Ambientes sedimentarios después de la ruptura de la plataforma carbonatada del Jurásico Inferior (Pliensbachiense- Toarciense, Subbético Externo, Zonas Externas Béticas)

Resumo

We study two sections of the Zegrí Fm (upper Pliensbachian-Aalenian) in the External Subbetic (Betic External Zones) and their palaeoenvironmental interpretation. These rocks were deposited in the South Iberian Paleomargin (Western Tethys). Five lithofacies are differentiated: 1) grey-yellow marl-marly limestone rhythmite; 2) dark marls; 3) thin bedded grey-ye- llow limestones, locally with chert and slumps; 4) grey marls and marly limestones; and 5) yellow-brown calcisiltites and calcarenites, intercalated in facies 3 and 4. Facies 1 to 4 are interpreted as hemipelagites. Facies 2 was deposited in rather depleted oxygen conditions with slightly dysoxic bottom waters but discarding completely anoxic conditions. The Toarcian Oceanic Anoxic Event (T-OAE) is recorded in this facies 2 at the Serpentinum Zone. Facies 5 are grainstone and packsto- ne-wackestone with peloids, bioclasts, ooids and foraminifera. These facies 5, locally with hummocky cross stratification, are interpreted as tempestites and/or internalites. The local facies distribution was controlled by the influence of adjacent emerged lands and carbonate platforms, differential subsidence, local tectonics, climate, sediment winnowing by currents, sedimentation rates, bioturbation, and diagenesis. The sedimentary basin evolution was mainly influenced by tectonics after the Pliensbachian break-up of the Lower Juras- sic platform, together with relative sea-level changes and the beginning of basaltic submarine volcanism in some nearby southern areas.