chemical composition and stratigraphic correlation of mesozoic basalt units of the newark basin new jersey and the hartford basin connecticut summary new major and trace element analyses of the messozoic basalts of the hartford basin of connecticut the talcott holyoke and hampden basalts indicate that the basalts are chemically very similar to the mesozoic basalts of the newark basin of new jersey the first second and third watchung basalts our geochemical data impose some constraints on any time stratigraphic correlation of the basalts in the two basins we suggest that the holyoke and second watchung basalts are fractionation products of a talcott first watchung parent magma we also suggest that the hampden and third watchung basalts are synchronous fractionation products of a magma unlike any of the eastern north american basalt types described in the literature but they may instead be the fractionation products of a magma resembling a magma of the same type as that of the mid atlantic ridge from a petrologic standpoint the most straight forward time stratigraphic interpretation is a one to one correlation of the three flows of the newark basin with the three flows of the hartford basin our geochemical and petrologic evidence is particularly supportive of time stratigraphic correlations between the first watchung and the talcott basalts and between the third watchung and the hampden basalts our data however are not inconsistent with the possibility that the second watchung may be slightly older than the holyoke basalt

differentiation of mesozoic basalts of the hartford basin connecticut the talcott oldest of the three basalts in the mesozoic hartford basin of connecticut contains abundant euhedral olivine and plagioclase phenocrysts and less common rounded augite plagioclase aggregates and orthopyroxene phenocrysts rimmed by augite and olivine the orthopyroxene which has a remarkably constant composition en 84 and is cr rich is believed to be a refractory residue from an upper mantle source region the holyoke basalt the middle unit is essentially aphyric with only minor plagioclase and olivine phenocrysts the hampden youngest of the three basalts contains abundant plagioclase and minor olivine and augite phenocrysts materials balance calculations using phenocryst compositions from the talcott basalt indicate that the holyoke can be derived from a talcott magma by addition of 7 8 orthopyroxene and removal of 7 9 olivine 15 clinopyroxene and 13 3 plagioclase the hampden basalt cannot be derived from a holyoke magma by any reasonable fractionation scheme but it can be derived from a talcott magma by removal of 4 4 olivine 12 0 clinopyroxene and 14 3 plagioclase one atmosphere melting experiments under controlled oxygen fugacities indicate successively lower liquidus temperatures for talcott holyoke and hampden basalts both the talcott and the holyoke have olivine and plagioclase on the liquidus simultaneously with augite and pigeonite appearing 15 c below the liquidus the hampden has plagioclase alone on the liquidus olivine and augite appear only 5 c below the liquidus orthopyroxene is not present in the low pressure experiments but is thought to have been stable on the liquidus at depths corresponding to pressures exceeding 8 kbar assimilation of orthopyroxene and crystallization of other phases necessary to produce the holyoke basalt from a talcott magma must have taken place at depth however because the low pressure phases obtained in the experiments are those required to produce the hampden from the talcott magma this fractionation likely occurred in a near surface magma chamber

anelastic response of the earth to a dip slip earthquake the deformation of the earth s surface immediately following an earthquake is well modeled by a dislocation in an elastic half space some time after the event however the elastic stresses begin to relax due to flow in the more fluid regions of the upper mantle the asthenosphere this relaxation causes further slow displacements observable at the earth s surface this paper examines the pattern and timing of these postseismic motions for a vertical dip slip fault and a 30 dip thrust fault a variety of rheological models are studied these models encompass variations in asthenosphere thickness mesosphere viscosity fault depth and most important power law flow both newtonian n 1 and non newtonian n 3 maxwell rheologies are considered for the asthenosphere and mesosphere the results for a vertical dip slip fault show that a peripheral upwarp develops within a distance of a few lithosphere thicknesses from the rupture zone on the downthrown side of the fault a comparable downwarp develops on the upthrown side these peripheral warps grow to a maximum height of about 5 of the total fault slip some time after the earthquake event and then collapse at much greater times the vertical motions for a 30 dip thrust fault show that after the earthquake a general uplift occurs in the region near the rupture zone horizontal displacements propagate asymmetrically away from the rupture zone the largest displacements occurring in the overthrust plate the principal result of the comparison of n 1 and n 3 rheological laws is that the basic pattern of uplifts and horizontal motions is very similar the major difference is the time dependence of the development of the pattern in spite of the complex geometrical structure of the subduction zone the displacements ui 1 t for newtonian rheology are nearly the same as ui 3 t for the non newtonian rheology if t t3 thus although the qualitative pattern of the displacements is not diagnostic of power law flow the great difference in time dependence allows a clear discrimination of the two flow laws

teleseismic evidence for a break off subducting slab under eastern turkey abstract we present seismic images of the upper mantle beneath eastern turkey determined by teleseismic tomography the data are measured precisely from seismograms recoded by the eastern turkey seismic experiment network consisting of 29 portable stations and 2 permanent stations our results show that obvious high velocity high v anomalies of up to 2 are interrupted beneath eastern turkey and subcrustal earthquakes occurred along these high v anomalies pronounced low velocity low v anomalies are visible from the arabian foreland basin in the southwest to the caucasus region in the northeast which extend down to about 400 km depth these low v anomalies are consistent with the existence of late cenozoic volcanism in the region these results provide new constraints on the geodynamic processes in the east anatolian plateau suggesting that the break off of the arabian slab may play an important role in the formation of the anatolian plateau and the volcanism in the region these processes might be related to the collision of the arabian plate with the eurasian plate

synthesis and revision of groups within the newark supergroup eastern north america the newark supergroup currently includes nine stratigraphic groups each of which applies to part or all of the rock column of only one or a few basins because the group nomenclature within the newark supergroup is neither inclusive nor parallel in its concepts nearly half of the strata within the newark supergroup lacks any group placement a new system is proposed herein that 1 establishes unambiguous group boundaries 2 places all newark supergroup strata into groups 3 reduces the number of group names from nine to three 4 creates parallelism between groups and three major successive tectonic events that created the rift basins containing the newark supergroup and 5 coincidentally provides isochronous or nearly isochronous group boundaries these proposed groups are 1 the chatham group middle triassic to basal lower jurassic sedimentary rocks 2 the meriden group lower jurassic extrusive volcanic and sedimentary rocks and 3 the agawam group new name lower jurassic sedimentary rocks above all early mesozoic igneous intrusive and extrusive rocks this new rock classification system makes use of the fact that a discrete interval of synchronous or nearly synchronous volcanism and plutonism occurred throughout the early mesozoic rift system of eastern north america the presence or absence of volcanic rocks provides a powerful stratigraphic tool for establishing regional groups and group boundaries the presence of sedimentary rocks injected by diabase dikes and sills in the absence of extrusive volcanic rocks places newark supergroup rocks in the chatham group the presence of extrusive volcanic rocks interbedded with sedimentary rocks injected by diabase dikes and sills places newark supergroup rocks in the meriden group the presence of sedimentary rocks lacking both extrusive volcanic rocks and diabase dikes and sills places newark supergroup rocks in the agawam group application of this new regional group stratigraphy to the early mesozoic rift basins requires revision of the stratigraphy of several basins to make formation boundaries match group boundaries

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

mars pathfinder landing site evidence for a change in wind regime from lander and orbiter data surface features related to the wind are observed in the vicinity of the mars pathfinder mpf landing site data from the lander and in data from orbit by the viking orbiter and mars global surveyor missions features seen from the surface include wind tails associated with small rocks barchanoid duneforms ripplelike patterns and ventifact flutes cut into some rocks features seen from orbit include wind tails associated with impact craters ridges inferred to be duneforms and modified crater rims interpreted to have been eroded and mantled by windblown material the orientations of these features show two prevailing directions one is inferred to represent winds from the northeast which is consistent with strongest winds predicted by a general circulation model to occur during the martian northern winter under current conditions a second wind blowing from the ese was responsible for modifying the crater rims and cutting some of the ventifacts the two wind regimes could reflect a change in climate related to mars obliquity or some other unknown factor regardless of the cause the mpf area has been subjected to a complex pattern of winds and supply of small particles and the original surface formed by sedimentary processes from tiu and ares vallis flooding events has been modified by repeated burial and exhumation

a new rhaetian δ13corg record carbon cycle disturbances volcanism end triassic mass extinction ete abstract the links between large scale volcanism carbon cycle perturbations and the biotic crises at the end triassic extinction event ete are not well understood the ete seems to be marked by three carbon isotope excursions cies likely triggered by different eruptive phases of the central atlantic magmatic province camp these three cies appear to occur during the late rhaetian close to the triassic jurassic boundary tjb but the relative timing connecting the volcanism carbon perturbations and extinctions is still subject to debate resulting from i the difficulties in long distance biostratigraphic correlations of rhaetian successions due to the step like extinction pattern characterizing the ete and to the lack of globally correlatable key fossil group s across the system boundary ii the limit of coverage of available 13c profiles to the system boundary interval rather than the entire rhaetian iii the inherent difficulties in correlating cies without clear biostratigraphic markers here we present a 13corg curve from the lombardy basin which covers for the first time the entire rhaetian using this chemostratigraphy we propose two possible correlations option 1 and option 2 with other late rhaetian to early hettangian successions worldwide these two possible correlations rely on a combination of paleontological ammonoids pollens conodonts lithostratigraphic and geochemical constraints option 2 in particular has important implications for the causality and geochronology of the ete events by suggesting that the sharp negative peak usually considered to be the initial cie in the lombardy might represent a carbon perturbation within the negative trend of the main cie this implies that a reconsideration of the succession of biotic events occurring during this time interval is required

observations of an aeolian landscape from surface to orbit in gale crater abstract landscapes derived solely from aeolian processes are rare on earth because of the dominance of subaqueous processes in contrast aeolian derived landscapes should typify mars because of the absence of liquid water the long exposure times of surfaces and the presence of wind as the default geomorphic agent using the full range of available orbital and mars science laboratory rover curiosity images wind formed features in gale crater were cataloged and analyzed in order to characterize the aeolian landscape and to derive the evolution of the crater wind regime over time inferred wind directions show a dominance of regional northerly winds over geologic time scales but a dominance of topography driven katabatic winds in modern times landscapes in gale crater show a preponderance of aeolian features at all spatial scales interpreted processes forming these features include first cycle aeolian abrasion of bedrock pervasive deflation organization of available sand into bedforms abundant cratering and gravity driven wasting all of which occur over a background of slow physical weathering the observed landscapes are proposed to represent a spectrum of progressive surface denudation from fractured bedrock to retreating bedrock capped mesas to remnant hills capped by bedrock rubble to desert pavement plains this model of landscape evolution provides the mechanism by which northerly winds acting over 3 ga excavated tens of thousands of cubic kilometers of material from the once sediment filled crater thus carving the intra crater moat and exhuming mount sharp aeolis mons the current crater surface is relatively sand starved indicating that potential sediment deflation from the crater is greater than sediment production and that most exhumation of mount sharp occurred in the ancient geologic past

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

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

the carnian pluvial event in western europe new data from iberia and correlation with the western neotethys and eastern north america nw africa regions abstract at the beginning of the late triassic a period of increased precipitation occurred over large tracts of central pangea the carnian pluvial event it was a short lived event 1 ma coeval with a marked sea level fall and active rifting new and classical sections of carnian age in the iberian peninsula have been studied and a new correlation scheme is proposed for the iberian domain integrating field data and subsurface electric log data this is the first time that the portuguese and spanish late triassic carnian sediments are correlated the carnian pluvial event is identified in the iberian peninsula as a continental clastic wedge manuel fm and coeval sediments in between marine evaporite formations during a marked sea level drop event its age is considered to be julian early carnian by palynological and paleogeographic considerations a new correlation of the late triassic sediments of the iberian peninsula with coeval sediments of western europe nw africa and eastern north america is proposed and a new paleogeographical map of central eastern pangea for this period is presented in order to demonstrate that the geographical extent of the siliciclastic sediments related to the carnian pluvial event was much larger than accepted before

thermal inertia of crater related wind streaks on mars data from the thermal emission spectrometer tes on board the mars global surveyor spacecraft are used to analyze the structure of and materials comprising crater related wind streaks comparisons of high resolution tes albedo and tes based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure the majority of the analyzed type i bright depositional streaks are distinct from the surrounding terrain in albedo but not in thermal inertia we conclude that these streaks consist of thin deposits of bright material greater than 1 pm thick but less than 1 3 mm thick the majority of the analyzed type i dark erosional streaks identified from viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks have been covered by a thin deposit of bright material greater than 1 m thick but less than 1 3 mm thick all of the analyzed type ii dark depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks consist of deposits greater than a few centimeters thick in this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material the values correspond to a broad range of sand sized particles easily mobilized by wind supporting the deflation deposition theory of type ii streak formation

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

a geographical information system gis study of triassic vertebrate biochronology geographical information systems gis have been applied extensively to analyse spatial data relating to varied environmental issues but have not so far been used to address biostratigraphical or macroevolutionary questions over extended spatial and temporal scales here we use gis techniques to test the stability validity and utility of proposed middle and late triassic land vertebrate faunachrons lvfs a global biostratigraphical framework based upon terrestrial freshwater tetrapod occurrences a database of tetrapod and megafloral localities was constructed for north america and western europe that also incorporated information on relevant palaeoenvironmental variables this database was subjected to various spatial analysis techniques our gis analysis found support at a global level for eocyclotosaurus as an anisian index taxon and probably aetosaurus as a norian indicator other tetrapod taxa are useful biostratigraphical biochronological markers on a regional basis such as longosuchus and doswellia for late carnian time other potential index fossils are hampered however by taxonomic instability mastodonsaurus metoposaurus typothorax paleorhinus pseudopalatus redondasaurus redondasuchus and or are not clearly restricted in temporal distribution paleorhinus angistorhinus stagonolepis metoposaurus and rutiodon this leads to instability in lvf diagnosis we found only in the western northern hemisphere is there some evidence for an anisian ladinian biochronological unit amalgamating the perovkan and berdyankian lvfs and a possible late carnian unit integrating the otischalkian and adamanian megaplants are generally not useful for biostratigraphical correlation in the middle and upper triassic of the study area but there is some evidence for a carnian age floral assemblage that corresponds to the combined otischalkian and adamanian lvfs environmental biases do not appear to strongly affect the spatial distribution of either the tetrapods or megaplants that have been proposed as index taxa in biostratigraphical schemes though several examples of apparent environmental bias were detected by the analysis consequently we argue that further revision and refinement of middle and late triassic lvfs is needed before they can be used to support global or multi regional biostratigraphical correlations caution should therefore be exercised when using the current scheme as a platform for macroevolutionary or palaeoecological hypotheses finally this study demonstrates the potential of gis as a powerful tool for tackling palaeontological questions over extended timescales

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

plate interface properties in the northeast hikurangi subduction zone new zealand from converted seismic waves arrival time inversion of local earthquakes in the northeast hikurangi subduction zone has indicated high vp vs at the plate interface but the thickness of the anomalous zone is poorly constrained by the p and s travel times we investigate this plate interface zone further by modeling s to p converted phases using synthetic seismograms for upgoing rays of earthquakes in the subducting plate mantle the modeling indicates a low velocity layer at the plate interface which is generally 1 2 km thick and has vp of 5 0 5 35 km s and vp vs of 2 this is consistent with a subducting sediment channel with near lithostatic fluid the low rigidity indicates a weak zone which will have a strong influence on the distribution of deformation the modeling approach shows promise in defining rheological parameters at the plate interface and mapping their variation across the seismogenic zone of the subduction thrust

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

continental subduction and exhumation of high pressure rocks insights from thermo mechanical laboratory modelling abstract thermo mechanical physical modelling of continental subduction is performed to investigate the exhumation of deeply subducted continental crust the model consists of two lithospheric plates made of new temperature sensitive analogue materials the lithosphere is underlain by liquid asthenosphere the continental lithosphere contains three layers the weak sedimentary layer the crust made of a stronger material and of a still stronger lithospheric mantle the whole model is subjected to a constant vertical thermal gradient causing the strength reduction with depth in each lithospheric layer subduction is driven by both push force and pull force during subduction the subducting lithosphere is heating and the strength of its layers reduces the weakening continental crust reaches maximal depth of about 120 km and cannot subduct deeper because its frontal part starts to flow up the subducted crust undergoes complex deformation including indicated upward ductile flow of the most deeply subducted portions and localised failure of the subducted upper crust at about 50 km depth this failure results in the formation of the first crustal slice which rises up between the plates under the buoyancy force this process is accompanied by the delamination of the crustal and mantle layers of the subducting lithosphere the delamination front propagates upwards into the interplate zone resulting in the formation of two other crustal slices that also rise up between the plates average equivalent exhumation rate of the crustal material during delamination is about 1 cm year the crust asthenosphere boundary near the interplate zone is uplifted the subducted mantle layer then breaks off removing the pull force and thereby stopping the delamination and increasing horizontal compression of the lithosphere the latter produces shortening of the formed orogen and the growth of relief the modelling reveals an interesting burial exhumation evolution of the sedimentary cover during initial stages of continental subduction the sediments of the continental margin are dragged to the overriding plate base and are partially accreted at the deep part of the interplate zone at 60 70 km depth these sediments remain there until the beginning of delamination during which the pressure between the subducted crust and the overriding plate increases this results in squeezing the underplated sediments out part of them is extruded upwards along the interplate zone to about 30 km depth at an equivalent rate of 5 10 cm year

discovery of metamorphic diamonds in central china an indication of a 4000 km long zone of deep subduction resulting from multiple continental collisions the central orogenic belt cob of china is a major continental collision zone that contains extensive outcrops of deeply subducted and exhumed rocks at both the eastern and the western end of the belt here we report discovery of microdiamonds from both eclogites and felsic gneisses in the north qinling zone in the central portion of the cob this discovery demonstrates that the country rocks of continental affinity shared in the ultra high pressure metamorphic uhpm event and provides a bridge connecting the two previously recognized uhpm terranes thereby establishing the existence of a uhpm belt extending more than 4000 km geochronological dating yields early palaeozoic ages in the west and early mesozoic ages in the east recording two separate continental collisions overprinted within the cob occurrence of uhp metamorphism during recurrent continental collision here and in the alps suggests that deep subduction of continental material during such collisions is probably common rather than exceptional with significant implications for processes of plate tectonic reorganization and mantle mixing over time

dust streaks on mars global mapping and photometry of selected areas on mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia data on the colors albedos and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter redder dust less than 20 of the ground need be covered by the optically thick dust in the brightest parts of the streaks the amount of dust in optically thick layers could be as little as 10 3 g cm2 dark streaks can be interpreted as erosional windows in a patchy dust cover our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous optically thin layers it has the advantage that large amounts of dust can be deposited without affecting regional albedos

global map of eolian features on mars ten basic categories of eolian features on mars were identified from a survey of mariner 9 and viking orbiter images the ten features mapped are 1 light streaks including frost streaks 2 dark streaks 3 sand sheets or splotches 4 barchari dunes 5 transverse dunes 6 crescentic dunes 7 anomalous dunes 8 yardangs 9 wind grooves and 10 deflation pits the features were mapped in groups not as individual landforms and recorded according to their geographic positions and orientations on maps of 1 12 5 million or 1 25 million scale in the north polar region light and dark streaks indicate winds from the west and northwest frost streaks show northeast and northwest winds barchan dunes show southwest and west winds transverse dunes show east and west winds local erosional features show winds from the northwest or southeast and northeast or southwest in the middle and low northern latitudes streaks show northeast winds yardangs and deflation pits show mostly easterly and northeasterly winds in the low southern latitudes light streaks and dunes record northwest and northeast winds dark streaks record southeast winds in high southern latitudes most streaks and dunes record southeast and east winds in the south polar region light and frost streaks record southwest and northwest winds whereas dark streaks and transverse dunes show southeast winds the patterns recorded for ephemeral features conform to global conditions of strong southern spring and summer northern fall and winter wind circulation erosional features in bedrock indicate long term and perhaps ancient wind trends whereas depositional features may record relatively more recent winds wind directions indicated by yardangs pits and other erosional features seldom correspond to those shown by streaks these erosional features indicating winds of different directions than those that formed the streaks may have been carved when the effective regional winds on mars were different due to relative hemisphere insolation differences which are related to obliquity variations alternatively many yardangs and pits may be largely controlled by structure and carved along surface structural patterns or features that channeled both ancient and present day winds deflation pits in the mantled terrain may contain the best record of ancient wind trends these pits seem to have stratigraphically related orientations different stratigraphic units composing the mantle contain wind erosion pits that possibly record large scale wind direction changes because of long term changes in the obliquity of the mars

surface properties of the pettit wind streak on mars implications for sediment transport abstract pettit crater 12 n 174 w is associated with a complex wind streak consisting of both type i bright streak and type ii dark streak materials broadband albedo measurements of the streak indicate a minimum of 20 and a maximum of 32 with 27 on the surrounding plains the darkest materials have the highest thermal inertias which can be related to an effective grain diameter typical of medium sand most of the dark streak materials have thermal inertias representative of fine sand the material most easily set in motion by the wind on mars the bright portions of the streak have thermal inertias higher than that of the surrounding plains the bright streak values are representative of very fine sand differences between temperatures measured at 11 and 20 m indicate there is no difference in the areal abundance of unresolved high thermal inertia materials e g blocks bedrock between the pettit streak and the surrounding plains the dark streak material is consistent with models involving sand saltation and transport but the bright streak thermal inertia is not consistent with a volumetrically significant enhancement of unconsolidated dust in the streak

aeolian saltation on mars at low wind speeds laboratory experiments indicate that the fluid threshold friction speed u tf required to initiate fully developed aeolian saltation is much higher on mars than on earth a discrepancy exists between mars climate models that do not predict winds this strong and observations that sand sized particles are indeed moving this paper describes how wind friction speeds well below u tf but above the impact threshold u ti required to sustain saltation can initiate sustained saltation on mars but at relatively low flux numerical experiments indicate that a sand grain on mars mobilized sporadically between u ti and u tf will develop over fetch lengths longer than generally available within low pressure wind tunnels trajectories capable of splashing grains that propagate saltation and collectively form a cluster of saltating grains that migrate downwind together the passage of a saltation cluster should leave behind a narrow zone of affected surface grains the cumulative effect of many clusters represents a low flux phenomenon that should produce slow changes to aeolian bedforms over periods in which winds remain close to u ti and never or rarely reach u tf field evidence from small impact ripples along rover traverses is consistent with effects of saltation at these low friction speeds without obvious evidence for events u tf the potential utility of this grain mobility process is that it can operate entirely at more common winds well below u tf and so help explain widespread sand movements observed on mars wherever evidence might be mostly absent for u tf being exceeded

the sedimentary cycle on early mars two decades of intensive research have demonstrated that early mars 2 gyr had an active sedimentary cycle including well preserved stratigraphic records understandable within a source to sink f

megaripple migration on mars aeolian megaripples with 5 to 50 m spacing are abundant on the surface of mars these features were repeatedly targeted by high resolution orbital images but they have never been observed to move thus aeolian megaripples especially the bright toned ones often referred as transverse aeolian ridges tars have been interpreted as relict features of a past climate in this report we show evidence for the migration of bright toned megaripples spaced 1 to 35 m 5 m on average in two equatorial areas on mars indicating that megaripples and small tars can be active today the moving megaripples display sand fluxes that are 2 orders of magnitudes lower than the surrounding dunes on average and unlike similar bedforms on earth can migrate obliquely and longitudinally in addition the active megaripples in the two study areas of syrtis major and mawrth vallis show very similar flux distributions echoing the similarities between dune crest fluxes in the two study areas and suggesting the existence of a relationship between dune and megaripple fluxes that can be explored elsewhere active megaripples together with high sand flux dunes represent a key indicator of strong winds at the surface of mars a past climate with a denser atmosphere is not necessary to explain their accumulation and migration

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

diagenetic history of fluvial and lacustrine sandstones of the hartford basin triassic jurassic newark supergroup usa abstract the early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay rich surface waters into grain framework or cutans formed from pedogenic processes the discovery of pedogenic mud aggregates as traction load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns this study compares diagenesis in fluvial subaerially exposed sandstones with lacustrine subaqueous sandstones in a triassic jurassic continental rift basin hartford basin newark supergroup diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment the fluvial sandstones in the new haven arkose east berlin formation and shuttle meadow formation of the hartford basin are dominated by concretionary calcite and early calcite cement infiltrated clays illite smectite pedogenic mud aggregates smectite and illite smectite grain coating clays illite hematite illite chlorite hematite quartz overgrowths late stage carbonate cements calcite ferroan calcite pore filling clays illite kaolinite with minor amounts of smectite smectite chlorite illite smectite and hematite however pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths and carbonate authigenesis as well as the quality of diagenetically enhanced porosity dark gray black lacustrine subaqueous sandstones and mudrocks in the east berlin and shuttle meadow formations are dominated by pyrite concretionary dolomite and early dolomite cement radial grain coating clays smectite chlorite illite smectite late stage carbonate cements dolomite ferroan dolomite ankerite albite and pore filling clays smectite chlorite illite smectite illite chlorite clay minerals exist as detrital mechanically infiltrated and neoformed clay the fluvial sandstones in the new haven arkose are dominated by illite the east berlin and shuttle meadow formations are dominated by illite in the fluvial sequences and smectite chlorite and illite smectite in the lacustrine sandstones dolomite ferroan dolomite and ankerite are restricted to lacustrine sandstones whereas calcite and ferroan calcite to fluvial sandstones albite predominantly precipitated in lacustrine rather than fluvial environments through intergranular dissolution of plagioclase by acidic meteoric water dissolution of unstable mafic minerals and sodium rich brines and evaporites developed from groundwater albitization and carbonate cementation are the most pronounced late stage diagenetic processes affecting both types of hartford sandstones

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

dune field pattern formation and recent transporting winds in the olympia undae dune field north polar region of mars high resolution imaging science experiment hirise imagery of the central olympia undae dune field in the north polar region of mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines with apparent slipfaces on the primary crests ubiquitous wind ripples areas of coarse grained wind ripples and deflated interdune areas geomorphic evidence and dune field pattern analysis of dune crest length spacing defect density and orientation indicates that the pattern is complex representing two constructional generations of dunes the oldest and best organized generation forms the primary crestlines and is transverse to circumpolar easterly winds gross bed form normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and ne winds and is reworking the older pattern mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the ne the younger pattern appears to represent an influx of sediment to the dune field associated with the development of the olympia cavi reentrant with ne katabatic winds channeling through the reentrant a model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography

dynamics of continental collision influence of the plate contact summary observations shows that continental collision may evolve in different ways resulting in a wide range of tectonic responses in search of the controlling conditions and parameters we start from the results of our previous work which demonstrated that the properties of the plate contact are important for the overall dynamics of convergent plate margins two fundamental types of subduction plate contact can be distinguished one based on a fault and the other based on a weak subduction channel in this study we investigate how the plate contact affects the initial stage of continental collision we use a finite element method to solve the heat and the time dependent momentum equations for elastic power law viscous and plastic rheologies for the same rheological properties and driving forces varying the nature of the plate contact leads to three types of responses the presence of a subduction channel promotes coherent and when the boundary conditions allow it plate like subduction of the continental margin in models with a subduction fault coherent subduction of the incoming continental lithosphere occurs when the colliding passive margin has a gentle slope the approaching continental sliver starts to subduct and the subduction is characterized by a non plate like behaviour slower subduction velocity than in channel models and strong slab deformation if the continental margin is steep and the strength of the incoming continental crust is high fault models result in locking of the trench eventually leading to slab break off if the crustal strength is relatively low shear delamination of part of the crust is expected in the channel model this type of delamination never occurs the tectonic settings used in our experiments prescribed plate velocity of the subducting plate versus fixed subducting plate corresponding to a landlocked basin setting do not significantly influence the nature of the model response we conclude that initial stages of continental collision are strongly affected by whether the subduction contact is a fault or a channel neither the slab pull magnitude nor the tectonic setting is very important to the overall geodynamics at this stage the plate contact type along with the slope of the incoming passive margin and the rheology of the continent controls whether the incoming crust 1 subducts entirely 2 separates partially or entirely from the lithospheric mantle or 3 blocks the trench likely leading to slab break off

mars wind streak production as related to obstacle type and size abstract the characteristics of wind streaks associated with martian craters and hills in the size range of 100 m to 80 km corresponding to obstacle heights of a few to several hundred meters have been analyzed from viking orbiter images both dark erosional and bright depositional streaks form over the entire obstacle size range but there are preferred obstacle sizes for producing streaks bright streaks form more readily in association with relatively smaller obstacles than do dark streaks small obstacles produce both types of streaks more effectively than do large ones hills produce streaks as effectively as do craters of comparable height alternative explanations of bright streak formation are evaluated in terms of their ability to account for these observations the most satisfactory models invoke blocking of atmospheric flow downwind of an obstacle and consequent deposition of dust within the sheltered zone

nature of a flood basalt magma reservoir based on the compositional variation in a single flood basalt flow and its feeder dike in the mesozoic hartford basin connecticut the erosional remains of the mesozoic holyoke basalt in the hartford pomperaug and deerfield basins of connecticut and massachusetts indicate an original flow volume of 1200 km3 its feeder dike which is about 50 m wide and 160 km long can be traced down through 2 km of mesozoic sediments and as a result of faulting associated with basin formation through an additional 6 km of paleozoic metamorphic rocks chemical profiles through the distal and proximal parts of the flow and through the dike at depths of 2 4 and 8 km provide sequential samples of the magma that rose during this one eruptive event the flow and dike have restricted compositions that indicate saturation with olivine augite and plagioclase at depth the flow consisted largely of a liquid at the pigeonite reaction point dike compositions can be modeled as mixtures of this liquid with up to 24 crystals of plagioclase augite and olivine the dike compositions indicate equilibration with these minerals at 3 8 kbar this pressure corresponds to a depth of 12 2 km which is believed to have been the depth of the brittle ductile transition in the crust at the time this transition appears to be the only reasonable barrier that could have caused ponding of the magma at the mid crustal level the holyoke liquid is interpreted to have segregated from a compacting crystal mush following 30 crystallization of the magma in this mid crustal reservoir eruption of the basalt exhausted the supply of segregated liquid and when the remaining crystal mush began to rise in the dike the average density of the magma column increased until it matched the average density of the intruded crust and the eruption ended by analogy with the differentiation that took place in the solidifying holyoke flow on the surface the mid crustal magma reservoir is estimated to have had a volume of at least 12 000 km3 the magma in this chamber must have come from a still deeper chamber because it was too fractionated to have come directly from a mantle source

the biostratigraphic importance of conchostracans in the continental triassic of the northern hemisphere conchostracans or clam shrimp order conchostraca sars are arthropods with a carapace consisting of two chitinous lateral valves triassic conchostracans range in size from 2 to 12 5 mm long and are common in deposits that formed in fresh water lakes isolated ponds and brackish areas their dessication and freeze resistant eggs can be dispersed by wind over long distances therefore many conchostracan species are distributed throughout the entire north ern hemisphere in the late permian to middle triassic interval several of these forms are also found in gondwana many wide ranging conchostracan species have short stratigraphic ranges making them excellent guide forms for subdivision of triassic time and for long range correlations the stratigraphic resolution that can be achieved with conchostracan zones is often as high as for ammonoid and conodont zones found in pelagic marine deposits this makes con chostracans the most useful group available for biostratigraphic subdivision and correlation in continental lake deposits upper triassic gondwanan conchostracan faunas are different from conchostracan faunas of the northern hemisphere in the norian some slight provincialism can be observed even within the northern hemisphere for example the sevatian redondestheria seems to be restricted to north america and acadiestheriella n gen so far has been found only in the sevatian deposits from the fundy basin of southeastern canada here we establish a con chostracan zonation for the changhsingian late permian to hettangian early jurassic of the northernhemispherethat forthemostpart isverywellcorrelatedwiththemarinescale thiszona tion is especially robust for the changhsingian to early anisian late ladinian to cordevolian and rhaetian to hettangian intervals for most of the middle and upper triassic this zonation is still preliminary five new genera six new species and a new subspecies of conchostracans are described that are stratigraphically important half of the eight stage boundaries of the triassic have been defined by a bio event within a marine global stratotype and point gssp locality and these definitions have been accepted by both the international subcommission on triassic stratigra phy and the international commission on stratigra phy the remaining four stage boundaries are nearing final definition in the lower triassic both the base of the induan priority brahmanian stage base of triassic and the base of the next younger olenekian stage have been firmly defined in the middle triassic there is wide agree ment that the defining species for the base of the anisian stage should be chiosella timorensis in the gssp candidate site at desli caira romania but there has not yet been a formal vote on this the base of the overlying ladinian stage however has been firmly defined in the upper triassic the base of the carnian has been firmly likewise defined but there is not yet a final defi nition for the boundaries of the overlying norian and rhaetian stages a consensus has not been reached on a defining species for the base of the norian or its gssp locality but all of the different proposals under consideration do at least fall within a rather narrow stratigraphic interval for the base of the rhaetian misikella posthernsteini kozur mock has been chosen as the defining species by the international working group on the rhaetian stage and the gssp candidate locality at steinbergkogel austria has been studied in detail by a group under the leadership of l krystyn vienna and presented to the participants of the international conference on upper triassic sub divisions zonations and events in bad goisern in the autumn of 2008 the base of the overlying hettangian stage base of the jurassic has been defined so far only by a working group as the fad first appearance datum of psiloceras spelae guex taylor rakus bucher the final definition of the triassic stages within marine gssp sections will be completed in the near future but more than 50 of known triassic rocks are of continental origin therefore the main task of triassic stratigraphers in thefuture will besubdivid ing and correlating terrestrial strata both between

unraveling the martian water cycle with high resolution global climate simulations global climate modeling of the mars water cycle is usually performed at relatively coarse resolution 200 300 km which may not be sufficient to properly represent the impact of waves fronts topography effects on the detailed structure of clouds and surface ice deposits here we present new numerical simulations of the annual water cycle performed at a resolution of 1 1 60 km in latitude the model includes the radiative effects of clouds whose influence on the thermal structure and atmospheric dynamics is significant thus we also examine simulations with inactive clouds to distinguish the direct impact of resolution on circulation and winds from the indirect impact of resolution via water ice clouds to first order we find that the high resolution does not dramatically change the behavior of the system and that simulations performed at 200 km resolution capture well the behavior of the simulated water cycle and mars climate nevertheless a detailed comparison between high and low resolution simulations with reference to observations reveal several significant changes that impact our understanding of the water cycle active today on mars the key northern cap edge dynamics are affected by an increase in baroclinic wave strength with a complication of northern summer dynamics south polar frost deposition is modified with a westward longitudinal shift since southern dynamics are also influenced baroclinic wave mode transitions are observed new transient phenomena appear like spiral and streak clouds already documented in the observations atmospheric circulation cells in the polar region exhibit a large variability and are fine structured with slope winds most modeled phenomena affected by high resolution give a picture of a more turbulent planet inducing further variability this is challenging for long period climate studies

constraints on mars recent equatorial wind regimes from layered deposits and comparison with general circulation model results aeolian modification has been a fundamental surface process on mars throughout the amazonian orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature s formation therefore observation of recently formed bedform orientations provides a way to probe mars recent wind regime and constrain test general circulation models gcms we collect statistical distributions of transverse bedform and yardang azimuths at nine sites on mars and compare measured feature orientations to those predicted by using vector wind field output from the marswrf gcm we focus on layered deposits because their erodible nature makes them applicable to determination of mars modern wind regime our methods of mapping from the long term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur sand flux equations and the direction of maximum gross bedform normal transport we find that all methods examined typically agree with each other to within 15 though there are some exceptions using high order wind stress weightings with multi directional annual wind fields generally use of higher wind stress thresholds produces improved matches to bedform orientations comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions yardangs match well to model predictions and sub populations in close proximity to each other are shown to match individual directional maxima in gcm output for a single site implying that topographic effects may produce very localised unidirectional wind fields unresolved by the gcm

wind streaks in tharsis and elysium implications for sediment transport by slope winds detailed maps of wind streaks in tharsis and elysium have been compiled from viking orbiter observations spanning one complete martian year the streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the tharsis bulge while the global circulation dominates in elysium dust erosion by downslope winds occurs over much of tharsis and in the vicinity of elysium mons this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes erosional streaks are largely absent in elysium planitia net deposition of dust might have occurred during the period of our observations surface properties such as slope thermal inertia and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions

presence of the dinosaur scelidosaurus indicates jurassic age for the kayenta formation glen canyon group northern arizona the glen canyon group moenave wingate kayenta and navajo formations of northern arizona represents an extensive outcrop of early mesozoic age terrestrial sediments the age of these formations has long been disputed because independent stratigraphic data from marine tie ins paleobotanical and palynological evidence and radiometric calibrations have been scanty or absent the fauna of the kayenta formation in particular has been problematic because it has appeared to contain both typical late triassic and early jurassic taxa here i report that the principal evidence for late triassic taxa dermal scutes previously assigned to an aetosaur in fact belongs to the thyreophoran ornithischian dinosaur scelidosaurus previously known only as a washed in form found in marine sediments in the early jurassic of england the presence of this dinosaur represents the first vertebrate biostratigraphic tie in of the glen canyon group horizons with reliably dated marine deposits in europe together with revised systematic assessments of other vertebrates and independent evidence from fossil pollen it supports an early jurassic age for the kayenta formation and most or all of the glen canyon group

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

early jurassic sedimentation of a rift valley lake culpeper basin northern virginia gray calcareous lacustrine strata of early jurassic age crop out adjacent to the faulted western margin of the culpeper basin a mesozoic graben dominated by fluviogenic red beds sedimentological mineralogical and paleontological aspects reveal a distinct zonation of littoral sublittoral and profundal deposits in the lacustrine sequence reconstructed physiographic profiles of the lake exhibit shore terrace slope and basin plain subenvironments dominant sedimentary processes in these domains were respectively sediment agitation by waves deposition from suspension slumping and proximal sediment gravity flows and suspension and distal turbidity current deposition deposition of the lacustrine sediments occurred in a eutrophic calcite precipitating permanently or normally stratified lake the lake occupied an elongate actively subsiding sub basin adjacent to or possibly straddling the western border fault the sedimentary fill of the sub basin is characterized by several cyclic fluvio lacustrine sequences which average 150 m in thickness and closely resemble sedimentary cycles of other newark rift basins the maximum areal extent of the lake may have exceeded 3 000 km2 with an average maximum depth of 35 m proterozoic and lower paleozoic strata of the blue ridge anticlinorium to the west constituted the major source of clastic sediments in the lacustrine sequence but uptilted basalt flows and interbedded sedimentary units of the culpeper group simultaneously shed detritus from the east

a new model to simulate the martian mesoscale and microscale atmospheric circulation validation and first results 1 the laboratoire de meteorologie dynamique lmd mesoscale model is a new versatile simulator of the martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters the model combines the national centers for environmental prediction ncep national center for atmospheric research ncar fully compressible nonhydrostatic advanced research weather research and forecasting arw wrf dynamical core adapted to mars with the lmd general circulation model gcm comprehensive set of physical parameterizations for the martian dust co2 water and photochemistry cycles since lmd gcm large scale simulations are also used to drive the mesoscale model at the boundaries of the chosen domain of interest a high level of downscaling consistency is reached to define the initial state and the atmosphere at the domain boundaries a specific hybrid vertical interpolation from the coarse resolution gcm fields to the high resolution mesoscale domain is used to ensure the stability and the physical relevancy of the simulations used in synoptic scale mode with a cyclic domain wrapped around the planet the mesoscale model correctly replicates the main large scale thermal structure and the zonally propagating waves the model diagnostics of the near surface pressure wind and temperature daily cycles in chryse planitia are in accordance with the viking and pathfinder measurements afternoon gustiness at the respective landing sites is adequately accounted for on the condition that convective adjustment is turned off in the mesoscale simulations on the rims of valles marineris intense daytime anabatic 30 m s 1 and nighttime katabatic 40 m s 1 winds are predicted within the canyon corridors topographical channeling can amplify the wind a few kilometers above the ground especially during the night through large eddy simulations in gusev crater the model describes the mixing layer growth during the afternoon and the associated dynamics convective motions overlying gravity waves and dust devil like vortices modeled temperature profiles are in satisfactory agreement with the miniature thermal emission spectrometer mini tes measurements the ability of the model to transport tracers at regional scales is exemplified by the model s prediction for the altitude of the tharsis topographical water ice clouds in the afternoon finally a nighttime warm ring at the base of olympus mons is identified in the simulations resulting from adiabatic warming by the intense downslope winds along the flanks of the volcano the surface temperature enhancement reaches 20 k throughout the night such a phenomenon may have adversely affected the thermal inertia derivations in the region

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

pre collisional high pressure metamorphism and nappe tectonics at active continental margins a numerical simulation the evolution of a subduction channel and orogenic wedge is simulated in 2d for an active continental margin with p t paths being displayed for selected markers in our simulation subduction erosion affects the active margin and a structural pattern develops within a few tens of millions of years with four zones from the trench into the forearc i an accretionary complex of low grade metamorphic sedimentary material ii a wedge of nappes with alternating upper and lower crustal provenance and minor interleaving of oceanic or hydrated mantle material iii a megascale melange composed of high pressure hp and ultra high pressure uhp metamorphic rocks extruded from the subduction channel and iv the upward tilted frontal part of the remaining lid the p t paths and time scales correspond to those typically recorded in orogenic belts the simulation shows that hp uhp metamorphism of continental crust does not necessarily indicate collision but that the material can be derived from the active margin by subduction erosion and extruded from the subduction channel beneath the forearc during ongoing subduction

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

paleoecology and sedimentology of a late triassic lake culpeper basin virginia u s a late triassic and early jurassic lacustrine sedimentary rocks in the culpeper basin northern virginia and maryland u s a locally contain abundant fossil ostracodes darwinula sp conchostracans clam shrimp cyzicus sp and cornia sp fish and plant fragments stromatolites pelecypods notostracans tadpole shrimp triops cf cancriformis and insects are known from some late triassic beds and freshwater gastropods have been reported from the early jurassic of the culpeper basin a 7 m thick late triassic lacustrine sequence exposed in the central part of the culpeper basin records the history of a perennial saline lake the lake deposits consist chiefly of olive gray mudstone and claystone with interbedded sandstone and siltstone and stromatolitic limestone in the upper part evaporite crystal molds and pseudomorphs are present locally in the central part of the sequence indicating saline conditions red laminated and cross laminated sandstone and siltstone beds at the top and near the bottom of the sequence were deposited by fresh water inflow to the lake marginal lacustrine deposits associated with these fluvial redbeds contain abundant faunal remains including ostracodes conchostracans notostracans and scarce fish remains and insects these organisms were restricted to relatively fresh water near the lake margins faunal remains are absent from the central saline part of the lake sequence

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

dynamics of sediment subduction accretion at convergent margins short term modes long term deformation and tectonic implications a conceptual model is proposed for the short term operation of subduction accretion systems at convergent margins the operation is described in terms of the mass fluxes among the four system components namely the accretionary or prowedge wedge p an uplifted plug u a retrowedge r and the subduction zone the latter consists of a conduit c of slowly moving and deforming material and an underlying subduction channel where material moves and deforms more rapidly a broad range of convergent margin types can be accommodated within the conceptual model framework with differing short term modes that depend on which of the p u r c components that are active finite element geodynamical model experiments are used to investigate whether these modes are dynamically feasible these experiments determine excitation of modes under controls that include model entry and exit mass fluxes flexural loading by accreted material and slab pull forces boundary velocities corresponding to subduction and subduction zone advance retreat distribution thickness and density of accreted sediment and internal frictional properties of the coulomb sediments that all modes with the exception of p in which only a prowedge is created are seen in the models provides support for the concepts and allows conditions that favor particular modes to be recognized in addition the finite deformation predicted by the models is used to infer the long term tectonic styles associated with both single mode evolutions and those that exhibit mode switching a steady state mass balance can occur for modes 0 pure subduction p c i e where components p and c are active or other modes when the surface mass denudation plus the subduction flux balances accretion plus tectonic underplating the p c mode is favored by subduction zone retreat and or an increasing subduction load and creates an apparent landward dipping backstop p u c is predicted to be the most common mode and it creates an apparent seaward dipping backstop p u r c is an inefficient mode but is favored by easily detached retrocrust or sediment and or a decreasing subduction load

the early mesozoic birdsboro central atlantic margin basin in the mid atlantic region eastern united states the early mesozoic birdsboro basin new name was a single elongate depositional trough in the present mid atlantic area of the eastern united states extending northeastward from central virginia across maryland pennsylvania and new jersey into southern new york what now remains after erosion comprises the barboursville culpeper gettysburg and newark remnants some 7 km of late triassic and early jurassic continental sediments of varying provenances entered and spread across in the birdsboro basin in several depositional environments the five resulting sedimentary lithosomes include feldspathic sandstone quartzose sandstone red silty mudstone gray shale and fanglomerate the extensive interbedding intertonguing and lateral gradation among these lithosomes suggest that they were contemporary and closely interrelated the feldspathic sandstone lithosome contains sediment with a southeastern provenance that accumulated in a bajada environment extending the length of the southeastern side of the basin sediment in the quartzose sandstone lithosome had a northwestern provenance the coarse grained fraction formed regional alluvial fans at the mouths of four major input centers the finer grained fraction was deposited in the distal reaches of these fans and in the playa environments in the interfan areas this fraction formed the red silty mudstone lithosome gray black shales and argillites of the gray shale lithosome accumulated in lacustrine environments in the interfan areas the fanglomerate lithosome comprises numerous small lobate deposits of poorly sorted sediment along both basin margins the location and time of activity of the northwest input centers largely determined the distribution and areal extent of the various depositional environments and consequent lithosomes along the length and across the width of the basin the birdsboro basin was deformed tilted faulted and folded sometime after the deposition of the youngest preserved rocks early sinemurian the deformation varied along the length of the basin producing differences in the amount of tilting structural elevation and subsequent erosion the present erosional remnants create the illusion of four originally separate depositional basins