Preliminary interpretation of the stable-isotope composition in lacustrine stromatolites of the Sierra de Alcubierre (Miocene, Ebro Basin, Spain)

La composición de isótopos estables de las láminas de dos estromatolitos lacustres del Mioceno medio de la Sierra de Alcubierre (unidad T6, Cuenca del Ebro) revela variaciones cíclicas entre láminas con diferente textura y clara evolución de la composición isotópica a lo largo del tiempo. Consisten en una alternancia de láminas claras, porosas (micrita-microesparita, de 0.65 mm a 6 mm de espesor) y láminas oscuras, densas (micrita, 0.5 m a 2 mm de espesor). La mayoría de estas láminas son compuestas. La significativa correlación entre δ13C y δ18O sugiere que la relación precitación/evaporación (P/E) controló en gran medida la evolución isotópica a corto plazo del ambiente lacustre salino de la unidad T6 en la Cuenca del Ebro. Las láminas oscuras tienen valores mayores de δ13C y δ18O que las claras, lo cual representa cambios cíclicos (estacionales a plurianuales) en la relación P/E. El decrecimiento en δ13C y δ18O y en el coeficiente de correlación (δ13C vs. δ18O) entre los estromatolitos estudiados indica una tendencia hacia una mayor relación P/E a lo largo del tiempo

Estudio estratigráfico y estructural del Sector de Cortes de Aragón, Teruel

Estudio tectosedimentario sobre las estructuras comprendidas en el sector de Cortes de Aragón-Muniesa donde se da un modelo de génesis coherente con el contexto tectónico y sedimentológico estudiado para la región E de la Cordillera Ibérica.<br /

Estudio geológico del sector de Tierga (Zaragoza): sector NW de la Rama Aragonesa de la Cordillera Ibérica

El trabajo se centra en el estudio de los materiales del Mesozoico en la zona de Tierga (Zaragoza) con especial énfasis en el análisis de las estructuras tectónicas que aparecen y en aspectos sedimentológicos de los materiales del Triásico Inferior. El objetivo principal es proponer una evolución tectónica para esta zona de la Cordillera Ibérica y un modelo paleoambiental para la facies Buntsadstein (Triásico Inferior)<br /

Estratigrafía y tectónica del Terciario en el sector Nigüella-Mesones de Isuela (Zaragoza)

This work is focussed on the Tertiary materials situated in the Nigüella-Mesones de Isuela sector (Zaragoza province, Spain). These materials unconformably overlie different Mesozoic units and are considered Miocene in age (Ramírez del Pozo et al., 1978). The main tectonic structure affecting the Tertiary is a NW-SE syncline, which extends towards NW outside the study area. We have studied their SE extreme. The main objectives of the study were the knowledge of the general geological history of the Nigüella-Mesones de Isuela sector, focussed on the Tertiary, including the interpretation of their sedimentary environment. To achieve these different objectives we made the geological cartography of the zone (1:10.000) and measured three stratigraphic sections (1:100) through the Tertiary. To interpret the structure, we have made three detailed geological cross sections. There are different small faults with an orientation N-S, E-W and WNW-ESE. However, the main macro-scale tectonic structures are 1) a normal-reverse fault (Nigüella Fault), which, to the North, has a sinestral component, and 2) a Tertiary syncline, both structures with a mean orientation NNW-SSE. The Nigüella Fault affects the Palaeozoic, Mesozoic and Tertiary materials. Tertiary materials were affected by the fault while they were deposited, causing their synsedimentary folding and resulting in the formation of the syncline. Four main Tertiary units were mapped based on lithological and textural criteria; the two intermediate units only crop out in the southern half of the syncline. The total thickness ranges from 112 m in the southern part, to 74 m in the northern part. However, in the central part the thickness is 48 m. Correlation and facies analysis of the measured sections allowed the interpretation and evolution of the sedimentary environment. The main facies associations (FA) are: A) alluvial FA: Fm-->[Gm1, Gm1b]‹—›(Gh); \[Gm1, Gm1a]-->Fm-->(Cm);, B) alluvial-fluvial FA: \,Gm2-->Fm; C) carbonate fluvio-lacustrine FA: [Cbt‹—›Cbtv]-->(Ce)-->[M, (Fm)]-->Cm; [Cbt‹—›Cbtv][M, (Fm)]-->Cm; and D) carbonate lacustrine FA: M-->Cm. The basin fill in this sector records three main sedimentary stages, with a clear expansion of lacustrine conditions through time: dominant fluvial-alluvial conditions, followed by dominant fluvial-lacustrine conditions and then dominant lacustrine conditions. The nature of the coarse alluvial-fluvial facies and the areal distribution of the lithofacies suggest a principal sediment source (mostly from carbonate Mesozoic drainage areas) from the East and North, with local coarse inputs from the West. However, further studies on a broader area would allow a better approach to this hypothesis. Tertiary compressive tectonics controlled both the sedimentation and the folding of all the sedimentary units, as it is evidenced by the thickness variations of the sedimentary units through the main cartographic-scale syncline. The main NW-SE trending cartographic fault represents an ancient NE dipping lower Mesozoic normal fault responsible for a hectometric-scale vertical slip. Tertiary compression, that controlled the source areas during sedimentation and location of a depocenter in the SW of the study area, gave rise to the buttressing of all the Tertiary record against the fault

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 /

Benthic diatoms on fluvial tufas of the Mesa River, Iberian Range, Spain

Background. The Mesa River (MR) in the Iberian Range (Spain) displays prominent, Pleistocene to present-day fluvial tufa deposits. Little of their associated microbiota has been studied to date despite the regional and historical relevance of these calcareous buildups. Goals. This paper is a preliminary exploration of the diatom (Bacillariophyta) genera associated with actively-growing tufa from 10 benthic environments along 24 km of the Mesa River. Methods. Bright- field microscopy, as well as consultation with specialists and specialized literature was used for taxonomic classification of diatoms. Results. We identified 25 diatom genera in three different types of sedimentary facies (porous and moss-algae rich, dense-laminated, and tufa-free gravel). Most diatoms were raphid pennate (class Bacillariophyceae), while few were centric (class Coscinodiscophyceae) or araphid pennate (class Fragilariophyceae). They appeared as integral components of the tufa structure along with cyanobacteria and other algae and mosses. Conclusions. Together with previous studies on the hydrochemistry and sedimentology of the MR, our interpretations suggest that HCO3-, pCO2, Ca2+, and TDIC negatively affect diatom richness and that their abundance is positively related to the presence of mosses and algae

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)

Tufa sedimentation in changing hydrological conditions : the River Mesa (Spain)

The processes controlling tufa deposition along the River Mesa (NE Spain) were studied from April 2003 to September 2009, based on six-monthly monitoring of physical and chemical parameters of the river water and sedimentological characteristics, including deposition rates on tablets. With a mean annual discharge around 1.5m3 /s, the sedimentation rate (mean 2mm/yr) recorded important spatial, seasonal and interannual variations. The river waters are of the calcium bicarbonate type. In this study, three distinct river stretches were distinguished based on the steady groundwater inputs, some of low-thermal nature. Groundwater discharges controlled the water chemical composition, and some sedimentation features too. At each stretch, an increase in pCO2 and conductivity was measured around the spring sites. Decreasing trends in conductivity or alkalinity with high enough saturation values with respect to calcite were only clearly observed in the intermediate stretch, which had higher tufa deposition rates than the other two. Tufa deposition rates were higher in cool (autumn+winter) than in warm (spring+summer) periods. In some low-rainfall warm periods, tufa deposition was inhibited or limited due to the low flow -mainly from groundwater inputs- and to the dryness of some river sites, which indeed favoured erosion during flooding. A decrease in yearly deposition rates from April 2006 onwards paralleled an important reduction in the river discharge. Groundwater inputs, drought periods and flood events should therefore be considered to understand fluvial tufa sedimentation in semi-arid conditions

Reconstrucción de la vegetación asociada al depósito tobáceo fluvial Holoceno del Nogal de El Batán, Las Parras del Martín, Cordillera Ibérica

El desarrollo de edificios tobáceos de origen fluvial se asocia a menudo con fases cálidas y húmedas cuaternarias y son comúnmente empleados como indicadores climáticos. En el presente trabajo se estudia el depósito tobáceo fluvial Holoceno del Nogal de El Batán, situado en el valle del río Las Parras (Cordillera Ibérica, NE España), bajo una perspectiva cronológica, estratigráfica y palinológica. La acumulación tobácea de 8, 2 m de espesor, intercala gravas, facies de rudstones de fitoclastos, boundstones de tallos, limos y arenas de composición carbonatada, además de margas, lime mud y niveles turbosos. La acumulación tobácea se emplaza en el Holoceno temprano final (ca. 8400 cal BP) y se correlaciona con los cambios ambientales ocurridos en la región, identificando tres fases principales. Los análisis polínicos señalan un paisaje dominado por coníferas en la base de la secuencia, esencialmente Pinus nigra/sylvestris tipo y Juniperus, mientras que localmente se desarrolla un bosque ripario donde destacan Corylus, Alnus, Salix, Populus, Celtis, Fraxinus, Tamarix y Rosaceae. En el Holoceno medio (ca. 8000-5000 cal BP) se produce la máxima expansión de las quercíneas, junto con taxones termófilos como Pistacia, Rhamnus, Arbutus y Olea. El incremento de taxones herbáceos y ruderales, y en especial la aparición de esporas coprófilas, marca la expansión agro-pastoril a lo largo del valle fluvial durante el Holoceno tardío (ca. 4300 cal BP). Development of Quaternary fluvial tufa buildings are often associated with warm and humid phases and are commonly used as climate indicators. El Nogal de El Batán Holocene fluvial tufa buildup, located in Las Parras River valley (Iberian Range, NE Spain), is investigated, following radiocarbon dating, stratigraphic description and palynological analysis. The studied deposit, 8.2 m-thick, is formed of gravels, phytoclast rudstones, calcite-coated stem boundstones and fine carbonate deposits (sands, silts and marls) with peaty horizons and carbonaceous debris. It has been dated within the upper early Holocene (ca. 8400 cal BP) and correlated with the environmental changes reconstructed for the region, identifying at least, three main phases. Pollen results highlight the existence of a conifer landscape, mainy dominated by Pinus nigra/sylvestris type and Juniperus, and locally dense riparian woodland with Corylus, Alnus, Salix, Populus, Celtis, Fraxinus, Tamarix and Rosaceae. Deciduous and evergreen oaks were the main spread regional forests accompanied by many warm-loving taxa like Pistacia, Rhamnus, Arbutus and Olea during the middle Holocene (ca. 8000-5000 cal BP). The transition towards the late Holocene (ca. 4300 cal BP) is evidenced by the rise of herbs and ruderal taxa, and especially the presence of coprophilous fungi, which are linked to the spread of agricultural and grazing practices along the river valley. © 2021, Asociacion Espanola para el Estudio del Cuaternario (AEQUA). All rights reserved