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Studies on rare earth elements (REEs) of river sediments from Kerala, India indicate that the average total REE (SREE) of clay and silt-sized fractions is much higher than in Post-Archaean average Australian Shale (PAAS). Peak high SREE for the clay fraction is found in the rivers of central Kerala and, for the silt fraction, it is in south and central Kerala. SREE shows a moderate to strong correlation with Mn and P and, no correlation with Al, Fe and Ti in both size fractions. SREE also shows no correlation with heavy metals in the clay fraction but a strong correlation in silt fraction. PAASnormalized REE shows MREE-enrichment in almost all the samples. Further, LREE-enriched and HREEdepleted REE patterns are characteristic of sediments from south and central Kerala, and HREE-enriched or flat REE patterns are characteristic of sediments from north Kerala. Weak positive or weak negative Ce anomalies are characteristic of the sediments. The Eu anomaly is negative in a few silt fractions from south Kerala and positive in all other sediments. Sm/Nd ratios are high in the clay fraction and decrease with increasing SREE for the sediments of central Kerala. REE enrichment and REE patterns are related to the felsic component and heavy mineral content in the sediments of south Kerala, adsorbed REE associated with the weathering products of laterites in the sediments of central Kerala, and the dominance of mafic component in the sediments of north Kerala. The river sediments of central Kerala may serve as a viable REE deposit because of their high REE content, inexpensive mining, easy recovery and extraction of REE. Only 21 out of 41 rivers of Kerala were analysed in this study. Detailed exploration in other rivers may expand and confirm the potential REE deposits and their economic viability. This REE deposit is different from the placer sand deposits on the beaches of south Kerala. [ABSTRACT FROM AUTHOR]

Understanding patterns of erosion and sedimentation and their driving mechanisms is important for formulating a variety of estuarine management issues (conservation, shoreline protection, navigation, dredging and embanking). Therefore, the present study aims to determine the factors influencing the seasonal distribution and dynamics of suspended particulate matter (SPM) of two meso-(Mandovi and Zuari) and four micro-tidal (Terekhol, Chapora, Sal, and Talpona) river estuaries of Goa, on the central west coast of India. These estuaries exhibited salinity stratification near their mouths during the wet season and well-mixed water columns during the dry season. The SPM concentrations were two times higher in the wet season than in the dry season. Estuarine turbidity maximum (ETM) was a consistent feature in both the seasons at the mouth of the estuaries, except in the estuary of the Sal River. The in situ vertical distribution of SPM volume concentration and mean particle size allowed for a better visualization of the ETM formation and distribution. The gravitational circulation as well as flocculation at the salt-freshwater interface during the wet season and the impact of tidal and wind-induced currents at the river mouths during the dry season were primarily responsible for the formation of the ETMs. [ABSTRACT FROM AUTHOR]

Organic carbon (OC), total nitrogen (TN) and stable carbon and nitrogen isotopic compositions were measured in suspended particulate matter (SPM) and surface sediment along estuaries of Mandovi and Zuari rivers, two small mountainous river systems in western India during wet and dry seasons, to characterize the sources of organic matter (OM) in these systems. Unlike major rivers, SPM concentrations increase seaward with a general trend of decreasing particulate organic carbon (POC) in these rivers, mostly due to the presence of estuarine turbidity maximum (ETM) located downstream of the estuaries. POC and particulate nitrogen (PN) were higher in the Mandovi than in the Zuari estuary. Except during wet season in the Mandovi, POC/PN and δ15N were altered by biogeochemical processes in both the estuaries and are not indicators of source organic matter. PN/POC and 13Corg indicated the dominance of terrestrial plant-derived OM and terrestrial soil-derived OM respectively, in the Mandovi and Zuari estuaries during wet season. The 13Corg versus salinity plot indicated increasing proportions of marine OM seaward in both estuaries during dry season. OC and TN in the sediments of both estuaries were much lower than in the overlying suspended matter. The mean δ13Corg in the sediment and SPM were similar in both the seasons in Mandovi and only during wet season in Zuari estuary. Uniform mean values of δ13Corg in the lower estuary and bay of Zuari indicated efficient mixing of sediments during wet season. Sediments with relatively high δ13Corg and low δ15N in the upper estuary of Zuari were related to anthropogenic contamination by sewage effluents during dry season. It is estimated that each river contributed at least ~20% terrestrial organic carbon (TOC) to the coastal system during wet season and received similar quantity of TOC during dry season. Since there are more than 10,000 small rivers originating from monsoon-dominated and/or mountainous regions globally, it must be appreciated that their total TOC contribution to the coastal system must be substantial. [ABSTRACT FROM AUTHOR]

Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June-September, October-January, February-April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June-September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1-5.6ms-1) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February-April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2-3.7ms-1) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition. [ABSTRACT FROM AUTHOR]

Mineralogy and Sr–Nd isotopic composition of the <2-μm fraction of the Holocene and late Pleistocene sediments from 12 gravity cores collected along the western margin of India were used to delineate the provenance and understand the response of isotopes with respect to the source rock composition. Holocene sediments show distinct clay mineral associations representing three major sources: illite, chlorite-rich sediments from the Indus, smectite-dominated sediments from the Deccan Traps, and kaolinite and smectite-enriched sediments from gneissic rocks. The mixing of Indus-derived sediment with the Deccan Traps-derived sediment or the Deccan Traps-derived sediment with gneissic rock-derived sediment occurs in the deeper water cores. Sr isotopes are very sensitive to weathering and laterization. Weathering does not influence Nd isotopes. The 87Sr/86Sr ratios of the Holocene sediments in shallow water cores are higher and fluctuated widely than those in deeper water cores. ∊Nd correlates well with the clay mineral associations, indicating source rock composition or mixing of source sediments. Kaolinite-enriched sediments coupled with high Sr ratios and low ∊Nd on the SW margin of India suggest intense chemical weathering in the hinterland. The influence of the sediment from the Ganges–Brahmaputra, transported by the Bay of Bengal waters during the NE monsoon surface current or SW monsoon underwater current, on the composition of the sediments of the SW Indian margin is insignificant. The late Pleistocene sediments reflect a decrease of hydrolytic processes resulting in decrease of smectite and Sr isotopic ratio. Clay minerals and ∊Nd values suggest that the provenance and transport pathways of the late Pleistocene sediments are the same as those of the Holocene for each region. [Copyright &y& Elsevier]

Environmental and sea level indicators were investigated using dredge samples from late Quaternary carbonate deposits along the shelf break between Goa and Cape Comorin, India. Geomorphic features in the area were identified from sonar profiles and included isolated patch reefs with a relief of up to 10 m, and linear reefs with reliefs between 2 and 15 m. The main clast types recovered from these features include fragmented corals and carbonate nodules dominated by either encrusted foraminifera or coralline algae. Some of these clast types are clearly of shallow-water origin. Fragments of reef-forming Poritid corals, for example, were collected off Mangalore at depths of 110–105 m and dated between 11,520 and 12,610 14C years BP (13.42–14.77 ka). Nodules of similar age dominated by Lithothamnium and capped by foraminiferal veneers were also collected at −90 m off Cape Comorin. Their altered algal tissues are consistent with formation in shallow water, high-energy conditions. In contrast, nodules recovered off Kochi and Mangalore–Goa are of deeper water origin, younger in age (10,980–7350 14C years BP), and are dominated by Gypsina encrustations with volumetrically less algal encrustation. They show cyclic succession of foraminiferal–algal, or foraminiferal–algal–coral laminations in which the algal species are typical of deeper waters. The age and elevation of corals and shallow-water nodules are both consistent with published glacio-eustatic sea-level curves. In addition, the alternate micro-encrustations of foraminifera, algae and encrusting corals could indicate changing conditions from nutrient-rich and turbid to nutrient-poor and clear water that may be attributable to seasonal variations in sediment flux caused by monsoons. [Copyright &y& Elsevier]

Detailed petrological, mineralogical, geochemical and radiogenic (U, Sr, Nd) and stable isotope (C, O, S) studies have been carried out on the Quaternary phosphorites of the continental margin off Chennai, southeast coast of India. These phosphorites are formed as a result of trapping and binding of sediments by microbial mats and are similar to phosphate stratiform stromatolites. Detrital and biogenic constituents enclosed in the phosphorites controlled the major and minor element composition. Except for Sr and U, the concentrations of most of the trace metals are lower than those in average shale and phosphorite. Middle rare earth element (MREE)-enriched patterns are the characteristic feature. The U–Th dating method indicates that the ages of the phosphorites are beyond 300,000 years. 87Sr/86Sr ratios of the phosphorites are higher than that of present-day seawater and &epsiv;Nd values are more negative than those of seawater of the Atlantic Ocean. Carbon isotope ratios are within the range expected for the oxic/suboxic zone but sulfur isotope ratios indicate suboxic conditions during phosphorite formation. These results imply that the benthic microbial mats thrived on the shallow shelf during the Quaternary low sea level conditions. Periodic or episodic sedimentation onto the mats led to their death. The bacteria associated with decaying microbial mats utilised phosphorus supplied by continental sources and rapidly precipitated phosphate. The availability of a high percentage of phosphorus in seawater seems to be an important controlling factor for the formation of phosphate stromatolites. The composition of these phosphorites differs from the modern phosphorites in upwelling regions, but are similar to Cambrian apatite stromatolites. These phosphorites provide evidence that the replicates of ancient phosphate stromatolites do exist in the Quaternary. [Copyright &y& Elsevier]

This paper presents the algebra of structural numbers, a new approach to the analysis of passive and active circuits. The theory is explained and applied to the passive and active circuits with reference to transistor circuits. The method is computer oriented and offers advantages of economizing computer time and space. The method eliminates lengthy algorithms for evaluation of determinants and the necessity of drawing the flow-graphs. [ABSTRACT FROM AUTHOR]