cenozoic topographic and climatic response to changing tectonic boundary conditions in western north america abstract this study presents an oxygen isotopic record from the paleocene to the pliocene based on the analysis of predominantly paleosol carbonate from intermontane basins in southwestern montana and eastern idaho 18 o values of calcite decrease by 7 to 10 between 50 and 47 ma in southwestern montana and idaho most likely as a result of an increase in elevation of 2 5 to 3 5 km this rise in elevation is roughly contemporaneous with the emplacement of the nearby challis volcanics and the formation of metamorphic core complexes in the hinterland of the sevier thrust belt moreover when compared to previous oxygen isotopic studies that show oxygen isotopic shifts of similar magnitude occurring later in the late eocene to early oligocene in northeastern nevada and late oligocene to miocene in southern nevada the results of this study add to a growing body of evidence for a spatial and temporal migration of high surface elevations from north to south in the great basin of western united states this surface uplift history supports tectonic models calling for north to south removal of the farallon slab or delamination of the mantle lithosphere

the geological isotopic botanical invertebrate and lower vertebrate surroundings of ardipithecus ramidus sediments containing ardipithecus ramidus were deposited 4 4 million years ago on an alluvial floodplain in ethiopia s western afar rift the lower aramis member hominid bearing unit now exposed across a 9 kilometer structural arc is sandwiched between two volcanic tuffs that have nearly identical 40ar 39ar ages geological data presented here along with floral invertebrate and vertebrate paleontological and taphonomic evidence associated with the hominids suggest that they occupied a wooded biotope over the western three fourths of the paleotransect phytoliths and oxygen and carbon stable isotopes of pedogenic carbonates provide evidence of humid cool woodlands with a grassy substrate

west wall structuring of equatorial plasma bubbles simulated by three dimensional hirb model plasma density depletions in the equatorial ionosphere or so called equatorial plasma bubbles epbs are generated in the postsunset period and tend to have a very complex spatial structure especially the east west asymmetry of epbs has been reported by various observations using a high resolution bubble hirb model which is a newly developed three dimensional numerical model for the equatorial ionosphere small scale structuring at the west wall of large scale f layer upwelling is clearly reproduced for the first time it is not an eastward neutral wind but a vertical shear of zonal plasma drift velocity at the bottomside of the f region that plays an important role in accelerating the instability growth at the west wall and generating the east west asymmetry of epbs

seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

thermal properties of lobate ejecta in syrtis major mars implications for the mechanisms of formation 1 this paper reports an analysis of the thermal properties of ejecta layers of single and double lobe impact craters on mars first observations of thermal properties were made at low resolution from the phobos 88 mission and did not allow mapping of variations of thermal properties inside the ejecta layer the themis instrument on board the mars odyssey mission provides new high resolution thermal mapping of the surface of mars from these data we observe a systematic temperature increase at night at the edge of the ejecta we evaluate first the possible influences on the surface temperatures at night of postimpact modification processes given the topography of an impact crater and its ejecta we show that the observed thermal signature is more likely related to a particle size distribution inherited immediately after the impact event during the emplacement of ejecta we propose that the kinetic sieving process observed in experimental and natural granular flows like pyroclastic flows is responsible for the accumulation of larger particles at the ejecta flow front and thus is responsible for the temperature increase despite evidence of aeolian activity at syrtis major these craters offer an example of preserved surface physical properties resulting from geological processes which have occurred since the formation of the volcanic shield of syrtis major further studies are underway with the mars express ongoing observations produced by the hrsc and omega instruments in order to explore the interplay between the surface physical properties and the spectroscopic signatures seen at syrtis major

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

phytoliths indicators of grassland dynamics during the late holocene in intertropical africa abstract the reconstruction of african tropical grassland history during the late holocene can be carried out using phytolith analysis fossil phytolith assemblages from lake guiers in the sahelian region of senegal and from lake sinnda in the guineo congolian region of congo were investigated the results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained tall or short grass associations are discriminated by their phytolith index iph saddle cross dumbel saddle while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths the phytolith data emphasize that in the guineo congolian region around lake sinnda the driest phase of the late holocene occurred between 4000 and 1200 yr b p commencing with the opening of the dense forest and its replacement by a short grass savanna from ca 1000 yr b p wetter climatic conditions developed as represented by the setting up of a tall grass savanna woodland the modern shrub and tall grass savanna was developed ca 700 yr b p in the sahelian region around lake guiers the driest phase occurred after about 2000 yr b p and has not been followed by moister conditions a tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs a short period of development of swampy vegetation which can be related to a lake level change interrupted the semi arid adaptation of the vegetation between about 2000 yr b p and the present

representational bias in phytoliths from modern soils of central north america implications for paleovegetation reconstructions abstract understanding localized patterns and community compositions of vegetation in an environment is critical to the reconstruction of climatic and ecological conditions across all spatiotemporal scales one of the most accurate and useful ways to characterize vegetation and therefore to describe the climatic and ecological conditions of a location is through the plant fossil record phytoliths plant silica microfossils are often preserved in the absence of other paleobotanical data and are becoming more widely used for deep time vegetation reconstructions significant work has been done to standardize the analytical methodology of phytolith extraction statistical analysis and interpretation but more detailed investigations are needed to understand how well a given soil assemblage represents the actual aboveground plant biomass for a given ecosystem we present results from paired soil phytolith assemblages and local vegetation assemblages across the central united states including temperate forest grassland and rangeland scrubland ecosystems phytolith assemblages obtained via extractions from soil a horizons were compared to percent cover of species and plant biomass estimates obtained via in situ field observations and aerial estimates of tree cover to analyze differences in the relative abundance of forest woody vegetation vs grasses soil phytolith assemblages from all sites average a 29 bias toward the grass morphotypes as compared to actual aboveground biomass observations and comparisons to percent cover yielded broadly comparable bias figures percent bias estimates do not show significant correlations to most environmental factors temperature precipitation local elevation however an extremely strong correlation p

mars express high resolution stereo camera spectrophotometric data characteristics and science analysis 1 the high resolution stereo camera hrsc on the mars express mex spacecraft in orbit about mars is delivering images of the mars surface and atmosphere from its high inclination elliptical orbit that are intended to cover most of the mars surface by the end of the mission these are acquired in four specific spectral passbands that sample the scene at different parts of the extended visual spectrum from near 0 4 m to about 1 m and in five additional channels four used for stereo and one nadir that use the same fifth spectral passband these channels view from different angles and can be used for photometric and spectral analysis the data allow a variety of studies of the surface and atmosphere of mars but these require detailed understanding of the data characteristics as there are several effects including of the observation geometry and the atmosphere that need to be treated this article is a report to the science community on the current understanding of the hrsc color data after an initial analysis and also a demonstration of their capabilities for study of mars which from this study appear to be considerable we first discuss the characteristics and calibration of the hrsc spectral data the atmospheric influence on the photometric appearance of the surface materials is explored and methods of compensating are considered reflectances are calculated for surface units by assuming the dark material is basalt and scaling the entire hrsc scene using a laboratory basalt spectrum for the selected dark material area the results and the correction factors for different orbits are compared we present several examples of what could become a large volume of future science results utilizing the hrsc spectrophotometric data in conjunction with photo interpretation for example we find relatively few but very important distinct spectral components at the hrsc resolution including what we interpret as iron oxide rich material unoxidized basalt and polar ice consistent with past works the major spectral components are distributed in ways that suggest compositional mixing and the need to revise the current geologic understanding of major regions

the occurrence and significance of biogenic opal in the regolith abstract biogenic opal produced by vascular plants diatoms and siliceous sponges have been found in soils and terrestrial sediments of all continents except antarctica since the middle of the 19th century the opal particles range in size from fine silt to fine sand almost all soils contain detectable opal up to levels of 2 3 and a significant number contain values in excess of 5 even higher values have been found from soils and sediments of all continents in a wide range of soil types the most important factor is poor soil drainage and seasonal to permanent water logging this encourages the proliferation of silica producing organisms such conditions have been found in the soils and aquatic sediments of the monsoonal tropics tropical rain forests temperate forests tropical savanna tropical islands semi arid grasslands and savanna and temperate woodland and grassland the presence of a volcanic substrate also appears favourable in some cases but is not necessary biogenic opal preferentially collects in the a horizon of soils and to a lesser extent in the b horizon this preferential distribution facilitates identification of palaeosols in stacked soil sequences biogenic opal is also a component of windblown dust even in arid environments biogenic opal is significant to regolith processes in a number of ways firstly as in the case in marine environments it is likely to be important in silica cycling and storage because of its greater lability compared to quartz secondly dissolution and reprecipitation of opal a as opal ct or micro quartz may play a role in cementation and silicification of regolith to form silica hardpans and silcrete thirdly the organisms that form biogenic opal can have considerable palaeoenvironmental significance and be valuable in reconstructing regolith evolution finally some forms of biogenic silica in particular sponge spicules can present a health hazard their high abundance in some soils and sediments needs to be considered when assessing the health implications of airborne dust

stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid miocene climatic optimum in idaho u s a abstract the effects of global climate change are manifested at the regional level consequently evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional scale climate data here we test whether climate change influenced faunal and floral patterns leading up to and during the mid miocene climatic optimum mmco based on datasets collected in the railroad canyon section rcs central eastern idaho u s a specifically we use isotope compositions of herbivore tooth enamel to investigate how mean annual precipitation map mean annual temperature mat cold month mean temperature cmmt and temperature seasonality varied through the rcs and how this local record compares to global climate reconstructions isotope compositions of teeth from the fossil equid merychippus and rhinocerotid diceratherium were compared across five time bins from c 23 to c 15 ma bulk 18o values of both taxa indicate that meteoric water compositions were unchanged through the study interval consistently c 15 6 but were c 1 9 higher than current regional meteoric water this difference points to warmer climates in central eastern idaho during the miocene post middle miocene topographic uplift in western north america and or shifts to air mass trajectories serial sampling of enamel shows seasonal fluctuations in water compositions and temperature bulk 13c values indicate an average map of 190 range 10 510 mm yr 1 with no significant change through the study interval comparable to today s map 236 mm yr 1 the reconstructed semi arid seasonal warm climate for the rcs agrees with phytolith assemblage data from the same strata indicating dominantly open grassy habitats however it is inconsistent with previously held ideas of warm wet mid miocene climates in the northern rocky mountains nrm based on paleosol analyses our inferred stable climate conditions for the mmco of the nrm contrast with coeval records from europe and asia indicating sustained or enhanced warm and wet climates these differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change

the spread of grass dominated habitats in turkey and surrounding areas during the cenozoic phytolith evidence abstract the arrival of hipparionine horses in the eastern mediterranean region around 11 ma was traditionally thought to mark the simultaneous westward expansion of savanna vegetation across eurasia however recent paleoecological reconstructions based on tooth wear carbon isotopes and functional morphology indicate that grasses played a minor role in late miocene ecosystems of the eastern mediterranean which were more likely dry woodlands or forests the scarcity of grass macrofossils and pollen in miocene floras of europe and asia minor has been used to support this interpretation based on the combined evidence it has therefore been suggested that late miocene ungulate faunal change in the eastern mediterranean signals increased aridity and landscape openness but not necessarily the development of grass dominated habitats to shed new light on the miocene evolution of eastern mediterranean ecosystems we used phytolith assemblages preserved in direct association with faunas as a proxy for paleovegetation structure grassland vs forest we extracted phytoliths and other biogenic silica from sediment samples from well known early to late miocene 20 7 ma faunal localities in greece turkey and iran in addition a middle eocene sample from turkey yielded phytoliths and served as a baseline comparison for vegetation inference phytolith analysis showed that the middle eocene assemblage consists of abundant grass phytoliths grass silica short cells interpreted as deriving from bambusoid grasses as well as diverse forest indicator phytoliths from dicotyledonous angiosperms and palms pointing to the presence of a woodland or forest with abundant bamboos in contrast the miocene assemblages are dominated by diverse silica short cells typical of pooid open habitat grasses forest indicator phytoliths are also present but are rare in the late miocene 9 7 ma assemblages our analysis of the miocene grass community composition is consistent with evidence from stable carbon isotopes from paleosols and ungulate tooth enamel showing that c4 grasses were rare in the mediterranean throughout the miocene these data indicate that relatively open habitats had become common in turkey and surrounding areas by at least the early miocene 20 ma 7 million years before hipparionine horses reached europe and arid conditions ensued as judged by faunal data

atmospheric effects on ejecta emplacement laboratory experiments allow the investigation of complex interactions between impacts and an atmosphere although small in scale they can provide essential first order constraints on the processes affecting late stage ballistic ejecta and styles of ejecta emplacement around much larger craters on planetary surfaces the laboratory experiments involved impacting different fine grained particulate targets under varying atmospheric pressure and density different gas compositions during crater formation ballistic ejecta form the classic cone shaped profile observed under vacuum conditions as atmospheric density increases for a given pressure however the ejecta curtain bulges at the base and pinches above this systematic change in the ejecta curtain reflects the combined effects of deceleration of ejecta smaller than a critical size and entrainment of these ejecta within atmospheric vortices created as the outward moving wall of ejecta displaces the atmosphere additionally a systematic change in emplacement style occurs as a function of atmospheric pressure largely independent of density contiguous ejecta rampart superposing ballistically emplaced deposits 0 06 to 0 3 bar ejecta flow lobes 0 3 to 0 7 bar and radial patterns 0 8 bar underlying processes controlling such systematic changes in emplacement style were revealed by observing the evolution of the ejecta curtain by changing target materials including layered targets and low density particulates by varying atmospheric density by changing impact angle and by comparing the ejecta run out distances with first order models of turbidity flows three distinct ejecta emplacement processes can be characterized ejecta ramparts result from coarser clasts sorted and driven outward by vortical winds behind the outward moving ejecta curtain this style of wind modified emplacement represents minimal ejecta entrainment and is enhanced by a bimodal size distribution in the ejecta such eddy supported flows are observed to increase in run out distance scaled to crater size with increasing atmospheric pressure by analogy with turbidity flows this scaled distance should increase as r1 2 for a given atmospheric pressure and degree of entrainment ejecta flows with much greater run out distances develop as the turbulent power in atmospheric response winds increase such flows overrun and scour the inner ejecta facies thereby producing distinct inner and outer facies the degree of ejecta entrainment depends on the dimensionless ratio of drag to gravity forces acting on individual ejecta and the intensity of the winds created by the outward moving curtain entrainment increases with increasing atmospheric density and ejection velocity crater size but decreases with ejecta density and size the intensity of curtain generated winds increases with ejection velocity crater size the dimensionless drag ratio characterizing the laboratory experiments can be applied to mars since the reduced atmospheric density is offset by the increased ejection velocities for kilometer scale events for a given crater size ejection velocity and atmospheric conditions a wide range of nonballistic ejecta emplacement styles could occur simply by varying ejecta sizes even without the presence of water alternatively the onset crater diameter for nonballistic emplacement styles can reflect the range of ejecta sizes possible from the diverse martian geologic history massive basalts to fine grained aeolian deposits scaling considerations further predict that ejecta run out distances scaled to crater size on mars should increase as r1 2 hence long run out flows dependent on crater diameter need not reflect depth to a buried reservoir of water on venus however the dense atmosphere maximizes entrainment and results in ejecta flow densities approaching a constant fraction of the atmospheric density under such conditions ejecta run out distances should decrease as r 1 2

mapping sub pixel surface roughness on mars using high resolution satellite image data 1 the ratio between co registered pixels in stereo or repeat image pairs is used to constrain the deviation of the martian surface from lambertian reflection due to unresolved shadows at the pixel scale of orbiting imagers relative differences between the ratios primarily reflect differences in the effective amount of shadows seen by the sensor in the two measurements and are thus used as a relative proxy for sub pixel surface roughness sr in scene atmospheric corrections enable simple application of this two look approach which facilitates robust sr mapping at spatial resolutions comparable to the image data relative two look sr estimates can be translated to physical sr parameters through empirical calibration using ground based measurements sr variation maps in gusev crater were derived from themis and hrsc images at 18 and 30 m pixel respectively the latter were calibrated using measurements from spirit to produce a quantitative clast coverage map of spirit s initial traverse in gusev crater

photometric anomalies of the lunar surface studied with smart 1 amie data we present new results from the mapping of lunar photometric function parameters using images acquired by the spacecraft smart 1 european space agency the source data for selected lunar areas imaged by the amie camera of smart 1 and the data processing are described we interpret the behavior of photometric function in terms of lunar regolith properties our study reveals photometric anomalies on both small sub kilometer and large tens of kilometers scales we found the regolith mesoscale roughness of lunar swirls to be similar in mare marginis mare ingenii and the surrounding terrains unique photometric properties related to peculiarities of the millimeter scale regolith structure for the reiner gamma swirl are confirmed we identified several impact craters of subkilometer sizes as the source of photometric anomalies created by an increase in mesoscale roughness within the proximal crater ejecta zones the extended ray systems reveal differences in the photometric properties between proximal and distant ejecta blankets basaltic lava flows within mare imbrium and oceanus procellarum indicate higher regolith porosity for the redder soils due to differences in the chemical composition of lavas

small scale spatial resolution of the soil phytolith record in a rainforest and a dry forest in costa rica applications to the deep time fossil phytolith record abstract phytolith analysis a well established tool in archaeology and quaternary paleoecology has become a source of data for deep time paleoecological studies only in the last 15 years recent years have also witnessed the publication of numerous soil phytolith inventories from extant vegetation types representing modern analogues however this work suffers from several methodological shortcomings limiting inter study comparisons and the development of a single and repeatable protocol for soil sample collection in this paper we focus on two fundamental methodological questions that must be answered before modern analogue studies can be meaningfully applied to deep time paleoecology 1 do phytoliths from the lower portion of the a horizon more commonly preserved in paleosols reflect standing vegetation equally well as the upper a horizon which is more commonly used in modern analogue studies but often truncated by erosion in paleosols 2 does a point soil sample usually collected from paleosols capture standing vegetation as accurately as a composite soil sample commonly used in modern analogue studies which is made from subsamples taken from a small area to address these questions we collected soil from 10 10 m quadrats in a rainforest la selva and a dry forest palo verde in costa rica and compared phytolith assemblages from upper vs lower soil a horizons and composites vs single phytolith assemblages at both sites phytolith assemblages from the lower vs upper a horizon and from single vs composite samples provide similar vegetation structure signal despite some compositional differences these results suggest that the typical approach in deep time paleoecology of taking point samples from the lower a horizon of paleosols is likely justifiable at least for paleosols reflecting rainforest and dry forest soils we discuss possible mechanisms driving differences between sites and future approaches to further expand and test our results

lunar topographic roughness maps from lunar orbiter laser altimeter lola data scale dependence and correlation with geologic features and units we present maps of the topographic roughness of the moon at hectometer and kilometer scales the maps are derived from range profiles obtained by the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter lro spacecraft as roughness measures we used the interquartile range of profile curvature at several baselines from 115 m to 1 8 km and plotted these in a global map format the maps provide a synoptic overview of variations of typical topographic textures and utilize the exceptional ranging precision of the lola instrument we found that hectometer scale roughness poorly correlates with kilometer scale roughness because they reflect different sets of processes and time scales hectometer scale roughness is controlled by regolith accumulation and modification processes and affected by the most recent events primarily geologically recent 1 2 ga meteoritic impacts kilometer scale roughness reflects major geological impact volcanic and tectonic events in earlier geological history young large impact craters are rough and their roughness decreases with age the global roughness maps revealed a few unusually dense clusters of hectometer and decameter size impact craters that differ in their morphology and settings from typical secondary crater clusters and chains the origin of these features is enigmatic the maps can assist in the geological mapping of the lunar maria by revealing contacts between volcanic plain units the global roughness maps also clearly reveal cryptomaria old volcanic plains superposed by younger materials primarily crater and basin ejecta

the cenozoic climatic and topographic evolution of the western north american cordillera herein we present oxygen isotope records from cretaceous to recent terrestrial sediments in the western north american cordillera the purpose of this analysis is to use oxygen isotope records to understand the coupled surface elevation and climate histories of this region through the cenozoic to do this we constructed 18o maps of surface waters for time intervals that trace the development of topography of western north america these maps are based on 4861 oxygen isotope analyses from both published 4478 and new 383 data we determined the 18o values of surface waters using paleotemperatures derived previously from floral assemblages and the appropriate isotope fractionation factors these data suggest that in the late cretaceous to early eocene the sevier hinterland formed a plateau of unknown height around 50 ma a topographic wave developed in british columbia and eastern washington that swept southward reaching northeastern nevada at 40 to 38 ma and southern nevada 23 ma this southward encroachment of an eocene plateau sweep caused reorganization of drainage patterns such that the intraforeland basins of wyoming and utah drainages extended deep within the sevier hinterland as the wave swept southward the landscape within the sevier hinterland developed into a rugged and high mountain range with the hypsometric mean elevation of 4 km and relief of 1 5 km this eocene highland was bordered on the west by a high sierra nevada ramp and on the east by the intraforeland basins that captured water draining these growing highlands the spatial and temporal evolution of this highland correlates with the timing of volcanism and extension these observations support tectonic models that call for north to south removal of the farallon slab or piecemeal removal of mantle lithosphere the isotopic data show that prior to growth of this highland the north american monsoon nam penetrated much farther north in the paleocene eocene than today the combined effects of global cooling increasing latitudinal temperature gradients and the generation of the orographic barrier created by the growing north to south highland produced a southward migration of the nam front by the oligocene the hydrologic regime that we observe today was in place it has been modified since then as a result of basin and range extension and collapse of the highlands in the mid miocene this collapse allowed the nam to penetrate farther north into the great basin of nevada and utah

land based evidence for tertiary climatic variations northern rockies paleoclimatic interpretations of sedimentation patterns paleosol mineralogy and vertebrate faunal assemblages of extensive tertiary continental clastic sediments of montana and idaho indicate four major changes in precipitation in this area during tertiary time wet to dry in late eocene dry to wet in late early miocene wet to dry in early middle miocene and dry to wet in late miocene pliocene time this climate pattern is synchronous with similar climatic changes inferred from deep ocean sedimentation rates for the indian pacific and atlantic oceans and to oxygen isotope paleo temperature data for the north pacific ocean and new zealand other paleoclimatic evidence supports the pattern the evidence suggests widespread synchronous tertiary climate changes that may provide useful time stratigraphic markers

vegetation and habitat change in southern california through the middle miocene climatic optimum paleoenvironmental records from the barstow formation mojave desert usa

high resolution isotopic record of c4 photosynthesis in a miocene grassland abstract the origin and spread of grasslands is one of the key evolutionary events in the cenozoic which is characterized by long term cooling and drying climatic conditions one way to examine the relationship between vegetation and climate is to study the isotopic composition of organic carbon preserved in paleosols paleosols that preserve organic matter in the form of carbonaceous root traces provide direct evidence of the proportion of c3 to c4 biomass that grew in the soil in contrast with pedogenic carbonate 13c values which may also reflect complicating factors including mixing from atmospheric 13c in low productivity ecosystems a high temporal and spatial resolution reconstruction of past ecosystems was derived from thirty five paleosols in a thirty four meter section of the sixmile creek formation at timber hills montana usa that was deposited during the miocene 10 2 8 9 ma ago phytoliths were extracted from paleosol samples to compare vegetation assemblages to inferences based on isotopic compositions with both proxies giving similar results isotopic results from organic matter indicate both a small component of c4 photosynthetic plants locally prior to their regional expansion to dominance in the late miocene through the early pleistocene and large variation in the abundance of c4 plants 0 25 in this ecosystem both laterally and on a 100 kyr timescale in contrast pedogenic carbonate 13c values from this site indicate a high proportion of c4 photosynthesis that is at odds with both phytolith and 13corg results suggesting that the carbonate values are biased by diagenesis or diffusion of atmospheric co2 and that a similar issue may impact previous paleovegetation reconstructions based on pedogenic carbonates quantitative reconstructions of mean annual temperature and mean annual precipitation indicate little local variability through time and that the fluctuations in c4 proportion were not climatically driven instead the variable proportion of c4 photosynthesis is best explained by ecosystem scale variables such as succession fluvial avulsion and fire regime

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

the volcanic history of central elysium planitia implications for martian magmatism abstract central elysium planitia cep is located south of elysium mons back to the era of the viking orbiters clues accumulated in favor of recent volcanism in relation with ground water release and the formation of long sub parallel fissures four aqueous flood channel systems emanate from linear fissures recent eruptions of low viscosity lavas originate from these fissures and from low shield volcanoes the objective of this paper is to constrain the volcanic history of this region and to determine the chronological relationships with fluvial erosional processes new observations e g new shield volcanoes and one new fluvial event are summarized on a context map thirty five surfaces have been dated from the count of about 15 000 impact craters ages have been cross checked with relative stratigraphy when possible a probabilistic approach has been introduced to compare similar ages and define periods of volcanic activity our results confirm that some volcanic features are extremely recent 2 my active periods are found at 2 5 3 my 4 3 my 13 5 16 2 my 19 my 21 32 my 58 my 71 my 85 95 my 134 my 173 my and 234 my not excluding the possibility that some of the gaps would be filled with additional crater counts the volcanic activity thus extended for at least the last 250 my the lava volumes have been estimated from the topographic modeling of the floor of depressions filled up by volcanic products including the volumes of several large crater cavities buried under lavas 20 of the total volume our new estimation of the total lava volume is 1 5 0 2 10 5 km 3 this value corresponds to an average thickness of one hundred meters of lavas for the young volcanic plain as a consequence the total eruption rate at cep defined as the total volume of lava divided by the time of emplacement 1 4 10 2 1 8 10 2 m 3 s is lower than values typically estimated for terrestrial hot spots or large igneous provinces suggesting longer inactive periods the concept of mantle plumes responsible for terrestrial flood volcanism may not be applicable to the case of cep and the mechanism proposed in schumacher and dreuer 2007 offers a plausible alternative to explain our observations

quantitative analysis of mars surface radar reflectivity at 20 mhz abstract the radar surface echoes taken from sharad observations are extracted to obtain a reflectivity map covering almost half of the martian surface and then compared to available roughness maps then we used a 2 step method based on a stochastic description of reflectivity in order to i separate the coherent incoherent components of the signal by means of a probability density function fitting of amplitude distributions and ii express these components with respect to roughness permittivity values by adapting common backscattering models to the nadir case scattering is found to be the most important process dominating reflectivity over the martian terrains reflectivity is best correlated with roughness maps derived from the slope parameter the stochastic behavior of reflectivity is confirmed by the excellent agreement of our models and demonstrates the low probability of retrieving permittivity from scattering surfaces the non stationary nature of most martian terrains is consolidated by a very good fit to k distributions justifying the use of the fractal theory for describing surface roughness on mars a few slightly rough regions exhibit both a coherent and incoherent component when surface correlation length is non significant within the resolution cell we show that the rms roughness at a decameters baseline can be derived with sub decimeter sensitivity without prior signal calibration improving the capabilities of sharad in determining surface roughness with a view to landing site selection sets of derived dielectric constants are obtained and analyzed with regard to the reference signal used for calibration given the very different implications of each set to the composition of martian terrains we emphasize the importance of good signal calibration as a major issue for sharad and the next interplanetary radar missions

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

vegetation response during the lead up to the middle miocene warming event in the northern rocky mountains usa abstract the mid miocene climatic optimum mmco initial warming beginning ca 18 ma and with peak warming ca 17 14 75 ma constitutes the earth s most recent greenhouse episode characterized by a transient shift to higher global atmospheric co 2 levels and warmer possibly wetter climatic conditions combined with the spread of grass dominated habitats it has been suggested that the mmco lead to significant turnover and modernization of fauna and flora however records documenting local vegetation change during the mmco are rare hence this hypothesis remains largely untested herein we combine phytolith assemblages and 13 c records from paleosol organic matter from the railroad canyon section rcs eastern idaho to provide the first direct detailed and continuous long term record of vegetation composition and structure in a single basin during the lead up to the mmco 22 9 15 2 ma late arikareean early barstovian phytolith assemblage analysis indicates that grasses primarily c 3 pooids dominated early middle miocene vegetation potential c 4 pacmad grasses were present by ca 21 6 20 7 ma late arikareean and vary in abundance 0 4 17 2 of diagnostic phytoliths through the section although relatively rare overall pacmad grasses decrease significantly through time in parallel with declining diatom abundances and an increase in pooid grasses in contrast paleosol 13 c org indicates 0 29 1 c 4 vegetation but no consistent temporal change where both phytolith and isotope based estimates are made from the same paleosol they are within error most 82 of the time thus the apparent discrepancy in temporal trends could either be due to differences in the resolution of the two records or could be explained if many pacmads were not c 4 grasses but instead water loving c 3 species overall these data suggest that open habitat mosaic vegetation with grass dominated grasslands and open woodlands occurred in the north rocky mountains usa by at least the early miocene more comparable to the timing for the spread of grass dominated habitats in the great plains than previously thought additionally phytolith data suggest that overall vegetation structure remained relatively stable throughout the rcs inconsistent with published paleosol morphology data this points to regionally unique floral patterns decoupled from global climate change leading into the mmco

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

eocene vegetation and ecosystem fluctuations inferred from a high resolution phytolith record a thorough understanding of the ecosystem factors that can act as drivers of vegetation change an important factor for projecting impacts of future climate change requires adequately distinguishing between plant community changes that occur on the local scale or over ecological time scales and long term trends phytolith assemblages have the potential to provide this information but little work has been done so far to test their ability to do so in deep time we examined vegetation patterns inferred from phytoliths plant silica microfossils from a single section of the renova formation timberhills region montana dated to 39 2 3 ma late middle eocene the section is composed of fl uvial sediments overprinted by paleosols including alfi sols entisols inceptisols and composite paleosols phytolith assemblages from 27 paleosol samples were used to reconstruct a high resolution vegetation history for the area and were compared with paleosol data phytoliths are predominantly from forest plants and include tropical elements such as palms arecaceae and gingers zingiberales suggesting a paratropical forest the high resolution sampling records heterogeneous vegetation including shifts among closed forest moderately open forest forest gaps edges and woodland and grass dominated habitats grasses are interpreted as early open habitat plants tolerant of drier conditions but they appear to be replaced by forest vegetation with time resulting in poor correspondence between paleosol type and phytolith assemblage at some stratigraphic levels where paleosol morphology indicates a forest ecosystem and the phytolith assemblages indicate a changing grass forest mixture as a function of depth within the profi les this is the fi rst study that has used phytoliths to construct a high resolution record of vegetation from deep time and we demonstrate that dense sampling and multiproxy approaches to paleo environmental reconstruction are necessary to capture vegetation heterogeneity in time and across microhabitats

self affine behavior of martian topography at kilometer scale from mars orbiter laser altimeter data 1 we used mars orbiter laser altimeter mola data from the current mars global surveyor mission to characterize the topographic roughness of the martian surface and to provide a mean to evaluate clutter at long 10 300 m wavelengths such wavelengths are relevant for the marsis and sharad subsurface radars which will be flown in future missions to mars the method of analysis is based on the assumption that topography can be described as a self affine fractal 30 km long segments of mola altimetry profiles have thus been reduced to the topographic parameters rms height rms slope and hurst exponent this last related to the fractal dimension which can be used as inputs to a near nadir radar scattering model the values of the hurst exponent are greater than 0 5 for most of the surface meaning a scaling behavior which is almost self similar maps of rms height and hurst exponent show that these two parameters have very different spatial distributions whereas the rms height is patterned after the north south dichotomy the hurst exponent follows a latitudinal trend we make use of a multivariate method called g mode to classify profiles in the three dimensional parameter space we find several roughness units some of which have a strong correlation with certain geologic units while others are bound by latitude however at scales between 300 m and 3 km large stretches of the surface of mars share common statistical properties of topography independent from the north south dichotomy

kilometer scale slopes on mars and their correlation with geologic units initial results from mars orbiter laser altimeter mola data martian surface slopes were calculated at baselines from 0 4 to 25 km using profiles obtained by the mars orbiter laser altimeter mola instrument during the aerobraking phase of the mars global surveyor mission median slope is proposed as a characteristic measurement of the typical surface roughness at each corresponding scale median slope is favored over rms slope because it is not influenced by the small number of higher slopes at the upper end of the slope frequency distribution tail median slope complements interquartile scale roughness characterization in that it is more sensitive to smaller baseline slopes a map of the median slope of the northern hemisphere is presented median slopes and their scale dependences are used to characterize typical kilometer scale roughness for a set of geologic units mapped in the northern hemisphere this analysis demonstrates that many individual units and groups of units are characterized by distinctive surface slopes and that these characteristics are sufficiently different that they hold promise for use in the definition and characterization of units characterization of the slope properties of geologic units provides information useful in the interpretation of their origin and evolution for example the generally smooth topography of the diverse vastitas borealis formation subunits is dominated by about 3 km 0 3 steep features almost indistinguishable in viking images the roughness characteristics of this unit differ from those of other geologic units on mars and suggest some distinctive process es of formation and or modification of kilometer scale topography common for all subunits the similarity of roughness characteristics of the several highland plateau units suggests that kilometer scale topography was largely inherited from the period of heavy bombardment the northern polar cap and layered terrains are largely very smooth at small scale the long steep sloped tails of the slope frequency distributions are compared for the dominant terrain types in the northern hemisphere of mars and are compared with earth continents the vastitas borealis formation found in the northern lowlands differs significantly from both cratered uplands and volcanic plains and these latter two units can be distinguished from each other on the basis of median slope terrestrial continents are smoother than cratered highlands but rougher than the vastitas borealis formation and most volcanic plains an inventory of all observed slopes much steeper than the angle of repose is presented steep slopes occur in the upper parts of tectonic scarps most likely representing bedrock exposures the presence of extremely steep slopes in the presumably ductile polar cap provides evidence for geologically recent and or ongoing formation of these slopes

meter scale slopes of candidate mer landing sites from point photoclinometry photoclinometry was used to analyze the small scale roughness of areas within the proposed mars science laboratory msl landing ellipses the landing ellipses presented in this study are those in eberswalde crater gale crater and holden crater the mawrth vallis site could not be measured due to its albedo variations we were able to constrain surface slopes on length scales comparable to the hirise image resolution 0 25 meters pixel the msl mission has various engineering constraints that each candidate landing ellipse must satisfy these constraints indicate that the statistical value of the slopes at one two and five meter baselines are an important criterion we used our technique to estimate surface slopes across large swaths of each image and built up slope statistics for the images in each landing ellipse we are confident that all three final msl landing site ellipses that could be measured in this study are within the small scale roughness constraints our results have provided input into the landing hazard assessment process

evidence of early c 4 grasses habitat heterogeneity and faunal response during the miocene climatic optimum in the mojave region abstract major changes to landscapes climate and mammalian faunas occurred at the regional scale in western north america during the miocene climatic optimum mco between 17 and 14 ma but few studies have looked at how the mco affected basin scale environments paleoenvironmental reconstructions coupled with mammalian fossil assemblages from the crowder and cajon valley formations in the mojave desert california contribute insights into local scale 10s of kilometers responses to warming during the hemingfordian and barstovian north american land mammal ages by integrating lithological descriptions phytolith analyses carbon isotope composition of preserved soil organic matter 13csom and elemental geochemistry of paleosols we provide reconstructions of depositional environments vegetation and precipitation through the mco phytolith and 13csom evidence suggest that paleoenvironments were predominately c3 grasslands with the earliest potential presence of c4 grasses in the region found within the crowder formation at 17 ma based on elemental geochemistry of paleosols mean annual precipitation estimates are 807 182 mm yr 1 at 17 ma in the crowder formation and 740 800 182 mm yr 1 from 16 to 15 ma in the cajon valley formation our multiproxy approach indicates that the crowder and cajon valley basins were stable large scale braided stream and floodplain systems with intermittent paleosol development and heterogeneity in vegetation and moisture conditions across spatial scales overall we find a signal of local paleoenvironmental stability during the mco however a significant drying trend in the crowder formation does correspond with faunal turnover and reduction in the number of taxa present high species diversity within faunal assemblages especially among small mammals and fewer shared species between the crowder and cajon valley assemblages than expected based on bootstrap analysis indicate that peak mammal diversity was accommodated at both local and regional scales during sustained tectonic activity and the mco in western north america

climate dust and fire across the eocene oligocene transition patagonia the eocene oligocene transition eot is typically interpreted as a time of drastic global cooling and drying associated with massive growth of a glacial icecap in antarctica and the shift to an icehouse climate the effects of this transition on the terrestrial environments floras and faunas of the southern hemisphere however have been unclear here we document simultaneous changes in fire regime and plant community in patagonia argentina decreases in the concentration of magnetite in loessites from the eocene oligocene vera member of the sarmiento formation correlate with decreases in the fraction of burnt palm phytoliths as well as more consistently palm dominated phytolith assemblages association of magnetite and burnt palm phytoliths suggests intense wildfires which appear to have been suppressed for 200 k y shortly after the eot the disappearance of fire related characteristics near the eot is possible if changes in regional wind patterns consistent with observed changes in sediment particle sizes caused changes in seasonal precipitation these results imply a more important role for fire in structuring eocene oligocene landscapes than previously thought

evolution of grasses and grassland ecosystems the evolution and subsequent ecological expansion of grasses poaceae since the late cretaceous have resulted in the establishment of one of earth s dominant biomes the temperate and tropical grasslands at the expense of forests in the past decades several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation the data indicate that the development of grassland ecosystems on most continents was a multistage process involving the paleogene appearance of c3 and c4 open habitat grasses the mid late cenozoic spread of c3 grass dominated habitats and finally the late neogene expansion of c4 grasses at tropical subtropical latitudes the evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open habitat grasses in addition the timing of these evolutionary and ecological events varied between regions consequently region by region investigations using both direct plant fossil

vegetational history of a site in the central amazon basin derived from phytolith and charcoal records from natural soils abstract analysis of phytoliths and macroscopic charcoal from natural soils near manaus brazil shows that the central amazonian terra firme forest has not been stable during the holocene phytolith taxonomic composition and radiocarbon ages indicate that a closed forest has continuously existed in the area since at least 4600 yr b p but that forest composition and species abundance changed significantly sometime during the holocene epoch there is no evidence that the vegetation experienced swidden cultivation the distribution and dates of the charcoal in the soils indicate that forest fires between 1795 and 550 yr b p burned an area of about 200 hectares vegetational changes and fires appear to be a result of climatic drying that may have affected large areas of the amazon basin over the past 5000 to 7000 years soil phytolith analysis is a promising tool for the study of environmental history in the humid tropics and may reduce the previous dependence on lake and swamp sediments at least for the holocene epoch

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

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

multi proxy evidence for tectonic control on the expansion of c4 grasses in northwest argentina the timing of the rise of c4 grasses and the climatic conditions driving their expansion are widely debated with recent studies suggesting that the expansion was more complex than previously thought proxy reconstructions from northwestern argentina record multiple increases and decreases in c4 abundance throughout the late miocene to early pliocene as well as variations in the timing of the spread of c4 grasses into the region here we present a multi proxy paleovegetation reconstruction of the proportions of c3 and c4 vegetation using organic carbon and phytoliths preserved in paleosols at entre rios in the santa maria basin of catamarca argentina between 6 2 and 3 3 ma both corg13 and phytolith assemblages indicate a c3 dominated ecosystem with no evidence for substantial amounts of c4 vegetation from the late miocene through mid pliocene despite their rise to dominance elsewhere during this time these data suggest that by 6 2 ma the santa maria basin floor was at an elevation high enough to create locally cool conditions that allowed c3 vegetation to outcompete c4 grasses phytolith assemblages show that later uplift of the sierra calchaquies and sierra aconquija ranges through the pliocene increased aridity and drove the expansion of c3 grasses at the expense of palms and other forest indicators this multi proxy paleovegetation reconstruction demonstrates that tectonics played an important role in controlling the late miocene expansion c4 grasses by suppressing their spread into northwest argentina

refining a pedogenic carbonate co2 paleobarometer to quantify a middle miocene greenhouse spike abstract estimates of respired soil co2 concentration in paleosols are needed to calculate past atmospheric co2 levels from the difference between organic and carbonate carbon isotopic values in paleosols a new compilation of co2 concentrations late in the growing season in modern calcareous soils can be used to estimate respired soil co2 by subtracting atmospheric co2 concentrations furthermore respired co2 shows a significant relationship with depth to calcic horizon and this relationship can be used to estimate respired co2 concentrations in paleosols these values as well as estimates of 13c of atmospheric co2 from 13c of soil organic matter and of paleotemperature from bw horizon chemical composition refine the cerling co2 paleobarometer these refinements are applied to quantify the middle miocene greenhouse which has been controversial because it was not detected by marine alkenone and boron paleobarometers new estimates of middle miocene atmospheric co2 from paleosols in railroad canyon idaho reveal levels at 16 ma of 852 86 ppmv this is similar to predicted values by 2100 and 3 times pre industrial values pil 280 ppmv

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

multiproxy studies of early miocene pedogenic calcretes in the santa cruz formation of southern patagonia argentina indicate the existence of a temperate warm vegetation adapted to a fluctuating water table abstract the lower miocene santa cruz formation in southern patagonia austral basin argentina contains several horizons of pedogenic calcretes which record 17 5 myr old vegetation adapted to a shallow and fluctuating water table at paleolatitude of 56 s to reconstruct the paleoenvironment paleoclimate and paleoecosystem we performed a multiproxy study of the calcretes examining abiotic and biotic components the calcretes exhibit a variety of morphologies horizontal and vertical rhizoliths laminar structure nodules massive crusts microfabrics beta predominant over alpha microfabrics and 18o and 13c values that fluctuate within each morphotype and throughout the analysed interval microfossils and phytoliths in the host material of the calcretes indicate fluctuating terrestrial freshwater and marine conditions and record an ecosystem dominated by herbaceous plants and arboreal elements in association with a typical coastal santacrucian vertebrate fauna we propose that the calcretes developed in soils in a coastal fluvial setting during pauses in floodplain aggradation that typically lasted between 8 25 ka and 400 ka years variable sedimentation rates in different parts of the coastal fluvial floodplain the fine texture of the host sediment and the influence of a fluctuating water table also influenced the formation of the calcrete a high water table in low relief areas of the floodplain created the conditions necessary to form a horizontally extended rhizolithic system that jointly with the biotic proxy can be correlated with a radicular pattern similar to the arboreal elements from coastal settings abiotic and biotic proxies of the studied interval attest to environmental fluctuations recorded at different scales that took place under temperate warm and subhumid climates with a marked rainfall seasonality with a slight increase in the aridity towards the top of the studied interval under these conditions a subtropical fauna and a c3 dominated ecosystem developed coincident with the onset of the mid miocene climatic optimum in patagonia

mars orbiter laser altimeter pulse width measurements and footprint scale roughness the mars orbiter laser altimeter mola measured the pulse width and energy of altimetric laser returns during the course of two mars years of operations as secondary science objectives mola obtains the footprint scale roughness and the bidirectional reflectivity of mars mola underwent extensive preflight calibration and pulse measurements were monitored continuously in flight but anomalous values of roughness have been inferred a calibration of pulse widths using inflight data yields a slope corrected roughness over 75 m diameter footprints that may be used for quantitative geomorphic surface characterization required for example for landing site selection the recalibration uses a total least squares estimation of pulse characteristics that generalizes the method of abshire et al 2000 this method utilizing the timing at voltage threshold crossings and the area between crossings accounts for observation errors and shows that surface roughness as small as 1 m can be resolved

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

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

coupling of marine and continental oxygen isotope records during the eocene oligocene transition while marine records of the eocene oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on antarctica continental records indicate substantial spatial variability marine eocene oligocene transition records are marked by an 1 1 foraminiferal 18o shift but continental records rarely record the same geochemical signature making both correlation and linking of causal mechanisms between marine and continental records challenging here a new high resolution continental 18o record derived from the freshwater gill breathing gastropod viviparus lentus is presented from the hampshire basin uk the solent group records marine incursions and has an established magnetostratigraphy making it possible to correlate the succession directly with marine records the v lentus 18o record indicates a penecontemporaneous higher magnitude shift 1 4 than marine records which reflects both cooling and a source moisture compositional shift consistent with the growth of antarctic ice when combined with clumped isotope measurements from the same succession about half of the isotopic shift can be attributed to cooling and about half to source moisture change proportions similar to marine foraminiferal records thus the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the eocene oligocene transition not observed in continental interior records

multiscale analysis of topographic surface roughness in the midland valley scotland surface roughness is an important geomorphological variable which has been used in the earth and planetary sciences to infer material properties current past processes and the time elapsed since formation no single definition exists however within the context of geomorphometry we use surface roughness as an expression of the variability of a topographic surface at a given scale where the scale of analysis is determined by the size of the landforms or geomorphic features of interest six techniques for the calculation of surface roughness were selected for an assessment of the parameter s behavior at different spatial scales and data set resolutions area ratio operated independently of scale providing consistent results across spatial resolutions vector dispersion produced results with increasing roughness and homogenization of terrain at coarser resolutions and larger window sizes standard deviation of residual topography highlighted local features and did not detect regional relief standard deviation of elevation correctly identified breaks of slope and was good at detecting regional relief standard deviation of slope sdslope also correctly identified smooth sloping areas and breaks of slope providing the best results for geomorphological analysis standard deviation of profile curvature identified the breaks of slope although not as strongly as sdslope and it is sensitive to noise and spurious data in general sdslope offered good performance at a variety of scales while the simplicity of calculation is perhaps its single greatest benefit

planetary regolith surface analogs optimized determination of hapke parameters using multi angular spectro imaging laboratory data this work presents a method for a determination of the global set of parameters involved in hapke s model for planetary surface analogs when dealing with a set of angular conditions representative of the usual range of observation in planetary exploration for spaceborne optical instruments the present approach is founded on a genetic algorithm the whole set of hapke parameters is treated simultaneously without any a priori assumptions it limits the risk of meeting a local extreme and the stability and repeatability of the determination are improved moreover it requires less computational time than a monte carlo routine as a demonstration using multi angular measurements acquired by a new laboratory wide field multispectral imaging facility parameter values for various grain sizes and material compositions of planetary regolith surface analogs are derived and their potential wavelength dependence is studied the results coherent with the literature validate all the steps in our methodology we focus our interest in the understanding of the physical meaning of hapke s parameters in particular of the parameter of the shadowing function for macroscopic roughness it appears that the features smaller than the centimeter scale contribute predominantly to the photometric effect related to the rocky aspect of planetary soil surfaces the parameter may thus be mainly considered as an integral of the roughness properties in the submillimetric centimetric range indeed the most representative case for describing natural regolith surface lies in texture classes in the millimeter range not involving necessarily a high macroscopic roughness with large surface slopes at hundreds of meters scale these findings strengthen the case that depends on both the grain size and the material geological properties

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

global aridity during the early miocene a terrestrial paleoclimate record from the ebro basin spain abstract paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high resolution proxy for paleoclimate results from geochemical climofunctions applied to early miocene strata exposed in the ebro basin spain demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the early miocene by up to 1150 mm yr 1 in comparison to modern values placing it in a subhumid climatic regime rather than an arid semiarid regime as previously suggested by sedimentological and paleontological approaches by making comparisons with published data on paleoclimate during the early miocene this article stresses the importance of regional climatic changes in global paleoclimatic interpretation

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

miocene vegetation and climate dynamics in eastern and central paratethys southeastern europe abstract from the cretaceous to modern time the earth s climate system has changed repeatedly from a greenhouse to an icehouse the miocene appeared as the last warm episode in earth history prior to the establishment of large northern hemisphere ice sheets furthermore the miocene was characterized by both large scale marine transgressions and pronounced episodes of regressions e g opening and closure of marine corridors as well as appearance and disappearance of lakes and swamps the sea level changes and instability of the climate system strongly influenced not only marine ecosystems but also the terrestrial biota to throw new light on the miocene evolution of european ecosystems and climate dynamics we compared plant assemblages from southeastern europe palaeogeographically this area is a transitional belt between tethyan and paratethyan realms and it thus constitutes a crucial geographical position when one tries to comprehend the exchange pathways of various floristic elements appearance and evolution of steppe vegetation interaction between forest and steppe vegetation and of course the corresponding climates influencing the vegetation dynamics both macro and microfloristic plant associations were considered in our analysis large palaeofloristic and palaeocoenotic transformations occurred during the miocene the early to middle miocene flora is rich and diverse in thermophilous elements which formed polydominant mesophytic to hygromesophytic forests early miocene climate was warm and humid with mean annual temperatures mainly above 16 c and annual rainfalls over 1000 mm the middle miocene was the warmest period of the whole miocene with annual temperatures ranging from 17 c to 19 c and winter temperatures from 7 c to 12 5 c climatic changes after the miocene climatic optimum caused changes in floristic composition and vegetation structure the vegetation shows a decreasing trend in abundance of palaeotropic and thermophilous elements reduction of macrothermic elements and disappearance of evergreen laurel forests together with these changes is a corresponding increase in the role of arctotertiary species in plant communities and they became dominants in mesophytic forests the available data indicate that major vegetation changes occur in the late miocene this period is characterized by more diverse climatic conditions which were directed by global climatic changes and probably complicated by regional palaeogeographic reorganizations and tectonic processes slight cooling and some drying is recorded for the beginning of the late miocene followed by fluctuations of palaeoclimate parameters observed which display cycling change of humid dryer and warmer cooler conditions our study provides a new insights on the miocene vegetation and climate dynamics and evolution in southeastern europe

ecological dynamic equilibrium in an early miocene 21 73 ma forest ethiopia abstract miocene paleoecology of east africa has implications for human origins and understanding the vicariant legacy forests found today on either side of the east african rift fossil leaves preserved in 21 73 million year old lacustrine sediments from the mush valley ethiopia provide a unique opportunity to investigate forest composition and dominance diversity patterns at an ecological scale we classified and analyzed 2427 leaves in total from two to three quarries within each of six stratigraphic levels spanning 7 m of section we estimate each quarry census represents one to three centuries and 50 60 kyrs separate the oldest and youngest levels pollen phytolith and compound specific organic geochemical data were also collected in a detailed stratigraphic context to provide independent integrated lines of evidence for landscape evolution and lacustrine paleoecology of the system that preserves the macrofossils forty nine leaf morphotypes were documented and legume 1 dominated all samples nonmetric multidimensional scaling jaccard similarity analyses and diversity and evenness indices demonstrate a degree of change comparable to community ecology dynamics likely illustrating a dynamic stable state in forest vegetation surrounding the lake taxonomic assessments of leaves phytoliths and pollen are consistent with a closed canopy forest with limited palm diversity a high abundance of des a ring triterpenoid molecules diagenetic products formed by microbial degradation under anoxic conditions and very negative 13c values

carbon isotope fractionation during decomposition of organic matter in soils and paleosols implications for paleoecological interpretations of paleosols abstract stable isotope ratios reported as 13c of organic carbon preserved in paleosols have potential utility as a valuable paleoecological indicator if the isotopic composition of paleobiomass is preserved in the paleosol organic carbon without fractionation however soil organic matter is in a constant state of decomposition in an open system and frequently decomposes further during alteration after burial of the paleosol during this decomposition kinetic fractionation of 13c 12c in an open system results in concentration of 13c in the residual organic matter preserved in the soil and paleosol this paper summarizes studies of modern soils which show that this 13c enrichment follows a rayleigh distillation process whereby the 13c 12c ratio is a function of the natural logarithm of the fraction of remaining soil organic carbon leaving soil organic carbon 13c enriched by up to 6 with respect to the original biomass if the fraction of original biomass carbon remaining during these decomposition processes deviates significantly from 1 the soil organic carbon can be 13c enriched by several per mil and thus not a good paleoecological indicator of the 13c value of the original biomass therefore effective paleoecological studies of 13c preserved in paleosol organic carbon must therefore demonstrate that the measured concentration of organic carbon in the paleosol is near its maximum concentration during soil formation or that the paleosol organic matter does not include the 13c enriched products of microbial decomposition suggestions are made for interpreting the effects of carbon isotope fractionation of organic matter and for materials and methods most useful for paleoecological studies from bulk paleosol organic carbon

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

estimating sub pixel surface roughness using remotely sensed stereoscopic data abstract surface roughness at the scale of 10 2 10 1 m can be estimated using the ratio rr between surface reflected solar radiance measured from two view angles at nearly the same time as rr is primarily a function of the difference between effective sub pixel shading observed from the two view angles the divergence from unity rr values which are expected for smooth lambertian surfaces they have no shadows was found to be proportional to roughness at the 10 2 10 1 m scale of geomorphic desert surfaces ground based rr values at 1 m resolution as well as remotely acquired rr values at 4 15 and 50 m resolutions were compared with observed surface roughness in two hyperarid test sites located in death valley california usa and the southern negev desert in israel the aster advanced spaceborne thermal emission and reflection radiometer 15 m stereoscopic capability is identified as an effective resource for obtaining relative sub pixel surface roughness estimates that are largely independent of surface composition and relatively insensitive to atmospheric effects

surface roughness and geological mapping at subhectometer scale from the high resolution stereo camera onboard mars express the quantitative measurement of surface roughness of planetary surfaces at all scales provides insights into geological processes a characterization of roughness variations at the scale of a few tens of meters is proposed that complements the analysis of local topographic data of the martian surface at kilometer scale as achieved from the mars orbiter laser altimeter mola data and at the subcentimeter scale using photometric properties derived from multi angular observations relying on a gabor filtering process an algorithm developed in the context of image classification for the purpose of texture analysis has been adapted to handle data from the high resolution stereo camera hrsc the derivation of roughness within a wavelength range of tens of meters combined with analyses at even longer wavelengths gives an original view of the martian surface the potential of this approach is evaluated for different examples for which the geological processes are identified and the geological units are mapped and characterized in terms of roughness

geology and distribution of impact craters on venus what are they telling us magellan has revealed an ensemble of impact craters on venus that is unique in many important ways we have compiled a data base describing the 842 craters on 89 of venus surface mapped through orbit 2578 the craters range in diameter from 1 5 to 280 km we have studied the distribution size density morphology geology and associated surface properties of these craters both in the aggregate and for some craters in greater detail we find that 1 the spatial distribution of craters is highly uniform 2 the size density distribution of large craters diameters 35 km is similar to the young crater populations on other terrestrial planets but at a much lower density that indicates an average age of only about 0 5 ga based on the estimated population of venus crossing asteroids 3 unlike the case on other planets the density of small craters diameters 35 km declines rapidly with decreasing diameters because of atmospheric filtering 4 the spectrum of crater modification differs greatly from that on other planets 62 of all craters are pristine only 4 are embayed by lavas and the remainder are affected by tectonism but none are severely and progressively depleted as extrapolated from the size density distribution of larger craters 5 large craters have a progression of morphologies generally similar to those on other planets but small craters are typically irregular or multiple rather than bowl shaped 6 diffuse radar bright or dark features surround some craters and 367 similar diffuse splotches with no central crater are observed and 7 other crater features unique to venus include radar bright or dark parabolic arcs opening westward and extensive outflows originating in crater ejecta the first three of these observations are entirely unexpected we interpret them as indicating that the planet s cratering record was erased by a global resurfacing event or events the latest ending about 0 5 ga after which volcanic activity declined but did not cease entirely since the last resurfacing event a maximum of 10 of the planet has been resurfaced and only about 4 of the craters have been obliterated convective thermal evolution models support this interpretation arkani hamed and toksoz 1984 observations 3 7 confirm quantitatively the expectation that the dense atmosphere of venus has strongly affected the production of craters large impactors have been relatively unaffected intermediate sized ones have been fragmented and have produced overlapping or multiple craters a narrow size range has produced shock induced splotches but no craters and the smallest bodies have had no observable effect on the surface the number of craters eliminated by the atmospheric filter is enormous about 98 of the craters between 2 and 35 km in diameter that magellan might have observed on a hypothetical airless venus unique crater related features such as parabolas and outflow deposits demonstrate the roles of venus high atmospheric density and temperature in modifying the crater formation process finally heavily fractured craters and lava embayed craters are found to have higher than average densities along the major fracture belts and rifted uplands connecting aphrodite terra and atla beta themis and phoebe regiones these craters thus provide physical evidence for recent volcanic and tectonic activity at a low level

statistics of mars topography from the mars orbiter laser altimeter slopes correlations and physical models data obtained recently by the mars orbiter laser altimeter mola were used to study the statistical properties of the topography and slopes on mars we find that the hemispheric dichotomy manifested as an elevation difference can be described by long baseline tilts but in places is expressed as steeper slopes the bimodal hypsometry of elevations on mars becomes unimodal when referenced to the center of figure contrary to the earth for which the bimodality is retained however ruling out a model in which the elevation difference is expressed in a narrow equatorial topographic step cannot be done by the hypsometry alone mars slope distribution is longer tailed than those of earth and venus indicating a lower efficiency of planation processes relative to relief building tectonics and volcanics we define and compute global maps of statistical estimators including the interquartile scale rms and median slope and characteristic decorrelation length of the surface a correspondence between these parameters and geologic units on mars is inferred surface smoothness is distinctive in the vast northern hemisphere plains where slopes are typically 0 5 amazonis planitia exhibits a variation in topography of 1 m over 35 km baselines the region of hematite mineralization in sinus meridiani is also smooth with median slopes lower than 0 4 but does not form a closed basin the shallower long wavelength portion of the lowlands topographic power spectrum relative to the highlands can be accounted for by a simple model of sedimentation such as might be expected at an ocean s floor the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths among their application these mola derived roughness measurements can help characterize sites for landing missions

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

taphonomical aspects of silica phytoliths in the loess sediments of the argentinean pampas abstract although pampean loess and pedostratigraphy processes in the pampas have been widely studied phytoliths observed in these sediments have been only mentioned without further quantitative or qualitative studies the present work is a first step towards an understanding of the environmental significance of loess phytolith datasets and their validity for palaeoenvironmental reconstructions and to comprehend the environmental conditions of loess formation the research focused on the taphonomy of loess phytoliths investigating the loess morphological and sedimentological characteristics variability in the qualitative and quantitative assemblage composition the phytolith frequency and were also phytolith extraction techniques the results highlight that the phytolith pool of loess deposits still retains information about the past vegetation and phytolith analysis from these deposits can be a useful exercise to further comprehend past climatic and environmental conditions under which loess palaeosol sequences formed

the spectra of the topography of the earth venus and mars the global topography of the terrestrial bodies has been more or less determined from past planetary missions and from ground measurements and the behaviour of their spectra studied over the low frequencies only except the earth s case we here perform new spherical harmonic analysis of the topography of the earth venus and mars by using existing sometimes recently made available data sets to the highest possible degree and order so as to establish the decay of these spectra over a larger range of frequencies than before study the limit of validity of the used data sets and provide some new inputs to further geophysical analysis

surface roughness radar backscatter and visible and near infrared reflectance in death valley california the vast alluvial fans of death valley california provide an ideal environment to examine the remote sensing measurement of geologic surfaces one of the objectives of the shuttle imaging radar c sir c program in death valley is detection of the variation in surface microtopography with age of the surface we present results of extensive field measurements of surface roughness together with an analysis of the effects of the surface microtopography on radar backscatter and visible and near infrared vnir reflectance as measured by aircraft and satellite sensors this subject is addressed in both the forward and inverse sense surface simulation and forward modeling are used to determine expected roughness effects while a method of inverse analysis that uses finite impulse response fir filters is used to assess the potential for inversion of multifrequency polarimetric synthetic aperture radar sar and multispectral vnir imagery for surface roughness the interaction of radar and vnir radiation with the death valley surfaces is complicated simple roughness parameters such as rms height and slope and offset of surface power spectra do not represent a sufficiently complete description of surface roughness to predict the radar or vnir signature uniquely multiple scattering which is controlled to a large extent by aspects of the phase of the surface fourier transform also exerts a controlling influence on the observed signal the phase aspect of surface roughness has not been considered in existing roughness characterization our inversions demonstrate retrieval of roughness parameters with almost equal success from both sar data and landsat thematic mapper tm data and indicate much potential for joint sar vnir data analysis the solutions are not however very stable and include effects of additional parameters such as intermediate scale topography and vegetation cover which masquerade as roughness variation in designing a stable inversion of more general applicability the multifrequency and polarimetric aspect of sir c data is important nevertheless high resolution roughness recovery will probably require hierarchical analysis of radar and optical images and also sar acquisition at multiple look angles and directions

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

convergent cenozoic co2 history reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus it is time for systematic testing of the proxies against measurements and against each other

spectrophotometric properties of materials observed by pancam on the mars exploration rovers 2 opportunity 1 the panoramic camera pancam on the mars exploration rover opportunity acquired visible near infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in meridiani planum nearly 25 000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles 0 150 at eagle crater in the surrounding plains in endurance crater and in the plains between endurance and erebus craters through sol 492 corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission disparity maps created from pancam stereo images allowed inclusion of local facet orientation estimates outcrop rocks overall exhibited the highest single scattering albedos 0 9 at 753 nm and most spherule rich soils exhibited the lowest 0 6 at 753 nm macroscopic roughness among outcrop rocks varied but was typically larger than spherule rich soils data sets with sufficient phase angle coverage resulting in well constrained hapke parameters suggested that models using single term and two term henyey greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule rich soils rover tracks and other compressed soils exhibited forward scattering while outcrop rocks were intermediate in their scattering behaviors some phase functions exhibited wavelength dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission

gusev photometric variability as seen from orbit by hrsc mars express minnaert and two term phase function hapke models are used to describe the photometric properties of the martian surface using hrsc high resolution stereo camera multi angular observations acquired along the ongoing mars express mission these observations can be pieced together to derive integrated phase functions over a wide range of phase angles the photometric diversity at 675 nm as seen from orbit of the martian surface properties across gusev is depicted with seven units three photometric units widespread across the flanks of apollinaris patera flank and the floor of gusev crater are identified as having high single scattering albedo with rather forward scattering properties low to intermediate macroscopic roughness and porous or not compacted powdered surface state as indicated by the opposition parameters another unit has the highest single scattering albedo the smoothest surface in terms of macroscopic roughness associated with an extremely forward scattering behavior the opposition parameters are consistent with the presence of transparent particles in the surface powder layer the distribution of this unit appears quite intermittent across the crater and does not seem to indicate any relationship with a given morphological structure it may correspond to sparse areas where the structure of the surface dust layer is the most preserved the most pronounced photometric changes are observed in three units associated with the low albedo features corresponding to dark wind streaks these units have a low single scattering albedo are the most backscattering surfaces across gusev have a high surface roughness and present variable surface states as shown by the opposition parameters estimates consistent with the occurrence of large grains organized in more or less packed layers clear differences are seen among these units in terms of opposition effect while one exhibits typical characteristics for the opposition effect another appears more unusual in terms of lobe width and the third suggests the occurrence of a packed compressed narrow size distribution powder surface the opposition effect thus appears to play a significant role suggesting that the surface state optical properties across gusev are strongly influenced by the porosity and packing characteristics or grain size distribution of the upper layer of the martian soil the mapping aspect of the investigation is quite useful to get a better sense of the meaning of the observed photometric variations indeed the hapke modeling suggests that surface organization surface roughness packing state is more important than the simple physical characterization of the intrinsic optical properties of the constitutive particles given the overall spatial patterns derived from the photometric analysis the variations at least for the western and central part of gusev crater are likely partly driven by the prevailing wind regimes considered to be oriented north northwest south southeast and disturbing the very upper surface layer the present photometric results agree with independent investigations based on thermal inertia reflectance spectroscopy in situ photometric and microscopic imaging and support the idea of a thin layer of fine grained dust being stripped off in the low albedo units to reveal a dark basaltic substrate comprising coarse grained materials

late oligocene early miocene paleosols of distal fluvial systems ebro basin spain abstract the study of paleosols can be a vital tool in the paleoenvironmental interpretation of continental deposits because their physical and chemical characteristics are a reflection of variations in aspects of soil formation changes in paleosol characteristics can be used to determine the architecture and nature of parent material paleosol maturity topography climate and soil forming organisms including vegetation cover on the ancient floodplain and can be utilized to recreate a palaeocatena furthermore paleosols can provide quantitative data on paleoclimate where other sources such as organic matter and pedogenic carbonate are absent late oligocene early miocene strata exposed in the ebro basin spain have been identified as proximal alluvial fan fluvial and lacustrine continental facies in parts of the distal fluvial system pedogenically altered channel and overbank deposits interfinger with ephemeral lacustrine facies three main paleosol types developed in these sediments and have been described and compared to modern soils entisol like early successional soils inceptisol like young soils and alfisol like open woodland soils paleoenvironmental reconstructions suggest a mosaic of ecotypes with areas of open woodland composed of shrubs herbs and small trees and other plants of low stature and with each ecotype being controlled primarily by fluctuating paleohydrological conditions from field observations and geochemical analysis the climate was found to be humid continental mean annual temperature mat 10 14 c 4 c mean annual precipitation map 450 830 mm yr 1 200 mm yr 1 these results indicate that climatic conditions were wetter than the present day ebro basin mat 14 c map 320 mm yr 1 and differ from previous interpretations of an arid to semi arid environment based on sedimentological criteria alone