Late Cambrian microbial build-ups,Llano Area,Central Texas: A three-phase morphological evolution     

Pankaj Khanna  Heath H. Hopson  André W. Droxler  Dylan A. Droxler  Daniel Lehrmann  Brian Kubik  Jacob Proctor  Pulkit Singh  Paul M. Harris 《Sedimentology》2020,67(2):1135-1160

Although Late Cambrian microbial build-ups were recognized in the Point Peak Member of the Wilberns Formation in Central Texas (USA) nearly 70 years ago, only a few studies focused specifically on the build-ups themselves. This study focuses on the interpretation of the regional (15 measured sections described in literature representing an area of 8000 km²) and local (field and drone photogrammetry studies in a 25 km² area from within south Mason County) microbial build-up occurrence, describes their growth phases and details their interactions with the surrounding inter-build-up sediments. The study establishes the occurrence of microbial build-ups in the lower and upper Point Peak members (the Point Peak Member is informally broken up into the lower Point Peak and the upper Point Peak members separated by Plectotrophia zone). The lower Point Peak Member consists of three <1 m thick microbial bioherms and biostrome units, in addition to heterolithic and skeletal/ooid grainstone and packstone beds. One, up to 14 m thick, microbial unit associated with inter-build-up skeletal and ooid grainstone and packstone beds, intercalated with mixed siliciclastic–carbonate silt beds, characterizes the upper Point Peak member. The microbial unit in the upper Point Peak member displays a three-phase growth evolution, from an initial colonization phase on flat based, rip-up clast lenses, to a second aggradation and lateral expansion phase, into a third well-defined capping phase. The ultimate demise of the microbial build-ups is interpreted to have been triggered by an increase of water turbidity caused by a sudden influx of fine siliciclastics. The lower Point Peak member represents inner ramp shallow subtidal and intertidal facies and the upper Point Peak member corresponds to mid-outer ramp subtidal facies. Understanding the morphological architecture and depositional context of these features is of importance for identifying signatures of early life on Earth.  相似文献   

PCA–based composite drought index for drought assessment in Marathwada region of Maharashtra state,India     

Prajapati  V. K.  Khanna  M.  Singh  M.  Kaur  R.  Sahoo  R. N.  Singh  D. K. 《Theoretical and Applied Climatology》2022,149(1-2):207-220

Theoretical and Applied Climatology - This paper presents a composite approach for drought characterization and monitoring using in situ and remote sensing-based drought indicators. The study was...  相似文献   

Effect of time and space partitioning strategies of samples on regional landslide susceptibility modelling     

Khanna  Kirti  Martha  Tapas R.  Roy  Priyom  Kumar  K. Vinod 《Landslides》2021,18(6):2281-2294

Landslides - Assessment of the spatial probability of future landslide occurrences for disaster risk reduction is done through landslide susceptibility modelling. In this study, we investigated the...  相似文献   

Geospatial landslide inventory of India—an insight into occurrence and exposure on a national scale     

Martha  Tapas Ranjan  Roy  Priyom  Jain  Nirmala  Khanna  Kirti  Mrinalni  K.  Kumar  K. Vinod  Rao  P. V. N. 《Landslides》2021,18(6):2125-2141

Landslides - India ranks first in the world in terms of fatal landslides. Large vulnerable area (0.42 million km2), high population density and monsoon rainfall make India’s landslide...  相似文献   

Correction to: Effect of time and space partitioning strategies of samples on regional landslide susceptibility modelling     

Khanna  Kirti  Martha  Tapas R.  Roy  Priyom  Kumar  K. Vinod 《Landslides》2021,18(6):2295-2296

Landslides - A Correction to this paper has been published: https://doi.org/10.1007/s10346-021-01646-0.  相似文献   

Corrigendum to “Condensed species in Titan's stratosphere: Confirmation of crystalline cyanoacetylene (HC₃N) and evidence for crystalline acetylene (C₂H₂) on Titan” [Icarus 178 (2005) 165-170]     

R.K. Khanna 《Icarus》2007,186(2):589

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New observations on Rajahmundry Traps of the Krishna-Godavari Basin     

G. Lakshminarayana  C. Manikyamba  Tarun C. Khanna  Prachiti P. Kanakdande  K. Raju 《Journal of the Geological Society of India》2010,75(6):807-819

The Rajahmundry Traps of the Krishna Godavari Basin (K-G Basin) consist of three distinct basalt flows interbedded with two intertrappean sedimentary horizons, which in turn are underlain by the late Cretaceous fossiliferous limestone bed (infratrappean) and overlain by the Cenozoic Rajahmundry Formation (conglomerate/sandstone). Among the three, the lower flow is characterized by the presence of the physical volcanological features such as rootless cones, tumuli and dyke like forms along with single to multitier columnar and radial jointing. The middle and upper flows are simple, massive and vesicular and exhibit spheroidal weathering. Physical volcanological features and lithological attributes indicate that the lower flow was formed by an explosive volcanic activity in hydrous environment, followed by sub aerial eruption to form the middle and upper flows. The fossiliferous limestone bed is a representative horizon for the K-T boundary mass extinction caused due to intense volcanism. Intertrappean sediments exhibit weathered soil profiles (palaeosols) with limestone beds denoting a distinct time gap during various phases of lava eruption. Evaluation of the palaeogeographic scenario of the Krishna and Godavari Rivers does not provide any evidence for the existence of Cretaceous palaeovalley which would have provided pathway for lava transportation from the Deccan volcanic province of western India to the K-G Basin situated along the east coast. The present study opens up an alternative approach to explain the origin of basalt flows at Rajahmundry. In all probability the lavas could be intrabasinal. NW-SE and NESW faults or their intersection zones are probable pathways for lava eruption in the K-G Basin.  相似文献   

An acoustic emission landslide early warning system for communities in low-income and middle-income countries     

N. Dixon  A. Smith  J. A. Flint  R. Khanna  B. Clark  M. Andjelkovic 《Landslides》2018,15(8):1631-1644

Early warning systems for slope instability are needed to alert users of accelerating slope deformation behaviour, enable evacuation of vulnerable people, and conduct timely repair and maintenance of critical infrastructure. Communities exposed to landslide risk in low- and middle-income countries seldom currently instrument and monitor slopes to provide a warning of instability because existing techniques are complex and prohibitively expensive. Research and field trials have demonstrated conclusively that acoustic emission (AE) monitoring can be an effective approach to detect accelerating slope movements and to subsequently communicate warnings to users. The objective of this study was to develop and assess a simple, robust, low-cost AE monitoring system to warn of incipient landslides, which can be widely deployed and operated by communities globally to help protect vulnerable people. This paper describes a novel AE measurement sensor that has been designed and developed with the cost constrained to a few hundred dollars (US). Results are presented from physical model experiments that demonstrate performance of the AE system in measuring accelerating deformation behaviour, with quantifiable relationships between AE and displacement rates. Exceedance of a pre-determined trigger level of AE can be used to communicate an alarm to users in order to alert them of a slope failure. Use of this EWS approach by communities worldwide would reduce the number of fatalities caused by landslides.  相似文献   

The Cadmium Zinc Telluride Imager on AstroSat     

V. Bhalerao  D. Bhattacharya  A. Vibhute  P. Pawar  A. R. Rao  M. K. Hingar  Rakesh Khanna  A. P. K. Kutty  J. P. Malkar  M. H. Patil  Y. K. Arora  S. Sinha  P. Priya  Essy Samuel  S. Sreekumar  P. Vinod  N. P. S. Mithun  S. V. Vadawale  N. Vagshette  K. H. Navalgund  K. S. Sarma  R. Pandiyan  S. Seetha  K. Subbarao 《Journal of Astrophysics and Astronomy》2017,38(2):31

The Cadmium Zinc Telluride Imager (CZTI) is a high energy, wide-field imaging instrument on AstroSat. CZTI’s namesake Cadmium Zinc Telluride detectors cover an energy range from 20 keV to \(>200\) keV, with 11% energy resolution at 60 keV. The coded aperture mask attains an angular resolution of 17\(^\prime \) over a 4.6\(^\circ \) \(\times \) 4.6\(^\circ \)  (FWHM) field-of-view. CZTI functions as an open detector above 100 keV, continuously sensitive to GRBs and other transients in about 30% of the sky. The pixellated detectors are sensitive to polarization above \(\sim \)100 keV, with exciting possibilities for polarization studies of transients and bright persistent sources. In this paper, we provide details of the complete CZTI instrument, detectors, coded aperture mask, mechanical and electronic configuration, as well as data and products.  相似文献   

Condensed species in Titan's stratosphere: Confirmation of crystalline cyanoacetylene (HC₃N) and evidence for crystalline acetylene (C₂H₂) on Titan     

R.K. Khanna 《Icarus》2005,178(1):165-170

Infrared spectra of crystalline HC₃N and C₂H₂ were investigated at several temperatures between 15 and 150 K. The characteristics of the 505 and 753 cm⁻¹ bands of HC₃N are in complete agreement with the emission spectral data on Titan obtained by the Voyager IRIS instrument, thus confirming the identification of crystalline HC₃N on Titan. A composite spectrum in the 720-800 cm⁻¹ region, with contributions from HC₃N and C₂H₂ in crystalline phases, reproduces the Voyager emission data in that region, thus providing a suggestion for the identification of crystalline C₂H₂ on Titan.  相似文献