controls of eustasy and diagenesis on the 238u 235u of carbonates and evolution of the seawater 234u 238u during the last 1 4 myr using a leaching protocol designed for the study of u isotopes in recent carbonates we measured the u isotope composition both 238 u 235 u and 234 u 238 u of modern and ancient corals n 6 a limestone and a dolostone as well as 43 shallow water carbonate sediments from the odp leg 166 site 1009 drill core on the slope of the bahamas platform although bulk corals record the seawater 238 u value within 0 02 differences of up to 0 30 in the 238 u of individual leachates suggest a control of the coral structure and a more positive 238 u 235 u ratio in the centers of calcification the drill core 238 u data shows that the 238 u 235 u ratio of shallow water carbonates is controlled mainly by 1 variations in sea level through the mixing of different amounts of platform derived sediments with 238 u 0 50 0 60 heavier than seawater and pelagic sediments with seawater like 238 u values 2 authigenic u enrichment via pore watercirculation and u reduction both on the platform and down to 5 m below the surface mbsf after deposition of the sediment and to a lesser extent by 3 early diagenetic processes i e carbonate dissolution and or recrystallization during sediment burial the global effect of these processes leaves the 238 u values of shallow water carbonates offset relative to that of seawater by carbonates sw 0 24 0 06 95 ci including all samples this shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow water platform shelf and slope environments i e most of the carbonate sedimentary record prior to the mesozoic to account for the average effect of carbonate diagenesis assuming that the 238 u 235 u ratio of carbonate platform sediments directly records the seawater 238 u 235 u ratio would underestimate the extent of ocean seafloor anoxia by at least a factor 10 the rapid fluctuations in 238 u values due to sea level changes i is a factor that should be considered before interpreting 238 u variations as reflecting changes in oceanic paleoredox conditions and ii reinforces the need for statistically meaningful data sets the 234 u data suggest that the 234 u 238 u ratio of the seawater has remained within 20 of the modern seawater value during the last 1 1 4 myr furthermore we find that small scale 1 15 variations in seawater 234 u mirror sea level changes during the penultimate glacial interglacial period 140 to 200 ka thus confirming the record of lower 234 u sw during periods of low sea level stand and expanding it to at least the last two glacial interglacial events i e 0 23 ma such fluctuations in 234 u initial values should be taken into account when screening carbonate sediments u th ages on the basis of the initial 234 u 238 u ratios of the samples

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

mineralogy early marine diagenesis and the chemistry of shallow water carbonate sediments abstract shallow water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of earth s chemical and climatic history one of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post depositional diagenetic alteration in this study we use paired measurements of calcium 44ca 40ca or 44ca and magnesium 26mg 24mg or 26mg isotope ratios in sedimentary carbonates and associated pore fluids as a tool to understand the mineralogical and diagenetic history of neogene shallow water carbonate sediments from the bahamas and southwest australia we find that the ca and mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis the observed variability in bulk sediment ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid fluid buffered to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment sediment buffered our results indicate that this process together with variations in carbonate mineralogy aragonite calcite and dolomite plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers 13c 18o major minor and trace elements in shallow water carbonate sediments in the geologic record our results also provide evidence that a large shallow water carbonate sink that is enriched in 44ca can explain the mismatch between the 44 40ca value of rivers and deep sea carbonate sediments and call into question the hypothesis that the 44 40ca value of seawater depends on the mineralogy of primary carbonate precipitations e g aragonite seas and calcite seas finally our results for sedimentary dolomites suggest that paired measurements of ca and mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo environmental information preserved in these enigmatic but widespread carbonate minerals

early diagenesis of shallow water periplatform carbonate sediments leeward margin great bahama bank ocean drilling program leg 166 mineralogic petrographic and geochemical analyses of sediments recovered from two leg 166 ocean drilling program cores on the western slope of great bahama bank 308 m and 437 m water depth are used to characterize early marine diagenesis of these shallow water periplatform carbonates the most pronounced diagenetic products are well lithified intervals found almost exclusively in glacial lowstand deposits and interpreted to have formed at or near the seafloor i e hardgrounds hardground cements are composed of high mg calcite 14 mol mgco 3 and exhibit textures typically associated with seafloor cementation geochemically hardgrounds are characterized by increased 18 o and mg contents and decreased 13 c sr and na contents relative to their less lithified counterparts despite being deposited in shallow waters that are supersaturated with the common carbonate minerals it is clear that these sediments are also undergoing shallow subsurface diagenesis calculation of saturation states shows that pore waters become undersaturated with aragonite within the upper 10 m at both sites dissolution and likely recrystallization of metastable carbonates is manifested by increases in interstitial water sr and sr ca profiles with depth we infer that the reduction in mineral saturation states and subsequent dissolution are being driven by the oxidation of organic matter in this fe poor carbonate system precipitation of burial diagenetic phases is indicated by the down core appearance of dolomite and corresponding decrease in interstitial water mg and the presence of low mg calcite cements observed in scanning electron microscope photomicrographs

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

uranium and radium diffusion in organic rich sediments sapropels among the late quaternary mediterranean sapropels the s5 125 ka is one of the best preserved due to its high organic carbon content that has limited postdepositional oxidation the high uranium content in this sapropel 40 dpm g 1 makes this layer interesting for studying uranium series disequilibrium in organic rich sediments for this reason the present work provides isotopic measurements of the u decay series in a s5 sapropel by applying more precise mass spectrometric methods tims mc icpms and gamma spectrometry assuming that u in the sapropel mostly originated from seawater the 234u 238u 230th 238u 226ra 230th and 231pa 235u activity ratios show systematic deviations from the theoretical values for a closed system evolution of the u series over the 125 ka since sapropel formation the radiogenic 234urad and 226ra show clear evidence of migration in the sapropel with modeled diffusion coefficients of 7 1 1 1 10 12 cm2 s 1 and 1 6 0 2 10 10 cm2 s 1 respectively the diffusion of 234urad cannot explain the high 230th 238u and 231pa 235u activity ratios observed in the sapropel two possible mechanisms or a combination of both are proposed for explaining the irregular 230th 238u and 231pa 235u activity profiles in sapropel s5 the first one is an enhanced export flux of 230thxs and 231paxs excesses exceeding the production rate in seawater during the time of sapropel formation and the second one is diffusion of authigenic uauth in the sapropel however the ambiguous determination of 230thxs and 231paxs in the sapropel and the poorly understood processes that might lead to uauth migration in anoxic sediments still limit a final explanation for the deviation of 230th 238u and 231pa 235u activity ratios from their expected theoretical values

u th dating of carbonate nodules from methane seeps off joetsu eastern margin of japan sea abstract we performed u th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off joetsu of the eastern margin of japan sea to decipher the active period of the methane seep the carbonates contain 230th part of which is located in detritus such as silicate and organics at the time of precipitation the initial 230th renders accurate dating with u th radioactive disequilibrium method difficult we assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty a 230th 232th 234u 232th isochron drawn by three chips divided from a carbonate nodule pc05 04 50 passed through data points of local sediments we conclude that the problem of initial 230th can be resolved by measurements of local sediments results show that carbonate nodules include local sediment as impurities furthermore the results of trace element analyses such as rb zr nb ree pb and th also support the idea in all 18 carbonate samples were dated with correction of initial 230th using the mean value of local sediment in this study the u th correction ages show 12 35ka with an isochron age of 26 3ka results indicate that during the time interval of u th ages from 12ka to 35ka environmental conditions must have been favorable for enhanced methane flux through sediment the extensive methane flow period at 20ka accords with the lowest stand sea level during the last glacial age results of this study also suggest that u th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation in order to acquire u th ages of carbonate at methane seep sites however it is important to evaluate the amount of initial 230th accurately using the value of sediment

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

paleoseismic evidence from trench investigation along hajipur fault himalayan frontal thrust nw himalaya implications of the faulting pattern on landscape evolution and seismic hazard abstract the study area falls within the mesoseismal zone of 1905 kangra earthquake mw 7 8 two parallel nnw sse striking active fault scarps named as hajipur faults hf1 and hf2 along the northwestern end of the janauri anticline in the foothill zone have displaced floodplain sediments of the beas river the hf1 and hf2 represent the imbricate faults of the himalayan frontal thrust hft and are the result of lateral propagation of deformation from two fold segments i e jf1 and jf2 respectively in northwest direction along the strike ground penetrating radar gpr profiles and trenching across the hf2 reveal two low angle thrust fault strands f1 and f2 displacements of 7 5 m on f2 and 1 5 m on the associated branching faults f a f b and f c were observed total four stratigraphic units unit a gravel with a lens of medium sand unit a is the oldest overlain by units b medium to coarse sand unit c with fine to medium sand and unit d fine to medium sand with scattered gravel were observed in trench radiocarbon ages of the charcoal samples from unit b and unit d optical ages of sediments from units a b and c gpr data and trench log suggest two major events along f1 and f2 strands event i along f1 occurred during 2600 800 yr bp and event ii along f2 around 400 yr bp and before 300 yr bp given the uncertainty in dates it is suggested that the latest event occurred during 1500 1600 ad considering the oldest unit unit a exposed in trench with vertical displacement of 7 5 8 m age of 2600 500 yr bp and net displacement of 9 m during single event along low angle fault 25 implies slip rate 7 6 1 7 mm yr uplift rate 3 2 0 6 mm yr shortening rate 6 9 1 4 mm yr and recurrence interval 1160 250 yr for large magnitude event with mw 7 0 with the recurrence of 1100 yr the penultimate event probably occurred at around 1400 1500 yr bp given the recent gps based slip rate of 14 1 mm yr in kangra reentrant baneerjee and burgman 2002 the present study suggests that about half of this slip is consumed along the hft and that this fault is more active compared to those in the hinterland

active circulation of saline ground waters in carbonate platforms evidence from the great bahama bank measurements of salinity temperature and ground water discharges within the great bahama bank provide evidence of active circulation of near normal ocean water beneath north andros island elevated salinity waters 38 42 derived by density refulx from the great bahama bank flow eastward beneath the island and mix with normal salinity cold ground waters 19 20 c from deeper than 250 m in the adjacent oceans east to west flow of water from the straits of florida may be driven by head differences generated by the florida current which impinges on the western margins of the platform alternatively density differences between the reflux and tongue of the ocean sea waters may cause more local circulation on the eastern flanks these flows have important diagenetic implications particularly in the explanation of pervasive secondary dolomitization widely reported at shallow depths in the bahamas

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

lower triassic carbonate δ238u record demonstrates expanded oceanic anoxia during smithian thermal maximum and improved ventilation during smithian spathian boundary cooling event abstract the smithian spathian boundary ssb transition was recently identified as a major biocrisis on the road to marine ecosystem recovery following the end permian mass extinction marine anoxia is hypothesized to have played an important role in the ssb biocrisis however an understanding of the relationship of this biocrisis to contemporaneous marine redox conditions has been hampered by limited knowledge of the timing duration and extent of anoxia during the smithian spathian s s transition here we present a high resolution carbonate u isotope record from the jiarong section of south china that spans the mid smithian to mid spathian interval this record shows persistent negative 238u values averaging 0 56 in the late smithian followed by a rapid positive shift from 0 78 to 0 10 across the ssb and then a more gradual shift back to lower 238u values in the early to mid spathian u isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late smithian and the early to mid spathian but contracted sharply during the s s transition this redox pattern shows an excellent correspondence to previously published tropical sea surface temperature sst records with peak oceanic anoxia coinciding with the smithian thermal maximum stm and diminished anoxia during a pronounced global cooling event at the ssb although paleontological records commonly do not distinguish between terminations during the late smithian and ssb we hypothesize that the ssb biocrisis which was marked by sharp diversity losses among conodonts ammonoids and other marine invertebrates was primarily associated with the stm in which case oceanic anoxia is likely to have been a major stressor of mid olenekian marine biotas

u th stratigraphy of a cold seep carbonate crust on continental margins oxidation of methane rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor the biogeochemical processes involved during this carbonate precipitation are increasingly understood but little is known about the duration or mode of carbonate crust formation here we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement which provide the first stratigraphy for a cold seep carbonate crust the 5 5 cm thick crust nl7 cc2 was collected by submersible on the nile deep sea fan in an area of active fluid venting u th analyses must be corrected for initial th and measurement of co existing sediments indicates the presence of both scavenged and detrital initial 230th which must be considered during this correction the calculated 230th u age depth profile for nl7 cc2 provides evidence for continuous downward carbonate precipitation at the studied location over the last 5000 years three distinct phases can be distinguished from top to bottom with average growth rates of 0 4 5 and 0 8 cm kyr respectively corresponding to carbonate precipitation rates ranging from 7 to 92 mol m2 h 1 rates consistent with previous estimates high resolution 13c profiles gontharet s pierre c blanc valleron m m rouchy j m fouquet y bayon g foucher j p woodside j mascle j the nautinil scientific party 2007 nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the nile deep sea fan eastern mediterranean sea deep sea res ii 54 1292 1311 and major elements across nl7 cc2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition we suggest that these changes primarily reflect modification of the diagenetic environment i e a progressive depletion of dissolved sulphate through anaerobic oxidation of methane caused by the initial carbonate crust formation and the resulting reduction in bioirrigation overall u th dating of cold seep carbonates offers a promising tool to bring new insights into biogeochemical processes at cold seeps and to assess the timing and duration of fluid venting on continental margins

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

advected glacial seawater preserved in the subsurface of the maldives carbonate edifice abstract analysis of both conservative and reactive geochemical tracers in pore fluids extracted from sediment cores from the maldives inner sea reveal extensive interstitial water masses whose origins lie in glacial intermediate water advected laterally through the maldives carbonate edifice these drillcores recovered during expedition 359 of the international ocean discovery program penetrate late oligocene to recent sediments including carbonate platform slope pelagic and drift facies combined shipboard and shore based analyses of the pore fluids show linearly co varying changes in the concentration of chloride and 18 o and d values of 25 mm 1 2 and 9 respectively additionally pore fluid strontium concentrations and calcium isotope ratios are strongly anti correlated with each other multiple reversals in these geochemical properties with depth indicate the existence of several distinct interstitial water masses these variations are interpreted as representing the different ages and reactive histories of young pleistocene and holocene waters advecting through the much older sedimentary formations in particular the elevated chloride concentrations and water isotope ratios suggest that seawater from the last glacial maximum is preserved in the subsurface where it occupies over 400 m of the sediment column within mid to late miocene sediments these pore fluids constrain the properties of an intermediate depth glacial water mass that had higher salinity and 18 o and d values than the average glacial ocean this system represents a unique archive yielding the most direct observations of glacial seawater to date as well as a demonstration of the long lasting potential for water rock interaction in carbonate platform systems

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage

global ocean redox variations across the smithian spathian boundary linked to concurrent climatic and biotic changes abstract the smithian spathian boundary ssb was an interval characterized by a major global carbon cycle perturbation climatic cooling from a middle late smithian boundary hyperthermal condition and a major setback in the recovery of marine necto pelagic faunas from the end permian mass extinction although the ssb has been linked to changes in oceanic redox conditions key aspects of this redox variation e g duration extent and triggering mechanisms and its relationship to coeval climatic and biotic changes remain unresolved here we report a high resolution middle smithian to middle spathian u isotope 238u record based on marine carbonates of the zuodeng south china and jesmond british columbia sections to investigate the timing and global extent of ocean redox variation across the ssb our 238u record reveals values similar to or slightly heavier than modern seawater 0 39 during the middle smithian a rapid negative shift to highly negative values during the early late smithian a positive shift at the ssb and a rapid shift back to more negative values in the early middle spathian a simple u isotope mass balance modeling suggests that the global area of anoxic seafloor expanded strongly during the late smithian and the early middle spathian covering 11 of total seafloor area but that it contracted sharply during the ssb 2 the redox pattern documented by our 238u record shows a good first order correspondence to tropical sea surface temperature sst data for the smithian spathian in particular peak anoxia coincided with the middle late smithian boundary hyperthermal event and diminished anoxia with a pronounced decline in ssts at the ssb the temporal correlation between anoxia and low biodiversity levels of many marine clades e g conodonts and ammonoids during the late smithian indicates that oceanic anoxia may have played a role in the ssb biocrisis

numerical models of fluid flow in carbonate platforms implications for dolomitization abstract the role of fluid flow in dolomitization is evaluated through hydrologic simulations designed to capture and test numerically the essential elements of some common dolomitization models a two dimensional finite difference code bethke 1985 was used to simulate single phase flow of variable salinity fluids driven by compaction convection and topography in carbonate platforms and adjacent basinal sediments a simple hydrostratigraphic model consisting of a platform reef complex surrounded by basin filling shale was constructed to examine the magnitude and direction of compaction flow during the initial phase of subsidence most pore fluids in the shale migrate to the surface at velocities less than 0 1 mm yr and basin derived fluids are focused into the reef from only a limited distance of 10 km relatively porous and permeable basinal limestones and sandstones may act as conduits for updip fluid flow into the platform reef complex magnesium mass balance constraints coupled with hydrologic simulations suggest that burial compaction is not an efficient mechanism for regional dolomitization two layer hydrostratigraphic models involving variable salinity fluids show that evaporation of seawater results in downward and seaward fluid migration the magnitude of flow is a function of fluid density even fluids at salinities marginally elevated above normal seawater values are capable of penetration several hundreds of meters into the underlying sediments albeit at rates of less than 1 cm yr paleohydrologic simulations coupled with thermodynamic arguments support that reflux of surface derived waters evaporated past gypsum saturation is a viable dolomitization mechanism calculations utilizing rates of mg mass flux show that dolomitization of large carbonate platforms 10 km3 by fluids below halite saturation requires millions of years of reflux driven flow p thermal convection of seawater through carbonate platforms has been simulated by varying the basal heat flow the thermal pump produces a convection cell in which lateral and vertical flow achieve rates of 75 0 and 13 0 mm yr respectively the potential for dolomitization is high because a large reservoir of mg seawater is tapped elevated temperatures drive fluids further into the stability field for dolomite and kinetic inhibition of dolomite nucleation and growth is decreased simulations of high frequency glacio eustatic sea level oscillations suggest that a dynamic hydrologic regime may be established a sea level fall of 2 m lasting for 10 000 yr can drive lateral flow at rates up to 0 15 m yr dolomitization is possible because marine waters migrate through the carbonate platform in response to gradients of hydraulic head created by eustatic sea level fluctuations

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

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

early diagenetic processes in labrador sea sediments uranium isotope geochemistry the concentration and isotopic composition of u dissolved in pore waters from hemipelagic sediments of the labrador sea were determined by thermal ionization mass spectrometry in two 30 cm long box cores the present fluxes of seawater u that diffuses across the sediment seawater interface are on the order of 2 4 g cm2 ka this diffusion imposes decreasing gradients of dissolved u downwards but the u concentration in pore waters immediately below the surface is much lower than that of open ocean seawater this is a primary feature that cannot be explained by carbonate precipitation due to decompression during core retrieval more likely it reflects the presence of a stagnant benthic boundary layer above the sediment water interface in which molecular diffusion of u is slower than in the overlying turbulently mixed seawater and or of microzones near the interface where u is bioaccumulated uranium is adsorbed at depths onto the solid phase in response to changes in the redox conditions within the

seismites in the kathmandu basin and seismic hazard in central himalaya soft sediment deformation structures have been analyzed at six sites of the kathmandu valley microgranulometric study reveals that silty levels 60 to 80 silt favor the development of soft sediment deformation structures while sandy levels 60 to 80 sand are passively deformed nonetheless well sorted sand levels more than 80 sand generate over fluid pressure during compaction if located beneath a silty cap leading to fluidization and dike development 3 d geometry of seismites indicates a very strong horizontal shearing during their development using a physical approach based on soil liquefaction during horizontal acceleration we show that the fluidization zone progressively grows down section during the shaking but does not exactly begin at the surface the comparison of bed thickness and strength depth evolution indicates three cases i no soft sediment deformation occurs for thin few centimeters silty beds ii the thickness of soft sediment deformation above sandy beds is controlled by the lithological contrast iii the thickness of soft sediment deformation depends on the shaking intensity for very thick silty beds these 3 cases are evidenced in the kathmandu basin we use the 30 cm thick soft sediment deformation level formed during the 1833 earthquake as a reference the 1833 earthquake rupture zone extended very close to kathmandu inducing there mmi ix x damages a 90 cm thick sediment deformation has therefore to be induced by an event greater than mmi x from a compilation of paleo and historic seismology studies it is found that the great m 8 1 historical earthquakes are not characteristic of the greatest earthquakes of himalaya hence earthquakes greater than m 8 6 occurred kathmandu is located above one of the asperities that laterally limits the extent of mega earthquake ruptures and two successive catastrophic events already affected kathmandu in 1255 located to the west of this asperity and in 1100 to the east

untangling the diagenetic history of uranium isotopes in marine carbonates a case study tracing the δ238u composition of late silurian oceans using calcitic brachiopod shells abstract the u isotope composition of ancient marine carbonates has been used to determine the 238u of past oceans based on the premise that the 238u signatures of marine carbonates reflect the 238u of seawater at the time of deposition however recent work from the bahamas shows that diagenesis alters the 238u signatures of bulk carbonates by effectively creating a positive and variable offset from seawater therefore finding a sedimentary archive that reliably records and preserves the 238u signal from seawater becomes fundamental calcitic brachiopod shells may provide such an archive as their shell structure can endure the effects of diagenesis and thus their 238u signatures can record the u isotope composition of the seawater in which they lived to explore whether calcitic brachiopods can more robustly record seawater 238u than bulk carbonates we analyzed brachiopod shells and their host carbonate matrices from five different stratigraphic levels across the upper silurian lau carbon isotope excursion cie using the data from brachiopod shells our results suggest that seawater 238u values were relatively stable and lower than present day 238u 0 58 0 11 2sd n 17 indicative of a more anoxic ocean state across the positive cie we also find that carbonate matrices display a distinctive positive 238u offset from contemporaneous seawater that varies between beds some beds show a ca 0 30 offset similar to what is described in the bahamas whereas others display no offset from the inferred seawater u isotope composition we propose the variability of the observed 238u offset to be a function of the degree of u vi exchange between anoxic porewaters and seawater a diminished u vi exchange would define a closed system style of diagenesis and mute the net isotope offset expressed between sediments and contemporaneous seawater some of the factors affecting the degree of u vi exchange include organic matter fluxes into the sediments and diagenetic fluid flow rates which could vary due to relative sea level changes as a result the observed 238u variability of the analyzed carbonate matrix samples could be the result of the environmental changes caused by the sea level fluctuations described for the studied stratigraphic interval we conclude that calcitic brachiopod shells provide an important archive for evaluating the 238u of ancient oceans and the style of diagenesis of u in marine carbonates

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

uranium series dating applications in natural environmental science uranium series u series analyses are an essential component of many research projects in earth and environmental science oceanography hydrology and science based archaeology topics range from magma chamber evolution and volcanic hazard prediction global climatic change through dating of authigenic carbonate deposits human evolution through dating of bone to the study of groundwater evolution the u series decay chains contain many elements that can be fractionated in environmental and geological processes half lives of radioactive isotopes of such elements range from seconds to many millennia and application depends on the natural timeframe of the process or the elapsed time this review will be limited to some aspects of the 238u 234u 230th 226ra system with half lives of 245 kyr 76 kyr and 1 6 kyr respectively in environmental systems fractionation of uranium and thorium is a very efficient process because thorium is extremely insoluble while hexavalent uranium in oxidising conditions is relatively soluble many authigenic precipitates of calcite contain virtually no thorium and inorganic precipitates have u ca ratios very similar to the ratio of dissolved uranium and calcium almost no radiogenic 230th in the precipitate means that the radiogenic clock starts effectively at zero however pure authigenic precipitates are rare and many contain some allogenic material mostly silicate with 238u in secular equilibrium with significant 230th some of the characteristics of different types of samples and various methods to accommodate or correct for inherited 230th will be discussed authigenic material should remain a closed system with respect to the relevant isotopes but that requirement is sometimes difficult to maintain because radioactive decay results in damage to the crystal lattice of the host mineral consequences of this recoil effect and correction schemes will be discussed dating archaeological bone based on the systematics of diffusion and adsorption to effectively model open system behaviour is also included

recent movements along the main boundary thrust of the himalayas normal faulting in an over critical thrust wedge abstract the main boundary thrust mbt is one of the major himalayan thrusts occurring during the cainozoic and it is presently incorporated within the himalayan thrust wedge lesser and outer himalayas displaced above the indian lithosphere nonetheless the mbt shows recent normal displacement along most of its length we suggest that the orientation of the major principal stress within the himalayan thrust wedge deviates significantly from the horizontal and when this deviation exceeds the dip of the vectors normal to back tilted thrusts the normal component of displacement may act along these faults steep north dipping segments of the mbt therefore show a normal component of displacement if a geometrical definition is used but they are faults in a compressional regime where the major principal stress axis has deviated from the horizontal micro structural data recorded along the surkhet ghorahi segment of the mbt are consistent with a strong deviation of the state of stress the presence of such peculiar normal faulting along the mbt is used to calibrate the mechanical characteristics of the belt considered as a coulomb wedge the following characteristics are suggested a very poor strength contrast between basal decollement and rocks in the wedge body b a high pore fluid pressure ratio probably close to 0 8 0 9 and a higher fluid pressure ratio close to 1 0 along the active normal faults if a high internal friction angle close to the byerlee value is considered the strong deviation in principal stress direction may have recently increased due to a taper of the himalayan wedge exceeding the stability boundary and may be controlled by erosion and isostatic uplift rebound of the himalayan range

clinoptilolite as a new proxy of enhanced biogenic silica productivity in lower miocene carbonate sediments of the bahamas platform isotopic and thermodynamic evidence abstract massive clinoptilolite authigenesis was observed at about 1105 meters below sea floor mbsf in lower miocene well compacted carbonate periplatform sediments from the great bahama bank ocean drilling program odp leg 166 site 1007 the diagenetic assemblage comprises abundant zeolite crystallized within foraminifer tests and sedimentary matrix as well as mg smectites in carbonate rich deposits the formation of the zeolite requires a supply of silica thus the objective of the study is to determine the origin of the silica supply its diagenetic evolution and consequently the related implications on interpretation of the sedimentary record in terms of local or global paleoceanographic change for lack of evidence for any volcaniclastic input or traces of si enriched deep fluids circulation an in situ biogenic source of silica is validated by isotopic data and chemical modeling for the formation of such secondary minerals in shallow water carbonate sequences geochemical and strontium isotopic data clearly establish the marine signature of the diagenetic zeolite as well as its contemporaneous formation with the carbonate deposition sr model ages of 19 6 23 2 ma the test of saturation for the pore fluids specifies the equilibrium state of the present mineralogical assemblage seawater rock modeling specifies that clinoptilolite precipitates from the dissolution of biogenic silica which reacts with clay minerals the amount of silica opal a involved in the reaction has to be significant enough at least 10 wt to account for the observed content of clinoptilolite occurring at the most zeolite rich level modeling also shows that the observed amount of clinoptilolite 19 reflects an in situ and short term reaction due to the high reactivity of primary biogenic silica opal a until its complete depletion the episodic occurrence of these well lithified zeolite rich levels is consistent with the occurrence of seismic reflectors particularly the p2 seismic sequence boundary located at 1115 mbsf depth and dated as 23 2 ma the age range of most zeolitic sedimentary levels biostratigraphic ages of 21 5 22 ma correlates well with that of the early miocene glaciation mi 1 and mi 1a global events thus the clinoptilolite occurrence in the shallow carbonate platform environment far from volcanogenic supply or in other sensitive marine areas is potentially a significant new proxy for paleoproductivity and oceanic global events such as the miocene events which are usually recognized in deep sea pelagic sediments and high latitude deposits

an early diagenetic deglacial origin for basal ediacaran cap dolostones abstract the beginning of the ediacaran period 635 ma is marked by conspicuous dolostone units that cap marinoan glacial deposits worldwide the extent and sedimentary characteristics of the cap dolostones indicate that anomalous carbonate over saturation coincided with deglacial sea level rise and ocean warming however the geochemical variability within cap dolostones both between continents across single continental margins and within individual stratigraphic sections has been difficult to reconcile with depositional models using a compilation of new calcium and magnesium isotope measurements in marinoan cap dolostone successions worldwide we show that the geochemical variability can be explained by early diagenetic dolomitization of aragonite along a spectrum of fluid and sediment buffered conditions dolostones from the outer platform formed under fluid buffered conditions whereas dolostones on the inner platform and foreslope environment formed under sediment buffered conditions this spatial pattern of dolomitizing conditions is consistent with buoyant recirculation of glacial seawater within carbonate platforms driven by the deglacial sea level rise and development of a meltwater surface ocean using a numerical diagenetic model to evaluate the geochemical differences between sediment and fluid buffered cap dolostone units we constrain the chemical and isotopic composition of both the dolomitizing fluid glacial seawater 13 c 0 2 the meltwater lens 13 c 11 and the primary aragonite sediment 13 c 6 to 3 these model end members do not imply that primary geochemical variability did not exist but demonstrates that it is not necessary to change the chemistry of seawater to explain the global stratigraphic variability in the geochemistry of basal ediacaran cap dolostones our results provide a novel framework for understanding the geochemical variability of cap dolostone units including large excursions in carbon isotopes and how this variability is the product of local diagenetic processes expressed globally in continental margin environments following the last snowball earth

limit of strain partitioning in the himalaya marked by large earthquakes in western nepal great earthquakes in the himalaya are thought to occur mostly along the range front field mapping and radiocarbon dating reveal earthquake rupture on a previously unrecognized fault in the interior of the western himalaya which forms part of a key structural component of the mountain range implying that seismic risk evaluations should be revised

the geochemistry of uranium and thorium in coastal marine sediments and sediment pore waters pore water profiles of uranium and thorium isotopes in the muddy sediments of buzzards bay ma permit an assessment of the effect of diagenetic redox reactions on the geochemical behavior of these elements uranium shows a pronounced minimum pore water concentration 1 2 dpm kg near the sediment water interface 0 3 cm which coincides with the pore water fe maximum u concentrations increase with depth to a broad maximum which is greater than the overlying seawater value then decrease laboratory sediment tank experiments maintained without macrofauna also show the near interface minimum and increase and sediment incubation experiments show removal of u from the pore water to a constant value by about 40 days the 234u238u activity ratio is equal to the seawater value in all samples oxidation state separations of pore water u in hcl solution using anion exchange demonstrate that u is present in the pore water as u vi the coincidence of the pore water uranium and fe maximum is consistent with the hypothesis of reduction of u vi to u iv and removal from solution at about the same depth or pe as fe is reduced increases in pore water u with depth appear to be related to release of authigenic seawater u vi to solution possibly as alkalinity and ph increase and organic matter with which the u is associated is oxidized lower concentrations at depth in the sediment column may be linked to increases of effective u reducing agents like hydrogen sulfide in the pore water or to the activities of macrofauna in contrast pore water profiles of the long lived th isotopes 232th and 230th show low activities 02 dpm kg and relatively little change with depth although values are greater than those in the overlying water solid phase activities are similarly constant with depth and the distribution may be controlled by a sorption equilibrium between pore water and the solid phase the short lived isotope 234th shows greatest pore water activities in the upper 5 cm and is present at virtually zero activities elsewhere in the sediment column the upper few centimeters of the sediment generally contain excess 234th scavenged from the overlying water column and distributed by bioturbation as well as pore water fe and mn profiles which show maxima indicating reduction and dissolution of fe and mn oxyhydroxides the pore water 234th profile can be explained by release of 234th from the solid phase as femn oxide surface coatings are reduced and dissolved

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

redefining medlicott wadia s main boundary fault from jhelum to yamuna an active fault strand of the main boundary thrust in northwest himalaya abstract the mbt demarcates a tectonic boundary between the tertiary sub himalaya and the pre tertiary lesser himalaya south of the mbt another tectonically important fault extends from muzaffarabad and riasi in jammu kashmir to bilaspur and nahan in himachal medlicott and wadia had designated this fault the main boundary fault mbf in simla hills and jammu region respectively in between these two areas later workers gave local area names to the mbf as the riasi thrust in jammu palampur thrust in kangra bilaspur thrust in simla hills and nahan thrust in sirmur we have reviewed and established the tectonostratigraphic framework and physical continuity of the lower tertiary belt and the mbf the lower tertiary belt lying south of the mbt has characteristic tectonostratigraphic setting with discontinuous bodies of stromatolite bearing proterozoic limestone overlain with depositional contact by the paleocene lower part middle eocene marine subathu patala formation which in turn overlain by the upper oligocene lower miocene non marine dharamsala murree formation to avoid confusion with the mbt we designate collectively the mbf and related faults as the medlicott wadia thrust mwt the mwt extends east of hazara kashmir syntaxis to river yamuna covering a distance of 700 km further east of yamuna the lower tertiary belt pinches out and the mwt merges with the sensuo stricto mbt the proterozoic limestone represents the basement over which the lower tertiary sediments were deposited the limestone basement with its cover was detached by the mwt exhuming to the surface and thrusting over largely the siwalik group the reactivated balakot bagh fault causative fault for the 2005 kashmir earthquake extends southeast with right step to the riasi thrust the riasi thrust shows evidence of reactivation and active tectonic activity in jammu region it extends further east to the palampur thrust in kangra reentrant which lies within the 1905 kangra earthquake rupture zone the bilaspur thrust continuation of the palampur thrust shows active faulting south of simla hills between sataun and yamuna river these observations indicate that the mwt represents a southern strand of the sensuo stricto mbt and shows active faulting in some segments

first access to the ocean beneath ekstromisen antarctica by means of hot water drilling a hot water drill developed during the past 2 years at alfred wegener institute was used to penetrate the ekstrom ice shelf several times near the georg von neumayer station the drilling operation was successful and the initial large diameter 35 cm allowed easy access to the ocean one hole was used to install an ultrasonic echo sounder which recorded the ablation at the ice shelf bottom continuously another hole was used for emplacement of a thermistor string throughout the 237 m thick ice shelf for ice temperature measurements several ctd profiles in the 175 m deepwater column and the analysis of water samples provided valuable data for the understanding of ice shelf ocean interactions

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

high resolution characterization of the asian monsoon between 146 000 and 99 000 years b p from dongge cave china and global correlation of events surrounding termination ii abstract speleothem samples from hulu eastern china 32 30 n 119 10 e and dongge southern china 25 17 n 108 5 e caves provide a nearly continuous record of the asian monsoon over the last 160 ka wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 yuan d cheng h edwards r l dykoski c a kelly m j zhang m qing j lin y wang y wu j dorale j a an z cai y 2004 timing duration and transitions of the last interglacial asian monsoon science 304 575 578 we have obtained higher resolution data in the interval between 99 and 146 ka b p providing a detailed account of 18o variations over most of mis 5 and the latter portion of mis 6 precise 230th dating has replicated the chronology of the samples within error the higher resolution data set confirms the timing of asian monsoon termination ii the midpoint of the negative shift in 18o marking the onset of the last interglacial asian monsoon placing it at 129 0 0 9 ka b p the bulk of this transition 1 7 took place within approximately 70 years with the total range of the transition being 3 the most abrupt portion of the shift in 18o values 1 1 marking the end of the last interglacial asian monsoon occurred in 120 years the midpoint of which is 120 7 1 0 ka b p the dongge cave monsoon 18o record over late mis 6 exhibits a series of sub orbital millennial scale climate shifts that average 1 3 in magnitude and occur on average every 1 8 ky abrupt shifts in 18o of up to 1 also occurred throughout the last interglacial asian monsoon with periods at multi decadal to centennial timescales similar to the amplitude and periodicities of events found by dykoski et al dykoski c a edwards r l cheng h yuan d cai y zhang m lin y an z revenaugh j 2005 a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china earth and planetary science letters 233 71 86 during the holocene in the dongge record these shifts cover more than 1 2 of the amplitude of millennial scale and multi centennial scale interstadial events during the last glacial period wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 and millennial scale and multi centennial scale interstadial events during the penultimate glacial period in china this study abrupt decadal to millennial scale climate events therefore appear to be a general feature of both glacial and interglacial climate we demonstrate that monsoon intensity correlates well with atmospheric ch4 concentrations over the transition into the bolling allerod the bolling allerod and the younger dryas in addition we correlate an abrupt jump in ch4 concentration with asian monsoon termination ii on the basis of this correlation we conclude that the rise in atmospheric co2 antarctic warming and the gradual portion of the rise in ch4 around termination ii occur within our weak monsoon interval wmi an extended interval of heavy 18o between 135 5 1 0 and 129 0 1 0 ka b p prior to asian monsoon termination ii and northern hemisphere warming antarctic warming over the millennia immediately preceding abrupt northern warming may result from the bipolar seesaw mechanism as such warming albeit to a smaller extent also preceded asian monsoon termination i the bipolar seesaw mechanism may play a critical role in glacial terminations

congruent permian triassic δ238u records at panthalassic and tethyan sites confirmation of global oceanic anoxia and validation of the u isotope paleoredox proxy

seawater 234 u 238 u during the last 800 thousand years abstract constraining the history of seawater 234u 238u is important because this ratio is used to assess the validity of u th ages and because it provides information about the past rate of physical weathering on the continents this study makes use of u rich slope sediments from the bahamas in an attempt to reconstruct seawater 234u 238u for the last 800 kyr for the last 360 kyr u th dating of these sediments provides ages and initial 234u 238u values sixty seven samples largely from marine highstands have initial 234u 238u which scatter somewhat about the modern seawater value 1 145 but neither this scatter nor the average value increases with age of sample these data contrast with published coral data and suggest that seawater 234u 238u has remained within 15 of the modern value for the last 360 kyr this confirms the rejection of coral u th ages where the initial 234u 238u is significantly different from modern seawater data from older highstands dated with 18o stratigraphy or by the presence of the brunhes matuyama b m reversal at 780 kyr allow seawater 234u 238u to be assessed prior to the range of the 230th chronometer unfortunately diagenetic scatter in the data between the b m reversal and 360 kyr is rather large probably relating to low u concentrations for these samples but there is no indication of a trend in seawater 234u 238u with age high u samples from close to the b m reversal show less diagenetic scatter and an initial 234u 238u that averages 1 102 this lower value can be explained by lower seawater 234u 238u at the time of the b m reversal or by progressive loss of 234u from the sediment by recoil a simple box model is presented to illustrate the response of seawater 234u 238u to variations in riverine input such as might be caused by changes in continental weathering comparison of the bahamas 234u 238u data with model results indicates that riverine 234u 238u has not varied by more than 65 for any 100 kyr period during the last 360 kyr it also indicates that the ratio of physical to chemical weathering on the continents has not been higher than at present for any extended period during the last 800 kyr

coupled uranium isotope and sea level variations in the oceans abstract globally rivers supply uranium to the oceans with excess 234 u relative to secular equilibrium and 234 u taken up by corals can be used for dating in addition the 234 u abundance in sea water at the time the coral was growing can be measured independently the veracity of u series ages used in determining past sea level variations is dependent on selecting pristine corals free from diagenetic alteration a quantitative test for alteration assumes invariant 234 u abundances in the oceans for at least the past half a million years and results from samples outside of a narrow range in modern ocean 234 u abundance are excluded from data sets here we have used previously published data to show that 234 u in the oceans appears to be variable and directly related to changes in sea level not only over long glacial interglacial timescales but also at very short centennial timescales most of the previously discarded data can be used to provide valuable additional sea level information the process permits a unique insight into the interplay between sources and sinks of uranium in the oceans mediated by sea level changes at rates far faster than previously thought possible similar rapid sea level forcing of other trace element abundances in the oceans is likely

the siwaliks of western nepal i geometry and kinematics abstract the siwalik group which forms the southern zone of the himalayan orogen constitutes the deformed part of the neogene foreland basin situated above the downflexed indian lithosphere it forms the outer part of the thin skinned thrust belt of the himalaya a belt where the faults branch off a major decollement md that is the external part of the basal detachment of himalayan thrust belt this decollement is located beneath 13 ma sediments in far western nepal and beneath 14 6 ma sediments in mid western nepal i e above the base of the siwalik group unconformities have been observed in the upper siwalik member of western nepal both on satellite images and in the field and suggest that tectonics has affected the frontal part of the outer belt since more than 1 8 ma several north dipping thrusts delineate tectonic boundaries in the siwalik group of western nepal the main dun thrust mdt is formed by a succession of 4 laterally relayed thrusts and the main frontal thrust mft is formed by three segments that die out laterally in propagating folds or branch and relay faults along lateral transfer zones one of the major transfer zones is the west dang transfer zone wdtz which has a north northeast strike and is formed by strike slip faults sigmoid folds and sigmoid reverse faults the width of the outer belt of the himalaya varies from 25 km west of the wdtz to 40 km east of the wdtz the wdtz is probably related to an underlying fault that induces a a change of the stratigraphic thickness of the siwalik members involved in the thin skinned thrust belt and particularly of the middle siwalik member b an increase from west to east of the depth of the decollement level and c a lateral ramp that transfers displacement from one thrust to another large wedge top basins duns of western nepal have developed east of the wdtz the superposition of two decollement levels in the lower siwalik member is clear in a large portion of the siwalik group of western nepal where it induces duplexes development the duplexes are formed either by far travelled horses that crop out at the hangingwall of the internal decollement thrust id to the south of the main boundary thrust or by horses that remain hidden below the middle siwaliks or lesser himalayan rocks most of the thrusts sheets of the outer belt of western nepal have moved toward the s sw and balanced cross sections show at least 40 km shortening through the outer belt this value probably under estimates the shortening because erosion has removed the hangingwall cut off of the siwalik series the mean shortening rate has been 17 mm yr in the outer belt for the last 2 3 ma

accumulation of bank top sediment on the western slope of great bahama bank rapid progradation of a carbonate megabank high resolution seismic profiles and submersible observations along the leeward slope of western great bahama bank show large scale export of bank top sediment and rapid progradation of the slope during the holocene a wedge shaped sequence up to 90 m thick is present along most of the slope and consists of predominantly aragonite mud derived from the bank since flooding of the platform 6 8 ka total sediment volume of the slope sequence is 40 80 that of holocene sediment currently retained on the bank maximum rates of vertical accumulation and lateral progradation are 11 15 m ka and 80 110 m ka respectively 10 to 100 times greater than previously known for periplatform muds slope deposition of exported mud during sea level highs appears to have been a major mechanism for the westward progradation of great bahama bank throughout the quaternary this may provide a critical modern analogue for ancient progradational margins

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

paleoseismic evidence of a surface rupture along the northwestern himalayan frontal thrust hft abstract new paleoseismic evidence is presented from the bhatpur n 31 18 16 28 e 76 9 50 00 trench site along the himalayan frontal thrust hft on western margin of the janauri anticline in nw himachal himalaya india the latest surface rupture at this site demonstrates coseismic displacement of at least 9 3 m radiocarbon dating of trench samples indicates that the surface ruptures occurred at a d 1400 1460 after comparison with other trench results along the himalayan front two scenarios are presented of the latest surface rupturing earthquake event in the northwestern indian himalaya 1 a single event surface rupturing for a minimum fault length of 450 km or 2 two events of different lateral extent according to the former scenario the latest surface rupture occurred between a d 1404 and 1422 the latter scenario suggests the latest surface rupture occurred between a d 1404 and a d 1460 in the northwestern extent from kala amb to hajipur with 9 0 m of coseismic displacement over a minimum fault length of 200 km yet another surface rupture event in the southeastern extent from kala amb to ramnagar has occurred between a d 1282 and a d 1422 with displacement ranging from 16 0 m to 26 0 m and a minimum surface rupture length of 230 km on the basis of these observations and historical earthquakes it is suggested that the potential for earthquakes larger than those in the historical records are capable of producing surface rupture lengths greater than the 200 to 230 km or 450 km in the northwestern indian himalayan front

fluid flow through carbonate platforms constraints from 234u 238u and cl in bahamas pore waters the geometry timing and rate of fluid flow through carbonate margins and platforms is not well constrained in this study we use u concentrations and isotope ratios measured on small volumes of pore water from bahamas slope sediment coupled with existing chlorinity data to place constraints on the fluid flow in this region and by implication other carbonate platforms these data also allow an assessment of the behaviour of u isotopes in an unusually well constrained water rock system we report pore water u concentrations which are controlled by dissolution of high u organic material at shallow depths in the sediment and by reduction of u to its insoluble 4c state at greater depths the dominant process influencing pore water 234 u 238 u is alpha recoil in holocene sediments the increase of pore water 234 u 238 u due to recoil provides an estimate of the horizontal flow rate of 11 cm year but with considerable uncertainty at depths in the sediment where conditions are reducing features in the u concentration and 234 u 238 u profiles are offset from one another which constrains the effective diffusivity for u in these sediments to be1 2 10 8 cm 2 s 1 at depths between the holocene and these reducing sediments pore water 234 u 238 u values are unusually low due to a recent increase in the dissolution rate of grain surfaces this suggests a strengthening of fluid flow probably due to the flooding of the banks at the last deglaciation and the re initiation of thermally driven venting of fluid on the bank top and accompanying recharge on the slopes interpretation of existing chlorinity data in the light of this change in flow rate constrain the recent horizontal flow rate to be 10 6 3 4 cm year estimates of flow rate from 234 u 238 u and cl are therefore in agreement and suggest flow rates close to those predicted by thermally driven models of fluid flow this agreement supports the idea that flow within the bahamas banks is mostly thermally driven and suggests that flow rates on the order of 10 cm year are typical for carbonate platforms where such flow occurs 1999 elsevier science b v all rights reserved

algal uptake of u and some other metals implications for global geochemical cycling abstract freshwater green algae ankistrodesmus sp cultured in dilute solutions of metals chelated with edta revealed massive uptake of u examination of thames river waters and selected micro organisms of its aquatic ecosystem revealed an average dissolved u concentration of 1 46 ppb representing about twice the global mean riverine solute concentration of 0 6 ppb u suspended particulates principally algae contain u at 103 to 105 times that of their river habitat averaging 28 300 ppb u one community of the filamentous algae spirogyra sp contained intracellular crystals tentatively identified as the ca oxylate weddelite studies of algae from a variety of environments have shown large concentration factors for a wide range of elements algae from an acid u mine tailings site contain up to 2 7 u dry weight plus very high concentrations of other metals micro organisms may act as an important sink for metal solutes in the hydrosphere

fate of reflux brines in carbonate platforms active reflux may occur during periods of platform top brine generation but the role and fate of these brines after reflux events are uncertain we have used a numerical flow model to investigate and quantify the response of reflux brines to changes in platform top salinity simulations suggest that reflux brines originally concentrated to gypsum saturation 150 have a relatively long platform residence time on the order of 100 times the duration of the reflux event when brine generating conditions cease brines will continue to sink through the platform entraining seawater a variant of reflux circulation we term latent reflux mesosaline brines intercepted by drilling of carbonate margins by the ocean drilling program may have originated from pleistocene reflux event s on the adjacent platform top and be currently moving by latent reflux latent reflux circulation could deliver a significant quantity of dissolved reactants to platform carbonates including mg for dolomitization

direct u th dating of marine sediments from the two most recent interglacial periods a knowledge of the age of marine sediments is necessary to determine the timing of events and rates of processes in the marine realm and the relationships among marine and other climatically sensitive records the establishment of an accurate chronology for pleistocene marine sediments beyond the range of radiocarbon dating approximately the past 45 kyr has therefore been a goal of palaeoceanographers for decades early attempts1 2 based on measurements of the radionuclides 230th and 231pa were beset with problems and subsequent studies focused on tying fluctuations in marine sediment oxygen isotope records to events such as the formation of coral reef terraces and changes in the earth s magnetic polarity3 4 and tuning the resultant chronologies to the earth s orbitally driven insolation variations5 8 but these chronologies especially the age and duration of the last interglacial period have been challenged by several studies9 12 raising questions about the fundamental cause of pleistocene climate fluctuations here we report the direct u th dating of aragonite rich marine sediments from the bahamas and present an accurately dated marine oxygen isotope record for the last two interglacials we obtain dates of 120 127 kyr bp for the last interglacial and 189 190 kyr bp for the late stage 7 interglacial these dates are in accord with the general theory of orbitally forced climate fluctuations and demonstrate the potential of our direct dating approach for developing an absolute chronology for the pleistocene marine oxygen isotope record

control on 234u 238u in lake water a study in the dry valleys of antarctica abstract the 234 u 238 u ratio in surface waters is generally higher than secular equilibrium due to nuclide recoil during alpha decay of 238 u the size of the deviation from secular equilibrium contains information about the environment in which the water is found this potential tool for environmental reconstruction has previously been studied in rivers groundwater and sediment pore water here we conduct a first assessment of the controls on 234 u 238 u in lakewaters thirty three waters from glacial melt streams and lakes of the mcmurdo dry valleys antarctica were analysed for u concentration and isotope ratio glacial melt has a low u concentration and a 234 u 238 u identical to seawater suggesting that u in antarctic ice is largely sourced from sea salt aerosols stream waters have higher u concentration 0 009 to 1 282 ppb and 234 u 238 u 1 280 to 1 832 due to chemical weathering of sediment in stream channels and 234 u recoil from this sediment average 234 u 238 u is 1 502 close to the average of observations from other surface waters worldwide the absence of groundwaters in the dry valleys indicates that reasonably high 234 u 238 u ratios do not require groundwater sources of u so care should be taken before using high 234 u 238 u as an indicator of groundwater inputs to stream waters lakewaters have u concentrations ranging from 0 027 to 46 ppb i e up to 14 times the seawater concentration and 234 u 238 u from 1 05 to 4 50 young lakes have 234 u 238 u which reflects the sources of u in one case lake joyce a 234 u 238 u lower than seawater may suggest u sourced from melting of old ice in which 234 u excess has partially decayed in older lakes 234 u 238 u is significantly higher than that in the inputs due to addition of recoil 234 u from sediments underlying the lake the size of the deviation from secular equilibrium can only be explained however if recoil from a large area of sediment is considered this is reasonable for the two lakes with particularly high 234 u 238 u bonney vanda which are both relicts of much larger lakes present during the last glacial period on the basis of this study the addition of recoil 234 u to lake water is expected to be a general feature and to cause a noticeable increase in 234 u 238 u for lakes with a u residence time of more than a few thousand years

diagenetic effects on uranium isotope fractionation in carbonate sediments from the bahamas abstract uranium isotope variations 238u recorded in sedimentary carbonate rocks are a promising new proxy for the extent of oceanic anoxia through geological time however the effects of diagenetic alteration on the u isotopic composition in carbonate sediments which are crucial to understand the accurate reconstruction of marine 238u are currently poorly constrained here we examine the effects of the aragonite to calcite transition in the pleistocene key largo limestone of south florida and assess the effects of vadose meteoric phreatic meteoric and phreatic marine diagenesis on u isotope fractionation in carbonate sediments from the bahamas transect including the well studied clino unda and odp site 1006 drill cores our results suggest that early diagenetic processes in bahamas carbonate sediments fractionate u isotopes by an average of 0 27 0 14 1 sd heavier than contemporaneous seawater downcore variations of 238u in slope and basin sediments display little if any correlation with u concentration and common geochemical indicators of diagenesis 13c 18o mn sr mg ca sr ca enrichments of redox sensitive elements or rare earth elements anomalies we propose two possible mechanisms to interpret the positive change in the 238u during carbonate diagenesis authigenic enrichment of isotopically positive u iv in carbonates and preferential incorporation of isotopically positive aqueous u vi species into carbonates these processes likely operate during early syndepositional diagenesis on the banktop further diagenesis during deeper burial is limited by the low solubility of u iv under reducing pore water conditions the early diagenetic behavior of u isotopes in bahamas carbonate sediments is likely broadly representative of carbonate diagenesis in the geological past we suggest that the mean diagenetic offset determined in this study be applied when reconstructing seawater 238u from ancient carbonates furthermore early diagenesis induces significant statistical variability in sediment 238u values pointing to the need for large high resolution data sets in order to average out stochastic variations in individual bulk sediment samples

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

behaviour and mobility of u series radionuclides in madeira abyssal plain turbidites over the past 750 000 years the irregular u profiles developed in madeira abyssal plain turbidites shortly after emplacement are preserved thereafter in the sediments for at least 750 kyr and can be correlated between widely spaced cores such profiles at 22 29 m depth in units 650 730 kyr old have been exploited to study steady state diffusion of the longer lived u decay series radionuclides and to derive effective in situ diffusion coefficients applicable to post oxic conditions a model developed for comparison of parent daughter pair data 238u 234u 234u 230th 230th 226ra 226ra 210po confirms that the only nuclide to exhibit convincing evidence of migration is 226ra effective diffusion coefficients d in the range 6 10 9 1 10 9 cm2 s 1 have been calculated for 226ra in these sediments with between 35 and 70 of total 226ra available for pore water diffusion the symmetrical distribution of 226ra around the 230th peaks indicates that pore water advection is absent other nuclides which might be expected to show evidence of migration are 234u and 222rn although leaching experiments demonstrate that 234u is potentially preferentially mobile relative to 238u this is not observed in the sediments and suggests that the post oxic geochemical environment immobilises 234u a maximum possible d of 10 15 10 14 cm2 s for 234u can be derived 230th is not expected to diffuse in pore waters and this is confirmed by the maximum d of 10 14 5 10 13 cm2 s 1 found the profiles of 226ra and 210po show good agreement which indicates that diffusion of 222rn is limited by its short half life

extensive marine anoxia associated with the late devonian hangenberg crisis abstract the global hangenberg crisis near the devonian carboniferous boundary dcb represents one of the major phanerozoic mass extinction events which shaped the roots of modern vertebrate biodiversity marine anoxia has been cited as the proximate kill mechanism for this event however the detailed timing duration and extent of global marine redox chemistry changes across this critical interval remain controversial because most of the studies to date only constrain changes in local or regional redox chemistry thus opinions on the significance of anoxia as a kill mechanism are variable from anoxia being a primary driver to being relatively unimportant in this study we explore the evolution of global marine redox chemistry using u isotopes of marine limestones the 238 u trends at long an section in south china document systematic oscillations with three negative shifts punctuated by two positive events in between the magnitude of the 238 u oscillations implies that the sediments do not record contemporaneous seawater with a constant offset at all times the lack of covariation between 238 u data and diagenetic indicators e g mn and sr contents mn sr ratio 18 o suggests that the 238 u trends are not produced by the same post depositional diagenetic processes instead trace metal enrichments suggest that more reducing conditions prevailed during the deposition of the two positive events we present plausible model scenarios that fit the observed 238 u trends in the context of redox sensitive trace metal data suggesting marine anoxia expanded in the latest devonian oceans to cover 5 of the continental shelf seafloor area the rapid expansion of marine anoxia coincident with the onset of the hangenberg crisis supports marine anoxia as an important kill mechanism biogeochemical modeling of the coupled c p u cycles suggests that intensified continental weathering for example assisted by the spread of seed plants with deeper root systems at this time could have triggered expansion of marine anoxia and other global changes e g positive excursion in 13 ccarb and decrease in sea surface temperature in the latest devonian the anoxic event is inferred to have been transient as climatic cooling would have reduced weathering fluxes

surface ruptures of large himalayan earthquakes in western nepal evidence along a reactivated strand of the main boundary thrust the chronology of the seismic ruptures along the active faults of western nepal remains almost unconstrained despite their high seismogenic potential we present here a slip history of one of these structures a 120 km long reactivated segment of the main boundary thrust named the surkhet gorahi fault this slip history is based on geomorphologic and neotectonic mapping of active faults deduced from the analysis of a high resolution total station digital elevation model and 15 detrital charcoals radiocarbon ages constraining the age of deposition or abandonment of 4 alluvial terraces of the bheri river in botechaur our results show that the last two earthquakes occurred on this fault after 1860 and 640 bp respectively and accommodated slip greater than 8 m each a value corresponding to the incremental vertical offset of the terraces such events released a significant part of the slip deficit accumulated on the main himalayan thrust fault however given the geometry of this fault system as well as the date of occurrence of the last events the ruptures could be associated with major earthquakes also rupturing the main frontal thrust such as the great 1505 earthquake

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

splay fault slip in a subduction margin a new model of evolution in subduction zones major thrusts called splay faults are thought to slip coseismically during large earthquakes affecting the main plate interface we propose an analytical condition for the activation of a splay fault based on force balance calculations and suggest thrusting along the splay fault is generally conditioned by the growth of the accretionary wedge or by the erosion of the hanging wall in theory normal slip on the splay fault may occur when the decollement has a very low friction coefficient seaward such a low friction also implies an unstable extensional state within the outer wedge finite element elasto plastic calculations with a geometry based on the nankai kumano section were performed and confirm that this analytical condition is a valid approximation furthermore localized extension at a shallow level in the splay hanging wall is observed in models for a wide range of friction coefficients from 0 to the value of internal friction coefficient of the rock here equals to 0 4 the timing of slip established for the splay fault branch drilled on nankai kumano transect suggests a phase of concurrent splay and accretionary wedge growth 2 ma to 1 5 ma followed by a locking of the splay 1 3 ma active extension is observed in the hanging wall this evolution can be explained by the activation of a deeper and weaker decollement followed by an interruption of accretion activation of a splay as a normal fault as hypothesized in the case of the tohoku 2011 earthquake can be achieved only if the friction coefficient on the decollement drops to near zero we conclude that the tectonic stress state largely determines long term variations of tightly related splay fault and outer decollement activity and thus influences where and how coseismic rupture ends but that occurrence of normal slip on a splay fault requires coseismic friction reduction

medieval pulse of great earthquakes in the central himalaya viewing past activities on the frontal thrust the himalaya has experienced three great earthquakes during the last century1934 nepal bihar 1950 upper assam and arguably the 1905 kangra focus here is on the central himalayan segment between the 1905 and the 1934 ruptures where previous studies have identified a great earthquake between thirteenth and sixteenth centuries historical data suggest damaging earthquakes in a d 1255 1344 1505 1803 and 1833 although their sources and magnitudes remain debated we present new evidence for a great earthquake from a trench across the base of a 13m high scarp near ramnagar at the himalayan frontal thrust the section exposed four south verging fault strands and a backthrust offsetting a broad spectrum of lithounits including colluvial deposits age data suggest that the last great earthquake in the central himalaya most likely occurred between a d 1259 and 1433 while evidence for this rupture is unmistakable the stratigraphic clues imply an earlier event which can most tentatively be placed between a d 1050 and 1250 the postulated existence of this earlier event however requires further validation if the two earthquake scenario is realistic then the successive ruptures may have occurred in close intervals and were sourced on adjacent segments that overlapped at the trench site rupture s identified in the trench closely correlate with two damaging earthquakes of 1255 and 1344 reported from nepal the present study suggests that the frontal thrust in central himalaya may have remained seismically inactive during the last similar to 700years considering this long elapsed time a great earthquake may be due in the region

u th dating of carbonate platform and slope sediments absolute chronology of marine sediment beyond the 14c age range provides a test for models of climate change and has many other applications u th techniques have been used for such chronology by dating corals but extending these techniques to marine sediment is complicated by the presence of significant initial 230th both in detrital material and scavenged from seawater in this study we investigate four methods of solving the initial 230th problem for a particular type of marine sediment the aragonite rich sediments of carbonate platforms and slopes bulk sediment u th analyses can be corrected for initial th to yield ages with 2 to 3 kyr precision for highstand periods when sediment aragonite contents are particularly high uncertainty on the corrections causes inadequate precision for sediment from other periods however removal of scavenged th before analysis would enable a dramatic increase in this precision but has not proved successful despite a range of chemical leach approaches using heavy liquids to separate the various carbonate minerals found in bahamas sediment enables an isochron approach to correct for initial th but the presence of initial th from two sources requires correction or removal of one source of initial th before the other is deconvolved by the isochron quantitative removal of detrital material before isochron analysis proves a successful approach such isochron data demonstrate that although sediment remains closed to u th on a centimetre scale nuclides are moved from grain to grain by recoil such intergrain exchange is expected to be observed in all sediments containing mineral grains with different u concentrations measured 234u 238u allows the recoil movement to be corrected and results in isochron ages with precision sometimes as low as 3 kyr the accuracy of this approach has been proved by dating samples within the 14c age range sediments spanning the penultimate deglaciation have also been dated after a small correction for bioturbation the age for this event is found to be 135 2 3 5 ka this date is 8 kyr before the peak in northern hemisphere insolation and suggests that deglaciation is initiated by a mechanism in the southern hemisphere or tropics this isochron approach shows considerable promise for dating of sediments older than this event which will provide further information about the timing and mechanisms of global climate change

the effects of diagenesis on lithium isotope ratios of shallow marine carbonates in this study we present new data on the 7li values and li ca mg ratios of carbonate cores from the great bahama bank clino unda a deep water core off of the bank top odp leg 166 site 1007 and the coralline key largo limestone we use these samples to evaluate the influence of meteoric diagenesis marine burial diagenesis and dolomitization on the li isotope system in carbonates we find that recrystallization of aragonite to low mg calcite in the presence of meteoric fluids results in a systematic decrease of the li ca mg ratio in clino unda and key largo samples due to the lower li ca mg ratio in meteoric fluids compared to seawater for li isotopes we observe that the 7li of meteorically altered low mg calcite is 22 0 3 8 n 28 1 which is coincidentally similar to the original aragonite rich sediments 22 1 in the bahamas 18 1 in key largo but with a larger variability from 15 to 27 we interpret these features as reflecting the overprinting of primary li during meteoric alteration with a highly variable isotope signature that may be controlled by a combination of local porewater and or global climatic conditions in either case meteoric diagenesis produces isotopic signatures that are unrelated to seawater composition in contrast marine burial diagenesis and dolomitization of clino and unda sediments under fluid buffered conditions result in li isotope composition that is similar 30 2 1 5 n 36 1 to modern seawater 31 for site 1007 the 7li values range between 23 permil and 31 permil we interpret this range as reflecting a combination of varying diagenesis style fluid to sediment buffered and varying contribution of calcite derived from pelagic sediments with distinct isotopic composition due to primary mineralogy altogether our results show that diagenesis does not invalidate the use of bulk carbonates for deriving li isotope paleo records but the reliability of past carbonates as recorders of seawater 7li values will depend on carefully characterizing their diagenetic history

uranium isotope systematics of ferromanganese crusts in the pacific ocean implications for the marine 238u 235u isotope system abstract variations of 238u 235u ratio 238u in sedimentary rocks have been proposed as a possible proxy for the paleo oceanic redox conditions although the marine 238u system is not fully understood here we investigate the spatial variation of 238u in modern ferromanganese fe mn crusts by analyzing u isotopes in the surface 0 3 mm depth layer of 19 fe mn crusts collected from 6 seamounts in the pacific ocean 238u values in the surface layers show little variation and range from 0 59 to 0 69 the uniformity of 238u values is consistent with the long residence time of u in modern seawater although the 238u values are lighter than that of present day seawater by 0 24 the light 238u values are consistent with the isotope offset observed in previously reported adsorption experiment of u to mn oxide these results indicate that removal of u from seawater to mn oxide is responsible for the second largest u isotope fractionation in the modern marine system and could contribute to isotopically heavy u to seawater depth profiles of u isotopes 234u and 238u in two fe mn crusts mr12 03 d06 r01 and mc10 cb07 b dated by os isotope stratigraphy were investigated to reconstruct the evolution of the oceanic redox state during the cenozoic the 238u depth profiles show very limited ranges 0 57 to 0 67 for mr12 03 d06 r01 and 0 56 to 0 69 for mc10 cb07 b and have values that are similar to those of the surface layers of fe mn crusts the absence of any resolvable variation in the 238u depth profiles may suggest that the relative amounts of oxic and reducing u sinks have not varied significantly over the past 45 myr however the 234u depth profiles of the same samples show evidence for the possible redistribution of 234u after deposition therefore the depth profile of 238u in fe mn crusts may have been also overprinted by later chemical exchange with pore water or seawater and may not reflect the paleo oceanic environmental changes to assess the potential role of u removal by mn oxides on seawater 238u we calculated seawater 238u with different u sink fluxes into mn oxides using a simple mass balance model the results of these calculations suggest that seawater 238u could have varied significantly throughout earth s history due to changes in the accumulation rate of mn oxides

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

using 234u 238u to assess diffusion rates of isotope tracers in ferromanganese crusts abstract ferromanganese crusts record seawater isotope history for several elements useful for paleoceanography interpreting crust isotope profiles however requires an assessment of the rate of diffusion of each element within the crust we address this issue using u and th isotope profiles coupled with concentration measurements of some trace elements whose isotopes are often measured in crusts a depth profile of 230thxs 234u for a north atlantic crust alv539 yields a growth rate of 3 05 mm myr consistent with an existing 10be 9be record but the growth rate implied by a 234u 238u profile in the same crust is 6 times faster due to diffusion of u in the crust the difference between the observed 234u 238u profile and that expected from 230thxs 234u enables the effective diffusivity of u to be calculated as 1 2 10 6 cm2 year recalculated literature data indicate that other crusts have diffusivities which range down to 4 7 10 8 cm2 yr this variation is to be expected given the range of porosity observed for ferromanganese crusts concentration measurements of various elements in the surface layer of the crust provide relative distribution coefficients for each element between seawater and crust these distribution coefficients enable the effective diffusivity of each element to be calculated by comparison with the diffusivity of u such diffusivities are assessed for crust alv539 and give a first indication of the expected preservation of isotope signals in ferromanganese crusts li os and sr have diffusivities of 2 10 4 3 10 5 and 2 10 5 cm2 year respectively and diffusion is expected to be sufficiently fast that crusts will not accurately preserve past seawater compositions th nd pb and be have diffusivities less than 10 9 cm2 year and are highly immobile in crusts a reassuring result for th and be crust chronologies and for nd and pb isotope tracing of past water masses using crusts hf has a diffusivity of 3 10 8 in alv539 fast enough to perturb but not destroy its isotope history for studies of hf in this and other crusts diffusion should therefore be considered measuring u isotope profiles provides a potential way of assessing such diffusion for hf or for other elements with relatively low distribution coefficients into ferromanganese crusts

a diagenetic origin for isotopic variability of sediments deposited on the margin of great bahama bank insights from clumped isotopes abstract the clumped isotope temperature proxy has been used to investigate the diagenetic history of carbonate sediments in two cores recovered during odp leg 166 on the margin of great bahama bank while periplatform sediments constitute a tempting archive of paleo ocean chemistry as they are unlikely to be subducted their primary limitation is a well documented susceptibility to post depositional diagenetic reworking the crystallization temperatures reconstructed using the clumped isotope proxy as well as the mineralogy and 13c and 18o values have been used to determine the relative effects of sediment mixing and sediment recrystallization results show that as sediments undergo diagenetic alteration at the seafloor their initially warm clumped isotope composition is overprinted at cooler benthic temperatures this process appears to occur in an environment with sufficient fluid exchange to overprint carbon isotopes an observation confirmed in a separate study by analyses of calcium a similarly rock buffered element this early reactive exchange between carbonates and fluids is likely driven by the conversion of metastable aragonite to calcite this partially occurs within the flushed zone where porewater compositions remain compositionally similar to seawater throughout the upper 40 meters of the sediment column sediments dominated by open system isotopic compositions correspond to a period of minimal sediment accumulation between 2 and 3 ma more deeply buried miocene sediments of the more platform proximal site 1003 show evidence of subsequent recrystallization incorporating the warmer geothermal t 47 values and more as well as modified water 18o values likely driven by co evolving porewater and carbonate oxygen isotopes reconstructed water 18o values of these deeper sediments at site 1003 are considerably more positive than the measured modern values suggesting that porewater 18o values were more positive during the miocene sediments deposited at the platform distal site 1006 between the early and middle miocene did not show evidence for this deeper recrystallization differences in diagenetic behavior between the two sites cannot be solely accounted for by differences in sediment accumulation rate to illustrate this time integrated models were constructed which simulated the burial of identically reactive material through the depositional history of each site the sediments deposited at site 1006 appear to stabilize after an initial phase of neomorphism whereas the more platform proximal site 1003 continues to recrystallize during deeper burial apparently in the presence of a parent fluid with a more positive 18o value than observed today we conclude that despite consisting of the same end member sediment sources and being spatially separated by less than 30 km the difference in clumped and oxygen isotopic composition between sites 1003 and 1006 can be predominantly attributed to differences in the rate and duration of recrystallization during burial

interseismic coupling on the main himalayan thrust we determine the slip rate and pattern of interseismic coupling on the main himalayan thrust along the entire himalayan arc based on a compilation of geodetic interferometric synthetic aperture radar and microseismicity data we show that convergence is perpendicular to the arc and increases eastwards from 13 3 1 7 mm yr to 21 2 2 0 mm yr these rates are comparable to geological and geomorphic estimates indicating an essentially elastic geodetic surface strain the interseismic uplift rate predicted from the coupling model closely mimics the topography suggesting that a small percentage of the interseismic strain is permanent we find that the fault is fully locked along its complete length over about 100 km width we don t find any resolvable aseismic barrier that could affect the seismic segmentation of the arc and limit the along strike propagation of seismic ruptures the moment deficit builds up at a rate of 15 1 1 10 19 n m yr for the entire length of the himalaya