A carbonate submarine fan in a fault-controlled basin of the Upper Jurassic, Betic Cordillera, southern Spain



    1. Department of Geology, Colegio Universitario de Jaén, and Department of Stratigraphy, Universidad de Granada, Spain
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      Departamento de Geologia, Colegio Universitario, Jaen, Spain.


ABSTRACT The middle member of the Loma del Toril formation (Kimmeridgian-Lower Tithonian, Intermediate units, Betic Cordillera) consists of up to 250 m of resedimented carbonate material. Three units have been distinguished. The lower, Unit A, is composed of conglomerates that are interpreted as deposited in a major valley on the lower slope of a basin margin. Unit B, calcarenites with some conglomerate intercalation, is interpreted as distributary channel deposits and Unit C, calcarenites, as the result of poorly developed depositional lobes of a submarine fan. The three units form a recessional sequence. They cannot be related to a transgression because the Kimmeridgian-Lower Tithonian in the Prebetic zone, where epicontinental sediments exist, is clearly regressive. The upper member of the Loma del Toril formation, made up of pelagic limestones with sporadic calcarenites or even thin conglomerate intercalations, is best interpreted as a basin plain facies. Lateral facies relationships suggest that down-faulting of the basin floor controlled the development of the fan. The scarce occurrence of turbidite beds in the basin plain facies, the prevailing channelized facies and the obvious lack of overbank deposits, suggest a transport system of low efficiency, with fan deposition at the base of slope. The underlying Jurassic strata cropping out along fault scarps, coeval carbonate shelf material, and upper slope deposits were the main sources of turbiditic resediments. With respect to basin morphology sedimentary processes and fan geometry, this Jurassic turbidite basin can be compared with the modern California continental borderland. Ancient analogues have been described by Reinhart (1977) and Price (1977).