the age of the medusae fossae formation evidence of hesperian emplacement from crater morphology stratigraphy and ancient lava contacts abstract the medusae fossae formation mff covering about 2 1 10 6 km 2 with an estimated volume of 1 4 10 6 km 3 and straddling the equatorial region of mars east of tharsis has historically been mapped and dated as amazonian in age analysis of the mff using a range of new observations from recent mission data at multiple resolutions reveals evidence that the formation is older than previously hypothesized with parts of the mff having formed in the hesperian and parts having been reworked and reformed throughout the amazonian up to the present ancient outcroppings of the mff edged with jagged yardangs became a mold for embaying hesperian aged lavas the erosion of the mff left solidified lava casts in the embaying lava unit this lava edge morphology permits the identification of ancient contacts between the mff and hesperian aged lava terrain additionally the flanking fan of the hesperian aged apollinaris patera volcano embays the formation at its foot indicating that parts of the mff were formed in the hesperian erosion has erased and inverted many of the superposed craters in the region showing that very young amazonian ages derived from impact crater size frequency distributions are resurfacing ages and not emplacement ages we find abundant evidence that the formation is extremely mobile and continuously reworked we conclude that a significant part of the mff may have originally been emplaced in the hesperian these observations place new constraints on the mode of origin of the mff

deltaic deposits at aeolis dorsa sedimentary evidence for a standing body of water on the northern plains of mars a fundamental long standing question regarding mars history is whether the flat and low lying northern plains ever hosted an ocean the best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy here we use high resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the aeolis dorsa region just north of the dichotomy boundary observations of stacked cross cutting channel bodies and stratal geometries indicate that these landforms represent exhumed distributary channel deposits observations of depositional trunk feeder channel bodies a lack of evidence for past topographic confinement channel avulsions at similar elevations and the presence of a strong break in dip slope between topset and foreset beds suggest that this distributary system was most likely a delta rather than an alluvial fan or submarine fan sediment transport calculations using both measured and derived channel geometries indicate a minimum delta deposition time on the order of 400 years the location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary unconfined by any observable craters suggests a standing body of water potentially 105 km2 in extent or greater and is spatially consistent with hypotheses for a northern ocean

vegetation succession in deglaciated landscapes implications for sediment and landscape stability landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed glacially influenced landscape to a stable diverse ecosystem which supports numerous species and communities large scale vegetation development and changes in sediment availability used as a proxy for paraglacial adjustment following rapid deglaciation were assessed using information from remote sensing delineation of broad successional vegetation cover types was undertaken using landsat satellite imagery covering a 22 year period to document the rate and trajectory of terrestrial vegetation development use of a space for time substitution in glacier bay national park alaska allowed back calculation of the age and stage of development of six catchments over 206 years the high accuracy 89 2 of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages bare sediment and alder in contrast later successional stages spruce and spruce hemlock dominated forest had high vegetation class retention and low turnover modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported these data when combined with the known influence of terrestrial succession on soil development and sediment availability suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation this study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio physical interactions within landscape evolution models 2014 the authors earth surface processes and landforms published by john wiley sons ltd

glacially induced organization of channel reach morphology in mountain streams 1 we examine the spatial distribution of channel reach morphologies in formerly glaciated mountain drainage basins of coastal british columbia canada using field and geographic information systems derived data we show that the local channel slope and the degree of colluvial alluvial coupling imposed by the glacial valley morphology dictate the spatial organization of channel types in particular the complex glacially induced channel long profile produces characteristic sequences of channel reaches that depart from the downstream succession colluvial boulder cascade step pool rapids riffle pool distinctive of simple unglaciated mountain streams typically the presence of one hanging valley in the river long profile produces and separates two full successions of channel types a headmost one characterized by an ephemeral seasonal hydrologic regime and a downstream one where water runoff is perennial we document that channel types are well separated in plots of slope versus shear stress area versus shear stress and slope versus relative roughness in agreement with these outcomes multivariate discriminant analyses coupled with principal component analysis of 98 study reaches yield a highly successful channel type classification when slope shear stress and relative roughness are considered success rates depending on whether or not boulder cascade reaches are pooled together with step pools are 88 and 75 respectively previous work in unglaciated settings has suggested that mountain channels have distinct bed morphology states that vary primarily with slope our study reveals that even in formerly glaciated valleys where slope is largely inherited from glacial times these distinct bed states exist and vary mostly with slope adding considerable strength to this empirical knowledge

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

regional metamorphic controls on alteration associated with gold mineralization in the eastern goldfields province western australia implications for the timing and origin of archean lode gold deposits alteration assemblages associated with archean epigenetic gold mineralization in the menzies kambalda area of the yilgarn craton western australia vary systematically with regional metamorphic grade up to and including upper amphibolite facies rocks k metasomatism is recorded by the presence of muscovite biotite and k feldspar at progressively higher metamorphic grades high metamorphic grades are commonly developed in broad thermal aureoles around fate syntectonic granitic intrusions metamorphic recrystallization of alteration assemblages is common in the thermal aureoles these relations suggest broad contemporaneity among granitoid intrusion regional metamorphism and mineralization during the final stages of the tectonic evolution of the granite greenstone terrain late syntectonic granitoids acted as centers of heat and fluid flux in large scale synmetamorphic hydrothermal systems that deposited gold possibly from modified mantle derived fluids

glacier fluctuations during the past millennium in garibaldi provincial park southern coast mountains british columbia the little ice age glacier history in garibaldi provincial park southern coast mountains british columbia was reconstructed using geomorphic mapping radiocarbon ages on fossil wood in glacier forefields dendrochronology and lichenometry the little ice age began in the 11th century glaciers reached their first maximum of the past millennium in the 12th century they were only slightly more extensive than today in the 13th century but advanced at least twice in the 14th and 15th centuries to near their maximum little ice age positions glaciers probably fluctuated around these advanced positions from the 15th century to the beginning of the 18th century they achieved their greatest extent between a d 1690 and 1720 moraines were deposited at positions beyond present day ice limits throughout the 19th and early 20th centuries glacier fluctuations appear to be synchronous throughout garibaldi park this chronology agrees well with similar records from other mountain ranges and with reconstructed n

an analysis of sinuous ridges in the southern argyre planitia mars using hirise and ctx images and mola data 1 a suite of sinuous ridges with branching and braided morphologies forms an anastomosing network in southern argyre planitia mars several modes of origin have been proposed for the argyre ridges imagery from the high resolution imaging science experiment hirise and context camera ctx aboard mars reconnaissance orbiter mro and mars orbiter laser altimeter mola topographic data sets from mars global surveyor mgs are used to constrain processes involved in formation of the argyre ridges we find the characteristics of the ridges and associated layered deposits consistent with glaciofluvial lacustrine processes and conclude that the ridges are most likely eskers in particular variations in ridge height appear to be related to the surrounding surface slope ridge height increases with descending slopes and decreases with ascending slopes this characteristic is observed in terrestrial eskers and is related to subice flow processes the nature of some eroding beds in the ridges suggests induration if the argyre ridges are indeed eskers the southern argyre basin was once covered by the margin of a large thick stagnating or retreating ice deposit that extended for hundreds of kilometers or more during ridge formation water flowed on top within or beneath the ice deposit the continuity and preservation of the ridges suggests that flow was primarily at the base of the ice the dimensions up to hundreds of meters tall and several kilometers wide aspect ratio and extent hundreds of kilometers of the ridges as well as preliminary calculations of discharge suggest that a significant amount of water was available

little ice age glacial activity in the mt waddington area british columbia coast mountains canada the establishment of fourteen little ice age lia glacier chronologies in the mt waddington area led to the development of an extended history of glacial activity in this portion of the southern british columbia coast mountains canada the glaciers were located within four different mountain ranges and were of varying size and aspect dendrochronological and lichenometric techniques were used to provide relative age estimates of moraines formed as glacier termini retreated from advanced positions evidence for pre lia glacial events is best preserved at tiedemann glacier where the oldest glacial advances date to a d 620 and 925 933 soil covered and well vegetated moraines built at cathedral pagoda and siva glaciers date to between a d 1203 and 1226 following this event moraines constructed at ragnarok siva and cathedral glaciers in the mid 14th century suggest glaciers in the region underwent a period of downwasting and retreat before readvancing the majority of moraines recorded in the mt waddington area describe late lia glacial events shown to have constructed moraines that date to a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 and 1942 1946 over the last 500 years these moraine building episodes were shown to occur on average every 65 years and suggest there has been prolonged synchronicity in the glaciological response to persistent climate forcing mechanisms nevertheless our analysis suggests that local factors such as aspect and size play an important role in individual glacial response notably ice termini of medium size glaciers facing eastwards showed a quicker response to climatically induced mass balance changes resume l historique de quatorze glaciers de vallee de la region du mont waddington sud de la chaine cotiere de colombie britannique canada durant le petit ge glaciaire pag fut evalue par l utilisation de techniques dendrochronologiques et lichenometriques procurant un ge minimum pour la formation des moraines laterales et frontales multiples les glaciers a l etude d aspect et de taille differents furent selectionnes a partir de quatre chaines de montagnes les evenements qui predatent le pag sont le mieux preserves sur le site du glacier tiedemann ou les plus vieilles avancees glaciaires date de a d 620 et 925 933 des moraines presentant une pedogenese avancee et recouvertes d une dense couverture vegetale furent datees entre a d 1203 et 1226 des moraines construites dans le milieu du 14 e siecle par les glaciers ragnarok siva et cathedral suggerent que les glaciers de la region se sont retires pour par la suite reavancer la majorite des moraines datees le furent vers la fin du pag soit en a d 1443 1458 1506 1524 1562 1575 1597 1621 1657 1660 1767 1784 1821 1837 1871 1900 1915 1928 et 1942 1946 au cours des 500 dernieres annees en moyenne 65 annees separent les differents episodes glaciaires ce qui suggerent un synchronisme des reponses glaciaires aux mecanismes climatiques des donnees preliminaires suggerent que l orientation et la taille des glaciers jouent un role important dans la reponse individualiste des glaciers en fait les terminus glaciaires des moyens glaciers d orientation est semblent repondre plus rapidement a un ajustement de volume interne glaciaire

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

the savage lode magnesian skarn in the marvel loch gold silver mine southern cross greenstone belt western australia part 2 pressure temperature estimates and constraints on fluid sources the savage lode gold skarn orebody in the marvel loch mine southern cross greenstone belt western australia replaces foliated metakomatiites in a subvertical ductile shear zone and is located within the broad metamorphic aureole of the ghooli dome granodiorite granite batholith pressure estimates based on metamorphic as well as alteration mineral parageneses indicate that skarn formation took place at p 4 1 kbar 1 kbar 100 mpa corresponding to a burial depth of about 13 km metamorphism reached temperatures of 550 630 c in the mine area and preceded skarn formation pressure temperature calculations constrain the maximum temperature of the hydrothermal fluid in the savage lode to 640 20 c during the formation of early olivine calcite and diopside amphibole rocks and to 500 600 c during the formation of phlogopite chlorite calcite schists and quartz diopside veins lower fluid temperatures 500 to 400 c are recorded by retrograde serpentine after olivine talc after tremolite a

metamorphic and structural setting of archaean amphibolitehosted gold deposits near southern cross southern cross province yilgarn block western australia abstract the southern cross archaean greenstone belt comprises dominantly low to mid amphibolite facies high strain domains which show evidence of a complex deformational and metamorphic history aeromagnetic field and petrographic data suggest that this complex structural metamorphic history was related to a single progressive deformation event which was broadly synchronous with granitoid emplacement between 2 68 and 2 62 ga lode gold deposits at corinthia hopes hill fraser s and polaris south occur in sequence from north to south along the fraser s corinthia shear zone in the southern cross greenstone belt corinthia and hopes hill are situated along a sheared granitoid greenstone contact whereas fraser s and polaris south occur within the greenstones about 200 m west of the contact gold mineralisation along the fraser s corinthia shear zone is associated predominantly with variably deformed quartz pyrrhotite pyrite plagioclase and or pyroxene calcite quartz plagioclase apatite veins with zoned alteration haloes of quartz plagioclase pyroxene calcite apatite and amphibole biotite chlorite there are accessory amounts of scheelite chalcopyrite arsenopyrite and galena with the fe sulphides bismuth and gold a variety of evidence including structural timing p t conditions deduced from critical metamorphic 550 c 2 5 3 7 kbars and metasomatic alteration assemblages 520 c 3 4 kbars the high thermodynamic variance of the metasomatic mineral assemblages and the zoning of individual alteration minerals indicates that gold related wallrock alteration occurred during or immediately after peak metamorphism there is some evidence for a sympathetic decline in metamorphic grade and the temperature of gold related alteration from south polaris south to north corinthia along the mineralised shear zone the shear zone acted as a major conduit for ore fluids at a depth of about 12 14 km 3 3 5 kbars lithostatic pressure in the crust gold mineralisation along the shear zone is related to large and small scale extensional crenulation cleavages the gold deposits might thus represent a relatively deep section of the crustal continuum of lode gold deposits proposed for the yilgarn block

valley formation on early mars by subglacial and fluvial erosion the southern highlands of mars are dissected by hundreds of valley networks which are evidence that water once sculpted the surface characterizing the mechanisms of valley incision may constrain early mars climate and the search for ancient life previous interpretations of the geological record require precipitation and surface water runoff to form the valley networks in contradiction with climate simulations that predict a cold icy ancient mars here we present a global comparative study of valley network morphometry using a principal component based analysis with physical models of fluvial groundwater sapping and glacial and subglacial erosion we found that valley formation involved all these processes but that subglacial and fluvial erosion are the predominant mechanisms this is supported by predictions from models of steady state erosion and geomorphological comparisons to terrestrial analogues the inference of subglacial channels among the valley networks supports the presence of ice sheets that covered the southern highlands during the time of valley network emplacement some valleys in the southern highlands of mars may have formed by subglacial erosion consistent with a cold and icy early mars according to a statistical analysis of valley morphometry

the hydrothermal fluid of archaean lode gold deposits at different metamorphic grades compositional constraints from ore and wallrock alteration assemblages a low salinity mixed aqueous carbonic fluid is common to all archaean lode gold deposits throughout the range of mineralising conditions from sub greenschist to lower granulite facies temperatures alteration assemblages and fluid inclusion data give constraints on the fluid composition fluid xco2 is 0 1 0 3 in typical greenschist facies mesothermal deposits at higher temperatures the assemblages are consistent with formation from a fluid of similar composition but slightly higher or lower xco2 cannot be ruled out and fluid inclusion data indicate that ch4 may be an important component in ore fluids at these temperatures fluid ph is neutral or weakly alkaline at all conditions a range of relative oxidation states of four orders of magnitude fo2 is indicated at any temperature with deposits more oxidising relative to qfm at lower temperature sulphur contents of the fluids vary from 10 to 10 3 5m s with a trend towards lower sulphur contents at lower temperatures the relative concentrations of major cations in solution are similar at all conditions with na k ca although ca may be less abundant at low temperatures the broad similarities in ore fluid composition at all temperatures give support to crustal continuum models in which archaean lode gold mineralisation involved either a single fluid moving through the middle and upper crust or derivation of ore fluids by similar processes at different crustal levels many of the compositional differences between high and lowtemperature ore fluids may be attributed to evolution of deep sourced hydrothermal solutions as they rise along structurally controlled conduits the constancy of major ore fluid component concentration e g co2 cl k suggests fluid buffering and high fluid rock ratios along fluid pathways fluid buffered conditions can also explain the ore fluid fo2 temperature relations with equilibria between oxidised and reduced aqueous carbon or sulphur species controlling the oxidation state in contrast the concentrations of components present in lesser abundance in archaean gold ore fluids e g s ca h were probably controlled either by saturation of one or more mineral phases brought on by decreasing temperature or were rock buffered through fluid rock reactions extrapolation to high temperatures of the k na and ca contents of the gold bearing fluids indicates that their composition is consistent with derivation from or final equilibration with rocks of intermediate granitic composition thus giving support to isotopic and geological arguments for ore fluid source regions external to the greenstone belts the fluid oxidation states are characteristic of a wide range of potential source rocks including mantle derived igneous rocks calc alkaline granitoids and magmas and seaflooraltered metabasalts strongly oxidised magmatic sources or unusually oxidising source processes e g co2 streaming during granulitisation of the lower crust are therefore not required in the genesis of arch an lode gold deposits

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

multi proxy record of holocene glacial history of the spearhead and fitzsimmons ranges southern coast mountains british columbia abstract evidence from glacier forefields and lakes is used to reconstruct holocene glacier fluctuations in the spearhead and fitzsimmons ranges in southwest british columbia radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early holocene to their maximum extents about two to three centuries ago during the little ice age the data indicate that glaciers advanced 8630 8020 6950 6750 3580 2990 and probably 4530 4090 cal yr bp and repeatedly during the past millennium little ice age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s limitations inherent in lacustrine and terrestrial based methods of documenting holocene glacier fluctuations are minimized by using the two records together

compositional re equilibration of fluid inclusions in quartz compositional modifications to salt water fluid inclusions in quartz were observed following exposure to disequilibrium conditions in a series of laboratory experiments in which samples containing inclusions of known composition were annealed at 3 kbar and 600 t 825 c in the presence of fluids having different compositions for time intervals ranging from a few days to one month changes in inclusion compositions following re equilibration were monitored using salt crystal dissolution temperatures and or ir infra red spectroscopy the behaviors of both synthetic and natural fluid inclusions were studied the synthetic samples were re equilibrated under pint pconf conditions to minimize stress in the crystal surrounding the inclusions and were subjected to both fh2ointfh2oconf and fh2ointfh2oconf after re equilibration for four days at t 600 c most inclusions displayed significant compositional changes without decrepitation salinity variations as large as 25 wt were inferred for brine inclusions exposed to fh2oint fh2oconf for 16 days at 825 c the majority of our observations are consistent with the net diffusion of water toward the reservior having the lowest h2o i e synthetic nacl h2o fluid inclusions exhibited increased tm nacl s implying lower relative h2o contents when re equilibrated in the presence of fluids having lower h2o whereas similar and in some cases the same inclusions exhibited decreased tm nacl s implying higher h2o contents after exposure to fluids having higher h2o the behavior of natural salt water fluid inclusions during re equilibration was generally consistent with corresponding observations on synthetic samples verifying that compositional changes are not restricted to synthetic inclusions our results clearly show that there was chemical communication between fluids trapped as inclusions in quartz and the external fluid reservoir additionally it is evident that although applied stress can significantly enhance the re equilibration rate strain in the crystal host around the inclusions resulting from large pressure differentials between the internal and confining fluids is not a necessary prerequisite for compositional change finally because significant compositional changes can be induced in brine inclusions in quartz during shortterm exposure to non equilibrium conditions at 600 t 825 c in the laboratory it is likely that similar changes may result at much lower temperatures during exposure of natural rocks to non equilibrium conditions over geologic time

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

extensive noachian fluvial systems in arabia terra implications for early martian climate valley networks are some of the strongest lines of evidence for extensive fluvial activity on early noachian 3 7 ga mars however their purported absence on certain ancient terrains such as arabia terra is at variance with patterns of precipitation as predicted by warm and wet climate models this disagreement has contributed to the development of an alternative icy highlands scenario whereby valley networks were formed by the melting of highland ice sheets here we show through regional mapping that arabia terra shows evidence for extensive networks of sinuous ridges we interpret these ridge features as inverted fluvial channels that formed in the noachian before being subject to burial and exhumation the inverted channels developed on extensive aggrading flood plains as the inverted channels are both sourced in and traverse across arabia terra their formation is inconsistent with discrete localized sources of water such as meltwater from highland ice sheets our results are instead more consistent with an early mars that supported widespread precipitation and runoff

effects of glacial retreat on proglacial streams and riparian zones in the coast and north cascade mountains proglacial stream development was studied in coastal british columbia and washington focusing on reaches exposed by post little ice age lia glacier retreat to address three principal questions i does the legacy of lia glaciation influence the evolution of channel morphology ii how long does it take for riparian forest to establish following glacier retreat iii can newly exposed proglacial streams provide suitable fish habitat channel morphologies were identified by field surveys of 69 reaches in 10 catchments riparian forest development and potential fish habitat were characterized in those reaches and an additional 22 catchments using gis analysis the landscape template imposed by the quaternary glaciation appears to override most of the modern effects of the lia in controlling channel reach morphology binary logistic regression analysis identified elevation and time since deglaciation as primary controls on the presence of riparian forest at higher elevations establishment of morphologically functional riparian forest could take several centuries prolonged by channel instability associated with post lia sediment inputs of the recently deglaciated streams included in this analysis the majority 86 of the total length was of suitable gradient for fish and could be accessed either by downstream populations or from adjacent lakes predicted maximum weekly average stream temperature mwat indicated that the post lia study streams were thermally suitable for cold water fish a future scenario of glacier loss would cause a 14 decline in accessible cold water thermal habitat in post lia streams decreased summer flows due to glacier retreat could further limit usable habitat by reducing stream depths and wetted perimeters copyright 2013 john wiley sons ltd

regional clastic sediment yield in british columbia the data archive of the water survey of canada supplemented by data of the british columbia hydro and power authority is used to investigate the areal pattern of fluvial sediment yield in british columbia the data represent suspended sediment loads at 63 stations derived from observations within the period 1966 1985 in most of the province there is a single annual peak in sediment transport in spring corresponding to the dominant snowmelt freshet however on the coast winter rainfall induces the sediment peak and in the coast and cascade mountains there is a transitional regime with two peaks from 65 to 90 of annual sediment yield occurs in the spring three months sediment yield per unit area specific sediment yield increases with drainage area at all scales from 10 up to 30 000 km2 the pattern persists seasonally throughout the year this contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from e

channel adjustment and a test of rational regime theory in a proglacial braided stream the upstream reach of the sunwapta river alberta provides a useful quasi experimental field case of channel adjustment in a proglacial stream historically the formation of a proglacial lake deprived the river of its coarse sediment supply for several decades and lead to a dramatic decrease in braiding intensity close to the lake while braiding intensity increased further downstream this response to the reduction of gravel input is consistent with previous experimental results subsequent construction activity and channelization close to the lake have contributed to the continuation of these temporal and spatial trends in channel pattern the current state of adjustment of the river morphology can be explained in the context of these historical changes using rational regime equations the study reach has no tributaries and bed material size decreases twofold along the reach while width and braiding intensity increase yet channel slope decreases by only 10 the absence of any significant change in discharge downstream along the reach allows testing of regime equations under conditions in which discharge is held constant the current downstream trends in slope and fluctuations in width are predicted reliably from rational regime equations but not by the existing empirical hydraulic geometry relations the rational equations incorporate the effect of grain size and slope on channel width and the effect of width and grain size on channel slope the regime equations are successful even though they were devised for single channel gravel streams the small 10 decrease in slope along the reach despite a halving of median grain size is attributed to the counteracting positive effect on slope of the downstream increase in braiding intensity and width the downstream increase in braiding intensity must be largely the result of decreasing grain size this confirms the influence of grain size on channel pattern thresholds and demonstrates using spatial transitions in channel pattern that channel pattern predictions based on stream power alone are inadequate

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

reach scale channel geometry of a mountain river mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall nonetheless adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers mountain rivers can differ in that imposed reach scale gradient is an especially important control on reach scale channel characteristics as indicated by examination of north st vrain creek in colorado north st vrain creek drains 250 km2 of the rocky mountains we used 25 study reaches within the basin to examine controls on reach scale channel geometry variables measured included channel geometry large woody debris grain size and mean velocity drainage area at the study reaches ranged from 2 2 to 245 km2 and gradient from 0 013 to 0 147 m m 1 we examined correlations among 1 potential reach scale response variables describing channel bankfull dimension and shape hydraulics bedform wavelength and amplitude grain size ow resistance standard deviation of hydraulic radius and volume of large woody debris and 2 potential control variables that change progressively downstream drainage area discharge or that are likely to re ect a reach speci c control bed gradient we tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels results from simple linear regression analyses indicate that most response variables correlate best with gradient although channel width and width depth ratio correlate best with discharge multiple regression analyses using mallow s cp selection criterion and log transformation of all variables produced similar results in that most response variables correlate strongly with gradient these results suggest that the hypothesis is partially supported channel bed gradient is likely to be a good predictor for many reach scale response variables along mountain rivers but discharge is also an important predictor for some response variables copyright 2004 john wiley sons ltd

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

spatial analysis of stream power using gis slk anomaly maps the stream length gradient index sl shows the variation in stream power along river reaches this index is very sensitive to changes in channel slope thus allowing the evaluation of recent tectonic activity and or rock resistance nevertheless the comparison of sl values from rivers of different length is biased due to the manner in which the index is formulated thus making correlations of sl anomalies along different rivers difficult therefore when undertaking a comparison of sl values of rivers of different lengths a normalization factor must be used the graded river gradient k has already been used in some studies to normalize the sl index in this work we explore the relationships between the graded river gradient k the sl index and the stream power proposing the use of a re named slk index which enables the comparison of variable length rivers as well as the drawing of slk anomaly maps we present here a gis based procedure to generate slk maps and to identify slk anomalies in order to verify the advantages of this methodology we compared an slk map of the ne border of the granada basin with both simple river profile knickpoint identification and with an sl map the results show that the slk map supplies good results with defined anomalies and suitably reflects the main tectonic and lithological features of the study area copyright 2008 john wiley sons ltd

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

on the origin of co2 rich fluid inclusions in migmatites nearly pure co2 fluid inclusions are abundant in migmatites although h2o rich fluids are predicted from the phase equilibria processes which may play a role in this observation include 1 the effects of decompression on melt 2 generation of a co2 bearing volatile phase by the reaction graphite quartz biotite plagioclase melt orthopyroxene co2 rich vapour 3 selective leakage of h2o from co2 h2o inclusions when the pressure in the inclusion exceeds the confining pressure during decompression and 4 enrichment of grain boundary vapour in co2 by subsolidus retrograde hydration reactions

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

colluvial sediment dynamics in mountain drainage basins abstract colluvial sediment dynamics are examined using a 70 year landslide inventory in formerly glaciated mountain drainage basins of coastal british columbia canada landslide sediment transfer is documented by identifying landslide types and by characterizing preferential sites of landslide initiation delivery and storage across spatial scales data analysis reveals that open slope landslides delivering material to seasonal or perennial channels and fluvial terraces are the dominant mechanisms of sediment transfer this finding suggests high instability of the low order channel network and its ongoing re organization degradation after generalized sediment recharge occurred in the last glacial maximum in the study period landslide activity across the landscape has generated net degradation on planar slopes and first order colluvial channels whereas unchannelled valleys higher order colluvial channels and alluvial channels have accumulated material the scaling relation of the landslide sediment yield appears to be controlled by the spatial arrangement of the relict glacial macro forms landslide yield is highest in unchannelled topography decreases at the scale of channel initiation ad 0 002 km2 and remains constant for drainage areas where length scales of cirque valley walls and hanging valley floors overlap 0 002

synmetamorphic lode gold deposits in high grade archean settings lode gold deposits that formed under conditions of the middle to upper amphibolite and granulite facies have been identified in the yilgarn block of western australia these deposits which form a continuum with lower metamorphic grade mesothermal gold depos its show that at least some of the fluids responsible for mesothermal gold deposits originated in or below the middle crust studies of 18 o suggest that fluid compositions were controlled by the wall rocks at least for some elements these more proximal gold deposits provide more information about deep fluid sources than do investigations of higher level mineralization deposited from fluids strongly modified by wall rock interaction during the early part of their ascent

glacial erosion evolution of river long profiles and the organization of process domains in mountain drainage basins of coastal british columbia 1 in glaciated british columbia canada quaternary climate changes are responsible for profound spatial reorganization of earth surface processes these changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs the evolution of glaciated landscapes is examined by analyzing the structure of geomorphic process domains and channel long profiles to identify process domains we use channel surveys and gis analysis to construct slope area transects of the channel network this analysis reveals generalized process form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains at the landscape scale of source colluvial channels contributing area 1 km2 the glacial paraglacial signature commonly overrides that produced by contemporary debris flows along the axis of former ice flows relict glacial cirques introduce a hanging fluvial domain at contributing areas as small as 8 10 2 km2 and produce complex channel long profiles similar to those observed for rivers responding to tectonic forcing slope area relations typical of unglaciated equilibrium environments do not apply here the concept of process domains appears to hold however some major glacially forced modifications in the alluvial colluvial transition are observed and the definition of a depositional colluvial subdomain is proposed comparison between field and gis measured slopes reveals that gis associated error is not uniform between process domains and that gis based plots do not successfully discriminate field based process domains the combination of glacial and post glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age

the legacy of pleistocene glaciation and the organization of lowland alluvial process domains in the puget sound region article i nfo alluvial rivers of the eastern puget lowland a landscape shaped by scour and fill from the cordilleran ice sheet continue to respond to patterns of deposition and scour by the last glacial age ice sheet 18 000 years after deglaciation topography revealed by valley cross sections created from high resolution lidar digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post glaciation slope area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts concavity indices in mountain headwaters 0 3b b0 9 compare to those of many world rivers 0 2b b1 0 but in the lowlands these indices differ between valleys created by subglacial fluvial erosion 5b b45 and post glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post glacial sea levels 1b b7 dramatic differences in river pattern landforms and dynamics occur in valleys having contrasting aggrading vs degrading and incomplete responses to pleistocene glaciation creating discrete valley scale hetero geneities in fluvial process domains along and between rivers these results point to the importance of valley scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from pleistocene glaciation they also point to the potential usefulness of slope area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes

the compositional limits of fluid immiscibility in the system h2onaclco2 as determined with the use of synthetic fluid inclusions in conjunction with mass spectrometry abstract the compositional limits of fluid immiscibility in the system nacl h2o co2 were investigated from 500 to 700 c at pressures of 1 2 and 3 kbar synthetic fluid inclusions formed in quartz prisms were equilibrated with high temperature high pressure fluids in hydrothermal pressure vessels the inclusions were analyzed optically by mass spectrometry and by microthermometry the fields of immiscibility were defined as a function of temperature and pressure mass spectrometry was used to validate the existence of the immiscible fluids and to determine the co 2 h 2 o ratios of the two coexisting phases microthermometry i e the measurement of the melting temperature of solid sodium chloride was used in conjunction with the results of the mass spectrometry measurements to define the tie lines within the two phase fields isochores and the location of a portion of the isopleth were determined for composition nacl8 9 h2o76 1 co215 0

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve

extensive hesperian aged south polar ice sheet on mars evidence for massive melting and retreat and lateral flow and ponding of meltwater local and regional mars orbiter laser altimeter mola topographic data support the presence of an extensive hesperian aged volatile rich south polar deposit the dorsa argentea formation hd and related units underlying the present amazonian aged polar cap api residual ice and apl layered terrain and covering a surface area that could be as large as 2 94 106 km2 about 2 of the surface of mars over twice the area of the present amazonian aged south polar deposits the deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present day polar deposits several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows including a large valley near the crater schmidt and the argyre basin narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of hd the new topographic data support the interpretation of these ridges as eskers representing meltwater distribution networks at the base of the receding deposit extensive development of large pits and depressions cavi have previously been interpreted as eolian etching or basal melting of ice rich deposits analysis of mola topography supports the interpretation that they represent basal melting of ice rich deposits and shows that they have links to the esker systems volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by apl and that some of the liquid water formed ponds and lakes in the distal parts of hd the presence of pedestal craters is further evidence of the removal of extensive volatile rich deposits and contributes to the quantitative measure of the former deposit thickness where did the melt products go inspection of the margins of the dorsa argentea formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the argyre basin some 3 5 4 0 km below their origin these channels do not exhibit tributaries their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the argyre basin over 1000 km away estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5 9 106 km3 equivalent to a global layer of water 20 m deep if the deposit consisted of 50 volatiles a portion of these volatiles migrated across the surface to pond in adjacent valleys and basins and into the groundwater system a significant portion of the volatiles remain in the deposit representing a net removal from the atmosphere and from the active hydrologic system in early to middle mars history and forming an accessible record of aqueous conditions and possible biological environments dating from that time

interpretation of post entrapment fluid inclusion re equilibration at the three mile hill marvel loch and griffins find high temperature lode gold deposits yilgarn craton western australia abstract fluid inclusions that are interpreted to be related to vein filling of quartz veins at the three mile hill and marvel loch gold deposits in amphibolite facies rocks and the griffins find deposits in granulite facies rocks in the yilgarn craton of western australia are dominantly low salinity h 2 o co 2 ch 4 mixtures or co 2 ch 4 fluids at each deposit inclusions have a wide range of compositions with respect to both the aqueous carbonic ratio and the co 2 ch 4 ratio of the carbonic phase and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock inclusion densities suggest a range of p t conditions of entrapment and are in general not consistent with the conditions of vein formation indicated by vein assemblages diffusional addition of h 2 into inclusions diffusional loss of h 2 o and reduction of inclusion volume are possible during cooling and uplift along the inferred p t path the inclusion populations could have been derived from an originally uniform population of low salinity aqueous dominated h 2 o co 2 inclusions by a combination of these processes inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition and to an extent by variations in fluid salinity if inclusion re equilibration is the cause of inclusion variability it was of variable intensity within a single vein system and within individual clusters of inclusions in some samples and is suggested to have been a function of the local petrological and textural environment

pervasive aqueous paleoflow features in the aeolis zephyria plana region mars abstract a survey of themis visible wavelength images in the aeolis zephyria plana region over the two western lobes of the equatorial medusae fossae formation mff shows 150 sinuous ridges having a variety of morphologies and contexts to systematize investigation we use a classification scheme including both individual ridge and ridge network types as well as associations with impact craters and fan shaped features the morphology of the ridges their location downslope from higher topography e g crater rims and scarps and their association with fan shaped forms indicate that most sinuous ridges formed through overland aqueous flow analysis of observations by individual ridge type leads to interpretation of most of these sinuous ridges as inverted fluvial channels or floodplains and a few as possible eskers with the origin of the remaining ridges under continuing investigation about 15 of the sinuous ridges are associated with impact craters but data analysis does not support a genetic relationship between the craters and the sinuous ridges instead analysis of one sinuous ridge network associated with a crater indicates that the water source for the network was atmospheric in origin namely precipitation runoff the broad areal distribution of these 150 ridges and the network morphologies in particular the branched and subparallel types suggest that an atmospheric water source is generally applicable to the population of sinuous ridges as a whole this concentration of sinuous ridges is the largest single population of such landforms on mars and among the youngest these ridges are situated at a paleoscarp between cerberus palus and the aeolis highlands suggesting that the precipitation that formed them was orographic in origin the ages of the equatorial mff units in which this population of sinuous ridges is found imply that this orographic rain and or snow fell during some period from the late hesperian through the middle amazonian

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

inverted fluvial features in the aeolis zephyria plana region mars formation mechanism and initial paleodischarge estimates 1 a subset of the sinuous ridges srs in the aeolis zephyria plana azp region of mars has been previously hypothesized to be inverted fluvial features although the precise induration and erosion mechanisms were not specified morphological observations and thermal inertia data presented here support this hypothesis a variety of mechanisms can cause inversion and identification of the specific events that lead to fluvial sr formation can provide insights into the sedimentological geochemical and climatic processes of the region reconnaissance of two terrestrial lava capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on mars but these criteria are not satisfied by the majority of the azp fluvial srs armoring also appears inconsistent with terrestrial analogs layering and surface textures of fluvial srs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments and that the primary erosional mechanism that exposed the fluvial srs was aeolian abrasion this analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form discharge approach to which we have applied scaling for martian gravity for those fluvial srs meeting a set of criteria for accurate paleodischarge estimates paleodischarge values generally range between 101 and 103 m3 s 1 the largest of these initial estimates are comparable to paleodischarge estimates for some late stage noachian fluvial channels on mars and provide a constraint on the atmospheric conditions at this equatorial location during the late hesperian to early amazonian time frame

spatial organization of process domains in headwater drainage basins of a glaciated foothills region with complex longitudinal profiles 1 lithologic transitions and glaciations create complex longitudinal profiles that control contemporary erosion and deposition processes in areas with these characteristics traditional morphometric approaches for predicting process domains such as area slope plots can be augmented by considering other predictors measured from high resolution lidar derived digital elevation models dems ordinal logistic regression was used to model the distribution of hillslope swale colluvial channel and fluvial channel domains as identified during field surveys the study area was a glaciated region of the rocky mountain foothills with a complex lithostructural setting relationships between domains and a suite of geographic information system derived descriptors were explored predictors included profile anomalies measured at the reach and basin scale using a normalized stream length gradient sl k index drainage area was the dominant factor controlling domains a model with area as the only predictor was 82 accurate reach slope relations were not consistent a model that also included lithology and basin scale sl k index variation was 87 accurate domain transitions had larger area thresholds in basins with resistant conglomerate versus sandstone or shale formations and where sl k index was more variable along a profile in a restricted model of hillslope swale and colluvial channel domains profile curvature measured over 100 m was also related to domain occurrence a model for regional scale mapping applications with six additional predictors was 95 accurate the results showed that ordinal logistic regression can be used to predict and map process domains in regions with complex physiography using descriptors measured from high resolution dems

interactions between instream wood and hydrogeomorphic development within recently deglaciated streams in glacier bay national park alaska the physical and structural characteristics of instream wood were examined within five streams that represented 200 years of stream development following glacial recession within glacier bay national park alaska wood characteristics altered with watershed age as terrestrial succession progressed and wood was recruited into the riverine environment the influence of wood characteristics on the development of geomorphic diversity and hydraulic variability within the streams were assessed using detailed habitat mapping sediment analysis and hydraulic assessment using an acoustic doppler current profiler at a number of transects upstream downstream and adjacent to wood results show that the size complexity and orientation of wood accumulations are the main drivers in determining the degree of influence instream wood have on stream geomorphic and hydraulic complexity adjacent terrestrial vegetation must be of a sufficient stage of development in terms of size and maturity in order to elicit significant hydrogeomorphic changes to benefit aquatic biota such as fish macroinvertebrates and plants

catalogue of large alluvial fans in martian impact craters abstract we conducted a systematic global survey using thermal emission imaging system infrared themis ir coverage 100 m pixel to search for large alluvial fans in impact craters on mars our survey has focused on large fans apron areas greater than 40 km 2 usually located in craters greater than 20 km in diameter due to the resolution of the themis images and mars orbiter laser altimeter mola coverage we find that the host craters are found to have a distinctive diameter range from 30 150 km the fans generally cluster in three geographic areas southern margaritifer terra southwestern terra sabaea and southwestern tyrrhena terra however several outliers do exist the alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter smaller fan aprons in general have higher more variable concavity the source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters

effects of coarse woody debris on morphology and sediment storage of a mountain stream system in western oregon effects of coarse woody debris cwd on channel morphology and sediment storage were investigated at five sites representative of first order to fifth order streams in the steep and bedrock confined stream first second order interaction between the channel and cwd was limited except where breakage upon falling produced cwd pieces shorter than channel width channel widening steepening and sediment storage associated with cwd were observed predominantly in third to fifth order streams variation in channel width and gradient was regulated by cwd in the fifth order stream most of the cwd pieces derived from the riparian forest interacted directly with the channel without being suspended by sideslopes in this system cwd promoted lateral channel migration but sediment storage was temporary with annual release and capture

evaluation of paleohydrologic models for terrestrial inverted channels implications for application to martian sinuous ridges abstract fluvial systems can be preserved in inverted relief on both earth and mars few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems the first phase of this investigation focused on an extensive spanning 12 km inverted paleochannel system that consists of four sandstone capped carbonate cemented sinuous ridges within the early cretaceous cedar mountain formation located southwest of green river utah morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data the models yield an envelope of plausible dominant discharge values 100 500 m 3 s reflecting the limitations of the approach and no single model can be used to reliably estimate paleodischarge on mars landforms with attributes consistent with inverted channels have been identified in spite of differences in the formation history between these martian landforms and the terrestrial analog described here including potential differences in cement composition and the erosional agent that was responsible for relief inversion these numerical models can be applied with modification to the martian landforms and yield an envelope of plausible values for dominant discharge

a conceptual model for alpine proglacial river channel evolution under changing climatic conditions this paper integrates concepts derived from the literature to focus upon interactions between riparian vegetation and river channel dynamics in alpine glacier basins discussion of the nature and variability of discharge and sediment regimes of alpine glacier fed rivers downstream variations in the physical character of the river channel and corridor consequent downstream variations in lateral processes and regional variations in alpine glacier dynamics lead to the proposal of a conceptual model of proglacial river channel riparian vegetation interactions under changing climatic conditions

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr