neotectonics of western india evidence from deformed quaternary fluvial sequences mahi river gujarat a quaternary fluvial sequence along the mahi river gujarat western india shows evidence for a discrete episode of normal faulting and related surface slumping four mapped nw striking faults have throws ranging from 1 m to over 3 m and have related growth folds in synchronous sediment units a slump sheet moved tens of metres northeastward down the 0 7 dip slope of one tilt block during displacement on its bounding fault the exposed part of the internally folded sheet is probably one side of a lobate slump mass several hundred metres in width fault activity began after deposition of a lower gravel which regional correlations suggest is about 300 ka old faulting ended just before deposition of an upper gravel sand complex dated by luminescence techniques in correlated sections at no younger than about 60 ka the mahi river section shows that neotectonic activity in peninsular india exemplified by the 1993 killari latur earthquake has a mid to late pleistocene component

multicomponent magnetization in western dolpo tethyan himalaya nepal tectonic implications abstract a palaeomagnetic study has been carried out in the tethyan himalaya th the northern margin of greater india twenty six palaeomagnetic sites have been sampled in triassic low grade metasediments of western dolpo two remanent components have been identified a pyrrhotite component characterized by unblocking temperatures of 270 335 c yields an in situ mean direction of d 191 7 i 30 9 k 29 5 95 5 7 n 23 sites the component fails the fold test at the 99 confidence level kin situ kbed 6 9 and is therefore of postfolding origin for reason of the low metamorphic grade this pyrrhotite magnetization is believed to be of thermo chemical origin geochronological data and inclination matching indicate an acquisition age around 35 ma the second remanence component has higher unblocking temperatures 400 c and up to 500 580 c range and resides in magnetite a positive fold test and comparison with expected triassic palaeomagnetic directions suggest a primary origin the postfolding character of the pyrrhotite component and its interpreted age of remanence acquisition implies that the main himalayan folding is older than 35 ma in the western dolpo area this study also suggests that the second metamorphic event neo himalayan was more significant in the dolpo area than the first eo himalayan one a clockwise rotation of 10 15 is inferred from the pyrrhotite component which is compatible with oroclinal bending and or rotational underthrusting models this rotation is also supported by the magnetite component indicating that no rotation of the tethyan himalaya relative to india took place before 35 ma

channel form and processes of the flood dominated narmada river india the 1300 km long narmada river flows along a structural lineament alternating between constricting rocky gorges and rapids and meandering wide alluvial reaches channel forms and processes were studied in a 120 km long section of an alluvial reach channel size shape and bedforms in the narmada river are related to very large floods which have occurred three times in this century during such floods the entire 400 m wide channel is utilized and 10 15 m high cliffs on both sides operate as riverbanks normally even the high flows of the south westem monsoon are insufficient to fill the whole channel and hence their effects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars a channel in channel topography is thus created the very large floods are also responsible for erosion of the rocky stretches and building of point bars the river meanders but its movement is restricted because of 1 rocky gorges and scablands operating as anchor points at intervals and 2 the presence of high alluvial cliffs which are topped on extremely rare occasions in spite of being located in a tectonically active zone in a monsoon setting it is the exceptional high magnitude floods at irregular intervals which control the form and behaviour of the narmada river

turbulence at a roughness transition in a depth limited flow over a gravel bed turbulence statistics derived from velocity measurements along a longitudinal transect characterized by a roughness transition are presented the bed morphology along the transect is dominated by composite scales of roughness ranging from an armoured bed in the upstream section to the presence of large protuberant clasts superimposed on the bed in the downstream section an array of four electromagnetic current meters operating at a frequency of 20 hz was used to measure the longitudinal and vertical velocities at various heights above the bed surface and at different positions along the transect emphasis is put on the longitudinal and vertical distributions of turbulent flow statistics such as reynolds shear stress uv cross correlation and quadrant analysis of velocity fluctuations the results indicate that the presence of protuberant clasts modifies the turbulence structure increases turbulence intensity and appears to dominate turbulence generation distinct flow zones are observed in particular a clear distinction is made between i a sublayer below the top of the major roughness elements identified by fluid motions predominantly towards the bed surface and characterized by intense eddying with some vortices or rollers possibly being trapped in this near bed flow region and ii an inner layer located immediately above the major protuberant clasts identified by positive vertical velocities and hence upward directed fluid motion the dominant generative mechanism of flow structure appears to be the shedding of vortices from the lee of obstacles interaction of vortices stretched by shear into the main body of flow downstream from major obstacles dominates the turbulence structure in depth limited flows over coarse and irregular bed surfaces

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

unequal mobility of gravel and sand in weakly bimodal river sediments bed load was trapped during flood events over a 20 month period at the lower end of the allt dubhaig a small river in scotland with rapid downstream fining of gravel bed material on a slowly aggrading concave long profile the channel bed near the trap is predominantly gravel with a secondary sand mode total transport in each event depended mainly on peak shear stress rather than duration over a threshold bed load was mainly sand in smaller events bimodal in intermediate events and mainly gravel in the biggest floods mean and maximum grain diameter both increased with peak shear stress but in different ways analysis of fractional transport rates and maximum grain size in relation to peak shear stress suggests that gravel transport is slightly size selective but sand transport is close to equal mobility the slight selectivity in gravel transport is consistent with previous field studies of near equilibrium unimodal beds and supports assumptions made in the numerical model of hoey and ferguson 1994 which successfully simulates the observed amount of downstream fining over the 2 5 km upstream of the bed load trap

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

evolution of coarse gravel bed forms field measurements at flood stage field measurements to investigate the origin and growth of mesoscale gravel bed forms in deep flows were made in the north fork toutle river washington sonar observations of the gravel streambed at a stationary point were recorded during two storm flows in december 1989 and january 1990 with concurrent bed load sampling and continuous velocity measurements mean diameter of bed load was about 3 cm flow depths were 1 4 2 4 m and bed shear stresses were 2 5 times the critical stress of mean bed load diameter as computed from the depth slope product these records document the hydrodynamic conditions under which dunelike coarse gravel bed forms were observed coarse gravel dunes height 20 cm length 6 15 m evolved more than 24 hours after peak stage primarily by accretion as inferred from bed form changes revealed in dual sonar records dune heights increased to 40 cm as mean trough elevation rose about 50 cm over several hours smaller dunes wavelength 1 3 m transitional from bed load sheets migrated on the backs of the large dunes the superposed dunes finally became indistinguishable from the large dunes which diminished in height by increasing the mean level of troughs gravel deposition occurred at the observation point in conjunction with migration of gravel dunes the direct comparison of known bed form regimes and gravel bar facies provides alternative interpretations of gravelly deposits

calcretes in semi arid alluvial systems formative pathways and sinks late quaternary deposits in gujarat western india show an abundant development of calcretes three major sinks of carbonate in the alluvial deposits are recognized 1 groundwater calcretes 2 pedogenic calcretes and 3 calcrete conglomerates groundwater calcretes originate from carbonate saturated waters travelling preferentially along stratification planes pedogenic calcretes form through soil forming processes typically in extra channel areas calcrete conglomerates occur as ribbons sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes as a result a pathway of calcretization develops that has the route groundwater calcrete to pedogenic calcrete to calcrete conglomerate the formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that 1 apart from aeolian dust river waters are also a major source of carbonate and 2 pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre existing groundwater calcretes consequently the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

the character and genesis of calcrete in late quaternary alluvial deposits gujarat western india and its bearing on the interpretation of ancient climates late quaternary deposits in mainland gujarat contain sediments deposited in subhumid and semi arid climates the 30 35 m succession shows the presence of vertisols at the base and a red bed horizon ferric calcisol when pedogenic in origin that roughly bisects the succession a widespread development of calcretes is observed throughout the succession the various varieties of calcrete include pedogenic calcrete groundwater calcrete calcrete conglomerate transported calcrete and rhizogenic calcrete pedogenic calcrete nodules associated with vertisols and the red soil show marked differences in morphology dimensions and the distribution of microscopic features these differences arise due to contrasting climate controlled physicochemical environs under which they formed pedogenic calcrete nodules associated with vertisols acquire large 5 10 cm dimensions and are characterised by either showing the presence of a nucleus of soil matter or showing a dense micritic groundmass cut by thick sparitic veins in contrast calcrete nodules that formed in the red soil are 3 cm in size and do not exhibit dense networks of sparitic veins calcretes associated with vertisols and the ferric calcisol also exhibit differences in the morphology of rhizoliths these differences also show up in the distribution of microfabrics of calcretes grain coats are present in rhizogenic and pedogenic calcretes but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes clotted micrite is present in all types except groundwater calcretes sparitic veins however are observed in each type but are relatively less developed in groundwater calcretes a similar distribution of displacive and replacive textures is also seen although some grains in groundwater calcretes showed signs of corrosion the vertisol associated calcretes represent a subhumid 500 700 mm climate whereas the red soil calcretes suggest a semi arid 100 500 mm climate calcretes from the vertisol association show a range in 13c composition constrained between 9 and 5 whereas the red soil calcretes exhibit the whole spectrum of values from 9 to 1 based on mineralogical associations calcretes usually taken to reflect semi arid episodes in the earth s history may be classified further calcretes when associated with sepiolite palygorskite suggest an arid climate mean annual rainfall 50 100 mm when associated with smectite haematite and the absence of hydromorphism a semi arid climate mean annual rainfall 100 500 mm and when found in smectitic vertisols subhumid climates mean annual rainfall 500 700 mm

measurements in a braided river chute and lobe 2 sorting of bed load during entrainment transport and deposition grain size distributions of bed material bed load and bar head deposition were sampled during the evolution of a chute and lobe in the braided gravel bed sunwapta river alberta although bed shear stress and total bed load transport rate varied substantially within the reach and from day to day ferguson et al this issue the median diameter d50 of bed load was remarkably constant the bed initially fined from chute to bar head but became more uniform sediment deposited on the bar head also had a near constant d50 similar to that of the bed load truncated at the same lower size limit both load and deposition were finer on average than the bed suggesting overall selective transport despite little sign of local sorting in contrast to median diameters maximum sizes dmax of sediment in motion and deposited on the bar head varied substantially and showed a weak but significant dependence on shear stress inferring selective entrainment from this evidence alone would be dubious because dmax was also found to increase systematically with the mass of sediment sampled however two different methods of analysis of fractional transport rates throughout the size range also showed size selective entrainment and transport in the marginal transport conditions of this study size sorting appears to occur but only weakly and mainly in the coarser fractions

ages of alpine tectonometamorphic events in the northwestern himalaya northern pakistan by 39ar 40ar method the main tectonometamorphic alpine events which occurred in the western part of the western himalayan virgation at south of the main suture in northern pakistan are dated by the 39ar 40ar method these events are as follows 1 the blueschist metamorphism 80 5 ma present in tectonic ophiolititic melanges along the suture this event occurred during an early subduction or obduction stage 2 the alpine barrovian metamorphism 50 30 ma developed in the sedimentary cover and orthogneisses of the indian plate during the postcollisional northward underthrusting of this plate below asia and 3 the emplacement of postmetamorphic leucogranites 23 ma resulting from the melting of the indian crust during the climax of the alpine metamorphism

bedform migration and bar evolution in a late quaternary monsoon influenced river gujarat western india abstract a study of a well exposed late quaternary calcrete conglomerate sheet from gujarat western india provides some insights on bedform migration and bar evolution in sub humid monsoon influenced rivers the architecture of the conglomerate sheet is defined by the presence of two elements channel ch and gravel bar gb this architectural simplicity is remarkable and may be typical of monsoon influenced rivers that show dominance of 3d dunes in the initial stage 1 the river was sand load dominated as seen in the presence of cross bedded sands at the base associated with this stage was a channel element ch1 at the northern extremity of the outcrop during stage 2 bank excavated blocks were redistributed in the channel which aided the appearance of gravel mesoforms within depressions on the channel bed and subsequent low stage sedimentation leading to the formation of channel element ch2 in stage 3 gravel dunes covered the entire channel bed and are separated from the preceding deposits by a channel lag falling stage dissection of the bar was accompanied by relocation of the flow along a smaller channel represented by channel element ch3 at the northern end of the outcrop and bar top dissection this history of bar evolution compares well with the central bar initiation and transverse bar braiding mechanisms described in flume studies except for change in bed material palaeocurrents during the termination of stage 3 showed typical patterns of convergence and divergence of bedforms in the southern extremity of the outcrop whereas the palaeocurrent directions are more consistent in the central regions this could be related to dune combination and splitting

trough cross bedded conglomerate facies abstract gravel bed river deposits contain a range of facies that includes planar cross bedded gravel gp massive gravel gm and trough cross bedded gravel gt of these the gt facies is commonly interpreted to represent deposits of channel fills and or three dimensional 3d gravel dunes and or scours or pools in this study a calcrete conglomerate sheet built up of gt facies is found to consist of trough cross beds of 3d dune origin gtd and of bedload sheet origin gtb whereas gtd occurs as sets gtb is found to occur as isolated large troughs the gtd facies is characterised by high dips low width height ratios and foreset bed thickness of about 100 140 mm in contrast the gtb facies has low dips high width height ratios and foreset bed thickness usually less than 50 mm the bivariate plot of width height of troughs vs maximum dip effectively discriminates between these varieties of troughs a third variety of gt may be recognised by the presence of a scoop or spoon shaped lower bounding surface as seen in the depositional dip direction this facies has been demonstrated in other works to represent filling of scours or pools on the streambed and is designated as gtc for the preservation of 3d gravel dunes in the stratigraphic record special flow conditions are necessitated of prime importance is the rapid recession of flow subsequent to a short duration of peak discharge such discharge patterns are critical to the preservation of gravel dunes in the stratigraphic record and appear to have been met with in the case of glacial outburst floods or floods in the seasonal tropics

unroofing history of the jambil and jawar carbonatite complexes from nw pakistan constraints from fission track dating of apatite abstract the peshawar plain alkaline igneous province paip is exposed north of the peshawar plain in nw pakistan it stretches from tarbela in the east up to loe shilman near the pakistan afghanistan border in the west within the paip carbonatites are found at loe shilman sillai patti jambil koga and tarbela small isolated sill like bodies and plugs of carbonatites are exposed in the jambil area about 10 km se of mingora in lower swat small isolated bodies of carbonatites have also recently been discovered at the locality of jawar about 4 km north west of the sillai patti carbonatite fission track dating studies on the apatite yielded ages of 15 7 0 4 and 25 2 1 0 ma for the jambil and jawar carbonatites respectively uplift induced denudation and cooling rates of 0 19 0 04 mm y 1 and 5 73 1 15 c ma 1 for jambil carbonatite 0 12 0 03 mm y 1 and 3 57 0 73 c ma 1 for jawar carbonatite and 0 13 0 03 mm y 1 and 3 97 0 82 c ma 1 for sillai patti carbonatite respectively were estimated comparison of the data indicates that all three carbonatite complexes have experienced similar uplift induced denudation and cooling rates during the past 25 15 ma

stratigraphy and structure of the indus suture in the lower swat pakistan nw himalaya abstract we present a geological map detailed structural description and new subdivisions of the indus suture zone lithologies in northeast pakistan lower swat region the indus suture zone is a dominantly fore arc related assemblage obducted onto the indian plate initial southward thrusting was followed by the reactivation of the indus suture as a ductile brittle normal fault significant strike slip faulting may have taken place at this stage later brittle reverse faults demonstrate that shortening outlasted normal faulting the comparison of the structural evolution of the indus suture zone and the indian plate shows that both terrains were sharing the deformational history possibly since the earliest stage of collision the lower swat area records a full orogenic cycle from early rifting through continent arc collision to orogenic collapse we present a geodynamic model that integrates all these elements

study of the tectonic uplift history of the sillai patti granitic gneiss pakistan constraints from zircon fission track dating abstract a group of alkaline igneous complexes called the peshawar plain alkaline igneous province paip is exposed in an arcuate fashion north of the peshawar plain in northwestern pakistan the paip which stretches from tarbela in the east to loe shilman near the pakistan afghanistan border in the west consists mainly of granites syenites gabbros ijolites and carbonatites field relationships suggest that the malakand granite and sillai patti carbonatite are younger than the malakand and sillai patti granitic gneisses however a zircon fission track age from the sillai patti granitic gneiss is less than the absolute ages of the malakand granite zircon u pb age 270 ma and sillai patti carbonatite calcite u pb age 30 ma biotite k ar age 31 2 ma zircon fission track age 32 3 1 4 ma therefore the zircon fission track age of 24 4 2 9 ma from the sillai patti granitic gneiss represents a time of post metamorphic denudation history of the area when these rocks passed through the 210 c isotherm this isotherm corresponds to a depth of about 6 7 km within the earth s crust from the present day surface

sedimentology of the upper burdekin river of north queensland australia an example of a tropical variable discharge river the burdekin river is an example of a class of tropical streams which experience two to four orders of magnitude variation in discharge in response to seasonal but erratic monsoonal rainfall floods of the burdekin rise abruptly reaching peak discharges of up to 40 000 m s in less than 24 h maintain peak flow for up to a few days and recede exponentially the geomorphology and deposits of these rivers reflect the extreme discharge fluctuations and have not previously been described a stretch of the upper burdekin river comprising four bends and one straight reach was examined near the town of charters towers the river bed is largely exposed for most of any year with a small misfit perennial channel carrying low stage flow major geomorphic elements of bends include point bars with ridge and swale topography three distinct types of chute channels avalanche slipfaces up to 5 m or more high around the downstream edges of bars and on the outer part of one point bar an elevated vegetated ridge straight reaches are flat or gently inclined sand and gravel covered surfaces much of the river bed is covered by well sorted in places gravelly coarse to very coarse grained sand with local accumulations of pebble to boulder gravel lower parts of the river bed are periodically draped by mud which is desiccated on exposure dunes and plane beds are the most commonly occurring bedforms with local development of gravelly antidunes most bank tops and upper vegetated bars are covered by silt and fine grained sand the river bed also hosts a low diversity but locally high abundance flood tolerant flora dominated by the paperbark tree melaleuca argentea which plays an important role in controlling the distribution of sediment the gross geomorphology of the river bed and most of the sedimentary features are interpreted as having formed during major bankfull or near bankfull flows which have a recurrence of about 18 years based on 65 years hydrographic data the initial rapid drop in discharge following flood peaks appears to preserve flood peak features on upper bars more or less intact whereas lower areas are subjected to variable degrees of modification during falling stage and by more frequent non bankfull discharge events

the influence of the south west indian monsoon on continental deposition over the past 130 kyr gujarat western india ocean and ice core records of the intensity of the south west indian monsoon swim show rapid shifts in most proxy indicators of climate over the past 125 kyr on decadal to millenial scales however the responses of continental environments to such perturbations remain unknown due to the absence of a suitable long term continental record the stratigraphic record from gujarat western india an area where all sedimentological processes are governed by the vagaries of the swim reveals three aggradation phases that represent deposits of seasonal rivers ap1 ephemeral rivers ap2 and dust storms ap3 based on a review of available dates and new esr dates on the oldest exposed calcretes from palaeovertisols these phases are assigned the time brackets 135 100 kyr bp ap1 100 20 kyr bp ap2 and 20 6 kyr bp ap3 these results suggest that continental depositional environments respond in a subdued manner and are separated by thresholds for climate shifts to effect durable changes in the continental depositional environment a period between 5 kyr and 16 kyr is the minimum time required to permanently change the landscape of an area alternatively catastrophic changes in terrestrial depositional environments may also be effected by abrupt climatic shifts that are beyond the tolerance limits of the depositional systems

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

first gps signals reflected from the interior of a tropical storm preliminary results from hurricane michael using gps signals reflected from the ocean surface is developing into a simple technique for measuring sea state and inferring surface wind speeds theoretical models have been developed which are considered valid to approximately 24 meters per second the gps reflection technique has an obvious extension to extremely high sea states cyclones and extra tropical storms in october of 2000 a gps system mounted in a noaa hurricane hunter research aircraft was flown into hurricane michael off the south carolina coast the first acquisition of gps signals reflected from the sea surface inside tropical cyclones was accomplished this paper presents some examples of the data sets as well as early wind speed retrieval results using direct extensions of current models data from the gps wind speed retrievals as well as from direct aircraft measurements are compared and discussed

record of deformation by secondary magnetic remanences and magnetic anisotropy in the nar phu valley central himalaya secondary magnetic remanences residing in pyrrhotite and anisotropy of magnetic susceptibility ams were studied in low grade metamorphic carbonates of the tethyan himalaya in nar phu valley central nepal and used for interpretation of tectonic deformations the characteristic remanence chrm is likely of thermomagnetic origin related to post peak metamorphic cooling occurring after the eohimalayan phase 35 32 ma the chrm postdates small scale folding main himalayan folding f1 and f2 as shown by a negative fold test of site mean directions at 99 confidence level and has been probably acquired between 32 and 25 ma late orogenic long wavelength folding associated with the chako antiform ca is recorded by the spatial dispersion of chrm directions and the distribution of the main axes of the ams tensor the mean tilting of the chrm direction since remanence acquisition c20 30j approximately coincides with the tilting of the ca 31j at the study area indicating that the pyrrhotite remanence predates the ca ca formed at 18 ma according to preliminary u pb dating however comparison of tilt angles of remanence directions and ams tensor axes suggests that remanence acquisition was not completed before the onset of the ca formation this could imply a younger age early miocene or even younger of the chrm using the distribution of remanence directions along a small circle as well as the distribution of ams tensor axes a clockwise mean rotation of 16j is obtained for a remanence age of c30 ma an early miocene remanence age would not change this result substantially compilation of rotations in the tethyan himalaya deduced from secondary pyrrhotite remanences reveals an increasing clockwise rotation from the hidden valley in the w to the shiar valley in the e c150 km distance incompatible with an oroclinal bending model d 2003 elsevier b v all rights reserved

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts