Delineation and Characterization of Waterlogged Salt Affected Soils in IGNP Using Remote Sensing and GIS

The India Remote Sensing data on 1:50,000 scale revealed the occurrence of permanent waterlogging in low-lying flats and depressions of the Indira Gandhi Nahar Pariyojona (IGNP) command area. Such data also indicated seasonal dynamics of waterlogging and soil salinization (Salt efflorescence/crusting) in irrigated areas. Mixed spectral signatures of high moisture content and poor crop stand indicated the presence of shallow aquifers close to the main canal. Digital analysis facilitated some indicators for segregating such land uses, limited to optical range. Ground truth study found patchy crop stand, moist soil profile and subsurface soil salinization indicating the presence of high water table (<1.5 m). It also found fluctuating (1.5–6.0 m) water table with poor vegetative growth indicating areas sensitive to waterlogging These were classified as potential waterlogging. Moderate to high soil salinity was found at surface and at the control section (0.2–0.8 m) of soil profiles indicating initiation of secondary salinization. Coarse to medium soil texture facilitated capillary rise of salts with the advancing water table in irrigated zone. The presence of fine textured and impermeable calcium carbonate layers at a depth below the surface enhanced waterlogging and rise of water table. The preponderance of chlorides and sulfates of sodium, calcium and magnesium was found in the salinized areas. The quality of ponded water was extremely poor and unfit for its reuse. The ground water was saline in some areas but normally lies within the prescribed limit. The quality of drainage water was poor in saline depression and unsuitable for reuse. These were moderate in other areas suggesting its safe reuse if mixed with good quality water. Suitable soil and water management practices are necessary for sustainable crop production in the irrigated areas     

Quantification of atmospheric oxygen levels during the Paleoproterozoic using paleosol compositions and iron oxidation kinetics

The increase in atmospheric oxygen during the Precambrian is a key to understand the co-evolution of life and environment and has remained as a debatable topic. Among various proxies for the estimation of atmospheric oxygen levels, paleosols, ancient weathering profiles, can provide a quantitative pattern of atmospheric oxygen increase during the Precambrian period of Earth history. We have re-evaluated the chemical compositions of paleosols, and presented a new method of applying Fe²⁺ oxidation kinetics to the Fe²⁺ and Fe³⁺ concentrations in paleosols to decipher the quantitative partial pressure of atmospheric oxygen (P_O2) between 2.5 and 2.0 Ga. We first estimated the compaction factor (CF, the fraction of original thickness) using the immobile elements such as Ti, Al and Zr on equal volume basis, which was then used to calculate retention fractions (M_R), a mass ratio of paleosol to parent rock, of redox-sensitive elements. The CF and Fe_R values were evaluated for factors such as homogeneity of immobile elements, erosion, and formation time of weathering. Fe_R increased gradually within the time window of ∼2.5-2.1 Ga and remained close to 1.0 since ∼2.1 Ga onwards. Mn_R also increased gradually similar to Fe_R but at a slower rate and near complete retention was observed ∼1.85 Ga, suggesting an almost continuous increase in the oxidation of Fe²⁺ and Mn²⁺ in paleosols ranging in age between ∼2.5 and 1.9 Ga.We have modeled P_O2 variations during the Paleoproterozoic by applying Fe²⁺ oxidation kinetics to the Fe²⁺ and Fe³⁺ concentrations in paleosols, which enabled us to derive an Fe²⁺ oxidation term referred to as ψ. Possible changes in temperature and P_CO2 during this time window and their effects on resulting models of P_O2 evolution have been also considered. We assumed four cases for the calculations of P_O2 variations between 2.5 and 2.0 Ga: no change in either temperature or P_CO2, long-term change in only P_CO2, long-term changes in both temperature and P_CO2, and short-term fluctuations of both temperature and P_CO2 during the possible, multiple global-scale glaciations. The calculations indicate that P_O2 increased gradually, linearly on the logarithmic scale, from <∼10⁻⁶ to >∼10⁻³ atm between 2.5 and 2.0 Ga. Our calculations show that the P_O2 levels would have fluctuated significantly, if intense, global glaciation(s) followed by period(s) of high temperature occurred during the Paleoproterozoic. This gradual rise model proposes a distinct, quantitative pattern for the first atmospheric oxygen rise with important implications for the evolution of life.     

Early Neogene Radiolarian faunal turnover in the northern Indian Ocean: Evidence from Andaman-Nicobar

Two intervals of faunal turnover are revealed by the study of radiolarians from the Early to Middle Miocene sequence of Andaman-Nicobar belonging to Stichocorys wolffii-Calocycletta costata-Dorcadospyris alata zones. These faunal changes are reflected in the values of species diversity, change in abundance of taxa, origination and extinction events and change in radiolarian assemblages. One such faunal change is identified in the latest Early Miocene. The time of this faunal change is marked by the extinction of species like Carpocanopsis cingulata and appearance of Calocycletta costata, Giraffospyris toxaria, Acrocubus octopylus and Liriospyris parkerae, an increasing trend in percentage of cold water species and a decreasing trend in species diversity upwards. The interval coincides with the time of initiation of cooling of sea surface water. Another, and the most prominent faunal turnover of radiolarians is recognized in the Middle Miocene Dorcadospyris alata Zone at about 14.8–12.7 Ma and is characterized by almost complete disappearance of an earlier dominant assemblage and an increase in abundance of an assemblage that was practically absent in the older sequence. The time of this turnover can be correlated with the time of Middle Miocene cooling identified in the examined sequence.