Geochemistry of the loessic sediments on Delhi ridge, eastern Thar desert, Rajasthan: implications for exogenic processes

Quartzite ridges in the Delhi region include in their local depressions thick piles of unconsolidated, unstratified, yellowish brown, homogenous loamy sediments. These Delhi ridge sediments (DRS) have textural, mineralogical and geochemical characteristics similar to those of loess sediments. Geochemically, DRS, just as other loess sediments, are similar to average exposed upper continental crust of Taylor and McLennan [Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, London, 311 pp.]. The calculated chemical index of alteration [Nesbitt, H.W., Young, G.M., 1984. Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations. Geochim. Cosmochim. Acta 54, 1523-1534; Nesbitt, H.W., Young, G. M., 1989. Formation and diagenesis of weathering profiles. J. Geol. 97, 129-147.] and other chemical parameters suggest a provenance of chemically less weathered rocks. During the process of wind transport and deposition, not only the dilution effect of silica on the REE abundance was counterbalanced but also the REE pattern was kept similar to the UCC and PAAS by the appropriate concentration and mixing of the REE bearing phases. The immediate source to these sediments is likely to be mechanically ground sediments of glacial origin. The last phase of the upliftment of the Himalayas, accompanied by Pleistocene glaciation could have provided a vast glacio-fluvial outwash plain. The aeolian processes associated with prevailing W to SW winds in the hot arid condition seem to have been selectively transporting fertile silt materials leaving behind infertile desert sands

Nd and Sr isotope characteristics of Quaternary Indo-Gangetic plain sediments: Source distinctiveness in different geographic regions and its geological significance

Quaternary sediments of the Himalayan foreland basin, known also as the Indo-Gangetic plains, have been studied for their Sr and Nd isotope geochemistry to constrain their sources and to infer their geological significance. The data show a large variation in the Sr-87/Sr-86 values and relatively a minor variation in the epsilon(Nd(0)) values, for compositionally homogeneous sediments. Sediments of the Ganga-Yamuna and Satluj systems have high Sr-87/Sr-86 (>0.75) and low epsilon(Nd(0)) ( 16), all relative to the previous group, suggesting their derivation from the Sub-Himalayan sediments including Tertiary Subathu Formation. The Subathu was likely derived from the Indus-Tsangpo Suture Zone basaltic volcanics and Tibetan Sedimentary Series. The Thar desert/Ghaggar river sediments are isotopically similar to those of the Indus plain indicating a shared provenance, either immediate or ultimate. The exposed sediments of the incised Yamuna river at Kalpi in the Ganga-Yamuna plains were derived from Peninsular India. These southern Ganga-Yamuna plain sediments are isotopically similar to the Thar Desert/Ghaggar river sediments although the juvenile components of their provenance differ - the Vindhyans-Deccan traps and Indus-Tsangpo suture zone volcanics, respectively. In the southern Ganga plain the Peninsular wedge of sediments could be present at depths below about 12 m, interbedded or mixed with Himalayan sediments. The isotope geochemistry of sediments also shows that the earliest influx of the Himalayan sediments to the Ganga-Yamuna interfluve occurred around 68-70 ka. This indicates that the Yamuna river has been flowing in the region at least since the Late Pleistocene. The dynamic relationship between the Yamuna and Chambal rivers in the region negates the idea of Yamuna being a tributary of Ghaggar-Saraswati river system during the Harappan time (3500 to 1900 BC

Geochemical, Sr and Nd isotopic studies on the Kalva Rangan Durga Quartzites of the Shimoga greenstone belt: Implications on weathering of Dharwarian continental crust

The Mesoarchean Kalva Rangan Durga Formation of the Shimoga greenstone belt in the western Dharwar Craton consists of orthoquartzite, ferruginous phyllite, banded ferruginous chert, and conglomerates. Thick beds of orthoquartzites of this formation are well exposed in Kalva Rangan Durga ridge, trending northeast to southwest for about 9 km, in the southwest part of the Honnali Dome. Quartzites are fine-grained in nature and mostly composed of quartz grains and fuchsite mica. In the present study, we have collected quartzite samples and carried out geochemical, Sr, and Nd isotope analyses to decipher their paleo-weathering conditions, provenance characteristics, and possible tectonic setting of deposition. Geochemical data indicate they are arkose to subarkose in nature. Moderate to intense chemical weathering of the source rocks of these quartzites during the Mesoarchean is suggested based on various weathering indices and ternary plots. Enriched LREE and flat to variably fractionated HREE patterns with negative Eu anomalies of quartzites indicate that they were mainly derived by weathering of tonalities, trondhjemite, and granodiorites (TTG) gneisses and granites. The relatively high concentration of Cr with variable Th/Sc and high Cr/Th ratios indicate both felsic and mafic sources for quartzites. Initial εNd values (t = 3.0 Ga) of quartzites range from −3.04 to +1.24 which further support their derivation from both older evolved continental crustal and juvenile sources. The presence of symmetrical ripple marks on the surface of quartzite indicates a shallow marine environment

Weathering of lower crustal rocks in the Kaveri river catchment, Southern India: implications to sediment geochemistry

In the upper catchment of the Kaveri river in the Sahyadri mountains of southern India, middle to lower crustal Archean granulite grade mafic and felsic rocks with similar structures and textures are exposed under the conditions of active tectonics, high rainfall and thick tropical vegetation. Occurrence of the two major rock types in close association under identical geological, geographical and biological conditions provides an uncommon situation for the study of weathering, elemental mobilization and sediment generation processes. Field observations, mineralogical and geochemical data including major, trace and rare earth elements (REE) of fresh rocks and variably weathered saprolite samples suggest that close association of mafic and felsic rocks accelerates the denudational processes by early weathering of mafic minerals in felsic rocks and mafic rocks in the terrain. Due to differential weathering of rocks, unweathered to less weathered felsic grains are likely transferred to the coarser fraction of fluvial sediments deposited on the floodplains of the river imposing an upper continental crust (UCC) geochemical signature. It is found that during chemical weathering, in addition to other factors, weatherability of host minerals of REE control the mobility of REE in the weathering profile. It is suggested from the observations on the weathering process and on the geochemistry of derivative sediments, that in a tectonically active system with a climate maximum, as in Sahyadris, an equilibrium could be dynamically maintained between weathering and erosional regimes. Also we infer from our study that there exist certain commonalities between surface denudational and mantle-magmatic geochemical differentiation processes. Similarity of these processes, therefore, may have implication to common UCC-like geochemistry of Post Archean sediments

Geochemistry of sediments of the Ganges alluvial plains: evidence of large-scale sediment recycling

The Himalaya, an amalgamation of different lithotectonic units brought together during, and even before, the Himalayan orogeny, has been subjected to various phases of denudation since the Palaeogene. Sediments derived by erosion of these lithotectonic units in different proportions were delivered to the Himalayan foreland. The nature and proportions of sediments from various lithotectonic units delivered to the foreland varied in response to the prevailing tectonic and climatic conditions during the orogeny. The geochemistry of sediments collected from floodplain, river channels and reworked aeolian sediments from the Delhi and Moradabad areas of the Ganges plain of the foreland basin indicates that they were derived from moderately weathered sedimentary sources. Further, the results also suggest that the sediments are not subjected to any significant post-depositional chemical weathering. High tectonic instability in the source area, and the geomorphology and cycles of aggradation and degradation in fluvial regimes in the Ganges Plain do not favor much chemical weathering. Homogenization of various lithotectonic units of the Himalaya through several episodes of sedimentary reworking is shown by the rare earth elements (REE) geochemistry of the sediments. The predominant source, for the homogeneous sediments, is likely the High Himalayan Crystalline or the Tertiary sub-Himalayan sediments, again the later was derived from High Himalayan Crystalline. If so, the Ganges alluvial plain is geochemically a Quaternary extension of Tertiary sub-Himalaya. The average composition of lithologies subjected to erosion in the Himalaya appears to be better represented by the alluvial mud present in the plain

Appraisal of Climate Response to Vegetation Indices over Tropical Climate Region in India

Extreme climate events are becoming increasingly frequent and intense due to the global climate change. The present investigation aims to ascertain the nature of the climatic variables association with the vegetation variables such as Leaf Area Index (LAI) and Normalized Difference Vegetation Index (NDVI). In this study, the impact of climate change with respect to vegetation dynamics has been investigated over the Indian state of Haryana based on the monthly and yearly time-scale during the time period of 2010 to 2020. A time-series analysis of the climatic variables was carried out using the MODIS-derived NDVI and LAI datasets. The spatial mean for all the climatic variables except rainfall (taken sum for rainfall data to compute the accumulated rainfall) and vegetation parameters has been analyzed over the study area on monthly and yearly basis. The liaison of NDVI and LAI with the climatic variables were assessed at multi-temporal scale on the basis of Pearson correlation coefficients. The results obtained from the present investigation reveals that NDVI and LAI has strong significant relationship with climatic variables during the cropping months over study area. In contrast, during the non-cropping months, the relationship weakens but remains significant at the 0.05 significance level. Furthermore, the rainfall and relative humidity depict strong positive relationship with NDVI and LAI. On the other, negative trends were observed in case of other climatic variables due to the limitations of NDVI viz. saturation of values and lower sensitivity at higher LAI. The influence of aerosol optical depth was observed to be much higher on LAI as compared to NDVI. The present findings confirmed that the satellite-derived vegetation indices are significantly useful towards the advancement of knowledge about the association between climate variables and vegetation dynamics

Correlation of age and hepatitis B virus DNA levels with histological activity in HBeAg negative chronic hepatitis B patients

The relationship between age and serum HBV DNA levels with histological activity in chronic hepatitis B inactive carriers is still unclear. We evaluated the correlation between age and hepatitis B viral DNA levels with Metavir score in inactive chronic HBV carriers. 50 patients (30 males and 20 females) were enrolled in the study after informed consent. Their blood samples were taken for routine investigations and specific tests for the study. Serum HBV DNA levels were quantified by real-time PCR. Metavir score was used for histologic grading. A1F0, A1F1, A1F2, A2F2 and A2F3 metavir scores were found in 41 (82%), 4 (8%), 1 (2%), 3 (6%), and 1 (2%) patients, respectively. There was significant correlation between age > 40 years and Metavir scores (p < 0.001). However there was no significant correlation between HBV DNA level with Metavir score (p = 0.074). Inactive carriers of 40 years of age or more should undergo liver biopsy to look for presence of significant histological findings despite having low HBV DNA level and normal SGPT level

Geochemical, stable isotopic, palynological characterization of surface dry soils and atmospheric particles over Jodhpur city (Thar Desert, Rajasthan) during peak summer of 2013

Atmospheric dust originating from the Thar Desert (India) acts as the local source of mineral dust in South Asia, spreading over an area of 0.32 x 10(6) km(2). Regional studies conducted during peak boreal summer are required to characterize this mineral dust that blows in form of episodic dust storms towards Indo-Gangetic Plains (IGP), using a multi-tracer approach. To achieve this goal, atmospheric PM10 particles were collected along with surface dry soils between 3 and 11 June, 2013, from in and around the Jodhpur city (26.2389 degrees N, 73.0243 degrees E) to glean elemental composition, stable isotopic and palynological (pollen types) database. Typical crustal elemental ratios, e.g. Si/Al, Ca/Al, Fe/Al, K/Al, Mg/Al, Ti/Al, varied in narrow ranges 8.1 +/- 1.21, 1.02 +/- 1.53, 0.50 +/- 0.14, 0.34 +/- 0.06, 0.19 +/- 0.06 and 0.06 +/- 0.02, respectively. Average Sr/Al, Rb/Al and Zr/Al ratios were found to be 39.70 +/- 12.24, 18.00 +/- 2.0 and 70.83 +/- 13.11 (mu g gm(-1)/wt%), respectively. Average delta C-13, delta N-15, delta S-34 values of surface soils were - 10.5 parts per thousand +/- 4.0, 11.4 parts per thousand +/- 1.6 and 3.6 parts per thousand +/- 2.1, while delta C-13 and delta N-15 of atmospheric PM10 particles varied in ranges - 25.6 parts per thousand +/- 0.67 and 9.9 parts per thousand +/- 1.7, respectively. Observed palynoassemblage indicated the open nature of vegetation that usually grows under warm-humid conditions with traces of few allergens and pathogens. Generated chemical-isotopic-pollen database could be utilized for deciphering origin of dust storms in IGP. Detailed multi-proxy characterization of mineral dust from the Thar Desert can further help to determine its role in influencing air quality and human health