Paleoflood events recorded by speleothems in caves

Speleothems are usually composed of thin layers of calcite (or aragonite). However, cemented detrital materials interlayered between laminae of speleothemic carbonate have been also observed in many caves. Flowstones comprising discontinuous carbonate layers form due to flowing water films, while flood events introduce fluviokarstic sediments in caves that, on occasion, are recorded as clayey layers inside flowstones and stalagmites. This record provides a potential means of understanding the frequency of palaeofloods using cave records. In this work, we investigate the origin of this type of detrital deposit in El Soplao Cave (Northern Spain). The age of the lowest aragonite layer of a flowstone reveals that the earliest flood period occurred before 500 ka, though most of the flowstone formed between 422 +69/‐43 ka and 400 +66/‐42 ka. This suggests that the cave was periodically affected by palaeoflood events that introduced detrital sediments from the surface as a result of occasional extreme rainfall events, especially at around 400 ka. The mineralogical data enable an evolutionary model for this flowstone to be generated based on the alternation of flood events with laminar flows and carbonate layers precipitation that can be extrapolated to other caves in which detrital sediments inside speleothems have been found. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessing precision and accuracy of atmospheric emission inventories

Assuming that state-of-the-art air quality models are accurate, then the precision and accuracy of their results directly depend on the precision and accuracy of their geographical, meteorological and emission input data. There are important applications, such as open pit mining, in which emission data are the main source of uncertainty. In such cases, historical air quality experimental data are typically available. The present work proposes a backward air quality simulation approach to assess the accuracy of emission inventories for these applications, with the goal of identifying sources that are over or underestimated. This approach consists of finding constants of the linear combination of the estimated emission that maximize R ² and make the slope equal to one in the linear correlation analysis when the results from the air quality model are compared to the experimental measurements of air quality. This methodology was applied to the case of the mining region in northern Colombia. As one of the largest open pit coal mining regions in the world, this region consists of seven independent mines with no relevant additional sources of emission. Use of the proposed methodology allowed quantification of the amount by which companies over or underestimated their emission, as well as quantification of uncertainties due to sources not considered in the model but that locally affect each monitoring station.     

Regional retrograde alteration of sub-greenschist facies chlorite to smectite

Dioctahedral smectite is present as a retrograde alteration product of chlorite in Permian-Triassic red slates of the Malaguide Complex in Sierra de Espuña (Betic Cordillera). Mineral assemblages and textures, illite crystallinity indices, and fluid inclusion data indicate sub-greenschist facies conditions that reached at least 180°C in the higher-grade tectonic unit of the Malaguide Complex, preceding formation of smectite. Smectite, having K as the dominant interlayer cation, occurs ubiquitously intercalated with trioctahedral chlorite as thin packets of layers and as individual layers that commonly change to chlorite along layers. Although some chlorite is typically homogeneous and trioctahedral, much chlorite shows signs of alteration and has compositions corresponding to different degrees of smectite contaimination. The incompatibility of metamorphic grade with the occurrence of smectite, the general association of chlorite and smectite, and the textural relations collectively show that dioctahedral smectite is derived through replacement of trioctahedral chlorite. Such replacement occurs on a regional basis and demonstrates that caution must be used in interpreting the occurrence of smectite in pelites as being due to prograde processes. Alteration of trioctahedral chlorite under oxidizing conditions due to introduction of phreatic water after uplift of the Betic Cordillera is proposed as the cause of formation of smectite.     

Evolution of the Cañadas edifice and its implications for the origin of the Cañadas Caldera (Tenerife, Canary Islands)

The volcano-stratigraphic and geochronologic data presented in this work show that the Tenerife central zone has been occupied during the last 3 Ma by shield or central composite volcanoes which reached more than 3000 m in height. The last volcanic system, the presently active Teide-Pico Viejo Complex began to form approximately 150 ka ago. The first Cañadas Edifice (CE) volcanic activity took place between about 3.5 Ma and 2.7 Ma. The CE-I is formed mainly by basalts, trachybasalts and trachytes. The remains of this phase outcrop in the Cañadas Wall (CW) sectors of La Angostura (3.5–3.0 Ma and 3.0–2.7 Ma), Boca de Tauce (3.0 Ma), and in the bottom of some external radial ravines (3.5 Ma). The position of its main emission center was located in the central part of the CC. The volcano could have reached 3000 m in height. This edifice underwent a partial destruction by failure and flank collapse, forming debris-avalanches during the 2.6–2.3 Ma period. The debris-avalanche deposits can be seen in the most distal zones in the N flank of the CE-I (Tigaiga Breccia). A new volcanic phase, whose deposits overlie the remains of CE-I and the former debris-avalanche deposits, constituted a new volcanic edifice, the CE-II. The dyke directions analysis and the morphological reconstruction suggest that the CE-II center was situated somewhat westward of the CE-I, reaching some 3200 m in height. The CE-II formations are well exposed on the CW, especially at the El Cedro (2.3–2.00 Ma) sector. They are also frequent in the S flank of the edifice (2.25–1.89 Ma) in Tejina (2.5–1.87 Ma) as well as in the Tigaiga massif to the N (2.23 Ma). During the last periods of activity of CE-II, important explosive eruptions took place forming ignimbrites, pyroclastic flows, and fall deposits of trachytic composition. Their ages vary between 1.5 and 1.6 Ma (Adeje ignimbrites, to the W). In the CW, the Upper Ucanca phonolitic Unit (1.4 Ma) could be the last main episode of the CE-II. Afterwards, the Cañadas III phase began. It is well represented in the CW sectors of Tigaiga (1.1 Ma–0.27 Ma), Las Pilas (1.03 Ma–0.78 Ma), Diego Hernández (0.54 Ma–0.17 Ma) and Guajara (1.1 Ma–0.7 Ma). The materials of this edifice are also found in the SE flank. These materials are trachybasaltic lava-flows and abundant phonolitic lava and pyroclastic flows (0.6 Ma–0.5 Ma) associated with abundant plinian falls. The CE-III was essentially built between 0.9 and 0.2 Ma, a period when the volcanic activity was also intense in the ‘Dorsal Edifice' situated in the easterly wing of Tenerife. The so called ‘valleys' of La Orotava and Güimar, transversals to the ridge axis, also formed during this period. In the central part of Tenerife, the CE-III completed its evolution with an explosive deposit resting on the top of the CE, for which ages from 0.173 to 0.13 Ma have been obtained. The CC age must be younger due to the fact that the present caldera scarp cuts these deposits. On the controversial origin of the CC (central vertical collapse vs. repeated flank failure and lateral collapse of mature volcanic edifices), the data discussed in this paper favor the second hypothesis. Clearly several debris-avalanche type events exist in the history of the volcano but most of the deposits are now under the sea. The caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent Teide-Pico Viejo volcanoes.     

Evolution of fluid geochemistry at the Turrialba volcano (Costa Rica) from 1998 to 2008

Turrialba (10°02′N, 83°45′W) is a 3,349-m high stratovolcano belonging to the Holocene “Cordillera Central” volcanic belt of Costa Rica. The summit consists of three EW-oriented craters (East, Central, and West). Since its last eruptive phase (1864–1866), the Central and West craters have displayed modest fumarolic activity, with outlet temperatures clustering around 90°C. In 2001, seismic swarms, ground deformation, and increasing fumarolic activity occurred. From 2005 to 2008, new fumarolic vents opened between and within the Central and West craters, and along the western and southwestern outer flanks of the volcanic edifice. These physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages: (1) hydrothermal (from 1998 to autumn 2001), characterized by the presence of H₂O, CO₂, H₂S, and, to a very minor extent, HCl and HF; (2) hydrothermal/magmatic (autumn 2001–2007), with the appearance of SO₂ and a significant increase of HCl and HF; and (3) magmatic-dominated (2007–2008), characterized by increased SO₂ content, SO₂/H₂S > 100, and temperatures up to 282°C. Accordingly, gas equilibrium in the CO₂-CH₄-H₂ system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions. The chemical–physical modifications of Turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems. Nevertheless, the risk of rejuvenation of the volcanic activity cannot be excluded, and an appropriate seismic, ground deformation, and geochemical monitoring program is highly recommended. Turrialba lies at a distance of 35 and 15 km from San José and Cartago, respectively, the two largest cities in Costa Rica.     

An environmental snapshot of the Bølling interstadial in Southern Iberia

The Bølling–Allerød interstadial is the closest warm time period to the Holocene. The study of the climate variability during this most recent warm scenario provides a natural record of potential environmental changes related with global temperature variations. Little is known about this interstadial in the Southern Iberian Peninsula. Therefore, the exceptional climatic record of the Otiñar paleo-lake (ca. 14.5–14.0 cal ka BP), provides environmental information about the first part of this interstadial (Bølling) in this key region. Although the studied high-resolution isotopic record point to almost invariant hydrological conditions in the paleo-lake, with little change in the carbon budget and important limestone dissolution, the pollen record shows an increase in forest species that can be interpreted as a warming trend and an increase in humidity during the Bølling in the area. This record is one of the few continental archives that show this climatic trend in Southern Iberia, agreeing with many other regional records from the western Mediterranean. This does not agree with higher latitude records that show an opposite trend. This opposite pattern in precipitation between the western Mediterranean and more northern latitudes could be explained by a persistent and increasing negative NAO mode during the Bølling in this area.     

Experimental study of the effect of pH and temperature on the kinetics of montmorillonite dissolution

The effect of pH on the kinetics of smectite (K-montmorillonite) dissolution was investigated at 50 and 70 °C in stirred flow-through reactors over the pH range of 1-13.5. Experiments done at very acidic and very basic pH were far from equilibrium. Near neutral pH experiments were closer to equilibrium. The Al/Si release ratio, while initially being incongruent, ultimately approached the stoichiometric value in most of the experiments. Temperature, extreme pH, and time favor congruency. Rates can be described by:

     

Assessment of nitrate contamination risk: The Italian experience

The purpose of this study is to show the results of the Italian research project of national interest (PRIN) launched in 2006 and finished in 2008, concerning the “assessment of groundwater contamination risk by nitrates assessment”. The project verified the IPNOA method for nitrate groundwater contamination risk assessment in four test-sites of Italy. The IPNOA is a parametric index which assesses the potential hazard of nitrate contamination originating from agriculture on a regional scale. The method integrates two categories of parameters: the hazard factors (HF), which represent all farming activities that cause, or might cause, an impact on soil quality in terms of nitrate (use of fertilisers, application of livestock and poultry manure, food industry wastewater and urban sludge), and the control factors (CF) which adapt the hazard factors to the characteristics of the site (geographical location, climatic conditions and agronomic practices). Finally, the Potential Risk Map is obtained by coupling the potential hazard of nitrate pollution (IPNOA) and the aquifer Contamination Vulnerability Map. The project was carried out by five Research Units (RU) from the Politecnico di Torino, Universities of Piacenza, Florence, Naples and Palermo. The geochemistry of groundwaters from the four test-sites was studied to determine the distribution of nitrate, and to evaluate groundwater chemical facies. All the study areas are affected by groundwater nitrate contamination and often by hydrogeochemical peculiarities. In some cases isotopic study, δ¹⁸O–NO₃δ¹⁵N–NO₃, allowed to differentiate nitrates of chemical fertilisers from those of biological origin, as well as denitrification processes.     

Volcanic complexes in the eastern ridge of the Canary Islands: the Miocene activity of the island of Fuerteventura

Fuerteventura has been since early stages of its growth the result of three different adjacent large volcanic complexes: Southern, Central and Northern. The definition of these volcanic complexes and their respective growing episodes is based on volcano-stratigraphic, morphological and structural criteria, particularly radial dyke swarms. Each complex has its own prolonged history that might be longer than 10 m.y. During that time, several periods of activity alternating with gaps accompanied by important erosion took place. The evolution of each volcanic complex has been partially independent but all the three are affected by at least three Miocene tectonic phases that controlled considerably their activity. The volcanic complexes are deeply eroded and partially submerged. In the core of the Northern and the Central volcanic complexes there is a set of submarine and plutonic rocks intensely traversed by a dyke swarm, known as the Basal Complex. The Basal Complex has been interpreted in different ways but all previous authors have considered it to be prior to the subaerial shield stage of the island. Here we advance the idea that the Basal Complex represent the submarine growing stage of the volcanic complexes and the hypabyssal roots (plutons and dykes) of their successive subaerial growing episodes.Two seamounts situated nearby, southwest of the island, might be interpreted as remains of two other major volcanoes. These two volcanoes, together with those forming the present emerged island of Fuerteventura, and finally those of Famara and Los Ajaches situated further north on Lanzarote constitute a chain of volcanoes located along a lineation which is subparallel to the northwestern African coastline and which may relate to early Atlantic spreading trends in the area.     

Mechanics of low-angle normal faulting: An example from Roosevelt Hot Springs geothermal area, Utah

Roosevelt Hot Springs geothermal area is located in the Mineral Mountains of southern Utah. The geothermal reservoir is formed by systems of faults and joints in Cenozoic plutonic and Precambrian metamorphic rocks. Low-angle denudation faults, dipping between 5° and 35° to the west, form an important component of the reservoir's structure. These faults developed simultaneously with steeply dipping faults that dissect the low-angle fault plates and merge into denudation faults at depth.Gently westward dipping joints provided planes of weakness along which the denudation faults nucleated. The average coefficient of sliding friction along the faults was less than 0.5 and probably ranged between 0.15 and 0.4. The maximum depth for formation of the denudation faults was estimated as 5 km. Hydrothermally altered cataclasite preserved in the fault zones indicates that faulting occurred under brittle conditions in the presence of chemically reactive fluids. The hydrothermal alteration may have significantly reduced friction in the fault zones.Hydrothermal alteration along fractures in the present geothermal reservoir is similar to that observed in the exhumed denudation faults, indicating that the frictional resistance along faults and joints in the reservoir could be significantly lower than along similar structures in unaltered granitic rock. Studies of the structural stability of the reservoir as a consequence of fluid withdrawal and reinjection should consider possible mechanical effects of this hydrothermal alteration.