Bacterial dolomite in ephemeral lacustrine carbonate-gypsum facies (Deza Formation, upper Eocene,Almazán Basin)

The lower sequence of the Deza Formation represents an ephemeral carbonate lacustrine environment revealed by the presence of limnic fossil and evidence of dry periods marked by the presence of numerous carbonate pseudomorphs, after lenticular interstitial gypsum crystals. In this work, the results of a petrological study of some dolomite facies in the lower sequence are shown to highlight the characteristics of dolomite crystals and to demonstrate their origin by biomineralization. The dolostones have massive or grumelar texture, with microfossils (gastropods and charophytes less than 2%) and carbonate pseudomorphs (calcite or dolomite) after interstitial lenticular gypsum crystals (20-60%); they have always palyigorskite as cement and may have undergone dedolomitization and silicification. Under SEM dolomite crystals are cylindrical, with sizes up to 40 microns in high. Due to their concentric inner vacuolar structure, high fluorescence, and the occasional occurrence of "dumbbell" forms, the dolomite is interpreted as formed as a result of sulfate reducing bacteria and EPS activity. This dolomite occurred in a micrite/biomicrite mud with interstitial gypsum crystals formed during drought periods. The biodolomite was formed at the expenses of the original calcareous matrix by replacement of gypsum crystalsLa secuencia inferior de la Formación Deza representa un ambiente carbonático lacustre efímero puesto de manifiesto por la presencia de fósiles límnicos y evidencias de desecación periódica marcadas por la existencia de numerosos pseudomorfos carbonáticos de cristales lenticulares de yeso intersticial. En este trabajo se muestran los resultados del estudio petrológico de determinadas facies dolomíticas de la secuencia inferior para resaltar el carácter de los cristales de dolomita y demostrar su origen por biomineralización. Las dolomías presentan textura masiva o grumelar con menos del 2% de microfósiles (gasterópodos, y caráceas) y entre un 20 y un 60% de pseudomorfos carbonáticos (calcita o dolomita) de cristales de yeso; siempre tienen paligorskita como cemento y pueden presentar evidencias de procesos de dedolomitización y silicificación. Los cristales de dolomita en MEB son cilíndricos con tamaños de hasta 40 µm de altura. Debido a su estructura interior vacuolar concéntrica, alta fluorescencia, y en ocasiones, su forma “en mancuerna” se interpreta que se originaron en relación con bacterias sulfato-reductoras y sus EPS. Esta dolomita precipitó en una micrita/biomicrita con cristales de yeso intersticial formados en épocas de emersión. La biodolomita se formó por remplazo de la matriz calcárea original y del yes

The origin of the saline waters in the Villafáfila lakes (NW Spain). A hydrogeological, hydrochemical, and geophysical approach

[EN]Villafáfila lakes are a natural reserve included in the intergovernmental RAMSAR agreements for conservation of wetlands, with special interest for their brackish-saline waters. These lakes are located at the western margin of the Duero basin, whose aquifer system has no evaporitic rocks upstream. Understanding the origin of the lake's salinity, the groundwater circulation and the distribution of the brackish-saline waters in the area is important not only for the preservation and management of the natural reserve, but for human water consumption as well. Three types of waters have been identified according to their chemical composition. Type 1 are calcium-bicarbonate fresh waters identified in the local recharge areas (surrounding hills); Type 2 are mixed waters dominated by sodium and chloride-bicarbonate, identified at the toe of the hills; Type 3 are brackish to saline sodium-chloride waters from the lakes, springs and boreholes. Time domain electromagnetic (TDEM) profiles have revealed the existence of a basement elevation that forces brackish regional groundwater flow to rise. Radiocarbon age of regional groundwaters points to residence times of 20–30 Ky. Villafáfila lakes are through-flow lakes nourished by meteoric waters (direct precipitation and shallow groundwaters) as deduced by stable isotopes (δ18OH2O, δDH2O), while the solutes are provided by ascendant deep groundwater flows in the lakes bottom and in the surrounding area. Sulphate stable isotopes (δ18OSO4=; δ34SSO4=) suggest that deep groundwaters have been in contact with Triassic and Cenozoic evaporites. Below the lake's bottom there is a brine (TDS = 27 g/L) contained within the lake-sediment aquitard that is concentrated by evaporation in the vadose zone and by salt recycling. A salinity inversion has been observed below the brine. The lack of saline crusts on the lake's bottom is favored by the SW outflow of the brine

3-D modelling of a fossil tufa outcrop. The example of La Peña del Manto (Soria, Spain)

[EN]Classical studies of tufas lack quantitative outcrop descriptions and facies models, and normally do not integrate data from subsurface in the stratigraphic and evolutive analysis. This paper describes themethodology followed to construct one of the first digital outcrop models of fossil tufas. This model incorporates 3-D lines and surfaces obtained from a terrestrial laser scanner, electric resistivity tomography (ERT) profiles, and stratigraphic and sedimentologic data from 18 measured sections. This study has identified seven sedimentary units (from SU-1 to SU-7) which are composed of tufa carbonates (SU-1; 3; 5; 6) and clastics (SU-2; 4; 7). Facies identified occur in different proportions: phytoherm limestones of bryophytes represent 43% of tufa volume, bioclastic limestones 20%, phytoherm limestones of stems 12%, oncolitic limestones 8%, and clastics 15%. Three main architectural elements have been identified: 1) Steeply dipping strata dominated by phytoherm limestones of bryophytes; 2) gently dipping strata dominated by phytoherm limestones of stems; and 3) horizontal strata dominated by bioclastic and oncoid limestones. The alternation of tufa growth and clastic input stages is interpreted as the result of climatic changes during Mid–Late Pleistocene.18.KA4A-463 A.C.01, Universidad de Salamanca CGL2014-54818-P of the Ministerio de Economía y Competitividad (MINECO)

Origin and hydrogeochemistry of a shallow flow-through lake on a Pleistocene piedmont, northern Spanish Meseta

The Cristo lagoon, situated on Neogene deposits in the northern Spanish Meseta, occupies a shallow depression on a Pleistocene piedmont. The development of the lacustrine depression on the piedmont was favoured by the fault network, reinforced by substrateloss by weathering, probably during the late Quaternary. Even during the hot summer season, salinity is low, with concentrations of total dissolved solids (TDS) being around 150 mg L–1. Only when the lagoon is almost dry do TDS concentrations exceed 500 mg L–1, sometimes rising as high as 1700 mg L–1. Whenthe lake level is high, lake chemistry is dominated by Na+, Ca2+, HCO3– and Cl–. During drier stages, there is a relative increase in Ca2+, Mg2+, Cl–, and SO42–, trending toward a calcium chloride-sulphate brine. Values of pH are above 9 during late spring and summer, resulting primarily from evaporative degassing favoured by the shallow depth of water, and secondarily from photosynthesis by the abundant submerged macrophytes. The infilling deposits, less than 0.5 m thick, are dark brown, massive, sandy muds consisting of quartz and clays (illite, kaolinite, smectite), all of which are allogenic in origin. The main source of dissolved sulphate was the oxidation of sulphides during weathering of lower Palaeozoic rocks in the catchment area. The 13C-depleted nature of dissolved inorganic carbon indicates an origin mostly by respiration and oxidation of organic matter. Geomorphology and hydrogeochemistry indicate a flow-through lake dominated essentially by groundwater flows. </p

Distribution and ecology of recent ostracods from the Villafáfila lakes (Zamora, Spain)

En este trabajo se estudian las asociaciones de ostrácodos que habitan en las Lagunas de Villafáfila (Zamora) y que han permitido caracterizar los diversos subambientes que se desarrollan en estos humedales. Así, se define un primer subambiente de cuerpos temporales de agua dulce con cierta hidrodinámica donde predomina Leucocythere aff. mirabilis. La abundancia de Ilyocypris bradyi caracteriza un segundo subambiente de margen lacustre somero al que llegan arroyos o pequeños riachuelos de agua corriente. El tercer subambiente consiste en aguas semipermanentes con poca corriente y moderada salinidad, definido por la abundancia de Limnocythere inopinata . Finalmente, se ha identificado un cuarto subambiente de humedal efímero con aguas con poca corriente y elevada salinidad en el que predomina Sarscypridopsis aculeata . Queda puesto de manifiesto con este trabajo que los principales factores ecológicos que condicionan la distribución de los ostrácodos en las Lagunas de Villafáfila son la hidrodinámica, el hidroperiodo y la salinidad del agua. Estos datos, además, servirán como comparativa o modelo actual para futuros trabajos de reconstrucción paleoambiental que se vayan a realizar en medios límnicos neógenos de la Península Ibérica, empleando las asociaciones de ostrácodosIn this work, the ostracod assemblages that inhabit in the Villafáfila lakes have been studied, allowing the characterization of several subenvironments developed in these wetlands. Thus, a first subenvironment of temporary fresh water bodies with some hydrodynamism where Leucocythere aff. mirabilis is dominant has been identified. The abundance of Ilyocypris bradyi characterized a second subenvironment of streams and small rivers of flowing waters that run into shallow lacustrine margins. The third subenvironment consists in semipermanent water bodies with low current and moderate salinity defined by the abundance of Limnocythere inopinata. Finally, a fourth subenvironment of ephemeral wetlands with slow currents and high salinity has been defined by the predominance of Sarscypridopsis aculeata . This work highlights that hydrodynamic, hydroperiod and water salinity are the main ecological factors that control the ostracods distribution along the Villafáfila lakes. Besides, these data will be used as comparison or recent model for future works focused on the neogene palaeoenvironmental reconstruction of other limnic settlements of the Iberian Peninsula using ostracod assemblage

Proyecto de difusión y promoción del nuevo Grado en Geología

Memoria ID-0209. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2015-2016

Geological-Geomorphological and Paleontological Heritage in the Algarve (Portugal) Applied to Geotourism and Geoeducation

A 3D virtual geological route on Digital Earth of the geological-geomorphological and paleontological heritage in the Algarve (Portugal) is presented, assessing the geological heritage of nine representative geosites. Eighteen quantitative parameters are used, weighing the scientific, didactic and cultural tourist interest of each site. A virtual route has been created in Google Earth, with overlaid georeferenced cartographies, as a field guide for students to participate and improve their learning. This free application allows loading thematic georeferenced information that has previously been evaluated by means of a series of parameters for identifying the importance and interest of a geosite (scientific, educational and/or tourist). The virtual route allows travelling from one geosite to another, interacting in real time from portable devices (e.g., smartphone and tablets), and thus making possible the ability to observe the relief and spatial geological distribution with representative images, as well as to access files with the description and analysis of each geosite. By using a field guide, each geosite is complemented with activities for carrying out and evaluating what has been learned; these resources allow a teaching–learning process where the student is an active part of the development and creation of content using new technologies that provide more entertaining and educational learning, teamwork and interaction with social networks. This itinerary allows the creation of attitudes and skills that involve geoconservation as an element for sustainable development