Uplift history of a Betic fold nappe inferred from Neogene-Quaternary sedimentation and tectonics (in the Sierra Alhamilla and Almeria, Sorbas and Tabernas Basins of the Betic Cordilleras, SE Spain)

Abstract

Structural, stratigraphical and sedimentological studies of the Alhamilla region show that the Sierra Alhamilla was elevated relative to the surrounding basins by open folding towards the end of the Tortonian period (about 7 Ma ago) and before the onset of Messinian sedimentation. The main arguments are: (1) the dominant current direction in the Neogene cover changes from southward to southeast- and southwestward during the Late Tortonian, (2) Late Tortonian seismites suggest contemporaneous major tectonic activity which is contrasted by low tectonic activity during the Messinian, (3) Messinian reefs colonise Nevado-Filabride basement exposed (near Polopos) in the eroded hinge of the Alhamilla Anticlinorium, (4) the Northern Boundary Fault which is interpreted to be cogenetic with the formation of the Alhamilla Anticlinorium transects Tortonian sediments but is covered (near Cantona) by unfaulted Messinian reefs, and (5) the base of an almost non-tectonised Messinian succession (in the Sorbas Basin) unconformably overlies an erosion surface of folded Tortonian sediments, Neogene uplift of the Alhamilla region is interpreted here to be due to isostatic recovery after the emplacement of the Alboran Diapir between 20 and 25 Ma ago. Estimates of the average uplift rates vary between 0.7 to 0.5 mm a-' for the Miocene and 0.15 to 0.1 mm a-t for the Pliocene and Quaternary. Pliocene and Quaternary uplift rates are almost identical to the sedimentation rates of 0.23 to 0.2 mm a-' estimated previously for the Alboran Basin.