Active (El Saladillo, Murcia) and fossil (Azuaje, Gran Canaria) travertines: similar facies in different geological settings

Comunicación presentada en el IX Congreso Geológico de España, Huelva, 12-14 septiembre 2016.[ES] En este trabajo se compara un travertino de un sistema activo (El Saladillo, Murcia) con uno fósil (Azuaje, Las Palmas) posiblemente Holoceno. Los dos presentan facies y mineralogías similares. En ambos el mineral dominante en las zonas cercanas a las surgencias es el aragonito (agregados esferulíticos) que disminuye distalmente, a favor de la calcita (morfologías trigonales). Las facies características son: shrubs, burbujas calcificadas, costras laminares, granos con cubiertas y micríticas con diatomeas. En conjunto ambos depósitos corresponden a un sistema de pozas y cascadas. El fuerte desequilibrio químico que caracteriza la zona de surgencia y su tendencia a equilibrarse aguas abajo son los responsables de la mineralogía, las facies, y de la variación de ambas a lo largo del sistema.[EN] An active travertine (El Saladillo, Murcia) and a fossil travertine (Azuaje, Las Palmas) have been compared in the present work. Both travertines show similar facies and mineralogy despite their formed under different geological settings (sedimentary and volcanic respectively). Aragonite, usually as spherulitic crystal aggregates, is the dominant mineral phase close to the spring. Aragonite content diminishes distally to spring, whereas trigonal calcite crystals become to be the dominant mineral phase. Characteristic facies found in both deposits are: shrubs, coated bubbles, laminated crusts, coated grains, and micrite deposits containing abundant diatoms. These deposits correspond to spring-fed pool-cascade systems. Strong chemical disequilibrium close to spring and downflow trend to chemical equilibrium control facies, mineralogy, and their variations along the system.Trabajo financiado por los proyectos CGL2014-54818- P (MINECO) y CGL-2011-27826-CO2-02 (MICINN).Peer reviewe

Chabazite and dolomite formation in a dolocrete profile an example of complex alkaline paragenesis in Lanzarote, Canary Islands

This paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the Mirador del Río dolocrete profile. The profile consists of a lower horizon of removilised weathered basalts, an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces. Formation occurred in arid to semiarid climates, giving place to a complex mineralogical association, including Mg-carbonates and chabazite, rarely described in cal/dolocretes profiles. Initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments, producing (Stage 1) red-smectites and dolomicrite. Dominant phreatic (Stage 2) conditions allowed precipitation of coarse-zoned dolomite and chabazite filling porosities. In Stages 3 and 4, mostly pedogenic, biogenic processes played an important role in dolomite and calcite accumulation in the profile. Overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock, to provide silica and Mg-rich alkaline waters, suitable for chabazite and dolomite formation, without a previous carbonate phase. Dolomite formed both abiogenically and biogenically, but without a previous carbonate precursor and in the absence of evaporites. Dominance of calcite towards the profile top is the result of Mg/Ca decrease in the interstitial meteoric waters due to decreased supply of Mg from weathering, and increased supply of Ca in aeolian dust. Meteoric origin of the water is confirmed by C and O isotope values, which also indicate lack of deep sourced CO2. The dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt-sourced rocks

The role of climate and aeolian dust input in calcrete formation in volcanic islands (Lanzarote and Fuerteventura, Spain)

[EN]Calcretes are widely described in non-marine settings with carbonates in their catchment, or vicinity areas, but in volcanic islands without carbonates in their substrate, calcretes are not very common. In Lanzarote and Fuerteventura Canary Islands, characterized by impressive volcanic landscapes, the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits. In these settings very well-developed calcretes cover large areas of the present landscape. The source of calcium required for the formation of these calcretes has not been discussed in much detail till now, although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes. The petrological and geochemical studies (87Sr/86Sr ratios, δ13C, δ18O, major, trace and REE) carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes. Canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits. Our study indicates that these interbeddings were the result of several stages in which, during dry periods, aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants, insects and bacteria played an important role in carbonate precipitation. The δ18O (− 2.70 to + 2.22‰ VPDB) and δ13C (− 8.21 to + 0.24‰ VPDB) values indicate that calcretes were formed by pedogenic processes. Comparison of calculated ∆18O values for the Canary calcretes with continental mid-latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island (oceanic) settings. Calcrete87Sr/86Sr ratios (0.706357 to 0.709208) show strong affinity with those obtained in aeolian carbonate dust and marine deposits, and are relatively different from those obtained in basalts. REE, major and trace element concentrations show that Ca-bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the Sahara and Sahel or sand dunes

El Edificio carbonático de Temisas: un ejemplo de un sistema tobáceo termógeno en la isla de Gran Canaria

El Edificio carbonático de Temisas (TCB) está situado en el barranco de Temisas al SW Gran Canaria. Se pueden reconocer cuatro facies distintas: detritica, “framestone”, fitoclástica y de transición, entre las dos últimas. Los depósitos carbonáticos son esencialmente de calcita. La secuencia sedimentaria indica que el TCB se ha formado en un sistema fluvial formado sobre todo por cascadas, canales y barras. Los depósitos estudiados en este trabajo corresponden a la parte distal de una surgencia carbonática y se podrían clasificar como toba. Los valores de isótopos estables sugieren un origen termal para estas aguas. Por ello el TCB puede ser considerado como una toba termogénaThe Temisas Carbonate Building (TCB) is situated in the Temisas ravine, at the SW part of the Gran Canaria Island. Four different facies were recognised: detrital, framestone, phytoclastic and a transition between the last two facies. The carbonate is mostly calcite. The sedimentary sequence indicates that the TCB was formed in a fluvial system with different subenvironments, such as cascades, channels and bars. The studied deposits correspond to the distal part of a calcareous spring deposit. Petrologically these deposits can be included in the term tufa. The stable isotope values indicate thermal origin for the CO2, so from the geochemical point of view the TCB should be considered a thermogene tuf

Las tobas/travertinos del barranco de Calabozo: Un ejemplo de construcción rápida de un edificio carbonático alimentado por una tubería de regadío

El barranco de Calabozo, en la Isla de Gran Canaria, muestra como rasgo excepcional la presencia de un edificio tobáceo/travertínico alimentado por una tubería de un sistema de regadío. La tubería se abasteció de pozos cuyas aguas son ricas en gases de origen volcánico y tienen temperaturas que alcanzan los 31ºC. En estas condiciones el agua se mineraliza con rapidez, enriqueciéndose en HCO3- y CO32-. Cuando sale de la tubería se desgasifica rápidamente (pierde el CO2) precipitando el carbonato que forma el edificio carbonático. El edificio del barranco de Calabozo es un edificio bioconstruido colgante, formado por: a) canal abastecedor (la tubería), b) pendiente c) barreras o cascadas y 4) pozas. El edificio funcionó escasas décadas y su tasa de crecimiento fue muy rápida. Esto explicaría los tres aspectos característicos de este edificio: 1) las barreras son bioconstrucciones de macrofitas, 2) las facies cristalinas gruesas son dominantes y responden a un desequilibrio fuerte por pérdida rápida de CO2 y 3) se observan rasgos diagéneticos a pesar de lo reciente que es el edificio. Las macrofitas ejercieron un papel de soporte para los precipitados inorgánicos, pero los microorganismos también jugaron un papel importante en la precipitación de las microfacies micríticas

Early diagenetic features in Holocene travertine and tufa from a volcanic setting (Azuaje, Gran Canaria, Spain)

The diagenesis of travertine and tufa is rarely considered an issue due to the common difficulty of distinguishing what is primary from secondary, as in most of cases these diagenetic changes occur very early. The main diagenetic features of travertine and tufa formed within a volcanic ravine in the north of Gran Canaria (Canary Islands, Spain) are cementation within pores and cavities, and of micropores (< 0.06 mm), micritization, aggrading neomorphism, aragonite-to-calcite transformation, and dissolution. One of the most striking features is cementation of micropores between fibrous crystals of shrubs, spherulites and crusts. Micropore cementation leads to a textural change of the primary aragonite and calcite fibres to a massive crystalline texture retaining the original fibres. Early cementation of micropores in fibrous textures can be significant in understanding their preservation in ancient shrubs and spherulites, such as those of Cretaceous Pre-salt reservoirs. These diagenetic changes are strongly controlled by their low porosity and permeability, whereas diagenesis occurred in a different way in the more porous and permeable textures. The diagenetic changes described here occurred very early in both tufa and travertine, being almost totally restricted to the period immediately after deposition

Changes in coated grain-types from travertine to tufa deposits in Azuaje carbonate building (Canary Islands, Spain)

along 3 km of Azuaje Ravine in the volcanic island of Gran Canaria (Canary Islands, Spain). The systems show a clear evolution from travertine to tufas along the Ravine. Coated grains have been grouped into ooids and oncoids based exclusively on their characteristics Ooids show regular concentric smooth envelopes and 0.1 mm-2 mm in size. Three main types of cortex have been distinguished: (i) radial fibre or acicular crystals comprising the whole cortex diameter and crosscutting the lamination, (ii) banded-radial arrangements with alternating layers of radial fibres and micritic layers, and (iii) micritic. Nuclei are intraclasts, peloids, spherulites, small plant part moulds, or may absent by dissolution, or undistinguishable from the cortex. Ooids are commonly spherical to ellipsoidal. Frequently two or more individual coated grains agglutinate and form compound grains. Mineralogy varies between aragonite and aragonite-calcite. Oncoids are 0.4 mm to several millimetres and exceptionally tens of centimetres (nuclei of palm tree leaf moulds). They display two main types of coatings: (i) thin, irregular, dense micritic laminae, and (ii) generally thicker porous laminae usually made of dendritic, shrubby, or columnar (branched) crystal aggregates, containing alternating lamination. Lamination is slightly wavy to mammillated. Nuclei are similar to those of the ooids, being intraclasts and plant moulds (leaving moldic porosity) the most common. Shapes are varied and generally irregular depending strongly on the shape of nuclei. Mineralogy varies from aragonite, to aragonite-calcite mixtures, and to exclusively calcite in tufa. Diagenetic changes are widespread, being apparently more intense in travertine than in tufa facies: aggrading recrystallization, aragonite inversion, dissolution, and cementation are the most common processes. δ13C-δ18O plots from each individual deposit show positive covariant trends. Isotope signals of coated grains are indistinguishable from other of the same deposit. δ13C decreases as the amount of calcite increases which suggest: a) that primary aragonite facies are heavier in carbon than those composed of calcite, and ii) diagenetic transformations deviate the primary signals to heavier 13C values. Ooids are restricted to travertines. Oncoids are ubiquitous, but changing strongly their features in downstream direction. Tufa deposits placed downstream only content oncoids with intraclasts and large plant moulds as nucleus, as well as thicker and more irregular coatings, than those found in upstream travertines. Coated grains formed with low to no displacement, as is suggested by their high diversity and the uncommon occurrence of deposits with mixed grains. Scarcity of detrital clasts as nuclei of coated grains suggests low clastic input from upstream but also from ravine walls. These may be related to slope stability, but also with the absence or attenuation of floods. Restricted distribution of ooids, sharp changes in oncoid type, mineralogy, isotopes and diagenesis suggest an abrupt change downstream in environmental conditions reflected in changes in vegetation and CaCO3 precipitation rates and mineralogy.This study was funded by Ayuda Grupos de Investigación-2014 GR3/14 granted to Research Group 910404-Petrología Aplicada al Análisis de Cuencas y a la Conservación del PatrimonioPeer reviewe

Variations of Tortajada fluvial-tufa sub-environments in a tectonically active basin, Teruel semigraben, NE Spain

Tortajada fluvial-tufa system is a freshwater fluvial carbonate deposit located approximately 6 km NE of Teruel (NE of Spain), in the eastern and tectonically active margin of the Teruel Basin. This margin was active during Neogene and Quaternary because of the movement of Concud and Teruel faults. The preserved deposit is divided in three main zones: upper terrace, lower terrace, and middle cascade-ponds. These terraces, cascades and ponded/shallow lacustrine areas, are composed of six facies: 1) framestone of stem facies formed by calcified macrophyte and bryophyte hanging stems, or some macrophytes growing upward, 2) phytoclastic rudstone facies consist of calcified macrophyte and bryophyte fragments distributed chaotically in micritic/microsparitic matrix, 3) framestone of bryophyte (moss) facies is a phytoherm of calcified bryophytes in living positions, 4) peloidal and filamentous stromatolite facies are slightly undulated stromatolite bodies with internal peloidal layers and organic filaments from which stromatolites could have been formed, 5) mudstone facies made up of micritic matrix with few grains (fragments of mosses and charophytes, ostracods, intraclasts…) and, 6) conglomerate and breccia facies containing stream fluvial polymictic gravels and slope-breccias. Besides, granular and peloidal microfacies appear in various facies (mainly in stromatolites) composed of intraclastic grains (previous moss and tufa fragments) and micritic peloids. Identifiable microbial microstructures in topmost parts of almost all facies micritized previously existing crystals. All six facies are organized in three sedimentary sequences, from east to west (downstream): terrace sequence, pond sequence and cascade sequence. All sequences start from fluvial conglomeratic base, with energy of water decreasing towards the top. These sequences were dependent of paleomorphology and, therefore, conditioned by Late Pliocene and Quaternary tectonic activity. Thus, secondary faults linked to the eastern margin of extensional Teruel Basin were, for instance, responsible for the cascade sequence. Also discontinuities made in Mesozoic host-rock allowed the upwelling of groundwater. Thereby, tectonic activity played an important role in diverse episodes of the formation of this fluvial-tufa system, beginning from the initial incision and establishment of fluvial network, and finalizing on tuffaceous ponds/shallow lacustrine and cascade areas. This is reflecting in various described facies and sequences formed along different sub-environments of the system. Negative isotopic values suggest that the origin of water for the formation of Tortajada fluvialtufa deposit was both meteoric rainfall and upwelling of shallow-groundwater, consistent with other data of tufas from the NE of Iberian Peninsula. Low ranges in δ18O indicates and open system with short residence time of water. In contrast, variations in δ13C values could be related to diverse processes, such as degassing during calcite physicochemical precipitation, photosynthesis or respiration of microbes, or even different residence times of the water. In conclusion, Tortajada fluvial-tufa deposit provides important information about fluvial sedimentation and tufa development during the evolution and different episodes of the formation of Teruel Basin.Peer reviewe

Controlling factors and implications for travertine and tufa deposition in a volcanic setting

This work studies a fossil system of perched and fluvial travertines passing distally to fluvial tufas within a volcanic ravine. Sedimentology, petrology and geochemistry of fossil aragonitic-calcitic travertines and downstream calcitic tufas from the Azuaje volcanic ravine were studied. These spring-related carbonates seem to be formed after the Mid-Holocene climate change, the transition from a monsoon-dominated humid climate to an arid-semiarid climate controlled by trade winds. The main travertine facies include rafts, dendrites/shrubs, ooids, oncoids and stromatolites among others, whereas tufas are characterised by phytoclasts, oncoids, coated stems, intraclasts and stromatolites. Facies observed can be (i) microbial-influenced when the microbial growth rate is greater than the precipitation rate and flow energy is not above the threshold value tolerated by microbes, or (ii) inorganic-dominated if the precipitation rate exceeds that of the microbial growth rate and/or flow energy is above the threshold tolerated by microbes. Travertine facies vary from mostly inorganic to microbially-dominated, whereas tufa facies are mostly microbially-influenced. Observed changes of facies in both travertines and tufas were interpreted as due to changes in environmental conditions from (a) less to more evaporative, (b) less saturated to oversaturated, and (c) high to low energy. Changes in textures, mineralogy, geochemistry and stable isotope composition downstream from travertine to tufa suggest a decrease in the CaCO3 precipitation rate and an increase in microbial influence from travertines (proximal part of the system) to (distal) tufas. Our study case illustrates the wide variety of facies and processes operating in spring-related travertine and tufa deposits. The details of arrangement, mineralogy, facies and geochemistry of the deposits were mostly controlled by climate and hydrogeology, although the volcanic setting, provided suitable conditions for spring‑carbonate deposition