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A seismic analysis of the Pliocene and Quaternary stratigraphy was conducted in the Alboran Sea (westernmost Mediterranean) using more than 1250 profiles consisting of single- and multi-channel seismic records. This allowed for the updating and renaming of the stratigraphic boundaries and the establishment of a new Pliocene and Quaternary seismic stratigraphy for the Alboran Sea, after the relocation of the base of the Quaternary from 1.8 to 2.6 Ma. The boundaries of the stratigraphic division are as follows: the Messinian (M at 5.96 to 5.33 Ma), the intra-lower Pliocene (P0 at ca. 4.5 Ma), the top of the Zanclean (P1 at ca.3.3 Ma), the base of the Quaternary (BQD at ca. 2.6 Ma), the top of the Gelasian (Q0 at ca. 1.8 Ma), the intra-lower Quaternary (Q1 at ca. 1.12 Ma), and the top of the Calabrian (Q2 at ca. 0.7 Ma). Additionally, for the first time, the seismic analysis allowed us to present and discuss the evidence of contourite features reaching the scale of the Alboran Basin. Contourite drifts (plastered, sheeted, elongated separated and confined monticular drifts) and erosive features (terraces, scarps, moats and channels) were developed under the continuous influence of Mediterranean water masses (light and dense), after the opening of the Strait of Gibraltar in the latest Miocene (5.46 Ma). There are at least two primary factors controlling the contourite features, based on the seismic analysis, as follows: i) tectonics, which has governed the relocation of the main Mediterranean flow pathways and their circulation patterns; and ii) climate, which has influenced both water mass conditions (interfaces) and hinterland sediment sources, conditioning the morpho-seismic expression and growth pattern of the drifts and terrace formation (dimensions). The distribution of contourite features through time and space has allowed us to propose the three following main scenarios for ocean circulation since the opening of the Strait of Gibraltar: Atlantic Zanclean flooding; the Pliocene sea, with two different stages for the dense circulation; and the Quaternary sea, with well-defined and stable interfaces for the Atlantic Waters (AW), light and dense Mediterranean waters.

A multiple Contourite Depositional System has been defined in the Plio-Quaternary sedimentary register in the Alboran Sea. This multiple system formed by the Atlantic and the low density and high density Mediterranean Waters, which shaped the margins and basins since the opening of the Gibraltar Strait. Three different (paleo)circulation scenarios are proposed since then: the Atlantic water Flooding;the Pliocene circulation, characterized by immature low and high density Mediterranean waters and a strong countercurrent in the Western Basin; and the Quaternary circulation, characterized by tabular Mediterranean water masses with multiple current dynamics,an increasing influence of density contrasts, and climate shifts causing major vertical and horizontal displacements of their interfaces., SI

New high-resolution seismic and swath bathymetry data reveal the detailed structure of nine mud volcanoes and two large fields of pockmarks at water depths of 400–1100 m in the western Alborán Sea. These features are related to episodes of focused fluid flow through Pliocene-Quaternary contourite deposits of the Ceuta Drift. We describe nine mud volcano systems, composed of two key structural elements: (i) extrusive edifices comprising cones, bicones and low-dip mudflows interfingering with adjacent drift sediments and (ii) intrusive feeder complexes comprising pipes and unstratified downward-tapering cones underlying the extrusive edifices. The mud volcano systems are grouped into four types: I: Complex edifices; II: Stacked single edifices; III: Single edifices fed by buried bicones and IV: Single edifices. All except the last record episodic extrusive activity since the Pliocene, the timing of which is constrained by correlation between the main mud extrusion episodes and dated unconformities within the Ceuta Drift. Complex mud volcanoes composed of twin to multiple seabed cones are the longest-lived systems, with at least six extrusive episodes since the mid-Pliocene; most of the mud volcanoes appear to have been reactivated in the mid-Pleistocene (~ 0.9 Ma, MPR discontinuity) and all at MIS12 (0.4 Ma). While the onset of focused fluid flow was triggered by mid-Pliocene tectonically-driven diapirism of Lower Miocene shales that form the rooting zone of the mud volcanoes, we suggest that some of the Pleistocene phases of mud extrusion might be related to erosion of the contourite drift during major sea-level falls. In addition to vertical focused fluid flow, we propose that leakages from the mud volcano feeder complexes into high-permeability contourite sediments may cause lateral fluid migration and form gas accumulations. Lateral fluid flow in the near surface sediments could be responsible of forming subsurface reservoirs and consequently, random pockmarks by fluidification and/or liquefaction of the non-consolidated shallow sediments. Stacked buried paleo-pockmarks indicate that this mechanism has been persistent along recent times, at least after the mid-Pleistocene. 3

The Alboran Sea is a Neogene extensional basin developed in a convergence tectonic setting that generates a complex physiography. The SW-NE-trending Alboran Ridge separates three main basins, Western, Eastern and Southern. The filling of the Alboran Basin is composed of Early Miocene to Quaternary deposits (CAMPILLO et alii, 1992). The Plio-Quaternary deposits lies over a strongly erosive surface (the Messininan surface -M reflector-) with three major types of features: the Zanclean Channel, several terraces, and canyons (ESTRADA et alii, 2011). The Plio-Quaternary sedimentary evolution has been controlled mainly by the interplay of tectonics, sea-level changes, and a complex ocean circulation (ERCILLA et alii, 1994). Most of the geological studies done since the 80’s in the Alboran Sea suggested that downslope processes were dominant, (ERCILLA et alii, 1992). Locally, contourite features had been defined in the westernmost slope of the Moroccan margin (ERCILLA et alii, 2002). Critical reviews of the available seismic records and of our previous literature allowed us re-nterpreting themorphosedimentary features that characterize the Alboran Sea. We propose the dominance of alongslope processes in the Alboran Sea, that are locally modified by the downslope processes at the margins, submarine fans, and walls of the Alboran Ridge and seamounts. 0

This paper presents a new view of recent sedimentation in the Alboran Sea, based on the analysis of the largest database of available seismic profiles in that sea. The results reveal that contourites represent the main morphosedimentary features that characterize the margins and basins. Several types of contourite features have been characterized, both depositional (plastered, sheeted, elongated-separated, confined, and channel-related) and erosive (moats, terraces and furrows). These elements are interrupted by the construction of turbidite fans, mainly in the Spanish margin, and by sedimentary instabilities that locally affect to the open slope, Alboran Ridge and morphological highs. This new morphosedimentary view of the Alboran Sea reveals for the first time the important role of along slope processes (transport, sedimentation and erosion) associated with Mediterranean water masses. En este trabajo se presenta una nueva visión de la sedimentación reciente en el Mar de Alborán, en base al análisis de la mayor base de datos con perfiles sísmicos disponibles en dicho mar. Los resultados obtenidos revelan que las contornitas representan el principal elemento morfosedimentario que caracteriza a los márgenes y las cuencas. Se han caracterizado varios tipos de elementos contorníticos deposicionales (crestas adosadas, laminares, elongadas-separadas, confinadas y de canal) y erosivos (fosas, terrazas y surcos). Estos elementos están interrumpidos por la construcción de abanicos turbidíticos, principalmente en el margen español, y por inestabilidades sedimentarias que afectan localmente al talud abierto, a la Dorsal de Alborán y a los altos morfológicos. Esta nueva visión morfosedimentaria del Mar de Alborán pone de manifiesto por primera vez el importante papel de los procesos sedimentarios longitudinales al margen (transporte, sedimentación y erosión) relacionados con las masas de agua mediterránea. 0

Several attempts for establishing a good Plio-Quaternary stratigraphy were proposed and disputed since the beginning of the studies in the Alboran Sea during the 80’s. Now, we have reviewed all the available data with the purpose of improving the detail of the previous stratigraphy by adding new chronostratigraphic boundaries (Lower Pliocene Revolution –LPR-, Base Quaternary Discontinuity –BQD- and Middle Pleistocene Revolution –MPR-) with paleoclimatic and paleoceanographic significances. Their addition have allowed tracking the effects of the Mediterranean water masses on the sedimentation since the opening the Strait of Gibraltar. The new results indicate that the Pliocene and Quaternary sedimentary record is mainly characterized by contourites, comprising both depositional and erosive features, that contribute to the outbuilding of the margins and infilling of the basins. Thus, a new Plio-Quaternary sedimentary evolution model with dominance of the alongslope processes has been established for the Alboran Sea., Desde el inicio de la investigación científica en el Mar de Alborán en los años 80 se han presentado varios trabajos de estratigrafía Plio-Cuaternaria. Recientemente hemos revisado todos los datos disponibles con el propósito de mejorar el nivel de detalle de la estratigrafía previa, añadiendo nuevos límites cronoestratigráficos (Lower Pliocene Revolution –LPR-, Base Quaternary Discontinuity –BQD- y Middle Pleistocene Revolution –MPR-) con significados paleoclimático y paleoceanográfico. Su inclusión nos ha permitido rastrear los efectos de las masas de agua mediterráneas sobre la sedimentación desde la apertura del Estrecho de Gibraltar. Los nuevos resultados indican que el registro sedimentario Plio-Cuaternario está principalmente caracterizado por contornitas, que comprenden tanto rasgos deposicionales como erosivos, que contribuyen a la construcción de los márgenes y relleno de las cuencas. Esto ha permitido establecer un nuevo modelo de evolución sedimentaria durante el Plio-Cuaternario con dominancia de los procesos longitudinales para el Mar de Alborán., Sí

Critical reviews of the available seismic records and analyses of CTD data in the Alboran Sea have changed the previous interpretations about the types of deposits making up the nearsurface sediments of the Alboran Sea. During the last 20 years many studies about sedimentation in the Alboran Sea suggested that turbiditic fans, gravitative deposits and hemipelagites characterized the slopes and sub-basins of the Alboran Sea. The new results suggest the dominance of contourites interrupted by submarine fans and sedimentary instabilities in those physiographic domains, Sí