Modelling the vulnerability of groundwater to contamination in an unconfined alluvial aquifer in Pakistan

The area of Thal Doab is located in the Indus Basin and is underlain by a thick alluvial aquifer called the Thal Doab aquifer (TDA). The TDA is undergone intense hydrological stress owing to rapid population growth and excessive groundwater use for livestock and irrigated agricultural land uses. The potential impact of these land uses on groundwater quality was assessed using a DRASTIC model in a Geographic Information System environment. Seven DRASTIC thematic maps were developed at fixed scale and then combined into a groundwater vulnerability map. The resultant vulnerability index values were grouped into four zones as low, moderate, high and very high. The study has established that 76% of the land area that is underlain by the TDA has a high to very high vulnerability to groundwater contamination mainly because of a thin soil profile, a shallow water table and the presence of soils and sediments with high hydraulic conductivity values. In addition, only 2 and 22% of the total area lie in low and moderate vulnerability zones, respectively. The outcomes of this study can be used to improve the sustainability of the groundwater resource through proper land-use management.     

Construction of the granitoid crust of an island arc part I: geochronological and geochemical constraints from the plutonic Kohistan (NW Pakistan)

We present major and trace element analyses and U–Pb zircon intrusion ages from I-type granitoids sampled along a crustal transect in the vicinity of the Chilas gabbronorite of the Kohistan paleo-arc. The aim is to investigate the roles of fractional crystallization of mantle-derived melts and partial melting of lower crustal amphibolites to produce the magmatic upper crust of an island arc. The analyzed samples span a wide calc-alkaline compositional range (diorite–tonalite–granodiorite–granite) and have typical subduction-related trace element signatures. Their intrusion ages (75.1 ± 4.5–42.1 ± 4.4 Ma) are younger than the Chilas Complex (~85 Ma). The new results indicate, in conjunction with literature data, that granitoid formation in the Kohistan arc was a continuous rather than punctuated process. Field observations and the presence of inherited zircons indicate the importance of assimilation processes. Field relations, petrographic observations and major and trace element compositions of the granitoid indicate the importance of amphibole fractionation for their origin. It is concluded that granitoids in the Kohistan arc are derivative products of mantle derived melts that evolved through amphibole-dominated fractionation and intra crustal assimilation.     

Geochemistry of Dharwar ultramafics and the Archaean mantle

Geochemical and petrological studies on serpentinised ultramafics of Kadakola, Mysore State, India, indicate that the Archaean mantle beneath the Indian Shield was of peridotitic in nature. This protomantle in the Archaean period was undifferentiated with higher concentrations of siderophile and transitional elements.     

Inventory of degraded lands of Palamau district, Bihar — A remote sensing approach

In this study, an attempt has keen made for the identification, categorisation and mapping of degraded lands in Palamau district of Bihar using remotely sensed data (IRS-1A, raise colour composite, on 1:50,000 scale), It was observed that water erosion is the main cause of land degradation affecting 6.27 per cent area of the district, of which 5.22 per cent is subjected to severe to very severe erosion and remaining 1.05 per cent is moderately to severely gulleid land Degradation due to rock quarries, mine spoils and dumps accounted for only 0.01 per cent of the district area. Degraded lands were mostly confined to agricultural areas (4.76%) follwed by forest lands (1.10%) and opert-scrub/pastures (0.42%), respectively, Subdivision-wise categorisation of degraded lands was also attempted for efficient location-speeific reclamation planning and easy monitoring.     

Lithologic characteristics and diagenesis of the Devonian Jauf sandstone at Ghawar Field, Eastern Saudi Arabia

The Lower Devonian Jauf Formation in Saudi Arabia is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Jauf Formation more specifically on the reservoir quality (including diagenesis), are very few. This study, which is based on core samples from two wells in the Ghawar Field, northeastern Saudi Arabia, reports the lithologic and diagenetic characteristics of this reservoir. The Jauf reservoir is a fine to medium-grained, moderate to well-sorted quartz arenite. The diagenetic processes recognized include compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cements and of feldspar grains. The widespread occurrences of early calcite cement suggest that the Jauf reservoir lost a significant amount of primary porosity at a very early stage of its diagenetic history. Early calcite cement, however, prevented the later compaction of the sandstone, thus preserving an unfilled part of the primary porosity. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-bridging clay cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late calcite cement occurs as isolated patches, and has little impact on reservoir quality of the sandstones.In addition to calcite, several different clay minerals including illite and chlorite occur as pore-filling and pore-lining cements. While the pore-filling illite and chlorite resulted in a considerable loss of porosity, the pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurs as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration to permeability of the reservoir. Diagenetic history of the Jauf Formation as established here is expected to help better understanding and exploitation of this reservoir.     

On the relationship between Indian Ocean Dipole events and the precipitation of Pakistan

This study investigated the relationship between the Indian Ocean Dipole (IOD) and the precipitation of Pakistan using data for the period of 1958–2010. The long-term evolution of the IOD index did not show interannual patterns similar to those of the annual precipitation of Pakistan. No linkage between the co-occurring trends of the IOD and the precipitation was traced during the period of investigation. The correlation between the IOD and the precipitation of Pakistan indicated a noteworthy impact over the monsoonal regions, especially the coastal area and the western region of Pakistan, which showed a significant positive correlation between the IOD index and annual and summer precipitation. A significant positive relationship was also revealed between the precipitation of the Balochistan Plateau and the IOD index for the summer monsoon season. No connection was observed between the IOD and the precipitation of the northern regions and the upper Indus Plain of Pakistan. Positive phases of the IOD have been noted to occur along with surplus precipitation during active monsoon conditions. The southeasterly wind moves from the Arabian Sea and transports additional moisture from the Arabian Sea to the coastal and southwestern parts of Pakistan during positive phases of the IOD.

     

Object-based urban land cover classification using rule inheritance over very high-resolution multisensor and multitemporal data

Very high spatial and temporal resolution remote sensing data facilitate mapping highly complex and diverse urban environments. This study analyzed and demonstrated the usefulness of combined high-resolution aerial digital images and elevation data, and its processing using object-based image analysis for mapping urban land covers and quantifying buildings. It is observed that mapping heterogeneous features across large urban areas is time consuming and challenging. This study presents and demonstrates an approach for formulating an optimal land cover classification rule set over small representative training urban area image, and its subsequent transfer to the multisensor, multitemporal images. The classification results over the training area showed an overall accuracy of 96%, and the application of rule set to different sensor images of other test areas resulted in reduced accuracies of 91% for the same sensor, 90% and 86% for the different sensors temporal data. The comparison of reference and classified buildings showed ±4% detection errors. Classification through a transferred rule set reduced the classification accuracy by about 5%–10%. However, the trade-off for this accuracy drop was about a 75% reduction in processing time for performing classification in the training area. The factors influencing the classification accuracies were mainly the shadow and temporal changes in the class characteristics.