Publication: Reinterpretación estratigráfica y sedimentológica de las formaciones Escucha y Utrillas de la Cordillera Ibérica
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2009
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Sociedad Geológica de España
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Abstract
El desarrollo de un sistema desértico arenoso (erg) cretácico ha sido reconocido a partir de estudios estratigráficos, sedimentológicos, paleoclimáticos, paleogeográficos y de relación tectónicasedimentación
en las Formaciones Escucha y Utrillas. Estos estudios indican que los potentes tramos arenosos, con tramos arcillosos y limosos de la parte superior de la Formación Escucha y totalidad dela Formación Utrillas en su área tipo y sectores adjacentes (Provincias de Teruel, Zaragoza y Soria),constituyen el registro sedimentario del primer sistema desértico arenoso (erg) cretácico de Europa.
El sistema desértico arenoso se desarrolló sobre la Superficie de Discontinuidad Regional (SDR) que se encuentra estratigráficamente dentro del registro de la Formación Escucha y marca la desaparición regional de los tramos de carbón que se explotan en la Comarca de las Cuencas Mineras de Teruel. Esta superficie está asociada a procesoso de exposición subaérea, erosión y tectónica sinsedimentaria,
y ha sido reconocida tanto en subsuelo como en superficie a lo largo de más de 230 km. Esta Superficie de Discontinuidad Regional separa dos sucesiones sedimentarias: una Sucesión
Sedimentaria Inferior (SSI), formada principalmente por arcillas y limos que contienen tramos de
carbón, areniscas y carbonatos y una Sucesión Sedimentaria Superior (SSS) formada por areniscas y
en menor proporción por arcillas y limos grises.
La Sucesión Sedimentaria Inferior (SSI) abarca la parte inferior y media de la Formación Escucha de
Pardo (1979) y contiene los tramos de carbón que siguen siendo explotados hoy día en la Comarca de
las Cuencas Mineras de Teruel.
Esta Sucesión Sedimentaria Inferior se encuentra estratigráficamente entre las plataformas urgonianas
en la base (Formaciones Oliete, Villarroya de los Pinares) o la Formación Benassal, dependiendo de los sectores estudiados, y la Superficie de Discontinuidad Regional (SDR) en el techo. Esta Sucesión
Sedimentaria Inferior tiene una edad Aptiense superior-Albiense inferior a partir de la bioestratigrafía
de nanofósiles, foraminíferos planctónicos, dinoflagelados y polen. Esta sucesión está formada por:
1) un Intervalo Basal con Carbonatos, que constituye el registro sedimentario de una plataforma
carbonatada con extensos lagoons; (2) Un Intervalo Intermedio con Carbón, formado en una costa siliciclástica con sistemas isla-barrera con marismas y 3) un Intervalo Arcilloso Superior caracterizado por potentes tramos arcillosos con rasgos pedogenéticos desarrollados en un sistema costero arcilloso de baja energía.
La Sucesión Sedimentaria Superior (SSS) incluye areniscas, limos y arcillas de la parte superior de la
Formación Escucha y las areniscas, limos y arcillas de la Formación Utrillas. Esta Sucesión
Sedimentaria Superior se encuentra comprendida entre la Superficie de Discontinuidad Regional (SDR) en su base y las plataformas carbonatadas del Cretácico Superior en su techo, y tiene una edad Albiense inferior-Cenomaniense inferior. La Sucesión Sedimentaria Superior constituye un sistema desértico arenoso (erg), que se desarrolló sobre la SDR, extensiéndose sobre un área mínima de más de 16.000
km2 en las Provincias de Soria, Zaragoza y Teruel.
El sistema desértico muestra una zonación espacial característica, como la descrita previamente para otros sistemas deposicionales desérticos antiguos (p.e. Porter, 1986): (a) back-erg; es el sector proximal
del erg, próximo al Macizo Ibérico (con una altitud elevada) y situado en las Provincias de Soria,
Zaragoza y Teruel y caracterizado por la interacción entre sistemas fluviales efímeros y procesos
eólicos; (b) central-erg: es la parte central del sistema desértico arenoso. Ha sido reconocido en la
Provincia de Teruel, y constituye una de las principales áreas de acumulación eólica con el desarrollo
de draas (dunas complejas); (c) fore-erg: es el area distal del erg (Provincia de Teruel) caracterizado
por la interacción entre el sistema desértico arenoso y el Tethys, donde los sedimentos eólicos fueron
retrabajados en ambientes sedimentarios costeros restringidos. Tras una transgresión regional sobre
el erg, se formó una costa árida en la que se desarrollaron marismas que generaron niveles de arcillas
carbonosas.
El desarrollo de este sistema desértico sufrió periodos de mayor y menor actividad eólica, asociados a variaciones en el aporte eólico que condicionaron la deflación y preservación de los sedimentos eólicos. Estas variaciones de los procesos alogenéticos dió lugar a una variedad de superficies limitantes que dividen el registro sedimentario eólico en diferentes estadios.
The development of a Cretaceous sandy desert system (erg) has been recognized from stratigraphic, sedimentological, paleoclimate, palaeogeographic and synsedimentary tectonics studies in the Escucha and Utrillas Formations. These studies show that, in their reference area and surounding areas in the Iberian Range (Teruel, Soria, and Zaragoza Provinces) the thick sandy intervals with mudstones and siltstones of the upper part of the Escucha Formation and the whole Utrillas Formation constitute the sedimentary record of the first Cretaceous erg reported from Europe. The desert system developed over the Regional Unconformity Surface (SDR) which is included in the sedimentary record of the Escucha Formation and marks the regional disappearance of the coalbearing deposits of the Comarca de las Cuencas Mineras (Teruel). This regional surface is associated to subaerial exposure, erosion and synsedimentary tectonics and has been recognized in outcrop and in the subsurface over more than 230 km. This regional unconformity surface (SDR) separates two sedimentary successions: a Lower Sedimentary Succession (SSI) largely formed by mudstones and siltstones with coal-bearing deposits, sandstones and carbonates and an Upper Sedimentary Succession (SSS) formed by sandstones and a minor proportion of muddy and grey siltstones. The Lower Sedimentary Succession (SSI) comprises part of the lower and middle parts of the Escucha Formation of Pardo (1979) and contains the coal-bearing deposits that have been mined in the Comarca de las Cuencas Mineras de Teruel since long. This sedimentary succession is located between the urgonian carbonate platfoms (Oliete, Villarroya de los Pinares Fms) and the Benassal Fm below, and the Regional Unconformity Surface (SDR) above. It is late Aptian-early Albian in age, based on nannofossils, planktonic foraminifera, dinoflagellates and pollen biostratigraphy. This sedimentary succession comprises 1) a Lower Interval with Carbonates, developed in a carbonate platform with broad lagoons; 2) a Middle Interval with Coal-bearing deposits, developed in a dominated siliciclastic coastal system with barrier islands and marshes; 3) an Upper Muddy Interval characterized by mustones with pedogenetic features developed in a low-energy coastal setting. The Upper Sedimentary Succession (SSS) includes sandstones, siltstones and mudstones of the upper part of the Escucha Formation and sandstones, siltstones and mudstones of the Utrillas Formation. This Upper Sedimentary Succession is located between the Regional Unconformity Surface (SDR) below, and the Upper Cretaceous Carbonate Platforms above. It is early Albian to early Cenomanian in age. This Upper Sedimentary Succession constitutes a sandy desert depositional system (erg) that developed over the regional unconformity surface, over an area of more than 16,000 km2 in the provinces of Soria, Zaragoza and Teruel. The desert system displays a characteristic spatial zonation as previously described for other ancient desert depositional systems (e.g. Porter, 1986): (a) back-erg; the proximal area of the desert system close to the – then high – Variscan Iberian Massif (Soria, Zaragoza and Teruel Provinces) with the interaction of ephemeral fluvial systems and aeolian processes; (b) central-erg; central part of the desert system (Teruel Province) which is one of the main areas of aeolian sediments accumulation and draa (complex dunes) development; (c) fore-erg; distal area of the desert system (Teruel Province) where the erg and the coeval marine environment interacted. During its evolution, the erg-margin was transgressed by the Tethys, and aeolian sediments were reworked by the sea in restricted marine environments. After regional transgression an arid coast formed where marshes and mangroves developed forming thin coally mudstone layers. The development of this desert system shows periods of greater and less aeolian activity, associated to variations in aeolian input that conditioned the deflation and preservation of aeolian sediments. Such variations of allogenic processes led to a variety of regional bounding surfaces that divide the aeolian sedimentary record in different stages.
The development of a Cretaceous sandy desert system (erg) has been recognized from stratigraphic, sedimentological, paleoclimate, palaeogeographic and synsedimentary tectonics studies in the Escucha and Utrillas Formations. These studies show that, in their reference area and surounding areas in the Iberian Range (Teruel, Soria, and Zaragoza Provinces) the thick sandy intervals with mudstones and siltstones of the upper part of the Escucha Formation and the whole Utrillas Formation constitute the sedimentary record of the first Cretaceous erg reported from Europe. The desert system developed over the Regional Unconformity Surface (SDR) which is included in the sedimentary record of the Escucha Formation and marks the regional disappearance of the coalbearing deposits of the Comarca de las Cuencas Mineras (Teruel). This regional surface is associated to subaerial exposure, erosion and synsedimentary tectonics and has been recognized in outcrop and in the subsurface over more than 230 km. This regional unconformity surface (SDR) separates two sedimentary successions: a Lower Sedimentary Succession (SSI) largely formed by mudstones and siltstones with coal-bearing deposits, sandstones and carbonates and an Upper Sedimentary Succession (SSS) formed by sandstones and a minor proportion of muddy and grey siltstones. The Lower Sedimentary Succession (SSI) comprises part of the lower and middle parts of the Escucha Formation of Pardo (1979) and contains the coal-bearing deposits that have been mined in the Comarca de las Cuencas Mineras de Teruel since long. This sedimentary succession is located between the urgonian carbonate platfoms (Oliete, Villarroya de los Pinares Fms) and the Benassal Fm below, and the Regional Unconformity Surface (SDR) above. It is late Aptian-early Albian in age, based on nannofossils, planktonic foraminifera, dinoflagellates and pollen biostratigraphy. This sedimentary succession comprises 1) a Lower Interval with Carbonates, developed in a carbonate platform with broad lagoons; 2) a Middle Interval with Coal-bearing deposits, developed in a dominated siliciclastic coastal system with barrier islands and marshes; 3) an Upper Muddy Interval characterized by mustones with pedogenetic features developed in a low-energy coastal setting. The Upper Sedimentary Succession (SSS) includes sandstones, siltstones and mudstones of the upper part of the Escucha Formation and sandstones, siltstones and mudstones of the Utrillas Formation. This Upper Sedimentary Succession is located between the Regional Unconformity Surface (SDR) below, and the Upper Cretaceous Carbonate Platforms above. It is early Albian to early Cenomanian in age. This Upper Sedimentary Succession constitutes a sandy desert depositional system (erg) that developed over the regional unconformity surface, over an area of more than 16,000 km2 in the provinces of Soria, Zaragoza and Teruel. The desert system displays a characteristic spatial zonation as previously described for other ancient desert depositional systems (e.g. Porter, 1986): (a) back-erg; the proximal area of the desert system close to the – then high – Variscan Iberian Massif (Soria, Zaragoza and Teruel Provinces) with the interaction of ephemeral fluvial systems and aeolian processes; (b) central-erg; central part of the desert system (Teruel Province) which is one of the main areas of aeolian sediments accumulation and draa (complex dunes) development; (c) fore-erg; distal area of the desert system (Teruel Province) where the erg and the coeval marine environment interacted. During its evolution, the erg-margin was transgressed by the Tethys, and aeolian sediments were reworked by the sea in restricted marine environments. After regional transgression an arid coast formed where marshes and mangroves developed forming thin coally mudstone layers. The development of this desert system shows periods of greater and less aeolian activity, associated to variations in aeolian input that conditioned the deflation and preservation of aeolian sediments. Such variations of allogenic processes led to a variety of regional bounding surfaces that divide the aeolian sedimentary record in different stages.