Microbial mat structures in profile: The Neoproterozoic Sonia Sandstone,Rajasthan, India

Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration.     

Characterization of hydrogeochemical process and evaluation of water quality of seven geothermal springs,Bakreswar, India

A study was conducted in seven geothermal springs located in Bakreswar, District Birbhum, West Bengal, India, in order to assess numerous geochemical processes which were responsible for chemical composition of thermal and mineralized water. The study area lies over the Sone, Narmada, and Tapti lineament of Precambrian Chotanagpur Gneissic Complex. Water chemistry has been carried out based on reaction stoichiometry and geo-statistical tools to identify geochemical process. Piper and Gibbs diagram suggest that the spring water belongs to Ca²⁺-Mg²⁺-HCO₃^??+?CO₃^2? water type and are controlled by rock dominance. Dissolution and precipitation of calcite, dolomite, gypsum, and fluorite minerals were identified as principle source of major ions in seven geothermal spring water. Principle component analyses revealed that major ions of spring water are derived from geogenic processes such as weathering, dissolution, and precipitation of various minerals. Overall results suggest that major ions of the spring’s water are derived from natural origin because no evidence of anthropogenic sources was observed during the study period. This study has also revealed that water quality of spring’s water is not suitable for drinking purposes and quite suitable for irrigation because of high abundance of Na⁺, K⁺, Cl^?, and HCO₃^? ions.     

Identification of water-bearing fractures in hard rock terrain by electrical conductivity logs, India

For the delineation of water-bearing fractures in hard rock areas, a new hydro-chemical technique has been developed which is based on electrical conductivity (EC) logs. The EC logs were carried out in experimental shallow bore wells (≈50 m) in three different parts of India. A sharp variation in EC was observed near water-bearing fractures in hard rock areas. To access applications of this technique, different locations in India were selected and experimental bore wells (≈50 m) were drilled. These were:

Evaluation and augmentation of safe drinking water supply schemes in Salur Mandal,Vizainagaram district,Andhra Pradesh

In order to assess the groundwater potentiality and augmentation of water supply schemes, estimation of the safe yield, well loss, formation loss, horse power of pump, depth of pump installation and duration of the pumping are essential. These parameters are estimated either by means of in-situ test or laboratory test. But the applicability of result from the laboratory test has limitations while in-situ tests give real representation of individual well of aquifer. The most common in-situ test is pumping test performed on well, which involves measurement of the fall and rise of water level with respect to time. The changes in water level (drawdown/recovery) and its quality are caused due to pumping of water from the well. Such study was carried out in Salur Mandal, Vizainagaram, Andhra Pradesh, India.     

Gravitational wave emission from a companion black hole in the presence of an accretion disc around a super-massive Kerr black hole

Gravitational wave signal characteristics from a binary black hole system in which the companion moves through the accretion disc of the primary are studied. We chose the primary to be a super-massive  ( M = 10⁸ M_⊙)  Kerr black hole and the companion to be a massive black hole  ( M = 10⁵ M_⊙)  to clearly demonstrate the effects. We show that the drag exerted on the companion by the disc is sufficient to reduce the coalescence time of the binary. The drag is primarily due to the fact that the accretion disc on a black hole deviates from a Keplerian disc and becomes sub-Keplerian due to inner boundary condition on the black hole horizon. We consider two types of accretion rates on to the companion. The companion is deeply immersed inside the disc and it can accrete at the Bondi rate which depends on the instantaneous density of the disc. However, an accretion disc can also form around the smaller black hole and it can accrete at its Eddington rate. Thus, this case is also studied and the results are compared. We find that the effect of the disc will be significant in reducing the coalescence time and one needs to incorporate this while interpreting gravitational wave signals emitted from such a binary system.