Contourite erosive features caused by the Mediterranean Outflow Water in the Gulf of Cadiz: Quaternary tectonic and oceanographic implications

Contourite depositional systems have been the focus of much recent research, but still relatively little is known about contourite erosive features and their associated processes. Based on multibeam bathymetry, side-scan imagery and different resolution seismic records, a detailed description and classification of the major erosive submarine valley features of the Contourite Depositional System of the Gulf of Cadiz middle slope is presented for the first time. Four types of erosive features have been differentiated, including contourite moats, contourite channels, marginal valleys and large isolated furrows, and interpreted in terms of their tectonic and oceanographic implications during the Quaternary. The study of the distribution and characteristics of erosive features is essential to better understand the present and past interaction of the Mediterranean Outflow Water (MOW) with the middle slope seafloor, and allows us to propose a new and more precise scheme for the MOW circulation patterns. This scheme includes a main along-slope circulation responsible for the excavation of the contourite moat and channels, and a secondary down-slope circulation responsible for the erosion of marginal valleys and isolated furrows. Three evolutionary stages have been observed in the development of the erosive system during the Quaternary, that can be related to changes in the distribution and splitting of the MOW as a consequence of the segmentation of the NE-SW diapiric ridges by neotectonic effects: 1) Early Pleistocene to Mid-Pleistocene: linear diapiric ridges; 2) Mid-Pleistocene to Late Pleistocene: diapiric reactivation and 3) Late Pleistocene to Holocene: main recent phase of diapiric ridges segmentation and rotation. This study provides important regional clues for establishing the evolution of the erosive features in relation with neotectonic effects, and represents a good example of the potential of erosive features as evidences for the reconstruction of the paleoceanography and recent tectonic changes. (C) 2008 Elsevier B.V. All rights reserved.