M. A. García del Cura

Palustrine sedimentation and associated features—grainification and pseudo-microkarst—in the Middle Miocene (intermediate unit) of the Madrid Basin, Spain

Abstract A rather thick sequence (50–75 m) of lacustrine limestones forms the uppermost part of the Intermediate Unit (Middle Miocene) in the NE part of the Madrid Basin, central Spain. A gradual change from distal alluvial to open lake facies is recorded in this area. Red mudstones passing vertically to strongly mottled limestones are typical of the transition from distal alluvial to marginal lake deposits. A wide variety of facies occur in the marginal lacustrine facies association, all of them showing pedogenic features (e.g. root traces, alveolar septal structures, pseudo-microkarst). Micrites and biomicrites are interpreted as open lacustrine deposits. Although not as strongly pedogenically modified as the marginal lacustrine facies, they still show evidence of subaerial exposure. The carbonate sequence was deposited in a low-gradient, shallow-lake system in which slight fluctuations in the water level caused extensive emergence. Pedogenic processes affected most of the lake deposits, but modification was more intense in the marginal facies. Biogenic activity and mechanical reworking at lake margins led to the formation of pedogenic-diagenetic pseudo-microkarst and peloidal and/or intraclastic limestones.

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.

Models of miocene marginal lacustrine sedimentation in response to varied depositional regimes and source areas in the Madrid Basin (Central Spain)

Abstract A succession of lake complexes formed through Miocene times in the Madrid Basin (Central Spain). The complex formed during the Aragonian stage provides an outstanding opportunity to evaluate the role of source areas and depositional regimes in the construction of coeval marginal lacustrine deposits. Sedimentary facies of the Aragonian lake indicate a shallow lake that was fringed to the NW and S by arkosic alluvium, to the N by litharenitic alluvial fans, and to the NE and E by alluvial fans distally dominated by large floodplains. Marginal lacustrine deposits in the arkosic realm mostly consist of Mg-smectites and dolomite sequences that laterally interfinger with sepiolite beds which were deposited in small discontinuous ponds in the distal alluvial fan areas. Occasionally, micaceous-rich sandy streams entered the lake forming sheets at their entry points. In contrast, the northern margin of the lake was formed by muddy flats which were influenced by fluctuation in the water table. In this setting, illitic mudstones are commonly interbedded with biotite-rich flood sands, showing a sheet-like geometry. Meandering channels occasionally cut into the mud flats. Facies assemblages on this side of the lake were mainly derived from low-grade metamorphic areas. To the northeast, the marginal lacustrine facies consist of silty clays, carbonate paleosols and paludal to lacustrine limestones. These facies reflect an interfingering between the lake and a wide stream-floodplain system derived from a carbonate source area. The mosaic of marginal lacustrine facies in the Madrid Basin during the Aragonian is discussed in the light of lithological and geochemical factors related to variations in source areas.

Pore size distribution and the durability of a porous limestone

Abstract A comparison of durability estimations based on mercury porosimeter data and experimental salt crystallization tests carried out on Bateig Stone from Alicante, Spain, establish that the main factor in the salt crystallization durability test is the ‘ink bottle’ pore system, identified by the presence of residual mercury in large pores after porosity testing. In addition, the results suggest that the commonly used indirect durability tests may not be considered a scientific definition of building stone behaviour.

Endolithic cyanobacteria in Maastricht limestone

Abstract The Maastricht limestone used for the construction of the 14th century O.L. Basilica in Tongeren, Belgium, is a light yellowish, porous, soft rock of the Late Cretaceous age. The limestone has a high carbonate content (> 95%); quartz and glauconite occur rarely. On the north side of the building, there is extensive growth of epilithic algae. On the south side, an assemblage of organisms was observed beneath the abiotic surface. This community, developed as a green layer 1 mm below the surface, is dominated by cyanobacteria. A moss was also present. The organisms were studied by transmitted light, phase contrast and scanning electron microscopy, and isolated in cultures. The cyanobacteria belong to the genera Synechococcus and Chroococcidiopsis, and the moss was identified as Tortula muralis Hedw. The organic matter present in the green layer was characterized in terms of molecular components using analytical pyrolysis. Pyrolysis products from polysaccharides and proteins, and evaporation/pyrolysis products from lipids, comprise the vast majority of identified compounds. The identification of specific biomarkers such as 7-methylheptadecane is further evidence of the presence of cyanobacteria. Phytenes and phytadienes are indicative of phototrophic organisms, as they are pyrolysis products from chlorophylls.

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.

SULFATED CRUSTS: A MICROSCOPIC, INORGANIC AND ORGANIC ANALYSIS

Summary Black sulfated crusts are widely represented in the cathedral of Sevilla, a 15th century building. They are characterized by high gypsum contents, as evidenced by FT–IR, EDAX, X-ray diffraction and thin section analyses. The organic fraction, as revealed by flash evaporation/pyrolysis, consisted of a complex mixture of aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (including 0-, N-, and S-heterocyclics) and terpenoids. All these compounds are signatures of fossil fuel combustion. Only isoprenoid hydrocarbons are indicative of biological input.

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.

Mineral-Forming Processes at Canelobre Cave (Alicante, SE Spain)

Canelobre cave presents a remarkable collection of speleothems, such as stalactites, coralloids, stalagmites, flowstones, draperies, columns, helictites, gours, spars, crusts and flowers. Most of them are calcitic in composition, although sulphate speleothems have been found in some lower chambers in the cave. Gypsum speleothems appear as white uniform crusts or as flowers (antholites). The younger speleothems recognized in the cave corresponds to soda-straw stalactites, helictites and some active stalagmites. Vadose speleothems clearly prevail the phreatic ones, which are represented mainly by calcite spar deposits. Different mechanisms of speleothem formation can be recognized in the cave: dripping or flowing water, seepage, capillarity, etc. The parameters that control the speleothem deposition are the characteristics of karstic waters and the cave microclimate.

DEGRADATION OF BUILDING MATERIALS OF THE TOLEDO CATHEDRAL (SPAIN)

The Toledo Cathedral was built with different types of stones (mainly granites and carbonates) which display varied weathering features. It is concluded that rock degradation induced by pollution is weak. The alteration has been mainly due to climatic controlled factors, such as humidity, thermal changes and frosting. These processes resulted in scaling of the stone blocks, alteration of the granite texture to sand, and the development of discontinuities within the rocks.