Folding by cataclastic flow: evolution of controlling factors during deformation

Folding at upper crustal levels occurs by bending of beds and flexural slip between beds. As a fold's interlimb angle decreases, changes in bed thickness and limb rotation are accommodated by various mechanisms, depending on deformation conditions. In the elastico-frictional (EF) regime, cataclastic flow may be the dominant mechanism for fold tightening. The Canyon Range (CR) syncline, located in the Sevier belt of central Utah, shows this type of deformation. The fold involves three thick quartzite units, with slight lithological variations between them. Fold tightening took place in the EF regime (<2 km overburden) by cataclastic flow, involving collective movement on a distributed network of fractures and deformation zones (DZs) from the micro- to the outcrop-scale. In detail, the degree of cataclastic deformation varies significantly across the fold due to minor variations in initial bedding thickness, grain size, matrix composition, etc. A cooperative relationship exists across different scales, and the fracture networks result in a fracture shape fabric that is relatively homogeneous at the outcrop-scale.The initial outcrop scale fracture/DZ network geometry is a product of the growth and linking of micro-scale cataclasite zones, which in turn is controlled by primary lithological variations. Once a fracture network forms, the material behavior of the fractured rock is unlike that of the original rock, with sliding of fracture-bound blocks accomplishing ‘block-controlled’ cataclastic flow. Thus, initial lithological variations at the micro-scale largely control the final deformation behavior at the largest scale. During progressive fold tightening, additional factors regulate cataclastic flow, such as fracture/DZ reactivation or healing, during folding. Although initial lithological variations in different units may produce unique network geometries, each unit's behavior may also depend upon the behavior of adjacent units. In the CR syncline, during the initial stages of cataclastic flow, the inherent nature of each quartzite unit results in unit-specific fracture network geometries. As deformation progresses, unit-specific networks begin to interact with those in surrounding units, resulting in feedback mechanisms regulating the later stages of network development. Thus, the nature of cataclastic flow changes dramatically from the initial to the final stages of folding.     

Laboratory investigation of pullout behavior of hollow and solid shaft helical nail in frictional soil

Acta Geotechnica - Helical soil nails are passive elements installed in the soil which attains its bond strength through skin friction and bearing from helices. The present study examines the...     

Reassembly of the Dharwar and Bastar cratons at ca. 1 Ga: Evidence from multiple tectonothermal events along the Karimnagar granulite belt and Khammam schist belt,southern India

The northern part of the Nellore–Khammam schist belt and the Karimnagar granulite belt, which are juxtaposed at high angle to each other have unique U–Pb zircon age records suggesting distinctive tectonothermal histories. Plate accretion and rifting in the eastern part of the Dharwar craton and between the Dharwar and Bastar craton indicate multiple and complex events from 2600 to 500 Ma. The Khammam schist belt, the Dharwar and the Bastar craton were joined together by the end of the Archaean. The Khammam schist belt had experienced additional tectonic events at \(\sim \)1900 and \(\sim \)1600 Ma. The Dharwar and Bastar cratons separated during development of the Pranhita–Godavari (P–G) valley basin at \(\sim \)1600 Ma, potentially linked to the breakup of the Columbia supercontinent and were reassembled during the Mesoproterozoic at about 1000 Ma. This amalgamation process in southern India could be associated with the formation of the Rodinia supercontinent. The Khammam schist belt and the Eastern Ghats mobile belt also show evidence for accretionary processes at around 500 Ma, which is interpreted as a record of Pan-African collisions during the Gondwana assembly. From then on, southern India, as is known today, formed an integral part of the Indian continent.     

Evaluation of the SWAT model for water balance study of a mountainous snowfed river basin of Nepal

In this study, a semi-distributed hydrologic model Soil and Water Assessment Tool (SWAT) has been employed for the Karnali River basin, Nepal to test its applicability for hydrological simulation. Further, model was evaluated to carry out the water balance study of the basin and to determine the snowmelt contribution in the river flow. Snowmelt Runoff Model (SRM) was also used to compare the snowmelt runoff simulated from the SWAT model. The statistical results show that performance of the SWAT model in the Karnali River basin is quite good (p-factor = 0.88 and 0.88, for daily calibration and validation, respectively; r-factor = 0.76 and 0.71, for daily calibration and validation, respectively). Baseflow alpha factor (ALPHA_BF) was found most sensitive parameter for the flow simulation. The study revealed that the average annual runoff volume available at the basin outlet is about 47.16 billion cubic metre out of which about 12% of runoff volume is contributed by the snowmelt runoff. About 25% of annual precipitation seems to be lost as evapotranspiration. The results revealed that both the models, SWAT and SRM, can be efficiently applied in the mountainous river basins of Nepal for planning and management of water resources.     

Spatio-temporal analysis of groundwater levels and projection of future trend of Agra city,Uttar Pradesh,India

Access to water resources is one of the major challenges being faced worldwide. Water scarcity, particularly groundwater resource, is the major ubiquitous concern for the country. Almost half of the country is reeling under severe ground water crisis due to anthropogenic and natural reasons (basalt rock surface). Agra region situated in the western part of Uttar Pradesh state of India has a semi-arid climate. The study area, which has a history of water scarcity since medieval ages, has seen a spurt of acute water shortage in recent times owing to the expansion of a very dense built-up area and excessive haulage accompanied by decline in rainfall. A study was under taken for identifying the trends in pre- and post-monsoon groundwater levels for Agra city, Uttar Pradesh. Pre-monsoon and post-monsoon groundwater depth data of 16 observation wells for the 2007–2016 period were collected and analyzed using ARC GIS 10.2 software. The rainfall trend during the study period was also studied to understand its role in groundwater fluctuation level. Statistical tests like Mann-Kendall, Sen’s slope estimator, and linear regression model were applied to understand the trend and rate of change in groundwater level. The land use/land cover map of the study area was integrated with groundwater map to have a primary understanding of the spatial trend of groundwater scenario of the study area. The result obtained is quite alarming for the city’s groundwater scenario. Results showed that the groundwater levels had significantly declined during 2007–2016. Average rates of water level decline were 0.228 and 0.267 m/year during pre- and post-monsoon seasons, respectively. There was a rapid decline in water level between 2008 and 2009 and between 2013 and 2014. The average rate of decline of pre- and post-monsoon groundwater level in the city during this period is 0.32 and 0.30 m/year, respectively. Significant decrease in groundwater level is found in 84.21% of wells for pre- and post-monsoon as obtained through Mann-Kendall analysis at 95% confidence level. During pre-monsoon season, the rate of decline according to Sen’s slope estimator varied between 0.74 and 2.05 m/year. Almost similar picture of decline is portrayed through linear regression slope wherein the computed rate of decline varied between 0.75 and 2.05 m/year. During post-monsoon, the rate of decline according to Sen’s slope varied between 0.13 and 1.94 m/year. Similar trend statistic is obtained through linear regression method where the declining rate is between 0.14 and 1.91 m/year. Comparison of the three statistical tests indicates similar nature of declining trend. The result of this research raises concern about the future of groundwater resources in Agra city. The findings of this study will assist planners and decision-makers in developing better land use and water resource management.     

An alternative interpretation for the map expression of “abrupt” changes in lateral stratigraphic level near transverse zones in fold-thrust belts

The map expression of "abrupt" changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of(1) a lateral(or oblique) thrust-ramp,or(2) a frontal ramp with displacement gradient、and/or(3) a combination of these geometries.These geometries have been used to interpret the structures near transverse /ones in fold-thrust belts(FTB).This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault.We describe the natural example of the Leamington transverse zone.which marks the southern margin of the Pennsy lvanian—Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier(TB.Thus.the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault.Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp.the observed structures along the Leamington zone most likely share the effects of the presence of a lateral(or oblique) ramp,lateral stratigraphic variations along the fault trace.and the displacement gradient.     

Sediment Yield Index mapping and prioritization of Madia subwatershed,Sagar District of Madhya Pradesh (India)

Assessment of soil loss through Sediment Yield Index (SYI) is important for watershed planning, prioritization, and development. In the absence of measured sediment data, SYI expressing the relative sediment yield from different basins work as a basis for grading another basin to adopt erosion control measures. An attempt was made to evaluate SYI in wider scale by using cost-effective tools like remote sensing and geographical information system (GIS). SYI was calculated for Madia subwatershed, which consists of 29 microwatersheds and located in Sagar District, Madhya Pradesh (M.P.) The IRS LISS III data and Shuttle Radar Topography Mission (SRTM) digital elevation models (DEM) of 90-m resolution were used to identify land use characteristics and geomorphometric analysis. Major land use was observed as agricultural land (24.7 %), water bodies (16.7 %), forest area (10.2 %), and settlement (21.3 %). In categorization, similar overall accuracy was observed for dense forest, barren land, settlement, and water bodies. The highest SYI with a value more than 20 was observed in microwatershed Mw6, Mw7, and Mw24, which comprises 33 % of the total watershed area. It gives the information about the watershed area that requires very high priority.     

Structural and textural development in Singhbhum shear zone,eastern India

The rocks within the Singhbhum shear zone in the North Singhbhum fold belt, eastern India, form a tectonic melange comprising granitic mylonite, quartz-mica phyllonite, quartz-tourmaline rock and deformed volcanic and volcaniclastic rocks. The granitic rocks show a textural gradation from the least-deformed variety having coarse-to medium-grained granitoid texture through augen-bearing protomylonite and mylonite to ultramylonite. Both type I and type II S-C mylonites are present. The most intensely deformed varieties include ultramylonite. The phyllosilicate-bearing supracrustal rocks are converted to phyllonites. The different minerals exhibit a variety of crystal plastic deformation features. Generation of successive sets of mylonitic foliation, folding of the earlier sets and their truncation by the later ones results from the progressive shearing movement. The shear sense indicators suggest a thrust-type deformation. The microstructural and textural evolution of the rocks took place in an environment of relatively low temperature, dislocation creep accompanied by dynamic recovery and dynamic recrystallization being the principal deformation mechanisms. Palaeostress estimation suggests a flow stress within the range of 50–190 MPa during mylonitization.     

Evaluation of TRMM multi-satellite precipitation analysis (TMPA) against terrestrial measurement over a humid sub-tropical basin,India

To support the GPM mission which is homologous to its predecessor, the Tropical Rainfall Measuring Mission (TRMM), this study has been undertaken to evaluate the accuracy of Tropical Rainfall Measuring Mission multi-satellite precipitation analysis (TMPA) daily-accumulated precipitation products for 5 years (2008–2012) using the statistical methods and contingency table method. The analysis was performed on daily, monthly, seasonal and yearly basis. The TMPA precipitation estimates were also evaluated for each grid point i.e. 0.25° × 0.25° and for 18 rain gauge stations of the Betwa River basin, India. Results indicated that TMPA precipitation overestimates the daily and monthly precipitation in general, particularly for the middle sub-basin in the non-monsoon season. Furthermore, precision of TMPA precipitation estimates declines with the decrease of altitude at both grid and sub-basin scale. The study also revealed that TMPA precipitation estimates provide better accuracy in the upstream of the basin compared to downstream basin. Nevertheless, the detection capability of daily TMPA precipitation improves with increase in altitude for drizzle rain events. However, the detection capability decreases during non-monsoon and monsoon seasons when capturing moderate and heavy rain events, respectively. The veracity of TMPA precipitation estimates was improved during the rainy season than during the dry season at all scenarios investigated. The analyses suggest that there is a need for better precipitation estimation algorithm and extensive accuracy verification against terrestrial precipitation measurement to capture the different types of rain events more reliably over the sub-humid tropical regions of India.