evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater 1 a single scoop of the rocknest aeolian deposit was sieved 150 m and four separate sample portions each with a mass of 50mg were delivered to individual cups inside the sample analysis at mars sam instrument by the mars science laboratory rover ss ample acquisition system the samples were analyzed separately by the sam pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes several chlorinated hydrocarbons including chloromethane dichloromethane trichloromethane a chloromethylpropene and chlorobenzene were identified by sam above background levels with abundances of 0 01 to 2 3nmol the evolution of the chloromethanes observed during pyrolysis is coincident with the increase in o2 released from the rocknest sample and the decomposition of a product of n methyl n tert butyldimethylsilyl trifluoroacetamide mtbstfa a chemical whose vapors were released from a derivatization cup inside sam the best candidate for the oxychlorine compounds in rocknest is a hydrated calcium perchlorate ca clo4 2 nh2o based on the temperature release of o2 that correlates with the release of the chlorinated hydrocarbons measured by sam although other chlorine bearing phases are being considered laboratory analog experiments suggest that the reaction of martian chlorine from perchlorate decomposition with terrestrial organic carbon from mtbstfa during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by sam chlorobenzene may be attributed to reactionsofmartian chlorine released during pyrolysiswith terrestrial benzene or toluene derived from 2 6 diphenylphenylene oxide tenax on the sam hydrocarbon trap at this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons nor do we exclude the possibility that future sam analyses will reveal the presence of organic compounds native to the martian regolith

modeling the thermal and physical evolution of mount sharp s sedimentary rocks gale crater mars implications for diagenesis on the msl curiosity rover traverse gale crater the mars science laboratory msl landing site contains a central mound named aeolis mons informally mount sharp that preserves 5 km of sedimentary stratigraphy formation scenarios include 1 complete filling of gale crater followed by partial sediment removal or 2 building of a central deposit with morphology controlled by slope winds and only incomplete sedimentary fill here we model temperature time paths for both scenarios compare results with analyses provided by msl curiosity and provide scenario dependent predictions of temperatures of diagenesis along curiosity s future traverse the effects of variable sediment thermal conductivity and historical heat flows are also discussed modeled erosion and deposition rates are 5 37 m yr consistent with previously published estimates from other mars locations the occurrence and spatial patterns of diagenesis depend on sedimentation scenario and surface paleotemperature for 1 temperatures experienced by sediments decrease monotonically along the traverse and up mount sharp stratigraphy whereas for 2 temperatures increase along the traverse reaching maximum temperatures higher up in mount sharp s lower units if early mars surface temperatures were similar to modern mars mean 50 c only select locations under select scenarios permit diagenetic fluids in contrast if early mars surface temperatures averaged 0 c or brines had lowered freezing points diagenesis is predicted in most locations with temperatures 225 c comparing our predictions with future msl results on diagenetic textures secondary mineral assemblages and their spatial variability will constrain past heat flow mount sharp s formation processes the availability of liquid water on early mars and sediment organic preservation potential

a model of the western laurentide ice sheet using observations of glacial isostatic adjustment we present the results of a new numerical model of the late glacial western laurentide ice sheet constrained by observations of glacial isostatic adjustment gia including relative sea level ind

formation of large beaches in an area of rapid differential isostatic rebound the three outlet control of lake agassiz abstract shorelines in basins undergoing differential isostatic rebound do not remain geographically fixed for long periods and are either transgressive or regressive during regression a relatively uniform blanket of shoreface sediment may be deposited but unless regression is slow or punctuated by periods of lake level equilibrium large beaches do not form in contrast along transgressive shorelines which migrate upslope large morphostratigraphic features commonly are maintained along the lake s margin these may subsequently be stranded when lake level declines beaches around isostatically rebounding proglacial lakes are commonly considered to have formed during a period of lake regression punctuated by abrupt drops in lake level however in basins that are differentially rebounding large beaches cannot form this way and only periods of transgressing waters allow enough time for large beaches to form and define a continuous shoreline around the basin with this in mind some of the largest and most extensive beaches in the glacial lake agassiz basin the norcross tintah and upper campbell constructed between 10 4 and 9 4 ka 14 c yr bp are reinterpreted as strandlines that were formed by transgression each of these three transgressions followed lower lake phases and resulted from in sequence differential isostatic rebound of the eastern outlet rebound and ice damming of the northwestern outlet and rebound of the northwestern outlet each of these transgressions ended when lake level reached the southern outlet stranding the norcross tintah and upper campbell beaches about 10 2 9 9 and 9 4 ka 14 c yr bp respectively

origin of the herman norcross tintah sequence of lake agassiz beaches in manitoba canada abstract the giant glacial lake agassiz basin is fringed by many strandlines which have long been used to trace the paleogeography of the former lake over its 5000 year history the oldest and highest of these strandlines were placed into three groups by warren upham in the 1890 s the herman norcross and tintah and form a staircase of small landforms the formation of these old strandlines began as early as 13 9 cal 12 0 14 c kyr bp and ended 12 8 cal 10 8 14 c kyr bp based on osl dates and the history of lake level in the agassiz basin new mapping and augering of beach ridges in southern manitoba canada associated with the earliest phase of the lake indicate that there are a series of up to 28 small discontinuous beach ridges that are generally only a few metres high and a few tens of metres wide these beaches mainly consist of weakly defined beds of poorly sorted sediments in many cases a central sandy diamicton unit lies stratigraphically between overlying beach sediments and clay diamicton till below spatially ridges are separated by silty or sandy units or gravel lags inter beach lagoonal organics were not found we discuss the possible origin of these lake agassiz beaches concluding that they were deposited over a few centuries by episodic storm events as lake level slowly declined we base this conclusion on the nature of the sediments in the beach ridges and the regional geomorphology as well theoretical considerations about sedimentation along a regressing shoreline of a large lake other origins are rejected although some other factors may have contributed to formation of some of the beaches such as temporary increases in sediment supply variable rate of outlet erosion and short increases in lake level that reworked sediment upslope into ridges using the time frame of 13 9 to 12 8 cal kyr bp for the formation of the beaches the average interval between formation of each beach is 39 years

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

mapping and measuring lake agassiz strandlines in north dakota and manitoba using lidar dem data comparing techniques revising correlations and interpreting anomalous isostatic rebound gradients based on light detection and ranging lidar digital elevation model dem data at 1 m spatial resolution lake agassiz strandlines were mapped and their elevations determined in northeastern north dakota and southern manitoba two different techniques for determining strandline elevations from lidar imagery are compared one based on measuring the crests of constructional beaches and the other using the elevation of slope breaks along the shorelines defined by shadows on the lidar hillshade map our measurements on lake agassiz strandlines show that previous correlations of younger strandlines around the pembina delta accepted for more than a century are incorrect the gladstone ojata and emerado strandlines south of the delta are offset by 10 m from their namesakes to the north and so are equivalent to the ojata emerado and hillsboro strandlines respectively furthermore anomalously low gradients for the ojata and emerado strandlines around the pembina delta are interpreted as resulting from postdepositional compaction of underlying fine sediment elevations on the isostatically rebounded strandlines confirm that older higher ones have steeper northward rising elevations and that gradients on those strandlines can be used as proxies for relative age

questioning the age of the moorhead phase in the glacial lake agassiz basin abstract the stratigraphy of sites within the lake agassiz basin that constrain the timing of the onset of the moorhead low water phase is reexamined stratigraphic interpretation of the oldest date 10 960 14 c yr bp from cross bedded sand of the ojata beach is questioned particularly in light of demonstrated long distance transport and reworking of older organic material from elsewhere in the basin a maximum onset age for the moorhead phase is suggested from a 10 675 60 14 c yr bp age from wood in gravel from the base of the southern outlet whereas radiocarbon dates from in situ peat indicate a later minimum onset age of 10 340 100 14 c bp

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

environment and paleoecology of a 12 ka mid north american younger dryas forest chronicled in tree rings abstract until now availability of wood from the younger dryas abrupt cooling event yde in n america ca 12 9 to 11 6 ka has been insufficient to develop high resolution chronologies for refining our understanding of yde conditions here we present a multi proxy tree ring chronology ring widths events evidenced by microanatomy and macro features stable isotopes from a buried black spruce forest in the great lakes area liverpool east site spanning 116 yr at ca 12 000 cal yr bp during this largely cold and wet period the proxies convey a coherent and precise forest history including frost events tilting drowning and burial in estuarine sands as the laurentide ice sheet deteriorated in the middle of the period a short mild interval appears to have launched the final and largest episode of tree recruitment ultimately the tops of the trees were sheared off after death perhaps by wind driven ice floes culminating an interval of rising water and sediment deposition around the base of the trees although relative influences of the continental ice sheet and local effects from ancestral lake michigan are indeterminate the tree ring proxies provide important insight into environment and ecology of a n american yde boreal forest stand

late pleistocene palaeoenvironments of the southern lake agassiz basin usa macroscopic plant remains pollen insect and mollusc fossils recovered from a cut bank on the red river in north dakota usa provide evidence that an extensive wetland occupied the southern basin of lake agassiz from 10 230 to 9900 14 c yr bp marsh dwelling plants and inver tebrates had colonised the surface of a prograding delta during the low water moorhead phase of lake agassiz a species of salix willow was abundant along distributary channels and stands of populus tremuloides aspen ulmus sp elm betula sp birch and picea sp spruce grew on the better drained sand bars and beach ridges most of the species of plants insects and molluscs represented as fossils are within their existing geographic ranges based on a few species with more northerly distributions mean summer temperature may have been about 1 2 c lower than the pre sent day no change in species composition occurred in the transition from the younger dryas to preboreal at the time that the wetland existed lake agassiz was draining either eastward to the north atlantic ocean or northwestward to the arctic ocean the wetland was drowned during the emerson phase transgression that resulted in meltwater draining southward to the gulf of mexico after 9900 14 c yr bp copyright 2005 john wiley sons ltd

factors controlling reservoir properties and hydrocarbon accumulation of the eocene lacustrine beach bar sandstones in the dongying depression bohai bay basin china abstract lacustrine beach bar sandstone reservoirs are economical important exploration targets in the dongying depression bohai bay basin the factors that controls reservoir quality and hydrocarbon accumulation in lacustrine beach bar sandstones were systematically investigated through an integrated petrographic petrophysical and diagenesis analysis the reservoir properties of the beach bar sandstones are mainly affected by compaction carbonate cementation and dissolution significant negative relationships exist between both the porosity and permeability and the volume of carbonate cement carbonate cement is mainly distributed along the sandstone mudstone contacts sandstones with thicknesses less than 1 m are generally tightly cemented to form zones with low petrophysical properties the material source of the carbonate cement in the tightly cemented zone was highly likely from the interbedded mudstone content of carbonate cements in the center of the thick sandstones is low whereas compaction is the dominant diagenetic process with some dissolution there is a positive correlation between the petrophysical properties of the beach bar sandstones and the content of kaolinite the petrophysical properties have an inverse correlation with the contents of illite and illite smectite mixed layer clays reservoir petrophysical property largely controls hydrocarbon accumulation in the beach bar sandstones compared with non oil bearing sandstones oil bearing sandstones have higher porosity and a larger pore throat size sandstones with a porosity of less than 8 5 and or low permeability of less than 1 02 10 3 m2 are mostly incapable of accumulating oil

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

the tintah campbell gap and implications for glacial lake agassiz drainage during the younger dryas cold interval abstract reconstructions of glacial lake agassiz paleogeography and drainage have been an important contribution to formulating a hypothesis in which glacial lake agassiz drainage to the atlantic ocean initiated the younger dryas cold interval this study evaluates the lake level and outlet history of lake agassiz as recorded by strandlines visible on lidar digital elevation models from north dakota and minnesota the former lake levels are warped due to glacial isostatic adjustment older levels have experienced more uplift and therefore have more curvature the strandline data establish that the moorhead lowstand of lake agassiz was bracketed by the strongly diverging campbell and tintah lake levels which creates a vertical gap between the former lake levels this gap exists due to a lake level drop of 90 m when the laurentide ice sheet retreat opened a lower outlet which must have been a northwest outlet to the arctic ocean by applying an exponential decay rebound model this event dates to 12 180 480 cal yr bp post dating the beginning of the younger dryas at 12 900 cal yr bp eastern drainage outlets to the atlantic ocean through the laurentian great lakes that were contemporaneous with the onset of the younger dryas cannot be ruled out but if these outlets existed their duration of occupation was short lived and not characterized by significant drawdown events within glacial lake agassiz

chronology of glacial lake agassiz meltwater routed to the gulf of mexico abstract sediment cores with new radiocarbon dates from the southern outlet of glacial lake agassiz indicate that meltwater delivery to the mississippi valley was disrupted at 10 800 14 c yr b p and the outlet was abandoned by 9400 14 c yr b p these findings confirm the timing of generally accepted terminations of the lockhart and emerson phases of lake agassiz additionally the radiocarbon chronology indicates that the spillway was fully formed by 10 800 14 c yr b p and that the occupancy in late emerson time was likely short lived with minimal spillway erosion

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

beach ridge development and lake level variation in southern lake michigan abstract the most accurate source of information on lake level fluctuations in the great lakes is the historical record from lake level gauges although it can be semiquantitatively extended back into the late 1700 s the historical record is too short to recognize long term patterns of lake level behavior to extend the historical record information must be obtained from the great lakes geologic record such information includes the elevation and age of geomorphic features and stratigraphic sequences one of the longest geologic records of late holocene lake level variation is preserved in a beach ridge complex along the southern shore of lake michigan called the toleston beach this strandplain contains over 150 beach ridges that arc across northwestern indiana and fan out into northeastern illinois each ridge was formed during the fall from a high lake level and the elevation of the foreshore deposits in each ridge provides information on the upper physical limit of lake level over the past 4000 years three scales of quasi periodic lake level variation were determined by radiocarbon dating basal peats of wetlands between the ridges and by measuring the elevation of foreshore swash deposits within ridges these three scales are 1 a short term and small scale fluctuation of 25 to 35 years with a range of about 0 5 to 0 6 m 2 an intermediate term and meso scale fluctuation of 140 to 160 years and a range of about 0 8 to 0 9 m and 3 a long term and large scale fluctuation of 500 to 600 years and a range of 1 8 to 3 7 m the short term and intermediate term fluctuations are reflected in the historical record an increase in the rate of shoreline progradation from east to west across indiana s shoreline causes differential preservation of the lake level fluctuations that is groups of four to six ridges in the western part of the strandplain that formed in response to the small scale fluctuations combine eastward into single ridges and groups of ridges representing the meso scale fluctuations the large scale fluctuations produced the most dramatic response in the western part of the toleston beach here following each high stand individual spits prograded southward off of a bedrock headland the successive spit extensions created several small lakes landward of the spits and started the 20 km eastward stream mouth deflection of the grand calumet river across indiana s western lakeshore

paleotopographic reconstructions of the eastern outlets of glacial lake agassiz paleotopographic reconstructions of the eastern outlets of glacial lake agassiz provide a foundation for understanding the complex manner in which terrain morphology controlled the routing of overflow through the eastern outlets during the lake s nipigon phase ca 9400 8000 14 c years bp and for understanding the causes of outlet driven declines in lake level during that period although flow paths across the divide between the agassiz and nipigon basins were numerous eastward releases from lake agassiz to glacial lake kelvin modern lake nipigon were channeled downslope into a relatively small number of major channels that included the valleys of modern kopka river ottertooth creek vale creek whitesand river pikitigushi river and little jackfish river from lake kelvin these waters overflowed into the superior basin the numerous lowerings in lake level between stages of the nipigon phase controlled by topography and the position of the retreating southern margin of the laurentide ice sheet had magnitudes of between 8 and 58 m although some of these drawdowns may have occurred as multiple individual events that could have been as small as several metres the total volumes of water released in association with these drops were as great as 8100 km 3 and for all nipigon stages were probably between about 140 and 250 km 3 per metre of lowering the topographic reconstructions demonstrate that lake agassiz occupied the area of glacial lake nakina located northeast of modern lake nipigon by the the pas stage ca 8000 14 c years bp and that lake agassiz drainage through the nipigon

timing and duration of north american glacial lake discharges and the younger dryas climate reversal abstract radiocarbon dated sediment cores from the champlain valley northeastern usa contain stratigraphic and micropaleontologic evidence for multiple high magnitude freshwater discharges from north american proglacial lakes to the north atlantic of particular interest are two large closely spaced outflows that entered the north atlantic ocean via the st lawrence estuary about 13 200 12 900 cal yr bp near the beginning of the younger dryas cold event we estimate from varve chronology sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0 1 sv 1 sverdrup 106 m3 s 1 the second outflow lasted about a century with a sustained discharge sufficient to keep the champlain sea relatively fresh for its duration according to climate models both outflows may have had sufficient discharge duration and timing to affect meridional ocean circulation and climate in this report we compare the proglacial lake discharge record in the champlain and st lawrence valleys to paleoclimate records from greenland ice cores and cariaco basin and discuss the two step nature of the inception of the younger dryas

organic molecules in the sheepbed mudstone gale crater mars the sample analysis at mars sam instrument on board the mars science laboratory curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of mars at gale crater central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin diagenesis concentration and long term preservation this will guide the future search for biosignatures here we report the definitive identification of chlorobenzene 150 300 parts per billion by weight ppbw and c2 to c4 dichloroalkanes up to 70 ppbw with the sam gas chromatograph mass spectrometer gcms and detection of chlorobenzene in the direct evolved gas analysis ega mode in multiple portions of the fines from the cumberland drill hole in the sheepbed mudstone at yellowknife bay when combined with gcms and ega data from multiple scooped and drilled samples blank runs and supporting laboratory analog studies the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in sam we conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources e g igneous hydrothermal atmospheric or biological or exogenous sources such as meteorites comets or interplanetary dust particles

megaflooding associated with glacial lake agassiz abstract significant baseline and episodic megaflooding from glacial lake agassiz was routed to the south east and north coasts of north america over the lake s nearly 6000 year history the five phases of lake level change were controlled by which outlet was active which in turn was controlled by ice margin position and glacioisostatic adjustment the southern outlet is the oldest and best understood outlet while successively younger outlets are progressively less understood eastern drainage synchronous with the younger dryas chronozone had been assumed by most studies but a spillway to accommodate the 90 m drop in lake level is yet to be described with the south and east outlets unable to accommodate the necessary lake level drawdown the northwest outlet has become the default outlet with arctic ocean core data supporting it however extant terrestrial data from the continent only provides data for a large flood from the fort mcmurray area closer to the end of the younger dryas coinciding with the timing of the preboreal oscillation the challenge remains to find agreement between the marine and terrestrial records uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the lake consisting of large spillways large boulders and in places giant current ripples composed of boulders flood discharge estimates into and out of the lake range from 0 04 to 1 sv with final subglacial drainage into the tyrell sea estimated at 5 sv sufficient to raise global sea level by 0 18 m and initiate the 8 2 ka stadial

northwest outlet channels of lake agassiz isostatic tilting and a migrating continental drainage divide saskatchewan canada lake cores obtained from the northwest outlet of glacial lake agassiz in northwest saskatchewan canada provide a minimum date for the cessation of the flood from the northwest outlet and a chronology for abandonment of mid holocene channels that presently straddle the mackenzie and churchill drainage divide the stratigraphy of a vibracore taken from long lake consists of a lower pebble gravel fining to massive sand silty clay and then fibrous peat wood fragments from the base of the clay yielded an accelerator mass spectrometry ams date of 9120 bp because the lake is scour in origin and is in the head of the spillway the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the emerson phase a vibracore taken at haas lake in an abandoned channel surrounded by muskeg with no influent streams consists of 0 8 m of stratified pebble gravel containing abundant shell and wood fragments overlain by 1 62 m of gyttja with a sharp conformable lower contact ams dates range from 5590 bp from the topmost gravel to 3080 bp within the gyttja the gravel is interpreted as fluvial recording a river draining wasekamio lake north into the clearwater river across the present day drainage divide today a drop of 2 m occurs from wasekamio lake southeast to lac ile a la crosse along 150 km of lake basins parallel to the cree lake moraine the dates from haas lake suggest that before 5200 bp the drainage divide was about 100 km further southeast implying that during the emerson phase lake level was controlled by a sill near flatstone lake at about 430 m instead of between wasekamio lake and the clearwater river as was previously proposed holocene differential isostatic uplift caused the flow reversal in the upper churchill basin anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today

glacial lake agassiz its northwest maximum extent and outlet in saskatchewan emerson phase abstract six different lines of evidence support the hypothesis that glacial lake agassiz expanded an additional 70 000 km2 over that previously mapped in northwestern saskatchewan and that the lake discharged out the northwestern clearwater outlet then through glacial lake mcconnell and mackenzie river to the arctic ocean elevations of formerly unmapped 1 strandlines and 2 glaciolacustrine sediments between the previously mapped northwest limit of lake agassiz and the clearwater lower athabasca spillway indicate that water extended 170 km farther northwest recently mapped strandlines at elevations up to 60 m above the previously mapped extent of lake agassiz can be traced along 3 isobases to the mouth of the spillway based upon 4 six radiocarbon dates recovered from spillway flood deposits in the athabasca river valley and its late pleistocene delta the 5 clearwater spillway was cut at 9 9 ka bp this date is synchronous with the initiation of the emerson phase 9 9 ka bp in the southern lake agassiz basin and 6 coincides with the position of the laurentide ice sheet at the cree lake moraine 10 ka bp along the northern margin of the lake following closure of the eastern outlets at the onset of the emerson phase lake agassiz transgressed toward the northwest into the deglaciated and isostatically depressed glacial foreland in the churchill river valley to an elevation of 490 m the pre flood elevation of the churchill mackenzie drainage divide at the head of the clearwater lower athabasca spillway the beaver river moraine an earthen drainage divide was breached resulting in lowering lake agassiz 52 m to a stable elevation at 438 m the lake discharged 21 000 km3 of water into the arctic ocean that raised global sea level by 6 cm

geochemical characteristics of glacial lake agassiz sediments and new ages for the moorhead phase at fargo north dakota usa the cause and age of the moorhead low water phase of glacial lake agassiz remains uncertain new geochemical x ray fluorescence xrf and elemental analysis and chronological optically stimulated luminescence osl data are used to test for evaporative enrichment within lacustrine sediment from rabbit lake a small basin just above the highest lake agassiz strandline and from two lake agassiz sediment cores at fargo north dakota increases in quartz and gypsum interpreted to be of aeolian origin suggest increased aridity at rabbit lake sometime after 13 540 13 750 cal years bp from the fargo cores lacustrine sediment of the brenna and sherack formations did not show convincing evidence for evaporative enrichment however this result is complicated by an erosional contact at the top of the brenna formation a thin middle sand unit between the brenna and sherack formation clays is stratigraphically equivalent to the poplar river formation west fargo member but its properties differ from the fluvial sand of the west fargo member four osl ages from the organic poor middle sand unit at fargo range between 12 8 0 2 and 13 5 0 2 ka with 1 6 ka uncertainty and suggest lake level fell at fargo at or before 13 1 0 2 ka the average of the osl ages with different sedimentological properties and a difference of 1750 years between the new osl ages and previously published ages on the west fargo member sand additional work is required to determine whether the middle sand unit is a new member of the poplar river formation recording an earlier and different depositional environment than the west fargo member from a plot of available ages for the moorhead phase the regression remains poorly constrained in time

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

ages for the big stone moraine and the oldest beaches of glacial lake agassiz implications for deglaciation chronology glacial lake agassiz has been implicated as the trigger for numerous episodes of abrupt climate change at the close of the last ice age yet the beginning age of the lake has never been determined here we report the fi rst numerical age data on the big stone moraine and the oldest beaches of glacial lake agassiz organic remains from lakes bogs and channels distal to and inset to the big stone moraine require that glacial activity at this moraine ceased prior to 12 000 14 c yr b p 13 950 cal calendar yr a site near new effi ng ton south dakota united states implies full glacial recession north of the topographic divide prior to 11 810 14 c yr b p 13 670 cal yr synchronous with the beginning of glacial lake agassiz lake agassiz shorelines inset to the moraine yield optically stimulated luminescence osl ages from 14 200 12 600 yr cal lower strandlines are younger but the similarity of ages suggests that initial lake lowering was faster than osl ages can currently resolve nevertheless the osl ages represent the fi rst numerical age assignments for the herman norcross and upham beach ridges setting the stage for future numerical age assignments within the lake agassiz basin these two dating methods yield strongly consistent results within stated uncertainties the age of the big stone moraine implies an interval of rapid retreat for the des moines lobe of the laurentide ice sheet during the bolling allerod warm interval the overlapping ages for the uppermost beach levels and abandonment of the highest lake agassiz spillway indicate a rapidly evolving lake until at least 13 500 yr cal

characterization of pebble fabrics in modern terrestrial glacigenic sediments pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers where sedimentary processes can be observed or inferred with relatively little ambiguity over 100 samples from contemporary environments illustrate fabrics characterizing melt out till deformed and undeformed lodgement till sediment flow deposits and ice slope colluvium lodgement till fabric variability is related to the two layer structure of these sediments a structureless friable upper layer with low shear strength and high consolidation coefficient overlying a very compact material of horizontal platy structure fabric strength assessed by eigenvalue analysis is weaker and pebble dip is more dispersed in the upper structureless horizon stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon alternatively upper horizon fabrics may be characteristic of all recently deposited lodgement tills with stronger fabrics developing at depth by dewatering and consolidation there is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt out tills through undeformed and deformed lodgement tills to sediment flow deposits and ice slope colluvium there is however considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some quaternary glacial sediments relatively strong fabrics characteristic of melt out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments

mars a review and synthesis of general environments and geological settings of magma h2o interactions the advent of a global cryosphere likely occurred very early in the history of mars and much of the available water and related volatiles co 2 clathrates etc were sequestered within and below the cryosphere this means that magmatism plutonism and volcanism as a geological process throughout the history of mars cannot be fully understood without accounting for the interaction of magma and water and related species in both solid and liquid form we review and outline the probable configuration of water and ice deposits in the history of mars describe environments and modes of magma h 2o interaction and provide specific examples from the geological record of mars magma and water ice interactions have been interpreted to have formed 1 massive pyroclastic deposits 2 large scale ground collapse and chaotic terrain 3 major outflow channels 4 mega lahars dwarfing terrestrial examples 5 sub ice sheet eruptions and edifices 6 pseudocraters 7 landslides on volcanic edifice flanks and 8 hydrothermal sites the global nature of the cryosphere its longevity and the diversity of environments means that mars is an excellent laboratory for the study of magma h 2o interactions and the role of related volatile species

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

glacial lake agassiz the northwestern outlet and paleoflood valley morphology and sediment in the fort mcmurray region of alberta indicate that a catastrophic flood discharged down the lower clearwater and athabasca river valleys 9900 yr b p geomorphic and chronologic evidence suggests that glacial lake agassiz emerson phase was the probable water source as the flood incised a drainage divide located near the alberta saskatchewan border the level of glacial lake agassiz decreased by 46 m discharged 2 4 x 106 m3 s for at least 78 days and stabilized at 438 m above sea level in the lake wasekamio area at that time water entered the arctic ocean via glacial lake mcconnell and the mackenzie river rather than the gulf of mexico via the mississippi river as previously thought such a large influx of fresh water 8 6 km3 h into the arctic at the close of the last glaciation may have had an abrupt major influence on northern climate

age determinations for glacial lake agassiz shorelines west of fargo north dakota usa understanding the evolution of lake agassiz is vital to developing a comprehensive late quaternary history of central north america although many of the geomorphic features of the lake are well known current reconstructions pri marily depend upon relative ages of landforms here we report new optically stimulated luminescence osl ages on a flight of strandlines located 140 km north of the southern outlet strandline ages at this location range from 14 3 0 2 to 10 0 0 2 ka cal spanning 4000 years of lake history using geomorphic relationships and osl age control it is pro posed that the herman through tintah strandlines developed over a period of 1000 years followed by a hiatus of strandline development until the campbell strandline developed at 10 3 0 2 ka cal there is agreement between our new osl dates and osl and radiocarbon ages from geomorphically correlative landforms elsewhere in the lake basin the use of high reso lution lidar imagery greatly aids localized mapping of shoreline features additional site specific field work and osl ages are necessary to further evaluate strandline tracing across the basin resume il est essentiel de comprendre l evolution du lac agassiz pour avoir un historique complet du quaternaire tardif du centre de l amerique du nord bien que plusieurs des caracteristiques geomorphologiques du lac soient bien connues les reconstructions actuelles sont surtout determinees par l ge relatif des formes de terrain dans cet article nous donnons de nouveaux ges determines par luminescence stimulee optiquement osl a d anciennes lignes de plage situees a 140 km au nord de l exutoire sud les ges des anciennes lignes de plage a cet endroit varient entre 14 3 0 2 et 10 0 0 2 ka cal soit 4000 ans d histoire du lac base sur des relations geomorphologiques et le controle de l ge par osl il est propose que les anciennes lignes de plage herman a tintah se soient developpees durant une periode de moins de 1000 ans une periode sans developpement de lignes de plage aurait suivi jusqu au developpement de la ligne de plage campbell vers 10 3 0 2 ka cal il y a concordance entre nos nouvelles dates osl et les ges determines par osl et par radiocar bone sur des formes de terrain correlees par geomorphologie ailleurs dans le bassin du lac l utilisation d imagerie lidar a haute resolution a grandement aide la cartographie locale des caracteristiques des lignes de rivage d autres travaux speci fiques au site et d autres ges osl sont necessaires pour continuer a tracer les anciennes lignes de plage a travers le bassin traduit par la redaction

early miocene adakite like volcanism in the balkuyumcu region central anatolia turkey petrology and geochemistry the balkuyumcu region located in the southwestern part of ankara in the izmir ankara suture zone central anatolia turkey consists of basic andesitic andesitic dacitic and rhyolitic rocks extruded during the early miocene 20 22 ma as a result of post collisional volcanism balkuyumcu volcanic rocks can be divided into two groups on the basis of their mineralogy and composition the basic andesitic ba and andesitic dacitic and rhyolitic adr groups the adr and ba group of rocks have adakite like and calc alkaline characteristics respectively the adr group has higher sio2 content sr y and la yb ratios and low mgo mg y and yb contents than the ba group both groups have nearly the same sr nd isotopic compositions and display similar normalized multi element patterns with enrichments in lile and lree depletions in nb ti zr p and a lack of eu anomalies major trace element and sr nd isotopic data indicate that both groups of rocks were derived from the same source but affected by different magmatic processes during ascent the adakite like rocks may have been produced by partial melting of thickened lower continental crust fractional crystallization also played a major role in their formation however the ba group rocks were derived from partial melting of lower continental crust that was probably delaminated these rocks appear to have had limited interaction with mantle peridodite during ascent to the surface

postglacial history and paleoecology of wampum manitoba a former lagoon in the lake agassiz basin a small paleolagoon along the margin of the glacial lake agassiz basin near wampum manitoba 130 km southeast of winnipeg contains an unusually thick and continuous sequence of late glacial and holocene organic sediment cores at 17 sites through this sequence provide insight into the fluctuations of the level of lake agassiz the timing of the construction of the lake9s most extensive strandline the upper campbell beach and the paleoecology of this area during the past 10 000 14 c yr the history of this area is established from 26 new ams radiocarbon dates siliceous microfossils plant macrofossils mineralogy sediment characteristics and stratigraphic relationships following deglaciation at wampum about 11 14 c ka deposition of largely unfossiliferous silty clay with occasional ice rafted clasts represents relatively deep water conditions in lake agassiz overlying this is a spatially and temporally variable mixture of silt sand peat gyttja and marl containing an allochthonous assemblage of siliceous microfossils and plant macrofossils with a wide range of radiocarbon dates these sediments were deposited in an embayment of lake agassiz mainly in shallow quiet waters as the lake transgressed about 10 ka over the moorhead low water phase surface between about 9 7 and 9 3 ka the wampum embayment was progressively isolated from lake agassiz by growth of the upper campbell spit resulting in the formation of a lagoon organic rich deposits on the lakeward side of the lagoon were buried 9 3 9 4 ka by sand and gravel of the spit and a thin overwash of sand marks this event throughout the lagoon at about this time lake agassiz fell below the upper campbell beach level subsequent accumulation at wampum consists mainly of algal gyttja during the early holocene and marl during the middle holocene only minor fluctuations in hydrological conditions occurred except for slightly warmer and drier conditions between 6 2 and 4 0 14 c ka these stable shallow water conditions may be due partly to persistent groundwater contributions to the site progressive encroachment of rooted aquatics led to present day fen conditions peat accumulation across the basin began by about 4 0 ka

using lidar digital elevation model data to map lake agassiz beaches measure their isostatically induced gradients and estimate their ages abstract high resolution lidar digital elevation model dem data were used to create dem mosaics and hillshade maps of a large region in north dakota for better defining and measuring the strandlines of glacial lake agassiz although many of the strandlines in this region had been identified and named more than a century ago by warren upham lidar images clearly reveal their complexity and identify additional small and low relief ridges not previously mapped the elevations of the crests of six well developed strandlines the campbell mccauleyville lower blanchard emerado upper ojata and lower ojata beaches were measured for each of these strandlines north south gradients were calculated which were produced by differential isostatic rebound the steepest gradient is on the uppermost campbell beach in the sequence and the gradient on each beach below is progressively lower confirming that these beaches were deposited in sequence from oldest to youngest as the level of lake agassiz declined because there were no anomalous beach gradients in this sequence the ojata beach formed after 9400 14 c 10 630 cal bp which is when the higher elevation campbell beach was deposited rather than at 10 000 14 c 11 480 cal years ago as some have suggested because of the age of organics below the ojata beach those organics and the subaerial surface on which they lie survived the moorhead transgression to the campbell beach and the ojata beach must have been deposited over the older organic unit later as lake level regressed a simple extrapolation model was used to estimate the ages of beaches in the sequence

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

optically stimulated luminescence ages from the lake agassiz basin in manitoba geomorphic analysis and optically stimulated luminescence osl ages from undated lake agassiz beaches and adjacent fluvial sediments on riding mountain in manitoba provide insight into their early history new osl ages of 14 5 2 4 and 13 4 0 7 ka on the oldest herman to norcross beaches of lake agassiz near the canada u s border indicate that the laurentide ice sheet lis retreated from that part of the agassiz basin by 14 5 ka to the north along riding mountain the herman strandlines are absent and osl ages on the oldest beach there average 12 9 ka which links it to the younger norcross tintah strandlines in adjacent riding mountain osl ages and geomorphological relationships of a large abandoned glacial spillway 200 m above the oldest beaches of lake agassiz indicate that this channel predates retreat of the lis and formation of beaches in this part of the agassiz basin with ice remaining in this area until after 14 5 ka osl ages on the gimli beach 170 km to the east are 3000 yr older than conventional assignments suggesting that it formed during the moorhead low water phase 12 8 10 6 ka luminescence ages support the conclusion that the campbell beach formed 10 9 ka near the end of the moorhead low water phase

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

strandline analysis in the southern basin of glacial lake agassiz minnesota and north and south dakota usa glacial lake agassiz a large pleistocene lake left behind strandlines at multiple elevations within its basin prior researchers have used these strandlines to identify four relatively stable water level stages but tracing them over long distances is often problematic in this study the elevation of the tintah strandline is returned to its original designation and a newly interpreted stable lake level at 1020 1030 ft 311 314 m is referred to as the upham level based on a concentration of ridges and a spit at that elevation cores from strandline and lagoon complexes from the milnor to tintah beaches reveal a decreasing thickness of strandline sediment associated with shorter aggregate length strandlines this relationship is most likely controlled by sediment starvation greater water level fluctuations and shallower water beaches near the head of the southern outlet spillway indicate that shoreline occupation at the lower campbell level was either very short lived or strandline development was hampered by shallow water the modern day sill elevation between the southern outlet spillway and the lake basin is found to be 3 km south of white rock minnesota at an elevation of 974 ft 297 m all but the campbell strandlines at the southern outlet are interpreted as the result of a regression driven by incision of the southern outlet spillway

the chronology climate and confusion of the moorhead phase of glacial lake agassiz new results from the ojata beach north dakota usa rapid drainage of glacial lake agassiz to the north atlantic ocean has been implicated as a triggering mechanism for the younger dryas yd cold event 13 11 6 ka cal a key component to this hypothesis is the interpretation that the ojata beach of lake agassiz in north dakota usa formed during a regression of the lake at the beginning of the yd this paper reviews the chronological data for the lowwater moorhead phase presents new radiocarbon and optically stimulated luminescence osl ages for the ojata beach and utilizes plant and insect macrofossils to reconstruct the paleoenvironmental conditions during the moorhead phase in eastern north dakota the integrated analysis of the geochronologic data emphasizes the need to distinguish between in situ and reworked plant macrofossils new ages obtained stratigraphically below the ojata beach sediments and reinterpreted chronologic data for the moorhead phase suggest that contrary to previous interpretations the ojata beach is a record of transgression of the lake in the later part of the yd and the oldest in situ minimum age for the moorhead phase is 10 47775 ka 14 c bp paleoenvironmental analysis indicates that a

testing northwest drainage from lake agassiz using extant ice margin and strandline data extant data on shorelines and ice margins in the glacial lake agassiz basin defines the limits of lake agassiz through deglacial time the ice sheet margin had not retreated far enough northwards by the beginning or end of the younger dryas chronozone for the lake to drain northwest however once lake agassiz reached the campbell beach stage at 10 800 10 300 cal bp then projections of lake agassiz strandlines were higher than the topography allowing for the first possible pathway to the northwest this relationship is used to reject the recent assertion that there was northwest drainage from lake agassiz at the beginning and end of the younger dryas chronozone

a chronology for glacial lake agassiz shorelines along upham s namesake transect abstract four traditionally recognized strandline complexes in the southern basin of glacial lake agassiz are the herman norcross tintah and campbell whose names correspond to towns in west central minnesota that lie on a linear transect defined by the great northern railroad grade the active corridor for commerce at the time when warren upham was mapping and naming the shorelines of lake agassiz ca 1880 1895 because shorelines represent static water planes their extension around the lake margin establishes time synchronous lake levels transitions between shoreline positions represent significant water level fluctuations however geologic ages have never been obtained from sites near the namesake towns in the vicinity of the southern outlet here we report the first geologic ages for lake agassiz shorelines obtained at field sites along the namesake transect and evaluate the emerging chronology in light of other paleoclimate records our current work from 11 sampling sites has yielded 16 independent ages these results combined with a growing osl age data set for lake agassiz s southern basin provide robust age constraints for the herman norcross and campbell strandlines with averages and standard deviations of 14 1 0 3 ka 13 6 0 2 ka and 10 5 0 3 ka respectively

abundances and implications of volatile bearing species from evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument on the mars science laboratory msl rover curiosity detected evolved gases during thermal analysis of soil samples from the rocknest aeolian deposit in gale crater major species detected in order of decreasing molar abundance were h2o so2 co2 and o2 all at the mol level with hcl h2s nh3 no and hcn present at the tens to hundreds of nmol level we compute weight numbers for the major gases evolved by assuming a likely source and calculate abundances between 0 5 and 3 wt the evolution of these gases implies the presence of both oxidized perchlorates and reduced sulfides or h bearing species as well as minerals formed under alkaline carbonates and possibly acidic sulfates conditions possible source phases in the rocknest material are hydrated amorphous material minor clay minerals and hydrated perchlorate salts all potential h2o sources carbonates co2 perchlorates o2 and hcl and potential n bearing materials e g martian nitrates terrestrial or martian nitrogenated organics ammonium salts that evolve nh3 no and or hcn we conclude that rocknest materials are a physical mixture in chemical disequilibrium consistent with aeolian mixing and that although weathering is not extensive it may be ongoing even under current martian surface conditions

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

evidence for indigenous nitrogen in sedimentary and aeolian deposits from the curiosity rover investigations at gale crater mars the sample analysis at mars sam investigation on the mars science laboratory msl curiosity rover has detected oxidized nitrogen bearing compounds during pyrolysis of scooped aeolian sediments and drilled sedimentary deposits within gale crater total n concentrations ranged from 20 to 250 nmol n per sample after subtraction of known n sources in sam our results support the equivalent of 110 300 ppm of nitrate in the rocknest rn aeolian samples and 70 260 and 330 1 100 ppm nitrate in john klein jk and cumberland cb mudstone deposits respectively discovery of indigenous martian nitrogen in mars surface materials has important implications for habitability and specifically for the potential evolution of a nitrogen cycle at some point in martian history the detection of nitrate in both wind drifted fines rn and in mudstone jk cb is likely a result of n2 fixation to nitrate generated by thermal shock from impact or volcanic plume lightning on ancient mars fixed nitrogen could have facilitated the development of a primitive nitrogen cycle on the surface of ancient mars potentially providing a biochemically accessible source of nitrogen

isostatic rebound in the northwestern part of the lake agassiz basin isobase changes and overflow abstract based on new gps elevation data on the upper and lower campbell strandlines in the northwestern part of the glacial lake agassiz basin the trend of isobases representing differential glacio isostatic rebound in that region is shown to bend and assume a nearly west east orientation this differs from the northwest southeast orientation to the southeast of the study area which others had projected into the northwestern corner of the lake agassiz basin this means that there was more isostatic depression than previously thought north of 53 n the difference in slopes on reconstructed water planes of the upper and lower campbell beaches is less with these isobases which better reflects the short period of time between their formation it is likely that the change in orientation of isobases reflects the presence of a thick keewatin ice center to the north our revised west east isobase reconstruction indicates that when the lake was at the campbell beach levels 9900 9400 14c b p lake agassiz overflowed across the paleo divide at wycherley lake saskatchewan which controlled flow through the northwestern outlet of lake agassiz during part of its history overflow would not have occurred through the wycherley lake channels at this time using the old isobase projections

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

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

preboreal oscillation caused by a glacial lake agassiz flood the preboreal oscillation pbo has been attributed to increased meltwater but the source of the meltwater and causative mechanism of the pbo has remained elusive here we attribute the source to a massive meltwater discharge event from an abrupt drainage of glacial lake agassiz canada via the mackenzie river into the arctic ocean a maximum volume of 21 000 km 3 was discharged over a 1 5 3 yr period with a peakdischarge of 0 500 sverdrups sv equivalent to a 6 m rise in the arctic ocean or 0 062 m rise in global sea level the flood occurred at about 11 335 cal yr bp and was followed by a b0 042 sv flow until 10 750 cal yr bp when the southern outlet of lake agassiz reopened and diverted drainage to the mississippi river system we estimate that only 2 4 of the flood water would have frozen into sea ice within the beaufort region but coupled with increased river ice production during winter and thicker pack ice growth throughout the arctic ocean a thicker longer lasting and more extensive packice may have been flushed through fram strait the thicker and more extensive packice and freshened sea surface may have triggered the pbo by increasing albedo and generating a low salinity anomaly upon melting in the north atlantic thus decreasing the formation of north atlantic deep water r 2002 elsevier science ltd all rights reserved

martian magmas contained abundant chlorine but little water the martian water cycle a key for the habitability of mars largely relies on the abundance of water in martian magmas and their mantle sources yet martian snc shergottite nakhlite and chassigny classes meteorites contain minimal water however some experimental studies have suggested that martian parental magmas contained as much as 2 h2o here we integrate mineral chemical experimental and cosmochemical constraints to show that martian magmas contained little water but abundant chlorine apatite and amphibole in martian meteorites are chlorine rich and water poor this constrains the chlorine contents in their parental magmas to 0 3 wt and water contents to 0 3 wt our experimental work has shown that large amounts of water are not needed to explain the mineralogy of the martian meteorites because chlorine has effects similar to those of water on crystallization such chlorine rich water poor martian magmas are consistent with mars being chlorine rich 2 5 compared with the earth furthermore the bulk cl composition of martian meteorites shows that they have not preferentially lost cl by degassing of an h2o rich vapor together these results show that chlorine not water was the dominant volatile species in martian basalts and that these basalts contributed little h2o to mars surface environment

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume