evaluation of kinetic uncertainty in numerical models of petroleum generation oil prone marine petroleum source rocks contain type i or type ii kerogen having rock eval pyrolysis hydrogen indices greater than 600 or 300 600 mg hydrocarbon g total organic carbon hi mg hc g toc respectively samples from 29 marine source rocks worldwide that contain mainly type ii kerogen hi 230 786 mg hc g toc were subjected to open system programmed pyrolysis to determine the activation energy distributions for petroleum generation assuming a burial heating rate of 1c m y for each measured activation energy distribution the calculated average temperature for 50 fractional conversion of the kerogen in the samples to petroleum is approximately 136 7c but the range spans about 30c 121 151c fifty two outcrop samples of thermally immature jurassic oxford clay formation were collected from five locations in the united kingdom to determine the variations of kinetic response for one source rock unit the samples contain mainly type i or type ii kerogens hi 230 774 mg hc g toc at a heating rate of 1c m y the calculated temperatures for 50 fractional conversion of the oxford clay kerogens to petroleum differ by as much as 23c 127 150c the data indicate that kerogen type as defined by hydrogen index is not systematically linked to kinetic response and that default kinetics for the thermal decomposition of type i or type ii kerogen can introduce unacceptable errors into numerical simulations furthermore custom kinetics based on one or a few samples may be inadequate to account for variations in organofacies within a source rock we propose three methods to evaluate the uncertainty contributed by kerogen kinetics to numerical simulations 1 use the average kinetic distribution for multiple samples of source rock and the standard deviation for each activation energy in that distribution 2 use source rock kinetics determined at several locations to describe different parts of the study area and 3 use a weighted average method that combines kinetics for samples from different locations in the source rock unit by giving the activation energy distribution for each sample a weight proportional to its rock eval pyrolysis s2 yield hydrocarbons generated by pyrolytic degradation of organic matter

permittivity estimation over mars by using sharad data the cerberus palus area 1 cerberus palus is a thoroughly studied region of mars characterized by evident platy textures that were interpreted either as evidence for a frozen sea close to mars equator or as being resultant of lava mud or ice flows coming from cerberus fossae through athabasca valles radargrams provided by radar sounder sharad clearly show the presence of subsurface layers in the area by exploiting the great amount of available data authors have performed an accurate quantitative analysis aimed to estimate electromagnetic properties of surface and subsurface layers in terms of permittivity and attenuation to this aim a simplified electromagnetic approach has been used but taking into account effects of scattering due to surface roughness for avoiding overestimated results this has been done by using theory of electromagnetic scattering from fractal surfaces and by estimating needed parameters from topographic data provided by mola three distinct geologic formations have been analyzed namely a part of zephyria planum the cerberus plains and the bedrock beneath the plains the retrieved electromagnetic parameters have been also modeled as a mixture of volcanic rocks with either ice or air the zephyria planum material was found to be significantly porous 50 60 with an attenuation more likely compatible with empty pores ambiguous results were obtained for the plains material being the resulting porosity high in both the cases of empty 40 50 and of ice filled 80 pores the obtained results do not allow for evidence of a frozen sea on cerberus palus area

dalton wells geology and significance of debris flow hosted dinosaur bonebeds in the cedar mountain formation lower cretaceous of eastern utah usa the lower cretaceous dalton wells dinosaur locality north of moab utah consists of a 2 m thick stacked succession of four fossil rich bonebeds with an estimated collective lateral extent of more than 4000 m2 to date 215 m2 of the bonebeds have been excavated and more than 4200 vertebrate fossil field specimens have been collected the site occurs at the base of the yellow cat member of the cedar mountain formation and lies unconformably on upper jurassic strata of the morrison formation the age of the assemblage is tentatively accepted as barremian nine dinosaur taxa are recognized making dalton wells one of the richest abundance and diversity lower cretaceous dinosaur localities in the world the bonebeds are rare examples of fossiliferous subaerial debris flow deposits at least four flows originated an undetermined distance up slope from an early cretaceous site of dinosaur bone concentration and flowed through the site carrying bones short distances toward an adjacent area of lakes ponds and wetlands host sediments most likely accumulated on the eastward dipping slopes of a backbulge in a foreland basin the overall depositional setting was alluvial lacustrine in a warm to hot and seasonally wet and dry climate the consistent expression and location of lacustrine facies in both the brushy basin member of the morrison formation and the yellow cat member of the cedar mountain formation indicate that high rates of subsidence typified the dalton wells area both before and after the j k transition and further suggest that there was some form of long term to episodic and localized influence on subsidence the depositional slope required to generate debris flows may have been established by forebulge crustal flexure but could also have been established or amplified by the high rates of subsidence that maintained the lacustrine paleoenvironments in the field area concretionary deposits in the yellow cat member at dalton wells are diagenetic and apparently resulted from groundwater precipitation likely enhanced by the presence of organics bones and lacustrine carbonates the regional and cross facies expression of calcretes in the yellow cat member combined with the rarity of pedogenic indicators confirms that they are not paleosols mineral precipitation likely occurred as groundwater flow was established in response to foreland basin development it remains unknown under what specific circumstances animals died and carcasses accumulated prior to being reworked by debris flows however the stratigraphic association of seasonally wet and dry facies throughout the yellow cat member suggests that drought induced mortality events were probably common in a seasonally wet and dry environment debris flows may have been triggered by intense rainfall or seismic events

local geoelectrical models of the martian subsurface for shallow groundwater detection using sounding radars received 15 february 2002 revised 20 july 2002 accepted 28 august 2002 published 6 march 2003 1 low frequency sounding radars should be able to probe the martian subsurface layers down to varying depths depending on the geoelectrical properties of the sounded sites we present in this work four frequency dependent geoelectrical models of the martian subsurface in the 1 20 mhz frequency band based on laboratory electromagnetic characterization of martian soil analogues those models correspond to local martian sites that we considered to be of particular interest in the search for water using mainly the ground penetrating radar gpr instrument of the netlander mission results and discussion are also valid for both sounding experiments marsis and sharad the four models of the martian subsurface are designed to represent terrains where recent fluviallike features suggest the presence of near subsurface ground ice and probably liquid water we performed measurements on volcanic and sedimentary materials that may be present on these sites under the appropriate geophysical conditions that may exist in those terrains we then simulated the backscattered radar echo arising from each site in the 2 mhz frequency band using the finite difference time domain fdtd algorithm in order to evaluate the instrument performances to probe the subsurface stratigraphy of each site our results confirm that the near subsurface rich iron oxide mineralogy controls the instrument performances in terms of penetration depth and signal to noise ratio in the 2 mhz frequency band we finally discuss the geophysical and geoelectrical sounding conditions that could lead to an ambiguous detection of shallow subsurface water on mars for the netlander gpr index terms 3210 mathematical geophysics modeling 1794 history of geophysics instruments and techniques 5144 physical properties of rocks wave attenuation 5109 physical properties of rocks magnetic and electrical properties keywords mars hydrology gpr sounding simulation fdtd

unveiling the taphonomy of elusive natural tank deposits a study case in the pleistocene of northeastern brazil abstract fossiliferous natural tanks are a singular type of sedimentary deposit restricted to northeastern brazil which usually preserves a diversified late pleistocene vertebrate fauna their fossil assemblages are taxonomically well known but their taphonomy is poorly understood this work presents a detailed taphonomic analysis of a tank deposit from jirau site ceara state northeastern brazil to improve understanding of the processes that influenced fossil deposition and preservation in natural tanks and to shed light on paleoecological and paleoenvironmental aspects related to the late pleistocene vertebrate fauna from northeastern brazil tank deposits from different localities were also compared to figure out potential taphonomic patterns among them additionally comparisons with other brazilian pleistocene deposits and other debris flow deposits bearing vertebrates were undertaken the study revealed the predominance of the megamammal eremotherium laurillardi in the deposit which we attributed to its abundance in late pleistocene biocoenosis as well as bone resistance scarcity of non mammalian vertebrates is likely related to their paucity in late pleistocene biocoenosis time averaging was evidenced by the co occurrence of different weathering petrographic and color patterns and may have affected the ontogenetic profile of the accumulation relative to the original biocoenosis analyses of weathering stages tooth and trample marks indicate wide exposition of the thanatocoenosis before burial abrasion and petrographic patterns allow reworking in the assemblage to be inferred permineralization and substitution are the fossilization processes observed taphonomy indicates that floods deposited clasts and bioclasts in the tank under an arid or semiarid climate in a debris flow regime comparison with other tank deposits revealed several similar taphonomic features and differences related to sedimentology and stratigraphy taphonomic similarities suggest rather homogeneous environmental conditions in the northeastern brazil during the late pleistocene as previously suggested by taxonomic studies comparison with other brazilian pleistocene deposits shows that tanks have more temporal fidelity than caves coastal and some fluvial deposits the jirau vertebrate accumulation was produced by the reworking and transport of skeletal elements accumulated in a nearby thanatocoenosis and is similar to other better known debris flow hosted vertebrate accumulations

response to comment on athabasca valles mars a lava draped channel system the recent geologic history of athabasca valles mars is controversial some studies report ice rich sediment in its channels whereas others find only lava data from the high resolution imaging science experiment camera now confirm that although certain features exhibit a superficial similarity to ice related landforms solidified lava coats the entire channel system

extensive valley glacier deposits in the northern mid latitudes of mars evidence for late amazonian obliquity driven climate change understanding spin orbital parameter driven climate change on mars prior to 20 ma ago requires geological evidence because numerical solutions for that period are chaotic and non unique we show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of mars 37 58 n originated through regional snow and ice accumulation and underwent glacial like flow breached upland craters and theater headed valleys reveal features typical of erosion in association with terrestrial glaciers parallel converging and chevron like lineations in potentially ice rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities together these martian deposits and erosional landforms resemble those of intermontaine glacial systems on earth particularly in their major morphology topographic shape planform and detailed surface features an inferred late amazonian age combined with predictions of climate models suggest that the obliquity of mars exceeded a mean of 458 for a sustained period during this time significant transfer of ice occurred from icerich regions e g the poles to mid latitudes causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers d 2005 elsevier b v all rights reserved

the morphologies of volcanic landforms at central elysium planitia evidence for recent and fluid lavas on mars abstract this paper focuses on physical parameters flow rates and rheological properties of lava flows observed in the central elysium planitia cep region of mars the flows are modeled as newtonian fluids using the jeffrey s equation and the concept of graetz number or alternatively as bingham fluids in addition to these approaches a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields providing independent quantifications of rheological variations between the shields this analysis indicates that of the five volcanoes studied two are partially buried by lava postdating their formation a result which has been confirmed independently in one case by high resolution images our observations reveal that two types of lava flows may be found in the cep region the first group is composed of large lava flows with viscosities around 2 5 10 5 pa s or yield strengths ranging from 100 to 500 pa the second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 103 pa s or yield strengths less than 200 pa when compared with other volcanic regions on mars investigated with similar approaches these latter values are at present the lowest inferred for martian lava flows several hypotheses for the formation of these lavas are discussed in the context of cep given that low viscosity can be the result of 1 high temperature 2 low crystal content 3 low si abundance of the liquid phase and or 4 the presence of dissolved volatiles two scenarios are considered in the first one it is demonstrated that low viscosity lavas of low silica content can be produced in the context proposed by schumacher and breuer schumacher s breuer d 2007 geophys res lett 34 l12202 for recent volcanism however geochemical maps derived from grs measurements do not provide support for anomalously low silica concentrations in this region in the second scenario a water rich magma is proposed although arguments in favor of a water rich mantle source below the cep are not available at the present time

ground penetrating radar sounding in mafic lava flows assessing attenuation and scattering losses in mars analog volcanic terrains we conducted low frequency 16 to 100 mhz ground penetrating radar surveys on the eroded lava flows at craters of the moon idaho usa volcanic field to evaluate the potential of future radar sounding investigations on mars to map shallow subsurface features radar sounding profiles were obtained from three locations above a lava tube across a volcanic rift and over a scoria cone results were combined with laboratory permittivity and magnetic permeability measurements of field collected samples to deconvolve the electromagnetic attenuation and scattering losses from the total losses and therefore separately quantify both effects on the radar penetration depth our results demonstrate a constrained performance for low frequency sounding radars to characterize mafic arid volcanic terrains that contain a significant amount of ferro oxides 14 mainly in the form of olivine and magnetite penetration depths of 35 m were achieved at a frequency of 100 mhz and depths of 80 m were achieved at 16 mhz with an effective dynamic range of 60 db results indicate that for frequencies below 100 mhz the electromagnetic attenuation dominated the signal losses while above this frequency threshold the volume scattering dominated the losses over our frequency range the observed electromagnetic attenuation and penetration depths were strongly dependent on the magnetic losses ground porosities and degree of heterogeneity rather than the sounding frequency in light of these results we suggest average attenuation and scattering losses measured in terms of db m and discuss the expected penetration depth for the mars orbital radar sounding instruments sharad and marsis in mafic volcanic terrains

mars radar mapping strong backscatter from the elysium basin and outflow channel abstract radar reflectivity maps of mars obtained at arecibo in 1990 using a modified delay doppler technique have revealed strong depolarized echoes coming from the elysium flood basin and outflow channel as well as from elysium mons this result is consistent with recent studies which show that much of the basin channel floor is covered with lava flows

taphonomy and preservation of a monospecific titanothere assemblage from the washakie formation late eocene southern wyoming an ecological accident in the fossil record abstract more than twenty partial skeletons all cf mesatirhinus sp were discovered in overbank deposits associated with sandstone channels within the adobe town member of the washakie formation washakie basin southwest wyoming taphonomic and sedimentologic data indicate a mass mortality event with reduced post mortem transport of the carcasses such a mass death assemblage of a large mammal taxon is a rare occurrence for the paleogene record accordingly position and orientation of all the bones were recorded to make possible an accurate detailed map of the deposit the remains principally include disarticulated skeletons of both sexes from juveniles to old adult some axial portions and limbs remained articulated others suggest partial articulation the collected remains were scattered in loose associations within an area of about 7 5 9 m recent erosion sheetwash has destroyed an unknown extent of the original mass burial to the east and south of the excavation but the 68 oriented bonebearing blocks collected represent about 50 of the exposed site the skeletal remains occurred within a single unit of poorly sorted but generally upward fining quartz grit with a basal mudflake conglomerate the bones are not abraded but have suffered from severe compaction damage and recent freeze thaw action the sediment represents a mass flow accumulation deposited during the waning stages of a flash flood the large number of individuals of a single taxon suggests that part of a herd of titanotheres was killed in a single mass mortality event the cause of death is not known but it is likely that the accumulation represents a small fraction of a large herd that was crossing a flooded river the carcasses drifted downstream to be left as a carcass jam on the flood plain as the floodwaters withdrew it follows that the assemblage represents a close approach to a single taxon slice from a terrestrial biocoenosis and allows interpretations to be made about the autecology social behavior age composition and community structure of titanotheres decomposition of the integument and other tissues of partially buried carcasses may have been a factor contributing to the pockety nature of the sediment

dielectric properties of asteroid vesta s surface as constrained by dawn vir observations abstract earth and orbital based radar observations of asteroids provide a unique opportunity to characterize surface roughness and the dielectric properties of their surfaces as well as potentially explore some of their shallow subsurface physical properties if the dielectric and topographic properties of asteroid s surfaces are defined one can constrain their surface textural characteristics as well as potential subsurface volatile enrichment using the observed radar backscatter to achieve this objective we establish the first dielectric model of asteroid vesta for the case of a dry volatile poor regolith employing an analogy to the dielectric properties of lunar soil and adjusted for the surface densities and temperatures deduced from dawn s visible and infrared mapping spectrometer vir our model suggests that the real part of the dielectric constant at the surface of vesta is relatively constant ranging from 2 3 to 2 5 from the night to day side of vesta while the loss tangent shows slight variation as a function of diurnal temperature ranging from 6 10 3 to 8 10 3 we estimate the surface porosity to be 55 in the upper meter of the regolith as derived from vir observations this is 12 higher than previous estimation of porosity derived from previous earth based x and s band radar observation we suggest that the radar backscattering properties of asteroid vesta will be mainly driven by the changes in surface roughness rather than potential dielectric variations in the upper regolith in the x and s band

fine grained debris flows and extraordinary vertebrate burials in the late cretaceous of madagascar vertebrate fossils are remarkably abundant and exceptionally well preserved within the upper cretaceous maevarano formation of northwestern madagascar the vast majority of these fossils including all of the currently known bone beds are entombed within deposits of fine grained cohesive debris flows these deposits are typically massive and are characterized by very poor sorting and a significant montmorillonite dominated silt clay mud fraction ranging from 17 to 46 by weight deposition is attributed to recurrent exceptional rainfall events that prompted erosion and flooded ancient channel belts with sediment laden flows these extraordinary burial events shielded vertebrate remains from destructive surface processes and also afforded protection for soft tissues taphonomic attributes of associated bone concentrations suggest that debris flows had limited transport potential and generally entombed subaerially exposed bone assemblages the remarkable and recurrent association of bone beds and debris flow deposits likely reflects marked seasonality in this late cretaceous terrestrial ecosystem with prolonged dry spells prompting mortality and subsequent rains setting debris flows in motion

age relationship of basaltic and andesitic surface compositions on mars analysis of high resolution tes observations of the northern hemisphere 1 previous mars global surveyor thermal emission spectrometer tes results have identified two principal surface compositions on mars basaltic surfaces are found primarily in the southern highlands while andesitic surfaces are found in the northern lowlands and in smaller concentrations distributed throughout the southern highlands in 1 pixel per degree composition maps the exact boundary between the basaltic and andesitic compositions is obscured by large amounts of equatorial surface dust in this work high resolution tes surface spectral data are used to identify and characterize isolated regions of basalt within the equatorial dust regions and northern lowlands generally between 20 s 60 n 0 360 w in an effort to better understand the nature of the boundary between the two compositions the purpose of refining this boundary is to more accurately determine the relationship of the compositional dichotomy with global surface morphology and derived crustal thickness results show that the basaltic surface composition is closely associated with the ancient cratered terrain morphology but is not well correlated with crustal thickness the northern extent of the tes basalt composition is also established with four exceptions there are no significant concentrations 30 surface cover of basalt greater than 400 km2 in area within the northern plains three are located within or adjacent to knobby terrain which has been suggested to be erosional remnants of the cratered highlands the fourth exception is in milankovic crater and may represent a local basalt flow or basaltic material excavated during crater formation results from this work suggest that there is a stratigraphic relationship between the basaltic and andesitic surface compositions with younger andesitic materials overlying older basaltic materials throughout the equatorial and northern plains regions

neotaphonomic measures of carnivore serial predation at ngamo pan as an analog for interpreting open air faunal assemblages abstract here i present a neotaphonomic account of natural bone accumulations that have resulted from carnivore serial predation at ngamo pan a vast complex of seasonal water holes located in hwange national park zimbabwe reconstructing the taphonomic histories of faunal assemblages from open air archaeological sites is burdened with a host of interpretive complications and this study is offered as a referential means for evaluating instances where stone tools and bone accumulations are associated in apparent archaeological contexts while the presence of stone tools implies some involvement on the part of humans open air sites near water would also have served as prime locations for serial predation by large carnivores to ambush prey a situation that over time can mimic archaeological bone accumulations the taphonomic and zooarchaeological signatures of carnivore serial predation at ngamo pan show marked similarities with the open air faunal accumulation from kalkbank a late pleistocene site in limpopo province south africa located along the margins of a relict pan many potential archaeological sites within the interior of southern africa dating to the middle stone age are known from open air settings near permanent or ephemeral bodies of water and the ability to decipher between hominin and non hominin carnivore involvement with bone accumulations is paramount in determining the hunting and scavenging behaviors of our early ancestors as much of our understanding of hominin subsistence during the middle stone age is drawn from coastal cave locations this study is intended to encourage a broadening of our perspective on the taphonomic histories of faunal accumulations dating to the middle stone age by incorporating supplementary evidence provided by these open air sites

surface modification on bone trampling versus butchery abstract previous researchers have reported difficulties in distinguishing between surface marks on bone formed by sedimentary abrasion and those inflicted while butchering trampling by large ungulates and humans has been credited with producing pseudocut marks natural alterations to the bone that mimic cultural ones the purposes of this research are 1 to re examine trampling as a taphonomic process and 2 to suggest criteria useful for distinguishing sedimentary abrasion including trampling from butchery macroscopic and microscopic comparison of experimentally trampled bones and those which have had soft tissue removed with a flint tool demonstrate significant differences between the surface modifications produced by the two 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

evidence from the mars express high resolution stereo camera for a frozen sea close to mars equator it is thought that the cerberus fossae fissures on mars were the source of both lava and water floods two to ten million years ago evidence for the resulting lava plains has been identified in eastern elysium but seas and lakes from these fissures and previous water flooding events were presumed to have evaporated and sublimed away here we present high resolution stereo camera images from the european space agency mars express spacecraft that indicate that such lakes may still exist we infer that the evidence is consistent with a frozen body of water with surface pack ice around 5 degrees north latitude and 150 degrees east longitude in southern elysium the frozen lake measures about 800 x 900 km in lateral extent and may be up to 45 metres deep similar in size and depth to the north sea from crater counts we determined its age to be 5 2 million years old if our interpretation is confirmed this is a place that might preserve evidence of primitive life if it has ever developed on mars

organic matter variation within upper and lower bakken shales of the williston basin by extracting kerogen pyrogram information abstract activation energy distribution from kerogen kinetics study contains some integral characteristics of the host source rock thermal history over geological time scales extracting relevant information from pyrogram is critical for reconstruction of source rock maturation and hydrocarbon generation histories in this study in order to improve understanding of the bakken shale source rock we present a new quantitative kinetic model by inversion of rock eval pyrograms of the bakken formation in williston basin a group of core samples from both upper and lower members of the bakken formation were collected for estimating transformation ratio tr and pyrolysis analysis and an inversion method with different kinetic statistic parameters was designed and conducted using the source rock tmax hydrogen index covariation combined with different burial histories the analysis of rock eval results on williston basin samples from both canada and us sides demonstrate basin wide organic matter characteristics of upper and lower bakken and identify variation of hydrocarbon generation histories the upper and lower bakken shales have different kerogen type characteristics based on activation energy distributions derived from tmax hi pair relationship which suggest variance of the preserved algal materials for upper and lower bakken the modeling results by the thermal history analysis with the rock eval dataset indicate a higher remanent generable kerogen in lower bakken shale and the thermal maturity results will be valuable for integrated assessment of the hydrocarbon systems of williston basin accurately

reconstructing habitats in central amazonia using megafauna sedimentology radiocarbon and isotope analyses abstract a paleomegafauna site from central amazonia with exceptional preservation of mastodons and ground sloths allows for the first time a precise age control based on 14 c analysis which together with sedimentological and 13 c isotope data provided the basis to discuss habitat evolution within the context of climate change during the past 15 000 yr the fossil bearing deposits trapped within a depression in the paleozoic basement record three episodes of sedimentation formed on floodplains with an intermediate unit recording a catastrophic deposition through debris flows probably favored during fast floodings the integrated approach presented herein supports a change in humidity in central amazonia through the past 15 000 yr with a shift from drier to arboreal savanna at 11 340 50 14 c yr b p and then to a dense forest like we see today at 4620 60 14 c yr b p

absorption and scattering in ground penetrating radar analysis of the bishop tuff 1 ground penetrating radar gpr signals are attenuated by both absorption and scattering we performed low frequency 100 mhz gpr surveys at the volcanic tableland of the bishop california tuff to evaluate the factors that control gpr depth of investigation and to develop insight into the capabilities of such radars for mars the subsurface reflection character was very different for two different commercial systems used together they revealed both internal welding contacts in the tuff and an abundance of discrete scatterers attenuation coefficients were computed from profiles that showed distributed scattering the semilogarithmic signal decay is directly analogous to seismic coda the absorption intrinsic loss was determined to be 1 db m from low frequency vertical electric soundings the residual attenuation that is the attenuation in the absence of absorption is attributed to scattering scattering attenuation of 1 db m at 25 50 mhz corresponds to mean free paths as short as 4 m a fraction of the two way propagation distances of 20 40 m therefore the bishop tuff is formally a strong scatterer to gpr the mean free path is also comparable to the subsurface radar wavelength in this case maximizing scattering loss the scatterers themselves likely originate as welding heterogeneities contrasts in dielectric constant due to density differences may be supplemented by moisture variations on mars scattering is likely to contribute significant losses to gpr signals in all but the most uniform materials and unfrozen thin films of water in the lower cryosphere could influence both absorption and scattering

pleistocene debris flow deposition of the hippopotamus bearing collecurti bonebed macerata central italy taphonomic and paleoenvironmental analysis abstract an integrated taphonomic sedimentological study provides insight into the origin preservation biases and paleobiological significance of the latest early earliest middle pleistocene bonebed of collecurti near colfiorito macerata central italy which represents an important benchmark in the european biochronological scale sedimentological evidence indicates that the bonebed is hosted in a debris flow deposit which was emplaced in a shallow lacustrine setting geologic and geomorphic controls on sedimentation in the intermontane colfiorito basin provided an ideal setting for the development of cohesive mass flows due to high relief and poorly integrated catchments along the basin margin and the abundance of detrital fines yielded by mesozoic sedimentary rocks of the local basement the fossil assemblage includes 496 bones with a minimum of 24 individuals representing 9 species and 8 genera dominated by hippopotamus antiquus the hippopotamus remains include partially articulated carcass parts as well as closely associated elements few disarticulated elements which are bones that can be more easily transported hydraulically were involved in pre debris flow winnowing and sorting and then entrained by the debris flows in nearby uplands transported a short distance down into a shallow pond or lake margin where the flow buried hippopotamus carcasses that had accumulated in the pond lake the hippopotamus carcasses were in an advanced state of decomposition when the debris flow entrained them their bones show no evidence of weathering trampling scavenging sorting or transportation prior to debris flow reworking which indicates that the animals were probably lying on the bottom of the pond where they lived or were already partially buried in mud previous palynological investigations have shown that the strata of interest at collecurti were deposited during a climatic trend toward ever increasing cooler conditions the low richness of the fauna confirms long exposure to harsh climatic and environmental conditions two are the plausible causes of the death of the collecurti animals i e severe cold and or drought taphonomic attributes rule out drought indicating that the assemblage accumulated in a short time as the result of a mass mortality event possibly due to a cold snap there are no other reported examples of quaternary debris flow hosted bonebeds in europe probably because this agent of taphonomic accumulation is rarely investigated in high energy paleogeomorphic settings it is likely that more such sedimentary events took place in the area and that similar fossil sites await to be discovered

role of material properties in the cratering record of young platy ridged lava on mars 1 platy ridged surfaces in the elysium planitia region of mars exhibit different crater densities on rafted plates and polygonally patterned areas between them rather than being indicative of different ages these differences provide insight into the variable strength of different types of lava surface the sizes of small craters and the resulting size frequency distribution sfd depend on the material strength of target surfaces brecciated lava surfaces are likely to have higher crater densities than coherent lava

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

esr dating of pleistocene mammal teeth and its implications for the biostratigraphy and geological evolution of the coastal plain rio grande do sul southern brazil abstract the fossiliferous deposits in the coastal plain of the rio grande do sul state southern brazil have been known since the late xix century however the biostratigraphic and chronostratigraphic context is still poorly understood the present work describes the results of electron spin resonance esr dating in eleven fossil teeth of three extinct taxa toxodon platensis stegomastodon waringi and hippidion principale collected along chui creek and nearshore continental shelf in an attempt to assess more accurately the ages of the fossils and its deposits this method is based upon the analysis of paramagnetic defects found in biominerals produced by ionizing radiation emitted by radioactive elements present in the surrounding sediment and by cosmic rays three fossils from chui creek collected from the same stratigraphic horizon exhibit ages between 42 3 ka and 34 7 ka using the combination uptake model for radioisotopes uptake while a incisor of toxodon platensis collected from a stratigraphic level below is much older fossils from the shelf have ages ranging from 7 1 10 5 ka to 18 3 ka indicating the mixing of fossils of different epochs the origin of the submarine fossiliferous deposits seems to be the result of multiple reworking and redeposition cycles by sea level changes caused by the glacial interglacial cycles during the quaternary the ages indicate that the fossiliferous outcrops at chui creek are much younger than previously thought and that the fossiliferous deposits from the continental shelf encompass ensenadan to late lujanian ages middle to late pleistocene

is the martian water table hidden from radar view 1 mars may possess a global sub surface groundwater table as an integral part of its current hydrological system however the mars advanced radar for subsurface and ionospheric sounding marsis onboard the mars express mex spacecraft has yet to make a definitive detection of such a body of liquid water in this work we quantify the conditions that would allow a detection of a deep aquifer and demonstrate that the lack of radar detection does not uniquely rule out the presence of such a body specifically if the overlying crustal material has a conductivity above 10 5 s m equivalent to a loss tanget of 0 008 a radar echo from an aquifer could be sufficiently attenuated by the intervening medium to prevent its detection by marsis as such the lack of direct detection by marsis a null result does not rule out the possibility of the water table s existence

taphonomy of jack s birthday site a diverse dinosaur bonebed from the upper cretaceous two medicine formation of montana jack s birthday site is a diverse vertebrate assemblage from the upper two medicine formation of western montana age is roughly 74 ma the site covers roughly 3000 m2 and excavations over 140 m2 a large bone sample 1600 skeletal elements allowed statistical evaluation of the preservational and compositional variation within the site evidence including sedimentary facies plant and invertebrate fossils and bone orientation and condition indicates jack s birthday site represents part of a small shallow floodplain lake lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m this variation represents a transition from lake through shoreline to marginal shoreline floodplain environments containing ten dinosaur taxa and a variety of non dinosaurs jack s birthday site provides one of the best single faunal samples of the region the vertebrate assemblage includes two taphonomic fractions the first consisting of attritional predominantly isolated and allochthonous elements represents a time averaged assemblage the other consists of associated parautochthonous remains restricted to a single horizon taxa represented by associated remains include three iguanodontoids hypacrosaurus prosaurolophus and gryposaurus and the theropod troodon associated individuals of these taxa have non random distributions within the site fisher s exact test p 0 01 and observed taxonomic clustering may reflect group behavior and or event mortality the four or more troodon represent the first described multi individual troodontid occurrence the diversity and spatial complexity of the parautochthonous fraction of the birthday site assemblage is difficult to explain discussion of possible event mortality mechanisms focuses on three drought botulism and cyanobacterial toxicosis these share an ability to act over an ecologically significant period of time affect a variety of species and concentrate mortality along water sources aspects that may have been important in generating the birthday site assemblage evidence at the site favors drought or perhaps a drought botulism hypothesis however taxonomic clusters could represent completely separate events with a variety of causes

mantled and exhumed terrains in terra meridiani mars 1 hematite bearing deposits in the terra meridiani region of mars constitute the top stratum of a partially eroded layered complex that covers dissected noachian aged cratered terrain the hematite unit consists of dark plains and dunes covering a bright substrate this substrate is fully exposed beyond the borders of the hematite bearing deposit and consists of polygonal ground separated by ridges or valleys together with layered deposits that have been eroded into a variety of landforms the complex is partially covered by a regional scale aeolian mantle that thickens toward the north the hematite bearing stratum exhibits low albedoes pulse widths and intermediate thermal inertias whereas the underlying unit exhibits high values of these parameters both units have spectral emissivity signatures similar to those for the low albedo cratered terrain to the south with the addition of hematite for the top stratum the complex is interpreted to consist of extensive plains forming lava flows and tephra deposits emplaced during an extensional regime and at least partially buried by an aeolian mantle aeolian stripping of the mantle exposed much of the complex and differentially eroded the deposits to produce the landforms existent today exploration of the hematite bearing deposits by the 2003 mars exploration rover opportunity will allow testing of the hypotheses presented since this stratum has been locally reworked into dunes that only partially cover the underlying brighter portion of the complex in particular the rover based measurements will allow us to test the extent to which the unusual remote sensing properties of the units indicate aqueous alteration

time averaging taphonomy and their impact on paleocommunity reconstruction death assemblages in texas bays the death assemblages in upper copano bay and upper laguna madre texas were compared with the living communities as sampled over a two year period in order to determine how taphonomy and time averaging affect paleocommunity reconstruction the living and death assemblages were compared using taxonomic composition numerical abundance diversity biomass and trophic and habitat proportions taxonomic composition particularly adult taxonomic composition and the biomass of the death assemblage more accurately reflect the characteristics of the living community than do numerical abundance and other community attributes based upon numerical abundance such as diversity taxonomic composition and biomass are less modified by taphonomy and time averaging because they are temporally more persistent characteristics of the community community and paleocommunity attributes are not equivalent because the paleocommunity is described using time averaged data ecological theory must be supplanted by paleoecological theory that takes into account this temporal component

classifying vertebrate assemblages preserved in quaternary tank deposits implications for vertebrate taphonomy and paleoecology abstract paleoecological interpretations require detailed taphonomic analyses which can reveal how fossil accumulations are related to the original site of life and death of organisms in other words only a taphonomic approach can unveil the quality of a fossil concentration and its potential for paleoecology a frequent issue in vertebrate taphonomy and paleoecology is the definition of autochthony parautochthony and allochthony these terms are widely employed to translate the spatial quality of a fossil assemblage however its application in terrestrial vertebrate accumulations especially in natural tank ones is quite confused this work proposes a form of classification of fossil vertebrate accumulations of natural tanks in relation to their proximity to the original place of death of the biocoenoses the terms autochthonous parautochthonous and allochthonous originally defined based on the analysis of marine shelly faunas are reinterpreted in attempt to clarify their application to vertebrate assemblages preserved in natural tank deposits this classification can also be applied to other trap assemblages such as fissures sinkholes and caves

bakken madison petroleum systems in the canadian williston basin part 3 geochemical evidence for significant bakken derived oils in madison group reservoirs there have been two different definitions of the upper devonian mississippian bakken madison petroleum systems in the canadian williston basin early studies proposed the bakken shales as the source for oils in both the bakken formation and madison group reservoirs more recent studies suggested two separate sources for these oils thus the bakken oils were interpreted to be derived from the bakken formation shales and the madison group oils from a carbonate source within the madison group the present study utilized quantitative results of molecular markers across gasoline range light hydrocarbons saturated and aromatic hydrocarbon fractions in 122 oil samples to re evaluate the oil oil and oil source relationships the steroid and hopanoid parameters collected in this study have confirmed the diagnostic features for end member bakken and lodgepole sources whereas a range of other molecular markers revealed compositional continuums occurring between the two oil families the recognition of more extensive mixing of bakken derived oils in madison group reservoirs along a sw ne trending fault fracture zone in southeastern saskatchewan indicates focused migration pathways for bakken oils and thus upward resource potentials the results also suggest caution with the use of conventional biomarker data in oil oil and oil source correlation when the different sources concerned contain biomarkers in drastically different concentrations

vertebrate preservation in fluvial channels abstract two taphonomic modes for attritional vertebrate assemblages in channels are proposed based on the sedimentary context of the vertebrate remains and taphonomic features of the bones themselves the channel lag mode includes bones that are buried with coarse lithologies near the bases of active channels the channel fill mode occurs in fine grained to mixed fills of abandoned channels the extreme for a channel lag assemblage would be a cluster of allochthonous abraded unidentifiable fragments and the extreme for a channel fill assemblage would be a cluster of autochthonous unbraded complete skeletons between these extremes there is a broad spectrum of possible taphonomic histories for bones in channels but distinct channel lag vs channel fill modes can be recognized in fluvial deposits in different tectonic and climatic settings throughout the phanerozoic physical and biological processes that affect the different modes produce different samples of vertebrate paleocommunities with bones in the channel lag mode representing transported remains from a variety of habitats whereas channel fill assemblages are more autochthonous and habitat specific channel facies channel pattern and alluvial architecture are used to develop hypotheses concerning how the taphonomic modes relate to different scales of fluvial processes fluvial systems with numerous abandoned channels provide more sites for preservation of relatively complete fossil vertebrates in channel fills while systems that continually rework sediments by lateral migration preserve more vertebrate remains as channel lags large scale physical controls on channel pattern and fluvial architecture probably have had significant effects on the quality and quantity of the vertebrate record throughout the history of land vertebrates taphonomic modes provide a basis for comparing faunas with similar preservational histories throughout the geologic record and they can help to minimize biases in important paleobiological parameters such as diversity estimates and the timing of appearance and extinction events

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

cerberus fossae elysium mars a source for lava and water cerberus fossae a long fracture system in the southeastern part of elysium has acted as a conduit for the release of both lava and water onto the surface the southeastern portion of the fracture system localized volcanic vents having varying morphology in addition low shields occur elsewhere on the cerberus plains three locations where the release of water has occurred have been identified along the northwest athabasca and grjota vallis and southeast rahway vallis portions of the fossae water was released both catastrophically and noncatastrophically from these locations a fluvial system that extends more than 2500 km has formed beginning at the lower flank of the elysium rise across the cerberus plains and out through marte vallis into amazonis planitia the timing of the events is late amazonian

u series dating and taphonomy of quaternary vertebrates from brazilian caves abstract the geochronology and taphonomy of internationally important fossil bearing cave deposits were studied both in the semi arid northern bahia area and the subtropical southeastern lagoa santa area of brazil taphonomic analysis suggests that the processes responsible for bone accumulation in the brazilian caves vary between sites and taphonomic bias can therefore be significant in causing differences in faunal composition in the toca da boa vista caves the presence of single articulated skeletons and the entrance related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation a process that biases the assemblage to smaller species and takes place over extended time periods in nearby toca dos ossos cave transport by runoff in the cave river is predominant and biases the fauna remains to larger more robust bones and species deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage similar processes were responsible for emplacement of the copious fossil remains in the more humid lagoa santa area where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers in this area runoff under a drier climate probably accounts for the sediment emplacement inside caves in both areas the mode of emplacement implies bias in the fossil record resulting in fossil assemblages that do not mirror surface faunas limiting palaeoenvironmental reconstruction mass spectrometric u series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition these ages confirm the previous view that many of the deposits derive from the late glacial but also show that much older material some 350 000 yr is also present the habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi arid northern bahia area taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted

continual geological activity in athabasca valles mars 1 comprehensive studies of the stratigraphic relationships in the athabasca valles region have been performed on imagery from the viking orbiters and the mars orbiter camera narrow and wide angle on board mars global surveyor as well as by making use of topographic data derived from the mars global surveyor laser altimeter mola instrument from superimposed crater frequencies we have derived absolute surface ages by applying the hartmann and neukum 2001 cratering chronology model the main channel has been incised into the cerberus volcanic plains with an average plains age of 3 4 ga the main fluvial or glacial erosion processes ended 2 6 ga ago this result shows that the age of the valley system itself is older than commonly believed one major possible fluvial event occurred in the topographically lower volcanic plains southwest of the valley 1 6 ga ago the valley itself was covered by lava episodically and ending 0 9 ga and in case of a few younger episodes 30 ma ago the surface texture south of the valley system suggests a younger possibly fluvial overprinting of the volcanic texture 30 ma ago the latest volcanic activity is dated to about 3 ma ago with the latter ages we have been able not only to confirm earlier age estimates by berman and hartmann 2002 but also to show that the valley system itself has undergone over a period of two billion years active geological cycles which were dominated by volcanic processes at the end

sounding the subsurface of athabasca valles using marsis radar data exploring the volcanic and fluvial hypotheses for the origin of the rafted plate terrain 1 to test the volcanic and fluvial hypotheses for the origin of the rafted plate terrain observed in the vicinity of athabasca valles 5 n 150 e central elysium planitia we investigated the subsurface radar echo from the mars advanced radar for subsurface and ionosphere sounding marsis 5 mhz band data over this area the backscattered signal losses were compared to finite difference time domain fdtd simulations of those arising from three hypothetical geoelectrical subsurface models which differed in their assumed composition percentage basalt versus ice and assumed mode of origin fluvial discharge frozen sea mudflow and low viscosity lavas the dielectric values used in these models are derived from laboratory measurements of mars analog materials under mars like conditions fdtd simulations suggest that if the near surface environment is ice rich it will result in an average loss rate of 0 053 db m for massive ice having less than 1 of suspended particulates and 0 065 db m for a mudflow consisting of a 50 50 mixture of ice and basaltic dust whereas the losses associated with a lava flow model increase to 0 19 db m in comparison the actual signal losses experienced by marsis within this region were on the order of 0 18 db m within the first 160 m beneath the surface this suggests that propagation characteristics of athabasca s near subsurface are more consistent with a volcanic rather than a fluvial or mudflow origin of the rafted plate terrain although limitations on radar sounding depth in this region cannot rule out the possibility of more deeply buried massive ice deposits

comment on athabasca valles mars a lava draped channel system jaeger et al reports 21 september 2007 p 1709 presented images of the athabasca valles channel system on mars and asserted that the observed deposits are composed of thin fluid lavas however all the features they described are secondary and postdate the surface by many millions of years as documented by structural relationships with small young impact craters

long bone fragmentation and interpretation of faunal assemblages approaches to comparative analysis abstract fragmentation of archaeological faunal assemblages has served as the basis for inferring a wide range of human behaviours however relationships between long bone breakage and past behaviours have often been expressed in terms of a direct equivalence between bone breakage and intensity of processing that is the greater the fragmentation the more intense the processing more refined interpretations based on bone breakage require a development of techniques to examine variability within the archaeological record data from western north american archaeological sites and several recent alaskan collections are used as the basis for documentation of assemblage variability in terms of 1 frequencies of complete bones 2 percentage difference values of proximal and distal articular ends 3 length of shaft attached to articular ends and 4 use of ratios of articular ends to shaft splinters and long bone shaft fragments in the development of minimum number of elements counts

radar evidence for ice in lobate debris aprons in the mid northern latitudes of mars 1 subsurface radar sounding data indicate that lobate debris aprons found in deuteronilus mensae in the mid northern latitudes of mars are composed predominantly of water ice the position in time delay and the relatively low amount of signal loss of the apparent basal reflectors below the debris aprons indicate that aprons contain only a minor component of lithic material the current presence of large ice masses at these latitudes has important implications for the climate evolution of mars and for future targets for in situ exploration

late devonian and early mississippian bakken and exshaw black shale source rocks western canada sedimentary basin a sequence stratigraphic interpretation the late devonian and early mississippian bakken and exshaw formations are a continuum of regionally correlated organic rich up to 35 total organic carbon black shale source rocks covering much of the western canada sedimentary basin the bakken formation is composed of 1 a black mudstone lower member 2 a gray mudstone sandstone middle member and 3 a black mudstone upper member the exshaw formation beneath the alberta plains and in exposures in the foothills and front ranges of the rocky mountains is composed of 1 a lower black shale member and 2 an upper siltstone member the basal black shale unit of the lower mississippian banff formation overlying the exshaw formation is a second organic rich interval these black shales are regionally significant hydrocarbon source rocks and local reservoirs the middle bakken member is a locally important reservoir rock with substantial economic potential the bakken and exshaw formations and the basal banff black shale are divisible into three systems tracts 1 a transgressive systems tract 2 a lowstand systems tract and 3 a second transgressive systems tract lodgepole and banff formation carbonates overlying the bakken and exshaw formations are part of a highstand systems tract a sequence boundary occurs between the lower and middle bakken members the conformable equivalent of this sequence boundary is within the exshaw black shale member variations in the internal composition of these systems tracts imply that two depocenters 1 the williston basin and 2 the prophet trough and the western margin of the north american craton were affected differently by relative sea level rise and fall during bakken and exshaw deposition because of differences in water depth and sediment accommodation spatial and temporal changes in black shale and gray mudstone sandstone as highlighted by this sequence stratigraphic interpretation may have significant impacts on source rock potential and hydrocarbon reservoir size location and quality

taphonomy of debris flow hosted dinosaur bonebeds at dalton wells utah lower cretaceous cedar mountain formation usa abstract a taphonomic study of the lower cretaceous dalton wells dw dinosaur bonebeds near moab utah provides insight into the origins preservational biases and paleobiological significance of one of the richest and most diverse early cretaceous dinosaur sites known the bonebeds occur in a stacked succession of debris flows at the base of the yellow cat member of the cedar mountain formation which was deposited in a seasonally dry alluvial lacustrine setting although only 5 of the locality has been collected more than 4200 bones were recovered representing an assemblage overwhelmingly dominated by dinosaurs with a minimum of 67 individuals that represent at least eight genera the assemblage also includes eight elements from four non dinosaurian reptiles the dinosaur fauna is sauropod dominated mni minimum number of individuals 41 a basal macronarian mni 15 venenosaurus mni 3 a camarasaurid mni 2 and a large number mni 21 of generically unassigned sauropod elements other dinosaurs include the theropods utahraptor mni 9 nedcolbertia mni 2 a possible ornithomimid mni 2 plus a large iguanodontid mni 4 and the ankylosaurid gastonia mni 9 patterns of skeletal articulation and clustering ontogenetic representation and bone surface modification indicate that the assemblage accumulated and was exposed for more than a year as the result one or more multiple mass mortality events likely droughts that culled large numbers of subadults from the biocoenose carcasses and disarticulated elements were reworked then later transported a short distance and buried by a succession of debris flows skeletal representation data patterns of sorting breakage burrows abrasion and scratch marks provide evidence for sorting trampling and scavenging prior to debris flow reworking pre debris flow sorting is attributed to earlier hydraulic winnowing of easily transported elements the intensity and thoroughness of breakage involving 97 of the elements suggest highly focused high load impacts compatible with trampling by sauropods and iguanodontids lightly abraded and vertically displaced elements indicate episodes of trampling in soft mud trampling occurred before and after debris flow transport theropod tooth marks are uncommon but bone scavenging by osteophagous insects was common and severe resulting in substantial damage to articular surfaces comparisons of dw and other debris flow hosted bonebeds indicate that there are few consistent patterns among fossil assemblage and bone modification data however there are numerous similarities in the geological and spatial taphonomy datasets from these sites resulting from the similar physico hydraulic conditions under which elements were transported reworked and buried geologically and taphonomically dalton wells is similar to the blagoveshchensk monodominant hadrosaur bonebed in the udurchukan formation of eastern russia which also is interpreted as a debris flow hyperconcentrated flow deposit dalton wells also shares geologic and taphonomic characteristics with four bonebeds southeast of the town of green river utah and all occur at the base of the yellow cat member the uniform stratigraphic occurrences of the dalton wells blagoveshchensk and the green river sites resting on an unconformity and their shared sedimentologic and taphonomic features indicate that these sites originated in response to similar tectonic depositional and biostratinomic factors

electron spin resonance dating of the late quaternary megafauna fossils from baixa grande bahia brazil abstract electron spin resonance esr spectroscopy was applied to date megafauna fossil teeth of stegomastodon waringi and toxodontinae two teeth found in baixa grande bahia brazil the co 2 signal with spectroscopic features g 2 0018 and g 1 9973 used for esr dating was detected in all fossil enamel the additive method was employed to construct the dose response curve and to calculate the equivalent dose d e neutron activation analysis of enamel dentine and soil where the samples were buried was used to determine the main radioisotopes concentration these data were used in the conversion of d e into age using the rosy esr dating software the results of age obtained were 50 10 ka for s waringi and 43 8 ka and 9 2 ka for toxodontinae teeth although late quaternary fossils from the extinct south american megafauna are relatively common in brazilian s northeast region few geochronological studies were conducted thus dating samples found in this region will allow a better time and space understanding of that fauna

spatial variation of bakken or lodgepole oils in the canadian williston basin there are two opposing schools of thought that infer either the bakken formation or the lodgepole formation as the primary source rock for the madison reservoired oils in the canadian williston basin a recent geochemical study revealed evidence indicating the existence of significant mixing of bakken and lodgepole oils in the madison reservoirs to investigate the geographic distribution of the oil compositions we employed a multivariate statistical method to extract source and maturity specific geochemical signatures from a geochemical data set for spatial analysis oil mixing appears to be geographically dependent and restricted by a northeast southwest striking zone torquay rocanville trend in southeast saskatchewan thus fracture or fault systems are inferred to have provided high permeability zones allowing bakken derived oil to migrate upward across the lodgepole formation the areas without significant fault or fracture systems favor lateral oil migration along porous beds restricting bakken derived oil accumulation to pools in bakken reservoirs and lodgepole derived oils to occur primarily in overlying reservoir beds of the madison group

radiocarbon dating and stable isotopes analyses of caiman latirostris daudin 1801 crocodylia alligatoridae from the late pleistocene of northeastern brazil with comments on spatial distribution of the species abstract caiman latirostris is a crocodilian reptile widely distributed in south america the fossil records for this species are limited in the continent and radiocarbon dating plus isotope analysis has not been performed to the existing records which prevent accurate paleoecological reconstructions thus the present study aimed to record the occurrence of a fossil of c latirostris in sergipe state northeastern brazil providing the first data of radiocarbon dating and stable isotopes 13 c and 18 o for this species as well as maps of the potential distribution for the present time and for the last glacial maximum 21 ka our results indicate that the analyzed specimen occurred in sergipe brazil between 11 068 11 211 cal bp 9680 30 bp and fed on mixed feeder animals 13 c 3 00 possibly insects shrimp snail fish and birds it appears that its body temperature was 26 c similar to the extant crocodilian species crocodylus niloticus indicating that the species lived in the nearby rivers or in tanks ancient lagoons a map displays the current distribution while the map for 21 ka indicates a restricted distribution for this species in south america perhaps caused by the dry and cold climate in the last glacial maximum which affected the distribution of water sources for this organism

the relationship between mola northern hemisphere topography and the 6 1 mbar atmospheric pressure surface of mars to assist in targeting of landers and to enable comparison of new elevation data to previous topography models we have re determined the position of the 6 l mbar atmospheric pressure surface on mars with respect to surface topography from the mars orbiter laser altimeter mola the 6 1 mbar surface lies on average 1600 m below the geoid defined zero level of mola topography which occurs at an average pressure of 5 2 mbars at ls o o the elevation of the 6 1 mbar surface is expected to vary by 1 5 2 5 km over the martian year due to the seasonal exchange of co2 between the atmosphere and polar caps for average martian atmospheric conditions the pressure at the mars surveyor 98 landing site is expected to be 5 0 mbars during the lander science phase of the mission assuming an elevation of 1600 meters above the zero level defined by mola topography

thermal analysis of fractures at cerberus fossae mars detection of air convection in the porous debris apron abstract this study investigates the cause of high nighttime temperatures within cerberus fossae a system of fractures affecting the central elysium planitia the inner parts walls and floor of the fractures are up to 40 k warmer than the surrounding plains however several temperature profiles exhibit a local temperature minima occurring in the central part of the fractures we examined first the influence of cooling efficiency at night in the case of a strong reduction of the sky proportion induced by the fracture s geometry however the lack of correlation between temperature and sky proportion calculated from extracted mars orbiter laser altimeter mola profiles argues against this hypothesis albedo variations were considered but appear to be limited within the fractures and are generally not correlated with the temperatures variations of the thermal properties of bedrocks exposures debris aprons and sand dunes inferred from high resolution images do not either correlate with temperature variations within the fractures as none of these factors taken alone or combined can satisfactorily explain the temperature variations within and near the fracture we suggest that geothermal heat transported by air convection within the porous debris aprons may contribute to explain high temperatures at night and the local minima on the fracture floor the conditions for the occurrence of the suggested phenomenon and the consequences on the surface temperature are numerically explored a conservative geothermal gradient of 20 mw m2 was used in the simulations this value being consistent with either inferred lithosphere elastic thicknesses below the shield volcanoes of the tharsis dome or values predicted from numerical simulations of the thermal evolution of mars the model results indicate that temperature differences of 10 20 k between the central and upper parts of the fracture are explained in the case of high darcy velocities which require high permeability values 5 10 6 m2 the presence of coarse material composing the debris aprons may explain why this key criteria was met in the context of cerberus fossae

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

equatorial and midlatitude distribution of chlorine measured by mars odyssey grs 1 the 2001 mars odyssey gamma ray spectrometer grs has made the first measurement of the equatorial and midlatitude distribution of cl at the near surface of mars a mean concentration value of 0 49 wt cl has been determined from a grand sum of grs spectra collected over the planet excluding high latitude regions cl is significantly enriched within the upper few tens of centimeters of the surface relative to the martian meteorites and estimates for the bulk composition of the planet however cl is not homogeneously distributed and varies by a factor of 4 even after smoothing of data with a 10 arc radius filter several contiguous geographically large 20 regions of high and low cl concentrations are present in particular a region centered over the medusae fossae formation west of tharsis shows significantly elevated cl a large region north of syrtis major extending into utopia planitia in the northern hemisphere shows the lowest cl concentrations on the basis of hierarchical multivariate correlations cl is positively associated with h while negatively associated with si and thermal inertia we discuss four possible geologic mechanisms aeolian volcanic aqueous and hydrothermal that may have affected the cl distribution seen by grs while some of the distribution may be due to cl rich dust deposits transported by aeolian processes this mechanism does not appear to account for all of the observed variability we propose that reactions with volcanic exhalations may have been important for enriching cl in medusae fossae formation material

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

multi phase evolution of gnammas weathering pits in a holocene deglacial granite landscape minnesota usa the morphometry of 85 gnammas weathering pits from big stone county in western minnesota allows the assessment of the relative ages of the gnamma population the ratio between maximum and minimum depths is independent of the initial size of the cavity and only depends on the weathering evolution therefore the distribution of depth ratios can be used to assess the gnamma population age and the history of weathering the asymmetrical distribution of depth ratios measured in big stone county forms three distinct populations when these sets are analyzed independently the correlation r2 between maximum and minimum depths is greater than 0 95 each single population has a normal distribution of depth ratios and the average depth ratios value for each population are 1 1 60 0 05 2 2 09 0 04 and 3 2 42 0 08 the initiation of gnamma formation followed the exhumation of the granite in the region this granite was till and saprolite covered upon retreat of the ice from the last glacial maximum nearby outcrops are striated but the study site remained buried until it was exhumed by paleofloods issuing from a proglacial lake these holocene aged gnammas in western minnesota were compared with gnammas of other ages from around the world our new results are in accordance with the hypothesis that values represent the evolution of gnammas with time under temperate to cold climate dynamics phases of the formation of new gnammas may result from changes in weathering processes related to climate changes copyright 2007 john wiley sons ltd

coherent and incoherent components in near nadir radar scattering applications to radar sounding of mars 1 we examine the relative importance of coherent and incoherent echo components in near nadir radar scattering from self affine surfaces the coherent component important only for observations at small incidence angles nadir looking sounders and altimeters is a function of both surface roughness and scattering area models for the incoherent component require a minimum scattering area for validity for smaller regions the radar echo is overestimated we propose a simple criterion for the horizontal scale that defines this shift in applicable scattering model and show the range of roughness parameters for which marsis sharad and possibly jimo radar sounder measurements may be modeled using the two approaches

investigation of target property effects on crater populations in long lava flows a study in the cerberus region mars with implications for magma source identification abstract young volcanism on mars is exemplified within the cerberus region which enables examination of relatively pristine lava flow surfaces in this investigation we derived model ages within the circum cerberus channelized lavas for sites proximal medial and distal to the lava flow sources finding that these ages decrease with increasing distance from the inferred source investigating multiple possible explanations for this downstream decrease in model ages we conclude that the most likely cause is changes in the rheological properties of the lava during emplacement analogous terrestrial lava flows exhibit rheological changes along their length during emplacement supporting the hypothesis that target properties affect crater size frequency distributions csfds on extraterrestrial bodies using scaling methods we investigated how possible material property changes in the cerberus channelized lavas affected csfds to derive a single model age for each channel we arithmetically size scaled the distal and proximal crater sizes we also used pi group scaling to estimate the effect of material strength and porosity on the final csfds we infer that the athabasca grjota and marte valles lavas underwent minor moderate and major rheological changes respectively to account for the progressively larger age discrepancies along their respective flow lengths the arithmetic size scaling yields relative lava emplacement ages from oldest to youngest respectively as grjota marte and athabasca this lack of a consistent progressive directional emplacement east to west or west to east of lava model ages implies that the magma source was spatially distributed beneath the cerberus region although magma contributions from the two bordering volcanic provinces cannot be ruled out the results of this study support the findings of previous lunar and martian studies that inferred target property changes affected csfds which may have some bearing on age dating of young lava surfaces across the inner solar system

vertebrate fossil bearing paleosol units willwood formation lower eocene northwest wyoming u s a implications for taphonomy biostratigraphy and assemblage analysis abstract in the lower 300 m of the fluvial willwood formation of northwest wyoming most large concentrations of vertebrate fossils consist of disarticulated and broken skeletal remains that occur in widespread tubular thin 2 cm 1 m greenish and bluish gray mudstones that are low in percentage of free iron aluminum and manganese relatively high in percentages of organic carbon and often show evidence of clay eluviation these units lie atop sesquioxide rich sometimes clay illuviated variegated unit red yellow purple and mottled variants and are relicts of the a horizons of podzolic spodosols aquods the wide distribution of bone fragments the numerical proportions of bone elements weathering of the fragments and biogenic evidence indicate the vertebrate remains accumulated gradually as litter on the surface of the soils and became incorporated into the a horizon the bones were disarticulated broken and otherwise disturbed by the action of scavengers prior to burial occurrence of abundant vertebrate remains in discrete readily identifiable and widespread paleosol units makes these units valuable biostratigraphic markers zonules faunules evidence of geologically short term lag accumulation of the bones is important to assemblage analysis the paleosol concentrations result from attritional mortalities that more closely reflect composition of the life assemblage than do remains concentrated by fluvial transport or predators

late cretaceous cenomanian to campanian paleoenvironmental history of the eastern canadian margin of the western interior seaway bonebeds and anoxic events abstract upper cretaceous strata in the pasquia hills of the northern manitoba escarpment eastern saskatchewan canada provide a detailed paleoenvironmental and sea level record of the eastern margin of the western interior seaway sediments deposited during the cenomanian turonian greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column with bottom water anoxia recurrently reaching into the photic zone a middle cenomanian sea level lowstand event followed by transgression left a series of bonebeds within the belle fourche member of the ashville formation indicating a sedimentary environment starved of coarse siliciclastics maximum sea level resulted in the formation of limestone beds within the favel formation further favoured by reduced terrigenous sediment input compared to the western margin limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions and reducing zoo and phytoplankton diversities during final greenhorn regression eastern saskatchewan probably turned into a restricted basin severely limiting marine circulation poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the cenomanian turonian transgressive regressive cycle this was caused either by a freshwater lid stratification of boreal and tethyan derived watermasses or both to various intensities affected by changing sea level basin oxygenation during niobrara time varies between localities along the eastern margin as documented by presence absence of benthic and planktic foraminifera

transport induced abrasion of fossil reptilian teeth implications for the existence of tertiary dinosaurs in the hell creek formation montana the experimental transport induced abrasion of five fossil teeth from a crocodilian and the tyrannosaurid dinosaur albertosaurus demonstrates that enamel coated teeth are minimally affected by abrasion associated with sediment transport processes after the equivalent of 360 480 km of transport two teeth showed slight loss of weight scratches were developed on the surface of one tooth there were slight enlargements of the areas between adjacent serrations of one tooth and a pit in the exposed dentine of one tooth was abraded smooth these changes would have been difficult to recognize if the teeth had not been examined before the start of the experiment our results suggest that dinosaur teeth are abraded so slowly by transport processes that they provide equivocal evidence for limited transport and reworking

taphonomy of mammalian fossils across the blancan irvingtonian boundary palm spring formation anza borrego desert of southern california abstract a taphonomic analysis of terrestrial mammal fossils from the fish creek vallecito creek area of the salton trough in southern california is presented the analysis is the first of its kind for these biochronologically important fossils and is the first step toward future paleoecological studies of these fossils paleoecological study of the fish creek vallecito creek fossils is important because the study may reveal changes in paleocommunity parameters related to faunal change across the blancan irvingtonian boundary fossils were collected from the palm spring and uppermost imperial formations consisting of 4300 m of continuously deposited tidal flat lacustrine and fluvial sediments based on superposed faunas deposition occurred during the blancan and irvingtonian land mammal ages seventy five genera of terrestrial mammals are recorded the analysis is based mainly on 109 productive sites 10 identifiable specimens small mammals fossils most often are found in low energy fine grained fluvial sediments floodplain channel fill floodplains acted as the source area for skeletal elements found in channel lag channel fill lacustrine and tidal flat sediments so that the assemblages from these depositional environments are comparable to each other throughout the 3 3 m y history of the fish creek vallecito creek area fluvial transport and sorting of skeletal elements of from the death site is minimal as shown by the lack of hydraulic sorting lack of abrasion and presence of elements characteristic of voorhies groups i iii in any one fossil assemblage physical condition and proportions of preserved skeletal elements suggest that physical chemical and biological processes occurring prior to fluvial transport were more important in biasing assemblages than hydraulic sorting by currents the consistency of the results suggests that the assemblages departed from the biocenoesis to the same degree most fossils accumulated in sediments deposited by streams originating in the local drainage basin the probability of mixing species from different paleocommunities is negligible and only one paleocommunity existed at any one time the significant aspect of the taphonomic history of the fossil assemblages is concerned with the degree to which paleoecologic information e g structure diversity relative abundance is preserved in the paleocommunity diversity and relative abundance appear to be accurately preserved for large mammals and underestimated to some degree for small mammals the analysis concludes that robust paleoecologic data can be retrieved from the suite of assemblages

a study of low albedo deposits within amazonis planitia craters evidence for locally derived ultramafic to mafic materials 1 we studied low albedo deposits in the floors of craters within the amazonis planitia region using infrared data from mars global surveyor thermal emission spectrometer tes and mars odyssey thermal emission imaging system themis high resolution visible images from the mars orbiter camera and themis and topographic data from the mars orbiter laser altimeter these deposits are found within subdued to sharp rimmed craters that impacted into thick basaltic lava flows from olympus mons these lava flows flooded the region and were subsequently eroded by aeolian processes tes spectral modeling of the low albedo deposits reveals a mineralogy that is dominated by mafic minerals olivine pyroxene with a derived bulk chemistry that ranges from ultramafic to mafic 40 52 wt sio2 in composition these bulk compositions are comparable to some martian lithologies but represent some of the lowest silica contents identified on mars the compositional range could be produced by either primary igneous processes or subsequent alteration by aeolian processes the spatial distribution of the compositions reveals weak to absent groupings and does not distinguish between the igneous or aeolian scenarios in some craters possible local sources have been identified within the crater walls floors and interiors local sources may be present in additional craters but obscured by dust no regional sources were identified within a reasonable distance in terms of sand transport but may also be obscured by dust therefore the low albedo deposits probably resulted from aeolian erosion of local intracrater basaltic materials that were subsequently redistributed within the floors of these craters

weathering phases recorded by gnammas developed since last glaciation at serra da estrela portugal abstract the morphometrical analysis of gnammas weathering pits in granite landscapes has been used to establish the relative chronology of recent erosive surfaces and to provide the weathering history in a region to test the validity of gnammas as relative chronometer indicators and the reliability of the obtained weathering record two sites have been studied in serra da estrela portugal the first site is within the limits of the glacier that existed in these mountains during the last glaciation whereas the second site is located in an unglaciated sector of the mountains which preserves a longer record of weathering in the bedrock surface the number of gnamma weathering phases recorded in the latter site 8 is larger than those from the former 6 correlation between both measurement stations based on morphometrical criteria is excellent for the younger six weathering phases 1 to 6 consequently the parameter used for relative chronology value has been verified to be age dependent although absolute values are modulated by microclimate due to altitude variations the weathering record was essentially duplicated once the surfaces at both sites were exposed demonstrating the reliability of gnamma evolution as a post glacial environmental indicator for the region

a data driven model for studying kerogen kinetics with application examples from canadian sedimentary basins abstract source rock is an essential element in unconventional resource play evaluation while kerogen kinetics is one of the most important components in source rock evaluation traditional approach for determining oil generation kinetics is done through laboratory pyrolysis analysis by mimicking the hydrocarbon generation processes with variable accelerated heating rates thus the thermal energy required for hydrocarbon generation under geological conditions is inferred study suggests that for a given kerogen type numerical kinetic models derived from a limited number of laboratory tests may result in unacceptable errors because of under representation of variation in activation energy related to organic facies change and source rock heterogeneity as economic margin of developing an unconventional resource play can be small business success often depends on early identification of favourable area a quick and robust method for resource play evaluation is critical this study proposes a data driven statistical approach that utilizes existing rock eval toc data by fitting the measured hydrogen index and tmax to an exponential model the model is designed so that all parameters have an explicit physical meaning and the ranges of parameter values are predictable once the empirical statistical model is established hydrocarbon transformation ratio can be calculated to represent the hydrocarbon generation kinetics of the source rock the main advantage of the proposed approach is the utilization of widely available rock eval datasets so that 1 no additional specifically designed laboratory pyrolysis experiments are required 2 the uncertainty due to facies variation or source rock heterogeneity nature and poor data quality human can be quantified through the statistical analysis of a large dataset and 3 validation for temperature and geothermal rates in situ pressure and other environmental conditions is not necessary as the input data for the model are all based on naturally matured samples rock eval datasets from four well known canadian source rock intervals representing the most common kerogen types are tested and used as examples to demonstrate the application of the proposed method the examined source rocks with different kerogen types show distinct kinetic behaviours and this is consistent with models derived from laboratory tests applications also indicate that the proposed method appears to be robust and convenient for modelling kerogen kinetics from rock eval data directly

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick