longriba fault zone in eastern tibet an important tectonic boundary marking the westernmost edge of the yangtze block global positioning system gps measurements across eastern tibet reveal a sharp velocity gradient zone located about 150 km west of the longmen shan frontal thrust zone where eastward block motion of tibet decreases from 12 mm yr to 3 mm yr over a distance of less than 10 km in order to investigate the tectonic cause for this rapid change in gps velocity together with systematic review on the available geological and geophysical data in easternmost tibet we provide new constraints on the tectonic feature of the longriba fault zone from advanced land observing satellite phased array type l band synthetic aperture radar data we propose that the ne striking longriba fault zone is the key structure responsible for the observed sharp gradient in gps velocities in addition the evidence indicates that the longriba fault zone instead of the longmen shan fault zone marks the westernmost edge of the yangtze crustal block given the irregular western margin of the yangtze block the longriba fault zone represents part of the actual tectonic boundary between the songpan ganzi terrane and the yangtze block the newly identified western edge of the yangtze block implies a paleocontinent ocean boundary at depth this boundary was a potential weak zone and may have been exploited during the formation of the longriba fault zone the results of this paper should advance our understanding of the tectonic relationship between the songpan ganzi terrane and yangtze block and provide additional constraints for studies of the geodynamic response of eastern tibet to the ongoing india eurasia collision

40ar 39ar dating and magnetostratigraphic correlation of the terrestrial cretaceous paleogene boundary and puercan mammal age hell creek tullock formations eastern montana the recovery and subsequent prolific radiation of mammals in the northern western interior of north america following the cretaceous paleogene k p boundary is well documented in rocks attributed to the puercan land mammal age the most complete puercan record is that of the tullock formation which crops out widely in garfield and mccone counties eastern montana the tullock formation overlies the dinosaur bearing hell creek formation and consists of a stratigraphic series of channel and overbank deposits from which well preserved puercan faunas have been collected these channel deposits are typically bracketed by widespread coal beds the irz and z coals mark the base of the puercan at the k p boundary as defined by the highest appearing local occurrences of in situ dinosaur fossils the highest stratigraphic occurrence of cretaceous pollen and an anomalously high concentration of the element iridium ir the irz coal is overlain sequentially by the z hfz y w and u coals fossil vertebrates

high temperature overprint in u hpm rocks exhumed from subduction zones a product of isothermal decompression or a consequence of slab break off slab rollback abstract this paper presents and discusses petrological observations from high to ultrahigh pressure u hp metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts the interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic meta eclogite and ultramafic garnet peridotite and pyroxenite exposed in collisional orogens the inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain pt paths of hp uhp rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks the bohemian massif of the european variscides is used as the basis for a model example to explain these processes but u hp rocks from various other terrains are taken into consideration to discuss available pt paths in relation to proposed subduction and exhumation rates of u hp rocks based on geophysical and geochronological data primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many u hp rocks which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of pt paths prior to initiation of exhumation and may have continued even with cooling if exhumation rates were rapid the commonly applied interpretation of isothermal decompression during exhumation is critically appraised considering whether a simple thermal relaxation and radiogenic heating during exhumation is responsible for formation of post peak pressure retrograde mineral assemblages and textures observed in u hp rocks we go on to consider whether this can satisfactorily explain the often pervasive medium pressure high temperature metamorphic re equilibration of u hp rocks or whether an additional external source of heat is a better explanation we conclude that the commonly observed high temperature metamorphic overprint exhibited by u hp rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions when mantle upwelling resulting from slab breakoff delamination or slab rollback takes place at the onset of continent continent collision we also explore contrasting pt trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation pt paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and once entrained share a common evolution that depends on the exhumation mechanism and rate considering all of the data presented in this work we conclude that the diverse polyphase metamorphic evolution exhibited by u hp terrains embodied in the pt paths of hp and uhp rocks has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

upper cretaceous paleocene biostratigraphy and magnetostratigraphy hell creek and tullock formations northeastern montana fossils from the hell creek and tullock formations in northeastern montana provide detailed documentation of terrestrial faunal and floral evolution during latest cretaceous lancian and early paleocene puercan time here the replacement of lancian faunas by those of puercan age most obviously signaled by the extinction of dinosaurs and the changes in pollen floras sometimes used to mark the cretaceous tertiary boundary occurred during a period of reversed magnetic polarity paleontological correlations suggest that dinosaur extinction and the change in pollen floras took place in the red deer valley area alberta during the same period of reversed polarity furthermore also on the basis of paleontological correlations the extinction of dinosaurs in the san juan basin new mexico appears to have occurred either during the same period of reversed polarity or possibly during the preceding period of normal polarity

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

the neotectonics of the tibetan plateau part of the continuing northward convergence between india and eurasia is probably taken up by strike slip displacement with tibet as a whole moving eastward away from the collision zone and undergoing east west extension molnar and tapponnier 1975 ni and york 1978 on the basis of our interpretation of landsat images we propose that strike slip faulting occurs throughout the tibetan plateau such that its north south cross section is being shortened with little contemporary folding or thrusting

palynologically calibrated vertebrate record from north dakota consistent with abrupt dinosaur extinction at the cretaceous tertiary boundary new data from 17 cretaceous tertiary k t boundary sections and 53 vertebrate sites in the hell creek and fort union formations in southwestern north dakota document a 1 76 m barren interval between the highest cretaceous vertebrate fossils and the palynologically recognized k t boundary the boundary is above the formational contact at 15 localities and coincident with it at two demonstrating that the formational contact is diachronous dinosaurs are common in the highest cretaceous vertebrate samples and a partial dinosaur skeleton in the fort union formation is the highest recorded cretaceous vertebrate fossil in this area

sedimentology stratigraphy and extinctions during the cretaceous paleogene transition at bug creek montana bug creek valley the source of an unusual and controversial cretaceous paleogene coincidence of mammals dinosaurs pollen and indium exemplifies the importance of depositional process in the reconstruction of evolutionary events five sedimentary facies are recognized at bug creek a cross stratified sandstone a green and purple siltstone a lateral accretionary sandstone a coal and a variegated siltstone repeated fluvial channeling restricts the accuracy of lateral correlations and the relationship of the fossil assemblage to the presumed cretaceous paleogene boundary cannot be established sedimentologically the cretaceous paleogene transition is represented here by cretaceous meandering channels that gave way initially to paleogene swamp deposition

seismic signature of the collision between the east tibetan escape flow and the sichuan basin abstract gps displacement vectors show that the crust in east tibet is being squeezed in an easterly direction by the northward motion of the indian plate and the sichuan basin is resisting this stream and redirecting it mainly towards indochina the longmen shan containing the steepest rise to the high plateau anywhere in tibet results from the strong interaction between the east tibetan escape flow and the rigid yangtze block sichuan basin but the kinematics and dynamics of this interaction are still the subject of some debates we herein present results from a dense passive source seismic profile from the sichuan basin into eastern tibet in order to study the deep structure of this collision zone using p and s receiver function images we observe a sudden rise of the lithosphere asthenosphere boundary lab from 120 to 150 km beneath the sichuan basin and from 70 to 80 km beneath eastern tibet in contrast the depth of the crust mantle boundary moho increases from 36 to 40 km beneath the sichuan basin and from 55 to 60 km beneath eastern tibet the 410 km discontinuity is depressed below eastern tibet by about 30 km although the 660 remains at nearly the same depth throughout the lms from these observations we conclude that the mode of collision that occurs between tibet and the sichuan basin is very different to that found between india and tibet in southern tibet we observe in essence the subduction of the indian plate which penetrates northwards for several hundred kilometers under central tibet the very thin mantle part of the lithosphere beneath eastern tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow this process leads to the exceptionally steep topography at the eastern tibetan margin as a result of gravitational buoyancy this view is supported by the very unusual depression of the 410 km discontinuity beneath eastern tibet which could be caused by the dynamics of the sub vertical downward asthenospheric flow

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

multi proxy record of the chicxulub impact at the cretaceous paleogene boundary from gorgonilla island colombia a 40 m stratigraphic section at gorgonilla island colombia provides a unique deepmarine low latitude southern hemisphere record of events related to the end cretaceous chicxulub impact and the

focal mechanisms and aftershock locations of the songpan earthquakes of august 1976 in sichuan china the precursory swarm three mainshocks m 7 2 6 7 7 2 and aftershocks of the songpan earthquakes have been reanalyzed using both local and teleseismic data the three mainshocks of this sequence occurred on the huya fault over a 7 day period relocations of the aftershocks using local arrival times show that three fault strands were activated during this sequence each mainshock occurred on a separate strand each one south of the strand activated in the previous mainshock and the aftershock zones of each mainshock appear to abut rather than overlap fault plane solutions determined by matching teleseismic p waveforms at world wide standard seismograph network stations with synthetic seismograms are consistent with the observed aftershock zones the first and third mainshocks m 0 1 3 10 19 and 8 4 10 18 n m respectively showed almost identical senses of motion a combination of reverse and left lateral strike slip motion on parallel strands striking n15 w that were separated by a large rightstepping en echelon offset the second mainshock m 0 4 0 10 18 n m occurred in this offset on a fault at a steep angle 125 to the other two strands and showed almost pure reverse motion differences in the orientations of the slip vectors of the three mainshocks show that the first mainshock increased the normal and shear stresses on the fault segment that moved in the second mainshock and that the second mainshock decreased the normal stress on the fault segment activated by the third mainshock these changes in normal stresses may have given rise to the longer time between the first and second events 5 days as compared with the time between the second and third events 30 hours a precursory swarm that preceded the songpan sequence by 3 years occurred in a volume that surrounded the northernmost part of the planar aftershock zone the time between the start of the swarm and the mainshocks and the magnitude of the largest event in the swarm are similar to those seen for precursory swarms in soviet central asia

cf wortmania from the early paleocene of montana and an evaluation of the fossil record of the initial diversification of the taeniodonta mammalia the garbani channel deposits part of the tullock formation exposed in northeastern montana have yielded a large sample of vertebrates that probably lived during the puercan 3 north american land mammal age nalma four fossils in this sample three isolated teeth and a medial phalanx document the presence of a stylinodontid taeniodont cf wortmania discovery of cf wortmania in the tullock formation extends the documented range of taeniodonts during puercan 3 approximately 500 miles 800 km northward from the san juan basin new mexico evaluation of the oldest records of taeniodonts from the lancian puercan and torrejonian nalmas highlights biases warranting future research recent phylogenetic analyses that resulted in numerous ghost lineages indicate that the available fossil record is far from complete they open the possibility that the origin and initial radiation of taeniodonts occurred in areas yet to be sampled and their first occurrences might reflect immigration of invasive species

extinction patterns δ18 o trends and magnetostratigraphy from a southern high latitude cretaceous paleogene section links with deccan volcanism although abundant evidence now exists for a massive bolide impact coincident with the cretaceous paleogene k pg mass extinction event 65 5 ma the relative importance of this impact as an extinction mechanism is still the subject of debate on seymour island antarctic peninsula the lopez de bertodano formation yields one of the most expanded k pg boundary sections known using a new chronology from magnetostratigraphy and isotopic data from carbonate secreting macrofauna we present a high resolution high latitude paleotemperature record spanning this time interval we find two prominent warming events synchronous with the three main phases of deccan traps flood volcanism and the onset of the second is contemporaneous with a local extinction that pre dates the bolide impact what has been termed the k pg extinction is potentially the sum of multiple independent events at least at high latitudes

quaternary and active faulting observed on the 1985 academia sinica royal society geotraverse of tibet active and recent faulting along the main north south road in tibet is dominated by normal faulting occurring on northerly trending planes and by strike slip faulting both of which reflect an east west extension of the plateau normal faulting is prevalent in the southern half of the plateau but we saw no evidence for any major graben in the northern half strike slip faulting on roughly easterly trending structures is m ore prevalent in the northern half but conjugate faulting with right lateral slip on northwesterly trending planes and left lateral slip on northeasterly trending planes is common in the southern half in two areas we also observed components of thrust faulting apparently in association with young strikeslip faulting our most important results are bounds on the rates of slip on the two main strands of the kunlun strike slip fault system which trends east w est through the kunlun range ground moraine containing boulders of pyroxenite is separated by 30 km from the nearest outcrop of such rock implying that amount of displacement in the last 1 5 to 3 m a therefore the average rate of slip during the quaternary period has been between 10 and 20 mm a with a likely value of 13 mm a abundant fresh tension cracks and mole tracks imply continued slip on the main strand the xidatan tuosuohu maqu fault and the likely occurrence of a major earthquake in the last few hundred years consistent offsets of gullies and dry stream channels of about 10 m may reflect slip of that amount during such an earthquake and possible multiple offsets at one site suggest that slip may occur by large displacements of 10 m during infrequent great earthquakes along the other strand the kunlun pass fault offsets of roughly 50 to 150 m of apparently post glacial valleys and of one glacier and its terminal moraine suggest a holocene rate of slip between 5 and 20 mm a and most likely about 10 mm a on this fault these rapid rates of displacement imply that tibet is being extruded rapidly eastward at a rate com parable to the rate at which india is penetrating into eurasia and therefore that at present a substantial fraction of this penetration is being absorbed by the eastward extrusion of tibet

field evidence for active normal faulting in tibet crustal thickening does not now occur in southern tibet field observations made during the chinese french expedition of 1980 support an earlier hypothesis based on a combined analysis of satellite images and fault plane solutions of earthquakes immediately north of the highest peaks of the himalayas the tectonic regime is dominated by east west extension we have mapped a large number of north south normal faults which sharply cut the glacial and post glacial morphology and followed several recent earthquake breaks along faults detected on satellite and aerial photographs microtectonic measurements in the quaternary suggest that the maximum principal stress is vertical

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

millennial slip rates of the tazang fault the eastern termination of kunlun fault implications for strain partitioning in eastern tibet abstract the way of slip transformation and strain partitioning at the eastern termination of the kunlun fault system remains unclear and the question of whether this fault system is an important part for lateral extrusion of tibetan crust is debatable the tazang fault is regarded as the easternmost continuation of the kunlun fault system and its late quaternary activity is unknown in this paper we use displaced geomorphic features combined with radiocarbon and optically stimulated luminescence osl dating to determine millennial slip rates along the tazang fault our data yield a 1 4 3 2 mm yr left slip rate on the western tazang fault similar to that on the maqu segment of the kunlun fault tectonic geomorphology proposes that displacement on the kunlun fault is probably transferred to the tazang fault via a pull apart basin the eastern tazang fault has a dominant reverse motion that decreases eastward from 1 5 mm yr to 0 2 0 3 mm yr at the easternmost part displaced terraces indicate that the eastern strand of the northern longriba fault is active in the holocene and has a 0 8 mm yr right lateral slip rate with a 0 3 mm yr reverse component millennial slip rates and geodetic results show that the decrease of left lateral motion along the tazang fault is mainly transformed into crustal shortening along the nearly n s trending longriba minjiang and huya faults probably resulting in uplift of the min shan our results also indicate that the deformation along the tazang fault is not transferred to beyond the border of the plateau and the kunlun fault is not an important tectonics for tibetan extrusion

late maastrichtian paleoclimatic and paleoceanographic changes inferred from sr ca ratio and stable isotopes abstract milankovitch scale cycles can be recognized in high resolution 13c 18o sr ca mineralogical and magnetic susceptibility data in hemipelagic sediments that span the last 700 kyr of the maastrichtian at elles tunisia oxygen isotope data reveal three cool periods between 65 50 and 65 55 ma 21 5 23 5 m 65 26 and 65 33 ma 8 11 m and 65 04 and 65 12 ma 1 5 4 m and three warm periods between 65 33 and 65 38 ma 12 16 m 65 12 and 65 26 ma 4 8 m and 65 00 and 65 04 ma 0 1 5 m the cool periods are characterized by small surface to deep temperature gradients that reflect intensive mixing of the water column the surface to deep sr ca gradient generally correlates with the oscillating t trend temperature difference between surface and bottom waters the carbon isotope composition of planktonic foraminifera indicates a continuous decrease in surface bioproductivity during late maastrichtian decreasing 13c values difference between the 13c values of surface and bottom dwelling foraminifera and the carbon isotope ratios of the planktonic species at the onset of gradual warming at 65 50 ma reflect a reduction in surface productivity as a result of decreased upwelling that accompanied global warming and possibly increased atmospheric pco2 related to deccan trap volcanism time series analysis applied to magnetic susceptibility 18o and sr ca data identifies the 20 kyr precession 40 kyr obliquity and 100 kyr eccentricity milankovich cycles

cretaceous extinctions multiple causes figure 1 deccan plateau basalts lava from deccan volcanism formed distinct layering credit gsfc nasa in the review the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary p schulte et al 5 march p 1214 2 the terminal cretaceous

importance of titanohematite in detrital remanent magnetizations of strata spanning the cretaceous paleogene boundary hell creek region montana intermediate composition titanohematite fe2 ytiyo3 with 0 5 y 0 7 is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature while largely overlooked in magnetostratigraphic studies intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of late mesozoic and early cenozoic laramide clastic deposits throughout the central united states intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite except its unique self reversing property due to these similarities and with detrital remanent magnetizations masking its self reversing nature intermediate titanohematite is often misidentified in sedimentary deposits past studies relied upon nonmagnetic techniques including x ray diffraction and electron microprobe analysis while these techniques can identify the presence of intermediate titanohematite they fail to test whether the mineral is the primary recorder to facilitate the identification of intermediate titanohematite in sedimentary deposits we characterize this mineral using low temperature magnetometry and high temperature susceptibility experiments and present a new identification technique based on titanohematite s self reversing property for sediments that span the cretaceous paleogene boundary hell creek region montana results from the self reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field but that intermediate self reversing titanohematite y 0 53 0 63 is an important ancillary carrier of remanence while earlier literature suggests that intermediate titanohematite is rare in nature reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record particularly within depositional basins adjacent to calc alkaline volcanics than previously thought

a new species of the basal plesiadapiform purgatorius mammalia primates from the early paleocene ravenscrag formation cypress hills southwest saskatchewan canada further taxonomic and dietary diversity in the earliest primates the fossil record of the earliest primates purgatoriid plesiadapiforms has become increasingly well documented during the past two decades but their dietary preferences remain poorly understood while the available evidence which consists mostly of isolated teeth and incomplete jaws with teeth suggests that purgatoriids were insectivorous to omnivorous we describe here a new species of purgatorius purgatorius pinecreeensis sp nov that extends the range of purgatoriid dental disparity toward greater omnivory than had been known before purgatorius pinecreeensis sp nov from the early paleocene puercan ravenscrag formation of southwestern saskatchewan differs from other species of purgatorius in having slightly lower crowned teeth with a lower trigonid relative to talonid blunter and more swollen major cusps more transverse lower molar paracristids and m3 with a more robustly developed posterior lobe taken together these specializations enhanced the capacity for crushing and grinding at

active tectonics of the ganzi yushu fault in the southeastern tibetan plateau the ongoing convergence between india and eurasia apparently is accommodated not merely by crustal shortening in tibet instead also by motions along strike slip faults which are usually boundaries between tectonic blocks especially in the tibetan plateau quantification of this strike slip faulting is fundamental for understanding the collision between india and eurasia here we use a variety of geomorphic observations to place constraints on the late quaternary kinematics and slip rates of the ganzi yushu fault one of the significant strike slip faults in eastern tibet the ganzi yushu fault is an active dominantly left lateral strike slip structure that can be traced continuously for up to 500 km along the northern boundary of the clockwise rotating southeastern block of the tibetan plateau we analyse geomorphic evidence for deformation and calculate the late quaternary slip rates at four sites along the eastern portion of the fault trace the latest quaternary apparent throw rates are variable along strike but are typically 1 mm a rates of strike slip displacement are likely to be an order of magnitude higher 8 11 mm a trenching at two locations suggests that the active fault behaviour is dominated by strike slip faulting and reveals several earthquake events with refined information of timing the 2010 mw 6 9 yushu earthquake which occurred on the northwestern segment of the ganzi yushu fault zone provides additional evidence for fault activity these observations agree with gps derived estimates and show that late quaternary slip rates on the ganzi yushu fault are comparable to those on other major active strike slip faults in the eastern tibetan plateau

environmental change across a terrestrial cretaceous paleogene boundary section in eastern montana usa constrained by carbonate clumped isotope paleothermometry the cretaceous paleogene k pg mass extinction has been attributed to the impact of a large bolide at the end of the cretaceous period although other potential causes have also been proposed most notably climate change caused by deccan traps india flood volcanism reconstructing paleoclimate particularly in terrestrial settings has been hindered by a lack of reliable proxies the recent development of carbonate clumped isotope paleothermometry has contributed to temperature reconstructions using geochemical proxies in terrestrial settings we employ this method along with new stratigraphic constraints in the hell creek cretaceous and overlying fort union paleogene formations montana usa to examine changes in temperature leading to and across the k pg boundary we demonstrate that well preserved ca 66 ma aragonitic bivalves serve as suitable paleoclimate archives although there are limitations in the stratigraphic availability of fossil bivalves for clumped isotope analysis we record an apparent 8 c decrease in summer temperatures over the last 300 k y of the cretaceous that corresponds broadly with patterns observed in other paleotemperature proxies this observed decrease plausibly could be explained by an absolute temperature decrease or by other environmental stresses on the organisms but in either case suggests changing living conditions over the interval previously documented declines in vertebrate and invertebrate biodiversity occur over the same stratigraphic interval at this study location these results are consistent with published models of the end cretaceous mass extinction in which destabilized ecosystems become more susceptible to an abrupt event like a bolide impact

fold thrust belt evolution expressed in an internal thrust sheet sevier orogen the role of cataclastic flow large hinterland thrust sheets are the dominant structures in retroarc fold thrust belt ftb wedges these internal sheets remain active throughout the history of an ftb and strongly influence the kinematics of the external portions of the ftb and the overall behavior of the entire tectonic wedge their emplacement and deformation account for a significant portion of the total mechanical energy budget in ftb evolution based on estimates using deformation features preserved within such sheets moreover the deformation within dominant internal sheets can be used as a means to evaluate the tectonic history of the wedge as a whole the principal deformation mechanisms in different parts of an ftb wedge are strongly controlled by variations in the geothermal gradient retroarc ftbs typically show a steeper geothermal gradient in the hinterland than in the foreland resulting in a foreland ward slope of the brittl ductile transition therefore a change from plastic to elastico frictional ef mechanisms is expected not only with decreasing depth but also across strike as a dominant internal thrust sheet is transported toward the foreland and undergoes exhumation by synorogenic erosion however evidence for cataclasis overprinting early plastic deformation features is often not preserved in ancient ftbs because of extensive erosion of the wedge top even where evidence for lat stage cataclastic behavior exists in either ancient or modern i e active orogens it is often not recognized or studied our work in the canyon range central utah segment of the sevier ftb shows that unraveling the ef mechanisms such as lat stage cataclastic flow is critical to understanding the total deformation history of an internal thrust sheet after initial emplacement under plastic deformation conditions the cr thrust sheet was continuously reactivated under ef conditions thereby helping to maintain critical taper of the ftb wedge during its development structures preserved in the cr thrust sheet therefore record a significant portion of the deformation history of the ftb as a whole the canyon range cr syncline part of the cr sheet underwent fold tightening within the ef regime and the cataclasized rocks are well preserved the geometry and progressive deformation patterns of the cr syncline reveal four distinct to partly overlapping deformation stages the history of the rocks in the cr thrust sheet has been tracked by incrementally retro deforming the ftb and by unraveling details of the deformation within the cr syncline at various scales for each stage we use the cr syncline as a type example to show that unraveling ef mechanisms is critical to 1 understanding the state of a ftb wedge during its evolution 2 calculating the energy involved in ftb emplacement and 3 developing accurate restorations placing constraints on the depth of the rocks for successive stages of deformation is essential for developing retrodeformable balanced cross sections and in turn geometric and kinematic models for wedge evolution

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago an overview is presented of the theory that an asteroid hit the earth 65 million years ago wiping out large numbers of land and marine species this theory predicts that the clay layer found at the boundary of the cretaceous and tertiary periods would be substantially different chemically from the clays in the limestone above and below the boundary layer it also predicts the iridium enhancement seen in this boundary layer would be found worldwide both predictions have been found to be true a third prediction was made but not fulfilled that the five major extinctions which occurred in the last 570 million years were caused by an asteroid impact the transport mechanism of the dust created by the impact and four mechanisms for the extinction of species are discussed criticisms of the theory are also discussed

direct high precision u pb geochronology of the end cretaceous extinction and calibration of paleocene astronomical timescales abstract the cretaceous paleogene k pg boundary is the best known and most widely recognized global time horizon in earth history and coincides with one of the two largest known mass extinctions we present a series of new high precision uranium lead u pb age determinations by the chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims method from volcanic ash deposits within a tightly constrained magnetobiostratigraphic framework across the k pg boundary in the denver basin colorado usa this new timeline provides a precise interpolated absolute age for the k pg boundary of 66 021 0 024 0 039 0 081 ma constrains the ages of magnetic polarity chrons c28 to c30 and offers a direct and independent test of early paleogene astronomical and 40ar 39ar based timescales temporal calibration of paleontological and palynological data from the same deposits shows that the interval between the extinction of the dinosaurs and the appearance of earliest cenozoic mammals in the denver basin lasted 185 ky and no more than 570 ky and the fern spike lasted 1 ky and no more than 71 ky after the k pg boundary layer was deposited indicating rapid rates of biotic extinction and initial recovery in the denver basin during this event

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

modeling climatic effects of carbon dioxide emissions from deccan traps volcanic eruptions around the cretaceous paleogene boundary abstract warming events observed in paleotemperature proxy records within 500 kyr of the cretaceous paleogene k pg boundary have often been attributed to atmospheric co 2 increases due to deccan traps flood volcanism currently there is uncertainty in the size nature and timing of the deccan eruptions all of which lead to uncertainty in the likely climatic effects modeling the impact of deccan traps eruption on climate is complicated by the discrepancy between the lifetimes of emitted gasses and the length of the total eruptive sequence though so 2 emissions can have important climatic effects the short atmospheric lifetimes of so 2 and resulting aerosols mean these effects are unlikely to be recognized in the proxy record here we focus on the co 2 emissions and attempt to match paleotemperature proxy records with plausible emissions scenarios we also test the relevance for climate of the number length and arrangement e g increasing or decreasing size of individual eruptions as well as the total duration and size of the overall eruptive sequence we find that the number and length of individual eruptions are largely unimportant to co 2 based based climate effects but that the pattern and duration of eruption have measureable effects unsurprisingly the total emitted co 2 from the deccan traps exerts a strong control on climatic effects and better constraints on the volume of emitted gas are necessary at the high end of the uncertainty range the deccan traps eruptions are capable of generating warming events recorded in the proxy record but rates of silicate weathering above modern rates are necessary to draw down co 2 in accordance with those records

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

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

paleoseismological events in the seismic gap between the 2008 wenchuan and the 2013 lushan earthquakes and implications for future seismic potential abstract the aftershocks of the 2008 wenchuan and 2013 lushan earthquakes delineated a prominent 60 km long seismic gap the uncertainty regarding the near future seismic potential of this seismic gap has become of increasing importance to both the scientific community and the public using paleoseismology this study investigated the occurrence of the last major event in the seismic gap and then considered the future seismic potential based on image interpretation trench excavation radiocarbon and optically stimulated luminescence dating and comparisons with historical earthquake rupture lengths the most recent paleoearthquake estimated magnitude m6 5 7 0 along the shuangshi dachuan fault sdf which is the southern segment of the longmen shan fault was constrained to 640 1330 ce very possibly 876 ce according to the most recent geological and geophysical findings we suggest that the seismic gap i e the sdf could be capable of generating m6 0 7 0 earthquakes but that the likelihood of such an occurrence in the near future is not very high

active faulting and block movement associated with large earthquakes in the min shan and longmen mountains northeastern tibetan plateau the min shan and central and southern parts of the longmen mountains form the middle segment of the north trending earthquake zone at the eastern edge of the tibetan plateau the min shan mountains are a cenozoic to quaternary uplift zone that has undergone south directed block movements to produce the 1933 diexi earthquake m 7 5 on the min jiang fault and the 1976 songpan earthquake swarm m 7 2 6 7 7 2 on the huya fault the min jiang fault on the western boundary of the uplift zone is dominated by reverse movement with a right lateral component the huya fault on the eastern margin of the min shan uplift zone is also dominated by reverse movement but is associated with a left lateral component

rb sr and u pb dating of bentonites a 6 in 15 cm bentonite in the z coal cretaceous tertiary boundary in eastern montana was sampled at four different places and biotite sanidine and zircon were separated from the clay u pb analyses of purified zircons yielded small systematic variations from concordant u pb dates plotting the data on a concordia diagram a short linear discordia line intersects the concordia at with an mswd of 1 16 the systematic variation of the four sets of zircon u pb data on the concordia plot may be an artifact of the sampling and purification procedure or could result from natural sample variation from minor contamination biotite fractions of varying specific gravity were obtained for each of the four z coal bentonite samples and together with the matching purified sanidine fraction were analysed for rb sr dating excluding those lighter biotite fractions found to have lost 30 or more of their original rb an isochron was obtained giving an age of 63 7 0 3 ma with an initial 87sr 86sr ratio of 0 706

high angle fault responsible for the surface ruptures along the northern segment of the wenchuan earthquake fault zone evidence from the latest seismic reflection profiles abstract the inverse right lateral yingxiu beichuan fault ruptured during the wenchuan earthquake for 270 km we investigated the northeastern segment of that fault by analysing 3 newly acquired and 3 older seismic lines that cross the fault we combine this analysis with that of the surface ruptures and of the regional geology in order to discuss the geometry the style and the amount of motion of the fault we conclude that the yingxiu beichuan fault is very steep 70 at the surface and has still a dip 45 at 6 km depth the fault offsets all previous structures and particularly the tangwangzhai nappes from which a vertical offset of 3 to 6 km is evaluated the right lateral component of motion along the yingxiu beichuan fault appears to be larger at the surface than at depth and increases only slightly towards the ne we suggest that the yingxiu beichuan fault is continuous at depth between its northern and southern segments

constraints on the volume and rate of deccan traps flood basalt eruptions using a combination of high resolution terrestrial mercury records and geochemical box models abstract deccan traps continental flood basalt eruptions spanned the cretaceous paleogene mass extinction erupting over a million cubic kilometers of basalt over a total duration of approximately a million years the environmental consequences of flood basalt eruptions depend on the timing and amount of volatile release eruption rates are thus needed to evaluate their potential to cause climate change radioisotopic dates are not currently sufficient to resolve sub ten thousand year eruptive tempos necessary for constraining the effects of short lifetime volatiles including sulfur dioxide recent studies have demonstrated that increases in mercury concentration in sedimentary records correlate with flood basalt eruptions under some circumstances however mercury concentrations have primarily been used to show the presence or absence of flood basalt eruptions we show that this proxy can be used to quantitatively estimate eruptive rates using a mercury geochemical cycle framework we illustrate this using new mercury chemostratigraphic records from terrestrial cretaceous paleogene boundary sections in eastern montana usa with multiple high resolution chronologic constraints we estimate that deccan eruptions lasted on the order of centuries and released 500 3000 megagrams mg of mercury per year corresponding to 50 250 km3 a of lava the box model framework highlights the importance of carefully accounting for differences in sedimentation rate and sampling resolution when comparing mercury records from different locations and depositional environments while there are uncertainties in the box model estimates due to possible variation in flood basalt mercury emissions and sedimentation rates they provide a useful framework to quantitatively evaluate the global mercury budget change indicated by changing concentration in sedimentary records eruptions of the estimated size would have released enough so2 if it reached the stratosphere to cause significant cooling for the duration of the eruption however given our constraints on the duration of individual eruptions these colder periods are likely too brief to be clearly visible in most existing paleoclimate records

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

high resolution chronostratigraphy of the terrestrial cretaceous paleogene transition and recovery interval in the hell creek region montana detailed understanding of ecosystem decline and recovery attending the cretaceous paleogene boundary kpb mass extinctions is hindered by limited constraints on the pace and tempo of environmental events near the boundary to mitigate this shortcoming high resolution 40ar 39ar geochronology was performed on tephras intercalated between fossiliferous terrestrial sediments of the upper hell creek and lower fort union formations in the western williston basin of northeastern montana usa tephra samples were collected from 10 stratigraphic sections spanning an area of 5000 km2 several distinctive tephras can be correlated between sections separated spatially by as much as 60 km the tephras are thin distal deposits generally preserved only in lignite beds which are interbedded with clastic deposits yielding vertebrate faunas of lancian late maastrichtian to torrejonian early danian north american land mammal ages sanidine from 15 tephra samples was analyzed in 1649 total fusion experiments 1597 on single crystals and 12 incremental heating analyses of multigrain aliquots ages were determined for 13 distinct tephras ranging from 66 289 0 051 to 64 866 0 023 ma including only analytical uncertainties this level of precision is sufficient to resolve the ages of all of the coal beds that have served as a basis for a regional stratigraphic framework the data confirm that the hell creek fort union formational contact is diachronous and further support the age of the kpb impact layer at 66 043 0 010 ma or 0 043 ma considering systematic uncertainties application of the new results to previous magnetostratigraphic data indicates an appreciably compressed time interval between the base of chron c29r and the top of chron c28r with a maximum duration estimate of 1 421 0 066 ma most notable is the implied brevity of chron c29r with a maximum estimate of 457 54 ka and possibly as brief as 345 38 ka compared to the 710 ka estimate from the geologic time scale 2012 gts2012 further application of new results to terrestrial biostratigraphy adds higher precision to the timing and tempo of biotic change before and after the kpb our results indicate that the timing of pre kpb ecological decline is constrained to the last 200 ka of the cretaceous adding further support to the press pulse extinction hypothesis additionally the duration of the depauperate basal paleogene puercan 1 disaster fauna is confined to a 70 ka interval faunal recovery in this region indicated by the appearance of primitive members of the placental mammal radiation and the restoration of taxonomic richness and evenness occurred within 900 ka after the kpb these results show that biotic recovery after the mass extinction in the terrestrial realm was more rapid than in the marine

the tibetan side of the india eurasia collision results are reported from the 1980 joint french chinese field expedition in tibet the area covered was from the high himalaya in the south to the region of nagqu 250 km north of yangbajain ophiolites in the zangbo valley represent remnants of the crust of an ocean basin which lay adjacent to the gangdise granodiorite belt in the late mesozoic the ophiolites were thrust to the south onto the cretaceous melange and triassic flysch but the age of this event is unclear in the tertiary sediments of the indian margin and the xigaze basin were folded with steeply dipping cleavage which indicates some north south shortening of the crust however the tertiary volcanic sequence on the lhasa block and further north shows comparatively little folding and thrusting in the quaternary deformation of tibet was characterized by east west extension

u pb zircon age constraints on the earliest eruptions of the deccan large igneous province malwa plateau india abstract climate instability driven by emission of volatiles during emplacement of large igneous provinces lips is frequently invoked as a potential cause of mass extinctions however documenting this process in the geologic record requires a holistic understanding of eruption rates the location of eruptive centers and potential sources of climate changing volatiles we present new chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims u pb zircon geochronology from malwa plateau basalts on the northern margin of the deccan lip india these basalts have been previously interpreted as either an extension of the province s main volcanic stratigraphy or as an independent eruptive center active up to millions of years prior to the main eruptive phase our data instead demonstrate that the lower malwa plateau basalts are temporally correlative with the first pulse of deccan volcanism and provide new constraints on its initiation and duration paleomagnetic data further indicate that upper malwa plateau basalts may be age equivalent to the second third and fourth pulses of deccan volcanism the relative thicknesses of age equivalent packages of basalt are consistent with eruption of the deccan lip from a southward migrating eruptive center the first eruptive pulse is coeval with a 200 kyr late maastrichtian warming event preserved globally in contemporaneous stratigraphic sections we propose that the first pulse of deccan magmatism was more voluminous in the north where it erupted through organic rich sedimentary rocks of the narmada tapti rift basin thermal metamorphism of these sediments could have been a source of sufficient co2 to drive the late maastrichtian warming event which if true would reconcile the apparent dampened warming signals associated with later deccan eruptive pulses

a pedotype approach to latest cretaceous and earliest tertiary paleosols in eastern montana a pedotype approach to the study of paleosols emphasizes individual profiles it is an alternative approach to the study of geosols which are laterally extensive suites of paleosols or pedofacies which are pedogenically distinctive sedimentary facies this is the first pedotype study of paleosols across the cretaceous tertiary boundary in eastern montana pedotypes allow assessment of sedimentation and fossilization the sequence of paleosols across the cretaceous tertiary boundary at bug creek is one of high temporal resolution because most available geological time can be accounted for by differing degree of development inferred for each pedotype paleosols at bug creek include pedotypes that preserve plant fossils well but were unfavorable for preservation of fossil vertebrates pedotypes also allow reassessment of ecosystem change despite indications of catastrophe at the cretaceous tertiary boundary the array of paleocene and cretaceous pedotypes are not strikingly different the upper cretaceous hell creek formation includes pedotypes interpreted as gleyed alfisols inceptisols and entisols probably formed under seasonally water logged forest and mean annual rainfall of the order of 900 1200 mm most paleosols of the lower paleocene tullock formation were histosols but some can be interpreted as gleyed inceptisols and entisols probably formed under bald cypress swamps in a humid climate with 1200 mm mean annual rainfall broadly comparable pedotypes were present before and after the cretaceous tertiary boundary although paleocene flood plain forest lived in paleosols chemically a little more oligotrophic than cretaceous paleosols this modest difference supports the idea that change to coaly facies in the earliest paleocene was a local shift in sedimentary environment such local changes do not begin to account for profound disruption in specific composition of plant and animal communities at the cretaceous tertiary boundary in eastern montana

first high precision u pb ca id tims age for the battle formation upper cretaceous red deer river valley alberta canada implications for ages correlations and dinosaur biostratigraphy of the scollard frenchman and hell creek formations the battle formation bfm is a widespread upper cretaceous marker horizon in western canada that records a time of low sediment input and marks the boundary between the edmontonian and lancian lan

centennial to decadal vegetation community changes linked to orbital and solar forcing during the dan c2 hyperthermal event formed close to the k pg boundary the boltysh meteorite crater ukraine preserves 400 m of lacustrine sedimentary rocks that include a record of the early danian dan c2 hyperthermal event abundant pollen spores and algae recovered from these sediments have yielded a cyclic record of plant ecology change paced by c 21 kyr orbital precession cycles new higher resolution sampling across the inception of the dan c2 hyperthermal event has identified oscillations in vegetation community ecology at sub orbital periods of c 2 kyr c 200 years and c 11 years these are consistent with possible hallstatt devreis suess and schwabe solar cycles respectively rapid regime shift from savanna to a mesic forest ecosystem was paced by c 21 kyr precession with the shift probably occurring in c 2 kyr i e possible hallstatt oscillations between mesic and winterwet dominated plant communities increased in intensity suggestive of ecological flickering supplementary material detrended correspondence and changepoint analysis palynological frequency data for dca groups and core photographs are available at https doi org 10 6084 m9 figshare c 3803893

terminal cretaceous extinctions in the hell creek area montana compatible with catastrophic extinction inaccurate stratigraphic correlations in the hell creek area montana have led to the assumption that transitional vertebrate faunas bug creek anthills exist in the latest cretaceous refuting a catastrophic turnover at the cretaceous tertiary boundary establishment of the transitional faunas in paleocene channels that cut down through the cretaceous tertiary boundary renders the terrestrial faunal record compatible with the marine record and with catastrophic extinction

erratum to surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake china worldwide occurrence and documentation of reverse type ruptures are sparse near hongkou the wenchuan rupture passes through the broad baisha river valley and provides excellent opportunities to trace the surface faulting in fine details for 13 km distance one of the longest continuous sections along the entire rupture in this paper we present the results of our mapping of the surface rupture in this reach based on the discontinuities in slip and geometry the rupture was divided into four sections for convenience from west to east the shenxi gou the miaoba the gaoyuan and the bajiao miao sections respectively the vertical offset is large in the shenxi gou and the bajiao miao sections locally reaching 5 6 m in maxima and generally low in the miaoba section 1 2 m or less in most places the slip gradient for vertical offset is generally 10 3 locally up to 10 1 similar to that in well documented strike slip ruptures near gaoyuan village the surface rupture con sists of two subparallel branches with the northern one exhibiting right lateral slip with minor southeast side up thrusting while the southern one is almost pure south east side up thrusting this pattern mimics the incomplete slip partitioning of oblique thrusting on parallel faults but at a local scale in addition the sense of vertical throw on these two strands is opposite to the general northwest side up thrusting of the wenchuan rupture we propose that it is likely due to the inheritance at shallow depth from the southeast dipping geological faults and that old fault zone structures can have a strong effect on the dynamic rupture by guiding the rupture propagation onto paths of preexisting though locally unfavorable dipping fault planes we also discuss the cross cutting slickenside striations observed near bajiao miao which indicated temporal rake rotation during dynamic rupture and their geological and seismological implications

conceptual models for short eccentricity scale climate control on peat formation in a lower palaeocene fluvial system north eastern montana usa fluvial systems in which peat formation occurs are typified by autogenic processes such as river meandering crevasse splaying and channel avulsion nevertheless autogenic processes cannot satisfactorily explain the repetitive nature and lateral continuity of many coal seams compacted peats the fluvial lower palaeocene tullock member of the fort union formation western interior williston basin montana usa contains lignite rank coal seams that are traceable over distances of several kilometres this sequence is used to test the hypothesis that peat formation in the fluvial system was controlled by orbitally forced climate change interacting with autogenic processes major successions are documented with an average thickness of 6 8 m consisting of ca 6 m thick intervals of channel and overbank deposits overlain by ca 1 m thick coal seam units these major coal seams locally split and merge time stratigraphic correlation using a cretaceous palaeogene boundary event horizon several distinctive volcanic ash fall layers and the c29r c29n magnetic polarity reversal shows consistent lateral recurrence of seven successive major successions along a 10 km wide fence panel perpendicular to east south east palaeo flow the stratigraphic pattern complemented by stratigraphic age control and cyclostratigraphic tests suggests that the major peat forming phases resulting in major coal seams were driven by 100 kyr eccentricity related climate cycles two distinct conceptual models were developed both based on the hypothesis that the major peat forming phases ended when enhanced seasonal contrast at times of minimum precession during increasing eccentricity intensified mire degradation and flooding in model 1 orbitally forced climate change controls the timing of peat compaction leading to enhancement of autogenic channel avulsions in model 2 orbitally forced climate change controls upstream sediment supply and clastic influx determining the persistence of peat forming conditions at the scale of the major successions model 2 is supported because interfingering channel sandstones do not interrupt lateral continuity of major coal seams

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

slip rate gradients along the eastern kunlun fault 1 whether strike slip fault systems in eurasia accomplish eastward extrusion of tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip here we present new slip rate determinations using millennial scale geomorphic markers from sites along the easternmost segment of the kunlun fault in north central tibet this fault system represents one of the major strike slip faults within the indo asian collision zone has been argued to exhibit uniform slip rates along much of its length and plays a central role in models for eastward extrusion of tibetan lithosphere displaced fluvial terrace risers along tributaries of the yellow river coupled with 14c ages of terrace material provide constraints on slip rates over late pleistocene to holocene time results indicate that slip rates decrease systematically along the eastern 150 km of the fault from 10 to 2 mm yr these data challenge the view that slip along the kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips moreover slip along the fault appears to terminate within the thickened crust of the plateau and therefore any extrusion of tibetan lithosphere accomplished by slip along the kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip

chemical and pb isotope composition of phenocrysts from bentonites constrains the chronostratigraphy around the cretaceous paleogene boundary in the hell creek region montana an excellent record of environmental and paleobiological change around the cretaceous paleogene boundary is preserved in the hell creek and fort union formations in the western williston basin of northeastern montana these records are present in fluvial deposits whose lateral discontinuity hampers long distance correlation geochronology has been focused on bentonite beds that are often present in lignites to better identify unique bentonites for correlation across the region the chemical and pb isotopic composition of feldspar and titanite has been measured on 46 samples many of these samples have been dated by 40ar 39ar the combination of chemical and isotopic compositions of phenocrysts has enabled the identification of several unique bentonite beds in particular three horizons located at and above the cretaceous paleogene boundary can now be traced based on their unique compositions across the region clarifying previously ambiguous stratigraphic relationships other bentonites show unusual features such as pb isotope variations consistent with magma mixing or assimilation that will make them easy to recognize in future studies this technique is limited in some cases by more than one bentonite having compositions that cannot be distinguished or bentonites with abundant xenocrysts the pb isotopes are consistent with a derivation from the bitterroot batholith whose age range overlaps that of the tephra these data provide an improved stratigraphic framework for the hell creek region and provide a basis for more focused tephrostratigraphic work and more generally demonstrate that the combination of mineral chemistry and pb isotope compositions is an effective technique for tephra correlation

u pb constraints on pulsed eruption of the deccan traps across the end cretaceous mass extinction temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality with eruptive volatile release driving environmental degradation and extinction we tested this model for the deccan traps flood basalt province which along with the chicxulub bolide impact is implicated in the cretaceous paleogene k pg extinction approximately 66 million years ago we estimated deccan eruption rates with uranium lead u pb zircon geochronology and resolved four high volume eruptive periods according to this model maximum eruption rates occurred before and after the k pg extinction with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction these findings support extinction models that incorporate both catastrophic events as drivers of environmental deterioration associated with the k pg extinction and its aftermath

palaeomagnetic evidence for southward displacement of the chuan dian fragment of the yangtze block summary cretaceous red sandstones of the feitianshan formation and the xiaoba formation were sampled at 33 sites from the dadeli and mishi synclines of xichang 27 9 n 102 3 e the study area is a part of the chuan dian fragment bounded by the xianshuihe xiaojiang and the red river fault systems which in turn constitute the southwestern part of the yangtze block almost all the samples give a characteristic palaeomagnetic direction with unblocking temperatures up to 680 c the primary nature of magnetization is ascertained by a positive fold test with a 99 per cent confidence level for the dadeli syncline the tilt corrected overall mean direction of the 33 sites is d 3 7 i 41 5 95 3 4 with a corresponding palaeopole at 85 2 n 241 7 e a95 3 5 this pole occupies the near sided position with respect to the estimate of the cretaceous pole of the sichuan basin indicating that the xichang area experienced a significant southward displacement combined with earlier reported palaeomagnetic data from the chuan dian fragment a significant southward displacement of 6 7 3 5 in latitude is estimated for the whole fragment with respect to the sichuan basin since the late cretaceous extrusion dynamics in the asian continent due to its collision with india brought about the southward displacement of the chuan dian fragment declination data indicate that the southern part of the chuan dian fragment was subjected to clockwise sense rotation of up to 45 this significantly large tectonic rotation probably occurred during extrusion of this

early paleocene magnetostratigraphy and revised biostratigraphy of the ojo alamo sandstone and lower nacimiento formation san juan basin new mexico usa

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

interstation pg and sg differential traveltime tomography in the northeastern margin of the tibetan plateau implications for spatial extent of crustal flow and segmentation of the longmenshan fault zone abstract interstation pg and sg differential traveltime tomography is performed in the northeastern margin of the tibetan plateau providing reliable mid lower crustal velocity images while minimizing errors from earthquake mislocation and origin time prominent low p and s velocities p and s in the northeastern tibetan plateau are bound to the east by the minjiang fault and the southwest segment of the longmenshan fault zone lmsfz in contrast relatively high p and s velocities 6 1 km s for v p and 3 7 km s for v s are found beneath the sichuan basin and in the triangular region bound to the west by the minjiang fault and to the east of the northeast segment of the lmsfz significant low velocity anomalies suggest a weak mid lower crust that flows beneath the eastern tibetan plateau while the high velocities beneath the sichuan basin indicate a rigid cold and stable crust the strong lithospheric mantle beneath the sichuan basin inferred from previous studies may act as a barrier to the eastward escape of crustal flow from the eastern tibetan plateau the segmentation of the lmsfz is reconfirmed by the distinct mid lower crustal velocities in the southwest and northeast segments high velocity and low conductivity anomalies in the mid lower crust beneath the eastern minshan uplift and the western qinling orogen suggest that no crustal flow reaches this area

geometry and late pleistocene slip rates of the liangdang jiangluo fault in the western qinling mountains nw china abstract two groups of faults striking in different direction nww trending and nee trending within the western qinling mountains play important roles in the tectonic deformation and the transference slip along the east end of the east kunlun fault we investigated the fault geometry and kinematics properties in the area based on the displacements of landforms and optically stimulated luminescence osl dating techniques the late pleistocene slip rates along the liangdang jiangluo fault were determined to be 0 43 0 13 mm a thrust and 0 71 0 18 mm a left lateral strike slip we also investigated some other faults and obtained characteristically low slip rates these slip rates are consistent with decadal gps observations despite previous studies that point to a systematic decrease in the left lateral slip rates from 10 mm a to

astronomical calibration of upper campanian maastrichtian carbon isotope events and calcareous plankton biostratigraphy in the indian ocean odp hole 762c implication for the age of the campanian maastrichtian boundary abstract an integrated framework of magnetostratigraphy calcareous microfossil bio events cyclostratigraphy and 13c stratigraphy is established for the upper campanian maastrichtian of odp hole 762c exmouth plateau northwestern australian margin bulk carbonate 13c events and nannofossil bio events have been recorded and plotted against magnetostratigraphy and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the maastrichtian thirteen carbon isotope events and 40 nannofossil bio events are recognized and calibrated with cyclostratigraphy as well as 14 previously published foraminifer events thus constituting a solid basis for large scale correlations results show that this site is characterized by a nearly continuous sedimentation from the upper campanian to the k pg boundary except for a 500 kyr gap in magnetochron c31n correlation of the age calibrated 13c profile of odp hole 762c to the 13c profile of the tercis les bains section global stratotype section and point of the campanian maastrichtian boundary cmb allowed a precise recognition and dating of this stage boundary at 72 15 0 05 ma this accounts for a total duration of 6 15 0 05 ma for the maastrichtian stage correlation of the boundary level with northwest germany shows that the cmb as defined at the gssp is 800 kyr younger than the cmb as defined by belemnite zonation in the boreal realm odp hole 762c is the first section to bear at the same time an excellent recovery of sediments throughout the upper campanian maastrichtian a precise and well defined magnetostratigraphy a high resolution record of carbon isotope events and calcareous plankton biostratigraphy and a cyclostratigraphic study tied to the la2010a astronomical solution this section is thus proposed as an excellent reference for the upper campanian maastrichtian in the indian ocean

subsurface structure and spatial segmentation of the longmen shan fault zone at the eastern margin of tibetan plateau evidence from focal mechanism solutions and stress field inversion abstract as the eastern margin of the tibetan plateau the longmen shan fault zone lmsfz is characterized by a complex structural style and strong seismicity such as the 2008 wenchuan ms8 0 and 2013 lushan ms7 0 earthquakes in order to better understand the subsurface geometry of the lmsfz we inverted 391 focal mechanism solutions fms of earthquakes m 3 5 that occurred between 2009 and 2016 in the longmen shan region using seismic waveforms subsequently we calculated the stress field based on the fmss the results show that the lmsfz is dominated by a thrust faulting stress regime with subhorizontal nw se trending maximum principal stress 1 and subvertical minimum principal stress 3 indicating a lateral compression due to the southeastward movement of the bayan har block changes in fault dips at 10 km depth are inferred as the result of a shallow level detachment layer which may also promote shortening of the upper crust and uplift of the longmen shan based on differences in subsurface fault geometry stress field and geomorphological evidence we divide the lmsfz into two segments by beichuan county the southwestern segment has a listric fault geometry while the northeastern segment is dominated by subvertical transpressional strike slip faults according to the fmss results we suggest that the lixian fault is a tear fault accommodating different thrusting rates in the eastern margin of the bayan har block the normal faulting earthquakes in the lixian area are caused by local extension resulting from the sinistral shear movement of lixian fault in a strike slip faulting stress regime it is suggested that under the continuous southeastward movement of the bayan har block and the obstruction of the rigid sichuan basin stress is accumulating along the southwestern segment of the lmsfz to which accordingly a high seismic hazard is ascribed and which should be carefully monitored

high precision u pb ca id tims dating and chronostratigraphy of the dinosaur rich horseshoe canyon formation upper cretaceous campanian maastrichtian red deer river valley alberta canada the non marine horseshoe canyon formation hcfm southern alberta yields taxonomically diverse late campanian to middle maastrichtian dinosaur assemblages that play a central role in documenting

stress evolution before and after the 2008 wenchuan china earthquake abstract we examine the distribution of coulomb stress before and following the m 7 9 wenchuan earthquake and model the time dependent components of the stress field into the future our modelling shows that the combined coseismic plus postseismic viscoelastic stress change due to the preceding large events m 6 7 at the hypocentral area of the wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95 yr depending on the rake of the rupture on the other hand coseismic stress modelling of the wenchuan earthquake shows strong interaction particularly with the faults close to its sw and ne ends such interactions have previously been shown to trigger further large earthquakes in addition redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the xianshuihe kunlun and tazang faults postseismic viscoelastic stress load on these distant faults over the next 22 yr since the earthquake could be up to 2 5 times larger than that of the coseismic stress increase alone this would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes resulting in clustering of large earthquakes in the region this behaviour however strongly depends on the stage that these faults are in their seismic cycle which is not known currently given the high density of population in the area with several cities chengdu guangyuan and hanzhong of more than 1 million inhabitants our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

a radiometric age for the cretaceous tertiary boundary based upon k ar rb sr and u pb ages of bentonites from alberta saskatchewan and montana bentonites associated with coal seams at the north american cretaceous tertiary k t boundary in the red deer valley of alberta in the frenchman valley of saskatchewan and near hell creek montana were dated by the k ar rb sr and u pb methods based upon palynological stratigraphic correlation and the presence of a sharp iridium anomaly the three sampled bentonite horizons all occur less than 1 m above the established k t boundary there is evidence of possible systematic errors giving dating results outside nominal statistical error values despite possible constant errors the weighted mean of nine average dates is calculated as 64 3 1 2 ma 2 standard deviation an unweighted averaging produces a grand mean age of 64 4 1 2 ma

a seismically induced onshore surge deposit at the kpg boundary north dakota the most immediate effects of the terminal cretaceous chicxulub impact essential to understanding the global scale environmental and biotic collapses that mark the cretaceous paleogene extinction are poorly resolved despite extensive previous work here we help to resolve this by describing a rapidly emplaced high energy onshore surge deposit from the terrestrial hell creek formation in montana associated ejecta and a cap of iridium rich impactite reveal that its emplacement coincided with the chicxulub event acipenseriform fish densely packed in the deposit contain ejecta spherules in their gills and were buried by an inland directed surge that inundated a deeply incised river channel before accretion of the fine grained impactite although this deposit displays all of the physical characteristics of a tsunami runup the timing w 10 to 11 earthquake generated by the chicxulub impact identifying a seismically coupled seiche inundation as the likely cause our findings present high resolution chronology of the immediate aftereffects of the chicxulub impact event in the western interior and report an impact triggered onshore mix of marine and terrestrial sedimentation potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact