gravity anomalies and segmentation at the east coast usa continental margin summary the free air gravity edge effect anomaly at rifted continental margins has generally been attributed to the transition between thick continental and thin oceanic crust while crustal thinning is a major contributor recent studies suggest that sediment loading and magmatism may significantly modify the edge effect anomaly and cause it at some margins to be highly segmented along their strike in this paper we use a combined 3 d flexural backstripping and gravity anomaly modelling technique to determine the role that sediment loading has played in controlling the segmentation of atlantic type continental margins we focus on the east coast usa since a substantial amount of high quality seismic reflection and refraction gravity and magnetic data already exists for this margin by calculating the gravity anomaly associated with rifting and sediment loading and iteratively comparing it to the observed free air anomaly we have determined the best fit elastic thickness te structure of the margin we show that 0 10 5 a integrated strength of the lithosphere these results imply that weak regions abut strong ones at the east coast usa margin te generally decreases with increase in the amounts of crustal thinning and the flexed basement curvature k suggesting it is controlled at least in part by the mechanical structure of the pre rift lithosphere and yielding due to flexural loading however there is considerable scatter suggesting other factors such as along strike changes in crustal composition irrespective we show that an isostatic anomaly that takes into account the best fit te distribution is significantly reduced in spectral power compared with one which is computed assuming only airy compensation i e te 0 km this is not to imply that rifting and sediment loading completely accounts for the anomalies along strike and across strike the east coast usa margin to the contrary significant isostatic anomaly highs and lows persist especially in inner and middle shelf regions one of the most prominent is an arcuate 670 km long high with flanking lows offshore carolina that we attribute to magmatism during the initial stages of continental break up

mechanical and geological effects of impact cratering on ida asteroids respond to impact stresses differently from either laboratory specimens or large planets gravity is typically so small that seismic disturbances of a few cm s 1can devastate unconsolidated topography yet the presence of regolith and the likelihood that many asteroids are gravitational assemblages tell us that gravity cannot generally be ignored we use numerical models for impact fracture in solids to examine the initial stage of crater formation on asteroid 243 ida up to the cessation of fracture and the establishment of the cratering flow at this stage we can infer final crater diameters but not profiles we find that a modified strength scaling applies for craters up to a few 100 m in diameter forming in rock subject to ida s gravity and that gravity controls all craters larger than 1 km bright annuli around a number of intermediate craters may be the result of low velocity surface disturbances rather than bright proximal ejecta deposits we also consider large impactors to which ida presents a curved finite target surface with irregular gravity these can excavate asymmetrical concavities stresses from large events can refocus and cause fracture far from the crater using the shape of ida as a basis for 3d hydrocode simulations we show that impact genesis of the vienna regio concavity can cause fracture in pola regio where grooves are observed in spacecraft images other simulations indicate that the formation of the 10 km crater azzurra might have reopened these fractures which may account for their fresh appearance this mechanism of groove formation requires an interior which coherently transmits elastic stress while this precludes a classic rubble pile asteroid it does allow well joined fault planes and welded blocks or pores smaller than the stress pulse

recurrent hierarchical patterns and the fractal distribution of fossil localities understanding the spatial structure of fossil localities is critical for interpreting earth system processes based on their geographic distribution coordinates of marine and terrestrial sites in the conterminous united states for 17 time bins were analyzed using point pattern statistics lacunarity analysis shows that the spatial distributions of sites are fractal for almost every studied interval indicating that clumping of localities occurs at multiple scales random hierarchical multiplicative processes provide a theoretical null model for the distribution of collecting sites consistent with their occurrence being a complex product of numerous biological geological and anthropogenic processes acting at many spatial and temporal scales mechanistic models for the formation preservation and exposure of fossil localities and other geologic entities can be tested using point pattern and related spatial statistics

testing the fossil record sampling proxies and scaling in the british triassic jurassic the quality of the fossil record varies immensely across taxa geographic regions environments and time intervals because much of this variation can be confounded when examining global patterns we present a detailed investigation of the british triassic and jurassic one of the most intensively studied pairs of systems in the world marine jurassic palaeodiversity is at least partly controlled by rock availability and accessibility the terrestrial record is patchier and effects of rock availability are overprinted by a stronger signal of sporadic preservation these results also fit a sea level driven common cause explanation as one would expect to see close correlation between rock availability and palaeodiversity in the marine realm but less so in the terrestrial formation counts and palaeodiversity do not correlate a surprising result given the number of earlier studies that have found close correlations however this study differs from most others in that formation counts and palaeodiversity metrics are derived from independent data sources and so within study redundancy is avoided the study confirms the complexity of rock fossil time series and the likelihood that the fossil record documents a complex mix of potential biological signal common cause signal and rock record and sampling bias it may be impossible to identify a useful simple sampling proxy for the fossil record that captures every bias and sampling error ironically when preservation is good sampling proxies representing rock availability such as outcrop area can be used to predict palaeodiversity but are ineffectual when the fossil record is patchy

a 56 million year rhythm in north american sedimentation during the phanerozoic abstract long term 10 myr fluctuations in climate sea level and sedimentation have been documented in the stratigraphic record but the lack of well constrained data series has made it difficult to rigorously evaluate cyclic periodic or quasi periodic changes at this scale here we utilize a new compilation of the coverage area of sedimentary rocks in north america to investigate the dominant modes orders of stratigraphic variability and to evaluate potential long period cyclic changes in sedimentation on the continent during the phanerozoic our analysis resolves two principal temporal modes of variability 1 a strongly sinusoidal mode with a periodicity of 56 myr 3 myr and 2 a longer term phanerozoic mode the m curve linked to the wilson cycle which is indistinguishable from a stochastic autoregressive process the newly identified 56 myr cycle in sedimentation delineates most of the cratonic sequences that have previously been identified qualitatively in north america but here we propose a quantitative redefinition that includes nine distinct units and two mega sequences the timing of the 56 myr beat in sedimentation is consistent with an orogenic oscillator source or an oscillatory dynamic in mantle convection and its tempo is statistically similar to a known rhythm in number of marine animal genera in the global fossil record thus the identification of a significant periodic signal in the sedimentary record of north america provides new evidence for an important tectonic and or mantle scale cyclic process that links both large scale biological evolution and physical environmental change

the fluvial geochemistry of the rivers of eastern siberia i tributaries of the lena river draining the sedimentary platform of the siberian craton abstract the response of continental weathering rates to changing climate and atmospheric pco 2 is of considerable importance both to the interpretation of the geological sedimentary record and to predictions of the effects of future anthropogenic influences while comprehensive work on the controlling mechanisms of contemporary chemical and mechanical weathering has been carried out in the tropics and to a lesser extent in the strongly perturbed northern temperate latitudes very little is known about the peri glacial environments in the subarctic and arctic thus the effects of climate essentially temperature and runoff on the rates of atmospheric co 2 consumption by weathering are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large rivers of eastern siberia the lena yana indigirka kolyma anadyr and numerous lesser streams which drain a pristine high latitude region that has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts common to western eurasia and north america the scale of the terrain sampled in terms of area is comparable to that of the continental united states or the amazon orinoco and includes a similarly diverse range of geologic and climatic environments in this paper the chemical fluxes from the western region the very large ancient and geologically stable sedimentary basin precambrian to quaternary of the siberian platform will be presented and compared to published results from analogous terrains in the tropical basins of china while the range in the chemical signatures of the various tributaries included here 60 sampled is large this mainly reflects lithology rather than the weathering environment the areal chemical fluxes are comparable to those of the chinese rivers being dominated by the dissolution of carbonates and evaporites the net consumption of atmospheric co 2 by aluminosilicate weathering is minor as it is in the tropical basins it is much smaller than in active orogenic belts in similar latitudes e g the fraser and yukon but comparable to those of the mackenzie tributaries that drain the eastern slope of the rockies lithology exerts the dominant influence in determining the weathering yield from sedimentary terrains and for a largely carbonate evaporite terrain climate does not have a direct effect

the late messinian event a worldwide tectonic revolution a review of geological and geophysical observations points towards a worldwide kinematic change at around 6 ma the synchronicity of many manifestations tectonics magmatism kinematics ecological events among others at 6 ma similar to those recognized from time to time on the geological time scale argues for a global geodynamic event that has led to many regional consequences on earth s surface in particular we propose that this global event was the main trigger for the three fold increase in sediment deposits in the world ocean over the last 5 ma but also for the onset of the messinian salinity crisis in the mediterranean area one of the most severe ecological crises in the earth s history we suggest this messinian revolution to be the last occurrence of cyclic successions of global events

construction of the cambrian and ordovician seawater 87sr 86sr curve abstract the estimated path of seawater 87 sr 86 sr during the cambrian and ordovician is based on 172 analyses the sample suite is largely from locations in oklahoma new york tennessee and texas where rocks of this age are widely exposed and well studied the oldest reliable samples examined in this study are of middle cambrian age and yield an 87 sr 86 sr near 0 70888 sw 19 the estimated ratio rises to near 0 70915 sw 8 in the lower upper cambrian the highest value during the phanerozoic and probably for all geologic time the estimated path drifts lower to near 0 70903 sw 4 at the cambrian ordovician boundary this further declines to near 0 70875 sw 32 at the end of the ibexian and reaches a value near 0 70821 sw 86 at the whiterockian mohawkian boundary the decline in the seawater 87 sr 86 sr continues into later mohawkian time to flatten abruptly near 0 70782 sw 125 this ratio is essentially constant through the latest ordovician the curve rises near to a ordovician silurian boundary value poorly constrained from our data near 0 70784 sw 123 the early paleozoic seawater curve shows the alternating dominance of continental and oceanic sources of sr continental sr dominated seawater from the beginning of the cambrian into late cambrian from that time as the cambrian transgression proceeded and radiogenic crystalline rocks were covered oceanic sr began to dominate sr from low ratio oceanic sources dominated through early mohawkian time an abrupt balance is struck between oceanic and continental sources to end the decline in the late ordovician and maintained until near the end of the ordovician the general curve shape follows the pattern suggested by proposed sealevel changes the rise and fall of seawater 87 sr 86 sr during the cambrian and ordovician characterized seawater variation during all the paleozoic

origination and extinction through the phanerozoic a new approach abstract temporal patterns of origination and extinction are essential components of many paleontological studies but it has been difficult to obtain accurate rate estimates because the observed record of first and last appearances is distorted by the incompleteness of the fossil record here i analyze observed first and last appearances of marine animal and microfossil genera in a way that explicitly takes incompleteness and its variation into consideration this approach allows estimates of true rates of origination and extinction throughout the phanerozoic substantial support is provided for the proposition that most rate peaks in the raw data are real in the sense that they do not arise as a consequence of temporal variability in the overall quality of the fossil record even though the existence of rate anomalies is supported their timing is nevertheless open to question in many cases if one assumes that rates of origination and extinction are constant through a given stratigraphic interval then

interaction of rising and sinking mantle plumes the frequency of plume formation in fully developed thermal convection is determined experimentally because the fluid has a temperature dependent viscosity the cold and hot thermal boundary layers have different thicknesses and viscosities as a result plumes are released from these layers with different frequencies there also appears to be a direct temporal interaction between the cold and hot boundary layers in particular whereas there is a single frequency for cold plume formation hot plumes form with multiple frequencies one of which is similar to the frequency of cold plumes the measurements thus suggest that cold sinking plumes may induce hot rising plumes

the influence of recent major crater impacts on the surrounding surfaces of 21 lutetia we present 3 d simulations of impacts into asteroid 21 lutetia the subject of a fly by by the european space agency s rosetta mission to comet 67p churyumov gerasimenko using a 3 d shape model of the asteroid impacts of sizes sufficient to reproduce the observed craters in lutetia s north polar crater cluster npcc as observed by the osiris experiment have been simulated using the smoothed particle hydrodynamics technique the asteroid itself has been modelled both as a homogeneous body and as a body with an iron core crater erasure in the vicinity of the npcc has been observed by osiris the results show that this erasure has most probably been caused by ejecta deposition following the impact of a 2 3 km diameter projectile impacting at a velocity of 5 km s 1 or an impact with similar energy this would produce a crater of roughly 34 km in diameter comparable to the largest and oldest member of the npcc erasure of craters via the shock associated with such an impact is shown to be less significant and does not reproduce the observed spatial distribution of erased craters or ghost craters time series of the surface velocity fields resulting from the simulated impacts are also presented it is suggested that the surface velocity field and velocity shear may play a role in the generation of lineaments our model calculations show that the velocity field lines around 50 s after impact exhibit a reasonable qualitative correlation with the orientation of lineaments observed on the entire visible surface of lutetia it is also shown that incorporation of a core of 25 30 km in diameter does not modify the velocity field evolution with time and as such the presence or otherwise of such a core cannot be inferred from lineament observations if this concept for their formation is valid

time series analysis of large igneous provinces 3500 ma to present abstract we outline an efficient integrated wavelet a spectral and a cross spectral approach for the time series analysis of geologic data here these techniques are applied to a database of 154 large igneous provinces lips in order to test for cycles trends and abrupt changes in temporal distribution since 3500 ma the average frequency of events is relatively constant and supports an overall model of semicontinuous temporal emplacement of lips however several weak cycles were obtained in the analysis those of longest duration are a 170 m yr cycle from 1600 ma to present and in the late archean a 330 m yr cycle from about 3000 to 1000 ma a cycle decreasing in length from 730 to 550 m yr over the interval 3500 ma to present and a still weaker cycle increasing from 900 to 1000 m yr over the interval 2000 ma to present additional cycles of shorter duration include a 250 m yr cycle in the late archean a 230 m yr cycle in the phanerozoic a 105 m yr cycle in the early proterozoic an

sediment cycling on continental and oceanic crust sedimentary rocks are often described as declining in quantity with increasing age due to the cumulative effects of crustal deformation and erosion one important implication of such a model is that the geological record becomes progressively less voluminous and less complete with increasing age here we show that the predictions of a model in which the destruction of sedimentary rock is the predominant process signal are borne out only among sediments deposited on oceanic crust and among sediments deposited above sea level in non marine environments most of the surviving volume of sedimentary rock 75 was deposited in and adjacent to shallow seas on continental crust and does not exhibit any steady decrease in quantity with increasing age instead shallow marine sediments exhibit large fluctuations in quantity that were driven by shifting global tectonic boundary conditions such as those that occur during the breakup and coalescence of supercontinents the accumulation of sediments on the continents has not been uniform in rate but it does record a primary signal of net growth that has many implications for the long term evolution of earth s surface environment

critical crater diameter and asteroid impact seismology if impact stress reverberation is the primary gradational process on an asteroid at global scales then the largest undegraded crater records an asteroid s seismological response the critical crater diameter dcrit is defined as the smallest crater whose formation disrupts all previous craters globally up to its size it is solved for by combining relationships for crater growth and for stress attenuation the computation for dcrit gives a simple explanation for the curious observation that small asteroids have only modest undegraded craters in comparison to their size whereas large asteroids have giant undegraded craters dcrit can even exceed the asteroid diameter in which case all craters are local and the asteroid becomes crowded with giant craters dcrit is the most recent crater to have formed on a blank slate when it is equated to the measured diameter of the largest undegraded crater on known asteroids peak particle velocities are found to attenuate with the 1 2 1 3 power of distance less attenuative than strong shocks and more characteristic of powerful seismic disturbances this is to be expected since global degradation can result from seismic cm s 1 particle velocities on small asteroids attenuation as modeled appears to be higher on asteroids known to be porous although these are also bodies for which different crater scaling rules might apply

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

use of hydrogen and carbon stable isotopes characterizing oils from the potiguar basin onshore northeastern brazil hydrogen and carbon isotopic abundances were measured in representative samples of marine evaporitic lacustrine and mixed oils from the onshore potiguar basin the isotopic data together with chemical compositions and geological information were used to investigate relationships among ddoil and d13coil and source thermal maturity biodegradation mixing and the distance of secondary migration of these oils the marine evaporitic oils are depleted in deuterium 135 to 114 and the lacustrine oils are enriched 101 to 88 values of dd for mixed oils are intermediate 113 to 104 between those of marine evaporitic and lacustrine oils showing that ddoil is a reliable tool to identify oils that differ genetically values of ddoil were not directly related to thermal maturation biodegradation or distance of the secondary migration hydrogen isotopic compositions of the oils can be related mainly to the ddwater in the paleoenvironments in which the primary producers lived therefore ddoil values can provide rough estimates of ddwater in the depositional environments of the source rocks and consequently may provide evidence about paleoclimatic conditions at the site marine evaporitic oils are enriched in 13c 26 5 to 25 7 and lacustrine oils are depleted 33 6 to 30 2 in 13c relative contributions of marine evaporitic and lacustrine sources to mixed oils thus can be calculated independently from carbon or hydrogen isotopic mixing models when these calculations are done independently the mixed oils separate into two families and a previously unrecognized component possibly associated with environments that formed during the lacustrine to marine transition is revealed the investigation thus demonstrates the superior resolving power of two element mixing systematics

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

on the relationship between macrostratigraphy and geological processes quantitative information capture and sampling robustness abstract spatial and temporal patterns in the sedimentary record are controlled by a wide range of forcing mechanisms macrostratigraphy uses the temporal ranges of gap bound rock packages compiled separately for different geographic locations to quantify these patterns the total number of gap bound packages d and the rates of package initiation and truncation p and q respectively distill depositional geometries into time series that preserve information on both the spatial extent and the temporal continuity of deposition these macrostratigraphic quantities should in principle relate quantitatively to the underlying forcing mechanisms that govern sedimentation here we use a numerical model of continental margin sedimentation to test the extent to which time varying forcing mechanisms including subsidence sediment supply and sea level change can be detected quantitatively by the application of macrostratigraphy spectral and information theoretic analyses of time series of d p and q show

macrostrat a platform for geological data integration and deep time earth crust research characterizing the lithology age and physical chemical properties of rocks and sediments in the earths upper crust is necessary to fully assess energy water and mineral resources and to address many fundamental questions in the earth sciences although a large number of geological maps regional geological syntheses and sample based measurements have been produced there is no openly available database that integrates rock record derived data while facilitating large scale quantitative characterization of the volume age and material properties of the upper crust here we describe macrostrat a relational geospatial database and supporting cyberinfrastructure that is designed to enable quantitative spatial and geochronological analyses of the entire assemblage of surface and subsurface sedimentary igneous and metamorphic rocks macrostrat now contains general comprehensive summaries of the age and properties of 33 903 lithologically and chronologically defined geological units distributed across 1 474 regions in north and south america the caribbean new zealand and the deep sea sample derived data including fossil occurrences in the paleobiology database more than 180 000 geochemical and outcrop derived measurements and more than 2 1 million bedrock geologic map units from over 170 map sources are linked to specific macrostrat units and or lithologies macrostrat has generated numerous quantitative results and its data infrastructure is being used in several independently developed mobile applications however it is necessary to expand geographic coverage and to refine age models and material properties to arrive at a more precise characterization of the upper crust globally

an assessment of the hydrogeochemistry of two wetlands located in bihar state in the subtropical climatic zone of india a total of 30 water samples and 8 sediment samples were collected and chemically analysed for major ions na k mg2 ca2 hco3 so42 cl no3 silica po43 f trace elements fe mn ni cd zn pb cu minerals and nutrients to determine the factors that control the chemistry of water in the kawar tal and kusheshwar asthan wetlands in the bihar state of india these analyses indicate that ca2 and hco3 ions are the most dominant ions in both of the wetlands it also indicates rock weathering is a major source of ions in these wetlands particularly the dissolution of carbonate minerals the hydrogeochemistry of water in kusheshwar asthan is favouring kaolinite formation and in kawar tal favouring kaolinite gibbsite formation quartz 36 clay minerals 21 and chlorite 10 are the dominant minerals in both the wetlands orthoclase 12 49 calcite 7 51 and illite 4 89 minerals are only available in kawar tal surface sediment while albite 6 29 and biotite 13 6 minerals are only available in kusheshwar asthan total carbon 3 inorganic carbon 0 9 organic carbon 2 1 total sulphur 0 0008 nitrogen 0 55 and phosphate 0 96 are available in kawar tal surface sediments while total carbon 2 38 inorganic carbon 0 55 organic carbon 1 84 total sulphur 0 001 nitrogen 0 62 and phosphate 0 64 are available in kusheshwar asthan surface sediments the study indicates wetlands are rich in nutrient for biological activities and are sufficient to support the biodiversity but few locations are influenced by anthropogenic activities which cause the increase of sulphur chloride iron and lead

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

asteroid 2867 steins shape topography and global physical properties from osiris observations the rosetta spacecraft flew by asteroid 2867 steins on 5 september 2008 allowing the onboard osiris cameras to collect the first images of an e type asteroid we implemented several three dimensional reconstruction techniques to retrieve its shape limb profiles combined with stereo control points were used to reconstruct an approximate shape model this model was refined using a stereophotoclinometry technique to accurately retrieve the topography of the hemisphere observed by osiris the unseen part of the surface was constrained by the technique of light curves inversion the global shape resembles a top with dimensions along the principal axes of inertia of 6 83 x 5 70 x 4 42 km it is conspicuously more regular than other small asteroids like 233 eros and 25143 itokawa its mean radius is r m 2 70 km and its equivalent radius radius of a sphere of equivalent volume is r v 2 63 km the north pole is oriented at ra 99 5 degrees and dec 59 5 degrees which implies a very large obliquity of 172 degrees and a retrograde rotation maps of the gravitational field and slopes were calculated for the well imaged part of the asteroid together with the shape they helped characterizing the most prominent topographic features identified at the surface of 2867 steins an equatorial ridge restricted to the extremities of the long axis a large crater having dimensions of 2100 x 1800 m in the southern hemisphere and an elongated hill in the northern hemisphere we conjecture that the equatorial ridge was formed by centrifugal acceleration as the asteroid was spun up by the yarkovsky o keefe radzievskii paddack effect c 2012 elsevier inc all rights reserved

geology of 243 ida abstract the surface of 243 ida is dominated by the effects of impacts no complex crater morphologies are observed a complete range of crater degradation states is present which also reveals optical maturation of the surface darkening and reddening of materials with increasing exposure age regions of bright material associated with the freshest craters might be ballistically emplaced deposits or the result of seismic disturbance of loosely bound surface materials diameter depth ratios for fresh craters on ida are 1 6 5 similar to gaspra results but greater than the 1 5 ratios common on other rocky bodies contributing causes include rim degradation by whole body ringing relatively thin ejecta blankets around crater rims or an extended strength gradient in near surface materials due to low gravitational self packing grooves probably represent expressions in surface debris of reactivated fractures in the deeper interior isolated positive relief features as large as 150 m are probably ejecta blocks related to large impacts evidence for the presence of debris on the surface includes resolved ejecta blocks mass wasting scars contrasts in color and albedo of fresh crater materials and albedo streaks oriented down local slopes color data indicate relatively uniform calcium abundance in pyroxenes and constant pyroxene olivine ratio a large relatively blue unit across the northern polar area is probably related to regolith processes involving ejecta from azzurra rather than representing internal compositional heterogeneity a small number of bluer brighter craters are randomly distributed across the surface unlike on gaspra where these features are concentrated along ridges this implies that debris on ida is less mobile and or consistently thicker than on gaspra estimates of the average depth of mobile materials derived from chute depths 20 60 m grooves 30 m and shallowing of the largest degraded craters 20 50 m minimum 100 m maximum suggest a thickness of potentially mobile materials of 50 m and a typical thickness for the debris layer of 50 100 m

tectonic subsidence analysis of the illinois basin tectonic subsidence curves calculated from three wells indicate that the illinois basin formed through initial fault controlled mechanical subsidence and subsequent thermal subsidence thermal subsidence involved an early stage of thermal linear 520 460 ma and subsequent thermal asymptotic subsidence 460 350 ma this thermal subsidence was in response to mantle intrusion which formed a three arm rift system a second subsidence episode of unknown origin was documented from middle mississippian through early permian time subsidence mechanisms controlled sedimentation and subsidence rate trends and also sedimentation patterns for each of the four distinct tectonic subsidence phases tectonic subsidence curves were extended across the sauk tippecanoe ordovician silurian and tippecanoe kaskaskia unconformities and fit a post rift thermal contraction model the sauk tippecanoe ordovician silurian and possibly the kaskaskia absaroka unconformities formed because rates of eustatic sea level fall exceede

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

neoproterozoic glacial origin of the great unconformity the great unconformity a profound gap in earth s stratigraphic record often evident below the base of the cambrian system has remained among the most enigmatic field observations in earth science for over a century while long associated directly or indirectly with the occurrence of the earliest complex animal fossils a conclusive explanation for the formation and global extent of the great unconformity has remained elusive here we show that the great unconformity is associated with a set of large global oxygen and hafnium isotope excursions in magmatic zircon that suggest a late neoproterozoic crustal erosion and sediment subduction event of unprecedented scale these excursions the great unconformity preservational irregularities in the terrestrial bolide impact record and the first order pattern of phanerozoic sedimentation can together be explained by spatially heterogeneous neoproterozoic glacial erosion totaling a global average of 3 5 vertical kilometers along with the subsequent thermal and isostatic consequences of this erosion for global continental freeboard

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

precipitation as meteoric sediment and scaling laws of bedrock incision assessing the sadler effect abstractalthough it has been several decades since sadler 1981 first showed that sediment accumulation rates exhibit a negative power law dependence on measurement interval i e the sadler effect only recently has a manifestation of covariance in rate with duration become more widely appreciated in degradational settings because our collective understanding of rates of deposition and erosion are widely utilized to constrain the importance of active tectonism and climate forcing in shaping the surface of our planet cognizance of the dependence of rate on duration of observation is of critical importance relations between elevation change deposition erosion and rate scaling laws have often been examined by stochastic random walk simulations but this approach is generally confounded by insufficient data on amounts of land surface change on durations of land surface change and on hiatal durations separating time intervals of change deposition or erosion rates measured over short intervals suc

hierarchical subdivision of the cenozoic era a venerable solution and a critique of current proposals abstract if tertiary and quaternary are to be formally defined and ranked then only one topology and two ranking options for the major subdivisions of the cenozoic era are consistent with the principles of hierarchical classification these are 1 for the tertiary and quaternary to be ranked as suberas with the paleogene and neogene ranked as periods of the tertiary or 2 for the tertiary and quaternary to be ranked as periods with the paleogene and neogene ranked as subperiods of the tertiary the first option would leave the period rank empty for quaternary time however so the second option is preferred here in neither case is an extension of the neogene to the present permitted if desired however early cenozoic and late cenozoic could be defined as formal unranked chrons with the latter term providing an unambiguous expression for the same concept as the extended neogene attempts to justify an extended neogene by reference to a statement arising from the 1948 international geological congress fail because they are based on a misinterpretation of that statement likewise an appeal to the alleged original meaning of the neogene fails because it is factually superficial and would also have unacceptable consequences if applied as a general principle to the rest of the time scale four arguments against a ranked tertiary and or quaternary involve the status of these names as parts of an obsolete classification the disparity in their durations an analogy between them and the unranked precambrian and their supposed ambiguity these arguments are readily refuted arguments in favor of a ranked tertiary and quaternary include the continuing widespread use of these names their practical relevance for geologic maps and their role in honoring the pioneers of stratigraphy a recent recommendation by the international commission on stratigraphy ics would decouple the beginning of the quaternary from the beginning of the pleistocene have the neogene and pliocene overlap the tertiary quaternary boundary and have the gelasian age belong to both the pliocene and the quaternary these results violate the existing guidelines of the ics this same proposal would also regard the quaternary as a subera within the neogene period the latter being extended to the present however this arrangement violates the most fundamental rule of hierarchical classification in that a unit of superior rank would be included entirely within a unit of inferior rank given these problems the international union of geological sciences iugs must reject the ics recommendation an improved version of the ics proposal with the quaternary ranked as a period and the paleogene and extended neogene ranked as suberas would still prohibit the tertiary from being ranked and would either violate simpson s rule or else require a new name for the traditional concept of the neogene because the classification of the cenozoic advocated here is strictly hierarchical violates none of the existing guidelines of the ics obeys simpson s rule requires no new names allows the tertiary quaternary paleogene and neogene to be formally ranked and has been in general use for more than a century it is to be preferred only two current options for defining the quaternary and pleistocene are valid namely to leave the beginnings of these units where they are now vrica gssp at 1 8 ma or to move both to the piacenzian gelasian boundary monte san nicola gssp at 2 6 ma the latter option is not prohibited by lyell s types of the older pliocene nor after 2008 by the existing guidelines of the ics but if enacted could jeopardize the stability of the rest of the standard global time scale

near s flyby of 253 mathilde images of a c asteroid on 27 june 1997 the near earth asteroid rendezvous near spacecraft flew within 1212 kilometers of asteroid 253 mathilde mathilde is an irregular heavily cratered body measuring 66 kilometers by 48 kilometers by 46 kilometers the asteroid s surface is dark estimated albedo between 0 035 and 0 050 and similar in color to some cm carbonaceous chondrites no albedo or color variations were detected the volume derived from the images and the mass from doppler tracking of the spacecraft yield a mean density of 1 3 0 2 grams per cubic centimeter about half that of cm chondrites indicating a porous interior structure

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

an 60 million year periodicity is common to marine 87sr 86sr fossil biodiversity and large scale sedimentation what does the periodicity reflect abstractwe find that the marine 87sr 86sr record shows a significant periodicity of m yr the 87sr 86sr record is out of phase with a 62 3 m yr periodicity previously reported in the record of marine animal diversity these periodicities are close to 58 4 m yr cycles found for the number of gap bounded sedimentary carbonate packages of north america we propose that these periodicities reflect the operation of a periodic pulse of the earth in large scale earth processes these may be linked to mantle or plate tectonic events possibly uplift which affects the earth s climate and oceans and thus the geochemistry sedimentation and biodiversity of the marine realm

the first half of tetrapod evolution sampling proxies and fossil record quality abstract the first half of tetrapod evolution witnessed substantial diversification of the clade and several major turnovers and mass extinctions in the time since their origin more than 380 myr ago to the beginning of the middle jurassic 175 myr ago tetrapods apparently diversified fitfully reaching their highest level in the middle permian and showing major diversity declines in the late moscovian early permian wordian lower wuchiapingian end permian lower anisian lower ladinian late triassic lower norian to upper rhaetian end triassic and early jurassic upper sinemurian lower pliensbachian of these diversity drops only the end permian and end triassic correspond to recognised mass extinctions and the late moscovian and early norian drops to other previously identified environmental crises the remainder could be real extinction or turnover events or partially artefacts of biased sampling there are strong correlations between formation counts and tetrapod palaeodiversity suggesting a sampling component in the raw data but the covariation is not uniform through the whole time span being poor from devonian to middle permian and better from late permian to early jurassic there is limited evidence for covariation between the tetrapod palaeodiversity time series and other putative sampling metrics such as specimen completeness numbers of publications map areas gap bounded sedimentary units rock volumes formations and fossil collections modelling by multiple correlations shows that formation count is generally the best explanatory model either on its own or combined with other sampling time series however it is not clear that formation count is independent of the palaeodiversity time series because rises and falls in both signals could reflect variations in original diversity or in preservation or in sampling

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

intercalibration of radioisotopic and astrochronologic time scales for the cenomanian turonian boundary interval western interior basin usa we develop an intercalibrated astrochronologic and radioisotopic time scale for the cenomanian turonian boundary ctb interval near the global stratotype section and point in colorado usa where orbitally influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40ar 39ar and u pb dating paired 40ar 39ar and u pb ages are determined from four bentonites that span the vascoceras diartianum to pseudaspidoceras flexuosum ammonite biozones utilizing both newly collected material and legacy sanidine samples of j obradovich comparison of the 40ar 39ar and u pb results underscores the strengths and limitations of each system and supports an astronomically calibrated fish canyon sanidine standard age of 28 201 ma the radioisotopic data and published astrochronology are employed to develop a new ctb time scale using two statistical approaches 1 a simple integration that yields a ctb age of 93 89 0 14 ma 2 total radioisotopic uncertainty and 2 a bayesian intercalibration that explicitly accounts for orbital time scale uncertainty and yields a ctb age of 93 90 0 15 ma 95 credible interval total radioisotopic and orbital time scale uncertainty both approaches firmly anchor the floating orbital time scale and the bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites with analytical uncertainties at the permil level of resolution and total uncertainties below 2 using our new results the duration between the cenomanian turonian and the cretaceous paleogene boundaries is 27 94 0 16 ma with an uncertainty of less than one half of a long eccentricity cycle

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

indirect detection of subsurface outflow from a rift valley lake abstract naivasha highest of the kenya gregory rift valley lakes has no surface outlet however unlike other rift lakes it has not become saline despite high potential evaporation rates which indicates that there must be some subsurface drainage the fate of this outflow has been the subject of speculation for many years especially during the general decline in lake water level during the 1980 s particularly to the south of the lake there are few opportunities to obtain information from direct groundwater sampling however the stable isotopic composition of fumarole steam from late quaternary volcanic centres in the area has been used to infer groundwater composition using a simple mixing model between rift flank groundwater and highly evaporated lakewater this has enabled subsurface water flow to be contoured by its lakewater content by this method outflow can still be detected some 30 km to the south of the lake stable isotope data also confirm that much of the steam used by the local olkaria geothermal power station is derived from lakewater though simple balance considerations show that steam use cannot alone be responsible for the fall in lake level observed during the 1980 s

covariation in macrostratigraphic and macroevolutionary patterns in the marine record of north america students of earth history have long recog nized the correlation between the quantity of preserved sedimentary rock and the diversity of life recorded as fossils but paleontologists have yet to determine whether this pattern refl ects a causal relationship or a unidirec tional sampling bias in fossil data imposed by preserved rock quantity distinguishing between these two alternatives has been com plicated by the fact that many of the basic patterns of paleontologic and lithologic co variation have yet to be quantifi ed rigorously here we present the fi rst analyses of the co variation between the macrostratigraphic and macroevolutionary histories of north america based on geographically and tem porally explicit co occurrences of rocks and fossils the analyses use independent quan titative summaries of the stratigraphic and fossil records by integrating the paleobiology database paleodb and macrostrat a mac rostratigraphy database for north america which allows a more direct comparison of the stratigraphic and biological histories of the continent than has heretofore been possible within the macrostrat database the rock re cord is divided into discrete packages of sedi ment that are bound by hiatuses resolvable at the stage level using per interval per pack age rates of sediment package initiation and truncation and genus fi rst and last appear ances herein regional origination and extinc tion we fia substantially stronger positive correlation between sediments and biology for extinction like parameters than we do for origination like parameters four of the largest coincident pulses of regional extinc tion and sediment truncation occur during the widely recognized end ordovician late permian end triassic and end cretaceous mass extinction intervals a further compari son of the global ranges of north american genera to north american macrostratigra phy indicates that the regional and global extinction of genera are more likely to oc cur in the same stage than are global and regional originations together these results suggest that our general understanding of biodiversity dynamics from the fossil record may not be strongly biased by the preserva tion of sediments and leaves open the pos sibility that certain large perturbations to the earth system are responsible for major changes of state in both the sedimentary and biological systems

stratigraphic distribution of marine fossils in north america the stratigraphic distribution of fossils reflects a combination of physical and biological factors although many studies have addressed the distribution of fossils at a basin scale and within sedimentary sequences spanning 10 4 10 6 yr little is known about the distribution of fossils within longer duration sedimentary successions covering broad geographic regions here we combine a north american macrostratigraphic database with fossil occurrence data from the paleobiology database to quantify the stratigraphic distribution of fossils within hiatus bound marine sedimentary rock packages that have a mean duration of 10 7 yr we find that fossil collections and marine genera are when averaged over all phanerozoic sedimentary rock packages more abundant than expected in the top 40 of package durations and less common than expected in the bottom 25 generic first and last appearance datums fads and lads in north america are not randomly distributed among fossil collections instead lads are more common than expected in the top 20 of package durations whereas fads are more uniformly distributed this result is not consistent with an unconformity related sampling bias but is indicative of greater congruence in the temporal scales over which genus extinction and regression occur than genus initiation and transgression these results support the hypothesis that macroevolution particularly genus extinction and large scale patterns of sedimentation share a common set of forcing mechanisms that are related to the formation and destruction of shallow marine habitats

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

surface expressions of structural features on eros abstract near shoemaker imaging of the asteroid eros has revealed a variety of surface forms that probably reflect underlying structures they range from global to local in scale the most prominent positive topographic feature is a long ridge rahe dorsum which extends over 18 km and has the morphology of a thrust fault two large ancient trough systems are also present grooves are ubiquitous commonly occur in suborthogonal sets and have linear or scalloped outlines the grooves on eros are similar in morphology and scale to those on other small bodies such as gaspra ida and phobos and are likely to have a similar mode of origin namely drainage of regolith into underlying fractures models that use groove dimensions as indicators of regolith thickness imply depths of up to several tens of meters many craters have been subjected to structural control resulting in squared outlines we find no evidence that specific groove sets are associated with individual impact events however evidence exists that preexisting structures have been reactivated by later impact activity the large scale of rahe dorsum and many grooves on eros s surface suggests that the asteroid is a largely coherent but fractured body

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

tectonic and depositional model of the arabian and adjoining plates during the silurian devonian during the late ordovician and early silurian the western part of the arabian peninsula was covered by polar glaciers that advanced from the south pole in african gondwana during this period nondeposition erosion or marginal marine conditions prevailed in eastern and northern arabia when the glaciers melted in the early silurian sea level rose sharply and the paleo tethys ocean transgressed the arabian and adjoining plates depositing a thick organic rich shale directly over the glaciogenic and periglacial rocks and related unconformities the post glacial sequence coarsens upward reflecting the passage of a coastline prograding northward from african and arabian gondwana to northern arabia a sea level drop in the late silurian placed the study area in a terrestrial environment however as sea level recovered in the early devonian a carbonate sequence blanketed most of the area the transgression however was interrupted by regional uplift and local orogenic movements in the middle and late devonian these movements constitute the onset of hercynian tectonism which resulted in erosion of the older sequences depositional hiatuses and regional facies changes

major episodes of geologic change correlations time structure and possible causes abstract published data sets of major geologic events of the past 250myr extinction events sea level lows continental flood basalt eruptions mountain building events abrupt changes in sea floor spreading ocean anoxic and blackshale events and the largest evaporite deposits have been synthesized with estimated errors these events show evidence for a statistically significant periodic component with an underlying periodicity formally equal to 26 6 myr and a recent maximum close to the present time the cycle may not be strictly periodic but a periodicity of 30myr is robust to probable errors in dating of the geologic events the intervals of geologic change seem to involve jumps in sea floor spreading associated with episodic continental rifting volcanism enhanced orogeny global sea level changes and fluctuations in climate the period may represent a purely internal earth pulsation but evidence of planetesimal impacts at several extinction boundaries and a possible underlying cycle of 28 36 myr in crater ages suggests that highly energetic impacts may be affecting global tectonics a cyclic increase in the flux of planetesimals might result from the passage of the solar system through the central plane of the milky way galaxy an event with a periodicity and mean phasing similar to that detected in the geologic changes

433 eros lineaments global mapping and analysis using images and laser ranging data from the near shoemaker mission we map lineaments on the surface of eros in order to investigate the relationship between surface morphology and interior structure several sets of lineations are clearly related to visible impact craters while others suggest that different parts of the asteroid may have undergone different stress histories some of these sets infer internal structure at least on a local level this structure may derive from eros parent body and suggest although largely coherent eros interior may have portions that have not undergone a common history

the rise and fall of stromatolites in shallow marine environments stromatolites are abundant in shallow marine sediments deposited before the evolution of animals but in the modern ocean they are restricted to locations where the activity of animals is limited overall decline in the abundance of stromatolites has therefore been attributed to the evolution of substrate modifying metazoans with phanerozoic stromatolite resurgences attributed to the aftermaths of mass extinctions here we use a comprehensive stratigraphic database the published literature and a machine reading system to show that the rock record normalized occurrence of stromatolites in marine environments in north america exhibits three phases an initial paleoproterozoic ca 2500 ma increase a sustained interval of dominance during the proterozoic 2500 800 ma and a late neoproterozoic 700 541 ma decline to lower mean prevalence during the phanerozoic 541 0 ma stromatolites continued to exhibit large changes in prevalence after the evolution of metazoans and they transiently achieved proterozoic like prevalence during the paleozoic the aftermaths of major mass extinctions are not well correlated with stromatolite resurgence instead stromatolite occurrence is well predicted by the prevalence of dolomite a shift in carbonate mineralogy that is sensitive to changes in water column and pore water chemistry occurring during continent scale marine transgressive regressive cycles

chemical and isotopic changes in williston basin brines during long term oil production an example from the poplar dome montana brine samples were collected from 30 conventional oil wells producing mostly from the charles formation of the madison group in the east and northwest poplar oil fields on the fort peck indian reservation montana dissolved concentrations of major ions trace metals sr isotopes and stable isotopes oxygen and hydrogen were analyzed to compare with a brine contaminant that affected groundwater northeast of the town of poplar two groups of brine compositions designated group i and group ii are identified on the basis of chemistry and 87sr 86sr ratios the solute chemistry and sr isotopic composition of group i brines are consistent with long term residency in mississippian carbonate rocks and brines similar to these contaminated the groundwater group ii brines probably resided in clastic rocks younger than the mississippian limestones before moving into the poplar dome to replenish the long term fluid extraction from the charles formation collapse of strata at the crest of the poplar dome resulting from dissolution of charles salt in the early paleogene probably developed pathways for the ingress of group ii brines from overlying clastic aquifers into the charles reservoir such changes in brine chemistry associated with long term oil production may be a widespread phenomenon in the williston basin

using quartz grain size and shape analysis to distinguish between aeolian and fluvial deposits in the dallol bosso of niger west africa size and fourier shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the dallol bosso in niger factor analysis of grain size distributions gave four sand end members that can be related to fluvial transport dynamics operating when the sediments were initially deposited the medium to fine and more angular shaped sand fractions are being reworked by wind aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape although gross shape characteristics lower harmonics of fourier series expansion indicated a common source rock for all sands the aeolian sands were well rounded whereas the fluvial sands tended to be more angular upper harmonics of fourier series

properties of craters on the achaia region of asteroid 21 lutetia we report on the physical properties of the craters of achaia region of the main belt asteroid 21 lutetia based on images obtained with the osiris instrument during the rosetta flyby that took place on 10 july 2010 images of the surface were acquired with its narrow angle camera from which digital terrain models dtm of the surface were constructed these dtms give access to the geometrical properties of the craters of the asteroid on a complex asteroid shape slopes and depth to diameter ratios d d of craters should be carefully measured taking into account the local topography to obtain a value that is physically related to the work of forces resisting to mass displacement associated with gravity and or material strength occurring in either excavation or degradation processes we present new measurements of d d and internal slopes of impact craters of the achaia region which offers optimal conditions of observations and a large population of craters we find that d d values for achaia craters differ from previous works on lutetia and are consistent with the values found on other asteroids such as 243 ida or 951 gaspra the achaia region may be divided into three units based on geomorphological analysis the mean d d values of the three units are different revealing differences in resurfacing history by impact related ejecta blanketing and seismic shaking some of these geological events may be recent compared to the age of the region since several lineaments intersect most craters of one of the three units independent evidence for ejecta blanket have been given for the unit associated with low d d values confirming the contribution of this process to crater modification moreover we suggest that displacements along faults identified as surface lineaments may have been responsible for the erasure of small craters our results are finally integrated into a chronology sequence of events explaining the present characteristics of the achaia region

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

a genetic link between konzentrat and konservat lagerstatten in the fezouata shale lower ordovician morocco abstract in the central anti atlas morocco zagora region the fezouata shale has yielded an extraordinary fossil lagerstatte documenting the initial stages of the great ordovician biodiversification event this lagerstatte contains abundant and exceptionally well preserved fossils epf exhibiting soft bodied preservation as well as hard mineralized parts of extinct organisms while soft bodied preservation in the fezouata shale is confined to a few stratigraphic intervals other fossiliferous intervals contain only shelly fossils in sandstone lenses sl placed in the context of a previously established depositional model epf are interpreted as autochthonous assemblages buried by storm deposits close to storm wave base there the current component of storms is reduced compared to proximal settings and weak oscillation is dominant resulting in the record of oscillation ripples in contrast bioclastic accumulations were generated upslope in shallower more proximal lower shoreface environments there the current component of storms was significant as suggested by the disarticulation of skeletal remains bioclastic materials are localized in sl which are lenses a few tens of centimeters in thickness and a few meters in width and length these lenses commonly display erosive bases and convex tops resulting in a lobate or a channel lobe morphology a large amount of sediment was thus rapidly deposited resulting in the rapid burial of allochthonous material across a strongly localized surface of the sea floor integrating both sedimentological and paleontological evidence intervals yielding epf are considered as konservat lagerstatten ksl in contrast with bioclastic accumulations defined as konzentrat lagerstatten kzl thus ksl assemblages are interpreted to approximate biocenoses in which organisms experienced rapid burial by distal tempestites while kzl assemblages more likely correspond to thanatocenoses locally deposited by storm back currents here a genetic link between ksl and kzl is suggested within the fezouata shale both types of lagerstatten were related to storm activity but at different depths

the tertiary and the quaternary are here to stay in 1989 and 2000 the international commission on stratigraphy ics published geologic time scales in which the term tertiary had been eliminated in the time scales published by the ics in 2004 the term quaternary was also eliminated the cenozoic shown as composed of two systems the paleogene and the neogene the neogene extending to the present was there any logical basis for these changes a review of the geologic literature since 1980 19 journals of extensive distribution and a considerable number of geologic maps time scales and stratigraphy textbooks as well as the georef clearly indicates that the tertiary and the quaternary have long been and are now in widespread use by geologists the world over and that their use has not declined at all during the last 25 yr they are very useful terms in geologic work essential for clear communication among geologists paleogene and neogene have received increasing use during the last 10 yr because they are also useful terms quaternary is probably the stratigraphic term most frequently used in the geologic literature tertiary is used as the pre quaternary part of the cenozoic by most geologists some however prefer to use paleogene and neogene instead of tertiary but it should not be a question of either tertiary or paleogene and neogene all three are needed as are cenozoic paleocene eocene oligocene miocene and pliocene to express various degrees of precision in stratigraphic assignation and dating all should be recognized as units of a standard geologic time scale geologists should retain a choice of what they think better fits their needs the preferred time scale therefore should have the cenozoic erathem comprising the tertiary and quaternary systems and the tertiary including the paleogene and neogene subsystems past attempts to eliminate the tertiary and quaternary have been ignored recent attempts will not succeed either the tertiary and the quaternary are here to stay certainly as long as geologists continue to use them as they have and continue to oppose the ill advised efforts to discard them from the geologic time scale

climate change and the selective signature of the late ordovician mass extinction selectivity patterns provide insights into the causes of ancient extinction events the late ordovician mass extinction was related to gondwanan glaciation however it is still unclear whether elevated extinction rates were attributable to record failure habitat loss or climatic cooling we examined middle ordovician early silurian north american fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the katian stage were particularly hard hit the duration of the subsequent sampling gaps had little effect on extinction risk suggesting that this extinction pulse cannot be entirely attributed to rock record failure rather it was caused in part by habitat loss extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled a macroecological trait linked to thermal tolerance a model trained on the relationship between 16 explanatory variables and extinction patterns during the early katian interval substantially underestimates the extinction of exclusively tropical taxa during the late katian interval these results indicate that glacioeustatic sea level fall and tropical ocean cooling played important roles in the first pulse of the late ordovician mass extinction in laurentia

characterizing and navigating small bodies with imaging data recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed the principal data output is an ensemble of landmark maps l maps high resolution topography albedo maps of varying resolution that tile the surface of the body because they can have a resolution comparable to the best images and can be located on a global reference frame to high accuracy l maps provide a significant improvement in discriminatory power for studies of small bodies ranging from regolith processes to interior structure these techniques are now being used to map larger bodies such as the moon and mercury l maps are combined to produce a standard global topography model gtm with about 1 57 million vectors and having a wide variety of applications they can also be combined to produce high resolution topography maps that describe local areas with much greater detail than the gtm when combined with nominal predictions from other data sources and available data from other instruments such as lidar or radar solutions for the spacecraft position and camera pointing are the most accurate available examples are drawn from studies of phobos eros and itokawa including surface characterization gravity analysis spacecraft navigation and incorporation of lidar or radar data this work has important implications for potential future missions such as deep interior and the level of navigation and science that can be achieved

marine diversity in the geological record and its relationship to surviving bedrock area lithofacies diversity and original marine shelf area biological principles suggest that recorded species diversity should increase as sampled area and habitat diversity increase however the interactions between earth system drivers of these physical quantities their representation in the preserved rock record and fossil species counts are debated we tracked marine bedrock area lithofacies diversity and echinoid species diversity through an 80 m y sea level cycle as recorded in the cretaceous of the united kingdom to test these relationships relative completeness of the rock record rises during transgression but drops rapidly at maximum flooding and continues to fall during highstand lithofacies diversity peaks during transgression but drops sharply as maximum flooding is reached whereas bedrock area peaks at maximum flooding then declines progressively through the highstand interval as a result of post cretaceous erosion both bedrock area and number of lithofacies units correlate with species diversity but species diversity is predicted best by the two combined there are no simple relationships between bedrock area and lithofacies diversity or the original area of marine sediments and range of habitats that once existed these variables are strongly shaped by stratigraphic architecture while the geological record left by a major sea level cycle accurately captures the biological evolution of local communities it is incomplete and systematically biased in its coverage of environments and communities erosional truncation of sediment packages and species ranges in the later stages of sea level cycles explains the reported asymmetric relationship between macroevolution and macrostratigraphy

large scale troughs on vesta a signature of planetary tectonics abstract images of vesta taken by the dawn spacecraft reveal large scale linear structural features on the surface of the asteroid we evaluate the morphology of the vesta structures to determine what processes caused them to form and what implications this has for the history of vesta as a planetary body the dimensions and shape of these features suggest that they are graben similar to those observed on terrestrial planets not fractures or grooves such as are found on smaller asteroids as graben their vertical displacement versus length relationship could be evaluated to describe and interpret the evolution of the component faults linear structures are commonly observed on smaller asteroids and their formation has been tied to impact events while the orientation of the large scale vesta structures does imply that their formation is related to the impact events that formed the rheasilvia and veneneia basins their size and morphology is greatly different from impact formed fractures on the smaller bodies this is consistent with new analyses that suggest that vesta is fully differentiated with a mantle and core we suggest that impact into a differentiated asteroid such as vesta could result in graben while grooves and fractures would form on undifferentiated asteroids

non biotic controls of observed diversity in the paleontologic record an example from the permo triassic karoo basin of south africa paleodiversity trends through geologic time can be affected by a number of geologic taphonomic and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record although much work has concentrated on the relationship between geologic exposure sample size and taxonomic richness i e number of taxa few studies have investigated the potential effects of dataset quality and changing taxonomy we use four different specimen level datasets of permo triassic tetrapods from the karoo basin of south africa to investigate how sample size geologic outcrop dataset quality and taxonomic revision all affect observed estimates of generic richness evenness and relative abundance our results indicate that large scale patterns of richness evenness and abundance such as the effects of the end permian mass extinction are generally robust to these potential biases across the four different datasets in contrast absolute values vary significantly as do finer scale patterns in agreement with past studies taxonomic errors revised taxonomy and new taxa have little effect on patterns of richness and evenness instead the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics despite application of sample standardization we conclude that although large specimen datasets hundreds to thousands of specimens are robust to various potential biases and can recover large scale paleobiologic trends they are still affected by many non biotic controls and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns

contrasting patterns and connections of rock and biotic diversity in the marine and non marine fossil records of north america abstract macrostratigraphy uses packages of continuous sedimentation that are bound by hiatuses of non deposition erosion or alternations between environments lithologies to characterize spatiotemporal patterns of sedimentation previous work has linked the macrostratigraphy of marine shelf environments to many different macroevolutionary patterns in the marine animal fossil record here we use an improved macrostratigraphic database for north america combined with fossil occurrence data in the paleobiology database to show that macroevolutionary and macrostratigraphic patterns are correlated more strongly in marine environments than in non marine environments we also test the hypothesis that the temporal distribution of lithological diversity measured as evenness similar to ecological evenness based on the number of lithostratigraphic units with a given lithologic type within each time interval has a relationship to genus level taxonomic diversity in both the marine and non marine realms uneven sampling of lithologies and their corresponding depositional environments can bias our perception of taxonomic diversity by causing taxa from poorly sampled environments to be underrepresented in the fossil record our results show a negative correlation between lithologic evenness and marine vertebrate generic richness less even sampling of lithologies corresponds to a higher observed taxonomic richness and no correlation with lithologic evenness and non marine diversity measures this suggests a difference in the relationship between biologic and sedimentary processes at work in the marine and non marine realms and possibly differences in the magnitude of the bias imposed by the rock record on the underlying biologic patterns

impacts of speciation and extinction measured by an evolutionary decay clock the hypothesis that destructive mass extinctions enable creative evolutionary radiations creative destruction is central to classic concepts of macroevolution1 2 however the relative impacts of extinction and radiation on the co occurrence of species have not been directly quantitatively compared across the phanerozoic eon here we apply machine learning to generate a spatial embedding multidimensional ordination of the temporal co occurrence structure of the phanerozoic fossil record covering 1 273 254 occurrences in the paleobiology database for 171 231 embedded species this facilitates the simultaneous comparison of macroevolutionary disruptions using measures independent of secular diversity trends among the 5 most significant periods of disruption we identify the big five mass extinction events2 seven additional mass extinctions two combined mass extinction radiation events and 15 mass radiations in contrast to narratives that emphasize post extinction radiations1 3 we find that the proportionally most comparable mass radiations and extinctions such as the cambrian explosion and the end permian mass extinction are typically decoupled in time refuting any direct causal relationship between them moreover in addition to extinctions4 evolutionary radiations themselves cause evolutionary decay modelled co occurrence probability and shared fraction of species between times approaching zero a concept that we describe as destructive creation a direct test of the time to over threshold macroevolutionary decay4 shared fraction of species between two times 0 1 counted by the decay clock reveals saw toothed fluctuations around a phanerozoic mean of 18 6 million years as the quaternary period began at a below average decay clock time of 11 million years modern extinctions further increase life s decay clock debt analysis of data on species co occurrence in the paleobiology database using a new machine learning algorithm reveals that mass extinctions and mass radiations are not coupled in evolutionary history

completeness of the fossil record and the validity of sampling proxies a case study from the triassic of england and wales many studies have highlighted correlations between palaeodiversity and sampling proxies these correlations have been interpreted as evidence for bias common cause or redundancy between signals here we compare a number of sampling proxies representing sedimentary rock volume rock accessibility and worker effort with palaeodiversity through the predominantly terrestrial triassic system in england and wales we find that proxies for sedimentary rock volume and accessibility do not correlate with palaeodiversity until the removal of facies related preservational and palaeoecological factors this indicates that a weak sampling signal may be present but the effects of changing palaeoenvironments are far more important at the regional scale significant correlations between worker effort and palaeodiversity are detected although this is likely to be a result of the preferential sampling of formations already known to be rich in fossils the fact that there is little evidence for sedimentary rock bias in the fossil record of the triassic of england and wales suggests that either 1 sampling bias is not a major source of error at the regional scale or 2 sampling proxies are inadequate representations of geological and human sampling bias supplementary material correlation test results and raw time series data from the study are available at www geolsoc org uk sup18567

sea level cycles during the growth of atlantic type oceans abstract first order changes in global sea level are commonly thought to be the result of short term fluctuations in oceanic spreading rate however eustatic high stands have occurred only twice in phanerozoic time and in both cases have followed supercontinent break up by a lag period of 50 100 ma therefore if pulses in spreading rate were the primary control of eustasy then for some reason rate increases would have had to have occurred with predictable periodicity with respect to major rifting events alternatively we propose that the major control on first order sea level cycles is the formation of atlantic type oceans with its attendant changes in the area age distribution of the global ocean floor and the formation of extensional passive margins our calculations indicate that both the approximate magnitude and relative timing of sea level highstands relative to supercontinent break up are predicted by this mechanism thus the importance of short term spreading rate variations in eustatic cycles becomes secondary

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

epicontinental seas versus open ocean settings the kinetics of mass extinction and origination environmental perturbations during mass extinctions were likely manifested differently in epicontinental seas than in open ocean facing habitats of comparable depth here we present a dissection of origination and extinction in epicontinental seas versus open ocean facing coastal regions in the permian through cretaceous periods an interval through which both settings are well represented in the fossil record results demonstrate that extinction rates were significantly higher in open ocean settings than in epicontinental seas during major mass extinctions but not at other times and that origination rates were significantly higher in open ocean settings for a protracted interval from the late jurassic through the late cretaceous these patterns are manifested even when other paleogeographic and environmental variables are held fixed indicating that epicontinental seas and open ocean facing coastlines carry distinct macroevolutionary signatures

tracking an upper limit of the carnian crisis and or carnian stage in the western carpathians slovakia the late triassic timescale especially the carnian norian boundary is poorly constrained mainly due to a paucity of high precision radio isotopic ages that can be related accurately to contradictions between the biostratigraphic and magnetostratigraphic correlations la icp ms dating of detrital zircons from five samples of the lunz formation the upper triassic siliciclastic sediments from the western carpathians slovakia provided a wide spectrum of ages that vary from late archaean ca 2582 ma to triassic ca 216 ma these marine delta sediments represent a typical product of the carnian crisis a major climate change and biotic turnover that occurred during the carnian stage in the tethys ocean within the carbonate shelf and intrashelf basins in the northern calcareous alps and the western carpathians the supply of clastic material in the studied lunz formation was derived from several sources especially i from the recycled variscan orogen ii from the remote east european platform and iii from the contemporaneous triassic volcanic sources syn sedimentary volcanic zircons with a concordia age of 221 2 1 6 ma calculated from 12 single analyses represent the maximum age of deposition of the lunz formation and demonstrate that the upper limit of the carnian crisis and or the carnian stage in the alpine carpathians realm is younger than the current age of the carnian norian boundary at ca 227 ma listed on the international chronostratigraphic chart international commission on stratigraphy 2016 12 edition

the structure of the asteroid 4 vesta as revealed by models of planet scale collisions three dimensional simulations of the global evolution of asteroid 4 vesta under two overlapping planet scale collisions closely reproduce its observed shape but expected large areas of olivine rich rocks and pure diogenites are not observed on the surface possibly implying that the outer 100 km is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites nasa s dawn mission to the asteroid 4 vesta revealed some unexpected surface features including a huge crater named veneneia underlying the even larger crater rheasilvia that was formed about a billion years ago the juxtaposition of these two impact basins provides an opportunity to develop an accurate model of vesta s topography martin jutzi et al report three dimensional simulations of vesta s global evolution through two successive planet scale collisions their model closely reproduces vesta s observed shape and provides a firm basis for the interpretation of the surface mineralogy and geology of vesta and by extension other small solar system bodies asteroid 4 vesta seems to be a major intact protoplanet with a surface composition similar to that of the hed howardite eucrite diogenite meteorites1 2 3 4 the southern hemisphere is dominated by a giant impact scar5 but previous impact models6 7 8 have failed to reproduce the observed topography the recent discovery that vesta s southern hemisphere is dominated by two overlapping basins9 provides an opportunity to model vesta s topography more accurately here we report three dimensional simulations of vesta s global evolution under two overlapping planet scale collisions we closely reproduce its observed shape and provide maps of impact excavation and ejecta deposition spiral patterns observed in the younger basin rheasilvia9 about one billion years old10 are attributed to coriolis forces during crater collapse surface materials exposed in the north come from a depth of about 20 kilometres according to our models whereas materials exposed inside the southern double excavation come from depths of about 60 100 kilometres if vesta began as a layered completely differentiated protoplanet then our model predicts large areas of pure diogenites and olivine rich rocks these are not seen11 12 13 possibly implying that the outer 100 kilometres or so of vesta is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites

organic geochemistry of mid continent middle and late ordovician oils ordovician oils in mohawkian and cincinnatian reservoirs of the united states mid continent retain the biochemical imprint of middle and upper ordovician oceanic life before the evolution of land plants and most vertebrates thus these oils have some geochemical features that distinguish them from younger oils these features include 1 a predominance of n c15 n c17 and n c19 alkanes in the saturated hydrocarbon fraction 2 relatively low amounts of longer chain n alkanes 3 low amounts of chlorophyll derived isoprenoids such as pristane and phytane and 4 abundant c29 sterane relative to c27 with rearranged forms diasteranes predominant over normal steranes ordovician oils also generally contain little sulfur and have a somewhat variable light stable carbon isotopic composition with dgr13csat and dgr13caro values of 28 to 31 pmil pdb but these features are typical of many marine oils the unusual chemistry of these ordovician oils supports the interpretation of reed illich and horsfield 1986 that prokaryotic organisms provided the organic matter for most ordovician oils although their claim for gloeocapsamorpha a problematic unicellular prokaryote possibly a blue green alga or an unusually large bacterium cannot be proven from oil chemistry alone knowing that indigenous mid continent ordovician oils were derived from prokaryotic organisms may aid in future exploration for these reservoirs

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

links between eccentricity forcing and the 100 000 year glacial cycle the 100 000 year glacial cycles are generally thought to be driven by the eccentricity of the earth s orbit statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100 000 year eccentricity cycle variations in the eccentricity 100 000 yr obliquity 41 000 yr and precession 23 000 yr of earth s orbit have been linked to glacial interglacial climate cycles it is generally thought that the 100 000 yr glacial cycles of the past 800 000 yr are a result of orbital eccentricity1 2 3 4 however the eccentricity cycle produces negligible 100 kyr power in seasonal or mean annual insolation although it does modulate the amplitude of the precession cycle alternatively it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle5 6 7 here i use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100 000 yr glacial cycles using cross wavelet phase analysis i show that the relative phase of eccentricity and glacial cycles has been stable since 1 2 myr ago supporting the hypothesis that 100 000 yr glacial cycles are paced8 9 10 by eccentricity4 11 however i find that the time dependent 100 000 yr power of eccentricity has been anticorrelated with that of climate since 5 myr ago with strong eccentricity forcing associated with weaker power in the 100 000 yr glacial cycle i propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing which disrupts the internal climate feedbacks that drive the 100 000 yr glacial cycle this supports the hypothesis that internally driven climate feedbacks are the source of the 100 000 yr climate variations12