Palaeoenvironments and evolution of the upper Maastrichtian platform in the Betic continental margin, SE Spain
Abstract In the Betic passive margin (SE Iberia) the latest Cretaceous (Late Maastrichtian) was a period of great tectonic activity that resulted in the reactivation of major NE-SW trending listric faults. In this unstable setting, a narrow (tens of km wide) but long (hundred of kilometres) mixed carbonate-siliciclastic platform developed over a “middle” Maastrichtian tectonically-induced unconformity. The environments developed in this platform and the changes they underwent during its evolution are interpreted and their facies and biotic associations described. These environments include: (1) the coastal lakes, which formed freshwater to hyposaline, shallow lacustrine systems; (2) the tidal flats, developed in a narrow coastal area under conditions of low turbulence and high freshwater influence; (3) the lagoon, characterized by normal marine salinity and by a variety of subenvironments, including radiolitid patches; (4) the platform edge, the dominant features of which developed under high-energy conditions, varying from mainly siliciclastic shoals to carbonate reef complexes, depending on the terrigenous influx; (5) the mid platform, corresponding to the shallower areas below fair-weather wave base, in which the fossil assemblages are still dominated by benthic forms; and (6) the outer platform, characterized by hemipelagic sedimentation. The evolutionary history of the platform comprises four main successive episodes: (1) Installation of a mixed carbonate-siliciclastic ramp, after an initial rapid transgressive event; (2) Evolution of the mixed ramp into an incipient rimmed carbonate shelf, induced by the accretion of the edge of the platform during an aggradational-progradational episode; (3) Interruption of the platform's evolution by a regional tectonic event that caused a minor transgressive pulse accompanied by a new arrival of abundant terrigenous material into the platform; (4) Reconstruction of the carbonate platform during a second progradational-aggradational episode. The end of the platform was controlled by the latest Maastrichtian regional tectonic event that caused strong changes in the palaeogeography and in the basinal configuration.