channel extends 2 km further into the basin than two other systems previously interpreted from one palaeogeographic timeslice, and this could be explained by structural confinement of the channel course. (3) The Solitary Channel fill is characterized at lower levels by large sandy bedforms indicating strong current conditions. (4) The distinction can be made between relatively long-lived sand-conduits in otherwise mud-prone sectors of basins, such as the two examples in this paper, and short-lived, sand-prone and mobile channels in more sandy areas.