Weathering Of Crystalline Rocks Research Articles

Temporal and Seasonal Variations of Silicate Svratka River and Sediment Characterization, Czech Republic: Geochemical and Stable Isotopic Approach

This study investigated weathering and hydrobiogeochemical processes in a silicate dominated watershed (Svratka river) in the Czech Republic in comparison with nearby carbonate dominated catchments. Elemental and isotopic analysis of river waters, particulates and sediments provided a more holistic view of weathering contributions, anthropogenic contamination, biological activity and evasion or sinks of CO2 to the atmosphere. In water samples, we determined total alkalinity after Gran 1974, and cations and anions were determined with inductively coupled plasma–optical emission spectrometer and ion chromatograph. δ13CDIC in water samples was determined with isotope ratio mass spectrometer. pCO2 and saturation indexes of calcite and dolomite were calculated with PHREEQC speciation program. Evasion fluxes were calculated after Broecker, 1974. Isotopic composition of carbon and nitrogen in particulate matter and sediments were determined with isotope ratio mass spectrometer. Mineral composition of sediments was determined with XRD method and elements with XRF method. Further enrichment factors of elements were calculated. The Svratka river, which is the major tributary of the Dyje river, is dominated by Ca2+ > Na+ > Mg2+ > K+ and HCO3− (as total alkalinity). Partial pressure (pCO2) concentrations range from close to 0–572-fold of atmospheric pressure. Isotopic composition of carbon in dissolved inorganic carbon (δ13CDIC) value ranged from − 13.3 to − 8.0‰ reflecting degradation of organic matter and exchange with the atmosphere. Bicarbonate weathering intensity for the Svratka river at its mouth is 11.8 mol/(l⋅km2⋅s), more on par with silicate terrains and lower than nearby carbonate watersheds. Isotopic composition of carbon (δ13C) and isotopic composition of nitrogen (δ15N) values of river sediment reflect soil and temperate plant (C3 plant) values, while higher δ15N values could be attributed to application of organic fertilizers in lower reaches. The river sediments, which came from weathering of crystalline rocks, are dominated by silt size, geochemically less mature quartz, feldspar and muscovite particles. All the stream sediments examined revealed slightly increased amounts of Zn, Cu and Pb. However, using Al as the normalization element to calculate enrichment factors, Zn, Cu and Pb are only elevated downstream, related to industrial contamination. This study is important for local and global level since it deals with contribution of weathering rates and contribution of CO2 to the atmosphere in silicate watershed.

Evaluation of the geothermal effects caused by the weathering of crystalline rocks

Abstract The acquisition of a permeability high enough to constitute an aquifer in crystalline rocks is a result of physico-chemical weathering through the transformation of minerals by the chemical processes of oxidation and hydration. The volumetric changes resulting from hydration induce stresses that fracture unweathered rocks. These reactions are exothermic, suggesting that the heat produced may generate a geothermal signature and even some hydrothermal effects. This paper develops a simplified model of thermal disturbance related to exothermic hydration to determine the relevance of this potential thermal effect. The fundamental thermal parameter is the rate of heat production, which is the product of the heat generation per unit volume multiplied by the velocity of the propagation of the front. When the front velocity is c. ≤1 mm a −1 , the temperature disturbance is negligible. The thermal effect only becomes significant if propagation of the front is extremely rapid (several centimetres per year). This observation led to an investigation of the instantaneous value of the front propagation velocity. This parameter was evaluated using a physical model coupling diffusion and chemical reactions with rock fracturing. Such extreme front velocities were only reached in exceptional circumstances; in most common situations, the weathering of crystalline rocks does not cause geothermal effects.

Field Monitoring in Sample Sites: Hydrological Response of Slopes with Reference to Widespread Landslide Events

The field monitoring is an essential tool to define geotechnical model able to assess landslide stability conditions, with particular reference to the hydrological response of the slopes in presence of widespread landslide events — the occurrence of several landslides trough wide areas. The results relative to two sample sites, representative of study areas characterised by homogeneous geological elements and where field monitoring has been carried out for adequate time intervals, are illustrated in the paper. In particular, we consider an area with outcroppings formed by a sort of “melange structure” made up of blocks and fragments of phyllites, clays, shales, ect., in a prevalently clayey matrix (Lungro sample site), and an area where are present rocks and soils deriving from weathering of crystalline rocks (“Serra di Buda”, Acri, sample site). In the Lungro sample site a piezometer monitoring network and a rain gauge give indications about the hydrological response of the slopes in an urban area; in the “Serra di Buda” sample site the piezometer levels measured for a long time period, and the rainfall, permit to identify some relationships between the cumulative rainfall and the piezometric levels. Values of cumulative rainfall of about 700mm on 120 days represent a necessary, but not sufficient, condition for critical stability conditions in the considered sample sites, in relation to possible scenarios of widespread landslide events.

Chemical and ecological evolution of the Miocene Ries impact crater lake, Germany: A reinterpretation based on the Enkingen (SUBO 18) drill core

Scientific drilling conducted at the inner slope of the Miocene central Ries impact crater recovered a partial section of crater lake sediments. Four sequences were recovered, composed of suevite-derived sandstones, thin lignite seams, bituminous shales, and marlstones to claystones. These flooding-evaporation sequences reflect the impact of short-term climatic fluctuations on a hydrologically closed basin. The superimposed trend from sequences rich in bituminous shales in the lower parts of the section to sequences dominated by organic-poor claystones and intercalated lignites in the upper parts of the section resembles that of the 300-m-thick central crater basin succession, which has previously been considered to reflect a climate-controlled development from an alkaline saline lake to a freshwater lake with temporary coal swamps. In the sediment core of Enkingen, however, the change from bituminous shales to organic-poor claystones with intercalated lignites is associated with a general increase in salinity, as indicated by (1) palynomorphs, (2) increase in δ13C of the lipid biomarker archaeol (bis-O-phytanylglycerol), and (3) the occurrence of 13C-enriched C20/C25-archaeol (O-phytanyl-O-sesterterpanylglycerol) specific to halophilic Archaea. In addition, the unidirectional trend in 87Sr/86Sr of carbonates, declining from ratios of Variscan basement rocks toward marine ratios, indicates a change from (1) weathering of crystalline rocks and suevite to (2) ejected Jurassic sediments (Bunte Breccia) in the catchment area as the major source of ion influx to the lake. From that trend, a change in lake water composition and a general increase in ion concentrations are inferred. These new results can be applied to a reassessment of major parts of the lacustrine succession of the Ries crater. We use these data to propose a new hypothetical model for the chemical and ecological evolution of the Ries crater lake: (1) After the establishment of a stratified brackish eutrophic soda lake due to silicate weathering and evaporation, the increasing influx of waters from the Bunte Breccia carbonate and authigenic silicate precipitation led to a mesotrophic halite lake with marine-like ion ratios and concentrations. (2) Further increase in ions, among them Mg2+ and Sr2+, resulted in hypersaline conditions with gypsum precipitation, low primary production, and phreatic Sr-rich dolomitization in marginal carbonates. (3) The final, sudden change to oligotrophic freshwater conditions is explained by the formation of an outlet late in the lake history. We conclude that the chemical and ecological evolution of the Ries lake therefore appears to have been mainly controlled by the weathering history of the catchment area, with climate fluctuations causing superimposed cycles. Similarly, changes in terrestrial palynomorph associations may at least partly reflect a change in soil types in the catchment area, from fertile, moist soils on suevite to dry karst soils and soils on Bunte Breccia. These interpretations imply that the initial suevite blanket of the Ries crater was much more continuous and widespread than previously assumed.

Halloysite-to-kaolinite transformation by dissolution and recrystallization during weathering of crystalline rocks

AbstractThe present study, which was carried out on a deep weathering profile of quartz diorite in the San'in district, Japan, along with two lateritic samples from India and Sri Lanka, provides convincing evidence supporting the dissolution and recrystallization mechanism for the halloysite-to-kaolinite transformation during weathering of crystalline rocks. In all the samples studied, tubular halloysite formed prior to kaolinite via the dissolution of feldspars and precipitation from solution. The crystal size distribution of tubular halloysite formed early was characterized by a lognormal curve having a positive asymmetry. When the activity of water decreased in the weathering profile, halloysite as well as goethite began to dehydrate, which acted as a trigger for dissolving halloysite. The heterogeneous nucleation of kaolinite took place on the edges and in the shrinkage pores of dehydrated halloysite tubes. The topotactic relationship of b*halloysite//b*kaolinite was kept between the substrate halloysite and the product kaolinite in the incipient growing stages of kaolinite. As a consequence, early formed halloysite transforms to kaolinite in a cannibalistic manner over a long period of time, owing to the intermittent supply of solution undersaturated with respect to halloysite in natural open systems.

Discussion of the Occurrence and Origin of Sedimentary Palygorskite-Sepiolite Deposits

AbstractMarine and non-marine palygorskite-sepiolite deposits are found throughout the world and occur interbedded with chert, dolomite, limestone, phosphates and other non-detrital sedimentary rocks. The origin of these high-magnesium clays has long been attributed to either alteration of volcanic ash or the structural transformation of smectite clays. More recently, others have argued origin by direct crystallization (neo-formation). Recent laboratory studies support this latter concept, particularly in environments where the concentration of alumina is low, the silica concentration high, and the pH alkaline. Such an origin is proposed for the Georgia-Florida deposits in southeastern United States, since major obstacles exist against formation by alteration of volcanic ash or by transformation of smectites. Lateritic weathering during the Miocene would have favored direct precipitation of these clays in the shallow, marginal seas. The basinward increase in the MgO: Al2O3 ratio is further support.Deep weathering of crystalline rocks in northern British Honduras and Guatemala would have produced similar high silica, low alumina conditions on the adjacent submerged Yucatan Platform during the late Tertiary. The seaward increase in the MgO: A12O3 ratio, the lack of associated detrital constituents, and the absence of associated smectites strongly indicate a similar origin by direct crystallization of these Yucatan palygorskite-sepiolite clays.Some occurrences of palygorskite and sepiolite may well be related to the alteration of smectite clays or volcanic ash. However, many of the large sedimentary deposits are more probably the result of direct crystallization adjacent to areas undergoing tropical or subtropical weathering.