Neoformation Of Clay Minerals Research Articles

Diagênese de Arenitos do Grupo Bauru no Estado de São Paulo

In the state of São Paulo, the Bauru Group units cover about 47% of the territory, constituting an aquifer of great interest, in particular for public watersupply. In this study, core samples were taken for petrographic and diagenetic characterization of different units, seeking to improve the knowledge of the Bauru Aquifer System. The samples were submitted to analysis by optical microscopy and scanning electron microscopy. The units of this aquifer system are mostly subarkoses (67% of the samples), except the Marilia Formation, which is composed of sublitharenite and quartzarenite. These sandstones were submitted to shallow and low-intensity diagenesis. The main diagenetic phases identified were dissolution of the detrital minerals, notably feldspar and pyroxene, neoformation of clay minerals, iron oxi-hydroxide, calcite and analcime. Locally there is precipitation of quartz, feldspar and titanium oxide.

Experimental constraints on Li isotope fractionation during the interaction between kaolinite and seawater

In this study, to better understand the factors controlling the concentration and isotope composition of lithium (Li) in the ocean, we investigated the behaviour of Li during interaction of kaolinite with artificial seawater. Dissolution of kaolinite in Li-free seawater at acidic conditions (exp. 1) results in a strong preferential release of light Li isotopes, with △7Liaq-kaol ∼ −19‰, likely reflecting both the preferential breaking of 6LiO bonds over 7LiO bonds and the release of Li from the isotopically lighter AlO6 octahedral sites. Sorption experiments on kaolinite (exp. 2) revealed a partition coefficient between kaolinite and fluid of up to 28, and an isotopic fractionation of −24‰. Thermodynamic calculation indicates authigenic smectites formed from the dissolution of kaolinite in seawater at pH 8.4 (exp. 3). The formation of authigenic phase strongly removed Li from the solution (with a partition coefficient between the solid and the fluid equal to 89) and led to an increase of ca. 25‰ in seawater δ7Li. This fractionation can be described by a Rayleigh fractionation model at the early stage of the experiment during rapid clay precipitation, followed, at longer reaction time, by equilibrium isotope fractionation during the much slower removal of aqueous Li via co-precipitation and adsorption. Both processes are consistent with a fractionation factor between the solid and the aqueous solution of ∼−20‰. These experiments have implications for interpreting the Li isotopic composition of both continental and marine waters. For instance, the preferential release of 6Li observed during kaolinite far-from-equilibrium dissolution could explain the transient enrichments in 6Li observed in soil profiles. With regard to the evolution of seawater δ7Li over geological time scales, our experimental results suggest that detrital material discharged by rivers to the ocean and ensuing “reverse chemical weathering” have the potential to strongly impact the isotopic signature of the ocean through the neoformation of clay minerals.

Unraveling Multiple Thermotectonic Events Accommodated by Crustal‐Scale Faults in Northern Iberia, Spain: Insights From K‐Ar Dating of Clay Gouges

AbstractLarge‐scale faults in the continental crust are significant features that control the evolution of sedimentary basins and intraplate mountain chains. Deciphering their evolution is a significant task because faults slip and reactivate in a variety of geological settings. In this work, clay gouges of two major orogen‐scale, long‐lived faults in northern Iberia, the Río Grío and Vallès‐Penedès Faults, were investigated by X‐ray diffraction and K‐Ar isotopic analysis. Illite polytype determinations of 44 subfractions (from <0.1 to 10 μm) allowed us to discriminate between authigenic/synkinematic illite crystals formed during faulting and detrital illite crystals inherited from the host rock. K‐Ar dating provided a detailed set of ages corresponding to key stages of the thermotectonic evolution of the Iberian Plate: (a) the Permian to Late Triassic extensional/transtensional activity associated to the emplacement of Late Variscan magmatic bodies and hydrothermal mineralizations, (b) the opening of the Central Atlantic Rift during Late Triassic‐Early Jurassic times, (c) the Late Jurassic‐Early Cretaceous rifting that led to the development of Mesozoic extensional/transtensional basins in northern Iberia, (d) the final stage of the anticlockwise rotation of the Iberian Plate with respect to Eurasia and the accommodation of the first Pyrenean compressional pulses in Campanian time, and (e) the positive inversion of Mesozoic extensional basins due to far‐field stresses associated with the Alpine orogeny during the Paleogene. The results highlight that thermotectonic conditions characterized by high‐geothermal gradients strongly favor fault movement and neoformation of clay minerals in fault gouges, regardless of the prevailing tectonic regime.

Chemical and mineralogical composition of fluvial sediments (Bistrita River, Romania): Geogenic vs. anthropogenic input into rivers on its way through mining areas

The upper reaches of the Bistrita drainage system were selected as a natural test site to determine the geogenic and anthropogenic input into fluvio-lacustrine systems in humid mid-latitude morphoclimatic zones. The reason for this selection lies in the complex geology and its metallogenic evolution leading to a great variety of Fe, Mn, U, and polymetallic sulfides ore deposits. It sparked an intense mining activity during the past centuries with a strong impact on the drainage system similar to many mineralized sites in the world which are still under exploitation. Sediment samples from Bistrita River were analyzed by means of X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), near-infrared (NIR) and micro-Raman spectroscopy (μ-Raman).Our results revealed that the chemical and mineralogical built-up of the stream sediments is mainly geogenic, with most of the trace elements accumulated in the river sediments derived from the source rocks exposed in catchment area of the River Bistrita. A strong input by man has been detected in the drainage system near abandoned mining sites. The trace elements are mainly accommodated in the structure of detrital minerals representative of the clastic aureole around the source rocks, and to a lesser extent adsorbed onto the surface of clay minerals. The REE incorporated into muscovite furnish evidence of having derived from the source rocks, prevalently mica schists exposed by supergene processes in the provenance area and rule out a neoformation of clay minerals on transport and deposition.

Understanding the hydrogeochemical evolution of groundwater in Precambrian basement aquifers: A case study of Bugesera region in Burundi

This study investigates hydrogeochemical processes controlling groundwater evolution in a Precambrian basement aquifer situated in northeastern Burundi, in Bugesera region. The hydrogeochemistry has been evaluated based on the analytical results of 143 water samples comprising 66 samples from shallow wells, 61 samples from springs, and 16 samples from the shallow lakes. While the stability diagrams, the evolutionary sequence of groundwater inferred from the Piper diagram and bivariate plots highlight the weathering of aluminosilicates as the primary process controlling groundwater chemistry in this aquifer, the increasing trend of chloride levels between the highlands (recharge area) and the depression of Bugesera (discharge area) and the random distribution of high nitrate content even in water samples from springs suggest that additional processes such as evaporative concentration and anthropogenic pollution play a secondary role in the hydrogeochemical evolution of groundwater. The spatial distribution of different hydrogeochemical parameters shows a general increasing trend from the highlands where water samples, mainly from springs, show low mineralisation (TDS=26–152mg/l) and low pH (field pH=4.6–6.6), towards the depression of Bugesera where higher values of mineralisation (TDS=44–3229mg/l) and pH (field pH=5.6–7.7) are observed. The overriding control of aluminosilicates weathering on the hydrogeochemical evolution of groundwater in Bugesera region is clearly demonstrated by the predominance of NaHCO3 and CaHCO3 water types and the cross-plots which show an increasing trend of alkaline and alkaline earth cations (Na++K++Ca2++Mg2+) released from the weathering of aluminosilicates along the flow line. Moreover, the poor correlation between the concentrations of SiO2 and Na+, Ca2+, Mg2+, K+, HCO3– and TDS reflects the incongruent character of the weathering of aluminosilicates which causes part of the silica released from the weathering of silicates to be taken up into the neoformation of clay minerals. The anthropogenic pollution is reflected by the occurrence of NaNO3, CaNO3, KNO3 and NaSO4 types even in spring water.

Development of Fe-rich clay minerals in a weathering profile derived from serpentinized ultramafic rock in Nui Nua massif, Vietnam

We investigated the chemical and mineralogical characteristics of a weathering profile of the Nui Nua serpentinized ultramafic-mafic massif (Thanh Hoa Province, Vietnam) using TEM-EDX, XRD, and FT-IR methods to understand the effects of monsoon climate conditions on weathering processes and clay minerals, especially transformation and neoformation of clay minerals. Clay minerals of this profile were characterized by a temporariness of serpentine clay minerals though chlorite seemed to be stable and increased from the bottom layer to the top layer. The nature of Fe changed rapidly from ferrous Fe (close to parent rocks) to ferric Fe and additionally it was incorporated into the octahedral sheet of dioctahedral smectite. Consequently, a Fe-rich smectite formed at the beginning of the weathering process and was detected as a dominant phase in the clay fraction of the profile. This phase was later transformed progressively to Al-rich smectite because of Fe-oxidation and corresponding Si-mitigation. Chemically, the contents of Fe and Mg reduced from the bottom layer to the top layer but Al developed vice versa. Magnetite in top layer was formed by bacterial activities. The transformations of clay minerals were controlled strongly by leaching conditions in the weathering system and by the effects of oxidation of Fe (Fe2+→Fe3+) on clay minerals paragenesis.

Pedodiagenetic Characterization of Cretaceous Paleosols in Southwest Minas Gerais, Brazil

ABSTRACT The influence of post-burial geological processes on preserving pedogenic properties has great importance in identifying ancient paleosols both in the field and in a laboratory. However there are not many publications that focus on characterizing paleosol diagenesis. As temperature and pressure progressively increase, evidence of pedogenesis is modified and destroyed, hindering paleoenvironment characterization and interpretation. This paper discusses diagenetic evidence and its relation to strictly pedogenic features, like structure, cements, nodules, and neoformation of clay minerals using the carbonate paleosols of the Marilia Formation in the upper unit of the Bauru Basin as a case study. Despite the long geotectonic and thermal history of the Marilia Fomation, paleosols bring us pedogenic evidence that can undergo micromorphological analyses, such as cementation, clay illuviation, bioturbation, and ped structures. The results of analyses in 25 paleopedogenic horizons indicate that the paleotopographic features were responsible for distribution of the diagenetic processes and preservation of the paleosol properties. The maturity of those paleosols controls lithification. In mature paleosols that developed in more stable portions of the landscape, characteristics such as carbonate cementation and development of pedogenic structures are the main factors that inhibit diagenesis. However diagenetic processes that influence poorly-developed paleosols are controlled by depositional characteristics and by changes in the water table, enabling more advanced diagenetic processes, compared to mature paleosols.

Volcanic soil formation in Calabria (southern Italy): The Cecita Lake geosol in the late Quaternary geomorphological evolution of the Sila uplands

This paper focuses on the main morphological, physical, chemical and mineralogical features of an andic-like soil, widely outcropping in the Sila upland plateau of Calabria (southern Italy), and its potential role in tephrostratigraphy. A multidisciplinary and multiscale approach allowed identification of this soil as a “masked” distal archive of volcanic products, developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis. The study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence, limited extent or poor preservation of primary eruptive products. The soil has an Andisol-like appearance, despite laboratory data that do not match the entire suite of diagnostic criteria for the Andisol taxonomic order. Geomorphological, stratigraphic and pedologic results, coupled with tephrostratigraphic and radiometric data, concur to suggest a Late Pleistocene(?) to Holocene age of the Andisol-like soil. In particular, the rhyolitic chemical composition of small-sized glass fragments (identified by SEM–EDS analyses) indicates soil genesis contributed by volcanic ash, probably sourced from Aeolian Arc explosive activity spanning the last 30 ka. Accordingly, the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties (in turn related to the neoformation of clay minerals from the weathering of volcanic glass) are consistent with a climatic shift from a seasonally-contrasted to a constantly humid pedoenvironment. This change can be ascribed to the Lateglacial(?) or Early–Middle Holocene to Late Holocene transition. Calibrated AMS 14C dates performed on charcoal fragments sampled from three representative soil profiles, provide Late Holocene ages (3136 ± 19, 343 ± 16 and 92 ± 24 yr BP), in accord with archaeological finds. On the basis of the consistent stratigraphic position, lateral continuity and wide extent, the soil can be considered a good pedostratigraphic marker in the Sila highlands and is informally defined as the “Cecita Lake geosol”. It supplies valuable time constraints for the underlying (occasionally overlying) deposits and/or soils. Moreover, it allows regional-scale morphostratigraphic correlations and detailed reconstruction of Late Pleistocene–Holocene geomorphic events in Calabria, a very suitable region for distal tephra deposition in the central Mediterranean peri-volcanic area. The effects of high-energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals.

Weathering of gneiss in Calabria, Southern Italy

The effects of weathering in a Mediterranean climate on the mineralogy and microfabric of Paleozoic gneiss of the Sila Massif, Calabria, southern Italy, have been studied. Field observations show highly weathered rock forms a residual soil. Micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages, having two distinct rock microfabrics. In the first stage, the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing, and large portions of the rock remain unaltered. The second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals. This latter stage occurs along both compositional and microstructural discontinuities, with etch pitting of feldspar, and neoformation of clay minerals and ferruginous products replacing feldspar, biotite, and iron-bearing garnet. The determination of quantitative petrographic indices provides a measure of the various stages of weathering.

Sources of strontium and calcium in desert soil and calcrete

The carbon-cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals. In the petrocalcic horizon (calcrete) of a Pleistocene soil from the USDA–SCS Desert Project area near Las Cruces, NM, approximately 1.5 g Ca/cm 3 has been added, with an associated expansion of the profile of ∼200%. Strontium isotope values for the labile cations and carbonate from the A, B and K soil horizons have 87Sr/ 86Sr values that range from 0.7087 to 0.7093, similar to the values for easily soluble local dust and rain. The parent material, non-calcareous Camp Rice alluvial sediment, has a 87Sr/ 86Sr ratio of ∼0.7165. Mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of ∼94%; the more likely scenarios indicate at least 98% of the Ca originated from atmospheric input. The variations in 87Sr/ 86Sr ratios of soil silicate (0.7131 to 0.7173) are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon. Moreover, the Sr isotope data suggest that 50–70% of silicate in the uppermost 25 cm of the profile could be atmosphere-derived. The isotopic composition of labile strontium in the A horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering. Steady-state models of the whole profile yield a Sr weathering flux ranging from ∼200 to 400 μg cm −2 Ma −1. The results indicate that both the present-day and long-term contribution of calcium from silicate weathering is less than 2% of that supplied from the atmosphere, and confirm that desert soil formation is not a significant sink for atmospheric carbon.

Relative ages of loess and till in two Quaternary palaeosols in Gorges Valley, Mount Kenya, East Africa

Two compound palaeosol profiles formed in loess and till were studied in the oldest early Quaternary end moraine (Gorges age) system on Mount Kenya. Although both tills appear to have similar weathering histories, the overlying loessic sediments, serving as secondary parent materials for the palaeosols, are considered to have different ages on the basis of colour, presence or absence of clay films, and field texture (especially percentage of silt). Palaeomagnetic determinations showed both tills to have reversed remanent magnetism, suggesting that they were emplaced during the Matuyama Chron. The overlying loessic sediments in profiles GOR55 and GOR58 show normal magnetism and grade upward into the lower zone of bioturbation in the A horizon complex. However, in GOR58 the surface loessic sediments have normal remanent magnetism with considerable secular variations, suggesting it was emplaced over a longer time frame during the Brunhes Chron (i.e. < 0.78 Ma). Profile GOR55 contains larger amounts of gibbsite, indicating more aggressive leaching over time, and an absence of secular magnetic variations suggests deposition over a shorter time interval. The study of volcanic feldspars and ash, using scanning electron microscopy, in the two profiles, shows that sand grain (63–250 μm) weathering is slightly different in the two tills; relative weathering effects (e.g. corrosion of grain surfaces and neoformation of clay minerals) are greater in profile GOR55 than in profile GOR58. Overall the data indicate that some sites in the lower tropical Afroalpine timberline environment may have aeolian covers that are considerably younger than the deposits they overlie. © 1997 by John Wiley & Sons, Ltd.

Characteristics of Clay Minerals in Saline Alkaline Soils in Alberta, Canada

AbstractThe stability of clay minerals in extremely saline alkaline soils is not well understood, but may be expected to differ from those in other soils due to differences in the geochemical environment. A survey of the clay mineralogy of surface horizons of 39 salt‐affected soils in Alberta, Canada, showed that many samples had unusual x‐ray diffraction characteristics in that essentially no basal reflections for smectite minerals were recorded. Four sites were subsequently selected for detailed mineralogical characterization. Extremely diffuse smectite diffraction maxima were found to occur primarily in the coarse clay fraction of surface soils, and appear to be the result of interaction with organic matter. After traditional pretreatments to remove organic matter and carbonates, the clay mineralogy of salt‐affected soils was found to be similar to nonsaline soils. Slight changes were sometimes noted in the diffraction maxima of the smectite minerals, possibly indicating lower crystallinity and layer charge. Tetrahedrally substituted smectites were not identified, while variable amounts of high‐charge smectite or vermiculite were detected in most samples. Despite very high ionic strengths and pH values as high as 10, little or no degradation of clay minerals appears to be occurring in these soils. Analysis of immiscibly displaced pore water indicated that the soil solutions were supersaturated with respect to common phyllosilicates. Relatively low amounts of fine clay, however, indicate that neoformation of clay minerals is unlikely.

Origin and Diagenesis of Clay Minerals in Relation to Sandstone Paragenesis: An Example in Eolian Dune Reservoirs and Associated Rocks, Permian Upper Part of the Minnelusa Formation, Powder River Basin, Wyoming

Eolian dune sandstones are the principal reservoir rocks in the Permian upper part of the Minnelusa Formation, Powder River basin, Wyoming. These sandstones formed as shorelines retreated and dunes migrated across siliciclastic sabkhas. Sandstones are mainly quartzarenites; on average, clay minerals constitute about 5 wt.% the whole rock. Although present in minor amounts, clay minerals play an important role in the diagenetic evolution of these sandstones. Allogenic clay minerals are present in shaly rock fragments and laminae. Early infiltration of clays into porous sabkha sands commonly form characteristic menisei or bridges between framework grains or, when more extensive, form coatings or rims on grain surfaces. Authigenic clays include nearly pure smectite, mixed-layer illite/smectite (I/S), and late diagenetic illite and corrensite; these clay minerals are present as pore-lining cements. In addition to the deposition and neoformation of clay minerals throughout sandstone paragenesis, the conversion of smectite to illite occurred as temperatures increased with progressive burial. A temperature of 103C is calculated at a present depth of 3,200 m using a geothermal gradient of 30C/km and a mean annual surface temperature of 7C. After correction for uplift and erosion (250 m), the maximum calculated temperature for the conversion of all random I/Smore » to ordered I/S is 100C. This calculated temperature is in excellent agreement with temperatures of 100-110C implied from I/S geothermometry.« less

Scanning electron microscopy of feldspar and volcanic glass weathering and neoformation of clay minerals in a quaternary paleosol sequence, Mount Kenya, East Africa

Volcanic glass, feldspar, magnetite, quartz, and trace amounts of other minerals (e.g. nepheline, biotite, amphibole) are the detrital components of the 63–250 μm sand fractions of the samples studied. Halloysite/metahalloysite, showing fibrous, tubular, platey and nodular shapes, and gibbsite (essentially nodular) occur as important weathering products. They formed essentially through weathering of volcanic glass reflecting the high precipitation and low evapotranspiration expected in a tropical bamboo forest as well as great amounts of time. Feldspar weathering occurs mainly as dissolution etching. The distribution of gibbsite and halloysite/metahalloysite are interpreted with regard to the paleoclimatic conditions under which the paleosols developed during pre-Teleki and Teleki/Liki interglacial periods.

Paleocene to lower Eocene clay sedimentation in the Bay of Biscay

A study of the mineralogy of red clay sequences overlying basalt in the Bay of Biscay revealed two successive units: unit one (lower unit) indicates that clay minerals are the result of subaerial weathering of acid or basic continental rocks, occurring in the Galice province (northwest Spain); and unit two (upper unit) consists of fine-grained particles which suggest distinct volcanic activity. Clay materials from the first unit (Paleocene) are deposited in shallow environments, whereas the second unit materials (lower Eocene) Occur in deeper environments followed by neoformation of clay Minerals and concentration of chemical elements (cobalt, nickel, lead, zinc, and barium).

Bestand, Umwandlung und Neubildung von Tonmineralen in küstennahen Sedimenten der Nordsee

Content, Transformation and Neoformation of Clay Minerals in near shore Sediments of the North SeaFrom literature and our own results, approximate quantitative values are given on the mineral content of clay and silt fractions of marine sediments from the Wadden Sea. Besides this, the extent of clay mineral transformation and neoformation in a marine environment is discussed.According to our knowledge, the extent of clay mineral transformation and neoformation must be unimportant because the sea water and pore solution of the sediments seems to be ‐ with the exception of a small Mg‐surplus — something like an equilibrium solution for three‐and fourlayer minerals, which neither favors a considerable base fixation nor base release. Therefore illite neoformation during halmyrolysis or early diagenesis seems to be impossible because of unfavourable relations of potassium to all other cations in the sea water. Obviously the neoformation of illite is connected with later diagenesis. The processes of clay mineral neoformation in a marine evironment are probably restricted to the formation of amorphous (Mg‐) Fe‐Si‐particles, which may be first steps in the formation of chamosites, chlorites or smectites.

Formation of glauconie in foraminiferal shells on the continental shelf off Norway

Glauconie inside shells of foraminifers, assumed to be formed during the timespan from the Last Glaciation to the present, is reported. The process is thought to take place at water temperatures of 6–7°C. The nature of the infilling process is suggested to be neoformation of clay minerals rather than transformation of pre-infilled clay.

The neoformation of clay minerals in brackish and marine environments

AbstractIt is suggested (1) that large amounts of Al, Fe and Si carried in solution by fresh water are chemically precipitated as hydroxide gels in the brackish water environment of estuaries and deltas, and (2) that these gels are subsequently deposited in both the brackish water environment and in the neighbouring seas, where they become parental material for the neoformation of clay minerals, and various other silicate and iron minerals. The types of neoformed minerals will depend upon both the composition of the parental gels and the physico-chemical milieu of their crystallization. Evidence is discussed supporting this hypothesis from the following sources (1) the concentrations of Al, Fe and Si dissolved in fresh water and in sea-water, (2) experimental work on the crystallization of alumino-siliceous gels, and (3) a study of the precipitation of Si from the waters of the Mississippi River delta.Because of the unusual sediment pattern of present times, this source of neoformed clay minerals and other minerals contributes only a small proportion of the sediments of the brackish parts of estuaries, deltas and the adjacent seas, which are dominated by fine-grained continental detritus. In earlier geological eras, when the world's river systems carried only relatively minor amounts of fine-grained continental detritus, this source of neoformed minerals is likely to have contributed a considerable proportion of the fine-grained sediments of these areas of sedimentation. Three possible examples are discussed.