forced regressive and lowstand hudson paleo delta system latest pliocene growth of the outer new jersey shelf abstract interpretation of the latest pleistocene stratigraphy of the outer new jersey shelf has evolved over the last three decades with addition of new geological and geophysical data during the last decade new results have described and interpreted various depositional elements within the latest pleistocene that overlie the regional reflector known as the r horizon on the basis of observations made from detailed mapping of the r horizon and the overlying sediment wedge s using high resolution shallow seismic chirp data acquired in several phases between 2001 and 2006 we revise the depositional model for the offlapping multi clinothem sediment wedge on the latest pleistocene outer new jersey shelf as strike elongated lobes of a falling stage wave influenced delta system fed by a pre lgm paleo hudson river channel s that probably reached the late pleistocene shelf edge off new jersey this sediment wedge is composed of a series of prograding and offlapping clinothems of varying thickness within our data which does not extend to the basinward termination of the wedge we seldom observe preserved topsets of these clinothems parts of the foresets of some clinothems are also not preserved particularly in the proximal part of the wedge the sediment wedge is elongated in strike direction nne ssw which suggests along strike sediment movement and possible redistribution of sediment in that direction by ambient shore parallel currents our data do not record any time equivalent fluvial channels at the proximal end of the sediment wedge though there are channel features that cap and cut down into several of the clinothems that make up the wedge farther seaward we suggest that this can be explained in two possible ways 1 relatively large spatial separation between the prograding front of the delta system and the delta plain topset deposits as is very common under a falling stage sea level condition and 2 lack of preservation of the stratigraphic record of the delta plain channels because of the likely vigorous falling stage erosion of topsets during the fall of sea level and possibly also during the subsequent transgressive ravinement and flooding after the lgm the clinothems within the sediment wedge show systematic variation in thickness indicating a northward shift of the main depocenter this shift might also be an indication of gradual northward migration of the principal fluvial feeder such a possibility is supported by previously reported late pleistocene paleo hudson channel deposits south of the modern hudson shelf valley

morphology and filling of incised submarine valleys on the continental shelf near the mouth of the fly river gulf of papua 1 much historical perspective about terrestrial and marine processes can be obtained from examination of fluvial valleys formed during lower sea level on surfaces that are now continental shelves the continental shelf near the mouth of the fly river gulf of papua has three incised valleys which were not extensively modified or filled during the holocene transgression multibeam mapping of the valleys documents their morphology seismic profiling reveals stratigraphy of sediment fill and coring within and near the valleys suggests mechanisms of filling kiwai valley is deep 20 50 m relief narrow 1 km wide steep sided and meandering due to river flows that caused its excavation through competent sedimentary deposits purutu valley is shallow 10 20 m relief and broad 2 km wide umuda valley is widest 14 km and has multiple channels with variable incision depths suggesting more extensive fluvial activity than the other two valleys valley filling has occurred in several ways reflecting valley morphology and location relative to the present river mouth kiwai and umuda valleys reveal three stages of infill 1 hemipelagic sedimentation at distal sites 2 gravity driven flows spreading down the valley and 3 subsequent clinoform progradation that completely fills the valley purutu valley fill is dominated by clinoform progradation clinoform progradation in umuda valley is driven by intense sediment reworking on the surrounding topset regions and its large width allows progradation from the sides as well as down its axis most shelf valleys around the world were filled long ago and available techniques have severe limitations for documenting the details of morphology and the mechanisms of filling the shelf valleys described in this paper provide a unique perspective to terrestrial and marine processes before during and after the holocene transgression

nd isotopic variations of phanerozoic paleoceans abstract the size of various phanerozoic paleoceans determined from paleogeographic maps provides a framework for assigningend measurements of primary authigenic marine minerals to individual paleoceans and for establishing theirend versus age curves we report newend data in the range from 80 to 750 ma for the largest phanerozoic and late precambrian paleocean the pacific panthalassa ocean ppo and limited data on some small paleozoic paleoceans these new data and all other published data on paleoceanend values are used to determine the trends through time ofend in seven phanerozoic paleoceans the variations in paleoceanend curves are due to changes in the rate of crustal additions and in paleoceanic geometry from these data we can calculate a meanend curve and a mean nd model age curve for phanerozoic seawater these curves show large variations with age and reflect the variations ofend in erosion products from the continents as a function of age the high erosion rates of young uplifted areas enhanceend and nd model age variations of phanerozoic seawater this makes it difficult to quantitatively recover crustal addition rates from these curves however it makes the episodic nature of continental additions more evident

tracking the last sea level cycle seafloor morphology and shallow stratigraphy of the latest quaternary new jersey middle continental shelf seafloor geomorphology and surficial stratigraphy of the new jersey middle continental shelf provide a detailed record of sea level change during the last advance and retreat of the laurentide ice sheet 120 kyr b p to present a nw se oriented corridor on the middle shelf between water depths of 40 m the mid shelf paleo shore and 100 m the franklin paleo shore encompasses 500 line km of 2d huntec boomer profiles 500 3500 hz an embedded 4 6 km2 3d volume and a 490 km2 swath bathymetry map we use these data to develop a relative stratigraphy core samples from published studies also provide some chronological and sedimentological constraints on the upper 5 m of the stratigraphic succession the following stratigraphic units and surfaces occur from bottom to top 1 r a high amplitude reflection that separates sediment 46 5 kyr old by ams 14c dating from overlying sediment wedges 2 the outer shelf wedge a marine unit up to 50 m thick that onlaps r 3 channels a reflection sub parallel to the seafloor that incises r and appears as a dendritic system of channels in map view 4 channels fill the upper portion of which is sampled and known to represent deepening upward marine sediments 12 3 kyr in age 5 the t horizon a seismically discontinuous surface that caps channels fill 6 oblique ridge deposits coarse grained shelly units comprised of km scale shallow shelf bedforms and 7 ribbon floored swales bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits we interpret this succession of features in light of a global eustatic sea level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr the morphology of the new jersey middle shelf shows a discrete sequence of stratigraphic elements and reflects the pulsed episodicity of the last sea level cycle r is a complicated marine non marine erosional surface formed during the last regression while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum wisconsin lowstand i e marine oxygen isotope stage 3 1 channels is a widespread fluvial subarial erosion surface formed at the late wisconsin glacial maximum 22 kyr b p the shoreline migrated back across the mid shelf corridor non uniformly during the period represented by channels fill oblique ridges are relict features on the new jersey middle shelf while the ribbon floored swales represent modern shelf erosion there is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession

the late proterozoic glacial era abstract the late proterozoic glacial record is reviewed on a global basis as a setting and introduction for that part of the symposium concerned with west african tillites no unequivocal glacial deposits have yet been recorded in the interval 1 0 2 0 ga late proterozoic glacial epochs have been grouped into three main periods namely lower congo c 0 9 ga sturtian c 0 8 ga and varangian c 0 65 ga and a possible final late sinian epoch near the precambrian cambrian boundary the ediacaran epoch with its metazoan fauna follows varangian and in part at least precedes late sinian the sturtian and varangian glacial periods each comprise at least two main glacial epochs the tillites of which are widespread chronometric ages are currently disputed and the values given are for identification in the literature rather than to provide chronometric definition of all the glacial epochs only those of the varangian glacial period appear to be represented in west africa it has been argued that varangian tillites were of global extent many forming in tropical latitudes though some authors prefer a hypothesis of polar wandering to limit glaciation to polar latitudes

tectonic evolution of juventae chasma mars and the deformational and depositional structural attributes of the four major light toned rock exposures therein abstract juventae chasma a canyon peripheral to the valles marineris trough system is the product of a unique merger of a martian chaotic terrain depression and an extensional tectonic chasm the chaotic terrain portion is set along a nne ssw axis while a linear trough the chasm component is present along a wnw ese axis within the chasm are four discrete bodies of layered light toned rocks of sedimentary origin features a d the chaotic terrain component formed during the early hesperian as a result of expulsion of liquid water along pre existing planes of weaknesses resulting from a wnw ene compression the chasm component formed in response to ne sw extension during the middle to late amazonian the light toned features a d are layered at

stratigraphic variability due to uncertainty in model boundary conditions a case study of the new jersey shelf over the last 40 000 years abstract prediction of stratigraphy by numerical sedimentary models is influenced by a series of geological boundary conditions paleo bathymetry sediment supply sea level ocean storm climate and tectonics these boundary conditions evolve non linearly over time and have considerable uncertainty this study explores the impact of the uncertainty of complex boundary conditions on stratigraphic prediction two numerical models are sequentially run the climate driven hydrological model hydrotrend generates a time series of discharge and sediment load at the river mouth which then feed into the process based stratigraphic model sedflux 2d sedflux disperses sediment in the fluvio marine domain the bedload fluxes drive floodplain and mouthbar deposition while suspended sediment is dispersed in the ocean through hypopycnal plumes seafloor sediment is reworked by ocean storms failures and subsequent transport as sediment gravity flows sedflux records the thickness of the deposited sediment and the grain size preserved over time along a longitudinal profile one base case simulation and 20 sensitivity tests of the new jersey shallow margin over the last 40 000 yr serve to explore the impact of uncertain boundary conditions initially the shelf is exposed and arctic conditions prevail in the drainage area paleo temperature and precipitation estimates differ significantly between different community climate system model realizations impacting river sediment flux predictions subsequently high sediment supply from the rivers draining the melting laurentide ice sheet has a dominant impact on the shelf stratigraphy drainage basin characteristics are strongly controlled by the hard to define details of the laurentide ice sheet dynamics over the last 10 000 yr the shelf becomes sediment starved and storm dominated but the paleo storm conditions are uncertain and thus require a wide range of values shallow seismic data have been used to validate the large scale deposited thicknesses of the sedflux prediction the base case sedflux prediction for the sedimentary architecture of the new jersey shelf is consistent with the acoustically observed distribution of major sediment wedges due to the strong forcing of the relatively well constrained sea level changes the range in thickness predictions over the sensitivity tests is well within the lateral variations reconstructed from the observed seismic data sedflux predictions and a data set of 654 seafloor samples taken on the new jersey shelf between 50 and 150 m water depth shows a subtle fining towards deeper water sedflux systematically overpredicts the component of fine sediments at the seafloor likely because the model does not predict shell hash paleo storm climate is found to have a high uncertainty and strongly impacts the predicted grain size distributions we advocate a modeling approach which couples a series of sensitivity experiments to a predicted base case experiment in that way the stratigraphic variability caused by uncertainty in the boundary conditions is evident for later users

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

high resolution seismic imaging of outcrop scale channels and an incised valley system within the fluvial dominated lower freshwater molasse aquitanian western swiss molasse basin abstract high resolution seismic reflection surveys on lake geneva near lausanne switzerland allow the interpretation of outcrop scale sedimentary features within the fluvial dominated lower miocene lower freshwater molasse bedrock seismic modelling of an outcrop is used to calibrate the seismic data and assist with interpretation seismic resolution is sufficient to image sandstone channel fill complexes 4 5 m thick five seismic facies are recognized and interpreted as fluvial architectural elements of the lower freshwater molasse two of these facies are characterized by fairly continuous reflections of variable frequency and low to moderate amplitude interpreted as metre thick channel fill complexes the lateral extent of such channels ranges from 100 to 170 m the other three seismic facies are characterized by moderate to high amplitude sub parallel continuous reflections the three facies are mainly distinguished using reflection frequency and continuity they correspond to distinct floodplain settings i e proximal intermediate and distal with respect to the active channel belt on a larger scale a portion of a ca 50 m deep incised valley system probably caused by a relative base level fall was identified two distinct valley fill units are recognized the lower unit was interpreted as comprising valley edge slump units by comparison with outcrop data the upper unit is interpreted as the fluvial fill deposited in the most landward portion of the valley

morphology and processes associated with the accumulation of the fine grained sediment deposit on the southern new england shelf abstract a 13 000 km2 area of the southern new england continental shelf which is covered by anomalously fine grained sediment has been surveyed by means of high resolution seismic reflection and side scan sonar techniques to map its morphology and structure and a near bottom instrument system contributed to understanding present activity of the deposit seismic reflection profiles show that the fine grained deposit which is as much as 13 m thick has accumulated during the last transgression because it rests on a reflector that is geomorphically similar to and continuous with the holocene transgressive sand sheet still exposed on the shelf to the west the ridge and swale topography comprising the sand sheet on the shelf off new jersey and long island are relict in origin as the e same features are found buried under the fine sediment deposit southwestward migrating megaripples observed on the sonographs in the eastern part of the deposit are evidence that sediment is still actively accumulating in this area in the western part of the deposit where surface sediment is composed of silt plus clay evidence of present sediment mobility consists of changes in the near bottom suspended matter concentrations primarily associated with storms nantucket shoals and georges bank are thought to be the sources for the fine textured sediment storms and strong tidal currents in these shoal areas may still erode available fine grained material which then is transported westward by the mean drift to the southern new england shelf where a comparatively tranquil environmen permits deposition of the fine material

the lower middle cambrian stages and stratotypes from the iberian peninsula a revision lower middle cambrian regional stages of the iberian peninsula cordubian ovetian marianian bilbilian acadoparadoxides and solenopleuropsidae stages are now reconsidered in the light of new stratigraphic and palaeontological trace fossils trilobites and archaeocyaths studies these stages are re described with selected stratotypes and chronostratigraphic boundaries the names leonian and caesaraugustian are formally proposed to replace the provisional stages of acadoparadoxides and solenopleuropsidae respectively a correlation chart of the lower middle cambrian lithostratigraphic units from the iberian peninsula is also presented two regessive transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the lower middle cambrian sequence in the iberian peninsula

shallow radar sharad sounding observations of the medusae fossae formation mars the sharad shallow radar sounding radar on the mars reconnaissance orbiter detects subsurface reflections in the eastern and western parts of the medusae fossae formation mff the radar waves penetrate up to 580 m of the mff and detect clear subsurface interfaces in two locations west mff between 150 and 155 e and east mff between 209 and 213 e analysis of sharad radargrams suggests that the real part of the permittivity is 3 0 which falls within the range of permittivity values inferred from marsis data for thicker parts of the mff the sharad data cannot uniquely determine the composition of the mff material but the low permittivity implies that the upper few hundred meters of the mff material has a high porosity one possibility is that the mff is comprised of low density welded or interlocked pyroclastic deposits that are capable of sustaining the steep sided yardangs and ridges seen in imagery the sharad surface echo power across the mff is low relative to typical martian plains and completely disappears in parts of the east mff that correspond to the radar dark stealth region these areas are extremely rough at centimeter to meter scales and the lack of echo power is most likely due to a combination of surface roughness and a low near surface permittivity that reduces the echo strength from any locally flat regions there is also no radar evidence for internal layering in any of the sharad data for the mff despite the fact that tens of meters scale layering is apparent in infrared and visible wavelength images of nearby areas these interfaces may not be detected in sharad data if their permittivity contrasts are low or if the layers are discontinuous the lack of closely spaced internal radar reflectors suggests that the mff is not an equatorial analog to the current martian polar deposits which show clear evidence of multiple internal layers in sharad data

using csem techniques to map the shallow section of seafloor from the coastline to the edges of the continental slope many important processes occur within the shallow section of the seafloor on the continental shelf and slope yet conventional geophysical constraints on the physical properties within this critical boundary layer are limited some of the key constraints involve quantification of fluids within the seafloor which can be provided by electrical methods this paper reviews the application of a towed em system to map the uppermost 20 m of seafloor in a variety of settings ranging from nearshore regions in water depths of approximately 10 m on the continental shelf out to water depths of 1300 m the system is a mapping tool that provides areal maps of seafloor resistivity and has been used for a variety of purposes including sedimentary characterization and facies mapping evaluation of groundwater discharge and mapping seafloor mounds in the gulf of mexico thought to contain massive deposits of gas hydrate

high resolution 3d seismic reflection and coring techniques applied to late quaternary deposits on the new jersey shelf studies of variable small scale features typical of quaternary glacimarine environments require an interdisciplinary approach precisely navigated high resolution 3d seismic surveys nested within a regional 2d seismic framework and integrated with a precisely navigated coring program designed to sample specific shallow acoustic facies we illustrate this approach with examples from continuing studies of sediments on the new jersey continental shelf surficial stratigraphy associated with the latest pleistocene holocene deglaciation has been imaged twice in true 3d using the huntec dts system a deep towed high frequency 500 3500 hz boomer source in both cases nominal profile spacing was 10 m 2 5 m shot points penetration of 40 ms 30 m was achieved seismic facies in the upper 5 m have been interpreted using differential gps navigated vibra cores accuracy of position of both seismic profiles and core locations approaches 5 m much smaller than the wavelengths of the geologic features being imaged sampled survey results show multiple sediment filled channels buried beneath the modern outer shelf meandering south and southeast in the general direction of the shelf edge channels are typically a few meters deep and 100 200 m across lateral continuity between the channeled surfaces within the outer shelf wedge and the mid shelf cannot be demonstrated because of later erosion but both sets of channels incise reflector r believed to be a pre late wisconsinan exposure surface ams14c dates on benthic foraminifers from cores show that channels on the midshelf are cut into sediment 45 000 yrs old and filled with muddy sediment as young as 12 500 yrs whereas channels on the outer shelf are filled with coarser and perhaps older sediment both sets of filled channels are buried beneath a surficial sand layer the integrated approach described here can remove some uncertainties and considerably sharpen the quaternary stratigraphic picture without the perspective obtained from 3d seismic surveys and equally precise sampling interpretations based on broader regional seismic surveys and spot coring are inevitably constrained by the potential for mismatching shallow acoustic and sedimentary facies

geology and insolation driven climatic history of amazonian north polar materials on mars a wealth of image and topographic data from the mars global surveyor and mars odyssey missions has been combined in a detailed geological map of the north polar region of mars one intriguing finding is a cycle of ice deposition similar in duration to a 1 470 year climate cycle of unknown origin on earth if both are externally driven a mechanism that affects both planets such as variation in solar luminosity must be involved mariner 9 and viking spacecraft images revealed that the polar regions of mars like those of earth record the planet s climate history however fundamental uncertainties regarding the materials features ages and processes constituting the geologic record remained1 2 3 4 5 6 recently acquired mars orbiter laser altimeter data7 and mars orbiter camera high resolution images8 from the mars global surveyor spacecraft and moderately high resolution thermal emission imaging system visible images9 from the mars odyssey spacecraft permit more comprehensive geologic and climatic analyses10 11 12 13 14 15 16 17 here i map and show the history of geologic materials and features in the north polar region that span the amazonian period 3 0 gyr ago to present 18 19 erosion and redeposition of putative circumpolar mud volcano deposits15 formed by eruption of liquefied fine grained material led to the formation of an early amazonian polar plateau consisting of dark layered materials crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the amazonian suggesting generally higher obliquity and insolation conditions at the poles than at present brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4 5 myr ref 20 finally the uppermost layers post date the latest downtrend in obliquity 20 000 years ago20

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

paleoenvironmental evidence for latest pleistocene sea level fluctuations on the new jersey outer continental shelf combining high resolution sequence stratigraphy and foraminiferal analysis foraminiferal assemblages in vibracored sediments within 5 m of the seafloor document high resolution sea level fluctuations and confirm the complex quaternary depositional history of the new jersey margin biostratigraphic data have been integrated with ongoing 2 d 3 d high resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle to outer shelf cluster analysis of foraminiferal assemblages sampled every 20 cm average define four sample groups a d dominated by benthic species group a characterized by cibicides lobatulus is a middle to outer shelf assemblage 60 100 m water depths group b is composed of middle shelf species 30 60 m water depths and is characterized by low abundances and a fairly uniform distribution of foraminifera which suggests reworking and or a high rate of sediment accumulation group c dominated by elphidium excavatum is an inner to middle shelf assemblage 10 40 m water depths group d present in only one core and dominated by ammonia beccarii represents marginal marine environments 0 10 m water depths with fluctuations in salinity in general the modern sedimentary veneer i e the upper 20 cm is characterized by the deeper water fauna of group a sediments below these modern deposits are characterized by groups b and c reflecting shallower water depths and variable sediment accumulation rates on the inner and middle shelf taken together the group succession in the cores suggests an overall se to nw landward transgression in these latest pleistocene holocene deposits seismic analysis indicates that one core 27 penetrates the flank of a buried channel including its fill and the pre channel section within the channel three alternations of groups c and d suggest fluctuations between marginal marine and middle shelf paleoenvironments high frequency perhaps very small 10 m changes in base level are indicated using previously published ams 14c dates these fluctuations can be constrained as having occurred between 45 000 yr b p channel incision and 12 500 yr b p channel filling suggesting the non uniform nature of the last wisconsinan deglaciation

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

mars landscape evolution influence of stratigraphy on geomorphology in the north polar region abstract lithology and physical properties of strata exposed at the earth s surface have direct influence on the erosion and geomorphic expression of landforms while this is well known on our planet examples on mars are just coming to light among the tens of thousands of airphoto quality images resolutions 1 5 12 m pixel acquired since 1997 by the mars global surveyor mgs mars orbiter camera moc specific examples occur among martian north polar layered materials which moc images reveal are divided into two distinct stratigraphic units a lower dark toned layered unit and a younger upper lighter toned layered unit the lower unit is less resistant to wind erosion than the upper unit the upper unit most likely consists of stratified dust and ice while the lower unit contains abundant poorly cemented sand sand is more easily mobilized by wind than dust the lower resistance to erosion of the lower unit results from the presence of sand where wind erosion in polar troughs has penetrated to the lower unit geomorphic change has proceeded more rapidly sand has been liberated from the lower unit and arcuate scarps have formed as the upper unit has been undermined wind erosion of the lower unit thus influences the geomorphology of the north polar region this result likely explains the genesis of the large polar trough chasma boreale and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades the properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30 50 less than previously estimated

seismic facies and regional architecture of the oak ridges moraine area southern ontario analysis of over 50 line kilometres of land based shallow seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

relict iceberg keel marks on the new jersey outer shelf southern hudson apron swath sonar bathymetry reveals sinuous furrows 400 m wide kilometers long and 4 m deep inscribed in semilithified clays on the southern hudson apron we interpret these as keel marks created by floating icebergs detached from the retreating laurentide ice sheet since ca 25 ka keel mark orientations suggest two phases of iceberg rafting these phases could correlate with heinrich meltwater events h2 and h1 ca 25 and 17 ka bracketing the late wisconsinan glacial maximum ca 22 ka during holocene transgression some keel marks were reworked and reformed into oblique ridges where older sandier sediments crop out at the seafloor relict glacial features on the new jersey outer shelf provide a tie between the timing of laurentide glacial retreat and the evolution of shallow stratigraphy on this mid latitude shelf during the last global sea level cycle ca 120 ka to present

late quaternary sedimentation on the outer and middle new jersey continental shelf result of two local deglaciations high resolution seismic profiles show two prominent late quaternary sediment wedges on the outer and middle new jersey continental shelf an extensive wedge along the outermost shelf and upper slope up to 50 m thick appears to have been deposited on the hudson apron during an early melting of the late wisconsin laurentide ice sheet subsequent southward transport of this sediment occurred during sea level regression still stand and transgression a mid shelf sediment wedge which forms the fortune shore probably was deposited during a second melt event 11 to 12 ka as sea level was transgressing over the shelf

origin and characteristics of the mars north polar basal unit and implications for polar geologic history building upon previous studies we have used mars orbiter camera and mars orbiter laser altimeter data to characterize in detail the newly discovered north polar basal unit lying stratigraphically between the polar layered deposits from which it is likely separated by an unconformity and the vastitas borealis formation this unit has introduced new complexity into north polar stratigraphy and has important implications for polar history exposures of the basal unit in olympia planitia and chasma boreale reveal relatively dark layers which exhibit differential erosion eroded primarily by wind the basal unit may be the major if not sole source for the north polar dunes and ergs and has contributed material to the lower polar cap layers we investigate four possible origins for the basal unit outflow channel oceanic deposits basal ice paleopolar deposits and eolian deposits the patchy layering within the unit its likely sandy grain size and presence only in the north polar basin suggest that it is primarily an eolian deposit supporting byrne and murray s 2002 earlier conclusion this implies that at some time during the early to late amazonian migrating sand was mixed with water ice forming a relatively dark sandy deposit during this time either no classic polar layered deposits were forming or smaller caps were growing and shrinking possibly adding material to the basal unit

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

towards high resolution 3d marine seismic surveying using boomer sources the use of boomer sources for 3d seismic imaging of shallow marine structures was investigated in a feasibility study boomers show sufficient stability to be used in multichannel seismic surveys the acquisition of a high frequency densely sampled seismic data volume was successfully performed in the baltic sea a pleistocene fluvial channel system and shallow gas accumulations were revealed beneath the unconsolidated sediments which constitute the sea floor in the southern kiel bay

shell structure and distribution of cloudina a potential index fossil for the terminal proterozoic cloudina bearing biosparites and biomicrites in the lower part of the nama group namibia contain a wide morphological diversity of shell fragments that can all be attributed to the two named species c hartmannae and c riemkeae the curved to sinuous tubular shells of cloudina were multi layered each shell layer was 8 to 50 micrometers thick and in the form of a slightly flaring tube with one end open and the other closed growth appears to have been periodic with successive shell layers forming within older layers each added layer was slightly elevated from the previous layer at the proximal end and was asymmetrically placed within the older layer so that only a portion of the new shell layer was fused to the previous layer this type of growth left a relatively large unminerialized area between the shell layers which was often partially or fully occluded by early marine cements the thin shell layers exhibit both plastic and brittle deformation and were likely formed of a rigid caco3 impregnated organic rich material often the shell layers are preferentially dolomitized suggesting an original mineralogy of high magnesian calcite both species in the nama group formed thickets or perhaps bioherms and this sedentary and gregarious habit suggests that cloudina was probably a filter feeding metazoan of at least a cnidarian grade of organization the unusual shell structure of cloudina gives rise to a characteristic suite of taphonomic and diagenetic features that can be used to identify cloudina bearing deposits within the nama group and in other terminal proterozoic deposits around the world species of cloudina occur in limestones from brazil spain china and oman in sequences consistent with a latest proterozoic age assignment in addition supposed lower cambrian pre trilobitic shelly fossils from northwest mexico and the white inyo mountains in california and nevada including sinotubulites nevadatubulus and wyattia are all either closely related to or con generic with cloudina hence it is probable that these outcrops are latest proterozoic in age and that cloudina or cloudina like organisms were widely distributed at that time it is possible moreover to suggest that metazoan biomineralization occurred on a global scale by the latest proterozoic at the same time that evidence for complex multicellularity and locomotion in animals appears in siliciclastic ediacaran rocks in the form of body and trace fossils

surface ages and resurfacing rates of the polar layered deposits on mars interpretation of the polar stratigraphy of mars in terms of global climate changes is complicated by the significant difference in surface ages between the north and south polar layered terrains inferred from crater statistics we have reassessed the cratering record in both polar regions using viking orbiter and mariner 9 images no craters have been found in the north polar layered terrain but the surface of most of the south polar layered deposits appears to have been stable for many of the orbital axial cycles that are thought to have induced global climate changes on mars the inferred surface age of the south polar layered deposits about 10 ma is two orders of magnitude greater than the surface age of the north polar layered deposits and residual cap at most 100 ka similarly modeled resurfacing rates are at least 20 times greater in the north than in the south these results are consistent with the hypotheses that polar layered deposit resurfacing rates are highest in areas covered by perennial ice and that the differences in polar resurfacing rates result from the 6 4 km difference in elevation between the polar regions deposition on the portion of the south polar layered deposits that is not covered by the perennial ice cap may have ceased about 5 million years ago when the obliquity of mars no longer exceeded 40

late quaternary sedimentation off new jersey new results using 3 d seismic profiles and cores abstract regional seismic reflection surveys have delineated a wedge of late quaternary sediment extending 150 km south from the hudson apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector r assumed to represent an erosional surface carved during a low stand of sea level probably corresponding to the wisconsinan maximum glaciation a 3 d reflection survey of a 5 0 5 km area of the southern part of the wedge was carried out in october 1989 line spacing was 10 m and shot spacing 2 5 m navigation achieved position accuracies to the survey shows that the outer shelf sediment wedge has a complex internal structure unrelated to the present seafloor morphology the sedimentary sequence appears to have been formed by a series of depositional events related to glacial melting and interrupted by at least one erosional episode marked by a seismic surface that defines a system of meandering channels faunal studies of samples from cores indicate that the sediments were deposited at shallower depths than at present but there is no evidence for deposition in shallower water or closer proximity to land than the modern mid shelf it appears that the history of periglacial marine sedimentation which accompanied the post wisconsinan deglaciation is no less complex than its continental counterpart

buried paleo channels on the new jersey continental margin channel porosity structures from electromagnetic surveying abstract we report on a marine electromagnetic em survey across two portions of the new jersey continental margin that have been previously shown to contain buried paleo channels the em method used provides bulk porosity estimates to depths of around 20 m below the seafloor and is thus able to place porosity constraints on the nature of the channel infill and the contrast in physical properties across the channel boundaries our data show that a key condition for the channels to have an electrical signature is that they incise an underlying regional unconformity r thought to represent a subaerially eroded surface exposed during the late wisconsinan glaciation channels that cut r are seen through increases in apparent porosity another seismically imaged channel sequence which lies within the outer shelf sediment wedge sequence above r does not have an electrical signature indicating that the sediments above and below the channel boundaries have similar physical properties

martian pedestal craters marginal sublimation pits implicate a climate related formation mechanism 1 pedestal craters on mars are defined by an outward facing scarp forming a plateau perched tens of meters above the surrounding terrain their origin has been attributed to impact armoring of the surface and subsequent removal of inter crater terrain by either eolian deflation or sublimation of an ice rich substrate we identified 2696 pedestal craters between 60 n and 60 s latitude 98 are poleward of 33 n and 40 s the majority of pedestal crater margins are smoothly sloped but 3 concentrated in utopia planitia and malea planum display distinctive marginal pits these pedestal crater scarps are anomalously tall usually 80 100 m and the pits resemble sublimation depressions seen on earth and elsewhere on mars providing evidence for sublimation of volatiles in the scarp where the armored surface has tapered the pitted scarps provide insight into the origin of the general pedestal crater population favoring formation via deposition of a volatile rich substrate impact armoring and sublimation of intervening volatiles crater densities and overlapping pedestal craters suggest multiple periods of emplacement and loss of these climate related latitude dependent deposits throughout the amazonian

the origin of conical mounds at the mouth of chasma boreale 1 one hundred and six isolated conical mound landforms were identified proximal to the north polar cap of mars at the mouth of chasma boreale five unique morphologies were identified including moderately sloped 4 6 cratered mound forms including two mounds of abalos colles flat topped moderately sloped 4 6 polygonal mound forms steeper 6 13 conical mound forms subdued mound forms with low angle slopes 0 5 3 and small 2 km diameter clustered conical forms with low to moderate angle 1 5 flank slopes from first order relationships between flank slope and the volcano productivity index volume diameter ratio 16 mounds were found to be morphologically similar to terrestrial low angle basaltic shield volcanoes thirteen mounds exhibit summit craters that range in depth d to diameter d ratio from 1 9 to 1 320 the circularity and d d ratios of mound summit craters are consistent with highly modified northern plains impact craters image analysis of shield like mounds reveals morphologic characteristics inconsistent with pristine volcanic landforms for most features horizontal flank layering 10 100 m thick polygonal map view morphology topographic relationships and spatial association with retreating polar scarps suggest that mound forms at the mouth of chasma boreale represent remnants of a once thicker more continuous sequence of near polar layered material evidence for northward scarp retreat is visible along rupes tenuis a sinuous scarp located west of chasma boreale along this scarp a single 100 m thick resistant cap unit part of the early amazonian age rupes tenuis unit is being undermined by aeolian erosion solar ablation and mass wasting remnants of the cap unit rest along the scarp margin and in places form small conical mound clusters at the base of the scarp fracture controlled retreat of the scarp is visible along the eastern portion of rupes tenuis and along the escorial crater remnant mesa where small tongue like promontories have been sculpted into the cap unit isolation of these irregularities by scarp retreat has formed several volcanic like scarp and mesa proximal mounds mound forms located closest to the retreating rupes tenuis scarp above 78 n were found to be the steepest and tallest mound landforms in the region mounds located distal to rupes tenuis were found to be broad and subdued this observation is consistent with long term retreat of a once more extensive rupes tenuis scarp and long term modification of isolated conical remnants

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

temporal relationship between cratonization and glaciation the vendian early cambrian glaciation in western gondwana abstract cratonization has long been said to favour glaciation cratons would be ideal cradles for the development of continental ice caps in western africa the widespread continental glaciation developed near the proterozoic paleozoic boundary can no longer be considered as vendian according to the recent discovery of an early cambrian microfauna in eastern senegal it extends until atdabanian time 530 520 ma the age of its beginning lacks in precision it can be vendian or early cambrian in the hoggar fold belt it constitutes the lower part of molassic intermontane sequences where it is about 30 40 ma younger than the pan african cratonization dated at 600 ma this extensive cratonization closed the old long lived pan african brasiliano cycle 1000 600 ma and is responsible for the aggregation of west gondwana in the south american paraguay belt glacial sequences also postdate brasiliano cratonization dated at 590 ma they are probably vendian overlain by an ediacara like fauna and slightly older than those of western africa the glaciation was restricted to the shoulders of rifted basins initiating the young short lived pan african brasiliano cycle 600 or slightly younger to 520 ma world distribution of continents indicate that the widespread late vendian early cambrian ice cap glaciation of west africa developed at middle latitudes 50 30 whereas the probably vendian glaciation of the paraguay belt restricted to local highlands occupied high to middle latitudes 60 in western gondwana glaciation and cratonization occurring near the proterozoic cambrian boundary appear as distinct and temporary unrelated phenomena

polar basal melting on mars if ice is present throughout the cryosphere anywhere on mars thermodynamic considerations suggest that it is most likely at the poles given this condition the deposition of dust and h2o at the polar surface will ultimately result in a situation where the equilibrium depth to the melting isotherm has been exceeded melting ice at the base of the cryosphere until thermal equilibrium is once again established should deposition persist the polar deposits will ultimately reach a thickness where melting will occur at their actual base at this point the cap may reach a state of equilibrium where the deposition of any additional ice is balanced by geothermal melting thermal calculations yield basal melting thicknesses that are consistent with the inferred 4 6 km thickness of the present north polar cap however in the south the deposits appear sufficiently thin 1 2 km that geothermal melting is likely to be relegated to a depth that lies well below the regolith polar cap interface similar conclusions are reached from consideration of the polar caps theoretical equilibrium profiles in the north a basal yield stress characteristic of ice at or near the melting point is indicated while in the south it appears the cap has yet to achieve the necessary height for significant deformation to occur at its base the potential importance of basal melting is illustrated through the discussion of four examples 1 the origin of the major polar reentrants 2 the removal and storage of an ancient martian ice sheet 3 the mass balance of the polar terrains and 4 the possibility of basal melting at temperate latitudes this analysis suggests that the process of basal melting may play a key role in understanding the evolution of the martian polar terrains and the long term climatic behavior of water on mars

phosphorus phosphorites and skeletal evolution at the precambrian cambrian boundary clustering of sedimentary phosphate deposits around the precambrian cambrian boundary is related to a global phosphogenic event this event probably resulted from a complex interplay of factors and had a profound effect on the biota with high concentrations of phosphorus in the photic zone producing an increase in the total shallow marine biomass faunal diversification the precipitation of skeletal structures and explosive evolution

latitude dependence of martian pedestal craters evidence for a sublimation driven formation mechanism we report on the results of a survey to document and characterize pedestal craters on mars equatorward of similar to 60 degrees n and 65 degrees s latitude the identification of 2696 pedestal craters reveals a strong latitude dependence with the vast majority found poleward of 33 degrees n and 40 degrees s this latitudinal extent is correlated with many climate indicators consistent with the presence of an ice rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the amazonian we have measured key physical attributes of pedestal craters including the farthest radial extents of the pedestals pedestal heights and the circularity of the pedestal margins in conjunction with the geographic distribution our measurements strongly support a sublimation related formation mechanism this is in contrast to previous hypotheses which have relied on eolian deflation to produce the elevated plateaus the identification of marginal pits on the scarps of some pedestal craters interpreted to be sublimation pits provide direct evidence for the presence of ice rich material underlying the armored surface of pedestal craters on the basis of our findings we propose a formation mechanism whereby projectiles impact into a volatile rich dust snow ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith the area surrounding the resulting crater becomes armored pedestals extend to a distance of multiple crater radii farther than typical ejecta deposits necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta return to low obliquity causes sublimation of the volatile rich layer from the intercrater plains lowering the elevation of the regional terrain this yields generally circular pedestal craters elevated above the surrounding plains as a result the armored surfaces of pedestal craters have preserved a significant record of amazonian climate history in the form of ice rich deposits

stable isotope geochemistry and palynology of the late precambrian to early cambrian sequence in newfoundland a sequence of clastic sediments in southeastern newfoundland straddling the precambrian cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid resistant organic walled microfossils a detailed study of the chapel island formation which includes the boundary interval has revealed fluctuations in the isotopic composition of organic carbon these are largely interpreted as caused by differences in the depositional environments highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite forming process sometimes under sulfate limited conditions palynological results are quite limited with respect to diagnostic microfossils

chasma boreale mars topographic characterization from mars orbiter laser altimeter data and implications for mechanisms of formation 1 chasma boreale a large reentrant in the north polar cap of mars is distinct in scale detailed topography and orientation from the spiraling troughs that characterize the majority of the polar cap we use new high resolution mars orbiter laser altimeter mola data and mars orbiter camera moc and viking images of the chasma region to assess hypotheses of origin of chasma boreale these hypotheses include formation by glacial flow and ablation by eolian processes such as katabatic winds and sublimation by outflow of meltwater or by a combination of two or more of these processes we find that these new data support initial formation by outflow of meltwater with later modification by katabatic winds and sublimation on the basis of our analysis we suggest a possible scenario in which outflow has occurred in several stages the outflow appears to have begun near an enclosed depression at the head of the chasma meltwater migrated within and below the ice down the regional slope and eventually broke out to the surface removal of material by melting caused subsidence and erosion of the polar deposits forming the chasma which has subsequently undergone modification by eolian and sublimation processes the outflow deposited most of its sediment in the form of a lobe that stratigraphically overlies the polygonal plains mapped at the mouth of the chasma and scoured some of the circumpolar sediment mantle in the surrounding region the lowest portions of the north polar basin received the rest of the sediment as a deposit a few meters thick mola data also reveal evidence for similar events of smaller magnitude elsewhere on the margins of the polar cap

geologic history of the polar regions of mars based on mars global surveyor data ii amazonian period based on mars orbiter laser altimeter mola and mars orbiter camera moc observations of amazonian polar layered deposits pld morphology composition and thickness we conclude that the plds are composed of porous unconsolidated layers that have not experienced significant basal melting or other glacial type processes morphologic features and associations within the pld chasmata including preserved craters and sinuous ridges indicate that the dominant process of chasmata formation is wind scouring our detailed analysis of south polar spiral trough topography in conjunction with the identification of similar layered stratigraphy within north polar spiral troughs suggests that trough migration due to preferential ablation of sun facing slopes cannot be demonstrated within the layered sequences we have not identified widespread unconformities discontinuities or pinch outs that would indicate an accublation origin of the plds we therefore postulate that the well defined plds at both poles eventually reached and maintained their present form following deposition without extensive deformation or redeposition large cuspate ridges in the ultimi lobe of planum australe appear to be layered and may be unusual erosional remnants of a once thicker pld in this area beneath the north polar layered deposits in planum boreum we have identified a platform of older highly degraded polar deposits as much as a kilometer thick that may have once covered an area larger than planum boreum

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

seismic geomorphology of buried channel systems on the new jersey outer shelf assessing past environmental conditions abstract quantitative geomorphologic analysis of shallowly buried dendritic channel systems on the new jersey shelf provides estimates of paleo hydrologic parameters needed to link channel morphology to the former hydrodynamic setting these channels observed in 1 4 khz deep towed chirp seismic data formed presumably as fluvial systems when the shelf was exposed during the last glacial maximum lgm the presumed fluvial origin of these channels is supported by their incision into underlying pleistocene strata a chaotic seismic fill unit at their bases which may be indicative of non marine gravel lag and measured stream junction angles that are consistent with a riverine origin the channels would also have been subjected to estuarine tidal environments during ensuing sea level rise we employ empirically derived hydraulic equations for modern rivers and estuaries to estimate paleo discharges velocities and maximum shear stresses using the preserved and interpolated paleo channel geometries as a guide generally trunk main channels have box like symmetric cross sections with width depth ratios of 100 whereas smaller tributary channels have more v shaped asymmetric cross sections with width depth ratios of 40 70 the high width depth ratios along with low sinuosities 1 1 and slopes

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

planum boreum basal unit topography mars irregularities and insights from sharad shallow radar investigations of planum boreum mars basal unit bu deposit have revealed multiple reentrants morphologic irregularities and thickness trends that differ from those of the overlying north polar layered deposits we present detailed subsurface maps for these features and offer explanation for genesis of the deposit s morphologic asymmetry expressed in different erosional characteristics between 0 e 180 e and 180 e 360 e additionally this work revealed a depression in the basal unit that may have provided a site for spiral trough initiation interpretations of the findings suggest that antecedent bu topography has a marked impact on modern morphology and that aeolian forces have been the dominant driver of polar deposit accumulation since at least the end of rupes unit emplacement we find no results requiring explanation beyond common martian surface processes including aeolian erosion and impact armoring to add to the detailed morphologic study of the bu we mapped the variability of the bu radar reflection character combining generalized katabatic wind flow with the radar mapping results suggests that rupes unit material sourced the younger cavi we present clear evidence that while compositionally distinct from the overlying layered deposits the bu and its morphology are intimately linked to the morphology of the north polar layered deposits combining geologic evidence with paleoclimate modeling the deposits contain evidence for a long history of aeolian emplacement and modification

formation constraints on martian north polar volcanic edifices 1 this study focuses on probable volcanic features in the north polar region of mars in an effort to constrain their formation mechanisms and to estimate the thickness of a possible former ice sheet using mars orbiter laser altimeter mola high resolution imaging science experiment hirise thermal emission imaging system themis and context camera ctx data we conduct topographic analyses of 108 putative volcanic edifices in the borealis volcanic field within 69 n 81 n and 197 e 330 e as it is rarely possible to identify rock types on mars such as hyaloclastite or palagonite we are limited to the use of topographic data and images alone in our study therefore we use available data for volcanic features in iceland to predict the formational mechanisms of similar features on mars we examined 21 icelandic volcanoes of subglacial and postglacial origin using digital elevation models dems as well as limited differential gps data and suggest by analogy that many of the features in the borealis volcanic field were likely formed subglacially we use these data to estimate a minimum ice sheet thickness for the area and suggest a range of minimum ice sheet thickness that varies between 57 and 610m with an average value of 283 m

the role of eolian processes in forming surface features of the martian polar layered deposits abstract the major topographic features of the martian polar layered deposits include the conspicuous spiral troughs subtle undulations broad reentrants chasma steep arcuate scarps and dune fields a prominent role for eolian processes in the formation of all of these features is proposed strong katabatic winds occur on the north polar cap producing widespread frost streaks these cold drainage winds are analogous to those on the terrestrial antarctic cap in the chasmae convergent katabatic winds create yardangs and erode arcuate scarps in the layered deposits that are also the source for local dune fields migrating outward from the polar cap the chasmae are postulated to originate by long term erosion by katabatic wind wind plays a role in formation of the troughs and scarps primarily through removal of dust freed from exposed layered deposits by ablation of ice on defrosted equator facing slopes the undulations are created by interaction between surface erosion or deposition of perennial ice and standing waves in the shallow katabatic windflow the south polar layered deposits exhibit topographic features similar to those at the north polar cap but erosion and depositional processes creating these features may be inactive during the current epoch because of the lack of an extensive perennial ice cover and associated katabatic wind

importance of aeolian processes in the origin of the north polar chasmata mars abstract a detailed examination of the location and orientation of sand dunes and other aeolian features within the north polar chasmata indicates that steep scarps strongly influence the direction and intensity of prevailing winds these steep scarps are present at the heads and along the margins of the north polar chasmata topographic profiles of the arcuate head scarps and equator facing wall of chasma boreale reveal unusually steep polar slopes ranging from 6 30 the relatively steep sloped 8 sinuous scarp at the head of two smaller chasmata located west of chasma boreale exhibits an obvious resistant cap forming unit scarp retreat is occurring in places where the cap unit is actively being undercut by descending slope winds low albedo surfaces lacking sand dunes or dust mantles are present at the base of the polar scarps a 100 300 m deep moat located at the base of the scarps corresponds with these surfaces and indicates an area of active aeolian scour from descending katabatic winds small local dust storms observed along the equator facing wall of chasma boreale imply that slope wind velocities in chasma boreale are sufficient to mobilize dust and sand sized particles in the polar layered deposits pld two amphitheater forms located above the cap forming unit of the sinuous scarp and west of chasma boreale may represent an early stage of polar scarp and chasma formation these two forms are developing within a younger section of polar layered materials the unusually steep scarps associated with the polar chasmata have developed where resistant layers are present in the pld offering resistance during the headward erosion and poleward retreat of the scarps steep slopes that formed under these circumstances enhance the flow of down scarp katabatic winds on the basis of these observations we reject the fluvial outflood hypothesis for the origin of the north polar chasmata and embrace a wind erosion model for their long term development in the aeolian model off pole katabatic winds progressively remove materials from the steep slopes below chasmata scarps undermining resistant layers at the tops of scarps and causing retreat by headward erosion assuming a minimum age for the onset of formation of chasma boreale 105 yr results in a maximum volumetric erosion rate of 0 35 km 3 yr 1 removal of this volume of material from the equator facing wall and head scarps of chasma would require a rate for scarp retreat of 0 5 m yr 1

resurfacing history of the northern plains of mars based on geologic mapping of mars global surveyor data 1 geologic mapping of the northern plains of mars based on mars orbiter laser altimeter topography and viking and mars orbiter camera images reveals new insights into geologic processes and events in this region during the hesperian and amazonian periods we propose four successive stages of lowland resurfacing likely related to the activity of near surface volatiles commencing at the highland lowland boundary hlb and progressing to lower topographic levels as follows highest elevations indicated stage 1 upper boundary plains early hesperian 2 0 to 2 9 km stage 2 lower boundary plains and outflow channel dissection late hesperian 2 7 to 4 0 km stage 3 vastitas borealis formation vbf surface late hesperian to early amazonian 3 1 to 4 1 km and stage 4 local chaos zones early amazonian 3 8 to 5 0 km at acidalia mensa stage 2 and 3 levels may be lower 4 4 and 4 8 km respectively contractional ridges form the dominant structure in the plains and developed from near the end of the early hesperian to the early amazonian geomorphic evidence for a northern plains filling ocean during stage 2 is absent because one did not form or its evidence was destroyed by stage 3 resurfacing remnants of possible amazonian dust mantles occur on top of the vbf the north polar layered deposits appear to be made up of an up to kilometer thick lower sequence of sandy layers early to middle amazonian in age overlain by late amazonian ice rich dust layers both units appear to have outliers suggesting that they once were more extensive

basal inflection controlled shelf edge wedges off new jersey track sea level fall a key marker for examining the latest pleistocene history of the new jersey margin is the high amplitude long recognized r horizon reflector this time transgressive surface was formed 47 33 ka and represents the integrated topographic and bathymetric surface developed during the complicated sea level oscillation associated with the regression that preceded the last glacial maximum lgm from landward to seaward across the outer shelf the r reflector changes from subhorizontal in most locations 9 m beneath the modern seafloor to seaward dipping forming the base of two offlapping sediment wedges the previously described outer shelf wedge and a deep shelf wedge seaward of it this transition occurs across two inflection zones where the dip of the r reflector steepens seaward that can be traced for tens of kilometers along strike and mark the landward limits of these wedges these inflection zones are possibly former wave dominated shorefaces these represent the primary topographic elements present during the last regression we speculate that these inflections dictated both the locations for deposition of the two prograding offlapping wedges that developed during the complex sea level fall prior to the lgm and their successive erosion before and after the lgm we suggest that such inflection zones and their associated wedges are important markers of regression in clastic dominated outer shelf settings along passive margins

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

orbital radar imagery and atmospheric modeling reveal an aeolian origin for abalos mensa mars 1 icy deposits surrounding planum boreum mars contain crucial information for deciphering paleoclimate and past geologic processes at the martian north pole one such deposit abalos mensa is an enigmatic wedge of material located near the 1 km high rupes tenuis its unique location and lobate morphology have fostered formation hypotheses that assume either fluvial or aeolian erosion of a once larger ice deposit the aeolian scenario posed previously requires impact shielding of ancient basal unit material to provide an erosional remnant which seeds later deposition while the fluvial hypotheses invoke cryovolcanism beneath the younger north polar layered deposits npld and associated outflow to erode the adjacent chasmata here we combine newly available radar sounding data high resolution imagery digital elevation models and atmospheric modeling to examine internal structure and infer both the mechanisms for and timing of abalos mensa formation from this integrative approach we conclude that abalos mensa formed as a distinct feature via atmospheric deposition following erosion of rupes tenuis and grew concurrently with the rest of planum boreum as the npld accumulated the required processes are consistent with those observed today no exotic phenomena cryovolcanism fluvial activity or impact shielding appear necessary to explain the formation of abalos mensa

topographic evidence for geologically recent near polar volcanism on mars abstract the mars orbiter laser altimeter mola was used to measure the topography of several putative near polar martian volcanic craterforms we believe they were formed by effusive lava shield building eruptions and were not hydromagmatic events as previously suggested furthermore these craterforms appear to be geologically recent with ages between 1 and 20 million years and may provide new evidence of localized thermal anomalies in the upper martian crustal column

drainage of late wisconsin glacial lakes and the morphology and late quaternary stratigraphy of the new jersey southern new england continental shelf and slope abstract we propose that late wisconsin deposition and erosion hudson shelf and block island valleys on the shelf and slope from new jersey to southern new england were a consequence of the catastrophic drainage of glacial lakes behind terminal moraine systems and the huge volume of water stored beneath the laurentian ice sheet and subsequent erosion of the lake sediments by flash floods the morphology imparted by glaciation regulated the discharge associated with the ablation of the glaciers associated with the deposits west of hudson shelf valley are the remains of mammoth and mastodon which were transported from their living habitats along the lake shores to their present burial sites on the shelf the floods also triggered gravity flows on the upper continental slope which made possible the transportation of coarse debris over hundreds of km into the deep sea that these catastrophic flood morphologies can still be recognized on the middle to outer shelf suggest that much of its surface was little modified during the late pleistocene holocene transgression thus the late pleistocene holocene transgression may have been characterized by short periods when sea level rose rapidly allowing for the preservation of relict features

mars observer camera the mars observer camera moc is a three component system one narrow angle and two wide angle cameras designed to take high spatial resolution pictures of the surface of mars and to obtain lower spatial resolution synoptic coverage of the planet s surface and atmosphere the cameras are based on the push broom technique that is they do not take frames but rather build pictures one line at a time as the spacecraft moves around the planet in its orbit moc is primarily a telescope for taking extremely high resolution pictures of selected locations on mars using the narrow angle camera areas ranging from 2 8 km 2 8 km to 2 8 km 25 2 km depending on available internal digital buffer memory can be photographed at about 1 4 m pixel additionally lower resolution pictures to a lowest resolution of about 11 m pixel can be acquired by pixel averaging these images can be much longer ranging up to 2 8 500 km at 11 m pixel high resolution data will be used to study sediments and sedimentary processes polar processes and deposits volcanism and other geologic geomorphic processes the moc wide angle cameras are capable of viewing mars from horizon to horizon and are designed for low resolution global and intermediate resolution regional studies low resolution observations can be made every orbit so that in a single 24 hour period a complete global picture of the planet can be assembled at a resolution of at least 7 5 km pixel regional areas covering hundreds of kilometers on a side may be photographed at a resolution of better than 250 m pixel at the nadir such images will be particularly useful in studying time variable features such as lee clouds the polar cap edge and wind streaks as well as acquiring stereoscopic coverage of areas of geological interest the limb can be imaged at a vertical and along track resolution of better than 1 5 km different color filters within the two wide angle cameras permit color images of the surface and atmosphere to be made to distinguish between clouds and the ground and between clouds of different composition

precambrian cambrian boundary and correlation from southwestern and central part of spain this paper comprises the first palaeontological correlation between the upper proterozoic lower cambrian series of ossa morena luso oriental alcudica and galaico castellana zones of the iberian peninsula the authors show the palaeontological events on acritarchs stromatolites cyanophyta soft bodied metazoa trilobites archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the precambrian cambrian boundary in the sequences the sierra de cordoba general series ossa morena zone has an erosive discontinuity between the rocks with the first record of cambrian metazoan activity skolithos sp monomorphichnus sp phycodes pedum and rusophycus sp and the rocks with a palynological association bavlinella faveolata protosphaeridium flexosum trachisphaeridium sp aff octoedryxium truncatum phycomicetes sp and cf ooidium sp which suggests a lower middle vendian age for this reason we suggest that the precambrian cambrian boundary be placed at this unconformity the upper part of the sierra de guadalupe series luso oriental alcudica zone includes detrital beds with phycodes pedum planolites sp and treptichnus sp which are also the first record of cambrian metazoan activity in the middle part of the sequences acritarchs attributed to the genus micrhystridium are found at the top of the calcareous beds this is taken to indicate an early cambrian age vendotaenids and bavlinella faveolata are found in abundance thus indicating a late vendian age for the middle part of this unit thus we propose the precambrian cambrian boundary be located in the upper part of the calcareous beds in the rio uso series galaico castellana zone the azorejo sandstones contain rusophycus gr radwanskii planolites sp and gordia sp trace fossils produced by trilobite like arthropoda monomorphichnus have been cited in the upper part of the underlying pusa shales moreover octoedryxium truncatum and bavlinella faveolata are found in the lower part of this unit which suggest that the precambrian cambrian boundary could be situated in the pusa shales calcareous microfossils related to annelid polychaetes are found associated with upper vendian acritarchs in the calcareous beds of sierra de guadalupe they are the oldest record of skeletal metazoa in the spanish series the medusoids found are associated with a vendian flora and they are also the oldest non skeletal metazoa record known in the iberian peninsula

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and

an ultrahigh resolution 3 d survey of the shallow subsurface on the continental shelf of new jersey regional seismic surveys have identified a wedge of late quaternary sediment extending 150 km south from the hudson river apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector that is assumed to be an erosional surface carved during a lowstand of sea level probably corresponding to the wisconsin maximum glaciation about 18 000 years ago an extremely high resolution 3 d seismic reflection survey of the southern part of the wedge figure 1 was carried out in 1993 as part of the strataform strata formation on margins initiative funded by the u s office of naval research