timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

intrabasin variability of the carbon isotope record across the permian triassic transition sverdrup basin arctic canada abstract a major late paleozoic depocentre the sverdrup basin canadian high arctic has been largely left out of the latest permian extinction debate as early workers presumed middle to late permian strata were absent basin scale sequence stratigraphic and chemostratigraphic correlations indicate late permian strata are only missing on the basin margins where they were removed by sub triassic erosion whereas continuous deposition is recorded in the basin centre the varying degree of sub triassic erosion has significant impact on the carbon isotope record across the latest permian extinction event where both the apparent rate and magnitude of carbon isotope shift vary as a function of basin position the intrabasin variability in apparent 13corg shift across the event is equivalent to that observed globally in contrast to the abrupt isotope shifts recorded on the basin margin similar to many records reported globally the basin centre section shows a systematic shift associated with the latest permian extinction the earth likely underwent a prolonged period of increasing environmental stress leading up to the event

the space time relationship of taxonomic diversity and morphological disparity in the middle jurassic ammonite radiation the middle jurassic ammonite radiation from the late aalenian to the end of the mid bathonian is traced using combined analyses of morphological disparity and taxonomic diversity the global signals of disparity and diversity are compared these signals are then broken down by paleogeographical provinces to detect any heterogeneity in the radiation an examination of the global signals reveals three biodiversity crises discordances between signals where morphological disparity grows while taxonomic diversity declines the subdivision of the signals indicates the radiation was heterogeneous between provinces the global signal is an aggregate of signals from each province the three biological crises have different paleogeographical signatures the first is visible in a few provinces only while the other two are visible in most provinces first order crises can be distinguished from second order ones by studying the number of paleogeographical provinces affected

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

hydrothermal eruptions at unstable crater lakes insights from the boiling lake dominica lesser antilles abstract the boiling lake a major touristic attraction in the morne trois pitons national park dominica s west indies world heritage site is located in an area of high hydrothermal activity in the southern part of the island this spectacular lake is characterized by unstable behavior which has been interpreted to result from the presence of a water body above a fluctuating gas filled or multi phase vent system the system produces a near boiling lake that occasionally drains and refills with water without any simple periodicity despite the fact that such unstable draining lakes are thought to be non eruptive the boiling lake is known to have sourced occasional small hydrothermal eruptions as well as toxic gas emissions which accompany the refilling phase of these drainage events similar explosive events seem also to be likely after landslide slumped rocks from steep altered crater walls cover the vent area in the lake leading to overpressurized conditions in both cases rock expulsion and gas release continue to pose serious threats for tourists and tour guides while conceptual models exist describing possible mechanisms of the boiling lake drainage itself little information exists to date regarding the trigger mechanisms related to the explosive events further no estimation of the eruption processes and dynamics of these events has previously been attempted to address this knowledge gap we employ here a combined field and laboratory based approach in order to i characterize the properties of the dominant lithologies from the crater walls at boiling lake ii determine how the ongoing alteration may affect their petrophysical properties e g porosity and permeability and iii evaluate how water saturated unconsolidated wall rock materials behave when rapidly decompressed from a slightly elevated pressure and temperature conditions here we propose that it is the petrophysical state of the materials involved e g porosity permeability and alteration related strength which controls the style and energy of these eruptions as well as the potential for landslides from the crater walls the experimentally simulated scenarios included in this study are i decompression from only slightly elevated pressure conditions inferred for small hydrothermal eruptions occurring after lake drainage events and ii decompression from rapidly enhanced pressure conditions produced by the capping and overpressurization of the vent area following landslide episodes ejection velocities obtained from rapid decompression experiments were used as input parameters for ballistic trajectory calculations allowing for estimation of the potential area impacted by ejected debris we anticipate that this study will serve as a contribution to the understanding of the hazard potential of future hydrothermal eruptions at unstable crater lakes in general as well as providing direct insights into the ongoing hydrothermal activity at the boiling lake

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

hydrothermal alteration of surficial rocks at solfatara campi flegrei petrophysical properties and implications for phreatic eruption processes abstract solfatara crater is located within the campi flegrei caldera to the west of naples italy it is one of the largest fumarolic manifestations known and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration alteration can result in changes of degassing behavior and in the formation of a cap rock thereby increasing the probability of phreatic eruptions here we investigate the effects of alunitic solfataric alteration on the mineralogy the physical properties porosity density permeability and the mechanical properties strength of the rocks involved as well as its influence on fragmentation and ejection behavior our results show that the pristine mineralogy of deposits from the vicinity of the solfatara cryptodome and from pisciarelli is almost completely replaced by amorphous silica and alunite the differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles alunitic alteration increases porosity and permeability whereas it reduces density elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study our results also show that alteration results in the generation of a high fraction of fines particle sizes

an integrated biomarker isotopic and palaeoenvironmental study through the late permian event at lusitaniadalen spitsbergen abstract the largest extinction of the phanerozoic occurred near the permian triassic p tr boundary some 252 ma ago several scenarios and drivers have been proposed for this event here we report for the first time an integrated study comprising sedimentological data biomarker distributions abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes 34spyrite 13ccarb 13corg for a late permian section from lusitaniadalen spitsbergen norway sedimentological and geochemical data support a marine transgression and collapse of the marine ecosystem in the late permian strong evidence for waxing and waning of photic zone euxinia throughout the late permian is provided by chlorobiaceae derived biomarkers including 13c data and 34spyrite implying multiple phases of h2s outgassing and potentially several pulses of extinction a rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event indicates a dramatic decline of land plants during the late permian and or increasing distance from palaeoshoreline as a consequence of sea level rise changes in d of selected biomarkers also suggest a change in source of organic matter om or sea level rise we also found biomarker and isotopic evidence for a phytoplanktonic bloom triggered by eutrophication as a consequence of the marine collapse compound specific isotope analyses csia of algal and land plant derived biomarkers as well as 13c of carbonate and bulk om provide strong evidence for synchronous changes in 13c of marine and atmospheric co2 attributed to a 13c depleted source the source could be associated with isotopically depleted methane released from the melting of gas clathrates and or from respired om due to collapse of the marine ecosystem

the origin of decoupled carbonate and organic carbon isotope signatures in the early cambrian ca 542 520 ma yangtze platform abstract the early cambrian ca 542 520 ma strata in south china record two prominent negative carbonate carbon isotope 13ccarb excursions of early nemakit daldynian n d and early tommotian ages across each of these excursions carbonate and organic carbon isotopes 13ccarb and 13corg are strongly decoupled regional correlation across a shelf to basin transect shows lateral heterogeneity of 13corg during the early middle n d but more homogenized 13corg values across the basin during the late n d and tommotian the temporal and lateral variations in 13corg suggest that decoupled 13ccarb and 13corg across the n d 13ccarb excursion were possibly caused by diagenetic alteration of organic matter and or amplification of detrital organic carbon isotope signature in low toc carbonates in contrast decoupled 13ccarb and 13corg of the upper n d and tommotian were likely resulted from chemoautotrophic methanotrophic biomass contribution to toc in organic rich black shale and carbonates the decoupled 13ccarb 13corg pattern from the lower n d strata ca 542 ma shows striking similarities with those from the basal ca 635 ma and upper ca 551 ma doushantuo formation in all three cases decoupled 13ccarb 13corg are seen in organic poor carbonates toc 0 1 and coupled 13ccarb 13corg occur in organic rich black shale and carbonates at the end of the negative 13ccarb excursion these similarities suggest that the shift from decoupled to coupled 13ccarb 13corg has no causal link with the terminal oxidation of a large oceanic doc reservoir given the pervasive anoxia euxinia in ediacaran early cambrian oceans local doc rich environments may have been common but a large oceanic doc reservoir capable of buffering the 13c of marine organic matter requires independent evidence

the early triassic ammonoid recovery paleoclimatic significance of diversity gradients ammonoids recovered much faster than other marine shelly invertebrates after the end permian mass extinction based on a refined global data set at the basin level we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the early triassic such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution i e at the basin level during the early triassic the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally restricted distributions this led to the emergence of a clear latitudinal diversity gradient during most of the smithian and spathian stages which entails increased steepness of the sea surface temperature gradient during the late early triassic however two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the smithian and at its very end the longitudinal analysis of smithian distributions indicates a westward decrease of diversity within the tethys which faded away during the spathian analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient

multidisciplinary constraints of hydrothermal explosions based on the 2013 gengissig lake events kverkfjoll volcano iceland hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity their deposits though generally hardly recognised or badly preserved provide important insights to quantify the dynamics and energy of these poorly understood explosive events furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion we present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at kverkfjoll a central volcano at the northern edge of vatnajokull on august 15th 2013 a small jokulhlaup occurred when the gengissig ice dammed lake drained at kverkfjoll the lake level dropped by approximately 30 m decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th here a multidisciplinary approach combining detailed field work laboratory studies and models of the energetics of explosions with information on duration and amplitudes of seismic signals has been used to analyse the mechanisms and characteristics of these hydrothermal explosions field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event the explosions lasted for 40 50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio lacustrine deposit composed of pyroclasts lavas scoriaceous fragments and fine grained welded or loosely consolidated aggregates interbedded with clay rich levels several small fans of ejecta were formed reaching a distance of 1 km north of the lake and covering an area of approximately 0 3 km2 with a maximum thickness of 40 cm at the crater walls the material volume of approximately 104 m3 has been ejected by the expanding boiling fluid generated by a pressure failure affecting the surficial geothermal reservoir the maximum thermal craterisation and ejection energies calculated for the explosion areas are on the order of 1011 1010 and 109 j respectively comparison of these with those estimated by the volume of the ejecta and the crater sizes yields good agreement we estimate that approximately 30 of the available thermal energy was converted into mechanical energy during this event the residual energy was largely dissipated as heat while only a small portion was converted into seismic energy estimation of the amount of freshly fragmented clasts in the ejected material obtained from sem morphological analyses reveals that a low but significant energy consumption by fragmentation occurred decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation whereas most of the fresh fragments derive from the disaggregation of aggregates furthermore ejection velocities of the particles 40 50 m s measured via high speed videos are consistent with those estimated from the field the multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small size yet hazardous steam explosion events

association of 34s depleted pyrite layers with negative carbonate δ13c excursions at the permian triassic boundary evidence for upwelling of sulfidic deep ocean water masses 1 a marine permian triassic boundary ptb section at nhi tao vietnam contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite s 34spy and carbonate c isotopic compositions 13ccarb the first and largest of the events that precipitated these pyritic horizons was coincident with the late permian mass extinction while subsequent events were generally smaller and occurred at quasiperiodic intervals of 20 to 30 ka a near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters among other considerations argues against a diagenetic control for these relationships rather the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep ocean waters containing 34s depleted hydrogen sulfide and 13c depleted dissolved inorganic carbon the sulfide 34s record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite formed via in situ bacterial sulfate reduction with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the late permian marine mass extinction this is the first study to 1 document patterns of pyrite 13ccarb covariation that strongly support upwelling as a major process at the ptb and 2 provide evidence of multiple quasiperiodic upwelling events that may reflect reinvigoration of global ocean overturn following a prolonged interval of late permian deep ocean stagnation

the stable carbon isotopic composition of organic material in platform derived sediments implications for reconstructing the global carbon cycle in pelagic carbonate sediments the degree to which the 13c values of inorganic and organic fractions co vary has been used to interpret rates of production burial and decomposition of organic carbon this relationship is relatively consistent through time permitting estimates of organic carbon production and preservation however as the majority of pelagic sediments older than 200 myr have been subducted carbonate sediments deposited in epeiric seas and platforms are often substituted for pelagic carbonates in analyses of ancient global carbon cycling there are well known pitfalls to using shallow marine carbonate materials including diagenesis semi isolation of depositional environments and input of different types of sediments with varying inorganic 13c 13cinorganic values which can obscure any global signatures one method used to assess whether global changes in 13c are accurately represented by 13cinorganic records is to examine variations in the 13c of co occurring organic material 13corganic if a 13corganic record co varies with a co occurring 13cinorganic record it is argued that the signals must be related to variations in the global carbon cycle this assumption has been investigated by analysing the isotopic composition of the organic carbon preserved in the uppermost 150 m of periplatform sediments recovered during odp leg 166 from the western margin of great bahama bank the 13corganic values measured in this study were compared to previously published 13cinorganic records measured on identical samples thus allowing a study of the correlation between the two records through time these analyses showed that the correlation coefficient between 13cinorganic and 13corganic increased from the proximal location site 1005 r2 0 1 to the distal site site 1006 r2 0 63 the importance of platform derived carbonate and organic material at the proximal location site 1005 is reflected in the absence of a co variation between inorganic and organic 13c records which exhibit no correlation on the platform itself in contrast the co variance in 13c values at the basinal location site 1006 is explained by a two point mixing model which demonstrates the importance of both pelagic and platform derived carbonate and organic carbon in generating the positive correlation between the organic and inorganic 13c values this results in a correlation between 13cinorganic and 13corganic records at site 1006 that is unrelated to global carbon cycling such data question the applicability of using 13corganic values to support the ability of 13cinorganic values to record global carbon cycling in carbonates recovered from environments where multiple sources of carbonate and organic carbon contribute to the bulk 13c signal

lower triassic conodont sequence in chaohu anhui province china and its global correlation abstract the early triassic paleogeographical setting of the chaohu section in china was in a deep part of the yangtze platform and this has resulted in a rather complete lower triassic sequence with rich ammonoid and conodont successions three lower triassic sections west pingdingshan north pingdingshan and south majiashan have been sampled in detail for a systematic conodont study eight conodont zones are recognized in ascending order these are the zones of hindeodus typicalis neogondolella krystyni neospathodus kummeli neospathodus dieneri neospathodus waageni neospathodus pingdingshanensis neospathodus homeri and neospathodus anhuinensis these are correlated with the sequences in north america and other areas of the world the succession provides a good basis for the definition of the global stratotype of the induan olenekian boundary gssp which has been proposed at the base of the neospathodus waageni zone in west pingdingshan seven new species are introduced neospathodus chaohuensis n chii n concavus n eotriangularis n pingdingshanensis n posterolongatus n tongi a new subspecies n waageni eowaageni and three morphotypes of n dieneri

evolution of oceanic redox conditions during the permo triassic transition evidence from deepwater radiolarian facies abstract the 90 biodiversity loss among marine invertebrate species during the end permian mass extinction the most severe phanerozoic biocrisis has been attributed to widespread oceanic anoxia superanoxia recent studies of the lithofacies inorganic geochemistry and biomarkers of permian triassic boundary ptb sections have yielded an inferred pattern of oceanic redox changes that is complex and sometimes inconsistent in this contribution we review the ecology of radiolarians an important microzooplankton group during the permo triassic transition and consider its implications for contemporaneous changes in paleoceanographic conditions our analysis shows that 1 late permian radiolarian faunas were cosmopolitan with different orders having specific depth preferences i e albaillellarians favoring deeper waters and spherical forms entactinarians and spumellarians shallower waters 2 deep water taxa declined earlier than shallow water taxa 3 many paleozoic type taxa survived into the early triassic but went extinct during a second crisis in the dienerian dead clade walking followed by the appearance or expansion of mesozoic type taxa during the olenekian and 4 the survival of paleozoic type taxa during the early triassic was greater at higher paleolatitudes than in the tropics these observations are consistent with a first order redox control on radiolarian faunal distributions specifically a shallowing and poleward expansion of the oceanic oxygen minimum zone during the ptb crisis the consequent adaptation of some deepwater taxa to shallower environments resulted in early triassic radiolarian faunas in continental basins becoming more similar to those in pelagic settings enhanced survival of paleozoic type taxa in high latitude regions indicates that the main stressor on permo triassic radiolarian communities was reduced oceanic oxygen levels stronger in the tropics rather than climatic warming stronger at the poles

the historic magmatic hydrothermal eruption of the breccia di commenda vulcano italy the historic breccia di commenda bc explosive eruption of vulcano aeolian islands italy opened with a phase that generated a gray fine ash layer dispersed to the northwest phase 1 the eruption continued with a dilute pyroclastic density current pdc that was dispersed to the east followed by the emplacement of radially distributed topographically controlled pdc deposits phase 2 the last phase of the eruption produced a sequence of accretionary lapilli and gray fine ash dispersed toward the southeast phase 3 the most impressive feature of the bc is its high lithic juvenile clast ratio and the yellow color of the deposits of phase 2 lithic fragments are mainly hydrothermally altered rocks in the silicic and advanced argillic facies juvenile fragments ranging from 20 to 40 by volume are mainly confined to the ash component of the deposits and comprise rhyolitic to trachyandesite poorly to non vesicular fragments the fine ash fraction of the deposits is richer in s cu zn pb and as than the bc juvenile lapilli and bombs and also the juvenile components of other la fossa units suggesting that the bc formed in the presence of an anomalously high amount of s and metals sulfur and metals may have been carried as aerosols by chloride and sulfate bearing micro crystals derived from the condensation of magmatic gas in the eruptive cloud the high content of hydrothermally altered lithic clasts in the deposits suggests that explosions involved the fluid saturated hydrothermally altered rocks residing in the conduit zone however the presence of a juvenile component in the deposits supports the idea that this explosion may have been triggered by the ascent of new magma we categorize this eruption as magmatic hydrothermal to emphasize that in this type of phreatomagmatic eruption the external water was an active hydrothermal system rock magnetic temperatures of non altered lava lithic fragments indicate a uniform deposit temperature for the pdc deposits of between 200 and 260 c with a maximum at 280 c these homogeneous relatively low temperatures are consistent with the idea that the phase 2 explosions involved the expansion of abundant steam from the flashing of the hydrothermal system in addition recent paleomagnetic dating of the bc provides an age of between 1000 and 1200 ad younger than that reported in the previously published data suggesting that previous interpretations and the recent history of la fossa and mt pilato require re evaluation

vertical δ13corg gradients record changes in planktonic microbial community composition during the end permian mass extinction abstract the global carbon cycle experienced a major perturbation during the permian triassic transition reflected inter alia in a large increase in the vertical shallow to deep gradient of carbonate 13c 13ccarb in early triassic seas however the effect of this perturbation on the vertical gradient of organic matter 13c in seawater 13corg is less known to date here we examine geographic and secular variations in 13corg in late permian early triassic seas of the south china craton and their implications for contemporaneous changes in microbial community composition and paleoredox conditions vertical 13corg gradients document the existence of a narrow and relatively shallow oxygen minimum zone omz within the open ocean northern deepwater basin ndw and a deeper and thicker omz within the semi restricted nanpanjiang basin npjb for the pre extinction interval 13corg gradients between the shallow and intermediate watermasses of the ndb and between the shallow and deep watermasses of the npjb record contributions to the sediment of organic matter from bacteria living below the ocean surface layer these bacteria were mainly anaerobic chemoautotrophs that inhabited suboxic to anoxic waters of an omz and that produced more strongly 13c depleted organic matter than surface water eukaryotic algae thus increasing 13corg for the post extinction interval a reversed 13corg in the ndb is attributed to blooms of green sulfur bacteria or other anaerobic photoautotrophic bacteria that were resident in a deep chlorophyll maximum layer and that had smaller carbon isotopic fractionation than surface water algae although quantitatively important in intermediate to deep water areas during the early triassic such bacteria were absent in coeval shallow water sections reflecting water depth controls on microbial community composition a concurrent flatting of the 13corg gradient in the npjb was caused by a return of oxic conditions and or a decline of primary productivity in the surface ocean

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

vent temperature trends at the vulcano fossa fumarole field the role of permeability between 1994 and 2010 we completed 16 thermal surveys of vulcano s fossa fumarole field aeolian islands italy in each survey between 400 and 1 200 vent temperatures were collected using a thermal infrared thermometer from distances of 1 m the results show a general decrease in average vent temperature during 1994 2003 with the average for the entire field falling from 220 c in 1994 to 150 c by 2003 however between 2004 and 2010 we witnessed heating with the average increasing to 190 c by 2010 alongside these annual scale field wide trends we record a spatial re organisation of the fumarole field characterised by shut down of vent zones towards the crater floor matched by rejuvenation of zones located towards the crater rim heating may be expected to be associated with deflation because increased amounts of vaporisation will remove volume from the hydrothermal system gambino and guglielmino j geophys res 113 b07402 2008 however over the 2004 2010 heating period no ground deformation was observed instead the number of seismic events increased from a typical rate of 37 events per month during 1994 2000 to 195 events per month during 2004 2010 as part of this increase we noticed a much greater number of high frequency events associated with rock fracturing we thus suggest that the heating event of 2004 2010 was the result of changed permeability conditions rather than change in the heat supply from the deeper magmatic source within this scenario cooling causes shut down of lower sectors and re establishment of pathways located towards the crater rim causing fracturing increased seismicity and heat flow in these regions this is consistent with the zone of rejuvenation which lies towards and at the rim being the most favourable location for fracturing given the stress field of the fossa cone schopa et al j volcanol geotherm res 203 133 145 2011 it is also the most established zone having been active at least since the early twentieth century our data show the value of deploying multi disciplinary geophysical campaigns at degassing fumarolic hydrothermal systems this allows more complete and constrained understanding of the true heat loss dynamics of the system in the case study presented here it allows us to distinguish true heating from apparent heating phases while the former are triggered from the bottom up i e they are driven by increases in heat supply from the magmatic source the latter are triggered from the top down i e by changing permeability conditions in the uppermost portion of the system to allow more efficient heat flow over zones predisposed to fracturing

role of apparent cohesion in the stability of dominician allophane soil slopes this study examines the effect of loss of apparent cohesion from rainwater infiltration upon the stability of partly saturated allophanic soil slopes of dominica west indies the parent material of the dominican allophanic soils are the andesitic and dacitic volcanic rocks from ten volcanic centres of mainly pleistocene age although simplifying assumptions are made to assess the depth of wetting front and magnitudes of true and apparent cohesion values of the partly saturated allophanic soils certain inferences of practical significance emerge from the study matric suction contributes to the effective stress of unsaturated soils and increases the shear strength of these soils by imparting them an apparent cohesion strength component this apparent cohesion strength component of the partly saturated dominican allophanic soils is considered to be related to the matric suction term u a u w by a parabolic relationship the partly saturated allophanic soil slopes of dominica would invariably fail from loss of apparent cohesion upon saturation of the soil mantle by the infiltrating water front only if a the average slope angle beta is greater than or equal to the drained shear strength parameter of the unsaturated soil phi d slopes with beta greater than or equal to phi d are referred to as category 1 slopes in this study and b the drained cohesion parameter c d belonging to the partly saturated soil of the category 1 slope is mainly contributed by matric suction induced apparent cohesion c app and contribution from true cohesion c is absent however the possibility of the category 1 slopes for the case 1 situation failing in the saturated condition from effective stress reduction due to rise in ground water table is shown to be an unfeasible proposition in contrast for the case 1 situation the partly saturated category 2 slopes beta phi d are insusceptible to failure from reduction in effective stress due to loss of matric suction but fail in the saturated condition from effective stress reduction due to rise in ground water table if the allophanic soils were to possess a sufficient magnitude of true cohesion c even the partly saturated category 1 slopes possessing slope angles beta much in excess of their phi d values beta phi d 15 1 degrees would remain stable upon total elimination of the matric suction induced cohesion however partly saturated category 1 slopes possessing a true cohesion component and insusceptible to failure from reduction in effective stress upon loss of matric suction invariably fail in the saturated condition from reduction in effective stress due to rise in ground water table using the methodology developed in this study two previously reported case histories pertaining to rain induced translational landslides in the residual soil areas of brazil are re examined and the results obtained in this study are found to be in agreement with the findings of the previous researchers

two pulses of extinction during the permian triassic crisis over 90 of marine species were lost during the end permian extinction fossil data show that the crisis in china was marked by two distinct phases of marine extinction separated by a 180 000 year recovery period

changes in ocean denitrification during late carboniferous glacial interglacial cycles rates of denitrification below some oceanic upwelling zones reach a maximum during periods when sea level rise was fastest throughout the pleistocene glacial cycles nitrogen isotope data from north american shales deposited 300 million years ago during palaeozoic glaciations are indicative of a similar pattern

palaeoenvironments of the permian triassic transition sections in kashmir india abstract detailed measurements of two permian triassic boundary sections at guryul ravine and pahlgam in kashmir indicate continuous sedimentation across the boundary though with a marked change from shallow storm influenced shelf to deeper shelf below wave base successive shell beds through the 2 5 m thick transitional latest permian section at guryul formed as in situ accumulations with little sign of either erosional breaks or condensation faunal change takes place gradually in the late permian transition beds as elsewhere in the tethyan sections there is no major event layer at the permian triassic boundary and little evidence for dysaerobic conditions both the kashmir and east greenland permian triassic sections have sedimentation rates that are orders of magnitude greater than at the condensed meishan reference section they show that the end permian extinction was associated with transgression but not with immediate onset of anoxic conditions macrofaunal extinction seems associated with reduction in primary production which would also explain the dwarfism of fossils found in all permian triassic sections studied so far

multiple early triassic greenhouse crises impeded recovery from late permian mass extinction the late permian mass extinction was not only the most catastrophic known loss of biodiversity but was followed by unusually prolonged recovery through the early triassic opinion has been divided on whether delayed recovery was a legacy of especially profound ecological disruption or due to additional environmental perturbations new records from the sydney basin in southeastern australia now reveal five successive late permian and early triassic spikes of unusually high atmospheric co2 and profound chemical weathering these successive atmospheric co2 greenhouse crises coincided with unusually warm and wet paleoclimates for a paleolatitude of 61 s successive transient greenhouse crises punctuated long term cool dry and low co2 conditions and may account for the persistence of low diversity and small size in early triassic plants and animals

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

phreatic activity and hydrothermal alteration in the valley of desolation dominica lesser antilles phreatic eruptions are possibly the most dramatic surface expressions of hydrothermal activity and they remain poorly understood the near absence of precursory signals makes phreatic eruptions unpredictable with respect to both time and magnitude the valley of desolation vod dominica located close to the boiling lake the second largest high temperature volcanic crater lake in the world hosts vigorous hydrothermal activity with hot springs mud pools fumaroles and steaming ground a phreatic or phreatomagmatic eruption from this site is considered to be the most likely scenario for future volcanic activity on dominica yet there is little information regarding the trigger mechanisms and eruption processes of explosive events at this active hydrothermal center and only a very small number of studies have investigated hydrothermal activity in the vod we therefore conducted two field campaigns in the vod to map hydrothermal activity and its surficial phenomena we also investigated alteration processes and their effects on degassing and phreatic eruption processes we collected in situ petrophysical properties of clay rich unconsolidated samples and together with consolidated rock samples we investigated the range of supergene and hydrothermal alteration in the laboratory in addition we performed rapid decompression experiments on unconsolidated soil samples our results show that alteration leads to an increasing abundance of clay minerals and a decrease in both strength and permeability of the rocks in the immediate vicinity of degassing acid sulfate fluids advanced argillic alteration yields a mineral zoning which is influenced by meteoric water the water saturated basal zone is dominated by kaolinite run 0whereas alunite formation is favored at and above the groundwater table where atmospheric oxidation of h2s to h2so4 occurs e g steam heated alteration alteration effects may in turn inhibit degassing at the surface increasing the potential for pressurization in the subsurface and thus lead to phreatic eruptions rapid decompression experiments together with ballistic trajectory calculations constrain estimates of the conditions prior to the 1997 small scale phreatic event in the vod the results presented here may serve as a contribution to the understanding of the hazard potential of ongoing hydrothermal activity within the vod on a broader perspective our results will help evaluate hydrothermal activity in similar areas worldwide which might also have the potential for phreatic eruptions for instance poas costa rica or tongariro and waimangu new zealand

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

seismic images and rock properties of the very shallow structure of campi flegrei caldera southern italy in september 2001 an extensive active seismic investigation serapis experiment was carried out in the gulfs of naples and pozzuoli with the aim of investigating and reconstructing the shallow crustal structure of the campi flegrei caldera and possibly identifying its feeding system at depth the present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the serapis dataset this is achieved by reflection seismic sections obtained by the 3d data gathering and through refined p velocity images of the shallowest layer of pozzuoli gulf z 3 500 m s correlates with units made up of agglomerate tuffs and interbedded lava which form the southern edge of the caldera which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study the upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses the depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt vp increase on the one dimensional 1d profiles extracted from the 3d tomographic model and by the presence of a strong reflector located at about 0 6 0 7 s two way time twt on common mid point gathers the move out velocity analysis and stack of the p p and p s reflections at the layer bottom allowed to estimate relatively high vp vs values 3 7 0 9 this hypothesis has been tested by a theoretical rock physical modeling of the vp vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent water saturated volcanic and marine sediments that filled pozzuoli bay during the post caldera activity

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

volcanically induced environmental change at the permian triassic boundary xiakou hubei province south china related to west siberian coal field methane releases a detailed geochemical investigation of the permian triassic boundary in a carbonate ramp setting at xiakou south china provides new insights regarding the role of volcanism in the largest mass extinction in earth history the xiakou section records 9 intervals of volcanic activity some producing up to 25 cm thick composite ash layers during the latest permian and earliest triassic each volcanic episode coincided with major changes in marine environments the largest changes occurred in conjunction with volcanic interval vi 4 correlative with the latest permian mass extinction during which 1 the oceanic oxygen minimum zone expanded as shown by framboidal pyrite flux 2 marine productivity declined sharply as shown by multiple productivity proxies and 3 climate conditions became more humid as shown by increased clay fluxes the mechanism by which volcanic eruptions forced marine environmental changes may be inferred from the relationship between ash layer thickness and the magnitude of the associated negative c isotope excursion the most likely connection is through volcanogenic methane release to the atmosphere possibly as a result of magmatic intrusions into the west siberian coal basin triggering increases in global temperature and humidity these climate changes in turn resulted in stronger oceanic stratification oxygen minimum zone expansion and a decline in marine productivity the xiakou section is important in demonstrating links between volcanism and the marine environment during the permian triassic transition interval

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

diversity dynamics of toarcian aalenian jurassic ammonites and transgressions regressions in the greater caucasus basin caucasian sea northern neo tethys ocean an evidence of partial dependence abstract possible dependence of ammonite diversity dynamics on shoreline shifts i e transgressions and regressions is yet to be understood data from the greater caucasus basin which was located on the northern active margin of the neo tethys ocean in the mesozoic permit to analyze the noted dependence at the toarcian aalenian time interval distribution of 161 species and 40 genera in each regional ammonite based biozone of this interval allows to evaluate the diversity dynamics of ammonites the total number of both species and genera changed cyclically the diversity maxima occurred in the h bifrons g thouarsense and l murchisonae zones the diversity minima occurred in the d semicelatum h variabilis p aalensis and g concavum zones semi quantitative analysis of facies distribution in 28 areas of the basin indicates a stepwise early toarcian middle aalenian transgression followed by a late aalenian regression the general trend towards species diversification through the study interval coincided with the noted transgression this is an evidence of partial dependence but no dependence between the generic diversity dynamics and shoreline shifts is visible it is hypothesized that transgressions facilitated the growth of the ammonite diversity but when they stopped the diversity was controlled by other factors changes in the spatial distribution of deep marine palaeoenvironments might also affect the ammonite diversity dynamics but no regional evidence of importance of oxygen depletion and seawater temperature fluctuations is found the minimal ammonite diversity in the d semicelatum zone could be a consequence of the early toarcian mass extinction in the greater caucasus basin the latter occurred at a peak of regression

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

high speed imaging of strombolian explosions the ejection velocity of pyroclasts explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the earth s crust knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption and yet direct measurements are still a difficult task with largely variable results here we apply pioneering high speed imaging to measure the ejection velocity of pyroclasts from strombolian explosive eruptions with an unparalleled temporal resolution measured supersonic velocities up to 405 m s are twice higher than previously reported for such eruptions individual strombolian explosions include multiple sub second lasting ejection pulses characterized by an exponential decay of velocity when fitted with an empirical model from shock tube experiments literature this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses these results directly impact eruption modeling and related hazard assessment as well as the interpretation of geophysical signals from monitoring networks

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

brachiopod miniaturization and its possible causes during the permian triassic crisis in deep water environments south china abstract brachiopod miniaturization is both the reduction in size of individuals of a species over time and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time this paper investigates this phenomenon prior to and during the end permian crisis in a deep water setting in south china based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species the process of miniaturization near the permian triassic boundary in deep water environments is characterized by 1 larger species including martinia sp costatumulus dongpanensis and anidanthus mucronata reduced in average body size and abundance over time towards the end permian brachiopod extinction event 2 small species including attenuatella mengi and spinomarginifera semicircridge showed a mixed response with either no size change or a reduction in average body size while these species increased in abundance over time indicating they were less sensitive to the stressed environmental setting 3 both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end permian crisis regression an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization based on the biotic replacement and changes in sea water chemistry among these factors the fall in sea level is perhaps the primary factor and led to a decline in productivity and an increased input of terrestrial material into the marine setting

bioessential element depleted ocean following the euxinic maximum of the end permian mass extinction abstract we describe variations in trace element compositions that occurred on the deep seafloor of palaeo superocean panthalassa during the end permian mass extinction based on samples of sedimentary rock from one of the most continuous permian triassic boundary sections of the pelagic deep sea exposed in north eastern japan our measurements revealed low manganese mn enrichment factor normalised by the composition of the average upper continental crust and high cerium anomaly values throughout the section suggesting that a reducing condition already existed in the depositional environment in the changhsingian late permian other redox sensitive trace element vanadium v chromium cr molybdenum mo and uranium u enrichment factors provide a detailed redox history ranging from the upper permian to the end of the permian a single v increase representing the first reduction state of a two step v reduction process detected in uppermost changhsingian chert beds suggests development into a mildly reducing deep sea condition less than 1 million years before the end permian mass extinction subsequently a more reducing condition inferred from increases in cr v and mo developed in overlying changhsingian grey siliceous claystone beds the most reducing sulphidic condition is recognised by the highest peaks of mo and v second reduction state in the uppermost siliceous claystone and overlying lowermost black claystone beds in accordance with the end permian mass extinction event this significant increase in mo in the upper changhsingian led to a high mo u ratio much larger than that of modern sulphidic ocean regions this trend suggests that sulphidic water conditions developed both at the sediment water interface and in the water column above the end permian mass extinction horizon mo v and cr decrease significantly on this trend we provide an interpretation of drawdown of these elements in seawater after the massive element precipitation event during the end permian maximum development of the reducing water column a decrease in the mo u ratio despite enrichment of mo and u also supports that of mo calculations of the total amounts of these elements precipitated compared with the global seawater inventory suggest that when more than 6 10 of the global ocean became euxinic as much as the study section most of the dissolved elements would precipitate into sediments resulting in a global element depleted seawater condition mo v and cr act as bioessential elements for both primary producers and animals the continuing reducing water column and the lack of bioessential elements could have had a considerable effect on primary producer turnover and marine life metabolism not only in the pelagic environment but also in surrounding marine environments

volcanic soil properties in dominica west indies abstract the unusual geotechnical and hydrological characteristics of the tropical clay soils involved in landslides in dominica resulting from hurricanes david and frederic in 1979 are examined these highly porous soils exhibit very high field moisture contents 42 180 for allophane latosols void ratios are very high up to 6 for allophanes and therefore field dry unit weights are very low 5 47 10 01 kn m3 for allophanes although predrying does not greatly affect the atterberg limits of kandoids it causes great reductions in the limits of allophane rich soils the degree of difference depending on the allophane content allophane soils also form a distinct group on cassagrande s plasticity chart falling below the a line as liquid limit increases predrying increases the r values by around 7 for kandoids but does not affect the allophanes and smectoids values of r vary with clay mineralogy allophanes 30 38 smectoids 32 35 dry kandoids 33 34 wet kandoids 25 29 all are abovevalues for temperate clays and are more akin to granular soils none of the direct shear tests showed any change of n as n n increased a marked contrast to temperate clays a detailed understanding of runoff processes notably zones of percolation impedance perched saturation and throughflow is essential to explanations of slope failure patterns although topsoil permeabilities and porosities of all dominican soils are extremely high subsurface soil hydrology varies strikingly with soil type impermeable subsoils and pans impede percolation at a shallow depth in smectoid and allophane podzolic soils in kandoids and allophane latosolics two zones of impedance above the b horizon and at the soilk rock interface are important but sufficient vertical development of saturation zonesto initiate landslides can only occur in the exceptionally prolonged high intensity rainfalls of cyclones

geological history and potential hazards of the late pleistocene to recent plat pays volcanic complex dominica lesser antilles during 1998 2000 the island of dominica in the lesser antilles experienced a major volcanic earthquake swarm spatially associated with volcanic centres in the south of the island this swarm provided the motivation for a major re assessment of geologic history and volcanic hazards in this region this has led to a re interpretation of the south western most corner of the island as a large volcanic complex termed the plat pays volcanic complex which has exhibited a wide range of past eruptive activity and which in the quaternary experienced a major caldera collapse triggered by a voluminous pyroclastic eruption stratigraphy and new 14c age determinations reveal a complicated history of development the earliest activity is represented by the formation of the plat pays stratovolcano and associated parasitic domes a major explosive eruption 39 000 years b p produced the grand bay ignimbrite and triggered a major caldera collapse of the summit and south western flank of the plat pays stratovolcano following the major eruption re injection of plat pays magma resulted in the extrusion of approximately 12 lava domes both within and outside the resulting depression caldera collapse was followed by at least one catastrophic flank collapse but it is unclear whether or not this was triggered by caldera formation the only on shore evidence of flank collapse is the breach of the caldera rim and truncation of post caldera deposits emplaced on or near the caldera rim we find no evidence of on shore large magnitude rock avalanche deposits within the stratigraphic framework of the plat pays volcanic complex frequent seismic swarms of volcanic earthquakes and vigorous geothermal activity indicate that south dominica is still underlain by an active magma reservoir system our new geological observations combined with an interpretation of recent seismic swarm activity suggest that an eruption probably dome forming from the plat pays volcanic complex is probable within the next 100 years

thermodynamics of gas and steam blast eruptions eruptions of gas or steam and non juvenile debris are common in volcanic and hydrothermal areas from reports of non juvenile eruptions or eruptive sequences world wide at least three types or end members can be identified 1 those involving rock and liquid water initially at boiling point temperatures boiling point eruptions 2 those powered by gas primarily water vapor at initial temperatures approaching magmatic gas eruptions and 3 those caused by rapid mixing of hot rock and ground or surface water mixing eruptions for these eruption types the mechanical energy released final temperatures liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate then decompress isentropically from initial near surface pressure 10 mpa to atmospheric pressure maximum mechanical energy release is by far greatest for gas eruptions 1 3 mj kg of fluid rock mixture about one half that of an equivalent mass of gunpowder and one fourth that of tnt it is somewhat less for mixing eruptions 0 4 mj kg and least for boiling point eruptions 0 25 mj kg the final water contents of crupted boiling point mixtures are usually high producing wet sloppy deposits final erupted mixtures from gas eruptions are nearly always dry whereas those from mixing eruptions vary from wet to dry if all the enthalpy released in the eruptions were converted to kinetic energy the final velocity v max of these mixtures could range up to 670 m s for boiling point eruptions and 1820 m s for gas eruptions highest for high initial pressure and mass fractions of rock m r near zero for mixing eruptions v max ranges up to 1150 m s all observed eruption velocities are less than 400 m s largely because 1 most solid material is expelled when m r is high hence v max is low 2 observations are made of large blocks the velocities of which may be less than the average for the mixture 3 heat from solid particles is not efficiently transferred to the fluid during the eruptions and 4 maximum velocities are reduced by choked flow or friction in the conduit

gas and water geochemistry of geothermal systems in dominica lesser antilles island arc abstract four of the nine potentially active volcanoes on the island of dominica in the lesser antilles volcanic island arc have associated active volcanic hydrothermal systems between 2000 and 2006 the gas and thermal waters from these systems were investigated to geochemically characterise the fluids gain insight into the temperature and equilibrium state of the underlying reservoirs and evaluate the feasibility of monitoring geothermal features as a volcano surveillance tool in dominica the geothermal gases are typical of those found in arc type settings with n2 excess and low amounts of he and ar the dry gas is dominated by co2 ranging from 492 to 993 mmol mol and has a hydrothermal signature with hydrogen sulphide as the main sulphurous gas the waters are predominantly acid sulphate so4 100 4200 mg l ph 4 and likely formed as a result of dilution of acidic gases in near surface oxygenated groundwater enrichment in both 18o and d with respect to the global meteoric water line gmwl confirms that the waters are of primarily meteoric origin but have been affected by evaporation processes quartz geothermometers gave equilibrium temperatures of 83 c 203 c these temperatures contrast with the higher equilibrium temperature ranges 170 c 350 c obtained for the gases using the h2 ar ch4 co2 gas ratios plot suggesting that the quartz geothermometers are affected by non attainment of equilibrium this may be a result of precipitation of the dissolved silica and or dilution by relatively cold shallow aquifers of the thermal fluids generally no significant variations in fluid gas chemistry of the hydrothermal systems were observed during the study period and we propose that there were no changes in the state of volcanic activity in this period one exception to this occurred in a feature known as the boiling lake which underwent a month long period of significant compositional temperature and water level fluctuations ascribed to a drastic decrease of hydrothermal input related to a perturbation in the lake probably seismically induced this geochemical study is part of an ongoing monitoring programme of dominica geothermal systems aimed at establishing long term geochemical observations for the purpose of volcano monitoring

morphological disparity of ammonoids and the mark of permian mass extinctions the taxonomic diversity of ammonoids in terms of the number of taxa preserved provides an incomplete picture of the extinction pattern during the permian because of a strongly biased fossil record the analysis of morphological disparity the variety of shell shapes is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns first a trend of decreasing disparity ranging for about 30 million years led to a minimum disparity immediately before the permian triassic boundary second the strongly selective capitanian crisis fits a model of background extinction driven by standard environmental changes third the end permian mass extinction operated as a random nonselective sorting of morphologies which is consistent with a catastrophic cause

the effect of variations in rainfall on the chemical composition of vulcano fumaroles italy analytical data for samples collected over a period of 17 months at the crater fumaroles of vulcano are given

dynamics of shallow hydrothermal eruptions new insights from vulcano s breccia di commenda eruption understanding the dynamics and effects of hydrothermal eruptions is crucial to the hazard assessment in both volcanic and geothermal areas eruptions from hydrothermal centres may occur associated with magmatic phases but also as isolated events without magmatic input with the most recent examples being those of te maari tongariro new zealand in 2012 and ontake japan in 2014 the most recent caldera of the island of vulcano southern italy hosts in its centre the la fossa cone active since 5 5 ka and now characterised by continuous fumarolic degassing in historical times la fossa cone has experienced several hydrothermal eruptions with the most violent event being the breccia di commenda eruption that occurred during the thirteenth century ad based on analysis of 170 stratigraphic logs we show that the breccia di commenda eruption occurred in three main phases after an opening low intensity ash emission phase phase 1 the eruption energy climaxed during phase 2 when a series of violent explosions produced an asymmetric shower of ballistic blocks and the contemporaneous emplacement of highly dispersed lithic rich blast like pyroclastic density currents pdcs the tephra units emplaced during phase 2 ranging in volume from 0 2 to 2 7 105 m3 were covered in turn by thin ash fall deposits phase 3 the dynamics of the most violent and intense stage of the eruption phase 2 was investigated by numerical simulations a three dimensional numerical model was applied describing the eruptive mixture as a eulerian eulerian two phase non equilibrium gas particle fluid plus a one way coupled lagrangian ballistic block fraction at the initial simulation time a mass of about 109 kg with initial overpressure above 10 mpa and a temperature of 250 c was suddenly ejected from a 200 m long eastward inclined nne ssw trending fissure the mass release formed blast like pdcs on both sides of the fissure and launched ballistic blocks eastwards field investigations and numerical simulations confirm that hydrothermal explosions at la fossa cone include intense ballistic fallout of blocks emission of pdcs potentially travelling beyond the la fossa caldera and significant ash fallout the hazard associated with both ballistic impact and pdc ingress as associated with hydrothermal eruption is significantly larger with respect to that associated with vulcanian type events of la fossa

the permian triassic boundary event a geochemical study of three chinese sections abstract trace elements were determined in two well documented chinese permian triassic p tr boundary sections meishan and shangsi and in a new section liangfenya iridium concentrations range from 3 to 87 pg g at or below levels in common sedimentary rocks the results contrast with previous reports of high ir concentration in the meishan and shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the permian a notable feature in each of these widely separated p tr sections 500 1500 km is the existence of 2 5 light colored clay layers at and near the boundary these clay layers are strongly enriched in cs zr hf ta and th and depleted in cr co and ir indicating that they are altered ash apparently from the same massive silicic volcanic eruptions we estimate the magnitude of these eruptions to be a few thousand km3 of magma a volume comparable to the great toba eruption

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

experimental constraints on phreatic eruption processes at whakaari white island volcano vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at whakaari white island volcano new zealand here we investigate the influence of sample type hydrothermally altered cemented ash tuffs and unconsolidated ash lapilli and fragmentation mechanism steam flashing versus gas expansion on fragmentation and ejection velocities as well as on particle size and shape our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs cemented by alunite and amorphous opal increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs as less energy is consumed by fragmentation fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front neither fragmentation mechanisms nor sample type show a significant influence on the shape our results emphasize that under identical pressure and temperature conditions eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion therefore phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments

disparity fluctuations in jurassic ammonoids by means of conch geometry abstract we investigated the jurassic ammonoids of southern germany with respect to their temporal patterns of morphospace occupation a fourier analysis of whorl outline shapes was performed based on 1200 species within 72 discriminated biostratigraphic zones three general modes of temporal patterns in morphospace occupation can be distinguished by combining the sum of range the sum of variance and the position of the centroid of the morphological spectrum 1 morphospace stasis 2 morphospace enlargement and 3 morphospace reduction we applied this classification scheme in the study of the jurassic ammonoids demonstrating that the evolutionary history of jurassic ammonoids in southern germany can be subdivided into three phases with increased morphological range ending with incisions in the early aalenian late bathonian and end tithonian morphological variance differs partly from the range showing a general increase during the jurassic with incisions at the toarcian aalenian boundary within the callovian and the late tithonian a conducted subsampling as well as the comparison of disparity analyses of different temporal resolutions shows strikingly varying effects in morphospace patterns different resolutions and subsampled data provide strong correlations between sample size and the sum of range in particular

diversity and morphological evolution of jurassic belemnites from south germany abstract belemnites are extinct cephalopods whose evolutionary history is representative of successful adaptive radiations during the mesozoic nevertheless a detailed understanding of the dynamics and palaeoenvironmental drivers of this evolution is still lacking in order to fill this gap we analyze the diversity and morphological disparity of jurassic rostra from south germany and compare these patterns with other euro boreal trends we show that after an early apparition of few dissimilar groups during the hettangian sinemurian interval belemnites experienced four periods of diversification i e early pliensbachian middle late toarcian early bajocian and oxfordian marked by morphological disparifications of rostra towards forms potentially optimized for different hydrodynamic properties these adaptive radiations were interrupted at regional scale by four biological crises corresponding to morphological bottlenecks i e pliensbachian toarcian aalenian late bajocian and kimmeridgian most of them were morphoselective except the aalenian extinction which could be related to a prominent sea level fall by comparing our results to palaeoenvironmental data we show that warm temperate seawater temperatures might have favoured the diversification of belemnites potentially by accelerating their metabolic rates the population turnovers and the evolutionary rates on the long term conversely cooling or hyperthermal events correspond with biological crises migrations towards refuge areas located in the arctic and mediterranean domains could have been key factors for rapid post crisis recoveries finally the available data suggest a trend towards increased streamlining of the rostrum through the jurassic

morphological fluctuations of ammonoid assemblages from the muschelkalk middle triassic of the germanic basin indicators of their ecology extinctions and immigrations abstract for a stratophenetic analysis of middle triassic ammonoids from the german muschelkalk anisian ladinian whorl expansion rates whorl width indexes umbilical width indexes maximal conch sizes body chamber lengths the orientations of the aperture and a number of sculpture parameters of approximately 500 specimens were identified 274 of these data sets sorted according to their stratigraphic age were evaluated in scatter plots as well as canonical discriminant function analyses several of the diagrams that were produced in these analyses reflect more or less steady changes in conch morphology through geological time except for some intervals with abrupt and rather drastic transformations these morphological discontinuities are synchronous with immigrations into the germanic basin of crinoid and brachiopod taxa this discovery indicates disturbances in the endemic evolution of the ammonoids caused by such immigrations at a small scale this case study demonstrates that a rising sea level may have boosted the faunal exchange between an open marine and a restricted epicontinental basin causing a minor regional increase in biodiversity it also demonstrates that the evolution of germanic ceratites happened mainly within the germanic basin but partially probably also within the tethyan sea the ecology of the ceratites from this basin is discussed accordingly they were stenohaline good backward swimmers with a good manoeuvrability and able to achieve neutral buoyancy

the recovery and radiation of early jurassic ammonoids morphologic versus palaeobiogeographical patterns abstract the recovery and radiation of the early jurassic ammonoid morphospace as represented by nine morphologic groups identified in an earlier study are traced through the first 36 subzones of the hettangian to domerian time interval a quantitative survey of the dispersion of 436 species over 15 palaeogeographical areas reveals seven palaeobiogeographical patterns each corresponding to an exclusive set of species exhibiting similar characteristics in terms of distribution and abundance this study combines morphologic chronostratigraphical and palaeobiogeographical data in an attempt to investigate possible connections between morphologic recovery and radiation patterns and the history of ammonoid distribution on a global scale two out of nine morphologic groups are found to be prevalent in a single palaeobiogeographical pattern through the major part of the studied time interval and a single morphologic group prevails in all the marine areas considered during domerian times all the other relationships identified are less tightly constrained in space and time and indicate loose ties over more limited periods and narrower distributions the present results suggest that such complex relationships can be deciphered more successfully by using analytical palaeobiogeographical patterns as proposed here rather than classical palaeobiogeographical units biochores

update on the fluid geochemistry monitoring time series for geothermal systems in dominica lesser antilles island arc 2009 2017 abstract with updated geochemical and isotopic compositions obtained over the period 2009 to 2017 this study presents revised fluid characterizations for the active volcanic hydrothermal systems on the island of dominica in the lesser antilles which were first reported in 2011 hydrothermal waters of dominica cover a wide spectrum of ph temperatures and chemical composition the ph of the thermal waters ranges from acidic to neutral ph values of 1 7 8 and the waters are predominantly na so4 in character na 14 2127 mg l so4 1 1725 mg l likely formed as a result of dilution of acidic h2s rich gases in near surface oxygenated groundwater and have experienced limited water rock interaction the geochemical composition of the waters for most of the hydrothermal systems studied indicate no significant changes with the exception of the boiling lake which experienced a short 6 week episode of instability in november 2016 which appeared to be associated with a small mud rich explosion unlike the last such event in december 2004 which was reported to be earthquake triggered this event is possibly the consequence of a moderate sized landslide into the lake the lake draining episodes have been accompanied by changes in composition between na so4 and na cl which is attributed to hydrothermal fluid contributions from two different aquifers a shallower acid sulphate hydrothermal aquifer and a deeply sourced brine aquifer reservoir temperatures determined by quartz geothermometers have not changed significantly over the monitoring period suggesting steady state degassing of the magma chambers in two areas temperatures have increased watten waven from 83 90 c to 89 139 c and sulphur springs from 145 152 c to 93 243 c the elevated reservoir temperatures have affected the isotopic composition of the waters 18o 5 7 to 9 1 and d 8 to 20 5 that reflect a dominantly meteoric source with boiling degassing and evaporation also playing an important role the time series data suggests that some hydrothermal areas are experiencing increased steam evaporation over time whereas other waters are becoming more meteoric the 13cdic is decoupled from the deuterium and oxygen 18 isotopes and shows very little variation over time but a broad range in values from 11 to 5 the dominant process contributing to 13cdic is degassing of primarily magmatic co2 as exhibited by the bubbling pools hydrothermal streams have experienced mixing with biogenic co2 sources including plant respiration and methanogenesis the slight variations observed from site to site are likely a consequence of fractional degassing of the magma chamber during exsolution of co2 over the sampling period 2014 2017 the temperatures and 13c values do not change which suggests a current steady state of degassing

formation of rock coatings induced by the acid fumarole plume of the passively degassing volcano of la fossa vulcano island italy at la fossa volcano vulcano island and in the surrounding environment rock coatings rc develop owing to exposure of the ground surface to a volcanic acid plume this plume is produced by the passive degassing of la fossa active cone proximal and distal with respect to the high temperature fumarolic field rc have been identified which differ in mineralogy texture and chemical composition proximal rc are characterised by high silica content massive texture and strong leaching at the expense of the pyroclastic material distal rc are characterised by the presence of silica jarosite and minor goethite laminated texture and less developed evidence of leaching the rc are produced by direct interaction between the acid fumarolic aerosol and rocks and by reaction of dews and rains acidified by the absorption of acid gases so2 hcl hf of the fumarole plume with volcanic material proximal rc are produced at conditions of ph 2 distal rc form at ph 2 3 based on the presence of jarosite although the occurrence of goethite in some samples suggests higher values of ph the influence of the volcanic plume in the development of these rc is indicated also by the coincidence of the rc areal distribution with the distribution of the volcanic plume controlled by the local wind field this is furthermore supported by the presence in rc of chloride and or sulphur bearing compounds enriched in volatile elements and metals commonly carried by volcanic aerosols

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

the spatial nearshore offshore distribution of latest permian phytoplankton from the yangtze block south china abstract in order to analyze the spatial paleoecological distribution of the organic walled microphytoplankton in the late permian five sections from the yangtze block south china displaying different sediment facies types from neritic to offshore paleoenvironments including basinal facies have been investigated palynologically based on the diversity and relative abundance of acritarch species and genera the new data from the permian provide similar patterns as those described from other geological periods 1 low diversities with 2 to 4 acritarch species occur in nearshore environments whereas the higher diversities more than ten acritarch species appear in the offshore environments 2 at the generic level the genera leiosphaeridia reduviasporonites and micrhystridium are distributed widely from nearshore facies corresponding to shallow water environments to offshore facies corresponding to deeper water settings whereas some genera such as dictyotidium and veryhachium have a narrower distribution occurring on the continental shelf and towards the basin indicating open marine environments 3 the genus schizosporis only occurs around the permian triassic boundary ptb when the sea level declined probably indicating nearshore environments with shallow water settings 4 at the specific level the species micrhystridium breve displaying short spines and leiosphaeridia minutissima are indicative of neritic facies whereas the other species of micrhystridium and veryhachium with longer spines e g micrhystridium stellatum and veryhachium hyalodermum and leiosphaeridia microgranifera indicate more open marine environments big spherical acritarch species over 80 m in diameter such as dictyotidium reticulatum indicate shallow water environments and 5 in the ptb strata the relative abundance of the enigmatic reduviasporonites interpreted by some authors as a fungal spore is not higher than 14 in every sample indicating that a spike of reduviasporonites does not occur in the yangtze area reduviasporonites chalastus 40 m in length obviously dominates in shelf environments of shallow water whereas the smaller reduviasporonites catenulatus 15 m in length are more common in deeper water

changes in biomarker abundances and sulfur isotopes of pyrite across the permian triassic p tr schuchert dal section east greenland abstract in this study we report on biomarker abundances through parts of the permian triassic boundary ptb of schuchert dal east greenland that contains rich marine faunal records and excellent terrestrial palynological records biomarker abundances and sulfur isotopes are used to correlate the series of events including changes in element cycling and associated redox conditions of the ocean surrounding the collapse of the marine and terrestrial ecosystems through this record of a major crisis of life on earth during a mass extinction episode the upper schuchert dal formation contains a low diversity palynological assemblage ascribed to arborescent cordiaite conifer pteridosperm vegetation samples from this pre collapse interval are characterised by high abundances of dibenzofuran dbf dibenzothiophene dbt and biphenyl since these compounds have similar base structures and show comparable abundance curves it is plausible that they probably derive from a common source we propose that phenolic compounds of lignin of the woody plants present during this period could be the source for dbf dbt and biphenyl the redox conditions during this period of time also support the formation of dbf and dbt just above the extinction interval there is a dramatic decrease in the abundances of dbf and dbt which occurs at the same time as a sudden change in the stable sulfur isotopic composition 34s of pyrite indicating a change in redox conditions from oxic to anoxic euxinic conditions 34s values leading up to the extinction are highly depleted in the heavy sulfur isotope about 40 vs vcdt whilst shortly after the extinction interval much more positive isotope values are observed about 25 an inferred change in the biogeochemical sulfur cycle is supported by facies evidence from similar neighbouring sections it is suggested that two processes are operating closely here 1 changes in redox conditions and 2 extinction and or transgression accounting for the absence of woody material

hydrothermal eruptions of nisyros dodecanese greece past events and present hazard abstract the detailed analysis of the craters of hydrothermal eruptions and related products present on nisyros island demonstrates the ephemerality of these morphological forms in other words the mere recognizable existence of the craters and associated deposits implies recency of hydrothermal activity the minimum temperature required to cause the explosive phenomenon and possibly the depth of the reservoir which can be evaluated on the basis of the correlation between the diameter of the crater and the depth of explosion as proposed by fytikas and marinelli 1976 are therefore closely representative of the current hydrothermal circulation both field evidence and historical records indicate that all the deposits of hydrothermal eruption recognized on nisyros island were emplaced as debris flows almost all the ballistic ejecta were entrained in these debris flows and either redeposited far from their landing sites or involved in later crater collapse and erosion this emplacing mechanism implies that the original products were characterized by a water content higher than about 5 by weight steam driven hydrothermal eruptions one of which took place in 1871 originated deposits of limited dispersion as no sign of these erodible products can be found in the field today surface geology and fluid geochemistry together with subsurface information e g primary and hydrothermal lithologies distribution of temperature with depth physical chemical characteristics of deep water bearing zones indicate that two distinct hydrothermal aquifers are present underneath the southeastern part of the caldera floor both aquifers were probably involved in the most important historically documented hydrothermal eruptions which occurred in 1873 at that time violent earthquakes fractured the brittle aquiclude separating the two aquifers and caused a sudden transfer of fluids from the deep to the shallow aquifer thus triggering the hydrothermal eruptions hydrothermal eruptions will probably occur in future and this hazard must be taken into serious consideration the southern half of lakki plain where all past eruptions took place and active fumaroles are concentrated is the zone at highest risk at present gas geochemistry represents an effective tool to detect changes in the p t conditions of the shallow aquifer and particularly the phenomena of pressure build up that may lead to a hydrothermal eruption

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

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

thermal surveys of the vulcano fossa fumarole field 1994 1999 evidence for fumarole migration and sealing abstract between 1994 and 1999 we carried out five thermal surveys of the vulcano fossa fumarole field each consisted of 485 1213 vent temperature measurements distributed across the field these show that the field has been cooling and expanding where mean and maximum vent temperatures decreased from 216 to180 c and 541 to 428 c respectively between 1994 and 1997 however expansion of the field resulted in increased heat loss from 45 to 67 mw we suggest that cooling and expansion has been caused by increased gas flux and or permeability where increased flow of fluids of magmatic origin during 1996 is implied by chemical and isotopic data capasso g favara r francofonte s inguaggiato s 1999 chemical and isotopic variations in fumarolic discharge and thermal waters at vulcano island aeolian islands italy during 1996 evidence of resumed volcanic activity j volcanol geotherm res 88 1999 167 175 we propose that the size of the conduit has increased causing the fumarole field to expand and vent temperatures to generally decline as gas and heat losses become distributed over a wider area the increase in exhaling area has outweighed the modulating effect of cooling on total heat losses so that heat loss has increased due to an increased input from the magmatic source and or an increase in system permeability within these field wide trends the rim and then the middle zones have been cooling conversely the lower zone showed evidence of warming during 1994 98 before cooling in 1999 throughout the measurement period a se s thermal migration has been apparent and a new hot zone has developed on the field s southern edge we suggest that sealing of fumaroles by complete boiling of marine fluids on the northern edge of the system and higher permeability on the southern edge may have influenced this expansion direction if vent temperatures drop below 100 c then shallow sulfur sealing will quickly diminish fumarole life expectancy and contribute to the abandonment of vents in cooling zones in our model increased gas flux and or permeability e g due to increased magmatic degassing and or fracturing is the primary mechanism driving observed changes in the field temperature size and location deep and shallow conduit sealing are secondary mechanisms influencing the location of new zones once increased gas and heat fluxes have been triggered

seismic signals in geothermal areas of active volcanism a case study from la fossa vulcano italy since the last eruption 1888 1890 volcanism at vulcano aeolian archipelago southern tyrrhenian sea has taken the form of persistent fumarolic activity the gas vapour phases of the geothermal systems are mainly discharged within two restricted areas about 1 km apart from each other in the northern part of the island these areas are la fossa crater and the beach fumaroles of the baia di levante fluids released at the two main fumarolic fields display quite different chemical and temperature characteristics implying different origins the local seismicity essentially takes the form of discrete shocks of shallow origin depth 1 km at la fossa usually with energy 1013ergs they are thought to be related to the uprise of pressurized hot gases and vapours discharged at the crater fumaroles the present investigation points to the existence of two principal categories of seismic events called m shocks and n shocks these are short events normally 10 s m type shocks are thought to be due to resonance vibrations within the interior of the volcano probably driven by the excitation of shock waves within cavities deeply affected by deposition and alteration of self sealant hydrothermal minerals n type events display features that resemble those of volcano tectonic earthquakes but have no recognizable s phases here they are tentatively attributed to microfracturing of rocks which have been extensively hydrothermally altered results of the present study permit a preliminary conceptual model of the local shallow seismic processes in the framework of geochemical modelling of fumarolic activity and geological inferences from geothermal drilling

cessation of a productive coastal upwelling system in the panthalassic ocean at the permian triassic boundary abstract while the end permian extinction in the marine realm is well known from the tethys ocean it remains little studied in the vast panthalassic ocean opal creek alberta canada is a biostratigraphically continuous permian triassic boundary ptb section that is interpreted to have been deposited in a deep outer shelf setting along the panthalassic western margin of pangaea significant organic carbon and nitrogen isotope excursions precede the extinction of the dominant late permian benthic organisms siliceous sponges geochemical comparison with underlying guadalupian age rocks and analysis of the conodont fauna suggest that the latest permian at opal creek records the shutdown of a productive cold water upwelling ecosystem with a mid water column oxygen minimum followed by the transition to a warm and less vigorously circulating system with a bottom water oxygen minimum the transition from a low diversity cold water conodont fauna in the middle permian to a more diverse latest permian fauna containing equatorial species coincides with a transition from elevated 15n values characteristic of coastal zones with denitrification in a mid water oxygen minimum to more normal marine values a spike in the 13c of organic carbon following a latest permian marine transgression along western pangaea is here attributed to transient increased productivity in the photic zone preceding the main extinction likely related to the synergistic effects of warming increased nutrient runoff and residual upwelling this is followed by an equilibration to lower 13corg values characteristic of a lower productivity regime in the early triassic

energy consumption by magmatic fragmentation and pyroclast ejection during vulcanian eruptions abstract magmatic fragmentation during explosive eruptions consumes a significant amount of energy by the creation of new surface via fracturing this process reduces the energy that can be imparted to the resulting pyroclasts in the form of kinetic energy to date models of vulcanian eruptions have neglected the energy balance consumed by magmatic fragmentation we present a 1 d model of vulcanian eruption that considers the energy balance in rapid decompression of a pressurized magma below a caprock followed by fragmentation and acceleration of particles we then tested the model via decompression experiments at different temperatures room vs 850 c and initial pressure different series of experiments involving either fragmentation of an intact volcanic rock followed by ejection of the particles or simply the ejection of loose particles were performed to quantify the energy consumed by fragmentation and the kinetic energy available to eject the particles the ejection velocities observed in the fragmentation experiments of intact rocks are systematically lower than the ones with loose particles due to the energy consumed by fragmentation this energy depends on the fragmentation threshold i e the minimum pressure required to completely fragment the sample and is inversely proportional to the fraction of pressurized pores we propose that the effective pressure propelling the gas particle mixtures after fragmentation corresponds to the pressure initially stored in the pore fraction minus the fragmentation threshold we applied our caprock model to vulcanian eruptions of popocatepetl volcano february 2003 and colima volcano 10 february 1999 and obtained gas pressures at the onset of fragmentation of 11 13 mpa and 19 22 mpa respectively these pressures might correspond to the gas pressures required to disrupt the caprock fragment the underlying porous magma and eject the ballistics at the observed distances the model presented herein may help describe the dynamics of vulcanian eruptions and improve hazard assessment

influence of alteration on the mechanical behaviour and failure mode of andesite implications for shallow seismicity and volcano monitoring volcanoes often host hydrothermal systems that alter the host rock to understand the influence of alteration on mechanical behaviour of edifice forming rock we performed a series of triaxial deformation experiments on variably altered andesite from mt ruapehu new zealand under constant effective pressure under the imposed conditions andesite with intermediate argillic alteration deforms in a brittle manner forming fractures by contrast andesite with advanced argillic alteration deforms in a ductile manner with sample failure driven by distributed cataclastic pore collapse we consider this the result of an increase in porosity and clay content with increasing alteration ancillary experiments highlight that the brittle ductile transition occurs at lower effective pressure i e at shallower depths in andesites with advanced argillic alteration relative to unaltered andesites of comparable porosity we conclude that advanced argillic alteration can create an anomalous shallow ductile zone which has important implications for fluid flow and pre eruptive seismicity

hydrothermal activity and subsoil complexity implication for degassing processes at solfatara crater campi flegrei caldera the solfatara area and its fumaroles are the main surface expression of the vigorous hydrothermal activity within the active campi flegrei caldera system at depth a range of volcanic and structural processes dictate the actual state of the hydrothermal system below the crater the presence of a large variety of volcanic products at shallow depth including pyroclastic fallout ash beds pyroclastic density current deposits breccias and lavas and the existence of a maar related fault system appears to exert major controls on the degassing and alteration behavior adding further to the complexity of this environment variations in permeability and porosity due to subsoil lithology and alteration effects may further influence fluid flow towards the surface here we report results from a field campaign conducted in july 2015 that was designed to characterize the in situ physical temperature humidity and mechanical permeability strength stiffness properties of the solfatara crater subsoil the survey also included a mapping of the surficial hydrothermal features and their distributions finally laboratory measurements porosity granulometry of selected samples were performed our results enable the discrimination of four main subsoils around the crater 1 the fangaia domain located in a topographic low in the southwestern sector 2 the silica flat domain on the western altered side 3 the new crust domain in the central area and 4 the crusted hummocks domain that dominates the north east and south parts these domains are surrounded by encrusted areas reworked material and vegetated soil the distribution of these heterogeneous subsoils suggests that their formation is mostly related to i the presence of the fangaia domain within the crater and ii a system of ring faults bordering it the subsoils show an alternation between very high and very low permeabilities a fact which seems to affect both the temperature distribution and surficial degassing a large range of surface temperatures from 25 up to 95 degrees c has been measured across these surfaces with the hottest spot corresponding to the mud pools the area of new crust formation and the crusted hummocks in the subsoil the distribution of temperature is more complex and controlled by the presence of coarser and more permeable sandy pebbly levels these act as preferential pathways for hot hydrothermal fluid circulation in contrast low permeability fine grained levels act as thermal insulators that remain relatively cold and hinder fluid escape to the surface hot gases reach the surface predominantly along vertical fractures when this occurs mound like structures can be formed by a cracking and healing process associated with significant degassing it is anticipated that the results presented here may contribute to an improved understanding of the hazard potential associated with the ongoing hydrothermal activity within the solfatara crater at this site the permeability of the near surface environment and its changes in space and time can affect the spatial and temporal distribution of gas and heat emission particularly in areas where reduction in permeability occurs it can produce pore pressure augmentation that may result in explosive events

10be and ba concentrations in west african sediments trace productivity in the past particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles in order to determine the influence of these processes on the depositional fluxes of10be and barium we have performed high resolution measurements on sediment core geob 1008 3 from the congo fan because the core is dominated by terrigenous matter supplied by the congo river it has a high average mass accumulation rate of 6 5 cm kyr biogenic10be and ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10be and ba which are assumed to be proportional to the flux of al2o3 the meanba al weight ratio of the terrigenous component was determined to be 0 0045 the unusualy high terrigenous10be concentrations of 9 1 109 atoms g al2o3 are either due to input of particles with high10be content by the congo river or due to scavenging of oceanic10be by riverine particles the maxima of biogenic10be and ba concentrations coincide with maxima of the paleoproductivity rates time series analysis of the10be and of ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr which also controls the rates of paleoproductivity in this core during the maxima of productivity the flux of biogenic ba is enhanced to a larger extent than that of biogenic10be applying a model for coastal scavenging we ascribe the observed higher sensitivity of ba to biogenic particle fluxes to the fact that the ocean residence time of ba is approximately 10 times longer than that of10be

the pliensbachian and tithonian extinction events the claim by raup and sepkoski1 that an approximately 26 myr mass extinction periodicity can be recognized on a global scale at family level over the past 250 myr has excited much attention and provoked speculation about an ultimate extraterrestrial cause2 10 while the purported periodicity can be challenged on grounds of both the inaccuracy of the geological timescale11 and the method of extinction analysis12 there can be no doubting the reality of at least some of the 12 proposed extinction events such as those at or near the end of the permian triassic and cretaceous others are less widely acknowledged further analysis by raup and sepkoski13 confirms the importance of two of these events within the jurassic at the end of the pliensbachian and tithonian stages i demonstrate here that marine invertebrate mass extinctions at approximately these times occurred on a regional not a global scale they can be related to severe reductions in habitat area provoked either by regression of epicontinental sea or by widespread anoxia

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

conodont zonation across the permian triassic boundary at the xiakou section yichang city hubei province and its correlation with the global stratotype section and point of the ptb xiakou section is situated north of the central yangtze platform with successive late permian to early triassic strata thicker than the global stratotype section and point gssp of the permian triassic boundary ptb we recognized three conodont zones across the ptb in this section by high precision biostratigraphy they are the hindeodus latidentatus clarkina meishanensis zone hindeodus parvus zone and isarcicella isarcica zone in ascending order which correspond well with the gssp the present biostratigraphic work on xiakou section certainly confirmed the conodont zonation through the ptb at the gssp and also testified to the correctness of the ptb demarcation in xiakou section based on this precise demarcation of the ptb the appearance of a clay layer bed zsji266 just beneath the ptb should be an important advantage over the gssp because this clay layer approaches to the ptb much in contrast with those two clay layers bed 26 and bed 28 in the gssp therefore the radiometric isotopic da

scale dependent location of hydrothermal vents stress field models and infrared field observations on the fossa cone vulcano island italy article i nfo hydrothermal venting occurs on numerous volcanoes of various age setting topographic and structural expression vent locations are commonly found not within volcanic craters only but predominantly at the crater margins and topographic highs a case example is vulcano island italy where the control on such vent locations along crater margins remained poorly understood however this paper describes numerical models combined with field observations and infrared imaging to explore the mechanisms that control the ascent paths of fluids in the fossa cone on vulcano using finite element modelling we calculate the gravitational stress in the volcanic edifice imposed by the topography results predict hydrofractures to be arranged in radial patterns at depth and in concentric patterns close to the surface furthermore low compressive stress values are found at the rims of the nested craters we compare the stress models to fumarole field data using a forward looking infrared camera we recorded images of the entire cone images were assembled to a mosaic and geocoded providing the first map of a remotely sensed temperature field in high resolution at la fossa the degassing and high temperature anomalies are found to be located mainly at the crests of the craters predominately in the northern and southern sector of the main crater therefore the stress distribution favours and indeed corresponds to the occurrence of fumaroles at la fossa the stress models also yield compression at the bottom of the crater where temperatures are cool thus we consider that the overall distribution of the fumaroles at the fossa cone is controlled by topography additional mechanisms contribute to the exact position of the degassing sites the influence of the lithological control seems to be strong in the southwestern part of the crater where the fumaroles are located 10 20 m below the inner crater rim in bedded strata in the northern part of the crater the exhalation sites can mainly be found at surface fractures and cracks emphasizing the structural control on the location of the fumaroles at this sector of the fossa cone using combined theoretical modelling and field observations this study helps to shed light into the processes directing fluids in volcanic edifices elsewhere and might contribute to the evaluation of upcoming hazard scenarios

fluids in early stage hydrothermal alteration of high sulfidation epithermal systems a view from the vulcano active hydrothermal system aeolian island italy abstract high sulfidation hs epithermal systems have elements in common with passively degassing volcanoes associated with high t acid fumarole fields or acid crater lakes they are considered to form in two stages the first of which involves advanced argillic alteration resulting from intense strongly acidic fluid rock interaction the la fossa hydrothermal system vulcano island represents a classic example of such an active hs system and can be considered as a modern analogue of this early stage of alteration resulting in a core of intense silicic 90 95 pure sio2 alteration surrounded by alunitic alteration zones this paper focuses on a geochemical and stable isotope study of the surficial alteration facies of vulcano particularly the horizon characterized by strong silicic alteration and on deep seated xenoliths ejected during the last eruption of la fossa volcano 1888 90 that can be considered as representative of fragments of the deep conduit system of la fossa volcano using directly measured temperatures at the sites of sampling we have calculated fluid composition in isotopic equilibrium with the alteration products the large range of measured silica 18o 12 3 to 29 reflects the wide range of formation temperatures 80 240 c the fluid compositions calculated for intense silicic alteration vary from 0 9 to 6 5 these are significantly heavier than local meteoric water 6 and are consistent with derivation from the condensation of high temperature fumarolic gases dominated by magmatic fluids and rich in acid gases so2 h2s hcl hf into shallow groundwaters of meteoric origin with dynamically variable ratios of fumarolic steam meteoric water the calculated 18o and d of water in equilibrium with alunite also suggest the mixing of magmatic and meteoric waters for the fluids involved in the genesis of advanced argillic alteration facies the calculated 18o of water in equilibrium with hedenbergitic clinopyroxene found in a veinlet in a metasomatized xenolith is 8 9 this value cannot reasonably result from water rock interaction between the host volcanic rocks and surface water instead it most likely represents a fluid brine exsolved from magma which was responsible for high temperature metasomatism in the deep conduit system

uranium diagenesis in sediments underlying bottom waters with high oxygen content we measured u in sediments both pore waters and solid phase from three locations on the middle atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments en433 1 212 mol c cm2 y oc426 120 10 mol c cm2 y en433 2 33 mol c cm2 y pore water oxygen goes to zero by 1 4 1 5 cm at en433 1 and oc426 and slightly deeper oxygen penetration depths were measured at en433 2 4 cm all of the pore water profiles show removal of u from pore waters calculated pore water fluxes are greatest at en433 1 0 66 0 08 nmol cm2 y and less at en433 2 and oc426 0 24 0 05 and 0 13 0 05 nmol cm2 y respectively solid phase profiles show authigenic u enrichment in sediments from all three locations the average authigenic u concentrations are greater at en433 1 and oc426 5 8 0 7 nmol g and 5 4 0 2 nmol g respectively relative to en433 2 4 1 0 8 nmol g this progression is consistent with their relative ordering of reduction intensity with greatest reducing conditions in sediments from en433 1 less at oc426 and least at en433 2 the authigenic u accumulation rate is largest at en433 1 0 47 0 05 nmol cm2 y but the average among the three sites on the mab is 0 2 nmol cm2 y pore water profiles suggest diffusive fluxes across the sediment water interface that are 1 4 1 7 times greater than authigenic accumulation rates at en433 1 and en433 2 these differences are consistent with oxidation and loss of u from the solid phase via irrigation and or bioturbation which may compromise the sequestration of u in continental margin sediments that underlie bottom waters with high oxygen concentrations previous literature compilations that include data exclusively from locations where o2 bw 150 m suggest compelling correlations between authigenic u accumulation and organic carbon flux to sediments or organic carbon burial rate sediments that underlie waters with high o2 bw have lower authigenic u accumulation rates than would be predicted from relationships developed from results that include locations where o2 bw 150 m

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

kerogen morphology and geochemistry at the permian triassic transition in the meishan section south china implication for paleoenvironmental variation abstract detailed fluorescent microscopic observations and organic geochemical analyses for insoluble sedimentary organic matter kerogens are conducted on the end permian to earliest triassic sediments in the meishan section a of south china the main objectives of the present study are to reconstruct variations of marine and terrestrial environments and to evaluate bulk characteristics of terrestrial input in the palaeo tethys ocean for the permian triassic boundary ptb most of kerogens in the meishan section are mainly composed of marine algae derived amorphous organic matter while terrestrial plant derived amorphous organic matter is remarkably dominant in the mass extinction horizon reported previously the relative abundances of marine organic matter may vary depending on marine production rather than terrestrial input in the palaeo tethys associated with changing terrestrial vegetation we also identified aromatic furans as major compounds in kerogen pyrolysate of all layers it is possible that sources of aromatic furans with alkyl group fungi and lichen proliferated as disaster biota in terrestrial ecosystem through the ptb higher abundances of herbaceous organic matter are observed in the layers above the mass extinction horizon however the conifer biomarker retene can be identified in kerogen pyrolysates of all layers these results imply that the productions of herbaceous plants increased as dominant pioneer biota in early stage of recovery for terrestrial ecosystem after its collapse but also that woody plant potentially continued to be produced in land area throughout the end permian and earliest triassic

volcano flank instability in the lesser antilles arc diversity of scale processes and temporal recurrence 1 the 1997 boxing day collapse a remarkable feature of the ongoing eruption of soufriere hills on montserrat has prompted new interest in the study of volcano stability in the lesser antilles building on a few cases documented in the literature we have now identified at least 47 flank collapse events on volcanoes of the caribbean arc where this type of behavior is characteristic and repetitive about 15 events occurred on active volcanoes within the last 12 000 years in the northern part of the arc flank collapses are repetitive do not exceed 1 km3 in volume occur in all directions and are promoted by intense hydrothermal alteration and well developed fracturing of the summit part of the edifices in contrast infrequent but large sector collapses with volumes up to tens of km3 are typical of the southern volcanoes they are always directed to the west as a result of the high overall slopes of the islands toward the deep back arc grenada basin because caribbean islands are small a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the grenada basin deposits from such submarine flows have been identified during the recent aguadomar and caraval oceanographic cruises and traced to their source structures on land edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential