Publication: Las facies continentales del Cretácico Inferior en la zona meridional de la Sierra de Altomira (Cordillera Ibérica) : estratigrafía, sedimentología y discusión sobre su correlación regional.
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Publication Date
2004
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Sociedad Geológica de España
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Abstract
Se han estudiado materiales sedimentarios continentales de la Sierra de Altomira meridional atribuidos recientemente al Cretácico Inferior en Facies Weald. Se distinguen dos unidades litoestratigráficas que denominamos: unidad inferior de lutitas y calizas, y unidad superior de conglomerados calcáreos. Ambas unidades están limitadas por discontinuidades. La unidad inferior se compone de calizas margosas, calizas dolomíticas, lutitas verdes y lutitas rojas. Representa un sistema deposicional de tipo llanura aluvial lutítica – lacustre carbonatado somero. La evolución de esta unidad es progradante y se discuten los posibles factores de control. La unidad superior se compone de
conglomerados y olistolitos calcáreos, procedentes de calizas jurásicas. Se interpreta como un sistema
deposicional de abanicos aluviales con inestabilidades gravitacionales. La distribución vertical y lateral
de facies, las potencias y el tipo de discontinuidad basal permiten deducir algunos rasgos paleoestructurales, con variaciones importantes para cada unidad; estas variaciones originan una fuerte ruptura sedimentaria entre ambas unidades. Se discuten los criterios estratigráficos que permiten atribuir estas unidades al Cretácico Inferior y se plantean las distintas posibilidades de correlación.
This work deals with continental sedimentary rocks that crop out in the Altomira Range (Central Spain). Two unconformity bounded units have been distinguished: a mudrocks and dolomitic limestones lower unit, and a calcareous conglomerates upper unit. The lower unit is composed of shallow lacustrine carbonates, and redoximorphicaly modified clayey marginal lacustrine to mudflat mudrocks. Facies associations are arranged in shallowing-upwards sequences composed from base to top of marly limestones, limestones and green/red mudrocks. Lacustrine environments dominate the lower part of the unit, and grade upwards to mudflat environments. We interpret the lower unit evolution as related to decreasing subsidence. The upper unit consists of calcareous conglomerates, olistoliths, and very scarce siliceous sandstones. Source rocks of both conglomerate and olistoliths are Jurassic limestones. An alluvial fan depositional system is interpreted for this unit which represents an important change in the structural framework of the basin with the appearance of active faults creating large topographic gradients. Regional evolution of the tectonic context and facies similarities point towards a Lower Cretaceous age. Accepting this age as an hypothesis, we propose two possible regional correlations between southern Altomira Range and south-western Iberian Chain; we also propose the elementary palaeo-structural features during this time period in the southern Altomira Range.
This work deals with continental sedimentary rocks that crop out in the Altomira Range (Central Spain). Two unconformity bounded units have been distinguished: a mudrocks and dolomitic limestones lower unit, and a calcareous conglomerates upper unit. The lower unit is composed of shallow lacustrine carbonates, and redoximorphicaly modified clayey marginal lacustrine to mudflat mudrocks. Facies associations are arranged in shallowing-upwards sequences composed from base to top of marly limestones, limestones and green/red mudrocks. Lacustrine environments dominate the lower part of the unit, and grade upwards to mudflat environments. We interpret the lower unit evolution as related to decreasing subsidence. The upper unit consists of calcareous conglomerates, olistoliths, and very scarce siliceous sandstones. Source rocks of both conglomerate and olistoliths are Jurassic limestones. An alluvial fan depositional system is interpreted for this unit which represents an important change in the structural framework of the basin with the appearance of active faults creating large topographic gradients. Regional evolution of the tectonic context and facies similarities point towards a Lower Cretaceous age. Accepting this age as an hypothesis, we propose two possible regional correlations between southern Altomira Range and south-western Iberian Chain; we also propose the elementary palaeo-structural features during this time period in the southern Altomira Range.