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Las facies lacustres del Oligoceno de Campins (Vallés Oriental, prov. de Barcelona)

AuthorsAnadón, Pere CSIC ORCID
Facies lacustres
Issue Date1986
PublisherUniversidad Complutense de Madrid
CitationCuadernos Geología Ibérica Vol, l0 Págs. 271-294 Madrid 1986
Abstract[ES] En los materiales oligocenos de Campins se han podido distinguir tres unidades principales. La unidad inferior y la superior están constituidas por areniscas arcósicas con intercalaciones de conglomerados y lutitas y poseen un origen aluvial. En la unidad intermedia, de origen lacustre, se han podido diferenciar unas facies lacustres someras, localizadas en la base y en el techo de la sucesión lacustre, y unas facies lacustres profundas. En éstas se han podido distinguir dos tipos extremos: carbonatadas y detríticas, observándose el paso gradual de unas a otras. El análisis sedimentológico de las diversas facies permite deducir que durante el depósito de las facies lacustres el lago fue meromíctico, con un fondo anóxico donde se formaban sedimentos ricos en materia orgánica. En zonas marginales del lago se depositaron materiales detríticos de grano grueso, principalmente por mecanismos de flujos gravitatorios de sedimentos. Tras la fase profunda, el lago se somerizó y finalmente sobre facies lacustres someras se depositaron materiales detríticos gruesos de origen aluvial.
[EN] The Oligocene Campins Basin is located close to the Vallés Fault which belongs to the Paleogene strike-slip tault system of the Catalan Coastal Ranges (Fig. 1). During the Neogene the major faults of this system acted as normal faults that produced grabens. The Oligocene deposits of Campins are small remnants of an ancient Oligocene basin now located in a Neogene graben (Fig. 2). A basement-slice of paleoZoic metamorphic rocks related to convergent wrenching along the Vallés Fault overthrust the Oligocene sediments of Campins (Fig. 2 and 3). The strike-slip in the Paleogene Vallés Fault produced also fault-gouge development. Several sequences of the basin fill deposits have been studied (Fig. 4) and three main units can be distinguished: — Lower, alluvial, unit. Mainly composed by variegated arkosic sands with interbedded red mudstones and conglomerates. The thickness of this unit ranges from 100 to 400 m. — Intermediate, lacustrine, unit (Fig. 4 and 5). The lower part of this unit up to 20 m thick is formed by variegated sandstones and mudstones, limestones and, locally, travertines or coal. Ihese lower levels are interpreted as shallow lacustrine deposits and are overlain by deep lacustrine deposits up to 200 m thick. Two main facies can be differenciated in the deep lacustrine sediments: carbonate facies and clastic facies. The carbonate facies is formed by a complex arrangement of thin bedded limestones and dolostones, carbonate mudstones, massive and laminated mudstones and oil-shales. Varves (calcite, organic-rich clays couplets) are locally present. The uppermost leveis of the carbonate facies are formed by carbonate mudstones with abundant mollusks, ostracods and charophyte remains. Ihe clastic facies is formed fainly by massive or laminated siltstones, up to 5 m thick with interbedded sandstone to microconglomerate beds up to 1,5 m thick. The coarse grained sediments display massive or graded bedding. The gradation between the clastic and carbonate facies is observed. — Upper, alluvial, unit. This unit overlies the carbonate facies of the intermediate unit. Is formed by red arkosic sandstones and conglomerates, up to 120 m thick. The overall megasequence indicates a basin-formation phase, with related alluvial deposits followed by the development of a shallo-w lacustrine environment that evolves to a deep lacustrine environment. The sedimentary features indicate that in this phase the lake was meromictic and organic-rich sediments were formed mainly due to algal contribution. Coarse-grained terrigenous deposits accumulated in marginal iones. They were formed by mass-flow processes. Later, the studied sequences indicate a shallow water sedimentation phase and a late alluvial sedimentation phase.
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