Salvador Ordóñez

Does climate control the morphological fabric of freshwater carbonates? A comparative study of Holocene barrage tufas from Spain and Britain

Abstract Calcium carbonate production in most freshwater tufa systems is controlled by a combination of physico-chemical precipitation, and biomediation associated with procaryote-microphyte biofilms. Inorganic precipitation is dominant under turbulent flow regimes, whereas biomediation necessitates sluggish flow or static water. We show here that temperature is also likely to affect tufa formation rates and architecture, leading to the development of a clearly definable range of fabrics. Two contrasting models are proposed: Warm semi-arid tufas: well seen in the Ruidera Pools National Park, Albacete Province, Central Spain, where tufa barrages consist of vertical, narrow rimmed arcuate structures. Frequently these are bounded both upstream and downstream by deep lakes. Laterally accreting mammilate stromatolites dominate the upper two thirds of lake margin subaqueous overhangs, whereas conical growth-forms dominate shady basal parts of subaqueous overhangs. Dense reed stands grow in thin peats on top of the vertical lake margin walls. Resistivity survey and percussion augering show up to 20 m of earlier lake fill which is banded into dark and pale beds. The upper 10 m accumulated in 4600 years. There is little or no preservation of organic material within these deposits. Cool temperate tufas: typified by slowly accumulating barrage tufas at Caerwys (N. Wales) and Alport (N. Derbyshire, UK). Transverse barriers across valleys are dominated by arcuate buttress developments built up of downstream-facing tabular carbonate sheets. Pools upstream of the barriers are shallow, dominated by clotted lime mud and organic sapropels in their depocentres, and stromatolite-dominated (laminar to low domes, or oncoidal) facies in broad marginal zones. Marginal stands of semi-aquatic vegetation are rooted in thick peats but frequently are also encrusted around their exposed stems by oncoidal carbonate. Fabric preservation is good for the carbonate material, however, marginal peats rapidly oxidise and stem encrustations collapse to produce cylindrical oncoid beds. Depocentre sapropels are always preserved and contain important pollen records otherwise rare in carbonate regions. Carbonates in both models accumulate relatively rapidly. They have a moderate preservation potential within Late Cenozoic terrestrial successions. The distinctly different characteristics of their preserved fabrics should allow recognition of two contrasting “climatic” models for fluvial barrage tufas in ancient deposits.

Quantification of salt weathering in porous stones using an experimental continuous partial immersion method

Abstract In this study, an experimental salt weathering simulation and porous stone durability classification are proposed. There are many laboratory tests that quantify durability against salt crystallisation weathering action. These are usually based on the total immersion of samples into a saline solution, which is not representative of the salt weathering mechanism. An experimental test based on partial immersion is suggested. This is a comparable study of weight loss and degradation of visual appearance due to salt crystallisation using, on the one hand, a standard durability test (UNE), and, on the other, the proposed durability test. The weight loss and visual appearance in our test is comparable to the degradation of building stone. The differences between weight loss data in both tests depend on the petrophysical properties: porous media and degree of coherence. From this testing, a new durability classification as a function of dry weight loss in the partial immersion test is proposed. Four divisions of different types of materials can be made in this classification, which quantifies salt weathering action mainly in environments and mild climatic conditions.

Predicting the Capillary Imbibition of Porous Rocks from Microstructure

The kinetics of capillary imbibition into porous rocks is studied experimentally and theoretically. The Washburn law is modified by introducing various corrections relating to the microstructure of the rocks, such as tortuosity, pore shape (obtained experimentally), and applying the effective medium approximation (EMA) in order to calculate the effective radius that defines the hydraulic conductance and the topology of the capillary imbibition. The application of the EMA shows that capillary imbibition is mainly produced in 1-D, and the pore structure is constituted by different pore throats in series, linked by chamber pores. The capillary process has been discussed as a function of their petrography and pore structure. Our study of the Washburn equation and the addition of correction factors for the pore structure allows a very accurate prediction of the weight rate.

Dedolomites associated with karstification. An example of early dedolomitization in lacustrine sequences from the Tertiary Madrid basin, central Spain

A variety of calcite fabrics formed by dedolomitization of middle to upper Miocene continental sediments of the Madrid basin, central Spain. The dedolomites are associated with other carbonates that show abundant diagenetic features. The diagenetic carbonates (Diagenetic Carbonate Zone, DCZ) overlies and grades laterally into lacustrine dolomite (Lower Dolomite Unit, LDU) and evaporites (Evaporitic Unit, EU), and in turn is capped by a paleokarst surface.The main dedolomite fabrics include sutured calcites and radial-fibrous calcites, the latter consisting of pseudospherulite mosaics and fibrous crusts. Other subordinate dedolomite fabrics consist of micro to mesocrystalline mosaics of rhombic, occasionally zoned calcites as well as reworked pseudospherulite crystals. These fabrics are interpreted to have been formed from extensive calcitization of dolostones and associated evaporite facies, the process being triggered and fostered by input of meteoric waters throughout a karstic system. The origin of the radial- fibrous calcites is discussed more specifically in view of their similarities to other calcite fabrics (e.g. Microcodium) often described in meteoric diagenetic environments.Geochemical evidence indicates that dedolomitization occurred in the shallow subsurface (<40m depth) and was achieved by oxidizing meteoric-derived ground waters. The diagenetic system behaved as an open system for nearly all trace elements analyzed; but in the shallower zone (vadose zone) the system is partially close respect to strontium. Vertical trends of the stable isotopes also support the proposed paleokarst model characterized by an irregular shallow water table and a narrow vadose zone.The results obtained from the geochemical simulation support that dedolomitization could develop by two combined hydrographical pattems: authigenic recharge through limestones and allogenic recharge. The dissolution/precipitation rates calculated for the main minerals involved in the process are consistent with petrographic- and geochemical evidence.

Orderly arrayed deposit of urate crystals in gout suggest epitaxial formation

The mechanisms responsible for the initial deposit of monosodium urate (MSU) crystals in gouty joints remain obscure. We report on nine small fragments of tissue that showed an arranged deposit MSU crystals, which were obtained along with synovial fluid (SF) from asymptomatic gouty joints. Three of the fragments had chondrocytic islands, indicating their cartilaginous nature; MSU crystals were found in their depth, all oriented in the same direction and in two of them, a parallel fibrillar appearance of its matrix was apparent following the MSU crystals in the same direction as the fibres (fig 1A). Bundles of undulating parallel fibres—probably of cartilage collagen—detached from two of these fragments. The remaining fragments were composed by similar bundles of undulating parallel fibres without a cellular component, and may constitute remanents of fibrillating cartilage. In four of these fragments, individual crystals were deposited densely packed in transverse rows, following the undulations of the fibres, and always positioned alongside them (fig 1B). Finally, in two additional fragments fewer crystals were seen, always laying parallel to …

Salt influence on evaporation from porous building rocks

The evaporation process of saline solutions within porous building rocks has been studied. Twelve different porous rocks saturated in pure water and a NaCl solution, were dried in a moisture balance. The influence of pore structure, environmental relative humidity and saline solution on the evaporation process has been studied from the experimental results. In order to explain the influence of these parameters simultaneously on the evaporation process, a detailed study of the thermodynamic equations is realised. This study explains the evaporation process in 0.01–100 μm pore size interval, predicting that saline solutions remain a long time within porous media, and therefore, intensify weathering processes.

Gout: the mechanism of urate crystal nucleation and growth. A hypothesis based in facts.

Joint Bone Spine - In Press.Proof corrected by the author Available online since jeudi 27 septembre 2012

The physicochemical weathering of monumental dolostones, granites and limestones; dimension stones of the Cathedral of Toledo (Spain)

Abstract Physical and chemical response to weathering has been evaluated for the building stones (granites and carbonate rocks) of the Cathedral of Toledo, Spain. Several aspects have been studied in detail: distribution of porosity and its relation to the fabric within the weathered material, chemical composition of weathering-related surficial crusts, and the order of crystallization of the soluble salts derived from the weathering processes. In addition, the study places some emphasis on the calculation of the crystallization pressures of these salts within the porous material resulting from weathering. Highest pressures are due to gypsum crystallization and, in decreasing order, to: anhydrite, mirabilite, epsomite, bloedite, thenardite and kieserite.

The water balance equations in saline playa lakes: comparison between experimental and recent data from Quero Playa Lake (central Spain)

Abstract The Quero Playa Lake is an ephemeral saline playa lake located in the La Mancha region of central Spain. In this study, a daily monitoring of the brine physical properties, water activity, brine depth and main climatic parameters was simultaneously carried out together with determining the precipitation sequence of minerals. Field data were compared with the results of simulating the water evaporation in an environmental chamber. In this simulation, a similar hydrochemical composition for the saline lake was used, and the main climatic parameters, temperature and humidity, were controlled. The water balance equation for saline lakes has usually been described using the Wood and Sanford equation [Econ. Geol., 85(1990) 1226–1235]. Our experimental results required us to revise the water balance equation for the brine depth variations (dh/dt), that may be expressed as follows: d h d t =p 1+k A B A L +S I −S O −ξ−H+D, where p (mm) is the precipitation; k is the drainage coefficient of the lake; AL is the lake surface; AB is the drainage basin surface; SI and SO are the contribution of influent and effluent seepage to the depth of brine in the lake. The term ξ is the evaporation/condensation, defined as ξ=kpW(aW−RH), where k is the mass transfer coefficient (Daltons equation); pW is the water pressure in equilibrium with the air; aW is the water activity of the brine; RH is the relative humidity. The other terms: H and D, correct the brine depth loss or/and gain a consequence of hydrated saline mineral precipitation and early diagenetic hydration/dehydration reactions. As a consequence of the above, we suggest that the water balance equation for saline lakes can be an important consideration in the interpretation of their evolution. The precipitation of hydrated saline minerals and the early diagenetic dehydration/hydration reactions imply changes in the dh/dt curves. As a result, the interpretation of the sequence of primary saline minerals in older evaporitic deposits may be used as a paleoenvironmental marker.

Impact of salt and frost weathering on the physical and durability properties of travertines and carbonate tufas used as building material

This study aims to understand the effect of salt and frost crystallisation on the petrophysical and durability properties of representative types of travertine and carbonate tufas. Results demonstrate that the studied travertines and tufas exhibit a very high durability against salt and ice crystallisation cycles, compared to carbonates rocks with similar porosity values. The variation of the loss of mass, effective porosity, capillary absorption coefficient, ultrasonic wave velocity and attenuation, and compressive strength was scarce during weathering tests. The evolution of petrophysical properties was slightly more intense after 30 cycles of salt crystallisation than 100 cycles of freeze–thaw. Petrophysical and durability properties of the travertines and carbonate tufas depend on porosity fraction and on the manner in which the vuggy porosity is connected. In the travertine facies, vuggy macropores show little connection and can be considered as separate-vug porosity. Their addition to interparticle porosity increases effective porosity and reduces their mechanical strength but does not significantly increase capillary transport and the effectiveness of salt and ice action over the stone. On the contrary, in the carbonate tufas, vugs act as touching-vug pores, as capillary imbibition coefficients reveal. However, scanning electron microscopy displays that they underwent microcracking processes related mainly to both thermal stresses and/or ice and salt pressures. These microcracks present little connection, and they do not enhance noticeably the water flow or decrease the mechanical properties. These results are finally discussed in terms of a nonlinear decay pattern, which with long periods of apparent stability might be followed by rapid and catastrophic decay.