S. Sarkar

Research Article| February 01, 2002 1.6 Ga U-Pb zircon age for the Chorhat Sandstone, lower Vindhyan, India: Possible implications for early evolution of animals Birger Rasmussen; Birger Rasmussen 1Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Search for other works by this author on: GSW Google Scholar Pradip K. Bose; Pradip K. Bose 2Department of Geological Sciences, Jadavpur University, Calcutta 700 032, India Search for other works by this author on: GSW Google Scholar Subir Sarkar; Subir Sarkar 2Department of Geological Sciences, Jadavpur University, Calcutta 700 032, India Search for other works by this author on: GSW Google Scholar Santanu Banerjee; Santanu Banerjee 3Department of Earth Sciences, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India Search for other works by this author on: GSW Google Scholar Ian R. Fletcher; Ian R. Fletcher 4Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Search for other works by this author on: GSW Google Scholar Neal J. McNaughton Neal J. McNaughton 4Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Birger Rasmussen 1Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Pradip K. Bose 2Department of Geological Sciences, Jadavpur University, Calcutta 700 032, India Subir Sarkar 2Department of Geological Sciences, Jadavpur University, Calcutta 700 032, India Santanu Banerjee 3Department of Earth Sciences, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India Ian R. Fletcher 4Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Neal J. McNaughton 4Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia, Crawley 6009, Australia Publisher: Geological Society of America Received: 17 May 2001 Revision Received: 26 Sep 2001 Accepted: 17 Oct 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2002) 30 (2): 103–106. https://doi.org/10.1130/0091-7613(2002)030<0103:GUPZAF>2.0.CO;2 Article history Received: 17 May 2001 Revision Received: 26 Sep 2001 Accepted: 17 Oct 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Birger Rasmussen, Pradip K. Bose, Subir Sarkar, Santanu Banerjee, Ian R. Fletcher, Neal J. McNaughton; 1.6 Ga U-Pb zircon age for the Chorhat Sandstone, lower Vindhyan, India: Possible implications for early evolution of animals. Geology 2002;; 30 (2): 103–106. doi: https://doi.org/10.1130/0091-7613(2002)030<0103:GUPZAF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Bedding-plane markings in the Chorhat Sandstone (lower Vindhyan), central India, were recently interpreted as burrows produced by triploblastic animals. Because the rocks were thought to be older than 1000 Ma, these structures were regarded as the oldest fossil evidence for metazoan life. However, the biological origin of the markings has been questioned, as has their age. Current age estimates are based on K-Ar, Rb-Sr, and fission- track dates, though some contentious evidence suggests that the rocks may be only 540 Ma. Here we provide the first robust age data for the lower Vindhyan by using SHRIMP (sensitive, high-resolution ion microprobe) U-Pb zircon geochronology to date silicified tuffs bounding the Chorhat Sandstone. Our results show that the sediments were deposited between 1628 ± 8 Ma and 1599 ± 8 Ma. If the Chorhat markings are burrows left by worm-like animals, then our data suggest that complex metazoans had evolved before 1600 Ma, 1 b.y. before the “Cambrian explosion” when animals rapidly diversified and became ecologically dominant. However, given the doubts expressed about the origin of the bedding-plane structures, as well as the surprisingly “old” age of the host rocks, further studies are urgently required to provide supportive evidence. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

We study the cosmology of the Supersymmetric Standard Model augmented by a gauge singlet to solve the μ-problem and describe the evolution of the domain walls which are created during electroweak symmetry breaking due to the discrete Z3 symmetry in this model. The usual assumption that (gravitationally induced) non-renormalisable terms which explicitly break this symmetry may cause the walls to collapse on a cosmologically safe timescale, is reconsidered. Such terms are constrained by considerations of primordial nucleosynthesis, and also because (by not respecting the Z3 symmetry) they induce divergences which destabilise the hierarchy and reintroduce the μ-problem. We find that, even when the Kähler potential is 'non-minimal' (i.e. when the hidden sector couples directly to the visible), the model is either ruled out cosmologically or suffers from a naturalness problem.

Despite its origin in a stable intracratonic basin, the Vindhyan Supergroup, central India, embodies tectonic-driven depositional cycles of various orders. A marked change in sedimentation pattern was coupled with a transient plate-margin compression in the otherwise extensional regime. An unconformity laterally correlatable with a conformity, that divides the Supergroup in two sequences arose in consequence. Maximum flooding surfaces (MFS) within the sequences can generally be correlated with intrabasinal volcanism that drastically diminished through the initial rift to later sag stage of basin evolution. Concomitantly with the change in tectonic milieu, paleoseismic deformation structures and related deposits also became drastically reduced in scale. Nevertheless, metre- and decametre-scale depositional cycles correlate well with the subtle record of paleoseismicity. Intermittent tilting of the depositional substratum is demonstrable in systematic bed-dip changes in metre-scale fining upward depositional cycles in the rift stage. In the sag stage, it is reflected merely in consistent deflection of paleocurrent directions at the top of the decametre-scale parasequence sets. Towards the top of the Supergroup, progressive thickening and decreasing frequency of parasequences indicates a declining rate of basin subsidence. Progradation, despite punctuation, thus resulted in basin-filling.

Drawing on a combination of modern occurrences and likely ancient counterparts, this atlas is a treatise of mat-related sedimentary features that one may expect to see in ancient terrigenous clastic sedimentary successions. By combining modern and ancient examples, the connection is made to likely formative processes and the utilization of these features in the interpretation of ancient sedimentary rocks. * The first full compilation of microbial mat features/structures preserved in the sliciclastic rock record * High quality, full color photographs fully support the text * Modern and ancient examples connect the formative processes and utilization of mat-related features in the interpretation of sedimentary rocks

The ephemeral nature of most sedimentation processes and the fragmentary character of the sedimentary record are of first-order importance. Despite a basic uniformity of external controls on sedimentation resulting in markedly similar lithologies, facies, facies associations and depositional elements within the rock record across time, there are a number of secular changes, particularly in rates and intensities of processes that resulted in contrasts between preserved Precambrian and Phanerozoic successions. Secular change encompassed (1) variations in mantle heat, rates of plate drift and of continental crustal growth, the gravitational effects of the Moon, and in rates of weathering, erosion, transport, deposition and diagenesis; (2) a decreasing planetary rotation rate over time; (3) no vegetation in the Precambrian, but prolific microbial mats, with the opposite pertaining to the Phanerozoic; (4) the long-term evolution of the hydrosphere–atmosphere–biosphere system. A relatively abrupt and sharp turning point was reached in the Neoarchaean, with spikes in mantle plume flux and tectonothermal activity and possibly concomitant onset of the supercontinent cycle. Substantial and irreversible change occurred subsequently in the Palaeoproterozoic, whereby the dramatic change from reducing to oxidizing volcanic gases ushered in change to an oxic environment, to be followed at ca. 2.4–2.3 Ga by the “Great Oxidation Event” (GOE); rise in atmospheric oxygen was accompanied by expansion of oxygenic photosynthesis in the cyanobacteria. A possible global tectono-thermal “slowdown” from ca. 2.45–2.2 Ga may have separated a preceding plate regime which interacted with a higher energy mantle from a ca. 2.2–2.0 Ga Phanerozoic-style plate tectonic regime; the “slowdown” period also encompassed the first known global-scale glaciation and overlapped with the GOE. While large palaeodeserts emerged from ca. 2.0–1.8 Ga, possibly associated with the evolution of the supercontinent cycle, widespread euxinia by ca. 1.85 Ga ushered in the “boring billion” year period. A second time of significant and irreversible change, in the Neoproterozoic, saw a second major oxidation event and several low palaeolatitude Cryogenian (740–630 Ma) glaciations. With the veracity of the “Snowball Earth” model for Neoproterozoic glaciation being under dispute, genesis of Pre-Ediacaran low-palaeolatitude glaciation remains enigmatic. Ediacaran (635–542 Ma) glaciation with a wide palaeolatitudinal range contrasts with the circum-polar nature of Phanerozoic glaciation. The observed change from low latitude to circum-polar glaciation parallels advent and diversification of the Metazoa and the Neoproterozoic oxygenation (ca. 580 Ma), and was succeeded by the Ediacaran–Cambrian transition which ushered in biomineralization, with all its implications for the chemical sedimentary record.

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry. Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe. The network may be made unstable by invoking a `tilt' in the axion potential due to Planck scale suppressed non-renormalisable operators. Alternatively the random walk of the axion field during inflation can generate a `bias' favouring one of the degenerate vacua, but we find that this mechanism is in practice irrelevant. Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather low -- thus ruling out e.g. the DFSZ axion with mass below 11 meV, where most experimental searches are in fact focussed.

The Collider Detector at Fermilab (CDF) experiment's Silicon Vertex Trigger (SVT) is a system of 150 custom 9U VME boards that reconstructs axial tracks in the CDF silicon strip detector in a 15μs pipeline. SVT's 35μm impact parameter resolution enables CDF's Level 2 trigger to distinguish primary and secondary particles, and hence to collect large samples of hadronic bottom and charm decays. We review some of SVT's key design features. Speed is achieved with custom VLSI pattern recognition, linearized track fitting, pipelining, and parallel processing. Testing and reliability are aided by built-in logic state analysis and test-data sourcing at each board's input and output, a common interboard data link, and a universal “Merger” board for data fan-in/fan-out. Speed and adaptability are enhanced by use of modern FPGAs.

Although the similarities between depositional processes and products as well as the analogous controls on basin-filling and evolution appear to have enjoyed great uniformity throughout the sedimentary rock record, a noticeable distinction exists in the rates and intensities of a broad range of geological processes in the Precambrian epoch. This paper searches for distinctiveness in the Precambrian sedimentary record, both siliciclastic and carbonate, through an extensive, though not exhaustive, review of the relevant literature augmented by new observations. While differences in Precambrian deltaic, aeolian, glacial and possibly also lacustrine deposits and settings appear to have been small, their large-scale development was controlled largely by a combination of temporal and geodynamic influences, essentially of global compass. In this regard the onset of the supercontinent cycle and major perturbations in palaeo-atmospheric composition appear to have been significant. Marine environments provide a poor platform for Precambrian–Phanerozoic comparisons of sedimentation patterns, as those from the former period are preserved almost exclusively in epeiric settings, an environment essentially lacking on modern Earth. For the shallow marine carbonates, biological mediation of chemical sediment deposition changed radically from dominance by microbial biota in the Precambrian to a combination of metazons, protozoans and algae for the skeletal carbonates of the Phanerozoic. Despite it being widely recognized that Precambrian channel systems were braided in all environments (deltaic, tidal, alluvial, fluvial) as a consequence of the lack of vegetation and poor development of soils, the fluvial setting has some enigmatic aspects. Amongst these is evidence for ponding of muddy detritus in apparently sandstone bed-load dominated braided systems, with effects on local palaeoslopes which have resulted in unusual palaeohydraulic parameters for Precambrian fluvial systems. This is perhaps a field of research which holds greater promise when investigating sedimentation patterns prior to the Phanerozoic.

The 2.7–2.0 Ga volcano-sedimentary records of the African, Indian and Australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas, concomitant with lowered freeboard. Carbonate-banded iron formation (BIF) platforms characterised the first such event, at ca 2.6–2.4 Ga (Africa and Australia) to 2.7 Ga (India). These earlier globally enhanced sea levels are ascribed to increased mid-ocean ridge activity, possibly related to breakup of a postulated Late Archaean 'southern' supercontinent. Alternatively, a transition from global-scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the Late Archaean (Nelson, 1998. Earth Planet. Sci. Lett. 158, 109–119). Both explanations of increased mid-ocean ridge activity are compatible with significant Early to Middle Archaean crustal growth (Armstrong, 1981. Phil. Trans. R Soc. London A 301, 443–472), with the emergent high freeboard cratons being subjected to aggressive weathering and erosion. Enhanced continental crustal growth near the Archaean–Proterozoic boundary (McLennan and Taylor, 1982. J. Geol. 90, 347–361), related to the development of significant island arc complexes, would have resulted in common lowered freeboard–enhanced sea level conditions at the passive margins of the 'southern' cratons. The diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and/or the thermal state of the cratons. From ca 2.4–2.2 Ga, cratons that make up the present-day continents of India, Africa and Australia had relatively high continental freeboard and lowered sea levels. Glacigenic deposits are preserved on the Kaapvaal (Africa), Singhbhum (India) and Pilbara (Australia) cratons. The second broadly defined drowning event, at ca <2.2 and >2.15 Ga, was probably due to post-glacial climatic amelioration. Freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned. In India, carbonates were more prominent than the siliciclastic sediments (including prominent black shales) seen in Africa and Australia.

The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. A few W-Sn deposits associated with granites are also known in the complex. Based on tectono-lithological features, the following domains are distinguished: the Archaean basement consisting of the Banded Gneissic Complex and granites, the Early Proterozoic Bhilwara, Aravalli, Jharol, and north Delhi belts and the Middle to Late Proterozoic south Delhi belt and the Vindhyan basin. Intra-cratonic rifting of the Archaean basement commencing ∼ 2.2 Ga ago resulted in the rock association of the Bhilwara belt, a thick pile of detritus derived largely from felsic sources and, to a minor extent, from tholeiitic sills with the geochemical characteristics of ocean-floor basalts. Stratiform Zn-Pb(-Cu) sulphide deposits at Rajpura-Dariba, Rampura-Agucha and also possibly those at Pur-Banera and Jahazpur formed 1.8 ± 0.04 Ga ago by convective seawater circulation in zones of crustal extension. The metal content of exhalative brines was precipitated in troughs where biologic activity was prolific. The shelf sediments of the Aravalli belt, characterized by dolomites with stromatolitic phosphorites, were deposited on a passive continental margin at the rifted western edge of the Archaean basement complex. The monotonous pelitic pile of the Jharol belt represents deep-pelagic continental-rise sediments. The Rakhabdev lineament delineates the shelf-rise boundary. The mafic-ultramafic bodies along this lineament represent Aravalli oceanic crust which subducted westward and eventually obducted as a consequence of an initial collision of the Aravalli continental margin with an incipient arc to the west around 1.5 Ga ago. In the Aravalli belt at Zawar, strongly radiogenic stratabound Pb-Zn deposits were formed close to the basement in second-order basins with biologic activity, by hydrothermal solutions convecting through a heterogeneous source. The north Delhi belt comprises three sedimentation domains: the Khetri sub-basin, the Alwar sub-basin and the Lalsot-Bayana sub-basin. Sedimentation in this belt commenced with shelf carbonates, followed by coarse clastic sediments and volcanites. Finally, pelites and semi-pelites were deposited in a multi-lagoonal, shallow-water, locally evaporitic environment. Synkinematic granitic intrusives in the north Delhi rocks are in the age range of 1.7-1.5 Ga. The stratabound Cu sulphide deposits of the Khetri belt and the pyrite-pyrrhotite deposits at Saladipura with a Pb-Pb model age of ∼ 1.8 Ga were formed from hydrothermal seawater and partly bacteriogenic sulphur in small, shallow, rift-related basins. The south Delhi belt, with extensive mafic volcanism, localized felsic volcanism, argillaceous-arenaceous-carbonate accumulations in successive, elongated basins and conspicuous felsic plutonism, is interpreted as an island arc. The geochemistry of pillowed and massive metavolcanites and an ophiolite assemblage indicate subduction in the western side of the arc. Part of the rocks of the Delhi belt may also have formed in rift-related back-arc basins as suggested by the ocean-floor characteristics of metavolcanic rocks. Subduction on the western side of the arc ultimately led to its terminal collision with the Aravalli continental margin around 1.0 Ga, involving intense progressive strain and oblique convergence. Small Cu-(Zn) deposits were formed within sedimentary intercalations in calc-alkaline basalts close to the hypothetical subduction zone. Extensional tectonics in the back-arc basins produced stratiform Zn-Pb-Cu deposits (Ambaji-Deri) around 1.1 Ga ago by high-temperature reduction of seawater convecting through multiple sources. Sn-W mineralizations are apparently related to the Malani felsic igneous phase of 735 Ma Rb-Sr age.

The Palaeoproterozoic Dhanjori Formation, eastern India is a terrestrial (dominantly fluvial) volcano-sedimentary succession. Basal conglomerate, coarse-grained sandstone, and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex. Sieve, sheet flood, mass flow and alluvial channel and overbank deposits comprise the fan segment. The rest of the formation is entirely constituted by fining upward fluvial cycles. An event of basin tilting and volcanic eruption intervened and resulted a second phase of Dhanjori sedimentation, although the general fluvial depositional framework remained unaltered. The two members of the Dhanjori Formation display different paleocurrent trends related to fluvial response to basin tilting. In the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development. Unlike the first phase, the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits. These volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short-lived lacustrine deposition. Composition of the volcanics varies upward from ultramafic to mafic. The Dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits. Interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption. A semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits.

This paper addresses macroscopic signatures of microbial mat-related structures within the 1.6Ga-old Chorhat Sandstone of the Semri Group — the basal stratigraphic unit of the Vindhyan succession in Son valley. The Chorhat Sandstone broadly represents a prograding succession of three depositional facies ranging from shallow shelf to coastal margin with aeolian sandsheet. The mat-mediated structures were generated because of plastic or brittle deformation of sand, turned cohesive and even thixotropic because of microbial mat growth. Mat growth also favoured abundant preservation of structures that usually have low preservation potential. Prolific growth of microbial mat in the subtidal to intertidal zone of the Chorhat sea was facilitated due to lack of grazing and burrowing activities of organisms in the Precambrian. It further indicates low rate of sedimentation between the storms, as also attested by frequent superposition of storm-beds, even near the storm wave base. It also reduces erosion and that, in turn, would imply low sediment concentration in flows leading to development of bedforms that are likely to be smaller in size and isolated from each other in a single train in contrast to those that form in mat-free sands.

Abstract Numerous soft-sediment deformation structures occur within the Proterozoic Bhander Limestone of an intracratonic sag basin in a 750 m long section along the Thomas River, near Maihar, central India. Part of these deformation structures have most probably a non-seismic origin, but other structures are interpreted as resulting from earthquake-induced shocks. These seismic structures are concentrated in a 60 cm thick interval, which is interpreted as three stacked seismi-tes. These three seismites are traceable over the entire length of the section. They divide the sedimentary succession in a lower part (including the seismites) deposited in a hypersaline lagoon, and an upper open-marine (shelf) part. Most of the soft-sediment deformations outside the seismite interval occur in a lagoonal intraclastic and muddy facies association. The SSDS within the seismite interval show a lateral continuity. They record simultaneous fluidisation and liquefaction. The bases of each of the three composing seismite bands are defined by small-scale shear folds, probably recording an earthquake and aftershocks. The presence of the three seismite bands at the boundary between the lagoonal and the overlying open-marine oolitic facies association suggests that the seismic event also triggered basin subsidence.

Lack of high quality zircon U-Pb age data has hampered us from ascertaining the relative positions of various continental blocks within East Gondwana, which also resulted in age-fossil inconsistencies in the Neoproterozoic successions particularly within India Peninsular region. By means of analyzing detrital zircons from the Neoproterozoic sedimentary rocks of Peninsular India and NW Australia, we found similar age spectra among NW India, Himalaya, NW Australia and Cathaysia Block that are indications of their proximity with each other. A scenario can be envisaged that following delivery of detritus (1.3–1.1 Ga) to northern India during early to middle Ediacaran Period, South China together with Australia probably clockwise rotated during late Ediacaran to Cambrian Period which prompted South China to receive detritus (1.3–1.1 Ga) from Western and northwestern Australia. New radiometric dates suggest an Ediacaran age for the Marwar and Bhander groups, thus confirming previous biostratigraphic correlations among the Marwar, Kurnool, Bhima and Bhander Groups. Given their diverse age spectra, the Maihar Sandstone and the Sonia Sandstone were possibly deposited in different time intervals/slices. Uncertainties in obtaining the youngest age of detrital zircons mean care must be taken when using detrital zircon age for tectonic regime classification.

An integrated chronicle of major events leading to the growth of the pre-2.0 Ga Indian Craton, which is the aim of this paper, is an essential requirement to constrain the possibility of Neoarchaean unification between Africa and India. The primordial sialic crust that eventually developed into the early Indian Craton segregated from the mantle before 3.8 Ga. Intially there were two seperate Indian blocks, the northern (NIB) and the southern (SIB), and they possibly amalgamated before 2.5 Ga. Rapid and extensive crustal growth at ca 3.1, 2.5 and 2.0 Ga, in conjunction with a related rise in relative sea level due to ocean basin volume reduction, kept the continental freeboard at a moderate level. The 2.5 Ga event was the greatest in magnitude and is likely to have led to the formation of an Indian supercontinent. Four sedimentary basins, one in the NIB and three in the SIB, developed on the typical Archaean tonal ite-trondhjemite-granodiorite basement, through rifting induced by mantle upwelling. Continental freeboard was lowered as a consequence and transgressions generally followed. Rifting persisted in all the pre-2.0 Ga basins, except one (Bastar) in the SIB, which only underwent a Wilson cycle as the two blocks collided. All the SIB basins were closed by 2.0 Ga, while the basin in the NIB, which only developed at ca 2.5 Ga, still persisted. Neoarchaean continuity between the Central Indian Tectonic Zone and the Limpopo Belt appears likely from all major aspects, but for the deformation history, which still remains elusive. Le but de cet article est de construire le calendrier complet desévénements majeurs qui ont conduitàla croissance du craton indien avant 2 Ga. Un tel calendrier est indispensable pourévaluer la possibilitéde l'unification de l'Afrique et de l'Inde au Néoprotérozoïque. La crouˆte sialique primitive qui s'est transformée ensuite en craton indien pŕecoce s'est séparée du manteau avant 3.8 Ga. Au début, il y avait deux blocs indiens séparés, celui du nord (NIB) et celui du sud (SIB), qui ont probablement fusionnéun peu avant 2.5 Ga. La marge continentale libre est restéeàune altitude basse,àcause de la croissance rapide et intense de la croute au cours desévénementsà3.1, 2.5 et 2.0 Ga, s'ajoutantàl'élévation du niveau de la meràla suite de la réduction de volume des bassins océaniques. L'événement de 2.5 Ga, le plus important en magnitude, a vraisemblablement aboutiàla formation d'un supercontinent indien. Quatre bassins sédimentaires, l'un sur le NIB et les trois autres sur le SIB, se sont développés sur un socle archéen typique de tonalite-trondhjémite-granodiorite par rifting induit par la remontée du manteau. Par conséquent, la marge continentale libre s'est abaissée et des transgressions ont généralement suivi. Le rifting a persiste dans tous les bassins avant 2.0 Ga,àl'exception d'un seul (Bastar) sur le SIB, qui a subi un cycle de Wilson seulement quand les deux blocs sont entrés en collision. Tous les bassins situés sur le SIB se sont fermés il y a 2.0 Ga, alors que le bassin sur le NIB qui s'est dévelopeéseulement il y a 2.5 Ga a persiste encore. La continuitéau cours du Néoprotérozoïque de la Zone Tectonique de I'Inde Centrale et de la Ceinture du Limpopo semble vraisemblable d'après toutes leurs caractéristiques majeures,àl'exception de la déformation dont l'histoire reste encore mal définie.

Precambrian and younger basins reflect the interaction of sediment supply and subsidence; the latter is generally ascribed to tectonic, magmatic and related thermal processes. The interplay of supply and subsidence is further modified by eustasy and palaeoclimate. Problems and enigmas inherent in analysis of Precambrian basin-fills include: a spectrum of ideas on the maximum age of Phanerozoic-style plate tectonics in the rock record; Archaean heat flow up to two to three times present values; changes in magmatism over time (including global magmatic events); the evolution of atmospheric composition and of life and their influence on weathering, erosion and sediment supply rates; degree of preservation, deformation and metamorphism, and preservational bias (especially of intracratonic basins which would lack evidence for early plate tectonics); a limited rock record; poor age constraints, inherent errors in geochronological techniques and difficulty in dating the time of deposition of sedimentary rocks. Major influences on Precambrian basin formation are assumed to include magmatism, plate tectonics, eustasy and palaeoclimate, all of which interacted. Models for greenstone belt evolution include plate tectonic intra-oceanic generation, plume-generated oceanic plateau, and global catastrophic magmatic events that may have been transitional to a plate tectonic regime over several hundred million years. The latter transition may have included the onset of the supercontinent cycle. Insignificant preservation of Precambrian ocean floor makes evaluation of these models problematic. Eustasy was intrinsically related to continental crustal growth rates, continental freeboard and the hypsometric curves of emerging cratons. Possible maximum crustal growth rates near the Archaean–Proterozoic boundary led to globally elevated sea levels, and the formation of enormous carbonate-banded iron formation platforms where cyanobacterial mats, which produced oxygen, flourished. The combination of changes in cratonic growth rates, thermal elevation of cratons, eustasy, weathering and palaeo-atmosphere composition may have combined to produce the first global glaciation at ca. 2.4–2.2 Ga. Examples of basins discussed here emphasise the interaction of tectonism, magmatism, eustasy and palaeoclimate in their evolution. For the Neoarchaean Witwatersrand basin (Kaapvaal craton, South Africa), evidence for all these factors is preserved in the basin-fill, whereas for the Neoproterozoic Macaúbas basin (São Francisco craton, Brazil), clear evidence for eustasy is more limited. The ca. <2.45–<1.9 Ga preserved Hurwitz basin (Hearne domain, Canada) suggests a predominant tectonic control, but with significant influences from magmatic processes, eustasy and palaeoclimate. For the ca. 2.7 Ga Ventersdorp Supergroup, which succeeded the Witwatersrand Supergroup, a strong case can be made for magmatism as a prime influence, with an inferred mantle plume having caused lithospheric stretching and thermal subsidence. The Ventersdorp formed part of an inferred global magmatic event, succeeded on the Pilbara and Kaapvaal cratons by the NeoArchaean–Palaeoproterozoic Hamersley and Lower Transvaal carbonate-banded iron formation platform successions, ascribed largely to globally high sea levels, allied to an aggressive weathering regime. Evidence for both eustasy and weathering are limited in the preserved basin-fill of the Palaeoproterozoic Timeball Hill (upper Transvaal Supergroup, Kaapvaal) depository, formed during the ca. 2.4–2.2 Ga global glaciation, probably due to tectonic subsidence. For the ca. 1.7–1.5 Ga Espinhaço basin (São Francisco craton, Brazil) evidence supports lithospheric stretching and thermal subsidence as prime influences. The origin of greenstone basins remains contentious. That magmatism was a major factor in their evolution is accepted by most, but whether this was plate-independent or plate-driven is less certain; the role of mantle plumes and the possibility of greenstones having been ridge-generated are also discussed by some workers. Episodic magmatism on a global scale may have played a role in the evolution of early basins such as the greenstones, Witwatersrand and Ventersdorp, and with a possible transition to plate tectonics into the Palaeoproterozoic, mid-ocean ridge growth related to either supercontinent break-up or to continental crustal growth rates probably influenced the eustatically controlled Hamersley and Lower Transvaal basin sedimentation. The possibility that early plate tectonics was characterised by variable spreading and subduction rates is discussed in the light of evidence from the Witwatersrand basin, the North American, Baltic and Siberian cratons, and the Transvaal Supergroup. In conclusion, Precambrian basin evolution probably reflects the variable interaction of tectonism, magmatism, eustasy and palaeoclimate (as also found for Phanerozoic basins), with the most significant difference compared to younger basins lying in the relative rates of processes such as ridge-spreading, subduction, crustal growth, weathering and atmospheric compositional change.

An attempt has been made to understand, within a cause-and-effect framework, the sequence-building pattern in Proterozoic time that witnessed non-uniformiteranean microbial mat growth and epeiric sea development. Marine or marginal marine successions in three Neoproterozoic formations, the Sonia Sandstone in western India, and the Sirbu Shale and Upper Bhander Sandstone in central India have been examined here for this purpose. The strikingly common feature of all three formations is vertical stacking of highstand systems tracts without intervention of any significant transgressive deposits. In one instance only, the transgressive systems tract is represented by a thin granular transgressive lag, and in all other cases the evidence of transgression is simply marked by the presence of marine flooding surfaces. The absence of transgressive strata relates to the low sea floor gradients, which facilitated rapid transgressions, combined with a generally low sediment supply. Aggradation under normal regressive highstand conditions, in spite of the low sediment supply, was promoted by the prolific growth of microbial mats, which reduced the effects of wave and current reworking by organic binding of clastic particles.

The occurrence of patchy preservation of ripples and of palimpsest ripples on many sandstone bed surfaces of the c. 2.1 Ga Magaliesberg Formation (Pretoria Group, Transvaal Supergroup), South Africa, suggests that microbial mats grew within the upper parts of sandy deposits of the braid-deltaic—tidally controlled epeiric marine coastline palaeoenvironment inferred for this stratigraphic unit. Recently, limited occurrences of petee ridges, cracked sand layers, “elephant skin textures”, wrinkle structures and “Manchuriophycus”-like cracks have been found, substantiating the envisaged role for microbial mats, binding sandy sediment and providing cohesion during active sedimentation by fluvial and tidal processes. Ripple marks associated with most of these biogenic sedimentary structures enable evaluation of genetic processes for the ripples (currents, waves, wind) as well as estimation of wave heights and water depths (cf. Tanner, W.F., 1967. Ripple mark indices and their uses. Sedimentology 9, 89–104. Tanner, W.F., 1971. Numerical estimates of ancient waves, water depths and fetch. Sedimentology 16, 71–88.). The petee ridges are interpreted as reflecting spring low tidal desiccation which cracked the mats, followed by disruption of sand beneath the mat due to loading from incoming tides or subsequent deposits. Slightly sinuous sand cracks on ripple crests are related to a similar combination of low tidal desiccation (and formation of wind ripples) with subsequent high tides providing the deeper water conditions and larger wave heights calculated from the (Tanner, W.F., 1971. Numerical estimates of ancient waves, water depths and fetch. Sedimentology 16, 71–88.) formula. Synaeresis cracking is inferred for both “elephant skin” cracks and “Manchuriophycus” structures. These inferred suspect-microbial sedimentary structures, when studied in relation to data derived from associated ripples, thus enable better estimation of depositional conditions within the Magaliesberg palaeoenvironment, and indicate minimum epeiric tidal ranges of c. 112 cm. In general, these structures are found associated with evidence for shallower water and higher energy conditions, which probably protected the microbial mats from degradation by heterotrophic bacteria, through fast burial. A possible association of such mat-related structures with epeiric marine or passive margin coastline conditions may be pertinent for much of the Precambrian clastic record.

The principle of uniformitarianism may be applied to Precambrian basin evolution and to the sedimentary record as a whole. The major difference in the Precambrian Eon lay in variability of rates and intensities of processes controlling weathering, erosion, transport, deposition, lithification, and diagenesis. This paper examines Precambrian sedimentation patterns within the larger framework of Earth evolution. Pre-rock record sedimentation probably comprised deep water oceanic realms within which meteoritic and cometary impact events generated very large tsunamis, resulting in very coarse volcaniclastic detritus combined with fine dust settling out of suspension, all reworked by marine current systems and localised turbidites. From c. 4 to 3.2 Ga, greenstone belts provided the predominant settings for the thin passive margin carbonates, BIF, stromatolitic evaporites, pelites and quartzites, and lesser synorogenic turbidites, conglomerates, and sandstones that accompanied the volcanic and volcaniclastic rocks typical of these settings. Common palaeoenvironments were high gradient alluvial fans, low sinuosity braided rivers, and relatively shallow marine settings, subject to wave and tidal action, and turbidity currents. Although continental crustal growth continued largely through greenstone belts until c. 2.7 Ga, the Witwatersrand basin (c. 3.0–2.7 Ga; Kaapvaal craton, South Africa) reflects initial stabilisation of the oldest craton, with an epeiric sea accumulating largely fluvial detritus subject to tidal (inland) and storm-wave (craton-marginal) reworking within a retroarc foreland basin setting. Neoarchaean–Palaeoproterozoic sedimentation is discussed within a framework of two global “superevents”, at c. 2.7 Ga and 2.2–1.8 Ga, each encompassing major changes in Earth's evolution related to the supercontinent cycle, mantle superplumes, peaks in crustal growth rates, and significant biochemical changes within the atmosphere–hydrosphere system. Concomitant globally raised sea levels led to chemical and clastic epeiric seas within which the first giant carbonate platforms developed, and deposition of iron-formation peaked globally at c. 2.5 Ga. The first global glaciation at c. 2.4–2.2 Ga provides little support for the “Snowball Earth” theory, but does suggest a negative feedback loop model whereby intraglacial CO2-related warming and synglacial decreases in weathering alternated up to three times. Models for palaeo-atmospheric and -oceanic evolution are mutually exclusive, but by c.1.8 Ga, the existence of large landmasses and free oxygen in Earth's atmosphere enabled erg development and red bed sedimentation globally; the full spectrum of Phanerozoic–Modern sedimentary environments was thus present on Earth. A third postulated “superevent” at c. 0.8–0.6 Ga essentially recreated conditions experienced at c. 2.2–1.8 Ga, with, additionally, at least three global refrigeration events.

Incorporation of the Kaapvaal craton within a speculative Neoarchaean–Palaeoproterozoic supercontinent has long been debated, and this idea provides a potential solution to solving the apparently enigmatic provenance of the huge quantities of gold within the famous Witwatersrand auriferous deposits of Kaapvaal. Within a framework of a postulated Neoarchaean “Kenorland” (“northern”; present-day reference) supercontinent, we examine possible “southern” cratons that may have been contiguous with Kaapvaal: Pilbara, Zimbabwe, Dharwar, São Francisco, Amazon, Congo. Brief reviews of their basic geology and inferred evolution in syn-Witwatersrand basin times (c. 3.1–2.8 Ga) show no obvious support for any such supercontinental amalgamations. An alternative idea to explain a measure of gross similarity amongst several Neoarchaean cratons is through global events, such as a c. 3125–3000 Ma cratonic-scale erosive event interpreted for both Pilbara and Kaapvaal, and a much more widespread magmatic event at c. 2760–2680 Ma. We postulate that a global superplume event at c. 3.0 Ga included a plume beneath the Kaapvaal cratonic nucleus, thus halting any subduction around that terrane due to the thermal anomaly. Such a speculative global magmatic event is assumed to have enhanced production of juvenile oceanic crust at mid-ocean ridges, including those “offshore” of the thermally elevated Kaapvaal nucleus. Intra-oceanic obduction complexes may have built up fairly rapidly under such conditions, globally, and once the plume event had abated, “normal” plate tectonics would have resulted in composite (greenstone-tonalite, possibly also including granite) terranes accreting with nuclei such as Kaapvaal. This enhanced plume-related cratonic growth can be seen as a rapid accretion event. Formation of the envisaged ophiolite complexes possibly encompassed deformation-related first-order concentration of gold, and once accretion occurred around Kaapvaal's nucleus, from north and west (present-day frame of reference), a second-order (deformation-related) gold concentration may have resulted. The third order of gold concentration would logically have occurred once placer systems reworked detritus derived from the orogens along the N and W margins of Kaapvaal. Such conditions and placer gold deposits are known from many Neoarchaean cratons. The initial source of gold was presumably from the much hotter Mesoarchaean mantle and may have been related to major changes in Earth's tectonic regime at c. 3.0 Ga. The unique nature of Kaapvaal is probably its early stabilization, enabling formation of a complex flexural foreland basin system, in which vast quantities of placer sediments and heavy minerals could be deposited, and preserved from younger denudation through a unique post-Witwatersrand history.

Microbial mat-related structures (MRS) in siliciclastics have been investigated from four Proterozic formations in India, namely the Marwar Supergroup, the Vindhyan Supergroup, the Chhatisgarh Supergroup and the Khariar Group for their spectral variations, genetic aspects, palaeo–environmental significance and influence on sequence stratigraphic architecture. The maximum diversification of MRS has been experienced in shallow marine coastal Precambrian successions. Observations made from modern environment as well as Precambrian rock records clearly indicates that the features like petee ridges, sand-cracks, gas domes, multi-directed ripples, reticulate surfaces, sieve-like surfaces and setulf are most likely to form in the shallowest part of the marine basins, in upper intertidal to supratidal conditions while wrinkle structures, roll-up structures and patchy ripples had a broader range of palaeogeographic settings from the supratidal to subtidal conditions. Discoidal microbial colony (DMC) represents a special variety of the mat-layer feature in modern environment that may have diverse internal architecture, sometimes falsely resembles Ediacaran medusoids. The uniqueness in sequence stratigraphic architecture of the microbial mat-covered sediment is reflected by the presence of more amalgamated HSTs compare to that of TSTs. The preservation of forced and normal regressive deposits on low-gradient epeiric shelf under low continental freeboard indicates microbial mat-infested sea-floor impedes erosion and concomitant sediment supply may facilitate formation and preservation of regressive packages.

Stratigraphic architecture of the fluvial interval at the base of the Neoproterozoic Sonia Sandstone, Rajasthan, India has been evaluated in consideration of the vegetationless Precambrian depositional environment. For its critical appreciation, facies, architectural elements, bounding surfaces, deductive palaeohydraulics, palaeocurrents, distribution of soft sediment deformation structures, as well as sequence stratigraphic status of the interval have been taken into account. Confined between an unconformity at the base and an overlying transgressive lag, the interval is considered a lowstand product. Temporal shifts in base profile, nevertheless, affected the tripartite division of the LST, systems tract developed during relative sea level lowstand. Palaeocurrent diversions across division boundaries as well as preferred concentration of soft sediment deformation structures along the top of the middle division make the role of tectonics evident. Facies, architectural elements, palaeohydraulic derivations as well as the degree of palaeocurrent consistency depict significant differences in channel patterns between the divisions. The axiom regarding braided patterns, frequent avulsion, and the ephemeral nature and flashy behavior of Precambrian rivers find conformity only in Division II. The river systems in Divisions I and III had frequently become meandering, due to valley constriction in the former and bank stability in the latter. Division I accumulated through sediment aggradation within a constricted valley incised deeply into the bedrock during the preceding course of base profile fall. Channel amalgamation characterizes Division I and more profoundly, Division II. The sharp upward transition from Division II to III records rapid enhancement in the rate of rise of base profile due to basin subsidence leading to encroachment of the contemporary sea. Mud settling was encouraged because of ponding at the downstream end turning the river channels fixed. Eventually the depositional site was drowned under the sea.

Abstract This chapter attempts an understanding of the Proterozoic Vindhyan Basin history in the broad framework of central India. Although the entire Vindhyan Supergroup is within the scope of this work, particular attention is paid to the little-known northwestern fringe exposures. Distinctive facies assemblages and diverse palaeocurrents in these exposures of the Lower Vindhyan play a pivotal role in the interpretation. Analysis of outcrop and subsurface data that extend under the Gangetic alluvium to the north of the Vindhyan outcrops further supports the hypothesis that an east–west-elongated basement ridge initially separated the master Vindhyan Basin from smaller contemporary basins to the north. Deposition took place in isolated lacustrine and fluvial basins north of the divide and largely in a marine realm south. Dextral shear accompanying rifting generated ridges that criss-crossed the Lower Vindhyan seafloor to the south. The uniform character of the Upper Vindhyan throughout, nevertheless, testifies to later drowning of the divide and unification of all of the basins as a consequence of regional tilt northward. However, the extended Vindhyan Sea was restricted by a second east–west-elongated ridge from merger with the contemporary Proterozoic sea further north, disparate sediments of which have been encountered in a few drill cores only.

We have searched for electrons scattered in the forward direction by neutrinos produced by dumping a 400 GeV/c proton beam on a copper target. We estimate the number of tau neutrinos produced from the decays of Ds mesons in the dump. The data limit the possible magnetic moment of tau neutrinos to be below 5.4×10−7 ωB. This rules out the suggestion that tau neutrinos of mass O(MeV) constitute the dark matter in the universe.

Ubiquitous microorganisms, especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats. In the absence of grazers and bioturbators, microbial mat is a unique feature of the Proterozoic. Most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding. Nonetheless, bed surface exposures are relatively rare in rock records. This limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed-across sections is needed. The 60 m thick coastal marine interval of the Sonia Sandstone Formation is bounded between two terrestrial intervals, a transgressive lag at the base and an unconformity at the top, and has been chosen for exploration of microbial mat structures in bed-across sections. A wide variety of microbial mat-induced structures in bed-across sections are preserved within the coastal interval of the Sonia Sandstone. Though many of these structures are similar in some aspects with bed surface structures, some of those presented here are new. The palaeogeographic range of these microbial structures extends from supralittoral to neritic. Diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains. SEM and EDAX analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the Sonia Sandstone. Effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous. The mat-cover on sediment surfaces hinders reworking and/or erosion of the sediments thereby increases the net sedimentation rate. Successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these Proterozoic formations could be a target for exploration.

Characteristics and tectonic settings of massive sulphide deposits, Southern Appalachian Blue Ridge Belt, USA gokld-minneralization in south-western Tanzania - a tecto-geochemical study Manganese deposition in the Proterozoic - global perspective and Indian scenario Breccia-related metallogenesis in the Proterozoic core of Wernecke mountains, Northwest Canada. (Part Contents)

The geological history and evolution of the Dharwar craton from ca. 3.5–2.5 Ga is reviewed and briefly compared with a second craton, Kaapvaal, to allow some speculation on the nature of global tectonic regimes in this period. The Dharwar craton is divided into western (WDC) and eastern (EDC) parts (separated possibly by the Closepet Granite Batholith), based on lithological differences and inferred metamorphic and magmatic genetic events. A tentative evolution of the WDC encompasses an early, ca. 3.5 Ga protocrust possibly forming the basement to the ca. 3.35–3.2 Ga Sargur Group greenstone belts. The latter are interpreted as having formed through accretion of plume-related ocean plateaux. The approximately coeval Peninsular Gneiss Complex (PGC) was possibly sourced from beneath plateau remnants, and resulted in high-grade metamorphism of Sargur Group belts at ca. 3.13–2.96 Ga. At about 2.9–2.6 Ga, the Dharwar Supergroup formed, comprising lower Bababudan (largely braided fluvial and subaerial volcanic deposits) and upper Chitradurga (marine mixed clastic and chemical sedimentary rocks and subaqueous volcanics) groups. This supergroup is preserved in younger greenstone belts with two distinct magmatic events, at 2.7–2.6 and 2.58–2.54 Ga, the latter approximately coincident with ca. 2.6–2.5 Ga granitic magmatism which essentially completed cratonization in the WDC. The EDC comprises 2.7–2.55 Ga tonalite–trondhjemite–granodiorite (TTG) gneisses and migmatites, approximately coeval greenstone belts (dominated by volcanic lithologies), with minor inferred remnants of ca. 3.38–3.0 Ga crust, and voluminous 2.56–2.5 Ga granitoid intrusions (including the Closepet Batholith). An east-to-west accretion of EDC island arcs (or of an assembled arc – granitic terrane) onto the WDC is debated, with a postulate that the Closepet Granite accreted earlier onto the WDC as part of a “central Dharwar” terrane. A final voluminous granitic cratonization event is envisaged to have affected the entire, assembled Dharwar craton at ca. 2.5 Ga. When Dharwar evolution is compared with that of Kaapvaal, while possibly global magmatic events and freeboard–eustatic changes at ca. 2.7–2.5 Ga may be identified on both, the much earlier cratonization (by ca. 3.1 Ga) of Kaapvaal contrasts strongly with the ca. 2.5 Ga stabilization of Dharwar. From comparing only two cratons, it appears that genetic and chronologic relationships between mantle thermal and plate tectonic processes were complex on the Archaean Earth. The sizes of the Kaapvaal and Dharwar cratons might have been too limited yet to support effective thermal blanketing and thus accommodate Wilson Cycle onset. However, tectonically driven accretion and amalgamation appear to have predominated on both evolving cratons.

Microbiota has always been the dominant life form, records of which are preserved in delicate forms within siliciclastic rocks. More pronounced record in the form of stromatolites possibly obscured the fact that many of the same delicate structures may be recognizable within carbonate rocks too. The Neoproterozoic Bhander Limestone in central India bears many such structures that are quintessentially similar to microbial mat-related structures reported from the Paleoproterozoic Chorhat Sandstone preserved within the same, Vindhyan Basin. Extensive microscopic, ultramicroscopic, and geochemical studies address the apprehension that such bedding plane structures in carbonate rocks could be merely weathering products. Trapping, binding and stabilitization of sediment by microbial mats are all evident. Preferred pyritization along the inferred, predefined microbial mats confirmed on the basis of EPMA (Electron Probe Microanalysis) results, and the enhanced carbon content along these mats layers and within suspected mat chips associated with them, are revealing. Raman spectroscopy, indeed, evinces enhanced kerogen content within both mats and mat chips. Interestingly, these microbial mat layers are recognized selectively within the lower of the two tiers of the Bhander Limestone. The lagoonal carbonate of the lower tier of the Bhander Limestone is muddy and contains a substantial proportion of silt-sized quartz grains that possibly impeded stromatolite growth. Stromatolites abound in the wave agitated upper tier of the Bhander Limestone which is dominated by oosparite. This paper provides evidence that the delicate microbial mat-related structures reported so far only from siliciclastic rocks can also be recognized within carbonate formations, and hopes to stimulate the search for additional such features, more preferably within carbonates originated in shallow and quiet water.

The long-standing dilemma between two extremes in palaeogeographic interpretation is resolved for the basal 115 m of the eastern exposures of the Lower Cretaceous Bhuj Formation, at the top of the hydrocarbon prospective Mesozoics of Kutch, India. An explicit record of a mega-scale event of relative sea level rise is found sandwiched between two fluvial stratigraphic intervals that amalgamate only at the eastern extremity of the exposure of the Formation. A localized estuary in the middle had its axis roughly parallel to the pre and post-inundation river channels, although a tributary made a significant detour. Variation in the fine sandstone-mudstone lithology documents decline in depositional energy in the mid-estuary amenable to coal formation. Sediment within the estuary had been routed through both the ends, palaeocurrent turning shore-parallel only at the estuary-mouth. Exception arises in case of some isolated lenses of very poorly sorted and coarse-grained deposits depicting flash floods in the tributary. Burrow characteristics change delicately in response to the inferred changes in the depositional scenario along the estuary. Resting on a coarsening upward ramp the initially fining and then coarsening upward estuarine succession is prograding, though not steadily. It was wave-dominated, but tide left imprint behind the estuary mouth bar gaining in intensity because of valley constriction. Macroscale changes in relative sea level, perhaps eliciting local tectonics, are recorded in the transient hysteresis in the stratigraphic trend with or without palaeocurrent diversions. The fluvial stratigraphic intervals encasing the marine interval have, in terms of architectural elements, many commonalities, but also some significant disparities. The latter indicates channel meandering in the pre-inundation period and braiding after inundation. Unlike the marine sandstones, bar-channel sandstones of the riverine deposits are distinctly less sorted, bimodal, even polymodal in grain-size distribution. Mineralogical composition identifies the sandstones as craton-derived, but their geochemical distinctions point to variation in parent rock composition under the maze of palaeogeographic overprints.

This study presents detailed sedimentological, geochemical, and mineralogical evidence of green clay formation at the basal part of the early Maastrichtian Kallankurichchi Formation, Cauvery Basin, India. Immediately overlying a basal scree conglomerate, the highly fossiliferous Kallankurichchi Formation hosted a ∼ 3.5 m thick dark grey limestone containing abundant green clay minerals formed by the alteration of metastable framework grains. Abundant fresh to partially palagonitized sideromelane glass and occasional preservation of gas bubble structures in green clays strongly suggest a volcaniclastic source. Petrographic observations manifested primary occurrences of the green grain pseudomorphs mimicking the shape of the precursor volcanic grains. The X-Ray Diffraction analysis of the randomly oriented bulk sample and oriented, smear-mounted green clay separates identified the berthierine by the strong ∼7 Å basal spacing. The mineral chemical data of the berthierine grain pseudomorphs recorded substantial compositional variation from Mg-, Si- and Al-rich core and Fe-rich rim, characterizing the maturation of berthierine from volcaniclastic substrate through 'proto'-berthierine. Tiny berthierine flakes (1–5 μm long) grew vertically from the mineral grain boundary and feldspar cleavages, suggesting its authigenic origin. Contemporaneous tectonic events, marked by abundant slide planes, suggested continuous sagging of the basin, causing oxygen-depleted bottom water conditions. The unusual appearance of berthierine as grain pseudomorphs, rarely reported from the rock record, revealed the dissolution of metastable volcaniclastic grains in a slightly acidic, oxygen-depleted depositional environment as the primary mechanism of authigenesis. The early diagenetic calcite cementation ceased the berthierine formation, preventing compaction and transformation.

The intracratonic rift-related Mesoproterozoic Rampur Shale in Kudri, India formed in the marine mid- and outer shelf domain. It bears a dominant imprint of shore-parallel, storm-driven flow, as predicted by oceanographers for modern shelves, and thus differs from other ancient storm deposits in the geological record. In the Rampur Shale, gutters are shore-parallel, while tool marks of various kinds are both shore-parallel and shore-normal, and show bipolarity in both directions. Hydrodynamic analysis and inter-relationships between the flow features suggest that the storm-driven flow was shore-parallel, dominantly unidirectional and steady initially, and that it became increasingly unsteady thereafter, while also becoming dominantly shore-normal during peak oscillation. As storm conditions waned, the gutters were filled by sediments under dominant wave influence. These Rampur data are consistent with observations made in modern seas and suggest that storm-driven flows, in general, have evolved in the same way over time, although their geological records may vary in details because of local constraints.

Seismites are difficult to identify in a sedimentary sequence that has been exposed to a number of other synsedimentary disturbances. The paper identifies some possible signatures of earthquakes in a lower submarine fan complex that formed in an extensional basin at the northwestern margin of the Indian plate. Dying growth faults, preferential basal brecciation of shale beds, frequent local intraformational unconformities, reverse grading attributed to mechanical sieving and intrabasinal mass flows through sand volcanoes bear the distinctive records of seismicity. Abundant synsedimentary grabens and horsts and profuse signs of liquifaction are suggestive. In this association, the thinning and fining up channel-fill sequences with evidence of gradually declining mass flow regimes also corroborate.

Variations of carbon and oxygen isotopic ratios in response to cyclical sea level fluctuations have been documented from a Paleoproterozoic peritidal stromatolite succession. The upper division of the Kajrahat Limestone, Vindhyan Supergroup of central India consists of several shallowing upward stromatolite cycles identified by regular and systematic changes in stromatolite size. Normally, larger stromatolites are followed upward in the succession by smaller stromatolites and microbial laminites that occupy the top of the cycle. Desiccation cracks are found in all the facies indicating subaerial exposure. We investigated the stable isotope compositional variations across nine complete stromatolite cycles showing frequent subaerial emergence. Carbon and oxygen isotopic values of the limestones, in general, are comparable to contemporary marine values available from earlier studies but show regular depletion in response to shallowing of the water level. The δ13C and δ18O values of the limestones vary within an individual stromatolite cycle; depleted values characterize the topmost part of the cycles. The isotope pattern is explained by micritic carbonate deposition in different sub environments of the shallow marine domain having different salinity and variable duration of exposure. These variations also probably caused the observed scatter in δ13C and δ18O values of supratidal microbial laminites.

Abstract Setulfs or inverted flutes, both in growth stage and in fossilized state, are addressed here. This account resolves the long-standing questions about their formative mechanism, depositional prerequisites, and preservation bias, as well as their palaeoenvironmental implications. These structures were observed to grow by accretion of wind deflated sand in the lee of miniscule obstructions, in the littoral–supralittoral transition zone, a little above the high-water mark on top of a partially-emerged bar at Chandipur, eastern India. Pseudopellets of crabs and scarce chips of microbial mat create the obstructions, as shells might also do in the case of other modern analogs reported from essentially similar environmental conditions. Moisture on the beach sand limited the lifting power of the wind, so that even miniscule obstructions could have a well-developed wake zone at their lee side, resulting in localized accumulation of a small ridge of sand extending downwind from the obstruction. Setulfs arrested under microbial mats were also found in Chandipur on the seaward fringe of a shallow marsh encircled by a spit. Like those in growth stage these mat-covered setulfs also had their tapering ends directed landward, as the wind was directed onshore during the period of observation. Fossilized setulfs in swarms are also described here from two Neoproterozoic formations in India, viz., the Sonia Sandstone and the Upper Bhander Sandstone. In both the cases, setulfs are preserved in well-sorted sandstones, and are associated with planar laminae, profound wave ripples, bifurcated parting lineations, infrequent rill marks and local swarms of current crescents on bedsurfaces. Additionally, recorded fossil setulfs are found in association with inversely graded translatent strata, crinkled adhesion laminae, patches of impact ripples and isolated small sets of alternate grain-flow and grain-fall cross-strata of aeolian origin. This suggests preservation in the high littoral–supralittoral zone as in case of all known modern setulf occurrences. The palaeowind direction derived from the ancient setulfs conforms in orientation to that recorded from other aeolian structures in the strata, supporting their wind deflation origin. Although shells and biogenic pellets were altogether absent from these Neoproterozoic rocks, microbial mat curls and fragments had presumably been abundantly present in the Proterozoic high littoral–supralittoral zone to facilitate formation of setulfs. Pertinently many microbial mat-related features are present within both the siliciclastic formations studied. In polished sections some of the studied Proterozoic setulfs reveal the existence of crinkled carbonaceous lamina covers that signify microbial mat growth on top of them. An a priori assumption is that microbial mats must have enhanced the preservation potential of these delicate structures, which would otherwise be extremely unlikely to be preserved. The seeming preference of fossil setulf occurrences from the Proterozoic–Early Palaeozoic time is most likely due to a lack of burrowers and grazers that would devastate the protective microbial mat later in the Phanerozoic. These observations suggest that swarms of setulfs are, in general, wind sculpted, and their presence in the rock record prefers palaeoenvironment interpretration as a high littoral–supralittoral transition zone, and also stands as proxy records of syn-depositional microbial mat growth.

This paper aims to unveil neotectonic imprints in topography, drainage and sediments in the 46.25 km long course of the River Chel from its source down to its alluvial fan at the base of the Himalayan Mountain Front in the Darjeeling–Jalpaiguri districts of India. A semi-circular ridge delimits its primary catchment. Within confinement of this watershed basin the drainage pattern is composite being convergent along the periphery and divergent on a butte inside. All these geomorphic neotectonic imprints are accompanied by ramp and flat structures and spectacular mylonitization of rocks. High hypsometric index and convex shape of the hypsometric curve derived from the central near-straight course of the river between the primary catchment and the Main Frontal Thrust (MFT) also reflects tectonic youthfulness of the river course. It is well manifested also in widely variable stream index and stream gradient index ratios (SL/K) often exceeding 2. In response to neotectonism, this river course as a whole shifted westward between 1962 and 2007. Maximum reduction of the stream gradient on top of the MFT is eloquent enough about recent uplift of the thrust ridge. The high average slope gradient of canyon wall about 45.68° is well consistent with this uplift. Very low channel-width/valley-height ratio along the river further corroborates the uplift. The alluvial fan system of the River Chel is comprised of five morphogenetic fans stacked one above another with a tendency to shrink and shift progressively upslope. They differ from each other in terms of tilt, axial orientation, primary depositional surface gradient and convexity in transverse section and thus present a writ of ongoing tectonism. Progressive upward increase in the share of distal crystalline rocks in clast composition within alluvial fan package is a clear proxy for southerly advancement of the MFT. Concomitant increase in maximum clast size is in good agreement with sediment source uplift. All the five fans are, however, dormant now. Present-day River Chel deeply incises through all of them and suggests further basement uplift in the context of frequent evidences of neotectonism all around, although the role of climate remains uncertain in absence of adequate data.

Sodic soil, characterized with high ESP (Exchangeable Sodium Percentage) (>15%), SAR (Sodium Adsorption Ratio) (>13) and pH (8.5-10) is considered as one of the important soil constraints causing reduced crop productivity. Out of the estimated 2.8 million hectares of sodic soils, about 2.5 million hectares occur in the Indo-Ganga plains. There are three distinct stages in the evaluation of sodic soils viz. salt accumulation, salinization and finally alkalization. Productivity of sodic soil is severely jeopardized by dispersion of soil colloid leading to slow infiltration, low permeability, water logging, poor soil tilth, cracking behaviour, soil crusting and poor microbial activities etc. The reclamation of sodic soil is an important step to increase the productivity of agricultural lands which includes chemical methods like application of gypsum, iron pyrite (FeS2), sulphur, etc.; biological methods like application of organic wastes, mulching, crop rotation etc.; cultural methods like proper drainage, deep ploughing, frequently irrigation, land labelling and physical methods like proper tillage operation, flushing, scraping etc. Further research is required in this field to bring back more areas under cultivation from the menace of soil sodicity to sustain productivity and to ensure food security.

The Vindhyan sedimentary succession in central India spans a wide time bracket from the Paleoproterozoic to the Neoproterozoic period. Chronostratigraphic significance of stable carbon and oxygen isotope ratios of the carbonate phase in Vindhyan sediments has been discussed in some recent studies. However, the subtle controls of facies variation, depositional setting and post-depositional diagenesis on stable isotope compositions are not yet clearly understood. The Vindhyan Supergroup hosts four carbonate units, exhibiting a wide variability in depositional processes and paleogeography. A detailed facies-specific carbon and oxygen isotope study of the carbonate units was undertaken by us to investigate the effect of these processes and to identify the least altered isotope values. It is seen that both carbon and oxygen isotope compositions have been affected by early meteoric water diagenesis. The effect of diagenetic alteration is, however, more pronounced in case of oxygen isotopes than carbon isotopes. Stable isotope compositions remained insensitive to facies only when sediments accumulated in a shallow shelf setting without being exposed. Major alteration of original isotope ratios was observed in case of shallow marine carbonates, which became exposed to meteoric fluids during early diagenetic stage. Duration of exposure possibly determined the magnitude of alteration and shift from the original values. Moreover, dolomitization is found to be accompanied by appreciable alteration of isotope compositions in some of the carbonates. The present study suggests that variations in sediment depositional settings, in particular the possibility of subaerial exposure, need to be considered while extracting chronostratigraphic significance from δ13C data.

Observational upper limits on anomalous neutral-current events in a proton beam dump experiment are used to constrain the possible hadroproduction and decay of light gluinos. These results require ifmg̃$̆4 GeV for ifmq̃ - minw.

Although the principle of uniformitarianism may be applied to the Precambrian sedimentary record as a whole, certain periods of the Archaean and Palaeoproterozoic witnessed a changing pattern of prime influences controlling the depositional systems.This paper examines the major controls on sedimentation systems and environments during the Archaean and Palaeoproterozoic within the broader perspective of Earth evolution.Earth's earliest sedimentary system (4.4?-3.7 Ga) was presumably comprised of deep oceanic realms and probably influenced primarily by bolide impacts, major tsunamis, localized traction and global contour current patterns, and bathymetry.As continental crust began to form, the impact-dominated, tsunami type sedimentation gave way to wider varieties of sedimentary environments, known from the oldest sedimentary records.During early continental crustal evolution (c.3.7-2.7 Ga), sedimentation was essentially of greenstone-type.Volcanic and volcaniclastic rocks were the major components of the greenstone belts, associated with thin carbonates, stromatolitic evaporites, BIF, pelites and quartzites and lesser synorogenic turbidites, conglomerates and sandstones.Volcanism and active tectonism (reflecting dynamic depositional settings during island arc and proto-continental nucleus formation) were the predominant factors openUP (November 2007) influencing sedimentation during this phase of Earth evolution.Transgressions and regressions under the combined influence of tectonics and eustasy are reflected in finingand coarsening-upwards successions from the proto-cratonic settings; low freeboard enabled the transgression to affect large areas of the proto-cratons.As the earliest, relatively stable craton formed, through a combination of plate tectonic and mantlethermal processes, continents and supercontinents with the potential for supercontinental cycles started to influence sedimentation strongly.Major controls on Neoarchaean-Palaeoproterozoic sedimentation systems (2.7-1.6 Ga) were provided by a combination of superplume events and plate tectonics.Two global-scale 'superevents' at c. 2.7 Ga and c. 2.2-1.8Ga were accompanied by eustatic rise concomitant with peaks in crustal growth rates, and large epeiric seas developed.The operation of first-order controls leading to development of vast chemical sedimentary platforms in these epeiric seas and concomitant palaeo-atmospheric and palaeo-oceanic evolution combined to provide a second-order control on global sedimentary systems in the Neoarchaean-Palaeoproterozoic period.The supercontinental cycle had become well established by the end of the Palaeoproterozoic, with the existence of large cratons across broad spectrums of palaeolatitude enabling erg development.The entire spectrum of sedimentary systems and environments came into existence by c. 1.8 Ga, prime influences on sedimentation and depositional system possibly remaining essentially uniform thereafter.

The role of biological influences in forming carbonate rocks (e.g., Altermann et al., 2006) is almost universally accepted within geology. In contrast, many see clastic sedimentary rocks as being formed primarily through physical and chemical processes, with biological mediation of their genesis being considered as of relatively minor importance (Schieber et al., 2007a). While sedimentologists and most geologists are familiar with the importance of trace fossils within clastic deposits (cf., the seminal work of Seilacher (1964) and many others since), the role of microbial mats in terrigenous sediment accretion, and in the formation and preservation of a whole host of mat-induced (mi) and mat-related structures within clastic sedimentary rocks, is less well known.

Palaeohydraulic estimates have been made using time-tested standard empirical formula involving channel dimensions, especially channel depth, in four Indian Proterozoic fluvial formations. These are the Mesoproterozoic Ramdurg, younger Mesoproterozoic Muchkundi and Neoproterozoic Cave Temple Arenite in Karnataka, and Upper Rewa Sandstone in central India. The basic data came from direct measurement of decompacted thicknesses of completely preserved channel-fills or bedforms, and more commonly of cross-sets. The result, in combination with data derived by others in a similar way from a few other Precambrian fluvial formations helps to provide a new insight into the palaeohydraulics of Precambrian rivers. River gradients appear to have been steeper during the Precambrian; the possibly continuous range of variation in river gradients from alluvial fans to the plains, as a whole shifted to higher values during the Precambrian epoch. The likely reason is a greater possibility of sediment bypassing on vegetation-free land. Concomitant downstream increase in discharge was enhanced in Precambrian rivers due to lack of withdrawal of groundwater through biogenic activity. Precambrian rivers were commonly ephemeral, but downstream the ephemerality index was reduced and some rivers might have been perennial where they debouched into standing bodies of water. The Precambrian river deposits studied generally had smaller width and depth with respect to Phanerozoic and modern rivers, possibly due to unstable substratum causing surface run-off tended to be impelled along multiple independent minor channels.

An integrated field, petrographical and geochemical investigation reveals a shallow marine dys-oxic depositional setting for the glauconite at the top of the Mesoproterozoic Lower Quartzite Member of the Vindhyan Supergroup. A thorough facies and paleogeographic analysis indicates a storm-influenced, shallow subtidal depositional condition for the glauconitic sandstone, occupying the mid-level of a transgressive systems tract (TST) deposit, which is capped by the maximum flooding zone (MFZ). The X-ray diffractional parameters confirm the evolved character of the glauconite. The mineral chemical analysis indicates the glauconite is enriched in K2O, MgO and Al2O3 and depleted in Fe2O3(total), compared to the Phanerozoic variety. It formed by the pseudomorphic replacement of the K-feldspar, by the addition of Fe2O3 at consistently high content of K2O, unlike most Phanerozoic examples. The elevated level of H3SiO4, Cl, K, Na, Mg and Fe, possibly derived by the continental weathering and/or contemporary volcanism, facilitated the glauconitization process. The high content of Mg in the glauconite corresponds to the Mg-rich, Mesoproterozoic seawater. A dys-oxic depositional condition, associated with a major marine flooding surface, favoured the formation of glauconite. While the onset of anoxic regime caused the disappearance of glauconite and the deposition of pyritiferous and carbonaceous shale in the overlying condensed zone deposits.

ABSTRACT Straight-crested and internally bipolar cross-stratified eolian dunes are common in the upper part of progradational cycles within the late Proterozoic Upper Bhander Sandstone, Son Valley, India. The Sandstone formed in a coastal setting, and it encompasses supralittoral storm, eolian sand sheet, draa, pond, and ephemeral stream deposits. Ripples of three different size and vector populations typically occur within the dune deposits. The smallest population shows migration parallel to the dune crests, and other two show migration obliquely towards the dune crests. Simple interpolation reveals only 9° deviation of the dune trend from the long-term resultant wind direction. In addition to the two primary wind vectors that control the duneforms, the sand transport ratio less than 1.2 suggests that these are longitudinal dunes. Forward computer modeling and calculation of the maximum gross bedform-normal transport direction further corroborate that the dunes were longitudinal. The dunes are smaller and architecturally simpler than most other longitudinal dunes described in the literature. The methodology adopted here is a useful approach to evaluate longitudinal dunes in the rock record.

The recent confirmation that at least some gamma-ray bursters (GRBs) are indeed at cosmological distances raises the possibility that observations of these could provide interesting constraints on the fundamental laws of physics. Here we demonstrate that the fine-scale time structure and hard spectra of GRB emissions are very sensitive to the possible dispersion of electromagnetic waves in vacuo with velocity differences $\delta v \sim E/E_{\QG}$, as suggested in some approaches to quantum gravity. A simple estimate shows that GRB measurements might be sensitive to a dispersion scale $E_{QG}$ comparable to the Planck energy scale $E_{P} \sim 10^{19}$ GeV, sufficient to test some of these theories, and we outline aspects of an observational programme that could address this goal.

The placement of the boundary between the Lower and the Upper Vindhyan in the Son valley, an unconformity, has long been at the centre of a raging debate. At the Bundelkhand sector, it is placed between the Rohtas Limestone and the Sasaram Sandstone (Lower Quartzite). On the other hand, in the Son valley sector, it is placed between the Bhagwar Shale and the Kaimur Formation. The recent study reveals the existence of ca. 12 m thick sandstone between the Bhagwar Shale and Rohtas Limestone, traced over 150 km in the Son valley sector. Based on in-depth facies constituents and facies tracts, this sandstone is an exact equivalent of the Sasaram Sandstone in the Bundelkhand sector. Its base is strongly erosional and limestone and chert clasts derived from the underlying Rohtas Limestone are abundantly present at the basal part of the sandstone and the unconformity between the Upper and Lower Vindhyan are likely to be present in between.

A Higgs particle produced in association with a Z boson and decaying into two photons is searched for in the data collected by the L3 experiment at LEP. All possible decay modes of the Z boson are investigated. No signal is observed in 447.5 pb^-1 of data recorded at centre-of-mass energies up to 209 GeV. Limits on the branching fraction of the Higgs boson decay into two photons as a function of the Higgs mass are derived. A lower limit on the mass of a fermiophobic Higgs boson is set at 105.4 GeV at 95% confidence level.

The Precambrian Chanda Limestone Formation in Adilabad District, Andhra Pradesh, India transcribes carbonate mass flow deposition in an extensional basin within the Godavari rift valley system. In the lower part of the formation, conglomerate beds which commonly interrupt the sequence of thin-bedded lime-mud turbidites, register pulsatory reinvigoration of mass flow processes. These gravelly mass flow products are significant because they indicate (i) deposition far below the wave base, (ii) intrabasinal origin, (iii) disassociation with any depositional slope like reef margins, (iv) occurrence in discrete vertical packages, (v) clear signals for sediment gravity flows, and (vi) invariable facies successions. The conglomerate bodies are extensive, parallel to the depositional strike, but restricted across the latter. The main mode of accretion is dominantly vertical aggradation, only the muddy turbidites spreading far and wide into the basin. The course of temporal evolution of the mass flows are also interpreted from vertical facies transitions. Although every flow eventually gave rise to turbidity currents, their initial states differred in three distinct ways which are correlated with gradient of the translational slope. Gradual decrease in declivity of the depositional substrate through time is interpreted.

Various methods, such as those developed by the Medical Internal Radiation Dosimetry (MIRD) Committee of the Society of Nuclear Medicine or employing dose point kernels, have been applied to the radiation dosimetry of (131)I radionuclide therapy. However, studies have not shown a strong relationship between tumour absorbed dose and its overall therapeutic response, probably due in part to inaccuracies in activity and dose estimation. In the current study, the GATE Monte Carlo computer code was used to facilitate voxel-level radiation dosimetry for organ activities measured in an (131)I-treated thyroid cancer patient. This approach allows incorporation of the size, shape and composition of organs (in the current study, in the Zubal anthropomorphic phantom) and intra-organ and intra-tumour inhomogeneities in the activity distributions. The total activities of the tumours and their heterogeneous distributions were measured from the SPECT images to calculate the dose maps. For investigating the effect of activity distribution on dose distribution, a hypothetical homogeneous distribution of the same total activity was considered in the tumours. It was observed that the tumour mean absorbed dose rates per unit cumulated activity were 0.65E-5 and 0.61E-5 mGY MBq(-1) s(-1) for the uniform and non-uniform distributions in the tumour, respectively, which do not differ considerably. However, the dose-volume histograms (DVH) show that the tumour non-uniform activity distribution decreases the absorbed dose to portions of the tumour volume. In such a case, it can be misleading to quote the mean or maximum absorbed dose, because overall response is likely limited by the tumour volume that receives low (i.e. non-cytocidal) doses. Three-dimensional radiation dosimetry, and calculation of tumour DVHs, may lead to the derivation of clinically reliable dose-response relationships and therefore may ultimately improve treatment planning as well as response assessment for radionuclide therapy.

Abstract This paper addresses a distinctive event bedset encased by coastal erg-margin deposits, at a preferred stratigraphic level near the base of the Neoproterozoic Upper Bhander Sandstone in central India. The bedset is composed of couplets of sandstone beds that exhibit incisive amalgamation although they differ in geometry, structures (at soles, within and at tops of beds), vertical grain-size variation as well as palaeocurrent pattern and direction. The wide extent of the bedset is evident from several exposures spread over a distance of more than 50 km roughly in strike-parallel direction. Flow and depositional dynamics interpreted from the coupled event beds are more consistent with a tsunami origin than alternative palaeogeography-compatible models of climate-induced storm, flash flood or accentuated tide deposits. A palaeotsunamiite model is thus discussed, with separate incoming and outgoing components. Considering the overall depositional setting to be an epeiric sea coast in an intracratonic sag basin, the relevant bedset is inferred to reflect the record of a teletsunamiite; it would also be one of the very few Precambrian tsunamiites known so far. Exceptional preservation of this possible tsunamiite was facilitated by sheltered deposition behind the backshore zone and the berm, as well as by rapid burial by wind-deflated sands and advancing aeolian dunes.

Abstract Mixed siliciclastic–carbonate rocks constitute the Upper Cretaceous Garuda-mangalam Sandstone Formation, Ariyalur (India), and offer an opportunity to look into the broad spectrum of mixing of compositionally and genetically different components. The palaeogeographic reconstruction indicates that deposition in the nearshore zone differed strongly in energy and active processes operatives due to the presence of a shore-parallel river-mouth bar. The western wing of the Mississippi bird-foot delta is considered to be a present-day analogon. Facies analysis in combination with petrography clearly shows the variability in palaeoenvironmental characteristics, both biogenic and non-biogenic. It also indicates diagenetic uptake of carbonate that filled empty spaces and actively replaced original components. Chemical staining followed by limited application of cathodoluminescence and energy dispersive X-ray analysis (EDAX) hint at intricacies in mixing arising from the compositional variations in the carbonate components. A model of siliciclastic–carbonate sediment mixing, including both the depositional and diagenetic developments, is presented; it is aimed at generating a better overview of, and a deeper insight into, the physical and chemical mechanisms involved.

Trace metal concentration in black shales can hold valuable information regarding ancient deep-ocean redox state.The size of marine reservoir of redoxsensitive elements (particularly molybdenum and chromium) is principally controlled by the extent of anoxicity in marine conditions following the onset of oxidative weathering post Great Oxygenation Event (~2.5-2.3Ga).Hence, it is considered that coupled analysis involving redox-sensitive element/s and primary organic productivity (total organic carbon) may provide a clue for redox behaviour of ancient deep ocean.Here, we use the redox behaviour of Mo and total organic carbon values of Vindhyan shales to show that the Vindhyan hydrosphere although initiated as a stratified sea with anoxic and sulphidic deep water as exemplified by the geochemical character of the Arangi Shale, the extent and veracity of anoxicity and euxinicity was never pervasive.It further suggests that the Vindhyan hydrosphere developed euxinic deep water only during deposition of Arangi, Rampur and Bijaygarh black shale and was anoxic but certainly not euxinic during Koldaha and Rewa sedimentation.The low concentration of Mo and Cr, in general, in argillaceous intervals suggests that the Vindhyan Sea behaved as a moderate Mo and depleted Cr reservoir.The consistent low concentration of Cr within the Vindhyan shales also suggests restriction in the availability of Cr in the water column in the absence of any significant detrital supply of Cr at very low atmospheric oxygen level (<0.1% PAL; present atmospheric level).

Literature review underlines uncertainty in the configuration of the Neoproterozoic supercontinent, (with Rodinia and Palaeopangaea reconstructions enjoying wide support), that stems primarily from inadequate palaeomagnetic data. Nonetheless, breakup of this supercontinent at ca. 0.65 Ga was conducive for epeiric sea formation globally. In the Vindhyan basin, India, a carbonate depositing sea developed over a fluvial-aeolian plain, at approximately 0.6 Ga. The top part of the Vindhyan Supergroup, the Upper Bhander Sandstone, was, however, able to prograde because of a decline in the rate of relative sea level rise. Within this general setting, temporal increases in this rate caused storm deposition at the coastline, largely in a supralittoral setting. Bizarre amalgamation of these storm beds without erosion likely owes its origin to severe curtailment of the velocity of the downwelling flow on the very gentle, muddy coastal slopes, and is thought to be a hallmark of deposition in an open epeiric setting. The storm domination in the Bhander embayment shelf is compatible with the Palaeopangaea supercontinental configuration.

Mechanisms of charging-up and charging-down of Gas Electron Multiplier (GEM) have been studied. Experimental investigations have been carried out on both dielectric polarization and radiation charging of GEMs. Environmental parameters, such as pressure and temperature have been monitored to normalize their effects on the charging-up and charging-down measurements. Variation in gain due to the combined, as well as individual, effects of the mentioned parameters, have been illustrated.

Glauconite forms authigenically by the replacement of quartz and feldspar substrates within the Precambrian Lower Bhander Sandstone (LBS) of the Vindhyan Basin. The glauconite exhibits consistently high K2O (7.08–8.62 wt%) and low to moderate TFe2O3 (6.20–18.5 wt%). The X-Ray Diffraction study reveals an evolved to highly evolved glauconitic mica structure. The deposition of mudstone-dominated LBS took place in a shallow marginal marine environment within a low gradient epeiric sea. The overall fining upward succession of the LBS comprises multi-storied, meter scale progradational cycles defined by red mudstone and sandstone–siltstone alternation in ascending order. The repetitive cycles indicate recurrent low-magnitude basin subsidence of the epeiric seafloor. Slump folds and slide planes, associated with the wedge-shaped mud pebble conglomerate, mark each episodes of basin subsidence. The glauconite occurs within sandstone and the sandy matrix of a wedge-shaped conglomerate at the base of a shallowing upward cycle which starts with a grey colored mudstone. The enrichment factors of redox-sensitive elements elucidate sub-oxic depositional condition during the glauconitization. The redox-sensitive element ratios (V/Cr, V/Sc) corroborates the sub-oxic depositional condition for the glauconitic interval and oxic environment for the encasing sediments. The formation of glauconite in the LBS corresponds to the deepening of the basin in response to the tectonic subsidence. The meter scale progradational cycles, recording the transition from suboxic to oxic conditions, corresponds to tectonically-induced deepening and subsequent filling. This study recognizes the significance of intrabasinal tectonics in facilitating suitable redox conditions for the glauconitization process within Proterozoic shallow epeiric sea deposit.

Biogenic signatures in Precambrian rocks are often difficult to confirm and debatable. We present some unusual features associated with microbial-mat related structures (MRS) from the freshly-exposed rippled bed surface of 1.6 Ga old Chorhat Sandstone, Vindhyan Supergroup, India. The features discussed here, are present within intertidal to supratidal environments often affected by storms. One of the features includes ridge-groove couplets that run across the ripple crests. Locally, the ridge-groove couplet forms a braid-like pattern. Along the ripple troughs, the ridges are considerably long and maintain a uniform width on the mm scale. Another feature shows meandering grooves bordered by ridges. The grooves swerve, form loops, cut across older grooves, and branch up. None of them have comparable equivalents in the Precambrian record described thus far. The invariably uniform width of the ridges for both the two features cannot be compared with undersurface gas bubble migration, and the swerving and reversing nature of the grooves denies passive movement of any inorganic/organic masses under the influence of an external force. They seem to have been created by movement through a microbiota-rich surficial sediment. Such unusual features raise questions about the biosphere and biotic structures during the Boring Billion (1.8–0.8 Ga). Les signatures biogéniques dans les roches précambriennes sont souvent difficiles à confirmer et elles sont très régulièrement débatues. Dans ce travail, nous présentons des structures inhabituelles associées aux tapis microbiens (MRS) ondulés et localisés à la surface des bancs de grès de Chorhat vieux de 1,6 Ga, bien preservés et appartenant au Supergroupe de Vindhyan, Inde. Les caractéristiques discutées sont décrites comme relevant d'environnements intertidaux à supratidaux souvent affectés par des courants de tempêtes. L'une de ces caractéristiques comprend des couplets de crêtes-rainures qui traversent des crêtes d'ondulation. Localement, le couple crêtes-rainures forme un motif en forme de tresse. Le long des creux ondulés, les crêtes sont considérablement longues et conservent une largeur uniforme à l'échelle du millimètre. Une autre caractéristique montre des rainures sinueuses bordées de crêtes. Les rainures s'écartent, forment des boucles, coupent les rainures plus anciennes et se ramifient. Aucun d'entre elles n'a d'équivalents comparables dans les archives précambriennes décrites jusqu'à présent. La largeur invariablement uniforme des arêtes pour les deux caractéristiques ne peut être comparée à la migration des bulles de gaz sous la surface. En plus, la nature déviée et inversée des rainures empêche le mouvement passif de toute masse inorganique/organique sous l'influence d'une force externe. Ils semblent avoir été formées par mouvement à travers un sédiment superficiel riche en microbiota. Ces caractéristiques inhabituelles soulèvent des questions à propos de la biosphère et les structures biotiques au cours du « Boring Billion » (1,8–0,8 Ga).

Significant variability in stromatolite growth patterns over a transition from basin plain to the nearshore zone is established for a Late Proterozoic marine sequence in India, so far undescribed. The attendant hydrodynamic changes are inferred and correlated in cause-and-effect terms. The stromatolite columns in wave-agitated reefs are larger, widening and branching upward and have a preferred directional growth. The intercolumnar areas are wide and filled up with broken stromatolite fragments among other things. The stromatolite bodies tend to be linear, ridge-like with broad bases and narrow tops. In the relatively less agitated tide affected nearshore subtidal plain the columns are smaller, less branching and widening. They have a preferred, but reversing, directional growth. The intercolumnar areas are proportionately wide and contain broken stromatolite fragments. The internal laminae are both continuous and discontinuous between the columns owing largely to tidal velocity asymmetry. The stromatolite bodies assume a tabular geometry. In the calm and quiet slope margin zone the stromatolite columns, small though like the tidal forms, are close-nested leaving little of intercolumnar areas. The columns are vertical, uniform in thickness and unbranching. The bodies assume a cylindrical form, albeit with rather irregular lateral boundaries.

The early Mesoproterozoic Rohtas Limestone in the Son valley area of central India represents an overall shallowing-upward carbonate succession. Detailed facies analysis of the limestone reveals outer- to inner-shelf deposition in an open marine setting. Wave-ripples, hummocky cross stratifications and edgewise conglomerates argue against a deep marine depositional model for the Rohtas Limestone proposed earlier. Stable isotope analysis of the limestone shows that δ13C and δ18O values are compatible with the early Mesoproterozoic open seawater composition. The ribbon limestone facies in the Rohtas Limestone is characterized by micritic beds, each decoupled in a lower band enriched and an upper band depleted in dissolution seams. Band-wise isotopic analysis reveals systematic short-term variations. Comparative enrichment of the heavier isotopes in the upper bands is attributed to early cementation from sea water and water derived from the lower band undergoing dissolution because of lowering of pH at depth. The short-term positive shifts in isotopic compositions in almost every upward gradational transition from a seamed band to a non-seamed band support the contention that dissolution seams here are of early diagenetic origin, although their formation was accentuated under overburden pressure.

The Cretaceous (Albian–Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic–Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation, exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous (Barremian–Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association (FA 1), records the first carbonate marine transgression within the basin, comprising a bar–lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite–glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association (FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement. Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association (FA 3). A tidal bar–interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational.

This paper examines the upper section (<185 m) of the late Proterozoic Sirbu Shale, central India, laid down in a storm-dominated shelf and lagoonal palaeoenvironment. Five of the six facies are laterally extensive, cyclical, interbedded shale-siltstone/fine sandstone. They generally have gradational mutual transitions and are amenable to palaeogeographical interpretation. The sixth facies is a coarse sandstone of low textural/ mineralogical maturity, confined to a localized occurrence and encased by one of the deeper shelf facies. The coarser interbeds bear storm signatures in all the facies. Current-formed features below storm beds record dominantly shore-parallel flow, although a shore-normal component is also evident. In the westward-opening intracratonic sag basin where deposition took place, the shelf succession built up as an overall prograding highstand systems tract that is divisible into a number of metre-scale parasequences. Slump features on top of each of the parasequences correlate the intervening marine flooding events with NE–SW extensional events and resultant landward subsidence. Fischer plots of parasequences reveal another, cryptic low-frequency depositional cyclicity. Troughs in the Fischer curves, denoting the longer cycle, roughly coincide with selective occurrence of NE–SW trending slide planes, implying superimposition of a NW–SE extension on the more frequent NE–SW extension. Enhanced subsidence is thus suggested at longer intervals owing to simultaneous orthogonal extension. The NE–SW extension reflects occasional readjustment of underlying rift blocks, whereas the NW–SE extension was possibly related to a plate-margin process. The resultant shelf basin probably assumed a NW–SE elongated, oval geometry with a dominant NE or landward-sloping flank. Plotting of shelf succession thickness downwards from a datum plane at a large number of locations simulates a three-dimensional basin configuration, as predicted from the inferred basin dynamics.

Ediacaran fossils represent a distinct group of large and structurally complex, enigmatic, soft-bodied organisms dominating the end-Precambrian (Ediacaran) oceans, with an age range from 630 to 542 Ma (Martin et al., 2000; Knoll et al., 2004, 2006). Microbes constituted the Precambrian biosphere almost entirely, and formed mats on wet sediment surfaces in the absence of grazers and burrowers. Evidence for microbial mats in the rock record dates back to 3.5 Ga (Altermann et al., 2006; Altermann, 2008) and mats continue to exist today, although largely confined to stressful environments due to metazoan activities.

Abstract A stretch of the modern hypersaline coastal plain of the Gulf of Cambay was chosen to examine the distribution of the microbial mat-related structures (MRS) on siliciclastic sediments in the intertidal and supratidal zones. The abundance of MRS increases from the lower intertidal zone to the upper supratidal zone while the type of MRS records a systematic change. While the lower intertidal zone exhibits wrinkle structures, sieve-like surfaces and patchy ripples in places, the upper intertidal zone exhibits diverse MRS related to reduced current activity on the mat layer and intermittent exposure. MRS in the upper intertidal zone include wrinkle structures, sieve-like surfaces, gas domes, reticulated surfaces, multi-directional ripples, patchy ripples, rolled-up mat fragments, setulfs and occasional petee ridges and cracked mat surfaces. The lower supratidal zone is characterized by increased occurrence of petee ridges, gas domes and cracked mat surfaces compared to the upper intertidal zone. The upper supratidal zone is distinguished by the presence of abundant cracked mat surfaces, petee ridges, gas domes and wrinkle structures. The presence of cm-scale, disc-shaped microbial colonies (DMC) with a variety of internal structures is a unique feature of the Gulf of Cambay study area. While wrinkle structures occur in all the coastal zones, setulfs occur close to the boundary between the upper intertidal and lower supratidal zones. An attempt has been made to compare the distribution of MRS in this modern environment with those in the ~1.6 Ga Chorhat Sandstone of the Vindhyan Supergroup for high-resolution palaeoenvironmental interpretation. The upper part of the intertidal segment of the Chorhat Sandstone is distinguished from its lower part by the presence of abundant cracked mat surfaces, petee ridges and gas domes in the former, while wrinkle structures, Kinneyia , rolled-up mat fragments, patchy ripples and multi-directional ripples are equally abundant in both parts. The lower part of the intertidal segment of the Chorhat Sandstone is thus analogous to the upper intertidal zone of the modern Gulf of Cambay environment, while the upper part of the Chorhat intertidal segment reflects prolonged exposure close to the high tide line. The bottom-most part of the intertidal segment of the Chorhat Sandstone with fewer MRS corresponds to the lower intertidal zone at Cambay. Inferred disc-shaped microbial fossils within Vindhyan sandstones are analogous to the DMC found in the modern environment and these features do not have any biostratigraphic implication.

The extraordinary lateral continuity of isopachous stromatolite laminae in the ∼87 m-thick Mesoproterozoic Lakshanhatti Dolomite (India) evinces chemical precipitation. Fan-shaped crystals grown on lamina surfaces further corroborate this contention; growth of fan-shaped crystals under the overhanging stromatolite column-margin indicates direct carbonate precipitation from ambient waters. The fan-shaped crystals are stacked up, separated only by thin dark micritic laminae. In a relatively upper stratigraphic interval of the formation, lighter laminae characterized by a clotted texture and traversed by numerous winding tubular voids change gradually upwards into dark micritic laminae. Some sporadically distributed lenticular intraclastic beds also have the similarly dark micritic coatings. Clear carbonate cement crusts also occur between laminae and between successive dark micritic coats around intraclasts. Dull cathodoluminescence (CL) characterizes this cement as well as the cement lining within early diagenetic voids. In contrast, the laminae with clotted textures show dirty orange luminescence, while the dark micritic laminae and the dark micritic grain-coats display clear bright orange luminescence. Pyrite and its pseudomorphs are preferably concentrated along the dark micritic laminae. Carbon content in these dark micritic components, whether laminae or coats, is much higher than in the lighter components, exceeding what can be accounted for their CaMg(CO3)2 composition. A large part of this carbon is kerogen, plausibly biogenic. The dark components are, therefore, reasonably, though not unequivocally, assumed to be microbial mats. Degradation of the mats might have given rise to the light laminae with clotted textures. The fuzzy-margin tubes within the light laminae probably manifest the escape of gases generated during organic matter decomposition. Si–Al-rich terrigenous fines thinly draping the dark carbonaceous laminae was possibly the result of baffling and trapping of terrigenous fines by filamentous microbiota. Dark carbonaceous laminae encasing intraclasts was considered to be the result of binding and stabilization by microbiota. Spike-like growth of discrete laminae strongly suggests an occasional breakdown of colonial homeostasis of phototrophic microbiota. The microbial community thus appears to have played an active role in stromatolite-building in the Lakshanhatti Dolomite Member, even though the simultaneous existence of direct carbonate precipitates from sea water indicates a hybrid origin of these stromatolites. Resting on shelf sandstone and being capped by dark offshore shale, the Lakshanhatti Dolomite had been deposited in distal offshore, but not at the great depth, perhaps in an epeiric sea. Progressive deepening inhibited direct carbonate precipitation. δ13C and δ18O values suggest normal open marine salinity during deposition.

Lead isotope ratios from three base metal deposits, Rangpo, Gorubathan in the eastern Lesser Himalaya and Bageswar in the Lesser Himalaya of Kumaun have been studied. The first two deposits, generally stratiform and stratabound, occur within pelitic, psammopelitic/wacke type metasediments which are locally carbonaceous. The Bageswar deposit is hosted by silicified dolomitic carbonate rocks. The Pb-isotope ratios appear to be homogenous in two and heterogenous in one of the deposits. Model Pb–Pb ages obtained for the Rangpo and Gorubathan deposits are 1800 Ma and for the Bageswar deposit, 1550–1700 Ma. Dispersion in isotopic ratios reflect the geochemical heterogeneity, particularly with respect to μ. Larger variation in the composition of Pb-isotope ratios in the Bageswar deposit may be explained by the participation of Pb from heterogenous sources. Pb-isotope characteristics of the Himalayan deposits are compared with those of a number of base metal deposits in the Delhi–Aravalli belt in Rajasthan, NW India. Ore lead from the deposits of both the Himalaya and of Rajasthan are enriched in 206Pb and 207Pb. However, lead in all cases plots on the evolution lines, corresponding to sources with higher U/Pb ratios. But the sources of lead in the Himalayan deposits had a lower Th/U ratio. The geologic observations as well as the Pb-isotope compositions are consistent with a sedimentary-diagenetic origin of the Himalayan base metal deposits.

The CDF Online Silicon Vertex Tracker (SVT) reconstructs 2D tracks by linking hit positions measured by the Silicon Vertex Detector to the Central Outer Chamber tracks found by the eXtremely Fast Tracker (XFT). The system has been completely built and assembled and it is now being commissioned using the first CDF run II data. The precision measurement of the track impact parameter will allow triggering on B hadron decay vertices and thus investigating important areas in the B sector, like CP violation and Bs mixing. In this paper we briefly review the architecture and the tracking algorithms implemented in the SVT and we report on the performance of the system achieved in the early phase of CDF run II.

The online silicon vertex tracker (SVT) is the new trigger processor dedicated to the two-dimensional (2-D) reconstruction of charged particle trajectories at the Level 2 of the Collider Detector at Fermilab (CDF) trigger. The SVT links the digitized pulse heights found within the silicon vertex detector to the tracks reconstructed in the central outer tracker by the Level 1 fast-track finder. Preliminary tests of the system took place during the October 2000 commissioning run of the Tevatron Collider. During the April-October 2001 data taking, it was possible to evaluate the performance of the system. In this paper, we review the tracking algorithms implemented in the SVT and we report on the performance achieved during the early phase of run II.

Source-signature imbibed within geochemistry and detrital mineralogy gets blurred when correlated with physical characteristics in the Barremian-Aptian siliciclastic-fill of the Pondicherry Sub-basin, India. Six alluvial conglomerate-shale facies associations linked with paleocurrent patterns present a facsimile of basin-margin scree/alluvial fans transiting into a low-sinuosity axial river system, in turn passing into a distal floodplain traversed by high-sinuosity channel branches. The QFL-plot for the sandstones indicates cratonic source gaining relative maturity toward the distal depositional setting. Geochemical data clearly document variable degrees of mixing of felsic and mafic components, and source-shifting in concert with rifting. Weathering had been moderate with an annual temperature around 12°C and rainfall 844–1060 mm, although geophysical reconstructions suggest high paleolatitude. Intrabasinal sediment transport and diagenesis, nonetheless, left a noteworthy overprint.

This study presents a review of the wide spectrum of biotic signatures within the Precambrian Vindhyan Supergroup deposited during the ‘boring billion’ and assesses their biological affinity and age implications. The sedimentation took place in wide–ranging palaeo–environments from fluvial to offshore through shallow marine. While the lower part of the ~ 4500 m thick Vindhyan succession is older than 1650 Ma, the age at its top part is poorly constrained, ranging from 1000 to 650 Ma. Microbial records are abundant in the form of stromatolites in limestone and microbially induced sedimentary structures (MISS) on both siliciclastics and carbonates across the Vindhyan succession. The wide morphological variation of these two features corresponds to depositional processes, early cementation, as well as lithological variations. The stromatolite record, as well as calcified and chertified microbial fossils, attest to the Mesoproterozoic to Neoproterozoic age of the sediments. Although the carbonaceous body fossils do not have age implications, they indicate the proliferation of algal life during the Meso– to Neoproterozoic time. The Ediacaran–like fossils mostly relate either to ‘discoidal microbial colony’ or detached pieces of microbial mat. Wide–ranging putative metazoan fossil reports remain the focal point of attention for many years. Although most of these reports are found to be microbially originated, some of these features have the potential to highlight the evolution of multicellular life during the Precambrian.

Microbes had been the sole occupant of the early biosphere and they strongly controlled the evolution of lithosphere, hydrosphere, biosphere and atmosphere.Many Microbes could form mat like structure on sea floor.During the Precambrian these microbial mats had a strong influence on sedimentation, and they facilitated the formation of a variety of mat-induced sedimentary structures (MRS/MISS) in siliciclastic and carbonate rocks.In last two decades many of these structures have been identified from the Indian Proterozoic rocks.Observation from modern environments indicates the formation of mat related structures in preferred segments of the shallow marine domain.We also investigate the cause and effect relationship between the mat-growth and the sequence building pattern during the Precambrian.The commonly present HSTs compared to those of corresponding TSTs possibly indicates that microbial mat-infested sea floor impedes erosion, while concomitant sediment supply facilitated formation and preservation of regressive packages during the Precambrian.

We have measured the probability, n(g->cc~), of a gluon splitting into a charm-quark pair using 1.7 million hadronic Z decays collected by the L3 detector. Two independent methods have been applied to events with a three-jet topology. One method relies on tagging charmed hadrons by identifying a lepton in the lowest energy jet. The other method uses a neural network based on global event shape parameters. Combining both methods, we measure n(g->cc~)= [2.45 +/- 0.29 +/- 0.53]%.

The present study deals with the Neoproterozoic mat-infested substrate sculptured by inferred bioturbations, excellently preserved within the ca. 600 Ma Sonia Sandstone, northwest India. The bioturbations are horizontal, being preserved on the bed-surfaces and have been classified into linear grooves and discoidal structures. The linear grooves are of two types, one group represents a straight to meandering pattern with raised sand ridges on either side, while the other group represents a mostly meandering pattern with changing width along the length, without raised ridges. Both types of grooves resemble trails of advanced organisms. The discoidal structures have five internal lobes emerging from the centre and merging with the outer ring and may represent body impressions of an organism; alternatively may represent variants of Ediacara or other soft bodied organisms. The interaction of the substrate with these possible bioturbators has great significance in establishing the evolutionary history of the substrate and resulting bioturbations during the Proterozoic. Microbial mats possibly provided oxygen and nutrients to the organisms and played an important role in their preservation. The study also tries to extrapolate the life style of these trace-makers. All these traces may raise speculation about the onset-time of some higher order organisms.

This book generates understanding of the course of sedimentation in Proterozoic Vindhyan Basin and the potential record of ancient life imbibed within the rocks and provides 75 color photographs and hand-sketches to bring the key aspects of the Vindhyan Geology readily within grasp of the readers

During normal data taking CMS expects to support potentially as many as 2000 analysis users. Since the beginning of 2008 there have been more than 800 individuals who submitted a remote analysis job to the CMS computing infrastructure. The bulk of these users will be supported at the over 40 CMS Tier-2 centres. Supporting a globally distributed community of users on a globally distributed set of computing clusters is a task that requires reconsidering the normal methods of user support for Analysis Operations. In 2008 CMS formed an Analysis Support Task Force in preparation for large-scale physics analysis activities. The charge of the task force was to evaluate the available support tools, the user support techniques, and the direct feedback of users with the goal of improving the success rate and user experience when utilizing the distributed computing environment. The task force determined the tools needed to assess and reduce the number of non-zero exit code applications submitted through the grid interfaces and worked with the CMS experiment dashboard developers to obtain the necessary information to quickly and proactively identify issues with user jobs and data sets hosted at various sites. Results of the analysis group surveys were compiled. Reference platforms for testing and debugging problems were established in various geographic regions. The task force also assessed the resources needed to make the transition to a permanent Analysis Operations task. In this presentation the results of the task force will be discussed as well as the CMS Analysis Operations plans for the start of data taking.

Within the hydrocarbon-producing Cretaceous marine Uttatur Group, Cauvery Basin, India, the Garudamangalam Sandstone Formation is at top of a TST-HST transit. The δ13C value is expectedly depleted within the calcareous Garudamangalam Sandstone, which is the top most unit of the Uttatur Group, overlying the Karai Shale. The calcareous sandstone was deposited in a coastal setting around a shore-parallel river mouth bar. Instances of excessive depletion of δ13C up to −44.5‰ in the carbonate cement is suggestive of methane generation and its subsequent sequestration. The common occurrence of early diagenetic pyrite in these rocks testifies to the proliferation of sulfate-reducing bacteria and is suggestive of methane generation beneath the sulfate reduction zone. Upward-moving diffusive methane was possibly consumed by methanotrophs at the base of the sulfate-reduction zone. Abundant fabric-selective carbonate cement corroborates microbially-controlled anaerobic oxidation of methane. The presumed high rate of nutrient supply, abundance of vegetative material and moderately high organic carbon content in sediments (av. 1.6%), support this contention. All the samples which have the greatest δ13C depletion are characterized by enriched organic carbon and are derived from a tidal inlet-mouth facies, and selectively from mud drapes on cross-bedding in tidal strata. Calcarenite at the base of the same cross-strata are invariably much less depleted in δC13. This range of relationships indicates the transport of methanotrophs that settled on foreset beds mostly as tides slackened under the broader control of neap-spring cycles.

The Sikkim-Darjeeling Himalaya contains the stretch of tectonically active Eastern Himalaya. It is composed of three main tectonic units: Higher Himalaya, Lower Himalaya and Siwaliks separated by thrusts, but joined by great fluvial system of the Tista River. The Higher Himalaya with relief up to 2,000–4,000 m was uplifted by about 2,000 m in the Quaternary rising above the snowline. Its mountain massifs previously had fluvial relief which later had been totally transformed by glacial and cryonival processes. The Lower Himalaya dissected 1,000–2,000 m locally with remains of mature relief fragments are continuously in the forest belt. The Siwaliks in this part of the Himalayan Range are reduced to a narrow belt, which blende with Lower Himalaya. Along the Frontal Fault it rises above 1,000 m directly over the alluvial plains of the Sub-Himalayan foredeep, which is still active and split into blocks of various tectonic tendency. Steep edge of the Himalaya is exposed to high monsoon rainfalls and is afflicted by heavy downpours and continuous rains. Following deforestation this marginal part and also the southern Sikkim area have been affected by large-scale mass movement processes and floods. Only the Tista and several large rivers are transporting heavy sediment loads down to the Brahmaputra River. The smaller streams dissecting the mountain edge form a belt composed of fans.

Abstract South–southwestward palaeocurrent swerved to east–southeast and then broadly to southeast over the transition from alluvial fan to axial channel and then to the flood plain in the Mio–Pliocene foreland system within which the Siwalik Group depositd in Darjeeling-Jalpaiguri Districts, eastern India. Palaeocurrent pattern is found to be multi-modal on the fans, virtually unimodal on the axial channel zone and again multi-modal, more profoundly, on the flood plain. Coarse siliciclastic mass-flows were progressively eliminated and gave way to predominant bed-load transport downfan and the axial river, and then to suspension-load dominance in fine siliciclastics on the flood plain. Distal flood plain lacustrine sediment included most of the coals and the entire bulk of the dolomitic limestone. Further resolution in palaeogeography within the frame of aforementioned foursome facies associations is elicited in twenty-six distinctive facies altogether. Critical evaluation of chemical indices (CIA, CIW, ICV, PIA, as well as Rb/Sr ratio) for weathering and depleted δ 18 O values indicate a high precipitation rate. The contention is further corroborated by the high discharge rate calculated from cross-set thicknesses within the main channel deposits. Reconciliation of various relevant data sets collected or calculated from all known worksites along the entire 2000 km-long exposure belt of the Siwaliks along the Himalayan foothills reveal confluence of two tributaries, one from the west and the other from the east, close to the present study area before escaping onto the Indian plains. Channel parameters, channel-belt width and discharge thus attained maxima in the present study area. The precipitation rate and temperature increased eastward overall as a prelude to the modern trend in this regard. 13 C enrichment indicates that the transition from C 3 to C 4 vegetation had already set in.

India offers a graceful natural laboratory for time traveling to the CretaceousCretaceous world. The present chapter attempts a review of Cretaceous geology from India heading for its stance on evolution of basin, stratigraphy, sedimentation, climate, volcanism, relative sea levelRelative sea level (RSL), biogeography and mass extinction. It was the era when India separated from the GondwanalandGondwanaland next to the South Pole and initiated the longest passage in a northward direction. Tectonic spurt and reformation steered the geography of the island continent. Margins of the land got novel shape, new ocean and bays opened up, coastlines were formed and new sedimentary basins developed at the continental margins as well as in the interior part. Later, Gondwana sedimentation was ceased. Relative sea levelRelative sea level (RSL) (RSL) was set to fluctuate at a similar pace to global transgression and regression. Sediments were deposited on the east coast, west coast, and offshore basins in response to the rise in RSL during AlbianAlbian, TuronianTuronian and Campanian. A Late CretaceousCretaceous transgression in central India came from the west. The maximum fossil foraminifer diversity was in theCenomanian late Cenomanian/earliest TuronianTuronian and this time-interval is corresponding with the maximum sea-level recorded during the MesozoicMesozoic. Apparently, a warm temperate humid palaeoclimate prevailed with a tendency of increasing humidity at the end of the CretaceousCretaceous. The paleotemperature graph was higher in Late Cretaceous too. India witnessed three renowned volcanic episodes during this period: Rajmahal and Sylhet flood basalts in the eastern part and Deccan volcanismDeccan volcanism in the western sector. India perhaps retained the biotic link with Africa via Madagascar and South America till Early CretaceousCretaceous. Terrestrial vertebrates are found cosmopolitan with a lack of evidence of endemism. Besides, diversity prevailed in floral distribution pattern, as gymnospermGymnosperm dominated and angiosperm appeared. The MaastrichtianMaastrichtian sections in India report the evolution of Gondwana fauna in isolation on top of amalgamation of Laurasian taxa. The K-Pg boundary is marked by a severe loss of fauna: the disappearance of dinosaurs, ammonitesAmmonites, flying reptiles, scleractinian corals, belemnitesBelemnite and some groups of bivalves, gastropods and echinoderms; acutely affecting calcareous planktons and reef invertebrates.

A kind of fairweather high-energy mesoscale flute-like scours is observed in the intertidal zone in Chandipur, at the northwestern corner of the Bay of Bengal, India. The scours are localized immediately in front of three sharp breaks within three contrasting environmental subzones. Their open ends point to the local slope directions that vary between adjacent subzones. Shapes and dimensions of the scours in association with a low intertidal bar vary subtly but significantly with bar height. Roller eddies caused by ephemeral hydraulic jumps provide a plausible explanation for their generation. Extended covering of rippled silt or very fine sand on the scoured intertidal flat denotes a rapid fall in depositional energy soon after scouring. This is a consequence of submergence-emergence tidal cycles. Occurrence of such mesoscale flute-like scours in ancient tidal flats would provide positive help in recognizing palaeoreliefs such as bars. There is, however, no reason for these scours to remain confined either to the sea margins or to the fairweather. The prerequisites for their formation are a sharp change in gradient of the depositional substrate and a periodic or episodic sedimentation process. Possible analogues of such scours are cited from a few ancient sequences.

Flat pebbles and edge‐wise fabric in the Mesoproterozoic Rohtas Limestone Formation (RLF) and the Chikkshelikere Limestone Member (CLM), India, generate a new insight into their formation. Simple stacks of alternating dark micritic and light‐coloured microsparite planar layers in the targeted sedimentary successions manifest a low‐energy depositional background, disturbed only occasionally by weak storms. While the dark layers are homogeneous, light‐coloured layers are generally planar, wavy ripple laminated, and bear frequent load casts. The dark layers often display varieties of 2‐D microbial mat structures little known from carbonate formations. In compliance with their identity, they are comparatively enriched in carbon, a large part of which is organic and kerogen. The said structures with their intrinsic deformations indicate delayed cementation. Notwithstanding delayed cementation, the flat clasts in these formations are readily traceable to the dark laminae possibly because of early acquisition of their selective cohesiveness. Resultant stress led to brittle deformation in the mat layers, while the light‐coloured layers underwent ductile deformation. All the studied breccias bodies are in situ, but this fact does not preclude either the possibility of reworking of the clasts while exposed to high‐energy current or generation of intraclasts by high‐energy currents eroding the depositional surface.

Since the beginning of Run II in 2001 the Fermilab Tevatron has been delivering proton‐antiproton collisions to CDF with a steadily increasing performance. By the end of Run II up to 8 fb−1 of integrated luminosity are expected to be available on tape. In order to provide the CDF Collaboration members with adequate computing resources for analyzing those data, a globally distributed pool of dedicated PC farms has been commissioned and is currently being successfully deployed. This paper describes the main features of the CDF Analysis Farm with particular attention to the user perspective. The last part is devoted to a brief overview of the more relevant technical details on the farm implementation and, finally, the future developments toward its integration in the GRID framework are outlined.

Detailed facies analysis in late Proterozoic Rewa Shale reveals three physically distinctive facies that differ in their paleogeography. Between shoreface and outer shelf the facies types are distributed as (I) shale with thin siltstone/Fine sandstone interbeds of outer shelf, (II) shale interbedded with HCS bearing sheet sandstone of inner shelf within storm wave base and (III) sandstone interbedded with silty shale of distal shoreface paleogeography. High resolution facies succession analysis reveals three different orders of depositional cyclicity, the lowest of which may be correlated with third order depositional 'sequence'. Thin (av 3 5 cm) discrete levels of emergence with their invariable associations and sharp transitions from inner shelf to shoreface facies mark the subaerial discontinuities, which punctuate the apparently monotonous. Rewa Shale succession Far from the coastline on a siliciclastic ramp that lacks shelf slope break, these features, even though cryptic, can provide important clues for sea level falls in shale dominated successions.

The multistoried siliciclastic succession at the base of basal Kerur Formation of the Neoproterozoic Badami Group shows ample variations in sequence building pattern within the ambit of the Precambrian fluvial sedimentation system. Detailed facies, architectural element, paleocurrent as well as stratigraphic architectural analysis invariably revealed a frequently avulsive braided pattern, with flashy discharges, for the paleoriver system; which is consistent with the basic tenet of the Precambrian alluvial sedimentation. Rare eolian features suggest seasonal flow fluctuations, referring to the semiperennial nature of the fluvial system. The studied interval represents a single valley fill, internally constituted by seven vertically juxtaposed channel belts. Each channel belt is fining upward along with the overall grain-size reduction up the succession. While the older channel belts inferred to be braided, channels possibly become more sinuous towards the top of the succession, as inferred from the appearance of bank-attached bars along with the omnipresent longitudidal bars. Flow durability within channel also increases with time, as the lower two belts appear to be ephemeral with highest energy flashy discharges, changing into semiperennial to perennial one upward. Bounded between an unconformity below and a thoroughly wave-featured limestone unit above, the coarse and poorly sorted clastic sedimentary rocks at the base of the basal Kerur Formation are interpreted as a base-level lowstand product, indicating gradual filling of the paleoriver valley under the backdrop of slow rise in base profile. Tectonics-related generation of accommodation space as well as the rejuvenation of slope along and across the basin-margin dictated the sediment distribution and sequence building pattern primarily. The increase in channel sinuosity up-the-succession is governed by the raised rate of base profile rise, which ultimately leads to termination of the terrestrial depositional system by complete marine inundation.

Abstract Poorly-sorted conglomerate patches rich in granules or sturdy fossils or both, and reddish mud matrix within the interstices stand out amidst fine-grained siliciclastic shelf sediments of the trangressive systems tract (TST) of the Lower Cretaceous Ukra Member, Kutch Basin, India. The siliciclastic shelf sediments contrast the conglomerates with their remarkable lateral extension. The fossils belong to a low-diversity group of sedentary bivalves that can be traced into the shoreface facies assemblage. The shelf sandstones are almost always sculpted by wave structures, especially hummocky cross-stratification while textures in the conglomerates suggest that the sediment settling was generally from suspensions. Textural variations in conglomerates reflect an immediate variation in flow viscosity prior to the downloading. The current structures obtained from the conglomerates record offshoreward palaeocurrent, in contrast to the shore-parallel palaeocurrent in the TST. The hummocky cross-stratified (HCS) beds are interpreted as seasonal storm deposits, while the conglomerate patches are taken as rip current deposits induced by waves of much longer periods. The glauconite-rich shale that alternates with conglomerates is probable fair-weather products. The conglomerates could not be recognized either in the coarse-grained shoreface deposits occupying the lower part of the overall fining-upward TST or in the coarsening-upward and glauconite-depleted highstand systems tract (HST). In contrast to the TST, the HST is dominantly tide-imprinted, having shore-normal palaeocurrent direction. It appears that intensification of waves and weakening of tides during transgression favored strong rip currents generation, which had presumably caused severe damage to the sea coast and to the shell banks growing preferably at the necks of the rip current channels. Rapid lateral facies transitions in the shoreface deposits at the basal part of the TST suggest enhanced irregularity in the coastline, possibly because of the mega cusps indented upon it. Frequency and intensity of storms enhanced during periods of global warming caused the transgression of the Early Cretaceous Ukra Sea.

The Great Unconformity that separates the early Cambrian sandstones from the Proterozoic metamorphosed sedimentary rocks has been recognized in many blocks on Earth. However, whether it represents a globally synchronous event or a composite of a series of diachronous events, and its formation mechanism remain largely unknown. In this study, we carry out detrital zircon U-Pb analyses for seven samples collected from the Paleoproterozoic Quanji Group and the overlying Neoproterozoic strata in the Olongbuluke terrane (OLT) of Northwest China. The results show that apart from age populations of ∼ 1.8–2.0 Ga and ∼ 2.2–2.5 Ga for all samples, additional ∼ 1.55–1.65 Ga age population occurs in sample from the Zhoujieshan Formation, and more scattered age populations ranging from ∼ 0.75 to ∼ 1.7 Ga are present in samples from the Heitupo and Hongtiegou formations. The ∼ 1.8–2.0 Ga and ∼ 2.2–2.5 Ga zircons correlate well with the magmatic and metamorphic events in the OLT basement, indicating their local provenances, while other zircons were possibly derived from the North China craton (NCC) or other adjacent blocks. Combined with published paleontological, stratigraphic, and geochronological data, the present study supports previous inference that the OLT had a close paleogeographic affinity to the NCC during late Paleoproterozoic to Neoproterozoic. New zircon U-Pb ages indicate that the Heitupo Formation was deposited later than ∼ 750 Ma, and the underlying Hongzaoshan Formation was deposited at ∼ 1.66 Ga, implying a huge break between them. Whereas the duration of the sedimentary break between the Heitupo Formation and the overlying Hongtiegou Formation is uncertain, biostratigraphic data suggest that a break of ∼ 30 Myr may exist between the late Ediacaran Zhoujieshan Formation and the overlying early Cambrian Xiaogaolu Group. The occurrences of these multiple unconformities in OLT are comparable to those in NCC, indicating that the Great Unconformity is represented by a series of lengthy denudations during the Proterozoic-early Cambrian in both the OLT and NCC, which may result from multiple tectonic activities in these two blocks.

The Collider Detector at Fermilab (CDF) Silicon Vertex Tracker (SVT) is a device that works inside the CDF Level 2 trigger to find and fit tracks in real time using the central silicon vertex detector information. SVT starts from tracks found by the Level 1 central chamber fast trigger and adds the silicon information to compute transverse track parameters with offline quality in about 15μs. The CDF SVT is fully installed and functional and has been exercised with real data during the spring and summer 2001. It is a complex digital device of more than 100 VME boards that performs a dramatic data reduction (only about one event in a thousand is accepted by the trigger). Diagnosing rare failures poses a special challenge and SVT internal data flow is monitored by dedicated hardware and software. This paper briefly covers the SVT architecture and design and reports on the SVT building/commissioning experience (hardware and software) and on the first results from the initial running.

Detecting thermal Unruh radiation from accelerated electrons has presented a formidable challenge due not only to technical difficulties but also for lack of conceptual clarity about what is actually seen by a laboratory observer. We give a summary of the current interpretations along with a simpler heuristic description that draws on the analogy between the Unruh effect and radiation from a two-level atomic system. We propose an experiment to test whether there is emission of thermal photons from an accelerated electron.

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry.Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe.The network may be made unstable by invoking a 'tilt' in the axion potential due to Planck scale suppressed non-renormalisable operators.Alternatively the random walk of the axion field during inflation can generate a 'bias' favouring one of the degenerate vacua, but we find that this mechanism is in practice irrelevant.Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather lowthus ruling out e.g. the DFSZ axion with mass below 33 meV, where most experimental searches are in fact focussed.

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry.Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe.The network may be made unstable by invoking a 'tilt' in the axion potential due to Planck scale suppressed non-renormalisable operators.Alternatively the random walk of the axion field during inflation can generate a 'bias' favouring one of the degenerate vacuua, but we find that this mechanism is in practice irrelevant.Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather lowthus ruling out e.g. the DFSZ axion with mass below ∼ 60 meV, where most experimental searches are in fact focussed.

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry.Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe.The network may be made unstable by invoking a 'tilt' in the axion potential due to Planck scale suppressed non-renormalisable operators.Alternatively the random walk of the axion field during inflation can generate a 'bias' favouring one of the degenerate vacuua, but we find that this mechanism is in practice irrelevant.Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather lowthus ruling out e.g. the DFSZ axion with mass below ∼ 60 meV, where most experimental searches are in fact focussed.

The neutrinoless double beta decay is a pivotal weak nuclear process that holds the potential to unveil the Majorana nature of neutrinos and predict their absolute masses. In this study, we delve into examining the impact of spin-dependent short-range correlations (SRC) on the nuclear matrix elements (NMEs) for the light neutrino-exchange mechanism in neutrinoless double beta ($0\nu\beta\beta$) decay of $^{48}$Ca, employing an extensive interacting nuclear shell model. All computations are performed employing the effective shell model Hamiltonian GXPF1A, encompassing the entire $fp$ model space through the closure approximation. Our investigation examines the NMEs' dependencies on factors such as the number of intermediate states, coupled spin-parity attributes of neutrons and protons, neutrino momentum, inter-nucleon separation, and closure energy. This scrutiny is performed with respect to both the conventional Jastrow-type approach of SRC, employing various parameterizations, and the spin-dependent SRC paradigm. Our findings illuminate a discernible distinction in NMEs induced by spin-dependent SRC, differing by approximately 10-20\% from those computed through the conventional Jastrow-type SRC, incorporating distinct parameterizations.

Monte Carlo production for the CMS experiment is carried out in a distributed computing environment; the goal of producing 30M simulated events per month in the first half of 2007 has been reached. A brief overview of the production operations and statistics is presented.

Monte Carlo production in CMS has received a major boost in performance and scale since the past CHEP06 conference. The production system has been re-engineered in order to incorporate the experience gained in running the previous system and to integrate production with the new CMS event data model, data management system and data processing framework. The system is interfaced to the two major computing Grids used by CMS, the LHC Computing Grid (LCG) and the Open Science Grid (OSG).

The Vindhyan rocks exposed in the Son valley unconformably overlies the granites/metasediments of the Mahakoshal Group. The Supergroup with its excellent preservation records the interplay between sediments and different sedimentological processes. Excellent preservation of primary sedimentary structures allows a detailed process-based facies analysis. The following section deals with the detailed facies descriptions and interpretations of the formations constituting the Vindhyan Supergroup, followed by paleogeographic interpretations. Facies of the constituent formations and members are presented in tables. The sequence stratigraphic framework of the Vindhyan Supergroup has been summarized at the end. Coordinates of the places are provided at the end of this chapter.

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