La secuencia aluvial a palustre-lacustre del Mioceno de Faido-Samiano (cuenca Miranda – Treviño, Pirineos occidentales)

This work presents the results from the study of the lower to middle? Miocene continental succession exposed in the Faido-Samiano section, on the south-east flank of the Miranda – Treviño piggy-back basin. Facies analysis allowed accurate interpretation of the constituent deposits and the corresponding depositional settings they characterize, from alluvial to varied palustrine-lacustrine sub-environments. Logging and mapping across an area of about 15 km2 revealed a distinct recurrent stratigraphic arrangement that reflects successive cycles of progressive expansion and abrupt subsequent retraction of the km-wide palustrine-lacustrine wetlands developed on the basin depocentre. The scale and distinct asymmetry of the successive stratigraphic cycles point to an origin likely related to high-frequency pulsating tectonic activity affecting the rising basin marginsEste trabajo expone los resultados del estudio de la sucesión continental del Mioceno inferior-medio? aflorante en la sección de Faido-Samiano, en el flanco sureste de la cuenca piggy-back de Miranda-Treviño. El análisis de facies ha conducido a la interpretación de un sistema sedimentario integrado por ambientes de abanico aluvial, palustre y lacustre. El levantamiento de la sección estratigráfica y la cartografía de los diferentes tramos ha permitido reconocer un patrón de facies recurrente, que refleja varios ciclos de expansión progresiva y retracción brusca de los humedales palustres-lacustres desarrollados en el centro de la cuenca. La escala y la asimetría de estos ciclos estratigráficos se ha relacionado con pulsos tectónicos de alta frecuencia afectando a los márgenes activos de la cuenc

Estratigrafía y sedimentología del Mioceno de la Plana Negra-Sancho Abarca (sector central-occidental de la Cuenca del Ebro)

Este trabajo abarca el estudio sedimentológico y estratigráfico de los depósitos del Burdigaliense (Mioceno inferior) y Langhiense (Mioceno medio) de la Plana Negra y la Plana de Sancho Abarca, sector central-occidental de la Cuenca del Ebro (NE de la Península Ibérica). Se han identificado un total de 5 litofacies (unidades cartografiables) constituidas por areniscas, lutitas, margas y calizas en variables proporciones, equiparables a miembros (informales) de la Formación Tudela. Se han realizado dos perfiles estratigráficos que abarcan las unidades tectosedimentarias T5 y T6 definidas para la Cuenca del Ebro; dicho límite es una conformidad que se reconoce como el paso de lutitas con intercalaciones de areniscas y calizas a predominio de calizas, y constituye un nivel excelente de correlación. Los depósitos de T5 tienen 130 m de espesor y los de T6 tienen 63 m. Las paleocorrientes medidas en la unidad T5 señalan procedencia del margen pirenaico. Se han caracterizado 17 facies sedimentarias (detríticas, mixtas y carbonatadas) que muestran gran variedad biótica (ostrácodos, carófitos y gasterópodos) y rasgos pedogenéticos. Se agrupan verticalmente en 5 asociaciones de facies que caracterizan los ambientes fluvial-aluvial distal, palustre y lacustre somero. El modelo de sedimentación propuesto se basa en la distribución espacial de esas asociaciones y expresa la relación entre dichos ambientes. La correlación de las secciones estudiadas con otras tres de áreas adyacentes que disponen de datación magneto-bioestratigráfica ha permitido datar con precisión la sucesión estudiada y el límite T5/T6 (C5Cn.1n, entre 16,062 y 16,099 Ma). La integración de las cinco secciones permite distinguir cuatro estadios evolutivos, definidos por la progradación-retrogradación del medio aluvial o retracción-expansión de los ambientes palustres y lacustres. Se relacionan con la tectónica y el clima, que controlaron la evolución de los sistemas sedimentarios a través de variaciones de los aportes y del nivel lacustre en el área estudiada.<br /

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

The stratigraphic and sedimentologic study of Miocene deposits in the Plana Negra-Sancho Abarca area fills a gap in the Ebro Basin knowledge. Five main lithofacies were characterized and mapped. The boundary between regional tectosedimentary units T5 and T6 is recognized as a conformity at a major facies change. Unit T5, up to 130m thick, consists of mudstones with interbedded sandstones and limestones. Unit T6, with 30 to 62m of preserved thickness, is made of limestones, marls and minor mudstones. Correlation of the studied outcrops with nearby sections that already had detailed magnetoestratigraphic and biostratigraphic data allows dating the studied succession as Burdigalian (early Miocene)-Langhian (middle Miocene), from C5Dr to C5Cn, and the boundary between units T5 and T6 to be located at 16.062-16.099 Ma. Seventeen sedimentary facies associated in seven vertical facies sequences document deposition in fluvial-distal alluvial, palustrine and lacustrine environments. A shallow (2-4m deep) lake body was locus for charophytes, ostracods, bivalves and gastropods to thrive. Occasional bottom currents reworked and transported allochems and fine-siliciclastic sediment offshore, forming laminated limestones. Bioturbation and desiccation features are abundant, indicating wide palustrine areas and episodic exposure. Low-sinuosity channels associated to the Pyrenean-derived Luna fluvial system run across the alluvial-plain. Four evolutionary stages of alluvial progradation-retrogradation and retraction-expansion of the palustrine-lacustrine system, likely related to Pyrenean tectonic activity, are distinguished. Maximum lacustrine expansion took place at the beginning of unit T6 deposition. This is consistent with initial conditions of increasing humidity of the Middle Miocene Climatic Optimum (MMCO)

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

The stratigraphic and sedimentologic study of Miocene deposits in the Plana Negra-Sancho Abarca area fills a gap in the Ebro Basin knowledge. Five main lithofacies were characterized and mapped. The boundary between regional tectosedimentary units T5 and T6 is recognized as a conformity at a major facies change. Unit T5, up to 130m thick, consists of mudstones with interbedded sandstones and limestones. Unit T6, with 30 to 62m of preserved thickness, is made of limestones, marls and minor mudstones. Correlation of the studied outcrops with nearby sections that already had detailed magnetoestratigraphic and biostratigraphic data allows dating the studied succession as Burdigalian (early Miocene)-Langhian (middle Miocene), from C5Dr to C5Cn, and the boundary between units T5 and T6 to be located at 16.062-16.099 Ma. Seventeen sedimentary facies associated in seven vertical facies sequences document deposition in fluvial-distal alluvial, palustrine and lacustrine environments. A shallow (2-4m deep) lake body was locus for charophytes, ostracods, bivalves and gastropods to thrive. Occasional bottom currents reworked and transported allochems and fine-siliciclastic sediment offshore, forming laminated limestones. Bioturbation and desiccation features are abundant, indicating wide palustrine areas and episodic exposure. Low-sinuosity channels associated to the Pyrenean-derived Luna fluvial system run across the alluvial-plain. Four evolutionary stages of alluvial progradation-retrogradation and retraction-expansion of the palustrine-lacustrine system, likely related to Pyrenean tectonic activity, are distinguished. Maximum lacustrine expansion took place at the beginning of unit T6 deposition. This is consistent with initial conditions of increasing humidity of the Middle Miocene Climatic Optimum (MMCO)

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

Stratigraphic and sedimentological study of distal alluvial and lacustrine deposits in the Plana de la Negra-Sancho Abarca area (western-central Ebro Basin, NE Iberia) within the early and middle Miocene allows five main lithofacies to be characterized and mapped within two tectosedimentary units, construction of a sedimentary facies model and discussion on allogenic controls on sedimentation. In this area, the boundary between tectosedimentary units T5 and T6 appears to be conformable and is marked by the change from dominant clastics to carbonates. Correlation of the studied outcrops with nearby sections that already had magnetostratigraphic and biostratigraphic data allows the studied succession to be dated from C5Dr to C5Cn (Burdigalian-Langhian), placing the boundary T5/T6 at ca. 16.1-16.05Ma.&nbsp;Seven vertical facies sequences document deposition of distal alluvial clastics and palustrine and lacustrine carbonates. Sandstones and mudstones represent low-sinuosity channels and lateral and terminal splays by unconfined flows runnig across the alluvial plain, associated to the Pyrenean-derived Luna fluvial system. The carbonates contain charophytes, ostracods, bivalves and gastropods, indicating deposition in 2-4m deep lakes. Laminated carbonate facies record reworking of shore carbonates and the influx fine-siliciclastic sediment offshore. Abundant bioturbation and desiccation features indicate episodic submergence and subaerial exposure.&nbsp;Four main episodes of alluvial and associated palustrine/lacustrine facies belt shifts are identified. Alluvial deposition in the studied T5 unit is related to low lake level conditions, rather than to a Pyrenean uplift. The maximum extent of the freshwater carbonates occur at the base of unit T6. This is consistent with conditions of increasing humidity of the Middle Miocene Climatic Optimum