Rajni Tewari

Deformation texture and microtexture developments in a cold rolled single phase hexagonal Zircaloy 2

Abstract A single phase hexagonal close packed Zircaloy 2 was cold deformed to different reductions by laboratory rolling. Systematic characterisations of the structural developments were carried out. Bulk texture developments were gradual, strongest developments being noticed at the highest strain. Although formation of well defined deformation fibre(s) could not be identified, overall developments in deformation texture were best captured through Taylor type models incorporating only prismatic slip. Strain localisations were observed as single or double walled dislocation structures at approximately 45 and 60° to the rolling direction. Such strain localisations were always associated with significant lattice reorientations or misorientation developments. Relative softening in lattice strain, observed at the higher reductions, can possibly be explained by the appearance of extensive strain localisations and the associated concurrent local dynamic recovery. The grains or orientations with dominant presence of strain localisations could be indirectly related to negative textural softening.

A Dicroidium flora from the Triassic of Allan Hills, South Victoria Land, Transantarctic Mountains, Antarctica

Chatterjee, S., Tewari, R. & Agnihotri, D., 2013. A Dicroidium flora from the Triassic of Allan Hills, South Victoria Land, Transantarctic Mountains, Antarctica. Alcheringa 37, 207-219. ISSN 0311-5518. A heterogenous and well-preserved assemblage of Triassic plants, including pteridophytes and gymnosperms, is described from the Lashly Formation of the Allan Hills, South Victoria Land, Antarctica. The pteridophytes include the sphenopsids Calamites aliwalensis, unidentified calamitalean axes, Neocalamites carreri and Neocalamites sp. The gymnosperms include Corystospermales, Peltaspermales and Pinales. Corystosperms dominate the megafloral assemblage and include Dicroidium odontopteroides, D. crassinervis, D. fremouwensis, D. coriaceum subsp. dutoitii, together with a microsporangiate structure Pteruchus sp. Peltaspermales include microsporangiate and ovuliferous reproductive structures namely Townrovia polaris and Matatiella dejerseyi, respectively. Conifers are represented by Heidiphyllum elongatum foliage and an unidentified cone. The megafossil assemblage is similar to those recorded from the late Early Triassic of New South Wales and Antarctica, Middle Triassic of Argentina, New Zealand and southeast Queensland, Middle to Late Triassic of South Africa, India, northern Argentina and Australia, early to middle Late Triassic of the central Transantarctic Mountains, Antarctica, and Late Triassic of Chile and North Victoria Land, East Antarctica. The records of Calamites aliwalensis, Neocalamites carreri, Dicroidium fremouwensis, Pteruchus sp., Townrovia polaris, Matatiella dejerseyi and a conifer cone are the first of these taxa from the Allan Hills. Recent finds from the Permian beds of India and Jordan indicate a much earlier origin of Dicroidium than previously suspected. Persistence of greenhouse conditions from the end of the Permian through the Triassic allowed the rich and diverse Dicroidium forests to develop in the polar regions of Antarctica. Sankar Chatterjee [sankar.chatterjee@ttu.edu], Texas Tech University, Lubbock, TX 79401, USA; Rajni Tewari [rajni.tewari@gmail.com], Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India; Deepa Agnihotri [deepa_302033@yahoo.com], Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226007, India. Received 9.4.2012; revised 20.9.2012; accepted 2.10.2012.

Thecamoebians (Testate Amoebae) Straddling the Permian-Triassic Boundary in the Guryul Ravine Section, India: Evolutionary and Palaeoecological Implications.

Exceptionally well-preserved organic remains of thecamoebians (testate amoebae) were preserved in marine sediments that straddle the greatest extinction event in the Phanerozoic: the Permian-Triassic Boundary. Outcrops from the Late Permian Zewan Formation and the Early Triassic Khunamuh Formation are represented by a complete sedimentary sequence at the Guryul Ravine Section in Kashmir, India, which is an archetypal Permian-Triassic boundary sequence [1]. Previous biostratigraphic analysis provides chronological control for the section, and a perspective of faunal turnover in the brachiopods, ammonoids, bivalves, conodonts, gastropods and foraminifera. Thecamoebians were concentrated from bulk sediments using palynological procedures, which isolated the organic constituents of preserved thecamoebian tests. The recovered individuals demonstrate exceptional similarity to the modern thecamoebian families Centropyxidae, Arcellidae, Hyalospheniidae and Trigonopyxidae, however, the vast majority belong to the Centropyxidae. This study further confirms the morphologic stability of the thecamoebian lineages through the Phanerozoic, and most importantly, their apparent little response to an infamous biological crisis in Earth’s history.

An Early Permian Glossopteris flora from the Umrer Coalfield, Wardha Basin, Maharashtra, India

Tewari, R., Pandita, S.K., Agnihotri, D., Pillai, S.S.K. & Bernardes-De-Oliveira, M.E.C., September 2012. An Early Permian Glossopteris flora from the Umrer Coalfield, Wardha Basin, Maharashtra, India. Alcheringa 36, 359–376. ISSN 0311-5518. A rich and well-preserved Glossopteris-dominated plant fossil assemblage is described from the Barakar Formation of the Makardhokra and Umrer open-cast projects, Umrer Coalfield, Nagpur District, Wardha Basin, Maharashtra, India. The assemblage includes equisetalean axes, cordaitalean leaves (Noeggerathiopsis hislopii), Gangamopteris clarkeana and diverse Glossopteris leaves and a fertile organ assigned to Scutum sp. cf. S. leslii. The flora, although similar to that of the Barakar Formation of the Damodar Basin complex (the reference basin system with respect to the qualitative and quantitative distribution of Indian Permian plant taxa), exhibits unique characteristics and is Artinskian to Kungurian in age. Besides supplementing knowledge of the broader Wardha Basin flora, this is the first systematic documentation of the Glossopteris flora from the Barakar Formation of this basin.

Early Triassic palynomorphs from Kuraloi Block, Belphar area, Ib-River coalfield, Mahanadi basin, Odisha

A rich assemblage of palynomorphs including miospores and megaspores has been recorded from the bore core no. IBKAN-2 drilled at a depth of 17.80m in Kuraloi Block-A, south-west part of the Ib-River Coalfield, Jharsuguda district, Odisha. The miofloral assemblage recovered shows prominence of cingulate, zonate, taeniate, non-striate and non saccate palynotaxa which indicate an early Triassic age and is comparable with the palynoassemblages of the same age known from the Damodar basin, India. The megaspore assemblage includes eight genera and fifteen species namely, Banksisporites karanpuraensis, B. indicus, B. utkalensis, Banksisporites sp., Barakarella pantii, Barakarella sp., Biharisporites spinosus, Biharisporites sp., Erlansonisporites triassicus, Erlansonisporites cf. erlansonii, Erlansonisporites sp. Jhariatriletes sp., Singhisporites sp., Ramispinatispora sp. and Talchirella trivedii. Records of megaspores are sparse in the early Triassic of Gondwana basins of India. The present study records the first occurrence of miospores and megaspores from the early Triassic of Mahanadi basin besides substantiating the earlier data.

Multipass warm/hot rolling of single phase Zircaloy 2: developments in crystallographic texture and in lattice strain

Abstract Zircaloy 2, a cast and hot forged alloy with a Widmanstätten structure, was warm/hot rolled to 40 and 80% reductions at approximate working temperatures of 200, 400, 600 and 800°C. The bulk crystallographic texture had clearly different patterns of developments between 200/400 and 600/800°C deformed structures. The estimated lattice strain, on the other hand, had shown noticeable relative softening and hardening after the respective deformation temperatures of 600 and 800°C. The patterns of macroscopic developments, both in bulk crystallographic texture and in lattice strain, could be explained from the microstructural observations. The difference in bulk crystallographic texture was primarily related to the preferred appearance of recrystallised grains. The 600°C rolled structure was associated with recovery/recrystallisation and a concurrent softening while the effects of a similar softening was suppressed through significant intermetallic precipitations and associated strain localisations in the 800°C rolled material.

Incêndios vegetacionais Indo-Brasileiros no Neopaleozoico: uma revisão dos registros de carvão vegetal macroscópico

Sedimentary charcoal is widely accepted as a direct indicator for the occurrence of paleo-wildfires and, in Upper Paleozoic sediments of Euramerica and Cathaysia, reports on such remains are relatively common and (regionally and stratigraphically) more or less homogeneously distributed. On the contrary, just a few reliable records have been published for the Late Paleozoic of Gondwana and only recently it has been demonstrated that macroscopic charcoals (and thus fires) were also common in the southern continent during this period. The most important Gondwanan records are predominantly charred gymnosperm woods mainly related to coal bearing strata. Late Paleozoic macro-charcoal occurs in both, the Damodar Basin (India) and the Paraná Basin (Brazil), demonstrating that paleo-wildfires were spread out in different sequences and distinct stratigraphic intervals during this period in Gondwana. Based on the so far published records as well as new samples from the Seam-VI coalfield, Raniganj Formation (Damodar Basin – Lopingian of India), an overview of the Late Paleozoic Indo-Brazilian macro-charcoal remains is presented. The hitherto unpublished samples were anatomically analyzed under Scanning Electron Microscope and a gymnosperm affinity could be established. The data presented here reinforce the relevance of paleo-wildfire as a source of environmental disturbance over large areas of Gondwana during the Late Paleozoic.

Experimental Studies on the Rain Attenuation Characteristics of Centimetre Waves

Frequencies above 10 GHz are adversely affected by rain. Experimental studies have been carried out to study the rain attenuation characteristics of radiowaves in and around Dehra Dun by establishing short distance experimental links at 11 and 17 GHz. Results thus obtained have been reported and a comparison has been made with those given in [2]. A method has also been suggested to evaluate the attenuation statistics fram point rain rate statistics for engineering terrestrial links.