the red river fault system in the tonkin gulf vietnam abstract the red river fault system in the tonkin gulf offshore haiphong was studied using seismic profiles calibrated by deep wells well characterised left lateral strike slip occurred continuously within a narrow 30 km wide zone southwest of the vinh minh fault between 30 ma and 5 5 ma however the corresponding amount of offset probably does not exceed a few tens of kilometres no sign of post 5 5 ma right lateral motion can be detected prior to 30 ma there is a widespread extension in a wider 100 km wide zone which could be related to a significant amount of left lateral motion the motion of the fault splays to the northeast of the vinh minh fault prior to 30 ma was absorbed in the rifting of the gulf of beibu a 15 5 ma unconformity separates the transtensional regime from a later transpresional regime this 15 5 ma date coincides with the cessation of sea floor spreading in the south china sea

quantifying the missing sink for global organic carbon burial during a cretaceous oceanic anoxic event abstract the cretaceous experienced numerous global and local climatic perturbations to the ocean atmosphere system especially during periods of known widespread organic carbon burial termed oceanic anoxic events oaes the cenomanian turonian boundary event 93 9 ma or oae 2 is the best documented and widespread organic carbon oc burial event in earth history with more than 170 sections published despite the substantial number of locations the majority is found within the proto atlantic ocean tethys ocean and epicontinental seaways it has been hypothesized that the pervasive burial of oc during oae 2 caused the observed positive carbon isotope excursion 2 to 7 average 3 the isotope excursion can help constrain the global burial of oc even for unstudied portions of the global ocean this approach can solve for missing oc sinks by comparing model estimates with the known distribution of oae 2 sediments and their oc contents specifically mapping the known spatial extent of oc burial in terms of mass accumulation rates mars and comparing those results with the prediction using a forward box model to derive the amount of oc burial to reproduce the globally observed positive carbon isotope excursion the available oc data from outcrop and drill core with reasonable extrapolation to analogous settings without data quantifies 13 of the total seafloor mostly from marginal marine and epicontinental epeiric settings however this extrapolation for oc burial plus using most appropriate mars to unknown portions of the seafloor fail to account for the amount of oc burial predicted for a 3 positive carbon isotope excursion this discrepancy remains even when considering additional sinks of organic carbon burial such as coal lacustrine environments authigenic carbonate and the loss of oc associated with hydrocarbon reservoirs this outcome points to a large reservoir of oc that is not currently constrained such as highly productive margins and or equatorial regions or a small but significant increase deep ocean oc burial another possibility is that the carbon fluxes are less than those used in the model which would require less oc burial to explain a 3 carbon isotope excursion

sulfur isotopes track the global extent and dynamics of euxinia during cretaceous oceanic anoxic event 2 the mesozoic era is characterized by numerous oceanic anoxic events oaes that are diagnostically expressed by widespread marine organic carbon burial and coeval carbon isotope excursions here we present coupled high resolution carbon and sulfur isotope data from four european oae 2 sections spanning the cenomanian turonian boundary that show roughly parallel positive excursions significantly however the interval of peak magnitude for carbon isotopes precedes that of sulfur isotopes with an estimated offset of a few hundred thousand years based on geochemical box modeling of organic carbon and pyrite burial the sulfur isotope excursion can be generated by transiently increasing the marine burial rate of pyrite precipitated under euxinic i e anoxic and sulfidic water column conditions to replicate the observed isotopic offset the model requires that enhanced levels of organic carbon and pyrite burial continued a few hundred thousand years after peak organic carbon burial but that their isotope records responded differently due to dramatically different residence times for dissolved inorganic carbon and sulfate in seawater the significant inference is that euxinia persisted post oae but with its global extent dwindling over this time period the model further suggests that only 5 of the global seafloor area was overlain by euxinic bottom waters during oae 2 although this figure is 30 greater than the small euxinic fraction present today 0 15 the result challenges previous suggestions that one of the best documented oaes was defined by globally pervasive euxinic deep waters our results place important controls instead on local conditions and point to the difficulty in sustaining whole ocean euxinia

earthquake fault superhighways abstract motivated by the observation that the rare earthquakes which propagated for significant distances at supershear speeds occurred on very long straight segments of faults we examine every known major active strike slip fault system on land worldwide and identify those with long 100 km straight portions capable not only of sustained supershear rupture speeds but having the potential to reach compressional wave speeds over significant distances and call them fault superhighways the criteria used for identifying these are discussed these superhighways include portions of the 1000 km long red river fault in china and vietnam passing through hanoi the 1050 km long san andreas fault in california passing close to los angeles santa barbara and san francisco the 1100 km long chaman fault system in pakistan north of karachi the 700 km long sagaing fault connecting the first and second cities of burma rangoon and mandalay the 1600 km great sumatra fault and the 1000 km dead sea fault of the 11 faults so classified nine are in asia and two in north america with seven located near areas of very dense populations based on the current population distribution within 50 km of each fault superhighway we find that more than 60 million people today have increased seismic hazards due to them

finite extension across the south vietnam basins from 3d gravimetric modelling relation to south china sea kinematics abstract we derive a crustal thickness map over the south vietnam basins from a 3d inversion of gravity data that takes into account the sedimentary infill and its density variation with depth this map is used to estimate the total amount of stretching across these basins that varies from 190 km to the east at 111 e to 30 km to the west at 107 e comparison with south china sea kinematics amount and timing of oceanic opening implies large decoupling with respect to the indochina block and supports the hypothesis of formation of the south china sea in upper oligocene to lower miocene by southward subduction of the proto south china sea

basin scale controls on the molybdenum isotope composition of seawater during oceanic anoxic event 2 late cretaceous abstract it is well established that the burial of organic carbon in marine sediments increased dramatically at a global scale at the cenomanian turonian boundary oceanic anoxic event 2 oae 2 94 myr ago late cretaceous many localities containing chemostratigraphic expressions of this event are not however enriched in organic carbon and point to a heterogeneous set of oceanographic and environmental processes operating in different ocean basins these processes are difficult to reconstruct because of the uneven geographical distribution of sites recording oae 2 thus limiting our understanding of the causes and palaeoceanographic consequences of the environmental changes that occurred at this time a new highly resolved molybdenum isotope dataset is presented from the cape verde basin southern proto north atlantic ocean and a lower resolution record from the tarfaya basin morocco the new data reveal periodic oscillations in the mo isotope composition of proto north atlantic ocean sediments from which coupled changes in the dissolved sulphide concentration and mo inventories of the basin seawater can be inferred the cyclic variations in sedimentary mo isotope compositions can be hypothetically linked to regional changes in the depth of the chemocline and in the rate of seawater exchange between basinal waters and global seawater the new data suggest that a global seawater mo isotope composition of 1 2 was reached very soon after the onset of oae 2 implying a rapid expansion of marine deoxygenation coeval with or slightly preceding enhanced global rates of organic carbon burial during oae 2 the modelled flux of mo into anoxic sediments is likely to have been 60 125 times greater than at the present day although the spatial extent of anoxia is unlikely to have been greater than 10 of the total seafloor

a review of nitrogen isotopic alteration in marine sediments key points use of sedimentary nitrogen isotopes is examined on average sediment 15n 14n increases approx 2 per mil during early burial isotopic alteration scales with water depth abstract nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record however bulk sedimentary nitrogen isotope ratios which can be determined routinely and at minimal cost may be altered during burial and early sedimentary diagenesis particularly outside of continental margin settings the causes and detailed mechanisms of isotopic alteration are still under investigation case studies of the mediterranean and south china seas underscore the complexities of investigating isotopic alteration in an effort to evaluate the evidence for alteration of the sedimentary n isotopic signal and try to quantify the net effect we have compiled and compared data demonstrating alteration from the published literature a 100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that at sites located off of the continental margins an increase in sediment 15n 14n occurs during early burial likely at the seafloor the extent of isotopic alteration appears to be a function of water depth depth related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of n isotopic alteration moreover the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global n cycle

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

high resolution seismic reflections in a potash mine high resolution seismic reflections underground in a deep potash mine in canada have been collected using a hammer for a seismic source 50 hz geophones and a digital stacking seismograph with 0 1 ms sampling rate data were obtained with 12 fold redundancy in both downward and upward directions from the mine openings reflections with dominant frequency up to 1100 hz were observed between 20 and 80 ms time both single geophones and arrays of geophones were tested for the roof profiles geophones were bolted to the rock with specially designed base plates computer processing used deconvolution filters to remove spurious high frequency resonance of the geophones constant velocity for salt was used for all static corrections and normal moveout corrections an unexpected result was the appearance of near vertical reflected waves that traveled both ways at the shear wave speed these are thought to have been caused by near surface fractures or near surface anisotropy of the rock synthetic seismograms c

empirical links between trace metal cycling and marine microbial ecology during a large perturbation to earth s carbon cycle abstract understanding the global redox state of the oceans and its cause and effect relationship with periods of widespread organic carbon deposition is vital to interpretations of earth s climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency here we present a compilation of new and published data from an organic rich locality within the proto north atlantic ocean during the cenomanian turonian boundary event that shows a dramatic drawdown of redox sensitive trace elements iron geochemistry independently suggests euxinic deposition i e anoxic and sulfidic bottom waters for the entire section thus confirming its potential as an archive of global marine metal inventories in particular depleted molybdenum mo and vanadium v concentrations effectively record the global expansion of euxinic and oxygen deficient but non sulfidic waters respectively the v drawdown precedes the oae fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia molybdenum drawdown in contrast is delayed with respect to v and coincides with the onset of oae2 parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the oae in this region of the proto north atlantic with the smallest relative eukaryotic contributions to total primary production occurring during metal depleted intervals this relationship may be related to decreasing supplies of enzymatically important trace elements similarly box modeling suggests that oceanic drawdown of mo may have approached levels capable of affecting marine nitrogen fixation predictions of possible nitrogen stress on eukaryotic production locally and globally are consistent with the low observed levels of mo and a rise in 2 methylhopane index values during the peak of the oae at the same time the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades calcareous nanofossils and foraminifera suggesting that the temporal patterns of anoxia euxinia and associated nutrient limitation may have contributed to the fabric of oae2 related turnover

intraplate tectonics in asia a precise age for large scale miocene movement along the ailao shan red river shear zone china tertiary left lateral movement along the 1000 km long ailao shan red river shear zone appears to have played an important role in absorbing post collisional northward penetration of india into asia crustal strike slip shear along this zone caused the formation of a gneiss belt metamorphosed to amphibolite grade including anatectic melting both metamorphism and melting were induced by ductile deformation yielding the possibility to date the major tectonometamorphic event that shaped the ailao shan red river belt 17 u pb isotope analyses were performed on small size fractions of zircon monazite and xenotime extracted from two different leucogranitic layers the two samples are located about 50 km apart in the central segment of ailao shan in structurally well controlled settings where the melts crystallized within the strongly foliated gneisses during late stages of deformation all mineral u pb analyses had to be corrected for excess or deficit amounts of radiogenic 206 pb originating from initial 230 th disequilibrium in the 238 u decay series in monazite such disequilibrium 206 pb reaches 20 of total radiogenic 206 pb the corrected u pb ages of monazite and xenotime lie between 22 1 and 23 9 ma whereas zircon yields significantly discordant u pb ages between 30 5 and 33 9 ma pointing to precambrian material in the magma source region inherited components could also be detected in monazite the set of u pb data shows that monazite and xenotime formed simultaneously in both localities substantiating an early miocene age of 23 0 0 2ma for late kinematic crystallization of anatectic melts in the metamorphic belt of the ailao shan red river shear zone

onset timing of left lateral movement along the ailao shan red river shear zone 40ar 39ar dating constraint from the nam dinh area northeastern vietnam left lateral motion along the ailao shan red river asrr shear zone has been widely advocated to be the result of the collision between the indian and eurasian plates and to account for sea floor spreading in the south china sea our new 40 ar 39 ar data on the south easternmost outcrop of the day nui con voi metamorphic massif northern vietnam suggest that the exhumation of metamorphic massif by shearing along the asrr zone began 027 ma and lasted until 022 ma a perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of 0 6c m y 1 such a good correlation also indicates that the onset of the leftlateral movement of the shear zone may have occurred later than 027 5 ma this conclusion is consistent with our previous interpretation that collision induced southeastward extrusion of indochina along the asrr shear zone postdates the opening of the south china sea and that extrusion tectonics in se china may not be responsible for the opening of the south china sea 2000 elsevier science ltd all rights reserved

chemocline collapse in lake kivu as an analogue for nitrogen cycling during oceanic anoxic events abstract one of the outstanding issues in the study of nutrient dynamics during oceanic anoxic events oaes is the preservation of 15n depleted nitrogen isotope signals which are not observed in analogous modern environments the favored mechanism for 15 n values below 0 is utilization of excess ammonium derived from underlying anoxic waters by primary producers however there are few modern examples available for testing this hypothesis due to the overall well oxygenated state of modern oceans here we present sedimentary 13 corg and 15 nbulk data as well as pigment biomarker ratios from the sediments of lake kivu a meromictic lake in east africa this system serves as a potential analogue for the development of strongly depleted 15 nbulk in oae black shales we focus on intervals of organic carbon enrichment sapropels that are interpreted to have been the result of lake water column mixing events sediment 13 corg and 15 nbulk decrease by up to 6 and 4 respectively near the base of sapropel layers these negative excursions provide evidence for the mixing of 13c depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need derived from the deeper anoxic basin of the lake support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers

climatic control of the late quaternary turbidite sedimentology of lake kivu east africa implications for deep mixing and geologic hazards the lake kivu catchment in the east african rift is subject to various geologic hazards including frequent volcanic eruptions earthquakes and potential limnic overturns and degassing events integration of high resolution seismic reflection data 14 c dated sediment cores and lake floor bathymetry reveals large axial and transverse turbidite systems in the eastern basin of the lake the turbidites were sourced by hyperpycnal river flows during exceptional floods and the temporal occurrence of the turbidites was climatically controlled the turbidite record over the past 12 k y is correlated with the regional paleohydrologic records from tropical east africa our study suggests that flood introduced turbidites preserved in deep lakes are indicators of hydrological changes and that extreme floods in lake kivu9s recent history may have triggered deep mixing events this study also has implications for the current degassing efforts in lake kivu potential geologic hazards may be triggered by extraordinary turbidity currents and need to be considered in the design and deployment of gas extraction facilities

crustal contamination of late neogene basalts in the dien bien phu basin nw vietnam some insights from petrological and geochronological studies early pliocene zanclean basalts in the dien bien phu pull apart basin in nw vietnam associated with the presently sinistral dien bien phu fault zone have been dated by the k ar method at 4 4 4 9 and 5 4 5 2 ma rapid migration of basaltic magma to the surface in the dien bien phu fault zone may be due to pliocene transtension of the crust in this region resulting from asthenospheric upwelling induced by lateral displacement of the mantle the basalts are moderately phyric 10 and consist of olivine hyalosiderite plagioclase bytownite labradorite and orthopyroxene bytownite labradorite phenocrysts and a fine grained crystalline matrix olivine hortonolite plagioclase labradorite clinopyroxene pigeonite and augite k feldspar the presence of fe rich olivine and orthopyroxene phenocrysts indicates that the basalts are sio2 saturated oversaturated olivine tholeiites which formed under water undersaturated conditions the dien bien phu basalts contain both mantle derived pyroxenites dunites gabbros and crustal sillimanite mullite mg fe spinel wallrock xenoliths indicative of crustal contamination during the ascent of the basaltic magma the basalts show selective enrichment in some mobile elements k rb sr and th a feature considered to be a result of metasomatism these rocks classified on the basis of their normative composition as quartz tholeiites could represent primary olivine tholeiites basalts in which the geochemical signatures were modified by the processes of contamination 2006 elsevier ltd all rights reserved

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

formation of the jinchuan ultramafic intrusion and the world s third largest ni cu sulfide deposit associated with the 825 ma south china mantle plume we report here shrimp u pb geochronological geochemical and nd isotopic data for the jinchuan ultramafic intrusion gansu province china which hosts the world s third largest magmatic ni cu sulfide deposits u pb baddeleyite analyses yield an age of 812 26 ma for the ultramafic intrusion this age is indistinguishable within analytical uncertainties from the u pb zircon ages of 827 8 ma and 828 3 ma for the sulfide bearing ultramafic rocks and the dolerite dykes that cut the ultramafic intrusion respectively these u pb dating results show beyond doubt that the jinchuan ultramafic intrusion and associated ni cu sulfide deposit were formed at 825 ma rather than 1500 ma as has been widely believed the ultramafic rocks exhibit large negative nd t values 8 9 to 12 0 that decrease with increasing la sm suggesting that their parental magmas were derived from a long term enriched lithospheric mantle and experienced crustal contamination mineralogical petrological and geochemical data all indicate that the jinchuan intrusion was generated by melting of the enriched lithospheric mantle heated by an anomalously hot plume the u pb ages of 825 ma for igneous baddeleyites and zircons and 900 880 ma for inherited zircons in the jinchuan mafic ultramafic rocks are comparable with those in the qaidam block and qilian belt the western extension of the qinling belt that was likely derived from northern yangtze craton the jinchuan ni cu sulfide bearing intrusion along with coeval regional plume related mafic dykes and tholeiites and mafic ultramafic complexes with associated v ti and ni cu pge mineralization is interpreted to be genetically related to the 825 ma south china mantle plume

indochina peninsula and the collision of india and eurasia the collision of india with asia results in a rapidly changing stress pattern around both himalayan syntaxes the maximum compressive stress which is north south north of the indenter fans radially through nearly 180 around the syntaxes to accommodate the necessary strike slip motion on the edges of the indenter thus the whole indochina peninsula was swept by the migrating stress and associated strain pattern as the eastern syntaxis moved to the north as a result the maximum horizontal component of the stress field is predicted to have been first oriented east west then north south we propose that this changing stress field controlled the opening of the sedimentary basins and of the south china sea as well as the direction of motion of the major strike slip faults

nitrogen isotope evidence for water mass denitrification during the early toarcian jurassic oceanic anoxic event bulk sedimentary nitrogen isotope 15ntot data have been generated from lower jurassic black carbon rich shales in the british isles and northern italy deposited during the early toarcian oceanic anoxic event a pronounced positive 15ntot excursion through the exaratum subzone of the falciferum zone defined by characteristic ammonites in the british isles broadly correlates with a relative maximum in weight percent total organic carbon and in some sections with a negative 13corg excursion upwelling of a deoxygenated water mass that had undergone partial denitrification is the likely explanation for relative enrichment of 15ntot and parallels may be drawn with quaternary sediments of the arabian sea gulf of california and northwest mexican margin the development of early toarcian suboxic water masses and consequent partial denitrification is attributed to increases in organic productivity approximately coincident phenomena include the following a relative climatic optimum realignment of major oceanic current systems and a possible release of methane gas hydrates from continental margin sediments early in the history of the oceanic anoxic event

biogeochemical controls on black shale deposition during the frasnian famennian biotic crisis in the illinois and appalachian basins usa inferred from stable isotopes of nitrogen and carbon abstract the frasnian famennian biotic crisis is marked by two distinct intervals known as the lower and upper kellwasser events kwes that in many locations are associated with deposition of organic rich shales sedimentary nitrogen and carbon isotopes offer insight into the biogeochemical processing of nutrients production of organic matter and palaeoceanographic conditions during the kwes here we present new bulk nitrogen 15nbulk and organic carbon 13corg isotope data from the late devonian appalachian and illinois basins ab and ib with a focus on intervals encompassing the kwes black shales from the ib and ab including the kwes are 15n depleted 1 0 2 0 and have significantly lower 15nbulk than interbedded grey shales 0 5 4 0 a trend consistent with many instances of black shale deposition in the phanerozoic organic carbon isotopes exhibit the broad positive excursions 3 5 from background that are typical of the kwes globally superimposed over these positive excursions in 13corg are sharp decreases of up to 3 0 within the black shale beds to as low as 30 5 the pattern of 15nbulk and 13corg values suggests that the depth of the chemocline and the degree of water column stratification exert a primary control on both 15nbulk and 13corg during black shale deposition in the context of the frasnian famennian biotic crisis the oscillating redox state and changing temperatures would have likely placed extreme stress on organisms within the marine environment of the ab and ib and may potentially have been a contributing factor to diversity loss over this time period

denudation history of onshore central vietnam constraints on the cenozoic evolution of the western margin of the south china sea abstract apatite fission track analysis is used to monitor the timing and rate of upper crustal cooling and denudation across central vietnam in response to rifting of the south china sea results show regional denudation in the syn and post rift phases of the south china sea occurred at a similar rate 40 10 m myr consistent with the sedimentation record in adjacent offshore basins this suggests that extension was not the dominant factor controlling cenozoic denudation probably because the study area was sufficiently distant from the actively rifted continental margin a significant change in regional cooling rate during the upper miocene inferred denudation rates also shift from 34 m myr to 390 500 m myr is linked to enhanced erosion and deposition of prograding sediments in adjacent offshore basins this shift in denudation is associated and contemporaneous with initiation of regional basaltic magmatism and development of topography

nitrogen cycle dynamics in the late cretaceous greenhouse abstract great attention has been paid to the origin of anomalously low nitrogen isotope values during the late cretaceous nitrogen isotope values are often as low as 3 and are typically less than 2 even in relatively organic matter lean sediments here we evaluate nitrogen isotope variability during a relatively quiescent phase of the late cretaceous greenhouse between oceanic anoxic events 2 and 3 using the black shales of demerara rise dr selection of this site allows us to isolate some of the factors that control nitrogen cycle dynamics and contribute to low nitrogen isotope values new n isotope measurements from odp site 1259 reveal 15 n values that range from 0 2 to 3 5 and oscillate by 1 5 to 3 over 1 6 million years ma temporal calibration of our data using a new astronomical time scale reveals a strong 100 thousand year ka eccentricity cyclicity in 15 n we attribute this cyclicity to oscillations in the position of the intertropical convergence zone itcz over dr that modulate upwelling intensity chemocline depth and the degree of 15n depletion we also recognize a statistically significant correlation p 0 0022 between the tex86 indices and 15 n with the lowest 15 n corresponding to the highest tex86 indices this relationship suggests that the activity and ecology of ammonia oxidizing thaumarchaeota and the 15 n of dissolved inorganic nitrogen utilized by primary producers are linked we therefore interpret the observed variability in the 15 n data and tex86 indices as primarily reflecting fluctuation of upwelling intensity and chemocline depth and the significant inverse relationship between these data sets suggests that caution should be exercised when interpreting the tex86 in terms of temperature in similar paleoenvironmental settings

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

bounds on strain in large tertiary shear zones of se asia from boudinage restoration we have used surface balanced restoration of stretched boudinaged layers to estimate minimum amounts of finite strain in the mylonitic gneisses of the oligo miocene red river ailao shan shear zone yunnan china and of the wang chao shear zone thailand the layer parallel extension values thus obtained range between 250 and 870 we discuss how to use such extension values to place bounds on amounts of finite shear strain in these large crustal shear zones assuming simple shear these values imply minimum total and late shear strains of respectively 33 6 and 7 3 at several sites along the red river ailao shan shear zone for the wang chao shear zone a minimum shear strain of 7 4 is deduced assuming homogeneous shear would imply that minimum strike slip displacements along these two left lateral shear zones which have been interpreted to result from the india asia collision have been of the order of 330 60 km red river ailao shan and 35 20 km wang chao

water and gas chemistry at lake kivu drc geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure 1 waters and dissolved gases collected along vertical profiles in the five basins main kabuno bay kalehe ishungu and bukavu forming the 485 m deep lake kivu democratic republic of the congo were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry the measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by 1 different contribution from long circulating fluid system containing magmatic co2 responsible of the huge co2 ch4 rich reservoir hosted within the deep lake water 2 spatial variations of the biomass distribution and or speciation and 3 solutes from water rock interactions the kabuno bay basin is characterized by the highest rate of magmatic fluid input accordingly this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the nyiragongo and nyamulagira volcanoes located a few kilometers north of the lake

displacement along the red river fault constrained by extension estimates and plate reconstructions significant e w extension and or compression must have been generated by displacements along the red river fault rrf since its curvature does not match a small circle centered at the euler pole for the indochina south china plate pair the amount of extension perpendicular to the rrf offshore vietnam depends on the magnitude of left lateral displacement along the rrf in general the larger the left lateral displacement along the fault the smaller the amount of e w extension all purely strike slip models of the opening of the south china sea that assume large displacements 250 km along the rrf encounter major problems because they imply little extension or even considerable shortening offshore east vietnam this is inconsistent with the presence of large elongated basins offshore vietnam using a plate tectonic model we compare continental extension values implied by different magnitudes of displacement along the rrf with crustal stretching estimates derived from 2 d profiles modeled from gravity data we utilize 2 d gravity forward models to restore the extended continental margin crust to its original position prior to extension we find that substantial amounts of extension for offshore vietnam can only be modeled assuming moderate displacements along the rrf compatible with the presence of a southward subducting proto south china sea the total amount of ene wsw extension offshore northern vietnam constrained by our 2 d gravity profiles and gravity inversion increases southward from 36 to 89 km along the yinggehai basin these values of ene wsw extension are consistent with 250 km of left lateral displacement along the rrf