Stratigraphic evolution of the Proterozoic succession in the western part of the Chattisgarh basin,India

The Meso to Neoproterozoic succession in the western Chattisgarh basin around Rajnandgaon has been classified into coarse siliciclastic dominated proximal and fine siliciclastic-carbonate dominated distal assemblages. The proximal assemblage, the Chandarpur Group, unconformably overlies the Neoarchean to Paleoproterozoic Dongargarh- Kotri volcanics (c.2.2-2.3 Ga), Bengpal Granite (c.2.5-2.6 Ga) and BIF of the Dalli-Rajhara Group (~2.4 Ga). The Chandarpur Group consists of 15-20 m thick conglomerate and feldspathic sandstone at the basal part of the succession, which is mapped as a lateral equivalent of the Lohardih Formation. The coarse clastics, conglomerate succession gradationally passes up to ~280 m thick succession of supermature sandstone, the Kansapathar Formation. The thick mudstone dominated heterolithic unit, the Gomarda Formation and its lateral equivalent, the Chaporadih Formation is not present in the western part of the Chattisgarh basin. The fine siliciclastic-carbonate assemblage of the Raipur Group conformably overlies the Chandarpur Group. The Raipur Group consists of Charmuria Limestone (~320 m), Gunderdehi Shale (~450 m), Chandi Limestone (~ 550 m) with Deodongar Member (~50 m) and Tarenga Shale. The sediments of Chandarpur Group were deposited in a shallow marine environment with occasional fluvial input in a relatively fluctuating sea level. The palaeoshoreline was NW-SE oriented with an open sea towards north which remained same throughout the deposition of the Chandarpur-Raipur sequence. It has also been inferred that the Lohardih Formation and the Kansapathar Formation represents a rifting phase followed by a stable subsidence stage when the basin evolved into a large epicontinental sea. The sequences further display signatures of passive margin sedimentation with multiple events of carbonate-shale rhythmite deposition.     

Chemical evolution in the high arsenic groundwater of the Huhhot basin (Inner Mongolia,PR China) and its difference from the western Bengal basin (India)

Elevated As concentrations in groundwater of the Huhhot basin (HB), Inner Mongolia, China, and the western Bengal basin (WBB), India, have been known for decades. However, few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the HB. In this study, the controls on solute chemistry in the HB have been interpreted and compared with the well-studied WBB, which has a very different climate, physiography, lithology, and aquifer characteristics than the HB. In general, there are marked differences in solute chemistry between HB and WBB groundwaters. Stable isotopic signatures indicate meteoric recharge in the HB in a colder climate, distant from the source of moisture, in comparison to the warm, humid WBB. The major-ion composition of the moderately reducing HB groundwater is dominated by a mixed-ion (Ca–Na–HCO₃–Cl) hydrochemical facies with an evolutionary trend along the regional hydraulic gradient. Molar ratios and thermodynamic calculations show that HB groundwater has not been affected by cation exchange, but is dominated by weathering of feldspars (allitization) and equilibrium with gibbsite and anorthite. Mineral weathering and mobilization of As could occur as recharging water flows through fractured, argillaceous, metamorphic or volcanic rocks in the adjoining mountain-front areas, and deposits solutes near the center of the basin. In contrast, WBB groundwater is Ca–HCO₃-dominated, indicative of calcite weathering, with some cation exchange and silicate weathering (monosiallitization).     

Synergistic Application of Optical and Radar Data for Archaeological Exploration in the Talakadu Region,Karnataka

Talakadu is a well known historic place situated on bank of the river Cauvery in Mysore district of Karnataka. The place is close to concave side of a prominent meander where large amount of sand has accumulated. It is believed that after construction of a reservoir upstream, sand was exposed to wind action burying the structures of Ganga dynasty and other later kingdoms. A number of buried sites have been identified by archaeological excavations conducted so far. Presently the area forms sand dunes with thick plantation cover. Analysis of RADAR data (fine beam RADARSAT and ENVISAT ASAR) led to identifying a hitherto unknown buried channel through the Old Talakadu town adjoining the excavated archaeological sites. The study suggests that RADAR penetration through the plantation canopy seems to have occurred as observed by comparing with corresponding optical data of LISS-IV. Below the canopy, sand and shrubs on top of the channel (topographically low area) are acting as smooth surface providing dark tone on radar imagery. During field validation GPS was extensively used to navigate through the forest canopy and locate the buried channel, excavated archaeological sites as well as other anomalous patterns. Synergistic application of optical (RESOURCESAT-1 LISS-IV and CARTOSAT-1 & 2) and radar (fine beam RADARSAT and ENVISAT ASAR) data led to identifying remote sensing based guides for archaeological exploration. Integration of known archaeological sites with the identified anomalous patterns was done in GIS environment. This study adds on to the knowledge base of the site and compliments already known information and suggested new areas for further archaeological exploration.     

Linkage of paraglacial processes from last glacial to recent inferred from Spituk sequence,Leh valley,Ladakh Himalaya

The paraglacial sequence in the Leh valley, Ladakh Himalaya preserves imprints of various processes active during deglaciation in the late phase of Last Glacial. In present work, a high resolution sedimentological record generated for Spituk is presented identifying aeolian episodes, mudflow events from Ladakh Range and debris flows extending from Zanskar Range across present Indus River. Two temporal phases of water ponding within Spituk Sequence are also identified. The seismites recorded at various stratigraphic depths and their association with the sediment facies signifies gravity induced process besides possible seismic activity as an added phenomena. Linkage between paraglacial processes since Last Glacial to Recent is tracked and evaluated.     

Diverse signatures of deformation, pressure-temperature and anatexis in the Rayagada sector of the Eastern Ghats granulite terrane

The granulites and granitoids around Rayagada in the north central part of the Eastern Ghats belt display structural and petrological differences when compared to similar rocks from Chilka and Jenapore in the northern Eastern Ghats. The impress of F₁ deformation is almost erased while that ofF ₃ is muted. The metapelites have a restricted chemical range and are non-migmatitic. There are two varieties of leptynitic granitoids, one of which is interlayered with yet another S-type granite containing cordierite. The maximum recorded temperature from geothermometers is 780‡C, but the magnitude of pressure is comparatively low, the highest value being 6.3 kbar. Another distinctive feature of the pressuretemperature record is the absence of evidence of decompression in the lower realms of pressure and temperature. Metamorphic reactions that could be identified indicate cooling, a noteworthy reaction being the sillimanite to andalusite transformation. Integration of data from pressure-temperature sensors suggest cooling at two pressures, 6 and 5 kbar. The generation of two types of granitoids from metapelites is interpreted to be due to intersection with solidus curves for pelitic and graywacke-like compositions, constrained by recent experiments, at 6 and 5 kbar. The first melting occurred on a prograde path while the second one was due to increase in temperature during exhumation at tectonic rates. Thus inspite of a broad similarity in the geodynamic scenario across the northern part of the Eastern Ghat belt, differences in exhumation rates and in style of melting were responsible for producing different signatures in the Rayagada granulite terrane.     

Hydraulic Effects of Shales in Fluvial-Deltaic Deposits: Ground-Penetrating Radar, Outcrop Observations, Geostatistics, and Three-Dimensional Flow Modeling for the Ferron Sandstone, Utah

Ground-penetrating radar (GPR) surveys, outcrop measurements, and cores provide a high-resolution 3D geologic model to investigate the hydraulic effects of shales in marine-influenced lower delta-plain distributary channel deposits within the Cretaceous-age Ferron Sandstone at Corbula Gulch in central Utah, USA. Shale statistics are computed from outcrop observations. Although slight anisotropy was observed in mean length and variogram ranges parallel and perpendicular to pale of low , the anisotropy is not statistically significant and the estimated mean length is 5.4 m. Truncated Gaussian simulation was used to create maps of shales that are placed on variably dipping stratigraphic surfaces interpreted from high-resolution 3D GPR surveys, outcrop interpretations, and boreholes. Sandstone permeability is estimated from radar responses calibrated to permeability measurements from core samples. Experimentally designed flow simulations examine the effects of variogram range, shale coverage fraction, and trends in shale coverage on predicted upscaled permeability, breakthrough time, and sweep efficiency. Approximately 1500 flow simulations examine three different geologic models, flow in the 3 coordinate directions, 16 geostatistical parameter combinations, and 10 realizations for each model. ANOVA and response models computed from the flow simulations demonstrate that shales decrease sweep, recovery, and permeability, especially in the vertical direction. The effect on horizontal flow is smaller. Flow predictions for ideal tracer displacements at Corbula Gulch are sensitive to shale-coverage fraction, but are relatively insensitive to twofold variations in variogram range or to vertical trends in shale coverage. Although the hydraulic effects of shale are statistically significant, the changes in flow responses rarely exceed 20%. As a result, it may be reasonable to use simple models when incorporating analogous shales into models of reservoirs or aquifers.     

Significance of transition between Talchir Formation and Karharbari Formation in Lower Gondwana basin evolution — A study in West Bokaro Coal basin, Jharkhand, India

Basal part of the Gondwana Supergroup represented by Talchir and Karharbari Formations (Permo-Carboniferous) records an abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment. The contact between the two is an unconformity. Facies analysis of the glacio-marine Talchir Formation reveals that basal glaciogenic and reworked glaciogenic sediments are buried under storm influenced inner and outer shelf sediments. Facies associations of the Karharbari Formation suggest deposition as fluvio-lacustrine deposits in fault-controlled troughs. An attempt has been made in this paper to explain the sedimentation pattern in Talchir and Karharbari basins, and the abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment in terms of glacio-isostacy.     

Felsic tuff from Rutland Island — A pyroclastic flow deposit in Miocene-sediments of Andaman-Java subduction complex

The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies:

Platinum group of elements in Semra komatiites, Palamau District, Jharkhand: A preliminary observation

Semra komatiites that occur at the NW fringe of the Chotanagpur Gneissic Complex represent high PGE content, associated with the pyrrhotite, pentlandite, chalcopyrite and pyrite. They display wide variation in the IPGE concentration and characterized by Pd/Pt values (> 1) similar to that of primitive mantle. The negative Ir anomaly is attributed to temperature dependant solubility limit, therefore, not a reflection of bulk mantle IPGE content. Wide variation in the Au content indicates its highly mobile nature. Metasomatism and serpentinisation possibly have played significant role in the Au enrichment.     

Wave-influenced deltas: geomorphological implications for facies reconstruction

ABSTRACT A process‐based facies model for asymmetric wave‐influenced deltas predicts significant river‐borne muds with potentially lower quality reservoir facies in prodelta and downdrift areas, and better quality sand in updrift areas. Many ancient barrier‐lagoon systems and ‘offshore bars’ may be better reinterpreted as components of large‐scale asymmetric wave‐influenced deltaic systems. The proposed model is based on a re‐evaluation of several modern examples. An asymmetry index A is defined as the ratio between the net longshore transport rate at the mouth (in m³ year^?1) and river discharge (in 10⁶ m³ month^?1). Symmetry is favoured in deltas with an index below ≈ 200 (e.g. Tiber, lobes of the Godavari delta, Rosetta lobe of the Nile, Ebro), whereas deltas with a higher index are asymmetric (e.g. Danube – Sf. Gheorghe lobe, Brazos, Damietta lobe of the Nile). Periodic deflection of the river mouth for significant distances in the downdrift direction occurs in extreme cases of littoral drift dominance (e.g. Mahanadi), resulting in a series of randomly distributed, quasi‐parallel series of sand spits and channel fills. Asymmetric deltas show variable proportions of river‐, wave‐ and tide‐dominated facies both among and within their lobes. Bayhead deltas, lagoons and barrier islands form naturally in prograding asymmetric deltas and are not necessarily associated with transgressive systems. This complexity underlines the necessity of interpreting ancient depositional systems in a larger palaeogeographic context.