buried topography of utopia mars persistence of a giant impact depression knobs partially buried craters ring fractures and some mesas permit a qualitative determination of the topography buried beneath younger northern plains materials these features are widely distributed in the utopia area but are absent in a large roughly circular region centered at about 48 degree n 240 degree w this implies the existence of a circular depression about 3 300 km in diameter buried beneath utopia planitia that is here interpreted to represent the central part of a very large impact basin the presence of buried curved massifs around part of this depression and a roughly coincident mascon lend further support present topography areal geology and paleotopography of buried surfaces all point to the persistence of this major depression for almost the entire history of mars

thermal stresses differential subsidence and flexure at oceanic fracture zones geosat geoid undulations over four pacific fracture zones have been analyzed after correcting for the isostatic thermal edge effect the amplitudes of the residuals are shown to be proportional to the age offset the shape of the residuals seems to broaden with increasing age both geoid anomalies and available ship bathymetry data suggest that slip must sometimes occur on the main fracture zone or secondary faults existing models for flexure at fracture zones cannot explain the observed anomalies a combination model accounting for slip and including flexure from thermal stresses and differential subsidence is presented our model accounts for lateral variations in flexural rigidity from brittle and ductile yielding due to both thermal and flexural stresses and explains both the amplitudes and the shape of the anomalies along each fracture zone the best fitting models have mechanical plate thicknesses that are described by the depth to the 600 700 c isotherms

pleniglacial sedimentation process reconstruction on laminated lacustrine sediments from lava dammed paleolake alf west eifel volcanic field germany abstract differentiating between regularly seasonal irregular and event based clastic sedimentation is difficult if sedimentation structures resemble and dating methods are imprecise in this study clastic light and dark laminae from lava dammed paleolake alf in the late pleistocene in the quaternary west eifel volcanic field are analyzed to clarify how they formed and if they are of annual origin and comparable to assumed periglacial varves from neighboring lake holzmaar therefore a multiproxy approach is applied combining sediment thin section analysis which focuses on composition and structure with 14c dates the results are compared to recently formed annually laminated clastic sediments of e g the high canadian arctic observed sedimentation structures reveal sediment delivery by over and interflows and deposition from suspension forming two characteristic microfacies type i graded laminae and type ii laminae with graded sublayers additionally erosional bases and event deposits indicate episodic underflows thus lamination is potentially seasonal but is significantly veiled by extreme runoff causing erosion and resuspension processes or a mixed water body preventing sediment delivery into the lake basin however sedimentation processes between watershed and lake could be reconstructed by comparing recent and paleosediment structures

how does venus lose heat the tectonics and volcanism of the terrestrial planets are controlled by the loss of heat from the planetary interior on the earth about 70 of the heat flow through the mantle is attributed to the subduction of cold lithosphere in order to understand the tectonic and volcanic processes on venus it is necessary to understand how heat is transported through its mantle in this paper three alternative end member hypotheses are considered the first is the steady state loss of heat through the mantle to the surface in analogy to the earth however without plate tectonics and subduction on venus a steady state requires either a very high plume flux or very rapid rates of lithospheric delamination the required plume flux would be equivalent to about 80 plumes with the strength of the hawaiian plume the required delamination flux implies a 50 delamination of the entire venus lithosphere every 10 m y neither appears possible so that it is concluded that venus cannot transport heat through its mantle to its surface on a steady state basis the second hypothesis is that there has been a strong upward concentration of the heat producing elements into the crust of venus the heat generated is then lost by conduction surface measurements of the concentrations of the heat producing elements place constraints on this model if everything is favorable this hypothesis might be marginally acceptable but it is considered to be highly unlikely the third hypothesis is that heat is lost by episodic global subduction events followed by long periods of surface quiescence the near random distribution of craters suggests that the last subduction event occurred about 500 ma this model implies a thick thermal lithosphere 300 km at the present time which is consistent with a variety of surface observations lava lakes on the earth are considered as analogies to plate tectonics they also exhibit episodic subduction events

a nonlinear rheology model for mid ocean ridge axis topography this paper describes a mechanical model of the mid ocean ridge axis based on a nonlinear rheology the oceanic lithosphere is modeled as a strongly temperature dependent power law material with the byerlee s friction law describing the brittle behavior of the upper oceanic lithosphere we examined two simple models a mantle only model predicted an axial rift valley 1 2 km deep and 10 15 km wide at slow half rates of 5 25 mm yr which is in fair agreement with observations however the rift valley did not completely vanish at fast spreading rates even though its width and relief became much smaller thus the mantle only model failed to explain the observed transition in axial topography with spreading rate by including a uniform thickness oceanic crust with theological properties different from the mantle our second model produced the first order variation of axial topography with spreading rate a pronounced rift valley with 1 2 km relief at slow rates a smaller relief 500 m rift valley at intermediate rates and no rift valley at fast rates there are two additional results of the nonlinear rheology model which are distinctively different from the previous uniform viscosity mantle models first horizontal velocity at the seafloor changes sharply in a very narrow zone at the ridge axis i e the stresses are concentrated in a very narrow zone for the nonlinear rheology this conclusion is remarkably independent of the boundary conditions at the seafloor second the computed width of the axial plastic failure zone decreases with spreading rate a result very different from that of a uniform viscosity model this is caused by the strong temperature dependence of the power law rheology and the fact that the temperature of the oceanic lithosphere depends greatly on the spreading rate beyond some distance from the ridge axis the brittle plate roughly the region above the 750 c isotherm deforms very little both the horizontal strain rate 11 and the maximum shear strain rate max are less than 10 17 s 1 which is in good agreement with the 10 18 s 1 average for oceanic brittle plate deformation inferred from seismic moment data within the ductile region area beneath the 750 c isotherm the strain rates are in the range of 10 14 10 16 s 1 except within a narrow band near the ridge axis where higher strain rates are located we found that the thermal structure of the oceanic lithosphere is not very sensitive to the details of the mantle flow pattern or the rheology but is very sensitive to the cooling by hydrothermal circulation near the ridge axis axial structure is also influenced by factors other than the spreading rate within the range of slow and intermediate rates our calculations show that the size of an axial rift valley decreases with an increase in either the thickness of the oceanic crust or the mantle temperature in other words a thinner crust or a cooler mantle temperature will produce a more pronounced rift valley in the vicinity of hotspots the absence of an axial rift valley even at slow spreading rates such as the reykjanes ridge can be well explained by the anomalously thicker crust and higher mantle temperatures in contrast at the australian antarctic discordance a deeper than normal section of an intermediate spreading ridge has very rough topography not present on the adjacent sections of the ridge this can be explained by our model as due to an anomalously low mantle temperature as has been suggested or perhaps also due to a thinner oceanic crust

the acheron dorsum on mars a novel interpretation of its linear depressions and a model for its evolution abstract the acheron dorsum north of olympus mons on mars is a unique 800 km long arcuate ridge apparently unrelated to other adjacent morphologies acheron dorsum is crossed by deep and wide fractures fossae here referred to also as linear depressions or lds commonly interpreted as grabens formed by local lithosphere stress in response to endogenous mantle upwelling we suggest an alternate view that the linear depressions may result from gravitational self adjustment of a loose deposit similar to the deep seated gravitational slope deformations dsgsd or sackung a kind of slow mass movement well documented on earth numerical simulations based on a finite difference numerical model devised for terrestrial dsgsds reproduce the timing and position of lds reasonably well provided that the viscosity of the viscoplastic layer is between 7 10 15 and 10 17 pa s while rock masses typically exhibit much higher values based on comparison with glacial examples we find that these viscosities could be compatible to a rock ice mixture this leads to the hypothesis that the rock underneath acheron dorsum may be highly fragmented and that ice might have been involved in its deformation our hypothesis could shed light on the puzzling stress pattern on acheron dorsum which follows approximately the ridge without requiring the presence of hypothetical small scale endogenous currents

challenges in c 14 dating towards the limit of the method inferred from anchoring a floating tree ring radiocarbon chronology to ice core records around the laschamp geomagnetic field minimum the c 14 dating method is the cornerstone for inferring age estimates for natural archives covering the last 50 000 yrs however c 14 age calibration for the last ice age relies mostly on records that only indirectly reflect the atmospheric c 14 concentrations in consequence calendar age estimates are significantly more uncertain for the period of the last ice age compared to the past 14000 yrs where tree ring based calibration records exist here we connect a c 14 tree ring chronology from kauri trees in new zealand to ice core be 10 records via the common signal in the galactic cosmic ray flux around the period of the laschamp geomagnetic field minimum ca 41 000 yrs bp synchronous changes of modelled c 14 and c 14 inferred from u th dated speleothems support the ice core chronology independently and suggest that the published ice core time scale errors are rather conservative for this period our analysis puts c 14 age determinations directly into the context of ice core climate records and it shows that the c 14 records underlying the c 14 calibration curve overestimate the atmospheric c 14 concentration by more than 200 parts per thousand consequently c 14 age calibration presently yields too old calendar age estimates by about 1200 yrs for this period c 2014 elsevier b v all rights reserved less

on the initiation of subduction estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation three environments proposed as preferential sites of incipient subduction are investigated passive continental margins transform faults fracture zones and extinct ridges none of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins the attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates this is the only tectonic force sufficient to trigger the nucleation of a new subduction zone the ubiquitous distribution of transform faults and fracture zones combined with the common proximity of these features to mature subduction complexes suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere

the loess and coversands of northern france and southern england loess and coversands are widespread on either side of the english channel in southern england loess is generally thin and discontinuous but locally reaches thickness of about 4 m in east kent coversands occur mainly in areas well north of the channel such as parts of east anglia and the southern side of the bristol channel most of the loess and coversand deposits in southern england date from the late devensian cold stage marine oxygen isotope stage mois 2 but there are also a few localised patches of older mainly mois 6 and 12 loess which are the dissected remnants of originally more extensive covers in france loess is widespread and locally very thick up to 12 m especially in northern and northeastern france in normandy and in the somme basin some long records indicate that accumulation began at the end of the lower pleistocene at about 900 ka nevertheless the main accumulations of typical calcareous loess are related to the upper weichselian and upper saalian stages mois 2 and end of mois 3 and mois 6 indeed before about 160 170 ka loess deposition was generally restricted to special sediment traps such as fluvial and marine terraces exposed to the east or northeast these older deposits are characterised by more sandy facies derived from local fluvial sources mainly by northwest to north northwest winds coversands occur locally along the coast of the mont saint michel bay and over the northern part of the seine estuary near le havre the main differences in thickness and extent of the loess deposits between southern england and northern france are linked to their location in relation to the source areas channel and north sea to ice sheets and to the main wind directions northwest to north northwest in france and western england but northeast in eastern england copyright 2003 john wiley sons ltd

an application of hierarchical bayesian modeling to better constrain the chronologies of upper paleolithic archaeological cultures in france between ca 32 000 21 000 calibrated years before present abstract investigations of chronology play a key role in the majority of archaeological research endeavors and are particularly pertinent to examinations of culture environment relationships especially during periods characterized by rapid and marked climatic variability and environmental reorganization rigorous evaluations of available data and robust methods are required if one wishes to reconstruct reliable chronologies and this is especially the case when examining periods that are associated with a relatively few radiometric measurements such is the case for the upper paleolithic archaeological record documented in present day france from 32 000 to 21 000 calibrated years bp we take into account critically examined radiocarbon measurements from contextually secure archaeological contexts and employ a recently developed method of hierarchical bayesian modeling to reconstruct the chronology of archaeological cultures from the middle gravettian to the badegoulian the calculated chronological intervals for each typo technologically defined culture phase are compared to the greenland ice core climatic record and a terrestrial paleoenvironmental record from bergsee lake southern germany itself expressed in calendar years calculated with the same calibration curve employed in our age model thereby permitting each archaeological culture to be correlated accurately with documented paleoclimatic variability

temporally transitional mantle convection implications for mars 1 the thermal evolution of terrestrial planets such as earth mars and venus is strongly dominated by the convective processes in the planet s silicate mantle the actual style of convection controls the efficiency of heat transport and thus the cooling behavior of the whole planet in the present study we investigate the heat transport properties of variable viscosity convection focusing on the temporally transitional behavior discovered recently while the difference of the newly found convective regime to the already known stagnant lid and episodic behavior has been elaborated in our previous study the present work investigates the applicability of the observed intermittent behavior to the thermal evolution of terrestrial planets a 3 d numerical mantle convection code is applied and calculations are carried out in the parameter range for which the temporally transitional behavior has been found using the described approach it is possible to investigate the transition from a temporarily mobilized to a stagnant surface in a fluid dynamically consistent manner while such a scenario has been suggested for mars early history it has so far been investigated only by means of parameterized convection models we show that the sporadic surface mobilization events may indeed occur on time scales relevant for mars in order to assess their influence on the subsequent thermal evolution of planetary bodies an internal heating of the mantle and a secular cooling of the core are additionally taken into account the obtained results are compared to the findings of thermal evolution studies employing parameterized convection models we show that the thermal consequences of a temporal transition from a mobile to a stagnant surface are indeed correctly described by parameterized models as done in previous studies

chasma boreale mars a sapping and outflow channel with a tectono thermal origin abstract a detailed geomorphological study of chasma boreale a widely known feature of mars north polar cap has been carried out for the first time along with a quantitative paleohydrological model it is concluded that the chasma was eroded by a flow whose discharge was on the order of magnitude of 10 9 m sec 1 this catastrophic flow is thought to have been preceded by a powerful sapping process caused by a tectonically focused thermal event several lines of evidence indicate tectonic control in the distribution and present aspect of most of the polar troughs this tectonic forcing probably played a major role in the inception of not only chasma boreale but also other polar reentrants as well

investigating links between ecology and bifacial tool types in western europe during the last glacial maximum we apply eco cultural niche modeling ecnm using the genetic algorithm for rule set prediction to reconstruct the ecological niches exploited by middle solutrean and upper solutrean populations during the latter stages of heinrich event 2 and the early part of the last glacial maximum respectively we focus on the upper solutrean technocomplex and its regionally distinct styles of hunting weaponry to investigate whether regional cultural variability reflects a link between material culture and ecology our analytical approach uses archaeological and geographic data in conjunction with high resolution paleoclimatic simulations and vegetation reconstructions for the two climatic phases in question our results indicate that cultural choices behind the production of specific projectile point types have at some level an ecological basis and are linked to particular environments we also find that the identified pattern of upper solutrean territoriality has an ecological foundation but that its stylistic expression in the variation of diagnostic armature types is likely a byproduct of cultural drift we argue that ecnm is an effective means with which to evaluate the paleoecological pertinence of archaeologically defined artifact types and to identify the ecological and cultural mechanisms underlying material culture variability

an improved gravity model for mars goddard mars model 1 doppler tracking data of three orbiting spacecraft have been reanalyzed to develop a new gravitational field model for the planet mars goddard mars model 1 gmm 1 this model employs nearly all available data consisting of approximately 1100 days of s band tracking data collected by nasa s deep space network from the mariner 9 and viking 1 and viking 2 spacecraft in seven different orbits between 1971 and 1979 gmm 1 is complete to spherical harmonic degree and order 50 which corresponds to a half wavelength spatial resolution of 200 300 km where the data permit gmm 1 represents satellite orbits with considerably better accuracy than previous mars gravity models and shows greater resolution of identifiable geological structures the notable improvement in gmm 1 over previous models is a consequence of several factors improved computational capabilities the use of optimum weighting and least squares collocation solution techniques which stabilized the behavior of the solution at high degree and order and the use of longer satellite arcs than employed in previous solutions that were made possible by improved force and measurement models the inclusion of x band tracking data from the 379 km altitude near polar orbiting mars observer spacecraft should provide a significant improvement over gmm 1 particularly at high latitudes where current data poorly resolve the gravitational signature of the planet

faunal dietary response to the heinrich event 4 in southwestern europe abstract the dietary traits of the ungulates from the canyars assemblage late pleistocene gava barcelona spain are analysed through tooth mesowear and microwear to study their feeding behaviour as well as the climatic conditions during the time of the arrival of the early modern europeans in the northeast of the iberian peninsula during the heinrich event 4 he4 between 39 and 40 kyr b p the dietary adaptations of ungulates to grazing dominated the community and included horses as well as some red deer aurochs and ibex results show a rigorous climate with the presence of grasslands capable of sustaining a high ungulate biomass the composition of the canyars ungulate community and its dietary adaptations clearly reveals some particularity of the he4 in the northeast of the iberian peninsula these open landscapes certainly favoured the migration routes of large mammals along the mediterranean basin and also favoured the dispersal of modern humans into the northeast of the iberian peninsula

muted change in atlantic overturning circulation over some glacial aged heinrich events several periods of massive iceberg discharge into the north atlantic and widespread cooling marked the last glacial period reconstructions of northward flow along the florida margin suggest that not all cold events were associated with a change in the strength of the atlantic meridional overturning circulation

the martian hemispheric dichotomy may be due to a giant impact mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1 3 the more southerly province is heavily cratered contains relatively old geological units and superficially resembles the lunar and mercurian highlands the northern province is relatively lightly cratered and contains younger geological units including extensive plains volcanic edifices and volcanic calderas except for the tharsis and elysium regions and other large volcanoes most of the younger northern province consists of lowlands which lie an average of 3 km below the highlands lowlands occupy about one third of mars they are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits fig 1 the transition is characterized by a variety of landforms unknown on other planets the highlands and lowlands are in isostatic equilibrium across the transitional zone4 no generally accepted explanation for the cause of the highland lowland dichotomy has been proposed although thinning of the lithosph re in the northern hemisphere by internal processes has been suggested5 large impacts which were a feature of early solar system history have also been suggested as an important cause of such early planetary surface heterogeneities3 6 7 subcircular lowlands such as argyre chryse hellas and isidis planitia and the plains south of tharsis occupy previously recognized impact basins8 10 we propose here that the largest expanse of lowlands also results from formation of a large impact basin early in mars history that has profoundly shaped the planet s surface

the magma ocean as an impediment to lunar plate tectonics potential for plate tectonics on a planet is determined by several factors besides the obvious one of temperature one of the most important of these is the ratio zc zl where zc and zl are the thicknesses of the crust and tectonic lithosphere respectively a high zc zl ratio imparts a low bulk density and thus a high buoyancy to the lithosphere cooling of the lithosphere can offset a limited degree of compositional buoyancy but for realistic assumptions regarding crustal and mantle densities lithosphere geotherms and the spatial variability of the zc zl ratio systematic lithosphere subduction i e plate tectonics is unlikely on any planet with average zc zl ratio greater than about 0 25 during a magma ocean phase zc zl must be 1 so systematic lithosphere subduction is impossible in general zl is closely linked to the average planet temperature whereas zc is only weakly related to t but is sensitive to the planet s pressure depth gradient dp dz i e its size which governs the fate of al during deep melting crystallization processes the moon has probably always had zc zl too high or in later times lithosphere thickness too high to sustain plate tectonics conceivably plate tectonics operated over the first few million years of lunar evolution particularly if the early interior was cooler than generally assumed and a true magma ocean never developed or only developed after gradual warming of the deep interior however weighing against this scenario in addition to the wide array of evidence in favor of the magma ocean hypothesis are the consistently moderate to young by lunar standards ages of geochemically evolved lunar rocks

vegetation response to abrupt climate changes in western europe from 45 to 14 7k cal a bp the bergsee lacustrine record black forest germany

fluid dynamics of local martian magma oceans the evolution of a melt region produced by a large impact during mars formation is addressed while some impact induced melt is redistributed during crater excavation sufficiently large impacts much larger than basin forming impacts generate an intact melt region which is retained beneath the excavation zone i e a local magma ocean local magma ocean evolution depends on the effective rheology controlling large scale deformation of the solid part of the planet mechanism of crystallization and melt region size within the uncertainties of various parameters two scenarios are possible for sufficiently weak rheology or large melt region size evolution is characterized by rapid extrusion and formation of a global magma ocean for sufficiently strong rheology or small melt region size in situ crystallization to a partially molten solid state occurs prior to isostatic adjustment subsequent to in situ crystallization local magma ocean evolution depends on melt region size and efficiency of lateral redistribution compared to bulk conductive cooling for large melt regions lateral spreading occurs via plastic deformation and results in an asymmetric global partial melt layer for small melt region size viscous spreading viscous can result in bulk cooling below the solidus prior to formation of a global layer a hypothesis for the origin of the hemispherical crustal dichotomy and tharsis rise is suggested the dichotomy is associated with a global partial melt layer produced by evolution of a large local magma ocean after dichotomy formation evolution of a second smaller local magma ocean is related to tharsis development

early transient cooling of mars previous evolution models for one plate planets have commonly assumed steady state cooling beneath a rigid lid recent 3d numerical models indicate however that conductive lid cooling exhibits early transient stages where the quasi static assumption is not valid we apply scaling laws for these transient stages to mars a wide range of initial conditions for the martian mantle reflects the possible consequence of the early differentiation of the planet our results display large variations for the timing of early transient cooling from several 100 ma up to a few ga indicating that classical quasi static models cannot describe a significant part of the planet s evolution this suggests new scenarios for mars early history with initial heat fluxes in good agreement with values inferred from both gravity and topography data from the mgs mission

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

the effect of rheological parameters on plate behaviour in a self consistent model of mantle convection abstract in a three dimensional numerical model of mantle convection we have explored the self consistent formation and evolution of plates this was done by investigating the influence of temperature stress and pressure dependence of the viscosity on plate like behaviour further the role of a depth dependent thermal expansivity and of internal heating was examined first order self consistent plate tectonics can be obtained for temperature and stress dependent viscosity we observe virtually undeformed moving plates and the phenomenon of trench migration however plate motion only appears during short intervals which are interrupted by long phases characterised by an immobile lid an improvement is achieved by adding pressure dependence of the viscosity and of the thermal expansivity to the model this leads to extended plates with continuous plate motion and the appearance of a low viscosity zone internal heating accelerates subduction and gives an increase in plate velocity the plates are otherwise left intact we find that the surface velocity is largely determined by subduction rather than by upwellings plate like behaviour is restricted to a narrow parameter window the window is bordered by an episodic or a stagnant lid type of flow on the one side and by a domain in which convection is akin to constant viscosity flow on the other side with these different convective regimes the behaviour of various terrestrial planets can be described self consistently occasionally even a change from the plate regime to the stagnant lid regime occurs such a type of transition has possibly changed the style of tectonics on some terrestrial planets such as mars

tectonic implications of mars crustal magnetism mars currently has no global magnetic field of internal origin but must have had one in the past when the crust acquired intense magnetization presumably by cooling in the presence of an earth like magnetic field thermoremanent magnetization a new map of the magnetic field of mars compiled by using measurements acquired at an 400 km mapping altitude by the mars global surveyor spacecraft is presented here the increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the mars crust variations in the crustal magnetic field appear in association with major faults some previously identified in imagery and topography cerberus rupes and valles marineris two parallel great faults are identified in terra meridiani by offset magnetic field contours they appear similar to transform faults that occur in oceanic crust on earth and support the notion that the mars crust formed during an early era of plate tectonics

origin of the martian global dichotomy by crustal thinning in the late noachian or early hesperian the marked dichotomy in topography surface age and crustal thickness between the northern lowland and southern upland of mars has been explained as due to an initially inhomogeneous crust a single mega impact event several overlapping large basin impacts and first order convective overturn of the martian mantle all of the published hypotheses propose that the dichotomy was formed early in martian history before the end of the primordial heavy bombardment a primordial origin is inherent in the initial crustal inhomogeneity hypothesis and required for both impact hypotheses endogenic hypotheses are not so constrained geological data indicate episodes of fracturing and faulting in the late noachian and the early hesperian this fracturing and faulting occurred primarily within the northern lowland and along the boundary between lowland and highland igneous activity also peaked in the late noachian and early hesperian these data suggest a tectonic event near the noachian hesperian boundary characterized by enhanced heat loss and extensive fracturing including formation of the faults that define much of the highland lowland boundary we argue that the major result of this tectonic event was formation of the dichotomy by thinning of the crust above a large convection cell or plume

a new aurignacian engraving from abri blanchard france implications for understanding aurignacian graphic expression in western and central europe abstract in the excitement of the widely publicized new finds of aurignacian art from chauvet from the swabian jura and from as far afield as pestera coliboaia in romania it has almost been forgotten that a rich corpus of aurignacian wall painting engraving and bas relief sculpture had been recognized and studied before world war i in the vezere valley of sw france scientific knowledge of the chronological and cultural context of that early discovered graphic record has been limited by the crude archaeological methods of that pioneering era and the loss and dispersal of many of the works discovered in 2011 we launched new excavations and a re analysis of one of the key sites for such early discoveries the collapsed rock shelter of abri blanchard in 2012 we discovered in situ a limestone slab engraved with a complex composition combining an aurochs and dozens of aligned punctuations this new find recovered by modern methods and dated by molecular filtration and hydroxyproline 14c provides new information on the context and dating of aurignacian graphic imagery in sw france and its relationship to that of other regions the support is not a fragment of collapsed shelter ceiling and is situated in the midst of quotidian occupational debris the image shows significant technical and thematic similarities to chauvet that are reinforced by our reanalysis of engraved slabs from the older excavations at blanchard the aligned punctuations find their counterparts at chauvet in the south german sites and on several other objects from blanchard and surrounding aurignacian sites in sum we argue that dispersing aurignacian groups show a broad commonality in graphic expression against which a certain number of more regionalized characteristics stand out a pattern that fits well with social geography models that focus on the material construction of identity at regional group and individual levels

buried impact craters a topographic analysis of quasi circular depressions utopia basin mars 1 many quasi circular depressions qcds revealed in the mars orbiter laser altimeter data set have no obvious structural representation in visible images of mars it has been suggested that these qcds are surface representations of buried impact craters and on the basis of this assumption cumulative count versus diameter plots of qcds in the northern lowlands have been constructed to date the buried lowland floor if the qcds are in fact buried impact craters their surface relief should scale directly with their diameter this relationship holds true for 115 qcds with diameters ranging from 7 to 100 km within roughly 1500 km of the center of the utopia basin the coefficient of determination r2 of the relationship more closely approaches 1 when qcds in zones of comparable cover thickness are evaluated the surface relief versus diameter relationship of 55 randomly selected pseudo qcds was also determined their poor correlation indicates that the direct relationship of surface relief to diameter of actual qcds is due to differential compaction of a cover material over buried impact craters and is not just a random effect of qcd diameter the slope of the trend of the qcds surface relief versus diameter when divided into zones of comparable cover thickness can be used to determine which zones have thicker or thinner cover

impact constraints on the age and origin of the lowlands of mars 1 visible and buried impact basins seen as quasi circular depressions qcds in mola data provide important new constraints on the age of the martian lowlands the buried lowlands are no younger than early noachian at least as old as the oldest exposed visible surface units in the highlands a model absolute age for these buried lowlands is 4 04 4 11 gy or earlier but similar model ages for the largest lowland basins are older yet 4 08 4 18 gy the lowland crust both formed and became low no later than 500 million years after mars formed and likely even earlier this constrains models for the origin of the fundamental crustal topographic dichotomy on mars mechanisms which operated both early and quickly during the earliest history of mars e g large impacts may be more likely than those requiring extended periods of time i e endogenic models

heinrich events sediments a history of terminology and recommendations for future usage abstract we document the history of terms used to describe heinrich h layers and events and which mark major glaciological iceberg discharge events in the north atlantic we argue that the usage heinrich layer heinrich zone or heinrich event should be restricted to only those sediments that can be ascribed to an origin from the hudson strait ice stream and the laurentide ice sheet we also argue that the commonplace understanding of these events as dominated by massive iceberg discharges fails to include the earlier well documented evidence that these events were also massive meltwater events linked to deposition along the north atlantic mid ocean channel namoc in the labrador sea we make five recommendations for future usage of heinrich events which include restricting the usage to those events that can be mineralogically geochemically linked to hudson strait abandoning the term heinrich stadial and promote local terminology for ice rafted events that may be correlated or not with hudson strait heinrich events based on calibrated radiocarbon dates or other appropriate chronological markers

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

origin of the martian crustal dichotomy evaluating hypotheses abstract any hypothesis for the origin of the martian global dichotomy should survive three elementary tests 1 it must account for the observed plan shape and apparent depth of the martian northern lowland 2 it must be physically consistent and 3 it must be compatible with available geological and geophysical data at present there are three contending types of hypotheses for the origin of the dichotomy creation by some endogenic process or processes creation by a single mega impact or creation by several overlapping large impacts none of these hypotheses can survive all three tests without the incorporation of additional processes the endogenic and mega impact hypotheses require the presence of additional impact basins to explain many of the topographic details of the martian northern lowland and of the dichotomy boundary and the mega impact hypothesis probably also requires extensive primordial erosion the multiple impact hypothesis requires an additional process or processes to account for the large portion of the northern lowland that is external to the rims of the basins inferred to be the cause of the lowland while we believe that aspects of the multiple impact hypothesis are required to account for some topographic details of the boundary and of the lowland other processes appear better able to account for the dichotomy as a whole these could include an early mega impact endogenic processes or some combination of these

subduction origin on early earth a hypothesis i propose a hypothesis for the origin of subduction on early earth that is directly coupled with mantle upwelling and the formation of mafi c crust the hypothesis invokes spatial and temporal overlap of both endogenic and exogenic processes broad quasi cylindrical mantle upwelling and large bolide impact respectively leading to subduction and spreading two signature processes of modern plate tectonics the spatial and temporal intersection of these processes could have occurred variably across early earth and thus subduction could have begun at different locations and times globally the hypothesis postulates that the ability of a terrestrial planet to evolve plate tectonics results from a balance between the strength of its lithosphere and the size bolide it can attract and survive both factors to a fi rst order are a function of planet size

episodic flood inundations of the northern plains of mars throughout the recorded history of mars liquid water has distinctly shaped its landscape including the prominent circum chryse and the northwestern slope valleys outflow channel systems and the extremely flat northern plains topography at the distal reaches of these outflow channel systems paleotopographic reconstructions of the tharsis magmatic complex reveal the existence of an europe sized noachian drainage basin and subsequent aquifer system in eastern tharsis this basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels and ponded to form various hypothesized oceans seas and lakes episodically through time these floodwaters decreased in volume with time due to inadequate groundwater recharge of the tharsis aquifer system martian topography as observed from the mars orbiter laser altimeter corresponds well to these ancient flood inundations including the approximated shorelines that have been proposed for the northern plains stratigraphy geomorphology and topography record at least one great noachian early hesperian northern plains ocean a late hesperian sea inset within the margin of the high water marks of the previous ocean and a number of widely distributed minor lakes that may represent a reduced late hesperian sea or ponded waters in the deepest reaches of the northern plains related to minor tharsis and elysium induced amazonian flooding

low degree mantle convection with strongly temperature and depth dependent viscosity in a three dimensional spherical shell 1 a series of numerical simulations of thermal convection of boussinesq fluid with infinite prandtl number with rayleigh number 10 7 and with the strongly temperature and depth dependent viscosity in a three dimensional spherical shell is carried out to study the mantle convection of single plate terrestrial planets like venus or mars without an earth like plate tectonics the strongly temperature dependent viscosity the viscosity contrast across the shell is 10 5 makes the convection under stagnant lid short wavelength structures numerous cylindrical upwelling plumes are developed because of the secondary downwelling plumes arising from the bottom of lid this convection pattern is inconsistent with that inferred from the geodesic observation of the venus or mars additional effect of the stratified viscosity at the upper lower mantle the viscosity contrast is varied from 30 to 300 are investigated it is found that the combination of the strongly temperature and depth dependent viscosity causes long wavelength structures of convection in which the spherical harmonic degree l is dominant at 1 4 the geoid anomaly calculated by the simulated convections shows a long wavelength structure which is compared with observations the degree one l 1 convection like the martian mantle is realized in the wide range of viscosity contrast from 30 to 100 when the viscosity is continuously increased with depth at the lower mantle

a stratigraphical basis for the last glacial maximum lgm abstract the last glacial maximum lgm is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest however the boundaries of the interval are ill defined and the term and acronym have no formal stratigraphical basis this is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels spanning the interval 23 19 or 24 18 ka and centred on 21 ka in terrestrial records the lgm is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle for example glaciers and ice sheets reached their maximum extents at widely differing times in different places in fact most terrestrial records display spatial variation in response to global climate fluctuations and changes recorded on land are often diachronous asynchronous or both leading to difficulties in global correlation however variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes whilst regional dust accumulation is recorded in loess deposits global dust flux is best recorded in high resolution polar ice core records providing an opportunity to define the lgm on land and establish a clear stratigraphical basis for its definition on this basis one option is to define the global lgm as an event between the top end of greenland interstadial 3 and the base onset of greenland interstadial 2 spanning the interval 27 540 23 340 ka greenland stadial 3 this corresponds closely to the peak dust concentration in both the greenland and antarctic ice cores and to records of the global sea level minima this suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume the later part of the lgm event is marked by heinrich event 2 which reflects the onset of the collapse of the laurentide at c 24 ka together with other ice sheets in the north atlantic region a longer and later span for the lgm may be desirable although defining this in chronostratigraphical terms is problematic whichever formal definition is chosen this requires the contribution of the wider quaternary community

the landes de gascogne southwest france periglacial desert and cultural frontier during the palaeolithic abstract during the last glacial period a large part of the aquitaine basin southwest france was a periglacial desert comprising coversands with low relief dune fields surrounded by loess accumulations osl and radiocarbon dates show that the phase of maximum sand deposition coincides with marine isotope stage mis 2 peats and gleyic palaeosoils intercalated within the sands at some sites indicate that vegetation cover was able to develop locally during short events possibly d o interstadials due to raised groundwater levels in interdunal depressions few palaeolithic sites have been discovered in the coversand area in contrast to the peripheral loess region systematic survey along a future highway corridor demonstrates that this paucity of sites is not the result of insufficient survey nor deep site burial but rather reflects an archaeological reality this strongly suggests that the sand area was not attractive for hunter gatherer populations due to its reduced levels of water resources and available vegetation and animal biomass the distribution of cultural markers such as art items and projectile points also shows that the coversand area probably acted as a barrier separating two different cultural sub areas one in the pyrenees and cantabria the other in the perigord as a consequence the commonly accepted view that southwest france as a whole served as a refugia during the cold and arid phases of the pleistocene should be replaced by a more complex one that reflects the fact that a large part of the territory was almost unoccupied and that human populations were concentrated along alluvial valleys

late noachian to hesperian climate change on mars evidence of episodic warming from transient crater lakes near ares vallis 1 the ares vallis region is surrounded by highland terrain containing both degraded and pristine large impact craters that suggest a change in climate during the late noachian early hesperian from warmer wetter conditions to colder dryer conditions however the regional occurrence of hesperian age crater outlet channels indicates that this period on mars was characterized by episodic climate fluctuations that caused transient warming facilitating the stability of liquid water at the surface an extensive survey of the morphology and topography of 75 impact basins in the region indicates that of the largest degraded craters 4 were identified with single outlet channels that suggest the former presence of water infill these basins lack inlets indicating that water influx was likely derived from sapping of groundwater a comparison of measured crater rim heights to modeled rim heights suggests that the bulk of the depth diameter reduction on these craters was the result of infilling possibly by sediments crater statistics indicate that crater degradation and infill occurred during a short 200 ma interval in the late noachian from 3 8 ga to 3 6 ga craters that formed after 3 6 ga exhibit a near pristine morphology our results support the hypothesis of rapid climate change at the end of the noachian period however geologic relationships between the crater outlet channels and ares vallis indicate that drainage occurred only after the period of intense crater modification during the hesperian 3 5 2 9 ga this suggests a delay between the time of infill of the craters and the time of drainage

ocean bathymetry and mantle convection 2 small scale flow numerical models demonstrate that a boundary layer instability of the lower lithosphere does not stop the lithosphere from subsiding and so it cannot explain the so called flattening of old seafloor the slower subsidence of the old seafloor is in any case better seen as a perturbation probably due to plumes furthermore if a boundary layer instability or any mode of upper mantle convection transported most of the heat emerging from old seafloor there would be pervasive large amplitude local bathymetrie gravity and geoid anomalies such anomalies have never been convincingly differentiated from the effects of the cooling lithosphere and hotspot tracks except for some low amplitude linear geoid anomalies near spreading centers the only modes of mantle convection with horizontal scales less than those of plates for which there is reasonably clear evidence are hotspot plumes and some possible near ridge boundary layer instabilities hotspots transport less than about 10 of the earth s heat flux and other small scale modes are probably less important

phase transitions and the three dimensional planform of thermal convection in the martian mantle previous convection models for earth have shown that the endothermic phase transition from spinel to perovskite plus magnesiowustite at 660 km depth has a strong effect on mantle convection for mars the depth of the main phase transitions is estimated using a set of 32 000 density models with randomly perturbed input parameters it is found that on average the depth of the spinel to perovskite transformation is 1910 km thus a perovskite layer exists in the martian mantle only if the core radius is less than 0 45 of the planetary radius recent results on the density of fes at pressure and temperature conditions relevant to the martiam core indicate that such a small core size is consistent with the cosmochemical estimate of around 14 sulphur content of the core numerical simulations of three dimensional spherical convection demonstrate that the presence of the endothermic phase transition close to the core mantle boundary is the crucial factor determining the style of convection in addition to the endothermic phase boundary the simulations assume an isoviscous mantle which is heated both from below and within a rigid upper boundary and rayleigh numbers of the order of 106 under these conditions it is shown that the natural planform of mantle convection exhibits only one or two strong mantle plumes the number of plumes decreases with time during planetary evolution for high rayleigh numbers the plumes start to oscillate about a mean position and pulsate in time strongly localized mantle upwellings are obtained even when the proportion of basal heating is only 10 these results are robust in the sense that they do not critically depend on the parameters of the phase transition the rayleigh number or the rate of basal heating this planform of mantle convection is consistent with the volcanic history of mars where early volcanism was widespread but later concentrated in two provinces tharsis and elysium and finally in tharsis alone

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

wet to dry climatic trend in north western iberia within heinrich events abstract the direct sea land correlation applied to core md99 2331 retrieved from the north western iberian margin shows a two phase pattern within heinrich events 4 2 and 1 in the ocean and in the adjacent landmasses changes between wet cold and dry cool conditions in the iberian peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the atlantic meridional overturning circulation here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the md99 2331 record and other available palaeoclimate sequences from the north atlantic region 18 75 n and 0 75 w the climatic asymmetry observed between mid and subtropical eastern north atlantic latitudes wet dry and the blake outer ridge dry wet during h4 h2 and h1 can be explained by changes in the position of the atlantic jet stream during the first phase of h4 h2 and h1 the atlantic jet stream was located further south following the southward displacement of the oceanic thermal front as far south as 35 37 n on the contrary during the second phase of h4 h2 and h1 the jet stream was located further north following the northward displacement of this thermal front as far north as 42 n from the atmospheric point of view these two phases are reminiscent of the present day negative and positive prevailing modes of the north atlantic oscillation nao respectively but high resolution studies of additional north atlantic key sites and climate simulations are needed to confirm the hypothesis of a nao like mechanism operating on millennial timescales

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

chronostratigraphy of two late pleistocene loess palaeosol sequences in the rhone valley southeast france abstract a sedimentological and chronostratigraphical investigation was carried out on two loess sections located in the mediterranean area in southeast france along the rhone river lautagne and the lower reach of a tributary of the rhone river collias high resolution sampling 5 20 cm for magnetic susceptibility grain size distribution including non parametric end member modelling colour reflectance and geochemistry was performed the chronology was based on luminescence dating of quartz grains and radiocarbon dating of small gastropod shells coupled with hierarchical bayesian modelling the collias section 8 m thick records the whole last climatic cycle it comprises a thick red basal pedocomplex s1 developed during the last interglacial and the early glacial similar to that observed elsewhere in southern and southeastern europe loess deposition occurred during the lower l1l2 and the upper pleniglacial l1l1 it was interrupted by soil formation during the middle pleniglacial of which a brown bwk horizon has been preserved l1s1 by contrast the 5 m thick lautagne section provides a detailed record of the upper pleniglacial weakly developed hydromorphic soils are correlated with the greenland interstadials gi 4 to gi 2 while the main period of coarse loess sedimentation corresponds to the greenland stadials gs 5 to gs 2 at a regional scale the time of loess deposition ranges between 38 5 ka and 12 ka with a peak at 28 24 ka overlapping with the maximal advance of the alpine ice sheet ais this strongly suggests that regional glacier dynamics was the main driver of loess sedimentation

scenarios for the evolution of life on mars received 10 march 2005 revised 2 august 2005 accepted 7 september 2005 published 22 november 2005 1 as the environmental histories of earth and mars have diverged drastically after the first few hundred million years so would the history of any life on them while earth has had liquid water on its surface for billions of years mars most likely had long dry and cold environments interspersed with warmer and wetter periods life thrived on earth but may have been severely restricted on mars there it could be present today in liquid water in or beneath ice sheets or glaciers in subterranean aqueous reservoirs especially in regions of elevated heat flow or in protected habitats such as lava tubes caves or cracks and fissures the potential for life is enhanced in regions where elevated heat flow may occur such as in parts of the tharsis and elysium volcanic provinces possible organisms would be chemoautotrophic psychrophiles adapted to a nutrient poor environment or photoautotrophic life in selected near surface habitats alternatively life may have evolved alternating cycles between active and dormant forms in which case microbes could be present in dormant forms close to the surface and in active forms in protected environments periodic liquid water on mars could have provided opportunities for biologic activity as well as evolutionary progress at the surface during the short lived climatic perturbations ancient organisms from any of these environments may also have left a detectable fossil record

tropical north atlantic subsurface warming events as a fingerprint for amoc variability during marine isotope stage 3 the role of atlantic meridional overturning circulation amoc as the driver of dansgaard oeschger do variability that characterized marine isotope stage 3 mis 3 has long been hypothesized although there is ample proxy evidence suggesting that do events were robust features of glacial climate there is little data supporting a link with amoc recently modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical north atlantic can be used to fingerprint a weakened amoc during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics to determine if amoc variability played a role during the do cycles of mis 3 we present new high resolution mg ca and 18o records spanning 24 52 kyr from the near surface dwelling planktonic foraminifera globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera globorotalia truncatulinoides in southern caribbean core vm12 107 11 33 n 66 63 w 1079 m depth our subsurface mg ca record reveals abrupt increases in mg ca ratios the largest equal to a 4 c warming during the interstadial stadial transition of most do events during this period this change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core additionally our data support the conclusion reached by a recently published study from the florida straits that amoc did not undergo significant reductions during heinrich events 2 and 3 this record presents some of the first high resolution marine sediment derived evidence for variable amoc during mis 3

temporal variation of the hawaiian plume flux abstract the magnitude of the hawaiian swell which surrounds the hawaiian volcanic chain does not decline monotonically and smoothly with distance along the chain the observed undulations are interpreted here as reflecting past variations in the buoyancy flux of the hawaiian plume rather than the monotonic thermal decline of the swell with age as has been inferred previously this interpretation is supported by seismic evidence that indicates there has been little thinning of the lithosphere which it is shown further implies that the time scale for thermal subsidence will be very long the largest change in flux was an increase in the plume flux by more than a factor of two about 25 30 myr ago the size of the volcanic edifices shows a broad correlation with the variations in the swell supporting this interpretation

tracing time in the ocean a brief review of chronological constraints 60 8 kyr on north atlantic marine event based stratigraphies abstract well resolved event based stratigraphies in marine sediments spanning a significant portion of the last glacial period 60 8 kyr provide a unique opportunity for time stratigraphic correlation in the north atlantic region here we review the current methods available to chronologically constrain these event based stratigraphies highlighting in particular the value of tephrochronology as an independent tool to validate correlations between records while the intimate protocols lowe et al 2008 blockley et al 2011 are equally applicable to marine and terrestrial records spatially and temporally variable marine radiocarbon reservoir age effects mres provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool despite the inherent uncertainties associated with tuning we conclude that the mid points of the common abrupt warming transitions associated with the well defined millennial scale climate oscillations the dansgaard oeschger d o cycles observed in the oxygen isotopes of the greenland ice cores and north atlantic sea surface temperature sst records currently provide the most robust correlation tie points from which to derive age control in this invited intimate special issue article we propose a new protocol for establishing marine event based chronostratigraphies in the north atlantic region and focus on areas of chronological potential in palaeoceanographic research

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

calibration of radiocarbon results pertaining to related archaeological events with the advent of the high precision radiocarbon calibration curve there is an increasing demand from archaeologists for results previously reported on the radiocarbon scale to be expressed on the calendar scale furthermore there is a general realization within the archaeological community that much more information can be derived from radiocarbon dating if the samples are taken from coherent well chosen contexts and if any available substantive archaeological information is included in the data analysis this paper describes how the bayesian approach to statistical data analysis can be used for the calibration of groups of radiocarbon results in situations where archaeological information is available a priori about the relationships between the contexts being dated recent innovations in the implementation of the bayesian paradigm are used and the methodology is illustrated by the analysis of data arising from two archaeological excavations

a regional tephrostratigraphic framework for central and southern european climate archives during the last glacial to interglacial transition comparisons north and south of the alps abstract this paper summarises the results of tephrochronological investigations into a suite of central and southern european records which include rotmeer southern germany soppensee and rotsee central swiss plateau lago di lavarone and lago piccolo di avigliana italian southern alpine foreland these sites provide records of palaeoenvironmental changes for the last glacial to interglacial transition lgit at the boundary between north atlantic and mediterranean climatic influences chemical characterisation of glass shards in volcanic ash layers indicates that multiple volcanic sources have contributed to the central european tephra record amongst other volcanic markers the laacher see tephra originating from the eifel region of germany c 12 9 0 1 ka and the vedde ash from iceland c 12 1 0 1 ka are found co located within the sediments of rotmeer soppensee rotsee and lago piccolo di avigliana these key horizons which bracket the onset of the younger dryas stadial provide precise calendrically dated tie points around which a detailed picture of the timing of local and regional environmental transitions can be constructed using the co located tephra layers the re colonisation of northern italian catchment areas by quercus is shown to occur just prior to the deposition of the laacher see tephra layer whereas to the north of the alps quercus and other thermophilous trees do not reappear until several centuries after the deposition of the vedde ash furthermore the discovery of the vedde ash in lago piccolo di avigliana and lago di lavarone is indicative of atmospheric transport of polar air into southern europe during the younger dryas stadial matching evidence proposed for such transport of polar air during the last glacial maximum lgm

deformational history of an outlier of metasedimentary rocks coast plutonic complex british columbia canada the khutzeymateen assemblage records a portion of the polyphase deformation experienced by rocks within the core of the coast plutonic complex this series of deformational events probably took place during late cretaceous to early eocene regional orogenic activity the khutzeymateen assemblage is dominated by metamorphosed graywackes and volcaniclastic material the earliest recognizable deformation involves thrust faulting that juxtaposed rocks of the khutzeymateen assemblage and central gneiss complex the next deformational event produced isoclinal folds f1 a penetrative foliation s1 and a strong mineral lineation l1 both f1 and l1 have a 340 15 orientation peak metamorphism p 450 50 mpa t 650 50 c was synchronous with this isoclinal folding event f1 folding was followed by a brittle chevron folding event f2 with a 335 20 orientation there is a strong lithologic control on the development of f2 minor folds which are developed predominantly within regularly layered qua

search for signs of ancient life on mars expectations from hydromagnesite microbialites salda lake turkey the 9white rock9 constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater c 90 km across in sabaea terra mars measures 18 15 km 180 540 m high it is re interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake were life to have emerged on mars as seems feasible then the 9white rock9 might be expected to comprise a complex of stromatolitic mounds salda golu lake in turkey is taken as an analogue this enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite hydromagnesite stromatolites microbialites up to 7 m high coalesce to form a group of small islands 200 m across the microbialites are seen to be growing near the mouth of the usually dry salda river in the southwestern sector smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter these columns terminate in domes a centimetre or so across the domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments the columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale the coarser layers near the surface still contain traces of the biofilm fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments though the structures of the individual microbes have not survived instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity annular structures on their upper surfaces can be seen in places the intervening and overlying material also comprised of hydromagnesite is a semi lithified mud bulbous megascopic structures separated by finer grained magnesium carbonate mudstone within strata in the 9white rock9 would be strong evidence of a photosynthetic microbial genesis another deposit of white rock on the western margin of juventae chasma could have a similar origin

evidences for a noachian hesperian orogeny in mars a number of tectonic structures have been located at the thaumasia plateau daedalia planum and aonia terra mars they include isolated folds with axial traces up to 200 km long trains of tightly folded structures tens of km long and thrusts their size and geometry are similar to those on earth and the direction of compression seems to have varied amply with time suggesting a complex tectonic evolution crater counts on the deformed terrain point to noachian to early hesperian ages on the basis of the geometry and geological relations of these structures we propose that they form part of an old martian orogen the thaumasia aonia orogen which embraced not only the thaumasia plateau but areas of daedalia planum aonia terra and nereidum montes as well a regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

contrasting impacts of dansgaard oeschger events over a western european latitudinal transect modulated by orbital parameters abstract terrestrial and marine proxies pollen planktic and benthic foraminiferal oxygen isotopes alkenone and foraminifer derived sea surface temperatures ssts ice rafted debris from images deep sea cores md95 2042 and su81 18 37 n 10 w md99 2331 and md03 2697 42 n 9 w and md04 2845 45 n 5 w show that western european and offshore environments were strongly affected by dansgaard oeschger d o and heinrich h events we concentrate here on latitudinal variability in the forest cover extent and composition of western europe during the succession of d o events showing new pollen records for core md04 2845 and for marine isotopic stages mis 3 and 4 of core md99 2331 in general cold ssts characteristic of greenland stadials were contemporaneous with the expansion of semi desert or steppic vegetation while greenland interstadials were synchronous with the expansion of forest our data reveal that the amplitude of atlantic and mediterranean forest expansions differs for any given d o warming during the glacial period 74 18 ka in the western mediterranean d o 16 17 and d o 8 and 7 corresponding to minima in precession were associated with strong expansion of forest cover contrasting with weak expansion of forest cover during d o 14 and 12 the opposite pattern is revealed at the atlantic sites further north the strongest greenland warmings are recorded for d o 19 11 and 8 this contrasting latitudinal climatic scenario is compared with other northern hemisphere records revealing similarities between the mediterranean climate and the asian monsoon regime which may relate to a summer atmospheric teleconnection between the two regions comparable to the present day situation parallels between mediterranean climate enhancement and peaks in global methane ch 4 during the last glacial period suggest a significant role of monsoon activity in determining ch 4 emission from wetlands

on the relation between transform fault resistance and plate motion a simple model for power dissipation due to friction along transform faults is used to examine the relations between relative velocity and power dissipation across transforms transform lengths and plate motions comparison is made between ridge transforms i e those that are part of spreading systems and major boundary transforms such as the san andreas fault power dissipation is calculated using velocity across the transform area above the 400 c oceanic or 350 c continental isotherm transform thermal structure is modeled by averaging the temperatures on either side of the transform whereas ridge transforms across which the relative plate velocity is slow can be of any length fast relative velocities only appear across short transforms when all transforms are used in this comparison a maximum speed as a function of transform length is suggested a minimum speed of 13 5 mm yr across ridge transforms was found in a case study of the pacific plate the transform lengths were found to have varied with time which has minimized the total power dissipation across the plate s transforms

crustal thickness and the average depth and degree of melting in fractional melting models of passive flow beneath mid ocean ridges in simple models of passive flow beneath mid ocean ridges fractional melting of the upwelling mantle produces unexpected relationships amongst crustal thickness degree of partial melting and the average depth of melting if the degree of melting is estimated on the basis of basalt composition then the average degree of melting is one third the maximum degree of melting and the average depth of melting is about two thirds the maximum depth in the simplest models the crustal thickness is about 1 5 times the product of the average fraction of melting and the height of the melting column if the average degree of melting represented in mid ocean ridge basalts were 10 and melt production continued to the base of the crust then only a 40 km high residual melting column would be required to produce a 6 km thick crust in more realistic models melting beginning at 60 km below the base of the crust and continuing to the top of the mantle would produce a 6 km thick crust with average degree of melting of 6 67 or melting beginning at 67 km and ending at 30 km below the base of the crust would produce a 6 km thick crust with an average degree of melting of only about 5 4 models of composition produced by fractional melting must consider the rate of melt production and the degree of melting throughout the melting region at the points where the melt is actually produced

estimation of oceanic hydrothermal heat flux from heat flow and depths of midocean ridge seismicity and magma chambers the difference between the heat flow predicted by thermal models of the lithosphere and that measured at the seafloor can be used to estimate the cooling by hydrothermal circulation however this approach may yield an overestimate because measurements in thinly sedimented young crust are typically made at topographic lows where hydrothermal circulation may systematically lower heat flow to circumvent this bias we estimate the cooling using the depths of midocean ridge earthquakes and magma chambers in addition to heat flow data the results indicate deeper hydrothermal circulation at slow spreading ridges and higher near axial hydrothermal heat loss at fast spreading ridges the predicted global hydrothermal heat flux is 80 of that for models constrained only by heat flow

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

rift valley no rift valley transition at mid ocean ridges a simple mechanical model for the axial topographic and gravity variations with spreading rate is developed the model emphasizes the rapid transition from one mechanism to another with changing spreading rate our model has a brittle layer over a ductile layer which are being pulled by forces away from the ridge axis there exists a potential failure zone of width lf where the stresses within the brittle plate exceeds its yield strength if the yield strength of the brittle plate is nearly constant this width is largely determined by the strain rate and the viscosity of the strong mantle the high ductility of oceanic crust at high temperatures relative to that of mantle at the same temperatures leads to the concept of a decoupling region a critical feature in this model the size of the decoupling region ld is determined by the thickness of the oceanic crust and temperatures within the crust if the decoupling region is small ld lf as shown to be the case for fast spreading ridges then each of the two layers responds separately to the horizontal stretching the brittle plate will be broken only at the axis and any buoyant force of the region would lift it up to form the rise crest high as a result of local isostasy the changing size of the decoupling region gives rise to the transition from atlantic type axial topography to pacific type as well as the transition from a high amplitude highly variable gravity signature to a low amplitude very uniform gravity signature parameters can be chosen so that such a transition occurs at a half rate of 35 mm yr which is the critical half rate suggested by both topographic and gravity data

large impact basins and the mega impact origin for the crustal dichotomy on mars the origin of the fundamental crustal dichotomy on mars remains the outstanding unsolved problem in martian geologic evolution the hypothesis that this dichotomy is due to a single giant mega impact early in martian history is tested by comparing the observed number of large impact basins on mars with the number expected from a d 2 distribution this test is based on the assumption that the mega impact borealis basin is the largest member of such a distribution the difference between observed and expected basins is the number of missing basins that might have been obscured by subsequent geologic events if the borealis basin were the largest member of a d 2 impact population there would be a very large number of missing basins on mars 1 larger than 5000 km 10 larger than 2000 km and 40 50 larger than about 1000 km diameter the area occupied by these missing basins allowing for overlap is too large to be hidden by the younger surface units a large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands by contrast if chryse is the largest member of a d 2 impact population the more modest number of missing basins could in principle be confined to areas of mars that have been resurfaced or reworked by subsequent geologic processes a possible alternative to the mega impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large but not giant impacts

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

seismic detection of meteorite impacts on mars abstract meteorite impacts provide a potentially important seismic source for probing mars interior it has recently been shown that new craters can be detected from orbit using high resolution imaging which means the location of any impact related seismic event could be accurately determined thus improving the constraints that could be placed on internal structure using a single seismic station this is not true of other seismic sources on mars such as sub surface faulting which require location using multiple seismic stations this study aims to determine the seismic detectability of meteorite impacts and assess whether they are a viable means of probing deep internal structure first we derive a relation between crater diameter and equivalent seismic moment based on observational data compiled from impact tests controlled explosions and earthquake seismology second this relation was combined with updated cratering rates based on newly observed craters to derive the impact induced seismicity on mars which we estimate to total 10 13 10 14 n m per year finally seismic waveform modelling was used to determine the detectability of these impacts based on reasonable assumptions about likely seismometer performance and background noise levels for our nominal noise instrument case we find that detectable impacts at teleseismic distances source receiver offsets greater than 60 are very rare and occur approximately once every 10 years for our most optimistic noise instrument case approximately one such event occurs each year this suggests that using solely meteorite impacts is not a reliable way of probing the martian interior although local impacts are more frequently detectable and could provide important constraints on near surface seismic properties

evidence for an ancient impact basin in daedalia planum mars geologic mapping has provided observations that some features on mars are morphologically similar to lunar imbrium sculpture materials these grooved features occur in clustered sets of a dozen or more are spaced 1 to 10 km apart and are unlike other linear martian features such as yardangs faults ancient valley networks and mass wasting features we propose that they represent impact materials from an ancient basin the orientations of these features were plotted as lines on a schmidt net and the density of the resulting intersections suggests a likely source area at approximately 26 0 125 0 or roughly the center of daedalia planum numerous features geologic materials and earth based radar data indicate that a basin with a diameter of approximately 4500 km with an early noachian age is centered at this location four interior rings with diameters of 1100 1500 2200 and 3200 km and an exterior ring with a diameter of approximately 6400 km were found the rings are spaced with a ratio of 2 0 1 which is similar to the basin ring spacing on the other terrestrial planets both concentric and infrequently radial basin related faults were recognized including claritas fossae gordii dorsum and the thaumasia graben faults or zones of weakness related to the basin rings may have influenced the position of the mangala valles source area and arsia mons based on the location and morphology of early hesperian to early amazonian volcanics composing daedalia planum the daedalia basin may also have extensive deep seated interior faults capable of extruding mare materials to the surface

high precision dating and correlation of ice marine and terrestrial sequences spanning heinrich event 3 testing mechanisms of interhemispheric change using new zealand ancient kauri agathis australis robustly testing hypotheses of geographic synchroneity of abrupt and extreme change during the late pleistocene 60 000 to 11 650 years ago requires a level of chronological precision often lacking in ice marine and terrestrial sequences here we report a bidecadally resolved new zealand kauri agathis australis tree ring sequence spanning two millennia that preserves a record of atmospheric radiocarbon 14c during ice rafted debris event heinrich event 3 he3 in the north atlantic and antarctic isotope maximum 4 aim4 in the southern hemisphere using 14c in the marine cariaco basin and 10be preserved in greenland ice the kauri 14c sequence allows us to precisely align sequences across this period we observe no significant difference between atmospheric and marine 14c records during he3 suggesting no stratification of surface waters and collapse in atlantic meridional overturning circulation amoc instead our results support recent evidence for a weakened amoc across at least two millennia of the glacial period our work adds to a growing body of literature confirming that heinrich events are not the cause of stadial cooling and suggests changes in the amoc were not the primary driver of antiphase temperature trends between the hemispheres decadally resolved 14c in ancient kauri offers a powerful new and complementary approach to polar ice core ch4 alignment for testing hypotheses of abrupt and extreme climate change

volcanic ash reveals time transgressive abrupt climate change during the younger dryas knowledge of regional variations in response to abrupt climatic transitions is essential to understanding the climate system and anticipating future changes global climate models typically assume that major climatic changes occur synchronously over continental to hemispheric distances the last major reorganization of the ocean atmosphere system in the north atlantic realm took place during the younger dryas yd an 1100 yr cold period at the end of the last glaciation within this region several terrestrial records of the yd show at least two phases an initial cold phase followed by a second phase of climatic amelioration related to a resumption of north atlantic overturning we show that the onset of climatic amelioration during the yd cold period was locally abrupt but time transgressive across europe atmospheric proxy signals record the resumption of thermohaline circulation midway through the younger dryas occurring 100 yr before deposition of ash from the icelandic vedde eruption in a german varve lake record and 20 yr after the same isochron in western norway 1350 km farther north synchronization of two high resolution continental records using the vedde ash layer 12 140 40 varve yr b p allows us to trace the shifting of the polar front as a major control of regional climate amelioration during the yd in the north atlantic realm it is critical that future climate models are able to resolve such small spatial and chronological differences in order to properly encapsulate complex regional responses to global climate change

an episodic hypothesis for venusian tectonics it is suggested that episodic plate tectonics occurs on venus episodes of rapid plate tectonics are separated by periods of surface quiescence for the last 500 200 m y it is postulated that the surface of venus has been a single rigid plate that has been thickening due to conductive cooling a near uniform surface age is consistent with observed crater densities and the relatively small number of craters modified by surface tectonics or embayed by lava flows a lithosphere that has conductively thickened for some 500 m y has a thickness of about 300 km nearly an order of magnitude greater than the thickness associated with steady state conductive heat loss such a thick lithosphere can support the high topography and associated gravity anomalies on venus as well as the unrelaxed craters studies of lithospheric flexure at coronae are also consistent with a thick elastic lithosphere incipient subduction associated with large coronae may represent the onset of a new episode of rapid plate tectonics on the earth 75 90 of mantle heat transport is attributed to the creation of new oceanic lithosphere at ocean ridges this process is not operative on venus this paper suggests that episodic plate tectonics on venus constitutes the primary mechanism for mantle heat transport on that planet

formation ages and evolution of shergotty and its parent planet from u th pb systematics the isotopic composition of lead was determined in different phases from shergotty zagami and eeta 79001 using phases with low 238 u 204 pb the initial leads of these meteorites could be well defined and are distinct from each other and have high 204 pb 206 pb from 0 0652 to 0 0739 these leads evolved in different reservoirs over most of solar system history in a low 238 u 204 pb 5 environment it follows that the parent planet of the shergottites has a high 204 pb concentration relative to u and must also be high in other volatiles if the parent planet of the shergottites is mars then this planet must be volatile rich compared to the earth by a factor of 1 8 this implies that mars lost its original atmosphere and that the present atmosphere was derived from a previously outgassed martian upper mantle the u th pb isotopic relationships involving phases with high 238 u 204 pb are quite regular and give ages for three shergottites which indicate an event of u th pb fractionation at 200 m y the initial leads at that time were highly evolved relative to the primordial lead the absence of substantial additions of radiogenic lead above the initial lead in high u phases precludes an older age for the u th pb fractionation however details of the data arrays are complex the young age is in general agreement with some of the ages obtained by other methods but precise concordance between the different methods is not established it is suggested that the shock event that produced maskelynite may possibly be associated with the late stage breakup at 2 5 m y and not necessarily related to the 180 m y record the major event of chronometer resetting is taken to be 180 m y this event does not appear to be an endogenic igneous event but an almost complete equilibration during a major impact on more ancient igneous rocks which were contained in the target problems of the polymetamorphic history of meteorites appear as complicated as those of polymetamorphic terrestrial terranes

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

european climatic response to millennial scale changes in the atmosphere ocean system during the last glacial period abstract pollen foraminifer dinocyst and coarse lithic high resolution analyses and 18 o measurements have been carried out for the last glacial section of marine core md95 2042 located near the southwestern margin of the iberian peninsula the pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period suggesting a climatic variability very similar to that of the dansgaard oeschger cycles recorded by the greenland ice cores the detailed direct correlation of the terrestrial and marine proxy data from core md95 2042 indicates a three phase pattern of heinrich events in land and ocean environments the first and last phases of the h5 and h4 events are characterized by a mild and humid climate in southwestern europe probably associated with the european origin of the ice rafted detritus the middle phase exhibits a cold and dry climate in iberia linked with the maximum input of ice rafted detritus this phase seems to correspond with the laurentide ice sheet surges between the heinrich events several cold and dry periods on land are correlated with stades of the dansgaard oeschger cycles the impact of the dansgaard oeschger stades in southwestern europe seems to be preferentially connected to the cold winter air masses reaching this mid latitude region

inverted fluvial features in the aeolis zephyria plana western medusae fossae formation mars evidence for post formation modification 1 the aeolis and zephyria plana contain the western most portion of the medusae fossae formation mff an enigmatic and extensive light toned deposit located in the martian equatorial region and dated from the hesperian to amazonian epochs this area hosts a large population of sinuous ridges srs interpreted as inverted fluvial features formed by precipitation indurated by chemical cementation buried by subsequent deposition and finally exhumed this interpretation of srs as uniformly fluvial represents a modification to an earlier hypothesis for one particular sr of possible glaciofluvial i e esker formation these srs provide a tool to investigate the degree and character of post fluvial modification processes in this region we combined digital terrain models made from context camera ctx and high resolution imaging science experiment hirise stereo image pairs with individual data points from the mars orbiter laser altimeter mola to estimate relief cross sectional profiles longitudinal profiles and slope directions of selected srs longitudinal profiles of several srs display undulations with amplitudes of up to order 100 m while some of the lower amplitude undulations may be due to differential erosion undulations having amplitudes in excess of sr relief require alternative explanations our combined morphologic and topographic analysis suggests that multiple post flow processes including compaction of the deposits and tectonic displacements have modified the original sr profiles specification of the type s and magnitudes of these modification processes will contribute to understanding both the potential of post flow modification of fluvial profiles elsewhere on mars as well as the nature and properties of the mff

claritas rise mars pre tharsis magmatism claritas rise is a prominent ancient noachian center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of mars this center is interpreted to be the result of magmatic driven activity including uplift and associated tectonism as well as possible hydrothermal activity coupled with its ancient stratigraphy high density of impact craters and complex structure a possible magnetic signature may indicate that it formed during an ancient period of mars evolution such as when the dynamo was in operation as tharsis lacks magnetic signatures claritas rise may pre date the development of tharsis or mark incipient development since some of the crustal materials underlying tharsis and older parts of the magmatic complex respectively could have been highly resurfaced destroying any remanent magnetism here we detail the significant characteristics of the claritas rise and present a case for why it should be targeted by the mars odyssey mars reconnaissance orbiter and mars express spacecrafts as well as be considered as a prime target for future tier scalable robotic reconnaissance