Climatic signatures in shallow-water carbonates: high-resolution stratigraphic markers in structurally controlled carbonate buildups (Late Miocene, southern Spain)

Abstract

Neogene intramontane basins of the Betic Cordillera (SE Spain) have a complex tectonic and sedimentary history. In the eastern Almerı́a province movements along the Carboneras strike-slip fault system (N50°E) and its conjugated faults (N140°E) controlled the distributions of depocenters and stratigraphic architectures of Late Miocene sediments. We have chosen the Agua Amarga area (1) to exemplify the potential of climatic signatures of biogenic associations in shallow-water carbonates for high-resolution chronostratigraphic correlations and (2) to describe stratigraphic architectures and facies distributions in a setting subject to synsedimentary tectonics. The southwestern margin (La Higuera) is formed by a gentle ramp dipping in a N50°E direction. Late Tortonian and Messinian deep and shallow-water carbonates divide into eight depositional units. Neptunian autoclastic breccias, neptunian dikes, and submarine biogenic pavements (unit H 1) document rapid flooding of the basin during a phase of intense tectonic dilatation (Late Tortonian). Units H 2–7 (Late Tortonian–Early Messinian) form wedges which dip and thicken in a basinward direction. Little lateral facies change and internal stratifications parallel with the basal surfaces imply deposition on a subhorizontal substratum. The upper bounding surfaces are erosional and formed by truncation of tilted strata. From wedge to wedge, the angle of dip decreases upsection and is near zero in between the last units which have parallel bounding surfaces and rest subhorizontally (unit H 7–8). This pattern results from cumulative rotational uplift which decreased upward, but does not necessarily exclude vertical displacements of the youngest units. The southeastern margin of the basin is mostly eroded but may have trended N50°E as indicated by the distribution of slumped reef blocks. A relict of the margin is preserved at Mesa de Roldán and exhibits steep clinoforms dipping towards the NW (N300°E) and W (N250°E). Synsedimentary tectonics are documented by nine shallow-marine depositional units (unit R 1: conglomerates associated with neptunian dikes; units R 2–9: skeletal carbonates and reefs) bounded by deep erosion surfaces and/or truncation of individual units along a Miocene fault. At both flanks, the shallow-water biofacies record an identical trend of climatic warming and therefore bracket a similar amount of time. Temperate conditions prevailed during the latest Tortonian and earliest Messinian, whereas tropical temperatures existed during the Early and Late Messinian and perhaps during the Tortonian/Messinian transition. The number of depositional units reflecting these climatic periods of time, and the stratal geometries, however, differ at both sites and within the basin, which implies spatial variations in the generation of accomodation space on independent fault blocks. These data also suggest that there cannot be any universal sequence stratigraphic model for Late Miocene shallow-water carbonates of SE Spain, and that the downstepping geometries observed in many other Early Messinian reefs of the Betic Cordillera reflect tectonic uplift.