tectonic forcing of drainages and geomorphic features developed across himalayan mountain frontal part of western limb of siang antiform arunachal himalaya drainages display tectonic forcing of their channels on the frontal region of the arunachal himalaya due to structural control dikari a transverse river flowing along the n s trending western limb of the major siang antiform exhibits structurally controlled nature of its drainage on its downstream flow towards south through a network of ne sw and nw se trending conjugate faults the river shows compressed meandering as the regional structural trend of ene wsw seems to be reactivated by the transverse nw se trend of neotectonic fault activity the himalayan frontal thrust hft tracing along the himalaya mountain front has been displaced sinisterly for a distance of 7 km by a wnw ese trending fault running along the sileng stream development of parallel drainages in the southern part of the sub himalaya is interpreted to have formed as a result of uplifting related to the above mentioned strike slip movement along the hft zone the frontal streams and rivers exhibit deflection of their channels from ne sw to ene wsw directions channel of the transverse siang river has been deflected for a length of 3 km along the nne ssw direction across the himalayan frontal part in this part of the himalaya previous workers did not give much emphasis on the role of siang antiform as far as neotectonic with respect to the tectonics related to the hft is concerned there is a syntectonic relationship between the active ne sw oriented compression direction and the tectonic forcing of the drainages including development of the tectonic geomorphology

late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

influence of neotectonism on geomorphology and depositional architecture of the gandak megafan middle ganga plain india abstract the gandak megafan formed by episodic tilting of tectonic block followed by an eastward shift of the gandak river the study area has been identified with 5 distinct depositional units which were chronologically named as oldest gandak plain osgp old gandak plain olgp gandak terminal fan gtfn i ii and iii an integrated approach including morphometry pedology gpr study and osl dating was adopted to study morphotectonics of the megafan dem of the megafan and anomalies in drainage of the area helped to delineate ne sw trending normal faults which divide the megafan block into 3 tectonic sub blocks present day channels reciprocate the fault movements through anomalies in drainage and change in sinuosity around the faults sinuosity of the gandak chhoti gandak and other small streams daha gandaki and rohini varies from 1 6 4 5 and 3 5 respectively which suddenly increases across faults the concurred variations in longitudinal river profiles and sl index appear to be attributable to the tectonic controls the development of these faults and subsequent tilting of the sub blocks influenced the sedimentary architecture and fluvial geomorphology of the megafan a linear arrangement of natural waterlogs and paleochannels observed in satellite images imply lateral shifting of the gandak river older depositional units osgp and olgp show well developed thick solum formation 2 2 m and 1 9 m respectively comparatively the younger units i e terminal fans show poor to no development of soil with 1 2 m to 0 8 m thick successions osl dates indicate that older and younger units were deposited between 10 7 and 8 5 ka and 5 7 and 1 4 ka respectively the tectonically stable period of 3 ka is also exhibited by non depositional surfaces in soil successions

sone megafan a non himalayan megafan of craton origin on the southern margin of the middle ganga basin india abstract researchers in the last few decades have focused on the fluvial megafans at the base of himalayan foothills in the ganga basin no major effort has so far been made to delineate any such large depositional environment at the base of the northern indian peninsular craton at the distal parts of the basin in this work for the first time we document a megafan unusually created by the cratonic sone river in the marginal plains south of the ganga the geomorphology of the megafan surface distribution of palaeochannels sedimentology and areal extent of the megafan are described the study also reconstructs the tectonic and palaeoclimatic conditions which might have helped in sediment supply from the cratonic catchment areas of the sone we suggest tectonic control over the sone river channel dynamics and development of the megafan the oval and fan shaped craton derived sediment body covers an area of around 12 000 km2 in the marginal plains and about 9000 km2 in the central alluvium north of the ganga river the megafan is around 190 km long and 240 km wide the mean slope of the megafan surface is 0 03 an onlap of himalayan sediments has occurred over the megafan at its toe parts caused by southward encroachment of the ganga during the holocene the megafan sediments comprise brownish yellow fine to coarse sand and gravels with an admixture of carbonaceous nodules kankars the thickness of the megafan sediment which directly overlies the precambrian basement varies from only a few meters in the south near the peninsular craton to 1000 m at the north in the central alluvial plain the granular zones form prolific aquifer systems in an otherwise poor hydrogeological setting of the marginal plains

dropstones their origin and significance abstract dropstones are clasts which pose a hydrodynamic paradox or which have an exotic or extra basinal lithology with uncertain provenance recently dropstones have been consistently interpreted as the product of ice rafting and have been used to substantiate the presence of cool climatic phases in the geological record this review illustrates that not all dropstones are reliable as palaeoclimatic indicators dropstones are the product of two distinct entrainment and transport mechanisms by a rafting agent or as a projectile four main processes of transport and formation are identified biological rafting ice rafting floatation and projectiles biological rafting agents include vertebrate gastroliths and other stomach contents vegetational rafting and anthropomorphic activity ice rafting can be the product of ice bergs or seasonal sea river or lake ice floatation of clasts in calm waters has been recorded for stones up to 25 mm in length projectiles are most commonly of volcanic origin given the range of transport and depositional mechanisms reviewed we argue that great care is required in the interpretation of the origin of dropstones

shallow sub surface stratigraphy of the ganga basin himalayan foreland present status and future perspectives the ganga basin in northern india is one of the world s largest fluvial basins and has attracted enormous attention from earth scientists across the globe with a view to understanding large river processes and landforms despite the scarcity of hydrological data from the ganga basin some important studies have been carried out in the last several decades however the unavailability of deep sections in this vast alluvial tract has always limited understanding of the sub surface stratigraphy of these plains during the last decade some important developments have taken place in integrating exposed cliff section data with the drill cores in pre defined transects and with targeted geophysical investigations additionally new areas of the basin have been studied for understanding landscape evolution including the effects of active tectonics this special issue of quaternary international highlights some of these developments from the stratigraphic archives of this large basin this collection of papers covers a wide gamut of subjects including terrace development in the frontal parts of the ganga basin resistivity based mapping of sub surface stratigraphy micromorphology of soils from plains drill core samples historical scale avulsion of large dynamic system such as the kosi active tectonics and landform development in southern ganga plains and finally some policy issues for management of dynamic river systems this introductory paper provides a background and present status of research in the ganga basin it attempts to summarise some of the recent research developments in the ganga basin research and highlights the unresolved issues some of which have been addressed through the contributions in this special issue

distribution diversity and geomorphic evolution of floodplain wetlands and wetland complexes in the ganga plains of north bihar india abstract floodplain wetlands are important features in alluvial settings across the world because of their ecological and hydrological significance understanding the geomorphic evolution of such wetlands is therefore not only interesting from an academic viewpoint but also necessary for their conservation and protection using a hierarchical system of geomorphological elements and units detailed geomorphic investigations have been carried out in the kosi ganga interfluve eastern ganga plain egp in the himalayan foreland to understand the distribution and diversity of the floodplain wetlands in this region the major geomorphic elements in this region consisting of lentic wetlands lakes and lotic streams water bodies were mapped using multispectral satellite images the distribution of the wetlands analysed through chord diagrams suggests that these are highly localised and associated with the regional geomorphic setting and the fluvial dynamicity the morphometric characterisation of these wetlands using their count area average area and total area shows significant variability among the geomorphic units the equal area circle eac such as the shoreline development index dl was found to be inadequate to assess the geomorphic maturity of the lentic water bodies and hence a new maturity index mch has been designed in this work using the convexity and area of the water bodies further the space for time substitution approach has been used to develop the evolutionary pathway for the wetlands and the wetland complexes in this interfluve over time scale of 10 102 years we suggest that the evolution of the wetlands in a dynamic fluvial system such as the interfluve region of the egp is governed by two different processes firstly fluvial scouring and channel abandonment provide negative relief at a regional scale and secondly erosional processes cut and fill acting on the local scale transform the narrow and deep fluvial scours into large and shallow wetland systems

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

uplift and convergence along the himalayan frontal thrust of india along the himalayan thrust front in northwestern india terrace deposits exposed 20 to 30 m above modern stream level are interpreted to have been uplifted by displacement on the underlying himalayan frontal thrust a radiocarbon age limits the age of the terrace to 1665 215 calendar bc 3663 215 radiocarbon years before present yielding a vertical uplift rate of 6 9 1 8 mm yr in combination with published studies constraining the dip of the himalayan frontal thrust fault to about 30 in the study area the observed uplift rate equates to horizontal shortening across the himalayan frontal thrust of 11 9 3 1 mm yr and the slip rate of the himalayan frontal thrust of 13 8 3 6 mm yr this is similar to previously reported rate estimates along the himalayan arc based on displacement of older plio miocene age rocks or the much shorter records of geodesy and historical seismicity the similarity is consistent with the idea that convergence across the himalayan front has occurred at a relatively steady rate through time the seismic expression of this deformation includes several great m 8 historical earthquakes which due to lack of surface rupture during those events have been attributed to their occurrence on blind thrusts yet the occurrence of a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismic scarps these observations suggest a potential for earthquakes along the himalayan frontal thrust larger than those observed historically

evidence for a buried fault system in the coastal plain of the carolinas and virginia implications for neotectonics in the southeastern united states geomorphic geologic and geophysical data suggest the presence of an 600 km long north northeast trending buried fault system in the coastal plain of the carolinas and virginia herein named the east coast fault system the east coast fault system is expressed by anomalous changes in fluvial geomorphology that locally coincide with one or more of the following features linear aeromagnetic anomalies buried faults interpreted from seismic reflection data surface faults offsetting pliocene pleistocene surficial units locally brecciated phyllites and argillites gently upwarped sediments topographic highs and seismicity near summerville south carolina river anomalies where the rivers traverse unconsolidated upper pleistocene holocene flood plain sediments are evidence of deformation along the east coast fault system during the past 130 to 10 k y which may be ongoing the fault system traverses the epicentral area of the 1886 charleston south carolina earthquake and lies west of paleoliquefaction sites along the outer south carolina coastal plain thus the fault system could be the source of the charleston earthquake and other large prehistoric earthquakes therefore confirmation and demarcation of the east coast fault system and elucidation of its history will help better assess seismic hazards in the southeastern united states

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

the late carboniferous glacial to postglacial transition facies and sequence stratigraphy western paganzo basin argentina abstract namurian early westphalian glacial postglacial deposits have been documented in the paganzo basin argentina but integrated sequence stratigraphic and sedimentological analyses of the glacial postglacial transition are rare in the cuesta de huaco section the glacial postglacial transition encompasses the lower sequence of the existing schemes glacioeustatic changes in sea level controlled the architecture and vertical arrangement of facies the basal sequence boundary is coeval with the onset of glaciation when sea level fell contemporaneous with glacial erosion and bypass of sediment the upper sequence boundary is a high frequency sequence boundary the basal deposits are interpreted as an early transgressive systems tract etst initiated during glacial retreat the interval fines upward contains current reworked diamictites conglomerates and sandstones deposited in a subglacial to proglacial environment facies i ii and ice rafted glaciomarine rhythmites facies iii postglacial brackish marine black shales facies iv represent the late transgressive systems tract ltst micritic limestone beds were deposited during a period of sediment starvation coeval with the maximum marine inundation in the basin mfz it marks a turnaround in the stacking pattern that became coarsening and thickening upward during the overlying highstand systems tract hst it consists of fine grained turbidites facies v and classical turbidites with wave reworked beds at the top facies vi deposited in a shallow deltaic systems intervening postglacial brackish deposits contain an ichnofauna dominated by trackways of arthropods and minor grazing traces preserved in bedding planes that resemble nonmarine ichnocoenoses and differ from the archetypal brackish ichnofaunas even when palynological data support the saline depleted environment

the permo carboniferous dwyka formation of southern africa deposition by a predominantly subpolar marine ice sheet abstract the 800 m thick glacigene dwyka formation was deposited along the northern margin of the permo carboniferous dwyka basin which covered an area of approximately 2 10 6 km 2 in southwestern gondwana the palaeogeographic setting geochemical data of the mudrocks and diamictites and the palaeontology indicate marine conditions during sedimentation ice lobes from spreading centres in the north east and south coalesced in the basin to form an extensive ice cover from the westphalian to the late sakmarian lodgement rain out and subaqueous debris flow diamictons subaqueous and subglacial melt water sands suspended mud and turbidity current sands and silts accumulated in the dwyka basin sedimentation started on the continental shelf during a grounded ice sheet stage predominantly lodgement processes then a floating ice stage predominantly debris rain out and finally an ice sheet disintegration stage debris rain out sand fall out and suspension settling of mud the palaeogeographic setting presence of marine conditions in the basin and the scale of glaciation indicate deposition from a predominantly mid latitudinal marine ice sheet the overall characteristics of the glacial sequence are neither typical of a polar nor a temperate setting and for such ancient glaciations a subpolar setting with the presence of unstable ice shelves is suggested

braiding and meandering parameters modifications to standard definttrons of brarding and meandertng are proposed to indicate the morphology of every rrver channel reach quantrtatrvely whether tt has srngle channel or multiple chinnels srnuosrty p rs defined as p l llr where l ts the length of the midline of the channel rn single channel rivers or the wldest channel inlnulti channel rivers and lp is the overall length of the reach braiding rs a measure of channel multiplicity and a new term brard channel ratlo b has been defined as b l rorll o where l o is the total of the mrd channel lengths of a ll the channels tn a reactt anoiiiir e p ssion for the brard channel ratto which gives the same numerical rcsult is b p rorl p where the total sinuosity p o l o1 lp and p has been defined above scatter pio on braid channel ratlo slnuoslty axes show a negatlve correlatton between these parameters as would be expected from the above relatlonshrps stnglechannel rivers b l have relatrvely hrgher srnuosrtres and the upper hmrt of these rs the point at which cut off becomes hrghly probable for multi channel rivers a i sinuoslty iemains low reflecting the limrtrng effect of braid bars on the development of fully dcveloped spiral seconciary flow data analyses showing that increasesin channel slope and bankfull diiharge are associated with changes from meandering to braided morpiology are diverting attenti on from the importance of the rncreased avarlability of bed load grade sediment as a control a variety of river systems supplying water and sediment to the gangetic al luvial plarns of indta have been investigated these alluvral plains are some of the most extensive in the world so the examination has dcpcndcd hcirvi ly t l thc tr c l topographical maps and satel l l te imagcs i he degree of braiding and meanderrng displayed by these rivers varies greatly from rlver to rtver and along the course of part lcular r lve rs ollc of thc first steps has therefore been to devise methods of measuring the degree of brardrng and meandering which can be applied to al l the rivers using maps and satel l i te tmagcs wrth exist ing schemes a r ivcr channel rcach cun either be expressed ln terms of brardrng or meandering sinuosrty although arguments have been developed against the thresholds between brarding and meandering that were suggested by leopold wolman 1957 there have been very few attempts at devlsing common parameters to quantl tat ively express the morphology of channels that vary from one type to the other the f irst part of this paper discusses definit ions of braiding and nrcanderrng rnd thc modif icat ions of these definrtrons that havc been adopted variat ions of thcsc nume rtcal measurements are then r l lustrated hrghhghting some of thc factors that may bc tnvolvcd tn causlng the variatton the meandering parameter sinuosity two minor modrf icat ions have been adopted to the procedures previously used in defining the slnuosity of channcls e g l copold wolman 1957 first ly the channel length has been measured along a l ine that runs mid way between the channel banks this has al lowed mcasuremcnt readl ly from topographical maps aenal photographs and satel lr te images and also has the advantage that the channel length is unlrkely to change ln a major way with changes of r rver water leve l secondly the r ivers rn india show so many transit ions between srngle channel and brarded morphologies that i t was found necessary to abandon the hard and fast dist inct ion be ween braided and meandering classes of r ivers and employ definit ions of brarding and meandering that can each be applied to every rrver no matter whether i t has single or multrple channels or both therefore the meandering sinuostty parameter has been extended to mult i channel situations where i t is based on the mid channel length o f the channe l tha t rs wtdes t tn each reach of the channel belt the modif ied sinuosttv parameter p rs

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

palynological biozones and radiometric data at the carboniferous permian boundary in western gondwana absolute radiometric data obtained recently in upper paleozoic basins of south america and southern africa are available to constrain the age of some palynological biozones defined in the western gondwana some dates obtained from argentina coincide with southern africa s and are useful to constrain the palynological associations in this way the permian argentinian lueckisporites weylandites lw biozone is compared with the lueckisporites virkkiae biozone of brazil and zone 3 of south africa on the other hand the palynofloras from dwyka south africa are comparable with argentinian and brazilian associations recovered near the carboniferous permian boundary tuffaceous intervals of the dwyka group in south africa suggest the beginning of that sequence at 307 ma reaching the 290 ma at the top the available palynological paleoenvironmental and radiometric data from these three western gondwanan areas are analyzed and compared 2006 international association for gondwana research published by elsevier b v all rights reserved

evaluating influence of active tectonics on spatial distribution pattern of floods along eastern tamil nadu india flooding is a naturally recurrent phenomenon that causes severe damage to lives and property predictions on flood prone zones are made based on intensity duration of rainfall carrying capacity of drainage and natural or man made obstructions particularly the lower part of the drainage system and its adjacent geomorphic landforms like floodplains and deltaic plains are considered for analysis but stagnation in parts of basins that are far away from major riverine systems is less unveiled similarly uncharacteristic flooding in the upper and middle parts of drainage especially in zones of an anomalous drainage pattern is also least understood even though topographic differences are attributed for such anomalous spatial occurrence of floods its genetic cause has to be identified for effective management practice added to structural and lithological variations tectonic movements too impart micro scale terrain undulations because active tectonic movements are slow occurring long term geological processes its resultant topographical variations and drainage anomalies are least correlated with floods the recent floods of tamil nadu also exhibit a unique distribution pattern emphasizing the role of tectonics over it hence a detailed geoinformatics based analysis was carried out to envisage the relationship between spatial distribution of flood and active tectonic elements such as regional arches and deeps block faults and graben and drainage anomalies such as deflected drainage compressed meander and eyed drainages the analysis reveals that micro scale topographic highs and lows imparted by active tectonic movements and its further induced drainage anomalies have substantially controlled the distribution pattern of flood

understanding confluence dynamics in the alluvial ganga ramganga valley india an integrated approach using geomorphology and hydrology abstract confluence dynamics in the ganga ramganga valley in the western ganga plains of india has been studied through systematic mapping of channel configuration using multi date remote sensing images and topographic sheets for a period spanning nearly 100 years 1911 2000 the study has been supplemented with a detailed analysis of the channel morphology hydrology and sediment transport characteristics of the different rivers our study indicates that new confluences have been created during this period and that the confluence points have moved both upstream and downstream on a historical time scale apart from major avulsions other processes that have controlled the confluence movements include river capture cut offs and aggradation in the confluence area river capture occurs through lateral bank erosion and migration encroachment by the master stream and beheading of smaller rivers resulting in upstream movement of the confluence point another process which influences the upstream migration of the confluence is an increase in sinuosity of one of the channels near the confluence and then a cut off aggradation in the confluence area and local avulsions of the primary channel in a multi channel system seem to be the major process controlling the downstream movement of the confluence point analysis of channel morphology hydrology and sediment budget for the study period supports our interpretations

quaternary of the pantanal west central brazil abstract the pantanal is a tectonic depression located at the left margin of the upper paraguay river the paraguay is the trunk river of an alluvial depositional tract composed by several large marginal alluvial fans the taquari fan being the largest one the present landscape is a complex tropical wetland characterized by month long floods every year with geomorphic features derived from the present conditions and others inherited from successive pleistocene and holocene climates some areas containing ponds are landscape relicts generated by eolian deflation during the last glacial maximum many ponds closed depressions isolated from the superficial waters by vegetated crescent ridges of fine sands were interpreted as salt pans bordered by lunette sand dunes initiation of the modern wetland has occurred during the pleistocene holocene transition with the change to a more humid climate and the individualization of lacustrine systems active tectonics has been playing an important role in the development of the pantanal landscape nowadays the paraguay river meanders in a large flood plain with extensive swamp surfaces being structurally constrained by faults in the west border of the basin sedimentation within the pantanal wetland is also affected by tectonic activity especially along faults associated with the transbrasiliano lineament

tectonic footprints and landscape evaluation along kulur river valley kumaun lesser himalaya india abstract tectonic reactivation along the major boundary thrusts and subsidiary thrust faults in the himalaya during the quaternary period has resulted in the rejuvenation of the landforms considering the role of neotectonic activity in the hazardous kumaun region we aim to study the neotectonically formed landscape along the kulur river valley a non glacier fed tributary of the saryu river in the zone of the berinag thrust bt the field evidences encompassing a variety of geomorphic indicators e g unpaired fluvial terraces palaeo river channels alluvial fans active and stabilized landslides lineaments waterfalls alignment of springs deeply dissected hills straight meandering course of rivers streams v shaped valleys triangular fault facets and water logged river ponding along with integrated values of eight morphometric parameters and stream steepness index ks indices characterize the modification of landscape in the kulur river valley the computed morphometric parameters in the kulur river drainage and its tributaries show that the basin has been tilted and uplifted forming v shaped valleys along with deformed and disequilibrium longitudinal profile thereof suggesting it to be controlled by lithology and tectonics based on the response of active tectonics in form of geomorphic features and quantitative measurements of river channels the entire basin has been divided into three segments in which the northern and southern segments are active compared to the middle sector a possible nne ssw trending lineament fault running parallel to the kulur river has been observed in the upper catchment and is characterized by fluvial terraces river ponding and deflection and offsetting of drainage with rectangular pattern etc this may have given rise to the widening and straightening of river courses which provide the favorable room for river ponding resulting in deposition of about 2 m thick lacustrine mud deposit

geomorphic evidences and chronology of multiple neotectonic events in a cratonic area results from the gavilgarh fault zone central india abstract the ene wsw trending gavilgarh fault zone gfz is an important tectonic lineament within the central indian shield geomorphological mapping and spatial analyses of rivers were carried out to elucidate the imprints of active tectonics on the fluvial systems of this region the sinuosity index width depth ratio of river valleys longitudinal profile s l index and hypsometric index of the rivers flowing from north to south across the gfz lineament suggest that the northern side of gfz was tectonically uplifted luminescence dating of sediments from river terraces and calculation of knickpoint migration rates in the rivers indicate occurrence of multiple neotectonic events in gfz at ca 65 80 ka ca 50 ka ca 30 40 ka and ca 14 ka evidences of neotectonic activity presence of active geothermal springs and occurrence of recent earthquakes along gfz suggest that this lineament is tectonically active and there is a need for proper seismic monitoring of this fault zone

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

tectonic evolution of kashmir basin in northwest himalayas abstract geomorphology has long been recognised as a key to evaluate the interplay between tectonics and landscape geometry in the regions of active deformation we use geomorphic signatures at varied spatial scales interpreted from srtm dem landsat etm data supplemented with field observations to review the tectonic evolution of kashmir basin in northwest himalayas geomorphic evidence is persuasive of a credible nnw sse trending dextral strike slip structure central kashmir fault ckf with the strike length of 165 km stretched centrally over the nnw sse length of the kashmir basin as a result of the strike slip motion and subsequent erosion significant deformation has taken place along the ckf in addition broad geomorphic architecture of the basin reveals typical pull apart characteristics hence we deduce that the kashmir basin has evolved as a pull apart quaternary sediment depression owing to the deformation along the central kashmir fault the spatial distribution pattern of seismic events neic catalogue 1973 2013 and gps measurements published collectively substantiate our geomorphic interpretations

fluvial dynamics of an anabranching river system in himalayan foreland basin baghmati river north bihar plains india abstract anabranching river systems are now regarded as a separate class in river classifications owing to their distinctive morphological hydrological characteristics and fluvial processes a better understanding of anabranching rivers still needs detailed data from different environmental and geographical settings this paper presents a detailed account of an anabranching river system from the himalayan foreland basin the baghmati river system from north bihar plains eastern india provides a typical example of an anabranching river system located in the interfan area between the kosi and the gandak megafans the river system is braided in upstream reaches and meandering in downstream reaches but the midstream anabranching reach is characterized by low width depth ratio 11 16 gentle gradient 0 00018 0 00015 variable peak discharge frequent flooding and high sediment load the anabranching in the midstream reaches is a response to its inability to transport high sediment load due to gentle channel slope and dominance of aggradation process the development of anabranches is related to rapid and frequent avulsions of the river channels with eight major avulsions observed in the 30 km wide floodplain in the last 230 years the decadal scale avulsion history of the baghmati river system makes it hyperavulsive and the major causative factors for such channel instability are sedimentological readjustments and active tectonics in the basin area

eolian permian deposits in west and northwest argentina abstract the sedimentary and stratigraphic characteristics of eolian permian deposits exposed in mendoza la rioja and san juan provinces west and northwest argentina are described in this paper the eolianites are fine and medium sandstones with large scale cross bedding multiple parallel truncation planes and some asymmetrical ripples three genetic types of deposits have been identified dune facies eolian sand sheet facies and mixed fluvial eolian facies fine and medium sandstones with large scale cross bedding and multiple parallel truncation planes are here interpreted as dune deposits mainly crescentic dunes and unstratified or flat bedded sandstones as eolian sand sheet deposits mixed fluvial and eolian sequences composed of sandstones mudstones and some matrix supported conglomerates represent a transitional facies between those formed in eolian and fluvial environments this considerable deposition of eolian sediments was probably brought about by the existence of an extensive medium to low latitude continent and the withdrawal of marine environments the environments with highest aridity occurred towards the south and west of the region the eolian circulation pattern was controlled by a long ensialic volcanic arc emerging towards the west of the basin

spatial and temporal evolution of an avulsion on the taquari river distributive fluvial system from satellite image analysis avulsion processes have been observed and analyzed using field based studies however they have rarely been analyzed through use of satellite imagery even though such an approach allows documentation of spatial and temporal variations of the resulting deposits in order to document changes that are occurring at the caronal avulsion on the taquari river brazil a time series of landsat imagery from 1985 to present 2010 was compiled as of july 2010 the imagery shows that the avulsion is not yet complete with discharge being routed to both the parent channel and the avulsion channel in the floodbasin the avulsion was initiated as flow was diverted from the parent channel to the floodbasin through two small crevasses allowing the development and evolution of splays with a single splay stabilizing only since 1999 the avulsion area is marked by the growth of new splays the formation of an avulsion belt and progradation of avulsion deposits into the floodbasin the parent channel downstream of the avulsion site has experienced decreasing width through time associated with the higher volumes of water and sediment being captured by the avulsion channel because this avulsion is not yet complete we expect more morphological changes to occur as the avulsion belt evolves into the primary channel rapid sedimentation caused by this avulsion and the 24 year time series of imagery that captured this change allowed us to construct a 3d block representing the evolution of depositional environments associated with avulsion using time in the vertical dimension thus we could represent the evolution of geomorphological patterns including floodbasin proximal levee distal levee and channel deposits and project their distributions through time this block of evolving sedimentary settings can be used as a guide for future sedimentologic studies by offering visual clues regarding the way which depositional systems track avulsion initiated changes

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

seasonal cycle variations on the supercontinent of pangaea the seasonal cycle of temperatures on pangaea early late permian configuration is simulated with a two dimensional energy balance climate model results indicate that the annual range of temperatures in the southern hemisphere of pangaea was considerably larger than any occurring at present maximum mean monthly summer temperatures are 38 c daytime highs probably exceed 45 c in some regions however summer temperatures in polar regions are considerably lower 0 5 c and are favorable for persistence of ice in eastern australia and glaciation in siberia conditions that receive some support from geologic data these simulations suggest that very high summer temperatures and a large annual range are major features of supercontinent environments such conditions may have significantly influenced the distribution of terrestrial permian biota our results are difficult to reconcile with postulated equable climates for some supercontinent configurations

geomorphic evidence of unrecognized balapur fault segment in the southwest kashmir basin of northwest himalayas abstract the balapur fault bf is a high angle thrust fault reverse dipping 60 ne with an established length of 40 km striking nw se of the kashmir basin however geomorphic traces suggest that the strike of the bf propagates beyond what has been documented previously the present investigation aims to identify the unrecognized segment of the bf in the sw of the kashmir basin using hypsometric variability in longitudinal profiles knickpoints zones followed by validation through stream gradient index sl calculations of the rivers draining the area the longitudinal profiles of all the streams indicate prominent and consistent anomalies in the upper and mid reaches even on the coarse resolution data survey of india topographic maps 1 50 000 40 m dem srtm 90 m the profile anomalies in the upper reaches hard rock zone of the streams may be attributed to lithological contacts i e panjal trap agglomeratic slate shale limestone however the river profile convex segments and course deflection specifically in the mid reaches soft rock zone are most likely associated with recent tectonic activity geomorphic signatures suggest that these anomalies coincide with the strike of the recognized segment of the bf moreover the sl values of each stream express a clear agreement with the anomalies shown by the long profiles of the rivers hence we infer that the strike of the bf extends for a significant distance 95 km over the northeastern flank of the pir panjal range in the nw se direction

historical geomorphology and pedology of the gandak megafan middle gangetic plains india the gandak megafan of eastern uttar pradesh and northwestern bihar lies in the middle gangetic plains the gandak river has shifted about 80 km to the east due to tilting in the last 5000 years this has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces this chronoassociation has five members qgd1 5 they are distinguished on the basis of profile development clay mineralogy and calcium carbonate content chlorite transforms to vermiculite on a large scale from qgd1 to qgd3 and decreases drastically in member qgd4 kaolinite and interstratified kaolinite smectite are abundant in the older members of the chronoassociation the youngest soils qgd1 500 b p while qgd3 soils like those on the older gandak plain and old rapti plains date back to 2500 b p qgd4 soils like those on the oldest gandak plain are dated as 5000 years b p whilst the oldest qgd5 soils as on the old ghaghra plain and ganga ghaghra interfluve date back to 10000 b p these soils which include pedogenic calcite and a saline epipedon indicate a dry climatic spell during the period 9000 11000 b p faults developed on the megafan are not related to the basement structures

soft sediment deformation associated with the east patna fault south of the ganga river northern india influence of the himalayan tectonics on the southern ganga plain abstract the geomorphic tectonic and seismic aspects of the ganga plain have been studied by several workers in the recent decades however the northern part of this tectonically active plain has been the prime focus in most of the studies the region to the south of the ganga river requires necessary attention especially regarding the seismic activities the region lying immediately south of the outer himalayas i e the ganga plain responds to the stress regime of the himalayan frontal thrust zone by movement along the existing basement faults extending from the indian peninsula and creating new surface faults within the sediment cover as well as a result several earthquakes have been recorded along these basement faults such as the great earthquakes of 1934 and 1988 associated with the east patna fault large zones of ground failure and liquefaction in north bihar close to the himalayan front have been recorded associated with these earthquakes the present study reports the soft sediment deformation structures from the south bihar associated with the prehistoric earthquakes near the east patna fault for the first time the seismites have been observed in the riverine sand bed of the dardha river close to the east patna fault several types of liquefaction induced deformation structures such as pillar and pocket structure thixotropic wedge liquefaction cusps and other water escape structures have been identified the location of the observed seismites within the deformed zone of the east patna fault clearly indicates their formation due to activities along this fault however the distance of the liquefaction site from the recorded epicenters suggests its dissociation with the recorded earthquakes so far and hence possibly relates to any prehistoric seismic event the occurrence of the earthquakes of a magnitude capable of forming liquefaction structure in the southern ganga plain indicates the transfer of stress regime far from the himalayan front into the peninsular region through these basement faults northward extension of the east patna fault coincides with the region of the himalayan front which corresponds to a less slip potential therefore an association of frequent earthquakes in this region indicates strain release along the east patna fault

luminescence dating of late quaternary fluvial sediments in the rapti basin north central gangetic plains there is evidence in parts of the southern gangetic plain of river incision and terrace formation although the elevation ranges across the plains are small relative to the seasonal variation of stage in the main rivers in the northern parts of the plain there is interaction between the longitudinal rivers and lateral influx of water and sediment in rivers crossing fans such as the gandhak and the kosi and the inter fan areas are locations where aggradation and avulsion are dominant thus the fluvial history of the ganges and its tributaries and the relationship of that history to environmental changes including climate change tectonic history and variation in relative sea level is likely to be very complex unravelling the history will require systematic dating of fluvial sediments with luminescence methods tl and osl being of significance given the absence of datable organics and the ambiguities associated with dating carbonates shells kankar this preliminary exercise involves applying these methods to test hypotheses about the ages of fluvial surfaces in the case of the lower rapti river tl dates are likely to be unreliable given the water turbidity and lack of zeroing but osl dates on both modern and recent sediments provide useful information on the ages of fluvial sediments in the region the evidence is consistent with the view that the rapti has had a post glacial history of aggradation and avulsion with shifts in its position and changes in locations of deposition therefore not being directly related to allogenic environmental changes

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

active transverse features in the central portion of the himalaya abstract many transverse lineaments or faults across the himalaya are already known interpretation of satellite images of the central portion of the himalaya given here adds to that number and suggests their continuity from the himalaya to its foredeep several such faults appear to be seismically active their shear motion recognized from geologic data and focal mechanism solutions compares well with a classical stress model when applied to northward progress of india under the himalayan collision front

holocene tectono geomorphic evolution of parts of the upper and middle gangetic plains india abstract using multispectral scanning mss images and digital elevation models dems 26 terrain morphological units were delineated in the study area between the rapti and kosi rivers in the gangetic plains based on the degree of soil development and the infrared stimulated luminescence chronology these terrain morphological units have been grouped into six members of a morphostratigraphic sequence with ages 1 65 1 65 5 3 5 3 7 5 7 5 8 5 8 5 10 and 10 ka integrated use of geomorphic markers including different drainage patterns identified from mss images significant breaks in topographic profiles terminal fans and artifact terrain features e g cliffs and significant breaks in slopes in dems digital terrain models dtms with highly exaggerated vertical dimensions were made to infer and map 20 nascent faults in the region between the ghaghara and kosi rivers in the flat gangetic plains the three major tectonic blocks are the upland ghaghara rapti block of the upper gangetic plain and the rapti gandak and gandak kosi blocks of the middle gangetic plain marked by high rates of subsidence and sedimentation the ghaghara rapti block bounded by the incised ghaghara and rapti rivers is an upland region and is primarily overlain by 10 ka old soils subsequent activity along the ne sw trending transverse normal faults led to deposition of young terminal fans southward tilt of the ghaghara rapti block generated two e w trending terraces on the left bank of the ghaghara river southwestward tilting of the upper part of the ghaghara rapti block led to development of the widest old ghaghara plain and rapti floodplain in the sw direction northeastward tilting of the rapti gandak block shifted the gandak river from west to east over a distance of 80 km during the period from 10 to 8 5 ka further compression from the sw caused development of four extensional normal faults the activity of three faults between 5 7 and 1 0 ka generated four terminal alluvial fans on this block the gandak kosi block is marked by a set of seven thrust splays off the himalayan frontal thrust hft in the footwall activity of these thrust splays in the foothill region caused progradation of the gravel piedmont and thus developed the widest piedmont zone 124 km in the gangetic plains this is the first report of gravel piedmont progradation from a modern environment and role of thrust splays in such a progradation in the southernmost part of this block the continuous occurrence of terminal fans over a length of 140 km south of the south muzaffarpur fault forms a terminal fan piedmont bajada orientation of the faults was used to interpret compression from the sw in the ghaghara rapti interfluve plain in the west since 10 ka and compression from the south in the gandak kosi interfan region in the east after 4 5 ka the rapti gandak region in the central part shows the effects of mainly compression from the sw and compression from the south at different times in addition to terminal fans formed because of low relief terrain features created by the activity of faults by involvement of the entire discharge of small meandering braided streams a new type of fan formed by splays from a large river on the downthrown sides of faults called splay terminal fans is observed from the rapti gandak block

terminal fans and the ganga plain tectonism a study of neotectonism and segmentation episodes of the indo gangetic foreland basin india abstract the study of spatial and temporal distribution of holocene terminal inland fans in the indo gangetic foreland basin suggests that the segmentation of the basin was initiated at 9 3 ka and continued up to 0 75 ka in three distinct episodes the earliest episode 9 3 7 3 ka was exclusively confined in the upper gangetic plain this episode covers 29 of total time span and contributes 13 of total faults including their reactivations development of six faults associated with terminal fans having large age gaps indicate relatively slow rate of faulting activities in the early holocene the second faulting episode was started at 6 4 ka and continued up to 2 3 ka covering 60 time of the total time span and contributed 69 of total faults including their reactivations though in most of the time the faulting events were confined in the upper gangetic plain but development of few faults in the middle gangetic plain in the middle of this episode shows a transitional shift of tectonic front from the upper to the middle gangetic plain the third faulting episode 1 5 0 75 ka is mainly confined in the middle gangetic plain this episode covers 11 time of the total time span and contributes 18 of faults out of the eight faults seven of them are in the middle gangetic plains though these three episodes have contributed in segmentation of the gangetic plains but the second episode was responsible for major segmentation of the region two major tectonically stable periods 7 3 6 4 ka and 2 3 1 5 ka and three minor periods in duration of 0 5 ka have been observed in the region episodic development of faults in individual tectonic blocks indicates that the stress distribution along the plains is non uniform which can also be correlated to the adjacent corresponding segments of the himalayan tectonics it has been observed that in each fault bounded block the faulting events start slowly and later becomes more frequent previous work pointed out four tectonically active episodes between the ghaghara and kosi rivers with the oldest faulting event at 7 89 ka however the region west of it i e between the ghaghara and ghaggar rivers which includes rest of the upper gangetic plain shows that neotectonic activities are earlier than 7 89 ka the oldest faulting event observed by previous study the youngest faulting episode of the present study coincides with that of previous study and suggests that the region between the gandak and kosi rivers is tectonically most active at present the tectonically stable periods pointed out in the previous study between the ghaghara kosi region is occupied by the faulting events in the upper gangetic plains hence instead of four tectonically active episodes the whole ganga plain witnesses three segmentation episodes with two major intervening stable periods the change of orientation of the faults in the plain may be correlated to directional change of indian plate motion differential convergence and upliftment rates along the himalayan front and the spatial extension of subsurface precambrian basement ridges into the plains

development of the late paleozoic glaciations of the south american gondwana in western argentina abstract the late paleozoic ice age in the south american segment of gondwana consisted of several glaciations which can be grouped into two main glacial periods the oldest of them occurred in late early to early late carboniferous time and the younger in early permian time paleontological evidence in the western argentine precordillera supports a late visean age for the beginning and a probable early westphalian age for the end of the carboniferous glacial period in this span of time subsidence and deposition of glacial debris took place in the western mobile belt and in patagonia but no sediments of that age were deposited in the eastern portion of the south american gondwana where subsidence started later a carboniferous glacial sequence is remarkably well preserved in the san eduardo group on the western flank of the precordillera where at least three distinct glaciations are recognized this sequence can be taken as a reference section for the carboniferous glacial deposits shorter than the former and probably restricted to the asselian epoch the permian glacial period is better known the evidence for it is well developed in eastern south american gondwana although a relic is also present in the precordillera the recognition of two glacial periods within the late paleozoic ice age is supported by the existence of a long lasting interglacial which seemingly began in the late westphalian and lasted until the end of the carboniferous period this major interglacial period is inferred from the total absence of glacial features in the upper carboniferous sequences in spite of the existence of a mountainous belt parallel to the pacific during the carboniferous period the presence of marine beds and glacial drift well to the east of these ranges suggests that it was not altitude that was the main factor in determining the formation of glaciers but latitude plus a global change in temperature it is argued that the ice sheets extended greatly during the carboniferous glaciations and reached neighboring areas of the paganzo basin in central argentina

active tectonics and geomorphology in the sone ganga alluvial tract in mid ganga basin india active tectonics plays a major role in landscape evolution by bringing changes in topography and channel slopes the alluvial plains in ganga basin are divided into a number of tectonic blocks by several active subsurface faults the associated disturbances along these faults have given rise to a distinctive fluvial regime and geomorphology in the region in sone ganga alluvial plain in parts of south ganga plains in middle ganga basin the sone and ganga rivers have responded to the ongoing tectonic deformation in the area the study reports a classical example of tilt induced avulsion and channel migration during holocene from the parts of south ganga plains within the extensional half graben between east patna fault epf and west patna fault wpf the rate of lateral tilt appears to control the style of channel movement with gradual migration occurring at low tilt rates and avulsion at higher rates the river sone lying laterally close to the line of uplift has undergone avulsions at different times of tilting whereas the ganga river located at the lower parts of the tilting block away from the line of uplift has migrated in the down tilt direction various fluvial anomalies such as gradient reversals in the longitudinal profile of channels sinuosity variations channel incision frequency in the braid bar distribution and variation in the cross sectional parameters of the channels most probably created by tectonics have been studied satellite images and maps coupled with relative bank height measurements and other geomorphologic studies in field have helped in identifying such fluvial signatures and their relevance to tectonics the subsurface faults in the sone ganga plains cut across and also run parallel the river channels showing the effects of transverse and lateral tilting manifested in channel avulsions and migrations

active tectonics landscape evolution and sediment dynamics in dehra dun northwest himalaya inferred from geomorphic indices and gis tools abstract geomorphic evolution of the frontal parts of active mountain belts is strongly influenced by tectonic processes usually manifested in fluvial structural and morphotectonic parameters of the landscape geomorphic indices have long been used for understanding the tectonic imprints in river basins however their applicability and validation from field observations in the himalayan basins have often been debated here we test the applicability of several geomorphic indices in the western dehra dun intermontane valley that includes well known tectonic elements such as main boundary thrust mbt main frontal thrust mft santaurgarh thrust st and other smaller faults based on the spatial distribution of the values of different geomorphic indices we map four different tectonic zones to represent the relative tectonic activity from low to very high we conclude from morphometric analysis that the mbt and the st are active faults however we do not find any geomorphic evidence of recent activity along several other faults mapped in this region or any deformation in the major fan units we argue that active tectonics has not played a significant role in shaping the landforms in this region except for providing accommodation space and sediment supply for the deposition of fan units we have further employed dem and limited borehole data to understand the sediment storage and excavation at late late quaternary time scale we compute the average stored volume of sediments since 50 ka as 8 03 1010 m3 using borehole data and 12 24 1010 m3 gis approach total eroded volume has been computed as 0 47 1010 m3 using borehole data and 0 64 1010 m3 gis approach these volumes give a time averaged sediment discharge leaving the dun as 0 21 0 39 106 m3 yr over late quaternary period we note that the estimated average eroded material during the incision phase is only 5 6 of the total accumulated sediment volume further the average estimated volume 8 03 12 24 1010 m3 in the valley is nearly half of the volume of the sediment that can be accommodated 27 2 1010 m3 in the valley also the present day sediment supply to the dun 0 14 106 m3 yr is low in comparison to estimated average erosion rate our results therefore suggest that the valley is only half filled and is in excavation phase since late quaternary mostly driven by climatic perturbations

fluvial archives a valuable record of vertical crustal deformation abstract the study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms but also for identifying the nature of crustal deformation and its history in recent decades geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens here we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions the effects of horizontal deformation are not addressed channel long profiles have received considerable attention in the literature and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady state characteristics then we review the literature dealing with the transient response of rivers to tectonic perturbation through the production of knickpoints propagating through the drainage network inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories finally we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes as well as the erosional imprint of tectonic forcing sedimentary deposits such as fluvial terrace staircases are also considered as a classical component of tectonic geomorphology we show that these studies have recently benefited from rapid advances in dating techniques allowing more reliable reconstruction of incision histories and estimation of incision rates the combination of progress in the understanding of transient river profiles and larger more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation i e extrapolation of local data to entire profiles finally planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the dis equilibrium state of drainage systems across regional drainage divides

oxygen and hydrogen isotope compositions of permian pedogenic phyllosilicates development of modern surface domain arrays and implications for paleotemperature reconstructions abstract mineralogic chemical and oxygen and hydrogen isotope compositions of 15 different phyllosilicate samples from permo pennsylvanian age paleosols of the eastern shelf of the midland basin of texas and the southern anadarko basin are presented mixtures of 2 1 phyllosilicates and kaolinite dominate most samples although some samples consist of relatively pure 2 1 phyllosilicates chemical and mineralogic data are used in conjunction with published thermodynamic data to calculate hydrogen and oxygen isotope fractionation factors for each sample in turn application of measured oxygen and hydrogen isotope compositions of the phyllosilicates to temperature dependent fractionation equations are used to calculate paleotemperatures of crystallization the d values of the phyllosilicates range from 69 to 55 the 18 o values range from 19 5 to 22 7 if these samples preserve a record of equilibrium with paleo meteoric waters the isotopic compositions of the phyllosilicates correspond to paleotemperatures of phyllosilicate crystallization ranging from 22 3 c to 35 3 c in particular the stratigraphic trend of calculated temperatures from midland basin samples suggests that early permian surface temperatures may have been up to 10 c warmer than those of the latest pennsylvanian

high precision u pb zircon age calibration of the global carboniferous time scale and milankovitch band cyclicity in the donets basin eastern ukraine 1 high precision id tims u pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic cyclostratigraphic and biostratigraphic framework of the carboniferous donets basin of eastern europe chemical abrasion of zircons use of the internationally calibrated earthtime mixed u pb isotope dilution tracer and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of 0 05 or 100 ka for these carboniferous volcanics this precision allows the resolution of time in the milankovitch band and confirms the long standing hypothesis that individual high frequency pennsylvanian cyclothems and bundles of cyclothems into fourth order sequences are the eustatic response to orbital eccentricity 100 and 400 ka forcing tuning of the fourth order sequences in the donets basin to the long period eccentricity cycle results in a continuous age model for the middle to late pennsylvanian moscovian kasimovian ghzelian strata of the basin and their record of biological and climatic changes through the latter portion of the late paleozoic ice age detailed fusulinid and conodont zonations allow the export of this age model to sections throughout euramerica additional ages for mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations

new insights into the effect of the quaternary fault activity on river knickpoints in the central alborz iran abstract this study examines the knickpoints in a region to provide new insights for assessing the tectonically formed knickpoints tfks in this paper we have used a quantitative method to recognize tfks using two different river steepness methods the stream gradient gd and the normalized steepness index ksn analysis of the extracted tfks with the longitudinal profile logarithm slope area plots and natural logarithm gradient distance plots suggests that these knickpoints correlate with the active segments of faults in addition evaluation of the tfks indicates that the different length and height of the tfks can be related to the different features of each fault the investigation of tfks was implemented in the central alborz located at the southern margin of the caspian basin in northern iran which is a part of an active deformation region of the arabian and eurasian plate collision zone the investigation of tfks suggests that the quaternary faults activities are related to the recent tectonic activity in the northern flank of the central alborz as well as the central part of the central alborz which is consistent with global positioning system gps studies and increased uplift rate the results are in agreement with field observations in terms of geomorphic features and geology

tectonic constraints on watershed development on frontal ridges mohand ridge nw himalaya india abstract uplifting frontal ridges are one of the most conspicuous geomorphic features that mark the frontal parts of actively converging mountain belts growth of these ridges can lead to the simultaneous development of a drainage system that is defined by watersheds stream network and long profiles of channels in the present study shape parameters of watersheds stream network characteristics and pattern of network growth shape of long profiles and the sl index have been investigated in a part of nw himalaya to understand the relationship between endogenic tectonic processes and exogenic fluvial processes this explains the tectonic control on drainage systems in the uplifting frontal ridge this watershed analysis was carried out using a digital elevation model dem and a number of anomalies have been identified and analysed the most striking is the asymmetric development of watersheds on either side of an almost straight ridge crest watershed asymmetry along the ridge crest is characterized by larger area and less elongated watersheds in the southern flank forelimb in comparison to the northern flank backlimb drainage network and long profile analysis establishes that the larger watershed area in the forelimb is due to dominance of headward erosion and its impact on drainage network growth dominance of headward erosion is due to slope variation in response to forelimb development along a fault related fold even through headward erosion has shifted the ridge crest it is parallel with the trace of the himalayan frontal thrust hft the parallel ridge crest with reference to the hft is indicative of the tectonic control of the hft on the development of the watersheds hence a well developed linkage between tectonic processes fold development and surface processes headward erosion is responsible for variation in watershed and drainage network pattern across the ridge crest the study also investigates the role of planform ridge curvature on watershed development the effect is more pronounced on an asymmetric ridge such as the mohand ridge than on a symmetric ridge

tectono geomorphic indices of the erin basin ne kashmir valley india abstract the present study aims to assess the tectonic activity in the erin basin ne kashmir on the basis of several relevant geomorphic indices and field observations we use digital elevation model srtm and survey of india soi topographic maps in gis environment to compute the geomorphic indices the indices i e convex hypsometric curve high hypsometric integral value h i 0 5 low basin elongation ratio eb 0 17 low mountain front sinuosity values s mf 1 08 average low valley floor width ratios vf 4 suggest that the area is tectonically active moreover prominent irregularities knickpoints knickzones along longitudinal profile of the erin river even in homogenous resistant lithology panjal trap and anomalous stream gradient index sl values reflect that the erin basin is dissected by two faults ef 1 and ef 2 with nnw sse and ssw nne trends respectively the results of this preliminary study further substantiate the recent gps studies which argue that the maximum strain is accumulating in the ne part of the kashmir himalaya

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

more major earthquakes at the nepal himalaya study on coulomb stress perspective abstract on april 2015 a major earthquake of 7 9 mw occurred in the nepal himalaya followed by 553 earthquakes of local magnitude greater than 4 0 within the first 43 days including another major event of 7 3 mw we resolve the static coulomb failure stress cfs change onto the finite fault models of 7 9 mw after elliott et al 2016 and galezka et al 2015 and its effect on associated receiver faults correlation of aftershocks with the enhanced cfs condition shows that the elliott et al 2016 model explains 60 4 and the galezka et al 2015 model explains about 47 7 of the aftershocks in high stress regions aftershocks were poorly spatially correlated with the enhanced cfs condition after the 7 9 mw main shock and can be explained by correlation with release of seismic energy from the associated secondarily stressed prominent thrust planes and transverse faults stress resolved on the associated receiver faults show increased stress on both transverse and thrust fault systems with the potential of triggering significant aftershocks or subsequent main shocks

palaeo climate controlled diagenesis of the westphalian c d fluvial sandstones in the campine basin north east belgium the westphalian c and d fluvial sandstones in the campine basin north east belgium are potential reservoirs for the sequestration of co2 and interesting analogues of the hydrocarbon reservoirs in the southern north sea although these sandstones were deposited in a relatively short period of time their reservoir properties and mineralogical compositions are very different a petrographic study complemented with stable isotope analyses fluid inclusion microthermometry and x ray diffraction analyses of the clay fractions of the sandstones which were sampled from deep boreholes 1000 m in the campine basin revealed that these differences are related mainly to the climate at the time of deposition the most important eogenetic processes affecting the westphalian sandstones were the generation of a pseudomatrix by physical compaction of al silicates and lithic fragments that were strongly altered by extensive meteoric leaching kaolinitization of unstable silicates and precipitation of siderite these processes had a detrimental influence on the reservoir properties of westphalian c sandstones but their impact on the westphalian d sandstones was minimal the difference is assumed to be related to the climate at the time of deposition which changed from tropical humid in the westphalian c to semi arid arid during the late westphalian d both the westphalian c and d sandstones were affected by similar mesogenetic processes mesogenetic quartz cementation resulted from chemical compaction and illitization of kaolinite k feldspar and smectitic clays illitization of kaolinite was controlled by the available quantities of co existing kaolinite and k feldspar and mainly affected the westphalian d sandstones illitization of k feldspar was controlled by the k feldspar content it had a much larger impact on the reservoir properties of the westphalian d as in these sandstones k feldspar was less affected by eogenetic alteration the illitization of smectitic clays resulted in illite quartz and ankerite cementation in both reservoirs this process had a more important impact on the westphalian c reservoir since cementation here also resulted from smectite to illite conversion in the interbedded and underlying shales the effect of mesogenetic alterations on the reservoir properties was much less drastic than the impact of eodiagenesis mesogenetic alterations do exert a significant control on the properties of the westphalian d the vast impact of eodiagenesis on the westphalian c sandstones made them less susceptible to mesogenetic alteration the effect of telogenetic processes on the porosity and permeability of the westphalian sandstones was small and restricted to the top reservoir intervals that directly underlie the cimmerian unconformity no significant telogenetic alterations related to the variscan unconformity were observed

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

tectonic versus climate influence on landscape evolution a case study from the upper spiti valley nw himalaya abstract we have undertaken structural geomorphological and morphometric analyses to investigate the role of tectonism and climate in the landscape evolution in the upper spiti valley nw himalayas geomorphometric analyses coupled with field investigations reveal active tectonic deformation in the spiti region the calculated geomorphic indices steepness concavity and hack demonstrate uplift subsidence along the kaurik chango fault whereas transverse topographic index t index reveals basin tilting associated with active faulting near hansa and lingti valley investigation of well dated mane palaeolake sediments also provides evidence of regional tectonic instability four episodes ca 7 8 7 4 6 5 and 6 1 cal ka of neotectonic activity have been identified during the period of the lake s existence we have also compiled data on the regional climate variability and compared it with the age of the mane palaeo landslide our results indicate that the landslide occurred towards the end of the early holocene intensified monsoon phase and is located near an active fault our data on regional tectonic instability and the coincidences of modern and palaeo landslides with zones of active deformation suggest that tectonism is an important factor governing landscape stability in the spiti region

alluvial river response to neotectonic deformation in louisiana and mississippi repeat geodetic surveys show uplift of the monroe and wiggins anticlines in louisiana and mississippi there are deformed quaternary terraces which indicate long term deformation in the valleys of the alluvial rivers that cross these structures and there are floodplain and channel convexities that provide evidence of modern deformation in addition the channels show significant variations of morphology sinuosity gradient and depth and behavior appropriate to reaches of increased and decreased valley slope these alluvial rivers are adjusting to modern deformation and their adjustment confirms two geodetic leveling anomalies

extreme freshwater release during the late paleozoic gondwana deglaciation and its impact on coastal ecosystems abstractstrata in the paganzo tarija and parana basins of argentina and brazil provideevidence for reconstructing the effects of late paleozoic glacial retreat the depositionalenvironment of the transgressive and early highstand ne grained deposits has been con troversial with interpretations ranging from normal marine shelves to estuaries to lakes whereas their counterparts from shallow marine settings not in uenced by glaciation hostdiverse fully marine ichnofaunas these ne grained postglacial deposits are dominatedby nonspecialized grazing trails simple feeding traces arthropod trackways and shtrails they are typical of freshwater environments and represent examples of the mermia and scoyenia ichnofacies however the local presence of acritarchs indicates sporadicmarine in uence these observations suggest a new interpretation that freshwater con ditions in fjordlike settings across south america were widespread because gondwananbasins were overwhelmed by strong meltwater discharge issuing from melting of the con tinental ice masses keywords

palaeoenvironmental framework of the glacial postglacial transition late paleozoic in the paganzo calingasta basin southern south america and the great karoo kalahari basin southern africa ichnological implications sedimentological palaeontological and geological data from the glacial to postglacial transition in the late paleozoic successions of the paganzo calingasta basin pc in southern south america and the great karoo kalahari basin gkk in southern africa are analysed revised and reinterpreted a brackish depositional setting is inferred for main areas previously considered to be nonmarine based upon ichnological interpretations three stratigraphic intervals have been defined based on changes in sedimentary facies and trace fossils association the glacial interval gi early postglacial interval epi and late postglacial interval lpi the gi and epi contain a dominance of arthropod trackways fish trails with and subordinate grazing and feeding traces the epi in the pc basin comprises both nonmarine and brackish marine ichnocoenoses without significant differences in ichnological composition trace fossils are preserved in underflow and turbidite beds of deltaic deposits opportunistic grazing traces constitute a post event ichnocoenosis while a pre event ichnocoenosis is preserved at the base of turbidite beds in the gkk basin ichnofossils were documented in turbidite fans the lpi in the gkk basin contains the first evidence of shallow water deltaic infauna and subordinate grazing traces conversely in the pc basin the infauna is lacking the gi and particularly the epi ichnofauna resemble the nonmarine mermia ichnofacies but they occur in large and long lived stable marine basins which received enormous inputs of melt water that markedly reduced the salinity they are not ichnologically comparable with brackish marginal marine environments that are affected by frequent sometimes diurnal fluctuations in physical parameters such as salinity and temperature the lpi in the gkk basin constitutes a typical record of the classical marginal marine ichnofaunas but in the pc basin the ichnofacies assignment is problematic grazing traces of the mermia ichnofacies appear in middle estuarine deposits where both palynomorphs and the presence of tidal features suggest brackishness the paganzo basin ichnology therefore shows some difficulties in differentiating nonmarine from subtle brackish environments without the full integration of sedimentological information ichnocoenoses dominated by trackways of arthropods are particularly inappropriate to distinguish between these types of depositional settings

remote sensing revealed drainage anomalies and related tectonics of south india abstract drainages have characteristic pattern and life histories with youthful stage in hilly areas mature stage in plains and old stage in the coastal zones the deviations from their normal life histories especially aberrations in their flow pattern in the form of various drainage anomalies have been inferred to be the indications of dominantly the eustatic and isostatic changes this especially after the advent of earth observing satellites has attracted the geoscientists from all over the world for studying such drainage anomalies in this connection a study has been undertaken in parts of south india falling south of 14 south latitude to comprehensively map some drainage anomalies like deflected drainages eyed drainages and compressed meanders and to evolve the tectonic scenario therefrom the mapping of such mega drainage anomalies and the related lineaments faults from the satellite digital data and the integration of such lineaments faults with the overall lineament map of south india showed that the study area is marked by active n s block faults and ne sw sinistral and nw se dextral strike slip faults such an architecture of active tectonic grains indicates that the northerly directed compressive force which has originally drifted the indian plate towards northerly is still active and deforming the indian plate

channel morphology hydrology and geomorphic positioning of a middle miocene river system of the siwalik foreland basin india systematic lithofacies palaeocurrent palaeomorphological and palaeohydrological analyses have provided detailed information about a hitherto unstudied river system of the siwalik foreland basin of the himalaya three distinct lithofacies associations each representing a specific depositional setting have been identified and named as facies association a facies association b and facies association c the facies association a comprises pebbly sandstone cross bedded sandstone ripple laminated sandy siltstone and bioturbated mudstone lithofacies and represents deposits of a braided channel the facies association b comprises cross bedded sandstone bioturbated mudstone fine sandstone mudstone alternation and lensoid to prismatic sandstone lithofacies and represents deposits of a channel natural levee crevasse splay and flood plain of a meandering stream the facies association c comprises mottled siltstone mudstone heterolith and fine sandstone lithofacies and represents deposits of the upland interfluve region the braided stream had a maximum depth of 4 15 m maximum width of 305 m and maximum discharge of 7045 cumec whereas the meandering stream had a sinuosity of 1 26 maximum depth of 3 71 m maximum width of 180 m and maximum discharge of 4070 cumec the area had a regional radial outward flow pattern but dominantly towards the ssw however the braided river had a bimodal flow pattern due to an active basement high induced bend along its course a comparison of the sediment characters and morphological and hydrological parameters of these streams with those of the modern rivers of the ganga gangetic basin has enabled us to infer that this river system was located in the medial distal megafan interfan setting of the basin

facies and architecture of a carboniferous grounding line system from the guandacol formation paganzo basin northwestern argentina abstract new outcrops of middle carboniferous glacigenic deposits found in the guandacol formation western paganzo basin are described in this paper the study locality of los pozuelos creek northwestern argentina includes coarse grained diamictites rhythmites laminated pebbly mudstones and shales that represent an expanded column of the gondwanic glaciation in this region thirteen lithofacies recorded at the measured section have been grouped into three facies associations facies association i is composed of coarse grained massive and stratified diamictites lithofacies dmm dms dmg dcs laminated siltstones with dropstones fld and interstratified sandstones and mudstones fl sr these rocks represent both tillites and resedimented diamictites closely associated to small water bodies where laminated siltstones with dropstones and stratified sandstones and mudstones were deposited facies association ii comprises couplets of matrix supported thinly bedded diamictites dmld and laminated mudstones with dropstones fld this facies association results from the combination of three different processes subaqueous cohesionless debris flows coeval rainout of ice rafted debris and settling of fine grained particles from supension finally facies association iii is made up of laminated mudstones without dropstones thin marl levels and scarce fine to very fine grained sandstones this assemblage clearly suggests sedimentation in a deep marine environment below the wave base the architecture of the glacigenic deposits has been investigated using photomosaic panels the geometry of the depositional bodies and facies suggest that los pozuelos creek outcrops exhibit a well preserved three dimensional example of a grounding line system in particular three different subenvironments of a morainal bank were interpreted a bank front a bank core and a bank back the bank front assemblage is characterized by coarse grained mainly resedimented diamictites grading laterally to prograding clinoforms composed of interbedded matrix supported thinly bedded diamictite and mudstones the bank core assemblage is formed by a stacking of coarse grained diamictites where at least five major erosional surfaces bounding four multistory diamictite bodies can be recognized finally the bank back assemblage corresponds to discontinuous intervals of striated lodgement till and coarse grained resedimented diamictites showing important post depositional deformation the retrogradational stacking of the morainal banks indicate an overall glacial retreat and a glacioeustatic sea level rise erosional surfaces at the base of each morainal bank suggest intervening short term episodes of ice advance the new data presented here confirm the existence of true tillites in western paganzo basin and suggest several at least four pulses of glacial advance and retreat during the namurian glaciation in the region and permit a more refined interpretation of the glacial deposits in the huaco area

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

foreland sedimentation in himalayan tectonic regime a relook at the orogenic process by raiverman v 2002 bishen singh mahendra pal singh publishers 23 a connaught place p o box 137 dehradun 248 001 india 378 pp price us 125

magma chamber and eruptive processes at izu oshima volcano japan buoyancy control of magma migration underground magmatic processes are modeled for a sequence of eruptions that started on november 15 1986 at izu oshima volcano it is predicted from the seismic gap the seismic velocity structure the deformation center and the gravity minimum that there should be a magma chamber at a depth of about 4 km beneath the northwestern flank of the volcano the effusion of basalt that began at the summit crater established a well connected conduit system between the magma chamber and the summit crater the following eruption from new fissures a few days later produced more felsic and less homogeneous compositions basaltic andesite to andesite because of cooling and fractional crystallization of ascending magma subsequently four small eruptions were caused by gravitational sliding of sluggish semisolid magma into openings in and along the sides of the shallow conduit as magma was returning to the magma chamber systematic tilt changes due to transmission of pressure pulses from the summit crater to the magma chamber were observed during a small explosion on november 18 1987 and for many periods of episodic volcanic tremor the migration of magma is interpreted to have been driven by a buoyancy force associated with bubbles in the magma in this regard dominant ascent of magma beneath the summit crater and new fissures in november 1986 was triggered by vesiculation of volatiles in the magma and the subsequent return flow of magma resulted from the release of bubbles through degassing the observed response of volcanic processes following earthquake swarms northwest of the island is also explained by buoyancy controlled magma migration that could intensify the effect of small fluctuations in the crustal stress

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

channel slope reversal near the martian dichotomy boundary testing tectonic hypotheses abstract faults along the martian dichotomy boundary are evidence of tectonic activity which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles in the eastern hemisphere between 30 e and 150 e this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure for which loading e g by material deposition of the northern lowlands is a possible cause watters 2003a nimmo 2005 the topographic slope changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them although other processes may complicate interpretations of reversed longitudinal profiles two fan shaped networks of inverted channels are located near 150 e in the aeolis dorsa region just north of the dichotomy boundary their original flow directions inferred from planform morphology suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest this contrast indicates slope reversal we investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses 1 lower crustal flow 2 flexure caused by material erosion from the highlands and deposition in the lowlands and 3 flexure caused by highland erosion and deposition in the lowlands plus deposition of the medusae fossae formation in the lowlands we test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes taking the possibility of non tectonic i e collapse processes into account our results suggest that among these three models the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the medusae fossae formation contrary to previous findings our results do not support the mechanism of lateral crustal flow although they do not rule it out because lower crustal flow and erosion may both have been operating but on different time scales the result of this hypothesis testing provides insight into the evolution of the dichotomy boundary and martian crust in this location

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

response of active tectonics on the alluvial baghmati river himalayan foreland basin eastern india active tectonics in a basin plays an important role in controlling a fluvial system through the change in channel slope the baghmati an anabranching foothills fed river system draining the plains of north bihar in eastern india has responded to ongoing tectonic deformation in the basin the relatively flat alluvial plains are traversed by several active subsurface faults which divide the area in four tectonic blocks each tectonic block is characterized by association of fluvial anomalies viz compressed meanders knick point in longitudinal profiles channel incision anomalous sinuosity variations sudden change in river flow direction river flow against the local gradient and distribution of overbank flooding lakes and waterlogged area such fluvial anomalies have been identified on the repetitive satellite images and maps and interpreted through dem and field observations to understand the nature of vertical movements in the area the sub surface faults in the baghmati plains cut across the river channel and also run parallel which have allowed us to observe the effects of longitudinal and lateral tilting manifested in avulsions and morphological changes

spatial and temporal distribution of inland fans terminal fans between the ghaghara and kosi rivers indicate eastward shift of neotectonic activities along the himalayan front a study from parts of the upper and middle gangetic plains india abstract neotectonic deformation in the indo gangetic plains is primarily manifested by surface ruptures caused by both normal faults and thrust splays the topographic breaks along these faults provide suitable sites for the formation of inland fans terminal fans on the down thrown blocks as these depositional features invariably form along the faults contemporaneously or soon after faulting they have widely been used as potential geomorphic markers in mapping faults in the flat gangetic plains based on this association infrared stimulated luminescence irsl dating of the fans has successfully been used for dating the faulting episodes in the gangetic plains thus the spatial and temporal distribution of inland fans terminal fans suggests migration of faulting activities from west to east with time and successive faulting events occur over periods of several hundreds of years to 10 3 years in the present study the correlation of eighteen dated inland fans terminal fans aligned along the faults and using the surficial and buried soil profiles suggests four deformation episodes 7 89 7 30 ka 5 84 3 99 ka 3 18 2 73 ka and 1 41 0 75 ka in the region between the ghaghara and kosi rivers in the gangetic plains these deformation episodes were witnessed by the development and reactivation of the extensional normal faults transverse to the himalayan frontal thrust hft in the ghaghara rapti interfluve and the thrust splays parallel sub parallel to the hft in the gandak kosi interfan regions the rapti gandak region in the middle serves as a transition zone in between the interfluve and the interfan region and shows both types of fault development at different times six inland fans terminal fans in the ghaghara rapti interfluve were formed between 7 89 and 2 73 ka in three deformation faulting episodes two in each phase the broad age difference between those and strongly developed soils suggests the faulting activities to be less frequent in this region the fan building episodes in the gandak kosi interfan region started at 4 92 ka by the initiation of thrusting activities out of eight inland fans terminal fans five of them were formed during 1 41 0 75 ka in association with various thrust splays these depositional features are characterised by a narrow age gap and weak to no surface soils which indicate early burial by high sediment supply from frequent thrusting activities segments of the plains having a high low population of inland fans terminal fans of narrow broad age gaps and with relatively weakly strongly developed soils lie close to or opposite to the segments having the highest lowest rate of convergence and upliftment of the himalayas along the hft

global cooling inferred from dropstones in the cretaceous fact or wishful thinking traditionally the cretaceous has been considered as a long period of global warmth a greenhouse world this view has been challenged in recent years by several lines of evidence palaeobotany stable isotopes and palaeoclimatic modelling in particular however although these data demonstrate that cooling is likely the only first hand evidence which demonstrates the presence of substantial ice build up in cretaceous high palaeolatititudes are dropstones these outsized or exotic clasts set in a fine grained sediment are often interpreted as a direct result of ice rafting the reliability of this dropstone evidence and particularly its validity is questioned in demonstrating ice age interludes within the cretaceous greenhouse

morphotectonic and neotectonic control on river pattern in the sierra de la cantera piedmont central precordillera province of san juan argentina article i nfo the drainagepattern on the western piedmontof thesierra de lacantera isdivergent typical of alluvialfansand showing anomalies that are directly related to the trace of la cantera thrust in previous studies two types of anomalies were identified upstream of the fault scarp rivers have a broom shaped pattern while downstream in the hanging block streams become denser more sinuous and incised in this contribution these morphotectonic aspects were analyzed in detail making direct and indirect analysis to quantify the relationship between theseanomaliesandthe faults affectingalluvialfans inaddition theinfluenceofneotectonicactivityon smaller water course patterns in the alluvial fan areas was investigated in order to find indicators of on going vertical movements since the spatial arrangements of these piedmont channels are determined by slope and structure where active faults cause diversions or anomalies topographic profiles in two selected channels cutting across the trace of the fault were performed using a differential gps in order to establish the relationship between the sinuosity and slope of these rivers the results obtained allow us to state that the most sinuous channels have lower slopes and are located in the hanging wall of the fault morphometric analysis of scarps stated that active tectonics have played an essential role in controlling the drainage pattern in the piedmont leading the rivers to adjust to these slope variations finally based on the geomorphologic stratigraphic structural and seismological characteristics and parameters analyzed la cantera thrust is considered a seismogenic source of significance to the nearby towns n700 000 inhabitants and also to the large scale dams built downstream along the san juan river published by elsevier b v