early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

q of the indian shield we analyze spectral attenuation of lg waves to determine q of the indian shield the dataset consists of four earthquakes recorded in the distance range of 240 2400 km the new estimate q f 800f 0 42 0 1 hz f 20 hz is based on a larger dataset than a previous estimate q f 508f 0 48 1 hz f 20 hz the new q f of the indian shield is comparable to the q in regions of eastern north america where its value is relatively high for example the adirondack mountains it is also in agreement with previously reported lg coda q at f 1 hz for the indian subcontinent the revised q f has important implications for the estimation of ground motions in the indian shield region using the stochastic method since the recorded data presently come mostly from large distances

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

transverse tectonics in the sikkim himalaya evidence from seismicity and focal mechanism data abstract in the present study about 356 local earthquakes in the region of the sikkim himalaya have been accurately located and analyzed using 2181 p travel times and 2161 s travel times from a network of 11 broadband seismic stations operated by the national geophysical research institute during january 2006 to november 2007 further refinement of the hypocentral parameters using the hypodd relocation program resulted in 198 well constrained locations interestingly this study reveals several characteristic features that distinguish sikkim from the rest of the himalaya the seismicity distribution is found to be confined mostly between the main boundary thrust mbt and the main central thrust mct but not quite associated with either while the entire himalayan front is generally characterized by shallow angle thrust faulting focal mechanisms in this region are predominantly of strike slip type in conformity with a right lateral strike slip mechanism along the northwest trending tista and gangtok lineaments the p axis trends of earthquake focal mechanisms are clearly oriented north northwest marking a clear transition from the ambient north northeast trending direction of indian plate motion with respect to the eurasian plate all along the himalayan front moderate sized earthquakes occur down to 70 km depth in this region compared to an average focal depth of 15 20 km in the rest of the himalaya also a high average crustal p velocity of 6 66 km sec and a fairly low b value of 0 83 0 04 are obtained indicating the probability of occurrence of a higher magnitude earthquake in the future a north south section in the sikkim region shows a relatively flat topography unlike in the rest of the himalayan mountain chain and suggestive of lower rates of convergence in the recent geologic past it is proposed that crustal shortening in the sikkim himalaya has been substantially accommodated by transverse tectonics rather than underthrusting in recent times

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

correlation of basinal carbonate cycles to nearshore parasequences in the late cretaceous greenhorn seaway western interior u s a upper cretaceous limestone shale couplets developed within the late transgressive stage of the greenhorn cyclothem may be correlated from carbonate dominated basinal sequences in central kansas and colorado westward to clastic cycles in southern utah six such basinal couplets have been traced to corresponding upward coarsening progradational cycles developed on the western margin of the western interior basin in the central basin in colorado and kansas these sedimentary cycles are represented by limestone shale and marlstone shale couplets 0 5 1 0 m in thickness more calcareous parts of these couplets may be correlated westward into condensed fossiliferous concretion and shell beds in proximal offshore lithofacies of arizona and utah these concretion and shell beds are physically traceable farther landward westward into bioturbated fossil rich transgressive lag deposits that bound 10 to 20 m thick coarsening upward progradational strand plain deposits parasequences in southwestern utah thus the progra dational phase of parasequence deposition correlates with accumulation of clay rich sediment in the central basin and the transgressive phase is characterized by reduced terrigenous input and deposition of carbonate rich sediment we consider milankovitch style orbital forcing of climate and tectonically induced fluctuations in rates of foredeep basin subsidence as possible forcing mechanisms for these basinwide events based on the widespread distribution of the limestone shale couplets as well as on estimated sedimentation rates and geochronology it has been widely speculated that these carbonate cycles reflect milankovitch cycles with periodicities on the order of 20 k y to 100 k y if so then stratigraphic data suggest that orbital forcing of climate affected eustasy and or sediment input and biogenic production in the western interior basin alternatively thrusting events in the sevier orogenic belt may have produced episodic changes in the rates of foredeep basin subsidence and consequent changes in base level which could have controlled the deposition of the greenhorn parasequences and carbonate cycles in either case correlation of these units demonstrates a consistent basinwide sedimentary response to high frequency base level or sediment input changes in the western interior epicontinental basin

sedimentary mercury enrichments as a marker for submarine large igneous province volcanism evidence from the mid cenomanian event and oceanic anoxic event 2 late cretaceous oceanic anoxic event 2 oae 2 during the cenomanian turonian transition 94 ma was the largest perturbation of the global carbon cycle in the mid cretaceous and can be recognized by a positive carbon isotope excursion in sedimentary strata although oae 2 has been linked to large scale volcanism several large igneous provinces lips were active at this time e g caribbean high arctic madagascan ontong java and little clear evidence links oae 2 to a specific lip the mid cenomanian event mce 96 ma identified by a small 1 positive carbon isotope excursion is often referred to as a prelude to oae 2 however no underlying cause has yet been demonstrated and its relationship to oae 2 is poorly constrained here we report sedimentary mercury hg concentration data from four sites three from the southern margin of the western interior seaway and one from demerara rise in the equatorial proto north atlantic ocean we find that in both areas increases in mercury concentrations and hg toc ratios coincide with the mce and the oae 2 however the increases found in these sites are of a lower magnitude than those found in records of many other mesozoic events possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events combined the new mercury data presented here are consistent with an initial magmatic pulse at the time of the mce with a second greater pulse at the onset of oae 2 possibly related to the emplacement of lips in the pacific ocean and or the high arctic

s wave attenuation and site effects in the region of friuli italy we used strong motion records from the 1976 friuli earthquake m 6 4 and 10 of the biggest aftershocks recorded by the national accelerograph network of the electrical power company of italy to estimate the quality factor q of s waves in this region the wide distance range of the recordings 10 r 190 km permits us to analyze the spectral amplitude decay of the records using a nonparametric approach e g anderson and quaas 1988 castro et al 1990 anderson 1991 we obtained attenuation functions for a set of 18 frequencies ranging between 0 4 and 25 0 hz the values of q retrieved from the attenuation functions obtained follow the frequency dependent relation q 20 4f a test of the method was made using a second data set consisting of digital seismograms from the friuli venezia giulia seismograph network in spite of the different size of the volume sampled by these data 10 r 131 km the frequency dependence of q obtained q 16 1f0 92 is similar to that obtained with the strong motion data set the near surface attenuation was also estimated using the model proposed by anderson and hough 1984 and anderson 1991 we found that 0 is smaller for the strong motion stations located on rock compared to stations located on either shallow or soft sediments to estimate the site response of the strong motion stations we corrected the spectral records for the attenuation effect and then inverted the corrected records to separate source and site effects using the inversion scheme proposed by andrews 1986 to verify the site amplification estimates obtained we also calculated the transfer function of each site using nakamura s 1989 method for s wave e g lermo and chavez garcia 1993 in general the shapes of the site functions obtained with the inversion are consistent with the transfer functions obtained calculating the horizontal to vertical component ratio

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

stomatal proxy record of co2 concentrations from the last termination suggests an important role for co2 at climate change transitions a new stomatal proxy based record of co2 concentrations co2 based on betula nana dwarf birch leaves from the hasseldala port sedimentary sequence in south eastern sweden is presented the record is of high chronological resolution and spans most of greenland interstadial 1 gi 1a to 1c allerod pollen zone greenland stadial 1 gs 1 younger dryas pollen zone and the very beginning of the holocene preboreal pollen zone the record clearly demonstrates that i co2 were significantly higher than usually reported for the last termination and ii the overall pattern of co2 evolution through the studied time period is fairly dynamic with significant abrupt fluctuations in co2 when the climate moved from interstadial to stadial state and vice versa a new loss on ignition chemical record used here as a proxy for temperature lends independent support to the hasseldala port co2 record the large amplitude fluctuations around the climate change transitions may indicate unstable climates and that tippingpoint situations were involved in last termination climate evolution the scenario presented here is in contrast to co2 records reconstructed from air bubbles trapped in ice which indicate lower concentrations and a gradual linear increase of co2 through time the prevalent explanation for the main climate forcer during the last termination being ocean circulation patterns needs to re examined and a larger role for atmospheric co2 considered

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

geophysical evidence for post miocene rotation of the island of viti levu fiji and its relationship to the tectonic development of the north fiji basin geophysical studies of the island of viti levu fiji show largeamplitude magnetic anomalies of up to 1500 nt to be located above the tavua volcanic center field sampling of the volcanic rocks from the intrusive and extrusive centers of the volcano show the rock samples to have initial intensities of natural remanent magnetization of up to 380 a m radiometric dating of fifteen oriented samples show an age range of 2 9 to 7 0 m y b p for the suite of rocks collected from the mba basaltic group paleomagnetic analysis of the dated rocksshows declination vectors ranging from 325 9 for an age of 2 9 0 2 m y b p to 290 4 for an age of 7 0 0 4 m y b p as a group the paleomagnetic declination values of the samples systematically decrease with age this decrease is attributed to progressive anticlockwise rotation of viti levu during the process of formation of the north fiji basin a linear least squares analysis of the paleomagnetic data indicates that the island has rotated in an anticlockwise direction through 90 during the past 7 m y at a rate of 13 7 per million years declination values as low as 245 measured for some sites not dated suggest that anticlockwise rotation of viti levu and development of the north fiji basin could have commenced as early as 10 m y b p following the breakup of the ancient solomons new hebrides fiji lau island arc large rotations of microplates may have occurred along other island arcs and marginal basin systems elsewhere in the western pacific and such rotational histories may reflect in detail the evolutionary development of these arcs and basins

a new proxy for cretaceous paleoceanographic and paleoclimatic reconstructions coiling direction changes in the planktonic foraminifera muricohedbergella delrioensis among some modern and recent fossil species of planktonic foraminifera the proportion of left to right coiled shells in a population appears to be temperature dependent the relative abundance of each morphotype reflecting ecological preferences a similar relationship is identified among muricohedbergella delrioensis carsey 1926 at the cenomanian turonian stage boundary in mid latitude sites of the western interior seaway including the pueblo type section the increase of sinistral m delrioensis in the assemblage is related to higher 18 o carb values and decrease in inner porosity which suggests that changes in the coiling direction in this morphospecies could represent a new proxy for constraining sea surface temperature sst variations as surface dwellers muricohedbergellids were not accepted manuscript 2 affected by oceanic anoxic event oae2 and provide a continuous paleoclimatic signal throughout the cenomanian turonian boundary interval furthermore genetic evidence obtained from extant foraminifera indicates that shifts of coiling ratios in planktonic foraminifera species can express the signature of distinct genetic types which are revealed through their opposite coiling directions coiling direction could be a genetic trait implying that cryptic species may occur in the mesozoic

basalt seawater interaction the plenus cold event enhanced weathering and geochemical change deconstructing oceanic anoxic event 2 cenomanian turonian late cretaceous oceanic anoxic event 2 cenomanian turonian ca 94 ma represents a major palaeoceanographic phenomenon that took place during an interval of extreme global warmth when large amounts of organic matter entered the marine burial record probably triggered by increased availability of nutrients for planktonic biota three sections eastbourne sussex uk raia del pedale campania italy and tarfaya morocco recording this event illustrate the influence on marine geochemistry of mafic volcanic rock seawater interaction anoxia to euxinia and re oxygenation and cooling during the so called plenus cold event the eastbourne section represents the organic lean epicontinental pelagic deposits of the english chalk the raia del pedale section represents a shallow water platform carbonate on the tethyan continental margin also largely devoid of organic matter and the tarfaya core represents an atlantic margin site where cyclically bedded organic rich sediments were well developed correlation between all three sections is readily achieved by biostratigraphy and carbon isotope stratigraphy 13ccarb and 13corg over the oceanic anoxic event 2 interval represented by a characteristic broad positive carbon isotope excursion the stratigraphic range of the plenus cold event defined by the presence in two discrete levels of boreal fauna and an excursion to heavier oxygen isotope values in the english chalk can be identified in raia del pedale and tarfaya by using the carbon isotope curve as a correlative tool similarly a section in southern france allows its co existing osmium isotope excursion to relatively unradiogenic values to be placed in the context of the oceanic anoxic event in all three analysed sections a fall to lower osmium isotope values clearly pre dated the onset of oceanic anoxic event 2 as defined by the initial rise in carbon isotope values allowing the putative magmatic mafic event as a trigger for the oceanic anoxic event an initial drop in sulphur isotope ratios 34scas at eastbourne correlates with the osmium isotope curve suggesting that isotopically light sulphur could have been derived from a mafic igneous source re oxygenation of sediments of all three investigated sections during the plenus cold event is variably illustrated by change in cerium calcium iodine calcium molybedenum calcium and uranium calcium ratios according to the redox behaviour of the elements in question and whether controls on seawater chemistry were local or global in nature changes in molybdenum isotope ratios from tarfaya and portions of the sulphur isotope curve from eastbourne and raia del pedale also indicate the probable presence of more oxygen rich bottom waters during the plenus cold event oxidation by such waters of previously deposited organic rich shales as well as loss of anoxic euxinic sinks is credited with temporarily enriching global seawater in a range of other redox sensitive trace metals for example v cr co ni cu zn and cd during ongoing basalt seawater interaction indicated by persistent relatively non radiogenic osmium isotope seawater values however early diagenetic enrichment of manganese in the english chalk over much of the oceanic anoxic event interval is broadly correlative in time with relatively low osmium isotope values in sections elsewhere a relationship that may be due to the lack of affinity of manganese with carbon rich shales hence allowing relatively elevated concentrations of the element in marine waters to persist during leaching of mafic rocks unlike other redox sensitive species the calcium isotope and lithium isotope ratios from eastbourne and raia del pedale indicate an increase in global weathering during the initial phase of oceanic anoxic event 2 and the shift in strontium isotopes and osmium isotopes to more unradiogenic values during the event suggests that not only construction but also destruction of one or more large igneous provinces was probably a proximal cause of this major palaeoceanographic phenomenon by elevating nutrient levels and planktonic productivity in large tracts of the world ocean globally widespread carbon burial and silicate weathering are both identified as important mechanisms for drawing down atmospheric carbon dioxide that in the absence of overwhelming volcanogenic replenishment of this greenhouse gas during the early phase of oceanic anoxic event 2 caused the plenus cold event

late miocene to pliocene palaeogeography of viti levu fiji islands abstract the island of viti levu is located on the fiji platform in an area that has been tectonically active since at least the late eocene the geological history of viti levu during this time is one of the competing influence of tectonics volcanism and eustatic sea level change in shaping the preserved stratigraphic and therefore palaeogeographic record the focus of this paper is the palaeogeographic evolution of viti levu from the period following the deformation of the tuva group and all older rock units of the vityaz arc around 7 5 ma to the present initial sedimentation during following the deformational event was influenced by the sinistral oblique slip deformation associated with anticlockwise rotation of the platform this tectonically dominated period of island evolution saw the establishment of a number of sedimentary basins many of which continued to receive sediments through until at least the earliest pliocene from 6 5 ma onward volcanic activity became the main influence on the stratigraphic record although evidence for major eustatic events miocene pliocene boundary are recorded in some sequences toward the end of the early pliocene tectonic uplift of viti levu resulted in a poor geological record for this time the quaternary stratigraphic record reflects relatively minor mostly eustatic events in coastal areas around major river systems

a seismic hazard scenario in the sikkim himalaya from seismotectonics spectral amplification source parameterization and spectral attenuation laws using strong motion seismometry 1 in this paper we present a seismic hazard map of the indian himalayan state of sikkim lying between nepal and bhutan himalaya in terms of horizontal peak ground accelerations with 10 exceedance probability over the next 50 years these figures the first for the region were calculated through a stepwise process based on 1 an estimation of the maximum credible earthquake mce from the seismicity of the region and global seismic hazard assessment program considerations and 2 four seismotectonic parameters abstracted from accelerograms recorded at nine stations of the sikkim strong motion array specifically installed for this study the latter include 1 the frequency dependent power law for the shear wave quality factor qs 2 the site response function at each station using receiver function analysis and generalized inversion 3 source parameterization of various events recorded by the array and application of the resulting relationships between m0 and mw and corner frequency fc and mw to simulate spectral accelerations due to higher magnitude events corresponding to the estimated mce and 4 abstraction of regional as well as site specific local spectral attenuation laws at different geometrically central frequencies in low moderate and high frequency bands

strontium isotope stratigraphy in the upper cenomanian shallow water carbonates of the southern apennines short term perturbations of marine 87sr 86sr during the oceanic anoxic event 2 abstract strontium isotope stratigraphy of shallow water carbonates from the southern apennines italy indicates that the late cenomanian early turonian evolution of marine 87sr 86sr is not accurately depicted by the marine reference curve using the low mg biotic calcite of well preserved rudist shells as a study material and carbon isotope stratigraphy for correlation to the standard ammonite biozonal scheme of northern europe new 87sr 86sr values are proposed for four different stratigraphic levels the middle and uppermost part of the guerangeri zone the lower and upper part of the geslinianum zone the southern apennines data suggest that a sharp positive shift at the onset of oceanic anoxic event 2 precedes the well known sr isotope negative shift the positive shift is interpreted in terms of enhanced rates of chemical weathering driven by global warming forced by volcanogenic co2 outgassing a stratified ocean is invoked to reconcile the high gradient and the short lag time of the perturbation with estimates of present day total mass and residence time of strontium in the ocean the sharp switch to the negative shift is related to the collapse of water column density gradient driven by thermal instability during a late cenomanian cool event more active ocean circulation suddenly delivered to surface waters the signal of increased submarine volcanism that had accumulated in deep waters

volcanism accompanying back arc basin development in the southwest pacific abstract the age and composition of magmatism in fiji and to a lesser extent vanuatu and tonga are evaluated in the light of the fragmentation which has sundered the island arc system they once collectively constituted any of six magmatic phenomena during the past 10 m y may be consequences of adjacent plate reconfigurations trondhjemitic plutonism about 10 m y change from tholeiitic to more calc alkaline volcanism between 10 and 6 m y eruption near the rifted arc margin of voluminous crustally derived high si low k rhyolites 7 m y ago shoshonite dominated basaltic volcanism 5 5 to 3 0 m y change to ocean island like basaltic volcanism at 3 0 0 2 m y and geochemically peculiar as well as tectonically anomalous acid andesites 0 7 3 0 m y ago in kandavu southwestern fiji crustal derivation of the low k rhyolites may reflect maximal heating during initial rifting shoshonites may accompany extreme regional extension above a still arc like source eruption of ocean island like basalts begins once subducted lithosphere no longer contributes to erupted melts or separates fiji from ocean island sources coeval eruption of hybrid andesites may accompany oblique subduction of south fiji basin crust beneath kandavu along the northeast hunter fracture zone

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

co2 forced climate thresholds during the phanerozoic abstract the correspondence between atmospheric co2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity here i compare 490 published proxy records of co2 spanning the ordovician to neogene with records of global cool events to evaluate the strength of co2 temperature coupling over the phanerozoic last 542 my for periods with sufficient co2 coverage all cool events are associated with co2 levels below 1000 ppm a co2 threshold of below 500 ppm is suggested for the initiation of widespread continental glaciations although this threshold was likely higher during the paleozoic due to a lower solar luminosity at that time also based on data from the jurassic and cretaceous a co2 threshold of below 1000 ppm is proposed for the initiation of cool non glacial conditions a pervasive tight correlation between co2 and temperature is found both at coarse 10 my timescales and fine resolutions up to the temporal limits of the data set million year timescales indicating that co2 operating in combination with many other factors such as solar luminosity and paleogeography has imparted strong control over global temperatures for much of the phanerozoic

geometry of upper cretaceous bentonite beds implications about volcanic source areas and paleowind patterns western interior united states four bentonite beds near the cenomanian turonian stage boundary ca 90 ma can be traced through much of the western interior of the united states isopach maps constructed for these bentonite beds indicate that volcanic source areas were positioned both northwest and southwest of the central u s western interior basin and also indicate both easterly and southeasterly paleowind directions volcanism of this age has not been reported previously in the southern source area

assessment of maximum earthquake potential of the kopili fault zone in northeast india and strong ground motion simulation abstract maximum magnitude mm earthquake in the kopili fault zone of north east india has been assessed using different approaches which are primarily dependent on various parameters such as fault geometry slip rate geodetic moment rate and convergence rate the analyses reveal that the source zone has accumulated strain energy during the last 72 years since 1943 enough to produce a strong earthquake of magnitude 7 on supplementing with the historical data we conclude mw7 3 as the maximum potential earthquake for the kopili source zone such large earthquake on its occurrence may cause widespread significant ground shakings and damage to infrastructures in the study region we therefore also simulated strong ground motion in the form of peak ground acceleration pga for the mw7 3 potential earthquake using empirical green s function egf approach for ten different sites in the analysis an earthquake of magnitude mw6 5 which has been simulated using a recorded mw5 3 earthquake is used as green s function the two step approach is adopted in the simulation process as the required criteria i e moment ratio of

the tavua caldera fiji a complex shoshonitic caldera formed by concurrent faulting and downsagging the shoshonitic tavua volcano in viti levu fiji developed from a submarine to a subaerial environment and comprises lava flows dominantly of absarokite composition with debris flows and conglomerates on its flanks the tavua caldera formed in the centre of the volcano within the caldera avalanche deposits are overlain by the turtle pool formation which consists of lacustrine sediments shoshonite lavas and hydrovolcanic pyroclastic lapilli tuffs subsequently the inner caldera formed in the centre of the tavua caldera this was infilled by the morrisons pool formation which comprises lavas and pyroclastic rocks of banakite composition with minor intercalated sediment thus the magmas became progressively more evolved in addition to normal movement along regional and concentric faults subsidence which exceeds 3 km was accomplished via substantial downsagging evidence for this is the consistent centripetal dip of caldera fill material which locally exceeds 50 in parts of the turtle pool formation centripetal dips are also recognized in pre caldera rocks immediately outside the tavua caldera subsidence was episodic caused by periodic non explosive withdrawal of underlying magma to erupt on the flanks and in part within the caldera downsagging and fault movement were responsible for approximately equal amounts of subsidence and their interaction produced a caldera with the shape of a stepped funnel

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

organically bound iodine as a bottom water redox proxy preliminary validation and application abstract carbonate associated iodine i ca has been used as a proxy of local upper ocean redox conditions and has successfully demonstrated highly dynamic spatial and temporal patterns across different time scales of earth history to further explore the utility of iodine as a paleo environmental proxy we present here a new method of extracting organically bound iodine iorg from shale using volumes of samples on the order of tens of milligrams thus offering the potential for high resolution work across thin shale beds the ratio of iorg to total organic carbon i toc in modern surface and subsurface sediments decreases with decreasing bottom water oxygen which may be used to reconstruct paleo redox changes as a proof of concept we evaluate the i toc proxy in holocene sediments from the baltic sea landsort deep iodp 347 and discuss those data within a framework of additional independent redox proxies e g iron speciation and mo the results imply that i toc may be sensitive to hypoxic suboxic conditions complementary to proxies sensitive to more reducing anoxic euxinic conditions then we test the usage of i toc in sediments deposited during late cretaceous cenomanian turonian oceanic anoxic event oae 2 from 94 million years ago ma we generated i toc and iorg records from six oae 2 sections tarfaya morocco furlo central italy demerara rise western equatorial atlantic cape verde basin eastern equatorial atlantic south ferriby uk and kerguelen plateau southern indian ocean which provide a broad spatial coverage generally i toc decreases over the interval recorded by the positive carbon isotope excursion the global signature of oae 2 suggesting an expansion of more reducing bottom water conditions and consistent with independent constraints from iron speciation and redox sensitive trace metals e g mo relatively higher i toc values thus more oxic conditions are recorded at two high latitude sites for oae 2 supporting previous model simulations cgenie that indicated higher bottom water oxygen concentrations in these regions our results also indicate that organic rich and oxygenated seafloors are likely a major sink of iodine and correspondingly influence its global seawater inventory

organic rich sedimentation in the south pacific ocean associated with late paleocene climatic cooling abstract a distinctive organic rich marine mudstone of late paleocene age occurs in most of new zealand s sedimentary basins and has been identified as a potential source rock for oil and gas identified as the waipawa formation in the east coast basin and the tartan formation in the great south and canterbury basins the unit is a relatively uniform massive mudstone that varies greatly in thickness 2 70 m and grades laterally into distinctive facies equivalents notably greensand and a thin bedded siliceous mudstone all these facies are characterised by relatively high toc 0 5 10 wt and 13 c enrichment 13 c toc 24 and we refer to them collectively as waipawa organofacies our detailed stratigraphic and geochemical studies refine the age 58 7 to 59 4 ma distribution and nature of the waipawa organofacies we have determined that deposition occurred in continental margin settings throughout much of the southwest pacific under cool dysoxic conditions associated with a significant influx of terrestrial organic matter high marine productivity a global fall in sea level and a regional unconformity across shallow and deep marine settings the combination of cool temperatures lowered sea level and bathyal erosion suggests that deposition was linked to short lived growth of an antarctic ice sheet in the earliest late paleocene 59 ma

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

magmatism and associated hydrothermal activity during the evolution of the tavua caldera 40 ar 39 ar dating of the volcanic intrusive and hydrothermal events the tavua caldera in viti levu fiji occurs in the upper part of the shoshonitic tavua volcano precaldera rocks forming the edifice of the volcano are predominantly mafic absarokite in composition whereas intracaldera rocks are intermediate shoshonite and banakite in composition the caldera hosts subeconomic porphyry style copper gold mineralization and minor weakly auriferous acid sulfate epithermal alteration both associated with monzonite intrusions in the center of the caldera and adularia sericite epithermal mineralization the emperor gold deposit on the caldera margin ten tavua samples ranging from hydrothermally altered or mineralized to relatively fresh material were dated by the 40 ar 39 ar incremental heating technique these dates establish that caldera collapse occurred between 4 6 and 4 5 ma precaldera absarokites have an age greater than 4 6 ma and probably as much as 4 7 ma while intracaldera shoshonites and banakites have a maximum age of 4 51 ma so there was a gap of at least 0 1 m y between mafic and major intermediate volcanism in this area monzonite intrusion and concurrent porphyry style alteration in the center of the caldera occurred between 4 51 and 4 44 ma essentially synchronous with intracaldera volcanism the last magmatic event within the caldera a banakite vent phase pyroclastic unit occurred at 4 14 or 0 08 ma adularia deposited during epithermal mineralization at emperor was formed at 3 71 or 0 13 ma this history which is clearly indicated by 40 ar 39 ar data would not have been possible to deduce by conventional k ar dating the results are similar to those obtained in other porphyry and epithermal systems where porphyry style magmatic hydrothermal activity is deemed to be synchronous with magmatism but a measurable interval occurs between magmatism and epithermal mineralization tavua is unusual in that samples of both types of mineralization are available are amenable to dating techniques and can be tied to the history of the caldera

late pleistocene holocene development of the tista megafan west bengal india 10 be cosmogenic and irsl age constraints abstract the himalayan proximal foreland is characterized by quaternary megafans of which the formational mechanisms remain debated the tista megafan spreads over more than 16 000 km2 from the mountain front where it is strongly incised to the confluence of the tista river with the jamuna brahmaputra river and stores sediments produced in the sikkim himalaya we propose a scenario for the late pleistocene holocene development of the tista megafan based on new 10be cosmogenic and infra red stimulated luminescence irsl age constraints and discuss the main potential controls on its evolution we suggest that two distal lobes developed successively downstream from a common proximal lobe deposition in the proximal lobe took place since at least 135 ka and incision began at 3 7 0 7 1 0 ka the western distal lobe of the megafan was deposited early in the history of the megafan when the sikkim himalaya catchment was drained by a tributary of the ganga river and was abandoned in the early holocene 10 11 ka the eastern recent

rupture of the indian slab in the 2011 mw 6 9 sikkim himalaya earthquake and its tectonic implications unlike the other himalayan plate boundary segments the eastern nepal to bhutan himalayan region is not known to have generated prominent shallow thrust faulting earthquakes typical of the ongoing convergence this region features strike slip earthquakes over the depth ranges of 40 120 km indicating intraslab deformation here we present for the first time a slip distribution model for the largest recorded intraslab strike slip earthquake in this region the mw 6 9 sikkim event that occurred on 18 september 2011 relying on kinematic source process modeling our results indicate a ne sw trending steeply dipping sinistral source zone within the underthrusting indian slab the rupture propagated radially with a low rupture velocity of 1 7 km s breaking a large asperity of 20 a 20 km 2 with a maximum slip of 1 6 m the rupture nucleated at a depth of 45 km and reached upper mantle depths the computed coseismic stress drop value is 13 6 mpa we suggest that most of the aftershocks occurred on the conjugate plane possibly due to stress triggering stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike slip regime in the upper mantle we observed a unimodal distribution of earthquakes beneath the higher himalaya this indicates a strong brittle indian slab and unravels a scenario of an eventual breakup of the lithosphere the key trigger might be variation in the convergence rates along the himalayan arc 2019 american geophysical union all rights reserved

modeling some empirical vertical component lg relations abstract higher mode surface wave theory is used to model the vertical component lg wave observed in eastern north america at regional distances tests of the model are made to determine whether it is capable of describing empirical spectral scaling laws spatial attenuation and peak time domain lg amplitudes it is found that a simple crustal model and a rough estimate of crustal qb are all that are required to accomplish this good results are obtained if the average crustal qp is equated to the coda q of the same frequency introduction the lg wave is a wave observed on short period seismograms of local and regional seismic events which travels with a group velocity of approximately 3 5 km sec in the central united states it is usually the largest arrival on the seismogram which makes it suitable for defining a magnitude scale nuttli 1973 herrmann and nuttli 1982 as part of developing the magnitude scale there have been many studies on the spatial attenuation of the lg wave nuttli 1973 street 1976 bollinger 1979 singh and herrmann 1982 the lg wave is usually thought of as a superposition of higher mode surface waves propagating within the crustal wave guide herrmann and nuttli 1975a b attempted to deterministically model observed lg amplitudes in terms of focal mechanism focal depth and seismic moment using surface wave techniques they were limited by their inability to compute surface wave eigenfunctions at frequencies greater than 0 5 hz however their results were encouraging harkrider 1979 drawing upon the work of apsel 1979 discovered a way to compute surface wave energy integrals of the higher modes very precisely bache

a pliocene shoaling basaltic seamount ba volcanic group at rakiraki fiji abstract at rakiraki in northeastern viti levu the pliocene ba volcanic group comprises gently dipping pyroxene phyric basaltic lavas including pillow lava and texturally diverse volcanic breccia interbedded with conglomerate and sandstone three main facies associations have been identified 1 the primary volcanic facies association includes massive basalt flows and sills pillow lava and related in situ breccia pillow fragment breccia autobreccia in situ hyaloclastite peperite 2 the resedimented volcaniclastic facies association consists of bedded monomict volcanic breccia and scoria lapilli rich breccia 3 the volcanogenic sedimentary facies association is composed of bedded polymict conglomerate and breccia together with volcanic sandstone and siltstone mudstone facies pillow lava and coarse hyaloclastite breccia indicate a submarine depositional setting for most of the sequence thick massive to graded beds of polymict breccia and conglomerate are interpreted as volcaniclastic mass flow deposits emplaced below wave base well rounded clasts in conglomerate were reworked during subaerial transport and or temporary storage in shoreline or shallow water environments prior to redeposition red oxidised lava and scoria clasts in bedded breccia and conglomerate also imply that the source was partly subaerial the facies assemblage is consistent with a setting on the submerged flanks of a shoaling basaltic seamount the coarse grade and large volume of conglomerate and breccia reflect the high supply rate of clasts and the propensity for collapse and redeposition on steep palaeoslopes the clast supply may have been boosted by vigorous fragmentation processes accompanying transition of lava from subaerial to submarine settings the greater proportion of primary volcanic facies compared with resedimented volcaniclastic and volcanogenic sedimentary facies in central and northwestern exposures near rakiraki indicates they are more proximal than those in the southeast towards viti levu bay the proximal area coincides with one of two zones where nw se trending mafic dykes are especially abundant and it is close to several small dome like intrusions of intermediate and felsic igneous rocks the original surface morphology of the volcano is no longer preserved though the partial fan of bedding dip azimuths in the south and east and the wide diameter exceeding 20 km are consistent with a broad shield

a κ model for mainland france an important parameter for the characterization of strong ground motion at high frequencies 1 hz is kappa which models a linear decay of the acceleration spectrum a f in log linear space i e a f a 0 exp f for f f e where f is frequency f e is a low frequency limit and a 0 controls the amplitude of the spectrum is a key input parameter in the stochastic method for the simulation of strong ground motion which is particularly useful for areas with insufficient strong motion data to enable the derivation of robust empirical ground motion prediction equations such as mainland france numerous studies using strong motion data from western north america wna an active tectonic region where surface rock is predominantly soft and eastern north america ena a stable continental region where surface rock is predominantly very hard have demonstrated that varies with region and surface geology with wna rock sites having a of about 0 04 s and ena rock sites having a of about 0 006 s lower s are one reason why high frequency strong ground motions in stable regions are generally higher than in active regions for the same magnitude and distance few if any estimates of s for french sites have been published therefore the purpose of this study is to estimate using data recorded by the french national strong motion network rap for various sites in different regions of mainland france for each record a value of is estimated by following the procedure developed by anderson and hough bull seismol soc am 74 1969 1993 1984 this method is based on the analysis of the s wave spectrum which has to be performed manually thus leading to some uncertainties for the three french regions where most records are available the pyrenees the alps and the cotes d azur a regional model is developed using weighted regression on the local geology soil or rock and source to site distance it is found that the studied regions have a mean between the values found for wna and ena for example for the alps region a value of 0 0254 s is found for rock sites an estimate reasonably consistent with previous studies

estimation of source parameters of m w 6 9 sikkim earthquake and modeling of ground motions to determine causative fault in this study source parameters of the september 18 2011 m w 6 9 sikkim earthquake were determined using acceleration records these parameters were then used to generate strong motion at a number of sites using the stochastic finite fault modeling technique to constrain the causative fault plane for this earthquake the average values of corner frequency seismic moment stress drop and source radius were 0 12 hz 3 07 1026 dyne cm 115 bars and 9 68 km respectively the fault plane solution showed strike slip movement with two nodal planes oriented along two prominent lineaments in the region the ne oriented kanchendzonga and nw oriented tista lineaments the ground motions were estimated considering both the nodal planes as causative faults and the results in terms of the peak ground accelerations pga and fourier spectra were then compared with the actual recordings we found that the nw se striking nodal plane along the tista lineament may have been the causative fault for the sikkim earthquake as pga estimates are comparable with the observed recordings we also observed that the fourier spectrum is not a good parameter in deciding the causative fault plane

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

cyanobacteria proliferation in the cenomanian turonian boundary interval of the apennine carbonate platform immediate response to the environmental perturbations associated with oae 2

magmatic evolution of late cenozoic volcanic rocks of the lau ridge fiji three main groups of lavas are exposed on islands of the lau ridge the lau volcanic group lvg 14 0 5 4 ma are predominantly andesite korobasaga volcanic group kvg 4 4 2 4 ma are predominantly basalt and mago volcanic group mvg 2 0 0 3 ma are basalt hawaiite lvg and kvg lavas are mostly medium k tholeiitic rocks with high lile hfse ratios characteristic of islands ares while mvg lavas are ne normative alkalic rocks with high lile and hfse characteristic of ocean island basalts lvg lavas have high nd 8 0 8 4 and low 87sr 86sr 0 70273 0 70349 similar to n morb whereas kvg lavas have slightly more radiogenic values nd 7 5 8 4 87sr 86sr 0 70323 0 70397 mvg lavas form an isotopically distinct group having lower nd 4 6 4 9 and 87sr 86sr ranging from 0 70347 0 70375 lvg lavas were erupted in a primary oceanic island arc vitiaz arc during the miocene basaltic lavas were derived by approximately 19 partial melting of mantle wedge peridotite with only minor subduction component andesites and dacites were produced by low pressure plagioclase pyroxene titanomagnetite dominated crystal fractionation kvg lavas were erupted during the period immediately prior to or during the initial stages of rifting in the lau basin and like lvg lavas show significant chemical differences at the northern and southern ends of the lau ridge lavas at the northern end type ii appear to be derived from a more depleted source than lvg but with a greater amount of subduction component those at the southern end type i probably came from a slightly more enriched source with less subduction component mvg basalts and hawaiites were derived from an enriched mantle with little or no subduction input the hawaiites type i could not have been derived from the basalts type ii and the two magma types must have come from different sources indicating mantle heterogeneity the lack of subduction influence indicates the mvg lavas are tectonically unrelated to the present day tonga arc and the lack of depletion indicators suggests they have tapped a different new part of the mantle wedge this may reflect introduction of sub pacific mantle through the present tonga lau subduction system

sedimentation and volcanism in an oligocene miocene intra oceanic are and fore are southwestern viti levu fiji rocks belonging to the lower oligocene to middle miocene wainimala group in southwestern viti levu can be divided into an are assemblage representing the axial part of a volcanic are and a basinal assemblage representing the trenchward flank of the are and the inner part of the fore are basin the are assemblage consists mainly of volcaniclastic rudites and lava flows with minor shallow water limestones and is intruded by mid to late miocene gabbro and tonalite stocks the basinal assemblage to the north is floored by part of an earlier eocene to lower oligocene are the lower part of this assemblage includes volcaniclastic rudites representing the dispersal aprons of major volcanic edifices to the trenchward of the are axis and basaltic lavas and fissure fed rhyolite lava domes and breceia ridges erupted in deeper water away from these centres the rhyolites are directly related to the acidic members of a dense compositionally bimodal dyke swarm that intrudes the underlying earlier are rocks recording substantial crustal extension the basinal volcanic rocks are interbedded with and overlain by a sequence of pelagic carbonates thin bedded epiclastic turbidites and acidic tuffs the basinal succession evolved from an intra are to an inner fore are setting as volcanism within the assemblage died away in the early miocene in the late early miocene increased uplift and emergence of the are massif increased the sediment yield to the fore are basin resulting in the deposition of thicker bedded coarser grained turbidites

synchronous records of pco2 and δ14c suggest rapid ocean derived pco2 fluctuations at the onset of younger dryas just before the onset of the younger dryas yd cold event several stomatal proxy based pco2 records have shown a sharp increase in atmospheric co2 concentration pco2 of between ca 50 and 100 ppm followed by a rapid decrease of similar or even larger magnitude here we compare one of these records a high resolution pco2 record from southern sweden with the intcal13 record of radiocarbon d 14 c the two records show broadly synchronous fluctuations at the yd onset specifically the intcal13 record documents decreasing d 14 c just before the yd onset when pco2 peaks consistent with a source of old co2 from the deep ocean we propose that this fluctuation occurred due to a major ocean flushing event the cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor we confirm that the earth system can produce such large multidecadal timescale fluctuations in pco2 through simulating an artificial ocean flushing event with the genie earth system model we suggest that sharp transitions of pco2 may have remained undetected so far in ice cores due to inter firn gas exchange and time averaging the stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change

the nadi basin neogene strike slip faulting and sedimentation in a fragmented arc western viti levu fiji the nadi basin in western viti levu is one of a number of sedimentary basins controlled by e w to ne sw faults that developed on the fiji platform in the late miocene the initial basin fill belonging to the upper miocene nadi sedimentary group consists of mainly basement derived breccias and sandstones deposited at bathyal depths by sediment gravity flows on a basin floor dissected by braided e w faults the main source area lay to the south across the actively down faulting basin margin in the latest miocene a change in provenance took place as debris spread southward from a newly developed e w chain of shoshonitic volcanoes koroimavua volcanic group some 12 km north of the southern basin margin continued normal displacement along the southern margin allowed the deposition of a thick sequence of shoshonitic sandstones at bathyal depths on the downthrown side in the earliest pliocene the onset of basin inversion was marked by shallowing to neritic depths and the onlap of sandstones and shoshonitic conglomerates southward onto pre nadi sedimentary group basement as inversion proceeded the basin fill was folded and southward directed reverse displacement took place along the southern basin margin evidence from the nadi and other late miocene basins indicates that they developed as a result of broadly e w directed sinistral strike slip probably related to a shearing collision of the melanesian border plateau with the northern margin of the fiji platform during the breakup of the formerly continuous outer melanesian arc it is suggested that prior to the establishment of the fiji fracture zone at 7 6 ma much of the left lateral displacement currently taking place along that plate boundary was accommodated by strike slip deformation within the fiji platform

phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 four sections documenting the impact of the late cenomanian oceanic anoxic event oae 2 were studied in basins with different paleoenvironmental regimes accumulation rates of phosphorus p bound to iron organic matter and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of oae 2 with an associated increase in 13 c values accumulation rates of p return to preexcursion values in the interval where the 13 c record reaches its fi rst maximum an offset in time between the maximum in p accumulation and peaks in organic carbon burial hydrogen indices and corg preact molar ratios is explained by the evolution of oae 2 in the following steps 1 an increase in productivity increased the fl ux of organic matter and p into the sediments the preservation of organic matter was low and its oxidation released p which was predominantly mineralized 2 enhanced productivity and oxidation of organic matter created dysoxic bottom waters the preservation potential for organic matter increased whereas the sediment retention potential for p decreased 3 the latter effect sustained high primary productivity which led to an increase in the abundance of free oxygen in the ocean and atmosphere system after the sequestration of co 2 in the form of black shales this oxygen helped push the ocean back into equilibrium terminating black shale deposition and removing bioavailable p from the water column

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

contemporaneous massive subaerial volcanism and late cretaceous oceanic anoxic event 2 abstract oceanic anoxic events oaes are geological time intervals characterized by extremely high burial rates of organic carbon that led to deposition of organic rich black shales in the global ocean it has been proposed that oceanic anoxic events are ultimately caused by massive volcanism associated with formation of large igneous provinces lips because of chronological similarities but no general consensus has developed yet to investigate the possibility of lip volcanism instigating oaes we measured stable isotopic compositions of bulk organic carbon 13 c org and lead pb isotopic compositions in the silicate sediment fraction across the bonarelli black shale italy a type stratigraphic section for the end cenomanian oae oae 2 94 ma ultra high resolution 13 c org records determined every 1 5 mm capture a 3 sharp negative shift at the base of the bonarelli at the same stratigraphic level pb isotopic compositions in the silicate sediment fraction exhibit significant shifts toward characteristic values of volcanic rocks from contemporaneous lips caribbean and madagascar flood basalts these data suggest a rapid substantial increase in the relative supply of silicate minerals from the two lips massive subaerial volcanism associated with lip formation provides a simple explanation for these two isotopic geochemical signals via release of a huge amount of carbon dioxide 10 5 gt co 2 and particulate materials into the atmosphere which resulted in a rapid negative shift of 13 c in sea water and changes in pb isotopic compositions in the silicate sediment fraction respectively we interpret that massive volcanism triggered significant climatic changes inducing biotic crises and oceanic anoxia

cretaceous oceanic red beds as possible consequence of oceanic anoxic events article i nfo oceanic anoxic events oaes represent brief periods of burial of large amounts of organic carbon in the oceans during cretaceous time burial of organic carbon which preferentially sequestered isotopically lighter carbon during oaes resulted in positive 13 c excursions of 2 3 recognizable in global ocean these deposits are typically dark grey to black shales considered to be the result of interaction between extreme warm climate ocean circulation high bioproductivity and organic carbon preservation less interest has been given to periods between oaes when oxic deep sea deposits such as red marls and red shales were deposited during mid and late cretaceous the latter deposits are associated with very low content of organic carbon and oxic depositional environments which dominated western tethys in post turonian time up to the early eocene feedbacks among geochemical cycles in response to decreasing global temperatures increasing deep ocean circulation forced by high latitude deep water formation along the antarctic margin and widening and deepening of the interconnections between the oceanic basins may have been responsible for the major paleoceanographic change from deposition of organic carbon rich black shales during mid cretaceous to world wide deposition of cretaceous oceanic red beds corbs in the late cretaceous the presence of corbs sandwiched between mid cretaceous oaes may reflect major climate and paleoceanographic changes in a contrast to extremely warm climates during the oaes the corbs suggest cold periods and therefore oscillating climate shifts that have seldom been considered during modeling of cretaceous

potential links between ocean plateau volcanism and global ocean anoxia at the cenomanian turonian boundary the cenomanian turonian boundary is marked globally by the extinction of marine invertebrates and an increase in the accumulation and preservation of organic carbon rich sediments black shales the timing of this boundary also coincides with large scale volcanism from at least three large igneous provinces the caribbean and ontong java oceanic plateaus and the madagascar flood basalts in this paper we assess the possibility that hydrothermalism associated with large scale submarine magmatism was responsible for the reduction of dissolved o 2 in the oceans we investigate two potential mechanisms the oxidation of reduced material in hydrothermal effluents and the stimulation of primary productivity in the water column due to the injection of hydrothermal fe into surface waters with the first mechanism we find that a 10 000 km 3 submarine basalt eruption three orders of magnitude larger than recent midocean ridge eruptions could release enough reduced hydrothermal material to consume at least 6 percent of the dissolved o 2 in seawater in a well ventilated ocean such as the present ocean with the second mechanism we calculate that even a small percentage of the hydrothermal fe released from a single large flow could have led to a significant increase in primary productivity in areas where fe was the biolimiting nutrient such as open ocean areas in the pacific the potential impact of both of these o 2 reducing mechanisms at the cenomanian turonian boundary would have been significantly greater if cretaceous oceans were less well ventilated than the present oceans

the 2011 sikkim earthquake mw 6 9 of the himalaya estimates of earthquake source parameters and representability of attenuation characteristics abstract the empirical accelerograms of the september 18 2011 sikkim earthquake m w 6 9 have been used in the present study to estimate its source parameters and to identify a representative relation for the attenuation of peak ground acceleration with distance the spectra of high energy packets observed in the sh waves approximated by transverse components of accelerograms has been modeled using brune s model a two step procedure has been adopted for this purpose the estimated source parameters of the 2011 sikkim earthquake have been found to be as corner frequency f c 0 09 hz seismic moment m 0 2 43 0 5 10 26 dyne cm stress drop 50 4 9 28 bars and the moment magnitude m w 6 87 0 05 these estimated values have been found to be consistent with those of reported values obtained using different data sets and procedures the high frequency earthquake ground motions are governed by stress drop at the source therefore a value of stress drop estimated here is useful for the simulation of earthquake strong ground motions in the region the attenuation characteristics of observed peak ground acceleration as a function of distance have been compared with those of obtained using five empirical relations it has been found that a relation given by mcguire 1978 represents the attenuation characteristics of peak ground acceleration is relatively better this relation may be used for estimating the peak ground acceleration of similar magnitude for future earthquakes in the region this relation is also useful for the simulation of earthquake strong ground motions in the region using envelope technique the outcome of the present study is useful for the estimation of the seismic hazard of the sikkim region of the himalaya

the northern gulf of mexico during oae2 and the relationship between water depth and black shale development despite their name oceanic anoxic events oaes are not periods of uniform anoxia and black shale deposition in ancient oceans shelf environments account for the majority of productivity and organic carbon burial in the modern ocean and this was likely true in the cretaceous as well however it is unlikely that the mechanisms for such an increase were uniform across all shelf environments some like the northwest margin of africa were characterized by strong upwelling but what might drive enhanced productivity on shelves not geographically suited for upwelling to address this we use micropaleontology carbon isotopes and sedimentology to present the first record of oceanic anoxic event 2 oae2 from the northern gulf of mexico shelf here oae2 occurred during the deposition of the well oxygenated inner neritic lower estuarine lower tuscaloosa sandstone the overlying organic rich oxygen poor marine tuscaloosa shale is entirely turonian in age we trace organic matter enrichment from the spinks core into the deepwater gulf of mexico where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the cenomanian turonian boundary interval redox change and organic matter preservation across the gulf of mexico shelf were driven by sea level rise prior to the early turonian highstand which caused the advection of nutrient rich oxygen poor waters onto the shelf this results in organic matter mass accumulation rates 1 2 orders of magnitude lower than upwelling sites like the nw african margin but it likely occurred over a much larger geographic area suggesting that sea level rise was an important component of the overall increase in carbon burial during oae2

crustal and lithospheric structure of inactive volcanic arc terrains in fiji abstract the crustal and lithospheric velocity structure of the fiji area may place important constraints on the evolution of island arcs in the region here we obtain receiver functions from one permanent seismic station and three temporary networks on the fiji platform the lau ridge and other small islands to develop point estimates of crustal thickness under the networks we obtain preliminary estimates of crustal thickness and poisson s ratio from h stacking of the receiver functions we then perform an inversion for shear wave velocity structure using a joint inversion of receiver functions and rayleigh wave dispersion curves from ambient seismic noise and teleseismic events the joint inversion results show an average crustal thickness of 30 km beneath viti levu the largest fiji island suggesting an extensive period of arc crustal formation and thickening in contrast we find shallower moho depths averaging 22 km beneath the smaller fiji islands and the lau ridge the limited thickness of the high velocity lid obtained by inversion indicates that the lithosphere is thinned beneath the marginal fiji islands which may be due to the early rifting event forming the lau basin together with the crustal thinning of this area as well and to thermal lithospheric erosion processes associated with adjacent back arc spreading a relatively slow velocity middle crustal layer roughly of 11 16 km thickness exists throughout fiji suggesting that remnant arcs contain significant volumes of felsic crustal rocks necessary for continental crust formation

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

site effect evaluation using spectral ratios with only one station the spectral ratio technique is a common useful way to estimate empirical transfer function to evaluate site effects in regions of moderate to high seismicity the purpose of this paper is to show that it is possible to estimate empirical transfer function using spectral ratios between horizontal and vertical components of motion without a reference station the technique originally proposed by nakamura to analyze rayleigh waves in the microtremor records is presented briefly and it is discussed why it may be applicable to study the intense s wave part in earthquake records results are presented for three different cities in mexico oaxaca oax acapulco gro and mexico city these cities are very different by their geological and tectonic contexts and also by the very different epicentral distances to the main seismogenic zones affecting each city each time we compare the results of nakamura s technique with standard spectral ratios in all three cases the results are very encouraging we conclude that if site effects are caused by simple geology a first estimate of dominant period and local amplification level can be obtained using records of only one station

postseismic deformation following the 2015 mw7 8 gorkha nepal earthquake new gps data kinematic and dynamic models and the roles of afterslip and viscoelastic relaxation we report global positioning system gps measurements of postseismic deformation following the 2015 mw7 8 gorkha nepal earthquake including previously unpublished data from 13 continuous gps stations installed in southern tibet shortly after the earthquake we use variational bayesian independent component analysis vbica to extract the signal of postseismic deformation from the gps timeseries revealing a broad displacement field extending 150 km northward from the rupture kinematic inversions and dynamic forward models show that these displacements could have been produced solely by afterslip on the main himalayan thrust mht but would require a broad distribution of afterslip extending similarly far north this would require the constitutive parameter a b to decrease northward on the mht to 0 05 mpa an extreme sensitivity of creep rate to stress change and seems unlikely in light of the low interseismic coupling and high midcrustal temperatures beneath southern tibet we conclude that the northward reach of postseismic deformation more likely results from distributed viscoelastic relaxation possibly in a midcrustal shear zone extending northward from the seismogenic mht assuming a shear zone 5 20 km thick we estimate an effective shear zone viscosity of 3 10 3 10 pa s over the first 1 12 postseismic years near field deformation can be more plausibly explained by afterslip itself and implies a b 0 5 1 mpa consistent with other afterslip studies this near field afterslip by itself would have re increased the coulomb stress by 0 05 mpa over 30 of the gorkha rupture zone in the first postseismic year and deformation further north would have compounded this reloading

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

frequency modulation reveals the phasing of orbital eccentricity during cretaceous oceanic anoxic event ii and the eocene hyperthermals abstract major advances in our understanding of paleoclimate change derive from a precise reconstruction of the periods amplitudes and phases of the milankovitch cycles of precession obliquity and eccentricity while numerous quantitative approaches exist for the identification of these astronomical cycles in stratigraphic data limitations in radioisotopic dating and instability of the theoretical astronomical solutions beyond 50 myr ago can challenge identification of the phase relationships needed to constrain climate response and anchor floating astrochronologies here we demonstrate that interference patterns accompanying frequency modulation fm of short eccentricity provide a robust basis for identifying the phase of long eccentricity forcing in stratigraphic data one and two dimensional models of sedimentary distortion of the astronomical signal are used to evaluate the veracity of the fm method and indicate that pristine eccentricity fm can be readily distinguished in paleo records apart from paleoclimatic implications the fm approach provides a quantitative technique for testing and calibrating theoretical astronomical solutions and for refining chronologies for the deep past we present two case studies that use the fm approach to evaluate major carbon cycle perturbations of the eocene and late cretaceous interference patterns in the short eccentricity band reveal that eocene hyperthermals etm2 elmo h2 i1 and etm3 x 52 54 myr ago were associated with maxima in the 405 kyr cycle of orbital eccentricity the same eccentricity configuration favored regional anoxic episodes in the mediterranean during the middle and late cenomanian 94 5 97 myr ago the initial phase of the global oceanic anoxic event ii oae ii 93 9 94 5 myr ago coincides with maximum and falling 405 kyr eccentricity and the recovery phase occurs during minimum and rising 405 kyr eccentricity on a myr scale the event overlaps with a node in eccentricity amplitudes both studies underscore the importance of seasonality in pacing major climatic perturbations during greenhouse times

a study of source parameters site amplification functions and average effective shear wave quality factor qseff from analysis of accelerograms of the 1999 chamoli earthquake himalaya the accelerograms of the 1999 chamoli earthquake and nine of its aftershocks which occurred in uttaranchal himalaya have been analyzed to investigate their source parameters the site amplification functions and the average effective shear wave quality factor qseff in the region the fault plane solution of the main shock is obtained using the spectral amplitudes of sh waves approximated by transverse components of accelerograms of the high energy packets observed in the accelerograms of the main shock it is found to be comparable with the reported solutions in other studies similarly the other source parameters viz seismic moment 5 03 1 7 1025 dyne cm stress drop 65 bars source duration 5 2 s and moment magnitude 6 4 estimated for the main shock are consistent with the values obtained in other studies the stress drops estimated for the aftershocks vary from 23 bars to 153 bars and the seismic moment from 1 4 1023 dyne cm to 2 9 1023 dyne cm the average estimated values of the effective shear wave quality factor qseff vary from 655 359 in the uttaranchal sector of himalaya and 1475 130 in the delhi region in general the qseff value increases with an increase in the epicentral distance reflecting the penetration of the waves into deeper layers of the crust as the epicentral distance of the observation point increases these values of qseff indicate that in general the curst is at low temperatures that will promote brittle behavior and conditions for episodic failure as compared to creep under the accumulated strains from plate collision at the himalaya plate boundary the site amplification characteristics at sites have been identified from the frequency bands of significant amplification observed in the spectral ratios of the horizontal to the vertical component records the decay of peak ground acceleration pga values with distance has been investigated using the empirical regression curves vis a vis the site amplification factors

the eltanin asteroid impact possible south pacific palaeomegatsunami footprint and potential implications for the pliocene pleistocene transition large asteroid impacts are rare and those into the deep ocean are rarer still the eltanin asteroid impact around 2 51 0 07 ma occurred at a time of great climatic and geological change associated with the pliocene pleistocene boundary numerical models of the event indicate that a megatsunami was generated although there is debate concerning its magnitude and the region wide extent of its influence we summarise the existing evidence for possible eltanin megatsunami deposits in antarctica chile and new zealand while also examining other potential sites from several locations mainly around the south pacific region in reviewing these data we note that these events were unfolding at the same time as those associated with the pliocene pleistocene boundary and as such most of the geological evidence from that time has a climatic interpretation the potential climatic and geological ramifications of the eltanin asteroid impact however have failed to be considered by most researchers studying this time period although we are not advocating that all geological activity at that time is connected with the eltanin asteroid impact it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions copyright 2012 john wiley sons ltd

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

early geochemical evolution of an oceanic island arc and backarc fiji and the south fiji basin the initial 25 to 35 ma of oceanic arc volcanism in fiji the early arc stage was dominated by eruption of lree depleted low k tholeiitic basalts and andesites the oldest volcanics include the highest hfse group morb like in composition plus high mg basalts and basic andesites with flat ree patterns as low as 4x chondritic concentrations these erupted either within the volcanic arc during its first 5 ma or in an adjacent backarc during its first ma of formation subsequent volcanics of the early arc stage apparently erupted onto early backarc basin crust most are intermediate between earlier extremes in hfse contents but at least one volcano produced strongly lree depleted island arc tholeiites in contrast medium k tholeiitic and calc alkaline andesites erupted during the mature arc stage parental basalts were enriched in lree but depleted in hree relative to earlier basalts due to a change in source composition counterflowing morb source asthenosphere within the mantle wedge dominated vol

himalayan main central thrust and its implications for himalayan inverted metamorphism abstract within the scheme of south directed orogenic polarity in the himalayan region the main central thrust mct developed at an intermediate stage between the collisional tectonics at the indus tsangpo suture in the north and the latest underthrusting at the main boundary thrust mbt in the south the proposition that the mct marks the base of the high himalayan central crystalline zone against the inner sedimentary belt of the lower himalayas creates confusion in its definition and its location in kashmir and especially in the eastern himalayas the problem can be resolved by defining the mct as the basal thrust of the crystalline nappe sequences either rooted at or detached as klippe from the central crystalline zone characteristically the nappe sequences show inverted metamorphism which generally starts at the basal thrust the redefined mct from the chlorite biotite grades and reaches the kyanite sillimanite grades with migmatites and anatectic granites in the highest tectonic levels the metamorphic rank of both the substrate and the overthrust rock units in the vicinity of the mct is generally low the inverted metamorphism may be explained by intracontinental underthrusting and resultant downbowing of the isotherms the redefined mct does not appear to represent the thrust zone along which the continental underthrusting was initiated it developed to the south of this zone as a possible sole thrust of the nappe stack of the crystalline rocks that overrode the parautochthonous sedimentary sequences of the lower himalayas the sequence of events associated with the mct would probably be repeated in the mbt

orbital time scale and new c isotope record for cenomanian turonian boundary stratotype previous time scales for the cenomanian turonian boundary ctb interval containing oceanic anoxic event ii oae ii vary by a factor of three in this paper we present a new orbital time scale for the ctb stratotype established independently of radiometric biostratigraphic or geochemical data sets update revisions of ctb biostratigraphic zonation and provide a new detailed carbon isotopic record for the ctb study interval the orbital time scale allows an independent assessment of basal biozone ages relative to the new ctb date of 93 55 ma gts04 the d 13 corg data document the abrupt onset of oae ii significant variability in d 13 corg values and values enriched to almost 222 these new data underscore the difficulty in defining oae ii termination using the new isotope curve and time scale estimates of oae ii duration can be determined and exported to other sites based on integration of well established chemostratigraphic and biostratigraphic datums the new data will allow more accurate calculations of biogeochemical and paleobiologic rates across the ctb

significant transient pco2 perturbation at the new zealand oligocene miocene transition recorded by fossil plant stomata abstract the reorganisation of earth s climate system from the oligocene to the miocene was influenced by complex interactions between tethyan tectonics orbital parameters oceanographic changes and carbon cycle feedbacks with climate modelling indicating that pco2 was an important factor oscillating episodes of climate change during the oligocene miocene transition omt have however been difficult to reconcile with existing pco2 records here we present a new pco2 record from the omt into the early miocene reconstructed using the stomatal proxy method with a database of fossil lauraceae leaves from new zealand the leaf database derives from three relatively well dated sites located in the south island of new zealand foulden maar mataura river and grey lake atmospheric pco2 values were obtained based on four separate calibrations with three nearest living equivalents using the stomatal ratio method as well as transfer functions our results based on the mean values of each of the four calibrations indicate pco2 ranging 582 732 ppm average 650 ppm at the omt falling precipitously to mean values of 430 538 ppm average 492 ppm for the earliest miocene and 454 542 ppm average 502 ppm in the early miocene the much higher values of pco2 at the omt indicate that pco played an important role in climate dynamics during this time potentially including the abrupt termination of glaciations