Seismic evidence of current-controlled sedimentation in the Alboran Sea during the Pliocene and Quaternary: Palaeoceanographic implications

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.