geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

evidences for cessation of indian plate subduction in the burmese arc region the issue of whether subduction is still active in the india burma plate boundary zone has been rather controversial while the presence of an eastward dipping indian lithospheric slab is undisputed different opinions have been voiced regarding the continuance of subduction at present analysis of the harvard cmt data in comparison with major subduction zones of the world demonstrates that the burmese arc is a unique region where there is a subducted slab but the direction of plate motion is nearly perpendicular to the down dip direction we propose a major right lateral shearing of the indian plate along with its subducted slab past the burmese plate in the nne direction

crustal structure and earthquake focal depths beneath northeastern india and southern tibet summary we use broad band teleseismic data recorded at eight sites along a north south profile from karimganj 24 84 n 92 34 e south of the eastern shillong plateau to bomdilla 27 27 n 92 41 e in the eastern lesser himalaya to determine the seismic characteristics of the crust in northeastern india we also analyse data from the chinese digital seismic network station at lhasa and indepthii stations located on the southern tibetan plateau north of our profile to extend the seismic images of the crust further northwards although the northeastern indian stations and the tibetan stations do not lie along a linear profile across the himalaya the wellrecognized uniformity of the himalaya along strike make this comparison of the two profiles meaningful receiver functions calculated from these data show that the crust is thinnest 35 38 km beneath the shillong plateau receiver functions at cherrapunji on the southern edge of the shillong plateau have a strong azimuthal dependence those from northern backazimuth events show that the moho beneath the southernmost shillong plateau is at a depth of 38 km while receiver functions from southern backazimuth events indicate that the moho beneath the northernmost bengal basin is at a depth of 44 km receiver functions from sites on the brahmaputra valley demonstrate that the moho is deeper by 5 7 km than below the shillong plateau a result which agrees with the hypothesis that the shillong plateau is supported by shearing stress on two steep faults that cut through the crust further north of the eastern himalayan foredeep the moho dips gently northwards reaching a depth of 48 km beneath bomdilla in the lesser himalaya and 88 km below lhasa in tibet using the crustal velocity models obtained from receiver function inversions we redetermined focal depths of wellrecorded earthquakes across this part of the indo tibetan collision zone and find all of these to occur within the crust hence we find no evidence for bimodal depth distribution of earthquakes beneath this region of northeastern india

earthquake prediction in northeast india a review a multidimensional geophysical approach is made to study earthquake precursors in northeast india resistivity gravity and seismological precursor anomalies for the two recent damaging earthquakes one on december 30 1984 magnitude 5 8 and the other on august 6 1988 magnitude 7 5 are very encouraging to intensify these studies in the region improved methods of magnetic and geohydrological precursor studies are suggested

revisiting the rare earth elements in foraminiferal tests are the rare earth elements rees in foraminifera a valuable proxy for use in paleoceanographic and climate change studies in order to investigate this we attempted a comprehensive study of rees in planktonic and benthic foraminifera several different cleaning protocols were tested although the hydroxylamine used to clean all foraminifera in this study removes an unidentified source of ree contamination it seems to remobilize metal oxides that are otherwise unaffected in flow through dissolution the calculated ree distribution coefficients kd ree s are between 100 and 500 for both planktonic and benthic foraminifera these kds are high compared to other elements in biogenic calcite but can be explained through a general model of element incorporation during foraminiferal calcification from data taken from eight core tops in the southeast pacific we conclude that the rees in planktonic foraminifera are indeed useful as a proxy for upper ocean water mass and mixed layer biogenic productivity alternatively the rees in benthic foraminifera are useful as a proxy for carbon flux to the sea floor these proxies should be robust down core unless the sediments have undergone anoxic diagenesis which stabilizes fe carbonate thus overprinting the primary ree signature however it is clear from ree distributions in foraminiferal tests if anoxic conditions have occurred

a seismotectonic study of the burma and andaman arc regions using centroid moment tensor data abstract the concept of a mean slip angle is introduced this enables a classification of focal mechanisms in any region into predominantly strike slip thrust and normal categories based on this concept the harvard centroid moment tensor cmt data in the burma and andaman arc regions from 1977 to 1992 comprising 167 focal mechanism solutions are examined and categorized distinct trends on the surface and in depth sections emerge on examination of these categories for instance in the burmese arc there is a clear segregation along the slab between strike slip type mechanisms down to a depth of about 90 km and thrust events which occur exclusively below this depth in addition a study of p and t axis orientations indicates that the stress pattern in the subducted slab is different from that farther east whereas the p axes of the thrust and strike slip mechanisms in the slab show a predominantly nne trend commensurate with the direction of motion of the indian plate with respect to the eurasian plate those in the region to the east show interestingly an average e w oriented compressive regime the northern and southern parts of the andaman are region exhibit distinct tectonic patterns whereas in the southern part the disposition of focal mechanisms along the slab and the p and t axis orientations indicate active subduction the mechanisms in the northern part exhibit a peculiar segregation into clusters of thrust normal and strike slip types without conforming to the local trend of the arc a similar study in the western aleutian trench region indicates a much simpler subduction pattern

perturbation of stress and oceanic rift extension across transform faults shown by earthquake focal mechanisms in iceland abstract major sources of stress perturbation are expected in the brittle crust and documented by local studies in iceland whether or not a significant average stress state may emerge from regional scale inversion of very large sets of focal mechanisms is thus subject to doubt we carried out stress inversion of double couple focal mechanisms recorded by the icelandic seismological network within a set of 126 588 shallow earthquakes from july 1991 to july 1999 we performed mass inversion of two main data sets of 12 191 and 71 889 focal mechanisms in the transform zone areas of north and south iceland respectively the inversion reveals surprisingly high levels of consistency within these data sets with regard to the expected dispersion adopting a threshold value of 40 in an individual fit scale from 100 total misfit to 100 perfect fit the proportion of acceptable data is as high as 78 for 65 571 focal mechanisms of the major regime in these two areas 53 for 18 519 mechanisms of the minor regime the major stress regimes thus calculated show nearly vertical intermediate principal axes and the azimuths of extension minimum stress 3 are 065 in the tjornes fracture zone and 140 in the south iceland seismic zone with respect to the 105 azimuth of plate separation these directions show nearly symmetrical angular deviations 40 anticlockwise in the right lateral transform zone area of north iceland and 35 clockwise in the left lateral one of south iceland such large deviations reveal first order stress perturbation in the areas where major rift offset resulted from late cainozoic rift jumps related to plate boundary migration with respect to the iceland mantle plume

seismotectonics in northeast india a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications summary in northeast india three major plates interact along two convergent boundaries the himalayas and the indo burma ranges which meet at the assam syntaxis to clarify this tectonic interaction and the underlying dynamics we determine the regional seismotectonic stress from the stress inversion of 285 double couple focal mechanism solutions of earthquakes with an average magnitude of 5 we then compare the reconstructed stress regimes with the available information about geodetically determined relative displacements north south compression in a direction consistent with india eurasia convergence prevails in the whole area from the eastern himalayas to the bengal basin through the shillong mikir massif and the upper assam valley e w extension in tibet is related to this n s india eurasia convergence not only does the major n s compression affect the outer segments of the indo burma ranges it also extends into the descending slab of indian lithosphere below these ranges although stresses at depth are controlled by bending of the slab beneath the burmese arc the existence of widespread n s compression in the bengal basin far away from the himalayan front is compatible with the previously proposed convergence between a shillong mikir assam valley block and the indian craton e w compression inside this block supports the hypothesis of a component of eastward extrusion stress inversion of focal mechanism solutions in the indo burma ranges reveals a complex stress pattern the burmese arc and its underlying lithosphere experience nearly arcperpendicular extension with ese wnw trends in the northernmost ne trending segment and ene wsw trends in the main n s arc segment such extensional stress documented from many arcs is likely a response to pull from and bending of the subducting plate at the same time the indo burma ranges are under compression as a result of oblique convergence between the sunda and indian plates the maximum compressive stress rotates from ne sw across the inner and northern arc to e w near the bengal basin this rotation is consistent with the deformation partitioning reflected in the rotation of relative displacement vectors from a ssw directed sunda burma motion to a wsw directed burma india motion as a consequence of this partitioning the major belt parallel fault zones show a variety of movements across the main n s arc segment from right lateral slip in the inner ranges to oblique reverse dextral slip in the outer ranges and pure thrusting in the westernmost foreland belt

coupled isotopic systematics of surface cerium and neodymium in the pacific ocean trace metals are known to be essential elements in marine ecosystems radiogenic isotopes of neodymium nd have been used as tracers in many recent oceanic trace metal studies although among rare earth elements cerium ce isotopes might be an interesting complementary tracer for particle reactive and lithogenic metals such as manganese this study determined the 138ce 142ce ratios in surface waters of the pacific ocean and its surrounding marginal seas the sulu sea the south china sea the east china sea and the south australian basin the 138ce 142ce and 143nd 144nd data are discussed in terms of the sources of rare earth elements and elemental fractionation between ce and nd in the marine environment in the western north pacific central water east china sea and south china sea isotopic compositions of ce ce 0 7 to 1 4 are most affected by radiogenic ce of continental origin in contrast less radiogenic isotopic compositions of ce ce 0 4 to 0 3 in the pacific equatorial water were observed locally near volcanic islands such as new guinea island suggesting the influence of mantle derived ce compared with nd the isotopic composition of ce showed a heterogeneous distribution in a given surface water mass reflecting the importance of local sources variations of isotopic compositions and concentrations of ce in the western equatorial pacific and the east china sea suggest that lithogenic ce is supplied and scavenged by particle dissolved interaction near the margins radiogenic ce in the western north pacific central water which is more continental like than nd isotopes suggests direct input by atmospheric dust into the north pacific ocean the isotopic distribution of ce is sensitive to aeolian supply to the surface waters of the open ocean this unique feature indicates that the 138ce 142ce ratio can be a useful chemical tracer for lithogenic trace elements such as iron and manganese which have short oceanic residence time

variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

application of the ce anomaly as a paleoredox indicator the ground rules much attention has been paid in recent years to the potential application of the ce anomaly measured in various marine phases as a paleoceanographic indicator of widespread marine anoxia in this paper we present and discuss results from recent studies of present day rare earth element ree distributions and hence ce anomaly distributions in the marine environment which are particularly pertinent to paleoceanography subsequently we review and discuss the validity of the recent literature in which ce anomalies have been employed as paleoredox indicators

transcurrent movements in the burma andaman sea region the drag produced by the northward movement of the indian plate has caused the indoburman ranges an accretionary prism to decouple from the burma plate along the kabaw fault and the burma plate itself has decoupled from the eastern highlands of burma along the sagaing fault the indoburman ranges have probably been dragged north slightly ahead of the burma plate although at times the two plates may have locked together to move as one unit it is suggested that the double arc formed by the indoburman ranges and the andaman nicobar sumatra islands was formerly one large single arc northward translation of this larger single arcuate structure has caused the tail end of the arc i e the andaman nicobar sumatra section to rotate into the burma plate causing a bending of the arc to form the present double arc and compression within the burma plate to form the pegu yoma folding northward movement of the burma plate has also resulted in offset by over 400 km of the irrawaddy river from its former connection through the channel of what is now the chindwin river

south pacific dissolved nd isotope compositions and rare earth element distributions water mass mixing versus biogeochemical cycling despite its enormous extent and importance for global climate the south pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography here we present the first detailed analysis of dissolved radiogenic nd isotopes end and rare earth elements rees in intermediate and deep waters of the mid latitude 40 s south pacific along a meridional transect between south america and new zealand the goal of our study is to gain better insight into the distribution and mixing of water masses in the south pacific and to evaluate the validity of nd isotopes as a water mass tracer in this remote region of the ocean the results demonstrate that biogeochemical cycling scavenging processes in the eastern equatorial pacific and release of lrees from the sediment clearly influence the distribution of the dissolved ree concentrations at certain locations nevertheless the nd isotope signatures clearly trace water masses including aaiw antarctic intermediate water average end 8 2 0 3 lcdw lower circumpolar deep water average end 8 3 0 3 npdw north pacific deep water average end 5 9 0 3 and the remnants of nadw north atlantic deep water average end 9 7 0 3 filtered water samples taken from the sediment water interface under the deep western boundary current off new zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process these data will serve as a basis for the paleoceanographic application of nd isotopes in the south pacific

sedimentary fe mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved ree in the marine environment authigenic ferromanganese fe mn oxides precipitate from seawater incorporating many dissolved trace elements such as nd pb whose isotopic composition is a direct proxy for ambient seawater thus isotopic studies of the fe mn oxyhydroxide component leached from sedimentary records can provide information on changes in erosional input or ocean circulation changes such studies may be complicated however by the presence of detrital material containing a fe mn oxide component which may mask the true seawater signal in addition the formation of fe mn oxyhydroxides in the marine environment remains poorly understood in particular the phase carbonates detrital particles that controls the delivery of authigenic fe mn oxides to the sediments has not yet been determined in this study we have analysed the ree and nd isotopic compositions of fe mn oxyhydroxide fractions dispersed in marine sediment cores from the cape and angola basins in the se atlantic cruise images ii for the angola basin deep sea core located at 1000 km south of the congo river mouth both the ree and nd isotopic compositions nd measured in recent fe mn oxyhydroxide fractions are typical of congo river borne fe mn oxides this shows that preformed fe mn oxides associated with detrital fractions can locally contaminate the seawater signal recorded by authigenic oxyhydroxides by contrast examination of ree distributions nd isotope data and mass accumulation rates in cape basin sediments shows paradoxically that the flux of fe mn oxides to sediments is controlled by aeolian particles from the nearby namib desert even though their ree and nd compositions point clearly to an authigenic origin it is proposed that partial dissolution of aeolian dust occurs in the water column releasing into solution its easily leachable fe mn component the dissolved fe2 and mn2 would then fuel the reprecipitation of authigenic fe mn oxyhydroxides scavenging additional dissolved trace elements from the ocean most probably from deep water masses in this case calculations suggest that aeolian deposition acts as a net sink for dissolved nd in the cape basin rather than a source and allows us to estimate the rate of removal of dissolved nd associated with atmospheric deposition yielding a global oceanic residence time for nd nd of between 500 and 1400 years

evaluation of the application of rare earth elements to paleoceanography anomalous departures of rare earth elements ree from similarity of chemical behaviour are most evident in a comparison of ce with its neighbors under reducing conditions ce3 acts like other ree but oxidized ce4 is adsorbed on mn fe oxyhydroxides or organic particulates and consequently the remaining solution will tend to exhibit a negative ce anomaly in addition more subtle fractionations may emphasize the light or the heavy or the middle ree a pattern of ree may be recorded by immediate diagenesis on a suitable chemical substrate such as apatite fish debris conodonts carbonate or chert this record was originally thought to reflect the paleoredox conditions of primary deposition however any such primary record may be overprinted by late diagenetic alteration early analyses of ree in conodonts from a wide range of sediments suggested a prevalence of reducing conditions no ce anomaly in pre carboniferous oceans and more common oxidation negative ce anomaly in the late paleozoic however recent research by other investigators indicates that variations in cean are more diverse in origin and in particular many are distorted to an unknown extent by late diagenesis in any case it is now clear that geological age does not show a consistent relationship to the level of the ce anomaly the ce anomaly apparently does not play any regular role in the isotopic events that accompany prominent mass extinctions further research is required to understand and thus make useful the controls on the ce anomaly

microscale neodymium distribution in sedimentary planktonic foraminiferal tests and associated mineral phases neodymium isotopic ratios recorded in calcareous foraminiferal tests shells and associated authigenic minerals were used to trace past water masses although the origin of preserved nd signals is still a matter of debate we determined for the first time the microscale nd distribution in two planktonic foraminifera species globigerinoides ruber and neogloboquadrina dutertrei and coexisting authigenic minerals from two selected time slices 15 6 and 129 kyr of a marine sediment core in the panama basin elemental mapping of nd ca fe mn and si was performed using nanosims ion probe and electron probe microanalysis epma on uncleaned tests together with scanning electron microscopy sem imagery epma and sem images revealed the presence of fe rich framboidal minerals inside test pores and inner chambers particularly in the old samples the young sample presented fe and mn rich patches on the inner test wall the nd intensity in fe mn rich patches and in some framboids was much higher than in foraminiferal calcite where the nd distribution was randomly heterogeneous with no systematic features such as an ontogenic nd rich layer or species specific differences the relationship between nd fe and mn confirmed a significant role of fe mn oxides as a nd carrier the high nd enrichment in some framboids could be explained by nd adsorption onto oxidized surface of fe sulfides particles rather than direct incorporation since the authigenic precipitates are major nd carrier phases the nd isotopic signals in sedimentary foraminiferal tests likely reflect bottom pore water values rather than surface water ones

synchronous deglacial overturning and water mass source changes understanding changes in ocean circulation during the last deglaciation is crucial to unraveling the dynamics of glacial interglacial and millennial climate shifts we used neodymium isotope measurements on postdepositional iron manganese oxide coatings precipitated on planktonic foraminifera to reconstruct changes in the bottom water source of the deep western north atlantic at the bermuda rise comparison of our deep water source record with overturning strength proxies shows that both the deep water mass source and the overturning rate shifted rapidly and synchronously during the last deglacial transition in contrast any freshwater perturbation caused by heinrich event 1 could have only affected shallow overturning these findings show how changes in upper ocean overturning associated with millennial scale events differ from those associated with whole ocean deglacial climate events

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

modern carbonate ooids preserve ambient aqueous ree signatures abstract skeletal and non skeletal components of marine sedimentary rocks have been analyzed for the purpose of reconstructing the rare earth element ree and yttrium y compositions of paleo seawater but skeletal carbonates frequently have proven to be unreliable recorders of seawater chemistry here we present a systematic multi technique assessment of rare earth and other trace elements in ooid sands from the modern great bahama bank gbb marine and great salt lake gsl continental based on strong acid hydrofluoric and nitric and weak acid acetic digestions as well as laser ablation la of ooid cortices and nuclei the results show that bahamian ooid cortices possess shale normalized ree y features nearly identical to those of shallow seawater including limited contamination from siliciclastic rees an admixture of even 0 2 of detritally sourced material can modify the primary marine ree y patterns by for example increasing the light ree lree content mean values of la data for bahamian ooid cortices exhibit similar ree y signatures to those produced by acetic acid digestion but la data are generally noisier primarily as a result of low ree concentrations and the small volume of carbonate ablated in analysis screening out samples with ree 0 9 ppm returns a flat pattern suggesting similar degrees of lree depletion controlled by carbonate complexation under similar aqueous alkalinity conditions in great salt lake and bahamian waters in summary ooids can be a reliable proxy for ree y characteristics of ambient surficial waters when adopting suitable analytical methods including laser ablation that allow the identification and isolation of a contamination signal from siliciclastic detritus

three dimensional seismic sedimentology and stratigraphic architecture of prograding clinoforms central taranaki basin new zealand three dimensional 3d seismic reflection analysis of a major miocene to pleistocene c 19 2 ma clinoform succession of the central taranaki basin offshore new zealand reveals two distinct intervals of downbuilding progradation c 7 5 6 ma and c 4 2 ma downbuilding clinoforms are of kilometre scale and characterized by straight upper foreset gullies that initiate near or at the clinoform breakpoint in places connected to topset distributary channels foreset mass transport complexes occur mainly in the basal parts of downbuilding clinoform successions upbuilding progradational clinoforms formed between c 6 5 5 ma and c 4 5 4 ma these clinoforms are generally smaller with topsets in places comprising beach ridges and tidal channels the foresets of the upbuilding clinoforms contain large gullies and sinuous deepwater channels locally connected to topset channels retrogradational deposits in the studied succession c 5 5 4 5 ma lack a distinct clinoform geometry show a few slope channels and gullies and are characterized by extensive landward stepping networks of shallow marine and fluvial channels 3d seismic reflection analysis of the c 2000 km2 study area allows an exemplary 3d documentation of migrating depositional systems along a highly progradational clastic margin constrained by a stratigraphic framework tightly defined by the two intervals of major depositional downbuilding the late miocene downbuilding is interpreted as forced by tectonic uplift along the cape egmont fault and neighbouring structures in the south of the study area in contrast the plio pleistocene downbuilding is interpreted as dominantly controlled by eustasy in a tectonic environment characterized by subsidence excellent preservation of the 4 2 ma clinoform topsets provides unique insights into depositional systems at and above the shelf break imaging palaeo shoreline and palaeo backshore environments the detailed 3d clinoform analyses presented contribute to the understanding of clastic sedimentation processes from shelf to slope which can be used to predict deepwater depositional facies

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

the sedimentary flux of dissolved rare earth elements to the ocean abstract we determined pore fluid rare earth element ree concentrations in near surface sediments retrieved from the continental margin off oregon and california usa these sites represent shelf to slope settings which lie above within and below the oxygen minimum zone of the northeast pacific the sediments are characterized by varying degrees of net iron reduction with pore fluids from the shelf sites being generally ferruginous and the slope sediments having less pronounced iron reduction zones that originate deeper in the sediment package ree concentrations show maxima in shallow upper 2 10 cm subsurface pore fluids across all sites with concentrations that rise more than two orders of magnitude higher than seawater these pore fluid enrichments highlight the importance of a sedimentary source of rees to the ocean s water column here we use our measurements to estimate the diffusive flux of nd out of ocean sediments resulting in a global flux between 18 and 110 10 6 mol nd yr 1 while we do assume that our pore fluid profiles as well as the very limited data previously published are representative of a wide array of ocean environments this calculated flux can account for the modeled missing nd source flux 76 10 6 mol nd yr 1 in global budgets arsouze et al 2009 pore fluid normalized ree patterns show distinct variation in the middle ree and heavy ree enrichments with sediment depth and amongst sites these patterns show that the heavy ree enrichment of pore fluids at our deep slope site 3000 m water depth is closest to the heavy ree enrichment of seawater this observation supports the view that ree cycling within the upper ten centimeters of deep sea marine sediments as opposed to shallower continental shelf and slope sediments plays a significant role in controlling the integrated global ree flux from the pore fluids and consequently the broad scale ree pattern in seawater

binding and transport of rare earth elements by organic and iron rich nanocolloids in alaskan rivers as revealed by field flow fractionation and icp ms abstract water samples were collected from six small rivers in the yukon river basin in central alaska to examine the role of nanocolloids 0 5 40 nm in the dynamics and transport of rare earth elements rees in northern high latitude watersheds influenced by permafrost total dissolved 40 nm colloids in a river sampled at higher altitude the

importance of vertical geochemical processes in controlling the oceanic profiles of dissolved rare earth elements in the northeastern indian ocean vertical profiles of dissolved rare earth elements rees were obtained in the bay of bengal and the andaman sea the ree concentrations at various depths in the bay of bengal are the highest in the indian ocean this is attributable ultimately to the large outflow of the ganges brahmaputra and irrawaddy rivers but the dissolved ree flux to surface waters alone cannot explain the large and near constant ree enrichment throughout the entire water column the underlying fan sediments serve as not a source but a sink for dissolved ree iii s absence of excess 228ra in the deep waters suggests that lateral input of dissolved rees from slope sediments is also small in these regions partial 0 3 dissolution of detrital particles which are carried by the rivers and lateral surface currents and subsequently settle through the water column appears to be a predominant source for the dissolved rees vertical profiles showing an almost linear increase with depth are common features for the light and middle rees everywhere but their concentration levels are variable from basin to basin and from element to element this suggests that their oceanic distributions respond quickly to the variation of particle flux and its ree composition through reversible exchange equilibrium with suspended and sinking particles much like the case for th the relative importance of the vertical geochemical processes of reversible scavenging over the horizontal basin scale ocean circulation with passive regeneration like nutrients decreases systematically from the light to the heavy rees using a model the mean oceanic residence times of rees in the bay of bengal are estimated to range from 37 years for ce to 140 1510 years for the strictly trivalent rees in the deep water of the andaman sea isolated from the bay of bengal by the andaman nicobar ridge maximum sill depth of 1800 m the ree concentrations are almost uniform presumably due to rapid vertical mixing the ree iii concentrations are similar to that of 1250 m depth water in the bay of bengal consistent with other oceanographic properties however the ree composition of the deep water appears to be altered slightly by preferential scavenging of the light ree iii at the bottom boundary of the basin

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

present day crustal deformation around sagaing fault myanmar 1 global positioning system gps measurement campaigns in myanmar conducted in 1998 and 2000 allow quantifying the present day crustal deformation around the sagaing fault system in central myanmar both a regional network installed at four points within the country and a local 18 station network centered on the city of mandalay across the sagaing fault demonstrate that active deformation related to the northward motion of india is distributed across myanmar in a platelet that extends from the western edge of the shan plateau in the east to the andaman trench in the west in this platelet deformation is rather diffuse and distributed over distinct fault systems in the east the sagaing shan scarp fault system absorbs 10 mm yr this gps study combined with an on land geotectonic survey demonstrate that oblique slip of india along the rigid sundaland block is accommodated by a partitioned system characterized by distribution of deformation over a wide zone index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8110 tectonophysics continental tectonics general 0905 8158 tectonophysics plate motions present and recent 3040 keywords tectonics gps fault southeast asia

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

dissolved rare earth elements in the southern ocean cerium oxidation and the influence of hydrography abstract analysis of dissolved ree distributions in the southeastern atlantic ocean has revealed that progressive oxidative removal of dissolved ce from deepwater 1 km occurs over the mixing time of the oceans ce anomaly ce ce values measured in deep waters from the southeastern atlantic are similar to but slightly higher than those from deep ocean stations throughout the indian and pacific oceans typically falling in the range 0 08ce ce 0 12 only deepwater samples from the north atlantic exhibit values greater than ce ce 0 12 with the exception of southeastern atlantic bottomwaters which are influenced by antarctic bottomwater covariation of dissolved ree concentrations with salinity and or dissolved si concentrations at this site has allowed dissolved ree compositions for various southern ocean water masses to be predicted end member concentrations for antarctic bottom water aabw derived in this way indicate high dissolved ree concentrations similar to average pacific deep water but with significantly enhanced dissolved ce concentrations and less pronounced hree enrichment this result is consistent with the proximity of our study site to active aabw deepwater formation and evolution of that water mass during transport to the pacific ocean

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

rare earth element association with foraminifera abstract neodymium isotopes are becoming widely used as a palaeoceanographic tool for reconstructing the source and flow direction of water masses a new method using planktonic foraminifera which have not been chemically cleaned has proven to be a promising means of avoiding contamination of the deep ocean palaeoceanographic signal by detrital material however the exact mechanism by which the nd isotope signal from bottom waters becomes associated with planktonic foraminifera the spatial distribution of rare earth element ree concentrations within the shell and the possible mobility of ree ions during changing redox conditions have not been fully investigated here we present ree concentration and nd isotope data from mixed species of planktonic foraminifera taken from plankton tows sediment traps and a sediment core from the nw atlantic we used multiple geochemical techniques to evaluate how where and when rees become associated with planktonic foraminifera as they settle through the water column reside at the surface and are buried in the sediment analyses of foraminifera shells from plankton tows and sediment traps between 200 and 2938 m water depth indicate that only 20 of their associated nd is biogenically incorporated into the calcite structure the remaining 80 is associated with authigenic metal oxides and organic matter which form in the water column and remain extraneous to the carbonate structure remineralisation of these organic and authigenic phases releases ions back into solution and creates new binding sites allowing the nd isotope ratio to undergo partial equilibration with the ambient seawater as the foraminifera fall through the water column analyses of fossil foraminifera shells from sediment cores show that their ree concentrations increase by up to 10 fold at the sediment water interface and acquire an isotopic signature of bottom water adsorption and complexation of ree3 ions between the inner layers of calcite contributes significantly to elevated ree concentrations in foraminifera the most likely source of ree ions at this stage of enrichment is from bottom waters and from the remineralisation of oxide phases which are in chemical equilibrium with the bottom waters as planktonic foraminifera are buried below the sediment water interface redox sensitive ion concentrations are adjusted within the shells depending on the pore water oxygen concentration the concentration of ions which are passively redox sensitive such as ree3 ions is also controlled to some extent by this process we infer that a the nd isotope signature of bottom water is preserved in planktonic foraminifera and b that it relies on the limited mobility of particle reactive ree3 ions aided in some environments by micron scale precipitation of mnco3 this study indicates that there may be sedimentary environments under which the bottom water nd isotope signature is not preserved by planktonic foraminifera tests to validate other core sites must be carried out before downcore records can be used to interpret palaeoceanographic changes

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

nd ca ratios in plankton towed and core top foraminifera confirmation of the water column acquisition of nd planktic foraminifera have been used as recorders of the neodymium nd isotopic composition of seawater although there is still controversy over the precise provenance of the nd signal we present an extensive multispecific plankton tow nd ca data set from several geographic locations se atlantic ne atlantic norwegian sea and western mediterranean together with core top samples from the mediterranean region the range of nd ca ratios in plankton towed foraminifera cleaned only of organic material from all regions 0 01 0 7 mol mol is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps with distribution coefficients kd ranging between 4 and 302 for the mediterranean where core top and plankton tow data are both available the range for plankton tows 0 05 0 7 mol mol is essentially identical to that for the core tops 0 1 0 5 mol mol readsorption of nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process we find a relationship between manganese mn and nd in plankton tow samples that is mirrored by a similar correlation in core top samples this relationship suggests that fe mn coatings are of negligible importance to the nd budgets of foraminifera as the nd mn ratio it implies is over an order of magnitude greater than that seen in other fe mn oxide phases rather since both plankton tows and core tops present a similar behavior the nd mn relationship must originate in the upper water column the data are consistent with the acquisition of nd and mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes collectively the results help to explain two abiding puzzles about nd in sedimentary planktic foraminifera their high ree contents and the fact that they record a surface water nd isotopic signal regardless of the cleaning procedure used

does sedimentary 231pa 230th from the bermuda rise monitor past atlantic meridional overturning circulation 1 ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes measurements of 231pa 230th ratios in a sediment core from the bermuda rise have been interpreted as evidence that the atlantic meridional overturning circulation amoc was weakened or completely eliminated during a period of catastrophic iceberg discharges heinrich event 1 h1 here we present new data from the bermuda rise that show further 231pa 230th peaks during heinrich 2 h2 and heinrich 3 h3 additionally a tight correlation between diatom abundances biogenic silica and 231pa 230th is discovered in this core our results redirect the interpretation of 231pa 230th from the bermuda rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties

stress permutations three dimensional distinct element analysis accounts for a common phenomenon in brittle tectonics 1 using three dimensional 3 d distinct element modeling we explored a variety of simulations to characterize and interpret the stress permutations in brittle tectonics stress inversions of fault slip data or earthquake focal mechanisms often revealed such permutations the main aim of our study is to produce simple mechanically consistent 3 d models that account for these switches between the principal stress axes 1 2 or 2 3 even with simple boundary conditions the stress changes induced by variations in rheology are large enough to modify the local tectonic behavior and to produce permutations of principal stress axes rather than simple directional changes of stress axes which exist but often remain limited the relative variations in principal stress magnitudes are the major cause of permutations 1 2 and 2 3 in nature permutations being left apart the orientations of axes often remain tightly clustered in our experiments we adopted a ratio 2 3 1 3 of 0 5 which makes permutations difficult low favors 2 3 permutations high favors 1 2 permutations and we explored a variety of tectonic situations involving compression extension and strike slip our experiments indicate that the major causes of stress permutations are the heterogeneity of the brittle deformation e g intact rock massifs between heavily faulted deformation zones and the anisotropy of the mechanical properties that results from fracturing and faulting which concur to modify the mechanical balance inside the analyzed volume and to produce stress permutations our models show that contrasts and anisotropy in rock properties favor stress permutations of major importance is the existence of relatively resistant zones at tips of the deformed zones acting as channels where stress concentrates and switches occur because in nature such zones move in time and space it is not surprising that stress permutations are so pervasive

rare earth elements in early diagenetic foraminifer coatings pore water controls and potential palaeoceanographic applications abstract rare earth element ree distributions in the ocean bear the fingerprints of several key environmental processes including vertical particle organic carbon fluxes water column pore water oxygenation and ocean transports the use of fossil ree analyses in the service of palaeoceanography as redox water transport or nutrient cycling proxies has long been a tantalizing possibility here we demonstrate the application of a novel laser ablation microanalysis approach for the rapid and accurate measurement of the ree composition of early diagenetic coatings on fossil foraminifera by applying this new method to a range of core top and multi core samples we show that authigenic ree enrichments on planktonic foraminifer surfaces reefs reflect a primary seawater signature that becomes overprinted during sediment burial due to early diagenetic processes that control the flux of rees to pore fluids thus light rees lrees and eventually middle rees mrees are generally enriched in foraminifer coatings relative to seawater while ce anomalies ce ce recorded in surface sediments are typically more positive than local seawater values and are further eroded during burial with the onset of anoxic conditions in the sediment similar patterns have previously been observed in pore fluid measurements indeed we show that mn and fe concentrations measured in foraminifer coatings track the availability of these elements in pore water indicating that they are not associated with a secondary oxide phase we propose that these elements along with rees are instead adsorbed directly from pore fluids in contrast u in authigenic coatings tracks the removal of this element from solution under sub oxic conditions supporting the use of u ca in foraminifer coatings as a redox proxy although our results confirm a significant early diagenetic influence on reefs we also demonstrate the potential utility of ce enrichment relative to expected seawater values as a palaeo oxygenation proxy we support this proposal with down core measurements of u ca and ce enrichment spanning the last deglaciation in the sub antarctic atlantic as well as a global array of lgm measurements which are found to co vary with parallel estimates of radiocarbon ventilation age consistent with a widespread drop in oxygen suggesting an increase in the efficiency of the biological pump our results suggest that laser ablation reefs measurements may hold some promise for palaeoceanographic reconstruction in particular through a shift in emphasis away from the reconstruction of primary seawater signals to the analysis of diagenetic impacts that are sensitive to changing hydrographic conditions

geochemical fingerprinting of trans atlantic african dust based on radiogenic sr nd hf isotopes and rare earth element anomalies mineral dust is an important component of earth s climate system and biogeochemical cycles on a global scale in order to understand the relationship between climate processes in the source areas and the properties of aerosols at distant receptor sites we must be able to identify the source provenance of dust here we present a multiproxy study that characterizes the temporal variability in the geochemical composition of long range african dust lrad collected between 2003 and 2011 in the trade winds on the caribbean island of barbados we find systematic differences between sr nd hf isotopic composition and rare earth element anomalies of individual dust events and evidence of seasonal shifts in dust source activity and transport these results indicate that coherent geochemical source signatures of lrad can be preserved even after transport across thousands of kilometers we investigated the possibility of identifying the potential source areas through comparisons with literature data however these data are almost entirely based on measurements of soil and sediment samples this could lead to biases because of soil aerosol particle size and composition differences nonetheless our data suggest that many samples are linked to sources in mali and sub saharan regions radiogenic nd hf composition of aerosols can potentially be a useful proxy to study the proximity of mineral dust sources to depositional sites in order to establish firmer links between lrad and dust source areas however we require much more data on the geochemical composition of aerosols from potential source areas in north africa

the geochemistry of rare earth elements in the amazon river estuary abstract the estuarine geochemistry of rare earth elements rees was studied using samples collected in the amazon river estuary from the amasseds amazon shelf sediment study cruise of august 1989 extensive removal of dissolved 0 22 m filtered trivalent rees from river water occurs in the low 0 6 salinity region removal by the salt induced coagulation of river colloids leads to fractionation among the ree iii series the order of removal is light rees middle rees heavy rees there also is the enhanced removal of ce relative to trivalent la and nd in the low salinity 0 6 zone and in the zone of high biological activity this is the first field observation of strong ce removal associated with coagulation of river colloids and biological productivity the argument is made that the decrease in the ce anomaly across a biological front is caused by biologically mediated oxidation of ce iii to ce iv coagulation of river colloids and biologically mediated oxidation of ce iii lead to fractionation of ree iii and redox modification of ce these processes result in the ree composition becoming fractionated relative to the amazon river water and crust and more evolved toward the ree composition of the oceans this study implies that reactions in estuaries play significant yet poorly understood roles in controlling the ree composition and ce anomaly of the oceans

estimates of interseismic deformation in northeast india from gps measurements abstract estimates of interseismic deformation in northeastern india based on gps measurements at eight permanent stations 2003 2006 and six campaign sites 1997 2006 are presented here the euler pole of rotation of indian tectonic plate in itrf2000 determined from the present data set is located at 51 7 0 5 n 15 1 1 5 e with angular velocity of 0 469 0 01 myr 1 the results show that there is a statistically insignificant present day active deformation within the shillong plateau and in the foreland spur north of the plateau in the brahmaputra valley convergence rate of the northeastern gps sites with respect to the igs station lhasa along baselines that are normal to the himalayan arc in this region is 16 0 5 mm yr this represents the arc normal indo eurasian convergence rate across the northeastern boundary similar to arc normal convergence rates determined in central nepal along the himalayan arc however unlike central nepal in the arunachal himalaya the 16 mm yr shortening is distributed between the lesser as well as higher and tethyan himalayas baselines between sites on the indo burmese fold and thrust belt ibftb and shillong plateau indicate variations in the shortening rate from 1 5 mm yr on the tripura mizoram salient trs south of the plateau to 6 mm yr in the imphal recess ir to the east and 8 mm yr in naga salient ns to the northeast this suggests that the deformation in the ibftb is segmented into n s blocks along e w transverse zones exhibiting dextral slip between ns ir and sinistral slip between ir and trs baselines between the ibftb sites also show 10 0 6 mm yr convergence pointing to the existence of an active transverse zone between aizawl and imphal

the geochemistry of rare earth elements in the seasonally anoxic water column and porewaters of chesapeake bay a twelve cruise time series study of a seasonally anoxic basin in chesapeake bay was carried out between february 1988 and february 1989 data from filtered bottom water and upper 0 1 cm porewater samples are presented this is the first study in which time series measurements have been employed to understand the low temperature geochemistry of rare earth elements rees the focus is on the coupling between redox reduction oxidation variations and ree cycling fractionation of trivalent rees and development of cerium anomalies the time series results demonstrate that rees have large seasonal cycles in both the water column and porewaters in response to the development of anoxia in the spring and reoxygenation in the fall the transition from oxic to suboxic to anoxic conditions results in the release of rees into the upper porewaters and bottom waters the release of rees and fe are coincident in the bottom waters while the release of rees lags fe by approximately 50 days in the upper porewaters this decoupling is explained in terms of a redox front which moves upward from the sediments to bottom waters during the development of seasonal anoxia the release of rees to the upper porewaters and bottom water are accompanied by 1 1 fractionation across the trivalent ree series and by 2 2 the preferential input of ce relative to its trivalent only ree neighbors ree iii fractionation is such that the relative rate of release increases from lu to la light ree middleree heavyree during reoxygenation removal of dissolved rees occurs from both the water column and upper porewaters and follows the same relative rates lree mree hree cerium removal occurs faster than its neighbor ree iii indicating a rapid oxidation of ce iii to ce iv

evolution of antarctic intermediate water during the plio pleistocene and implications for global climate evidence from the south atlantic abstract formed in the southern ocean antarctic intermediate water aaiw plays a fundamental role in the modern climate system as an important sink for atmospheric co2 and as a mid depth conduit supplying nutrient rich waters to subtropical and tropical upwelling regions during the transition from warm pliocene greenhouse conditions to pleistocene icehouse conditions around 3 ma model simulations suggest dramatic circulation changes in the southern ocean aaiw formation region due to cooling and expanded sea ice cover around antarctica however the history and properties of aaiw over this time period are still poorly understood here we trace aaiw source water provenance temperature and salinity changes over the last 4 myr using nd isotopes of fe mn oxyhydroxide encrusted foraminifera benthic foraminiferal mg ca and stable isotopes from southwest atlantic dsdp site 516 our results show that modern aaiw properties emerged gradually over the last 3 myr as evidenced by gradual cooling 6 c and freshening of intermediate waters over this same interval end values decrease and diverge away from those of pacific sourced waters and converge on values of present day circumpolar deep water cdw these observations are in accordance with model simulations indicating increased deep vertical mixing at the polar front associated with sea ice extension these modified aaiw source waters penetrated increasingly northward into the atlantic at intermediate depths enhancing nutrient supply and contributing to surface cooling along subtropical coastal upwelling sites these circulation changes may have facilitated ocean co2 storage providing a positive feedback amplifying global cooling and intensification of northern hemisphere glaciation

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

rare earth elements and yttrium in seawater icp ms determinations in the east caroline coral sea and south fiji basins of the western south pacific ocean abstract using inductively coupled plasma mass spectrometry icp ms vertical profiles of yttrium and all the rare earth elements rees in seawater were obtained at three locations in the western south pacific the east caroline coral sea and south fiji basins based on the data we have analyzed the inter ree iii relationships and found that ree iii s heavier than dy and particularly close neighbors show strong coherencies in their oceanic behavior considering that the heavy ree iii s are less particle reactive than the light and middle ree iii s and that they have very tight correlations with regressions passing almost through the origin the neighboring element ratios of the heavy ree iii s behave virtually conservatively and are suitable as tracers of water masses the dy ho er system is practically good because its dynamic range signal to noise ratio is large in the ocean the highest ho dy ratios 0 31 are found in intermediate and deep waters throughout the western south pacific which overlie the antarctic bottom water with a low ho dy ratio 0 27 these high ho dy waters are probably formed in the polar and subantarctic frontal zone and advect northward ree iii data provide better insights into the deep water recirculation in the south pacific than those discussed based upon the regular oceanographic properties alone

tectonic stress field in the indian subcontinent a map of maximum horizontal compressive stress orientation in the indian subcontinent has been prepared using orientations derived from three different stress indicators borehole elongation breakouts in situ hydraulic fracturing measurements and earthquake focal mechanisms most part of the subcontinent appears to be characterized by a compressional stress regime thrust and strikeslip faulting imposed by plate boundary forces although shmax orientations do not in general show clear correlation with the direction of motion of the indian plate four provinces are recognized on the basis of regionally consistent orientations these are the midcontinent stress province the southern shield the bengal basin and the assam wedge their boundaries have been determined taking into consideration regional tectonics and seismicity central and northern india including the shillong plateau stretching up to the great himalaya pakistan and nepal are included in a broad midcontinent stress province characterized by nne ene oriented shmax the mean orientation of shmax in this province is n23 e subparallel to the direction of compression expected to arise from the net resistive forces at the himalayan collision zone suggesting that it is largely determined by the tectonic collision processes much of southern india mysore plateau and the high grade metamorphic terrain south of the plateau appears to be part of a second stress province characterized by nw oriented shmax these appear close to those of the intraplate stress field prevailing in the central indian ocean a third stress province was recognized in the bengal basin including parts of west bengal tripura manipur and mizoram in northeastern india and most of bangladesh this province extends eastward from the marginal fault in the western margin of the bengal basin to the indo burma subduction zone and is bounded on the north by the e w striking dauki fault shmax within the sedimentary pile of the bengal basin is oriented in e w direction while p axes of earthquakes within the basement and the crust beneath the basin and within the subducted slab of the indian plate beneath the indo burman ranges generally trend north n30 e shmax orientations within the sedimentary pile of the basin are parallel to the local approximately e w direction of the convergence of indian and burmese plates suggesting a casual relation to the resistive forces at the subduction zone in the indo burma region interestingly the stress field in the basement and the crust beneath the bengal basin and in the subducted slab is similar to the one prevailing in the midcontinent stress province assam wedge stress region occupies the northeastern corner of the indian plate including upper assam arunachal pradesh and much of nagaland this region subducts beneath a sharply bent continental collision boundary consisting of the northeastern limb of the himalayan and northern limb of the indo burman fold belts as a result the stress field in this province is depth differentiated and most likely responsible for the absence of consistent shmax directions

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

siderophore promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater river and ocean water abstract the rare earth elements ree are a group of trace elements that have short marine residence times and that in river lake and marine surface waters are typically associated with organic and inorganic particles explosive volcanic eruptions such as the 2010 eruptions of eyjafjallajokull volcano in iceland produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms to become bioavailable however this iron needs to be solubilized by complexing agents such as siderophores a well studied example of such a chelator is the biogenic siderophore desferrioxamin b dfob based on results from incubation experiments with glacial meltwater rich river waters from southern iceland which are rich in suspended volcanic ash and that had been incubated with and without dfob respectively we here show that siderophores not only enhance the release of iron but also promote the mobilization of ree from these particles in the presence of dfob partial dissolution of volcanic ash and presumably other lithic particles produces a flux of dissolved ree into ambient waters that is characterized by depletion of the light ree over the middle ree and by selective enrichment of cerium due to the formation of dissolved ce iv dfob complexes in siderophore rich environments this siderophore bound ree flux has the potential to modify the concentrations and distribution of the dissolved ree and of the isotopic composition of dissolved nd in glacial meltwaters river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater which are assumed to account for the missing nd flux to seawater thermodynamic data further suggest that siderophore promoted element mobilization could also be important for other polyvalent trace elements such as hf

interpreting the style of faulting and paleoseismicity associated with the 1897 shillong northeast india earthquake implications for regional tectonism 1 the 1897 shillong assam northeast india earthquake is considered to be one of the largest in the modern history although oldham s 1899 classic memoir on this event opened new vistas in observational seismology many questions on its style of faulting remain unresolved most previous studies considered this as a detachment earthquake that occurred on a gently north dipping fault extending from the himalayan front a recent model proposed an alternate geometry governed by high angle faults to the north and south of the plateau and it suggested that the 1897 earthquake occurred on a south dipping reverse fault coinciding with the northern plateau margin in this paper we explore the available database together with the coseismic observations from the region to further understand the nature of faulting the geophysical and geological data examined in this paper conform to a south dipping structure but its location is inferred to be in the brahmaputra basin further north of the present plateau front our analyses of paleoseismic data suggest a 1200 year interval between the 1897 event and its predecessor and we identify the northern boundary fault as a major seismic source the shillong plateau bounded by major faults behaves as an independent tectonic entity with its own style of faulting seismic productivity and hazard potential distinct from the himalayan thrust front a point that provides fresh insight into the regional geodynamics

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

chromium isotope fractionation between modern seawater and biogenic carbonates from the great barrier reef australia implications for the paleo seawater δ53cr reconstruction abstract this study investigates chromium isotope variations 53 cr and ree patterns in present day biogenic carbonates and ocean waters from lady elliot island lei located in the southern great barrier reef gbr australia which is one of the world s largest carbonate producing shelf ecosystems our results from thoroughly cleaned biogenic carbonates collected at lei with no detectable evidence for lithogenic cr and or mn fe oxide coating contamination revealed a systematic and statistically significant correlation r 2 0 83 p 0 05 between 53 cr and cerium anomaly ce ce data in molluscan shells i e gastropods this in turn implies a redox controlled incorporation of cr from seawater into a shell during mineralization mediated by the organism in particular shells with higher 53 cr values which approach the cr isotope composition of local seawater tend to be associated with more negative ce ce importantly the intercept of the above 53 cr vs ce ce correlation points to the cr isotope composition of local ocean water which has an average 53 cr of 0 82 0 13 2 relative to srm 979 these findings thus indicate that the above multi proxy approach could be used to reconstruct the 53 cr signature of local paleo seawater based on ce ce and 53 cr data in a set of well preserved fossil skeletal carbonates i e molluscan shells collected at a specific site interestingly the only calcifying organism from lei that yielded identical 53 cr vs ce ce values as those in ambient ocean water was a microbial calcitic carbonate produced by red coralline algae lithothamnion sp this organism thus seems to incorporate cr isotopes and ree from seawater without additional biological discrimination and or isotope fractionation effects considering that calcite is a more stable caco3 polymorph during post depositional alternation and diagenetic stabilization of marine carbonates compared to aragonite the fossil counterparts of these algal microbial carbonates microbialites might thus represent ideal natural archives of the paleo seawater 53 cr and ce ce variations over geological time finally our compilation of 53 cr data from recent marine biogenic carbonates originating from the main oceanic provinces south north pacific south north atlantic caribbean mediterranean sea confirms that marine carbonates tend to be systematically enriched in light cr isotopes relative to local ocean waters trace element constraints however indicate that some of these shifts to lower 53 cr values i e approaching 0 1 per mil are related to a presence of lithogenic cr in the shells causing a diagenetic overprint of the primary marine 53 cr signal

strong and deep atlantic meridional overturning circulation during the last glacial cycle extreme abrupt northern hemisphere climate oscillations during the last glacial cycle 140 000 years ago to present were modulated by changes in ocean circulation and atmospheric forcing1 however the variability of the atlantic meridional overturning circulation amoc which has a role in controlling heat transport from low to high latitudes and in ocean co2 storage is still poorly constrained beyond the last glacial maximum2 3 4 here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle dominating ocean circulation in the atlantic whereas a shallower glacial mode with southern sourced waters filling the deep western north atlantic prevailed during glacial maxima3 5 our results are based on a reconstruction of both the strength and the direction of the amoc during the last glacial cycle from a highly resolved marine sedimentary record in the deep western north atlantic parallel measurements of two independent chemical water tracers the isotope ratios of 231pa 230th and 143nd 144nd 6 7 8 which are not directly affected by changes in the global cycle reveal consistent responses of the amoc during the last two glacial terminations any significant deviations from this configuration resulting in slowdowns of the amoc were restricted to centennial scale excursions during catastrophic iceberg discharges of the heinrich stadials severe and multicentennial weakening of north atlantic deep water formation occurred only during heinrich stadials close to glacial maxima with increased ice coverage probably as a result of increased fresh water input in contrast the amoc was relatively insensitive to submillennial meltwater pulses during warmer climate states and an active amoc prevailed during dansgaard oeschger interstadials greenland warm periods

microseismicity and tectonics in northeast india abstract three microearthquake surveys were carried out in shillong plateau mikir hills and assam valley areas during 1984 to 1986 some 422 events are relocated by the homogeneous station method the microseismicity map reveals intense crustal 10 to 40 km activity beneath the tura area of shillong plateau the areas to the west of shillong and the area around mikir hills also show high activity the microseismicity map further shows major tectonic lineaments that are compatible with the landsat imagery lineaments and the major faults composite focal mechanisms of the microearthquakes show spatial variation of the tectonic stresses in the region an ene wsw horizontal compressive stress is dominant in the tura area whereas a se nw horizontal compressive stress is dominant in the shillong and mikir hills areas

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

rare earth elements and nd isotopes tracing water mass mixing and particle seawater interactions in the se atlantic abstract distributions of dissolved and particulate rare earth elements rees and seawater neodymium isotopic composition e nd were established in samples from the bonus goodhope bgh ipy geotraces cruise in the se atlantic sector of the southern ocean 36 s 13 e to 57 s 0 feb mar 2008 close to the south african continent in the subtropical domain particulate rees show the highest concentrations and flat paas normalized patterns clearly tracing their lithogenic origin active cerium oxidation onto suspended particles is evidenced by the mirror image relationship of the cerium anomaly between dissolved and particulate phases unradiogenic dissolved neodymium in surface waters e nd 17 1 traces the influence of old sedimentary material brought by the agulhas current and rings to the cape basin area a mass balance calculation suggests that the release of nd from dissolution of lithogenic material corresponds to a remobilization of 154 10 6 t of sediment per year i e 5 of the total sediment delivered to the southeast african coast annually at open ocean stations both dissolved and particulate rees present negative cerium anomalies indicating that particles have acquired a marine signature the increasing ree concentrations with depth and the strong linear correlations of dissolved ree with silica indicate that surface removal and deep re mineralisation of rees are partially related to the biogeochemical cycle of silicate which involves biogenic silica diatoms combined with marine carbonates these authigenic phases could explain the observed ree patterns in suspended particles except for la we suggest that the positive la anomalies in both phases are linked to the oceanic barium cycle and the partial dissolution of barite crystals especially in the polar frontal zone the e nd composition behaves conservatively in intermediate and deep waters while input processes affect the isotopic signal of subtropical surface waters and weddell gyre bottom waters an indian ocean and an atlantic variety of aaiw have been isotopically differentiated e nd 9 3 0 3 and e nd 8 0 0 5 respectively homogeneous signatures characterize circumpolar waters e nd from 8 2 to 8 4 for cdw a binary mixing model has been used to assess the contribution of undiluted nadw reaching southern latitudes

evaluating the fidelity of the cerium paleoredox tracer during variable carbonate diagenesis on the great bahamas bank abstract inferring redox conditions for ancient marine environments is critical to our understanding of biogeochemical cycles over earth history because of the redox sensitivity of cerium ce relative to other rare earth elements rees and its uptake in marine carbonates the ce anomaly ce ce is widely applied to ancient carbonates as a proxy for local redox conditions in the water column however carbonate sediments and rocks are particularly vulnerable to multiple stages and styles of post depositional diagenetic alteration where the diagenetic redox conditions and fluid compositions can vary widely from overlying seawater evaluations of the effects of this post depositional alteration for the ce anomaly have mostly been limited to ancient carbonate rocks rather than recent well characterized analog facies here we report on analyses of ree plus yttrium concentrations rey and ce anomalies in bulk carbonate samples from drill cores collected in the bahamas clino and unda that allow us to track loss or retention of primary signals of initial oxic deposition through a range of subsequent alteration scenarios mostly under anoxic conditions specifically these materials have experienced well constrained overprints linked to meteoric processes and marine burial diagenesis including dolomitization our results show that regardless of mineralogy diagenetic fluid composition and redox state the rey patterns in these carbonates including the ce anomaly are similar to those of modern oxic seawater indicating that they likely record the seawater signatures of primary deposition as such the ce anomaly in shallow marine carbonates has the potential to preserve records of primary deposition even when subject to multiple stages and styles of diagenetic alteration confirming its utility in studies of ancient marine redox

the potential of sedimentary foraminiferal rare earth element patterns to trace water masses in the past dissolved rare earth element ree concentration data from intermediate and deep seawater form an array characterized by higher middle ree enrichments mree mree in the north atlantic and a progressive increase in heavy to light ree ratios hree lree as water masses age the rees in foraminifera are fractionated towards higher mree mree and lower hree lree relative to seawater calculations based on a scavenging model show that the ree patterns in uncleaned core top foraminifera resemble those adsorbed onto calcite particulate organic material and hydrous ferric oxides but the full extent of the ree fractionation measured in foraminifera was not reproduced by the model however differences in the hree lree mree mree ratios and the cerium anomaly between ocean basins are preserved and are in agreement with the seawater ree distribution under oxic conditions the hree lree and mree mree compositions of uncleaned foraminifera at the sediment seawater boundary are preserved during burial but the cerium anomaly is sensitive to burial depth in suboxic sedimentary environments all uncleaned foraminiferal ree concentrations are elevated relative to core top values indicating addition of rees from pore waters the hree lree ratio is highest when sedimentation rates were greatest lippold et al 2009 and when high fe ca ratios in the uncleaned foraminifera indicate that fe was mobile in sediments that have not experienced suboxic conditions during burial uncleaned foraminifera preserve the seawater signal taken up at the sediment seawater interface and are therefore suggested to be a suitable archive of changes in the ree signal of past bottom waters this article is protected by copyright all rights reserved

assessment of seawater nd isotope signatures extracted from foraminiferal shells and authigenic phases of gulf of guinea sediments the radiogenic neodymium nd isotope composition of foraminiferal shells provides a powerful archive to investigate past changes in sources and mixing of water masses however seawater nd isotope ratios extracted from foraminiferal shells can be biased by contaminant phases such as organic matter silicates or ferromanganese coatings the removal of which requires rigorous multiple step cleaning of the samples here we investigate the efficiency of flow through and batch cleaning methods to extract seawater nd isotope compositions from planktonic foraminifera in a shelf setting in the gulf of guinea that is strongly influenced by riverine sediment inputs nd isotope analyses of reductively and oxidatively cleaned mono specific planktonic foraminiferal samples and reductively cleaned mixed benthic foraminifera were complemented by analyses of non reductively cleaned mono specific planktonic foraminiferal samples fe mn coatings of de carbonated bulk sediment leachates and the residual detrital fraction of the same sediment al ca and mn ca ratios of fully cleaned foraminiferal samples reveal indistinguishable levels of cleaning efficiency between the batch and the flow through methods and the nd isotope compositions obtained from application of both methods are identical within error furthermore non reductively cleaned foraminiferal samples have the same nd isotope composition as reductively cleaned foraminifera at our study sites close to the niger river mouth the nd isotope composition of the foraminifera agree with the seawater nd isotope composition of nearby stations based on the combined extracted nd isotope signatures and element to calcium ratios as well as rare earth element distribution patterns we infer that the planktonic foraminiferal nd isotope signatures reflect bottom water pore water signatures the isotopic composition of the bulk de carbonated sediment leachates fe mn coatings differs significantly from the foraminiferal data at this site and probably reflects particles that acquired their ferromanganese pre formed pre formed ferromanganese coatings in nearby rivers therefore in such river influenced shelf settings foraminiferal shells should be used to obtain unbiased bottom seawater signatures

online preconcentration icp ms analysis of rare earth elements in seawater the rare earth elements rees with their systematically varying properties are powerful tracers of continental inputs particle scavenging intensity and the oxidation state of seawater however their generally low pmol kg concentrations in seawater and fractionation potential during chemical treatment makes them difficult to measure here we report a technique using an automated preconcentration system which efficiently separates seawater matrix elements and elutes the preconcentrated sample directly into the spray chamber of an icp ms instrument the commercially available seafast system elemental scientific inc makes use of a resin with ethylenediaminetriacetic acid and iminodiacetic acid functional groups to preconcentrate rees and other metals while anions and alkali and alkaline earth cations are washed out repeated measurements of seawater from 2000 m water depth in the southern ocean allows the external precision 2 of the technique to be estimated at 23 for all rees and 15 for most comparison of nd concentrations with isotope dilution measurements for 69 samples demonstrates that the two techniques generally agree within 15 accuracy was found to be good for all rees by using a five point standard addition analysis of one sample and comparing measurements of mine water reference materials diluted with a nacl matrix with recommended values in the literature this makes the online preconcentration icp ms technique advantageous for the minimal sample preparation required and the relatively small sample volume consumed 7 ml thus enabling large data sets for the rees in seawater to be rapidly acquired

seismotectonics of a newly formed transform zone near a hotspot earthquake mechanisms and regional stress in the south iceland seismic zone abstract we carry out mass inversion of focal mechanisms of earthquakes from 1991 to 2004 along the south iceland seismic zone within a quadrangle about 37 km wide and 65 km long with 33 878 earthquakes illuminating a crust volume of nearly 35 000 km3 our inversion aims at identifying the seismotectonic stress regimes that best account for the whole set of data not at examining local variations and stress perturbations in space and time regardless of magnitude selection the inversion reveals consistent orientations for both a primary regime with ne sw compression and nw se extension accounting for about three fourths of the data and a secondary regime with nw se compression and ne sw extension the corresponding earthquakes are highly intricate in space and time suggesting that the secondary regime which shows larger dispersion and slightly lower magnitudes as compared with the primary regime mainly results from the effects of elastic rebound stress drop and fluid migration because the data acquisition and our inversion technique are independent this analysis provides confirmation that even the negative magnitude earthquakes recorded by the icelandic seismic network sil are reliable our analysis reveals high levels of consistency between the seismotectonic stress pattern and the transform kinematics of the south iceland seismic zone the proximity of the icelandic mantle plume with a positive thermal anomaly modified the rheology of the upper lithosphere and hence influenced structural development simple shear probably prevails within a 20 km wide corridor in the underlying viscous layer inducing particular block faulting at the surface both the fault distribution and the effective block dimensions are consistent with a simple structural evolution model

source parameters of earthquakes and intraplate deformation beneath the shillong plateau and the northern indoburman ranges we determined the fault plane solutions and focal depths of 17 earthquakes beneath the shillong plateau and the northern indoburman ranges by combining results from the inversion of long period p and sh waveforms and amplitudes from polarities of first motions and from the identification of pp and sp phases on short period seismograms fault plane solutions of 15 earthquakes show mixtures of thrust and strike slip faulting but the p axes for these events are nearly horizontal and consistently oriented north northeast south southwest all of these earthquakes occurred at depths greater than 29 km beneath the shillong plateau one event occurred at a depth of 52 km the relatively large depths for earthquakes in an intraplate setting suggest that the indian lithosphere in this area is especially cold earthquakes beneath the northern indoburman ranges define a gently east southeast dipping zone from 30 to 45 km beneath the bengal basin to 40 to 90 km beneath the ranges this zone seems to steepen and connect with the zone of intermediate depth seismicity that dips eastward beneath burma these earthquakes cannot have occurred along the interface between a subducting indian plate and the overriding indoburman lithosphere because the p axes not the nodal planes are parallel to the north south trending seismic zone although a couple of the earthquakes might have occurred within the indoburman lithosphere most of this seismicity seems to have occurred within the indian plate recently and currently being subducted eastward beneath the indoburman ranges the consistent north northeast trend of the p axes implies that the orientation of maximum compressional strain in the indian plate throughout its northeastern pan is nearly perpendicular to that responsible for roughly north south trending folds of the indoburman ranges thus either recently in geologic time since 1 ma the orientation of maximum compression changed dramatically or more likely the deformation in the indoburman ranges is decoupled from that in the underlying indian plate meanwhile the seemingly identical northward displacement of india and the indoburman ranges with respect to south china must be accommodated farther east along the sagaing and other faults

deep structure and tectonics of the burmese arc constraints from earthquake and gravity data abstract active subduction of the indian plate is currently occurring beneath the burmese arc along an east dipping benioff zone which extends to a depth of about 180 km the overriding burma plate has an appearance of an inland seismic slab that is deflected downwards in the vicinity of the benioff zone a crustal seismic zone some 60 80 km east of the benioff zone correlates to backarc activity a triangular aseismic wedge in the top part of the crust outlines the central belt molasse basin east of the burmese foldbdt fault plane solutions show that the burmese benioff zone is characterized by shallow angle thrusting at its upper edge whereas down tip tensional events dominate its lower edge most of the backarc seismicity is accounted for by the sagaing transform or by the activity of the shan scarp normal fault zone at the margin of the asian plate a gravity anomaly pair with amplitude of 175 mgal coincides with the 1100 km long burmese arc lying in a north south direction the gravity anomalies along a profile in central burma and in adjacent areas of the bengal basin are interpreted in terms of plate subduction as well as near surface mass anomalies this suggests that sediments below the central belt may have an average thickness of the order of 10 km but may be as thick as 15 km at the subduction zone the oceanic crust underlying deeper parts of the bengal basin experiences phase transition at about 30 km depth in a benioff zone environment east of the burmese foldbelt several thrust planes are present within the folded and deformed cretaceous tertiary sediments of the fold belt these are often associated with ophiolites and basic to ultrabasic rocks a low density zone at least 60 km wide underlies the andesitic volcanic axis in the overriding plate

burma plate motion 1 plate motion in the indo burmese arc andaman sumatra region of burma plate is poorly resolved this is mainly due to lack of relevant data and complex tectonics of the region we analyze 1 azimuths of coseismic displacements due to the 2004 sumatra andaman and 2005 nias earthquakes 2 estimates of interseismic deformation in the indo burmese arc andaman sumatra and sagaing fault regions all based on gps measurements 3 long term plate motion rates across sumatra fault system sagaing fault and andaman sea from geomorphological and other geophysical studies and 4 the earthquake focal mechanisms in the region we suggest that the ssw motion of sunda plate with respect to indian plate may be partitioned into the dextral strike slip motion across the sagaing fault in the north and sumatra fault system in south in the back arc region and the arc normal motion across the sumatra subduction zone which becomes oblique in andaman and southern indo burmese arc region and dextral in the northern indo burmese arc region of the fore arc under the rigid plate approximation we estimate a pole for india burma plate pair at 27 1 n 82 1 1 e with an angular velocity of 0 845 0 12 ma and for burma sunda at 22 3 1 1 n 109 3 2 5 e with an angular velocity of 0 67 0 12 ma thus the plate motion in the northern and southern regions of burma plate namely the indo burmese arc and andaman sumatra arc may be explained by a single pole and does not require a boundary between the two