southern kermadec submarine caldera arc volcanoes sw pacific caldera formation by effusive and pyroclastic eruption abstract three newly identified submarine caldera volcanoes brothers healy and rumble ii west of the southern kermadec arc within water depths 80 and low density 0 3 0 5 g cm 3 erupted pumiceous clasts these observations are interpreted as evidence of subaqueously quenched pyroclastic eruption s sheathed by ambient water flashing to steam discharging some 5 km3 of pyroclastic material from healy volcano caldera collapse is inferred to be penecontemporeous with the pyroclastic eruption s although it is possible formation as an explosive crater occurred but we consider the latter unlikely given the volume of erupted material and water depth extrapolation of these observations to other submarine arcs indicates pyroclastic eruption of silicic magmas and syn eruptive caldera collapse is possible within water depths of 500 1000 m

conodont color and textural alteration an index to regional metamorphism contact metamorphism and hydrothermal alteration experimental and field data are used to extend the utility of conodonts as semi quantitative thermal indices into the regimes of regional and contact metamorphism as well as hydrothermal alteration an arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color alteration indices cai above 300 c that is for cai values of 5 through 8 such cai values occur in very low to medium grade regionally metamorphosed contact metamorphosed and hydrothermally altered rocks the uniformity or variability of cai values within a sample together with conodont texture can help to distinguish grades and environments of metamorphism particularly in metacarbonate sequences induced cai by pyrolysis in a water methane mixture at kbar results in retardation of cai and in a disparate mixture of both low and high cai values within each experimental sample in this system color alteration processes above a cai of 2 to 3 seem to change from predominantly carbonization to predominantly loss of organic matter presumably by oxidation and volatilization of oxides these experiments approximate the type of cai mixture characteristically found in conodonts recovered from hydrothermally altered rocks these data indicate that cai values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

a gravity and volcanostratigraphic interpretation of the lake toba region north sumatra indonesia abstract in northern and central sumatra a wide distribution of ignimbrite and volcanic sediments is observed some geologists consider that these volcanic products were erupted from lake toba the subduction of the indian ocean plate along the trench of central sumatra started at least as long ago as the late miocene fitch s model 1972 obtained the plate convergence vector 67 mm yr decomposed into its components perpendicular 58 mm yr and parallel 34 mm yr to the trench axis tears seaward of the mountain range created the sumatran fault about 2 ma ago at that time the edge of the plate reached a depth of almost 100 km and a large amount of dacite magma was generated the tuk tuk dacite a kind of ignimbrite was erupted along the sumatran fault and covered a broad area the age of this ignimbrite was obtained as 1 9 0 4 ma k arage and 2 0 0 3 ma fission track age since this eruption the hinterland of this fault has been changed to a tensional field forming a graben structure at the northern end of this graben west of harranggaoul the ignimbrite haranggaoul formation was erupted 1 3 0 3 ma ago forming a caldera the lacustrine sediments of samosir island have a normal magnetization and overlie the tuk tuk dacite unconformably from this we can conclude that the graben structure has been covered with water lake toba at 0 7 0 6 ma ago this tectonic movement has continued so that it is difficult to distinguish the caldera structure on the gravity anomaly map of the northern part of lake toba from the results of the gravity survey it can be concluded that at 0 1 ma ignimbrite flowed down along the asahan river and filled the old river along the lowland between parapat and porsea forming a caldera 30 000 years ago dacite and and esite eruptions have occurred around lake toba forming the volcanic cones

long term cycles of triassic climate change a new δ18o record from conodont apatite jat and isw gratefully acknowledge financial support from the australian research council dp1096252 mr is grateful for financial support from progetto d ateneo 2009 cpda090175 09 and 2012 cpda 121100 and prin 2008 2008bef5z7 005

paleogeographic differences in temperature water depth and conodont biofacies during the late devonian the famennian late devonian started after and ended with two of the seven largest crises of the phanerozoic the kellwasser and hangenberg events respectively in between global environmental trends have been identified involving cooling and eustatic regression tropical and subtropical marine faunas were largely cosmopolitan overall this suggests that the famennian was marked by long term environmental changes occurring in a relatively homogeneous manner despite being punctuated by several short term events of limited faunal impact how these trends were modulated according to geographic location is investigated in this study by comparing two continuous outcrops in the montagne noire col des tribes section france and in saxo thuringia buschteich section germany both were located in the subtropical area during this period and belonged to two former microcontinents bracketed between the closing rheic ocean and gondwana sedimentary facies oxygen isotopes and the generic conodont composition biofacies were studied in a high resolution and in the same rock samples sedimentary facies provided an estimate of water depth and oxygen isotopes were used as pa leotemperature proxy conodont biofacies were analyzed using a principal component analysis allowing the expression of the variations in the two outcrops on the same axes and a quantitative comparison with the other proxies sea level and temperature variations were different between the two areas saxo thuringia displayed stable deep and warm conditions throughout in contrast the environment of the montagne noire was shallower and cooler during the late and latest famennian compared to the early and middle famennian congruent with the global change evidenced elsewhere the location of saxo thuringia close to the first point of closure of the rheic ocean might have favored active tectonics causing a local departure from the eustatic trend the stable temperatures at bu during the late and latest famennian may be due to the position of saxo thuringia in the remnant rheic ocean limiting water mass exchange with open seas and favoring the persistence of warm conditions offshore taxa persisted later at high abundance in the saxo thuringian record the two conodont biofacies records were otherwise very comparable this suggests that other factors mitigated the water depth forcing on these conodont assemblages

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

the impacts of land plant evolution on earth s climate and oxygenation state an interdisciplinary review abstract the paleozoic emergence of terrestrial plants has been linked to a stepwise increase in earth s o2 levels and a cooling of earth s climate by drawdown of atmospheric co2 vegetation affects the earth s o2 and co2 levels in multiple ways including preferential organic carbon preservation by decay resistant biopolymers e g lignin and changing the continental weathering regime that governs oceanic nutrient supply and marine biological production over shorter time scales 1 myr land plant evolution is hypothesized to have occasionally enhanced p weathering and fertilized the oceans expanding marine anoxia and causing marine extinctions oceanic anoxia would eventually become limited by oceanic o2 uptake as oxygen accumulates in the atmosphere and surface oceans when excess organic carbon is buried in marine sediments here we review hypotheses and evidence for how the evolving terrestrial ecosystems impacted atmospheric and oceanic o2 and co2 from the ordovician and into the carboniferous 485 298 9 ma five major ecological stages in the terrestrial realm occurred during the prolonged time interval when land was colonized by plants animals and fungi marked by the evolution of 1 non vascular plants 2 vascular plants with lignified tissue 3 plants with shallow roots 4 arborescent and perennial vegetation with deep and complex root systems and 5 seed plants the prediction that land vegetation profoundly impacted the earth system is justified although it is still debated how the individual transitions affected the earth s o2 and co2 levels the geological record preserves multiple lines of indirect evidence for environmental transitions that can help us to reconstruct and quantify global controls on earth s oxygenation and climate state

timing and patterns of the frasnian famennian event evidences from high resolution conodont biostratigraphy and event stratigraphy at the yangdi section guangxi south china abstract continuous centimeter scale sampling for conodonts with microfacies and carbon isotope analysis has been carried out across the frasnian famennian f f transition at the yangdi section guangxi south china the newly revised conodont biostratigraphy reveals a succession of six zones ranging from the upper palmatolepis rhenana zone to lower palmatolepis crepida zone in ascending order based on a detailed analysis of conodont abundance and diversity changes through the section two intervals involving significant conodont faunal changes were recognized in the uppermost palmatolepis linguiformis zone at the yangdi section the first conodont change occurred at the transition between the lower and upper pa linguiformis zone and is marked by the disappearance of pa linguiformis accompanied by the successive disappearances of pa eureka pa rhenana pa nasuta pa gigas ad ioides and ad nodosa the second conodont change appeared in a horizon equivalent to the uppermost upper kellwasser horizon ukh and is indicated by the elimination of nearly all frasnian palmatolepids ancyrodellids and polygnathids furthermore the second conodont change is coincident with the decimation of ostracods and tentaculitids and is synchronous with the turnovers of conodont biofacies in addition the onset of the 13 c carb perturbation is a little earlier than the second conodont change with the maximum amplitude of excursion right at the start of the famennian therefore we conclude that the second conodont change represents the f f mass extinction based on the temporal correlation among 13 c carb excursions pelagic faunal changes and conodont biofacies turnovers during the f f boundary interval according to the high resolution conodont biostratigraphy together with cyclostratigraphy the uppermost ukh and whole ukh contain 1 and 12 bundle cycles respectively thus the time span of the mass extinction and the entire upper kellwasser crisis lasted 16 18 kyr and 200 kyr respectively

constraints imposed by rift inheritance on the compressional reactivation of a hyperextended margin mapping rift domains in the north iberian margin and in the cantabrian mountains the alpine pyrenean cantabrian orogen developed along the plate boundary between iberia and europe involving the inversion of mesozoic hyperextended basins along the southern biscay margin thus this margin represents a natural laboratory to analyze the control of structural rift inheritance on the compressional reactivation of a continental margin with the aim to identify former rift domains and investigate their role during the subsequent compression we performed a structural analysis of the central and western north iberian margin based on the interpretation of seismic reflection profiles and local constraints from drill hole data seismic interpretations and published seismic velocity models enabled the development of crustal thickness maps that helped to constrain further the offshore and onshore segmentation based on all these constraints we present a rift domain map across the central and western north iberian margin as far as the adjacent western cantabrian mountains furthermore we provide a first order description of the margin segmentation resulting from its polyphase tectonic evolution the most striking result is the presence of a hyperthinned domain e g asturian basin along the central continental platform that is bounded to the north by the le danois high interpreted as a rift related continental block separating two distinctive hyperextended domains from the analysis of the rift domain map and the distribution of reactivation structures we conclude that the landward limit of the necking domain and the hyperextended domains respectively guide and localize the compressional overprint the le danois block acted as a local buttress conditioning the inversion of the asturian basin

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

crystallinity and diagenesis of sedimentary apatites the crystallinity of sedimentary apatites was determined by fourier transform infrared spectroscopy ft ir using the splitting of a triply degenerate antisymmetric bending vibration of orthophosphate the crystallinity indices of recent marine apatites are low 3 0 3 6 while those of onland ancient apatites are high 4 5 7 8 indicating post depositional recrystallization the infrared spectra reveal that recrystallization is associated with a decrease in carbonate content substituting for po43 and an increase in fluoride order within the apatite structure the relationship between the crystallinity index and po43 18o suggests alteration of the primary isotopic composition by exchange reactions between po43 oxygens and surrounding waters the monterey samples have a large range of crystallinity index that reflects a set of complex and highly variable diagenetic conditions this demonstrates the use of ft ir criteria for differentiating between pristine and altered apatites and as a consequence for relating geochemical markers to formation or diagenetic environments it is suggested that only those samples that have low crystallinity indices c i 3 8 should be considered as pristine apatite spectra of fish remains indicate that differences in rare earth element ree patterns correspond to variations in crystallinity carbonate content and f order in the apatite lattice the fact that crystallinity is not correlated with geologic age suggests that environmental factors such as accumulation rate and pore water chemistry govern the recrystallization process in general sr content decreases and 18op exhibits high variability with increasing crystallinity

a gravity study of the island of vulcano tyrrhenian sea italy a detailed gravity survey was carried out on the island of vulcano aeolian islands italy gravity was measured on 107 stations and the bouguer anomalies were computed by assuming geological densities

potential field and bathymetric investigation of the monowai volcanic centre kermadec arc implications for caldera formation and volcanic evolution the dynamics of caldera formation are affected by internal factors such as magma chamber structure and properties and regional tectonic stresses understanding their interrelationship is important for assessing volcanic hazard and reconstructing the evolution of a volcano the monowai volcanic centre located at the tonga kermadec arc is a basaltic andesitic submarine stratovolcano and caldera recent surveys have shown that it is active but little is known about its structure and evolution here we present a combined analysis of swath bathymetry and potential field data from monowai acquired during cruise so215 on the r v sonne in 2011 april june the monowai caldera is associated with a 20 25 mgal bouguer gravity anomaly high and a broad positive magnetic anomaly short wavelength magnetic anomalies of up to 1400 and 800 nt are observed along the caldera rim and on the summit of monowai cone inversion of the bouguer gravity anomaly data shows that the caldera high is caused by a buried dense body with density contrast of up to 450 kg m 3 with respect to the surrounding arc crust the body has a volume of 250 km3 and is divided into a main unit extending from 3 to 6 km depth and a shallower ring structure that underlies the rim of monowai caldera we estimate the density of the body to be 2650 2850 kg m 3 suggesting a mafic composition the ring structure is interpreted as set of ring dykes and the main unit as a solidified or partly solidified magma chamber system the monowai pluton the observed magnetic anomalies are consistent with pluton intrusion within the bruhnes magnetic polarity analysis of the swath bathymetry data shows that monowai is located in a 20 km wide graben part of an en echelon left stepping horst and graben system that spans the length of the arc and backarc the monowai caldera is elongated perpendicular to the direction of rifting suggesting that it is affected by the regional stress regime geomorphological analysis suggests that the caldera was created by repeated collapse of a single caldera structure and that its complex shape and multiple ring faults can be attributed to prolonged activity and multiple cycles of inflation and collapse we propose a multiphase evolution of the monowai volcanic centre comprising initial magma emplacement and crustal inflation magma chamber evacuation and caldera collapse caldera resurgence and mass waisting southward migration of the eruptive vent and formation of monowai cone it remains unclear whether the current eruption at the monowai cone is fed directly from a small underlying magma chamber or laterally from the monowai pluton observation of radial fissure ridges on its flanks suggests that a shallow magma body may have been recently emplaced beneath the summit causing inflation and the formation of extensional cracks the summit appears unstable and may be prone to lateral or vertical collapse therefore the region remains a potential source of regional volcanic and tsunami hazard

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

carbon isotope geochemistry of the frasnian famennian transition abstract carbon isotope records for inorganic and total organic carbon toc as well as for individual organic biomarkers show two positive excursions in the late frasnian with comparable shape and amplitude in 13c the positive shifts in 13c can be correlated with the deposition of the kellwasser horizons the inorganic carbon isotope excursions are explained by an enhanced organic carbon burial that is expected to lower the concentration of oceanic dissolved co2 toc 13c values do not exhibit a larger shift than that recorded by inorganic carbon 13c values this is unexpected since a decrease in the dissolved co2 concentration should result in lower carbon isotope fractionation during photosynthesis ep 13c values of presumed algal biomarkers low molecular weight n alkanes pristane phytane although offset by 2 5 exhibit essentially identical records as toc and confirm this unexpected result it is proposed that high atmospheric and oceanic co2 concentrations during the devonian resulted in maximum photosynthetic fractionation any change in the co2 concentration would thus not affect ep as such 13c of primary organic carbon and 13ccarb will exhibit parallel excursions the data imply that carbon isotopes and the relationship between ep and co2 will not be effective to study changes in pco2 levels during the devonian since co2 concentrations were too high

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

size reduction of conodonts indicates high ecological stress during the late frasnian under greenhouse climate conditions in south china abstract the late frasnian mass extinction lfme during extreme greenhouse conditions had a serious impact on biotic evolution herein based on detailed size measurements of 1783 elements of the conodont genera polygnathus and palmatolepis at the lali and duan sections in south china conodont animals underwent significant size reduction at the genus level during the late frasnian the bergmann s rule controlled the evolution of frasnian conodont animals and their size reduction during the late frasnian may have resulted from long term global warming and indicated high ecological stress before the frasnian famennian boundary ffb this phenomenon can explain why the decline of benthic faunas such as corals brachiopods or metazoan reefs predated the extinction of pelagic faunas such as conodonts in the upper kellwasser ukw event and at the ffb

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

conodont biofacies patterns in the kellwasser facies upper frasnian lower famennian of the eastern anti atlas morocco abstract the abundant conodont fauna of a black limestone and shale lithology kellwasser facies of late frasnian early famennian age provides a significant example of environmental control on conodont distribution and abundance conodont collections from the upper gigas and upper crepida zones of the eastern anti atlas were examined biofacies maps for the conodont genera palmatolepis polygnathus icriodus ancyrodella and ancyrognathus were constructed and their facies distribution patterns analysed no significant restriction in conodont distribution was observed to be caused by the rise and extension of oxygen depleted water over the platform during the late frasnian early famennian the abundance of conodonts however appears to have been related to optimal food supply in the oxygenated portion of the water column conodont biofacies patterns observed in the upper devonian of the eastern anti atlas do not fit a simple ecological model involving distance from shore and depth of water the faunas of two intervals investigated exhibit a similar level of species diversity the pattern of which evidently follows the platform basin configuration but the majority of species shows a more or less random distribution the onset of black sediment deposition was characterized by the dominance of polygnathus and icriodus whereas towards its termination during the upper crepida zone time interval the genus palmatolepis clearly predominated this difference is a consequence of both a rise of sea level and of evolutionary changes in the composition of the conodont fauna during the early famennian

event stratigraphic markers within the kellwasser crisis near the frasnian famennian boundary upper devonian in germany abstract short time intervals of anomalous conditions often referred to as global events yield excellent tools for detailed stratigraphic correlations in addition to pronounced effects minor features may be applied for fine scale comparisons of rock sequences these include alternations within a given portion of rock or distinct layers at exactly the same position such marker horizons are often traceable over long distances recognition of these specific markers allows for a more detailed search for possible causes of anomalous events

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

age constraint for an earliest famennian forest and its implications for frasnian famennian boundary in west junggar northwest china abstract as one of the five major extinction events in earth history the frasnian famennian boundary ffb crisis caused dramatic reductions in marine and terrestrial diversity the effects of this event on terrestrial ecosystems are not well understood due to the limited preservation of terrestrial sedimentary rocks and the relative scarcity of plant fossils this study generates a robust zircon u pb age 371 5 0 9 ma earliest famennian for a new fossil assemblage containing lycopsida archaeopteridales and cladoxylopsida from the upper zhulumute formation of the west junggar basin nw china these taxa are typical arborescent plants of the late devonian and represent the oldest known forest in china documenting afforestation in west junggar coevally with or just after the upper kellwasser event 372 ma the new u pb ages generated in this study refine the placement of the ffb in west junggar to within the zhulumute formation instead of the hongguleleng formation as previously thought

record of climate driven morphological changes in 376 ma devonian fossils the lower and upper kellwasser horizons represent two anoxic events that mark the mass extinction at the frasnian famennian f f boundary among other groups conodont animals were severely affected but the genus palmatolepis survived with a complete turnover at the f f boundary here the fine morphological variations of the genus palmatolepis and the sea surface temperature evolution are quantified in two f f boundary sections using morphometrics and oxygen isotopic composition of apatite respectively in accordance with other f f sections the isotope records show two positive excursions of 1 during the lower and upper kellwasser anoxic events the conodont shape and the oxygen isotopic composition of the genus palmatolepis are significantly correlated within the frasnian and famennian stages suggesting a strong environmental influence on the morphology of the feeding apparatus of the conodont animal we propose that the morphological differences are linked to changes in the trophic position of palmatolepis enhanced organic carbon burial which is supported by global positive carbon isotope excursions in inorganic and organic carbon during both the lower and upper kellwasser events altered the primary biomass production and thus the subsequent nutrient supply to higher trophic levels while the carbon and oxygen isotopic shifts are of similar amplitude during lower and upper kellwasser events the variation of the shape of palmatolepis during the upper kellwasser i e the f f boundary is more pronounced than during the lower kellwasser

palaeokarst and its implication for the extinction event at the frasnian famennian boundary guilin south china a prominent palaeokarst within cyclic peritidal strata reported here at the frasnian famennian boundary in guilin southern china displays karren scalloped surfaces dissolution pits and pipes the last contain residual soil terra rossa and are then filled with marine sediment of the overlying strata the features of the palaeokarst depth of pipes and amount of missing strata indicate a significant and long lasting c 50 ka fall of sea level at the end of the frasnian the coincidence of the significant sea level fall with the first stage of the frasnian famennian mass extinction which mostly affected shallow marine and reef dwelling fauna and of the subsequent rapid sea level rise with the second stage of the extinction which mostly affected deeper water organisms reinforces the importance of sea level change in this mass extinction

pulses of enhanced continental weathering associated with multiple late devonian climate perturbations evidence from osmium isotope compositions anomalously high rates of continental weathering have frequently been proposed as a key stimulus for the development of widespread marine anoxia during a number of late devonian environmental and biospheric crises which included a major mass extinction during the frasnian famennian transition marked by the upper and lower kellwasser horizons here this model is investigated by presenting the first stratigraphic record of osmium isotope trends 187os 188os in upper devonian strata from the kowala quarry holy cross mountains poland changes in reconstructed 187os 188os seawater values to more radiogenic compositions are documented at the base of both the lower 0 42 to 0 83 and upper 0 31 to 0 81 kellwasser horizons characteristic of the frasnian famennian transition and additionally within upper famennian shales that record a more minor environmental perturbation known as the annulata event 0 20 to 0 53 these shifts indicate the occurrence of extremely enhanced continental weathering rates at the onsets of the kellwasser crises and during the later annulata event the similarity of 187os 188os values in this study from frasnian famennian boundary and lower famennian strata between 0 4 and 0 5 to those from north american stratigraphic equivalents suggests that the 187os 188os values record global trends these findings support a causal relationship between increased continental weathering and thus nutrient supply to the marine shelf and the environmental perturbations that occurred during numerous late devonian events including both of the biospherically catastrophic kellwasser crises as well as other less severe oceanic anoxic events

the influence of the late devonian kellwasser events on deep water ecosystems evidence from palaeontological and geochemical records from south china abstract the late devonian frasnian famennian f f event consisting of the lower and upper kellwasser events had a severe impact on shallow water ecosystems while the effect on deep water ecosystems is ambiguous in order to recognize the kellwasser events and to evaluate their influences on the deep water ecosystems a newly refined conodont biostratigraphic framework spanning the lower palmatolepis rhenana zone to the pa delicatula platys zone has been established in the nandong section basinal facies guangxi south china the upper devonian lower and upper kellwasser horizons lkh and ukh have been recognized in the deep water facies on the basis of lithological variations biological turnovers and positive carbon isotope 13ccarb excursions the lkh is characterized by the enrichment of marine nektonic communities e g conodonts homoctenids and entomozoacean ostracods whereas the top of the ukh is barren of fossil organisms suggesting that the upper kellwasser event had a more severe effect on nekton than the lower kellwasser event the upper kellwasser uk 13ccarb positive excursion lags behind the enrichment of cu ni mo and v indicating that the uk 13ccarb positive excursion was probably related to elevated primary productivity which induced oxygen depletion in the water column the uk 13ccarb positive excursion peak prior to the f f boundary indicates a more limited effect of riverine influx on the deep water setting which suggests that the regional palaeogeographic configuration played an important role in the carbon cycle

modelling of the oxygen isotope evolution of seawater implications for the climate interpretation of the δ18o of marine sediments it is often argued that the 18o value of oceanic water was maintained close to 0 for hundreds of millions of years as a consequence of oxygen isotope exchange between oceanic crust and seawater however for several decades the interpretation of the biosedimentary oxygen isotope record has conflicted with the igneous record because with increasing age a general trend of decreasing 18o values about 6 is observed in most carbonates cherts and phosphates especially for the paleozoic and early mesozoic we developed a dynamical model of seawater crust interaction that computes the 18o value in these two reservoirs as function of time this model takes into account the continuous production of crust at oceanic ridges its expansion rate the permeability profile with space and time the mineralogical mode of the crust and the kinetics of oxygen isotope exchange between rock forming minerals and seawater the model indicates that the 18o value of seawater may vary by 2 with a time response ranging from 5 to 50 ma for expansion rates of 1 to 10 cm a 1 the variation of 2 is fixed by both integrated water rock ratio and closure time of the seawater crust system by sediments variations in the oxygen isotope ratio of seawater through time have important implications for the interpretation of the systematically low 18o values of pre jurassic marine sediments according to our model marine paleotemperatures could be up to 10 c lower than those expected when applying the classical hypothesis of an ice free ocean with a 18o value of 1

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

the late devonian frasnian famennian event in south china patterns and causes of extinctions sea level changes and isotope variations abstract the frasnian famennian f f event may be recognized in various facies areas in south china in the pelagic cherty basin facies both lower and upper kellwasser events can seemingly be recognized in the deeper water carbonate facies the f f event level is well controlled in light of conodont biostratigraphy in the shallow water carbonate and mixed carbonate shale facies the f f boundary may be defined by clear taxonomic distinction in benthic fossils articulate brachiopods and corals as well as evidence from minor pelagic fossils post extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups in open shallow water platform to inter platform depression areas brachiopods seem to recover quickly probably in the middle pa triangularis zone benthic ostracodes seem to recover at a later stage recovery of rugose corals did not happen until the uppermost famennian three steps of the f f mass extinction are postulated 1 extinction of diverse brachiopods including most atrypids 2 extinction of pelagic conodonts 3 extinction of both benthic faunas very abundant and diverse rugose corals and ostracodes and pelagic conodonts evidence of an end frasnian regression in south china is clear particularly in shallow water settings however in deeper water settings the picture is complicated with evidence of both sea level rise and fall in the latest frasnian it may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic hydrothermal activities may have mainly caused frequent and rapid climatically warming cooling alterations and sea level changes as well as marine ecologic collapse eutrophication microbial blooming seawater acidification and anoxia which may explain the f f extinction pattern in south china

did climate changes trigger the late devonian kellwasser crisis evidence from a high resolution conodont δ18opo4 record from south china abstract the impact of climate change on biodiversity has been the focus of studies on the phanerozoic biotic crises however it is still controversial whether climate change has caused the frasnian famennian f f biotic crisis since there is no unequivocal view on the global climate change during this critical period in order to reconstruct palaeotemperatures during the f f transition in south china eastern palaeotethys a high resolution oxygen isotope 18 o po 4 record was obtained based on 104 measurements of conodont apatite from the yangdi section the oxygen isotope record based on mono generic samples reveals an increase in 18 o po 4 by 0 7 in the lower kellwasser horizon lkh and 1 4 in the upper kellwasser horizon ukh translating into low latitude surface water cooling of 3 c and 6 c respectively these two 18 o po 4 shifts agree well with the time equivalent 18 o po 4 records from the western palaeotethys suggesting that two climate cooling pulses in conjunction with the deposition of the kellwasser horizons are a global signal during the f f transition the positive shift of 18 o po 4 coincides with positive excursion in carbon isotope of carbonates 13 c carb in the ukh indicating that enhanced burial of organic carbon resulted in a drop in atmospheric p co 2 and thus global climate cooling cooling started immediately before the upper kellwasser biotic crisis with the lowest temperature documented at the top of the ukh climate cooling during the deposition of the lkh is observed in conjunction with the sharp decline in metazoan reefs the coincidence of cooling and the kellwasser biotic crisis suggests that global cooling played a major role in the collapse of ecosystems

orbital cyclostratigraphy of the devonian frasnian famennian transition in south china abstract superbundlesets bundlesets bundles and laminae were formed in the carbonate successions of the devonian frasnian famennian transition in guangxi south china their hierarchical structures ratio relationships and arrangement order within conodont zones are lasting and stable in the stratigraphical sequences and can be traced across the different facies belts and sedimentary basins the hierarchically organized superbundlesets bundlesets bundles and laminae correspond to a long eccentricity eccentricity obliquity and precession and sub milankovitch cyclothem respectively the ratio of long eccentricity to eccentricity is 1 4 below the boundary between frasnian famennian and 1 3 above the boundary between frasnian famennian eccentricity to obliquity is 1 3 and eccentricity to precession is 1 6 in the devonian since the eccentricity periodicity of 100 000 years remains essentially steady through geological time the periodicity of the long eccentricity obliquity precession and sub milankovitch cycle was 400 000 33 333 16 667 and 8000 or 17 000 years these ratios are different from those of the permian cretaceous and quaternary and coincide well with those calculated theoretically by berger et al science 255 1992 560 this reinforces the hypothesis of the slowing of the earth s rotation and the lengthening of precession and obliquity periods since at least the devonian time on the basis of the hierarchical milankovitch cyclothems the chronostratigraphical subdivision and correlation of the frasnian famennian transition can be made at the resolution of 100 000s and 10 000s of years the duration of the upper rhenana zone linguiformis zone and lower middle and upper triangularis zone is 0 6 0 8 0 3 0 3 and 0 3 ma respectively

late devonian tetrapod habitats indicated by palaeosols in pennsylvania abstract late devonian famennian tetrapods from the duncannon member of the catskill formation near hyner pennsylvania usa have been found within palaeosols that offer a new line of evidence for their ancient environments hyner has yielded at least two fossil tetrapod species hynerpeton basseti and densignathus rowei subhumid vertisol palaeosols and semiarid aridisol palaeosols alternate at hyner as in other catskill formation sedimentary cycles attributed to milankovitch eccentricity periods 100 ka tetrapods were found in palaeosols of subhumid not semiarid phases of 100 ka palaeoclimate cycles in addition palaeosols at hyner record an unusually warm and wet climatic episode compared with other palaeosols of the catskill formation and correlated with the european annulata black shale event tetrapod bones are cracked and disarticulated in red palaeosols of an oxbow lake margin as if victims of dry season death decay and subaerial weathering vegetation choked swales and floodplains would have afforded shelter from 3 4 m long predatory fish hyneria lindae of open water and offered food of large dead fish small live fish arachnids myriapods and scorpions if these early tetrapods lived on land at all it was during wet seasons of feeding and breeding rather than fatally dry seasons supplementary material chemical data are available at http www geolsoc org uk sup18373

a high resolution middle to late permian paleotemperature curve reconstructed using oxygen isotopes of well preserved brachiopod shells abstract climatic warming has been widely cited as a driver for many mass extinction events in earth history including the middle late permian guadalupian lopingian boundary glb mass extinction and end permian mass extinction epme investigated in this study however the role of warming in driving the epme event is under debate because current paleotemperature studies indicate the rapid increase in sea surface temperature postdate the onset of the epme event and a reliable paleotemperature record across the glb event is lacking here we present a high resolution and successive 18 o record using low mg calcite shells of brachiopods blmcs from a single stratigraphic section in central china to reconstruct paleotemperature changes from the middle to the latest permian after a rigorous screening for diagenesis our data show a 1 0 decrease in 18 ocalcite and thus climatic warming during the middle capitanian followed by a gradual 2 0 increase climatic cooling during the late wuchiapingian from the latest wuchiapingian to the early changhsingian 18 o decreased gradually and reached the lowest values of 4 0 and thus rapid climatic warming immediately before the permian triassic boundary the two warming events are coeval with the onset of the emeishan large igneous province and the siberian traps large igneous province respectively suggesting the two volcanic events are the plausible drivers of these climatic warming events a close comparison of paleontological and geochemical records indicates that the warming events occurred predate the glb and epme events this is in contrast with conodont 18 oapatite data which document the rapid climatic warming lagged the onset of the extinction event the comparison between 18 o of blmcs and 18 o of conodonts from the same section shows that the long term trends are similar but at higher temporal resolution discrepancies are present entailing further investigation in the near future our study confirms that 18 o of the brachiopod shells underwent important changes during the end of paleozoic highlighting that sea surface temperature is a key factor to understand the biosphere history since it changes simultaneously with the biological crises and that blmcs are invaluable archive for tracking physical and chemical conditions of past oceans

squeesar and gps ground deformation monitoring of santorini volcano 1992 2012 tectonic implications abstract the santorini volcanic complex svc has been in a dormant state for the last 60 years until january 2011 when upward influx of magma reawakened the volcano with intense radial ground deformation and inter caldera seismicity that lasted until january 2012 but declined afterwards this paper aims to study the ground deformation and the inferred tectonic implications of the svc for the period 1992 2012 mainly based on the squeesar technique and dgps campaign results of our local network which incorporates available data on internet from several continuous gps stations established on the island the spatial deformation of the svc during the quiet period 1992 2010 was deduced by joint analysis of ers1 and 2 and envisat it was found that the intra caldera palaea kammeni shield volcano was being uplifted 2 3 mm yr with increasing rate whilst the adjacent nea kammeni shield volcano was being subsided up to 6 mm yr with increasing rate the rest of the svc showed a velocity field varying from 1 to 2 mm yr indicating a rather linear deformation during that period the results from the gps network are in full agreement with the squeesar results based on the results of squeesar analysis of 12 envisat images and dgps cgps data to end 2012 the deformation for the unrest period 2011 2012 was non linear being characterized by strong radial deformation in the northern part of the caldera 50 120 mm yr and accelerating values 130 mm yr 2 combined gps squeesar mogi modeling indicated a source located north of nea kammeni at a shallow depth however a progressively decreasing rate in deformation was noted at most gps cgps station components after january 2012 indicating magma settlement consistent with the constantly decreasing rate of the inter caldera seismicity the faulting features seem to have a key role in the evolution of the deformation which continues up the end 2012 but at a very low level

temperatures and oxygen isotopic composition of phanerozoic oceans abstract the temperature of ancient oceans is an important constraint for understanding the climate history of our planet the classical oxygen isotope paleothermometry on fossil shells while very proficient when applied to the younger cenozoic portion of the geologic record is believed to yield only unreliable results for the phanerozoic deep time either because the empirically well documented secular trend to more negative 18 o values with increasing age was generated by post depositional recrystallization processes or if primary implies ecologically unpalatable hot early oceans here we present a compilation of 18 o measurements for 58 532 low mg calcite marine shells that cover almost the entire phanerozoic eon argue that the secular decline of about 6 is primary propose that it reflects the changing oxygen isotopic composition of sea water and define a new baseline trend for 18 o of paleo sea water the latter providing a new template for calculation of ambient habitat temperatures of fossil specimens the resulting pattern for fossil taxa foraminifera brachiopods belemnites and bivalves mimics their modern counterparts in temperature ranges and modes this conceptual framework enables application of actualistic concepts to ambient habitat temperatures of fossils and provides us with a long overdue tool for interpretation of deep time geologic history

temperature evolution and the oxygen isotope composition of phanerozoic oceans from carbonate clumped isotope thermometry abstract surface temperature is among the most important parameters describing planetary climate and habitability and yet there remains considerable debate about the temperature evolution of the earth s oceans during the phanerozoic eon 541 million years ago to present the time during which complex metazoan life radiated on earth here we critically assess the emerging record of phanerozoic ocean temperatures based on carbonate clumped isotope thermometry of fossil brachiopod and mollusk shells and we present new data that fill important gaps in the late paleozoic record we evaluate and reject the hypothesis that solid state reordering of 13c 18o bonds has destroyed the primary clumped isotope temperature signal of most fossils during sedimentary burial at elevated temperatures the resulting phanerozoic record which shows a general coupling between tropical seawater temperatures and atmospheric carbon dioxide co2 levels since the paleozoic indicates that tropical temperatures during the icehouse climate of the carboniferous period were broadly similar to present 25 30 c and suggests that benthic metazoans were able to thrive at temperatures of 35 40 c during intervals of the early and possibly the latest paleozoic when co2 levels were likely 5 10 higher than present day values equally important there is no resolvable trend in seawater oxygen isotope ratios 18 o over the past 500 million years indicating that the average temperature of oxygen exchange between seawater and the oceanic crust has been high 270 c since at least the early paleozoic which points to mid ocean ridges as the dominant locus of water rock interaction over the past half billion years

gravity model studies of newberry volcano oregon newberry volcano a large quaternary volcano located about 60 km east of the axis of the high cascades volcanoes in central oregon has a coincident positive residual gravity anomaly of about 12 mgals model calculations of the gravity anomaly field suggest that the volcano is underlain by an intrusive complex of mafic composition of about 20 km diameter and 2 km thickness at depths above 4 km below sea level however uplifted basement in a northwest trending ridge may form part of the underlying excess mass thus reducing the volume of the subvolcanic intrusive a ring dike of mafic composition is inferred to intrude to near surface levels along the caldera ring fractures and low density fill of the caldera floor probably has a thickness of 0 7 0 9 km the gravity anomaly attributable to the volcano is reduced to the east across a north northwest trending gravity anomaly gradient through newberry caldera and suggests that normal perhaps extensional faulting has occurred subsequent to caldera formation and may have controlled the location of some late stage basaltic and rhyolitic eruptions significant amounts of felsic intrusive material may exist above the mafic intrusive zone but cannot be resolved by the gravity data

elliptical calderas in active tectonic settings an experimental approach abstract caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber many field theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults in the simplest theoretical scenario circular magma chambers produce circular calderas many calderas however are elliptical in shape particularly those in extensional and compressive tectonic settings several factors may explain elliptical calderas the first is the presence of an elliptical magma chamber established by for instance preferential intrusion along pre existing basement structures or differential spalling of the magma chamber walls the second is the overlap nesting of several discrete calderas to form a single larger elliptical structure the third is asymmetric subsidence the fourth is variable pre collapse topography a fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation a sixth factor is the post collapse distortion of the caldera structure due to continued regional deformation to better understand relationships between caldera surface expression reservoir geometry and regional tectonic stresses we conducted scaled analogue experiments these experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs circular rubber balloons of known dimensions and depths the results show that in principle calderas produced in compression extension experiments are elongated parallel to the direction of minimum horizontal compressive stress despite the chamber beneath being circular in plan view as a consequence model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress to shallower dips where striking parallel to the minimum horizontal regional compressive stress this leads us to suggest that the influence of a regional stress field on caldera fault orientation during and or after caldera formation may be significant in the development of elliptical calderas in addition such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

rapid rates of growth and collapse of monowai submarine volcano in the kermadec arc most of earth s volcanoes are under water as a result of their relative inaccessibility little is known of the structure and evolution of submarine volcanoes advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing here we report the results of a bathymetric survey of monowai submarine volcano in the tonga kermadec arc which we mapped twice within 14 days we found marked differences in bathymetry between the two surveys including an increase in seafloor depth up to 18 8 m and a decrease in depth up to 71 9 m we attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows hydroacoustic t wave data reveal a 5 day long swarm of seismic events with unusually high amplitude between the surveys which directly link the depth changes to explosive activity at the volcano the collapse and growth rates implied by our data are extremely high compared with measured long term growth rates of the volcano demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor

conodont sr ca and δ18o record seawater changes at the frasnian famennian boundary abstract the oxygen isotopic composition 18 o p and strontium calcium sr ca p ratios have been measured in late devonian conodonts palmatolepis sp from contemporaneous sections at coumiac france and m rirt morocco the sequences encompass two anoxic horizons the lower kellwasser lkw and upper kellwasser ukw events with the top of the ukw coinciding with the mass extinction at the frasnian famennian boundary the genus palmatolepis survived the faunal crisis but exhibited plastic responses to the environmental changes which are recorded in the evolution of shape during the anoxic events the present study demonstrates that shape 18 o p and sr ca p values of conodonts are correlated in both localities excluding diagenesis as the driving process for the measured 18 o p and sr ca p values the conodonts 18 o p and sr ca p values are correlated in both localities and distributed into either a pre crisis and crisis group using the relationships between the 18 o p and sr ca p values we estimate that the variation of the seawater sr ca ratio during the frasnian famennian mass extinction was of about 20 its initial value this drastic decrease of the seawater sr ca ratio is discussed in the light of the reef demise that occurred during the faunal crisis

seismic stratigraphy of the central tonga ridge abstract seismic stratigraphic analyses of single and multichannel seismic reflection profiles from the central part of the tonga arc system sw pacific are used to interpret its geological evolution on the central tonga ridge a high standing part of the frontal arc as defined by karig 1970 and its flanks between 18 s and 22 s we identify and map six seismic sequences overlying inferred lower middle eocene volcanic acoustic basement available island sections and boreholes along with seismic facies suggest that the upper eocene to upper miocene stratigraphic succession on the central tonga ridge consists of volcaniclastic turbidites and hemipelagic sediments in contrast carbonate deposition predominates from the early pliocene to the present we interpret major hiatuses during the early oligocene early miocene and early pliocene based upon the available seismic data and previous results we infer that the extreme eastern tofua trough a partially filled basin that now separates the central tonga ridge from the tofua ridge the modern volcanic arc may be the site of latest eocene or oligocene extension which may be related to rifting and back arc spreading in the south fiji basin to the west another late miocene or early pliocene phase of rifting deformed strata deposited in the palaeogene basin and led to creation of at least part of the modern tofua trough available evidence suggests that the neogene extension is related to initiation of sea floor spreading in the lau basin widespread carbonate deposition beginning in the early pliocene suggests a decrease of volcanic activity in the vicinity of the central tonga ridge an apparent n s migration of miocene and younger depocentres may be related to sequential uplift of parts of the central tonga ridge in response to progressive southward subduction of the louisville ridge at the tonga trench

thermal excursions in the ocean at the cretaceous tertiary boundary northern morocco δ18o record of phosphatic fish debris c lecuyer p grandjean j r o neil h cappetta and f martineau 1993 thermal excursions in the ocean at the cretaceous tertiary boundary northern morocco c lso record of phosphatic fish debris palaeogeogr palaeoclimatol palaeoecol 105 235 243 high precision oxygen isotope analyses were made of phosphate extracted from 17 samples of nektonic and benthic fish debris sampled across the stratigraphic cretaceous tertiary boundary in northern morocco a refinement of the silver phosphate method was used to isolate phosphate from biogenic materials measured 180 values of 18 6 20 5 o are interpreted as reflecting high resolution thermal variations that affected the ocean water column of the western tethys the warm 27 c water masses that characterized maastrichtian times underwent rapid cooling and stabilized at an average temperature of 19 c during the dano montian and thanetian this period of constant and cool temperature was followed by a relatively rapid but more gradual warming to about 25 c achieved in the middle ypresian significant small shifts in 6180 values between nektonic and benthic fauna recorded only during the stages of rapid warming or cooling may correspond to averaged thermal differences within the water column that developed in response to global climatic changes the indicated temperature distribution could have been caused by thermal changes in the atmosphere rather than some signal carried by deep ocean currents the oxygen isotope data coupled with previous measurements of ree and end ti on the same samples support the suggestion that paleo pacific westward currents progressed as far as the northwestern part of the african platform at the end of the cretaceous period

evidence of wildfires and elevated atmospheric oxygen at the frasnian famennian boundary in new york usa implications for the late devonian mass extinction the devonian period experienced significant fluctuations of atmospheric oxygen o2 levels 25 13 for which the extent and timing are debated also characteristic of the devonian period at the frasnian famennian f f boundary is one of the big five mass extinction events of the phanerozoic fossilized charcoal inertinite provides a record of wildfire events which in turn can provide insight into the evolution of terrestrial ecosystems and the atmospheric composition here we report organic petrology programmed pyrolysis analysis major and trace element analyses and initial osmium isotope osi stratigraphy from five sections of upper devonian f f interval from western new york usa these data are discussed to infer evidence of a wildfire event at the f f boundary based on the evidence for a wildfire at the f f boundary we also provide an estimate of atmospheric o2 levels of 23 25 at this interval which is in agreement with the models that predict elevated po2 levels during the late devonian this coupled with our os isotope records support the currently published osi data that lacks any evidence for an extra terrestrial impact or volcanic event at the f f interval and therefore to act as a trigger for the f f mass extinction the elevated o2 level at the f f interval inferred from this study supports the hypothesis that pco2 drawdown and associated climate cooling may have acted as a driving mechanism of the f f mass extinction