Articles written in Journal of Earth System Science
Volume 89 Issue 1 March 1980 pp 23-29
The miliolite deposits of Saurashtra have been dated by234U,230Th,231Pa and14C methods. Concordant ages of 105 years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting a contemporaneous origin for both. The lower14C ages (≤40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute only ≤10% by weight, as such the aeolian characteristics of quartz grains may not be relevant to the origin of the miliolites.
Volume 92 Issue 3 November 1983 pp 255-260
Vertical profiles of137Cs and210Pb have been determined in a 9 m column of ice from accumulation zone of Changme-Khangpu glacier in north Sikkim valley.137Cs activity varies from 4 to 22 dpm/ L. In many samples210Pb occurs at a level of 20 to 65 dpm/ L which is much higher than the expected fallout value.137Cs and210Pb activities correlate well with each other but not with the dust content. Possibility of210Pb production in the nuclear explosions is discussed. Several peaks appear in the depth profile of137Cs and210Pb which can be matched with Chinese atmospheric nuclear explosions with some phase difference if a uniform ice accumulation rate of 0.7 m per year is assumed since 1969.
Volume 107 Issue 4 December 1998 pp 251-263
The boundary horizons of the Cretaceous-Tertiary (Um Sohryngkew River section, Meghalaya and Anjar section, Kutch), the Permo-Triassic (Guling, Lalung, Ganmachidam and Attargoo sections, Spiti valley) and the Eocene-Oligocene (Tapti River section, Gujarat) have been identified in the sedimentary records of the Indian subcontinent. These sections have been studied for geochemical anomalies. The results are discussed in the framework of extra-terrestrial and terrestrial causes proposed to explain the physical, chemical and mineralogical observations at these boundaries. A critical analysis suggests that although the astronomical causes, particularly the bolide impacts, can easily explain the geochemical and physical changes, the terrestrial causes (volcanism) may have played a significant role in creating the biological stress observed in fossil records (mass extinction) at or near some of these boundaries.
Volume 110 Issue 2 June 2001 pp 103-110
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.
Volume 110 Issue 2 June 2001 pp 111-132
Chemical analysis of nine Deccan flow basalts at Anjar, Kutch, western India, indicates that all, except the uppermost flow F-9, are alkaline. In their major and trace element composition, the alkali basalts resemble Ocean island basalts (OIB). Similarities of many diagnostic trace element ratios (e.g. Sm/Nd, Ba/Nb,Y/Nb and Zr/Nb) are similar to those found in the Réunion Island basalts. The uppermost basalt is tholeiitic and chemically resembles the least contaminated Deccan basalt (Ambenali type). The Anjar basalts have iridium concentration ranging between 2 and 178 pg/g. Some of these values are higher by about an order of magnitude compared to the Ir concentration in other basalts of the Deccan. A synthesis of chemical, palaeomagnetic and geochronologic data enables us to construct a chemical and magnetic stratigraphy for these flows.
The three flows below the iridium enriched intertrappean bed (IT III) show normal magnetic polarity whereas all except one of the upper basalts show reversed magnetic polarity. The sequence seems to have started in polarity zones 31N and probably continued up to 28R or 27R. The results presented here support the view that Deccan volcanism in Kutch occurred on a time span of a few million years.
Volume 114 Issue 2 April 2005 pp 111-124
We report the presence of a 3–5 cm thick loose fragmental layer in the Siliceous Earth at Matti ka Gol in the Barmer basin of Rajasthan. Petrographic, chemical and mineralogical study reveals the presence of abundant volcanic debris such as glass shards, agglutinates, hollow spheroids, kinked biotites, feldspars showing oscillatory zoning, olivines, ilmenite and native iron. The presence of similar particles in the whole section suggests that the Siliceous Earth is a volcanic ash. Stratigraphic correlation, palynological and microvertebrate data suggest that the Siliceous Earth may have deposited over a short span of time during the Upper Cretaceous to Lower Palaeocene. In view of the possibility that this section may contain K/T impact debris, we looked for grains having impact signatures. Some patches of the Siliceous Earth of Bariyara show the presence of Ni-rich (> 0.5%) vesicular glasses, sanidine spherules, magnesioferrite crystals, soot, etc., but because of their low abundance, it is not possible to establish if they are volcanic, micrometeorite ablation products or a part of the K/T impact ejecta.
Volume 114 Issue 6 December 2005 pp 573-575
Volume 114 Issue 6 December 2005 pp 601-607
During the accretion of planets such as Earth, which are formed by collisional accretion of plan-etesimals, the probability of capture of interplanetary bodies in planetocentric orbits is calculated following the approach of Hills (1973) and the n-body simulation, using simplectic integration method. The simulation, taking an input mass equal to about 50% of the present mass of the inner planets, distributed over a large number of planetoids, starting at 4 M y after the formation of solar system, yielded four inner planets within a period of 30 M y. None of these seed bodies, out of which the planets formed, remained at this time and almost 40% mass was transferred beyond 100 AU. Based on these calculations, we conclude that ∼ 1.4 times the mass of the present inner planets was needed to accumulate them. The probability of capture of planetoids in geocentric orbits is found to be negligible. The result emphasizes the computational difficulty in ’probability of capture’ of planetesimals around the Earth before the giant impact. This conclusion, however, is in contradiction to the recent observations of asteroids being frequently captured in transient orbits around the Earth, even when the current population of such interplanetary bodies is smaller by several orders of magnitude compared to the planetary accumulation era.
Volume 114 Issue 6 December 2005 pp 699-709
The primary objectives of the Chandrayaan-1 mission are simultaneous chemical,mineralogical and topographic mapping of the lunar surface at high spatial resolution.These data should enable us to understand compositional variation of major elements,which in turn,should lead to a better understanding of the stratigraphic relationships between various litho units occurring on the lunar surface.The major element distribution will be determined using an X-ray ﬂuorescence spectrometer (LEX),sensitive in the energy range of 1 –10 keV where Mg,Al,Si,Ca and Fe give their K 𝛼 lines.A solar X-ray monitor (SXM)to measure the energy spectrum of solar X-rays,which are responsible for the ﬂuorescent X-rays,is included.Radioactive elements like Th will be measured by its 238.6 keV line using a low energy gamma-ray spectrometer (HEX)operating in the 20 –250 keV region.The mineral composition will be determined by a hyper-spectral imaging spectrometer (HySI)sensitive in the 400 –920 nm range.The wavelength range is further extended to 2600 nm where some spectral features of the abundant lunar minerals and water occur,by using a near-infrared spectrometer (SIR-2),similar to that used on the Smart-1 mission,in collaboration with ESA.A terrain mapping camera (TMC)in the panchromatic band will provide a three-dimensional map of the lunar surface with a spatial resolution of about 5 m.Aided by a laser altimeter (LLRI) to determine the altitude of the lunar craft,to correct for spatial coverage by various instruments, TMC should enable us to prepare an elevation map with an accuracy of about 10 m.
Four additional instruments under international collaboration are being considered.These are: a Miniature Imaging Radar Instrument (mini-SAR),Sub Atomic Re ﬂecting Analyser (SARA), the Moon Mineral Mapper (M3)and a Radiation Monitor (RADOM).Apart from these scientiﬁc payloads,certain technology experiments have been proposed,which may include an impactor which will be released to land on the Moon during the mission.
Salient features of the mission are described here.The ensemble of instruments onboard Chandrayaan-1 should enable us to accomplish the science goals de ﬁned for this mission.
Volume 114 Issue 6 December 2005 pp 733-738
The Chandrayaan-1 mission to the Moon scheduled for launch in late 2007 will include a high energy X-ray spectrometer (HEX) for detection of naturally occurring emissions from the lunar surface due to radioactive decay of the238U and232Th series nuclides in the energy region 20–250 keV. The primary science objective is to study the transport of volatiles on the lunar surface by detection of the 46.5 keV line from radioactive210Pb, a decay product of the gaseous222Rn, both of which are members of the238U decay series. Mapping of U and Th concentration over the lunar surface, particularly in the polar and U-Th rich regions will also be attempted through detection of prominent lines from the U and Th decay series in the above energy range. The low signal strengths of these emissions require a detector with high sensitivity and good energy resolution. Pixelated Cadmium-Zinc-Telluride (CZT) array detectors having these characteristics will be used in this experiment. Here we describe the science considerations that led to this experiment, anticipated flux and background (lunar continuum), the choice of detectors, the proposed payload configuration and plans for its realization