atmospheric processes governing the changes in water isotopologues during enso events from model and satellite measurements enso el nino southern oscillation has profound effects on the global water cycle which can be examined at the process level by investigating the associated water isotopologues many isotope based studies are aimed at understanding enso variability in the tropics however focusing principally on near surface processes and isotopologue signals the goal of the present study is to investigate the atmospheric processes governing the changes in the isotopic composition of water vapor both near the surface and at midtroposphere in the pacific region during enso events using a combination of remote sensing data and model simulations for the lower atmosphere i e 1000 hpa our results show that rainout processes less rain reevaporation of falling droplets and increase of convective updrafts and diffusive exchange within the convective systems contribute to the isotope amount effect and isotopically deplete the water vapor during wet conditions in agreement with previous studies however we find that the enso associated isotopic signal in the midtroposphere i e 500 hpa diverges from the near surface response analysis suggests that transport of enriched water vapor from lower atmospheric layers through convective updrafts controls the enrichment of midtropospheric water vapor over the pacific ocean in the observations a strong positive correlation between the increase of convective precipitation and the isotopic composition of water vapor clearly points to such a mechanism r of 0 7 0 8 in the central pacific and 0 5 0 6 in the west pacific model results confirm this mechanisms though producing slightly lower correlation values with r values of 0 6 in the central pacific and 0 5 in the west pacific however the distinction between convective and stratiform precipitation remains a result of model dependent parameterization our analysis suggests that two issues should be investigated in more detail in further studies 1 the equilibrium and disequilibrium between rain droplets and surrounding vapor for convective and stratiform precipitation and 2 different convection schemes in the different isotopic general circulation models gcms describing the triggering of convection and uplift of lower layer air to higher layers ideally such a comparison of different isotopic gcms can provide us with an interesting benchmark test for the performance of the different convection schemes during enso and can help to disentangle the importance of the different processes contributing to the amount effect

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

palaeogeographical significance of clay mineral assemblages in the permian and triassic sediments of the se iberian ranges eastern spain the evolution of the palaeogeography of the se iberian basin during the permian and triassic represents a general evolution from continental to marine environments it has been recently studied from the sedimentological stratigraphical tectonic and palaeontological points of view in spite of these results many aspects of this palaeogeography are still a matter of discussion in this study clay mineralogy analysis complements previous studies representing a new aspect for understanding the evolution of the sedimentary environment and the palaeogeography of the iberian basin during the periods in question and thus of the palaeogeography and the location of the major high areas in the westernmost border of the tethys sea in spite of late diagenetic transformations the original clay mineral associations of the permian triassic sediments of the se iberian ranges can be reconstructed seventy seven samples of siliciclastic and carbonate sediments of these ages have been studied sem and xrd revealing six new aspects that help to precise the palaeogeographical interpretation of the area 1 two major mineral assemblages have been found illite kaolinite pyrophyllite in the continental facies and illite chlorite vermiculite mixed layer clays in the marine facies 2 the mg rich clay minerals are here considered to be of marine origin 3 active phases of basin boundary faults are marked in the sediments by the presence of pyrophyllite derived directly from the palaeozoic metamorphic basement 4 unconformities separating major depositional sequences also separate formations with different clay mineralogy 5 different groups of clay minerals can be separated clearly coinciding with the different palaeogeographical stages also distinguished in the westernmost border of the tethys sea 6 the clay mineral associations back up the data of a previous hypothesis of a humid climate for the end of the permian in the study area just prior to the first incursion of the tethys sea

proportions of convective and stratiform precipitation revealed in water isotope ratios distinguishing convective and stratiform rainfall is key to understanding how the water cycle responds to climate change an analysis of satellite and surface data shows that rain isotope ratios reflect the proportions of these types of rain

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

modeling the isotopic composition of precipitation the physics of the stable isotopes of water is incorporated into a two dimensional kinematic bulk cloud microphysical model the model is run for several idealized classical stratiform and convective storm situations and the resulting isotope ratios of precipitation and water vapor are diagnosed and compared to observations for stratiform snow the model produces low isotope ratios that decrease rapidly poleward of the warm front the lowest isotope ratios occur when the atmosphere is cold and when the vertical velocity attains its maximum value high in the troposphere for stratiform rains the model produces much higher isotope ratios without a significant poleward gradient as a result of isotope exchange between the falling rain and the surrounding vapor isotope ratios of rain are lowest when the melting level is near the ground and isotope exchange is minimized for air mass thunderstorms isotope ratios are uniformly high in warm air no matter what the cloud height unless hail approaches or reaches the ground the model also produces a significant amount effect for rain in which isotope ratios decrease with increasing rainfall totals isotope ratios are particularly low when the rain derives from a recirculation process in which air previously charged by vapor from falling rain subsequently rises under such conditions the model sometimes produces isotope ratios that decrease from the periphery to the core of the precipitation shield it is suggested that this recirculation process is responsible for extraordinarily low isotope ratios observed in some hurricanes and organized thunderstorms the dominant cloud microphysical processes can sometimes be inferred from isotope ratios of precipitation the model produces ice pellets with isotope ratios close to those of rain when the pellets are produced by homogeneous freezing of rain and close to those of snow when the pellets are produced by refreezing of partially melted snow a climatology of isotope values that matches the main features of the observed global data set and of a seven year record of storms at mohonk lake new york is generated by running the model for a wide range of conditions this includes the deuterium excess d d 8 18o for antarctic snows that increases markedly as d falls below 300 and the deuterium deficit observed for rain in warm dry regions

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

magnetic model of the subduction zone in the northeast japan arc abstract magnetic modeling of the forearc side of the tohoku northeastern japan arc was carried out using spectral analysis of shipborne magnetic data the original data show anomalies caused by volcanic rocks on the western shallow side and linear marine magnetic anomalies on the eastern deeper side throughout the forearc region as calculated from temperature gradient data of heat flow measurements and deep drilling the curie depth is deeper than the moho on the eastern deeper side this suggests that the moho may correspond to the base of the magnetic layer because analysis of upper mantle xenolith suites indicates that the upper mantle should be non magnetic in addition the conrad discontinuity may correspond to the apparent top of magnetic layer because the lower crustal layer would be more mafic than the upper layer it was estimated by 2d spectral analysis that the magnetic base and surface lie at about 20 km and 10 km respectively this suggests that the moho and the conrad may roughly correspond to the magnetic base and surface the magnetic anomalies in the pacific basin are traced towards and over the inner side of the trench and show a gradual decrease in amplitude disappearing eventually about 100 km west of the trench this reflects the descent of the oceanic slab the 1d spectral analysis indicates that the marine magnetic layer is descending at an angle of about 4 in the japan trench this angle increasing to 20 degrees below the coast where the marine magnetic layer reaches a depth of more than 30 km this agrees with the seismic reflection data from the trench and because the magnetic layer can be traced down to a depth of 30 km it may be suggested that the curie isotherm deepens to more than 30 km just east of the coast

emeishan basalts sw china reappraisal of the formation s type area stratigraphy and a discussion of its significance as a large igneous province the late permian emeishan basalt formation of sw china is one of earth s lips large igneous provinces yet its basic geology remains poorly documented recent work on sections close to the type area in sichuan province enable us in part to rectify this descriptions of the formation and associated units at two areas one on the lower flanks of mt emei and another from a series of outcrops in ebian county 50 70 km to the sw are presented the basalt pile is 180 270 m thick and in both areas comprises 12 flows that were erupted in relatively quick succession it rests conformably upon shallow marine limestones lignites suggesting emplacement close to sea level the upper half of the youngest basalt was intensively weathered but not eroded prior to it being conformably succeeded by complex body of rocks c 30 m thick that includes thin basalts pyroclastic rocks tuffs and organic rich terrestrial sediments this unit which has previously been described as a sedimentary package presumably because intense weathering has obscured the primary lithological fabric in key outcrops is considered to mark the volcanic waning phase uppermost permian and triassic terrestrial sediments conformably overlie the terminal volcanic rocks the sub regional stratigraphy is compared as best it can be with that described from two sections 400 km to the se one section matches reasonably well the other does not indicating that regional correlations need to be developed carefully the information is discussed in the context of lip generator models several key features of the emeishan basalt terrain are at odds with those commonly encountered in lip s the most important conclusion is that the unit marks a prematurely terminated system in which full bloodied rifting leading to the development of an ocean basin never started

sequence stratigraphy of continental triassic strata of southernmost brazil a contribution to southwestern gondwana palaeogeography and palaeoclimate abstract the continental triassic succession of southernmost brazil comprises two second order depositional sequences the sanga do cabral early triassic and the santa maria middle to late triassic supersequences the first one includes ephemeral low sinuosity fluvial deposits developed on a low gradient plain based on fossil tetrapods especially procolophonids an upper induan age is estimated for this sequence facies association of the santa maria supersequence indicates low sinuosity fluvial rivers deltas and lakes this supersequence can be further subdivided into three third order sequences age provided by palaeovertebrate biostratigraphic data as follows santa maria 1 ladinian santa maria 2 carnian to early norian and santa maria 3 probably raethian or early jurassic sequences the gondwanides paroxysms i and ii in the sierra de la ventana cape fold belt are directly related to the development of both supersequences the source area of the sanga do cabral supersequence was located to the south it consisted of an uplifted peripheral bulge situated landward of the retro foreland system from where older sedimentary rocks were eroded the source area of the santa maria supersequence was also positioned southwards and related to the uplifted sul rio grandense and uruguayan shields the santa maria supersequence stratigraphic architecture is comparable to the triassic rift basins of western argentina diagenesis facies and palaeontology of the studied succession suggest a dominantly semiarid climate during the triassic

pattern of vertebrate extinctions across an event bed at the permian triassic boundary in the karoo basin of south africa the extinction of vertebrates around the time of the permian triassic boundary has long been regarded as a gradual event occurring over millions of years our new field investigations of fluvial strata in the central and southern karoo basin of south africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora the bed is in a sedimentary sequence that is marked by a reddening of flood plain mud rocks and a change from high to low sinuosity river channel systems here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden possibly catastrophic event perhaps of 50 000 yr duration or less

magnetic petrology of arc xenoliths from japan and aleutian islands xenoliths from japan and the aleutian islands were studied for the purpose of identifying source rocks with sufficient magnetization to account for positive subduction zone magsat anomalies two types of magnetic lithologies are identified 1 amphibolites and homblende gabbros containing up to 8 6 titanomagnetite mostly as large unoxidized multidomain crystals and 2 pyroxene gabbros and metagabbros with up to 20 3 titanomagnetite usually in association with primary ilmenite the first type is represented by xenoliths from ichinomegata japan and adak island in the aleutians the second restricted to iki island japan and kanaga island aleutians has abundant coarse grained titanomagnetite which in most samples has been oxidized producing secondary trellis type ilmenite lamellae a few iki island xenoliths show more advanced oxidation arc xenoliths show 3 orders of magnitude range in natural remanent magnetization and saturation remanence and about 2 orders of magnitude range in magnetic susceptibility nearly all iki island rocks and many from ichinomegata and the aleutians possess induced magnetization 2 a m 1 and greater with the expectation of additional magnetization due to viscous remanence at elevated temperature the tio 2 content of titanomagnetite together with the presence ot appreciable al 2 o3 and mgo ensure that most xenoliths have curie points between 400 and 550 c remanence acquisition curves exhibit a range reflecting varying degrees of magnetic hardening due to oxidation correspondingly each xenolith site groups distinctly on a plot of magnetic hysteresis ratios this paper indicates that lithologies with total magnetizations of many a m 1 exist in lower crust arc settings their volumetric distribution is uncertain based on the limited xenolith population reported herein

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

sequence stratigraphic analysis and paleogeographic interpretation of the buntsandstein and muschelkalk facies permo triassic in the se iberian range e spain abstract the iberian ranges is an alpine structure trending nw se in central spain they first appeared as small intracratonic basins in the early permian and experienced different periods of extensional tectonics during the mesozoic and cenozoic controlled by ancient hercynian or older fracture systems and at least two periods of compressive inversion tectonics the permian and triassic of the se iberian ranges are of germanic type within the prevailing buntsandstein and muschelkalk facies eight formations are recognized pollen and spore assemblages and some ammonoid horizons allow for age assessments ranging from thuringian late permian to carnian late triassic two phases of sedimentation can be distinguished during the early extensional period the first phase rift phase led to the development of the lower buntsandstein facies bounded by two angular unconformities and subdivided into two depositional sequences ds 1 and ds 2 the lower one is dominated by alluvial fans deposited in half grabens and the upper one by sandy braided rivers in more symmetrical grabens the second phase thermal or flexural subsidence phase led to the deposition of the uppermost buntsanstein rot and muschelkalk facies mostly shallow marine carbonates subdivided into two depositional sequences ds 3 and ds 4 with well developed lowstand transgressive and highstand systems tracts lst tst and hst intervals the criteria for separating systems tracts and the interplay of tectonics eustatism and rate of sedimentation are discussed ds 3 and ds 4 broadly correspond to 2 1 and 2 2 third order cycles but their limits are about 3 4 m y younger this may be explained by local tectonic factors

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

crustal magnetization and long wavelength aeromagnetic anomalies of the minto block quebec measured susceptibilities of 3500 samples from a 500 500 km area of the minto block superior province quebec have an average value of 0 03 si equivalent to induced magnetizations of 1 5 a m charnockitic lithologies igneous orthopyroxene bearing granodiorite granite diorite that constitute large parts of the minto region yield the highest susceptibilities the variations in susceptibility show a good correlation with the variations in the observed magnetic field including those at long wavelengths 100 km suggesting that charnockitic and related granitoid rocks could be responsible for the long wavelength anomalies modeling of a magnetic profile perpendicular to the strike of mapped lithotectonic subprovinces in the minto block supports this contention charnockitic lithologies are not usually considered a possible sources of long wavelength anomalies mafic rock types are generally favored the dominant minto lithologies are more felsic but are more efficient in the production of magnetite from the available iron

mass extinction of peat forming plants and the effect on fluvial styles across the permian triassic boundary northern bowen basin australia abstract the most spectacular extinction event in earth s history occurred across the permian triassic boundary in the northern bowen basin a major coal bearing sedimentary basin in eastern australia a long lived c 9 myr cold climate peat mire ecosystem collapsed at the permian triassic boundary when the vast majority c 95 of peat producing plants became extinct the environmental change marked by the permian triassic boundary is expressed as an abrupt and sharp change in sedimentary regime at the contact between the rangal coal measures and the sagittarius sandstone the stratigraphic record shows no diminution in the thickness lateral extent or spatial distribution of coal seams prior to the boundary event the abrupt ecological shift at the permian triassic boundary was coincident with and interrelated to a change in landscape attributes and fluvial style the boundary shift is considered to reflect a short period radical atmospheric change accompanied by an abrupt change in plant ecosystems however palynological data indicate that it was preceded by a more gradual gross taxonomic progression in the floral succession the boundary shift is unlikely to reflect change in the tectonic setting of the northern bowen basin because the detrital character of clastic sediment supply shows no provenance change within the boundary sequence the late permian fluvial style is characterised by large scale up to 1 km wide sandstone dominated low sinuosity trunk river channel deposits the trunk river channels were flanked by extensive levee composite crevasse splay systems channel tracts were relatively stationary in position over enduring periods and developed stacked sediment accumulations up to 30 m thick the constrained character of the late permian trunk river systems was most likely due to progressive compaction of thick tracts of peat substrate and the stabilising effect of vegetation adjacent to the channel complex the well developed crevasse splays coupled with the low sinuosity style of the fluvial channels might suggest a perennial fluvial system characterised by short discharge periods as common in high latitude settings the fluvial architecture of the sagittarius sandstone the basal formation of the lower triassic rewan group is characterised by sheet like elements suggestive of broad shallow channels in a deforested braid plain setting the channel deposits are considered to represent highly mobile sandy systems dominated by a flashy runoff regime the mass extinction of plants in the northern bowen basin at the permian triassic boundary thus had a significant impact on the early triassic landscape and fluvial architecture

large scale bed configurations macroforms platte river basin colorado and nebraska primary structures and formative processes large scale current bed forms defined here as bed configurations having dimensions commensurate with the size of the turbulent boundary layer are considered by many workers to be hydrodynamically equivalent to the regime bed forms these bed forms were investigated at formative flows bankfull flows on the south platte and platte rivers in colorado and nebraska to determine structures and formative processes results of this study suggest that large scale bed forms here termed macroforms are not hydrodynamically equivalent to the regime bed forms but constitute a unique hierarchical class of bed configurations produced by turbulent vortices that involve the entire boundary layer macroforms are oriented obliquely to the mean flow direction and are attached to one or both channel banks three members of a continuum of geometries are recognized in the channels of the platte river basin the internal stratification for each of the three macroform types recognized in the basin is similar and in its simplest form consists of the coarsening upward sequence apron laminae foreset laminae topset laminae although it may not be possible to differentiate the three macroform types solely on the basis of internal stratification the presence of a distinctive coarsening upward sequence in coarse grained fluvial systems offers a potentially powerful tool for identifying these environments in the geologic record

the late permian climate what can be inferred from climate modelling concerning pangea scenarios and hercynian range altitude abstract a major unsolved geodynamic problem is the permian pangea plate configuration at the end of paleozoic era around 255 ma while consensual geology indicates a plate arrangement close to that of the jurassic prior to the atlantic opening pangea a paleomagnetic data indicates a nearly 3000 km more eastward position of gondwana with respect to laurussia leading to major plate and relieves reorganisation during permo triassic times pangea b using an atmospheric general circulation model agcm we simulate the climatic response to both configurations we also test the fundamental role of paleo elevations through sensitivity experiments each simulated climate is then compared with the aim of constraining the best fit to a particular paleogeographic scenario main trends of simulated late permian climate in agreement with paleoclimatic indicators are 1 a warm temperate climate accompanied by a monsoon circulation over the eastern side of gondwana 2 a cold temperate climate marked by strong annual thermal amplitude at high latitudes in gondwana and in siberia 3 an arid belt in the subtropics over the western side of gondwana and laurussia and 4 strong climatic differences over both hemispheres respectively main variance is found over laurussia with a simulated tropical climate while an arid climate is suggested by paleodata simulating different paleo elevations of the appalachian and the variscan fold belts can solve this discrepancy the best model data fit is reached for a mean altitude of 4500 m in the appalachians and appears to be dependent of pangea configuration with a southern europe variscan range of some 3000 m in a pangea a configuration or only 2000 m in for pangea b taking into account the geodynamic context we argue that pangea b appears to be the more probable configuration

age of the emeishan flood magmatism and relations to permian triassic boundary events the permian triassic p t mass extinction the greatest biological mortality event in the earth s history was probably caused by dramatic and global forcing mechanisms such as the siberian flood volcanism here we present the first set of high precision 40 ar 39 ar dating results of volcanic and intrusive rocks from the emeishan traps south china which define a main stage of the flood magmatism at v251 253 ma and a subordinate precursory activity at v255 ma this time span is generally coeval with or slightly older than the age of the p t boundary estimated by the ash beds in the meishan stratotype section and the main eruption of the siberian traps our data reinforces the notion that the eruption of the emeishan traps rather than eruption of the siberian traps accounted for the formation of the p t boundary ash beds in south china the emeishan flood magmatism which occurred in the continental margin comprising thick marine limestone formations moreover may have triggered rapid release of large volumes of methane and carbon dioxide that could have been responsible for the global n 13 c excursion and associated environmental crisis leading to the mass extinction at the p t boundary fl 2002 elsevier science b v all rights reserved

satellite magnetic anomalies over subduction zones the aleutian arc anomaly positive magnetic anomalies seen in magsat average scalar anomaly data overlying some subduction zones can be explained in terms of the magnetization contrast between the cold subducted oceanic slab and the surrounding hotter nonmagnetic mantle three dimensional modeling studies show that peak anomaly amplitude and location depend on slab length and dip a model for the aleutian arc anomaly matches the general trend of the observed magsat anomaly if a slab thickness of 7 km and a relatively high induced plus viscous magnetization contrast of 4 a m are used a second source body along the present day continental margin is required to match the observed anomaly in detail and may be modeled as a relic slab from subduction prior to 60 m y ago

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

mid latitude interhemispheric hydrologic seesaw over the past 550 000 years an interhemispheric hydrologic seesaw in which latitudinal migrations of the intertropical convergence zone itcz produce simultaneous wetting increased precipitation in one hemisphere and drying in the other has been discovered in some tropical and subtropical regions for instance chinese and brazilian subtropical speleothem cave formations such as stalactites and stalagmites records show opposite trends in time series of oxygen isotopes a proxy for precipitation variability at millennial to orbital timescales suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics this tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing the impacts of such an interhemispheric hydrologic seesaw on higher latitude regions and the global climate system however are unknown here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid latitude western pacific ocean our results are based on a new 550 000 year record of the growth frequency of speleothems from the korean peninsula which we compare to southern hemisphere equivalents the korean data are discontinuous and derived from 24 separate speleothems but still allow the identification of periods of peak speleothem growth and thus precipitation the clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550 000 years extended at least to the mid latitudes such as northeast asia and that orbital timescale itcz shifts can have serious effects on temperate climate systems furthermore our result implies that insolation driven itcz dynamics may provoke water vapour and vegetation feedbacks in northern mid latitude regions and could have regulated global climate conditions throughout the late quaternary ice age cycles

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

the upper permian boniches conglomerates formation evolution from alluvial fan to fluvial system environments and accompanying tectonic and climatic controls in the southeast iberian ranges central spain the boniches conglomerates fm upper permian represents the first episode of sedimentation in the southeast border margin of the iberian basin central spain the iberian basin commenced development as a rift basin running mainly nw se during the early permian and underwent its first general extensional period during the late permian the boniches fm was deposited as a small segment less than 100 km long and 9 10 km wide of the iberian basin that extended in a northeast direction during this period detailed mapping and palaeocurrent analysis have shown that the boniches fm is of a curvilinear wedge shaped morphology sediments close to the southwest main faulted border are of a maximum thickness of 230 m clear lateral variation in thickness controlled by the activity of secondary transfer faults perpendicular to the main nw se axis may be observed this network of faults permitted the formation of blocks limited laterally by the transfer faults these blocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation of reduced sub basins with different sedimentary characteristics based on facies and facies association the boniches fm is thought to have evolved vertically from two main alluvial fan systems in the lowest part of the formation into fluvial braided systems flowing southeast as expected no flow orientations towards the footwall block are observed during the first episodes of the refill this may be explained by erosion or simply a lack of sedimentation due to the gentle slope the change from alluvial fan to fluvial environments is interpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainage from a transfer zone located to the northwest three different reorganization episodes clearly marked in the boniches fm as main boundary surfaces mbs separate four members subdivided into 4 5 levels 34 m thick each level consists of fining upward successions less than 1 m thick tectonics and climatic factors clearly controlled sedimentation tectonic activity was probably of greatest importance and was conditioned by the movement of the main nw se and ne sw transfer faults the role of climate in ancient conglomerate sediments has not been well established palaeogeographical mineralogical sedimentological and clast analyses suggest that the boniches fm was deposited under humid conditions by running water the differentiation between proper alluvial fans and fluvial environments during the transition period of the boniches fro is not clear since in many recent alluvial fans braided fluvial systems are associated with fans

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

petrogenesis and alteration of tuffs associated with continental flood basalts from putorana northern siberia in the putorana region of the siberian continental flood basalt province tuffs form thin layers or small bodies between single basaltic lava flows based on our fieldwork these ash fall deposits have relatively small volumes 100 000 m 3 compared with the associated basaltic flows and the tuffs of the adjacent noril sk region in the north six tuff units with different degrees and modes of alteration were analysed by xrd sem and xrf in order to determine mineralogical and chemical changes which occurred during progressive alteration pyroxene compositions and immobile element ratios suggest that the tuffs were derived from a basaltic lava like the flood basalts post eruptive low temperature alteration processes have significantly changed the primary composition of the tuffs therefore the different tuffs have variable petrography mineralogy and geochemistry mgo 5 2 9 2 wt sio 2 33 6 69 1 wt and tio 2 0 6 1 6 wt compared to the tholeiitic basalts in which they are interbedded crystallization of secondary minerals such as carbonate clay minerals zeolites and analcime occurred from circulating fluids the results show that the fluid compositions varied significantly between the different tuffs this implies that the elements behaved differently depending on the circulating agent which led to the formation of different minerals in addition two samples show an input of quartz derived either by wind from terrigenous sediments or generated by magma sediment interaction and one sample was deposited in a subaqueous possibly lacustrine environment these results indicate that the conditions during alteration varied despite the close spatial relationship of the tuffs and that a generalization about the alteration processes cannot be made in the putorana region the analyses of the clay minerals show alteration of chlorite to vermiculite interestingly corrensite a regularly stacked 50 50 mixed layered clay mineral composed of chlorite and vermiculite is still preserved in two samples this indicates different alteration stages in the different tuff outcrops the state of alteration deduced from immobile element ratios plagioclase compositions and mineral assemblages shows contradictory results this suggests that the state of alteration is best deduced from clay minerals as one can follow this process step by step

the global continent ocean magnetization contrast abstract a schematic global model for the distribution of magnetization in the lithosphere is devised this model is characterized by a uniform stepwise change of radially integrated susceptibility at continent ocean boundaries and an axial dipolar inducing field a spherical harmonic expansion of the magnetic field produced by this source distribution is computed then the standard method of truncation at degree n 13 is used to determine the respective contribution of this field to the main field and to the lithospheric anomaly field the latter is shown to display significant anomalies near continental margins as well as within continents and oceanic basins the energy density spectrum of this field is shown to be very similar to the spectrum of the magsat derived lithospheric anomaly field furthermore several features of this field are shown to account for unexplained anomalies of the magsat field this supports the hypothesis that such an abrupt magnetization variation may occur at several continental margins and contribute to the signal in the magsat derived long wavelength anomaly maps this hypothesis provides an order of magnitude estimate for the magnetization difference between oceanic and continental lithospheres finally it is argued that the synthetic anomaly field produced by this model provides an upper bound to the energy density spectrum of the lithospheric field at low harmonic degrees and concluded that the lithospheric field does not contribute significantly to the earth s field below degree 13

global patterns of enso induced precipitation although there have been many analyses of el nino southern oscillation enso induced precipitation anomalies global patterns from these analyses remain incomplete here we combine recent satellite estimates of oceanic precipitation and historical rain gauge records to derive a global climatology of enso induced precipitation anomalies using empirical orthogonal function eof analyses the patterns suggest that the re arrangement of convection centers of the walker circulation during enso events induces large precipitation anomalies in the tropics while associated changes in the monsoon systems through the hadley cell over the pacific indian and atlantic oceans and their interactions with midlatitude westerlies generate coherent anomaly patterns over the extratropics our results can be used to evaluate climate models and forecast enso induced precipitation anomalies

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

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

combined measurements of 17oexcess and d excess in african monsoon precipitation implications for evaluating convective parameterizations water stable isotopes d18o dd are useful tools to depict and to understand the atmospheric water cycle in tropical regions they record the variations of convective activity and their implementation in convection schemes brings constraints on our understanding and parameterization of this phenomena here we present for the first time measurements of a new isotopic marker of the hydrological cycle 17oexcess resulting from the combination of d17o and d18o of water in convective regions on two different time scales i during the african monsoon onset and intra seasonal variability banizoumbou 2006 and ii during the squall line of the 11th of august 2006 niamey 17oexcess responds to the monsoon onset by a 30 per meg increase as well as to different convective processes in squall lines by 20 per meg variations these variations parallel those of d excess at first order and display significant correlation with relative humidity in the lower troposphere still higher correlation coefficients are observed between d excess and relative humidity than between 17oexcess and relative humidity suggesting a higher influence of relative humidity on d excess than on 17oexcess using a simple reevaporation model and a more sophisticated 2d model of a squall line we show that reevaporation is the process explaining the increase of d excess and 17oexcess with relative humidity for these two studies we also show that the combination of 17oexcess and d excess is a powerful tool to constrain the representation of isotopic processes during rain reevaporation in turn a good representation of such processes enables to use water isotopes to evaluate convective parameterization in atmospheric models 2010 elsevier b v

water isotopic variability in response to mesoscale convective system over the tropical ocean 1 in tropical regions the empirical negative relationship between the isotopic content of precipitation and rainfall amount known as the amount effect has been used as a rationale for paleohydroclimate reconstruction from isotope records however there is still no comprehensive physical explanation for this empirical effect here we reconsider the well known amount effect using newly available isotope data for both surface water vapor and precipitation obtained from shipboard observations in this study we hypothesized that stratiform rainfall associated with mesoscale convective systems mcss is a key process in reducing tropical water isotopic concentrations and tested this hypothesis with an idealized mcs model our conceptual model reasonably accounted for several observed features and indicated that isotopic reductions in tropical oceanic regions reflect a precipitating system s change relatively high isotope ratios corresponded to disorganized convection on the other hand mcss were characterized by lower isotope ratios with increasing stratiform area in addition the amplitude of this isotopic depletion was related to the scale of the precipitation system the lowest isotopic ratios were observed during the passage of large scale disturbances corresponding to the madden julian oscillation convective envelope in which mcss are embedded this means that the frequent appearance of mcss results in further decreases in the isotopic ratio of surface vapor and precipitation from this we conclude that the amount effect can be interpreted as the development of a precipitation system from an isolated convection cell into a large scale system containing several mcss and that past large scale convective activity can be reconstructed from isotope records

diurnal to interannual rainfall δ 18 o variations in northern borneo driven by regional hydrology the relationship between climate variability and rainfall oxygen isotopic 18o variability is poorly constrained especially in the tropics where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate here we present a daily resolved 5 yr long timeseries of rainfall 18o from gunung mulu national park located in northern borneo 4 n 114 e in the heart of the west pacific warm pool and compare it to local and regional climatic variables daily rainfall 18o values range from 0 7 to 18 5 and exhibit a weak but significant inverse relationship with daily local precipitation amount r 0 19 p 0 05 consistent with the tropical amount effect day to day 18o variability at mulu is best correlated to regional precipitation amount averaged over the preceding week r 0 64 p 0 01 the inverse relationship between mulu rainfall 18o and local regional precipitation amount increases with increased temporal averaging reaching r 0 56 r 0 72 on monthly timescales large negative multi day rainfall 18o anomalies of up to 16 occur every 30 90 days and are closely associated with wet phases of the intraseasonal madden julian oscillation a weak semi annual seasonal cycle in rainfall 18o of 2 3 bears little resemblance to seasonal precipitation variability pointing to a complex sequence of moisture sources and or trajectories over the course of the year interannual rainfall 18o variations of 6 8 are significantly correlated with indices of the el nino southern oscillation with increased rainfall 18o during relatively dry el nino conditions and vice versa during la nina events we find that mulu rainfall 18o outperforms mulu precipitation amount as a tracer of basin scale climate variability highlighting the time and space integrative nature of rainfall 18o taken together our results suggest that rainfall 18o variability at mulu is significantly influenced by the strength of regional convective activity as such our study provides further empirical support for the interpretation of 18o based paleo reconstructions from northern borneo stalagmites as robust indicators of regional scale hydroclimate variability where higher 18o reflects regional drying

water isotopologues as a quantitative paleosalinity proxy 1 paleosalinity reconstructions are a goal of paleoceanographic study because of their potential to provide insight into past ocean circulation while temperature reconstructions have been assessed by using multiple independent proxies the skill of existing salinity reconstructions remains poorly quantified we examine the applicability of two different approaches using a set of coupled water isotope enabled general circulation model experiments as a numerical analog for the real climate system these simulations for the holocene at roughly 1000 year time steps explicitly track variability in both the water isotopologues and salinity our simulations suggest that quantitative reconstructions of past salinity variability based solely on inferred 18osw variability have very large errors and uncertainties however we find that paired 18osw and d variability from combining biomarker and calcite proxies holds promise for providing better quantitative estimates of salinity variability

temporal and spatial variations in tectonic subsidence in the iberian basin eastern spain inferences from automated forward modelling of high resolution stratigraphy permian mesozoic by subsidence analysis on eighteen surface sections and 6 wells which cover large part of the iberian basin e spain and which are marked by high resolution stratigraphy of the permian triassic jurassic and cretaceous we quantify the complex permian and mesozoic tectonic subsidence history of the basin backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies the sections and wells have also been forward modelled with a new automated modelling technique with unlimited number of stretching phases in order to quantify variations in timing and magnitude of rifting it is demonstrated that the tectonic subsidence history in the iberian basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence the number of stretching phases appears to be much larger than found by earlier studies showing a close match with stretching phases found in other parts of the iberian peninsula and allowing a clear correlation with discrete phases in the opening of the tethys and atlantic

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

late permian to middle triassic correlations and palaeogeographical reconstructions in south western european basins new sedimentological data from minorca balearic islands spain description of sedimentary sections and interpretations of sequence stratigraphic evolution of permian triassic red beds of minorca allow a new proposal of palaeoenvironment reconstructions the permian sediments mainly correspond to floodplain and pond deposits with sheetflood sand bed rivers environment de 1 within a warm and semi arid climate and the preserved succession forms one complete stratigraphic cycle the retrogradational phase of this cycle is represented by alluvial colluvial deposits grading upwards to environment de 1 and to extensive floodplain and pond deposits the progradational phase is characterized by increasing fluvial influence with palaeocurrent mainly oriented to the sw palaeosol horizons and preservation of a late permian palynoflora the uppermost part of this succession is truncated by a major erosional surface the sediments above this unconformity are characterized by braided river deposits environment de 2 with palaeocurrent oriented to the ssw within the more basal conglomeratic facies and to the wnw in overlying units the absence of extensive floodplain deposits a paucity of evidence for biogenic activity and palaeosols together with the presence of ventifacts indicate an arid climatic setting for the succession this environment evolved from braided rivers palaeocurrents mainly oriented to the se environment de 3 with in situ palaeosols and reworked breccias to fluvial coastal and shallow marine deposits environment de 4 dated as upper anisian to ladinian this succession characterizes a retrogradational trend although the transition between de 2 and de 3 was not observed a switch in palaeocurrent directions may indicate a change in source area a comparison at a regional scale with other peri tethyan basins allows the succession to be placed within a broader palaeoenvironmental and stratigraphic context during late permian to middle triassic during the late permian sedimentation occurred in alluvial playa lake or ponded environments where fluvial systems generally flowed southward except in south eastern france oriented to the ne within these sw european basins such as minorca the late permian succession shows a major retrogradational evolution from fluvial or alluvial fan deposits to extensive lake playa or floodplain deposits and a progradational trend fluvial or alluvial fan deposits the permian triassic transition corresponds to an unconformity overlain by braided river deposits with arid climate indicators aeolian deposits ventifacts and aeolian dune sedimentation at the scale of western europe this arid episode is dated as smithian and the induan age sedimentation deposits seem to be preserved only in the central part of the germanic basin as with all other peri tethyan basins environment de 2 of minorca above the major erosional surface is attributed to the smithian in the upper part of the studied succession braided river deposits indicative of less arid climatic conditions are preserved this succession contains the earliest mesozoic palaeosols dated as anisian by palynomorphs and expresses a vertical evolution from fluvial to open marine depositional environments attributed to the muschelkalk transgression

a stable isotope tree ring timescale of the late glacial holocene boundary late glacial and holocene tree ring chronologies like deep sea sediments or polar ice cores contain information about past environments changes in tree ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere we have established a 9 928 year absolutely dated dendrochronological record of holocene oak quercus robur quercus petraea and a 1 604 year floating late glacial and early holocene chronology of pine pinus sylvestris from subfossil tree remnants deposited in alluvial terraces of south central european rivers the pine sequence provides records of dendro dated 14c 13c and 2h patterns for the late younger dryas and the entire preboreal 10 100 9 000 yr bp through the use of dendrochronology radiocarbon age calibration and stable isotope analysis we suggest that the late glacial holocene transition may be identified and dated by 13c and 2h tree ring chronologies

a small alluvial crevasse splay abstract a crevasse splay deposited on the floodplain of the clarence river in northeastern new south wales australia by a small ephemeral tributary provides a guide to the geometry and sedimentary structures of crevasse splays in general and to the processes affecting their final form the splay consists of a main lobe of sand with smaller sand fingers that end in slipfaces around its edges water seeping out of the channel reworks part of the splay into a gently thinning sheet small scale facies models derived from different parts of this splay explain the origins of solitary planar cross sets and gently inclined bedding in some ancient crevasse splay sandstones

emeishan basalts sw china and the end guadalupian crisis magnetobiostratigraphic constraints abstract a magnetostratigraphic investigation of the permian emeishan lip large igneous province was carried out on a composite section in ebian county close to the type area in sichuan sw china the main succession of twelve flows 175 m thick carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity the data enable a correlation to be proposed with an emeishan basalt sequence in western guizhou c 400 km to the se from our knowledge of the geomagnetic field9s reversal behaviour during the permian it suggests that the main lava pile along the eastern half of the emeishan basalt outcrop belt was erupted within a half to one million years using magnetobiostratigraphic data from the adjacent south china platform the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the maokou limestones constrained by conodont data the main emei basalts appear to be at least two biozones older 1 1 5 ma than the mid late permian boundary it is possible however that the emei basalt waning zone sequence which represents an explosive volcanic phase might be coeval with the end guadalupian biotic crisis thus arguments implicating emei basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative age constraints

preliminary interpretation of magnetic anomalies over japan and its surrounding area the anomalies of geomagnetic total force over japan and its surrounding area 20 50 n and 120 160 e were interpreted by a magnetization of the earth s surface layer in a direction parallel to the main magnetic field a negative magnetization anomaly in the japan sea may be attributable to the thinness of the magnetized part of the crust in comparison with the japan island this is in accordance with the underground high temperature gradient suggested from the observed high heat flow values in the japan sea area

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

vertebrate extinction across permian triassic boundary in karoo basin south africa distinct assemblages of paleosols above and below the permian triassic boundary in the karoo basin of south africa are evidence for reorganization of ecosystems following this greatest of all mass extinctions the permian triassic boundary is recognized from the last appearance of dicynodon and from a series of negative excursions in the isotopic composition of carbon within therapsid tusks pedogenic carbonate nodules and organic matter the boundary is also marked by laminated beds with very weakly developed paleosols a change from purple 10r to brownish red 2 5yr paleosols and a thin 10 cm claystone breccia of reworked soil clasts paleoclimatic changes include a shift from arid and highly seasonal paleoclimate inferred from diffuse and shallow calcareous nodules in permian paleosols to semiarid and less seasonal paleoclimate inferred from deep and well focused calcic horizons in triassic paleosols an earliest triassic shift to warmer and wetter paleoclimate is also indicated by increased chemical weathering abundance of lycopsids and diversity of labyrinthodonts permian paleosols have root traces comparable to those of open shrubland and riparian woodland whereas triassic paleosols have root traces and profile forms like soils of open woodland this is a significant paleoenvironmental change but not as dramatic a change as would be expected from the devastating extinctions of 88 of fossil vertebrate genera latest permian therapsid reptiles were diverse and ecologically specialized in contrast the principal earliest triassic therapsid lystrosaurus was a burrower with no specific habitat preference its short internal nares barrel chest and high neural spines would have given it greater aerobic scope than preexisting therapsids and may have been an advantage under conditions of hypercapnia and hypoxia these adaptations and associated ecosystem changes are compatible with widespread vertebrate mortality by acidosis and pulmonary edema in a post apocalyptic greenhouse created by the voluminous release of methane from shallow marine and permafrost clathrates

asian monsoon hydrometeorology from tes and sciamachy water vapor isotope measurements and lmdz simulations implications for speleothem climate record interpretation observations show that heavy oxygen isotope composition in precipitation 18 o p increases from coastal southeastern se china to interior northwestern nw china during the wet season contradicting expectations from simple rayleigh distillation theory here we employ stable isotopes of precipitation and vapor from satellite measurements and climate model simulations to characterize the moisture processes that control asian monsoon precipitation and relate these processes to speleothem paleoclimate records we find that 18 o p is low over se china as a result of local and upstream condensation and that 18 o p is high over nw china because of evaporative enrichment of 18 o as raindrops fall through dry air we show that 18 o p at cave sites over southern china is weakly correlated with upstream precipitation in the core of the indian monsoon region rather than local precipitation but it is well correlated with the 18 o p over large areas of southern and central china consistent with coherent speleothem 18 o p variations over different parts of china previous studies have documented high correlations between speleothem 18 o p and millennial timescale climate forcings and we suggest that the high correlation between insolation and speleothem 18 o p in southern china reflects the variations of hydrologic processes over the indian monsoon region on millennial and orbital timescales the 18 o p in the drier part north of 30 n of china on the other hand has consistently negative correlations with local precipitation and may capture local hydrologic processes related to changes in the extent of the hadley circulation

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

what are the climate controls on δd in precipitation in the zongo valley bolivia implications for the illimani ice core interpretation abstract controversy has surrounded the interpretation of the water isotopic composition d or 18o in tropical and subtropical ice cores in south america although recent modeling studies using agcm have provided useful constraints at interannual time scales no direct calibration based on modern observations has been achieved in the context of the recent ice core drilling at nevado illimani 16 39 s 67 47 w in bolivia we examine the climatic controls on the modern isotopic composition of precipitation in the zongo valley located on the northeast side of the cordillera real at about 55 km from nevado illimani monthly precipitation samples were collected from september 1999 to august 2004 at various altitudes along this valley first we examine the local and regional controls on the common d signal measured along this valley we show that 1 local temperature has definitely no control on d variations and 2 local rainout is a poor factor to explain d variations we thus seek regional controls upstream the valley potentially affecting air masses distillation based on backtrajectory calculations and using satellite data trmm precipitation noaa olr and direct observations of precipitation iaea gnip we show that moisture transport history and the degree of rainout upstream are more important factors explaining seasonal d variations analysis of a 92 yr simulation from the echam 4 model t30 version implemented with water stable isotopes confirms our observations at seasonal time scale and emphasize the role of air masses distillation upstream as a prominent factor controlling interannual d variations lastly we focus on the isotopic depletion along the valley when air masses are lifted up our results suggest that if the temperature gradient between the base and the top of the andes was higher by a few degrees during the last glacial maximum lgm less than 10 of the glacial to interglacial isotopic variation recorded in the illimani ice core could be accounted for by this temperature change it implies that the rest of the variation would originate from wetter conditions along air masses trajectory during lgm

comparison of atmospheric hydrology over convective continental regions using water vapor isotope measurements from space 1 global measurements of the 500 825 hpa layer mean hdo h2o ratio from the tropospheric emission spectrometer tes are used to expose differences in the dominant hydrologic processes in the amazon north australian and asian monsoon regions the data show high regional isotopic variability and numerous values unexpected from classical rayleigh theory correlation analysis shows that mixing with boundary layer air enhanced isotopic fractionation during precipitation and subsiding air parcels contribute to intraseasonal isotopic variability these local controls explain only 8 30 of total regional variance which suggests that the isotopes are primarily indicators of moist processes that occur upstream seasonal trajectory analysis demonstrates that rayleigh distillation in a lagrangrian framework underestimates the observed isotopic depletion during the monsoons and suggests substantial recycling of water within or below clouds the trajectory results for the dry seasons reveal that subsiding air parcels periodically introduce isotopically depleted air into the north australia and asian monsoon regions whereas vigorous low level convection over the amazon basin acts to quickly enrich and moisten dry subsiding air the analysis indicates variations in the strength of convective detrainment into the lower to middle troposphere over all regions which during the dry seasons of the north australian and asian monsoon regions correlate with increases in relative humidity this study shows that isotopic measurements provide unique diagnostics of mechanisms that control the seasonal sources of water and that these provide a refined understanding of the differences in the characteristics of hydrologic budgets in these monsoonal regions