chemical and mechanical processes during burial diagenesis of chalk an interpretation based on specific surface data of deep sea sediments burial diagenesis of chalk is a combination of mechanical compaction and chemical recrystallization as well as cementation we have predicted the characteristic trends in specific surface resulting from these processes the specific surface is normally measured by nitrogen adsorption but is here measured by image analysis of scanning electron micrographs this method concentrates on the micritic matrix alone deep sea sediments are ideally suited to the study of burial diagenesis because they accumulate in a relatively conservative tectonic setting we used material from the ontong java plateau in the pacific where a 1 km thick package of chalk facies sediments accumulated from the cretaceous to the present in the upper 200 300 m the sediment is unconsolidated carbonate ooze throughout this depth interval compaction is the principal porosity reducing agent but recrystallization has an equal or larger influence on the textural development in the chalk interval below compaction is not the only porosity reducing agent but it has a larger influence on texture than concurrent recrystallization below 850 m grain bridging cementation becomes important resulting in a lithified limestone below 1100 m this interpretation is based on specific surface data alone and modifies current diagenetic models

seismic pore space compressibility and gassmann s relation the pore space compressibility of a rock provides a robust model independent descriptor of porosity and pore fluid effects on effective moduli the pore space compressibility is also the direct physical link between the dry and fluid saturated moduli and is therefore the basis of gassmann s equation for fluid substitution for a fixed porosity an increase in pore space compressibility increases the sensitivity of the modulus to fluid substitution two simple techniques based on pore compressibility are presented for graphically applying gassmann s relation for fluid substitution in the first method the pore compressibility is simply reweighted with a factor that depends only on the ratio of fluid to mineral bulk modulus in the second technique the rock moduli are rescaled using the reuss average which again depends only on the fluid and mineral moduli

stream length gradient hotspot and cluster analysis sl hca to fine tune the detection and interpretation of knickzones on longitudinal profiles abstract this work presents a new approach for fine tuning the analysis of stream longitudinal profiles we show that applying hotspot and cluster analysis hca based on the getis ord gi statistic to the stream length gradient sl index improves the visualization of anomalous values assisting in the identification of tectonic structures and large landslides high positive gi values indicate the clustering of sl anomalies hotspots and mirror the occurrence of knickzones on the stream long profiles we applied this methodology to a mountainous sector of the eastern emilia romagna region in northern italy remote sensing and field surveys conducted on hotspot sites indicate that large landslides are the main process associated to over steepened long profile segments along streams connected to the valley slopes along stream changes in bedrock resistance accounts for the main anomalies within sectors where hillslopes and valley floors are disconnected we demonstrate that specific relationships between geometry and intensity of sl hotspots are indicative of the process responsible for the knickzone formation and in particular that tectonic structures generally provide the longest and highest anomalies the results of this work suggest that sl hca maps are more advantageous for detecting and interpreting knickzones compared with traditional sl maps since i they need less input data to be computed thus making them useful to investigate regions poorly covered by detailed geological data and or where field surveys are difficult to be carried out and ii the hotspot geometry can help discriminate the knickzones attributable to gravitational mass movements from litho structural ones

ava analysis and interpretation of a carbonate reservoir northwest java basin indonesia a detailed analysis is performed of amplitude variation with angle ava observations in six common midpoint gathers with reflection points that are over and beside carbonate reefs in the parigi formation in the northwest java basin both empirical analysis and full wavefield modeling of the ava data suggest that the presence of gas affects ava by reducing the bulk density of the reservoir decreasing of the overburden vp vs ratio and by local attenuation caused by gas sieving through the overlying sediments the slopes of ava curves for reflections from the top of the parigi are negative for brine saturation and strongly positive for gas saturation

significance of europium anomalies in silicate melts and crystal melt equilibria a re evaluation although europium speciation in silicate melts partly reflects prevailing oxygen fugacities melt composition and structure play the major role in determining eu2 eu3 ratios and europium partitioning into mineral phases experimental evidence by different investigators on the magnitude of the compositional effect on eu2 eu3 provides consistent results only if account is taken of the oxygen buffer system employed in the experiments the medium dependent reduction of europium can be understood in terms of the preferential stabilization of eu2 by a strong aluminosilicate complex in the melt phase and to a much lesser degree by metasilicate complexes the stability of these complexes increases as the field strength of the associated cation species decreases hence eu2 aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt the influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during anhydrous anatexis in high grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

static and dynamic effective stress coefficient of chalk deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it the effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction effective stress coefficient of the pore pressure the effective stress coefficient is thus relevant for studying reservoir deformation and for evaluating 4d seismic for the correct pore pressure prediction the static effective stress coefficient n is estimated from mechanical tests and is highly relevant for effective stress prediction because it is directly related to mechanical strain in the elastic stress regime the corresponding dynamic effective stress coefficient is easy to estimate from density and velocity of acoustic elastic waves we studied n and of chalk from the reservoir zone of the valhall field north sea and found that n and vary with differential stress overburden stress pore pressure for valhall reservoir chalk with 40 porosity ranges between 0 98 and 0 85 and decreases by 10 if the differential stress is increased by 25 mpa in contrast for chalk with 15 porosity from the same reservoir ranges between 0 85 and 0 70 and decreases by 5 due to a similar increase in differential stress our data indicate that measured from sonic velocity data falls in the same range as for n and that n is always below unity stress dependent behavior of n is similar decrease with increasing differential stress to that of during elastic deformation caused by pore pressure buildup for example during waterflooding by contrast during the increase in differential stress as in the case of pore pressure depletion due to production n increases with stress while decreases

stream analysis of small drainage basins in an ancient landform korean peninsula abstract much of the topography of korea is ancient but many quaternary fault outcrops and marine terraces have been observed in the southeastern part of the korean peninsula sufficient evidence of a quaternary fault is lacking in the geological features of the commercially developed jukbyun and uljin areas knickpoints that develop on streams can be formed by tectonic activity such as faulting and folding or can result simply from the differential erosion rates of bedrock in this study we investigated the relationship between stream steepness and faults in the jukbyun area stream profile analyses of the bugu and namdae basins were performed using a digital elevation model to estimate quaternary tectonic movements stream parameters obtained from analysis of the longitudinal stream profiles of the bugu and namdae drainage basins in the northeastern part of the korean peninsula indicated neotectonic movement thirty of the thirty nine knickpoints that developed in the downstream areas of the fluvial channels corresponded to fault zones it is thought that fault activity results in knickpoints in river systems the normalized relative slope k sn value 54 9 of the bs1 stream in the bugu drainage basin was higher than that 28 8 36 3 of the other streams in both basins despite a similar lithology to ns1 and ns2 therefore we concluded that stream steepness might be a result of tectonic forcing rather than a product of rock strength in the study area and that stream parameters could provide indirect evidence of quaternary tectonics in ancient landforms

3 d spherical shell modeling of mantle flow and its implication for global tectogenesis in order to study the relationship between mantle flow and global tectogenesis we present a 3 d spherical shell model with incompressible newtonian fluid medium to simulate mantle flow which fits the global tectogenesis quite well the governing equations are derived in spherical coordinates both the thermal buoyancy force and the self gravitation are taken into account the velocity and pressure coupled with temperature are computed using the finite element method with a punitive factor the results show that the lithosphere as the boundary layer of the earth s thermodynamic system moves with the entire mantle both its horizontal and vertical movements are the results of the earth s thermal motion the orogenesis occurs not only in the collision zones at the plates boundaries but also occurs within the plates if the core mantle boundary is impermeable and the viscosity of the lower mantle is considerable the vertical movement is mostly confined to the upper mantle the directions of the asthenospheric movements are not fully consistent with those of the lithospheric movements the depths of spreading movements beneath all ridges are less than 220 km in some regions the shear stresses acting on the base of the lithosphere by the asthenosphere are the main driving force but in other regions the shear stresses are the resisting force

how burial diagenesis of chalk sediments controls sonic velocity and porosity based on p wave velocity and density data a new elastic model for chalk sediments is established the model allows the construction of a series of isoframe if curves each representing a constant part of the mineral phase contributing to the solid frame the if curves can be related to the progress of burial diagenesis of chalk which is revised as follows newly deposited carbonate ooze and mixed sediments range in porosity from 60 to 80 depending on the prevalence of hollow microfossils despite the high porosity these sediments are not in suspension as reflected in ifs of 0 1 or higher upon burial the sediments lose porosity by mechanical compaction and concurrently the calcite particles recrystallize into progressively more equant shapes high compaction rates may keep the particles in relative motion whereas low compaction rates allow the formation of contact cement whereby if increases and chalk forms rock mechanical tests show that when compaction requires more than in situ stress porosity reduction is arrested during subsequent burial crystals and pores grow in size as a consequence of the continuing recrystallization the lack of porosity loss during this process testifies to the absence of chemical compaction by calcite calcite pressure dissolution as well as to the porosity preserving effect of contact cementation at sufficient burial stress the presence of stylolites indicates that pressure dissolution takes place between calcite and silicates and depending on pore water chemistry and temperature pore filling cementation may occur over a relatively short depth interval limestone and mixed sedimentary rock form and porosity may be reduced to less than 20 isoframe increases to more than 0 6 in hydrocarbon reservoirs in north sea chalk relatively high porosity and high ifs are found the reason may be that recrystallization and porosity preserving contact cementation progress whereas pore filling cementation is small probably because pressure dissolution along stylolites is arrested pressure dissolution may be arrested for two reasons 1 the introduction of hydrocarbons causes a fall in effective burial stress and 2 adsorption of polar hydrocarbons on the silicates may shield calcite from the silicates

geomorphological response of fluvial and coastal terraces to quaternary tectonics and climate as revealed by geostatistical topographic analysis geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces this work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the late quaternary we chose the major valleys of the adriatic foothills central italy affected since late miocene by a differential tectonic uplift which is still active in particular i we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the metauro river and cesano river mouths ii we performed correlations between the height distribution of the alluvial terrace sequences and the quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the metauro cesano misa and esino rivers the obtained averaged incision rates have been interpreted also in the light of the stream length gradient index sl index steepness index ks and concavity index as proxies of the stream power per unit length results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers in particular we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the metauro and cesano rivers already recognized in previous works through sedimentological morphostratigraphic and chronological data moreover we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late quaternary glacial periods despite the slope area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration we observed some space and time variability of averaged incision rates for adjacent valleys mainly explained by physiographic configuration and dynamics of drainage network copyright 2011 john wiley sons ltd

evaluation and prediction of shear wave velocities in calcareous marine sediment and rocks shear wave velocities from full waveform acoustic logs recorded in calcareous oozes and chalks were determined using the spectral ratio inversion method data were recorded during dsdp leg 95 drilling off the east coast of the united states dsdp site 613 sampled a progression of carbonaceous siliceous oozes through partially lithified chalk discrete shear wave velocities within a 350 meter interval were calculated the results of a method for predicting shear wave velocities using wood s equation correlate well with inversion results at shear wave velocities greater than 800 m sec predictions using wood s equation provide a theoretical maximum value for shear wave velocity to compare with inversion results inverted data fall just below the predicted theoretical maximum value from wood s equation and agree quite well with trends in wood s results and other related logging measurements at slower shear wave velocities the physical contrast between borehole fluid drilling mud and the formation ooze is not enough to excite normal borehole modes used in inversion processing resulting in inversion velocities greater than wood s maximum

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

response of the ganges dispersal system to climate change a source to sink view since the last interstade the forcing of sediment dispersal systems by climate is widely accepted but there remains disagreement on the general responses to climate change such as how resulting signals propagate downstream and ultimately how they are preserved in the stratigraphic record towards a better understanding of these issues this paper presents a comprehensive overview of ganges dispersal system behavior since the last interstade which reveals major coeval responses to changes in the south asian monsoon at 3000 km from its mountain headwaters to deep sea fan the ganges dispersal system is immense and yet shows tight coupling between source area catchment basin and coastal and marine depocenters furthermore system wide responses and downstream transfer of the signal appear to occur at least as fast as current temporal resolution of 1 2 ky this tight linkage of source to sink components is considered a function of the southwest summer monsoon s overwhelming control on regional hydrology about 80 of the ganges discharge and 95 of its sediment load are delivered to the margin during only 4 months making the system extremely sensitive to this seasonal forcing in addition the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents finally despite its present intensity strength of the summer monsoon has varied significantly over the past 150 ky under orbitally driven changes in insolation and global glacial boundary conditions the resulting changes in precipitation both well above and below modern values have forced system wide responses ranging from glacier advance retreat to sediment fluxes to the margin and deep sea fan the overall conclusions are 1 that this immense dispersal system responds to multimillennial scale 104 years climate change in a system wide and largely contemporaneous manner and 2 that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation furthermore these acute responses to climate change have produced sedimentary stratigraphic features that diverge from traditional sequence models in their nature and timing

solution properties of rare earth elements in silicate melts inferences from immiscible liquids abstract the partitioning behavior of rare earth elements ree between immiscible silicate liquids was investigated as a function of temperature and total ree oxide concentration ree preferentially partition into the end member liquids that are rich in network modifying cations with two liquid partition coefficients greater than any other cation the two liquid partition coefficients of ree in a given experiment are essentially identical to one another no evidence was seen to suggest that the solution mechanisms of ree in high silica liquids vary with differences in their ionic radii two lattice models of trace element solution behavior fail to remove the compositional dependence of ree two liquid partition coefficients due to the assumption that all network forming and network modifying cations mix ideally with one another as a result it is probably incorrect to derive physical interpretations from the results of the application of two lattice models the results are applied to the origins of the lree enriched phenocryst matrix partition coefficients seen for some ferromagnesian minerals in high silica rhyolites since liquids with extremely high concentrations of t o t linkages do not strongly discriminate between the ree on the basis of their ionic radii the anomalous ree crystal matrix partition coefficient patterns are best explained as the result of contamination of these minerals by lree accessory phases

cenozoic cooling history and fluvial terrace development of the western domain of the eastern kunlun range northern tibet abstract the growth of the tibetan plateau resulted primarily from cenozoic india asia collision and continued convergence and thus the deformation timing and geomorphic evolution of northern tibet are critical to understanding the dynamics of orogenic plateau growth although previous studies have suggested that the altyn tagh shan and the eastern kunlun range of northern tibet have experienced differential faulting and exhumation history our knowledge of the temporal and spatial distribution of the growth of the northwestern tibetan plateau is still lacking in this study we integrate new geologic mapping low temperature themochronometry 18 apatite fission track ages and optically stimulated luminescence osl dating to provide constraints on the cenozoic cooling history of northwestern tibet and late quaternary fluvial terrace development we focus on where altyn tagh shan structures are juxtaposed against eastern kunlun range structures new fission track cooling ages from one traverse along the aksu river yielded three cooling age domains paleocene miocene and early pliocene with this new knowledge of 12 10 ma initiation of jianxiashan thrusting and exhumation we suggest a refined n s shortening rate of this thrust system of 2 0 2 4 mm yr and strain rates of 8 9 10 16 s 1 thermal history modeling suggests that the study area experienced two broad events including slow cooling through the aft paz since the early eocene and rapid cooling during the late miocene our osl dating results from the aksu drainage reflect two separate processes of aggradation and incision that occurred during the late pleistocene and holocene respectively which are interpreted to result from long term forcing of incision by a constant rate of tectonic uplift modulated by late quaternary climatic variations we interpret that this incision occurred at a rate of 1 mm yr which is faster than exhumation rates inferred from the aft data 0 3 0 5 mm yr these quaternary exhumation rates may reflect faster recent exhumation or uplift associated with the proximal altyn tagh fault in accordance with previous studies we present a refined cenozoic tectonic model for the evolution history of northern tibet the deformation pattern of northern tibet results from clockwise rotation of preexisting weaknesses and transpressional deformation along the kunlun fault and the haiyuan fault

experimental evidence for a relationship between liquid immiscibility and ore formation in felsic magmas abstract geological studies demonstrate that liquid immiscibility in felsic magma closely associates with the ore forming process in order to obtain experimental evidence demonstrating the relationship between the ore forming process and liquid immiscibility in felsic magma we carried out a series of experiments at high temperature and atmospheric pressure the experimental results show that the granite kbf 4 na 2 moo 4 system is a homogeneous melt at high temperature with decrease in temperature however the melt decomposes into two immiscible melts silicate melt and ore forming melt the ore forming melt exists as globules in the silicate phase molybdenm ca na mg p mn f b and oh are concentrated in these globules the ore forming melt is characterized with very low sio 2 and al 2 o 3 concentrations but the concentration of moo 3 and cao is very high in contrast the silicate melts are significantly enriched in sio 2 and al 2 o 3 and depleted in moo 3 and cao in the silicate melt the concentrations of network modifying elements e g mo ca na p mg and volatiles f oh are very low the differences between the two immiscible melts exist not only in chemical composition but also in structure the ore forming melt structurally consists of moo 4 moof 4 b oh 4 and oh while the silicate melt is si0 4 because of the difference in composition and structure the two immiscible melts possess different physical properties compared to silicate melt the ore forming melt has a lower density and viscosity which permits the globules to behave as bubbles in granite magma and to move and concentrate in the upper part of magma chamber this process is probably responsible for the concentration of ore forming elements in the upper part of granite bodies and their immediate aureoles the present experimental results suggest that liquation in felsic magma can be the first step in the ore forming process during granitoid evolution

geological and mechanical study of argillaceous north sea chalk implications for the characterisation of fractured reservoirs abstract argillaceous chalk intervals from the north sea are characterised by matrix permeabilities lower than 0 2 md and therefore they are defined as tight chalks hence fracture networks within these chalks are of major importance to predict fluid flow and reservoir or seal behaviour this study aims to understand the geological parameters controlling the chalk petrophysical and mechanical properties using the outcrop analogue of the cenomanian chalk at cap blanc nez northern france sedimentological petrographic and petrophysical analyses were performed and show that the combination of the depositional environment and diagenetic imprint control the microtexture non carbonate content is ranging from 5 to 40 within the studied samples and is critical for the diagenetic imprint the fracture behaviour of the chalk was studied using a mechanical stratigraphy approach throughout the 70 m thick succession where a transition between lower cenomanian argillaceous chalk and middle upper cenomanian pure chalk is exposed twenty two mechanical units are distinguished and the amount of fractures crosscutting initiating and terminating on mechanical interfaces quantified manual scanlines show that fracture spacing ranges from 17 to 232 cm mechanical interfaces are associated with lithological heterogeneities with strong microtextural contrasts related to the non carbonate content and or degree of cementation the mechanical units are thus defined either by deposition or diagenesis the fracturing behaviour of about 10 m homogeneous pure chalk interval units defined as dfz densely fractured zones differs significantly from the rest of the succession large sigmoidal shaped fractures are confined to those intervals and a dense fracture network developed because of their plastic behaviour clay layers are able to accommodate part of the stress whereas homogeneous pure chalk show a more brittle behaviour

channel profiles around himalayan river anticlines constraints on their formation from digital elevation model analysis 1 we present a comparison between measured and numerically modeled channel profiles of rivers in two important drainage basins of central nepal the kali gandaki and the arun drainage basins modeled channel profiles are based on a simple stream power approach using best fit exponents defining the nonlinearities in the relative contributions of local channel gradient and water flux to erosion rate our analysis of the stream power in the whole river network confirms the work of other authors that a 50 to 80 km wide zone roughly corresponding to the high himalayan topography is subjected to rapid rock uplift we suggest a model where the uplift of this zone is driven by erosion and isostatic response so that centers of maximum uplift are located within the main channels of the north south draining rivers we also suggest that the rate of uplift slows down with increasing distance to the main channels such a spatial distribution of the uplift leads ultimately to the formation of river anticlines as observed along all major himalayan rivers we propose that the formation of river anticlines along south draining himalayan rivers was accelerated by a sudden increase of the drainage area and discharge when the rivers captured orogen parallel drainages on the north side of the range this may follow successive headward cutting into the tibetan plateau the model is confirmed by differences between main channels and east west running tributaries time dependent numerical models predict that capture events cause strongly elevated erosion rates in the main channel

drainage network geometry versus tectonics in the argentera massif french italian alps abstract the argentera massif french italian alps with its uniform lithology was selected to evaluate how known plio pleistocene tectonics have conditioned the drainage network geometry the drainage network was automatically derived and ordered from a 10 m resolution dem on hillshade images alignments of morphological features were identified the massif was subdivided into 22 domains of 50 km 2 within which the directions of every river channel segment and the direction of the aligned morphological features were compared and contrasted with the strike of tectonic structures measured in the field results suggest that the argentera drainage system is variously controlled by recent tectonics depending on the massif sector taken into account in the nw sector the vertical uplift is less because the strain has been accommodated in an oblique direction along a lateral thrust in the se sector strain in a predominantly vertical direction along a frontal thrust has resulted in a major vertical displacement accordingly the nw sector is characterized by i a strong geometric relationship between the main tectonic structures and the directions of river channels ii longitudinal main rivers bordering the massif and iii a general trellis pattern within the domains in the se sector the prolonged uplift has forced an original longitudinal drainage system to develop as a transverse system this change has occurred by means of fluvial captures that have been identified by the presence of windgaps fluvial elbows and knickpoints at the domain scale intense uplift of the se sector has prompted the drainage pattern to evolve as a dendritic type with no clear influence of structure in the channel orientations

active lower crustal deformation and himalayan seismic hazard revealed by stream channels and regional geology abstract thick tibetan crust stores energy driving large earthquakes along its margins at its southern margin it is hypothesized that its lower crust is extruded between two shear zones such that strain in the ductile lower crust is fed into the higher seismogenic portions of the crust predicting rock uplift between these structures the upper shear zone is regionally referred to as the south tibetan detachment std and the lower shear zone as the main central thrust mct we use field mapping and ksn channel steepness analysis to test this hypothesis in northwestern nepal within a notable gap in historic seismicity here we show an 170 km 40 km swath of rapid rock uplift at the southern margin of the tibetan plateau that overlaps a regional anticline suggesting active folding the area of rapid uplift coincides with peak interseismic strain determined by gps and overlies the inferred locked to creeping transition along the india asia plate boundary the fold is cored by thick ductiley deformed crust and defined by a shear zone interpreted as the std because the std is folded it cannot facilitate active extrusion of a mid crustal channel a regional cross section across the fold shows that while the uppercrust has little post miocene shortening the lower middle crust is anomalously thick we explain this by duplexing whereby thrust sense shear zones stack ductile lower middle crust beneath the std north downdip of the locked to creeping transition the plate boundary here last ruptured during the mw 8 2 ad 1505 earthquake whose inferred rupture area encompasses the region of rapid rock uplift shown here predicting a high slip potential integrating the structural geology and ksn analysis with microseismicity patterns and the 1505 surface rupture suggests that in western nepal the locked to creeping transition is 40 km wide and lies 100 120 km north of the himalayan thrust front

chalk porosity and sonic velocity versus burial depth influence of fluid pressure hydrocarbons and mineralogy seventy chalk samples from four formations in the overpressured danish central north sea have been analyzed to investigate how correlations of porosity and sonic velocity with burial depth are affected by varying mineralogy fluid pressure and early introduction of petroleum the results show that porosity and sonic velocity follow the most consistent depth trends when fluid pressure and pore volume compressibility are considered quartz content up to 10 has no marked effect but more than 5 clay causes lower porosity and velocity the mineralogical effect differs between p wave and shear velocity so that smectite bearing chalk has a high poisson s ratio in the water saturated case but a low value in the dry case oil bearing chalk has up to 25 units higher porosity than water saturated chalk at similar depth but similar velocity probably because hydrocarbons prevent pore filling cementation but not pore structure stiffening cementation in this presumably water wet chalk these results should improve the modeling of chalk background velocity for seismic inversion analysis when describing the porosity reducing process pore volume compressibility should probably be disregarded when correcting for fluid pressure because the cementing ions originate from stylolites which are mechanically similar to fractures we find that cementation occurs over a relatively short depth interval

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

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

a laboratory study of the dependence of elastic wave velocities on pore scale fluid distribution laboratory data have been collected during a continuous imbibition drainage experiment that show a clear dependence of elastic wave velocities on the details of the pore scale distribution of water and air in a sandstone compressional wave velocity vp was measured at a frequency of 1 mhz shear wave velocity vs was measured at a frequency of 600 khz during the experiment vp showed little variation with the level of water saturation sw during increasing sw through imbibition until sw 0 80 at which point vp increased dramatically when sw was decreased pronounced saturation induced hysteresis was observed in the region 03 0 4 as a simple model we consider the imbibition process as producing a partially saturated state in all pores i e all pores contain both air and water the drainage process in contrast favors the existence of either air filled or water filled pores as elastic wave velocities are very sensitive to the saturation state in the smaller crack like pores these variations in fluid distribution cause related variations in velocities

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

climatic and tectonic controls on fluvial incision and aggradation in the spanish pyrenees the influences of tectonic and climatic changes on upland river systems are investigated using data from plio pleistocene terraces of the rio cinca river in the southern pyrenees this river runs transverse to the main thrust fault structures and is a major conduit for sediment delivery to the ebro basin detailed field mapping combined with long profile and palaeohydraulic reconstructions yields a comprehensive picture of changes in palaeoriver character during the plio pleistocene as the area is over 150 km from the basin outlet in the mediterranean sea changes in base level are unlikely to have influenced terrace development although tectonic activity has exerted a strong control on the position of the river the main period of thrust propagation pre dates the terraces and activity has waned from the pliocene through to the present it is concluded that the main control on incision in this area is climate through its influence on sediment supply rivers which are starved of sediment by climate change will have the power to incise whereas aggradational phases are linked to periods of increased sediment flux

acoustic measures of partial gas saturation in tight sandstones the acoustic properties of tight sandstones are very sensitive to partial gas water saturation measurements at 5 khz show that compressional velocity drops sharply with undersaturation extensional and shear losses at 5 khz are large in both fully and partially saturated sands the shear loss qs 1 declines linearly with increasing gas content the extensional loss qe 1 peaks at 0 80 water saturation q 1 is frequency dependent the attenuation is well explained by hydrodynamic relaxation in the grain contacts the measurements indicate velocity dispersions consistent with this mechanism ultrasonic velocities at 500 khz are roughly 10 25 higher than acoustic velocities at 5 khz the ultrasonic velocities exhibit a weak dependence on saturation frame moduli are unrelaxed at these frequencies

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

mapping lithofacies and pore fluid probabilities in a north sea reservoir seismic inversions and statistical rock physics reliably predicting lithologic and saturation heterogeneities is one of the key problems in reservoir characterization in this study we show how statistical rock physics techniques combined with seismic information can be used to classify reservoir lithologies and pore fluids one of the innovations was to use a seismic impedance attribute related to the vp vs ratio that incorporates far offset data but at the same time can be practically obtained using normal incidence inversion algorithms the methods were applied to a north sea turbidite system we incorporated well log measurements with calibration from core data to estimate the near offset and far offset reflectivity and impedance attributes multivariate probability distributions were estimated from the data to identify the attribute clusters and their separability for different facies and fluid saturations a training data was set up using monte carlo simulations based on the well log derived probability distributions fluid substitution by ga

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

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

effective stresses and shear failure pressure from in situ biot s coefficient hejre field north sea we propose a combination of biot s equations for effective stress and the expression for shear failure in a rock to obtain an expression for minimum pore pressure in a stable vertical well bore we show that a biot s coefficient calculated from logging data in the hejre field north sea is significantly different from 1 the log derived biot s coefficient is above 0 8 in the shetland chalk group and in the tyne group and 0 6 0 8 in the heno sandstone formation we show that the effective vertical and horizontal stresses obtained using the log derived biot s coefficient result in a drilling window for a vertical well larger than if approximating biot s coefficient by 1 the estimation of the biot s coefficient is straightforward in formations with a stiff frame whereas in formations such as shales caution has to be taken we discuss the consequence of assumptions made on the mineral composition of shales as unphysical results could be obtained when choosing inappropriate mineral moduli

fission track evidence for quaternary uplift of the nanga parbat region pakistan the north striking nanga parbat haramosh massif protrudes into the northwestern himalaya along the axis of a great syntaxis1 2 fig 1 where the hindu kush karakorum and himalayan ranges converge as the indus suture zone3 enters this region from the east it bifurcates into two branches encircling what may be a docked island arc terrane4 the southern branch the main mantle thrust crops out on both flanks of the nanga parbat massif forming a tight structural loop5 this massif and the adjacent terrane contain some of the highest peaks in the himalaya nanga parbat and the indus river located just 20km away define the world s greatest continental relief 6 930 m we report here the discovery of unexpectedly young sphene zircon and apatite fission track dates from the nanga parbat haramosh massif these dates as low as 1 3 myr for zircon and 0 4 myr for apatite imply that during the pleistocene the nanga parbat region was uplifted and eroded at nearly 1 cm yr 1

target oriented avo inversion of data from valhall and hod fields a stratigraphic elastic inversion scheme has been applied to a real seismic data set from valhall and hod fields in the north sea avo inversion shows discontinuous high porosity zones that can be interpreted as evidence for stratigraphic traps in the upper chalk interval this was tested by exploration drilling after avo processing was completed and hydrocarbons were found

squeezing river catchments through tectonics shortening and erosion across the indus valley nw himalaya tectonic displacement of drainage divides and the consequent deformation of river networks during crustal shortening have been proposed for a number of mountain ranges but never tested in order to preserve crustal strain in surface topography surface displacements across thrust faults must be retained without being recovered by consequent erosion quantification of these competing processes and the implications for catchment topography have not previously been demonstrated here we use structural mapping combined with dating of terrace sediments to measure quaternary shortening across the indus river valley in ladakh nw himalaya we demonstrate 0 21 m k y 1 of horizontal displacement since ca 45 ka on the stok thrust in ladakh which defines the southwestern margin of the indus valley catchment and is the major back thrust to the tethyan himalaya in this region we use normalized river channel gradients of the tributaries that drain into the indus river to show that the lateral continuation of the stok thrust was active for at least 70 km along strike shortening rates combined with fault geometries yield vertical displacement rates that are compared to time equivalent erosion rates in the hanging wall derived from published detrital 10be analyses the results demonstrate that vertical displacement rates across the stok thrust were approximately twice that of the time equivalent erosion rates implying a net horizontal displacement of the surface topography and hence narrowing of the indus valley at 0 1 m k y 1 a fill terrace records debris flow emplacement linked to thrust activity resulting in damming of the valley and extensive lake development conglomerates beneath some of the modern alluvial fans indicate a northeastward shift of the indus river channel since ca 45 ka to its present course against the opposite side of the valley from the stok thrust the integration of structural topographic erosional and sedimentological data provides the first demonstration of the tectonic convergence of drainage divides in a mountain range and yields a model of the surface processes involved

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

the signature of an unbalanced earthquake cycle in himalayan topography fifty percent of the relative motion between the indian and asian plates is accommodated by active convergence at the himalayan range front hrf earthquake cycle processes on shallowly dipping hrf thrust faults generate large earthquakes mw 7 and contribute to the growth of hrf topography interseismic rock uplift rates reach a maximum north of the active main frontal thrust and have been suggested to significantly influence the collocated convex bulge in hrf topography using geodetically constrained models of interseismic rock uplift rates and simple channel erosion rate laws we show that convex channel profiles are predicted when interseismic deformation outpaces coseismic deformation applying this model to the observed elevation profiles of 20 hrf spanning channels in nepal yields a minimum mean residual elevation 72 m if interseismic deformation has outpaced coseismic deformation by a factor of four the long term earthquake deficit required for the application of this model is consistent with some estimates of historical moment imbalance but requires temporally variable fault system activity the spatial correlation between nominally interseismic rock uplift and the hrf topographic bulge may be explained by 1 a noncausal geometric coincidence 2 geodetic observations of significant deformation not directly related to earthquake cycle processes or 3 an unbalanced earthquake cycle at the hrf

integrated analysis of structures and landforms of an intermontane longitudinal valley pinjaur dun and its associated mountain fronts in the nw himalaya abstract frontal regions of the himalaya associated with topographic recesses are commonly marked by the development of intermontane valleys locally referred to as duns the relationship between structural evolution and landform development of an intermontane longitudinal valley pinjaur dun is explored to understand the role of tectonic processes on landform development the pinjaur dun has a length of 180 km it is divisible into a wider 20 km northwestern and a narrower 6 8 km southeastern segment the barsar thrust the nalagarh thrust and the himalayan frontal thrust form the mountain fronts in the area the proposed structural model integrates the transverse structures for e g ghaggar tear fault with the sequential development of imbricates in front of the main boundary thrust the pinjaur dun formed as a consequence of the fold thrust related uplift that formed the outermost siwalik hills most of the geomorphic units formed within the dun are the result of interactions between the imbricates such as the pinjaur thrust jhajara thrust and pinjaur garden fault these interactions also resulted in the development of a significant and prominent drainage divide between the jhajjara and the sirsa rivers of the pinjaur dun landform development and landscape evolution in this frontal region of the himalaya are a consequence of the interaction of thrust fold and transverse fault zone tectonics and constitute a record of transient 102

late quaternary fluvial aggradation and incision in the monsoon dominated alaknanda valley central himalaya uttrakhand india the present study aims to explain the spatial and temporal variability in phases of aggradation incision in response to changes in climate and seismicity during the late quaternary in the alaknanda river valley a major tributary of the river ganges or ganga geomorphology stratigraphy and optical dating of the fluvial sediment reveal that the oldest fluvial landforms preserved in the south of the main central thrust are debris flow terraces developed during the early part of pluvial marine isotopic stage 3 following this a period of accelerated incision erosion owing to an increase in uplift rate and more intense rainfall occurred in the lesser himalaya three phases of valley fill aggradation around 26 3 ka 18 2 ka and 15 1 ka and 8 1 ka occurred in response to changes in monsoon intensity and sediment flux the last phase was regionally extensive and corresponds to a strengthening of the early holocene indian summer monsoon a gradual decline in the monsoon strength after 8 1 ka resulted in reduced fluvial discharge and lower sediment transport capacity of the alaknanda river leading to valley fill incision and the development of terraces the study suggests that fluvial dynamics in the alaknanda valley were modulated by monsoon variability and the role of tectonics was subordinate limited to providing accommodation space and post deposition modification of the fluvial landforms copyright 2010 john wiley sons ltd

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

variations in trace element partition coefficients in sanidine in the cerro toledo rhyolite jemez mountains new mexico effects of composition temperature and volatiles trace element partition coefficients have been measured for one plagioclase and five sanidine mineral separates from the cerro toledo rhyolite new mexico sanidine partition coefficients vary substantially and systematically within the cerro toledo rhyolite partition coefficients for ca sr zn la and eu are lowest in the most evolved rhyolites whereas sm and hree partition coefficients are highest rubidium partition coefficients remain constant while those for ba ce and th are variable variations of the sr zn la and eu partition coefficients are correlated with the ca contents and partition coefficients of the sanidines calcium may have controlled the distribution of these elements in the sanidine by modifying the feldspar structure the low ca partition coefficients in sanidines for the most evolved rhyolites may be the consequence of modification of the melt structure possibly due to increased volatile contents at the top of the magma chamber s during evolution of the cerro toledo rhyolite the zn and la partition coefficients between sanidine and melt also may have been controlled by this change in melt structure modelling using major elements and the constant rb partition coefficient for sanidine indicates 70 crystallization of magma during cerro toledo rhyolite time by removal of 68 sanidine and 32 quartz estimates of the volume 1 of initial parental magma and 2 of the magma that crystallized during this period are 11 670 km3 and 8170 km3 respectively the average intrusion rate of silicic magma during cerro toledo rhyolite activity was 35 10 3 km3 a

catastrophic rock slope failures and late quaternary developments in the nanga parbat haramosh massif upper indus basin northern pakistan abstract the nanga parbat haramosh massif has some of the greatest relief on earth and highest measured rates of uplift denudation and river incision in bedrock many studies have sought to understand how its morphology relates to geotectonic evolution and glaciations however few catastrophic rock slope failures had been recognised and many of their impacts had been attributed to other processes recently more than 150 of these landslides have been found within a 100 km radius of nanga parbat 8125 m new discoveries are reported east north and west of nanga parbat along the indus streams most generated long run out rock avalanches that dammed the indus or its tributaries some impounding large lakes they initiated episodes of intermontane sedimentation followed by trenching and removal of sediment valley floor features record a complex interplay of impoundment and sedimentation episodes superimposition of streams in pre landslide valley floors and exhumation of buried features these findings depart from existing reconstructions of quaternary events a number of the rock avalanche deposits were previously misinterpreted as tills or moraine and their associated lacustrine deposits attributed to glacial lakes features up to 1000 m above the indus formerly seen as tectonically raised terraces are depositional features emplaced by landslides or erosion terraces recording the trenching of valley fill in landslide interrupted river reaches unquestionably tectonics and glaciation have been important but decisive and misread formative events of the holocene involve a post glacial landslide fragmented fluvial system the latter has kept valley developments in a chronic state of disequilibrium with respect to climatic and geotectonic controls accepted glacial chronologies are put in doubt particularly the extent and timing of the last major glaciation the pace and role processes in the holocene have been seriously underestimated

the status of central seismic gap a perspective based on the spatial and temporal aspects of the large himalayan earthquakes abstract the central himalaya considered as a prominent seismic gap is generally believed to be the most vulnerable segment due for a great plate boundary earthquake m 8 two significant historical earthquakes are known to have occurred in this region in ad 1505 and 1803 interpreted by some workers as great earthquakes occurrences of these events question the validity of central himalaya being a seismic gap here we analyze the macroseismal data from the central himalaya and the gangetic plains and suggest that neither of these earthquakes can be qualified as a plate boundary type event and the size of at least the 1803 does not exceed mw 7 7 our studies further indicate that the central himalayan frontal thrusts may be undergoing a quiescence of 1000 years in terms of generation of great earthquakes assuming a steady elastic strain accumulation due to plate convergence and its simple translation as periodic great earthquakes such long quiescence may appear intriguing we suggest that the long term quiescence and the spatial and temporal clustering that characterize the distribution of large earthquakes in the himalaya is a manifestation of the tectonic deformation associated with a highly evolved fold and thrust belt our analyses also indicate that the large moderate earthquakes are mostly concentrated on higher level thrusts these structures probably accommodate most of the seismogenic slip in the himalaya and the rest of the strain could possibly be expended on passive folding consequently great earthquakes m 8 are relatively infrequent as in the case of central himalaya apparently leading to long periods of quiescence

alkali zirconosilicates in peralkaline rocks based on the crystal chemistry of alkali zirconosilicates azs it is argued that zr in silicate melts is a network modifier rather than a complex former with the aid of silicate melt theory the late crystallization of azs in peralkaline melts can be explained the high ks ns and high q calculated in some norms of peralkaline rocks but not expected from the modes is the result of calculating zrsio4 rather than k na 2zrsio5 xsio2

the use of the stream length gradient index in morphotectonic analysis of small catchments a case study from central italy abstract the aim of this work is to test an integrated quantitative geomorphic approach based on stream length gradient index sl index analysis within the small catchment of the tarugo river in the northern marchean apennines central italy the tarugo river basin 92 km 2 wide strikes sw ne across the marchean ridge and the western sector of marchean piedmont the area is characterized by a series of nw se trending ne verging thrust folds affecting the meso cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks the area investigated has been affected since the pliocene by extensional tectonics accompanying a regional uplift decreasing in rate north eastwards in this work the sl index analysis has been integrated with the spatial analysis of the amplitude of relief a r and compared to geological and geomorphological field data results of this work indicate that the sl index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes i e regional uplift that is often undetectable by other morphotectonic parameters in contrast the sl index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one

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

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

impact of tectonics on drainage network evolution of suru basin kargil n w himalaya jammu and kashmir india the main objective of this paper is to work out quantitative measurement of various geomorphic parameters as well as analysis of geomorphic landforms to study the tectonic character of suru basin morphometric analysis being widely used to assess the drainage characteristics of the river basins has also been found to be a useful tool to delineate tectonically active zones a number of parameters including the mountain front sinuosity asymmetry factor transverse topography symmetry hypsometry longitudinal profile and the shape parameters have been used the low mountain front sinuosity values 1 4 indicate that the tectonic forces dominate over erosive activity also the asymmetry factor 66 98 suggests that the right side of the basin has experienced uplift with the development of unpaired river terraces hypsometric integral 0 96 convex up hypsometric curve and the gps data of year 2011 2013 indicate that the relief of the basin is high relative to mean is in youthful stage and actively uplifting at the rate of 2 18 0 99 mm year the shape parameters further suggest that the suru river basin having lower elongation ratio is indicative of elongate shape of basin with tectonic forces outpacing the erosion power area altitude analysis of the suru river basin indicates that about 72 of the area of the basin is steeply to very steeply sloping and 28 area is moderately to gently sloping the area altitude indicates 72 area of basin could slide when there is slight shift in terms of tectonic disturbance in addition to the geomorphic indices the field investigations reveal tectonically unstable character exhibit a complex topography and varied quaternary sedimentation the major geomorphic landforms viz alluvial terraces alluvial fans debris cone scree and talus cone at the foothills are present throughout the valley with tectonic structures like micro folds back tilted beds deeply incised valleys faults and tectonic deposits ophiolites indicating that the tectonic activity has affected the basin the synergized results of geomorphometry field investigations and gps data indicate that the suru basin is tectonically active and uplifting

aluminum coordination in metaaluminous and peralkaline silicate melts incremental amounts of na2o and k2o added to immiscible melts in the mgo cao tio2 al2o3 sio2 system cause a decrease in critical temperature phase separation and change in the pattern of al2o3 partitioning al2o3 which is concentrated in the low sio2 immiscible melts in the alkali free system is increasingly partitioned into the high sio2 immiscible melt as the alkali aluminium ratio is increased however k2o is more effective than na2o in stabilizing al2o2 in the sio2 rich melt the coordination changes occurring in the aluminosilicate melts upon the addition of the alkali oxides are described by caal2o4 2siok 2kalo2 siocaosi where k or na displaces ca as the charge balancing cation for the networkforming alo4 tetrahedra the increased stability of the alo4 species in the highly polymerized sio2 rich melt and the consequent shrinkage of the miscibility gap is ascribed to positive configurational entropy and negative enthalpy changes associated with the formation of k na alo4 species element partition systematics indicate that na k alo2 species favor the more polymerized caal2o4 and tio2 species the less polymerized silicate structure in the melt

a physical model for porosity reduction in sandstones the experimental elastic moduli porosity trends for clean sandstones can be described by the modified upper hashin shtrikman muhs bound one geometrical but not necessarily geological realization is as porosity decreases the number of the pores stays the same and each pore shrinks while maintaining its shape this concept of uniform porosity reduction implies that permeability is proportional to the effective porosity squared and that formation factor is proportional to the inverse of the effective porosity the effective porosity here refers to the part of the pore space that dominates fluid flow the proposed relations for permeability and formation factor agree well with the experimentally observed values these laws are different from the often used forms of the kozeny carman equation and archie s law where permeability is proportional to the total porosity cubed and formation factor is proportional to the inverse of the total porosity squared respectively we suggest that the uniform porosit

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

implications for elastic energy storage in the himalaya from the gorkha 2015 earthquake and other incomplete ruptures of the main himalayan thrust abstract rupture in the 2015 m7 8 gorkha earthquake nucleated at the downdip edge of the main himalayan thrust mht near the transition from interseismic locking to aseismic creep beneath the tibetan plateau and propagated incompletely towards the main frontal thrusts mft despite the imposition of a substantial static strain in the mid decollement afterslip on the mht within a year of the earthquake had decayed to negligible levels earthquakes that incompletely rupture the mht 7

porosity identification using amplitude variations with offset examples from south sumatra abstract this paper describes the use of a relatively new exploration technique in the modeling and interpretation of seismic data the technique holds promise for identification of primary lithology and of local lithological facies variations its underlying principle is that any single reflection within a cdp gather will show an amplitude variation between near and far offset traces given certain physical properties of rocks across the reflecting boundary stacking velocity information above the reflector and the cdp geometry it is possible to model the observed amplitude variation such modeling can result in useful information on lithology two examples will be shown of the application of this technique in the detection of porosity in miocene reefal buildups in south sumatra

impact of wind erosion on detecting active tectonics from geomorphic indexes in extremely arid areas a case study from the hero range qaidam basin nw china abstract geomorphologic analysis has been used widely to detect active tectonics in regions where fluvial incision is the major erosional process in this paper however we assess the feasibility of utilizing these frequently used geomorphic indexes e g hypsometric curves longitudinal channel profiles normalized stream length gradient slk index to determine active tectonics in extremely arid areas where wind erosion also plays an important role the case study is developed on the hero range in the western qaidam basin one of the driest regions on earth with severe wind erosion since late pliocene the result shows that in the west and south sectors as well as the western part of the east sector of the hero range where fluvial incision prevails these geomorphic indexes are good indicators of active faulting and consistent with the geological result based on study of fault traces scarps faulted holocene fans and historical seismicity within the past four decades in contrast along the northeastern margin the ne and the se parts of the east sector of the range where wind erosion is also important the results from the geomorphic indexes show quite active tectonics contrary with the geological evidence favoring weakly active tectonics moreover the positive slk anomaly lies oblique to the fault trace and the anticline axis but parallel to the wind direction to reconcile the contradiction we propose that wind erosion caused by northwestern winds has a tendency to make geomorphic indexes exhibit anomalous values that indicate higher activities by way of 1 lowering the base level to generate knickpoints on the longitudinal channel profiles and therefore positive slk anomalies and 2 lateral erosion of the mountain front making the hypsometric curves and even the longitudinal channel profiles more convex and producing obvious slope breaks

framework for avo gradient and intercept interpretation amplitude variation with offset avo interpretation may be facilitated by crossplotting the avo intercept a and gradient b under a variety of reasonable petrophysical assumptions brine saturated sandstones and shales follow a well defined background trend in the a b plane generally a and b are negatively correlated for background rocks but they may be positively correlated at very high vp vs ratios such as may occur in very soft shallow sediments thus even fully brine saturated shallow events with large reflection coefficients may exhibit large increases in avo deviations from the background trend may be indicative of hydrocarbons or lithologies with anomalous elastic properties however in contrast to the common assumptions that gas sand amplitude increases with offset or that the reflection coefficient becomes more negative with increasing offset gas sands may exhibit a variety of avo behaviors a classification of gas sands based on location in the a b plane rather than on normal

estimating rock porosity and fluid saturation using only seismic velocities evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting interpretation of seismic velocities and amplitudes is based on theories of fluid saturated and partially saturated rocks that have been available since the 1950s here we present a new synthesis of the same physical concepts that uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution the key idea revolves around the fact that the density and the lame elastic parameter are the only two parameters determining seismic velocities that also contain information about fluid saturation at low enough frequencies gassmann s well known equations show that the shear modulus is independent of the fluid saturation level we use these facts to

holocene activity and paleoseismicity of the selaha fault southeastern segment of the strike slip xianshuihe fault zone tibetan plateau abstract in this study we examine the holocene activity including slip rate and paleoseismicity of the selaha fault a branch of the left lateral strike slip xianshuihe fault zone located along the southeastern segment of the ganzhi yushu xianshuihe fault system gyxfs of the tibetan plateau interpretation of high resolution images and field investigations reveal that the selaha fault is characterized by left lateral strike slip faulting with an average horizontal slip rate of 9 0 mm year during the holocene trench excavations and 14c dating results show that at least three morphogenic earthquakes occurred during the past millennium the most recent event occurred in the past 450 years and corresponds to the 1786 m 7 75 earthquake the penultimate seismic event e2 occurred in the period between 560 and 820 year bp i e 1166 1428 ce and is probably associated with the 1327 m 7 5 earthquake the antepenultimate event e3 is inferred to have occurred in the period between 820 30 and 950 30 year bp our results confirm that the selaha fault as a portion of the gyxfs plays an important role as a tectonic boundary in releasing the strain energy accumulated during the northeastward motion of the tibetan plateau in response to the ongoing northward penetration of the indian plate into the eurasian plate the strain energy is released in the form of repeated large earthquakes that are recorded by strike slip displacements of stream channels and alluvial fans

elastic behaviour of north sea chalk a well log study we present two different elastic models for respectively cemented and uncemented north sea chalk well log data we find that low biot coefficients correlate with anomalously low cementation factors from resistivity measurements at low porosity and we interpret this as an indication of cementation in contrast higher biot coefficients and correspondingly higher cementation factors characterize uncemented chalk for the same low porosity accordingly the poisson s ratio porosity relationship for cemented chalk is different from that of uncemented chalk we have tested the application of the self consistent approximation which here represents the unrelaxed scenario where the pore spaces of the rock are assumed to be isolated and the gassmann theory which assumes that pore spaces are connected as tools for predicting the effect of hydrocarbons from the elastic properties of brine saturated north sea reservoir chalk in the acoustic impedance poisson s ratio plane we forecast variations in porosity and hydrocarbon saturation from their influence on the elastic behaviour of the chalk the gassmann model and the self consistent approximation give roughly similar predictions of the effect of fluid on acoustic impedance and poisson s ratio but we find that the high frequency self consistent approach gives a somewhat smaller predicted fluid saturation effect on poisson s ratio than the low frequency gassmann model the gassmann prediction for the near and potentially invaded zone corresponds more closely to logging data than the gassmann prediction for the far virgin zone we thus conclude that the gassmann approach predicts hydrocarbons accurately in chalk in the sonic frequency domain but the fluid effects as recorded by the acoustic tool are significantly affected by invasion of mud filtrate the amplitude versus angle ava response for the general north sea sequence of shale overlying chalk is predicted as a function of porosity and pore fill the ava response of both cemented and uncemented chalk generally shows a declining reflectivity coefficient versus offset and a decreasing normal incidence reflectivity with increasing porosity however for the uncemented model a phase reversal will appear at a relatively lower porosity compared to the cemented model

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

canyon incision and knickpoint propagation recorded by apatite 4he 3he thermochronometry abstract in many regions of the world deeply incised canyons demonstrate the net effects of physical processes active at earth s surface in response to surface uplift low temperature thermochronometry can constrain the timing and rates of bedrock incision which is necessary for relating canyon incision to surface uplift over geological timescales we analyzed four samples from the cotahuasi ocona canyon system in southwest peru using 4 he 3 he thermochronometry and we present a new inversion model to identify continuous low temperature cooling histories that are consistent with the observed data derived cooling histories limit the onset of fluvial incision to 13 to 8 ma this is in agreement with previously reported interpretations based on a three dimensional thermal model interpolation to a much larger set of conventional apatite u th he ages however because 4 he 3 he thermochronometry constrains an independent cooling history for each sample the results also permit testing of landscape evolution models with greater spatial variability in exhumation compared to those models that can be tested by a geographically scattered set of conventional u th he ages the different cooling histories of the four samples require asynchronous incision along at least part of the canyon system that is best explained by headward propagation of fluvial incision by knickpoint migration

microstructures and physical properties in carbonate rocks a comprehensive review abstract carbonate rocks are well known to be tremendously heterogeneous they mainly consist of component particles from biological and non biological origin embedded in a lime mud matrix and or in a cement composed of even smaller particles the size shape density and spatial arrangement of those particles alongside with natural fractures and cracks although those are certainly not exclusive to carbonate rocks define a microstructural pattern that is known to have a great influence on rock physical properties thus to understand carbonate rock systems at large scales formation reservoir geophysicists have to study them at the pore scale hoping to resolve the so called upscalling problem with this in mind unravelling and identifying the relations between physical properties and carbonate rock microstructures is paramount for a global comprehension of a carbonate rock system since the late nineties several research groups and authors have worked on documenting and providing significant insights into the microstructural parameters controlling the physical response of several rock properties porosity permeability electrical conductivity elastic seismic and mechanical properties in carbonates this article proposes a review of this specialized literature from the early and recent contributions in rock physics with emphasis on the recent studies on carbonate rocks from the paris basin

denudation processes and rates in the transverse ranges southern california erosional response of a transitional landscape to external and anthropogenic forcing 1 quantification of denudation in the transverse ranges of california permits reconstruction of spatial and temporal variations in erosion that represent both the response and evolution of interacting hillslopes and channels on the southern front of the san gabriel mountains observational records of the infilling of debris basins and dams define twentieth century landscape erosion rates averaging 1 6 and 0 9 mm yr 1 respectively although all major sediment transport occurs during intense winter storms debris production on hillslopes is greatly enhanced by recurrent fires consequently in this populated region anthropogenic fires have augmented the natural erosion rates we perform a global inversion to estimate the role of precipitation intensity burned areas and local slope on catchment denudation rates after subtracting the effects of anthropogenic fires we estimate landscape denudation rates given natural fire ignition rates increased fire during the past century has augmented sediment production in debris basins by an average of 60 and individual basins show increases up to 400 to identify the dominant hillslope erosion processes the volumetric contribution of landslides was estimated using repeat aerial photographs for the same time interval over which the debris basins have been operative between 1928 and 1973 landsliding produced only 10 of the sediment in debris basins even in the long term when infrequent but volumetrically important landslides occur bedrock landslides appear to contribute a maximum of 50 to the long term landscape denudation previous mapping of soil slippage in the san dimas experimental forest within the san gabriel mountains rice et al 1969 rice and foggin 1971 indicates that shallow landsliding is likely to be the dominant modern hillslope erosion process when compared to incision rates derived from a fluvial shear stress model and to exhumation rates based on low temperature thermochronological data blythe et al 2000 modern natural erosion rates are comparable to denudation rates since the pliocene comparisons of modern erosion rates suggest that debris production on hillslopes and first order channels is directly dependent on vegetation cover and precipitation intensity for higher order channels drainage areas 2 km2 only major storms convey the sediments down valley during the past century some temporal decorrelation occurs between small scale and large scale catchments because hillslope produced sediment is stored in second order and higher channels until major storms mobilize it thus the larger fluvial network damps the episodic fire induced hillslope sediment pulses that occur within small watersheds at a longer temporal scale however uplift and denudation may have been sustained sufficiently long in much of the san gabriel mountains for the topography to reach a macroscale steady state in contrast to rapidly eroding 2 mm yr 1 ranges for which quantification of bedrock landsliding will approximate the sediment flux the san gabriel mountains occupy a niche of intermediate rates 0 1 1 0 mm yr 1 in which a broad suite of hillslope processes including shallow seated and deep seated landslides debris flows and wet and dry ravel contribute to the sediment flux

testing gassmann fluid substitution sonic logs versus ultrasonic core measurements although gassmann fluid substitution is standard practice for time lapse studies its validity in the field environment rests upon a number of underlying assumptions the impact of violation on the predictions of gassmann equations can only ultimately be validated by in situ testing in real geological environments in this paper we show a workflow that we developed to test gassmann fluid substitution by comparing saturated p wave moduli computed from dry core measurements against those obtained from sonic and density logs the workflow has been tested on 43 samples taken from a 45 m turbidite reservoir from the campos basin offshore brazil the results show good statistical agreement between the p wave elastic moduli computed from cores using the gassmann equation with the corresponding moduli computed from log data this confirms that all the assumptions of the gassmann are adequate within the measurement error and natural variability of elastic properties these results provide further justification for using the gassmann theory to interpret time lapse effects in this sandstone reservoir and in similar geological formations

how perfect is the himalayan arc the himalayan plate boundary because it is entirely subaerial is both the most dramatic and the most accessible to direct observation of all active convergent boundaries on earth the shape of this boundary can be described as a small circle of radius 1696 55 km centered at long 91 6 1 6 e and lat 42 4 2 1 n for the extent of the arc between long 77 2 and 92 1 e the pole of this small circle is consistent whether seismicity topography or stress state is used to define the position of the tectonic boundary the defined small circle also coincides with a peak in microseismicity the maximum horizontal strain rate and a peak in the vertical velocity field this quantitative definition of a stable curved tectonic boundary is a prerequisite to modeling the dynamics of curvature in convergent arcs and applying appropriate boundary conditions to other regional models

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

late quaternary geomorphic scenario due to changing depositional regimes in the tangtse valley trans himalaya nw india abstract records from the tangtse valley in the trans himalaya reveal depositional history since 48 ka with fluvial aggradation followed by incision lacustrine sediment fill and later incision varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses flood events colluvial and glacial activity are preserved the valley is located west of the pangong tso bangong co one of the largest lakes in tibet which has served as a spillway flooding and damming the entire tangtse valley resulting in the formation of a lake today pangong tso consists of five basins separated by shallow sills and is fed by snow melt documentation based on 14 c and osl chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of pangong tso toward west occupying the present day tangtse valley between 9 6 5 1 ka this event coincides with periods of high lake levels in tibet china as well as intensified monsoon periods over the indian subcontinent a fluvial regime around 48 ka and 30 21 ka with comparatively arid conditions and dry phases interspersed by flooding is documented the valley has been incised to depths of 40 50 m in the upper part and to 130 m in the lower part the incision rate ranges from 0 3 to 1 2 mm yr 1 in the upper part and reaches as high as 10 8 mm yr 1 in the lower valley much of the incision took place between 22 and 9 6 ka although repeated sediment fill incision cycles in the valley from 30 22 ka 22 9 6 ka 9 6 5 1 ka 5 1 ka and even to present time were observed

velocities and propagation characteristics of pn and sn beneath the himalayan arc and tibetan plateau possible evidence for underthrusting of indian continental lithosphere beneath tibet new seismological observations on velocities and propagation characteristics of pn and sn waves beneath tibet can be interpreted although not uniquely to indicate the shallow angle underthrusting of the greater indian continental lithosphere beneath the tibetan plateau this is inferred from available geological and geophysical data and is now supported by new seismological observations the most significant observation is that high frequency sn waves shear waves that travel in the mantle lithosphere propagate efficiently in the uppermost mantle beneath the tibetan plateau except beneath the north central part of tibet the chang thang terrane furthermore sn propagates efficiently across the stable block of the tarim basin along the tien shan and himalayan mountains and across the indian shield apparent velocities of pn and sn waves that traverse the uppermost mantle beneath the tibetan plateau are 8 42 and 4 73 km s respectively these velocities are very similar to those beneath the himalayan mountains and the indian shield the efficient propagation and the velocities of pn and sn waves beneath tibet are also similar to those commonly observed beneath shield and stable continental regions these results are consistent with the underthrusting model and do not favor the class of alternative models in which the tibetan plateau is formed by shortening and thickening of hot crustal and uppermost mantle material in response to the convergence of india and asia

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

ultrasonic velocities of north sea chalk samples influence of porosity fluid content and texture we have studied 56 unfractured chalk samples of the upper cretaceous tor formation of the dan south arne and gorm fields danish north sea the samples have porosities of between 14 and 45 and calcite content of over 95 the ultrasonic compressional and shear wave velocities vp and vs for dry and water saturated samples were measured at up to 75 bar confining hydrostatic pressure corresponding to effective stress in the reservoir the porosity is the main control of the ultrasonic velocities and therefore of the elastic moduli the elastic moduli are slightly higher for samples from the south arne field than from the dan field for identical porosities this difference may be due to textural differences between the chalk at the two locations because we observe that large grains i e filled microfossils and fossil fragments that occur more frequently in samples from the dan field have a porosity reducing effect and that samples rich in large grains have a relatively low porosity for a given p wave modulus the clay content in the samples is low and is mainly represented by either kaolinite or smectite samples with smectite have a lower p wave modulus than samples with kaolinite at equal porosity we find that ultrasonic vp and vs of dry chalk samples can be satisfactorily estimated with gassmann s relationships from data for water saturated samples a pronounced difference between the vp vs ratios for dry and water saturated chalk samples indicates promising results for seismic amplitude versus offset analyses

unraveling chalk microtextural properties from indentation tests abstract the petrographical petrophysical and geomechanical properties of the less commonly studied low permeability or tight chalks are presented in this study the latter are relevant as potential unconventional reservoirs or intra reservoir seals tight chalks encompass different lithotypes in which the main factors controlling the petrophysical properties as shown in this study are the non carbonate content and the degree of cementation those parameters strongly modify chalk microtexture and thus its porous network reducing pore sizes hence altering poroperm properties in order to better understand the characteristics of tight chalks an integrated petrographical petrophysical and geomechanical study was carried out on a set of 65 chalk samples from northwestern european outcrops covering a wide range of lithotypes the dataset gathered covers a broad spectrum of values for the determined petrophysical e g porosities from 9 to 45 and geomechanical properties e g strengths from 3 to 60 mpa in the framework of this study indentation tests were performed on the chalk samples this technique proved to be a successful method to quickly estimate rock strength indeed a good linear correlation r2 0 90 has been established between indentation strength and ucs furthermore indentation tests yielded valuable information about the chalk properties both in terms of petrographical cementation clay content petrophysical exponential relationship with porosity and geomechanical in relation to the elastic parameter and plasticity index properties this cheap and easy to operate method is a promising tool to indirectly estimate the mechanical parameters of chalks when core samples are unavailable for laboratory testing in oil field wells

morphotectonic analysis of the hazara arc region of the himalayas north pakistan and northwest india abstract in the hazara arc region of northern pakistan some of the active basements structures buried below a thick detached sedimentary layer are inferred from the distribution of lineaments and the drainage patterns as viewed in landsat satellite imagery and from river profiles a prominent set of nw trending lineaments seen on satellite imagery coincides approximately with the southwest or updip side of the indus kohistan seismic zone iksz the most active basement structure of the region even though this structure is buried beneath and decoupled from a 12 km thick sedimentary layer the iksz has been interpreted as an extension of the himalayan basement thrust and is also associated with a prominent topographic step knickpoints on major rivers in the region lie on or north of the iksz all indus river tributaries examined north of the iksz show prominent knickpoints while two tributaries draining south of the iksz have no knickpoints these results suggest ongoing uplift above and north of the iksz and are consistent with the tectonic model obtained from the seismic data another prominent lineament set is detected along the north south section of the indus river this set is probably related to the indus river horst anticline and associated reentrant one of the two highest lineament concentrations occurs at the intersection between the nw trending iksz lineament and the n trending indus river lineament the other is along the west bank of the indus valley 25 km north of tarbela dam a topographic ridge swabi nowshera ridge appears to be forming along the west side of the indus river in the peshawar basin the rising ridge is ponding the kabul river upstream of nowshera where the drainage is braided