Alluvial Formation Research Articles

Analog-based meandering channel simulation

Characterizing the complex geometries and the heterogeneity of the deposits in meandering river systems is a long-standing issue for the 3-D modeling of alluvial formations. Such deposits are important sources of accessible groundwater in alluvial aquifers throughout the world and also play a major role as hydrocarbons reservoirs. In this paper, we present a method to generate meandering river centerlines that are stochastic, geologically realistic, connected, and conditioned to local observations or global geomorphological characteristics. The method is based on fast 1-D multiple-point statistics in a transformed curvilinear domain: the succession in directions observed in a real-world meandering river (the analog) is considered as statistical model for multiple-point statistics simulation. The integration of local data is accomplished by an inverse procedure ensuring that the channels pass through a given set of locations while conserving the high-order spatial characteristics of an analog. The methodology is applied on seven real-world case studies. This work demonstrates the flexibility and the applicability of multiple-point statistics outside the standard paradigm that considers the simulation of a 2-D or 3-D variable with spatial coordinates.

Influence ofGuadua paraguayanaDöll on the structure and regeneration of a remaining forest at the high lands of Tibagi River, Paraná state

Tão logo detectada a invasão do bambu Guadua paraguayana na planície aluvial do rio Tibagi, Ponta Grossa-PR, buscou-se avaliar, por meio de levantamento fitossociológico e indicadores associados à estrutura e funcionamento de formações florestais, a agressividade e influência da espécie sobre a estrutura e regeneração de um remanescente de Floresta Ombrófila Mista Aluvial. O estudo fitossociológico consistiu na instalação de dezesseis parcelas (50 m²) para inventário dos indivíduos arbóreos com CAP ≥ 15 cm e dezesseis parcelas (4 m²) para estudo da regeneração natural. Os resultados atestam que a presença de G. paraguayan a na riqueza de espécies da floresta, mortalidade, número de indivíduos arbóreos, vitalidade dos indivíduos remanescentes, profusão de epífitos vasculares e avasculares, na regeneração natural e incidência de radiação no interior das parcelas, é significativa. Mas, apesar de as alterações provocadas por este bambu comprometerem a dinâmica de regeneração no remanescente, a espécie é apenas um agravante, não a causa da degradação ambiental. Abstract As soon as the bamboo’s invasion was diagnosed in the alluvial floodplain of Tibagi’s river, Ponta Grossa-PR, the study started evaluating, through phytosociological study and indicators associated with the structure and functioning of the forest, the aggression and influence of the bamboo species on the structure and regeneration of a subtropical ombrophilous alluvial forest remnant. The phytosociological study was developed by an installation of sixteen plots (50m²) to inventory all the trees with CBH ≥ 15 cm and sixteen other plots (4m²) for studying the regeneration: individuals with up to 1.30 m high. The results show that the effect of G. paraguayana in species richness, mortality and number of trees, vitality of the remaining trees, abundance of vascular and nonvascular epiphytes, regeneration and in the incidence of radiation inside the plots, is very significant. But even though the changes caused by this bamboo compromise the regeneration dynamics of alluvial formations in the high Tibagi’s areas, the species is only an aggravating and not the cause of environmental degradation.

Influence of ionic strength and soil characteristics on the behavior of Cryptosporidium oocysts in saturated porous media

The physico-chemical behavior of Cryptosporidium oocysts was investigated during their transfer through an alluvial formation from Les Cayes (Haiti) via batch tests. Five approximately 3kg soil samples were collected and combined prior to batch tests from the alluvial formations. The experiments were carried out at soil pH by equilibrating different ranges of pure oocysts concentrations and soil samples with 3mM CaCl2 and 1mM NaBr as electrolyte. We used the Debye–Hückel equation describing ion activity in a solution for a given ionic strength. The equilibrium adsorption mechanism is used to enumerate the oocysts in the soil. The results suggest that the oocysts behavior in porous media depends on soil characteristics such as soil pH, the nature of the mineral and organic constituents of the soil and the ionic strength and activities in solution. These results show that a total transfer in batch containing NaBr solutions against a partial one in batch containing CaCl2 solutions depends on the oocysts media concentration. To confirm the oocysts number retained in soil, confocal microscopy was successfully used and the images demonstrate that the majority of oocysts were retained at the range of concentrations tested. The findings from this study demonstrated that the retention of C. Parvum in soils may be influenced by chemical conditions and soils characteristics, which are important for groundwater risk assessment.

The role of diagenesis and depositional facies on pore system evolution in a Triassic outcrop analogue (SE Spain)

This study aims at unravelling the diagenetic history and its effect on the pore system evolution of the Triassic redbeds exposed in SE Spain (TIBEM11TIBEM Triassic redbeds of the Iberian Meseta.), an outcrop analogue of the TAGI (Trias Argilo-Gréseux Inférieur) reservoir (Berkine-Ghadames Basin, Algeria). Similar climatic, base level and tectonic conditions of aforementioned alluvial formations developed analogue fluvial facies stacking patterns. Furthermore, interplay of similar detrital composition and depositional facies in both formations resulted in analogue early diagenetic features. Petrographic observations indicate lithic subarkosic (floodplain facies) and subarkosic (braidplain facies) compositions which are considered suitable frameworks for potential reservoir rocks. Primary porosity is mainly reduced during early diagenesis through moderate mechanical compaction and formation of K-feldspar overgrowth, gypsum, dolomite and phyllosilicate cements. Early mesodiagenesis is testified by low chemical compaction and quartz cementation. Telodiagenetic calcite filling fractures and K-feldspar dissolution determined the final configuration of analysed sandstones. Mercury injection-capillary pressure technique reveals overbank deposits in the floodplain as the least suitable potential reservoirs because of their lowest open porosity (OP < 16%), permeability (k < 5 mD) and small dimensions. On the other hand, braidplain deposits show the highest values of such properties (OP up to 31.6% and k > 95 mD) and greater thickness and lateral continuity, so being considered the best potential reservoir. The accurate estimation of TIBEM microscale attributes can provide important input for appraisal and enhanced oil recovery performance in TAGI and in others reservoirs consisting on similar fluvial sandy facies.

Efecto del silicio y plaguicidas en la fertilidad del suelo y rendimiento del arroz.

The objective of this work was to evaluate theeffect of silicon on the soil fertility, the incidence of diseasesand insect pests, the yield and quality of rice grains, varietyCR 4477. The study was conducted in La Vega, Florencia,San Carlos, Costa Rica between May and Octuber in 2010and 2011 in the same field. Five treatments were established:silicon to soil, silicon to soil plus pesticides (chemical alternatives),silicon to foliage, silicon to foliage plus pesticidesand a commercial control. Sources were silicon powder at70% of SiO2 applied 15 days before sowing at a dose of 100kg SiO2/ha and 40% SiO2 and 36% MgO concentrated liquidapplied to the foliage at a dose of 4 l/ha at 17 and 30 daysafter planting. The soil was an alluvial formation inceptisolorder, and at the beginning of the experiment had a pH of4.9, P and Si values of 29 and 44.7 ppm respectively, exchangeableacidity 1.2 cmol(+)/l and base sum 19.11 cmol(+)/l.The results showed no effect of silicon in soil fertility, the incidenceof pests and diseases, and milling quality, except thatthe combination of silicon applied at soil and the pesticidesused increased the zinc and copper content in the soil, alsothe zinc and magnesium in the leaves of rice, but this effectdid not result in yield and grain quality. Results also suggestthat the use of pesticides positively influenced weight andpaddy yield (p ≤ 0.05).

Early evidence of Acheulean settlement in northwestern Europe--la Noira site, a 700,000 year-old occupation in the center of France.

The human settlement of Europe during Pleistocene times was sporadic and several stages have been recognized, both from paleaoanthropological and archaeological records. If the first phase of hominin occupation (as early as 1.4 Ma) seems mainly restricted to the southern part of the continent, the second phase, characterized by specific lithic tools (handaxes), is linked to Acheulean settlements and to the emergence of Homo heidelbergensis, the ancestor of Neanderthals. This phase reached northwestern Europe and is documented in numerous sites in Germany, Great Britain and northern France, generally after 600 ka.At la Noira (Brinay, Central France), the Middle Pleistocene alluvial formation of the Cher River covers an archaeological level associated with a slope deposit (diamicton). The lithic assemblage from this level includes Large Cutting Tools (LCTs), flakes and cores, associated with numerous millstone slabs. The lithic series is classified as Acheulean on the basis of both technological and typological analyses. Cryoturbation features indicate that the slope deposits and associated archaeological level were strongly frozen and disturbed after hominin occupation and before fluvial deposition. Eight sediment samples were dated by the electron spin resonance (ESR) method and the weighted average age obtained for the fluvial sands overlying the slope deposits is 665±55 ka. This age is older than previous chronological data placing the first European Acheulean assemblages north of 45th parallel north at around 500 ka and modifies our current vision of the initial peopling of northern Europe. Acheulean settlements are older than previously assumed and the oldest evidences are not only located in southern Europe. La Noira is the oldest evidence of Acheulean presence in north-western Europe and attests to the possibility of pioneering phases of Acheulean settlement which would have taken place on a Mode 1-type substratum as early as 700 ka. The lithic assemblage from la Noira thus provides behavioral and technological data on early Acheulean occupation in Europe and contributes to our understanding of the diffusion of this tradition.

‘Steppe’ mammoth (Mammuthus trogontherii) remains in their geological and cultural context from Bełchatów (Poland): A consideration of human exploitation in the Middle Pleistocene

In 1981 and 1991, mammoth remains and associated fauna were found in central Poland, at the Bełchatów opencast mine in sandy gravel deposits. Most of them lay at approximately 160–175 m above mean sea level (a.s.l.), located in the lower and upper members of the alluvial Chojny Formation. This formation belongs to the Middle Pleistocene, and can be connected with the Mazovian (MIS-11, Holsteinian) or Zbójnian (MIS-9, Reinsdorf) Interglacial.The Bełchatów mammoth assemblage described here consists of cranial and postcranial elements. Analysis of their morphological characteristics and osteometrics are used to demonstrate that at least two molars and one tusk belong to Mammuthus trogontherii and that the tusk belonged to a male. On the basis of the minimum number of elements of the most common element (left incisors), the mammoth remains represent at least two individuals. Based upon the different ages of death for the various elements, it appears that they represent several individuals.The bulk of the mammoth remains were recovered from the oldest depositional cycle in the lower member of Chojny Formation, and are therefore coincident with a shrub tundra environment and cool temperate conditions. They were deposited in sediments formed by a meandering river with a fairly low power of flow, and were buried soon after transport over a short distance. This conclusion is also supported by the palaeobotanical data.An additional element, a costa, was recovered from the upper member of the Chojny Formation, which is associated with the cooling conditions. The enveloping deposit appears to be the result of a series of more rapid discharge events by a braided river. This element is distinguished from those elements recovered from the lower member due to the presence of a series of unusual striations. SEM analysis suggests that some of the striations were probably made by chipped stone tools used in a slicing action, as if the result of the filleting of flesh from the rib area. The time frame for the depositional context of the costa suggests that the striations may have been made by one of several possible human taxa that occurred in central Europe during this period, including Homo heidelbergensis. Given the dearth of human skeletal remains from this region and time period, this represents the earliest and only example of Middle Pleistocene human butchering activity in Poland. The remains discussed in this paper are presented in light of their depositional and cultural contexts, which not only increases our knowledge of the occurrence of M. trogontherii in Poland, but also provides increased evidence for Lower Palaeolithic human activity in central Europe during an early interglacial.

Climatic and tectonic control on fluvial and alluvial fan sequence formation in the Central Makran Range, SE-Iran

The geomorphic evolution of the Makran Range of SE-Iran and SW-Pakistan has been controlled by the prevailing SW-Asian monsoon and Mediterranean winter rainfall climate and the surface uplift processes resulting from the Arabia–Eurasia collision. The impact of climate on Quaternary fluvial and alluvial sequence formation and their regional correlation has been little investigated due to limited age control of these sequences. Using 10Be cosmogenic nuclide exposure ages we established a Middle to Late Pleistocene terrace chronology. Our record tentatively indicates that terrace levels were abandoned towards the transition to or during warmer/pluvial periods (interglacials and/or interstadials) back to Marine Isotope Stage (MIS) 7, but abandoned ages show a large spread. It is hypothesized that pluvial phases correspond with times of enhanced SW-monsoons and a northward shift of the Intertropical Convergence Zone (ITCZ). Furthermore, orbital periodicities can be deduced on frequencies related to obliquity and precession cycles. Overall, caution has to be placed in sampling and interpreting alluvial deposits, which may have complex inheritance patterns and spatially and temporarily variable catchment erosion histories and terrace-channel dynamics.Beside the dominant climate control on terrace formation, elevated channel steepness indices around major thrusts and numerous knickpoints indicate an additionally tectonic influence on terrace formation. Local incision rates (mean ~0.6–0.8mm·a−1) are variable in space and time but are similar to uplift rates obtained from coastal terraces and thus suggest a regional surface uplift.

Fluvial system response to external forcing and human impact – Late Pleistocene and Holocene fluvial dynamics of the lower Guadalete River in western Andalucía (Spain)

The 170 km long river course of the Guadalete River (western Andalucía) provides an excellent record of Late Pleistocene and Holocene fluvial sedimentation dynamics. Furthermore, its floodplain sediments are very well suited to describe geomorphic changes forced by climate fluctuations, sea‐level changes, tectonic influences and human activity. Multiproxy investigations were based on field mapping and the study of 18 profile sections, mainly including sedimentological characterisation, soil‐chemical analyses and radiocarbon dating of 34 samples. Findings were complemented by drillings and electrical resistivity tomography. The lowermost 50 km of the river section are divided into an upper and lower part (each 25 km long), based on different sediment preservation conditions. The boundary corresponds to the disappearance of the Late Pleistocene river terrace. Significant floodplain aggradation occurred at around 10 000 cal. years BP, while dynamics were strongly affected by sea‐level fluctuations until the early Holocene. Furthermore, sedimentation starting at 8000, 6100, 4600, 2200, 900 and 400 cal. years BP is related to enhanced fluvial dynamics due to environmental stress that presumably was triggered by climate fluctuations, that is, aridification. However, the strongest intensity of sedimentation at 400 cal. years BP points to climate anomalies in the course of the Little Ice Age. In contrast, several periods of stability associated with alluvial soil formation took place during the Bølling and Allerød interstadials, prior to 8000, 6100 and 5100, and after 4300 and 2000 cal. years BP. The anthropogenic signal in floodplain evolution is not clearly distinguishable from that of climate. However, human land use had the potential to amplify geomorphic processes, especially during periods of climate deteriorations that caused increasing stress on the environment.

Application of geostatistical simulation models in the charac- terization of complex geological structures

Geostatistical simulation methods are able to generate numerical models or relations of the spatial distribution of a continuous geologic variable (grade, thickness, density, etc.) or a categorical variable (geological units and lithofacies or rock types). In this work, a review of traditional simulation techniques, as the Sequential Indicator Simulation (SIS), reveals a major pitfall that comes from theoretical difficulties in the development of a valid cross covariance model. On the contrary, a valid indicator cross covariance model is automatically defined in the framework of the Truncated Gaussian Simulation Method (TGS). This method is based on the concept that the categorical variables are obtained by truncating one standard multigaussian random variable at different thresholds. Plurigaussian Simulation Method (PGS) is an extension of the TGS Method but based on the simultaneous truncation of several multigaussian variables. An application of Plurigaussian method to simulate the lithofacies in the alluvial formations of the West Thessaly Basin is finally presented. This method was shown to be effective in reproducing the spatial characteristics of the different lithofacies and their distribution across the studied area.

Occurrence and hydrogeochemistry of fluoride in alluvial aquifer of Weihe River, China

Fluoride (F−) has significant impacts on human health. High fluoride groundwater (up to 1.90 mg/L) has been found in upper confined aquifer underlying the first terrace of Weihe River during a hydrogeological investigation for water supply in 2005. To reveal the occurrence and hydrogeochemistry of high F− groundwater, hydrogeochemical tools such as saturation index, ionic ratios and correlation analysis were used in this study. The study shows that the concentrations of most physiochemical parameters from phreatic water, influenced by intensive evaporation and anthropogenic activities such as unregulated sewage and excreta disposal and agricultural practices in the area, are higher than those of confined water. The F− concentration in phreatic water is within the acceptable limits set by China and the World Health Organization (WHO), while that of upper confined water shows a decreasing trend northwestward as the Weihe River approaches, with F− concentration in the first terrace beyond the national and the WHO standards. High F− groundwater is observed in alkaline environment associated with high Na+, pH, HCO3 − and low Ca2+ and Mg2+. The enrichment of F− is controlled by geologic and hydrogeological conditions, fluorine-bearing minerals presented in alluvial formations and their dissolution/precipitation under the alkaline environment along groundwater flow. Ion exchange, human activities and the mixing of different recharge waters may influence the enrichment of F− as well.

Trace element study in∼Tisa River and Danube alluvial sediment in Serbia

The contaminated sediment serves as a long-term source of toxic elements, since that mobility and transport in the environment of these elements are strongly influenced to associated solid phase. In this study, the modified Tessier sequential extraction procedure was applied for the fractionation of Cd, As, Hg, Cu, Zn, Cr, Pb, Ni and V in the sediments (Tisa River and canal sediments - Danube alluvial formation), to obtain an overall classification of trace element pollution in these areas through its spatial distribution. Investigations of this region are important due to the widespread occurrence of metal mining activities throughout the Tisa and Danube drainage basins and possibilities of contamination with toxic elements at studies localities. Five steps of the sequential extraction procedure partitioned elements into CH3COONH4 extractable (F1), NH2OHHC carbonate extractable and easily reducible (F2), H2C2O4/(NH4)2C2O4 moderately reducible (F3), H2O2–HNO3 organic extractable (F4), and HCl acid soluble residue (F5). Analyses of the extracts were performed by flame atomic absorption spectrometry. To indicate the degree of risk of toxic elements, risk assessment code and contamination factor have been used. The results of partitioning study indicate that more easily mobilized forms (metals in adsorbed/exchangeable/carbonate forms or bound to amorphous Fe and Mn oxyhydroxides and Fe and Mn oxides) were predominant for copper, zinc, cadmium and lead, which can be used as indicators for input from anthropogenic source. In contrast, the largest amount of chromium and nickel were associated with the inert fraction, which reduced their solubility and rendered them immobile under natural conditions and indicative of natural origins. Most of remaining portion of metals was bound to ferromanganese oxides fraction. It is concluded that sequential extraction results proved useful to distinguish between anthropogenic and geochemical sources of elements in the sediments.

Características granulométricas de los depósitos aluviales en el campo de Cartagena

Granulometric characteristic of the alluvial formations in the Cartagena field (Spain). The succession semi-arid environmental conditions which have affected the area of Cartagena, in the southeast of Spain, from the Quaternary up to now, gave rise to torrential rainfalls which can be appreciated in the landscape's alluvial formations. The granulometric analysis of these accumulations helps to tell apart the dífferent morphogenetic processes affecting their deposit, as well asto characterize their sedimentalfacies. In this respect, the common índices ofheterometry, acuity, asymetry, and those of dynamic classification, energy rate (N) and thickness índex (X) of Riviére (1977) have been calculated. The interpretation of those facies with bends of accumulative frequency, and the description of the sedimentary structures, where the analyzed samples are located, round of this study on the alluvial formations of a semiarid Mediterranean area.

Stratigraphy of the Arriaga Palaeolithic sites. Implications for the geomorphological evolution recorded by thickened fluvial sequences within the Manzanares River valley (Madrid Neogene Basin, Central Spain)

The Arriaga Palaeolithic sites, located within the Middle–Late Pleistocene thickened terrace (TCMZ: +18–22m) of the Manzanares River valley (Madrid, Central Spain), were subject to intensive archaeological and palaeontological prospecting during the 1980s. Compilation of documents from these old excavations, together with new geoarchaeological, sedimentological, pedological and geophysical data, allow us to locate the morpho-stratigraphic position of the analysed sites within the overall stratigraphy of the TCMZ. This thickened terrace comprises two main fluvial sequences (Lower and Upper) topped by a thick (2.5–5m) alluvial–colluvial formation. The fluvial sequences are stacked in the study site located in the lowermost reach of the valley, but display complex inset relationships upstream, where they are individualized in two different terrace levels at +18–22 and +12–15m. Terrace thickening was primarily controlled by synsedimentary subsidence caused by dissolution of the evaporitic substratum and locally influenced and backfed by tectonic activity. The regional analysis of the dated (TL and OSL) fluvial sequences containing Palaeolithic sites within the TCMZ, together with new TL dates provided in this study, indicate that the three sedimentary sequences in the TCMZ are time-transgressive valley-fill bodies. Terrace thickening started before the Last Interglacial Period (MIS 6 or older) and continued during whole MIS 5 (lower fluvial sequence) and MIS 4 (upper fluvial sequence) reaching the MIS 3 (top alluvial formation), the latter characterized by the accumulation of alluvial–colluvial sequences derived from the main tributaries and valley slopes. The TCMZ records the Middle–Late Pleistocene boundary, but also the transition between the Lower and Middle Palaeolithic periods during the Late MIS 5 (ca. 96 to 74ka). The studied Arriaga sites contain evolved Lower Palaeolithic industry (evolved Acheulean techno-complexes) and warm faunal assemblages located within the Lower fluvial sequence, but apparently well constrained Middle Palaeolithic sites are placed within the Upper fluvial sequence at other upstream locations. Deposition of the thickened alluvium was mainly controlled by the upstream advance of dissolution-induced subsidence phenomena, blurring the impact of Late Pleistocene climatic cycles and producing time-transgressive longitudinal valley-fill bodies (i.e. sedimentary sequences). Late Quaternary climatic changes only seem to control the incision/aggradation cycles after the termination of the TCMZ from the Late MIS 3. Dates related to the development of younger inset terraces indicate that they are apparently linked with cold Heinrich events H4 to H1. These younger inset terraces yield cold faunal assemblages and abundant Middle Palaeolithic “Mousterian” assemblages.

Development of a stream–aquifer numerical flow model to assess river water management under water scarcity in a Mediterranean basin

Stream flow, as a part of a basin hydrological cycle, will be sensible to water scarcity as a result of climate change. Stream vulnerability should then be evaluated as a key component of the basin water budget. Numerical flow modeling has been applied to an alluvial formation in a small mountain basin to evaluate the stream–aquifer relationship under these future scenarios. The Arbúcies River basin (116km2) is located in the Catalan Inner Basins (NE Spain) and its lower reach, which is related to an alluvial aquifer, usually becomes dry during the summer period. This study seeks to determine the origin of such discharge losses whether from natural stream leakage and/or induced capture due to groundwater withdrawal. Our goal is also investigating how discharge variations from the basin headwaters, representing potential effects of climate change, may affect stream flow, aquifer recharge, and finally environmental preservation and human supply.A numerical flow model of the alluvial aquifer, based on MODFLOW and especially in the STREAM routine, reproduced the flow system after the usual calibration. Results indicate that, in the average, stream flow provides more than 50% of the water inputs to the alluvial aquifer, being responsible for the amount of stored water resources and for satisfying groundwater exploitation for human needs. Detailed simulations using daily time-steps permit setting threshold values for the stream flow entering at the beginning of the studied area so surface discharge is maintained along the whole watercourse and ecological flow requirements are satisfied as well. The effects of predicted rainfall and temperature variations on the Arbúcies River alluvial aquifer water balance are also discussed from the outcomes of the simulations. Finally, model results indicate the relevance of headwater discharge management under future climate scenarios to preserve downstream hydrological processes. They also point out that small mountain basins could be self-sufficient units so long as the response of the main hydrological components to external forces that produce water scarcity, as climate change or human pressures, is appropriately considered in water resource planning.

Genesis and geochemistry of high fluoride bearing groundwater from a semi-arid terrain of NW India

Occurrence of fluoride in natural water resources and the associated health hazards have been reported from many parts of India during the last decade. With the objective of organizing a systematic scientific programme to understand the geochemical behaviour of fluoride in natural water resources in relation to the local hydrogeological, climatic conditions and agricultural use, a typical semi-arid terrain in the northwestern part of India was chosen for detailed study. The present work is an attempt to study the fluoride contamination in groundwater in parts of Jaipur district, Rajasthan state, and to assess the origin and genesis of fluoride in groundwater. The area, falling under the semi-arid tract of central Rajasthan, is geologically occupied by alluvial formations and Precambrian rocks (gneisses and schists) where groundwater occurs under unconfined to semi-confined conditions. A total of 66 groundwater samples was collected during the pre-monsoon period and analysed, which gave a concentration of fluoride in water in the range of 0.35 to 9.3 mg/l with 62 % of the samples in excess of permissible limit of 1.5 mg/l. As compared to alluvial formations, fluoride enrichment in groundwater is higher in hard rock areas. The samples collected from the granite gneissic terrain show higher values when compared to those in the schist. The groundwater of the shallow aquifers (soil–clay complex weathered zone) has a higher concentration of fluoride than the deep (fractured hard rock) aquifer does. The possible sources of fluoride are chemical weathering and leaching of fluorine-bearing minerals present in hard rocks and alluvial formations under the alkaline environment in arid to semi-arid conditions. High pH as well as alkalinity and low levels of Ca, Mg and total hardness suggest favourable chemical conditions for the fluoride dissolution process. A higher rate of evapotranspiration, intensive and long-term irrigation and heavy use of fertilizers are the supplementary factors that further increase the fluoride content in the groundwater. A groundwater management programme is suggested.

A possible synoptic source of water for alluvial fan formation in southern Margaritifer Terra, Mars

The morphometry and occurrence of crater-bound fans in southern Margaritifer Terra that were active from around the Hesperian–Amazonian boundary into the Early Amazonian is consistent with emplacement related to synoptic precipitation. Precipitation, possibly occurring as snow, may have been locally influenced by topography and (or) orbital variations. It is not known how much of the total sediment inventory in the fans relates to this late activity versus possible earlier events where water may have been available from alternate sources such as impact-related melting of ground ice. Winds may have concentrated late occurring precipitation into existing relief and (or) preexisting alcoves that facilitated physical weathering to produce fine sediments later incorporated into fans. Two of the craters containing fan deposits, Holden and Eberswalde, were finalists for the MSL landing site. Results suggest that exposed and accessible fan sediments at both crater sites may record a late period of colder, drier conditions relative to early Mars that was punctuated by ephemeral water-driven activity.

A study on groundwater geochemistry and water quality in layered aquifers system of Pondicherry region, southeast India

Geochemical signatures of groundwater in the Pondicherry region, south India, were determined. The coastal aquifers are fragile and this situation becomes more intense in layered aquifer systems like that of the Pondicherry region. In this region, groundwater occurs in alluvium, Lower Cuddalore, Upper Cuddalore, Tertiary, Cretaceous and mixed aquifers. The geochemical signature of groundwater in these formations was studied by collecting 93 groundwater samples. The collected samples from specific formations were analysed for physical parameters, such as electrical conductivity (EC), pH and major ion concentrations, such as Ca, Mg, Na, K, Cl, HCO3, PO4 and SO4. The results of the analysis were interpreted with geology; the ionic concentrations in the groundwater vary spatially and temporally. The abundance of these ions are in the following order: Na > Ca > Mg > K = Cl > HCO3 > SO4. Interpretation of analytical data shows that Ca–Na and Cl–SO4–HCO3 is the dominant facies in all the formations. Groundwater in the area is generally hard and fresh-brackish in most of the formations and brackish in nature in alluvium formation. The sodium absorption ratio shows that most of the samples are grouped under excellent category to good category in all the formations. The residual sodium carbonate also are in good category in all the formations. Chloro-alkaline indices reveal that the majority of samples show negative values in all the litho units indicating the exchange of Na and K in groundwater with Mg or Ca in rock. Scholler classification of water indicates that longer residence time of water with more prominent base exchange. High EC and TDS values in certain locations of alluvial, Upper Cuddalore and Cretaceous formations prove to be unsuitable for drinking and irrigation purposes.

The Wealden (non-marine Lower Cretaceous) of the Wessex Sub-basin, southern England

The Wealden Beds (non-marine Lower Cretaceous) of the Wessex Sub-basin, southern England, are exposed principally in coastal sections on the Isle of Wight and in Dorset. Geological Conservation Review sites within these strata have been extensively documented since the earliest days of geological enquiry in Great Britain. The succession is dominated by the alluvial Wessex Formation which demonstrates a broad east–west transition from meanderplain lithofacies to coarser-grained alluvial sediments, in relative proximity to the Cornubian source massif. The meanderplain sediments on the Isle of Wight are of international importance for their plant and animal fossils, the latter including many dinosaurs and their trackways. Upper Barremian transgression resulted in the spread of muddy lakes and coastal lagoons from the Weald Sub-basin into the eastern part of the Wessex Sub-basin, around or through the Purbeck–Isle of Wight structure. The resulting richly fossiliferous mudrock-dominated strata are now represented by the Vectis Formation on the Isle of Wight and in Swanage Bay, Dorset. The Geological Conservation Review sites in the Wessex Sub-basin are documented and interpreted, with particular reference to research history, chronostratigraphy, structural context, palaeoenvironments, palaeobiology and palaeoclimatology. New directions for research are proposed, as applicable.

Geothermal fields of Hengill Volcano, Iceland

This paper provides a review of geological, geophysical, and geochemical studies for three geothermal zones of Hengill Volcano, Iceland: Nesjavellir, Hellisheidi, and Hveragerdi. We discuss the relationships between global tectonics and high-temperature geothermal systems in Iceland. The bulk of this review is devoted to studies of the physical, geochemical, and mineralogic parameters for the three areas. A separate discussion concerns surface phenomena, as well as the origin of thermal water. This review covers studies of the main aquifer complexes: Miocene/Lower Pliocene plateau basalts, Upper Pliocene/Pleistocene lavas and volcanoclastics involving tillite horizons, an aquifer complex of Holocene lava sheets as thick as 1 km, and an aquifer complex of Upper Pleistocene/Holocene alluvial eolian deposits and formations of bottom moraines. We consider a conceptual model of geothermal reservoirs characteristic for the Hengill geothermal fields.