Hydrogeochemistry of the Koyna River basin,India

Hydrogeochemistry of the Koyna River basin, famous for the Koyna earthquake (magnitude 7) of 1967, has been studied. Basalt is the primary aquifer; laterites, alluvium, and talus deposits form aquifers of secondary importance. Groundwater generally occurs under water table conditions in shallow aquifers. Deeper aquifers are associated only with basalts. One hundred and 87 water samples were collected from various sources, such as dugwells, borewells, springs, and surface water, including 40 samples for analysis of iron. Only major constituents were analyzed. Analyses show that the concentrations of Ca²⁺ exceed that of Mg²⁺ in almost all water samples; the concentrations of Na⁺ are generally next to Ca²⁺ and are always higher than that of K⁺; and CO₃ ^2– and SO₄ ^2– are very low and are often negligible. Groundwater in borewells tapping deeper aquifers has higher mineralization compared to that in dugwells representing shallow aquifers. Majority of the water samples are dominated by alkaline earths (Ca²⁺, Mg²⁺) and weak acids (HCO₃ ⁻, CO₃ ^2–). Groundwater from shallow aquifers is generally calcium-bicarbonate type (53%) and calcium-magnesium-bicarbonate type (27%). In case of deeper aquifer, it is mostly calcium-magnesium-bicarbonate type (29%), sodium-bicarbonate type (24%), calcium-bicarbonate type (19%), calcium-magnesium-sodium-bicarbonate type (19%) and sodium-calcium-bicarbonate type (9%). Groundwater water is generally fit for drinking and irrigation purposes, except in the lower reaches of the Koyna River basin, which is affected by near water logging conditions.     

Degana (Rajasthan, India) and Tigrinoe (Primorye, Russia) tungsten and tin-tungsten deposits: Composition of mineral-forming fluids and conditions of wolframite deposition

Formation conditions of orebodies and conditions of wolframite deposition at the Degana tungsten deposits in Rajasthan, India and the Tigrinoe tin-tungsten deposit in the Russian Far East were studied. Differences in the composition and state of fluid systems were established by microthermometric study of fluid inclusions (FI) and thorough petrographic examination of FI. At the Degana deposit, the ore veins in granite were formed from K-Na-Ca-(Mg, Fe, etc.) chloride solutions with a salinity up to 36 wt % NaCl equiv at a temperature of >420 to 120°C and under a pressure reaching 1550 bar. The formation temperature of the orebodies hosted in breccia reached 450°C and pressure was below 400 bar. The salinity of mainly Nachloride aqueous solutions was no higher than 18 wt % NaCl equiv. At the Tigrinoe deposit, the temperature during formation of quartz-wolframite-cassiterite veins varied from 420 to 240°C and the pressure was no higher than 300 bar. The salt concentration of Na-chloride solutions was 7-3 wt %. Wolframite crystallized at the very beginning of ore deposition. Probable sources of fluids are discussed. It is suggested that the factors controlling wolframite deposition could have been different even at the same deposit.     

Stable isotope analysis of carbon and nitrogen in angrites

Angrites are a small group of ancient basaltic achondrites, notable for their unusual chemistry and extreme volatile depletion. No comprehensive study of indigenous light elements currently exists for the group. Measurement of the abundances and isotopic composition of carbon and nitrogen could provide information pertaining to the evolution of the angrite parent body. Bulk‐sample stepped combustion analyses of five angrites and a glass separate from D'Orbigny were combined with earlier data and acid dissolution experiments of carbonates found in D'Orbigny to compile an inventory of indigenous carbon and nitrogen. Indigenous carbon combusted between 700 °C and 1200 °C, with abundances of 10–140 ppm and a mass‐weighted δ¹³C of ?25 to ?20‰ with the exception of D'Orbigny (δ¹³C approximately ?5‰). Nitrogen was released at 850–1200 ºC, 1–20 ppm with a δ¹⁵N ?3‰ to +4‰; again, D'Orbigny (δ¹⁵N approximately +20 to +25‰) was an exception. We interpret these components as largely indigenous and decoupled; the carbon in graphitic or amorphous form, while the nitrogen is present as a dissolved component in the silicates. No relationship with the textural sub‐classification of angrites is apparent. We suggest that the angrite parent body contains a reservoir of reduced carbon and thus may have undergone a change in redox conditions, although the timing and mechanism for this remain unclear.     

Comments on Placenticeras mintoi (Vredenburg, 1906) from the Bagh Beds (Late Cretaceous), central India with special reference to Turonian Nodular Limestone Horizon

The Late Cretaceous (Cenomanian to Coniacian) marine sediments of central India prevalently known as ‘Bagh Beds,’ have been deposited in the E-W extending Narmada Basin. The stratigraphy of these Cenomanian — Coniacian sediments has been reviewed and summarized. The Bagh Beds have been found to consist of three formations: Nimar Sandstone, Nodular Limestone and Corallian Limestone in ascending order. Main emphasis has been given to Nodular Limestone Formation (Turonian), which is the most fossiliferous horizon of the Bagh Beds. Nodular Limestone Formation has more or less alternating bands of varying thickness of nodular limestone and marl. It yielded numerous ammonoid specimens, which have been found to belong to a morphologically highly variable ammoniod taxon Placenticeras mintoi Vredenburg.     

Evolution of regoliths and landscapes in deeply weathered terrain — implications for geochemical exploration

Thick, commonly lateritic, regoliths are widespread in inter-tropical regions of the world and present particular challenges in exploration. These are best tackled through a sound understanding of the evolution of the landscapes in which they occur. The regoliths formed under humid, warm to tropical conditions and, although they may have been modified by later climatic changes, i.e., to more humid or more arid conditions, many chemical and mineralogical characteristics are retained. These include the geochemical expressions of concealed mineralization. Erosional and depositional processes control the preservation and occurrence of specific regolith units that may be used as sample media and, in turn, target size, element associations and contrast, thereby influencing sampling procedures, analysis and data interpretation. These parameters are best summarized in terms geochemical dispersion models based on the degree of preservation of the pre-existing lateritic regolith. Regolith–landform mapping permits an assessment of the terrain in terms of such models. In relict regolith–landform regimes, in which the lateritic regolith is largely preserved, broad multi-element anomalies in the upper ferruginous horizons (lateritic residuum) can be detected using sample intervals of 1 km or more. In contrast, in erosional regimes, where this material is absent, anomalies in upper saprolite, and the soil and lag derived from it, are more restricted in area and closer sampling intervals, (200×40 m or less) may be necessary. Lag and soil are, generally, ineffective in depositional areas, except where the sediments are very thin (e.g.,<2 m) or overburden provenance can be established. Stratigraphic drilling is necessary to establish whether the overburden overlies a buried lateritic horizon or an erosion surface cut in saprolite. Lateritic residuum remains an excellent sample medium if present, again with widespread haloes, but where it is absent, leaching and the restricted haloes in upper saprolite present formidable problems. Ferruginous saprolite or composites across the unconformity may be effective, but otherwise carefully targeted drilling and sampling through saprolite and saprock may be necessary. Partial extraction analyses have yet to demonstrate significant results except in very specific environments. In arid regions, pedogenic carbonate (calcrete, caliche) may be a valuable sample medium for Au exploration, principally in erosional regimes, and in depositional areas where the overburden is shallow. Sample intervals range from 1 km for regional surveys, through to 100×20 m in prospect evaluation. Saprolite is an essential sample medium in all landform environments, but the restricted halos and possibility of leaching requires that drilling and sampling should be at close intervals.     

Directional spread parameter at intermediate water depth

The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information.     

Mapping spatiotemporal patterns of events using social media: a case study of influenza trends

Tracking spatial and temporal trends of events (e.g. disease outbreaks and natural disasters) is important for situation awareness and timely response. Social media, with increasing popularity, provide an effective way to collect event-related data from massive populations and thus a significant opportunity to dynamically monitor events as they emerge and evolve. While existing research has demonstrated the value of social media as sensors in event detection, estimating potential time spans and influenced areas of an event from social media remains challenging. Challenges include the unstable volumes of available data, the spatial heterogeneity of event activities and social media data, and the data sparsity. This paper describes a systematic approach to detecting potential spatiotemporal patterns of events by resolving these challenges through several interrelated strategies: using kernel density estimation for smoothed social media intensity surfaces; utilizing event-unrelated social media posts to help map relative event prevalence; and normalizing event indicators based on historical fluctuation. This approach generates event indicator maps and significance maps explaining spatiotemporal variations of event prevalence to identify space-time regions with potentially abnormal event activities. The approach has been applied to detect influenza activity patterns in the conterminous US using Twitter data. A set of experiments demonstrated that our approach produces high-resolution influenza activity maps that could be explained by available ground truth data.     

Comparative study on projected clustering methods for hyperspectral imagery classification

In this study, projected clustering is introduced to hyperspectral imagery for unsupervised classification. The main advantage of projected clustering lies in its ability to simultaneously perform feature selection and clustering. This framework also allows selection of different sets of dimensions (features/bands) for different clusters. This framework provides an effective way to address the issues associated with the high dimensionality of the data. Experiments are conducted on both synthetic and real hyperspectral imagery. For this purpose, projected clustering algorithms are implemented and compared with k-means and k-means preceded by principal component analysis. Preliminary analyses of studied algorithms on synthetic hyperspectral imagery demonstrate good results. For real hyperspectral imagery, only ORCLUS is able to produce acceptable results as compared to other unsupervised methods. The main concern lies with identification of right parameter settings. More experiments are required in this direction.     

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m⁻³), low surface primary production (2.55 mg C m⁻³ day⁻¹) and low zooplankton biovolume (0.14 ml m⁻³). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO₃–N > 8.2 μM, PO₄–P > 0.8 μM, SiO₄–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m⁻³, PP – 9.23 mg C m⁻³ day⁻¹), and mesozooplankton biovolume (1.12 ml m⁻³) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.