development and demise of a fringing coral reef during holocene environmental change eastern ningaloo reef western australia abstract reefs lining the western exmouth gulf located at the northern limit of the 300 km long ningaloo reef in western australia represent modern incipient coral reefs and veneers of non reef building coral algal communities on exposed pleistocene or give up holocene reef surfaces acquisition of sixteen cores alongside u series tims dates were used to confirm the nature of the pleistocene foundation and characterise holocene reef development three calcretised pleistocene units were identified as 1 the last interglacial mis 5e reef directly underlying holocene units 2 a mid pleistocene mis 7 bioclastic conglomerate unit and 3 a pleistocene alluvial fanglomerate eight holocene reef facies total thickness of 1 8 5 3 m included coral framework facies domal arborescent mixed tabulate and encrusting and detrital facies carbonate sand skeletal rubble and alluvial fan deposits holocene ages range from 7 93 to 5 8 ka bp with vertical accretion ranging from 1 46 to 9 88 mm year avg 4 11 mm year highest rates of accretion and thickest accumulation occurred in the most seaward and deepest cores composed of massive coral framestone and coralline algal crusts a six stage holocene chronology is proposed including 1 coastal inundation from 8 to 8 5 ka bp 2 initiation start up from 8 to 7 5 ka bp 3 rapid growth catch up and back step from 7 5 to 7 ka bp 4 rapid aggradational growth catch up from 7 to 6 5 ka bp 5 reef decline give up and detrital buildup from 6 5 to 5 8 ka bp and 6 detrital buildup and progradation from 5 8 ka bp to present changes in reef facies and the ultimate demise of the holocene reef probably involved a combination of increased sea level coastal flooding and erosion during the mid holocene highstand with associated increase in sedimentation turbidity and decline in water quality burial by sediment buildup during the mid holocene highstand and detrital progradation during the mid to late holocene regression and the introduction of alluvial sediment during cyclones and other severe storms to an already stressed community modern communities have thus shifted from coral dominated to bored macroalgal pavements this study shows that integration of reef development processes with response to environmental change can be used to assess future pressures on coral reef ecosystems globally

surface rupture of the 2005 kashmir pakistan earthquake and its active tectonic implications to provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications we have conducted field mapping of the surface rupture associated with the 2005 m w 7 6 kashmir earthquake despite the difficulty arising from massive earthquake induced landslides along the surface rupture we found that typical pressure ridges and warps extend northwestward for a distance of 70 km with a northeast side up vertical separation of up to 7 m neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake but three active faults or fault segments within the sub himalaya collectively called the balakot bagh fault compose the causative fault although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures only a part of it had been mapped as active before the earthquake the location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern central segment boundary and propagated bilaterally to eventually break all three segments our obtained surface rupture traces and the along strike slip distribution are both in good agreement with results of prompt analyses of satellite images indicating that space geodesy can greatly aid in time consuming field mapping of surface ruptures assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka we tentatively estimate the earthquake recurrence interval and shortening rate on the balakot bagh fault to be 1000 3300 yr and 1 4 4 1 mm yr respectively these estimates indicate that the balakot bagh fault is not a main player of himalayan contraction accommodation graphic 1 selected field photographs and arcgis files of the mapped surface rupture traces and measured vertical separations are available in the electronic supplement to this article 1 embed inline graphic 1 gif

the sub himalayan fold thrust belt in the 1905 kangra earthquake zone a critical taper model perspective for seismic hazard analysis 1 we investigate the broader epicentral area of the m 7 8 1905 kangra earthquake s north india affecting the sub himalayan hills the tectonics of the area is characterized by two major rentrants kangra and dehradun interposed by the nahan salient the first order topography between the himalayan frontal thrust and the main boundary thrust shows a marked lateral variation along strike of the mean gradient characterized by a very small mean slope angle 1 in correspondence with the reentrants and higher values 3 in the salient these tectonic and topographic features also show a good correspondence with the peculiar macroseismic field of the 1905 event s which is characterized by two distinct intensity maxima separated by a distance of 150 km clearly overlapping the two major tectonic reentrants in this paper based on available geological and geophysical information and a critical analysis of the general mechanical constraints the seismogenic volume of the external sector of the chain is investigated in terms of critical taper model attempting to clarify the possible correlations between tectonics topography and seismicity in the sub himalayan belt based on different assumptions three possible seismotectonic scenarios are explored in order to constrain their likelihood and therefore to suggest a potential seismic gap in the area corresponding to the nahan salient which may experience an event of significant magnitude in the future

impact of riser reconstructions on estimation of secular variation in rates of strike slip faulting revisiting the cherchen river site along the altyn tagh fault nw china abstract slip rates are heavily contested for many of the first order strike slip faults within the indo asian collision zone rates determined geodetically are generally lower than those reported using reconstructions of offset landforms and it is unclear if this discrepancy reflects true secular variation in slip history systematic errors in interpretation or both here i examine the methods used to derive slip rates from reconstructions of displaced fluvial risers and show that such rates are subject to potentially important uncertainties that have largely been overlooked review of published data demonstrates that the slip rate can vary by a factor of 1 2 to 5 for the same site depending on whether the reconstruction uses the age of the upper or lower terrace for the initiation of riser offset to reduce this epistemic uncertainty i have developed six geomorphic indices that can be used to identify the most accurate end member reconstruction 1 comparison of riser offset with inset channel width 2 similarity of riser and tread displacements 3 morphological analysis of the scarp profile 4 riser deflection in plan view 5 diachroneity of terrace abandonment and 6 whether riser crests or bases yield the slip vector without the use of these geomorphic observations the epistemic uncertainty associated with current methods for determining slip rate from offset fluvial risers is likely to be so large that there is no resolvable discrepancy between the gps and geologic rates within the indo asian collision zone application of three of these indices to new field mapping of the cherchen he river site 86 4 e along the central altyn tagh fault yields a revised slip rate of 9 4 2 3 mm yr equivalent within error to the rates previously derived from gps and paleoseismic studies although reinterpretation of published data from the sulamu tagh site 87 4 is consistent with this revised rate additional work is needed to reconcile this result with some of the rates reported near aksay 94 e

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

facies outcrop gamma ray and c o isotopic signature of exposed miocene subtropical continental shelf carbonates north west cape western australia abstract exposed uplifted miocene carbonate sequences of the cape range north west cape western australia provide outcrop analogues of seismic sequences from offshore parts of the shelf facies include deep shelf marls very fine and fine packstone larger foram wackestone floatstone and muddy rudstone foram coralline algal skeletal fragment packstone wackestone shallow seagrass facies lagoonal wackestone mudstone with scattered corals and tidal flat laminites the exposed early miocene units include the mandu highstand a sequence in the tulki and one in the middle miocene trealla limestone sequences contain decameter scale 5 20 m thick 4th order parasequences evident on gamma ray logs and by facies stacking that shallow and coarsen up they appear to be due to eccentricity driven sea level changes which may have been up to 50 m higher frequency meter scale parasequences of deep water marl up into larger foram rudstone floatstone perhaps precession obliquity are evident at the base of the exposed mandu section these parasequences are not merely random storm deposits this is indicated by the covariance of c and o isotopes with the lighter values associated with deepening and deposition of deep shelf marls and the heavier values being associated with shallowing and deposition of larger foram facies the uplifted miocene continental shelf sediments of the north west cape preserve a record of eustasy paleoclimate and paleoceanography and thus provide a window into factors affecting the shelf that can be compared with coeval better studied deep sea cores

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

interseismic strain accumulation across the central north anatolian fault from iteratively unwrapped insar measurements the north anatolian fault naf is a major tectonic feature in the middle east and is the most active fault in turkey the central portion of the naf is a region of global navigation satellite systems gnss scarcity previous studies of interseismic deformation have focused on the aseismic creep near the town of ismetpasa using radar data acquired in a single line of sight direction requiring several modeling assumptions we have measured interseismic deformation across the naf using both ascending and descending data from the envisat satellite mission acquired between 2003 and 2010 rather than rejecting incorrectly unwrapped areas in the interferograms we develop a new iterative unwrapping procedure for small baseline interferometric synthetic aperture radar insar processing that expands the spatial coverage our method corrects unwrapping errors iteratively and increases the robustness of the unwrapping procedure we remove long wavelength trends from the insar data using gnss observations and deconvolve the insar velocities into fault parallel motion profiles of fault parallel velocity reveal a systematic eastward decrease in fault slip rate from 30 mm yr 25 34 95 confidence interval ci to 21 mm yr 14 27 95 ci over a distance of 200 km direct offset measurements across the fault reveal fault creep along a 130 km section of the central naf with an average creep rate of 8 2 mm yr and a maximum creep rate of 14 2 mm yr located 30 km east of ismetpasa as fault creep is releasing only 30 40 of the long term strain in the shallow crust the fault is still capable of producing large damaging earthquakes in this region

1991 1992 gps measurements across the nepal himalaya in march 1991 35 control points were measured in the collision zone between the indian and asian plates using the global positioning system gps twenty eight points are located in the nepal himalaya and 7 in s and e tibet in october 1992 6 of the nepal points were remeasured together with 3 bedrock points in bihar state india 5 points in e tibet and one in urumchi the average wrms gps position repeatability between 1991 and 1992 improved from 8 mm to 5 mm in the north 16 mm to 7 mm in the east and 32 mm to 25 mm in the vertical components himalayan convergence rates of 20 mm yr may be resolved to 10 accuracy within 5 years with these uncertainties unless improved vertical measurement techniques are introduced many decades must elapse before regional secular vertical motions may be resolved the 1991 3 1992 8 measurements are consistent with geologically determined himalayan convergence rates of less than 20 mm year

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

insar slip rate determination on the altyn tagh fault northern tibet in the presence of topographically correlated atmospheric delays 1 the interseismic strain across the altyn tagh fault at 85 e has been measured using 59 interferograms from 26 ers 1 2 sar acquisitions on a single track for the period 1993 2000 using an atmospheric delay correction that scales linearly with height we estimate the left lateral strike slip motion to be 11 1 5 mm yr assuming no relative vertical motion and a 15 km fault locking depth this is in agreement with sparse gps measurements the atmospheric delay corrections agree well with coarse contemporaneous modelled weather data reinforcing the importance of correcting for atmospheric delays in insar studies of interseismic strain accumulation particularly in areas of high topographic relief that strongly correlate with the expected tectonic signal we also find that in addition to the tropospheric water vapour wet delay the hydrostatic dry delay makes a significant contribution to the signal

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

interferometric synthetic aperture radar insar atmospheric correction gps moderate resolution imaging spectroradiometer modis and insar integration atmospheric effects represent one of the major limitations of repeat pass interferometric synthetic aperture radar insar in this paper gps and moderate resolution imaging spectroradiometer modis data were integrated to provide regional water vapor fields with a spatial resolution of 1 km 1 km and a water vapor correction model based on the resultant water vapor fields was successfully incorporated into the jet propulsion laboratory california institute of technology roi pac software the advantage of this integration approach is that only one continuous gps station is required within a 2030 km 1354 km modis scene application to ers 2 repeat pass data over the los angeles southern california integrated gps network scign area shows that this integration approach not only helps discriminate geophysical signals from atmospheric artifacts but also reduces water vapor effects significantly which is of great interest to a wide community of geophysicists

structural evolution of the frontal fold thrust belt nw himalayas from sequential restoration of balanced cross sections and its hydrocarbon potential abstract two sedimentary lithotectonic zones are traditionally recognized in the northwestern himalayan frontal fold thrust belt in the nahan salient the lesser himalaya zone lhz and the sub himalaya zone shz the lhz is made up of a sequence of proterozoic to early cambrian rocks and the shz is made up of cenozoic rock sequences which were deposited subsequent to the india asia collision serial balanced cross sections show that the structural geometries become increasingly complex from independent ramp anticlines near the foreland through imbricate fan duplex to stacked up horses towards the hinterland sequential restoration suggests a structural evolution in which a foreland propagating in sequence thrusting event was followed by out of sequence thrusting in an approximately break back style during the out of sequence movement some of the ramps formed during in sequence thrusting were repeatedly reactivated leading to very complex structural geometries particularly in the lhz in such a complexly deformed terrain a rigorous structural modelling approach combined with a robust geochemical and geochronological database should be used to carry out calibrated petroleum system modelling and thus reduce exploration risk

geosciences of the himalaya karakoram tibet orogen the himalaya karakoram tibet orogen a product of india eurasia collision 55 ma back continues to attract global attention for its many geoscientific uniqueness this orogen is the most exciting natural laboratory to study continental dynamics and its evolution during past few decades phenomenal progresses have been made in uplift and extrusion models dynamic metamorphism magmatism climate tectonics interaction etc this thematic volume on the geosciences of the himalaya karakoram tibet consists of eighteen papers and two geosites in the first paper kirby and harkins correlated variation in slip rate along the kunlun fault with topography of the anyemaqen shan mountain at the eastern tibetan plateau their work indicates that fault terminations might be associated with crustal thickening of the plateau and demonstrate that the upper crustal deformation of the tibetan plateau to be pervasive and dispersed throughout the crustal blocks rather than localized along narrow fault zones robinson and pearson compiled an orogen wide correlation of footwall and hanging wall units of the ramgarh and munsiari thrust sheets they considered the ramgarh munsiari thrust sheet as a single major orogenscale fault system they hypothesized that the extensional shear within the south tibetan detachment was triggered possibly by slip transfer from the main central thrust into the ramgarh munsiari thrust during the miocene thakur reviewed the tectonics of the siwalik range of the himalaya he concluded in sequence deformation and critical taper mechanism acted in this terrain presuming the crustal channel flow model to be correct mukherjee estimated a viscosity of 10 10 pa s and a prandtl number of 10 10 for the greater himalayan crystallines moharana et al described the munsiari thrust from kumaun himalaya to consist of a core and a damage zone and described their structural geology in detail mukherjee described a basal detachment of extensional ductile shear from the base of the greater himalayan crystallines at bhagirathi section of the indian himalaya and explained it in terms of a shifting crustal channel flow ubiquitous backthrusts within this terrain were another new finding and were explained by southward subduction of eurasian plate below the indian plate based on balanced crosssection studies khanal and robinson estimated slip along major himalayan faults from the budhi gandhaki river section of central nepal sen and collins inferred dextral transpression and changing angle of convergence of the formation of the ladakh magmatic arc they also reported late eocene s type granite magmatism in its central part mathew et al discuss the tectonothermal evolution of the arunachal himalaya they obtained isothermal decompression for the greater himalayan sequence and isobaric cooling from the main central thrust region jayangondaperumal et al reevaluated co seismic slip of the himalayan frontal thrust the estimated shortening around the himalayan frontal thrust would lead a bigger earthquake in the western part of indian himalaya shah presented a geomorphologic study from kashmir basin in india identified faults from remote sensing studies and predicted a future earthquake of mw 7 6 srivastava et al s mukherjee department of earth sciences indian institute of technology bombay mumbai india e mail soumyajitm gmail com

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

a chronology of the little ice age in the tropical andes of bolivia 16 s and its implications for climate reconstruction dating moraines by lichenometry enabled us to reconstruct glacier recession in the bolivian andes since the little ice age maximum on the 15 proglacial margins studied we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries moraines were dated by performing statistical analysis of lichen measurements based on the extreme values theory like glaciers in many mid latitude mountain areas bolivian glaciers reached their maximal extent during the second half of the 17th century this glacier maximum coincides with the maunder minimum of solar irradiance by reconstructing the equilibrium line altitude and changes in mass balance we think the glacier maximum may be due to a 20 to 30 increase in precipitation and a 1 1 to 1 2 c decrease in temperature compared with present conditions in the early 18th century glaciers started to retreat at varying rates until the late 19th to early 20th century this trend was generally associated with decreasing accumulation rates by contrast glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity these results are consistent with observations made in the study region based on other proxies

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

dynamic ridges and valleys in a strike slip environment strike slip faults have long been known for characteristic near fault landforms such as offset rivers and strike parallel valleys in this study we use a landscape evolution model to investigate the longer term catchment wide landscape response to horizontal fault motion our results show that strike slip faulting induces a persistent state of disequilibrium in the modeled landscapes brought about by river lengthening along the fault alternating with abrupt shortening due to stream capture the models also predict that in some cases ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion we find that ridge migration happens when slip rate is slow enough and or soil creep and river incision are efficient enough that the landscape can respond to the disequilibrium brought about by strike slip motion regional rock uplift relative to baselevel also plays a role as topographic relief is required for ridge migration in models with faster horizontal slip rates stronger rocks or less efficient hillslope transport ridge mobility is limited or arrested despite the continuance of river lengthening and capture in these cases prominent steep fault facing facets form along well developed fault valleys comparison of landscapes adjacent to fast slipping 30 mm yr and slower slipping 1 mm yr or less strike slip faults in california usa reveals features that are consistent with model predictions our results highlight a potential suite of geomorphic signatures that can be used as indicators of horizontal crustal motion and geomorphic processes in strike slip settings even after river capture has diminished or erased apparent offset along the fault

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

middle and upper miocene cyclostratigraphy of downhole logs and short to long term astronomical cycles in carbonate production of the great bahama bank abstract ocean drilling program site 1006 is located in the santaren channel off the western slope of the great bahama bank downhole logs of sediment physical and chemical properties from hole 1006a contain repetitive alternations cycles which using the nannofossil and planktic foraminifer biostratigraphy as a guide to the sedimentation rate we show to be paced by the earth s climatic precession the formation microscanner resistivity image log shows a high resolution record of the sedimentary cycles and we use it to measure cycle thicknesses the record of cycle thickness contains long term cycles that repeat about every 400 kyr which we correlate to the 400 kyr cycles in orbital eccentricity this broad scale tuning results in an age profile for the core that is largely consistent with previously astronomically tuned biostratigraphic dates it has previously been established that the bahama bank produces and exports carbonate preferentially during sea level highstands each highstand produces one sedimentary cycle hence we infer that sea level also fluctuates with a mainly precessional periodicity although obliquity is also found in the log records we attribute the 400 kyr period in cycle thickness to eccentricity modulation of the amplitude of sea level fluctuations a high amplitude sea level rise will cause more carbonate to be generated and deposited than a low amplitude sea level rise

evidence for a great medieval earthquake 1100 a d in the central himalayas nepal the himalayan orogen has produced three thrust earthquakes with moment magnitude m w 7 8 to 8 5 during the past century yet no surface ruptures associated with these great earthquakes have been documented here we present paleoseismic evidence from east central nepal that since 700 a d a single earthquake ruptured the frontal thrust fault at 1100 a d with a surface displacement of 17 5 3 meters and a lateral extent and size that could have exceeded 240 kilometers and m w 8 8 respectively ruptures associated with m w

widespread seagrass meadows during the early miocene burdigalian in southwestern australia paralleled modern seagrass distributions abstract the trealla limestone which forms a veneer of foraminiferal rich limestone and covers over 4000 km2 of the tectonically stable southern carnarvon platform contains the oldest evidence for seagrass meadows known in western australia it belongs to lower tf1 letter stage based on larger benthic foraminifers of the burdigalian within interval 19 16 ma and is the only miocene unit on the platform the trealla limestone here is coeval to the deeper water lower part of the much thicker trealla limestone in the exmouth sub basin to the northwest a seagrass meadow depositional environment is indicated by most of the studied microfacies based on comparisons with modern sediment composition and foraminiferal assemblages found in innermost shelf seagrass banks between 23 s and 32 s on the present western australian coast some levels in the trealla limestone on the platform e g with abundant miliolid foraminifers and absence of coral debris probably were deposited in and around dense seagrass meadows similar to those present today in the metahaline 40 55 ppt salinity reaches of shark bay whereas other levels e g coral floatstone were deposited under normal marine conditions based on comparisons with modern carbonate sediment and biota in the region the biogenic composition of the trealla limestone on the platform suggests winter minimum sea surface temperatures within the range of 17 22 c the nullabor limestone in the eucla basin at 10 further south on the southern australian margin is similar at least in part in composition and age to the trealla limestone on the southern carnarvon platform both may have been deposited during a burdigalian sea level rise and during part of the miocene climate optimum recognized elsewhere sediment composition and foraminiferal assemblages including epiphytic types found in the trealla and nullabor limestones are similar to those in the modern seagrass banks of the region this suggests that seagrasses similar to the extensive posidonia and amphibolus stands which are dominant today between 25 s and 35 s along the western australian coast were widespread during the burdigalian

early holocene delevelling and deglaciation of the cumberland sound region baffin island arctic canada radiocarbon cosmogenic surface exposure and relative sea level data are used to examine deglaciation and glacioisostatic adjustment of cumberland sound and cumberland peninsula and southeastern baffin island in the context of a new model for the glacial history of the eastern canadian arctic over the last decade a multidisciplinary effort on easternmost baffin island has documented far greater ice expansion during the last glacial maximum than previously believed including low gradient glaciation in marine embayments coexisting with ice free or thin cold based ice on adjacent upland crystalline terrain this study documents that the cumberland sound region underwent about twice as much glacioisostatic movement during the last glacial maximum as shown in previous reconstructions however the loading impact of the laurentide ice sheet and local glaciation on adjacent cumberland peninsula was limited the mapped zero isoline on emergence shows that postglacial eustatic rise exceeded glacial isostatic uplift for much of the eastern peninsula a finding that is consistent with that of prior studies the center of loading and the major source of glacial ice for the entire cumberland sound region were foxe basin and western baffin island strandlines dated 10 500 and 8500 1 4 c yr b p show that slow deglaciation of cumberland sound was punctuated by at least two periods of faster grounding line retreat coastal southeastern cumberland peninsula was deglaciated before 9400 1 4 c yr b p and other areas surrounding cumberland sound were deglaciated after ca 9000 1 4 c yr b p these land areas experienced relatively slow glacial retreat and restrained rebound cosmogenic surface exposure ages on glacially scoured bedrock support the 1 4 c based inferred timing for deglaciation of the sound although inheritance of nuclides from prior exposure is evident in samples indicating limited bedrock erosion in many areas for central cumberland sound a rapid rise of relative sea level of 4 5 m 100 1 4 c yr 4 6 m 100 yr and a half life for crustal response of 720 1 4 c yr 1400 yr are consistent with those values obtained in other studies of isostatic adjustment around the edges of the former northern hemisphere ice sheets where lithospheric influences were relatively dominant

a cosmogenic 10be chronology for the local last glacial maximum and termination in the cordillera oriental southern peruvian andes implications for the tropical role in global climate abstract resolving patterns of tropical climate variability during and since the last glacial maximum lgm is fundamental to assessing the role of the tropics in global change both on ice age and sub millennial timescales here we present a10be moraine chronology from the cordillera carabaya 14 3 s a sub range of the cordillera oriental in southern peru covering the lgm and the first half of the last glacial termination additionally we recalculate existing 10be ages using a new tropical high altitude production rate in order to put our record into broader spatial context our results indicate that glaciers deposited a series of moraines during marine isotope stage 2 broadly synchronous with global glacier maxima but that maximum glacier extent may have occurred prior to stage 2 thereafter atmospheric warming drove widespread deglaciation of the cordillera carabaya a subsequent glacier resurgence culminated at 16 100 yrs followed by a second period of glacier recession together the observed deglaciation corresponds to heinrich stadial 1 hs1 18 000 14 600 yrs during which pluvial lakes on the adjacent peruvian bolivian altiplano rose to their highest levels of the late pleistocene as a consequence of southward displacement of the inter tropical convergence zone and intensification of the south american summer monsoon deglaciation in the cordillera carabaya also coincided with the retreat of higher latitude mountain glaciers in the southern hemisphere our findings suggest that hs1 was characterised by atmospheric warming and indicate that deglaciation of the southern peruvian andes was driven by rising temperatures despite increased precipitation recalculated 10be data from other tropical andean sites support this model finally we suggest that the broadly uniform response during the lgm and termination of the glaciers examined here involved equatorial pacific sea surface temperature anomalies and propose a framework for testing the viability of this conceptual model

seismotectonic perspectives on the himalayan arc and contiguous areas inferences from past and recent earthquakes abstract spread over countries including pakistan india nepal bhutan and china the himalayan mountain chain the most spectacular result of the indo eurasian plate collision is a locus of destructive earthquakes past earthquakes from this region have impacted vast swathes of frontal himalaya and stretches of alluvial plains south of the range front risk from future earthquakes has increased considering the burgeoning population and an ever expanding built environment in the region while considerable ambiguities exist on the locations ruptures and sizes of the earthquakes during the first half of the last millennium 1255 1344 and 1505 ce those during the latter half 1803 and 1833 ce are quite well documented all reported from the central himalayan segment comprising eastern nepal kumaun and garhwal while dormancy prevailed in the central segment in the intervening period the himalayan arc elsewhere witnessed three large great earthquakes in the last century namely 1905 kangra mw 7 8 1934 bihar nepal mw 8 2 and 1950 upper assam mw 8 6 the last one being the largest intra continental earthquake in the recorded history the april 25 gorkha nepal earthquake mw 7 8 located in the central seismic gap terminated the period of low level seismic productivity that followed the 1950 event the himalayan arc and its contiguous regions are now being investigated using various tools including paleoseismology quite understandably the interpretations and tectonic models do not always converge given the diverse quality and type of data the data from variously sized modern day earthquakes sourced in the diverse structural settings of the himalaya provide better constraints on the source properties of the himalayan earthquakes the source complexity and diversity is a striking point of interest for the post 1950 events and at least some of them seem to deviate from the generally accepted model of great ruptures on a shallow dipping detachment a prime example of such anomalies is the 2005 kashmir earthquake mw 7 6 sourced on an out of sequence thrust the sources of the 1991 uttarkashi mw 6 8 1999 chamoli mw 6 6 and the 2015 gorkha nepal mw 7 8 earthquakes all in the central himalayan segment are attributed to the ramp flat on the down dip part of the main himalayan thrust mht in contrast the 2011 sikkim mw 6 9 and the 2016 imphal mw 6 7 earthquakes are intraplate events sourced within the subducting slab source models of modern day earthquakes 1991 2016 discussed in this paper bring out this plurality of mechanisms expected of a complex subduction cum collisional boundary this review presents the status of current seismotectonic understanding of the himalaya from the analyses of significant earthquakes from the past as well as recent events with a focus on the central himalayan segment

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

glacier and lake level variations in west central europe over the last 3500 years on the basis of glacier and lake level records this paper attempts for the first time a comparison between high resolution palaeohydrological and palaeoglaciological data in west central europe over the past 3500 years a data set of tree ring width radiocarbon and archaeological data in addition to historical sources were used to reconstruct fluctuations of the great aletsch the gorner and the lower grindelwald glaciers in the swiss alps the three ice streams experienced nearly synchronous advances at c 1000 600 bc and ad 500 600 800 900 1100 1200 and 1300 1860 these glacier fluctuations show strong correspondence with lake level variations reconstructed in eastern france jura mountains and pre alps and on the swiss plateau this supports the hypothesis of climatically driven fluctuations historical data available for the period since ad 1550 reveal in detail various meteorological conditions behind the successive glacier advances however in agreement with the general trend shown by th

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

investigating topographic metrics to decipher structural model and morphotectonic evolution of the frontal siwalik ranges central himalaya nepal abstract the fold and thrust belt in the himalayan front is marked by the upliftment of the frontal outermost siwalik hills along the main frontal thrust mft these frontal ranges display distinct morphology with prominent curved stair stepped and overlapping segments in the central himalaya in this study we analyse the structural framework morphology growth and relative uplift rates of the frontal ranges in the central himalaya using various topographic metrics the results suggest that the frontal ranges are folds developed along six mft segments that have interacted to form the present day topography these segments are also overlapping in some areas thus resulting in stress partitioning we also identify a nw se trending pre existing tear fault in the region that forms barrier to the growth and propagation of the mft segments and the frontal ranges along it the uplift rates are generally lower on relatively older fault segments due to initiation of the younger overlapping faults it is supported by the results of the morphometric indices as the older and less active mft segments yield high mountain front sinuosity ratio 1 3 2 2 and valley floor width to height ratio 3 3 14 6 and low values of steepness index 0 2 0 8 and hypsometric integral 0 4 0 5 growing folds along the mft segments have resulted in the deflection of the narayani and the east rapti rivers we establish a model for the initiation and growth of various structural segments in the study area and the resultant drainage reorganisation

insar observations of strain accumulation and fault creep along the chaman fault system pakistan and afghanistan we use 2004 2011 envisat synthetic aperture radar imagery and insar time series methods to estimate the contemporary rates of strain accumulation in the chaman fault system in pakistan and afghanistan at 29 n we find long term slip rates of 16 2 3 mm yr for the ghazaband fault and of 8 3 1 mm yr for the chaman fault this makes the ghazaband fault one of the most hazardous faults of the plate boundary zone we further identify a 340 km long segment displaying aseismic surface creep along the chaman fault with maximum surface creep rate of 8 1 2 mm yr the observation that the chaman fault accommodates only 30 of the relative plate motion between india and eurasia implies that the remainder is accommodated south and east of the katawaz block microplate

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

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

kinematics of thrust sheets within transverse zones a structural and paleomagnetic investigation in the appalachian thrust belt of georgia and alabama deformation styles of orogenic belts change along strike across transverse zones tzs hence the kinematics of tzs is indispensable for three dimensional restoration of thrust belts we investigate the causes of deviation in strike of fold axes and fault surfaces in two tzs of the southern appalachians using structural cross sections and paleomagnetism in the rising fawn tz of georgia hanging wall lateral ramp folds yield paleomagnetic rotations and variation in magnitude of thrust translation plunge of folds differential slip and rotations are associated with lateral ramp geometry and along strike variation in the rheology and thickness of units that host lower and upper detachment levels in alabama the internal geometry strike and paleomagnetic rotations of the helena thrust sheet change across the anniston tz these differences resulted from movement of the helena thrust sheet over different footwall blocks and sub decollement basement graben structures and from differential slip along an oblique ramp rotations of thrust sheets within tzs occur where a thrust sheet was translated over 1 an oblique lateral ramp with contrasting rock strengths at lower and upper detachment levels 2 a transverse basement fault that separates contrasting basement structural domains and 3 intersections between frontal ramps and transverse structures because of the local causes of rotations in lateral structures paleomagnetic and structural analyses of tzs are necessary for understanding the kinematics and restoration of both single thrust sheets and large scale curves in thrust belts

evaluation of recent glacier recession in the cordillera blanca peru ad 1962 1999 spatial distribution of mass loss and climatic forcing we use a combination of aerial photogrammetry satellite imagery andd ifferential gps mapping to quantify the volume of ice lost between ad 1962 and 1999 from three glaciers on nevado queshque in the cordillera blanca peru 101s the largest averagedsurface lowering thinning occurredin the southwest aspect 22 m andthe least in the eastern aspect 5 m a heuristic sensitivity analysis indicates that 9 3 w m 2 was requiredto melt the total observedice loss andthis can be explainedby sensible heat transfer relatedto a temperature rise of 1 1c combinedwith a latent heat d ecrease relatedto a 0 14 g kg 1 increase in specific humidity a first difference analysis of temperature records from 29 stations in the cordillera blanca shows an average rising trend of 0 261c per decade over the 37 year interval more than adequate to supply the hypothesized sensible heat transfer a simple transmittivity model within a digital elevation model indicates solar radiation related to altered cloudiness was not a predominant climatic forcing the distribution of glacier area with altitude calculated with the digital terrain model explains the observed asymmetrical ice melt r 2005 elsevier ltd all rights reserved

a 2 300 year long annually resolved record of the south american summer monsoon from the peruvian andes decadal and centennial mean state changes in south american summer monsoon sasm precipitation during the last 2 300 years are detailed using an annually resolved authigenic calcite record of precipitation 18o from a varved lake in the central peruvian andes this unique sediment record shows that 18o peaked during the medieval climate anomaly mca from a d 900 to 1100 providing evidence that the sasm weakened considerably during this period minimum 18o values occurred during the little ice age lia between a d 1400 and 1820 reflecting a prolonged intensification of the sasm that was regionally synchronous after the lia 18o increased rapidly particularly during the current warm period cwp a d 1900 to present indicating a return to reduced sasm precipitation that was more abrupt and sustained than the onset of the mca diminished sasm precipitation during the mca and cwp tracks reconstructed northern hemisphere and north atlantic warming and a northward displacement of the intertropical convergence zone itcz over the atlantic and likely the pacific intensified sasm precipitation during the lia follows reconstructed northern hemisphere and north atlantic cooling el nino like warming in the pacific and a southward displacement of the itcz over both oceans these results suggest that sasm mean state changes are sensitive to itcz variability as mediated by western hemisphere tropical sea surface temperatures particularly in the atlantic continued northern hemisphere and north atlantic warming may therefore help perpetuate the recent reductions in sasm precipitation that characterize the last 100 years which would negatively impact andean water resources

temperature change is the major driver of late glacial and holocene glacier fluctuations in new zealand advance and retreat of temperate glaciers is largely controlled by changes in temperature and precipitation but the relative importance of these drivers is debated numerical modeling of a new zealand glacier reveals that temperature is the dominant control on glacier length we find that a glacial advance dated to ca 13 000 yr b p requires a cooling event of 3 4 c this mid latitude southern hemisphere cooling is similar in magnitude to the antarctic cold reversal in the vostok ice core record and likely to be a response to the same climate signal

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

systematic insar tropospheric phase delay corrections from global meteorological reanalysis data 1 despite remarkable successes achieved by differential insar estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated mainly because of the topography related atmospheric phase screen aps in areas of high relief empirical removal of the stratified component of the aps may lead to biased estimations of tectonic deformation rates here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with sar acquisitions using the era interim global meteorological model the modeled phase delay is integrated along vertical profiles at the era i grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel this approach is validated on unwrapped interferograms we show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

structural control on along strike variation in the seismicity of the northwest himalaya an overview of seismicity along the northwest himalaya exhibit along strike segmentation intricately controlled by the subsurface topographic ridges on the underthrusting indian plate as well by rift and nappe structures in the overriding wedge of the himalaya the segmentation exists for thrust dominated large magnitude earthquakes m 6 seated on the active detachment beneath the outer and lesser himalaya segmentation also prevails for moderate and small magnitude earthquakes concentrated in a narrow himalaya seismic belt hsb straddling northern lesser himalaya and southern higher himalaya numerical calculations of stress distribution favour that the degree of seismicity in the hsb is a good proxy to the presence of mid crustal ramp connecting the locked section of active detachment to aseismically slipping detachment beneath higher himalaya further gap or diffused pattern in the concentrated seismicity in the hsb in agreement with mapped high electrical conductive structure suggests ramp structure may be absent where underthrusting delhi hardwar ridge interacts with the himalaya arc in the nappe dominated tectonics the accommodation of the accumulating strains on the listric thrust faults produces increased frequency of moderate magnitude earthquakes and thereby possibly influences stress level on the detachment this may explain relatively less frequent occurrences of large earthquake in the kangra chamba region compared to that in the garhwal himalaya the low level seismicity in the simla region may also be influenced by the active kaurik chango rift in the higher himalaya as the former casts a stress shadow on the latter

interferometric synthetic aperture radar atmospheric correction using a gps based iterative tropospheric decomposition model abstract atmospheric effects represent one of the major error sources of repeat pass interferometric synthetic aperture radar insar and could mask actual displacements due to tectonic or volcanic deformation the tropospheric delays vary both vertically and laterally and can be considered as the sum of i a vertically stratified component highly correlated with topography and ii a turbulent component resulting from turbulent processes in the troposphere varying both in space and time in this paper we outline a framework to routinely use pointwise gps data to reduce tropospheric effects on satellite radar measurements an iterative tropospheric decomposition itd model is used and further developed to separate tropospheric stratified and turbulent signals and then generate high resolution correction maps for sar interferograms cross validation is employed to assess the performance of the itd model and act as an indicator to users of when and where correction is feasible tests were carried out to assess the impact of gps station spacing on the itd model insar correction performance which provides insights into the trade off between station spacing and the achievable accuracy the application of this framework to sentinel 1a interferograms over the southern california usa and southern england uk regions shows approximately 45 78 of noise reduction even with a sparse 50 80 km station spacing gps network and or with strong and non random tropospheric turbulence this is about a 50 greater improvement than previous methods it is believed that this framework could lead to a generic insar atmospheric correction model while incorporating continuous and global tropospheric delay datasets e g numerical weather models

active transfer faulting in the nw sub himalaya india observed by space borne topographic analyses abstract the results of surface morphology and insar analyses carried out along a nne ssw oriented 7 km long transfer fault are presented this structure actively accommodates differential motion across two blocks in the western sub himalayan belt of india segmentation is most pronounced in this sector of the accretionary wedge where minimal climatic variations and a three fold sub division kangra renetrant nahan salient dehradun reentrant are well recognized segmentation is here clearly elucidated by variation in surface topography geologic structure and recorded seismicity over the last few decades however the transition from one segment to another is poorly documented and understood this article primarily documents surface topography and drainage anomalies within the transition zone between the kangra reentrant and the nahan salient through the study of space imageries spanning nearly six decades i e early 1960 s to present geomorphic observations and insar analyses demonstrate that the segmentation is largely governed by lateral variation in geological structure deformation patterns and mechanical stratigraphy and accommodated by transverse movement along the transfer fault it should be noted that transfer faults commonly represent a privileged pathway for the major drainage and therefore surface manifestations are rarely preserved e g yamuna tear ganga tear etc a rare instance of preserved surface topography associated with the recent activity along the sabilpur transfer fault at the transition between the kangra renetrant and the nahan salient is documented here our investigations demonstrate that the sabilpur active fault saf accommodates differential tectonic convergence between the two blocks predominantly by left lateral strike slip kinematics with a component of uplift related to thrusting at hft

natural and anthropogenic variations in atmospheric mercury deposition during the holocene near quelccaya ice cap peru mercury hg is a toxic metal that is transported globally through the atmosphere the emission of hg from mineral reservoirs and subsequent recycling in surface reservoirs i e soil biomass ocean and atmosphere are fundamental to the modern global hg cycle yet past emissions from anthropogenic and natural sources are not fully constrained we use a sediment core from yanacocha a headwater lake in southeastern peru to study the anthropogenic and natural controls on atmospheric hg deposition during the holocene from 12 3 to 3 5 ka hg fluxes in the record are relatively constant mean 1 1 4 0 6 g m 2 a 1 n 189 past hg deposition does not correlate with changes in regional temperature and precipitation inferred from nearby paleoclimate records or with most large volcanic events that occurred regionally in the andean central volcanic zone 300 400 km from yanacocha and globally in b c 1450 3 4 ka hg fluxes abruptly increased and reached the holocene maximum flux 6 7 g m 2 a 1 in b c 1200 concurrent with a 100 year peak in fe and chalcophile metals as ag tl and the presence of framboidal pyrite continuously elevated hg fluxes from b c 1200 500 suggest a protracted mining dust source near yanacocha that is identical in timing to documented pre incan cinnabar mining in central peru during incan and colonial time a d 1450 1650 hg deposition remains elevated relative to background levels but lower relative to other hg records from sediment cores in central peru indicating a limited spatial extent of preindustrial hg emissions hg fluxes from a d 1980 to 2011 4 0 1 0 g m 2 a 1 n 5 are 3 0 1 5 times greater than pre anthropogenic fluxes and are similar to modern fluxes documented in remote lakes around the world

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

late quaternary systematic stream offsets caused by repeated large seismic events along the kunlun fault northern tibet abstract the kunlun fault is one of the largest strike slip faults in northern tibet china in this paper we focus upon the kusai lake kunlun pass segment of the fault to understand the geomorphic development of offset streams caused by repeated large seismic events based on tectono geomorphic analysis of high resolution satellite remote sensing images combined with field studies the results indicate that systematic left lateral stream offsets appear at various scales across the fault zone lateral offsets of small gullies caused by the 2001 m w 7 8 kunlun earthquake vary typically from 3 m to 6 m meanwhile streams with cumulative offsets of 10 m 25 30 m 50 70 m 250 300 m and 750 1400 m have resulted from repeated large seismic events during the late quaternary an average slip rate of 10 1 mm year has been estimated from the lateral stream offsets and 14 c ages of alluvial fan surfaces incised by the streams a three dimensional model showing tectono geomorphic features along a left lateral strike slip fault is also presented the kusai lake kunlun pass segment provides an opportunity to understand the relationship between geomorphic features produced by individual large seismic events and long term geomorphic development caused by repeated large seismic events along a major strike slip fault

seismic geomorphology and growth architecture of a miocene barrier reef browse basin nw australia abstract the cenozoic succession of browse basin is characterized by a carbonate system that developed from a non tropical ramp in eocene lower miocene times to a tropical rimmed platform in the middle miocene the evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle miocene tropical reef system the first reef structures developed during the early middle miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction subsequently they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km the barrier reef itself comprises three distinct ridges separated by progradational steps the second and third step are separated by a karstified horizon which is interpreted to represent the global sea level fall shortly before the serravallian tortonian boundary the following third ridge formed in a slightly downstepped position during the sea level lowstand and initial transgressive phase further sea level rise during the early tortonian first drowned the barrier reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior the similar evolution of the browse basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea level changes relatively large subsidence rates in the study area possibly augmented the eustatic sea level rise in the tortonian and hence contributed to the drowning of the reef system however the initiation and final demise of the reef system was also governed by global and regional climate variations the first seismically defined reefs developed simultaneous to a maximum in the transport capacity of the indonesian throughflow which brings warm low salinity waters to the north west shelf reef drowning followed the restriction of this seaway close to the middle to early miocene boundary this near closure of the indonesian seaway possibly led to a regional amplification of the global middle to late miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea level

earthquake recurrence and rupture dynamics of himalayan frontal thrust india the black mango fault is a structural discontinuity that transforms motion between two segments of the active himalayan frontal thrust hft in northwestern india the black mango fault displays evidence of two large surface rupture earthquakes during the past 650 years subsequent to 1294 a d and 1423 a d and possibly another rupture at about 260 a d displacement during the last two earthquakes was at minimum 4 6 meters and 2 4 to 4 0 meters respectively and possibly larger for the 260 a d event abandoned terraces of the adjacent markanda river record uplift due to slip on the underlying hft of 4 8 0 9 millimeters per year or greater since the mid holocene the uplift rate is equivalent to rates of fault slip and crustal shortening of 9 6 3 5 7 0 millimeters per year and 8 4 3 6 7 3 millimeters per year respectively when it is assumed that the hft dips 30 10

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

sedimentary basins formed and carried piggyback on active thrust sheets small sedimentary basins that formed on the apennine southern margin of the po basin complex northern italy have been studied using borehole and seismic reflection information and their evolution can be dated using the largely marine biostratigraphy of the miocene to quaternary sediments these studies show that the basins formed and were filled while being carried on moving thrust sheets and they are therefore named piggyback basins each of these basins corresponds to the active phase of a different thrust front ramp on the pyrenean northern margin of the ebro basin complex northern spain similar piggyback basins formed between eocene and mid miocene time they have since been uplifted and eroded and may therefore be studied in outcrop in northern spain much of the basin fill sediment was deposited in nonmarine environments

palaeoprecipitation record using o isotope studies of the himalayan foreland basin sediments nw india abstract the himalayan foreland basin sediments were deposited during a crucial time period in the himalayan orogeny this period in the tertiary has become major focus of research because of the large scale uplift of the himalayan range which has greatly modified the climate of the asian continent the present south asian monsoonal climate is believed to be a consequence of himalayan uplift during this period also the himalayan orogeny comprises a major regional tectonic event of the earth hence the study of these himalayan foreland basin sediments are not only significant in revealing the palaeoclimatic history of the asian continent but also paves a way for understanding of the effects of himalayan orogeny on global climate here we report a palaeoprecipitation history of the ramnagar sub basin since miocene times and its regional correlation to other sub basins of the himalayan mountain belt an attempt has been made to use oxygen isotope ratios of pedogenic carbonates in siwalik palaeosols as proxy palaeo recorders to deduce the palaeoclimatic history of the jammu region in the ramnagar sub basin for the first time a total of 141 pedogenic carbonates have been analyzed from three siwalik sections covering a lateral stretch of approximately 40 50km along strike the 18 o values vary from 12 31 to 5 89 and when plotted against age indicate that 18 o values on average become 2 enriched from the oldest to the youngest analyzed sediments except for largely depleted 18 o values around 10 ma 5 ma and 1 8 ma this 2 increase in calculated 18 o values could have been possible by an 3 c increase in mean annual air temperature conversely the largely negative 18 o values indicate periods of intense rainfall or stronger monsoonal conditions an increase of 2 6 in 18 o values has been found from the 10 ma rainfall event to that at 1 8 ma which indicates a reduction of 173 mm in rainfall intensity and amount hence precipitation reconstructions indicate a progressive increase in aridity from 12 ma to recent excluding a short term increases in rainfall or monsoon intensity at around 10 ma 5 ma and 1 8 ma this pattern of palaeoprecipitation change is similar to the changes documented in other sub basins of the himalayan mountain range further monsoon intensification at around 10 ma 5 ma and 1 8 ma is also observable in various other proxy records thereby suggesting the role of significant regional tectonism in the evolution and intensification of the present south asian monsoon climate our results indicate that from the mid miocene to recent except for the periods of largely depleted 18 o values the average 18 o value increased by 2 the general increase in average 18 o values from lower to upper siwalik sediments can be explained by changes in both continentality and latitude of the moisture source it seems likely that this long term increase in 18 o values was due to the uplift of the himalayas and the tibetan plateau in the north which acted as a barrier to the passage of airmasses from central asia in the north thereupon with time restricting the source of airmasses to the south from the indian ocean

extrusion vs duplexing models of himalayan mountain building 1 discovery of the pabbar thrust confirms duplex dominated growth of the northwestern indian himalaya since mid miocene ongoing himalayan growth is generally thought to be dominated by duplexing and or extrusion processes these models may be tested by reconstructing himalayan fold thrust belt growth since the middle miocene however our knowledge of basic structural geometry remains too fragmentary to resolve the issue even in areas with rich stratigraphic diversity such as the northwestern indian himalaya in this region a primary outstanding question involves the uncertain relationship of the berinag thrust and the tons thrust structures with displacements of 80 km and 40 km respectively the uncertain geometry and kinematics allow for the complete range of duplexing or extrusion processes for the integrated kinematic history since the middle miocene to address this issue field mapping and kinematic analysis were performed to reconstruct the deformation of the lesser himalayan sequence in the northwest indian himalaya our results reveal a new discovery a 450 m thick top to southwest shear zone termed the pabbar thrust the pabbar thrust placed the outer lesser himalayan sequence the tons thrust hanging wall directly on the berinag group the berinag thrust hanging wall this discovery requires that the berinag thrust and tons thrust are in fact the same structure and discrete duplexing processes dominated growth of the northwest indian himalaya for the past 10 15 million years along strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the india west nepal border where prior work suggests that structures are continuous but stratigraphy does not match

recalibration of the yellow rhizocarpon growth curve in the cordillera blanca peru and implications for lia chronology abstract a new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the cordillera blanca peru during the little ice age lia our results reveal that an early lia glacial advance occurred around ad 1330 29 however a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers hence this second glacial stage dated from ad 1630 27 is considered as the lia maximum glacial advance in the cordillera blanca during the 17th 18th centuries at least three glacial advances were recorded synchronously for the different glaciers ad 1670 24 1730 21 and 1760 19 the moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18 in the total length of the glacier from the lia maximum extent to the beginning of the 20th century the 24 glaciers have retreated a distance of about 1000 m corresponding to a reduction of 30 in their length this rate is comparable to that observed during the 20th century estimates of palaeo equilibrium line altitudes show an increase in altitude of about 100 m from the lia maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century because long time series are not available for precipitation and temperature this glacial retreat is difficult to explain by past climate changes however there is a fair correspondence between changes in glacier length and the 18 o recorded in the quelccaya ice core at a century timescale our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet lia to the drier conditions of today finally a remarkable synchronicity is observed with glacial variations in bolivia suggesting a common regional climatic pattern during the lia

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

integration of gamma ray spectrometry magnetic susceptibility and calcareous nannofossils for interpreting environmental perturbations an example from the jenkyns event lower toarcian from south iberian palaeomargin median subbetic se spain abstract the pliensbachian toarcian sedimentary rocks of the median subbetic betic cordillera se spain were deposited in the south iberian palaeomargin under hemipelagic conditions in the arroyo mingarron section se spain these deposits are composed by a marl and marl and limestone alternation with abundant radiolarians the application of magnetic susceptibility and gamma ray spectrometry to these deposits allows to interpret environmental changes related to the fluctuations in the continental influx of terrigenous and phytodetritus to a hemipelagic setting in the south iberian palaeomargin the increase of terrigenous input was coincident with the negative carbon isotopic excursion cie at the base of the njt6 nannofossil zone that correlates with the jenkyns event the increase of th and k content is related to enhanced detrital input especially oxides and silicates including clay minerals the gamma ray signal derived from u is comparatively low with respect to k and th nevertheless the u content shows an increase in the base of njt6 nannofossil zone that indicates a relative increase of organic matter content coincident with the jenkyns event changes in the calcareous nannofossil assemblages at the beginning of the njt6a nannofossil subzone and in particular the sharp decrease in abundance of the species mitrolitus jansae during the negative cie of the jenkyns event are interpreted as related to sea water stratification and a probable poor oxygenation making inhospitable the deep photic zone during this event

field gamma ray patterns and stratigraphic reinterpretation of offshore well log data from lower jurassic organic rich units of the lusitanian basin portugal abstract lower jurassic sinemurian pliensbachian successions cropping out in onshore areas of the lusitanian basin provide detailed information of three well characterized organic rich intervals i the unit f from the coimbra formation ii the polvoeira member of the agua de madeiros formation and the iii marly limestones with organic rich facies mlof member of the vale das fontes formation despite decades of research these source rocks have not yet been properly identified and characterized in terms of extension and thickness in the basin s offshore this paper compares detailed gamma ray gr profiles from onshore outcrops coimbra montemor o velho figueira da foz monte real sao pedro de moel and peniche regions with seven offshore wells our objective is to recognise lower jurassic organic rich intervals in offshore areas of the basin highlighting their lateral extension and improving the overall stratigraphic definition of the lower jurassic in the lusitanian basin gr field measurements indicate that the highest gr values and u contents are consistently observed in the organic rich intervals reaching up to 134 api and 9 0 ppm of u in contrast the lowest api and u contents were determined in dominantly calcareous units ranging between 5 34 api and 0 1 1 4 ppm respectively wireline gamma ray logs show a good correspondence between field patterns and offshore well logs recognizing the organic rich intervals in offshore areas the highest gr values are interpreted to be linked with the 2nd and 3rd order maximum flooding intervals previously recognised in the sinemurian pliensbachian successions in the western iberian margin detailed gr maps linked to maximum flooding intervals highlight the variation of the vertical and lateral distributions of the organic rich units in offshore areas of the lusitanian basin

late holocene fluctuations of qori kalis outlet glacier quelccaya ice cap peruvian andes geology v 42 p 347 350 1 doi 10 1130 g35245 1 there was an error in determining the number of 10be atoms per gram of quartz for samples js 09 20 24 14 and 15 and thus the calculated 10be ages all usage of these samples and their ages has been corrected in the gsa data repository

crustal structure beneath the sub himalayan fold thrust belt kangra recess northwest india from seismic reflection profiling implications for late paleoproterozoic orogenesis and modern earthquake hazard abstract most compressional orogens include salients and recesses along their strike the age and origin of which can be hard to ascertain in the kangra recess in the trace of the main boundary thrust mbt the largest such recess within the active himalayan orogen the sub himalayan sedimentary fold thrust belt increases in width to as much as 90 km the kangra basin but narrows to as little as 10 km in the adjoining nahan salient of the mbt the subathu basin to the southeast new seismic reflection profiling places the himalayan decollement at 6 8 km depth above thin but reflective meso to neoproterozoic vindhyan lesser himalayan series equivalent strata these data show that the vindhyan sedimentary rocks are thinner in the kangra recess than further southeast allowing the hypothesis that the width of the lesser himalayan thrust belt and the existence of the kangra recess could be related to the pre deformation basin thickness this hypothesis obviates the need for control of the kangra recess by a lateral ramp in the main himalayan thrust so making it more likely that the kangra segment could rupture as part of an earthquake far larger than the devastating 1905 m 7 8 kangra earthquake below the proterozoic sedimentary rocks our reflection data show a west southwest dipping reflective fabric spanning a 30 km crustal thickness which we infer corresponds to a widespread ulleri wangtu orogenic event at c 1850 ma affecting a pre tethyan indian continental margin thickening the basement by c 20 the deepest 10 km of this 50 km thick crust shows a more horizontal arguably younger reflectivity though the moho is not clearly marked by strong reflectors

facies architecture of a late jurassic carbonate ramp the korallenoolith of the lower saxony basin the sedimentary succession of a late jurassic oxfordian to basal kimmeridgian carbonate ramp is described and interpreted the study area is located in the central part of the lower saxony basin in nw germany which forms part of the central european basin eight well exposed and undeformed sections of the study area suntel area wesergebirge and eastern part of the wiehengebirge provide detailed information about lithofacies and lateral thickness variations biostratigraphically the age of these sediments is poorly constrained twenty microfacies types are recognized that can be grouped into seven facies associations a strongly bioturbated marlstones deposited near storm wave base swb b foraminifera rich wackestones c wackestones and floatstones with biostromes and d bioclastic limestones deposited between swb and fair weather wave base fwwb e oolitic and iron oolitic limestones and f siliciclastic sediments deposited above fwwb and g lagoonal deposits these facies associations characterize a storm dominated shallow mixed carbonate siliciclastic ramp based on facies changes quartz content and gamma ray logs the korallenoolith formation can be subdivided into a lower carbonate dominated and an upper siliciclastic dominated part build up by different scales of small to large scale deepening and shallowing upward cycles a preliminary correlation of measured outcrops of this formation is presented

rates of deglaciation during the last glaciation and holocene in the cordillera vilcanota quelccaya ice cap region southeastern peru abstract moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the huancane valley on the west side of the quelccaya ice cap and the upismayo valley on the northwest side of the cordillera vilcanota the fastest rates of deglaciation 39 10 5 to 114 10 5 km3 yr 1 and 112 10 5 to 247 10 5 km3 yr 1 for each valley respectively were calculated for the most recent paleoglaciers corresponding to the last few centuries these results are consistent with observations in the venezuelan andes showing high rates of deglaciation since the little ice age these rates also fall within the range of 20th century rates of deglaciation measured on the quelccaya ice cap 29 10 5 to 220 10 5 km3 yr 1 brecher and thompson 1993 thompson 2000 these results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century equilibrium line altitude ela depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the quelccaya ice cap and 170 m for the cordillera vilcanota maximum ela depressions are lower than previously published

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia

glacier fluctuations in extratropical south america during the past 1000 years article i nfo this paper presents an updated extensive review of glacier fluctuations during the past 1000 years in the extratropical andes of south america between ca 17 and 55 s given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range regional accounts are given for the desert andes 17 31 s the andes of central chile and argentina 31 36 s and the north 36 45 s and south 45 55 s patagonian andes the techniques dating limitations and interpretations of the glacier records along this transect are also discussed information on glacier fluctuations in the desert andes is limited to the 20th century documentation on past glacier variations is more abundant in the central chilean argentinean andes but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited most records indicate that glaciers were generally more extensive prior to the 20th century with dates of maximum expansion ranging from the 16th to the 19th centuries the number and extent of glaciers increase significantly in the patagonian region where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area for some patagonian glaciers maximum little ice age lia or post lia advances have been precisely dated by dendro geomorphological determinations or in situ measurements however for most sites the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum lia expansion identified in most areas between the 16th and 19th centuries evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium these events were generally less extensive than the lia maximum pulses despite the occurrence of several post lia readvances over the past 100 110 years most areas in the andes of extratropical south america have experienced a general pattern of glacier recession and significant ice mass losses the differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and or the dating techniques used in each case together with the varying dominance of precipitation temperature and other climatic and non climatic factors on glacier mass balance and glacier dynamics these differences indicate that the late holocene glacier history of southern south america is more complex than commonly assumed the evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed well dated records of glacier fluctuations

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

sedimentology of plio pleistocene late orogenic deposits associated with intraplate subduction the upper siwalik subgroup of a part of panjab sub himalaya india abstract this study provides a detailed sedimentologic documentation of the lithofacies cyclicity sandbody geometry palaeoflow variability and depositional models of the youngest late orogenic deposits of the siwalik molasse these deposits represent one of the important examples of sedimentation in the zone of intraplate subduction of the himalayan collision belt lithofacies analysis has resulted in the recognition of four conglomerate facies massive matrix supported conglomerate crudely stratified conglomerate trough cross stratified conglomerate planar cross stratified conglomerate five sandstone facies erosional scour and fill pebbly sandstone medium to coarse grained sandstone fine to medium grained ripple drift laminated sandstone bioturbated calcareous fine grained sandstone and six mudstone facies parallel laminated bioturbated mudstone reddish brown massive mudstone variegated mudstone bluish grey to violet mudstone buff coloured mudstone pebbly mudstone in addition hard calcareous layers have been recognised as a separate facies state the deduced cyclic sequences of the tatrot and pinjor formations of the upper siwalik subgroup show fining upward characters from cs coarse sandstone to ms mudstone through fs fine sandstone and ss alternations of sandstone and siltstone the sandbodies of the tatrot and pinjor formations reveal a sheet like geometry and an internal dominance of inter storey scour surfaces the presence of intraformational debris mud drapes reactivation surfaces and a general fining upward of grain size indicates fluctuating hydrodynamic conditions with frequent channel abandonment and re occupation resulting in net vertical aggradation the dominant style of sedimentation both in the channel and overbank facies is through vertical aggradation data on the palaeoflow variability indicates that the upper siwalik subgroup can be subdivided into four and three sediment vector sequences in the khetpurali and ghaggar sections respectively the palaeodrainage pattern in the khetpurali section reveals a major influence of northerly drainage twice in the stratigraphic column the high percentage of overbank deposits in individual cycles the lack of vegetal debris organic poor palaeosol units and abundant syngenetic caco 3 activity warrant comparison with the modern anastomosed deposits described from arid central australia some intervals of the sequences are comparable to the sublinear subparallel drainages with local anastomosis of the modern piedmont zone of the himalaya the higher parts of the stratigraphic column indicate proximal braided stream deposits and finally proximal alluvial fan deposits syntectonic activity has controlled the deposition of the megasequences which are a response to episodicity in the activity of basin margin basin margin or basin margin intrabasin structures the vertical stacking of the siwalik megasequences appears to be episodic in character

geochemical events documented in inorganic carbon isotopes abstract screening of sampling and analytical data is crucial for the detection of real global shifts in marine 13c against the noise of diagenesis the real global shifts of 13c are of two types 1 long term secular shifts caused by changes in the fractional burial of organic carbon and 2 transient shifts caused by abrupt changes of biological productivity in the surface photic zone both are applicable to stratigraphic correlation but differ in their application to modelling of changes in oceanographic or atmospheric composition a recent compilation found 34 carbon isotope events in the phanerozoic and neoproterozoic equally distributed among positive and negative shifts this in itself attests to a variety of proximate causes of the shifts

the pinjaur dun intermontane longitudinal valley and associated active mountain fronts nw himalaya tectonic geomorphology and morphotectonic evolution abstract the himalayan orogenic belt formed as a result of collision tectonic processes shows abundant evidence of neotectonic activity active tectonics and the occurrence of historical earthquakes its frontal deformation zone is characterized in some segments by intermontane longitudinal valleys duns such frontal segments of the himalaya are marked by the occurrence of multiple mountain fronts in one such segment of the foothills of the nw himalaya the pinjaur dun is developed and marked by three mountain fronts mf1a and mf1b associated with the southernmost himalayan frontal thrust hft mf2 associated with the sirsa fault and mf3 associated with the barsar thrust along the southern margin of the relatively higher main part of the sub himalaya geomorphic responses to the tectonic activity of these and related structural features have been analyzed through the use of geomorphic indices drainage density stream longitudinal profiles drainage anomalies and hypsometric analysis also fault and fold growth and their expression on landform development was studied using a combination of surface profiles and field observations the values of valley floor width to height ratio v f for valleys associated with mf1 ranged between 0 07 and 0 74 and for valleys associated with mf2 ranged from 1 02 5 12 v f for the four major valleys associated with mf1b ranged from 1 1 1 7 the asymmetry factor for 26 drainage basins related to mf1a indicate these have developed under the influence of a transverse structure these results taken together with those obtained from the hack profiles and sl index values hypsometry drainage density and drainage anomalies suggest that the faults associated with the mountain fronts and related structures are active active tectonics and neotectonic activity have led to the formation of four surfaces in the pinjaur dun in addition an important drainage divide separating the sirsa and jhajara drainage networks also developed in the intermontane valley surface profile analysis helped in deciphering the growth history of the fault bend fold structures of the outermost siwalik hills the effects of tectonic activity on the proximal part of the indo gangetic plains are interpreted from the remarkable river deflections that are aligned linearly over tens of kilometers in a zone about 10 km south of the hft based on these integrated structural and tectonic geomorphological approaches a morphotectonic evolutionary model of the dun has been proposed this model highlights the role of uplift and growth history of the fault bend fold structures of the outermost siwalik hills on i the depositional landforms and drainage development of the pinjaur dun and ii valley development of the outermost siwalik hills importantly this study postulates the formation of an incipient mountain front that is evolving ahead of the hft and the outermost siwalik hills in the indo gangetic plains

recent fold growth and drainage development the janauri and chandigarh anticlines in the siwalik foothills northwest india the active growth of a fault and thrust belt in frontal zones of himalaya is a prominent topographical feature extending 2500 km from assam to pakistan in this paper kinematical analysis of frontal anticlines and spatial mapping of active faults based on geomorphological features such as drainage pattern development fault scarps and uplifted quaternary alluvial fans are presented we analyse the geomorphic and hydrographic expressions of the chandigarh and the janauri active anticlines in the nw india siwaliks to investigate the morphological scenario during the folding process we used spatial imagery geomorphometric parameters extracted from digital elevation models and fieldwork folding between the beas and sutlej rivers gives clear geomorphological evidence of recent fold growth presumably driven by movements of blind thrust faults structural style within the janauri and chandigarh anticlines is highly variable fault propagation folds pop up structures and transfer faults the approach presented here involves analysis of topography and drainage incision of selected landforms to detect growth of active anticlines and transfer faults landforms that indicate active folding above a southwest dipping frontal thrust and a northeast dipping back thrust are described along strike differences in ridge morphology are measured to describe the interaction of river channel patterns with folds and thrust faults and to define history of anticline growth the evolution of the apparently continuous janauri ridge has occurred by the coalescence of independent segments growing towards each other by contrast systematic drainage basin asymmetry shows that the chandigarh anticline ridge has propagated laterally from nw to se