Sedimentology and depositional architecture of tufas deposited in stepped fluvial systems of changing slope: Lessons from the quaternary añamaza valley (Iberian Range, Spain)

The Pleistocene and Holocene tufas of the Añamaza valley (stepped build-ups, up to 70 m thick, along the valley) consist of several depositional stages separated by erosional surfaces. Eight associations of tufa and related carbonate facies, plus minor polygenic detrital facies, represent the processes that occurred in different fluvial and related environments. The bedrock lithology and structure controlled the location of the knickpoints along the valley and allowed separation of two stepped stretches with distinct conceptual facies models. The moderate-slope model includes extensive standing-water areas dammed by barrage-cascades. In the lakes, bioclastic silts, sands and limestones along with phytoclastic and marly, at places peaty, sediments formed. Abundant stem phytoherms account for extensive palustrine areas. The high-slope model consists of smaller dammed areas between close-up cascades and barrage-cascades, which were composed primarily of moss phytoherms and phytoclastic tufas. An outstanding feature is the extensive steep reach with phytoclastic and polygenic detrital sediments, and stepped cascades consisting of stromatolitic and moss phytoherms. There, the steep slope limited the preservation of stem phytoherms and favoured erosion. The geometry and thickness of the sedimentary fill (wedge-shaped units composed of cascade and barrage-cascade deposits downstream, and dammed and gentle-sloped channel deposits upstream) are therefore different for each model. Multi-storey wedges are a distinctive feature of the high-slope model. The initial knickpoint geometry and the tufa aggradation/progradation ratio on such steep surfaces (for example, related to changes in discharge) controlled the growth style of the cascades or barrage-cascades and, hence, the extent, thickness and vertical evolution of the upstream deposits. The sedimentological attributes and stable-isotope composition of the carbonate facies suggest a higher and more variable precipitation/evaporation ratio during the Pleistocene than during the Holocene, consistent with an overall decrease in the river discharge. This evolution was coupled with warm conditions, which prevailed during the stages of tufa formation. These results may help to assess architectural patterns in interpreting other basins, and underscore the significance of tufas as records of past hydrology and climate

Intrinsic and extrinsic controls of spatial and temporal variations in modern fluvial tufa sedimentation: A thirteen-year record from a semi-arid environment

Sedimentological and hydrochemical parameters of the River Piedra (north-east Spain) were monitored every six months (from 1999 to 2012) at 24 sites, at which tablets were installed all along the river. The river water is of HCO3–SO4–Ca type and is notably influenced by inputs from upstream karstic springs. Tufa deposition was first detected 8 km downstream of these springs and greatly increased from there, primarily along the steeper stretch (i.e. within the Monasterio de Piedra Natural Park); then, deposition decreased through the most downstream stretch, with smaller ground water inputs. The spatial evolution of the tufa thickness, with parallel variations of PWP (Plummer, Wigley, Parkhurst) rates, was thus determined by the river water pCO2 which was controlled by ground water inputs and by the river bed slope. Five fluvial subenvironments and seven sedimentary facies were characterized. The water flow conditions are the primary factor responsible for the distinct deposition rates of facies, mainly through CO2-outgassing. Stromatolites and moss-tufa and alga-tufa had the highest rates, whereas loose tufa formed in slow-flowing water and tufa of spray areas had thinner deposition. A six-month pattern in the deposition rate was detected through thickness measurements. That pattern was parallel to the seasonal PWP rates. The increased deposition during warm periods (spring and summer; mean: 5·08 mm) compared with cool periods (autumn and winter; mean: 2·77 mm) is linked chiefly to temperature, which controlled the seasonal changes in the physico-chemical and biological processes; this finding is supported by a principal components analysis. Seasonal variations of insolation and day duration also contributed to such a deposition pattern. Large discharge events, which provoked erosion of tufa deposits and dilution of water, caused the reversal of the seasonal deposition rate pattern. Stromatolites are likely to preserve the most complete sedimentary record. Although tufas are a potentially sensitive record of climate-related parameters, erosion is an intrinsic process that may overwhelm the effects of such parameters. This issue should be considered in palaeoclimatic studies based on the tufa record, particularly in semi-arid conditions

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

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

Discerning the interactions between environmental parameters reflected in d13C and d18O of recent fluvial tufas: Lessons from a Mediterranean climate region

d13C and d18O of recent, continuous tufa records, obtained during a monitoring period spanning 3 to 13 years, are compared with the corresponding, known environmental conditions. Three rivers in NE Iberia (located along a 200-km N–S transect) are used for this comparison. The isotopic variations through space and time are discussed in terms of the environmental and geological parameters that operate on different scales, focusing on discerning the interactions between these parameters and providing examples of possible misinterpretation of climatic conditions, which is important to past climate studies based on isotopic data. The calculation of the actual isotopic fractionation coefficients, and the comparison with the literature-derived coefficients, demonstrates that the studied tufa formation was close to isotopic equilibrium to reflect the water temperature. The difference between mean measured water temperature (Tw) and mean calculated Tw (based on d18Ocalcite and measured d18Owater) is less than 2.7 °C. Tendencies of these calculated Tw are similar to the regional air temperature (Tair) tendencies through time, in particular in the case of the 13-year record, although certain deviations exist over shorter time spans. The best agreement between measured and calculated Tw and between d18Ocalcite-based Tw tendencies and Tair tendencies corresponds to the tufa stromatolite facies. Differences between the d18Ocalcite records of the three rivers cannot be attributed to temperature changes, but to the varying influences of groundwater inputs and isotopic rainfall composition in each river.Without considering these parameters, d18Ocalcite-based Tw calculations yield inaccurate results when comparing the study sites. d13Ccalcite values do not exhibit distinct patterns over time, and d13Ccalcite variations are likely caused by local processes that do not reflect general environmental changes. These findings underscore the significance of accounting for both groundwater behaviour and rainfall stable isotope composition when interpreting climate parameters in carbonate systems, particularly when differences between the isotopic signatures of deposits exist in the same region

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

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

Las tobas cuaternarias del río Añamaza (provincia de Soria, Cordillera Ibérica): aproximación cronológica

High-gradient, stepped fluvial tufa systems with dammed areas existed in the River Añamaza valley (NW Iberian Ranges, Spain) during Quaternary times. Single deposits range from a few meters to about 70 m thick, in which prograding-aggrading wedges separated by erosional surfaces exist. Several episodes of tufa formation have been distinguished by means of U-series, Amino-acid racemization and radiocarbon techniques. These correlate to MIS 8, 7, 5 and 1. The presence of MIS 9 is uncertain, as chronological data may also correspond to older stages. Most tufas in this area formed in MIS 5. Distinct tufa episodes can also be distinguished in the Holocene. These are the first chronological data presented for one of the northernmost Quaternary tufa systems in the Iberian Ranges

Análisis preliminar de las tobas cuaternarias del río Ebrón (Castielfabib, Valencia, Cordillera Ibérica)

In this paper the Alpine cleavage affecting the Permo-Triassic series of the Espadan Range (Castellón) is studied. Cleavage affects to argillites and sandstones in Saxonian and Buntsandstein facies. At cartographic scale it is linked with the Espadan box anticline with constant ONO-ESE trend. At microscoscopic scale it constitutes a “spaced cleavage” with a predominance of pressure solution and passive rotation mechanisms. At outcrop scale the cleavage characterizes by a sigmoidal geometry linked both the post-cleavage flexural slip as a cleavage-related flexural flow mechanism. The proposed kinematic model to explain its origin includes three main stages: 1) incipient development of cleavage linked to layer-parallel shortening, 2) buckling and increasing of cleavage penetrativity and 3) folfing amplification and layer-parallel shear. RESUMEN Se estudia la esquistosidad alpina que afecta a la serie Permo-Triásica de la Sierra de Espadán, (Castellón). La esquistosidad afecta a los tramos argilíticos y areniscosos en facies Saxoniense y Buntsandstein, con distinto grado de penetratividad. A escala cartográfica se asocia al anticlinal de Espadán con geometría en cofre y orientación ONO-ESE. A escala microestructural se clasifica como esquistosidad espaciada con predominio de los mecanismos de disolución por presión y rotación mecánica de filosilicatos. A escala de afloramiento destaca la geometría sigmoidal de las superficies de esquistosidad atribuida tanto a un mecanismo post-esquistoso de flexodeslizamiento en las capas competentes como a flexofluencia sin-esquistosa en capas incompetentes. El modelo cinemático para su génesis contempla tres estadios: 1) desarrollo incipiente de esquistosidad en relación a acortamiento paralelo a las capas, 2) buckling e incremento del grado de penetratividad y 3) amplificación de los pliegues y cizalla simple paralela a las capa