tracing euxinia by molybdenum concentrations in sediments using handheld x ray fluorescence spectroscopy hhxrf abstract elevated molybdenum mo contents in organic rich sediments are indicative of deposition from an anoxic and sulfide rich euxinic water column this can be used for tracing past euxinic conditions in ancient oceans from sedimentary archives conventional analytical detection of elevated molybdenum levels is however expensive and cannot be directly performed in the field here we show that handheld x ray absorption spectroscopy hhxrf on both rock powders and rock surfaces provides a powerful tool for laboratory or field based geochemical characterization of mo content and the tracing of euxinic depositional conditions we further present a sedimentary mo database compiled from over 300 globally distributed modern marine sites to show that modern euxinic marine basins are characterized by molybdenum enrichment 25 ppm relative to average crust 1 5 ppm and river suspended matter 3 ppm only mn oxide rich deposits from oxygenated deep sea settings match such high mo enrichments but these are easily distinguished from mo rich sediments from the continental shelves hence past and present organic rich sediments enriched in mo are indicative of at least intermittent water column euxinia we analyzed the molybdenum content of powdered and homogenized samples of holocene miocene triassic jurassic ordovician and cambrian age by hhxrf and inductively coupled plasma mass spectrometry icpms we further analyzed 2 certified nist standard references nist 2781 with mo 47 ppm and nist 2702 with mo 10 ppm for analytical control analytical precision 1 after 30 120 and 300 seconds of measuring time was 4 2 and 1 ppm with a respective detection limit of 11 5 3 ppm 3 noise level the data were accurate to within the given precision 1 after a daily calibration to samples covering a range of mo concentrations from 0 to 30 ppm hand held xrf equipment also allows mo measurements directly on fresh rock surfaces both in the field and under laboratory conditions rock samples from a cambrian drill core closely match icpms obtained mo concentrations from homogenous powders of the same rocks collectively our data show that hhxrf as a quick and reliable method for the precise and accurate quantification of molybdenum concentrations in both rock powders and at fresh rock surfaces the non destructive nature of the hhxrf measurements is combined with low per sample analytical costs minor sample preparation and easy applicability in the field

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

is the subtropical jet shifting poleward the tropics are expanding poleward at about 0 5 circ per decade in observations this poleward expansion of the circulation is consistently reported using hadley cell edge metrics and lower atmospheric tropical edge metrics however some upper atmospheric tropical metrics report smaller trends that are often not significant one such upper atmospheric metric is the subtropical jet latitude which has smaller trends compared to the hadley cell edge in this study we investigate the robustness of the weak trends in the subtropical jet position by introducing a new method for locating the subtropical jet and examining the trends and variability of the subtropical jet latitude we introduce the tropopause gradient method based on the peak gradient in potential temperature along the dynamic tropopause using this method we find the trends in the subtropical jet latitude are indeed much smaller than 0 5 circ per decade consistent with previous studies we also find that natural variability within the subtropical jet latitude would not prevent trends from being detected if they were similar to the hadley cell edge as trends greater than 0 24 circ per decade could reliably be detected using monthly data or 0 09 circ per decade using daily data despite the poleward expansion of the tropics there is no robust evidence to suggest the subtropical jet is shifting poleward in either hemisphere neither the current diagnostic methods nor natural variability can account for the small subtropical jet trends the most likely explanation which requires further investigation is that the subtropical jet position is not tied dynamically to the hadley cell edge

nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

a sagging spreading continuum of large volcano structure gravitational deformation strongly infl uences the structure and eruptive behavior of large volcanoes using scaled analog models we characterize a range of structural architectures produced by volcano sagging and volcano spreading these arise from the interplay of variable basement rigidity and volcano basement de coupling from comparison to volcanoes on earth la reunion and hawaii and mars elysium and olympus montes the models highlight a structural continuum in which large volcanoes throughout the solar system lie

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

molybdenum drawdown during cretaceous oceanic anoxic event 2 during the cretaceous greenhouse episodes of widespread ocean deoxygenation were associated with globally occurring events of black shale deposition possibly the most pronounced of these oceanic anoxic events oae s was the cenomanian turonian oae2 94 ma however although certain redox sensitive trace metals tend to be preferentially sequestered in sediments deposited under anoxic conditions with mo drawdown being specifically prone to euxinic settings these elements are generally somewhat depleted in sediments deposited during oae2 to understand the driving factors responsible for this depleted trace metal drawdown we have studied a low latitude section from the proto north atlantic ocean tarfaya s57 where existing biomarker and iron sulphur data point to a dominantly euxinic water column with periodic transitions to ferruginous fe rich water column conditions we utilise a variety of redox proxies fe speciation redox sensitive trace metals and mo isotopes which in combination allows us to evaluate the detailed nature of ocean redox conditions and hence controls on trace metal drawdown the results suggest that seawater 98mo values may have ranged between 0 6 and 1 1 during oae2 likely connected to changes in the local mo reservoir as a consequence of low and probably heterogeneous concentrations of mo in the ocean the very low mo toc ratios at tarfaya and elsewhere in the proto north atlantic may support a model in which deep water circulation was partially restricted within and between the north atlantic and other ocean basins we propose that the combination of a low and possibly heterogeneous 98mo of seawater mo together with low mo toc ratios points to a large decrease in the global oceanic mo reservoir during oae2 reflecting a major global scale increase in mo drawdown under persistent euxinic conditions 2016 elsevier b v

a new calibration to determine the closure temperatures of fe mg ordering in augite from nakhlites recently it has been shown that the relatively low closure temperature tc of 500 100 c calculated for augite from miller range nakhlite mil 03346 13 using the available geothermometers would correspond to a slow cooling rate inconsistent with the petrologic evidence for an origin from a fast cooled lava flow moreover previous annealing experiments combined with hr sc xrd on an augite crystal from mil 03346 clearly showed that at 600 c the fe2 mg degree of order remained unchanged thus suggesting that the actual tc is close to this temperature in order to clarify this discrepancy we undertook an ex situ annealing experimental study at 700 800 and 900 c until the equilibrium in the intracrystalline fe2 mg exchange is reached using an augite crystal from miller range nakhlite mil 03346 13 with a composition of about en36fs24wo40 these data allowed us to calculate the following new geothermometer calibration for martian nakhlites where the application of this new equation to other martian nakhlites nwa 988 and nakhla suggests that for augite with composition close to that of mil 03346 the tc is up to 170 c higher with respect to the one calculated using the previous available geothermometer equation thus suggesting a significantly faster cooling in agreement with petrologic evidence

portable x ray fluorescence spectroscopy as a tool for cyclostratigraphy cyclostratigraphic studies are used to create relative and high resolution timescales for sedimentary successions based on identification of regular cycles in climate proxy data this method typically requires the construction of long high resolution datasets in this study we have demonstrated the efficacy of portable x ray fluorescence spectroscopy pxrf as a non destructive method of generating compositional data for cyclostratigraphy the rapidity 100 samples per day and low cost of pxrf measurements provide advantages over relatively time consuming and costly elemental and stable isotopic measurements that are commonly used for cyclostratigraphy the non destructive nature of pxrf also allows other geochemical analyses on the same samples we present an optimized protocol for pxrf elemental concentration measurement in powdered rocks the efficacy of this protocol for cyclostratigraphy is demonstrated through analysis of 360 toarcian mudrock samples from north yorkshire uk that were previously shown to exhibit astronomical forcing of caco3 s and 13corg our study is the first to statistically compare the cyclostratigraphic results of pxrf analysis with more established combustion analysis there are strong linear correlations of pxrf ca with dry combustion elemental analyzer caco3 r2 0 7616 and pxrf s and fe with dry combustion elemental analyzer s r2 0 9632 and r2 0 9274 respectively spectral and cross spectral analysis demonstrates that cyclicity previously recognized in s significant above the 99 99 confidence level is present above the 99 92 and 99 99 confidence levels in pxrf s and fe data respectively cyclicity present in caco3 data above the 99 96 confidence level is also present in pxrf ca above the 98 12 confidence level

arctic black shale formation during cretaceous oceanic anoxic event 2 the late cretaceous oceanic anoxic event 2 oae2 represents a major perturbation of the global carbon cycle caused by the widespread deposition of organic rich black shales although the paleoceanographic response and the spatial extent of bottom water anoxia in low and mid paleolatitudes are reasonably well constrained for oae2 similar data from high paleolatitudes are lacking here we present palynostratigraphy and organic carbon isotope stratigraphy from the sverdrup basin axel heiberg island canada it is shown that episodes of high marine organic carbon burial at paleolatitudes of 70 n is contemporaneous with the widely observed occurrence of black shale deposition during oae2 paleontological lithological and geochemical data indicate normal marine conditions with persistent anoxic bottom waters during oae2 the results imply that the high marine primary productivity pulse during oae2 may have caused massive organic carbon burial on the arctic shelf in general with important implications for hydrocarbon source rock distribution in the arctic region

the morphologies of volcanic landforms at central elysium planitia evidence for recent and fluid lavas on mars abstract this paper focuses on physical parameters flow rates and rheological properties of lava flows observed in the central elysium planitia cep region of mars the flows are modeled as newtonian fluids using the jeffrey s equation and the concept of graetz number or alternatively as bingham fluids in addition to these approaches a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields providing independent quantifications of rheological variations between the shields this analysis indicates that of the five volcanoes studied two are partially buried by lava postdating their formation a result which has been confirmed independently in one case by high resolution images our observations reveal that two types of lava flows may be found in the cep region the first group is composed of large lava flows with viscosities around 2 5 10 5 pa s or yield strengths ranging from 100 to 500 pa the second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 103 pa s or yield strengths less than 200 pa when compared with other volcanic regions on mars investigated with similar approaches these latter values are at present the lowest inferred for martian lava flows several hypotheses for the formation of these lavas are discussed in the context of cep given that low viscosity can be the result of 1 high temperature 2 low crystal content 3 low si abundance of the liquid phase and or 4 the presence of dissolved volatiles two scenarios are considered in the first one it is demonstrated that low viscosity lavas of low silica content can be produced in the context proposed by schumacher and breuer schumacher s breuer d 2007 geophys res lett 34 l12202 for recent volcanism however geochemical maps derived from grs measurements do not provide support for anomalously low silica concentrations in this region in the second scenario a water rich magma is proposed although arguments in favor of a water rich mantle source below the cep are not available at the present time

effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels we numerically define the thermochemical evolution of a subduction related crystal bearing magmatic mass at mid crustal levels 0 7 gpa 20 25 km two main dynamic mechanisms are considered 1 a pure buoyancy driven system where the convective flow is induced by density changes during magma cooling 2 a buoyancy driven convective system governed by chaotic advection the non newtonian rheology of natural magmas is taken into account linking the herschel bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system the latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy driven convective system nearly 2 times faster our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems in particular 1 a time dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch 2 at the attainment of the maximum packing fraction i e just before the jamming condition homogeneous andesitic melts can be potentially extracted from the system and 3 the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy dominated system

orbital calibration of the late campanian carbon isotope event in the north sea a new record of carbon isotopes nannofossil biostratigraphy gamma ray and fe content variations is presented for the upper campanian of the adda 3 core danish central graben north sea the studied interval provides a revision of previously assigned late coniacian to early santonian ages new biostratigraphic data indicate a late campanian age for the 60 m thick studied interval the late campanian event lce is well recorded by a 1 5 negative excursion in the bulk 13 c along with two stepwise pre excursion negative shifts defining the pre lce the amplitude of the lce appears higher in the north sea than in other areas as seen from the correlation to germany the uk and france this correlation allows identification of a new 0 4 negative excursion defined as the conica event fe and gamma ray variations are used to calibrate the record with cyclostratigraphy fourteen 405 kyr cycles identified in the upper campanian of adda 3 can be correlated to north germany the compilation of previous results from north germany and correlation to adda 3 shows that the boreal upper campanian spans a total of 17 cycles each of 405 kyr that is 6 885 myr the duration of the lce is estimated to be c 1 myr at adda 3 and in north germany supplementary materials calibration of the hh xrf data is available at https doi org 10 6084 m9 figshare c 2134362

analytical numerical modeling of komatiite lava emplacement and thermal erosion at perseverance western australia abstract we have applied a thermal fluid dynamic geochemical model to investigate the emplacement and erosional potential of archean komatiite flows at perseverance western australia perseverance has been proposed as a site of large scale thermal erosion by large volume komatiite eruption s resulting in a 100 150 m deep lava channel containing one of the world s largest komatiite hosted fe ni cu pge sulfide deposits using constraints based on field theoretical and geochemical data we have modeled the emplacement of a range of flow thicknesses over felsic tuffaceous substrates with various degrees of consolidation and water contents thermo mechanical erosion becomes more effective for substrates that are increasingly unconsolidated and water rich for thermo mechanical erosion to be responsible for the formation of the 100 m deep concave perseverance embayment and the highly contaminated 10 20 perseverance komatiites the most likely scenarios require emplacement of thick e g 10 30 m turbulent channelized liquidus or superheated komatiite lavas over a welded or unconsolidated submarine tuff flow distances must have been long tens to hundreds of kilometers and flow volumes must have been very high hundreds to thousands of km 3 lava channels and tubes 110 km long have not been observed on earth but are consistent with those formed by low viscosity lavas on venus the moon mars and io flow volumes are consistent with those in continental flood basalt eruptions and oceanic plateau large igneous provinces and may represent the initial outpourings of komatiite lavas from archean mantle plume activity

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

crystallization kinetics of alkali feldspars in cooling and decompression induced crystallization experiments in trachytic melt cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar the effect of the degree of undercooling t t liquidus t experimental and time on nucleation and crystal growth process this experimental work gives us new data about crystallization kinetics of trachytic melts and it that will be useful to better understand the natural system of campi flegrei volcanoes experiments have been conducted using cold seal pressure vessel apparatus at pressure between 30 and 200 mpa temperature between 750 and 855 c time between 7 200 and 57 600 s and redox condition close to the nno 0 8 buffer these conditions are ideal to reproducing pre and syn eruptive conditions of the campi flegrei volcanoes where the conditions pertain to the complete range of pressures temperatures and time at which the experiments were performed alkali feldspar is the main phase present in this trachyte and its abundance can strongly vary with small changes in pressure temperature and water content in the melt implying appreciable variations in the textures and in the crystallization kinetics the obtained results show that crystallization kinetics are strictly related to t time final pressure superheating t and water content in the melt t is the driving force of the crystallization and it has a strong influence on nucleation and growth processes in fact the growth process dominates crystallization at small t whereas the nucleation dominates crystallization at large t time also is an important variable during crystallization process because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations this is an important aspect to understand magma evolution in the magma chamber and in the conduit which in turn has strong effects on magma rheology

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

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

on the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics abstractthe arid subtropics are situated at the edges of the tropical belt where subsidence in the hadley cells suppresses precipitation any meridional shift in these edge latitudes could have significant impacts on surface climate recent studies have investigated past and future changes in the tropical belt width and have found discrepancies in the rates of expansion estimated with different metrics and between climate models and reanalyses here cmip5 simulations and four modern reanalyses are analyzed using an ensemble of objective tropical belt width metrics to reexamine if such inconsistencies exist the authors do not find sufficient evidence to demonstrate this discrepancy between models and reanalyses as reanalysis trends in the tropical belt width fall within the range of model trends for any given metric furthermore only metrics based on the hadley cells are found to exhibit robust historical and future expansion metrics based on the subtropical jet and the tropopause show no robust resp

cretaceous black mud from the central arctic ocean perhaps the oldest sediment yet recovered from the central arctic ocean is a black organic carbon rich mud of late campanian or maastrichtian age the sediment is known in a single piston core f1 533 taken from the eastern alpha ridge the black mud has an average organic carbon content of 14 wt and contains abundant woody plant fragments and pollen in addition to amorphous organic matter in a marine dinoflagellate rich matrix moderate hydrogen and high oxygen indices determined by rock eval pyrolysis suggest a substantial contribution of terrestrial plant debris to the marine sediment the black mud is younger than organic rich strata deposited during the oceanic anoxic events proposed for aptian albian and late cenomanian to early turonian times in the atlantic and pacific oceans the high content of organic carbon and the abundance of terrestrial organic matter in the arctic black mud suggest a marine setting influenced by an abundant supply of organic detritus rather than by a low level of oxygenation in the water column sediment in this core demonstrates that the central arctic ocean may have been in existence by the late campanian to maastrichtian and that the area of core f1 533 probably was adjacent to an eroding vegetated land mass

sources and mechanisms for the enrichment of highly reactive iron in euxinic black sea sediments the deep basinal euxinic sediments of the black sea are enriched in iron that is highly susceptible to sulfidization compared to oxic suboxic continental margin sediments in the black sea and oxic dysoxic continental margin and deep sea sediments worldwide a mass balance treatment of iron speciation data from three deep basin sediment cores shows that this enrichment is due to a combination of 1 highly reactive iron bearing phases sulfides and oxides whose ultimate source was by diagenetic mobilization from the shelf wijsman and others 2001 and 2 enhanced iron reactivity in the lithogenous component of deep basinal sediments the cause of the enhanced reactivity of lithogenous iron is problematical possible mechanisms include microbial oxidation of non reactive iron silicates and the preferential deposi tion of a fine grained reactive iron enriched lithogenous component in the deep basin by the fractionation of the lithogenous flux during transport across the shelf the application of paleoredox indicators based on iron reactivity degree of pyritization indicator of anoxicity should take into account that the availability of highly reactive iron and hence the concentration of reactive iron phases in the sediment is controlled by a variety of chemical physical and biological factors some of which are not related directly to redox conditions in the water column

controls on regional marine redox evolution during permian triassic transition in south china abstract although oceanic anoxia is regarded as a leading cause of the permian triassic boundary ptb mass extinction its timing extent and underlying causes remain unclear here we conducted a high resolution fe s c mo geochemical study of the entire changhsingian and lowermost induan succession in a carbonate ramp setting at ganxi western hubei province south china six stratigraphic units representing discrete redox intervals were identified based on integrated fe s c mo data units i iii are of latest wuchiapingian to early changhsingian age with units i and iii characterized by euxinia and unit ii by uncertain redox conditions unit iv of mid changhsingian age records a gradual transition from euxinic to ferruginous conditions units v and vi spanning the latest permian mass extinction lpme to earliest triassic interval were deposited under dominantly ferruginous conditions punctuated by both euxinic and oxic episodes redox variations at ganxi were controlled by contemporaneous oceanographic changes in the upper oceanic thermocline region i euxinia in units i and iii may record elevated marine productivity as suggested by mean organic carbon accumulation rates or ocar of 6 5 and 5 1 mg cm2 kyr respectively that was possibly related to upwelling ii the euxinic to ferruginous transition from unit iv to units v vi can be attributed to a combination of reduced sulfate availability and rising terrigenous iron inputs mean fe of 1 7 and 3 9 respectively for units v iv and vi compared to 1 0 for units i iii and iii transient intervals of euxinia in units v and vi were facilitated by enhanced sulfate fluxes related to episodic volcanism during this interval an integration of the redox data from ganxi with previously published data from the shangsi and xiakou sections suggests that enhanced weathering fluxes were most likely the key factor controlling the marine redox transition from euxinic to ferruginous conditions during the latest permian across the south china region

role of tropical variability in driving decadal shifts in the southern hemisphere summertime eddy driven jet abstractthe southern hemisphere summertime eddy driven jet and storm tracks have shifted poleward over the recent few decades in previous studies explanations have mainly stressed the influence o

lipid biomarker stratigraphic records through the late devonian frasnian famennian boundary comparison of high and low latitude epicontinental marine settings abstract the pervasiveness of black shale preservation in association with late devonian biological crises suggests marine anoxia played a major role in driving ecological perturbations however devonian black shale deposition is still mechanistically poorly understood we have compiled detailed biomarker lipid chemostratigraphic records for 83 different rock samples using molecular constituents of bitumens of upper kellwasser equivalent black shales from two foreland basins from the low paleolatitude appalachian basin new york state and from the high paleolatitude madre de dios basin bolivia in order to better understand local environmental conditions and organic source inputs during this depositional event despite strong indications from stable nitrogen isotopic signatures for fixed nitrogen nutrient limitation the biomarker assemblages with consistently low moderate hopane sterane ratios 28 c 29 sterane ratios at higher paleolatitude in the more nutrient replete madre de dios basin suggest prasinophyte microalgae flourished in this setting in accordance with palynological evidence for high contributions of tasmanites cysts in these strata all samples contain only very low absolute amounts of aryl isoprenoids with 2 3 6 trimethyl substitution and other aromatic carotenoids up to several orders of magnitude lower than concentrations reported from other phanerozoic euxinic basins these data are consistent with local marine paleo redox models for both basins lacking a persistently shallow sulfidic aquatic zone and demonstrate that temporally persistent or spatially pervasive photic zone euxinia is not necessarily associated with all black shale sequences in the late devonian

direct measurements of latent heat during crystallization and melting of a ugandite and an olivine basalt received 19 october 1993 accepted 3 may 1994 abstract step scanning calorimetric measurements us ing a setaram ht1500 calorimeter were performed be tween 800 and 1400 on two natural samples a ugan dite from the east african rift and an olivine basalt from the western mexican arc our measurements provide the first in situ quantitative assessment of enthalpy dur ing melting of initially crystalline natural samples the distribution of latent heat across the liquidus solidus intervals of the two samples is distinctly different re flecting significant variation in the sequence and abun dance of mineral phases during melting clinopyroxene and leucite in the ugandite olivine clinopyroxene and plagioclase in the basalt our data further indicate that the common assumption of a uniform distribution of latent heat across the liquidus solidus interval of a mag ma is a reasonable approximation for the olivine basalt but is grossly in error for the ugandite this is due to cotectic precipitation of leucite and clinopyroxene lead ing to a large disproportionate release of latent heat early in the crystallization sequence the implication for the thermal history of a crystallizing ugandite magma is that the rate of heat loss during conductive cooling will initially be more rapid than the average rate the net result will be to produce lower magmatic temperatures after a given cooling interval relative to models assum ing a uniform release of latent heat an additional series of scanning calorimetric experiments were performed at variable rates 1 2 and 3 to evaluate the role of kinetics on the distribution of enthalpy during both melting and crystallization of the ugandite and olivine basalt the results indicate that clinopyroxene is the most important mineral phase in controlling the shapes of the enthalpy profiles during cooling this is due to its large enthalpy of fusion and its tendency for sluggish nucleation followed by rapid crystallization at temper atures that vary with cooling rate the resolution of the calorimeter in terms of heat detected per unit time is also important in determining the shapes of the observed enthalpy profiles during these rapid scans estimates based on the observed calorimetric signal associated with melting of olivine and the lack of a calorimetric signal during melting of leucite combined with known enthalpies of fusion for the two phases indicate detec tion limits of approximately 0 6 1 2 kj per 5 rain incre ments

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

formation of a martian pyroxenite a comparative study of the nakhlite meteorites and theo s flow the unusual composition of the nakhlites a group of pyroxenitic martian meteorites with young ages presents an opportunity to learn about nonbasaltic magmatic activity on another planet however the limited number of these meteorites makes unraveling their history difficult a promising terrestrial analog for the formation of the nakhlites is theo s flow in ontario canada this atypical 120 m thick flow differentiated in place forming distinct layered lithologies of peridotite pyroxenite and gabbro theo s pyroxenite and the nakhlites share strikingly similar petrographies with concentrated euhedral to subhedral augite grains set in a plagioclase rich matrix these two suites of rocks also share specific petrologic features mineral and whole rock compositional features and size and spatial distributions of cumulus grains the numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion their formation could have involved settling of crystals in a phenocryst laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow the latter case is more likely and requires steady state nucleation and growth of clusters of pyroxene grains and olivine in the nakhlites circulating in a strongly convecting melt pool followed by settling and continued growth in a thickening cumulate pile trapped pockets of intercumulus liquid in the pile gradually evolved finally growing fe enriched rims on cumulus grains with sufficient evolution the melt reached plagioclase supersaturation causing rapid growth of plagioclase sprays and late stage mesostasis growth

modeling organic carbon burial during sea level rise with reference to the cretaceous after three decades of research on the correlation between sea level and various proxies there has been very little quantification of the first order influence of sea level change on nutrient inventory marine productivity and burial of organic carbon we present a model aimed at quantifying the burial of organic carbon as a function of sea level rise the biogeochemical model explicitly considers the mean surface area distribution of the earth as a function of elevation also included is dissolved inorganic phosphate dip liberated from coastal sediments during transgression we quantify how sea level rise of magnitudes inferred for the mid cretaceous influences the phosphorus cycle and burial of organic carbon the burial efficiency is greater on the shelf therefore in the model the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given dip concentration and associated new production of organic matter np with a late cretaceous model shelf area the residence time of dip decreases by 60 relative to the present day reference thus in the final steady state dip and np in the open ocean are reduced compared to today when the biologically reactive phosphorus preac fluxes to the ocean from land are held constant the lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean finally the global organic carbon burial decreases by 30 relative to today in the model this decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to preac in buried sediments in contrast during sea level rise coastal erosion may increase the preac flux to the ocean by up to 20 relative to today and cause a temporary increase in dip concentration in the ocean the resulting increase in organic carbon burial is equivalent to a carbon isotope event of 0 5 to 1 larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise

influence of the high arctic igneous province on the cenomanian turonian boundary interval sverdrup basin high canadian arctic abstract emplacement of large igneous provinces lips had a major effect on global climate ocean chemistries as traced in sedimentary records and biotic turnovers the linkage between lips and oceanic anoxic events has been documented with the cenomanian turonian boundary event and oceanic anoxic event 2 oae2 the caribbean lip and high arctic large igneous province halip are regarded as possible triggers the pericratonic arctic sverdrup basin is the partial location of the halip where little is known about sedimentary geochemical and biotic responses to the halip phases sedimentary strata at glacier fiord axel heiberg island exhibit a dynamic cretaceous polar carbon burial history within the lower to middle cenomanian bastion ridge formation and upper cenomanian to turonian part of the kanguk formation we present the first initial 187os 188os osi composition profile for a polar cenomanian turonian boundary interval 100 93 9 ma linked to recently dated magmatic phases of the strand fiord formation part of the halip the carbon isotope record coupled with the osi profile show two events in the upper cenomanian interval marked by positive carbon perturbations and shifts to more non radiogenic osi compositions the earlier short lived event is interpreted as result of weathering of the surrounding strand fiord volcanics causing a local non radiogenic osi signal coinciding transgressive shorelines let to an increase in marine and terrestrially derived organic matter subsequently injection of mantle derived basalts into organic rich sediments is credited with causing the release of methane documented in a distinct negative carbon isotope excursion we speculate that the methane release of the halip was an important contribution for rapid global warming caused by increasing atmospheric co2 levels associated with the oae2 event likewise recognized in the sverdrup basin as climate cooled in the middle and late turonian carbon burial decreased under increasingly oxygenated benthic conditions epifaunal foraminiferal species adapted to low oxygen conditions persisted during the oae2 our cenomanian to turonian multiproxy record of the sverdrup basin distinguishes between local and global signals within a restricted high arctic basin our results demonstrate the interplay between basin tectonism and sea level change increased weathering during transgressive phases seafloor processes such as hydrothermal activity and methane release and biotic response to a complex paleoceanography with future reliable dated frameworks this unique polar record will facilitate correlations to other polar basins and records of lower paleolatitudes

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

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

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

a southern hemisphere record of global trace metal drawdown and orbital modulation of organic matter burial across the cenomanian turonian boundary ocean drilling program site 1138 kerguelen plateau despite its assumed global nature there are very few detailed stratigraphic records of the late cenomanian to the early turonian oceanic anoxic event 2 from the southern hemisphere a highly resolved record of environmental changes across the cenomanian turonian boundary interval is presented from ocean drilling program site 1138 on the central kerguelen plateau southern indian ocean the new data lead to three key observations firstly detailed biostratigraphy and chemostratigraphy indicate that the record of oceanic anoxic event 2 is not complete with a hiatus spanning the onset of the event a decrease in glauconite and highly weathered clays after the onset of oceanic anoxic event 2 marks the end of the hiatus interval which can be explained by a relative sea level rise that increased sediment accommodation space on the kerguelen plateau margin this change in depositional environment controlled the timing of the delayed peak in organic matter burial during oceanic anoxic event 2 at site 1138 compared with other oceanic anoxic event 2 locations worldwide a second key observation is the presence of cyclic fluctuations in the quantity and composition of organic matter being buried on the central kerguelen plateau throughout the latter stages of oceanic anoxic event 2 and the early turonian a close correspondence between organic matter sedimentary elemental compositions and sediments recording sea floor oxygenation suggests that the cycles were mainly productivity driven phenomena available age control points constrain the periodicity of the coupled changes in sedimentary parameters to ca 15 to 50 ka suggesting a link between carbon burial and astronomically forced climatic variations precession or obliquity in the southern hemisphere mid latitudes both during and after oceanic anoxic event 2 fluctuations that were superimposed on the impact of global scale processes finally trace metal data from the non sulphidic black shale unit at site 1138 provide the first evidence from outside of the proto north atlantic region for a global drawdown of seawater trace metal mo inventories during oceanic anoxic event 2 this article is protected by copyright all rights reserved

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

sources of iron for pyrite formation in marine sediments more than two hundred aerobic continental margin aerobic deep sea dysaerobic and anaerobic euxinic sediments have been examined for their variations in different operationally defined iron fractions each of which represents a different reactivity towards dissolved sulfide aerobic continental margin deep sea and dysaerobic sediments contain similar contents of highly reactive iron dithionite soluble iron plus pyrite iron poorly reactive iron iron soluble in hcl less that soluble in dithionite and unreactive iron total iron less that soluble in hcl by contrast non turbidite euxinic samples from the black sea as well as euxinic samples from the cariaco basin and framvaren are enriched in highly reactive iron these sediments contain a small lithogenous fraction and a large biogenous organic c rich fraction which decays by sulphate reduction in an iron rich water column to form pyrite rich sediment other anaerobic euxinic samples from the black sea orca basin and kau bay contain lower concentrations of biogenous sediment and are not therefore enriched in highly reactive iron degrees of pyritization dop for all the aerobic dysaerobic and anaerobic euxinix samples except those low in biogenous material are consistent with analogous ancient sediments and indicate that most pyrite formation occurs form the highly reactive iron fraction

a co2 decrease driven cooling and increased latitudinal temperature gradient during the mid cretaceous oceanic anoxic event 2 article i nfo the mid cretaceous is thought to be a greenhouse world with significantly higher atmospheric pco2 and sea surface temperatures as well as a much flatter latitudinal thermal gradient compared to the present this time interval was punctuated by the cenomanian turonian oceanic anoxic event oae 2 93 5 myr ago an episode of global massive organic carbon burial that likely resulted in a large and abrupt pco2 decline however the climatic consequences of this pco2 drop are yet poorly constrained we determined the first high resolution sea surface temperature sst record across oae 2 from a deep marine sedimentary sequence at ocean drilling program odp site 1276 in the mid latitudinal newfoundland basin nw atlantic by employing the organic palaeothermometer tex86 we found that ssts across the oae 2 interval were extremely high but were punctuated by a remarkably large cooling 5 11 c which is synchronous with the 2 5 5 5 c cooling in sst records from equatorial atlantic sites and the plenus cold event because this global cooling event is concurrent with increased organic carbon burial it likely acted in response to the associated pco2 drop our findings imply a substantial increase in the latitudinal sst gradient in the proto north atlantic during this period of global cooling and reduced atmospheric pco2 suggesting a strong coupling between pco2 and latitudinal thermal gradients under greenhouse climate conditions

lithium isotope evidence for enhanced weathering during oceanic anoxic event 2 the ocean anoxic event 2 oae2 about 93 5 million years ago was marked by high atmospheric co2 concentration rapid global warming and marine anoxia and euxinia the event lasted for about 440 000 years and led to habitat loss and mass extinction the marine anoxia is thought to be linked to enhanced biological productivity but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery here we use lithium isotope measurements from carbonates spanning the interval including oae2 to assess the role of silicate weathering we find the lightest values of the li isotope ratio 7li during oae2 indicating high levels of weathering and therefore atmospheric co2 removal which we attribute to an enhanced hydrological cycle we use a geochemical model to simulate the evolution of 7li and the ca sr and os isotope tracers our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric co2 concentrations and rapid global warming which initiated oae2 the simulated warming was accompanied by a roughly 200 000 year pulse of accelerated weathering of mafic silicate rocks which removed co2 from the atmosphere the weathering also delivered nutrients to the oceans that stimulated primary productivity we suggest that this process together with the burial of organic carbon allowed the rapid recovery and stabilization from the greenhouse state

the interplay of internal and forced modes of hadley cell expansion lessons from the global warming hiatus the poleward branches of the hadley cells and the edge of the tropics show a robust poleward shift during the satellite era leading to concerns over the possible encroachment of the globe s subtropical dry zones into currently temperate climates the extent to which this trend is caused by anthropogenic forcing versus internal variability remains the subject of considerable debate in this study we use a joint eof method to identify two distinct modes of tropical width variability 1 an anthropogenically forced mode which we identify using a 20 member simulation of the historical climate and 2 an internal mode which we identify using a 1000 year pre industrial control simulation the forced mode is found to be closely related to the top of the atmosphere radiative imbalance and exhibits a long term trend since 1860 while the internal mode is essentially indistinguishable from the el nino southern oscillation together these two modes explain an average of 70 of the interannual variability seen in model edge indices over the historical period since 1980 the superposition of forced and internal modes has resulted in a period of accelerated hadley cell expansion and decelerated global warming i e the hiatus a comparison of the change in these modes since 1980 indicates that by 2013 the signal has emerged above the noise of internal variability in the southern hemisphere but not in the northern hemisphere with the latter also exhibiting strong zonal asymmetry particularly in the north atlantic our results highlight the important interplay of internal and forced modes of tropical width change and improve our understanding of the interannual variability and long term trend seen in observations

thermo rheological magma control on the impact of highly fluid lava flows at mt nyiragongo 1 in january 2002 mount nyiragongo erupted foiditic lavas that covered the southern volcano flank devastating vast urban areas lava flows originated from vents at different heights on the eruptive fissure displayed different velocities from tens of km h at the highest vents to slow advance 0 1 1 km h in goma town several km away from the volcano to understand the different behavior of lava flows and their threat to the local population we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent we demonstrate that pre eruptive cooling and syn eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights venting at lower altitudes is expected to produce viscous slowly advancing lavas although development of fluid faster flows should be included among possible future eruptive scenarios

breakdown of the linear relationship between the southern hemisphere hadley cell edge and jet latitude changes in the last glacial maximum abstracta poleward displacement of the hadley cell hc edge and the eddy driven jet latitude has been observed in the southern hemisphere sh during the last few decades this change is further p

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

organic facies variability and paleoenvironmental changes on the moroccan atlantic coast across the cenomanian turonian oceanic anoxic event oae2 abstract the cenomanian turonian boundary is marked by worldwide paleoenvironmental and paleoceanographical changes that are associated with a perturbation of the global carbon cycle and black shale deposition called the oceanic anoxic event 2 oae2 the objective of this study is to precisely characterize the nature of the organic matter its variability paleoenvironmental significance and the preservation conditions of two areas located along the northwest african shelf where large scale organic carbon burial contributed significantly to the global carbon burial associated with oae2 with these premises an organic petrographic and geochemical approach to the cenomanian turonian record of the moroccan atlantic coast allowed the definition of the variability of the organic facies and the paleoenvironmental characterization of the upper cenomanian lower turonian sediments of the agadir section agadir basin and of the lower turonian record of the amma fatma section tarfaya basin at agadir the marine microplankton dominated assemblages with variable degree of amorphization allowed the characterization of a transgressive regressive cycle during the upper cenomanian followed during the lower turonian by a drowning event with establishment of a deep platform environment under reducing conditions increase in efu efv efmo the base of the succession base of w archaeocretacea biozone and the top of the upper cenomanian are characterized by two sea level lowstands and a high energy oxic environment that culminate in emersion surfaces high efmn and low organic matter preservation the organic facies in the lower turonian of amma fatma is largely dominated by bacterial material probably derived from sulfur bacteria indicating an outer shelf setting with some degree of restriction under euxinic conditions high efmo and high primary productivity high efcu efni efzn differences in terms of the redox conditions between the two basins during the lower turonian were determined with anoxia prevailing at agadir while euxinic conditions are established at tarfaya these are explained by different oceanic circulation patterns with the mixing of tethyan waters at agadir high primary productivity is recorded at both locations possibly promoted by the occurrence of upwelling currents this study further corroborates a delay in the anoxia in agadir that during the isotopic excursion of oae2 only reaches slight dysoxia upper cenomanian and the maintenance of reducing conditions in tarfaya post oae2

emplacement and erosive effects of lava in south kasei valles mars abstract although it has generally been accepted that the martian outflow channels were carved by floods of water observations of large channels on venus and mercury demonstrate that lava flows can cause substantial erosion recent observations of large lava flows within outflow channels on mars have revived discussion of the hypothesis that the martian channels are also produced by lava an excellent example is found in south kasei valles skv where the most recent major event was emplacement of a large lava flow calculations using high resolution digital terrain models dtms demonstrate that this flow was locally turbulent similar to a previously described flood lava flow in athabasca valles the modeled peak local flux of approximately 106 m3 s 1 was approximately an order of magnitude lower than that in athabasca which may be due to distance from the vent fluxes close to 107 m3 s 1 are estimated in some reaches but these values are probably records of local surges caused by a dam breach event within the flow the skv lava was locally erosive and likely caused significant kilometer scale headwall retreat at several cataracts with tens to hundreds of meters of relief however in other places the net effect of the flow was unambiguously aggradational and these are more representative of most of the flow the larger outflow channels have lengths of thousands of kilometers and incision of a kilometer or more therefore lava flows comparable to the skv flow did not carve the major martian outflow channels although the skv flow was among the largest and highest flux lava flows known in the solar system

stratigraphically controlled silicification in danian chalk and its implications for reservoir properties southern danish central graben abstract the effect of silica on reservoir quality in chalk is subject to continuing debate in particular the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently in this study a new approach is applied to constrain silica variability in reservoir chalk utilizing hand held x ray fluorescence hh xrf on samples from four maastrichtian danian cores from hydrocarbon producing fields in the southern danish central graben the results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area data display a common stratigraphic signature in all wells however with maximum silica concentrations and minimum porosities occurring in the lower part of the danian ekofisk formation correlation between hh xrf quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi regional silica event during the mid danian nannofossil zones nntp2f g to nntp4a d whereas the upper boundary of the peak silica unit is poorly constrained generally stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends however comparison between the hh xrf quantified silica content and reservoir data porosity permeability estimated pore radius and calculated specific surface area shows poor correlation indicating that silica content within the ekofisk reservoir is not the only factor controlling the reservoir quality unknown complex diagenetic interactions between calcite silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones making the ekofisk reservoir much less predictable than the underlying maastrichtian tor formation

viscous flow behavior of tholeiitic and alkaline fe rich martian basalts abstract the chemical compositions of martian basalts are enriched in iron with respect to terrestrial basalts their rheology is poorly known and liquids of this chemical composition have not been experimentally investigated here we determine the viscosity of five synthetic silicate liquids having compositions representative of the diversity of martian volcanic rocks including primary martian mantle melts and alkali basalts the concentric cylinder method has been employed between 1500 c and the respective liquidus temperatures of these liquids the viscosity near the glass transition has been derived from calorimetric measurements of the glass transition although some glass heterogeneity limits the accuracy of the data near the glass transition it was nevertheless possible to determine the parameters of the non arrhenian temperature dependence of viscosity over a wide temperature range 1500 c to the glass transition temperature at superliquidus conditions the martian basalt viscosities are as low as those of the fe ti rich lunar basalts similar to the lowest viscosities recorded for terrestrial ferrobasalts and 0 5 to 1 order of magnitude lower than terrestrial tholeiitic basalts comparison with empirical models reveals that giordano et al 2008 offers the best approximation whereas the model proposed by hui and zhang 2007 is inappropriate for the compositions considered the slightly lower viscosities exhibited by the melts produced by low degree of mantle partial melting versus melts produced at high degree of mantle partial melting likely corresponding to the early history of mars is not deemed sufficient to lead to viscosity variations large enough to produce an overall shift of martian lava flow morphologies over time rather the details of the crystallization sequence and in particular the ability of some of these magmas to form spinifex texture is proposed to be a dominant effect on the viscosity during martian lava flow emplacement and may explain the lower range of viscosities 10 2 10 4 pa s inferred from lava flow morphology further the differences between the rheological behaviors of tholeiitic vs trachy basalts are significant enough to affect their emplacement as intrusive bodies or as effusive lava flows the upper range of viscosities 10 6 10 8 pa s suggested from lava flow morphology is found consistent with the occurrence of alkali basalt documented from in situ analyses and does not necessarily imply the occurrence of basaltic andesite or andesitic rocks

relationship between plagioclase crystallization and cooling rate in basaltic melts rock textures commonly preserve a record of the near surface crystallization history of volcanic rocks under conditions of simple cooling without convection or mixing textures will reflect sample cooling rate the temperature at which crystallization was initiated and the distribution of mineral phase precipitation across the crystallization interval compilation of plagioclase size and number density data on natural dike sill and lava lake and experimental samples suggests that 1 growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate and 2 the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization evaluation of textural data in the context of recent numerical models of crystallization in simple one and two component systems provides new insight into regularities in the crystallization behavior of basaltic magmas for example the rate of change in crystal size and number density as dictated by mass balance has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems in natural samples plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width solidification time comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes distributions broaden and the grain size at peak frequency increases with increasing crystallization times decreasing cooling rates in contrast partially crystallized makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size measured size distributions in dikes can be explained by late stage modification of makaopuhi type distributions through loss of small crystals possibly the consequence of growth without nucleation finally this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near surface basaltic systems predicted growth rates will be slow and relatively constant 10 10 10 11 cm s for crystallization times expected in most shallow volcanic systems 1000 years

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

paleo redox conditions during oae 2 reflected in demerara rise sediment geochemistry odp leg 207 abstract cretaceous black shales deposited under severe oxygen depletion are carriers of proxy signals for paleoenvironmental conditions using high resolution patterns of iron and sulfur speciation stable sulfur isotope discrimination and trace element enrichment from black shale sequences of sites 1258 and 1260 we identified alterations of the depositional environment during the cenomanian turonian boundary event oae 2 in the southern north atlantic odp leg 207 demerara rise changes in redox conditions are suggested by high ratios of reactive to total iron which indicate that pyrite was formed both in the water column and within the sediment this corresponds to euxinic paleoenvironmental conditions with at least temporarily free dissolved sulfide in the water column a situation similar to the modern deep black sea in addition besides fixation of sulfide as iron sulfide organic matter acted as an important sulfur trap during early diagenesis stable sulfur isotope fractionation went through a minimum within the oae 2 interval indicating enhanced sulfur isotope discrimination during highest burial of organic matter om potentially due to lower burial efficiency of reduced sulfur and or a higher contributions from the oxidative part of the sulfur cycle e g in the water column or the surface sediments elevated fe al and co al values within the cenomanian turonian interval confirm euxinic conditions but at the same time require a zone where reducing but non sulfidic conditions prevail allowing reductive fe and co mobilization in oxygen depleted nearshore sediments the existence of an expanded oxygen minimum zone omz is demonstrated by extremely low mn al ratios a change in the trace metal tm inventory of seawater is postulated from a decline in seawater derived tm enrichment because hypoxic or even euxinic environments form an important sink for tm the enlargement of euxinic depositional areas at the global onset of black shale deposition during oae 2 have likely led to a drawdown of the seawater tm reservoir

geochemistry and re os geochronology of the organic rich sedimentary rocks in the jingtieshan fe cu deposit north qilian mountains nw china abstract the jingtieshan group in the north qilian mountains nw china is dominantly composed of banded iron formations bifs copper deposits and organic rich sedimentary rocks ors carbonaceous phyllite x ray diffraction analysis of the ors shows the mineral assemblage to be quartz clay minerals the total organic carbon contents show a range of 0 44 1 72 here we present the results of the geochemistry and re os geochronology of the ors from the jingtieshan group the high values of chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and th u ratio indicate intense weathering the al 2 o 3 tio 2 zr sc th sc la th ratios high rare earth elements abundances light rare earth elements enrichment normalized to chondrite and distinctly negative eu anomalies suggest that the jingtieshan group ors were derived mainly from felsic volcanic units the new re os isochron age of 1308 100 ma 2 n 6 mswd 23 broadly overlap with the previous published ages determined using sm nd and u pb isotope systems the new age represents the depositional age of the jingtieshan group as well that of bif in the jingtieshan area furthermore the initial 187 os 188 os ratios 0 44 0 07 indicate that the os in the seawater was dominantly derived from hydrothermal fluids 75 the ce anomaly ce ce 0 95 1 00 and v v ni ratios 0 71 0 86 as well as the lack of enrichment in redox sensitive trace elements such as u v zn pb cu ni cr co and mn together with the presence of overlying bif suggest that the jingtieshan area represents a ferruginous deep water succession this and intense submarine hydrothermal activities contributed to the deposition of the jingtieshan bif

viscosity measurements of subliquidus magmas alkali olivine basalt from the higashi matsuura district southwest japan abstract we carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the matsuura district sw japan at subliquidus temperatures from 1230 c to 1140 c under 1 atm with nno oxygen buffered conditions viscosity increased from 31 to 1235 pa s with a decrease in temperature from 1230 to 1140 c on cooling olivine first appeared at 1210 c followed by plagioclase at 1170 c the crystal content of the sample attained 31 vol at 1140 c plagioclase 22 olivine 9 non newtonian behaviors including thixotropy and shear thinning were pronounced in the presence of tabular plagioclase crystals the cause of such behavior is discussed in relation to shear induced changes in melt crystal textures relative viscosities r s m where s and m are the viscosities of the suspension and the melt respectively were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by giordano and dingwell giordano d dingwell d b 2003 non arrhenian multicomponent melt viscosity a model earth and planetary science letters 208 337 349 the obtained relative viscosities are generally consistent with the einstein roscoe relation which represents r for suspensions that contain equant and equigranular crystals even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes this consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size the applicability of the einstein roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results our experiments and those of sato sato h 2005 viscosity measurement of subliquidus magmas 1707 basalt of fuji volcano journal of mineralogical and petrological sciences 100 133 142 show that the relationship between relative viscosity and crystal fraction is consistent with the einstein roscoe relationship for axial ratios that are smaller than the critical value of 4 6 5 but discrepancies occur for higher ratios

metric dependent tendency of tropical belt width changes during the last glacial maximum abstractmotivated by studies of tropical expansion under modern global warming the behavior of the tropical belt during the last glacial maximum lgm relative to the preindustrial period has been

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

midlatitude fronts and variability in the southern hemisphere tropical width abstractthis study examines the relationship between midlatitude synoptic activity and variations in the width of the tropics in the southern hemisphere for the period 1979 2016 the edge of the tr

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

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

natural variations of tropical width and recent trends the temporal evolution of the tropical width since 1979 is investigated in observations and models by using metrics based on outgoing radiation 6 7 m brightness temperature and atmospheric reanalysis the maximum 20 year widening as seen in radiation by satellites occurred during 1993 2012 and was associated with a global sea surface temperature sst change that resembles the el nino southern oscillation pacific decadal oscillation in the pacific region idealized experiments with community atmospheric model version 5 reveal that tropical pacific sst pattern largely accounts for the widening a number of coupled model intercomparison project phase 5 coupled models can simulate without any type of forcing this satellite inferred tropical widening and its associated pacific sst pattern while model simulated widenings are consistent for all metrics the two reanalysis based widenings are inconsistent internally and with the satellite based and model widenings our results reinforce suggestions that observed widenings can be explained by internal variability as captured by climate models though this depends on whether reanalysis trends are regarded as reliable

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

the effects of undercooling and deformation rates on the crystallization kinetics of stromboli and etna basalts we have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from stromboli pumice from the march 15 2007 paroxysmal eruption and etna 1992 lava flow isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate t 1 157 1 187 c and dot gamma i 4 26 s 1 for stromboli t 1 131 1 182 c and dot gamma i 0 53 s 1 for etna melt viscosity increased due to the decrease in temperature and the increase in crystal content the mineralogical assemblage comprises sp plg dominant cpx with an overall crystal fraction between 0 06 and 0 27 increasing with undercooling and flow conditions both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process plagioclase nucleation incubation time strongly decreases with increasing t and flow while slow diffusion limited growth characterizes low t low deformation rate experiments both stromboli high strain rate and etna low strain rate plagioclase growth rates g display relative small variations with stromboli showing higher values 4 8 1 9 10 9 m s 1 compared to etna 2 1 1 6 10 9 m s 1 plagioclase average nucleation rates j continuously increase with undercooling from 1 4 106 to 6 7 106 m 3 s 1 for stromboli and from 3 6 104 to 4 0 106 m 3 s 1 for etna the extremely low value of 3 6 104 m 3 s 1 recorded at the lowest undercooling experiment for etna t 20 c indicates that the crystallization process is growth dominated and that possible effects of textural coarsening occur g values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions stirring of the melt simulating magma flow or convective conditions facilitates nucleation and growth of crystals via mechanical transportation of matter resulting in the higher j and g observed any modeling pertaining to magma dynamics in the conduit e g ascent rate and lava flow emplacement e g flow rate p hoehoe a transition should therefore take the effects of dynamic crystallization into account

glass forming ability and crystallisation behaviour of sub alkaline silicate melts abstract the intrinsic solidification behaviour and glass forming ability gfa of natural sub alkaline silicate melts have been experimentally quantified via cooling induced solidification approach gfa is measured by the critical cooling rate rc the rate at which a melt solidifies 2 area of crystals cooling rates of 9000 1800 180 60 7 and 1 c h have been run between 1300 c super liquidus region and 800 c quenching temperature at air f o 2 and ambient p for six silicate melts with compositions ranging from basalt b to rhyolite r i e b 100 b 80 r 20 b 60 r 40 b 40 r 60 b 20 r 80 and r 100 and water contents comprised between 53 b 100 and 384 b 20 r 80 ppm the ranges of cooling rates and chemical compositions used in this study are the broadest ever investigated in the earth sciences the phase proportions area were determined by image analysis on about 500 back scattered electron images collected over different magnifications phases are glass clinopyroxene cpx spinel sp and plagioclase plg sp is ubiquitous with abundance of few area and nucleates earlier than silicate crystals cpx solidifies in all runs except in r 100 and its abundance follows asymmetric broad gaussian like trends with tails towards low rates as a function of cooling rate moving from b 100 to b 40 r 60 these trends conserve their shape but shift progressively to lower cooling rates and mineral abundances plg crystallises only at low cooling rates and in sio 2 poor compositions run products with low amounts of crystals 5 area clearly show that cpx preferentially nucleates on surfaces of sp whereas a significant crystallisation of cpx 5 area is observed with decreasing cooling rate and with changing composition from b 100 to b 20 r 80 the crystallisation of silicate crystals is related to the chemical diffusivity of components in the melt also the initial crystallisation of plg occurs preferentially on cpx in general the amount of crystals decreases as the cooling rate increases however in some cases the amount of crystals remains constant or even decreases for b 80 r 20 with decreasing cooling rate rc values change over 5 orders of magnitude being 100 b 20 r 80 b 40 r 60 b 60 r 40 and b 80 r 20 and b 100 respectively the variation of rc can be modelled through nbo t nonbridging oxygen per tetrahedron parameter by the following equation rc a 1 e nbo t b c where a b and c are fitting parameters equal to 9214 0 297 and 0 040 respectively similarly to other glass forming liquids network metallic and molecular systems rc for natural sub alkaline silicate melts is inversely related to the reduced glass transition parameter trg trg tg tm and can be quantified with the equation rc a trg b where a and b are 1 19 10 4 and 28 7 respectively these results may be used to retrieve the solidification conditions of aphyric degassed and oxidised lavas in addition our data provide general constrains on the crystallisation kinetics of natural crystal bearing silicate melts erupted on earth e g lavas with phenocrysts the relationship between crystal content and cooling rate suggests that the solidification path induced by degassing can be also complex and nonlinear the growth of crystals with size up to 1 mm from a nearly anhydrous superheated silicate melt indicates that variable cooling conditions of lavas have to be accounted to discriminate among minerals formed before during and after eruptions moreover our results can be used to design glass ceramics from naturally available easy to find low cost starting materials

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

crystallization kinetics and rheology of leucite bearing tephriphonolite magmas from the colli albani volcano italy abstract we have investigated the rheology of liquid and crystal bearing tephriphonolite magmas from the colli albani volcanic district high 1124 1569 c and low 690 800 c temperature anhydrous liquid viscosities were determined by a combination of concentric cylinder 101 0 to 103 6 pa s and micropenetration 109 2 to 1012 1 pa s viscometry comparison with literature data reveals that at high temperatures viscosity seems to be related to the melts degree of polymerization nbo t while at low temperatures the dependency is not linear with values of viscosity higher than expected subliquidus isothermal crystallization experiments and viscosity determinations were carried out at high temperature 1150 1240 c in air using a concentric cylinder apparatus at constant shear strain rate 0 1 s 1 the overall crystal fraction varies between 0 06 at 1240 c leucite and 0 34 at 1150 c leucite 0 32 plagioclase 0 02 with a direct linear increase of crystal content with decreasing temperature which parallels the viscosity increase the inspection of products quenched at the end of the crystallization stage defined when viscosity reaches a constant value reveals strong evidence of leucite clustering after the first segment of the experiment performed at a constant shear rate a second stage of experiments at variable shear rate was performed comprised of an up ramp 0 1 s 1 0 9 s 1 and a down ramp 0 9 s 1 0 1 s 1 segment at the end of the down ramp leucite crystals appear sub spherical and unclustered for the same applied shear rate the viscosity values of the up ramp are not recovered within the experimental time scale indicating strain and strain rate dependent rheology for these suspensions while the down ramp viscosity data are shown to be in perfect agreement with literature models discrepancies between the up ramp data and pre existing predicting models have been observed we suggest that this complex behavior is related to the clustering of leucite crystals during the crystallization process and their breakage during the higher shear rate viscosity measurements the kinetics of crystallization in terms of nucleation and growth rates seems to be strongly affected by the degree of undercooling and dynamic stirring conditions we conclude that any modeling of tephriphonolite magma flow either in conduit or subaerial should take into account the effects of strain strain rate and internal textures i e clustering

formation of hrad vallis mars by low viscosity lava flows abstract hrad vallis is a martian outflow channel previously interpreted as a product of aqueous outbursts from the subsurface possibly involving mudflows associated with lahar like events however an alternative volcanic hypothesis for the development of the system is worthy of consideration on the basis of 1 the nature of landforms preserved along component channels and adjacent uplands and 2 similarities between the basic properties of this system and large volcanic channels of the inner solar system hrad vallis commences on the distal flanks of the elysium mons shield volcano terminates within extensive volcanic plains is associated with landforms typical of large volcanic channels and shows evidence for having been a conduit for large volumes of lava the properties of this system are consistent with incision by low viscosity lava crude thermal estimates suggest that this system could have formed through effusion of as little as 10 900 km 3 of magma to the surface or 6 of the volume of the terrestrial columbia river basalt group incision rates of up to several meters per day are estimated for mechanical and thermal processes involving lava flows with depths of 5 20 m and dynamic viscosities of 1 pa s flow of lava within the hrad vallis system is predicted to have been fully turbulent and characterized by discharges as great as 865 000 m 3 s predicted flow conditions are consistent with those previously determined for athabasca valles which also formed as a result of the expulsion of flows from structures associated with elysium mons

enhanced productivity rather than enhanced preservation led to increased organic carbon burial in the euxinic southern proto north atlantic ocean during the cenomanian turonian oceanic anoxic event three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

integrated biostratigraphy and carbon isotope stratigraphy for the upper cretaceous kanguk formation of the high arctic sverdrup basin canada

fissure eruptions in tharsis mars implications for eruption conditions and magma sources the tharsis region has been the focus of many studies of volcanism on mars not only are the largest volcanoes on the planet located here but also many of the youngest volcanic features are found within tharsis comparatively little attention has been given to understanding the origin of the smaller volcanoes within tharsis and these smaller structures may provide important information on both the regional tectonics of the area and the availability of magma from the shallow or deep crust we have identified six separate but physically close vent systems in eastern tharsis just to the east of the volcano jovis tholus these vents are typically linear fissures a few to 20 km in length that have built small shields rising to 50 85 m above the level of the surrounding topography the maximum length of individual lava flows from these fissures is 30 km but more typical lengths are 15 20 km mapping of the vent complexes reveals that smooth material interpreted to be spatter from fire fountaining is located on the rims of some of the fissures this spatter then formed either short 5 km flows or merged close to the fissure to form the longer flows there appears to have been some temporal evolution of the flow field as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows we find evidence of frozen lava ponds and channelized flows from central vents photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute originally identified by mouginis mark and christensen mouginis mark p j christensen p r 2005 new observations of volcanic features on mars from the themis instrument j geophys res 110 e8 doi 10 1029 2005je002421 of the flows from the central vent complex they are all 5 m thick which is a factor of 8 15 thinner than flows elsewhere on mars to investigate the unusual eruption conditions limited total volume of the construct and of individual flows we model the lava rheology the duration of emplacement the subsurface conditions that may have led to these eruptions and the volatile content of the magma we find lava viscosities and yield strengths to be 100 pa s and 100 pa respectively eruption rates to be 5000 m3 s 1 flow speeds to be 1 2 m s 1 durations of emplacement of individual flow units to be 5 h and the equivalent magma water content to be 0 1 0 2 mass these eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions small vents such as the ones studied here have also been identified in other parts of eastern tharsis so that the eruptions described here may characterize a common style of volcanism on mars that can only be identified now that image spatial resolution in the range 1 20 m pixel is available it is therefore possible that additional searches of other volcanic areas syrtis planum elysium planitia and hesperia planum may also show greater diversity of activity than is currently accepted