A mid to late Holocene record of palaeoclimatic changes from Nal Sarovar: a palaeodesert margin lake in western India

With a view to obtain palaeoclimatic data from a climatically sensitive region we have studied core samples from Nal Sarovar, a large shallow lake lying within the palaeodesert margin of Thar in western India. A combination of C/N ratios and δ¹³C on a radiocarbon-dated core section have been used as climatic proxies. A high-resolution record extending back to ca. 6.6 ka BP has been reconstructed. The data indicate that, in the past, climate has varied from drier to wetter than present on time-scales of few hundreds to few thousands of years. There are, however, significant differences on the timing of these wet and dry periods, when compared with the available data from lakes farther north, in Rajasthan. Further, it looks unlikely that during the 6.6 ka the catchment areas of Nal Sarovar experienced such a significant increase in rainfall as has been suggested for the Rajasthan lakes. Interestingly, drier periods in Nal Sarovar data appear to correlate well with periods of glacier expansion in Eurasia indicating that the palaeoclimatic variations recorded in Nal Sarovar are a regional feature. © 1997 John Wiley & Sons, Ltd.     

A NOTE ON DAMAGE-BASED INELASTIC SPECTRA

When a structure is subjected to moderate to severe ground motions, a few excursions of the response yield level may take place following the reductions usually enforced in the design forces. These excursions are associated with progressive damage in the structure. Thus, a choice of the design level has to be suitably based on the maximum damage to be allowed in the structure. In this paper, a stochastic technique of developing damage-based non-linear spectra has been proposed for the aseismic design of those structures which can be idealized through Single-Degree-Of-Freedom (SDOF) oscillators. The proposed technique has been illustrated by obtaining the non-linear spectra which can possibly be used for a damage-based design. Along with the spectra, allowable ductility demand which should be supplied through proper sizing and detailing of the members and is compatible with the damage has also been specified. The non-linear SDOF oscillators have been approximated for this purpose by equivalent linear oscillators using a new stochastic linearization technique. The proposed linearization technique has been validated through simulation results in the case of an idealized, non-hysteretic, Elasto-Plastic (EP) model.     

PROPAGATION OF TORSIONAL SURFACE WAVES IN VISCOELASTIC MEDIUM

It is well known that an elastic homogeneous half-space does not allow torsional surface waves to propagate. The present paper attempts to find out the possibility of propagation of such waves in a viscoelastic half-space. The study reveals that although the homogeneous elastic half-space does not allow torsional surface waves to propagate, a viscoelastic half-space does so. The wave is damped due to the viscoelastic parameter. It has also been found that as the viscoelastic parameter decreases, the medium becomes elastic and the torsional surface waves ceases to propagate.     

PERFORMANCE EVALUATION OF SUBMERGENCE RATIO OF A RECTANGULAR SUBMERGED VANE WITH A COLLAR

1 INTRODUCTION Odgaard and Kennedy (1983) suggested that for values of angle of attack, α greater than or equal to approximately 20o, a persistent scour hole is produced near the upstream end of a vane. As α was reduced the number of vanes producing obj…     

An isotopic investigation of a near-surface groundwater system

ABSTRACT

The distribution of environmental tritium, deuterium and oxygen-18 in the unsaturated zone and the underlying sandy phreatic aquifer was studied throughout 1981 in an area of high pine forests in the Rhine valley near Heidelberg. The observed vertical distribution of isotopes in the unsaturated zone can be satisfactorily explained by the combined use of a multi-cell model for moisture transport and an evapotranspiration model. The distribution in the underlying aquifer of the tracer input at the water table obtained using this method is found by replacing the total vertical diffusion coefficient in the diffusion equation with the dispersion coefficient. In this way observed tritium profiles are satisfactorily simulated for the period 1966–1981. The stable isotope profile in the unsaturated zone however remains largely unexplained due to inadequate data on the stable isotope content of precipitation over the investigated area.     

Major,Trace, and Rare Earth Elements in the Sediments of the Central Indian Ocean Basin: Their Source and Distribution

Abstract

A large number of surface sediments as well as short sediment cores collected in the Central Indian Ocean Basin have been subjected to various geochemical investigations during the last one and half decade. The studies varied, covering different aspects of sediments and resulting in a number of publications. In the present article, we have put together the data from 82 surface sediments and 14 short sediment cores, including 25 new analyses, to study the trend of their distribution and source at large. The distribution maps of elements show that highest concentrations of Mn, Cu, Ni, Zn, Co, and biogenic opal in the surface sediment occurs between 10°S and 16°S latitude, where diagenetic ferromanganese nodules rich in Mn, Cu, Ni, and Zn are present. The studies highlight that the excess element concentration (detrital unsupported) such as Mn, Cu, Ba, Ni, Co, Pb, and Zn have contributed >80% of their respective bulk composition. These excess elements exhibit strong positive correlation with each other suggesting their association with a single authigenic phase such as Mn oxide. Biogenic opal contributes 30–50% of the total silica in the siliceous sediment. Aluminum, Fe, and K have contributed >60% from terrigenous detrital source compared to their bulk composition. In calcareous ooze, Ca, and Sr excess contribute >95% while, in siliceous ooze it is only 50% of their bulk composition. Nearly 35% of structurally unsupported Al in the sediment raises doubt of using Al as a terrigenous index element to normalize the trace and minor elements. Biogenic apatite is evident by the positive correlation between Ca (<1%) and P. Calcium, Sr, and P depict a common source such as biogenic. Bulk element concentration such as Li, V, Cr, Sc, and Zr are positively correlated with Ti indicating their terrigenous detrital source. Rare earth element (REE) concentration increases from calcareous ooze to siliceous ooze and reaches a maximum in the red clay. Presence of positive Eu-anomaly in these sediments has been attributed to aeolian input. REE in these sediments are mostly carried by authigenic phases such as manganese oxide and biogenic apatite. Based on the distribution of transition elements in the sediment cores, three distinct zones—oxic at top, suboxic at intermediate depth, and a subsurface maxima—have been identified. Oxic and suboxic zones are incidentally associated with high and low micronodule abundance in the coarse fraction (>63 μm) respectively. Ash layers encountered at intermediate depth between 10 to 35 cm are correlative with the Youngest Toba eruption of ～74ka from Northern Sumatra. This ash is mainly responsible for the high bulk Al/Ti ratio up to 48.5 (three times higher than Post Archean Australian Shale), other than scavenging of dissolved Al by biogenic components.     

REFLECTIONS AND REFRACTIONS FROM CURVED INTERFACES: MODEL STUDY *

Reflections and refractions from curved interfaces were studied on two dimensional scale models. Time of arrival, amplitude and character of reflected, converted, and refracted waves were mainly used for this study. Some reflected refractions, refracted reflections and diffractions were also considered. It was possible to separate PS and SP waves and to study their amplitude and character separately. From the amplitude study of refracted arrivals it was concluded that the refracted ray path penetrates into the high velocity layer rather than propagating along the interface. Although most of the results are interesting from the theoretical point of view, a few applications to exploration problems are suggested.     

Flame and Graphite Furnace Atomic Absorption And Optical-Emission Spectroscopic Determination Of Yttrium and the Rare-Earth Contents of Sixteen International Reference Samples Of Rocks and Coal

A simplified calcium oxalate and ferric hydroxide coprecipitation procedure was applied for quantitative separation and concentration of yttrium and the rare-earth elements from eight USGS (STM-1, RGM-1, QLO-1, SCo-1, MAG-1, SDC-1, BHVO-1, SGR-1), three French (MA-N, AN-G, BE-N), four South African (NIM-35/71–38/71) reference rocks and one NBS coal (1632) before determination by flame and graphite furnace atomic absorption and optical-emission spectroscopy. The results agree or fall near mid-range of other published values, where available. The chondrite normalized distribution patterns are generally smooth and conform to the shapes of other analyzed samples of similar nature.