climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

permian and triassic greenhouse crises paleoclimatic time series from permian and triassic paleosols reveal transient episodes of unusually warm and wet conditions interrupting long periods of cool and dry conditions usual for calcareous red paleosols some of these paleoclimatic events are known from stomatal index of fossil lepidopteris leaves to have been episodes of elevated global atmospheric co2 the magnitude of 19 known permian and triassic greenhouse crises varied considerably and they offer new evidence for the relationship between paleoclimate and atmospheric co2 levels these greenhouse crises also had marked effects on global lowland vegetation introducing frost sensitive tropical lycopsids to high latitudes and drought tolerant conifers to low latitude lowlands greenhouse events punctuate phases in plant evolution ottokaria callipteris plumsteadia rufloria lidgettonia tatarina pleuromeia and dicroidium scytophyllum floras greenhouse events also punctuate the evolution of reptilian dynasties successive pelycosaur dinocephalian dicynodont rhynchosaur and dinosaur faunas and respiratory adaptations such as enlarged bony secondary palate greenhouse crises of the late and middle permian were the most severe known and suggest a role for atmospheric pollution with ch4 and co2 in those mass extinction events probably from thermogenic cracking of coals by intrusive feeder dikes of flood basalts because of formalities in boundary definition these mass extinctions are neither end permian nor end guadalupian but upper changhsingian and mid capitanian respectively

anomalous early triassic sediment fluxes due to elevated weathering rates and their biological consequences analysis of 16 marine permian triassic boundary sections with a near global distribution demonstrates systematic changes in sediment fluxes and lithologies in the aftermath of the end permian crisis sections from continent margin and platform settings exhibit higher bulk accumulation rates bars and more clay rich compositions in the griesbachian earliest triassic relative to the changhsingian latest permian these patterns which largely transcend regional variations in tectonic setting sequence stratigraphic factors and facies are hypothesized to have resulted from a substantial average 7 increase in the flux of eroded material from adjacent land areas owing to accelerated rates of chemical and physical weathering as a function of higher surface temperatures increased acidity of precipitation and changes in landscape stability tied to destruction of terrestrial ecosystems this sediment surge may have been a contributory factor to the latest permian marine biotic crisis as well as to the delayed recovery of early triassic marine ecosystems owing to the harmful effects of siltation and eutrophication contemporaneous deep sea sections show no increases in sediment flux across the permian triassic boundary owing to their remoteness from continental siliciclastic sources and location below the paleo carbonate compensation depth

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

determining crustal structure beneath seismic stations overlying a low velocity sedimentary layer using receiver functions the receiver function rf technique has been widely applied to investigate crustal and mantle layered structures using p to s converted ps phases from velocity discontinuities however the presence of low velocity relative to that of the bedrock sediments can give rise to strong reverberations in the resulting rfs frequently masking the ps phases from crustal and mantle boundaries such reverberations are caused by p to s conversions and their multiples associated with the strong impedance contrast across the bottom of the low velocity sedimentary layer here we propose and test an approach to effectively remove the near surface reverberations and decipher the ps phases associated with the moho discontinuity autocorrelation is first applied on the observed rfs to determine the strength and two way traveltime of the reverberations which are then used to construct a resonance removal filter in the frequency domain to remove or significantly reduce the reverberations the filtered rfs are time corrected to eliminate the delay effects of the sedimentary layer and applied to estimate the subsediment crustal thickness and vp vsusing a h k stacking procedure the resulting subsediment crustal parameters thickness and vp vs are subsequently used to determine the thickness and vp vs of the sedimentary layer using a revised version of the h k stacking procedure testing using both synthetic and real data suggests that this computationally inexpensive technique is efficient in resolving subsediment crustal properties beneath stations sitting on a low velocity sedimentary layer and can also satisfactorily determine the thickness and vp vs of the sedimentary layer

timing of mammal like reptile extinctions across the permian triassic boundary in south africa the rate timing and pattern of change in different regions and paleoenvironments are critical for distinguishing among potential causes for the permian triassic p t extinction carbon isotopic stratigraphy can provide global chronostratigraphic control we report a large 13 c excursion at the p t boundary and no long term permian 13 c trends for samples from the interior of pangea stratigraphic gaps between available samples limit the resolution of our 13 c curve but the excursion is within a 15 m thick zone of overlap between permian and triassic taxa sedimentological and taphonomic observations demonstrate that this 15 m interval does not represent geologically instantaneous deposition together these data support a rapid and globally synchronous p t event but suggest that it occurred over a geologically resolvable interval of time

chemical and isotopic investigations into the origin of clay minerals from the galapagos hydrothermal mounds field abstract a dark green authigenic nontronite is the major component of the galapagos hydrothermal mounds field sediments oxygen isotopic compositions of the chemically purified in situ mounds temperatures of up to 15 c assuming an authigenic origin the fe rich montmorillonite that dominates in the noncarbonate clay fraction of the surrounding pelagic ooze has isotopic formation temperatures of 27 to 39 c compared with measured in situ temperatures of ca 3 5 to 6 5 c the higher isotopic formation temperatures calculated for the hydrothermal nontronite suggest either complex patterns of fluid circulation and nontronite precipitation presently within the mounds or a higher thermal history associated with rapid and episodic periods of deposition during the holocene pleistocene the apparent high isotopic temperature of the fe rich montmorillonite may reflect 1 formation under hydrothermal conditions at spreading centers with subsequent dispersal by bottom currents 2 a detrital origin of the mineral or 3 a mixture of authigenic fe montmorillonite and detrital al montmorillonite in this region

fe si oxyhydroxide deposits at a slow spreading centre with thickened oceanic crust the lilliput hydrothermal field 9 33 s mid atlantic ridge diffuse and focused low temperature fluids emanate at 9 33 s mid atlantic ridge and precipitate fe sioxyhydroxides that form chimneys mounds and flat lying deposits this extensive vent field named lilliput lies at the axial zone of a spreading segment with a significantly thickened crust 11 km theoretically much more heat needs to be removed from a thick crust spreading center compared to a spreading center with typical thickness of 6 km therefore settings with thickened crust should be favourable for supporting very powerful hydrothermal systems capable of producing large mineral deposits this is the first report on the composition of seafloor hydrothermal deposits at abnormally thickened oceanic crust due to hotspot ridge interaction our studies revealed that generally the lilliput hydrothermal deposits are very similar in morphology structure composition and lateral extent to other low temperature hydrothermal deposits of mid ocean ridges and intraplate volcanoes deposits at the lilliput vent field are composed of si containing goethite and ferrihydrite have very low contents of a number of transition and rare earth elements and show ree distribution patterns with negative ce and eu anomalies the speciation and precipitation of the main deposit forming elements fe and si at the hydrothermal field appear to be partially controlled by live microbes and exuded organic compounds the 18o values of the precipitated silica containing feoxyhydroxides point to low temperature formation and sr nd pb isotope variations suggest that the hydrothermal precipitates scavenged metals predominantly from the ambient seawater these findings are in agreement with the biogeochemical scenario for their precipitation

latitudinal temperature gradient during the cretaceous upper campanian middle maastrichtian y18o record of continental vertebrates latitudinal variations in model biogenic apatite d18o values were calculated using fractionation equations of vertebrates and weighted rainfall y18o values along with mean annual air temperatures provided by iaea wmo meteorological stations the reference equation obtained was used to compute a continental temperature gradient for the late campanian middle maastrichtian interval by using published and new d18o values of phosphate from vertebrates samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83 4 n alaska to 32 3 s madagascar the temperature gradient was less steep 0 4 0 1 c latitude than the present day one 0 6 c latitude with temperatures that decreased from about 30 c near the equator to about 5 c at the poles above 30 of paleolatitude air temperatures were higher than at present the validity of these results is discussed by comparison with climatic criteria inferred from paleontological paleobotanical and sedimentological data the latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying mesozoic terrestrial climates

low temperature fluid flow through sulfidic sediments from tag modification of fluid chemistry and alteration of mineral deposits low temperature fluid flow has been identified as an important component of the heat mass and chemical flux at sites of active venting one way to study the movement of water through hydrothermal deposits is to analyse the pore fluids extracted from sulfidic sediments the composition of diffuse flow fluids in one sediment core from the south of the active tag mound reflects the dilution of high temperature black smoker fluids with modification inside the mound during ongoing circulation fluid modification includes conductive cooling removal of si from solution and entrainment and removal of u from seawater which can represent significant sinks of these elements precipitation of clay minerals and fe oxides is currently occurring within this sediment core generating ochreous type material subsurface extensive low temperature alteration of basaltic material at the core top is apparent in conjunction with supergene enrichment of cu and mn

precipitation of fe iii oxyhydroxide deposits from shallow water hydrothermal fluids in tutum bay ambitle island papua new guinea abstract previous research on sea floor fe iii oxyhydroxide deposits has focused primarily on deep sea hydrothermal systems found along volcanically active portions of the mid ocean ridges and on hydrogenetic deposits formed in deep basins and along continental shelves there is however not much known about their formation in shallow water settings associated with volcanic islands the hydrothermal system at ambitle island papua new guinea provides an excellent opportunity to study the formation of fe iii oxyhydroxides in a shallow water setting precipitation from the hydrothermal solution is caused by mixing with seawater based on a 87 sr 86 sr mixing model the calculated minimum and maximum seawater fractions are approximately 11 and 57 respectively thus precipitation of tutum bay fe iii oxyhydroxides takes place at a temperature range between approximately 60 and 93 c the chemical composition shows low mn contents fe mn 600 and elements that are usually enriched in fe iii oxyhydroxides such as co and v are below crustal abundance and well below their concentrations in island arc volcanics arsenic concentrations on the other hand are by two orders of magnitude higher than those in other marine deposits rare earth element ree concentrations reflect their concentration in the hydrothermal fluids rather than seawater the crystallinity of the deposits increases with age as protoferrihydrite is apparently altered to fe smectite and hematite and as bearing minerals are formed contact with seawater and therefore oxidizing conditions seems to be the factor increasing the crystallinity

formation of fe mn si oxide and nontronite deposits in hydrothermal fields on the valu fa ridge lau basin abstract hydrothermal fe mn si oxides and nontronite are pervasive in the hine hina vai lili and mariner hydrothermal fields along the central valu fa ridge lau basin morphometric and mineralogical analyses reveal that the iron rich filaments are the most important constituents of these fe mn si oxide deposits both the morphologies and chemical composition of the filaments indicate that neutrophilic fe oxidizing bacteria have played a key role in the formation of these deposits a key process of the formation of these deposits is the creation of a complicated filamentous network in which a series of metabolic activities and passive sorption and nucleation processes occur the precipitation of dissolved si in unsaturated and saturated states leads to a two generation growth model in the hydrothermal vents the precipitation of amorphous opal occurs in a relatively narrow temperature range 41 1 42 9 c based on oxygen isotope analyses indicating a fast precipitation rate of opal a when conductive cooling of the hydrothermal fluid occurrs patchy nontronite in the mariner fields is a product of the direct precipitation from hydrothermal fluids at a temperature of 87 9 c whereas the scattered nontronite at the hine hina field is the product of the replacement of hydrothermal fe si oxides at a temperature of 46 2 c

new geochemical and palaeontological data from the permian triassic boundary in the south african karoo basin test the synchronicity of terrestrial and marine extinctions abstract the end permian mass extinction epme is widely recognised as the largest mass extinction in phanerozoic history in marine strata the main extinction event is well constrained and has been radiometrically dated to an interval of some 60 kyr approximately 251 9 million years ago however the age and duration of the epme in the terrestrial realm as well as its possible synchronicity with that of the marine realm is debated here we shed light on issues pertaining to the identification and position of the terrestrial epme in southern africa using recently collected sedimentological facies sequences palaeontological biostratigraphic ranges geochemical stable isotope analyses and detrital zircon id tims data from a new site in the xhariep district of the south african karoo basin we demonstrate that the permian triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction we conclude that the terrestrial epme recorded in the karoo may be regarded as essentially synchronous with the epme currently defined in the marine realm and was likely the result of the same volcanically induced atmospheric disturbances this study describes the first single vertical succession of vertebrate and plant fossils that span the terrestrial permian triassic boundary that are also well constrained both by relative stable isotopes and absolute detrital zircon geochronology dating methods

hydrothermal activity on the southern mid atlantic ridge tectonically and volcanically controlled venting at 4 5 s we report results from an investigation of the geologic processes controlling hydrothermal activity along the previously unstudied southern mid atlantic ridge 3 7 s our study employed the noc uk deep tow sidescan sonar instrument tobi in concert with the whoi usa autonomous underwater vehicle abe to collect information concerning hydrothermal plume distributions in the water column co registered with geologic investigations of the underlying seafloor two areas of high temperature hydrothermal venting were identified the first was situated in a non transform discontinuity ntd between two adjacent second order ridge segments near 4 02 s distant from any neovolcanic activity this geologic setting is very similar to that of the ultramafic hosted and tectonically controlled rainbow vent site on the northern mid atlantic ridge the second site was located at 4 48 s at the axial summit centre of a second order ridge segment there high temperature venting is hosted in an 18 km2 area of young lava flows which in some cases are observed to have flowed over and engulfed pre existing chemosynthetic vent fauna in both appearance and extent these lava flows are directly reminiscent of those emplaced in winter 2005 06 at the east pacific rise 9 50 n and reference to global seismic catalogues reveals that a swarm of large m 4 6 5 6 seismic events was centred on the 5 s segment over a 24 h period in late june 2002 perhaps indicating the precise timing of this volcanic eruptive episode temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5 s mar turtle pits have subsequently revealed vent fluids that are actively phase separating under conditions very close to the critical point for seawater at 3000 m depth and 407 c the hottest vent fluids yet reported from anywhere along the global ridge crest

warming and increased aridity during the earliest triassic in the karoo basin south africa the permian triassic p t mass extinction is the largest extinction event of the phanerozoic and has been causally related to eruption of the siberian traps siberia russia through climatic and ecological effects of volcanically forced greenhouse gas emissions given anthropogenic changes to the atmosphere documenting details of links between greenhouse warming and catastrophic biological consequences has significance beyond better understanding of the p t boundary earliest triassic warming is supported by modeling and isotopic studies however the empirical data are limited in this paper we show that 18 o values of phosphate in therapsid tusks from the interior of pangea paleolatitude 60 s were relatively constant through the latest permian but increased by 2 during the earliest triassic over the same interval 18 o values of carbonate soil nodules increased by 5 the increases in both measurements and the disproportionately large shift among nodules indicate that the interior of pangea warmed and became markedly more arid immediately after the p t boundary

global warming and the end permian extinction event proxy and modeling perspectives abstract the mass extinction event that occurred at the close of the permian period 252 million years ago represents the most severe biodiversity loss in the ocean of the phanerozoic the links between the global carbon cycle climate change and mass extinction are complex and involve a whole range of often inter related geochemical biological ecologic and climatic factors it has become widely accepted that the end permian mass extinction was associated with a global warming event because the age of the siberian trap eruption a potentially massive source of carbon dioxide coincides within error with the extinction event however geologic data that are in support of this global warming event are relatively sparse the chain of events and the causal relationship between the eruption of siberian traps and mass extinction is not well established global warming in particular has only been reported from limited proxy data and climate models for which the pco2 in the atmosphere just before and during the end permian extinction event is poorly known this study critically assesses both the proxy climate data and the existing paleoclimate simulations with the goals of assessing our current understanding of the link between mass extinction and climate change and providing some guidance for future studies proxies indicate that prior to the end permian extinction event tropical sea surface temperatures ranged from 22 to 25 c and possible pco2 values ranged from 500 to 4000 ppm before the extinction event during the peak extinction tropical temperatures rose up to 30 c while pco2 perhaps increased up to 8000 ppm climate models that use different pre event pco2 values show similar amount of co2 doubling to replicate the observed carbon isotope excursions we find that the temperature anomaly during the end permian extinction is consistent with 1 5 doublings of atmospheric pco2 and that the implied climate sensitivity is 5 6 c within the upper range of values produced by climate models

end permian mass extinction in the oceans an ancient analog for the twenty first century the greatest loss of biodiversity in the history of animal life occurred at the end of the permian period 252 million years ago this biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of earth s largest continental flood basalt provinces the siberian traps volatile release from basaltic magma and sedimentary strata during emplacement of the siberian traps can account for most end permian paleontological and geochemical observations climate change and perhaps destruction of the ozone layer can explain extinctions on land whereas changes in ocean oxygen levels co2 ph and temperature can account for extinction selectivity across marine animals these emerging insights from geology geochemistry and paleobiology suggest that the end permian extinction may serve as an important ancient analog for twenty first century oceans

intensifying aeolian activity following the end permian mass extinction evidence from the late permian early triassic terrestrial sedimentary record of the ordos basin north china

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

oxygen isotopes from conodont apatite of the midcontinent us implications for late ordovician climate evolution abstract the major glaciation at the end of the ordovician is associated with the 2nd largest mass extinction event of the phanerozoic growth of late ordovician ice sheets requires a dramatic cooling from the greenhouse conditions that prevailed for most of the ordovician but when and how fast this cooling occurred are controversial issues the controversy is due in large part to a lack of good geochemical constraints on the temperature history of the katian 453 445 2 ma to address this uncertainty we measured phosphate 18o values from 3 conodont species collected from sections in the midcontinent region of the united states that span an 5 7 m yr long interval covering most of the katian results reveal a statistically significant offset in 18o values between some taxa and show up to 2 differences among samples however there are no apparent long term trends within or between sections rather values fluctuate around a 18o mean of 19 vsmow our study provides the longest relatively high resolution species specific conodont record generated for this interval and we found no evidence supporting progressive cooling during the katian

young volcanism and related hydrothermal activity at 5 s on the slow spreading southern mid atlantic ridge the effect of volcanic activity on submarine hydrothermal systems has been well documented along fast and intermediate spreading centers but not from slow spreading ridges indeed volcanic eruptions are expected to be rare on slow spreading axes here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated apparently magmatically robust segment center on the slow spreading southern mid atlantic ridge near 5 s three high temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase separated vapor type fluids exit temperatures at one of the fields reach up to 407 c at conditions of the critical point of seawater the highest temperatures ever recorded from the seafloor fluid and vent field characteristics show a large variability between the vent fields a variation that is not expected within such a limited area we conclude from mineralogical investigations of hydrothermal precipitates that vent fluid compositions have evolved recently from relatively oxidizing to more reducing conditions a shift that could also be related to renewed magmatic activity in the area current high exit temperatures reducing conditions low silica contents and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source probably related to a young volcanic eruption event nearby in which basaltic magma is actively crystallizing this is the first reported evidence for direct magmatic hydrothermal interaction on a slow spreading mid ocean ridge

coexistence of fe ii and mn ii oxidizing bacteria govern the formation of deep sea umber deposits the genesis of umber deposits has remained controversial for several decades recently microbial fe ii oxidation associated with low temperature diffuse venting has been identified as a key process for the formation of umber deposits but the exact biogeochemical mechanisms involved to the precipitation of mn oxides in umber deposits still remain unknown here we used nano secondary ion mass spectrometer synchrotron based x ray absorption spectroscopy electron microscopy and molecular techniques to demonstrate the coexistence of two types of metal oxidizing bacteria within deep sea hydrothermal umber deposits at the south mid atlantic ridge where we found unique spheroids composed of biogenic fe oxyhydroxides and mn oxides in the deposits our data show that fe oxyhydroxides and mn oxides are metabolic by products of lithotrophic fe ii oxidizing bacteria and heterotrophic mn ii oxidizing bacteria respectively the hydrothermal vents fuel lithotrophic microorganisms which constitute a trophic base that might support the activities of heterogenic mn ii oxidizing bacteria the biological origin of umber deposits shed light on the importance of geomicrobiological interaction in triggering the formation of metalliferous deposits with important implications for the generation of submarine mn deposits and crusts c 2015 elsevier ltd all rights reserved

palaeotethys seawater temperature rise and an intensified hydrological cycle following the end permian mass extinction abstract the end permian mass extinction has been associated with severe global warming main stage volcanism of the siberian traps occurred at or near the extinction interval and has been proposed as a likely greenhouse catalyst in this study a high resolution 18o record is established using diagenetically resistant apatite of conodonts and low mg calcite of brachiopods from stratigraphically well constrained permian triassic p tr boundary successions in northwestern iran a new evaluation is made for previously published conodont 18o values from south china and revised palaeotemperatures are presented together with new data from wuchiapingian to griesbachian sections in iran 18o data from p tr sections in iran document tropical sea surface temperatures sst of 27 33 c during the changhsingian with a negative shift in 18o starting at the extinction horizon translating into a warming of ssts to over 35 c the results are consistent with re calculated ssts of the south chinese sections warming was associated with an enhanced hydrological cycle involving increased tropical precipitation and monsoonal activity in the tethys sea global warming intensification of the hydrological cycle and associated processes vertical water column stratification eutrophication and subsequent local anoxia may all have facilitated an extinction event

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

nontronite from a low temperature hydrothermal system on the juan de fuca ridge abstract a deposit of fe rich al poor hydrothermal nontronite was recovered from the juan de fuca ridge analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities the deposit is located near the tip of a propagating segment of the juan de fuca ridge rare earth elements and sr isotopes indicate that the nontronite precipitated from seawater a formation temperature of 57 c is suggested by oxygen isotopic composition the low temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment more mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low temperature systems

is the vertebrate defined permian triassic boundary in the karoo basin south africa the terrestrial expression of the end permian marine event the end permian extinction records the greatest ecological catastrophe in earth history the vertebrate fossil record in the karoo basin south africa has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems recently claimed to be in synchrony with the marine crisis workers assumed that systematic turnover at the dicynodon assemblage zone boundary followed by the appearance of new taxa directly above the base of the lystrosaurus assemblage zone is the continental expression of the end permian event and recovery to test this hypothesis we present the first highprecision age on strata close to the inferred permian triassic boundary a u pb isotope dilution thermal ionization mass spectrometry zircon age of 253 48 0 15 ma early changhsingian is from a silicified ash layer 60 m below the current vertebrate defined boundary at old lootsberg pass southern south africa this section yields newly discovered plants and vertebrates and is dominated by a normal polarity signature our collective data suggest that the dicynodon lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported and older than the marine extinction event therefore the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end permian mass extinction the actual permian triassic boundary in the karoo basin is either higher in the katberg formation or is not preserved the currently accepted model of the terrestrial ecosystem response to the crisis both in this basin and its extension globally requires reevaluation

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

global climate perturbations during the permo triassic mass extinctions recorded by continental tetrapods from south africa several studies of the marine sedimentary record have documented the evolution of global climate during the permo triassic mass extinction by contrast the continental records have been less exploited due to the scarcity of continuous sections from the latest permian into the early triassic the south african karoo basin exposes one of the most continuous geological successions of this time interval thus offering the possibility to reconstruct climate variations in southern laurasia from the middle permian to middle triassic interval both air temperature and humidity variations were estimated using stable oxygen 18op and carbon 13cc isotope compositions of vertebrate apatite significant fluctuations in both 18op and 13cc values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution in terms of air temperature oxygen isotopes show an abrupt increase of about 8 c toward the end of the wuchiapingian this occurred during a slight cooling trend from the capitanian to the permo triassic boundary ptb at the end of the permian an intense and fast warming of 16 c occurred and kept increasing during the olenekian these thermal fluctuations may be related to the emeishan south china and siberian volcanic paroxysms that took place at the end of the capitanian and at the end of the permian respectively vertebrate apatite 13cc partly reflects the important fluctuations of the atmospheric 13c values the differences with marine curves being likely due to the evolution of local humidity both the oxygen and carbon isotope compositions indicate that the ptb was followed by a warm and arid phase that lasted 6 ma before temperatures decreased during the late anisian toward that of the end permian environmental fluctuations occurring around the ptb that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release

the origin of clay minerals in active and relict hydrothermal deposits samples of fe oxide rich hydrothermal sediments were collected from active and inactive portions of the transatlantic geotraverse tag hydrothermal field on the mid atlantic ridge clays separated from tag metalliferous sediments in this study all consist of al poor nontronite oxygen isotope thermometry of the clays yields formation temperatures of 54 67 c for samples from the inactive alvin mound compared with 81 96 c for samples from the active tag site the latter are the highest recorded temperatures for authigenic hydrothermal clays sr isotope analysis of the clays from the active mound suggests that they precipitated from seawater dominated fluids containing less than 15 hydrothermal end member fluid in contrast nontronite from the inactive alvin mound has 87sr 86sr values that closely resemble that of detrital north atlantic clays suggesting a dominantly continental source for the sr rare earth element data are consistent with a significant detrital input to the inactive site but also demonstrate the extent of hydrothermal input to the low temperature fluid crystallographic fractionation of the trivalent ree is apparent in the heavy ree enrichments for all nontronite samples the inferred formation mechanism for nontronite rich fe oxyhydroxide deposits at the surface of the active mound is by direct precipitation from low temperature fluids at the inactive alvin site in contrast the deposits form during alteration of pelagic sediments by diffuse fluids and replacement of biogenic carbonate with nontronite and fe oxyhydroxide these two modes of formation are both important in seafloor hydrothermal settings where clay minerals are a significant component of the hydrothermal deposit

high precision temporal calibration of late permian vertebrate biostratigraphy u pb zircon constraints from the karoo supergroup south africa therapsid and other tetrapod fossils from the south african karoo supergroup provide the most detailed and best studied terrestrial vertebrate record of the middle and late permian the resulting biostratigraphic scheme has global applicability establishing a temporal framework for these faunas has proven difficult magnetostratigraphy has been hampered by a jurassic overprint and intercorrelation with permian marine sequences has been equivocal here we report u pb zircon isotope dilution thermal ionization mass spectrometry id tims dates for five volcanic ashes interbedded with fossils from the pristerognathus tropidostoma and cistecephalus vertebrate biozones of the beaufort group this temporal framework allows correlation to marine zonations and improves understanding of rates of faunal evolution and patterns of basin evolution our results identify no correlative vertebrate extinctions in the karoo supergroup to the marine end guadalupian mass extinction and raise the question of whether there is any record of a terrestrial extinction related to the emeishan large igneous province

anatomy of a mass extinction sedimentological and taphonomic evidence for drought induced die offs at the permo triassic boundary in the main karoo basin south africa abstract the southern part of the karoo basin of south africa contains a near complete stratigraphic record of the permo triassic boundary ptb isotope and magneto stratigraphy confirm that these predominantly fluvial strata are approximately the same age as zircon dated marine ptb sections 252 mya by august 2013 our team had found 579 in situ vertebrate fossils mostly of the clade therapsida in ptb exposures at three widely separated locations in the southern karoo basin biostratigraphic ranges of the various taxa found in each of the sections reveal three separate phases of die off within the same roughly 75 metre thick stratigraphic interval displaying the same sequence of sedimentary facies interpreted as indicative of climatic drying increased seasonality and the onset of an unpredictable monsoon type rainfall regime the three phases of an inferred ecologically stepped mass extinction are phase 1 45 m 30 m below ptb datum brought on by lowered watertables which led to loss of shallow rooting groundcover in the more elevated proximal floodplain areas and the disappearance of the smaller groundcover grazing herbivorous dicynodonts and their attendant small carnivores phase 2 20 0 m below ptb datum is the main extinction that occurs in massive maroon grey mudrock culminating in an event bed of laminated reddish brown siltstone mudstone couplets this facies reflects progressively unreliable rainfall leading to vegetation loss in proximal and distal floodplain areas the larger tree browsing herbivores and their attendant carnivores are confined to watercourses before finally disappearing phase 3 25 30 m above ptb datum occurs in massive maroon siltstone facies with evidence of climatic aridity including the accumulation of mummified carcasses buried by windblown dust all of the surviving permian taxa disappear within 30 m of the ptb temporal resolution based on accretion rates and pedogenic maturity of each stratigraphic section reveals that phase 1 and phase 2 die offs lasted 21 000 and 33 000 years separated by a short period of 7000 years where no disappearances are recorded and this was followed by 50 000 years of stasis for the final extinction phase lasting only 8000 years that removed all the permian survivor taxa we propose that the recorded disappearances are real rather than preferential preservation failure and that they represent drought induced die offs moving progressively up the food chain as the terrestrial ecosystem collapsed the latter mostly likely caused by volcanogenic greenhouse gas emissions and rapid global warming

geological and hydrothermal controls on the distribution of megafauna in ashes vent field juan de fuca ridge a computerized data base was constructed to aid in the interpretation of biological and geological observations recorded from 7662 photographs taken of ashes vent field located along the sw wall of the summit caldera of axial volcano juan de fuca ridge during 1985 1986 using the pisces iv submersible and a towed camera system the transition region between the locus of high temperature vents in ashes vent field i e inferno 326 c hell 301 c and virgin mound 298 c and more typical environmental conditions for the summit caldera of axial volcano as a whole is zoned spatially with respect to sediment type and organism assemblage three general ecological zones are identified within the vent field 1 the central vent zone within 100 m of a high temperature vent dominated by vent associated organisms vestimentiferan tube worms clams bacterial mats and sedimentation high temperature plume derived and low temperature in situ deposits 2 the distal vent zone 100 725 m from any high temperature vent characterized by extensive fields of iron oxide iron silicate and silica chimneys and sediment nontronite assemblage material as well as maximum densities of most nonvent fauna and 3 the nonvent impact zone 725 1300 m indicated by elevated densities of nonvent organisms relative to regional i e caldera wide values and maximum bathydorus sp sponge densities the distribution of vestimentiferan tube worms is limited to within 90 m of known high temperature venting central vent zone and anemones were observed only between 30 and 40 m from hot vents clams and microbial mats are concentrated in the central vent zone as well but occur sporadically up to 1250 m from the hot vents in association with hydrothermal nontronite that is probably precipitating in situ from 60 c vent fluid thus megafaunal distributions are a useful indicator of poorly defined often diffuse low temperature hydrothermal activity on the seafloor maximum densities of nonvent echinoderms i e holothurians sea stars urchins are associated with the distal venting zone distributions of megafauna not endemic to the vent environment are sensitive to both local geology particularly the nature of the substrate and effects of hydrothermal activity such as enhanced food availability or hydrothermal sedimentation although evidence for active venting is not apparent in the nonvent impact zone photographic data suggest that the type and number of megafauna living in this region are significantly influenced by proximity to low and high temperature hydrothermal sources that support enhanced microbial production and produce sediment of hydrothermal origin which may be advected to the peripheral environment statistical interpretation of photographic data suggests an outer limit to the extent of vent influence on benthic megafauna i e bathydorus sp sponges of about 1000 1300 m for the hydrothermal system active at ashes vent field in 1985 1986 on the scale of a single vent field hydrothermal activity apparently results in a less patchy distribution of benthic nonvent organisms within the central and distal vent zones than is common in the nonvent environment

a new high resolution stratigraphic and palaeoenvironmental record spanning the end permian mass extinction and its aftermath in central spitsbergen svalbard abstract research on the permian triassic boundary ptb along the northern margins of pangaea exposed today in the arctic region has been heavily reliant on field observations where data resolution was consequently determined by outcrop condition and accessibility core drilling in central spitsbergen allowed for a near complete recovery of two 90 m cores through the ptb analyses of the core and nearby outcrops include stratigraphic logging and sampling xrf scanning petrography biostratigraphy isotope geochemistry and geochronology the first appearance datum fad of h parvus in svalbard places the base of the triassic ca 4 m above the base of the vikinghogda formation and ca 2 50 m above the end permian mass extinction epme and its associated sharp negative 13c the ptb therefore falls within the reduviasporonites chalastus assemblage zone in svalbard precise u pb tims dating of two zircon crystals in a tephra layer just above the first documented hindeodus parvus in svalbard gives an age of 252 13 0 62 ma high resolution palaeoenvironmental proxies including si kcps kilo counts per second zr rb k ti fe k and v cr indicate a transition towards a more arid climate in the earliest triassic contemporaneous with prolonged bottom water dysoxic anoxic conditions following an increase in volcanic activity in the late permian statistical analysis of zr rb k ti and v cr elemental ratios suggests that the system was impacted by long eccentricity 400 kyr cyclicity the 13c excursion in organic carbon 13corg record signals a large negative carbon isotope excursion cie associated with the mass extinction event but also records a second smaller negative cie ca 22 m above this interval this younger 13corg excursion correlates to similar cies in the dienerian late induan records of other sections notably in the tethys ocean which have been interpreted as recording a small biotic crisis during the post extinction recovery evidence of this negative cie in spitsbergen suggests that the dienerian crisis may have been global in extent the negative 13corg values are associated with evidence for dysoxia or anoxia in the core and the occurrence of tephra layers in the same interval suggests a possible connection between the dienerian crisis and a discrete episode of volcanic activity

low temperature hydrothermal deposits of franklin seamount woodlark basin papua new guinea abstract hydrothermal deposits of siliceous fe mn oxides from a few cm to 7 m in height are widespread at the summit and caldera floor of franklin seamount a 250 m high edifice of basaltic andesite lava tubes pillows and talus located near the western propagating tip of the woodlark spreading axis some deposits are venting clear fluid at about 30 c the hydrothermal constructions are composed predominantly of x ray amorphous protoferrihydrite mixed with variable amounts of opaline silica and greenish nontronite most deposits are covered by mm thick black crusts of vernadite and feroxyhyte which are mineralised bacterial formations genus leptothrix of hydrogenous origin microbes also influenced formation of the fe rich parts of the deposits as evidenced by filamentous protoferrihydrite pseudomorphs of gallionella blocky inorganic particles of protoferrihydrite and ferrihydrite occur as rare interior phases nontronite formed by precipitation from hydrothermal solutions commonly involving replacement of microbial protoferrihydrite and silica patchy and lenticular birnessite partly altered by biogenic processes to vernadite occurs within siliceous protoferrihydrite matrices in dark cm thick outer margins of some edifices this is considered hydrothermal in origin reflecting percolation of hydrothermal fluids through porous protoferrihydrite opal aggregates to more oxidised conditions near the exterior related to mixing with seawater the different mineralogical associations are reflected by geochemistry trace elements in the manganiferous phases were derived partly from the primary hydrothermal solution and partly from seawater with which this was extensively diluted at the depositional site and also deeper within the volcanic structure of franklin seamount most of the fe mn cu zn and pb was derived from the primary hydrothermal fluid from limited data nontronitic portions of the deposits contain more cu zn and pb than the siliceous protoferrihydrite rich portions migration of redox boundaries and redistribution of elements during flow through processes influence development of the typical zoned structure of the deposits uranium thorium decay series equilibria at both actively venting and inactive sites at franklin seamount yield ages not exceeding 43 years

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

rare earth element distribution in exhalites associated with broken hill type mineralisation at the pinnacles deposit new south wales australia abstract rare earth element ree concentrations in exhalites and pelites associated with strata bound base metal broken hill type mineralisation have been measured for the early proterozoic pinnacles deposit in western new south wales garnetites garnet rich rocks and sulphide rich garnet gahnite bearing rocks exhibit a wide variety of ree concentrations particularly lree and eu which cannot be related entirely to changes in mineralogy but show some correlation with stratigraphic position relative to the main orebody exhalites lying in the footwall to the mineralised rocks have negative eu anomalies and steep lree enriched patterns whereas exhalites in the hanging wall to the ores and silicate rich rocks from within the ore lenses have zero or positive eu anomalies and less lree enriched patterns hree have more consistent values throughout the deposit but in places are strongly depleted non mineralised pelites are slightly enriched in the ree relative to shale composite values and have negative eu anomalies it is argued in this paper that because the variations in data can be related to the stratigraphic location of samples relative to the orebodies that the observed ree distributions are due to fluctuations in ree concentrations in the primary exhalative fluids rather than differential mobilisation of ree during a second post depositional episode of hydrothermal alteration or mobilisation of the ree during prograde granulite facies metamorphism or retrograde amphibolite facies metamorphism which has affected the area the lack of association between metamorphic mineral assemblages and ree distribution and the absence of any homogenisation of the ree concentrations suggest that the data reflect the primary exhalative fluid composition and that the variations in ree data reflect changes in palaeoenvironmental conditions such as f o 2 and temperature a corollary to this conclusion is that there was minimal mobilisation of the ree during subsequent metamorphism

hydrothermal manganese oxide deposits from baby bare seamount in the northeast pacific ocean abstract manganese oxide crusts were recovered from baby bare seamount in order to investigate the history of off axis hydrothermal venting baby bare is a small basement high protruding from a regional sediment cover on the eastern flank of the juan de fuca ridge that acts as a focus for discharging crustal fluids stratabound mn oxide crusts were collected where warm venting has been observed near the seamount summit mn oxide crusts are composed primarily of 10 a manganate pyrolusite with minor nontronite saponite and or barite these assemblage and chemical characteristics such as high mn fe ratios and low trace metal and ree concentrations are indicative of a hydrothermal origin minimum ages for these deposits calculated using growth rates 324 to 1800 mm ma and estimated thicknesses of manganese outcrops show that baby bare has been hydrothermally active for at least 0 5 myr and possibly since its formation 1 7 2 7 ma hydrothermal manganese oxide crusts such as these from baby bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off axis hydrothermal activity

seismic stratigraphy and tectonic structure from a composite multi channel seismic profile across the entire dangerous grounds south china sea abstract we interpret a more than 500 km long composite multi channel seismic reflection profile across the entire dangerous grounds the south china sea five tectonostratigraphic units are determined together with seven sequence boundaries detailed analysis of extensional features based on measurements of fault heaves revealed two major phases of extension separated by a distinct unconformity which likely correspond with the beginning of sea floor spreading in the south china sea early extension occurred during continental rifting late cretaceous early oligocene and resulted in formation of half grabens and rotated blocks controlled by a deeply rooted detachment system extension continued in our study area during the drifting phase of the east subbasin of the south china sea late oligocene early miocene until the subsequent opening of the southwest subbasin at about 25 ma but its intensity decreased markedly thereafter deeply rooted detachment systems evolved possibly during this second phase of extension at the continent ocean transition area from a coincidence of the lowermost reflections and moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust mantle boundary it is suggested that the dangerous grounds reflect a magma poor rift system at the initial stage of mantle unroofing we suggest that a widespread carbonate platform developed across the dangerous grounds concurrent with the period of seafloor spreading in the southwest subbasin of the south china sea fault related stretching factors f along the line show discrepancies with the whole crustal stretching factors c the continental crust of the dangerous grounds may have experienced nonuniform thinning

diversity of biogenic minerals in low temperature si rich deposits from a newly discovered hydrothermal field on the ultraslow spreading southwest indian ridge 1 a newly discovered hydrothermal field on the ultraslow spreading southwest indian ridge expands the known ranges of biogenic minerals microbes and hydrothermal deposits the deposits from this vent site show typical characteristics of low temperature hydrothermal deposits rare earth element fractionation might be partly influenced by bacterial activity a physicochemical gradient is present across the layer of deposits providing suitable microhabitats for various microbes molecular phylogenetic analysis demonstrates a diverse range of bacteria some of which are involved in sulfur iron and nitrogen metabolism a high diversity of biogenic fe and si minerals are present in the deposits biogenic silica fe sulfides and fe oxides with distinctive morphologies are closely related to microbes several novel fe oxide structures are found and attributed to new types of biogenic minerals the precipitation of porous silica spherules and fe sulfides can be strongly promoted by extracellular polymer saccharides biomineralization features indicate that these deposits evolved through four stages these results help us to better understand the formation of biogenic minerals and low temperature deposits associated with microbes in the earth s modern and ancient seafloor hydrothermal vent fields

formation of fe silicates and fe oxides on bacterial surfaces in samples collected near hydrothermal vents on the southern explorer ridge in the northeast pacific ocean samples collected in low temperature 2 50 degrees c waters near hydrothermal vents of the southern explorer ridge in the northeast pacific ocean contained fine 500 nm fe and mn oxide and fe silicate particles coating bacterial surfaces partially to totally mineralized bacteria along with bacterial exopolymers were covered with a mixture of poorly ordered si rich fe oxides possibly ferrihydrite mn oxides and fe silicates possibly nontronite minerals occur as very fine 2 20 nm granular material fine 20 100 nm needles and sheets small 200 500 nm nodules and filaments i e mineralized exopolymers under saturation conditions we infer that bacterial surfaces provided nucleation sites for poorly ordered oxides and silicates the formation of fe and mn oxides was likely initiated by the direct binding of soluble fe and mn species to reactive sites like carboxyl phosphate and hydroxyl groups present within the bacterial cell wall and the exopolymers fe silicate formation involved a more complex binding mechanism whereas metal ions such as fe possibly bridged reactive sites within the cell walls to silicate anions to initiate silicate nucleation

hydrothermal clay mineral formation of east pacific rise and bauer basin sediments samples of surface metalliferous sediment recovered from the crest of the east pacific rise at 6 s and 10 s latitudes and from the adjacent bauer basin are characterized by an authigenically formed fe rich montmorillonite that dominates the non carbonate mineralogy of the clay fraction 2 m oxygen isotopic formation temperatures indicate that the fe montmorillonites are created by low temperature hydrothermal processes 30 50 c in the 10 s region of the east pacific rise and bauer basin possibly as a result of cooling and oxidation of unstable high temperature 380 30 c sulfide assemblages or as a result of the percolation of hydrothermally altered seawater solutions through underlying basalt and sediments the widespread sedimentation of the clay mineral is suggested to be caused by colloidal transport possibly as a result of erosion of hydrothermal mounds by bottom currents hydrothermal fe montmorillonite nontronite formation may act as a direct and significant oceanic sink for si and fe released by the high temperature hydrothermal alteration of basalt at ocean spreading centers

genesis of ferromanganese crusts from the tag hydrothermal field the rare earth element ree geochemistry and nd isotopic composition of marine ferromanganese crusts allow insight into their environment of deposition we present ree along with major and trace element data from a suite of samples collected near an active hydrothermal site from the mid atlantic ridge and demonstrate extreme ree variability over short spatial scales both positive and negative ce anomalies are observed along with varied fractionation of the rees some of the fe mn crusts are formed directly from low temperature hydrothermal fluids channelled over 3 km from any high temperature vent site a significant hydrothermal component is observed in one fe mn crust sampled other samples collected from the same area are predominantly hydrogenous and form at a wide range of accumulation rates depending on the hydrothermal plume input the identification of extreme heterogeneity in source and depositional environment within one hydrothermal field suggests that 1 this variability can be resolved both spatially and temporally within a fossil hydrothermal deposit and 2 the integrated record provided by bulk analysis should be interpreted with caution

first evidence for high temperature off axis venting of deep crustal mantle heat the nibelungen hydrothermal field southern mid atlantic ridge during segment scale studies of the southern mid atlantic ridge mar 7 12 s we found evidence in the water column for high temperature hydrothermal activity off axis east of ascension island extensive water column and seafloor work using both standard ctd and deep submergence auv and rov deployments led to the discovery and sampling of the drachenschlund dragon throat black smoker vent at 8 17 87 s 13 30 45 w in 2915 m water depth the vent is flanked by several inactive chimney structures in a field we have named nibelungen the site is located 6 km south of a non transform offset between two adjacent 2nd order ridge segments and 9 km east of the presently active northward propagating a2 ridge segment on a prominent outward facing fault scarp both vent fluid compositions and host rock analyses show this site to be an ultramafic hosted system the first of its kind to be found on the southern mar the thermal output of this single vent based on plume rise height information is estimated to be 60 15 mw this value is high for a single black smoker vent but small for an entire field the tectonic setting and low he content of the vent fluids imply that high temperature off axis venting at drachenschlund is driven not by magmatic processes as at the majority of on axis hydrothermal systems but by residual heat mined from the deeper lithosphere whether this heat is being extracted from high temperature mantle peridotites or deep crustal cumulates formed at the duelling non transfrom offset is unclear in either case the drachenschlund vent provides the first direct observations of how cooling of deeper parts of the lithosphere at least at slow spreading ridges may be occurring

calcic vertisols in the upper daptocephalus assemblage zone balfour formation karoo basin south africa implications for late permian climate

the formation of high temperature clay minerals from basalt alteration during hydrothermal discharge on the east pacific rise axis at 21 n abstract aluminous high temperature clay minerals form from alteration of tholeiitic basaltic glass and calcic plagioclase during hydrothermal venting on the crest of the east pacific rise at 21 n the clay alteration assemblages are layered crusts up to 1 mm thick completely replacing glass and calcic plagioclase adjacent to surfaces exposed to hydrothermal fluids the interiors of the affected basalt samples have unaltered appearances and oxygen isotopic compositions just slightly heavier than that of morb the surficial alteration crusts are mixtures of beidellitic smectite aluminous dioctahedral randomly interstratified mixed layer al rich chlorite smectite minor chlorite an x ray amorphous aluminosilicate material and possible minor serpentine amesite a 18 o value of 4 1 0 2 smow is determined for the beidellitic smectite assuming that this smectite equilibrated with hydrothermal fluid having an oxygen isotope value between that of seawater 0 and 350 c hydrothermal fluid from epr 21 n vents 1 6 an equilibration temperature between 290 c and 360 c is calculated for the beidellitic smectite this is substantially higher than any previously reported temperature for an oceanic smectite the mixed layer al rich chlorite smectite has a 18 o value of 3 5 which corresponds to equilibration at 295 360 c the aluminous composition of the alteration assemblage is uncommon for clay minerals produced by submarine hydrothermal basalt alteration we suggest that this assemblage is largely the product of high temperature interaction between basalt glass plagioclase and mg poor acidic hydrothermal fluids with possibly some contribution of mg from bottom seawater and that the aluminous clays either incorporate al 3 remobilized from basalt by lowph hydrothermal fluids or are residual phases remaining after intense alteration of basaltic glass plagioclase

catastrophic dispersion of coal fly ash into oceans during the latest permian extinction the eruption of the siberian trap flood basalts resulted in the heating and combustion of coals and organic rich sediments at the time of the permian mass extinction the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion and then dispersed globally creating toxic marine conditions

hydrothermal nontronite formation at eolo seamount aeolian volcanic arc tyrrhenian sea abstract a sediment core containing a yellowish green clay bed was recovered from an area of extensive hydrothermal deposition at the se slope of the eolo seamount tyrrhenian sea the clay bed is composed of pure nontronite described for the first time in the tyrrhenian sea which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits the high al content suggests precipitation from al containing hydrothermal solutions the ree distribution of the eolo nontronite has a v shape pattern the heavy ree enrichment is in part due to their preferential partitioning in the nontronite structure this enrichment was possibly further enhanced by the hree preferential sorption on bacterial cell walls the light ree enrichment is the result of scavenging uptake by one of the nontronite precursors i e poorly ordered fe oxyhydroxides from the hydrothermal fluids oxygen isotopic composition of the nontronite yields a formation temperature of 30 c consistent with a low temperature hydrothermal origin the relatively radiogenic nd isotopic signature of the nontronite compared to the present day mediterranean seawater indicates that approximately half of nd and presumably the rest of the lree are derived from local volcanic sources on the other hand 87 sr 86 sr is dominated by present day seawater sr scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube like filaments which are indicative of bacteria assisted precipitation bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly ordered hydrothermal fe oxyhydroxides and silica precipitated upon aging the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite finally the well balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero thus the ubiquitous nontronite precipitation along the active plate boundaries and around the hot spots has no significant impact on oceanic trace element chemistry

diking young volcanism and diffuse hydrothermal activity on the southern mid atlantic ridge the lilliput field at 9 33 s detailed exploration with remotely operated and autonomous deep submergence vehicles has revealed at 9 degrees 33 s the presence of the southernmost active hydrothermal field known so far on the mid atlantic ridge the size of the hydrothermal field which we have named lilliput is about 1000 m x 250 m it lies in a water depth of 1500 m on a ridge segment segment a3 with considerably thickened crust of 11 km four relatively small diffuse vent sites occur on a large young estimated 100 years old lava flow partly covering the flow with hydrothermal fe oxide hydroxide sediments based on homogeneous major element compositions of ca 25 lava samples this flow covers an area of at least 5 km x 0 6 km the lava flow erupted from a series of parallel fissures at the western edge of the flow and a volcanic ridge consisting of up to 30 m high pillow mounds the volcanic ridge probably represents the surface expression of an underlying dike which fed the flow several drained lava pond structures were observed within the flow but only one shows hydrothermal activity the hydrothermal venting and precipitation of abundant fe oxyhydroxides appear to be related to the young diking and eruption event and the four different hydrothermally active sites of the lilliput field lie along and almost equidistant from the eastern flank of the supposed dike although a hydrothermal plume some 500 m above the seafloor was found in two consecutive years 2005 and 2006 no high temperature venting associated with lilliput has been found in agreement with findings at other ridges with thick crust such as reykjanes high magma supply rate and frequent diking and eruption events may lead to hot hydrothermal vents being rare in slow spreading segments with thick crust whereas diffuse venting is abundant interestingly the fauna at the lilliput vents largely consists of small and apparently juvenile mussels bathymodiolus sp and did not show any signs of growth during the four years of continuing observations possibly reflecting pulsing hydrothermal activity

crustal thickness variations in the aegean region and implications for the extension of continental crust 1 we installed 5 broadband and 45 short period temporary seismic stations distributed partly as a dense 100 km long n s linear array and partly as a regional network throughout the menderes massif of western turkey in order to study crust upper mantle structure and seismicity in this study we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the aegean region receiver function studies at seven broadband stations using the h stacking method have yielded crustal thicknesses and vp vs ratios over a broad region of the aegean a more detailed crustal image was obtained in the central menderes massif where we applied common conversion point stacking to receiver functions obtained from the n s linear array the results show a general trend of westward crustal thinning from 36 km in central anatolia to 28 30 km in the central menderes massif to 25 km beneath the aegean sea the results also indicate that crustal thinning in the aegean is not uniform in the n s extensional direction the crust is thinner in the central menderes massif 28 30 km of crustal thicknesses and the cycladic massif 25 26 km than in surrounding regions where crustal thicknesses are 32 34 km the long lived elevated moho under the metamorphic core complexes suggests that the lower crust in the aegean region is at least 3 times more viscous than that in the basin and range province where the moho is much flatter

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

hydrothermal sulfide bearing fe si oxyhydroxide deposits from the coriolis troughs vanuatu backarc southwestern pacific abstract the coriolis troughs located in the vanuatu backarc of the southwestern pacific consist of the vate trough to the north the erromango basin in the middle and the futuna trough to the south major hydrothermal activity responsible for the formation of sulfides and barite bearing fe si oxyhydroxide deposits as well as biological communities of living galatheid crabs and gastropods occurs at the caldera rim of a submarine volcano in the northern vate trough the deposits consist of major nontronite and amorphous fe si oxyhydroxides minor sulfides and barite and are associated with traces of mn galena chalcopyrite pyrite sphalerite marcasite and covellite are the principle sulfide minerals the deposits occur sporadically on pillow lavas and breccias as small chimneys mounds flat slabs and infillings in water depths between 1100 and 1400 m the deposits are more than several tens of meters wide and extend about 1 km in one direction at the northwestern and eastern caldera rims the appearance of shimmering water was observed in the holes between the pillow lavas and tubes and was associated with a positive temperature anomaly by 0 2 c relative to the ambient seawater dark back scattered acoustic images obtained by side scan sonar revealed the occurrence of mounds this suggests the presence of several hydrothermal deposits on the eastern rim of the caldera in the futuna trough sulfide bearing fe si oxyhydroxide deposits are present as flat slabs and infillings of brownish fragments and reddish brown sediments and mn precipitation on volcanic rocks near the summit of a submarine volcano on the northwestern flank in water depths between 940 to 980 m the deposits are characterized by the presence of bacterial filaments high concentrations of fe max 42 wt and as max 2 7 wt major goethite and amorphous fe si oxyhydroxides birnessite and sulfides the hydrothermal nontronite deposits of the vate trough were formed under more reduced conditions than the goethite of the futuna trough sulfides and barite from the vate deposits were formed as a result of the precipitation from hydrothermal fluids in the deposits whereas sulfides of the futuna deposits were deposited from hydrothermal vents further away the presence of sulfides in the vate fe si oxyhydroxide deposits suggests that extensive sulfide deposits may exist in the volcanic pile of the caldera the coriolis troughs are still active especially in the vate trough there are a number of areas with the potential for hydrothermal precipitation of sulfide bearing fe si oxyhydroxide deposits in both the vate and futuna troughs

migration controls extinction and survival patterns of foraminifers during the permian triassic crisis in south china abstract the permian triassic mass extinction the greatest biotic crisis in earth history triggered the complete replacement of ecosystems with the 5 10 surviving species giving rise to the mesozoic fauna despite a long history of systematic studies on permian triassic foraminifera there have been few investigations into spatial and temporal patterns of survivorship and evolution during this critical interval we interrogate a high resolution data set comprising newly obtained and previously published foraminiferal data including 13 422 specimens in 173 species in 62 genera from seven well studied permian triassic successions that record a transect of platform to basin facies in south china shallow water settings seen at the cili and dajiang sections suffered a single pulse sudden extinction with high extinction rates at the end of the palaeofusulina sinensis zone deeper water and slope environments seen at liangfengya and meishan experienced a two pulse extinction in the clarkina yini and isarcicella staeschei zones basinal settings seen at shangsi gujiao and sidazhai record a single less devastating extinction pulse in and slightly above the c yini zone in the late permian foraminiferal diversity was greatest on the shallow platforms where 76 4 of species recorded in our study lived the two pulses of the permian triassic extinction prompted this foraminiferal diversity hotspot to move to deeper slope settings comprising 75 6 of contemporary species and finally basinal settings comprising 88 8 of species we propose that foraminifera migrated to deeper water to avoid overheating and toxicity in shallow waters that were driven by the emplacement of the siberian traps and coeval volcanic activities around the paleotethys ocean this study provides a methodological framework for investigating survival mechanisms for foraminifers and other taxonomic groups during mass extinction events

spatial and temporal variability in crystallization of celadonites within the troodos ophiolite cyprus implications for low temperature alteration of the oceanic crust celadonite a low temperature 30 c hydrothermal alteration mineral is a predominant fracture and void filling phase within the volcanic rocks of the troodos ophiolite the combined chemical and structural properties of celadonite i e high k2o and ar retentive along with its common occurrence provide a valuable tracer for studying the temporal and spatial variability of low temperature hydrothermal fluid circulation and alteration within this ancient oceanic crust some 54 new k ar age determinations of celadonites from various geographic and stratigraphic locations within the extrusive rocks of troodos yield crystallization ages ranging from 90 9 1 0 to 49 8 0 5 ma with the oldest in close agreement with the estimated 91 92 ma crystallization age of troodos igneous rocks the youngest age indicates that low temperature water rock chemical exchange continued for at least 40 m y after crustal formation this represents a 100 increase over previous estimates based on limited numbers of k ar dates of celadonite of the duration of low temperature mineral precipitation in troodos correlation between celadonite ages and field relationships suggests the following 1 there is no apparent relationship between celadonite crystallization and stratigraphic depth 2 celadonite crystallization occurs homogeneously on an outcrop scale with adjacent samples from a single flow unit yielding equivalent k ar ages 3 flow units with relatively high primary permeabilities e g pillows and breccias yield celadonites with younger k ar ages 4 celadonite precipitation at distinct locations occurred rapidly with little or no age difference between rim and core sections of single large deposits the above correlations suggest that low temperature hydrothermal fluid circulation and secondary mineral precipitation are controlled by the local alteration conditions such as intrinsic permeability degree of fracturing and water rock ratios and are independent of time and space integration of these local heterogeneities over the entire extrusive sequence suggests that the upper oceanic crust undergoes relatively homogeneous closure to hydrothermal fluid circulation no evidence is found to support a progressive upward sealing of the oceanic crust

abrupt and gradual extinction among late permian land vertebrates in the karoo basin south africa the karoo basin of south africa exposes a succession of upper permian to lower triassic terrestrial strata containing abundant terrestrial vertebrate fossils paleomagnetic magnetostratigraphic and carbon isotope data allow sections to be correlated across the basin with this stratigraphy the vertebrate fossil data show a gradual extinction in the upper permian punctuated by an enhanced extinction pulse at the permian triassic boundary interval particularly among the dicynodont therapsids coinciding with negative carbon isotope anomalies

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

latest permian paleosols from wapadsberg pass south africa implications for changhsingian climate terrestrial settings preceding the endpermian crisis are reported to trend toward increasingly dry and arid conditions resulting in landscape change and a shift in fl architectures and regimes much of the latest permian changhsingian stratigraphic record in the karoo basin south africa consists of paleosols which record the physical conditions across time and space preboundary sequences at wapadsberg pass eastern cape province provide insight into the climate regime that infl uenced paleosol formation at that time a high resolution sedimentological and geochemical study of two stacked aggradational paleosols in conjunction with stable isotope geochemical characterization of paleosol carbonate cemented concretions over a 90 m section at this locality demonstrates that these landscapes were predominantly wetland terrains without a demonstrable trend in increasing drying up to the permian triassic boundary as defi ned by vertebrates in the area two paleosols examined 70 m below the permian triassic boundary are identifi ed as protosols and the former soil air interface of each is marked by an autochthonous forestfl oor litter in which canopy leaves of glossopteris and groundcover plants of trizygia are preserved molecular weathering ratios e g base loss clayeyness chemical index of alteration minus potassium cia k etc determined from these horizons are indicative of immature soil development under watersaturated conditions assuming that paleosol matrix concentrations of trace elements are indicative of permian soil solution chemistries high concentrations of ni cu ba and cr may have been growth stress factors that may account for the small glossopterid leaf size in the megafl oras in contrast to current models that implicate stress in response to climate change stable isotope 18 o and 13 c values are presented for micritic and microspar 20 m calcite cements from carbonate nodules collected at 15 horizons through a 90 m stratigraphic interval up to and including the permian triassic boundary these isotopic ratios exhibit dissimilar trends no clear trend exists in 18 o peedee belemnite pdb values range from 14 7 to 21 8 in contrast a trend exists in 13 c values where carbonate cements almost certainly precipitated under well drained conditions in an interval that is 60 m below the permiantriassic boundary 5 3 while 13 c values as low as 16 9 indicative of water logged conditions begin 90 m below and continue up to the permian triassic boundary hence no evidence is found for a preboundary trend toward increasing aridity at this locality the fi rst estimates of the latest permian atmospheric pco2 from paleosols based on coexisting calcite and organic matter 13 c values from paleosols that developed under well drained conditions provide a range of values from 900 to 1900 and 500 to 1300 ppmv respectively which are signifi cantly lower than the latest early permian when terrestrial biome replacement is documented to have occurred

diagenesis and the reconstruction of paleoenvironments a method to restore original δ18o values of carbonate and phosphate from fossil tooth enamel abstract intra tooth 18 o variations within the carbonate 18 oc and phosphate 18 op components of tooth apatite were measured for miocene and pliocene hypsodont mammals from afghanistan greece and chad in order to evaluate the resistance of enamel to diagenetic alteration application of water apatite interaction models suggest that the different kinetic behaviours of the phosphate water and carbonate water systems can be used to detect subtle oxygen isotope disequilibria in fossil enamel when intra individual variations are considered selective alteration of the oxygen isotope composition from the carbonate component of afghan and greek enamels suggests inorganic isotopic exchange processes microbially induced isotopic exchange for phosphate is demonstrated for the first time in enamel samples from chad in association with extensive recrystallization in chad 18 op values were derived from partial isotopic exchange with fossil groundwater during early diagenesis mass balance calculations using average carbonate content in enamel as a proxy for recrystallization and the lowest 18 op value of dentine as a proxy for the isotopic composition of the diagenetic fluid indicate that diagenesis can alter 18 op by as much as 3 in some enamel samples this diagenetic alteration is also responsible for a decrease in intra individual variations of up to 1 in affected specimens the effects of diagenesis on 18 op values of fossil enamel are not systematic however and can only be estimated if sequential 18 op and 18 oc analyses are performed on fossil enamel and dentine reconstruction of large temporal or spatial scale paleoclimates based on 18 op analyses from mammalian teeth cannot be considered valid if enamel has been affected by bacterial activity or if the data cannot be corrected for diagenetic effects

hydrothermal nontronite formation associated with microbes from low temperature diffuse hydrothermal vents at the south mid atlantic ridge oceanic nontronite deposits have been identified to be closely related to low temperature hydrothermal activities however their formation mechanisms associated with microbes in diffuse hydrothermal vents still remain largely unknown the friable deposits collected from the low temperature diffuse flow at the southern atlantic ridge display a layered structure scanning electron microscope sem and transmission electron microscope tem analyses reveal that abundant filamentous spherical and rod shaped mineralized forms are preserved in the yellowish green layer of the deposits these mineralized forms primarily consist of si and fe selected area electron diffraction saed patterns of the mineralized forms indicate that they are composed of nontronite high intensities of 12c and 12c14n signals derived from cellular structures determined by nano secondary ion mass spectrometry nanosims suggest the intimate relationship between nontronite and microbes the results of 454 pyrosequencing analyses provide insights into the microbial communities involved in the biologically induced mineralization in the yellowish green layer we propose an evolutionary model for establishing paragenetic sequences among nontronite mn oxide and fe oxyhydroxide in the deposits this paragenetic sequence could be widespread in modern and ancient low temperature hydrothermal fields

hydrothermal exploration of mid ocean ridges where might the largest sulfide deposits be forming highlights black smokers on slow spreading ridges can host larger seafloor massive sulfide sms deposits than on fast ridges the largest slow ridge sms deposits are typically associated with long lived tectonic fractures sustained fluid flow ultramafic tectonic hosted sites exhibit high average cu 10wt and au 3ppm contents in their surface sms samples hydrothermal plume surveys are consistent with equal abundances of magmatic vs tectonic vent control along ultraslow ridges the first black smokers on any ultraslow ridges exhibit high cu au sms contents at both magmatic and tectonic vent sites abstract here we review the relationship between the distribution of modern day seafloor hydrothermal activity along the global mid ocean ridge crest and the nature of the mineral deposits being formed at those sites since the first discovery of seafloor venting a sustained body of exploration has now prospected for one form of hydrothermal activity in particular high temperature black smoker venting along 30 of the global mid ocean ridge crest while that still leaves most of that 60 000 km continuous network to be explored some important trends have already emerged first it is now known that submarine venting can occur along all mid ocean ridges regardless of spreading rate and in all ocean basins further to a first approximation the abundance of currently active venting as deduced from water column plume signals can be scaled linearly with seafloor spreading rate a simple proxy for magmatic heat flux what can also be recognized however is that there is an excess of high temperature venting along slow and ultra slow spreading ridges when compared to what was originally predicted from seafloor spreading magmatic heat budget models an examination of hydrothermal systems tracked to source on the slow spreading mid atlantic ridge reveals that no more than half of the sites responsible for the black smoker plume signals observed in the overlying water column are associated with magmatic systems comparable to those known from fast spreading ridges the other half of all currently known active high temperature submarine systems on the mid atlantic ridge are hosted under tectonic control these systems appear both to be longer lived than and to give rise to much larger sulfide deposits than their magmatic counterparts presumably as a result of sustained fluid flow a majority of these tectonic hosted systems also involve water rock interaction with ultramafic sources importantly from a mineral resource perspective this subset of tectonic hosted vent sites also represents the only actively forming seafloor massive sulfide deposits on mid ocean ridges that exhibit high concentrations of cu and au in their surface samples 10 wt average cu content and 3 ppm average au along ultraslow spreading ridges first detailed examinations of hydrothermally active sites suggest that sulfide deposit formation at those sites may depart even further from the spreading rate model than slow spreading ridges do hydrothermal plume distributions along ultraslow ridges follow the same 50 50 distribution of black smoker plume signals between magmatic and tectonic settings as the slow spreading mar however the first three black smoker sites tracked to source on any ultra slow ridges have all revealed high temperature vent sites that host large polymetallic sulfide deposits in both magmatic as well as tectonic settings further deposits in both types of setting have now been revealed to exhibit moderate to high concentrations of cu and au respectively an important implication is that ultra slow ridges may represent the strongest mineral resource potential for the global ridge crest despite being host to the lowest magmatic heat budget

the link between biomineralization and fossilization of bacteria insights from field and experimental studies abstract fossil biominerals and fossils of microorganisms in ancient rocks contain important biogeochemical signals decoding this record may reveal crucial information about the evolution of life on earth and terrestrial paleoenvironments however the identification of traces of life especially in very old rocks is extremely challenging because the morphological and chemical signatures of biominerals and microfossils are subtle of microscopic size and inevitably altered with aging in this review we stress on the fact that biomineralization is often the first step of fossilization and produces particular chemical structural and morphological features that can be preserved in fossil biominerals or microfossils with a special focus on fe biomineralization the taphonomic processes affecting biominerals and microfossils and altering their morphology and or chemical composition over time are then discussed in light of experimental fossilization simulations and field sample analyses we suggest that taxonomic biases observed in the fossil record may be related to differential abilities of species to trigger biomineralization this calls for studies of the effective biomineralizing activity and fossilization potential of each species present in highly diverse natural microbial communities finally recent analytical developments leave little doubt that very substantial progress in the study of biomineralization processes and ancient biostructures will be achieved in the near future

anomalously low δ18o values of high latitude permo triassic paleosol siderite abstract the most severe extinction in earth history occurred during a time of extreme climate change caused in part by a massive release of carbon into the atmosphere isotopic measurements of siderite occurring in paleosols during intervals of global warming suggest high latitude depletions in 18 o of precipitation often attributed to an amplified hydrologic cycle here late permian and early triassic paleosol siderite from alaska antarctica eastern australia siberia and south africa indicate similar or greater meridional gradients in siderite 18 o compared to other past warm intervals an isotope tracer enabled version of the global environmental and ecological simulation of interactive systems genesis general circulation model gcm was used to compare to siderite 18 o data the model when deriving siderite 18 o at a specified paleoatmospheric co 2 concentration of 12 7 the preindustrial atmospheric level pal matches a small subset of relatively less depleted high latitude siderites but does not produce the conditions necessary to explain the most depleted siderite 18 o values siderite has been thought to record mean annual precipitation 18 o though this study suggests that many may not a seasonal bias where siderite growth occurs in the summertime in wetlands that receive most of their recharge from melting winter precipitation may be responsible genesis indicates soil moisture recharge during the spring ahead of the rainy season for high latitude permo triassic pt siderite localities that reach below freezing winter temperatures drainage from high altitude regions throughout the growing season may also be responsible biological cloud feedbacks and monsoon related amount effects are not likely the cause for low siderite 18 o because the enrichment of water vapor 18 o associated with warming is too significant

local lithospheric relief associated with fracture zones and ponded plume material 1 buoyant plume material ponds at the base of oceanic lithosphere it is a natural probe for the relief on the base of the lithosphere owing to plate age because it flows laterally along an upside down drainage pattern geomorphic and geochemical studies of near ridge and on ridge hot spots indicate as expected that the oceanic lithosphere thickens as it ages corridors of thin lithosphere channel plume material along the axis while the thick lithosphere at the end of ridge segments dams this along axis flow channel hot spots extend from plumes toward ridge axes however a good correlation between local lithospheric thickness and local age is not evident at fracture zones within the old ocean basins such a correlation would be expected if the lithosphere cooled only by conduction then pressure release melting and volcanoes would occur preferentially near fracture zones where plume material cascades from thick old to thin young lithosphere this concentration of volcanic edifices does not occur this lack of correlation between lithosphere thickness and plate age is an expected consequence of small scale convection at the base of the lithosphere scaling relationships and numerical models indicate that modestly vigorous convection of several milliwatt per meter squared is sufficient to perturb local lithospheric relief beneath fracture zones without changing the gross correlation of lithospheric thickness with plate age typically the step in lithospheric thickness moves toward the old side of the fracture zone

hydrothermal oxide and nontronite deposits on seamounts in the eastern pacific deposits of fe oxide mud nontronite and fe mn crusts were sampled from the summits of two seamounts in the eastern pacific where low temperature 0 15 c hydrothermal fluids are issuing the deposits consist of x ray amorphous fe oxyhydroxide and are rich in fe 43 wt contain minor si and p 4 and 3 5 respectively and have very low mn 0 01 and other trace element contents other deposits where no current hydrothermal activity was observed consist of mud and crusts composed of amorphous material and poorly crystalline hematite goethite and smectite these deposits have slightly higher mn up to 2 and other trace element contents the mineralogical and chemical differences between the active and inactive deposits and crusts are interpreted to be due to recrystallization and contamination with detrital biogenic hydrogenous and possibly hydrothermal sulfide material nontronite deposits capped by fe mn oxides were sampled from one of the seamounts these deposits have compositions similar to other seafloor nontronite deposits and formed at low temperatures 30 c during mixing of low temperature hydrothermal fluids with seawater the oxide deposits consist almost entirely of long delicate filaments remarkably similar in morphology to genera of fe oxidizing bacteria such bacteria were probably important in catalyzing the oxidation and precipitation of iron from hydrothermal fluids on the seamounts the occurrence of nearly identical filament rich oxide deposits on two widely separated seamounts suggests that this type of deposit may be common on seamounts but previously unrecognized