subtidal occurrences of ladder back ripples their significance in palaeo environmental reconstruction ladder back ripples are common on modern intertidal flats and have been thought to be diagnostic of deposition in this environment recognition of superimposed asymmetric ladder back ripples in a subtidal back barrier estuary and superimposed symmetric ladder back ripples in an embayed shallow marine environment indicates that these features are not diagnostic of deposition in the intertidal zone only but can occur in other depositional environments produced by different mechanisms and on different scales the presence of ladder back ripples in the subtidal zones challenges aspects of a model used to determine the palaeotidal range of ancient tidal sequences

a late cretaceous turonian ichthyofauna from lac des bois northwest territories canada with paleobiogeographic comparisons with turonian ichthyofaunas of the western interior seaway a fish fauna from a turonian sequence of the great bear basin at lac des bois is described the fauna includes examples of ichthyodectes cf osmeroides a euteleost and several aulopiforrn fishes such as enchodus cimolichthys and a juvenile that cannot be further identified the fauna of lac des bois most closely resembles other arctic fish assemblages of the western interior seaway based on a upgma unweighted pair group method with arithmetic averages cluster analysis of various north american turonian localities there are also slight differences between eastern and western localities along the seaway the north south differences of the ichthyofauna can be explained by current patterns distributing the fishes in the seaway or transgressive events during the turonian the east west differences may be due to changes in water depth from east to west

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

orbital observations of contemporary dune activity in endeavor crater meridiani planum mars 1 although aeolian landforms are pervasive on mars evidence for contemporary activity has been limited the next major campaign for the mars exploration rover opportunity is the investigation of the 20 km diameter endeavor crater 6 km to southeast of the rover s position as of december 2010 we present evidence from orbital imagery that eight aeolian bed forms 14 000 m2 in endeavor crater have been active within the past decade 2001 2009 at a spatial scale that should be directly observable by opportunity from the crater rim two dunes appear to show translational migration 10 20 m but all dunes indicate erosion to be the dominant process with up to 100 sediment removal thermophysical properties of these dunes are consistent with very fine to fine sand sizes the particle sizes most easily moved by the martian atmosphere the dunes that show the most surface change have a rippled appearance without well defined slip faces based on their morphology elliptical shape we classify them as dome dunes mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system the major wind regimes from modeling are consistent with observations of wind streaks sand streamers ripples and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand the translation and erosion of these dunes constitutes the largest contemporary movement of sand sized sediment reported on mars to date and demonstrates that endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface daily seasonally and or episodically in the recent past

mapping and characterization of small scale aeolian structures on mars an example from the msl landing site in gale crater abstract a new set of methodologies which allow a simple and fast mapping and characterization of small scale aeolian structures on mars is introduced in this work we follow an object based approach in which the bedform crestlines are automatically mapped and characterized from the methodology validation we conclude that the quality of the obtained results is comparable with human produced photointerpretations we show that the accuracy associated with the measurement of mean trends from the automatically mapped patterns is less than 10 through the analysis of two areas located near the msl landing site in gale crater we explore some of the possibilities that the automatic mapping technique enables namely for multitemporal surveys and ripple pattern analysis we demonstrate how the mapped ripple patterns can be used to assess local wind orientations and we analyze some examples that illustrate the diversity of wavelength spatial distributions that can be found on mars we try to relate these pattern wavelength variations with the possible local influence of granulometry and wind shear velocity

strontium isotope correlation of the basal maastrichtian stage in antarctica to the european and us biostratigraphic schemes new 87 sr 86 sr dating allows the correlation of a marker horizon within the prolific late cretaceous gunnarites antarcticus faunal assemblage of the cape lamb member snow hill island formation vega island antarctica with reference sections in europe and the usa this horizon is between 81 5 and 96 5 m above the base of the g antarcticus assemblage replicate analysis of six macrofossils from within it yielded a mean value for 87 sr 86 sr of 0 707 735 9 0 000 004 3 2 s e n 17 this ratio in turn yields a numerical age of 71 0 0 2 ma when compared to the standard 87 sr s6 sr reference curve for the latest cretaceous for which the campanian maastrichtian boundary is placed at 71 3 0 5 ma the value of 0 707 735 9 0 000 004 3 correlates to a level in the belemnella lanceolata belemnite zone of the chalk of northwestern germany that is 2 5 5 m beneath the base of the overlying b pseudobtusa zone and 7 5 m above the campanian maastrichtian belemnite boundary and to an interval within the ammonite zonation of the us western interior that spans the early maastrichtian baculites baculus and b eliasi zones but with a most likely level within the b eliasi zone an earliest maastrichtian age is thereby determined for the antarctic horizon and indeed for the entire g antarcticus assemblage gunnarites sensu lato is an important ammonite marker for the base of the maastrichtian throughout the southern high latitude regions and the associated large heteromorph ammonite diplomoceras may comprise a macrofossil link back to the maastrichtian type sections

transverse aeolian ridges tars on mars aeolian processes are probably the dominant ongoing surface modification process on mars as demonstrated by observations of dunes ripples yardangs ventifacts wind streaks dust devils and dust storms large dark dunes ldds are particularly common and were first recognized in the 1960 s from mariner data however another population of smaller often brighter ripple like aeolian bed forms that are morphologically distinct from ldds has been observed in recent higher resolution images calculations of saltation path length under martian conditions suggest these small bed forms could have formed as small barchanoid dunes or as mega ripples also known as granule ripples these features have therefore been called transverse aeolian ridges tars as this label has no genetic inference we have begun a study of tars that examines all high resolution mars orbiter camera data 1 5 to 8 m pixel resolution in a 45o longitude wide pole to pole swath we aim to determine the geographic distribution of tars assess whether they are active and to identify possible sediment sources we have already made some key observations first we present a new classification of tar deposits based on crest ridge morphology of individual forms and the size and degree of topographic control of the entire sediment mass second we present associations of tars with ldds slope streaks dust devils tracks and small impact craters that provide clues as to whether tars are currently active finally we present preliminary pole to pole survey results for the northern hemisphere that show clusters of tar deposits in the low latitudes suggesting possible unique sediment sources in these regions

dark aeolian sediments in martian craters composition and sources our research focuses on the mineralogical characteristics of dark sediment deposits in martian craters dunes dune fields and sand sheets and their local sediment sources carried out on the basis of 70 selected localities morphological analyses reveal dark layers exposed in a number of crater walls showing indications of material transport from the layers downwall to the intracrater deposits additional sites show dark sediment emerging from several craters floors suggesting a dark material source beneath the crater floor spectral analyses of omega and crism data showed for the first time that a direct mineralogical connection exists between the dark layers in the crater walls and the intracrater dune and sand sheet material based on these findings it is shown that these layers are the local sources for the dark aeolian sediment inside the craters spectral analyses further indicate that all deposits are nearly of the same mafic mineralogical composition hinting at a similar origin we conclude that the mineralogical composition points to a volcanic origin of the material the dark layers which we infer to be the material sources might represent layers of volcanic ash almost globally deposited in early noachian times and subsequently covered by regolith groundwater impact erosion and crustal movement led to the highly fragmented situation of the dark layers today however burial protected the layers of dark sediment from chemical alteration caused by surficial fluvial processes impact erosion after the wet periods on mars led to the exposure and mobilization of the material today

martian surface winds insensitivity to orbital changes and implications for aeolian processes aeolian features observed on the surface of mars provide insight into current and potentially past surface wind systems in some cases the features are clearly transient and related to the lifting and settling of atmospheric dust other features like dunefields yardangs and ventifacts are more persistent and likely require significant time to form in this study we analyze the observed directions of selected aeolian features with the aid of the geophysical fluid dynamics laboratory mars general circulation model gcm initially we examine bright and dark streaks which have been observed to form in association with global dust storms the ability to match these features with mars gcm wind directions provides an important validation of the model more important we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the veverka et al 1981 model of bright and dark dust streak formation in addition these best fit times correspond well with the dark streak wind storm model of magalhaes and young 1995 the primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long term wind indicators for example the misalignment of rock tail and ventifact orientations at the mars pathfinder landing site specifically we assess whether changes in planetary obliquity precession or global dust opacity could significantly alter patterns of surface wind directions in all cases we find the seasonal and annual average wind direction patterns to be highly invariable while changes in the dust loading hence the partitioning of solar absorption between the surface and atmosphere and in the surface latitude of maximum solstitial insolation cause the vigor of the large scale circulation to increase especially the hadley cell the spatial patterns of the surface wind orientations remain essentially unchanged in the case of perihelion during northern summer opposite of the current perihelion position the northern summer hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere taken together these results cast significant doubt on orbital explanations for surface wind changes it is thus suggested that significant changes in topography e g tharsis uplift true polar wander or climate e g the existence of a significantly thicker atmosphere or an ocean at some point in the past are more likely explanations for long term wind indicators such as the ventifact orientations at the mars pathfinder landing site

ichthyornis aves from the early turonian late cretaceous of alberta an isolated left humerus from the cretaceous toothed bird ichthyornis is described the fossil comes from the vimy member of the kaskapau formation at watino alberta and is early turonian in age the watino specimen is the oldest well authenticated record of ichthyornis and the oldest cretaceous skeletal fossil of a bird from the western hemisphere the wide geographic distribution of ichthyornis within the western interior of north america is in keeping with nomadic habits as inferred from strongly flying modern marine birds

the occurrence and formation of ladderback ripples in subtidal shallow marine sands zululand south africa abstract until recently ladderback ripples have been considered diagnostic of late stage emergence run off in intertidal environments observations have demonstrated that ladderback ripples may also occur in the subtidal environment new underwater observations off the zululand coast support reddering s assertion that ladderback ripples are not confined to tide dominated environments two types of ladderback ripple are described they form in shallow submarine bioclastic and terrigenous sediments on the landward margin of offshore coral reefs the main ripple set in each instance is oriented sub parallel to the shoreline and is produced by the dominant southeasterly swell while superimposed ripple sets in the troughs of the larger sets are formed by two mechanisms 1 the approach of low amplitude high frequency northeasterly to easterly swells which are not sufficiently strong to change the orientation of the dominant larger set and 2 longshore currents produced by oblique wind driven swells in small coastal embayments when conditions change the superimposed ripples are rapidly reworked and incorporated into the main ripple set they therefore have a low preservation potential both the occurrences documented here and those reported previously are in microtidal wave dominated settings

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

active faults and paleoseismicity in fennoscandia especially sweden primary structures and secondary effects abstract fennoscandia today a region of low to moderately low seismicity was at the time of deglaciation with rates of uplift on the order of tens of centimetres per year a region of very high seismicity and active tectonics this is evident both from primary fault structures and from secondary sedimentary and hard rock effects in the region around the epicentral areas the map of active faults in fennoscandia includes numerous structures previously not recognised despite this the recording of active faults and paleoseismic events is still in its initial phase much more data will surely accumulate in the near future

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

the influence of local topography for wind direction on mars two examples of dune fields in crater basins in this work we perform an analysis of large dark dunes within moreux crater and herschel crater on mars using high resolution imaging science experiment hirise and context camera ctx data sets these data allow us to conduct a detailed analysis of dune morphology and slip faces concluding that the studied dune fields are influenced by topographically controlled complex wind directions our morphological analysis reveals that inside moreux crater in particular the topographic setting dominates the wind flow direction leading to the development of a sand transport pathway encircling the central peak of the crater the dune fields in herschel crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields our analysis indicate that the studied dune systems is not the result of paleo wind regimes furthermore we perform thermal inertia measurements using thermal emission spectrometer tes data which indicate that the studied dune fields consist of medium sand 250 500 mm in diameter

a progression of induration in medusae fossae formation transverse aeolian ridges evidence for ancient aeolian bedforms and extensive reworking a progression of induration erosion and redeposition of transverse and networked transverse aeolian ridges tars has been documented in the medusae fossae formation mff mars cratered and eroded aeolian bedforms are rarely observed on mars indicating that those found in the mff have been inactive for much longer than those found elsewhere indurated tars are observed to grade into faceted mff terrain indicating a genetic relationship between the two we propose that tar deposition induration and erosion have played a larger role in the surface morphology and evolution of the mff than previously recognized the deposition induration and erosion of tars indicate that the mff has undergone multiple cycles of reworking and that much of its current surface morphology does not reflect the circumstances of its primary emplacement copyright 2011 john wiley sons ltd

constraints on ripple migration at meridiani planum from opportunity and hirise observations of fresh craters 1 observations of fresh impact craters by the opportunity rover and in high resolution orbital images constrain the latest phase of granule ripple migration at meridiani planum to have occurred between 50 ka and 200 ka opportunity explored the fresh resolution crater cluster and concepcion crater that are superposed on and thus younger than the ripples these fresh craters have small dark pebbles scattered across their surfaces which are most likely fragments of the impactor suggesting that the dark pebbles and cobbles observed by opportunity at meridiani planum are a lag of impactor derived material either meteoritic or secondary impactors from elsewhere on mars two larger fresh rayed craters in meridiani planum bracket ripple migration secondaries from ada crater are clearly superposed on and secondaries from an unnamed 0 84 km diameter crater have been modified and overprinted by the ripples three methods were used to estimate the age of these craters and thus when the latest phase of ripple migration occurred the inactivity of the ripples over the past 50 ka at meridiani is also consistent with other evidence for the stability of the ripples the lack of observed eolian bed forms in craters that formed in the past 20 years and little evidence for much dune motion in the past 30 yr on mars observations of crater morphology and their interaction with the ripples allow the development of a general time scale for craters in meridiani planum over the past million years

mahli at the rocknest sand shadow science and science enabling activities 1 during martian solar days 57 100 the mars science laboratory curiosity rover acquired and processed a solid sediment sample and analyzed its mineralogy and geochemistry with the chemistry and mineralogy and sample analysis at mars instruments an aeolian deposit herein referred to as the rocknest sand shadow was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions during first time activities the mars hand lens imager mahli was used to support both science and engineering activities related to sample assessment collection and delivery here we report on mahli activities that directly supported sample analysis and provide mahli observations regarding the grain scale characteristics of the rocknest sand shadow mahli imaging confirms that the rocknest sand shadow is one of a family of bimodal aeolian accumulations on mars similar to the coarse grained ripples interrogated by the mars exploration rovers spirit and opportunity in which a surface veneer of coarse grained sediment stabilizes predominantly fine grained sediment of the deposit interior the similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on mars we suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation where winnowing of the fine sediment fraction results in a relatively low sediment load and a preferential increase in the coarse grained fraction of the sediment load the compositional similarity of martian aeolian deposits supports the potential for global redistribution of fine grained components combined with potential local contributions

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

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

wind streaks on mars meteorological control of occurence and mode of formation abstract why do some craters on mars produce depositional wind streaks while others produce erosional ones there is no evidence to suggest that crater morphology or topography plays the determining role some craters can form either type of streak at different times of the martian year suggesting that the controlling factor is meteorological we propose that atmospheric stability is the determining factor a stable atmosphere should lead to blocking of the wind flow by crater rims producing wind shadows over distances comparable to those of observed bright streaks such conditions should prevail in a belt about the equator at the time of major dust storms as the atmosphere becomes more transparent following the end of the dust storms the rate of surface heating increases and the stability of the atmosphere is reduced under such conditions blocking is not expected flow over obstacles results in increased surface stress downwind conditions which encourage the formation of erosional dark streaks these ideas are shown to be consistent with the seasons at which erosional and depositional streaks are formed as well as with their distribution on the planet specifically the scheme explains why craters which have both erosional and depositional streaks occur only within a very restricted latitude belt

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

soil grain analyses at meridiani planum mars 1 grain size analyses of the soils at meridiani planum have been used to identify rock sources for the grains and provide information about depositional processes under past and current conditions basaltic sand dust millimeter size hematite rich spherules interpreted as concretions spherule fragments coated partially buried spherules basalt fragments sedimentary outcrop fragments and centimeter size cobbles are concentrated on the upper surfaces of the soils as a lag deposit while finer basaltic sands and dust dominate the underlying soils there is a bimodal distribution of soil grain sizes with one population representing grains 125 m and the other falling between 1 4 5 mm soils within craters like eagle and endurance show a much greater diversity of grain morphologies compared to the plains the spherules found in the plains soils are approximately 1 2 mm smaller in size than those seen embedded in the outcrop rocks of eagle and endurance craters the average major axis for all unfractured spherules measured in the soils and outcrop rocks is 2 87 1 18 mm with a trend toward decreasing spherule sizes in both the soils and outcrop rocks as the rover drove southward wind ripples seen across the plains of meridiani are dominated by similar size 1 3 1 7 mm hematite rich grains and they match in size the larger grains on plains ripples at gusev crater larger clasts and centimeter size cobbles that are scattered on the soils have several spectral and compositional types reflecting multiple origins the cobbles tend to concentrate within ripple troughs along the plains and in association with outcrop exposures

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

paleoseismicity the swedish case abstract sweden is part of an old cratonic area it was repeatedly glaciated during the quaternary after the 20 ka glaciation maximum it has experienced a glacial isostatic uplift of over 800 m numerous paleoseismic indices have been recorded giving evidence of frequent high magnitude earthquakes from the time at around and just after the deglaciation late holocene archaeoseismic fracturing is also reported these observations violate all claims of a possible safe long term repository for high level nuclear waste some 500 m down in the bedrock

late cretaceous antarctic fish diversity new material from the santa marta formation late coniacian early maastrichtian of james ross island contributes significantly to the current knowledge of late cretaceous antarctic fish diversity the taxon list for the santa marta formation is extended and new records of neoselachians and teleosts are reported the stratigraphic ranges of some previously known taxa are enlarged and the palaeobiogeography and palaeoecology of late cretaceous antarctic fishes are discussed top predators that occupied the higher levels in the food chain along with marine tetrapods dominate the marine faunas from the santa marta and lopez de bertodano formations the only fish adapted to crushing hard shelled invertebrates were the chimeroids rays an important component of marine fish associations as well as fish from lower trophic levels remain unknown from the late cretaceous of antarctica

active aeolian processes on mars a regional study in arabia and meridiani terrae 1 we present evidence of widespread aeolian activity in the arabia terra meridiani region mars where different kinds of aeolian modifications have been detected and classified passing from the regional to the local scale we describe one particular dune field in meridiani planum where two ripple populations are distinguished by means of different migration rates moreover a consistent change in the ripple pattern is accompanied by significant dune advancement between 0 4 1 meter in one martian year that is locally triggered by large avalanche features this suggests that dune advancement may be common throughout the martian tropics

earth aeolian wind streaks comparison to wind data from model and stations wind streak is a collective term for a variety of aeolian features that display distinctive albedo surface patterns wind streaks have been used to map near surface winds and to estimate atmospheric circulation patterns on mars and venus however because wind streaks have been studied mostly on mars and venus much of the knowledge regarding the mechanism and time frame of their formation and their relationship to the atmospheric circulation cannot be verified this study aims to validate previous studies results by a comparison of real and modeled wind data with wind streak orientations as measured from remote sensing images orientations of earth wind streaks were statistically correlated to resultant drift direction rdd values calculated from reanalysis and wind data from 621 weather stations the results showed good agreement between wind streak orientations and reanalysis rdd r 0 78 a moderate correlation was found between the wind streak orientations and the weather station data r 0 47 a similar trend was revealed on a regional scale when the analysis was performed by continent with r ranging from 0 641 in north america to 0 922 in antarctica at sites where wind streak orientations did not correspond to the rdds i e a difference of 45 seasonal and diurnal variations in the wind flow were found to be responsible for deviation from the global pattern the study thus confirms that earth wind streaks were formed by the present wind regime and they are indeed indicative of the long term prevailing wind direction on global and regional scales

walvis ridge barrier its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early south atlantic ocean the early south atlantic was subdivided latitudinally by the proto walvis ridge which separated early cretaceous open marine conditions in the south from non marine environments to the north changes in the palaeogeography which can be monitored by the distribution of ostracod assemblages determined the establishment of a wide variety of depositional environments including evaporitic and total organic carbon rich facies limited northward marine influxes across the barrier are postulated for mid aptian time while largescale southward migrations of marine ostracods from the northern sector occurred in early cenomanian and or turonian times the latter established cosmopolitan faunas in the southern atlantic and effectively marked the breakdown of the walvis ridge as a physical barrier to north south migrations although possible oceanographic factors militated against longitudinal faunal movements variations in the composition of ostracod assemblages during so called oceanic anoxic events and the production of potential source rocks is briefly reviewed

reconstruction of eolian bed forms and paleocurrents from cross bedded strata at victoria crater meridiani planum mars outcrop exposures imaged by the opportunity rover at victoria crater a 750 m diameter crater in meridiani planum are used to delineate sedimentary structures and further develop a dune interdune depositional model for the region the stratigraphy at victoria crater observed during opportunity s partial traverse of its rim includes the best examples of meter scale eolian cross bedding observed on mars to date the cape st mary promontory located at the southern end of the rim traverse is characterized by meter scale sets of trough cross bedding suggesting northward migrating sinuous crested bed forms cape st vincent which is located at the opposite end of the traverse shows tabular planar stratification indicative of climbing bed forms with meter to decameter scale dune heights migrating southward promontories located between cape st mary and cape st vincent contain superposed stratigraphic units with northward and southward dipping beds separated by outcrop scale bounding surfaces these bounding surfaces are interpreted to be either reactivation and or superposition surfaces in a complex erg sea any depositional model used to explain the bedding must conform to reversing northward and southward paleomigration directions and include multiple scales of bed forms in addition to stratified outcrop a bright diagenetic band is observed to overprint bedding and to lie on an equipotential parallel to the preimpact surface meter scale cross bedding at victoria crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field comparable to jurassic age eolian deposits in the western united states

origin of longitudinal triangular ripples on the nova scotian continental rise since the recognition of current produced bedforms in the deep ocean attempts have been made to predict direction intensity and variability of abyssal flow from the nature of sea floor irregularities see refs 1 3 longitudinal triangular ripples ltrs are inter mediate scale bedforms 20 cm high metres long that are becoming recognized as important and geographically widespread predictors of bottom current flow i describe here recent sea floor photographs of ltr fields on the lower continental rise off nova scotia which show that the bedforms develop in fine grained cohesive sediment with an alignment parallel to the regional contours and to mean current direction an observational model for ltr formation is proposed wherein ltrs are deposited initially as tails behind large sea floor biological mounds and are subsequently constructed and propagate in the direction of mean current by sediment transport oblique to the bedform axis this transport is induced by short term currents that deviate from mean current direction and cause formation of a separation bubble on one side or the other of the ltr crest

gone with the wind eolian erasure of the mars rover tracks 1 the wheel tracks left by the mars exploration rovers spirit and opportunity are unique artificial markings on the surface of mars the tracks stretch several kilometers across diverse terrain in two widely separated regions of the planet the initial appearance and characteristics of the tracks were well documented by the science and navigation cameras aboard the vehicles at the time the tracks were formed orbital observations by mars global surveyor and mars reconnaissance orbiter document the erasure of the tracks over a period of more than 2 mars years close up examinations of track crossings where the rovers encountered tracks made hundreds of martian solar days earlier provide insights into the mechanisms and time scales of eolian alteration on mars these observations suggest that fallout of atmospheric dust plays only a minor role in obscuring rover tracks over time instead track erasure is dominated by sediment that is transported by surface winds both deposition and erosion act to erase the rover tracks the length scales for eolian sediment transport are hundreds of meters at least much larger than the size of the tracks gradual processes such as dust devils and sand saltation have minor effects that can nonetheless erase rover tracks over long time periods however short lived strong wind events associated with seasonal dust storms have much more pronounced effects significantly altering the tracks on time scales of days these episodic strong winds tend to occur annually during the perihelion season the time scale for track erasure is typically only 1 martian year

additions to the diversity of elasmosaurid plesiosaurs from the upper cretaceous of antarctica abstract three specimens of elasmosaurid plesiosaurs sauropterygia plesiosauria from upper cretaceous beds of antarctica are described here these include postcranial remains of a single adult individual recovered from late maastrichtian beds of marambio seymour island possessing a distinctive combination of features cervical vertebrae having centra with a triangular outline in transverse section a vertical groove on the rostral and caudal edge of the neural spines and a deep articulation over the neural arch for the following postzygapophysis while the scapula shows an unusually large and anteriorly recurved dorsal process this combination of features is unknown in any adult postcranial elasmosaurid genus recovered to date in the upper cretaceous of the weddellian biogeographic province and could represent a new form additional specimens from james ross island comprise the first record of an aristonectinae plesiosauria elasmosauridae in late campanian beds being the oldest known record of this sub family finally a third specimen from the same age and locality reveals the presence of very long necked elasmosaurids with affinities to typical representatives from the upper cretaceous of the northern hemisphere these findings add to the known diversity of upper cretaceous elasmosaurids in high latitudes of the southern hemisphere

a mass movement origin for cirques the glacial process of cirque initiation whereby small initial hillslope hollows grow by nivation until snow can form glacier ice and ice motion then enlarges the hollow to a fully developed cirque appears to have difficulty explaining the creation of large cirques in the time available during quaternary glaciations at the rates at which glaciers are reported to erode rock and in rapidly uplifting mountain ranges it also has difficulty explaining the striking proliferation of cirques in fiordland south island new zealand an area of harder rock and less glaciation than the nearby cirque poor area of south westland here we show that cirques can be initiated as large deep seated often coseismic rock slope failure source area depressions in which snow may accumulate to form cirque glaciers which can then remove detritus from smooth and enlarge the cirque we present an example of a classically shaped cirque that has never held a glacier we show that many similarities between the locations sizes and shapes of rock slope failure source area depressions and cirques are understandable on this basis as is the occurrence of cirques in presently aseismic intraplate locations and their relative paucity in actively uplifting ranges the extent to which cirques may be of mass movement origin has implications for their value as palaeoclimatic indicators copyright 2006 john wiley sons ltd

high resolution topomapping of candidate mer landing sites with mars orbiter camera narrow angle images 1 we analyzed narrow angle mars orbiter camera moc na images to produce high resolution digital elevation models dems in order to provide topographic and slope information needed to assess the safety of candidate landing sites for the mars exploration rovers mer and to assess the accuracy of our results by a variety of tests the mapping techniques developed also support geoscientific studies and can be used with all present and planned mars orbiting scanner cameras photogrammetric analysis of moc stereopairs yields dems with 3 pixel typically 10 m horizontal resolution vertical precision consistent with 0 22 pixel matching errors typically a few meters and slope errors of 1 3 these dems are controlled to the mars orbiter laser altimeter mola global data set and consistent with it at the limits of resolution photoclinometry yields dems with single pixel typically 3 m horizontal resolution and submeter vertical precision where the surface albedo is uniform the dominant error is 10 20 relative uncertainty in the amplitude of topography and slopes after calibrating photoclinometry against a stereo dem to account for the influence of atmospheric haze we mapped portions of seven candidate mer sites and the mars pathfinder site safety of the final four sites elysium gusev isidis and meridiani was assessed by mission engineers by simulating landings on our dems of hazard units mapped in the sites with results weighted by the probability of landing on those units summary slope statistics show that most hazard units are smooth with only small areas of etched terrain in gusev crater posing a slope hazard

intense earthquakes and seismotectonics as a function of glacial isostasy abstract old shields and plate interiors have often been assumed to exhibit a high crustal stability during the last decade or two we have learnt more and more about the fragility not to say untenability of this concept however high magnitude earthquakes and large scale fault movements have been recorded where they were not supposed to be able to occur within formerly glaciated areas like northern europe scotland and northern north america a rapidly increasing number of field observations indicates that the glacial isostatic readjustment process was linked to intense seismotectonic activity we will here investigate the fennoscandian situation and propose a novel causation model for the high deglaciation seismicity in comparison with the present day situation

comparison of remote sensing observations of planetary wind streaks abstract wind streaks are common aeolian features observed on terrestrial planets they were first identified on mars thus the associated terminology is based on mars related observations usually describing surface patterns with distinct albedos however terms related to reflected tones are only relevant to past knowledge for mars and not necessarily suitable for description of radar visible streaks located on venus titan or earth furthermore the sensor type used to observe wind streaks can influence the subsequent data analysis the purpose of this study was to examine the effects of sensor type on wind streak identification and interpretation six case studies featuring wind streaks on earth were performed using imaging by both radar and optical sensors the results indicate that wind streak identification is constrained to a specific combination of sensor settings appropriate for the local surface properties only half the optically visible wind streaks considered in this study were also radar visible but all the wind streaks observable in the radar images also appeared in the optical images furthermore bright and dark reflectance and backscatter are relative terms and should be used with caution these results suggest that the venusian wind streak database is most likely far from complete and that many more streaks exist

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

interpretation of the complex dune morphology on mars dune activity modelling and a terrestrial analogue in this work we analyze a dark erg on mars that could be considered a mega dune draa where secondary dunes of different morphology are superposed over a main crescent shaped bedform primary dune the presence of a complex multi directional wind regime is indicated as one of the main causes for the accumulation of a tall draa presenting an analogy to the great sand dunes in colorado in both cases main regional winds from the sw blow in opposition to winds from the ne which are enhanced by the topography such a complex wind regime leads to the development of star and reversing dunes and is accurately predicted by atmospheric models on a regional and local scale signs of activity in the form of grainflow scars are also noted over the slip faces of many dunes suggesting that easterly winds are actively shaping the study draa in the present day climatic setting the presence of this draa on mars suggests a complex interaction between regional and local topographically controlled flows and a consistent availability of sand the future study of an analogue terrestrial site such as the great sand dunes could be fundamental for understanding the evolution of similar martian dune fields copyright 2012 john wiley sons ltd

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

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

deglacial paleoseismicity in sweden the 9663 bp iggesund event abstract the iggeesund event is an example of the high seismicity which occurred in fennoscandia during deglaciation as a function of the high rate of glacial isostatic uplift this event is dated to varve 9663 bp the iggesund hudiksvall area is represented by intensive postglacial fracturing of the bedrock recorded over an area of at least 50 50 km the most remarkable locality is the boda cave system a hill fractured into a field of large detached blocks with a cave system of more than 2 km length in the varve year 9663 bp an extensive turbidite was spread over an area of 210 80 km liquefaction structures are recorded over an area of 80 30 km and can be assigned to the same varve year structures and deposits of a tsunami are recorded over 80 50 km

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

the use of varved clay chronology for dating paleoseismic events the erstavik record in the stockholm area south sweden abstract geological structures suggest that the fennoscandian shield was subjected to a higher seismicity at the end of the last glaciation than today this article demonstrates the use of varved clay chronology for dating paleoseismic events it is argued that the deposited annually layered glacial varves were sensitive to past ground movements in the stockholm area the erstavik varved clay chronology suggests four paleoseismic events a first i dating from varve year 10 473 to 10 468 bp a second ii 10 451 to 10 445 bp a third iii 10 429 to 10 425 bp and a fourth iv 10 409 to 10 404 bp in de geer s old 1940 chronology the first i dating corresponds with 1117 to 1112 the second ii with 1095 to 1089 the third iii with 1073 to 1069 and the fourth iv with 1053 to 1048 the most pronounced event was the one at around varve year 10 429 bp varve 1073 in de geer s old chronology the recurrence time of about 20 years suggests a totally different seismic regime at the time of deglaciation than what exists today it coincided with the period of maximum isostatic uplift the complexity of the varved clay response to seismic events is also discussed

high resolution measured and modelled three dimensional airflow over a coastal bowl blowout abstract blowouts are common landforms found within coastal dunes their dynamics are primarily driven by aeolian transport caused by surface wind stress though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex three dimensional wind flows around blowouts have yet to be properly quantified especially within zones of separation re attachment and acceleration this has been largely due to inadequate measurement of airflow and a lack of suitable airflow models with this in mind we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the belmullet peninsula ireland using ultrasonic three dimensional anemometry measuring at 50 hz and three dimensional computational fluid dynamic cfd modelling we measure and model for the first time in 3d a detailed picture of the heterogeneity of wind flow over this type of terrain during alongshore wind conditions wind speeds within the deflation basin were retarded by 50 compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim wind was directed into the deflation basin through a gap in a western erosional wall termed the blowout throat in oblique onshore wind airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30 compared to wind speed on the foredune in lee of the erosional wall adjacent to the blowout throat small zones of flow separation occurred close to the erosional wall in both cases the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls the results illustrate that wind is manipulated according to localised topography within the bowl blowout itself resulting zones of potential sediment transport erosion and deposition are spatially complex and alter with wind direction the presence of a blowout throat has a significant influence on airflow patterns within a deflation basin modelled cfd and measured anemometer data demonstrated excellent comparisons for wind direction and speed allowing much greater spatial measurement resolution than physical instrumentation simulated turbulence did not correlate well with measured data highlighting the requirement for high frequency three dimensional anemometry in areas of complex flow

submarine holocene sedimentary disturbances in the olkiluoto area of the gulf of bothnia baltic sea a case of postglacial palaeoseismicity abstract high resolution echo soundings were used to study the fault activity in the olkiluoto area of the gulf of bothnia southwestern finland echo sounding profiles in holocene submarine sediments show normal faults structures related to gas or groundwater seepage submarine slides and slumps and debris flow type structures the faults and other disturbance structures occur along two bedrock lineaments all faults occur at the same stratigraphical level whose age is estimated at 10 700 calendar years bp 9500 radiocarbon years bp it is suggested that their movement has been triggered by palaeoseismic event s when the late weichselian ice sheet was retreating from the site and bedrock stresses were released through lineaments and fracture zones these are the first observations of postglacial fault movements in quaternary sediments from southern finland but the timing of these movements is contemporaneous with the incidence of postglacial bedrock faulting 9000 10 000 radiocarbon years bp in northern fennoscandia the origin of the gas groundwater seepages remains unclear their reflections in the echo sounding profiles imply that part of the gas is derived from the organic bearing litorina and recent gyttja clays however at least some part of the gas is derived from the bedrock deep gas

origin of a complex and spatially diverse dune field pattern algodones southeastern california the algodones dune field of southeastern california shows a complex and spatially diverse dune field pattern that is superimposed upon a series of topographic lineations analysis of dune field pattern parameters dune crest length crest orientation dune spacing and defect density derived from aerial images indicates that the dune field pattern represents two constructional generations prominent compound crescentic dunes formed during the first constructional generation a younger generation consists of a variety of simple crescentic dunes linear dunes and zibars statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved and provide explanations for 1 diversity of dune types 2 range in implied constructional times 3 range in crest orientations and 4 the anomalous nature of the population of linear dunes the boundary conditions that have modified pattern development include orographic effects grain size vegetation areal extent and antecedent conditions topographic lineations in the algodones range from the western ramp which defines the field margin to subtle features masked by the pattern of dunes imaging of the western ramp using ground penetrating radar shows high angle cross strata migrating perpendicular to the lineation trend the most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent lake cahuilla which is the source of algodones sands the overall geomorphic complexity of the algodones originates from the emplacement of the dune ridges during stages of lake cahuilla the two generations of dune field construction and the controls exerted by boundary conditions

shifting sands on mars insights from tropical intra crater dunes evidence for sand motion is found in repeated observations of sand dunes at three sites in the martian tropics by the high resolution imaging science experiment on mars reconnaissance orbiter an eroding outcrop of layered sediments is identified as a possible source of the sand in pasteur crater ancient layered sediments in becquerel crater are actively being carved into flutes and yardangs by the blowing sands dunes in an un named crater in meridiani near the mars exploration rover opportunity landing site advanced as much as 50 cm over an interval of one martian year copyright 2012 john wiley sons ltd

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

neotectonics and paleoseismicity within the stockholm intracratonal region in sweden abstract a number of sites with fresh faults and fractures have been mapped in detail their postglacial and sometimes late glacial age is confirmed they form simple and similar patterns consistent with stress release due to a combination of acting forces they are associated with the peak rate of glacial isostasy and increased strain rates by two orders of magnitude they often cut straight across bedrock hills between so called weak zones the fault throws correspond to approximately magnitude 7 on the richter scale sedimentary and morphological data confirm the seismo tectonic origin newly discovered large scale network of crossing faults is found to have changed the course of the stockholm esker in a way that reveals at least two major seismo tectonic events this is consistent with paleoseismic events of magnitude 7 or more

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

fossil marine actinopterygian fishes from the kaskapau formation upper cretaceous turonian near watino alberta turonian fossil marine fishes occur at several localities near watino alberta in sandstones and in shale concretions of the vimy member kaskapau formation the actinopterygian fossils in the san

paleoseismicity and geodynamics in sweden abstract paleoseismicity denotes past pre instrumental earthquakes as recorded by bedrock structures morphological features and sedimentological criteria glacial varves eskers and deltas are excellent records of paleoseismic events data from sweden are presented faults fractures and various types of sedimentary disturbances of late pleistocene and holocene age frequently occur it is concluded that the seismic activity was very intensive in connection with the peak rates of glacial isostatic uplift and that this was a natural effect of the geodynamic processes operating

global changes the lithosphere internal processes and earth s dynamicity in view of quaternary observational data abstract observational data indicate that the earth has a much higher dynamicity than is generally believed and that internal processes occupy key positions in major integrated geophysical geodynamic systems are susceptible to much more rapid and larger changes than generally believed and hence are indispensable for the understanding of global changes studies of the internal processes must therefore be included in the global change project the quaternary provides an ideal time framework for such studies

localization and physical property experiments conducted by opportunity at meridiani planum the location of the opportunity landing site was determined to better than 10 m absolute accuracy from analyses of radio tracking data we determined rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images topographic profiles generated from rover data show that the plains are very smooth from meter to centimeter length scales consistent with analyses of orbital observations solar cell output decreased because of the deposition of airborne dust on the panels the lack of dust covered surfaces on meridiani planum indicates that high velocity winds must remove this material on a continuing basis the low mechanical strength of the evaporitic rocks as determined from grinding experiments and the abundance of coarse grained surface particles argue for differential erosion of meridiani planum

the birth and death of transverse aeolian ridges on mars transverse aeolian ridges tars are small bright windblown deposits found throughout the martian tropics that stand a few meters tall and are spaced a few tens of meters apart the origin of these features remains mysterious more than 20 years after their discovery on mars this paper presents a new hypothesis that some of the tars could be indurated dust deposits emplaced millions of years ago during periods of higher axial obliquity it suggests that these tars are primary depositional bed forms that accumulated in place from dust carried by the winds in suspension perhaps in a manner comparable to antidunes on earth and were subsequently indurated and eroded to their current states by eons of sandblasting it points out examples of modern dust drifts and dune like features that appear to have been recently formed by dust accumulating directly onto the surface from atmospheric suspension it shows how these pristine dust deposits could evolve to explain the range of morphologies of the tars finally it explains how the known properties of many tars are consistent with this hypothesis including their composition thermal behavior and distribution

an interpretation and catalogue of paleoseismicity in sweden abstract paleoseismic data provide a long term record of seismic activity to predict hazards for periods longer than one to a few centuries in sweden the analysis reveals there was a drastic change in dominant seismic mode from a high to super high deglacial mode to a low to moderately low mode in present and late holocene time paleoseismic criteria and characteristics include numerous different sources of information viz primary faults bedrock deformation sedimentary deformation rock and sediment slides liquefaction sorting by shaking tsunamis differing geomorphic expressions disordering and ordering of magnetic particles by applying multiple criteria it was possible to identify 44 paleoseismic events including 23 events of estimated m 6 7 12 events of m 7 8 and 6 events of m 8 varve dating often allows a precision as to a single year in one case even to the season of a year the key for paleoseismic reconstruction and testing is the application of multiple criteria

campanian maastrichtian cretaceous stratigraphy of the james ross island area antarctica one of the most important outcrops of uppermost cretaceous campanian maastrichtian sedimentary rocks in the southern high latitudes occurs within the james ross island group northeastern antarctic peninsula these rocks comprise a 1500 2000 m thick sequence of predominantly shallow marine clastic sediments that were deposited within a retro arc basin they are virtually undeformed and have yielded prolific invertebrate and vertebrate faunas and a wide range of plant taxa campanian maastrichtian strata are contained within two component formations of the upper cretaceous lower tertiary marambio group the lower santa marta formation is approximately 1100m thick and has three constituent members ammonites within the santa marta formation indicate an early to late campanian age assignment dinoflagellates suggest that the lower levels of the formation may range into the santonian stage in the northern james ross island to vega island region there is a conformable transition into the overlying lopez de bertodano formation here the basal cape lamb member is unconformably overlain by the sandwich bluff member although there are some lithological and fauna1 discrepancies which are attributed to marked lateral facies changes across the basin it is believed that the cape lamb member can be correlated with the lower to middle regions of the 1200 m thick sequence of undifferentiated lopez de bertodano formation lithologies exposed on seymour island molluscan data indicate a late campanian palaeocene age range for this upper formation dinoflagellates again suggest that the lowest beds may be slightly older the correlation presented provides the basis for a formal subdivision of the campanian and maastrichtian stages in the southern high latitudes it has also revealed two major basin shallowing events in the late campanian early maastrichtian and latest maastrichtian respectively and the existence of a major fault fault zone across southeastern james ross island the improved temporal framework will aid late cretaceous palaeoclimatic and palaeobiological studies in antarctica

overview of the opportunity mars exploration rover mission to meridiani planum eagle crater to purgatory ripple the mars exploration rover opportunity touched down at meridiani planum in january 2004 and since then has been conducting observations with the athena science payload the rover has traversed more than 5 km carrying out the first outcrop scale investigation of sedimentary rocks on mars the rocks of meridiani planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine grained siliciclastics and sulfates the siliciclastic fraction was produced by chemical alteration of a precursor basalt the sulfates are dominantly mg sulfates and also include ca sulfates and jarosite the stratigraphic section observed to date is dominated by eolian bedforms with subaqueous current ripples exposed near the top of the section after deposition interaction with groundwater produced a range of diagenetic features notably the hematite rich concretions known as blueberries the bedrock at meridiani is highly friable and has undergone substantial erosion by wind transported basaltic sand this sand along with concretions and concretion fragments eroded from the rock makes up a soil cover that thinly and discontinuously buries the bedrock the soil surface exhibits both ancient and active wind ripples that record past and present wind directions loose rocks on the soil surface are rare and include both impact ejecta and meteorites while opportunity s results show that liquid water was once present at meridiani planum below and occasionally at the surface the environmental conditions recorded were dominantly arid acidic and oxidizing and would have posed some significant challenges to the origin of life copyright 2006 by the american geophysical union

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

patterns in mobility and modification of middle and high latitude southern hemisphere dunes on mars nasa mars data analysis program mdap nnx14ao96g mdap grant nnx12aj38g nnx16aj43g 123117

development of spatially diverse and complex dune field patterns gran desierto dune field sonora mexico the pattern of dunes within the gran desierto of sonora mexico is both spatially diverse and complex identification of the pattern components from remote sensing images combined with statistical analysis of their measured parameters demonstrate that the composite pattern consists of separate populations of simple dune patterns age bracketing by optically stimulated luminescence osl indicates that the simple patterns represent relatively short lived aeolian constructional events since 25 ka the simple dune patterns consist of i late pleistocene relict linear dunes ii degraded crescentic dunes formed at 12 ka iii early holocene western crescentic dunes iv eastern crescentic dunes emplaced at 7 ka and v star dunes formed during the last 3 ka recognition of the simple patterns and their ages allows for the geomorphic backstripping of the composite pattern palaeowind reconstructions based upon the rule of gross bedform normal transport are largely in agreement with regional proxy data the sediment state over time for the gran desierto is one in which the sediment supply for aeolian constructional events is derived from previously stored sediment ancestral colorado river sediment and contemporaneous influx from the lower colorado river valley and coastal influx from the bahia del adair inlet aeolian constructional events are triggered by climatic shifts to greater aridity changes in the wind regime and the development of a sediment supply the rate of geomorphic change within the gran desierto is significantly greater than the rate of subsidence and burial of the accumulation surface upon which it rests

a new hesperornithiform aves specimen from the late cretaceous canadian high arctic with comments on high latitude hesperornithiform diet here we describe a new hesperornithiform specimen from the upper cretaceous kanguk formation of devon island nunavut canada this specimen nuvf 286 is referred to cf hesperornis sp based on size and shape of femora and teeth preserved with other skeletal elements previous osteohistologic analyses indicate a subadult ontogenetic stage at the time of death this new cf hesperornis specimen includes the first teeth associated with a high latitude hesperornithiform allowing for comments on the trophic behavior of these birds paleoecological reconstructions based on current knowledge of polar assemblages and comparisons to modern birds suggest that high latitude hesperornithiform birds may have had more varied diets than previously assumed

largest wind ripples on earth unique wind ripples attaining heights to 2 3 m wavelengths to 43 m and a crest maximum grain size of 19 mm occur on the argentine puna plateau at 4000 m altitude these are the largest ripples reported on earth comparable only to mars counterparts they form in the presence of high proportions of low density pumice clasts 0 91 g cm 3 although crests are exclusively composed of varnished normal density clasts 2 43 g cm 3 mature ripple profiles are partly excavated on bedrock so they form by a combination of deflation winnowing of finer grains minor wind drift of fine gravel and lagging of clasts 4 cm the large ripple size appears to be related to strong winds dense saltation layers and a long time for evolution ripple sizes are smaller on obstacles as compared to flat terrain there is a lack of correlation between clast size wavelength and the extreme ripple size in spite of the thin atmosphere all of which suggest that while small scale gravel ripples may form according to a reptation model their evolution into large scale types may relate to aerodynamic instabilities originating at the saltation curtain air interface

definition of late cretaceous stage boundaries in antarctica using strontium isotope stratigraphy abstract new 87sr 86sr analyses of macrofossils from 13 key marker horizons on james ross and vega islands antarctica allow the integration of the antarctic late cretaceous succession into the standard biostratigraphic zonation schemes of the northern hemisphere the 87sr 86sr data enable late cretaceous stage boundaries to be physically located with accuracy for the first time in a composite southern hemisphere reference section and so make the area one of global importance for documenting late cretaceous biotic evolution particularly radiation and extinction events the 87sr 86sr values allow the stage boundaries of the turonian coniacian coniacian santonian santonian campanian and campanian maastrichtian as well as other levels to be correlated with both the united kingdom and united states these correlations show that current stratigraphic ages in antarctica are too young by as much as a stage immediate implications of our new ages include the fact that inoceramus madagascariensis a useful

in absurdum long term predictions and nuclear waste handling abstract careful use of scientific knowledge allows predictions into the future when the time units for our predictions increases to hundreds of thousands of years we have extended our abilities in absurdum this is true for long term safety statements regarding the handling of our high level nuclear waste the fennoscandian shield has been claimed to offer exceptionally stable bedrock conditions over immense time periods we only need to go back to the last deglacial phase some 10 000 years ago to have a totally different situation from that of today at that time sweden was characterized by exceptionally high seismic activity both in amplitude and frequency these conditions like a number of related phenomena will be repeated at future ice ages in such an environment there can be no safe repository in the bedrock in the absence of true long term safety we can only recommend the utilization of the dry rock deposit drd method where the waste is stored in the bedrock under dry conditions under constant control and monitoring accessible for maintenance and possible future methods of rendering the waste harmless and even removal

late cretaceous extinction patterns in antarctica new correlations of marine clastic sedimentary rocks exposed within the james ross basin antarctica have shown that the mid to late cretaceous succession is in excess of 5 km thick plotting the ranges of the principal molluscan macrofossils against the revised stratigaphy indicates that inoceramid bivalves are totally absent and dimitobelid belemnites extremely rare throughout an extensive 1400 m thick maastrichtian succession these early extinction patterns are interpreted to be due to both a regional shallowing event and a pronounced phase of high latitude campanian maastrichtian cooling cool polar bottom waters may have been forming by as early as mid to late campanian times

persistent aeolian activity at endeavour crater meridiani planum mars new observations from orbit and the surface abstract aeolian driven bedform activity is now known to occur in many regions of mars based on surface and orbital observation of contemporary martian ripple and dune mobility events many of these sites have only been monitored with sufficient resolution data for the last few mars years when the high resolution imaging science experiment hirise began acquiring images of mars one exception is the well monitored endeavour crater in meridiani planum which was one of the first known sites of unambiguous dune activity migration and deflation however those early detections used lower resolution images over longer temporal baselines versus the hirise data now available leaving some measurements poorly constrained new orbital and surface observations of endeavour show multiple spatial cm m km and temporal seasons mars year scales of aeolian driven surface change which confirms earlier reports dome dunes in the eastern portion of the crater persistently deflate disseminating dark sand across lighter toned regolith and or eroded bright dust and likely contribute to the crater interior s episodic decreases in orbital albedo measurements other dome dunes are detected with the highest migration rates 4 12 m per mars year and volumetric sand fluxes reported yet for mars estimated dune construction times or turnover times here and elsewhere on mars are significantly shorter than martian obliquity cycles implying that it is not necessary to invoke paleoclimate wind regimes to explain current dune morphologies located on the crater rim the opportunity rover detected evidence for near and far field aeolian driven activity with observations of spherules sand movement in the rover workspace bedform albedo alteration and dust lifting events observations of intracrater dunes show periodic shifting dark streaks that significantly constrain local wind regimes directionality and seasonality constraints on wind directions from surface and orbital images show that aeolian bedforms can be extremely active in bi and possibly tri modal wind regimes and during periods without major dust storms

stratigraphy and vertebrate paleoecology of upper cretaceous lowest paleogene strata on vega island antarctica the upper cretaceous maastrichtian sandwich bluff member of the lopez de bertodano formation is well exposed on vega island in the james ross basin off the northeastern coast of the antarctic peninsula although this unit is one of the richest sources of end cretaceous vertebrate fossils in antarctica it is also one of the least sedimentologically and stratigraphically characterized units in the basin new facies and stratigraphic analyses of the sandwich bluff member and the underlying cape lamb member of the snow hill island formation were performed in tandem with intensive prospecting for fossil vertebrates and stratigraphic assessment of historic paleontological localities on vega island this effort has led to a revised stratigraphy for the sandwich bluff member and the precise stratigraphic placement of important terrestrial and marine vertebrate fossil localities facies analysis reveals a fining and shallowing upward trend through the section that culminates in a newly recognized sequence boundary near the top of the sandwich bluff member followed by the deposition of a previously unrecognized 6 m thick matrix supported pebble cobble conglomerate of probable alluvial origin immediately overlying this unit well developed thalassinoides burrow networks in fine grained transgressive sandstones and siltstones indicate a rapid return to marine conditions a similar stratigraphic pattern is well documented at the top of the lopez de bertodano formation and the base of the overlying paleocene sobral formation on seymour island in the southern part of the basin although no fossils were recovered to constrain the age of the upper 10 15 m of the succession on vega island that preserves the newly recognized upper sequence boundary strata below this level can be confidently placed within the manumiella bertodano interval zone which extends to a short distance below the k pg boundary on seymour island hence based on sequence stratigraphic and lithostratigraphic evidence the uppermost 10 15 m of the succession on vega island may encompass the cretaceous paleogene boundary together with a few meters of the paleocene sobral formation

aeolian dune field pattern boundary conditions aeolian dune field patterns reflect the complex external environment within which the pattern evolves these external environmental controls are the boundary conditions on aeolian dune field pattern formation the influences of boundary conditions such as wind regime and sediment supply are well known however boundary conditions represent a relatively unexplored area of dune field pattern formation source area geometry and areal limits are two newly recognized boundary conditions measurements of crest spacing and crest length from satellite images of dune field patterns with point and line source area geometries show an increase in spacing and crest length over distance whereas spacing and crest length in plane sourced patterns emerge equally across the dune field the impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area and that dune fields that are five times longer in the direction of dune migration than in the crest parallel direction can achieve the greatest spacing within a given area empirical measurements of spacing defect density and dune field area from ten different dune fields ranging over four orders of magnitude in size show that spacing increases and defect density decreases as dune field area increases because the formation of all dune fields involves a wind regime and sediment supply there must be interplay of boundary conditions within the same dune field at different stages of pattern development one boundary condition may dominate over others and with changing climatic eustatic or tectonic parameters boundary conditions may change to modify an existing pattern recognizing boundary condition controls on aeolian dune field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change