earthquake swarms precursory to moderate to great earthquakes in the northeast india region abstract the northeast india region has seen ten m 7 1 2 earthquakes since 1897 including two great earthquakes of m 8 7 in 1897 and 1950 the last m 7 1 2 earthquake occurred on august 17 1952 with the exception of three earthquakes others are found to be associated with periods of background normal seismicity precursory swarms quiescence and mainshocks and the associated foreshocks and aftershocks the dataset has been critically examined for completeness considering the current capabilities for defining locations and also considering other parameters regression equations relating the mainshock magnitude mm the average magnitude of the largest two events in the swarm mp and the time interval mp between the beginning of the swarm and the mainshock have been developed these are mm 1 37mp 1 41 and mm 3log10tp 3 27 it is important to recognize precursory swarms and quiescence in real time indeed we believe we have recognized one such sequence in the vicinity of the arakan yoma fold belt on the basis of mp and tp values the lateral extent of swarm activity and the fact that no event of m 6 has occurred since 1975 in the preparation zone defined by the 1963 1965 swarm we estimate that an m 8 earthquake could occur at any time in the area bounded by 21 and 25 1 2 n and 93 and 96 e the focal depth of this impending earthquake is estimated to be 100 40 km in view of the focal depths of the other events in the swarm

change from late tertiary compression to quaternary extension in southern tibet during the india asia collision field studies in southern tibet show that subsequent to folding resulting from the india asia collision 50 40 ma reverse faults and backthrusts formed as a result of nne ssw and nnw sse trending compressions they affect conglomerates of oligocene miocene age and are probably contemporaneous with shearing on the himalayan main central thrust and folding of paleogene basins along the northern border of southern tibet 25 16 ma rift systems postdate compressional structures they were active during the pleistocene and probably during the pliocene 5 2 ma change from a compressional to an extensional regime in tibet probably occurred during the late miocene 10 5 ma this change is tentatively correlated with uplift inferred by chinese workers from paleogene to present day variations of the tibetan vegetation recent and active faulting in the high plateau results from a wnw ese striking extension this is in agreement with tibetan focal mechanisms the himalayan lowlands are subjected to a nne ssw trending compression as demonstrated by superficial deformations and seismicity therefore the horizontal maximum compressive stress trajectory is roughly parallel to india asia convergence hmax being 1 in the lowlands and 2 in the high plateau this change results from the increase of the vertical principal stress value due to the weight of the elevated mass zz is 3 in the lowlands and 1 in the high plateau thus the third principal stress axis is 2 in the lowlands and 3 in the high plateau allowing extension to occur in the wnw ese direction extensional tectonics are significantly different in southern and northern tibet southern tibet being constrained between the himalayan syntaxes the e w extensional principal deviatoric stress value 3 is of rather small magnitude and the n s trending 2 value is extensional as demonstrated by analysis of recent faults normal components prevail along all the azimuths in the field this favors formation of rift systems of large axial extension on the contrary north of the himalayan syntaxes northern tibet flows easily eastward the e w extensional principal deviatoric stress value 3 is of higher magnitude and the n s stress 2 is compressional as shown by inversion of focal mechanism data this favors strike slip components on faults which deviate from the n s direction as expressed in the field by shorter n s trending graben linked with normal strike slip faults these faults permit some n s shortening in northern tibet without thickening in response to india asia collision in high plateaus which are subjected to lateral compression such as the andean altiplano and tibet the extensional direction is basically controlled by the convergence direction being roughly orthogonal to the latter

timing of intraplate deformation northeastern indian ocean abstract seismic stratigraphy and dsdp and odp drilling have demonstrated that two unconformities of early eocene and latest miocene age can be traced over much of the northeastern indian ocean the eocene event was a major hiatus in sedimentation following collision of india with asia and was the time of termination of deposition of a continental rise off the east side of india and the initiation of proximal bengal fan deposition the miocene event was the onset of north south compression in the indian plate during rapid uplift in tibet and the himalayas

timing of structural events in the himalayan foothills of northwestern pakistan the attock cherat range forms the southern boundary of the peshawar basin and includes rocks transitional between metasediments of the lesser himalaya and foreland basin strata to the south the attock cherat range comprises three fault bounded structural blocks which are from north to south 1 precambrian metaclastic strata overlain by unfossiliferous limestone which is itself apparently overlain by paleozoic strata with the contact not exposed 2 unfossiliferous flysch of precambrian age overlain by cretaceous and paleogene marine strata and murree red beds at least in part of early miocene age and 3 unfossiliferous limestone argillite and quartzite correlated in part to paleozoic strata in the peshawar basin overlain by a tertiary sequence generally similar to that in block 2 farther south in the kala chitta range strata of triassic to eocene age occur in south verging folds and thin thrust sheets the similarity of the tertiary sequences in the kala chitta range and in blocks 2 and 3 demonstrates that the pre tertiary sequences were juxtaposed by faults prior to deposition of the paleocene lockhart limestone this may coincide with initial contact of the west northwest facing passive margin of india with eurasia or nearby microplates major late tertiary imbricate thrusting and folding took place prior to uplift of the attock cherat range and to deposition of peshawar intermontane basin fill of pliocene pleistocene age the peshawar basin formed as the kala chitta range was faulted south on the main boundary thrust mbt forcing siwalik foreland basins still farther south late quaternary deformation in the southern peshawar basin occurred along a seismically active zone of en echelon stepped left faulted pressure ridges that may reflect a subsurface ramp on the older mbt

an early pliocene thermal disturbance of the main central thrust central nepal implications for himalayan tectonics since the beginning of the collision between india and asia at about 50 ma the convergence in the himalaya has largely been taken up along major thrust zones in this study samples of the lesser himalaya formations up to 10 km below the main central thrust mct and the greater himalaya sequence up to 12 km above the mct have been analyzed by the 40ar 39ar and u pb methods to investigate the thermal history of the mct the ages can be summarized as follows 1 the youngest ages from muscovites 3 1 ma biotites 3 4 ma and hornblendes 4 1 ma all come from within 1 km of the mct 2 there is a marked asymmetry of ages between the footwall and the hanging wall of the mct the maximum mica age in the hanging wall greater himalaya sequence is 13 ma whereas a muscovite 5 km below the mct in the footwall has an age spectrum with a gradient from 400 to 1400 ma 3 five k feldspars from 6 2 to 11 9 km above the mct all give minimum ages in the range 3 0 6 4 ma and 4 a 206pb 238u age on a brannerite from the greater himalayan sequence is 4 8 ma structural and petrologic observations preclude the possibility that this age distance distribution reflects faulting within the greater himalaya sequence and production of the necessary thermal energy by shear heating requires unrealistically high shear stresses infiltration of hot fluids through the mct zone appears to be the best hypothesis to explain these data simple numerical simulations which account for heat transfer by advection within the fluid flow zone and by conduction outside it indicate that the observed age distribution could have been produced by infiltration of hot fluids through the mct zone at circa 5 to 4 ma within the following range of conditions the fluids heated rocks to temperatures in the range 470 to 510 c for less than 1 million years in a region narrower than the entire mct zone the temperature of the thermal disturbance inferred from the 40ar 39ar data is consistent with petrologic data from albitic alteration assemblages in the greater himalaya sequence and the u pb age of the brannerite is similar to the youngest 40ar 39ar hornblende age this scenario hydrothermal heating culminating at about 4 ma is similar to the model of le fort 1981 for the generation of the high himalayan leucogranites in the late oligocene early miocene by dehydration of the footwall rocks of an active thrust in the younger instance we interpret that fluids derived from the footwall rocks of the main boundary thrust migrated upward through the lesser himalaya formations and were subsequently channeled along the mct producing the thermal disturbance

development of the himalayan frontal thrust zone salt range pakistan the salt range is the active frontal thrust zone of the himalaya in pakistan seismic reflection data show that a 1 km offset of the basement acted as a buttress that caused the central salt range potwar plateau thrust sheet to ramp to the surface exposing mesozoic and paleozoic strata the frontal part of the thrust sheet was folded passively as it overrode the subthrust surface on a ductile layer of eocambrian salt lack of internal deformation of the rear part of the thrust sheet is due to decoupling of sediments from the basement along this salt layer early to middle pliocene 4 5 ma conglomerate deposition in the southern potwar plateau previously interpreted in terms of compressional deformation may instead document uplift related to basement normal faulting stratigraphic evidence paleomagnetic dating of unconformities and sediment accumulation rates suggest that the thrust sheet began to override the basement offset from 2 1 to 1 6 ma cross section balancing demonstrates at least 20 to 23 km of shortening across the ramp the rate of himalayan convergence that can be attributed to underthrusting of indian basement beneath sediments in the pakistan foreland is therefore at least 9 14 mm yr about 20 35 of the total plate convergence rate

stable isotopic evidence for latest miocene sea level fall in the mediterranean region the discovery of a marked isochronous decrease of carbon isotope ratio values 0 5 0 8 in marine carbonates at about 6 2 myr has stimulated several speculations regarding the origin of this event1 3 here we report stable isotope studies of planktonic and benthic foraminifera from the late miocene carmona dos hermanos section in southwestern spain which suggest that 1 the carbon shift at 6 2 myr is directly associated with a eustatic sea level lowering recorded in the same section 2 the shift in 13c at 6 2 myr and other times may be related to an increased flux of marine and terrigenous organic matter depleted in 13c and eroded from the continental shelves during sea level lowstands and 3 the sea level fall at 6 2 myr triggered the rapid shift towards hypersaline conditions in the mediterranean well before the deposition of the messinian evaporites

neogene tectonics in the western mediterranean may have caused the messinian salinity crisis and an associated glacial event the messinian salinity crisis msc was a catastrophic event which led to the deposition of 106 km3 of evaporite in the mediterranean between 6 5 and 5 ma b p stratigraphic investigations have previously suggested that the progressive increase of salinity in the mediterranean leading to the msc may have been caused by tectonic narrowing and closure of seaways between the mediterranean and the atlantic detailed reconstruction of the tectonic history of the arc of gibraltar and adjacent alboran basin independently suggests 1 1 that the early miocene guadalquivir and alboran seaways closed and narrowed respectively near the end of the tortonian 7 ma b p and 2 2 that the tectonic arc of gibraltar progressively emerged above the sea level during the messinian 7 5 ma b p which caused together with a eustatic glacial lowering of the sea level the isolation and subsequent dessication of the mediterranean this is in agreement with a two stage history of the msc previously postulated on the basis of stratigraphical observations 1 1 deep basin deep water and 2 2 deep basin shallow water salt deposition the closure of the seaways between the mediterranean and the atlantic and the associated drop in world wide oceanic surface salinity may even have caused the kapitean optian glacial event about 5 5 ma b p

vegetation covers as indicator of seismo tectonic environment an integrated geophysical study in north baromura hill india spatial distributions of vegetation cover are closely related to topographical characters like slope steepness soil types elevations etc in seismo tectonic regions fault lines or tectonic lineaments are the most prominent surface signatures that can be reflected by vegetation distribution as tectonic displacement causes the change of topographical parameters in the present study a part of northern baromura hill between 23o 42 n to 23o49 n latitudes and 91o30 e to 91o36 e longitudes which is considered as an active seismo tectonic region of tripura as well as northeast india was selected for assessing the relationship between spatial variation of plant cover and topography geologically baromura hill is a north south extended fold belt and formed by late tertiary to quaternary depositions evidences show that tectonic events played very important role in landform evolution of this area during the geological past in this research an extensive fieldwork was conducted in the study area to understand the geomorphic and vegetation signatures and their environmental relationships various spectral resolutions of landsat etm were used for digital analysis to analyse the vegetation character of this area digital operation was done within the spectral range 0 63 1 75 m band 4 and band 3 were used for ndvi operation band 5 or mid wave infrared band was classified in unsupervised mode to understand the range of plant water in the study area overlay operation with those operated images shows the spatial distribution pattern of vegetation cover indicates the landform condition three clear tectonic lineaments faults were detected from the digital study in on the northern part baromura hill structural conditions of those fault lines were verified by geo electrical survey during fieldwork gps tool was used for fixing the ground control points resistivity characters of the study area assessed from ves profile strongly supports that vegetation cover analysis from remotely sensed data within 0 63 1 75 m spectral ranges can be a very useful tool for detecting surface tectonic signatures of the landform

the neotectonics of the tibetan plateau part of the continuing northward convergence between india and eurasia is probably taken up by strike slip displacement with tibet as a whole moving eastward away from the collision zone and undergoing east west extension molnar and tapponnier 1975 ni and york 1978 on the basis of our interpretation of landsat images we propose that strike slip faulting occurs throughout the tibetan plateau such that its north south cross section is being shortened with little contemporary folding or thrusting

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi sources approach for spatial data analysis this paper aims to assess the morphological signatures of tectonic features faults on the basis of multi sources spatial data analysis for that purpose the present authors selected the southern part of baromura hill of tripura which has been discussed very little in the scientific literatures an extensive field work was done in the assumed faulted areas to understand the geomorphic signatures of faulting in the field gps was used for fixing the ground control points scanned survey of india soi topographical sheets spot pan and land sat band 5 was used for digital analysis an old dem on irs liss iii fcc was also consulted for final mapping two clear lineaments faults were detected from field observation on southern baromura hill apart from these another one was found in the outer part of this hill range an attempt was made to explain the morphological signatures of those faults by density slicing on radiometric data based on emittance of different physical components finally a geomorphic map with main tectonic features of baromura was prepared for future disaster management planning

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

cenozoic uplift and deformation of the tibetan plateau the geomorphological evidence an erosion surface interpreted as a pediplain is traced across the tibetan plateau as a result of faulting and warping its elevation now varies from approximately 4500 6000m it was cut across folded and thrust eocene strata and mid miocene granites but was dislocated by major faults before the pliocene its age is thought to be mid to late miocene crustal shortening after pediplanation is small if the crust beneath the plateau was thickened by deformation during crustal shortening the thickening must mainly have occurred before the pediplanation

neogene history of the south pacific tradewinds evidence for hemispherical asymmetry of atmospheric circulation rea d k and bloomstme m k 1986 neogene history of the south pacific tradewmds evidence for hemlsphermal asymmetry of atmospherm circulation palaeogeogr palaeochmatol palaeoecol 55 55 64 eohan dust grains extracted from southeast pacific pelagic sediments provide a neogene record of southern hemisphere atmospherm processes the mass accumulation rate of dust has been low and generally constant at 1 4 mg cm 2 103 y since the late ohgocene eohan grains ze data show an increase from 8 20 3 40 t m older sediments to 7 20 6 80 t m younger materml this shift occurred about 10 5 m y ago and reflects a s gmfmant increase in the intensity of atmospheric circulation then there s no obwous response to the onset of northern hemisphere glacmtmn 2 5 m y ago m these eohan records from the south pacific compamson with existing lnformatmn from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the neogene and that this asymmetry reached its greatest extent between 10 5 and 2 5 ma

impact of faults on landslide in the atharamura hill along the nh 44 tripura the present study is aimed at assessing the relationship between existing faults and occurrence of landslides the geophysical techniques like geothermal imaging of fault zone soil electrical resistivity data and field verification identify the fault characteristic the present study reveals two prominent faults in the atharamura hill i e one north south extended faults and the other east west extended faults the change in the geothermal characteristic along the fault structural data dip strike and most significantly the locations of landslide close to faults provide strong correlation of the landslide and the existing faults the soil electrical resistivity data are low along the faults the subsurface resistivity profile clearly delineates the faults

seismic assessment in southern baromura hill northeast india considering geophysical aspects this paper aims to assess the geophysical signatures like morphology and structure of a fault line which is situated in a part of southern baromura hill of tripura northeast india in this work manual observations and technical applications were adopted for understanding the morphological and structural characters of the fault line as tectonic mapping is one of the main objectives of this study the remote sensing technique was used to prepare a tectonic map of the study area geothermal range of the area was measured by unsupervised classification of landsat tm thermal infrared band band 6 the classified thermal band was overlaid by another classified shortwave infrared band band 7 of landsat tm which explains the structural evidences of the study area in addition an automated digital elevation model dem was prepared to assess the morphological characters of the study area particularly near the confluence of r maharani and r gumti to analyse the structural condition of the faulted zone resistivity characters of the rocks were measured by vertical electrical sounding ves method the electrical resistivity character of this area strongly supports that a displacement occurred in this place finally an attempt was made to explain the character of faulting on the basis of morphological signatures and structural evidences for future disaster management planning

corals move boulders an unusual mechanism of sediment transport tidal currents over the sill of knight inlet a fjord on the western canadian coast are frequently in excess of 1 m s 2 this shallow sill 65 m is composed of cobble to boulder sized sediments that support extensive growths of large gorgonian corals although current generated shear stresses are normally far from sufficient to initiate boulder movement drag forces due to the attached corals do cause a significant rearrangement of the boulders on the sill

mn2 activated luminescence in dolomite calcite and magnesite quantitative determination of manganese and site distribution by epr and cl spectroscopy abstract dolomite calcite and magnesite were studied by epr and cl spectroscopy mn2 activated luminescence in calcite and magnesite is characterized by single gaussian peaks at 16 250 cm 1 615 nm and at 15 300 cm 1 654 nm respectively in calcite the mn2 content and the normalized epr area are linearly correlated when the mn2 content is deconvolution of corrected cl spectra from dolomite shows two overlapping peaks at 17 315 cm 1 578 nm and 15 270 cm 1 655 nm in rare cases only the 15 270 cm 1 655 nm gaussian peak is present the cl peak at 17 315 cm 1 578 nm ia is due to mn2 in the ca site and the peak at 15 270 cm 1 655 nm ib to mn2 in the mg position the mn2 content in dolomite is linearly correlated with the normalized epr areas of the two sites the distribution ratio kd of mn2 in the two sites of dolomite i e the ca and the mg position was determined by epr and cl spectroscopy a linear correlation exists between kd from epr and the intensity ratio i b i a from cl cl spectroscopy is thus an appropriate method to determine kd in dolomite evaporitic dolomites may be differentiated from non evaporitic dolomites by their kd values

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

neogene evolution of the himalayan tibetan region constraints from odp site 758 northern ninetyeast ridge bearing on climatic change abstract magnetic susceptibility remanence and lithostratigraphic profiles for the neogene quaternary sequence at site 758 odp leg 121 on the northern ninetyeast ridge show distinct changes dated from biostratigraphy and detailed magnetostratigraphy at 17 5 10 4 10 0 8 8 6 5 5 4 5 1 2 7 2 5 1 9 and 1 2 1 1 ma these magnetic and lithologic changes appear to reflect changes in the supply and character of terrigenous material from the himalayan tibetan region resulting from changes in gradient of the ganges brahmaputra and probably the ancient indus drainage systems the sedimentary changes can be correlated with changes in uplift sensitive markers such as the oceanic 87 sr 86 sr ratio and monsoonal induced upwelling but not clearly so with sealevel variations we interpret these sedimentary changes therefore to primarily reflect changes in the tectonic evolution of the himalayan tibetan region the changes in the distal marine sedimentary record of the northern ninetyeast ridge are compared with isotopic control on the timing of himalayan tibetan tectonic phases and magnetostratigraphic control on their reflection in the proximal siwalik molasse record this comparison indicates that the distal ninetyeast ridge record can be used to detail and to place minimal age constraints on tectonic phases in the wider himalayan region and on evolution of the proximal molasse sequence with a time lag determined for the four earliest changes at less than 1 m y the changes at 17 5 ma and 5 4 5 1 ma can be interpreted in terms of the causative chain enhanced plate motion uplift and sedimentation change climatic change supporting arguments that the late cainozoic global climatic deterioration is driven by uplift of large plateaus such as the himalayan tibetan region and the western cordillera

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

deep sea bio physical variables as surrogates for biological assemblages an example from the lord howe rise abstract little is known about diversity patterns of biological assemblages in deep sea environments primarily because sampling deep sea biota over vast areas is time consuming difficult and costly in contrast physical mapping capabilities are increasing rapidly and are becoming more cost effective consequently the growing need to manage and conserve marine resources particularly deep sea areas that are sensitive to anthropogenic disturbance and change is leading the promotion of physical data as surrogates to predict biological assemblages however few studies have directly examined the predictive ability of these surrogates the physical environment and biological assemblages were surveyed for two adjacent areas the western flank of lord howe rise lhr and the gifford guyot spanning combined water depths of 250 2200 m depth on the northern part of the lhr in the coral sea multibeam acoustic surveys were used to generate large scale geomorphic classification maps that were superimposed over the study area forty towed video stations were deployed across the area capturing 32 h of seabed video 6229 still photographs that generated 3413 seabed characterisations of physical and biological variables in addition sediment and biological samples were collected from 36 stations across the area the northern lord howe rise was characterised by diverse but sparsely distributed faunas for both the vast soft sediment environments as well as the discrete rock outcrops substratum type and depth were the main variables correlated with benthic assemblage composition soft sediments were characterised by low to moderate levels of bioturbation while rocky outcrops supported diverse but sparse assemblages of suspension feeding invertebrates such as cold water corals and sponges which in turn supported epifauna dominated by ophiuroids and crinoids while deep environments of the lhr flank and lower slopes of the gifford guyot were characterised by bioturbation with high occurrences of trails burrows and mounds evidence for bioturbation was significantly less on the upper sections of gifford guyot with mostly trails on the more sediment starved environments the seamount summit also supported a variety of taxa such as benthic ctenophores and rock associated fishes that were not recorded in the deeper basin habitats physical characteristics of the seabed particularly geomorphology were good predictors of biological assemblage composition and percent cover of key taxa of the nine geomorphic classes assessed in this study six predicted different physical habitats that supported distinct biological assemblages however other classes that were defined by spatial features e g valleys seamount dunes where surficial physical variables were not unique provided little predictive power of biological assemblages but rather had characteristics that were shared with adjacent surrounding geomorphic classes given the growing need to use surrogates in the management and conservation of marine environments these results are promising however our findings suggest that there is a pressing need for careful testing and validation of surrogates such as geomorphic classes before classification schemes can be deemed effective and employed as a management tool to predict seabed habitats and their biological assemblages

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

the magnetostratigraphy fission track dating and stratigraphic evolution of the peshawar intermontane basin northern pakistan the peshawar basin is situated along the junction of the northern margin of the indo gangetic foredeep and the southern margin of the hindu rush himalayan ranges during the late cenozoic southward encroachment of tectonic disruption into the foredeep terminated molasse deposition and delineated the peshawar intermontane basin through uplift of the attock range along the southern margin of the basin in this study magnetostratigraphy fission track dates on volcanic ashes and stratigraphic data are used to define the chronologic and stratigraphic evolution of the basin following a late miocene to pliocene interval of folding and thrusting of the preexisting molasse sediments deposition began in the peshawar basin by at least 2 8 m y ago subsequently 300 m of basin filling sediments accumulated at rates averaging 15 cm 1 000 yr northward progradation of alluvial fan deposits from the uplifted basin margin had begun by 2 6 m y ago and continued at an inferred rate of 2 cm yr proximal to the attock range in the south alluvial fan facies persisted until 0 6 m y ago contemporaneous sediments closer to the basin center demonstrate the presence of rapid facies transitions to extensive floodplain and shallow lacustrine depositional environments widespread intermontane basin sedimentation was terminated by accelerated uplift of the attock range after 0 6 m y ago subsequently during the brunhes chron catastrophic floods have periodically inundated the peshawar basin continuing tectonic deformation of the basin is indicated by uplifted flood deposits offset terraces and modern seismicity

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

high resolution strontium isotope stratigraphy and biostratigraphy of the miocene monterey formation central california detailed biostratigraphic and sr isotope studies on two outcrop sections of the miocene monterey formation of california demonstrate the applicability of the sr isotope method for detailed chronostratigraphic correlation multidisciplinary biostratigraphic ages generally agree with sr isotopic ages determined by correlating 87sr 86sr ratios with a standard 87sr 86sr versus age curve constructed of data from deep sea drilling project sites 575 and 590 diagenetic modification of sr isotopic ratios of the monterey formation was negligible strontium isotopes provide age resolutions of 0 1 to 0 2 ma in the lower miocene small faults and slump structures are identified as reversals within a general trend of increasing 87sr 86sr biostratigraphy yields the more definitive age assignments in the younger siliceous rocks where diatoms in particular have more utility than the corresponding flat and polytonal portion of the isotopic curve strontium isotopic correlation of the basal monterey formation with deep sea drilling project site 575 indicates that monterey deposition commenced at 17 85 0 10 ma within planktic foraminiferal zone n6 and calcareous nannofossil zone cn2 concomitant with an increase in slope of the sea water 87sr 86sr versus age curve this event dates 0 35 0 10 m y before the beginning of the pronounced shift of 13c and 1 4 m y before the shift of 18o observed at site 575 it is evident that sr isotope stratigraphy is a valuable supplement to biostratigraphy the techniques are complementary in refining chronostratigraphic interpretations

characterization of earthquake dynamics in northeastern india regions a modern nonlinear forecasting approach the northeastern india nei region is seismotectonically one of the most active regions of the world earlier studies of nei earthquake data have provided contrasting evidence for the presence of randomness and low dimensional strange attractor here in the present study we assess the dimensionality of an earthquake generating mechanism by nonlinear predictability analyses on phase portrait constructed by monthly frequency earthquake time series which was obtained from the noaa catalogue the result of nonlinear forecasting analyses suggests that the earthquake processes in the nei region evolve on a non random high dimensional chaotic system such a complex high dimensional earthquake behavior is indicative of heterogeneous geological structures in which weak fault zones and or individual fault interactions might have strength fluctuations due to pore pressure variation further k 2 entropy analysis was performed to isolate the non random component from the data the analysis reveals a quasi coherent time structure k 2 0 08 month which corresponds to a seasonal time scale of about 12 months we argue that stochastic resonance created by seasonality bias may have combined with noise to affect the pore pressure variation leading to subsequent earthquake triggering it is interesting to note that most earthquakes and swarm activities occurred during or after the monsoon season geological and geophysical evidence also reconciles with the above view evidence for high dimensional chaos associated with seasonal bias in the nei region may provide useful constraints for testing models and criteria to assess earthquake hazards on a more rigorous and quantitative basis

paleogeography glacially induced crustal displacement and late quaternary coastlines on the continental shelf of british columbia canada abstract subsequent to the last glacial maximum lgm complex isostatic adjustments resulted from deglaciation eustatic sea level change tectonic faulting and a relatively thin flexible lithosphere in the queen charlotte islands qci region a geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the late quaternary northeast pacific continental shelf between 14 2 and 8 7 ka bp wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath queen charlotte qc sound and hecate strait glacial ice 690 m thick began retreating from dixon entrance after 14 5 ka bp 14c years ago and prior to 12 6 ka bp permitting over 100 m of crustal uplift in northern hecate strait a forebulge persisted in hecate strait and qc sound from 13 2 until after 9 7 ka bp implying fixed glacial ice on the british columbia bc mainland until 10 ka bp paleogeographic reconstructions show two emergent ice free terrains one extending eastward from the qci and the other in qc sound by 11 7 ka bp a landbridge connected the bc mainland and the qci

acoustic discrimination of relatively homogeneous fine sediments using bayesian classification on mbes data highlights acoustically meaningful clustering correlating with ground truth data seascape scale acoustic mapping through classification per beam footprint bayesian approach for discriminating sedimentary units with low heterogeneity geo acoustic resolution a new measure of sedimentary acoustic class separability modern seafloor mapping is based on high resolution mbes systems that provide detailed bathymetric and acoustic intensity backscatter information we examine and validate the performance of two unsupervised mbes classification techniques for discriminating acoustic classes of sedimentary units with small grain size variability the first technique based on a principal components analysis pca is commonly used in literature and has been applied for comparison with the more recent approach of bayesian statistics by applying these techniques to a mbes dataset from an estuarine area in the netherlands we tested their ability to discriminate fine grained sediments at least 70 silt holding small percentages of coarser material such as sand shell hash or shells we focus on the bayesian technique as it outputs acoustically significant classes related to backscatter values this technique utilizes backscatter values averaged over scatter pixels projected pulse lengths inside the footprint of each beam the originality of our application lies in the fact that the optimal number of classes is derived by utilizing a number of beams simultaneously it is assumed that the backscatter values per beam vary relatively to the varying seafloor types by treating the beams separately across track variation in the seafloor type can also be accounted for thereby the classification is guided by outer more discriminative beams additionally we control the optimal number of classes by employing the quantitative criterion of goodness of fit 2 the bayesian acoustic classes show correlation with grain size parameters such as coarse fraction 500 m percentage and mean of the grain size 500 m when analyzed with multiple linear regression in order to examine the relative scale of the acoustic classification results we compare the bayesian acoustic classes with underwater video interpretation our results reveal that the bayesian approach enhances the sedimentological interpretation of mbes high resolution data by providing classification on seascape scale here meters to tens of meters hence we suggest that backscatter processing techniques are more commonly applied to produce classes that discriminate sediments with low grain size contrast to describe this ability we introduce the term geoacoustic resolution we want to encourage the use of the bayesian technique also in deep sea applications based on auv data where sediments express low variability but sampling would be time consuming and costly the advantages of this method would favor mapping of macro habitats which appear at meter scale and require datasets of sufficient resolution in order to be quantitatively described

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

origin and age of the mediterranean messinian evaporites implications from sr isotopes strontium isotope ratios from the messinian late miocene 6 4 to 4 85 ma evaporites of the mediterranean basin 1 2 support a subdivision into stratigraphically lower predominantly marine deposits lower evaporites lev lower gypsum and main salt characterized by sr isotopic ratios generally equivalent to those of messinian seawater and stratigraphically higher deposits upper evaporites uev with 87sr 86sr ratios lower than messinian seawater the range of 87sr 86sr ratios of the lev unit from the eastern mediterranean overlap with values obtained from essentially coeval red sea evaporites 3 strontium isotopic ratios measured from the upper evaporites however are lower and a high proportion of this sr was probably derived from low 87sr 86sr continental runoff that characterizes much of this basin 4 these results therefore strongly support depositional models utilizing a deep desiccated basin 1 with a constant marine inflow during the early stages including salt formation followed by a series of long lasting and sometimes isolated desiccation events that produced a strong but variable continental influence on the sr isotopic compositions of the uev strontium isotopic measurements can also be used to asses the actual timing of the deposition of the lev ratios obtained from oyster fragments and foraminifers from pre evaporitic units at odp site 654 tyrrhenian sea suggest that the major rifting phase in this region occurred between 8 and 6 5 ma ratios obtained from the early lev from the mediterranean sea suggest that initiation of evaporite deposition began about 5 65 ma ago results from units immediately overlying the uev in sicily suggest termination of evaporite deposition about 4 9 ma ago errors associated with these age estimates are about 0 5 ma 2

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi source approach for spatial data analysis a critical review in a recent work dey et al environ earth sci 59 353 361 2009 presented some new observations on the southern part of one of the anticlinal ridges of tripura viz the baromura range the work incorporated a number of irregularities and misinterpretations that need to be addressed to avoid future confusion the present article critically reviews dey et al s paper to bring out its inaccuracies

an early india asia contact paleomagnetic constraints from ninetyeast ridge odp leg 121 new paleomagnetic results from sedimentary rock and basement of the ninetyeast ridge ocean drilling program leg 121 sites 756 758 detail the northward movement of the indian plate for the past 80 m y analysis of the combined paleolatitude age profile indicates a distinct reduction in india9s northward movement rate at 55 ma interpreted as completion of suturing of greater india and asia india9s northward motion slowed from 18 19 5 cm yr to 4 5 cm yr for the location of site 758 comparison of this profile with paleomagnetic data from the wider himalayan region indicates that initial contact between northwestern greater india and southern asia was already established by cretaceous tertiary time this supports a possible causal link between the india asia convergence and the deccan traps extrusion

dolomite thermometry by electron spin resonance spectroscopy abstract electron spin resonance esr spectroscopy has been used to distinguish different genetic types of dolomite in the complex metamorphic terrain of the ballachullish area of nw scotland by measuring the esr signals of mn2 from the two inequivalent sites in dolomite the partition coefficient can be determined and related to temperature a systematic one hundred fold increase in the partition coefficient from the highest grade of contact metamorphic skarn to supergene dolomites was found the use of this partition coefficient complements fluid inclusion and gross chemical data and is a useful aid in geothermometry

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

the chronology of intermontane basin development in the northwestern himalaya and the evolution of the northwest syntaxis abstract the northwest syntaxis delineates a complex zone where the northwesterly trending himalayan ranges meet the northeasterly trending hindu kush and indus kohistan ranges the southern margin of the hindu kush himalayan collisional belt is delineated by a series of imbricate thrusts that transect the northern edge of the modern indo gangetic foredeep the kashmir and peshawar basins are embedded in this still developing thrust belt and are symmetrically oriented about the northwest syntaxis consideration of chronologic stratigraphic structural and geophysical data from the syntaxial zone permits the construction of a model for intermontane basin development and the evolution of the northwest syntaxis during the late cenozoic the formation of the kashmir and peshawar basins results from the transfer from the north of the locus of thrusting and uplift to the southern margins of the basins during the pliocene the morphotectonic emergence of the ancestral pir panjal and attock ranges along the southern margins of the two basins coincides with changes in the patterns of sedimentation and deformation both within the basins and in the bounding foredeep to the south contrasting styles of tectonic deformation on opposite sides of the syntaxis are interpreted as a response to differences in the strength of sediment basement coupling across the syntaxis

mineralogy and mn geochemistry of laboratory synthesized dolomite abstract dolomite was synthesized in hydrothermal bombs to assess influences on mn partitioning into the mg and ca sites calcite was added to magnesium chloride solutions doped with 0 10 20 or 50 ppm mn runs were made for 8 to 241 hr at 192 and 224 c the calcium content of dolomite increased to 60 64 after 75 hr at 192 c and reverted to stoichiometry thereafter increases in the mn content of the starter solution progressively retarded formation of dolomite for dolomites formed without added mn or formed in less than 40 hr with 10 ppm added mn the esr signals were too broad to permit determination of mn site distribution ratios measurable ratios of mn in the mg site to mn in the ca site vary as a linear function of time from 0 3 to 7 for samples prepared at 192 c and from 3 to 16 for those prepared at 224 c stoichiometric dolomites have higher mn partitioning ratios than nonstoichiometric dolomites as observed in natural systems dolomites formed in supratidal sabkha early groundwater and dorag conditions may differ in their mn signature from those formed during burial diagenesis

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

microseismicity and source mechanism study shillong plateau northeast india microearthquakes recorded by two surveys in the shillong plateau during december 1982 july 1983 and january february 1984 respectively have been analyzed for seismicity and tectonic study in the region of 1 000 events recorded during the surveys 180 events with reliable p and s readings which are observed within 50 km radius of the network are relocated by the homogeneous station method it is found that the events are mostly confined within a depth range of 10 to 35 km the seismicity in general may be correlated with the major geological structure lineaments in the area high rates of seismicity are observed in the shillong and tura areas on the other hand an aseismic zone is delineated to the east of shillong composite source mechanisms of two groups of microearthquakes show thrust fault mechanisms one group of microearthquakes 1982 to 1983 in the shillong area shows pure thrust faulting with a se nw compressive stress p axis whereas the other group of microearthquakes 1984 in the tura area shows thrust faulting with a strike slip component and a ene wsw compressive stress p axis the stress orientations are compatible with the known tectonics of the region collision of the indian plate with the eurasian plate at the himalaya and subduction of the indian plate beneath the burmese plate at the arakan yoma range

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

late neogene paleoceanography and paleoclimatology of the gulf of aden region based on calcareous nannofossils quantitative study of climatically sensitive nannofossils in the sediments of the gulf of aden has provided a climatic and oceanographic scenario for the northwestern indian ocean during the late neogene the surface water temperature was relatively cold during the latest middle miocene to late miocene 10 7 to 6 32 ma with a probable warm interval in the early late miocene 9 82 to 8 49 ma this cooling is attributed to increased upwelling in the northwestern indian ocean the surface water was relatively warm from the latest late miocene to the middle of the late pliocene 6 32 to 2 59 ma the most intense cooling took place during the late pliocene to early pleistocene 2 59 to 1 69 ma intense upwelling during this interval coincides with worldwide climatic deterioration a probable short warm interval 1 69 to 1 59 ma followed this cold interval in the pleistocene the surface water was cold from 1 59 to 1 00 ma and from 0 61 to 0 24 ma and warm from 1 00 to 0 61 ma and after 0 24 ma

sequential late cenozoic structural disruption of the northern himalayan foredeep chronologies for the siwalik molasse and intermontane basins along the southern margin of the himalaya and hindu kush ranges constrain the timing and pattern of facies migration and structural disruption of the indo gangetic foredeep this synthesis indicates that quiescent intervals are punctuated by pulses of rapid deformation as thrusting migrates in a stepwise fashion across the foredeep

the contact between the higher himalaya crystallines and the tibetan sedimentary series miocene large scale dextral shearing space and time evolution of the synmetamorphic structures across the metamorphic pile have been studied in several areas along the himalayan belt east and central nepal garhwal zanskar from one area to the other the evolution is very similar 1 at the base of the pile in the main central thrust mct shear zone the stretching lineation penetrative and regularly oriented n0 e to n30 e indicates the mct transport direction very constant all along the belt from the eohimalayan main metamorphic development up to the late metamorphic movements 2 at the top of the pile at the contact between the crystalline unit and its sedimentary cover gravity driven structures are confirmed north vergent folds ductile normal faulting however there are numerous local indications of late miocene syn to late emplacement of the leucogranitic plutons dextral shearing 3 in between across the medium part of the pile the stretching lineation shows a conspicuous progressive regional clockwise rotation clearly indicated by the strain trajectories mapped in nepal and garhwal points 1 and 2 show that the crystalline sedimentary boundary despite its apparent structural and metamorphic continuity is not only a normal fault but also an important dextral shear zone which has acted since the upper miocene as the main southern limit of the eastward extruding tibetan block

geochemical evidence supporting t c chamberlin s theory of glaciation in 1899 t c chamberlin proposed that the co sub 2 content of the atomsphere decreased during times of enhanced continental erosion ultimately resulting in glacial epochs he ascribed the increase in the rate of chemical weathering relative to the rate of supply of co sub 2 from earth s interior to increased orogenic activity and globally higher average elevations which promoted rapid chemical erosion of silicates the oceanic record of strontium isotopes preserved in marine sediment supports his suggestion that glacial climates during the phanerozoic are in part linked to increases in the rate of global chemical erosion relative to outgassing from earth s interior further the close correspondence of the major tectonic episodes of the late cenozoic to times of increased continental erosion and glaciation suggests that chamberlin s hypothesis of the cause of glacial periods should be revived

the late cenozoic chronologic and stratigraphic development of the kashmir intermontane basin northwestern himalaya abstract the intermontane basin of kashmir developed within the thrust faulted southern margin of the himalayan range detailed lithostratigraphies magnetic polarity stratigraphies and fission track dates on enclosed volcanic ashes were determined at four separate localities in order to develop a chronology of the late cenozoic evolution of the kashmir basin the results indicate that sedimentation had commenced by about 4 m y ago since then over 1300 m of sediments have aggraded at inferred average rates varying from 16 to 64 cm per 1000 yr lacustrine and deltaic sediments dominate the kashmiri sequences and appear to respond sensitively to tectonic events along the basin margins conglomerates shed from the faulted basin margins at about 1 7 2 1 2 7 and 3 0 3 5 m y ago punctuate the predominantly low energy fluviolacustrine depositional record paleocurrent analyses indicate a switch from northeasterly derived conglomeratic facies to southwesterly derived ones about 1 7 m y ago this transition reflects enhanced activity along the main boundary thrust complex to the southwest and an apparent diminution of faulting along the northeastern margin of the basin in the pir panjal range 1400 3000 m of uplift at inferred rates of up to 10 mm yr 1 have terminated widespread sedimentation within the kashmir basin since the middle pleistocene

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake abstract gupta h k and singh v p 1982 is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake in a l hales and z suzuki editors earthquake prediction tectonophysics 85 31 33

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

relationship between paleotemperatures of metamorphic dolomites and esr determined mn ii partitioning ratios abstract an electron spin resonance esr study of the distribution of mn ii between mg sites and ca sites in 28 contact metamorphic dolomite samples suggests that the distribution is temperature sensitive the data can be modelled by alternative interpretations in the first a polynomial equation approximates the trend of the data suggesting an exponential relation with mn ii ratios decreasing to a stable value of 10 with increasing temperature to near 900 c the second suggests two groups of dolomites one group close to the intrusion

mapping coral and sponge habitats on a shelf depth environment using multibeam sonar and rov video observations learmonth bank northern british columbia canada abstract efforts to locate and map deep water coral and sponge habitats are essential for the effective management and conservation of these vulnerable marine ecosystems here we test the applicability of a simple multibeam sonar classification method developed for fjord environments to map the distribution of shelf depth substrates and gorgonian coral and sponge dominated biotopes the studied area is a shelf depth feature learmonth bank northern british columbia canada and the method was applied aiming to map primarily non reef forming coral and sponge biotopes aside from producing high resolution maps 5 m2 raster grid biotope substrate associations were also investigated a multibeam sonar survey yielded bathymetry acoustic backscatter strength and slope from benthic video transects recorded by remotely operated vehicles rovs six primary substrate types and twelve biotope categories were identified defined by the primary sediment and dominant biological structure respectively substrate and biotope maps were produced using a supervised classification mostly based on the inter quartile range of the acoustic variables for each substrate type and biotope twenty five percent of the video observations were randomly reserved for testing the classification accuracy the dominant biotope defining corals were red tree coral primnoa pacifica and small styasterids of which stylaster parageus was common demosponges and hexactinellid sponges were frequently observed but no sponge reefs were observed the substrate classification readily distinguished fine sediment sand and bedrock from the other substrate types but had greater difficulty distinguishing bedrock from boulders and cobble the biotope classification accurately identified gardens dense aggregations of sponges and corals and primnoa dominated biotopes 67 accuracy but most other biotopes had lower accuracies there was a significant correspondence between learmonth s biotopes and substrate types with many biotopes strongly associated with only a single substrate type this strong correspondence allowed substrate types to function as a surrogate for helping to map biotope distributions our results add new information on the distribution of corals and sponges at learmonth bank which can be used to guide management at this location

growth rate variation and potential paleoceanographic proxies in primnoa pacifica insights from high resolution trace element microanalysis red tree coral primnoa pacifica is one of the more common habitat forming deep sea gorgonian corals in the northeast pacific ocean growing in colonies up to 2 m high and living for decades to hundreds of years growth characteristics of p pacifica were studied in dixon entrance northern british columbia and the olympic coast national marine sanctuary washington state usa based on samples collected in july 2008 to minimize the impact of scientific sampling on coral populations only dead coral skeletons and dislodged live corals were collected ages and growth rates were measured using band counts and checked against ams 14 c ages of gorgonin rings ba ca mg ca na ca and sr ca ratios in the calcite cortex were measured using radial secondary ion mass spectrometer sims transects with a spot size of 20 m and separation distance of 25 m growth banding was consistent in width between the central mixed zone consisting of calcite and gorgonin and the dominantly calcite cortex average annual radial growth rate of the nine corals analysed ranged from 0 23 to 0 58 mm yr with an average growth rate of 0 32 mm yr in dixon entrance and 0 36 m yr in ocnms these growth rates are slightly higher than p pacifica growth rates from the gulf of alaska and more than four times the growth rates of sister species primnoa resedaeformis in the northwest atlantic primary productivity is likely a more important driver of geographic variation in primnoa growth rates than temperature or current strength both dixon entrance and ocnms are areas with high primary productivity and strong tidal currents lack of post atomic bomb radiocarbon in all but one of the gorgonin samples and long radiocarbon reservoir ages in the northeast pacific made radiocarbon based verification of coral ages and growth rates difficult due to wide errors in calibrated age estimates mg ca and sr ca ratios were inversely correlated in two of the three corals analyzed and showed evidence of interannual variation mg ca ratios ranged from 70 to 136 mmol mol 1 and sr ca ratios from 2 041 to 3 14 mmol mol 1 previously published relationships between gorgonian calcite mg ca and seawater temperature yielded average temperatures matching ambient measurements but the intra and inter annual variation in apparent temperature based on the mg ca ratios was more than double the observed variation in modern seawater temperature ranges in the region annual variation in mg ca and sr ca could be related to seasonal changes in precipitation efficiency which is likely a function of short term fluctuations in coral growth rate in turn related to variation in primary productivity seasonal and interannual variations in food availability driven by primary productivity may affect skeletal growth rate hence mg ca and sr ca ratios primnoid coral skeletal microgeochemistry probably records temporal changes in both temperature and primary productivity

correlation of sidescan backscatter with grain size distribution of surficial seabed sediments the dependence of acoustic backscatter on sediment grain size distribution is examined using dual frequency 100 and 410 khz sidescan sonar and 22 sediment grab samples from the loch linnhe artificial reef site on the west coast of scotland the sidescan data were processed to remove an empirically estimated average grazing angle dependence on backscatter the processed data were analysed by forming histograms of pixels extracted from a 20 m 2 box around each ground truth site a positive correlation r 0 73 between mean backscatter intensity and mean grain size was obtained i e the coarsest samples had the brightest backscatter a positive correlation r 0 59 was also found between the standard deviations of the backscatter and grain size distributions i e poorly sorted sediments gave the most variable backscatter the performance of the sidescan data was compared to results from a co incident single beam echo sounder roxann survey the roxann roughness index e1 compared well with the sidescan whilst the roxann hardness index e2 did not this may be due to a physical link between the acoustic measures the comparison showed the sidescan to have delivered a significantly higher resolution image of the seabed for a similar amount of ship time imaging of the artificial reef modules themselves was found to be frequency dependent d 2004 elsevier b v all rights reserved

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less