Search

The Asurabandha area on the southern side of the main Sukinda Ultramafic Complex (SUC) in the State of Odisha hosts some irregular and sporadic chromitite bodies which are completely detached from the main SUC. The isolated chromitite bodies are highly altered. Chromitite samples from these isolated bodies have been studied using a polarising petrological microscope, scanning electron microscope (SEM), field emission-scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer and the findings are presented here. In this area, we have identified the associated silicate minerals with chromite to be primarily opal-CT and quartz, contrary to the conventional Fe–Mg silicates such as olivine, pyroxene, or serpentine, although in few instances, the Fe–Mg silicates are identified. The original Fe–Mg silicates have almost completely been replaced by the silica polymorphs. Occurrences of opal-CT and quartz have been identified from their prominent X-ray diffraction peaks at d-spacing of 4.10 Å (with a shoulder peak at 4.32 Å) and 3.34 Å, respectively. The phase compositions are also confirmed by SEM-EDAX analyses. The average composition of opal-CT was found to be (in wt.%) SiO2: 95.41, MgO: 1.75 and FeO: 1.74. The presence of MgO and FeO in the composition of opal-CT, along with relict mesh-like micro-structures, indicate its formation by silicification/opalization from serpentines. A low-temperature hydrothermal alteration process driven by Si- and CO2-rich fluids through fractures and fault zones might have caused the removal of Mg and Fe from primary ultramafic silicate minerals and precipitation of opal-CT. This replacement process involved the initial dissolution of serpentine with preferential leaching of the metallic ions (Mg, Fe) and simultaneous precipitation of amorphous silica to form possibly opal-A in the beginning and then to opal-CT which subsequently transforms to microquartz because of the ordering of structure and removal of water through the dissolution–precipitation mechanism. [ABSTRACT FROM AUTHOR]

Before proceeding with any type of analysis, the condition of preservation of microfossil shells must be determined. Preservation of the shell affects tasks, such as holotype specimen selection, distribution chart, and specimen selection for geochemical analysis. The typical way to determine the degree of alteration is to use a visual examination under the stereo microscope. The deviation of visual characteristics such as colour and smoothness of the shell surface from unaltered shells depicts the alteration status. However, our eyes are frequently misled by the roughness of the shell created by tiny crystals that form due to recrystallization during the diagenesis process and are perceived to be smooth. In turn, the shell is regarded as well-preserved. To address these limitations, we have analyzed scanning electron microscope (SEM) images of ostracod shells using ImageJ, an image processing software, to determine the roughness parameters based on the grey value of the image. In addition, we compared the values of several parameters with different types of alterations, such as recrystallization and dissolution. This study aims to characterize the surface roughness of eight selected ostracod specimens from Middle Callovian to Upper Oxfordian beds of the southern part of Mainland Kachchh. The selected eight species - Cytherella masuguluensis, Progonocythere sp. A, Progonocythere jaisalmerensis, Bythocypris rajasthanensis, Paracypris contermia, Galliaecytheridea remota, Cytherelloidea sp. A, Cytherelloidea sp. B - belong to six genera and five families. [ABSTRACT FROM AUTHOR]

Anopheles subpictus (Grassi, 1899) is a potent malarial vector responsible for transmission of malarial pathogens in different regions of the world. The present study was conducted to investigate different characteristic features of eggs and adult body parts of An. subpictus mosquito prevalent in Hooghly, West Bengal, India. The adult mosquitoes were collected from rural areas of Hooghly and maintained in the laboratory. Eggs and adult body parts of An. subpictus were prepared for the SEM study and observed through a scanning electron microscope. The eggs of An. subpictus were found to be single, black in color with average length and width of 499.68 ± 11.33 µm and 96.23 ± 3.0 µm, respectively. Most of the adult body parts were found to be covered with fine setae and scales of unique characteristic features. Several morphological characters of An. subpictus mosquito of Hooghly showed marked differences when compared with the same species of other geographical regions. These morphological features of different life stages of An. subpictus mosquito revealed through scanning electron microscopy will surely illuminate the current knowledge about the vector identification of the study areas, which might contribute to vector management programmes in the Hooghly district. [ABSTRACT FROM AUTHOR]

River sand samples have been collected from Ponnai river, Tamil Nadu, India for characterization of minerals and heavy metals by different spectroscopic techniques. Initially, the samples were subjected by Fourier Transform-Infra Red (FT-IR) spectroscopic technique and infra-red absorption bands values are observed in the range of 515–520, 695–700, 775–780 cm−1 which shows the presence of quartz in all the samples. Similarly, infra-red peaks were absorbed for feldspar, kaolinite, calcite, gibbsite and organic carbon and confirmed by X-Ray diffraction (XRD) technique. Additionally, zircon, aragonite, magnetite and kyanite minerals were identified in the samples using only the XRD method. The concentration of heavy metals such as Pb, Cr, Zn, Ni, Hg, As, Mn, Cu has been determined by flame atomic absorption spectrometry (FAAS). An average metal concentration measured in mg kg−1 were: Pb 0.12, As 0.15, Hg 0.13, Cu 2.80, Zn 10.15 Cr 12.70, Ni 2.86 and Mn 104.94 and hence found in the order of Mn > Cr > Zn > Ni > Cu > As > Hg > Pb. These average values do not exceed the world average value and hence potentially do not affect the quality of sand in the river. In addition to that, presences of heavy metals are confirmed by scanning electron microscope equipped with energy dispersive X-ray spectrometry (SEM/EDS) analysis. In order to understand the possible natural and anthropogenic sources of heavy metals, multivariate statistical techniques such as Pearson correlation, principal component and cluster analysis were performed. Results obtained from the statistical techniques were good agreement with each other. [ABSTRACT FROM AUTHOR]

A new petrified palm stem Palmoxylon dindoriensis Khan, Roy et Bera, sp. nov. from the latest Maastrichtian (late Cretaceous)-earliest Danian (early Paleocene) sediments of the Deccan Intertrappean beds of Madhya Pradesh, central India is reported. Sections from different parts of the recovered stem were prepared by using standard thin section techniques and studied under transmitted light compound and scanning electron microscopes. The significant anatomical characters of the present fossil stem are the presence of well-preserved fibrovascular bundles (fvbs) with reniform type of dorsal fibrous sclerenchymatous part (dcap), two metaxylem vessel elements in each fvb, well-developed two-layered tabular parenchyma around dcap of fvb, fibrous bundles throughout the CZ, highly compact ground parenchyma tissue and the absence of centrifugal differentiation of fibrous part of fvb. The aforesaid anatomical attributes reveal its close resemblance with the extant taxa of subfamily Coryphoideae of the family Arecaceae having Cocos-type general stem organization. The core distribution of modern palms and the presence of highly compact ground parenchyma of the present fossil suggest that they thrived under a tropical, terrestrial warm, humid environment during the time of deposition (latest Maastrichtianearliest Danian). [ABSTRACT FROM AUTHOR]

Due to inaccessibility and tough conditions (high-altitude low-oxygen region) very less information is available about the Indian Tethys Himalayan sequences, particularly geochemical data are scarce. An attempt is made in the present study to evaluate the sediment geochemistry and paleo-redox conditions of Devonian–Carboniferous black shales from the Spiti region, Tethys Himalaya, using multi proxy approach. Besides black shales, this paper also provides the first in-depth study of the geochemistry of phosphatic nodules (hosted by the black shales) that will allow primary and secondary processes to be understood. Geochemical investigations, particularly redox-sensitive trace element ratios (for e.g. V/(V + Ni) > 0.5; Ni/Co = 4.3–7.2; V/Cr > 2 and positive Ce anomalies), suggest deposition of these black shales under sub-oxic to anoxic marine conditions, thus recording an ocean anoxic event in the region. These ocean anoxic events of Devonian–Carboniferous Spiti black shales, which possess distinctive geochemical signatures, can very well be correlated with global events such as Hangenberg Events and the Lower Alum Shale Event. The span of the chemical index of alteration (CIA) values (54–78), variation of ∆4Si% parameter (82–3) and C values (0.1–0.6) recorded in the black shales strongly indicate varying degrees of weathering conditions in the source area, which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in Devonian–Carboniferous period in the Spiti region. The distinct geochemical characteristics such as Y, Sr and rare earth element (REE) enrichments (particularly middle REE enrichments with a "hat-shaped" pattern) with high P2O5 contents (up to 14 wt%) distinguish the nodules from the host rocks (black shales). SEM (scanning electron microscope) results, supplemented by XRD (X-ray diffraction) studies of the nodules, show the dominance of calcium, silica and phosphatic phases. The diversity of clay minerals, significant variations in mineralogical composition and lack of any continuous vertical trend in the nodules suggest a relatively low impact on the primary environmental signal by burial diagenesis. [ABSTRACT FROM AUTHOR]

The East coast of India is subject to continuous changes by high energy events. We sought to assess the depositional conditions along the coast from the geophysical and sedimentological character of the dune sands of the Gopalpur and Paradeep coast of Odisha, and the Sagarnagar coast of North Visakhapatnam. Quartz layers of the heavy mineral-rich zone collected at a depth of ~2 m from the landward foot of the dunes in the Visakhapatnam and Odisha coast, gave the OSL age estimates as 1,050 ± 50 and 260 ± 10 years respectively, revealing that the age of the dunes in Visakhapatnam are older than those on the Odisha coast. Episodic high energy events have affected the coast. Evidence from ground penetrating radar data consists of three stratigraphic units. The upper unit consists of vague reflections, parallel to the ground in continuous manner, most probably formed by wind action. On the other hand, the middle layer shows high amplitude reflections of heavy mineral-rich massive layers, possibly the result of tsunami activity. The lower massive layer parallel to the ground surface shows a low reflection pattern. The GPR studies showed that the thickness of the heavy mineral layers is greater on the landward foot of the dune as compared to that on the seaward side. According to the grain size analysis, the dune is composed of both wind generated and tsunamigenic sediments. The scanning electron microscope studies revealed that the heavy minerals present in the dunes are mainly sillimanite, ilmenite, garnet, pyroxene, rutile, sphene, biotite, hornblende, zircon, monazite and magnetite. The study demonstrates the origin of sand dunes in different ages along the East Coast of India by the effect of various natural phenomena. [ABSTRACT FROM AUTHOR]

Extreme wave events of 1000 and 1500 years (radiocarbon ages) have been recently reported in Mahabalipuram region, southeast coast of India. Subsequently, we carried out extensive sedimenttological analysis in regions covering a total lateral coverage of 12 km with a new archeological site as the central portion of the study area. Twelve trenches in shore normal profiles exhibit landward thinning sequences as well as upward fining sequences confirming with the global signatures of extreme wave events. The sediment size ranges from fine-to-medium and moderately well sorted-to-well sorted, and exhibit positive skewness with platykurtic-to-leptokurtic nature. We now propose the abrupt winnowing or back and forth motion including unidirectional transport of these deposited sediments, which results in positive skewness. Textural analyses derived from scanning electron microscope studies (SEM) demonstrate the alteration produced, in the ilmenite mineral with vivid presence of pits and crescents with deformation observed on the surface due to extreme wave activities. This is further confirmed with the predominance of high-density mineral such as magnetite (5.2) and other heavy minerals in these deposits inferred the high-intensity of the reworking process of the beach shelf sediments. [ABSTRACT FROM AUTHOR]

Cretaceous phosphorites from the onshore of Tamil Nadu have been investigated for their origin and compared with those in the offshore. Cretaceous phosphorites occur as light brown to yellowish brown or white nodules in Karai Shale of the Uttatur Group in the onshore Cauvery basin. Nodules exhibit phosphatic nucleus encrusted by a chalky shell of carbonate. The nucleus of the nodules consists of light and dark coloured laminae, phosphate peloids/coated grains and detrital particles interspersed between the laminae. Scanning electron microscope (SEM) studies reveal trapping and binding activity of microbial filaments. A mat structure with linearly arranged microbial filaments and hollow, cell-based coccoid cyanobacterial mat are present. Nodules contain abundant carbonate fluorapatite, followed by minor calcite, quartz and feldspar. The P2O5 content of the phosphorites ranges from 18 to 26%. The CaO/P2O5, Sr and F contents are higher than that of pure carbonate fluorapatite. Concentrations of Si, Al, K, Fe, and Ti are low. We suggest that the nuclei of the nodules represent phosphate clasts related to phosphate stromatolites formed at intertidal conditions. At high energy levels the microbial mats were disintegrated into phosphate clasts, coated with carbonate and then reworked into Karai Shale. On the other hand, Quaternary phosphorites occur as irregular to rounded, grey coloured phosphate clasts at water depths between 180 and 320m on the continental shelf of Tamil Nadu. They exhibit grain-supported texture. Despite Quaternary in age, they also resemble phosphate stromatolites of intertidal origin and reworked as phosphate clasts onto the shelf margin depressions. Benthic microbial mats probably supplied high phosphorus to the sediments. Availability of excess phosphorus seems to be a pre-requisite for the formation of phosphate stromatolites. [ABSTRACT FROM AUTHOR]