Resumen de Caracterización sedimentológica de los depósitos carbonatados de La Muela de Borja (sector central de la Cuenca del Ebro)
Marta Vázquez-Urbez, María Concepción Arenas Abad, Gonzalo Martín Pardo Tirapu
This contribution deals with the stratigraphy and sedimentology of the youngest deposits of the Muela de Borja (western-central part of the Ebro Basin) that constitute the tectosedimentary unit Tñ (Vallesian-Turolian in age, Pérez, 1989). In this area, the unit mostly consists of brown and beige limestones that are associated with minor marls, mudstones, sandstones and conglomerates;
the siliciclastic deposits only appear at the base of the unit.
Ten sedimentary facies are present: oncolitic, bioclastic and intraclastic limestones, boundstones of encrusted macrophytic stems, non concentric stromatolites, marls, siliciclastic conglomerates and sandstones with trough cross-stratification, massive carbonate conglomerates and massive mudstones. These facies are arranged in decimetre to metre sequences than can be lacustrine, fluvio-lacustrine and fluvial in origin.
Based on facies analysis and the areal distribution of facies, unit T8 is interpreted as having been deposited in a shallow, open lacustrine system related to oncolitic channels and palustrine areas to the south and west. The isotopic composition (513C and 8180 ) of the carbonate facies agrees with such a hidrologically open system. During deposition of the lowermost part of the unit, a siliciclastic, eastward flowing, trunk fluvial system existed. At various times, the fluvio-lacustrine system was accupied by carbonate gravel blankets, that indicate north and south, local source areas.
