Biostratigraphy and depositional environment of the Miocene limestone bed of Baripada,Mayurbhanj district,Odisha: Foraminiferal,sedimentological and bulk organic geochemical evidences

Baripada Marine Beds (BMB) have been studied extensively in terms of its mega fossil content. However, not much has been discussed about the foraminiferal content and the organic matter assemblage in these beds. The fossiliferous sequence of BMB consists of sandstone, shale and limestone units. The present study is persued on the limestone unit of BMB. Foraminiferal, thin section and rock-eval pyrolysis studies were performed on the 33 surface samples collected from five sections of Jamdapal and Mukurmatia region along the Budhabalang river bank. Foraminifera are less abundant in the samples of Jamdapal, whereas Mukurmatia is comparatively rich. First appearance datum of Globorotalia menardii[ranges since middle Miocene (12.6 Ma); FAD at planktic foraminiferal zone N12] and last appearance datum of Neogloboquadrina continuosa [ranges between early Miocene (23.2 Ma) to late Miocene (8.3 Ma); FAD at planktic foraminiferal zone N4B and LAD at N16] together suggest that the limestone unit was deposited in between 12.6 to 8.3 Ma within the upper Miocene. Also, the association of shallow water benthic foraminifera (Species of Ammonia, Asterorotalia, Bolivina, Buliminella, Cibicides, Challengerella, Criboelphidium, Cribononion, Elphidium, Hanzawaia, Nonionella) and planktic foraminifera (Globigerina falcoensis, Globigerina woodi, Globorotalia menardii, Neogloboquadrina continuosa) together with oyster bank and shark teeth suggest deposition of limestone within well oxygenated, tropical, shallow water, open marine condition (within 40m water depth). Lithological and thin section studies together with global sea level fluctuation history advocate that upper Miocene marine transgression promoted the formation of this unit. Bulk organic geochemical data obtained by the rock-eval pyrolysis studies on selected samples indicate a low total organic carbon (TOC), with low hydrogen index (HI), high oxygen index (OI). The organic facies is characterised by type-IV kerogen with major contribution from near shore terrestrial plants. This also suggests deposition in shallow, oxygenated environments that did not promote significant accumulation and preservation of organic content in sediments.     

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south‐central New York. All samples were collected ?1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [⁴He], thermogenic [CH₄], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon‐rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.     

The effect of pulse profile evolution on pulsar dispersion measure

In an earlier paper, based on simultaneous multifrequency observations with the Giant Metrewave Radio Telescope (GMRT), we reported the variation of pulsar dispersion measures (DMs) with frequency. A few different explanations are possible for such frequency dependence, and a possible candidate is the effect of pulse shape evolution on the DM estimation technique. In this paper we describe extensive simulations we have done to investigate the effect of pulse profile evolution on pulsar DM estimates. We find that it is only for asymmetric pulse shapes that the DM estimate is significantly affected due to profile evolution with frequency. Using multifrequency data sets from our earlier observations, we have carried out systematic analyses of PSR B0329+54 and PSR B1642−03. Both these pulsars have central core-dominated emission which does not show significant asymmetric profile evolution with frequency. Even so, we find that the estimated DM shows significant variation with frequency for these pulsars. We also report results from new, simultaneous multifrequency observations of PSR B1133+16 carried out using the GMRT in phased array mode. This pulsar has an asymmetric pulse profile with significant evolution with frequency. We show that in such a case, amplitude of the observed DM variations can be attributed to profile evolution with frequency. We suggest that genuine DM variations with frequency could arise due to propagation effects through the interstellar medium and/or the pulsar magnetosphere.     

Torsional vibration of a composite truncated conical bar

Summary Torsional vibration of a body composed of two conical bars, the upper one being made of non-homogeneous material and the lower of a homogeneous material, by the application of a shearing stress on the upper end has been considered in the problem. It is assumed that the lower end of the composite body is fixed and the lateral surface is free from shearing stress.     

Study of drainage pattern of Raniganj Coalfield (Burdwan district) as observed on Landsat-TM/IRS LISS II imagery

Drainage pattern of Raniganj Coalfield basin has been mapped as observed on false colour composites of Landsat TM and IRS-LISS II imagery and their characteristics have been interpreted in terms of basin morphology, surface materials and underlying rock types. The drainage system of the region is composed of 3 perennial rivers with 15 ephemeral nalas and jhors which as a whole flows on recent peneplain basin. Although, on an average, nalas and jhors of the area have smaller stream length and with smaller basinal area but they hold sufficient amount of water during monsoon and therefore by effective planning and management, surface water resources could be enhanced in the region.     

The disturbance due to periodic surface traction in a semi-infinite medium of varying elasticity and density

Summary In this paper, the shear displacement due to a transverse periodic surface traction on a semi-infinite elastic solid, in which the rigidity and density vary exponentially with the depth has been obtained. The normal modes are calculated for high frequencies and the surface displacement obtained numerically in a particular case for a low frequency.     

Crystal chemical and 57Fe Mössbauer study of chromite from the Nuggihalli schist belt (India)

Summary In the Nuggihalli schist belt (India), chromite bodies were affected by intense serpentinization followed by weathering. In spite of the strong oxidation of the chromite grains, some unaltered cores were preserved, and they were characterised using electron probe microanalysis, single-crystal X-ray diffraction and low temperature ⁵⁷Fe Mössbauer spectroscopy. Results of such investigations revealed that chromite cores from the Nuggihalli schist belt are effectively not oxidised, and their study revealed that chromite was not affected by greenschist-facies metamorphism. The apparently highly ordered cation distribution of the chromites, which would suggest low equilibration temperature, is just caused by the very high Cr contents, which prevent Mg–Al exchange between T and M sites. Using Fabries (1979) geothermometer a temperature of about 1180°C was retrieved (Mitra and Bidyananda, 2003), which therefore corresponds to the quenched-in igneous equilibrium.     

Photogeologic mapping north of Khairwara,Udaipur district,Rajasthan

Photogeologic mapping of a sample area defined by latitudes 24° O to 6′N and longitudes 73° 30′ to 45′ E from a part of the Aravalli orogen, illustrates the advantages, as well as limitations, of photo-interpretation (PI) in terrains comprsing, highly deformed ancient rock formations. Discrimination between psammitic and pelitic metasediments is easy, using micro-relief and drainage parameters as PI elements; but that between pelites, ultra-basic schists and impure marbles is difficult and less reliable. Trends of foliations, several sets of joints and faults are distinct on the aerial photographs, but complete reconstruction of the superposed fold geometry is not possible. Within the area studied, dominantly pelitic, psammitic and a little clacareous metasediments, intruded by ultra-basics, exhibit a prominent and persistent NNE trend defined by lithologic contacts, bedding and foliations, with steep northwesterly dips. In its central part, bands of psammites within the pelites exhibit a hook shaped fold interference pattern (type 3 of Ramsay, 1967) with the later upright (Fleuty, 1964) fold axial trace trending northwesterly.     

Significance of contrast in the early stages of the structural history of the Delhi and the pre-Delhi rock groups in the Proterozoic of Rajasthan, western India

Structures of four generations are decipherable both in the pre-Delhi rocks of central Rajasthan, and in the Delhi rocks of Khetri in northeastern Rajasthan and around Todgarh in central Rajasthan. There is a remarkable identity in the later phases of the deformational history of the two groups, with gravity-induced structures followed by conjugate folds due to longitudinal shortening (N-S in northeastern Rajasthan and NE-SW in central Rajasthan). The earlier stages of the structural history of the two groups are, however, significantly different. The E-W-trending reclined folds of the first generation in the pre-Delhi rocks are absent in the Delhi rocks throughout Rajasthan. The NNE- to NE-trending folds of the second generation in the pre-Delhi groups are upright, whereas these structures in the Delhi rocks are of two phases—recumbent folds, followed by coaxial upright folds. The folds of the first and the second phases in the Delhi rocks plunge gently NE or SW where they are not affected by subsequent deformations. But the NE-trending folds in the pre-Delhi rocks show an extreme variation in axial plunge from horizontal to vertical, even where they are unaffected by later movements. Evidence has been adduced to suggest that these differences in the earlier phases of the structural evolution of the two groups are due to an angular unconformity between the Delhi and the pre-Delhi rocks.