Anirban Das

Sr and 87Sr/86Sr in rivers draining the Deccan Traps (India): Implications to weathering, Sr fluxes, and the marine 87Sr/86Sr record around K/T

The concentration of dissolved Sr and its 87Sr/86Sr has been measured in the headwaters of the Krishna River System and west flowing Western Ghat rivers, all of which have their drainage almost entirely in the Deccan Traps. The Sr concentration follows that of Ca and Mg with Sr/Ca and Sr/Mg ratios similar to that of Deccan basalts, suggesting that all these alkaline earths are released to waters nearly congruently from the Deccan basalts during chemical weathering. The 87Sr/86Sr range from 0.70614 to 0.70986, within that reported for the Deccan basalts. The dissolved Sr flux from the Deccan calculated from the measured data is ∼1.35 × 108 moles yr−1, ∼0.4% of the global riverine flux, which is nearly the same as the proportion of area covered by Deccan basalts relative to the global drainage. The flux, however, is a factor of ∼3 lower than that reported for the Narmada-Tapti-Wainganga (NTW) rivers draining the northern Deccan. This difference in Sr flux among rivers draining the various regions of Deccan could be natural spatial/temporal variations and/or due to supply of Sr to NTW rivers from nonbasaltic sources. Model calculations on the role of emplacement and weathering of Deccan on marine Sr isotope evolution around KTB and late Tertiary show that Deccan basalts can be an important contributor to the decline in 87Sr/86Sr during these periods. It is shown that to account for the pre-KTB dip in 87Sr/86Sr, the flux requirement from Deccan at that time would have to be several times the contemporary flux with 87Sr/86Sr of 0.705–0.708. Considering that the area of Deccan at KTB was about thrice the present area and that the weathering rate of Deccan basalts may have been much higher in early stages following eruption, such high fluxes at about KTB seem feasible. The disproportionately higher flux requirement for Sr is similar to that invoked to explain the pre-KTB decrease in 187Os/188Os. The calculations also show that the supply of unradiogenic Sr from basalts can have significant control on the long-term, ∼66 to ∼55 Ma, decline of marine 87Sr/86Sr.

Disproportionately high rates of sulfide oxidation from mountainous river basins of Taiwan orogeny: Sulfur isotope evidence

[1]xa0Sulfur isotopic tracing of river sulfate (SO42−) suggests that sulfide oxidation accounts for 85 ± 7% of the dissolved SO42−in one of the largest river systems (the Kaoping) of the Taiwan orogeny in the high-discharge season. This corresponds to a basin-wide contribution of ∼1.2–1.6% of pyrite-derived SO42− exported by rivers globally, from a river basin, which is only ∼0.003% of the global drainage area. Intense rainfall, high relief and active tectonics all favor intense physical weathering of the Kaoping basin, which promotes continuous exposure of fresh (sulfide) mineral surfaces for oxidative weathering. This coupling between physical and chemical weathering sustains disproportionately high sulfide oxidation, ∼400 times relative to surface area, in the Kaoping basin.

Application of an improved ion exchange technique for the measurement of δ34S values from microgram quantities of sulfur by MC-ICPMS

Motivated by limitations of the existing solution-based Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) studies to low sulfur concentrations, analytical procedures are reported for δ34S measurements (2σ precision of 0.24–0.34‰) at sulfur concentration [S] of 2 μg mL−1, following its purification by anion exchange resin (AER). δ34S values of International Atomic Energy Agency (IAEA) standards S-1, S-2 and S-3, and IAPSO seawater measured in this study agree (within uncertainties) with the consensus values measured by conventional techniques. These values also are in close agreement with the reported numbers by an MC-ICPMS study in which δ34S was measured at [S] of 20 μg mL−1 following its purification by cation exchange resin (CER). Anion exchange purification offers significant advantages of less sample requirement (2 μg S vs. 500 μg S), lower procedural blanks (∼12 ng vs. ∼250 ng of S), and less chemical requirements and sample processing times, over the cation exchange; therefore, δ34S measurements attempted in this study would suffer significantly from procedural blank if CER is used. It is believed that the procedures reported in this study would establish the application of MC-ICPMS to δ34S measurements in low sulfur containing samples, and should find widespread application especially in studies related to glacier, snow, rainwater and aerosol samples.

High iridium concentration of alkaline rocks of Deccan and implications to K/T boundary

We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in hydrothermal activity.

Instability of electrostatic waves in nonuniform weakly ionized magnetized plasmas

Novel electrostatic instabilities are shown to exist in a weakly ionized magnetoplasma having equilibrium density and electron temperature gradients. The growth rate of the instabilities critically depends on collisions between charged particles and neutral atoms. It is suggested that the present instabilities could be potential candidates for generating enhanced fluctuations during strong auroral activities in the E region of Earth’s ionosphere, in cometary plasmas, as well as in controlled laboratory experiments.

Krishna River Basin

Humans derive a variety of benefits from rivers, and the interconnection between river systems and human civilizations is known since ages. Large-scale anthropogenic and natural perturbations affect river (basins), which in turn, often have negative impacts on humans. Indian Peninsular rivers (e.g. the Krishna, Kaveri and the Godavari) bear significance across regional and global domains. Concern on closing of the Krishna river basin has brought forward the issue of water allocation amongst the user states. Hence, it is imperative to have crucial understanding of the geology, climate, rainfall, water resources, geomorphology, soil types and structure of the Krishna river basin. Krishna ranks as fifth largest river basin in India with a catchment area of ~2.6 × 105 km2. The river traverses a length of ~1400 km across the states of Maharashtra, Karnataka and Andhra Pradesh, before draining into the Bay of Bengal. The geology of the basin is dominated by basalts and crystalline rocks with alluvium, lateritic soils as minor components. It has about thirteen major tributaries (the Bhima and the Tungabhadra are the two largest) and several small-to-large-scale reservoirs for irrigation and/or hydropower generation schemes (e.g. Nagarjuna Sagar and Srisailam). The climate of the region is mostly semi-arid and dry except for humid regions along the Western Ghats. Soils in the basin are generally shallow in depth, and they belong to the type Entisols, Alfisols and Vertisols (black soils for cotton and sugarcane). The major cultivations of the basin are rice, sugarcane and oil seeds. Concerns are raised about shrinkage of the basin, frequent emergence of extreme events such as floods and degradation of water quality of the Krishna and its tributaries. Despite no major annual rainfall variation, observation of large-scale decrease in water discharges in both upper and lower reaches of the basin has stressed the need of management and allocation of water resources in the basin. Flooding in the recent years, in 2006 and in 2009, highlights the role of various human activities that might have contributed to the causes of flooding. Significant actions need to be taken to reduce the socio-economic losses such extreme events bring into the KRB. Water quality issues have also been reported by several workers, resulting mostly from discharges from the industrial towns such as Pune, Satara, Kurnool and Vijayawada. In order to minimize the effect caused by anthropogenic perturbations, the need is to pursue the recommendation proposed by experts (engineers, management specialists, geologists, economists, agricultural scientists, water quality chemists, government experts, etc.). Humans need to extract the socio-economic benefit from a river (basin); however, it should come with greater accountability to preserve the basin.