palaeomagnetism and magnetostiatigraphy of triassic strata in the sangre de cristo mountains and tucumcari basin new mexico usa summary we report palaeomagnetic data and a composite magnetic polarity sequence for middle and upper triassic rocks assigned to the anton chico member of the moenkopi formation and chinle group respectively exposed along the eastern flank of the sangre de cristo mountains and in the tucumcari basin of eastern and northeastern new mexico thermal demagnetization isolates a well defined dual polarity characteristic magnetization carried in most cases by haematite and interpreted as an early acquired chemical remanent magnetization crm characteristic magnetizations from 74 palaeomagnetic sites one site one bed are used to define a magnetic polarity sequence which we correlate with previously published triassic data obtained from both marine and non marine rocks preliminary correlation suggests that the resolution of magnetostratigraphic data derived from continental strata is not necessarily of lesser quality than that from marine rocks on the basis of the magnetostratigraphic data a profound unconformity is believed to separate lower middle norian and upper norian rhaetian strata of the chinle group palaeomagnetic poles derived from selected sites in steeply dipping 85 strata for the middle triassic anisian 240 ma 50 n 121 e n 8 late carman early norian 225 ma 53 n 104 e n 16 and late norian rhaetian 208 ma 59 n 77 e n 8 are in relatively good agreement with previously published data for the moenkopi formation and chinle group and related strata in southwest north america none the less comparison with palaeomagnetic poles obtained from gently dipping or flat lying triassic strata from this study anisian 46 n 112 e n 13 late carnian 54 n 87 e n 12 and previously published triassic poles in southwest north america suggest that a modest apparent rotation not greater than about 5 affects declinations from steeply dipping rocks the distribution of palaeomagnetic poles indicates 25 angular distance of apparent polar wander between about 240 and 208 ma

morphology internal architecture and emplacement mechanisms of lava flows from the central atlantic magmatic province camp of argana basin morocco abstract the morphology internal architecture and emplacement mechanisms of the central atlantic magmatic province camp lava flows of argana basin in morocco are presented the volcanic pile was produced by two volcanic pulses the first represented by the tasguint formation corresponds to a succession of 3 13 individual flows created by 1 8 eruptions the second alemzi formation is composed of 2 7 individual flows formed by 1 4 eruptions these formations geochemically distinct are separated by thin silty or sandy horizons or by palaeosols they include compound pahoehoe flows and simple flows the first type is almost exclusive of the lower formation while the second type dominates the upper formation the lava flows show clear evidence of endogenous growth or inflation the characteristics of the volcanic pile suggest slow emplacement during sustained eruptive episodes and are compatible with a continental basaltic succession facies model

carnian norian biomagnetostratigraphy at silicka brezova slovakia correlation to other tethyan sections and to the newark basin correlations of upper triassic magnetic stratigraphies from tethyan sections have been hampered by difficulties with conodont biostratigraphy and taxonomy and discontinuous sedimentation particularly in the hallstatt limestones of turkey and austria the magnetic stratigraphy and conodont biostratigraphy from the upper carnian to upper norian limestones exposed at silickabrezova slovakia can be correlated to other tethyan sections and to the continental succession in the newark basin the resulting correlations help to resolve some of the apparent discrepancies in existing conodont zonations and result in a revised correlation to north american terrestrial vertebrate and palynological zones the correlations imply that the norian rhaetian boundary lies within newark polarity zone e17r at v207 ma the carnian norian boundary lies close to the base of newark polarity zone e7r at v226 ma this implies durations for the norian and rhaetian stages of 19 myr and 7 myr respectively 2002 elsevier science b v all rights reserved

sedimentology stratigraphy and paleoclimate at the late miocene coffee ranch fossil site in the texas panhandle abstract the late miocene coffee ranch fossil assemblage contains some of the earliest evidence of c4 herbivory in north america however little is known regarding the environmental setting associated with the fauna and a general lack of detailed paleoclimate data exists for the late miocene from the north american continental interior in this study the sedimentary environments stratigraphy geochronology and paleoclimate are interpreted for a series of outcrops of the late miocene ogallala formation in the texas panhandle that includes the coffee ranch locality updated magnetostratigraphy coupled with previously published geochronology indicates that all exposed strata were deposited over a 277 kyr interval within chron c3an 2n from 6 42 6 70 ma depositional environments include fluvial channels floodplain ponds floodplain paleosols eolian paleosols riverine tufa and reworked volcanic ash trunk and tributary fluvial channels are differentiated using channel dimensions sedimentary structures and bounding surface architecture and indicate seasonally variable discharge paleosols from nine pedofacies are described and preserve a spectrum of weakly developed entisols and weakly to moderately mature inceptisols and vertisols constitutive mass balance calculations reveal that mature paleosols formed along distinct pedogenic pathways calcic vertisols accumulated pedogenic carbonate and exhibited either net volumetric dilation or collapse as a result of mineral weathering in contrast non calcic vertisols show patterns of decalcification and variable degrees of volumetric dilation and collapse the presence of the paleosols described in this study requires paleoprecipitation between of 900 1150 mm yr approximately double modern values and a westward shift of the continental udic ustic soil moisture boundary by 400 km during the late miocene this finding suggests that climates in the southern midcontinent were not sufficiently arid to select for c4 photosynthetic pathways over c3 photosynthesis in the late miocene

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

paleoecology of aphelops and teleoceras rhinocerotidae through an interval of changing climate and vegetation in the neogene of the great plains central united states abstract the rhinocerotidae was one of most widespread and abundant mammalian groups in north america during the oligocene and miocene but were extinct by the early pliocene potential drivers of extinction include the expansion of c4 grasslands cooling climate and increased seasonality here we examine potential changes in the relative abundance of two common genera aphelops and teleoceras from the middle miocene to the pliocene of the great plains we also use stable isotopes in tooth enamel to test whether great plains rhinoceroses were able to incorporate c4 vegetation into their diet after the expansion of c4 grasslands relative abundance of rhinoceroses fluctuates during the middle to late miocene but then rapidly declines at the end of the miocene around 6 5 ma coinciding with the expansion of c4 grasslands on the great plains stable carbon isotopes indicate that both aphelops and teleoceras were predominantly c3 feeders for most of their history during c4 expansion some individuals were able to adapt to modest c4 consumption but were not as successful as contemporaneous horses our results suggest that the extinction of rhinoceroses was associated with environmental stress related to diminishing food resources following the expansion of c4 vegetation possibly coupled with a shorter growing season as climate cooled in addition tooth enamel 18o values in rhinoceroses do not support the interpretation that teleoceras a hippo ecomorph had a semi aquatic lifestyle tooth enamel 18o values reflect a strong latitudinal temperature gradient suggesting that rhinoceroses effectively track 18o values in surface waters and are potentially useful for paleoclimatic reconstructions

middle triassic pentasauropus dominated ichnofauna from western gondwana ichnotaxonomy palaeoenvironment biostratigraphy and palaeobiogeography abstract quadruped trackways of large pentadactyl footprints are reported from the middle triassic anisian ladinian cerro de las cabras formation of the cuyo basin mendoza province central western argentina the track bearing strata are interpreted as deposited by sheetfloods in a mixed flat where water was ponded in a playa lake setting the vertebrate trackways are assigned to the ichnogenus pentasauropus originally described from the upper triassic elliot formation of south africa based on the presence of five equally spaced digit imprints that form an anteriorly convex broad arcuate pattern a new ichnospecies pentasauropus argentinae nov isp is erected for the argentinian material because of the distinct heteropody inward rotation of the pes and outward rotation of the manus imprints and the presence of palm sole traces and the diagnosis of the ichnogenus is emended pes manus set arrangement and trackway patterns indicate a sprawling limbed trackmaker with an abducted posture for the fore limbs and at least a semi abducted posture for the hindlimbs which suggests that the trackmaker was a kannemeyeriiform dicynodont associated archosaur ichnotaxa chirotherium barthii chirotherium cf c rex isochirotherium cf i coureli point to a middle triassic age for the trackway bearing strata in agreement with bracketing geochronological data the rare occurrence of the therapsid footprint dicynodontipus isp is also compatible with the inferred age the moderate abundance and oldest occurrence of pentasauropus from three areas in argentina suggest an origin for this ichnogenus in southwestern gondwana and presumably this area was a faunal exchange gate between southeastern and southwestern gondwana and south gondwana and north america

time calibration of triassic jurassic microfloral turnover eastern north america abstract palynological data from the newark basin of the newark supergroup reveal a spike in the spore pollen ratio at the triassic jurassic boundary this spore spike is coincident with a 60 regional extinction of the palynoflora and approximately synchronous with terrestrial vertebrate extinctions orbitally controlled sedimentary cycles allow stratigraphic sections to be calibrated in time constraining the duration of the microfloral turnover to an interval of 21 ky the geologically brief palynofloral break is similar to cretaceous tertiary boundary fern spikes these data support a triassic jurassic boundary impact extinction scenario

diet reconstruction for an extinct deer cervidae cetartiodactyla from the quaternary of south america abstract among the extinct cervids of the pleistocene in south america morenelaphus has the most abundant fossil record and the broadest geographic distribution however the paleoecology of morenelaphus is poorly known especially its dietary patterns thus this study aims to recognize the feeding habits of this extinct cervid through analysis of microwear the microwear analysis indicated a mixed feeder diet for morenelaphus both high pit values and frequency of individuals with low number of fine scratches indicated the consumption of grasses possibly including grit siliciclastic sediment ingested during feeding also our results suggest that morenelaphus possibly went extinct at the pleistocene holocene transition as a result of climate environmental changes and or a physiological nutritional crisis

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

the indian summer monsoon drought of 2002 and its linkage with tropical convective activity over northwest pacific the indian subcontinent witnessed a severe monsoon drought in 2002 which largely resulted from a major rainfall deficiency in the month of july while moderate el nino conditions prevailed during this period the atmospheric convective activity was anomalously enhanced over northwest and north central pacific in the 10 20 n latitude belt and heavy rainfall occurred over this region in association with a series of northward moving tropical cyclones similar out of phase rainfall variations over the indian region and the northwest nw pacific have been observed during other instances of el nino southern oscillation enso the dynamical linkage corresponding to this out of phase rainfall variability is explored in this study by conducting a set of numerical experiments using an atmospheric general circulation model the results from the model simulations lend credence to the role of the tropical pacific sea surface temperature anomalies in forcing the out of phase precipitation variability over the nw pacific and the indian monsoon region it is seen that the enso induced circulation response reveals an anomalous pattern comprising of alternating highs and lows which extend meridionally from the equatorial region into the sub tropic and mid latitude regions of west central pacific this meridional pattern is associated with an anomalous cyclonic circulation over nw pacific which is found to favor enhanced tropical cyclonic activity and intensified convection over the region in turn the intensified convection over nw pacific induces subsidence and rainfall deficiency over the indian landmass through anomalous east west circulation in the 10 20 n latitude belt based on the present findings it is suggested that the convective activity over nw pacific is an important component in mediating the enso monsoon teleconnection dynamics

paleodietary reconstruction of fossil horses from the eocene through pleistocene of north america paleodietary trends for north american horses from hyracotherium early eocene through equus late pleistocene were examined using dental microwear analysis over 1200 fossil specimens were analyzed for enamel microwear and results were compared to an extensive microwear database of extant ungulates this study tests the hypothesis that eocene horses browsed on low abrasion foods whereas oligocene and later horses had more abrasive diets concomitant with the spread of more open habitats and examines the correlation between the acquisition of hypsodonty and the beginning of grazing microwear results indicate that early to middle eocene species engaged mostly in fruit browsing in contrast late eocene to oligocene taxa have microwear scratch numbers typical of grazing and mixed feeding ungulates but with very fine scratch textures which are unusual in modern c4 grazers and indicate consumption of relatively low abrasion grasses an increase in overall dietary abrasion is evident beginning in the early miocene but members of the anchitherinae sensu stricto engaged in leaf browsing while other forms committed to grazing or alternating between grass and leaves anchitherinae ss continue to rely on leaves until they became extinct in the late miocene while members of the equinae were either grazing or mixed feeding through the pleistocene dietary abrasion increased further beginning in the late miocene and continued to increase through the pleistocene most pleistocene horses were not grazing but rather alternating between grass and leaves or even browsing increased pitting of dental enamel and coarser scratch textures in plio pleistocene horses reinforces the idea that increased abrasion may be due to grit encroachment on food items and or a shift toward coarser grasses than due to a steady increase in the amount of grass consumed

influence of indian ocean dipole on poleward propagation of boreal summer intraseasonal oscillations abstract the influence of the indian ocean dipole iod on the poleward propagation of boreal summer intraseasonal oscillations bsisos is examined using observed datasets this study finds that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years disorganized poleward propagation of bsiso in the south equatorial indian ocean is observed during positive iod years the rationale behind such an anomaly in the poleward propagation of bsiso in contrasting iod years is identified based on the theory of northward propagating bsiso which suggests the influential role of air sea interaction on the genesis and propagation of bsiso it is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting iod years which in turn influences the meridional propagation of bsiso this study assumes significance considering the critical role of bsiso in modulat

fossil horses and carbon isotopes new evidence for cenozoic dietary habitat and ecosystem changes in north america abstract the transformation from low crowned to high crowned horse teeth during the miocene has traditionally been interpreted as an adaptive response to the spread of savanna grasslands during the middle miocene by about 15 m y ago carbon isotope data from 50 north american horse teeth spanning eocene to pleistocene age indicate that savanna grasslands presumably dominated by c 4 grasses as they are today first became widespread much later than do horses with high crowned teeth prior to 7 m y horses had a c 3 based diet and after 7 m y horses started eating c 4 grasses this change in diet occurred when the major drop in the diversity of horses occurs during the late miocene the change in vegetation reflected in horses diet may be related to a significant reduction in atmospheric co 2 level toward the end of the miocene which provided the c 4 grasses with an adaptive advantage and led to their expansion at the expense of c 3 plants

triassic vertebrates of gondwanan aspect from the richmond basin of virginia a new locality of early late triassic age in the richmond basin of east central virginia has yielded abundant remains of a diversified assemblage of small to medium sized tetrapods that closely resembles southern hemisphere gondwanan assemblages in the predominance of certain synapsids associated palynomorphs indicate an early middle carnian age for the fossiliferous strata the discovery suggests that previously recognized differences between tetrapod assemblages of early late triassic age from gondwana and laurasia at least in part reflect differences in stratigraphic age rather than geographic separation

the nonmarine triassic jurassic boundary in the newark supergroup of eastern north america abstract for the last three decades the position of the triassic jurassic boundary tjb in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the central atlantic magmatic province camp in the newark supergroup of eastern north america this boundary however is demonstrably older than the tjb as it is defined in marine strata thus the palynostratigraphic change used to place this tjb in the newark most resembles a late norian change in the european section and does not correspond to any palynological event at the marine defined tjb conchostracan biostratigraphy suggests that the tjb is in the newark extrusive zone above the oldest camp basalt and vertebrate biostratigraphy is consistent with this placement of the tjb radioisotopic ages indicate that the tjb defined in marine strata is no older than 200 ma but the oldest camp basalts of the newark supergroup consistently yield ages averaging about 201 ma magnetostratigraphic correlation of the newark section to the tjb section at st audrie s bay in england also indicates that the onset of camp volcanism in the newark supergroup is older than the marine tjb correlations based on carbon and osmium isotopes are also consistent with this correlation thus all data indicate that the tjb in the newark supergroup is above the lowest camp basalt in the newark extrusive zone correct placement of the tjb in the newark supergroup allows key nonmarine and marine events to be sequenced across the tjb indicating the following succession of events crurotarsan thecodont extinction the palynofloral turnover in the newark the first camp eruptions the extinctions of rhaetian ammonites and conodonts and the first appearance of jurassic psiloceratid ammonites

magnetostratigraphy of the sherwood sandstone group lower and middle triassic south devon uk detailed correlation of the marine and non marine anisian the sherwood sandstone group in south devon consists of the budleigh salterton pebble beds and the otter sandstone formation the otter sandstone formation comprises four lithostratigraphic sub units from the base labelled a d and contains tetrapods corresponding to the perovkan land vertebrate faunachron and is consequently a key european non marine anisian succession a total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal the magnetic properties and characteristic remanence is predominantly carried by haematite most of which probably formed early in the depositional and diagenetic history the lower part of the sherwood sandstone group budleigh salterton pebble beds and otter sandstone formation unit a lower part of unit b has predominantly normal polarity magnetozones bs1 bs2 and bs3n with three thin reversed polarity magnetozones the lower part of unit b to the lower part of unit c of the otter sandstone formation is predominantly reverse polarity magnetozones bs3r bs4 and bs5 but includes three short normal polarity intervals the upper ca 50 m of unit c shows a mix of normal and reverse polarity bs6 bs7 with normal dominating the ca 15 m thick unit d is entirely of normal polarity bs8n the magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in europe these show that the bs2 and bs3n magnetozones of the otter sandstone formation are lower aegean to middle pelsonian lower to middle anisian the bs3r to bs5r magnetozone interval is middle pelsonian to lower illyrian middle to upper anisian and the bs6 to bs8n magnetozone interval is middle illyrian to lower fassanian the top of unit d is correlated to an interval in the middle of the nevadites zone close to the anisian ladinian boundary consequently the otter sandstone formation correlates with the muschelkalk in the polish basin but is equivalent to only part of the germanic basin muschelkalk the continuous magnetostratigraphy from the sherwood sandstone group provides additional details of the polarity pattern through the pelsonian to illyrian interval which appears to be lacking in discontinuous marine sections a synthesis of adjacent european sedimentary basins in combination with the magnetostratigraphy suggests that the budleigh salterton pebble beds are probably late spathian to lower aegean

more than one event in the late triassic mass extinction the recent hypothesis that mass extinctions are discrete phenomena that have occurred with great regularity during the history of life1 2 is testable in several ways two essential elements of the hypothesis are 1 that each extinction event represents a significant departure from normal or background rates of extinction and 2 that such mass extinction events are spaced equally in time the analyses of the cyclicity of mass extinctions so far have concentrated on the past 250 myr with the first event occuring at the permian triassic boundary 245 myr ago1 5 the second event followed 26 33 myr later1 6 in the late triassic here i present a detailed analysis of the fossil record of marine and non marine life during the late triassic which suggests that there were at least two phases of mass extinction during that time separated by 12 17 myr

influence of the pacific japan pattern on indian summer monsoon rainfall abstractthis study discusses the impact of the pacific japan pj pattern on indian summer monsoon ism rainfall and its possible physical linkages through coupled and uncoupled pathways empirical orthogonal function analysis of 850 hpa relative vorticity over the western north pacific wnp is used to extract the pj pattern as the leading mode of circulation variability the partial correlation analysis of the leading principal component reveals that the positive pj pattern which features anticyclonic and cyclonic low level circulation anomalies over the tropical wnp and around japan respectively enhances the rainfall over the southern and northern parts of india the northwestward propagating rossby waves in response to intensified convection over the maritime continent reinforced by low level convergence in the southern flank of westward extended tropical wnp anticyclone increase rainfall over southern peninsular india meanwhile the anomalous moisture transport from the warm bay of bengal due t

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

tertiary history of c4 biomass in the great plains usa we use the carbon isotope composition of paleosols to reconstruct the history of c4 biomass on the great plains from ca 23 to 1 ma the proportion of c4 biomass was uniform and moderate 12 34 throughout the miocene increased between 6 4 and 4 0 ma and reached modern levels by 2 5 ma ecological changes in great plains ungulates preceded the increase in c4 biomass the contrasts in the paleosol and ungulate records may indicate initial development of c3 grasslands after the middle miocene or a greater role for ecological interactions within communities in structuring ungulate faunas contrasts in paleosol records from different continents point to regional rather than global controls on the evolution of c4 grasslands

the evolution of pco2 ice volume and climate during the middle miocene abstract the middle miocene climatic optimum 17 15 ma mco is a period of global warmth and relatively high co2 and is thought to be associated with a significant retreat of the antarctic ice sheet ais we present here a new planktic foraminiferal 11b record from 16 6 to 11 8 ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to co2 these new data demonstrate that the evolution of global climate during the middle miocene as reflected by changes in the cyrosphere was well correlated to variations in the concentration of atmospheric co2 what is more within our sampling resolution 1 sample per 300 kyr there is no evidence of hysteresis in the response of ice volume to co2 forcing during the middle miocene contrary to what is understood about the antarctic ice sheet from ice sheet modelling studies in agreement with previous data we show that absolute levels of co2 during the mco were relatively modest 350 400 ppm and levels either side of the mco are similar or lower than the pre industrial 200 260 ppm these new data imply the presence of either a very dynamic ais at relatively low co2 during the middle miocene or the advance and retreat of significant northern hemisphere ice recent drilling on the antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the ais did occur during the middle miocene but the complete loss of the ais was unlikely consequently it seems that ice volume and climate variations during the middle miocene probably involved a more dynamic ais than the modern but also some component of land based ice in the northern hemisphere

extremes of the indian summer monsoon rainfall enso and equatorial indian ocean oscillation it is well known that anomalies of the indian summer monsoon rainfall ismr are linked to el nino and southern oscillation enso we show that large anomalies of the ismr are also linked to the equatorial indian ocean oscillation equinoo between states with enhancement suppression of atmospheric convection over the western part of the equatorial indian ocean with suppression enhancement over the eastern part and associated changes in the anomaly of the zonal wind along the equator equinoo is the atmospheric component of the coupled indian ocean dipole mode there is a strong relation between the large anomalies of ismr and a composite index which is a linear combination of the indices for enso and equinoo with all seasons with large deficits excess characterized by small large values of the index however the variation of ismr within one standard deviation is more complex and does not appear to be related to the composite index

a new stable isotope record of neogene paleoenvironments and mammalian paleoecologies in the western great plains during the expansion of c4 grasslands abstract stable isotopes in horse teeth from the north american great plains show that equids began to incorporate c4 plants in their diets about 6 5 million years ago as c4 grasslands expanded however the ecological response of many other ungulates to this expansion is poorly documented we use stable carbon isotopes in mammalian tooth enamel to test whether other ungulates adapted by incorporating c4 vegetation in their diets the openness of habitats before the expansion of c4 grasslands is uncertain with plant phytolith studies suggesting a patchy environment with open habitat grasses and forest and pollen and macrofloral studies suggesting more forested habitats to address this problem we use a model that predicts carbon isotope values for tooth enamel for a variety of environments based on values in modern plants carbon and oxygen isotopes were analyzed in medium to large herbivores from three late miocene and three pliocene local faunas comprising a total of 13 and 7 genera respectively and 59 and 42 individuals results indicate that before the expansion of c4 grasslands taxa with high crowned teeth were consuming predominantly c3 vegetation in contrast by the late pliocene most taxa studied were consuming a component of c4 vegetation and only the peccary platygonus sp had a pure c3 diet c4 consumption increased in the late pliocene 3 0 ma big springs local fauna probably in response to increased c4 biomass most landscapes in the late miocene of nebraska were open such as woodland savanna or c3 grassland although low carbon values from the pratt slide local fauna suggest a denser presumably forested area this general pattern suggests an expansion of open habitats no later than 12 ma early clarendonian through the miocene pliocene transition there was an overall shift to lower 18o enamel values which parallels the long term decrease in global mean annual temperature inferred from the marine record our results indicate that major changes in the diets of medium and large herbivores broadly corresponded with increased c4 biomass and cooling climate from the latest miocene to the late pliocene

eastward propagating mjo during boreal summer and indian monsoon droughts improved understanding of underlying mechanism responsible for indian summer monsoon ism droughts is important due to their profound socio economic impact over the region while some droughts are associated with external forcing such as the el nino and southern oscillation enso many ism droughts are not related to any known external forcing here we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics we show that most ism droughts are associated with at least one very long break vlb breaks with duration of more than 10 days and that the processes responsible for vlbs may also be the mechanism responsible for ism droughts our analysis also reveals that all extended monsoon breaks whether co occurred with el nino or not are associated with an eastward propagating madden julian oscillation mjo in the equatorial indian ocean and western pacific extending to the dateline and westward propagating rossby waves between 10 and 25 n the divergent rossby wave associated with the dry phase of equatorial convection propagates westward towards indian land couple with the northward propagating dry phase and leads to the sustenance of breaks thus the propensity of eastward propagating mjo during boreal summer is largely the cause of monsoon droughts while short breaks are not accompanied by westerly wind events wwe over equatorial western pacific favorable for initiating air sea interaction all vlbs are accompanied by sustained wwe the wwes associated with all vlb during 1975 2005 initiate air sea interaction on intraseasonal time scale extend the warm pool eastward allowing the convectively coupled mjo to propagate further eastward and thereby sustaining the divergent circulation over india and the monsoon break the ocean atmosphere coupling on interannual time scale such as el nino can also produce vlb but not necessary

regional scale variability in the spread of grasslands in the late miocene abstract a new paleovegetation reconstruction based on both phytolith and paleosol carbon isotopic data is presented for the middle late miocene 11 2 9 5 ma of southwestern montana both sources of data indicate an open habitat c3 grassland ecosystem with a small c4 component

archosaur footprints cf brachychirotherium with unusual morphology from the upper triassic fleming fjord formation norian rhaetian of east greenland the orsted dal member of the upper triassic fleming fjord formation in east green land is well known for its rich vertebrate fauna represented by numerous specimens of both body and ichnofossils in particular the footprints of theropod dinosaurs have been described recently an international expedition discovered several slabs with 100 small chirotheriid pes and manus imprints pes length 4 4 5 cm in siliciclastic deposits of this unit they show strong similarities with brachychirotherium a characteristic upper triassic ichnogenus with a global distribution a peculiar feature in the fleming fjord specimens is the lack of a fifth digit even in more deeply impressed imprints therefore the specimens are assigned here tentatively to cf brachychirothe rium possibly this characteristic is related to the extremely small size and early ontogenetic stage of the trackmaker the record from greenland is the first evidence of this morphotype from the fleming fjord formation candidate trackmakers are crocodylian stem group archosaurs how ever a distinct correlation with known osteological taxa from this unit is not currently possible while the occurrence of sauropodomorph plateosaurs in the bone record links the greenland assemblage more closer to that from the germanic basin of central europe here the described foot prints suggest a pangaea wide exchange supplementary material three dimensional model of cf brachychirotherium pes manus set from mguh 31233b from the upper triassic fleming fjord formation norian rhaetian of east greenland as pdf ply and jpg files 3d model created by oliver wings photographs taken by jesper milan is available at https doi org 10 6084 m9 figshare c 2133546

asian summer monsoon simulated by a global cloud system resolving model diurnal to intra seasonal variability 1 interaction of convection and circulation is key to the asian summer monsoon but difficult to represent in global models here we report results from simulations for the summer of 2004 by a global cloud system resolving model nicam at both 14 and 7 km horizontal resolution nicam simulates the observed monsoon circulation patterns and the northward propagation of precipitation the 7 km run simulates summer mean precipitation maxima in narrow bands along the western ghats himalayan foothills the arakan yoma highlands and the annamite range precipitation 1 is modulated by orography 2 is affected by synoptic scale systems and 3 displays a pronounced diurnal cycle especially over indo china with its strong weak signal propagating westward eastward in the wet dry phase of the intraseasonal oscillation this set of simulations captures these intraseasonal changes of the indian monsoon with high fidelity from june to early july nicam exhibits a positive bias in precipitation over the indian ocean common to atmospheric models with prescribed sea surface temperature this calls for the inclusion of ocean atmosphere coupling process to improve monsoon simulation skills

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

cenozoic expansion of grasslands and climatic cooling abstract mountains ocean currents forests and swamps have played an important role in regulating global climate for hundreds of millions of years but the truly novel event of the cenozoic was the evolution and expansion of grasslands with their uniquely coevolved grasses and grazers neogene expansion of the climatic and geographic range of grasslands at the expense of woodlands is now revealed by recent studies of paleosols fossils and their stable isotopic compositions grasslands and their soils can be considered sinks for atmospheric co2 ch4 and water vapor and their cenozoic evolution a contribution to long term global climatic cooling grassland soils are richer in organic matter than are woodland and desert soils of comparable climates and when eroded their crumb clods form sediment unusually rich in organic matter grasslands also promote export of bicarbonate and nutrient cations to lakes and to the oceans where they stimulate productivity and c burial this increased productivity and

distribution and diversity patterns of triassic cynodonts therapsida cynodontia in gondwana abstract cynodonts are an important component of triassic tetrapod faunas and are frequently one of the dominant groups a summary of their record during the triassic of gondwana is presented cynodonts are represented by 63 species 57 genera in gondwana with diversification peaks occurring during the late anisian particularly in africa and the carnian of south america and india data on the number of faunas of each age and the duration in millions of years estimated for these faunas were integrated with cynodont generic diversity values one of the most important turnovers in cynodonts occurred at the late olenekian anisian involving changes in two directions a the record of complex bucco lingually expanded gomphodont postcanines with traversodontid cynodonts already representing an important group at the end of the anisian b the record particularly during the anisian of significantly large sized cynodonts e g cynognathus and diademodon with basal skull length between 30 to 40 cm considering that the global maximum peak of cynodont diversity is during the norian rhaetian the diversity of gondwanan cynodonts for that time eight taxa is remarkably low

an unusual new archosauromorph reptile from the upper triassic wolfville formation of nova scotia an unusual new reptile teraterpeton hrynewichorum is described based on a partial skeleton the holotype comes from the upper triassic wolfville formation newark supergroup of nova scotia the temporal region of the skull is of the euryapsid type the premaxillary rostrum and dentary symphysis are elongate and edentulous the dentition comprises distinctive occluding upper and lower teeth a phylogenetic analysis shows that teraterpeton hrynewichorum is an archosauromorph reptile trilophosaurus buettneri from the upper triassic dockum group of texas may represent a closely related species

environmental change in the great plains an isotopic record from fossil horses abstract carbon and oxygen isotope ratios of fossil horse tooth enamel from nebraska and texas show evidence for late neogene environmental changes in the great plains the earliest unambiguous c4 dietary signal among texas equids coincides with the age of the classic late hemphillian age coffee ranch fauna which we suggest is 6 6 ma based on volcanic ash correlations c4 vegetation was present in the diets of a small fraction of late hemphillian equids in nebraska and was thereafter ordinary in the diets of both nebraska and texas equids there is no unequivocal evidence for abundant c4 vegetation in the diets of pre late hemphillian equids and we suggest that the ensuing dietary change reflects c4 biomass expansion in the latest miocene carbon isotope ratios of post hemphillian horses in nebraska can be divided into two statistically distinct populations on the basis of whether tortoise remains co occur with horse remains indicating that the two proxies carbon isotopes and presence absence of tort

pedogenic carbonate stable isotope record of environmental change during the neogene in the southern great plains southwest kansas usa carbon isotopes and the evolution of c4 dominated grasslands fossiliferous strata in the meade basin southwest kansas preserve numerous superposed mammalian faunas and calcareous paleosols that range in age from the clarendonian north american land mammal age nalma 12 0 9 0 ma early late miocene to the early irvingtonian nalma ca 2 5 ca 1 0 ma early pleistocene faunas from these sections document the evolution of the small mammal community of the modern grassland ecosystem of the region and the stable isotope composition of paleosol carbonates provides a means by which the environmental context of the evolution of the modern ecosystem may be documented we used the stable carbon isotope composition 13 c relative to vienna peedee belemnite vpdb of 194 pedogenic carbonates from 19 measured sections to reconstruct the history of c 4 grass abundance in the meade basin paleosol carbonate 13 c values reflect the proportion of c 3 trees shrubs cool climate grasses and c 4 warm climate grasses plants that grew in an ancient soil and provide a means with which to reconstruct past mammalian habitats paleosol carbonate 13 c values record a three phase increase in the abundance of c 4 biomass during the neogene in the meade basin late miocene sections have mean 13 c values of 7 6 0 90 clarendonian and 6 5 0 31 hemphillian nalma 9 0 4 9 ma consistent with 17 and 26 c 4 biomass respectively miocene 13 c values from meade are statistically identical to published 13 c values for miocene paleosol carbonates elsewhere in the southern great plains supporting the widespread presence of 20 c 4 biomass on average in the region throughout the miocene the abundance of c 4 biomass increased between the end of the hemphillian section and the beginning of the early blancan nalma 5 0 3 0 ma early and middle blancan 3 0 2 5 ma carbonates have statistically identical 13 c values 4 9 0 90 and 5 0 1 10 respectively suggesting a stable ecosystem during the early pliocene although high 13 c variability in densely sampled intervals suggests a high degree of landscape scale variation in c 4 abundance the final phase geochronologically controlled by two well characterized ashes huckleberry ridge 2 10 ma cerro toledo b 1 47 1 23 ma and magnetostratigraphy is a trend to higher 13 c values from the late blancan to early irvingtonian ca 2 5 ca 1 0 ma from 4 at the base of the section to 1 at the top corresponding to an increase from almost 50 to 65 c 4 biomass the abundance of c 4 biomass first reaches modern levels for the region 78 10 9 around the level of the cerro toledo b ash indicating that a modern like grassland ecosystem first appeared in the region ca 1 3 ma although 13 c values do not remain consistently high through the rest of the section

investigating equid mobility in miocene florida usa using strontium isotope ratios abstract despite extensive research on the evolutionary history and ecology of horses surprisingly little is known about the daily and seasonal movements i e mobility of extinct species we used strontium isotope ratios 87sr 86sr in tooth enamel to estimate mobility patterns of equids from two miocene fossil sites in northern florida usa thomas farm ca 18 ma and love bone bed ca 9 5 9 ma the species included in our sample have a range of body sizes 45 252 kg and reconstructed diets gomphotheres and tapirs from love bone bed were also included to represent browsers based on modern species behavior we predicted small bodied and browsing taxa living in closed habitats had limited mobility and 87sr 86sr similar to local northern florida limestone we anticipated larger bodied and grazing taxa living in open environments had increased mobility with higher and more variable 87sr 86sr reflecting larger movements across differing geologies contrary to expectations the majority of taxa at both sites have higher 87sr 86sr than expected for local eocene bedrock and instead are similar to contemporary late oligocene to mid miocene seawater the most plausible explanation for these findings is that most individuals foraged close to the paleo coastline where vegetation would have been influenced by marine derived strontium via sea spray or precipitation tapirs have considerably higher and more variable 87sr 86sr than horses or gomphotheres at love bone bed which may reflect foraging on aquatic vegetation in the river channel that is preserved at the site our results suggest that horses were relatively sedentary in florida even during their peak radiation

pedogenic carbonate stable isotope record of environmental change during the neogene in the southern great plains southwest kansas usa oxygen isotopes and paleoclimate during the evolution of c4 dominated grasslands neogene strata in the meade basin southwest kansas preserve numerous superposed calcareous paleosols in sections that range in age from the clarendonian north american land mammal age nalma 12 0 9 0 ma early late miocene to the early irvingtonian nalma ca 2 5 ca 1 ma early pleistocene the carbon isotope compositions 13 c relative to vienna peedee belemnite vpdb of pedogenic carbonates from these sections record the protracted regional increase in the abundance of grasses using the c 4 photosynthetic pathway over this interval with the first appearance of a modern like grassland ecosystem having 70 c 4 biomass around 1 3 ma we use the stable oxygen isotope composition 18 o relative to vienna standard mean ocean water vsmow of 194 paleosol carbonates from 19 measured sections to reconstruct the climatic conditions in the meade basin during the rise of c 4 grasses to ecological dominance in the region pedogenic carbonate 18 o values are sensitive to soil temperature and the 18 o of soil water and hence they are a paleoclimate proxy carbonate 13 c values do not exhibit consistent trends in relation to 18 o values indicating no consistent relationship between short term climatic conditions in terms of temperature or aridity and the abundance of c 4 biomass mean carbonate 18 o values within biostratigraphic intervals decrease from the clarendonian 25 3 0 72 to the early and middle blancan 21 8 0 87 and 22 1 0 69 respectively and they also exhibit a decreasing trend in the late blancan early irvingtonian from 25 to 21 the increase in 18 o values between the end of the middle blancan and the beginning of the late blancan early irvingtonian sections could reflect the onset of northern hemisphere glaciation and a change in the isotope composition of the hydrosphere due to increased ice volume the long term trend in 18 o values suggests that c 4 biomass increased coincident with some combination of decreasing temperature increasing proportion of winter precipitation recharge of soil water and or increasing soil moisture thus the ecological dominance of c 4 grasses in the region today does not seem to be linked to warmer temperatures or increased aridity

the role of the secondary standard in stratigraphy the dsvelopment of a series of internationally acceptablc chronostratigraphical units initially grew up through agreed use today s requirement of endorsement by the international commission on stratigraphy has resulled in the official rejection of names which are perfectly valid and still essential in the parts of the world for which they were introduced recognition of this fact is urged by the acceptance of the secondary emerging geological systems in particular major lithological changes or unconformities often provided the ideal criterion for drawing a boundary at a particular place thus the base of the cambrian is well defined at most places in britain by a basal unconformity paradoxically in the type area of north wales the basal boundary may be conformable on the underlying recambrim cowie rushton stubblefield 1972 the base of the carboniferous was drawn where marine hmestandards as locall defined chronost the rxlssible future correlation with the rima standard litholorical base of the old red sandstone was eaualed with the the eeolorical time scale has been developed piecemeal over almost two centuries initial work was concerned with the naming of formations in enelish eeoloeical literature usuallv referred to as strata these were often adaptations of quarrymen s terms such as we find in william smith s contribution to townsend s 1813 table of strata which listed formations between the coal measures and the chalk this was developed from earlier manuscript versions the fist of which deal with the formations around bath dates from 1797 strata were then grouped togkther as a result of syntheses of earlier work into formations or into series thus smith s jurassic stratal tenns were grouped into an oolite formation buckland 1818 or an oolite series conybeae phillips 1822 these terms were compared with the jura limestone of humboldt 1795 and following brogniart s introduction of the term jurassic

ungulate diets reveal patterns of grassland evolution in north america abstract equids from the late miocene hemphillian north american land mammal age of texas evolved c4 dominated diets earlier than their nebraska counterparts leading researchers to hypothesize a northward expansion of c4 grasses between 8 and 6 ma however competing hypotheses from multiple paleoecological proxies support one of three hypotheses that northward c4 expansion occurred at the expense of c3 woodlands c3 grasslands or was not occurring during the hemphillian we test these alternative hypotheses by comparing the ecosystems of hemphillian texas and nebraska 6 3 7 5 ma using hoofed mammal dietary reconstruction hypsodonty and digestive strategy and by incorporating published tooth enamel isotopes paleosol isotopes and phytolith assemblage data we also use hypsodonty mesowear and microwear in a detailed comparison of two localities that are roughly contemporary cambridge nebraska at 7 ma and coffee ranch texas at 6 6 ma to rule out time averaging as an explanatory variable through analogy with modern african communities we reconstruct texas and nebraska ecosystems as bushland and woodland respectively using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217 mm year for nebraska and 1368 mm year for texas using rarefaction we also do not find differences in the richness of brachydont hypsodont and hindgut fermenting taxa we therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late miocene when compared to published paleosol and phytolith data which show no differences in c3 c4 biomass among latitudes our results allow us to reject hypotheses of northward c4 expansion during the late miocene we therefore suggest that the equid enamel isotopes may have been biased by two potential factors the primary reliance on a single locality of appropriate age and possible behavioural lag in c4 feeding among nebraska equids these results suggest that the formation of a modern c3 c4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes

prolonged monsoon droughts and links to indo pacific warm pool a holocene record from lonar lake central india abstract concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the indian summer monsoon ism also referred to as the indian ocean summer monsoon and the absence of long term palaeoclimate data from the central indian core monsoon zone cmz here we present the first high resolution well dated multiproxy reconstruction of holocene palaeoclimate from a 10 m long sediment core raised from the lonar lake in central india we show that while the early holocene onset of intensified monsoon in the cmz is similar to that reported from other ism records the lonar data shows two prolonged droughts pd multidecadal to centennial periods of weaker monsoon between 4 6 3 9 and 2 0 6 cal ka a comparison of our record with available data from other ism influenced sites shows that the impact of these pd was observed in varying degrees throughout the ism realm and coincides with intervals of higher solar irradiance we demonstrate that i the regional warming in the indo pacific warm pool ipwp plays an important role in causing ism pd through changes in meridional overturning circulation and position of the anomalous walker cell ii the long term influence of conditions like el nino southern oscillation enso on the ism began only ca 2 cal ka bp and is coincident with the warming of the southern ipwp iii the first settlements in central india coincided with the onset of the first pd and agricultural populations flourished between the two pd highlighting the significance of natural climate variability and pd as major environmental factors affecting human settlements

carbon and oxygen isotopic variability in neogene paleosol carbonates constraints on the evolution of the c4 grasslands of the great plains usa abstract understanding the development of grassland ecosystems is critical for understanding the evolution of their associated vertebrate faunas we focus on the central and southern portions of the great plains which is the largest continuous grassland in north america and has a well documented mammalian fossil record modern biomass in this region is dominated by c4 grasses but paleontological evidence indicates the region was forested prior to the middle miocene implying the region was formerly dominated by c3 plants we examine long and short term variations in the abundance of c4 grasses and climatic conditions in the central and southern great plains using the stable carbon and oxygen isotope composition of paleosol carbonates from 28 sections of 11 lithostratigraphic units in the region the carbon isotope composition 13c of paleosol carbonate reflects the proportion of c3 and c4 plants that grew in an ancient soil the long term pattern of 13c values indicates that the percentage of c4 grasses in the great plains was moderate ca 20 throughout most of the miocene increased from 6 4 to 4 0 ma and reached modern levels by 2 5 ma based on the range in 13c values within sections and the mean 13c values for different carbonate morphologies that reflect different intervals of carbonate accumulation the abundance of c4 biomass did not vary substantially on short time scales the variability in c4 biomass on short time scales does not correlate with age of section latitude longitude or the mean percentage of c4 biomass the oxygen isotope composition 18o of soil carbonate is controlled by soil temperature and the 18o value of soil water great plains paleosol 18o values vary considerably in relation to time and latitude removing the variation due to latitude with least squares linear regression reveals a temporal pattern that is consistent with the global pattern of neogene climate change quantitative interpretation of the 18o record is difficult without independent control on temperature or the oxygen isotope composition of soil water both of which have probably varied with long term climate change comparisons of measured 18o values for each section with predicted values based on modern temperature data and estimated modern meteoric water 18o values suggest that 1 most miocene sections have 18o values consistent with warmer temperatures and more positively shifted soil water 18o values than today 2 three miocene sections in western nebraska probably had soil water compositions that were more negative than similar aged localities in the region and 3 the plio pleistocene sections have 18o values consistent with cooler temperatures and more negative soil water 18o values than today the paleosol 13c values do not correlate strongly with the pattern of climate change recorded by the 18o values suggesting that long term change in mean temperature is not the main control on the abundance of 13c biomass in the great plains we propose two testable hypotheses to account for our data and other published data that bear on the evolution of the great plains ecosystem

triassic temnospondyls of the pranhita godavari basin india abstract the pranhita godavari p g basin of central india has yielded early middle and late triassic temnospondyl families bracyops laticeps the type for the family brachyopidae was first described from the lower triassic mangli beds of the northernmost extension of the p g basin in the northern and central parts of the p g basin itself the middle triassic yerrapalli formation has stanocephalosaurus rajareddyi a paracyclotosaurid and the upper triassic maleri formation has buettneria maleriensis a metoposaurid and two other chigutisaurid taxa compsocerops cosgriffi and kuttycephalus triangularis a critical review of triassic temnospondyls of the p g basin indicates that the affinities of s rajareddyi and k triangularis are somewhat uncertain and discovery of further material is necessary to establish their relationships among similar temnospondyls of the world it is also noted that b maleriensis is displaced by the two chigutisaurid genera and species at the carnian norian boundary thus p g basin is unique in having pangaean metoposaurids and exclusively gondwanan chigutisaurids in successive faunal zones within the same formation significantly the end of carnian is marked by the demise of metoposaurids in india as well as in africa and europe in north america their size appears to have diminished during that time

dynamics of breaks in the indian summer monsoon abstract in this paper the authors present results of diagnostic analysis of observations and complementary experiments with a simple numerical model that enable them to synthesize the morphology and dynamics of breaks in the indian summer monsoon ism almost one week ahead of the onset of a break spell over india a monotonically decreasing trend in convective activity is found to occur over the bay of bengal in response to a steady eastward spreading of dry convectively stable anomalies from the equatorial indian ocean a major intensification of the convectively stable anomalies over the bay of bengal is seen about 2 3 days prior to commencement of a monsoon break both observations and modeling experiments reveal that rapid northwest propagating rossby waves are triggered in response to such a large strengthening of the convectively stable anomalies it is shown that an abrupt movement of anomalous rossby waves from the bay of bengal into northwest and central india marks the initiation of a break

influence of indian ocean dipole on boreal summer intraseasonal oscillations in a coupled general circulation model 1 the role of indian ocean dipole iod on poleward propagation of boreal summer intraseasonal oscillations bsiso is examined using long simulation of a coupled ocean atmosphere general circulation model the model sintex f1 simulates the salient features of bsiso realistically it is found that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years the probable mechanisms behind such an anomaly in poleward propagation of bsiso in contrasting iod years are identified we find that the mean structure of meridional specific humidity distribution undergoes cardinal changes in contrasting iod years which in turn influences the meridional propagation of bsiso enhanced decreased air sea interaction in negative positive iod years also supports coherent incoherent poleward propagation of bsiso anomalies this study has important implications considering the critical role of bsiso in modulating the seasonal mean summer monsoon rainfall

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

niche modeling reveals lack of broad scale habitat partitioning in extinct horses of north america abstract the classic traits of modern horses equidae large body size high crowned teeth hypsodonty and a single toe monodactyly are often considered adaptations to grassland environments however extinct horses that varied in these three traits overlapped geographically for millions of years during the miocene and pliocene it has been hypothesized that co occurring horse species partitioned habitats with large bodied hypsodont and monodactyl equids dominating open grasslands while equids with different combinations of traits lived in more wooded areas we tested for the presence of broad scale habitat partitioning by compiling a large database of north american horse fossil occurrences with data on trait state body size hypsodonty index and toe number and paleoenvironment derived from paleovegetation records null modeling of niche overlap in each of the north american land mammal ages of the miocene and pliocene revealed that taxonomic and trait based groups show no differences in habitat occupancy cluster dendrograms visualizing niche overlap showed that some ecological guilds shared derived traits but derived traits were not associated exclusively with grassland habitats trait values are not predicted by the proportion of grassland habitats in time bins further the three traits show no co evolution across the equid tree when corrected for phylogenetic relatedness together these results suggest that the evolution of large body size hypsodonty and monodactyly in equids was not due to a shared selective regime in response to expanding grassland habitats instead these traits may have evolved separately likely due to a variety of small scale selective pressures acting across the variety of habitats present in the miocene and pliocene

global triassic tetrapod biostratigraphy and biochronology abstract eight temporally successive assemblage zones of tetrapod fossils provide the basis for dividing triassic time into eight land vertebrate faunachrons these land vertebrate faunachrons their type assemblage zones and their approximate correlation to the standard global chronostratigraphic scale are ascending order 1 lootsbergian lystrosaurus assemblage zone balfour katberg and burgersdorp formations karoo basin south africa late dorashamian induan 2 nonesian cynognathus assemblage zone burgersdorp formation karoo basin south africa olenikian 3 perovkan shansiodon assemblage zone donguz formation russian urals anisian 4 berdyankian mastodonsaurus assemblage zone bukobay formation russian urals ladinian early carnian 5 otischalkian paleorhinus assemblage zone chinle group chinle basin usa late early to early late carnian 6 adamanian rutiodon assemblage zone chinle group chinle basin usa latest carnian 7 revueltian pseudopalatus assemblage zone chinle group chinle basin usa norian 8 apachean redondasaurus assemblage zone chinle group chinle basin usa rhaetian the triassic land vertebrate faunachrons provide a framework for the correlation of triassic nonmarine deposits with a temporal resolution comparable to the seven triassic stage ages of the standard global chronostratigraphic scale

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

unusual tetrapod teeth from the upper triassic chinle formation arizona usa two teeth collected from the upper triasssic chinle formation of northeastern arizona are described here and named kraterokheirodon colberti gen et sp nov these teeth are novel in having an occlusal ridge with six cusps and a posterior shelf lacking dentine evidence for thecodont implantation of the root suggests amniote affinities for these teeth they do not match any teeth known for basal vertebrates or basal tetrapods although the teeth display some affinities with traversodont cynodonts there are significant differences that preclude a referral to this group these teeth most probably represent an unknown tetrapod clade and document the presence of a large amniote previ ously unknown from late triassic terrestrial faunas

isotopic age of the black forest bed petrified forest member chinle formation arizona an example of dating a continental sandstone zircons from the black forest bed petrified forest member chinle formation in petrified forest national park yield ages that range from late triassic to late archean grains were analyzed by multigrain tims thermal ionization mass spectrometry single crystal tims and shrimp sensitive high resolution ion microprobe multiple grain analysis yielded a discordia trajectory with a lower intercept of 207 6 2 ma which because of the nature of multiple grain sampling of a detrital bed is not considered conclusive analysis of 29 detrital zircon grains by tims yielded upb ages of 2706 6 6m a to 2066 6 ma eleven of these ages lie between 211 and 216 6 6 8 ma our statistical analysis of these grains indicates that the mean of the ages 213 6 1 7 ma reflects more analytical error than geologic variability in sources of the grains grains with ages of ca 1400 ma were derived from the widespread plutons of that age exposed throughout the southwestern cordillera and central united states twelve grains analyzed by shrimp provide 206 pb 238 u ages from 214 6 2m a to 200 6 4 ma we use these data to infer that cores of inherited material were present in many zircons and that single crystal analysis provides an accurate estimation of the age of the bed we further propose that even if some degree of reworking has occurred the very strong concentration of ages at ca 213 ma provides a maximum age for the black forest bed of 213 6 1 7 ma the actual age of the bed may be closer to 209 ma dating continental successions is very difficult when distinct ash beds are not clearly identified as is the case in the chinle formation detrital zircons in the black forest bed however are dominated by an acicular morphology with preserved delicate terminations the shape of these crystals and their inferred environment of deposition in slow water settings suggest that the crystals were not far removed from their site of deposition in space and likely not far in time plinian ash clouds derived from explosive eruptions along the early mesozoic cordilleran margin provided the crystals to the chinle basin where local conditions insured their preservation in the case of the black forest bed the products of one major eruption may dominate the volcanic contribution to the unit volcanic detritus in the chinle formation was derived from multiple distinct sources coarse pebble to cobble size material may have originated in eastern california and or western arizona where triassic plutons are exposed fine grained detritus in contrast was carried in ash clouds that derived from caldera eruptions in east central california or western nevada

seasonal to interannual time scale dynamics of the equatorial undercurrent in the indian ocean abstractthis paper investigates the structure and dynamics of the equatorial undercurrent euc of the indian ocean by analyzing in situ observations and reanalysis data and performing ocean model experiments using an ocean general circulation model and a linear continuously stratified ocean model the results show that the euc regularly occurs in each boreal winter and spring particularly during february and april consistent with existing studies the euc generally has a core depth near the 20 c isotherm and can be present across the equatorial basin the euc reappears during summer fall of most years with core depth located at different longitudes and depths in the western basin the euc results primarily from equatorial kelvin and rossby waves directly forced by equatorial easterly winds in the central and eastern basin however reflected rossby waves from the eastern boundary play a crucial role while the first two baroclinic modes make the largest contribution intermediate modes 3 8 are also

the age fauna and palaeoenvironment of the late triassic fissure deposits of tytherington south gloucestershire uk important vertebrate faunas occur in fissure deposits of late triassic jurassic age in sw britain although the faunas are well described their age and palaeoenvironment remain poorly understood one such fissure system was documented in detail during quarrying operations at tytherington and has yielded in situ palynomorphs that add much information concerning its age and palaeoenvironment significantly the tytherington fauna is of the sauropsid type that has generally been dated as norian or pre penarth group transgression and was also regarded as representing a distinct upland fauna the palynomorphs which include a significant marine component demonstrate that the tytherington triassic fissures are infilled with late triassic rhaetian sediments that match specific levels in the westbury formation in addition many of the tytherington solutional fissures probably formed during the rhaetian and are consistent with a fluctuating saline to freshwater environment there is no prima facie evidence of solutional formation and infilling of the reptile bearing deposits before the rhaetian trangression the fissure reptile fauna which includes the early dinosaur thecodontosaurus inhabited a small fire swept limestone island in the rhaetian sea the features of the herpetofauna are entirely consistent with this island model which has quaternary analogues

a sedimentological model for the continental upper triassic tadrart ouadou sandstone member recording an interplay of climate and tectonics argana valley south west morocco the continental upper triassic tadrart ouadou sandstone member was deposited in an extensional setting on the pangaean continent strongly influenced by a low latitude climatic regime 10 to 20 north complex interaction of basin subsidence and climatically driven processes led to high facies variability and a lack of correlatable units across the argana valley exposures a process orientated approach integrating detailed facies with architectural element analysis was undertaken which resulted in a multistage depositional model for the tadrart ouadou sandstone member the basin scale model shows that basal alluvial fan and braided river systems are confined to the centre of the argana valley exposures aeolian deposits occur throughout the sequence but dominate in the north after a phase of playa deposition prominent basin wide fluvial incision of up to 8 m marks the onset of perennial fluvial flow these well sorted internally complex and locally highly amalgamated fluvial sandstones are widespread throughout the basin and are focused in a north to south south west flowing channel system after a final stage of aeolian sedimentation sandstone deposition of the tadrart ouadou sandstone member in the argana valley is terminated rapidly by the onlap of lacustrine mudstones of the sidi mansour member the study revealed that except for one pronounced period of perennial conditions sedimentation is controlled largely by ephemeral fluvial flow alternating ground water tables deflation processes and periods with limited periodic local run off the study highlights that facies architecture in the basin is the result of complex interaction of local syn sedimentary tectonics and the climatic regime within the basin but also the climate of the catchment area to the east the data suggest a proximal to mid distal basin setting in the rain shadow to the west of a mountain range massif ancien which exerted a strong control on the depositional environments of triassic deposits exposed in this part of south west morocco

magnetostratigraphy across the triassic jurassic boundary in the main karoo basin abstract the end triassic mass extinction and the transition and explosive diversification of fauna over the triassic jurassic boundary is poorly understood and poorly represented in the rock record of the southern hemisphere this is despite the rich diversity in both body and trace fossils of triassic jurassic age in southern africa which is not found in coeval northern hemisphere localities we report here the first palaeomagnetic polarity zonation of the upper triassic lower jurassic continental red bed succession elliot formation stormberg group in southern africa the results from 10 partially overlapping sections with a composite thickness of 280 m provide a magnetic polarity chronology of the main karoo basin in south africa and lesotho palaeomagnetic analyses reveal that heating samples to between 150 c and 300 c removes the secondary moderately inclined 48 normal polarity component of remanent magnetization this component overlaps with the present day field and is comparable to the overprint direction expected from lower jurassic karoo dolerite intrusions in contrast a likely primary high unblocking temperature component of dual polarity consistently is of steeper inclination 63 this characteristic remanence passes the reversals test except where means are based on small sample populations there are only two resulting polarity zones for the 200 m thick lower elliot formation lef with potential for a thin 3rd magnetozone in the uppermost part the upper elliot formation uef in contrast which was sampled over a thickness of 80 m has five polarity zones the failure of the reversal test for the uef and combined elliot formation lef uef indicates that the normal polarity samples may be biased by a younger overprint of either the jurassic normal polarity of the karoo large igneous province or present day field the separate poles calculated for the four sites in the lef and ten sites in the uef overlap with the late triassic and early to middle jurassic gondwana poles respectively the combined elliot formation and uef pole positions are better constrained than the lef and therefore considered more reliable overall the lef shows considerable overlap with the late triassic apparent polar wander paths apwp poles

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

arctosaurus osborni a late triassic archosauromorph reptile from the canadian arctic archipelago arctosaurus osborni is known only from an incomplete cervical vertebra from the upper triassic heiberg formation of cameron island nunavut canada re examination of the unique specimen indicates that it represents an archosauromorph reptile possibly from the clade allokotosauria to date arctosaurus osborni represents the sole record of late triassic continental tetrapods from nunavut and the northernmost record of such animals anywhere in the world

dynamical response of the south asian monsoon trough to latent heating from stratiform and convective precipitation simulation experiments using a simplified atmospheric gcm and supplementary diagnostic analyses of observations are performed to understand how the south asian monsoon trough mt responds dynamically to latent heating from mesoscale convective systems mcss observations reveal that the mt during active monsoons is characterized by a deep cyclonic vorticity extending from the surface to 350 hpa and organized mcss covering over 3500 4000 km along the indo gangetic plains the mcss during active monsoons are composed of a relatively higher abundance of stratiform type precipitation mostly nimbostratus as compared to the convective type the results suggest that a stratiform type heating profile is very effective in promotingupward development of continental scale cyclonic circulation well above the midtroposphere over the mt region the vertical development involves a dynamical uplift of the layer of cyclonic circulation and is induced by midlevel 600 500 hpa convergence and vorticity stretching above 500 hpa by varying the population of stratiform and convective rain types in the simulation the horizontal scale of midlevel vorticity response is shown to increase significantly with stratiform population in contrast the midlevel response is more localized when the mcs is dominated by deep convective clouds for large stratiform populations the midlevel responseis found to extend far westward up to the northernflanks of the africanitcz indicativeof rossby wave dispersion of pv anomalies that are generated near the level of maximum heating gradient from the present findings one can conclude that the vertical deepening of mt during active monsoons is not merely a localized phenomenon instead it represents a large scale dynamical response to organized mcss that exert pivotal influence on the upward development of cyclonic circulation well above the midtroposphere

the leading mode of indian summer monsoon precipitation variability during the last millennium 1 the internally generated intraseasonal variability of the indian summer monsoon is characterized by intermittent periods of enhanced active and deficient break precipitation which produce a quasi east west precipitation dipole over the indian subcontinent here we present multicentennial length and near annually resolved reconstructions of monsoon precipitation inferred from absolute dated and instrumentally calibrated speleothem oxygen isotope records from regions central and northeast india that have diametric responses to active break monsoon circulation patterns on centennial timescales ad 1400 2008 precipitation variability from these two regions exhibit opposing behavior oscillating between periods with a persistently active dominated ad 1700 to 2007 and a break dominated ad 1400 to 1700 regime the switch between these regimes occurs abruptly within decades at a time ad 1650 1700 when a proxy record of upwelling intensity from the arabian sea suggest an abrupt increase in the monsoon winds on the basis of these observations we hypothesize that the frequency distribution of active break periods varies on centennial timescales implying a leading role of internal dynamics in governing the ism response to slowly evolving changes in the external boundary conditions

indian ocean monsoon coupled interactions and impending monsoon droughts 1 monsoon droughts over the indian subcontinent emanate from failures in the seasonal june september monsoon rains while prolonged dry spells monsoon breaks pervade on sub seasonal intra seasonal time scales the underlying causes for these long lasting anomalies remain elusive based on analyses of a suite of observed data sets we report an ocean atmosphere dynamical coupling on intra seasonal time scales in the tropical indian ocean which is pivotal in forcing extended monsoon breaks and causing droughts over the subcontinent this coupling involves a feedback between the monsoonal flow and thermocline depth in the equatorial eastern indian ocean eeio in which an anomaly of the summer monsoon circulation induces downwelling and maintains a higher than normal heat content the near equatorial anomalies induce strong and sustained suppression of monsoon rainfall over the subcontinent it is concluded that the intra seasonal evolution of the ocean monsoon coupled system is a vital key to unlocking the dynamics of monsoon droughts