Laterite Formation Research Articles

The Unique Role of Pore Water in Lateritic Bauxite Formation, Republic of Guinea

The Unique Role of Pore Water in Lateritic Bauxite Formation, Republic of Guinea

(U-Th)/He-dating of ferruginous duricrust: Insight into laterite formation at Boddington, WA

Geochronological characterization of pisolites and nodules in ferruginous duricrust from laterite profiles exposed near the Boddington gold mine (BGM) in Western Australia was undertaken by application of (UTh)/He dating. Optical microscopy, Raman spectroscopy, X-ray diffraction (XRD) analysis and TESCAN Integrated Mineral Analyser (TIMA) mineral mapping identified areas in pisolites and nodules in pisolitic and fragmental duricrust suitable for (UTh)/He-dating. (UTh)/He dates of 5.8–1.3 Ma for pisolites and fragmental duricrust nodules indicate late-Miocene/Pliocene to possible early-Pleistocene ages as a minimum age for the formation of pisolites and nodules and a maximum age for formation of the BGM duricrust. Averaged (UTh)/He ages suggest at least two main episodes in the evolution of pisolite formation, the oldest occurring at 5.8–5.2 Ma and a younger episode at 3.9–3.2 Ma, with indication of an even later episode of pisolite formation at 2.3–2.0 Ma. These results are comparable with (UTh)/He data for pisolitic duricrust approximately 50 km to the east of Perth (Toodyay), and are consistent with other age estimates for lateritization in Western Australia, suggesting that processes of regolith formation and/or modification in the Darling Range, to the east and south-west of Perth, were regionally synchronous. The significant difference in age of the rim (2.0 ± 0.2 Ma) compared to the core (3.9 ± 0.5 Ma) of a single pisolite, in conjunction with a difference in mineralogy and textural evidence, suggest that ancient, episodic bushfires may have affected or reset the (UTh)/He system of iron oxides. Despite this, geochronological characterization can provide quantitative constraints on the age and relative timing of regolith formation.

Erosion Studies on Lithomargic Clays

Lithomargic clays are found at shallow depths in lateritic formations, sandwiched between hard lateritic crust at top and the parent granitic gneiss underneath. Many earlier studies have proved that the behaviour of these soils is similar to dispersive soils, and they are also found to be highly erosive. Very few and detailed studies on erosion of lithomargic clays are available in the literature. Lithomargic clays along the western coastal belt of peninsular India are available with varying percentages of sands and fines (especially silts, with negligible amount of clays occasionally). In this study, a number of hole erosion tests are conducted on controlled lithomargic clay samples with varying percentage of fines to study their erosion characteristics. The influence of degree of compaction, moulding water content, head causing flow, percentage silt content and plasticity index on the erosion rate index and critical shear stress of controlled lithomargic clay samples are being studied. The results of this study indicate that the critical shear stress for soils with higher silt fraction and fine sand content varied from 45 to 125 N/m2, whereas for soils with higher clay fraction and fine sand content the critical shear stress varied from 200 to 400 N/m2. The erosion rate increased with a decrease in percentage compaction in all the samples, and critical shear stress is found to be highest at optimum moisture content conditions. It is generally observed that soils with fines whose plasticity indices are high, are less erodible compared to soils with fines whose plasticity indices are low.

The solubility of goethite with structurally incorporated nickel and cobalt: Implication for laterites

Both cobalt (Co) and nickel (Ni) substitute for Fe in goethite (α-FeOOH) as well as adsorb on goethite. Co and Ni-rich goethite are the dominant ore mineral in oxide-type laterite deposits. A quantitative understanding of the aqueous solubility of Ni- and Co-rich goethite would help in modelling the formation of laterites and developing methods for metal extraction. In this contribution, we determined the aqueous solubility of substituted nickel and cobalt goethite in both the binary and ternary systems as a function of pH < 1 to 5 and varying concentrations found in Ni laterites. We found the dependency of the solubility product (Ksp) of goethite to the type of incorporated ion, concentrations, and pH. The solubility of Ni substituted goethite increases with increasing pH and increasing Ni substitution. A similar trend is observed for Co, although its substitution in goethite appears to increase the stability of goethite. Ksp increases with increasing Ni and Co substitution in bi-metal (Ni and Co) goethite, and are generally low compared to those of single metal substituted goethite with the same concentration. These findings have some implication for substitution mechanism and Ni and Co extraction from laterites and soils. The Ni(OH)2-Co(OH)2-FeOOH solid solution simulation with PHREEQC is inconsistent with our experimental data and reveals “nonideality” of mixing systems with different chemical and thermodynamic properties as end members, but attained equilibrium with goethite at lower pH.

Reactive Transport Modeling Applied to Ni Laterite Ore Deposits in New Caledonia: Role of Hydrodynamic Factors and Geological Structures in Ni Mineralization

AbstractThis study is devoted to understanding the impact of topography and hydrodynamics on the formation of high‐grade supergene nickel deposits. The investigation proposes a new conceptual mineralization model that describes the formation of various exceptionally Ni‐enriched hot spots observed in lateritic profiles. Numerical analysis of the effects of local hydrodynamics on deposits formation is performed by means of PHREEQC geochemical simulator and COMSOL Multiphysics software. These are coupled through an iCP Java interface that allows to code their level of interaction and facilitates the exchange of parameters. The model developed extends the currently existing geochemical formulation of nickeliferous laterite formation from peridotite carried out in 1‐D and is additionally capable of simulating mass solute transport and geochemical processes within complex fractured‐porous systems. The simulations improve our understanding of metal enrichment in saprolite and bedrock zones. It was shown that, although the initial development of nickel lateritic ores takes a few million years, they are prone to relatively quick leaching and subsequent redistribution of Ni when the topography changes in response to tectonic processes. The latter leads to the formation of rich nickel deposits at the bottom of the slope, mostly due to leaching of the saprolite material. In addition to the role of changes in topography, the critical impact of fractures and fracture networks on metal mobility and distribution was identified. The model developed provides significant insight into the distribution of mineral resources, in particular Ni deposits, and can be of great help for future mineral prospecting in industry.

Weathering of Ophiolite Remnant and Formation of Ni Laterite in a Strong Uplifted Tectonic Region (Yuanjiang, Southwest China)

The Yuanjiang Ni deposit in southwestern margin of the Yunnan Plateau is the only economically important lateritic Ni deposit in China. It contains 21.2 Mt ore with an average grade of 1.05 wt % Ni and has been recognized as the second largest Ni producer in China following the Jinchuan super-large magmatic Ni–Cu deposit. This Ni deposit is hosted within the lateritic regolith derived from serpentinite within the regional Paleo-Tethyan Ophiolite remnants. Local landscape controls the distribution of the Ni mineralized regolith, and spatially it is characterized by developing on several stepped planation surfaces. Three types of lateritic Ni ores are identified based on Ni-hosting minerals, namely oxide ore, oxide-silicate mixed ore and silicate ore. In the dominant silicate ore, two phyllosilicate minerals (serpentine and talc) are the Ni-host minerals. Their Ni compositions, however, are remarkably different. Serpentine (0.34–1.2 wt % Ni) has a higher Ni concentration than talc (0.18–0.26 wt % Ni), indicating that the serpentine is more significantly enriched in Ni during weathering process compared to talc. This explains why talc veining reduces Ni grade. The geochemical index (S/SAF value = 0.33–0.81, UMIA values = 17–60) indicates that the serpentinite-derived regolith has experienced, at least, weak to moderate lateritization. Based on several lines of paleoclimate evidence, the history of lateritization at Yuanjiang area probably dates to the Oligocene-Miocene boundary and has extended to the present. With a hydrology-controlled lateritization process ongoing, continuous operation of Ni migration from the serpentinite-forming minerals to weathered minerals (goethite and serpentine) gave rise to the development of three types of Ni ore in the regolith. Notably, the formation and preservation of the Yuanjiang lateritic Ni deposit has been strongly impacted by regional multi-staged tectonic uplift during the development of Yunnan Plateau. This active tectonic setting has promoted weathering of serpentinite and supergene Ni enrichment, but is also responsible for its partial erosion.

Local Topographic Model using Position Index for Analyzing the Characteristics of Unserpentinized Lateritic Zones in Sorowako Nickeliferous Laterite Deposit, Indonesia

An investigation of the relationship between slope position classification and nickeliferous laterite zones over serpentinized ultramafic terrain in Sorowako, South Sulawesi has been conducted using topographic position index from Light Detection and Ranging data for digital elevation model as references with detail resolution of 5m. The index is calculated by comparing the elevation of each cell in the elevation model to the mean of a specified neighborhood around that cell. The classification has six classes, i.e., valleys, lower slopes, gentle slopes, middle slopes, upper slopes and the local ridges. Chemical properties data from 413 drill holes were used for analysis to confirm the laterite zones –limonite and saprolite. By topographic model, slope position class of local ridges, upper slopes and lower slopes with the slope average of 9.82°, 16.05°, and 14.61° respectively, generally indicated the distribution of thick limonite zones, while saprolite zones were in significantly different pattern due to less or no correlation. 2D semivariogram model for spatial thickness distribution also confirmed the corresponding factor between the significant direction of landform reliefs and limonite thickness. Based on the geochemistry profile of limonite zone, the rate of weathering process in laterite formation is longer than the physical process of removal top profile by erosion or accumulation by transported top materials.

Identification of Karstic Features in Lateritic Soil by an Integrated Geophysical Approach

Lateritic soils are widely spread across the southern and central parts of India. Lateritic formations usually have soft sediments, entrapped between hard to medium soft lateritic rock, which are leached due to the ingress of water during rainy seasons creating hollow sections or cavities which span over large lengths. Laterites are highly heterogeneous and prone to cavitation due to its weathering process; a sound knowledge of the subsurface condition is required before starting any construction. This study presents the application of integrated geophysical investigation for the identification of cavities at a mega construction site in Kerala State, India. Geophysical survey methods, namely ground penetrating radar (GPR) and multichannel analysis of surface waves (MASWs) techniques, are used to identify the heterogeneities in lateritic soils and localized cavities. The survey areas identified are critical sections of a mega construction project subjected to heavy dynamic and static loads. The preliminary GPR survey is carried out across the study areas at specific interval spacing to identify probable heterogeneities. Confirmative survey or detailed GPR and MASW surveys are carried out at the locations identified in the preliminary survey at close intervals to confirm the presence of an anomaly and identify its location. The anomalies in the GPR radargram are identified by visual inspection and trace amplitude approach. Using MASW survey, a 2D shear wave velocity profile is generated to identify low shear wave velocity zones which confirm the presence of an anomaly. On comparing the data from both GPR and MASW survey techniques, the underground cavities were successfully identified at multiple locations with further crosschecking with borings. The study further provided details on subsurface lithology at survey locations.

Silicon and chromium stable isotopic systematics during basalt weathering and lateritisation: A comparison of variably weathered basalt profiles in the Deccan Traps, India

Global biomass production is fundamentally affected by the hydrological cycling of elements at the Earth's surface. Continental weathering processes are the major source for most bio-essential elements in marine environments and therefore affect primary productivity. In addition, critical zone biomass depends on energy and chemical exchange reactions in weathering profiles. The latter reservoirs are in turn influenced by different climatic conditions that control weathering and pore water parameters like pH and Eh, which regulate mineral break down rates and dictate the mobility and mass flux of elements.Two Deccan Traps basalt weathering profiles of contrasting age and alteration intensity provide a natural laboratory for investigating the effects of rock alteration on Si and Cr and their isotopic systematics. The Quaternary Chhindwara profile has progressed to a moderate degree of alteration (saprolite), while the Paleogene Bidar example displays an extremely altered laterite. The Chhindwara saprolite profile shows a near uniform Cr and Si concentration and isotopic composition, whereas the Bidar laterite profile is characterised by an intense loss of Si, a large enrichment of Cr within the most altered uppermost levels, and a wide range of Cr stable isotope ratios (−0.85 to 0.36‰ δ53/52Cr). A co-variation between Si and Cr isotopes, as well as their co-variation with iron content, provides empirical evidence that iron redistribution within the profile has a large effect on Cr mobility and Si isotopic fractionation. Therefore, it is concluded that iron oxides exert a primary control over the isotopic composition of both Cr and Si in pore waters of laterites.Since laterite formation is promoted by tropical climates, the results of this study provide new evidence to suggest that the hydrological Cr and Si fluxes originating from continental weathering have changed in accordance with large-scale, deep time climate variation and continental plate configuration. An increased flux of Si and greater magnitude of Cr mobility and isotopic fractionation are possibly amplified under CO2-rich, greenhouse episodes and/or when large landmasses were tectonically arranged at near equatorial latitudes.

A New Building Material: Mixture of Rice Straw, Laterite and Cement

The aim of this study is to improve the proprieties of the mixtures of rice straw and laterite. Thus, we conduct this study related to the mixtures of rice straw, laterite and cement for their use as building material. The lateritic formations represent the most abundant economical materials resources available in tropical and equatorial Africa. Rice straw is rich in cellulose. Consequently, few animals are able to use it as food. We have determined by experiments the mechanical and thermal properties of samples. The Interesting results obtained show that the integration of mixtures of rice straw, laterite and cement in building materials are great opportunities to reduce the cost of social housing. It also improves the thermal comfort.

Impact of landuse on the groundwater quality along coastal aquifer of Thiruvallur district, South India

The present study was carried out to understand the impact of landuse pattern that includes agricultural and urban development on coastal aquifers of the SE coast of India. Regional geology includes marine sediments, alluvium, sandstone and laterite formations. Groundwater samples were collected from 50 dug wells and bore wells during pre-monsoon 2013 (May) and post-monsoon 2014 (January). Water samples were analyzed for physical and chemical parameters such as electrical conductivity (EC), pH, TDS, Na+, K+, Ca2+, Mg2+, Cl−, HCO3 −, SO4 2−, NO3 − and Total Hardness, using standard procedures. Results indicate the following order of concentration of ions: Na+ > Ca2+ > Mg2+ > K+, and Cl− > HCO3 − > SO4 2− > NO3 −. Further, total hardness (TH) was evaluated to understand the suitability of groundwater for drinking purpose. Na–Cl, Mixed Ca–Mg–Cl and Ca–HCO3 facies were the dominant groundwater types in the study area. Study findings gives a detail understanding of interrelations between geology and landuse practices with water quality. Statistical results indicate that leaching of secondary salts, sea water intrusion, infiltration of contaminated water and ion exchange processes are responsible for the groundwater chemistry variation.

Quartz arenites and laterites in the Moesian Group (Upper Triassic), northwestern Bulgaria: possible evidence for the effect of the Carnian Humid Episode

Quartz-rich sandstones and ironstone crusts occur in the lowermost part of the Upper Triassic Moesian Group exposed in the western Balkanides. On the basis of performed field studies, micropetrography, X-ray diffraction, and major-element chemistry, these deposits are defined as first-cycle quartz arenites and laterites, respectively. The former were deposited in an alluvial environment, while the latter developed in gravel-dominated fluvial sediments. The main control on their formation was warm to hot humid climate conditions combined with low relief, quiescent tectonic setting, mixed source area, and slow sedimentation rate. The decreasing compositional maturity of the sandstones forming the Glavatsi Member (quartz arenites→feldsarenites→litharenites), the disappearance of the lateritic crusts upwards in the continental succession, and the presence of thick overlying fluvial and playa deposits in the Komshtitsa Formation (or Chelyustnitsa Formation) reflect gradual transition from humid to subhumid climate, and then to persistent semi-arid climate regime. This irreversible trend correlates with other Upper Triassic strata deposited in the Western Tethys realm and adjacent areas. The coeval formation of quartz arenites and laterites must have been related to the most distinctive climate change during the Triassic, i.e., the global Carnian Humid Episode. The new results and interpretations appear to be the first geological record for the effect of pronounced mid-Carnian humidity reported from Eastern Europe. They also present indirect sedimentological evidence for the stratigraphical range of the Moesian Group in NW Bulgaria.

Revealing the conditions of Ni mineralization in the laterite profiles of New Caledonia: Insights from reactive geochemical transport modelling

New Caledonia is one of the world's largest nickel laterite deposits that form from intense chemical and mechanical weathering of a peridotite bedrock. As a result of such a weathering process a subsequent downward migration of Si, Mg and Ni takes place, which eventually leads to redistribution of the elements in depth and over time depending on their mobility. Being released from ultramafic parent rock to groundwater, the mobility of nickel is to a great extent controlled by sorption, substitution and dissolution/precipitation processes. Therefore, the final profile of nickel enrichment is the result of the superposition of these possible fates of nickel. The way how Ni is redistributed in between them represents and defines its mineralization in laterite. Knowledge of these processes along with factors, controlling them appears to be a key to detailed understanding of laterite formation. In this study a numerical model, which solves the reaction-transport differential equations, is used to simulate the formation of laterite profile from ultramafic bedrock with particular emphasis on modelled Ni enrichment curve, its comparison with in situ observations, and detailed understanding of trace elements mobility. Since nickel deposits in New Caledonia is characterized by oxide and hydrous Mg silicate ores, three different concurrent fates of Ni deposition in a profile were taken into account in the modelling: i) Ni in a goethite crystal lattice, ii) Ni sorbed on weak and strong goethite sorption sites, and iii) Ni precipitated with silicates (garnierite). Simulations were performed using PHREEQC associated with llnl.dat thermodynamic database that has been edited in order to account garnierite minerals used in the calculations. The work outline is represented by: i) long term (10 Ma) simulation of nickel laterite formation and evolution, ii) analysis of mobility of the elements and understanding its controlling factors, iii) comparison of modelled and in situ Ni enrichment profile and analysis of nickel distribution in between different retention processes, iv) modelling and in depth understanding of these retention processes. The modelling reveals that the vertical progression of the pH front controls thickening of iron-rich zone, explains the vertical mobility of the elements and governs the Ni enrichment. Adsorption itself plays an important role in lateritization process retarding Ni mobility, but i) becomes significant in a narrow range of pH (slightly alkaline) due to competition of Mg and Ni for sorption sites and ii) does not explain such a high nickel content in limonite nowadays, suggesting that Ni is held in goethite mostly by stronger ties i.e. substituted for Fe in the crystal lattice of iron oxide. 1-D modelling appears to be a powerful tool in understanding the general behavior of trace elements upon the formation of laterite and at the same time reveals that locally Ni mineralizations should be explained by more complex processes, such as lateral transfers, convective flows and preferential pathways.

Two Dimensional Flows on Degree of Porosity and Permeability Influences on Radial Flow in Lateritic and Silty Formation Patani Coastal Area of Niger Delta

This paper is monitor the deposition of radial flow applying deterministic modelling techniques, the system observed porosity and permeability to express lots of influences determined by geological setting from the soil. This expression were found imperative on the system in other to ensure that two dimensional phase of radial flowstudy are carried out. Permeability and porosity influences were observed to pressure it deposition in various soil formation in lateritic and silty formation. The influences are from the structural disintegration from porous rocks, the rates of permeation were observed to be paramount parameters deposited in two dimensional flow phase of the system. Investigation carried out express these stated parameters as one of the formation influences that may have pressured the variation of radial flow in lateritic and silty formation. The developed modelling approach were found imperative, the expressed model were generated base on the developed system through these variables, experts in soil engineering will applied these concepts as one way to monitor two dimensional radial flow in unconfined bed including other engineering purpose.

Why was iron lost without significant isotope fractionation during the lateritic process in tropical environments?

To investigate the formation of laterites and Fe cycling during tropical weathering, this study presents Fe isotope and major trace-element compositions of a laterite profile obtained from an equatorial rainforest, Southern Philippines. The lateritic profile is 7m deep from top soil to less-weathered peridotites. X-ray diffraction analyses reveal that the major Fe-bearing minerals are hematite and goethite. The profile shows a large variation in Fe2O3 concentrations (32.1–73.3wt%) and dramatic Fe loss based on τTi,Fe factors (τTi,Fe≈−50% to −90%) calculated from the open-system mass fraction transport function. Notably, δ56Fe depicts a small range from −0.03‰ in the peridotite to +0.10‰ in the extremely weathered saprolites.The small Fe isotopic fractionation and significant Fe loss provide important insights into Fe cycling during extreme weathering of peridotites in a tropical climate. Variations in Fe content and δ56Fe can be modeled by a Rayleigh distillation process with apparently small fractionation factors of 56Fe/54Fe between the saprolite and fluid (103lnαsaprolite–fluid) of 0.01 to 0.20, much smaller than those experimentally determined for reductive dissolution of goethite (103lnαgoethite-Fe(II)≈1.2; Icopini et al., 2004) and hematite (103lnαhematite-Fe(II)≈1.3; Beard et al., 2003). These observations suggest that Fe should have experienced a complete and in situ oxidation prior to Fe migration and Fe was probably transferred in the form of colloidal substances. Fe transport over the history of the laterite formation and evolution may not have had a discernible effect on the Fe isotopic composition of the ecosystem.

Statistical Analysis of the Effect of Mineralogical Composition on the Qualities of Compressed Stabilized Earth Blocks

AbstractCompressed stabilized earth blocks (CSEBs) are typically produced with laterites because of their abundance in the tropics. However, the formation of laterites is governed by the nature of the parent rock, the age of the land surface, climate, and topography and drainage conditions resulting in laterites with varying mineral compositions. Because the geotechnical composition of tropical residual soils appears to be largely controlled by their mineral composition, the first level of any classification system should take into account the factors giving rise to their development. This paper summarizes the results of an analysis of the effect of mineralogical composition on the performance characteristics of CSEBs. The results from the X-ray diffraction analysis show that the soil samples consist of varying proportions of quartz and kaolinite alongside other minerals. The results obtained from this investigation show that soils with higher quartz and kaolinite content produced blocks with better perfo...

Predictive Simulation of Seawater Intrusion in a Tropical Coastal Aquifer

AbstractThe solute transport in a tropical, coastal aquifer of southern India is numerically simulated considering the possible cases of aquifer recharge, freshwater draft, and seawater intrusion using numerical modeling software. The aquifer considered for the study is a shallow, unconfined aquifer with lateritic formations having good monsoon rains up to about 3,000 mm during June to September and the rest of the months almost dry. The model is calibrated for a two-year period and validated against the available dataset, which gave satisfactory results. The groundwater flow pattern during the calibration period shows that for the month of May a depleted water table and during the monsoon month of August a saturated water table was predicted. The sensitivity analysis of model parameters reveals that the hydraulic conductivity and recharge rate are the most sensitive parameters. Based on seasonal investigation, the seawater intrusion is found to be more sensitive to pumping and recharge rates compared to ...

Characterization and evolution of primary and secondary laterites in northwestern Bengal Basin, West Bengal, India

It is quite impossible to travel far in India without observing the remarkable ferruginous crust to which Buchanan in 1807 gave the name of laterite. In Indian peninsula, it is a post-Cretaceous stratigraphic succession with a polycyclic nature of evolution which marks the unconformity with recent Quaternary alluvium. There are perennial problems and research gaps in the investigation of laterites in India as well as in West Bengal: (1) defining, identifying and classifying lateritic materials, (2) mode of formation of laterite and its other horizons, (3) determining the ages of laterites, (4) reliability of laterites as palaeoclimatic indicators, (5) identifying topographic requirements and pedogeomorphic processes for laterite formation, and (6) reconstructions of former lateritized landscapes. The formation of north‒south lateritic hard crust (i.e. Rarh Bengal) on the Rajmahal Basalt Traps, Archean granite‒gneiss, Gondwana sediments, Paleogene gravels and older deltaic alluvium is analyzed here to resolve the aforesaid problems and to depict the variable characteristics of laterites with special reference to its tectono-climatic evolution in the northwestern marginal part of Bengal Basin. This paper reveals that the low-level secondary laterites (probably the Pliocene‒Early Pleistocene age) of Rarh Bengal are composed of heterogeneous Fe‒Al rich gravelly materials which were derived from the high-level primary laterites (probably the Eocene‒Miocene age) of plateau since the Paleogene Period by the peninsular river system, following the underlying structure of Bengal Basin. Alongside the roles of drifting of Indian Plate, establishment of monsoon climate, neo-tectonic uplifts and re-lateritization of ferruginous shelf deposits are determined here to unearth the palaeogenesis of primary and secondary laterites in West Bengal.

Estimation of Lateral Subsurface Flow in Lateritic Formations Using Well Hydrograph Analysis

The lateritic formations in west coast of India face a unique problem. In spite of good recharge in unconfined aquifer during monsoon every year, these aquifers drain very quickly in summer season. This is mainly due to the high porosity and permeability of these formations. Proper estimation of lateral subsurface flow from these formations is necessary for sustainable water management. This component is estimated by considering groundwater balance equation. Well hydrograph analysis has been carried out to obtain the gross and net recharge components. 42 open wells of varying diameters and depths spread over the entire microwatershed have been identified for the purpose. A recession equation is developed to predict the water level below ground level in the well at any particular time period of the dry season. Recession curve corresponding to dry periods is considered in obtaining specific yield (Sy)of the formation. The recession flow analysis carried out for the wells show an average value of recession constant for the shallow wells as 0.003 and for deep wells as 0.001. The specific yield determined from recession curves vary from 0.013 to 0.036. The average subsurface flow (SSF) from the microwatershed is found to be 0.09 m /year which is equal to 2.78% of the total annual rainfall. The lateral subsurface flow is estimated as a residue of groundwater balance equation.

Carbon Sequestration Potential of Teak Plantations of Different Agro-Climatic Zones and Age-Gradations of Southern India

Carbon sequestration potential of teak plantations in different agro-climatic zones of Southern India, viz. Northern Dry Zone, Northern Transition Zone, and Hilly Zone were studied. Teak plantations belonging to three age gradations viz. 10, 15 and 20 years were considered for the study. Above ground biomass was computed based on volume estimation and wood density after considering three 10 x 10 m plots. Carbon sequestration potential of teak plantations on farmlands differed significantly with respect to agro-climatic zones and age. Teak plantations raised on the farmlands of Northern Transition Zone had significantly higher above ground biomass than that in Northern Dry Zone and Hilly Zone at all the three age-gradations. Consequently, total above ground carbon sequestered was also significantly higher among the teak plantations of the Northern Transition Zone (247.47 t/ ha) than that in Hilly Zone (157.60 t/ha) and NDZ (103.73 t/ha). For obvious reasons total amount of carbon sequestered was significantly higher in 20-year plantations (330.00 t/ha) than in 15-year (108.53 t/ha) and 10-year plantations (70.27 t/ha). Perhaps optimal average annual rainfall of 749 mm and medium black soil in Northern Transition Zone have contributed to the higher biomass in teak. Poor rainfall in Northern Dry Zone (<585 mm) and poor soil conditions (lateritic formations) in Hilly Zone must have contributed to the poorer growth of teak in these zones. key words: Teak, Carbon sequestration, Biomass, Farmlands.