depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

active shoreline of ontario lacus titan a morphological study of the lake and its surroundings of more than 400 filled lakes now identified on titan the first and largest reported in the southern latitudes is ontario lacus which is dark in both infrared and microwave here we describe recent observations including synthetic aperture radar sar images by cassini s radar instrument 2 cm and show morphological evidence for active material transport and erosion ontario lacus lies in a shallow depression with greater relief on the southwestern shore and a gently sloping possibly wave generated beach to the northeast the lake has a closed internal drainage system fed by earth like rivers deltas and alluvial fans evidence for active shoreline processes including the wave modified lakefront and deltaic deposition indicates that ontario is a dynamic feature undergoing typical terrestrial forms of littoral modification

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

evolution of southern caribbean plate boundary vicinity of trinidad and tobago two processes oblique collision of an island arc and strike slip motion parallel to the south american coast have been suggested as dominant in the tectonic evolution of the southeastern corner of the caribbean field work in the el pilar fault zone of trinidad and interpretation of offshore seismic data lead us to conclude that the dominant process was strike slip motion on five or more major fault systems within a 250 km wide east west trending plate boundary zone extending north to south from grenada to the mouth of the orinoco river during the last 30 m y movements in this fault zone 1 diverted the orinoco river eastward 2 juxtaposed blocks with diverse stratigraphic characteristics and 3 generated secondary extensional compressional and strike slip str ctures including anticlines of northeast to north northeast trend of which the tobago arch the central range of trinidad and the deformed mud diapirs off the southeastern coast of trinidad are the most prominent

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

chemistry and petrography of calcite in the ktb pilot borehole bavarian oberpfalz germany the ktb kontinentales tiefbohrprogramm der bundesrepublik deutschland pilot borehole in northeast bavaria germany penetrates 4000 m of gneiss amphibolite and subordinate calc silicate lamprophyre and metagabbro there are three types of calcite in the drilled section 1 metamorphic calcite in calc silicate and marble 2 crack filling calcite in all lithologies and 3 replacement calcite in altered minerals crack filling and replacement calcite postdate metamorphic calcite multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks cracks that eventually filled with calcite carried water to sites where replacement calcite formed by plagioclase hydrolysis or other decarbonation reactions whole rock contents of all three calcite types range from 35 wt in near surface calc silicate to 0 1 wt in amphibolite with calcite filled cracks at 3872 m calcite contains average sr concentrations of 180 ppm and mn concentrations of 3980 ppm crack filling calcite microdrilled from thin sections has average 13c 9 0 2 2 and 18o 10 5 1 5 values are 1 standard deviation crack filling mineral assemblages that include calcite originally formed at temperatures of 150 350 c presently crack filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of 120 c the saline to brackish water contains a significant proportion of meteoric water re equilibration of crack filling calcite to lower temperatures means that calcite chemistry tells us little about water rock interactions in the crustal section at temperatures higher than 120 c

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

titan radar mapper observations from cassini s t3 fly by cassini s titan radar mapper imaged the surface of saturn s moon titan on its february 2005 fly by denoted t3 collecting high resolution synthetic aperture radar and larger scale radiometry and scatterometry data these data provide the first definitive identification of impact craters on the surface of titan networks of fluvial channels and surficial dark streaks that may be longitudinal dunes here we describe this great diversity of landforms we conclude that much of the surface thus far imaged by radar of the haze shrouded titan is very young with persistent geologic activity

latitudinal and altitudinal controls of titan s dune field morphometry dune fields dominate 13 of titan s surface and represent an important sink of carbon in the methane cycle herein we discuss correlations in dune morphometry with altitude and latitude these correlations which have important implications in terms of geological processes and climate on titan are investigated through the microwave electromagnetic signatures of dune fields using cassini radar and radiometry observations the backscatter and emissivity from titan s dune terrains are primarily controlled by the amount of interdune area within the radar footprint and are also expected to vary with the degree of the interdunal sand cover using sar derived topography we find that titan s main dune fields shangri la fensal belet and aztlan tend to occupy the lowest elevation areas in equatorial regions occurring at mean elevations between 400 and 0 m relative to the geoid in elevated dune terrains we show a definite trend towards a smaller dune to interdune ratio and possibly a thinner sand cover in the interdune areas a similar correlation is observed with latitude suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north the altitudinal trend among titan s sand seas is consistent with the idea that sediment source zones most probably occur in lowlands which would reduce the sand supply toward elevated regions the latitudinal preference could result from a gradual increase in dampness with latitude due to the asymmetric seasonal forcing associated with titan s current orbital configuration unless it is indicative of a latitudinal preference in the sand source distribution or wind transport capacity

relationship between continental area and elevation continental hypsographic curves derived from data gathered by kossinna1 show a similarity of shape that suggests a correlation between continental area including the continental shelf and average height2 3 i have considered the varied geological histories of the continental blocks and suggest here that this relationship is not fortuitous and that changes in continental groupings will have profound effects not only on ocean volumes and hence sea level but also on the three dimensional shapes of the continental blocks

late cenozoic history of the eastern llanos of venezuela geomorphology and stratigraphy of the mesa formation abstract the study area corresponds to the mapire river basin in the southern part of the state of anzoategui and constitutes a region of low relief covered by the pleistocene mesa formation this formation consists of horizontally bedded alluvial sediments represented by light gray coarse to fine grained quartz sand with cross bedding marked by ochre red and pink alteration and to a minor extent by marsh deposits represented by laminated and spotted shale the typical topography consists of mesas north of the left margin of the orinoco river the musinacio and mapire mesas to the north of the mesas there is a topography of low hills covered by blocks of ferruginous crusts a typical tropical savanna climate exists in the region with a strong dry season which lasts 4 6 months followed by a rainy season with excess humidity the dominant erosional process is scarp retreat due to the action of the savanna climate on the lithology of the partly unconsolidated sediments it has formed deep canyons in the headwaters and is magnified by tectonic uplift and the lowering of the regional base level however some topographic forms have been preserved due to the hardening of the sands by iron oxides preliminary thermoluminescence dating of sand from two stratigraphic sections confirms the pleistocene age of the mesa formation 0 5 1 ma bp previously suggested by its stratigraphic position and geomorphological interpretation

weathering processes and the composition of inorganic material transported through the orinoco river system venezuela and colombia abstract the composition of river borne material in the orinoco river system is related primarily to erosion regime which in turn is related to tectonic setting especially notable is the contrast between material derived from tectonically active mountain belts and that from stable cratonic regions for a particular morpho tectonic region the compositional suites of suspended sediment bed material overback deposits and dissolved phases are fairly uniform are are typically distinct from whose of other regions for each region a consistent set of chemical weathering reactions can be formulated to explain the composition of dissolved and solid loads in developing these formulations erosion on slopes and storage of solids in soils and alluvial sediments are important considerations compositionally verymature sediment is derived from areas of thick soils where erosion is transport limited and from areas where sediments are stored for extended periods of time in alluvial deposits compositionally immature sediments are derived from tectonically active mountain belts where erosion is weathering limited weathering limited erosion also is important in the elevated parts of the guayana shield within areas of sleep topography compared to the mountain belts sediments derived from elevated parts of the shield are more mature a greater degree of chemical weathering seems to be needed to erode the rock types typical of the shield the major element chemistry and mineral composition of sediment delivered by the orinoco river to the ocean are controlled by rivers that have their headwaters in mountain belts and cross the llanos a region of alluvial plains within the foreland basin the composition of sediments in rivers that drain the shield seems to be established primarily at the site of soil formation whereas for rivers that drain the mountain belts additional weathering occurs during s episodes of storage on alluvial plains as sediments are transported across the llanos to the main stem of the orinoco after mixing into the main stem there seems to be little subsequent alteration of sediment

hypsometry of titan cassini radar topography data are used to evaluate titan s hypsometric profile and to make comparisons with other planetary bodies titan s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets to investigate topographic extremes a novel variant on the classic hypsogram is introduced with a logarithmic abscissa to highlight mountainous terrain in such a plot the top of the terrestrial hypsogram is quite distinct from those of mars and venus due to the glacial buzz saw that clips terrestrial topography above the snowline in contrast to the positive skew seen in other hypsograms with a long tail of positive relief due to mountains there is an indication weak given the limited data for titan so far that the titan hypsogram appears slightly negatively skewed suggesting a significant population of unfilled depressions limited data permit only a simplistic comparison of titan topography with other icy satellites but we find that the standard deviation of terrain height albeit at different scales is similar to those of ganymede and europa

a search for co variance among seismicity groundwater chemistry and groundwater radon in southern california several wells and springs near active faults in southern california have been monitored for the concentration of rn na k mg 2 and cl for periods of up to 24 months in an effort to see if any of these constituents show variations which may be related to seismic activity or environmental phenomena a few of these sites have shown significant fluctuations one site in the san gabriel mountains has shown relatively high radon in the summer and low radon in the winter apparently following the annual precipitation cycle however this site showed no corresponding change in its chemistry a second site near wrightwood california has shown an annual cycle in its chemical composition but shows no change in radon ten days prior to the big bear earthquake m 4 9 70 km to the east one sample from this site showed a 50 increase in radon but no change in chemistry a third site 20 km north of the malibu earthquake m 5 0 showed radon variation ranging from 0 4 to 4 times the normal concentration for two months preceding and two months following the event the chemistry at this site did not change within this study area radon appears to exhibit anomalous variations within several tens of kilometers of impending earthquakes the mechanism creating these signals has not been elucidated but does not influence the composition of important ionic constituents groundwater radon concentrations may also reflect variations in precipitation but do not appear to reflect variations in atmospheric pressure data from cold springs are consistent with a model in which ionic constituents are controlled by reactions in the soil zone and radon concentrations are controlled by flow rates in the aquifer

the distribution of bright and dark material on ganymede in relationship to surface elevation and slopes abstract the unique high resolution digital terrain data set available for ganymede s uruk sulcus area and galileo regio is analyzed by quantitative image analysis techniques to identify relationships between surface brightness elevation and slopes broad and narrow ridges and grooves of the uruk sulcus terrain model are found to be aligned with bright and dark lineament patterns visible in images these prominent lineaments represent areas covered by bright and dark albedo material not effects of photometric shading there is a strong correlation between material locations and elevation bright material is found on topographic highs whereas dark material is located in depressions the relative abundance of the dark material increases with lower elevation in galileo regio we find that bright material is also located on slopes facing north we suggest that the bright material in uruk sulcus and galileo regio was emplaced or exposed during or after formation of the terrain in its present location whereas the dark material was eroded and redistributed down slope effects of net solar illumination may play a role in the peculiar azimuthal distribution of bright and dark material on slopes

regional controls on geomorphology hydrology and ecosystem integrity in the orinoco delta venezuela interacting river discharge tidal oscillation and tropical rainfall across the 22 000 km2 orinoco delta plain support diverse fresh and brackish water ecosystems to develop environmental baseline information for this largely unpopulated region we evaluate major coastal plain shallow marine and river systems of northeastern south america which serves to identify principal sources and controls of water and sediment flow into through and out of the orinoco delta the regional analysis includes a summary of the geology hydrodynamics sediment dynamics and geomorphic characteristics of the orinoco drainage basin river and delta system because the amazon river is a major source of sediment deposited along the orinoco coast we summarize amazon water and sediment input to the northeastern south american littoral zone we investigate sediment dynamics and geomorphology of the guiana coast where marine processes and holocene history are similar to the orinoco coast major factors controlling orinoco delta water and sediment dynamics include the pronounced annual flood discharge the uneven distribution of water and sediment discharge across the delta plain discharge of large volumes of water with low sediment concentrations through the rio grande and araguao distributaries water and sediment dynamics associated with the guayana littoral current along the northeastern south american coast inflow of large volumes of amazon sediment to the orinoco coast development of a fresh water plume seaward of boca grande disruption of the guayana current by trinidad boca de serpientes and gulf of paria and the constriction at boca de serpientes

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

disentangling abrupt deglacial hydrological changes in northern south america insolation versus oceanic forcing paleoenvironmental studies and climate models demonstrate that fl uvial runoff and moisture availability in the caribbean hinterland react very sensitively to climatic variations late pleistocene and holocene climate records document pronounced dry and wet periods over tropical south america mainly caused by shifts of the intertropical convergence zone itcz however forcing mechanisms for changes in the itcz position remain controversial here we present high resolution foraminiferal ba ca and 18oseawater records from a core located within the orinoco river outfl ow documenting abrupt hydrological changes in the orinoco catchment area during the deglacial and holocene our data obtained from the surface dwelling foraminifera globigerinoides ruber pink show an abrupt increase in ba ca ratios in the early holocene starting 600 yr after the end of the younger dryas yd cold interval at ca 10 8 ka and suggesting a massive reorganization of moisture sources in northern south america in contrast the salinity dependent 18oseawater from the same samples shows a gradual decrease starting at the end of the yd the offset of our ba ca peak excludes meltwater release in conjunction with the northern andean glacier retreat well before the end of the yd as a forcing mechanism we suggest that the ba ca record documents an abrupt increase in ba rich waters of a northern andean source caused by the insolation driven shift of the itcz and or enhanced monsoon activity

mesozoic radiolarites accumulation as a function of sea surface fertility on tethyan margins and in ocean basins radiolarites commonly comprising chert shale couplets feature prominently in the mesozoic stratigraphy of the neotethyan realm the origin and significance of these deposits especially with regard to understanding palaeoproductivity in that region remains controversial this study examines transport processes and accumulation rates of radiolarians radiolarites as well as the chronology of radiolarite sedimentation based on revised data from the southern alps and new data from the balagne nappes alpine corsica results suggest that the spatio temporal distribution of carbonate and silica on tethyan margins was governed by extensive lateral transport of radiolarian tests from topographic highs to basins palaeoclimatic rather than palaeotectonic changes seem to have triggered changes in surface fertility which in turn brought about major facies changes observed in tethyan marginal basins regional platform demise possibly due to eutrophication and onset of radiolarite deposition in the early bajocian can be correlated with a positive shift in the carbon isotope curve whereas platform recovery and the end of radiolarite accumulation correlates with a gradual decline in 13c values the existence of a vigorous trans pangaean equatorial current system that could have produced regional upwelling is questioned because of evidence for middle jurassic to early cretaceous oligotrophic conditions in the proto caribbean and the central atlantic the caribbean river plume model is proposed as a possible alternative to upwelling in the jurassic western tethys dissolved nutrients may have been dispersed in low salinity lids that originated from river plumes of rivers from tropical africa and warm temperate eurasia vast areas of the pre late cretaceous world ocean must have accumulated radiolarites at low rates 50 myr radiolarite sections observed in many circumpacific terranes radiolarian chert and claystone could be the normal pelagic sediment during ordovician to early cretaceous time in far offshore open oceanic settings where dilution by terrigenous material and periplatform shallow water carbonates was absent

topographic comparisons of uplift features on venus and earth implications for venus tectonics abstract venus and earth display different hypsography we use topographic profiles to search for well understood terrestrial analogs to venusian features specifically by using cross correlation we correlate average profiles for terrestrial rifts slow and fast ultra slow incipient and inactive and also hotspots oceanic and continental with those for venusian chasmata and regiones to draw inferences as to the processes responsible for shaping venus surface correlations tend to improve with faster spreading rates venus correlations rank considerably lower than terrestrial ones suggesting that if chasmata are analogous to terrestrial spreading centers then spreading on venus barely attains ultra slow rates individual features normalized average profiles are correlated with profiles of other such features to establish the degree of similarity which in turn allows for the construction of a covariance matrix principal component analysis of this covariance matrix shows that yellowstone more strongly resembles atla beta and w eistla regiones than it does the terrestrial oceanic hotspots and that venusian chasmata especially ganis most closely resemble the ultra slow spreading arctic ridge

smoothness of titan s ontario lacus constraints from cassini radar specular reflection data 1 cassini radar altimetry data collected on the 49th flyby of titan 2008 december 21 over ontario lacus in titan s south polar region provides strong evidence for an extremely smooth surface with less than 3 mm rms surface height variation over the 100m wide fresnel zone histograms of the raw radar echoes imply a mirror like specular reflection of the transmitted signal such an echo is possible only if the surface is extremely flat relative to our 2 2 cm wavelength the 3 mm upper bound follows from analyzing the strength of the specular return which declines exponentially with increasing surface height variance in this experiment the strength of the echo was larger than expected severely saturating the receiver we developed a method to partially correct the echoes for the distortion incurred while the implied mm scale smoothness is not proof that the surface is liquid it is unlikely that a solid surface is so smooth

periodic mudflat progradation northeastern coast of south america a hypothesis abstract the guiana coast of northeastern south america backed by mangrove swamps and fronted by migrating mudflats and associated subtidal mudbanks has developed during the holocene as a prograding mud wedge from amazon derived sediment a hypothesis is offered for the periodic stabilization of shifting mudflats a process that has been recognized previously as the mechanism for initiation of new land growth the hypothesis assumes that solar semiannual and 18 6 yr tidal components allow abnormal exposures of coastal mudflats and conditions that are favorable for establishment of avicennia mangroves once colonized mangrove roots displace muds upward thus decreasing the frequency of tidal inundation and increasing the ability of vegetation to trap and hold muds based on estimated ates of root growth and forecasted tide records for the coast of surinam land elevation will increase by 25 cm in 10 yr and frequency of tidal inundation above 2 45 m 8 0 ft will decrease from 106 to 2 per year during the same period

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

dynamics of an ice continent on titan 1 if the large high albedo surface feature on titan s leading hemisphere is an elevated continent composed mainly of water ice it will deform under its own weight we present a model for the axisymmetric spreading of this hypothesized continent based on the similarity solution of halfar 1983 and the approach of nye 2000 we find that the thickness of the model continent is dictated by the spreading time whereas topographic relief is controlled primarily by isostatic effects for a mantle density of 1000 kg m 3 the relief of an isostatically supported continent on titan is not likely to exceed 3 7 km

orinoco and amazon river sediment input to the eastern caribbean basin abstract carbonate and mineralogic analyses of piston cores from aves ridge eastern caribbean basin reveal climatically modulated relationship among quaternary carbonate deposition and terrigenous sediment influxes from the orinoco and amazon rivers low carbonate content and dark sediment color extending into the pleistocene suggest considerable dilution of pelagic components by terrigenous sediment on the western flank of aves ridge which is characterized by a southwest thickening sedimentary wedge contrary to typical trends observed in the more distal areas of the central basin west of aves ridge carbonate content is lowest during interglacial climates and highest during glacial climates a high clay mineral input correlates with interglacial climate however the orinoco tracer mineral pyrophyllite is low during interglacials and high during glacials the observed trends suggest that amazon sediment influx to the eastern caribbean is highest during interglacials or times of high sea level the amazon influx is promoted by deposition on the shelf and westward coastal transport of sediment during high sea level and reduced by shelf edge deposition and loss to the amazon canyon during low sea level the orinoco influx is similarly modulated but it undergoes a relative and possibly absolute increase during low sea level because of proximity to the depositional site the terrigenous dilution produces the reversal of carbonate trends however total sediment accumulation rates on southernmost aves ridge remain higher during glacials possibly as a result of increased carbonate production caused by upwelling

feasibility of estimating cementation rates in a brittle fault zone using sr ca partition coefficients for sedimentary diagenesis abstract cement phases such as calcite or quartz often incorporate trace elements from the parent fluids as they crystallize experimental sedimentary diagenesis indicates that trace element partition coefficients reflect rates of cementation the applicability of these findings to fault zone cementation is examined as we make a preliminary attempt to estimate calcite cementation rate in a brittle fault zone directly from the fault rock composition data samples for this study were collected from the knoxville outcrop of the saltville fault in tennessee the cementation rates for the fault rock samples range from 1 10 12 to 3 10 13 m 3 h per m in agreement with some experimental rates and the rates reported for samples from the dsdp sites when applied to a non responsive pore system model these rates result in rapid precipitation sealing indicating the influence exerted by the surface area volume ratio of the pore network we find it feasible to obtain a reasonable range of values for the cementation rate using the trace element partition method however the study also indicates the need for relatively accurate values for the trace carrier element ratio in the fault zone syntectonic pore fluid and exhumed cement

hydrocarbon lakes on titan distribution and interaction with a porous regolith from 10 to more than 100 000 km 2 the size and location of lakes provide constraints on parameters associated with subsurface transport using porous media properties inferred from huygens probe observations timescales for flow into and out of observed lakes are shown to be in the tens of years similar to seasonal cycles derived timescales are compared to the time between collocated sar observations in order to considertheroleofsubsurfacetransportintitan shydrologic cycle citation hayes a et al 2008 hydrocarbon lakes on titan distribution and interaction with a porous regolith geophys res lett 35 l09204 doi 10 1029 2008gl033409

the geomorphology of ceres introduction observations of ceres the largest object in the asteroid belt have suggested that the dwarf planet is a geologically differentiated body with a silicate core and an ice rich mantle data acquired by the dawn spacecraft were used to perform a three dimensional characterization of the surface to determine if the geomorphology of ceres is consistent with the models of an icy interior rationale instruments on dawn have collected data at a variety of resolutions including both clear filter and color images digital terrain models have been derived from stereo images a preliminary 1 10 m scale geologic map of ceres was constructed using images obtained during the approach and survey orbital phases of the mission we used the map along with higher resolution imagery to assess the geology of ceres at the global scale to identify geomorphic and structural features and to determine the geologic processes that have affected ceres globally results impact craters are the most prevalent geomorphic feature on ceres and several of the craters have fractured floors geomorphic analysis of the fracture patterns shows that they are similar to lunar floor fractured craters ffcs and an analysis of the depth to diameter ratios shows that they are anomalously shallow compared with average ceres craters both of these factors are consistent with ffc floors being uplifted due to an intrusion of cryomagma kilometer scale linear structures cross much of ceres some of these structures are oriented radially to large craters and most likely formed due to impact processes however a set of linear structures present only on a topographically high region do not have any obvious relationship to impact craters geomorphic analysis suggests that they represent subsurface faults and might have formed due to crustal uplift by cryomagmatic intrusion domes identified across the ceres surface present a wide range of sizes 100 km basal shapes and profiles whether a single formation mechanism is responsible for their formation is still an open question cryovolcanic extrusion is one plausible process for the larger domes although most small mounds 10 km diameter are more likely to be impact debris differences in lobate flow morphology suggest that multiple emplacement processes have operated on ceres where three types of flows have been identified type 1 flows are morphologically similar to ice cored flows on earth and mars type 2 flows are comparable to long runout landslides type 3 flows morphologically resemble the fluidized ejecta blankets of rampart craters which are hypothesized to form by impact into ice rich ground conclusion the global trend of lobate flows suggests that differences in their geomorphology could be explained by variations in ice content and temperature at the near surface geomorphic and topographic analyses of the ffcs suggest that cryomagmatism is active on ceres whereas the large domes are possibly formed by extrusions of cryolava although spectroscopic analysis to date has identified water ice in only one location on ceres the identification of these potentially ice related features suggests that there may be more ice within localized regions of ceres crust figure 1 dawn high altitude mapping orbit imagery 140 meters per pixel of example morphologic features a occator crater arrows point to floor fractures b linear structures denoted by arrows c a large dome at 42 n 10 e visible in the elevation map d a small mound at 45 5 s 295 7 e e type 1 lobate flow arrows point to the flow front analysis of dawn spacecraft framing camera image data allows evaluation of the topography and geomorphology of features on the surface of ceres the dwarf planet is dominated by numerous craters but other features are also common linear structures include both those associated with impact craters and those that do not appear to have any correlation to an impact event abundant lobate flows are identified and numerous domical features are found at a range of scales features suggestive of near surface ice cryomagmatism and cryovolcanism have been identified although spectroscopic analysis has currently detected surface water ice at only one location on ceres the identification of these potentially ice related features suggests that there may be at least some ice in localized regions in the crust 1 pending yes

geochemistry of water at cajon pass california preliminary results samples of water and associated gases were collected from the cajon pass well using downhole samplers and from the pipe stands at the completion of drill stem tests the fluids were recovered from fracture systems in granitic rocks from two uncased test intervals located at 1 829 to 1 905 m and 1 829 to 2 115 m results of chemical analysis indicate major differences in the composition of water from different fracture systems water from one fracture system in the first test interval has a salinity of 2 150 mg l dissolved solids and is relatively high in cl ca and fe but low in hco3 and so4 water salinity from a second fracture system is only 950 mg l and is dominated by na hco3 and so4 most of the water from the second interval likely originated from one fracture system it is alkaline low in hco3 has a salinity of 1 150 mg l and is a naso4 type water characteristic of pore water in the granitic rocks of the area the differences in water composition indicate different evolutionary paths and isolation of water within relatively proximal fracture systems

origin of amazon mudbanks along the northeastern coast of south america abstract seismic profiles sediment cores and water column measurements were collected along the northeastern coast of brazil to examine the origin of mudbanks in the amazon coastal mud belt these 10 60 km long shore attached features previously had been observed to migrate along the 1200 km coast of the guianas in response to wave forcing chirp 3 5 khz seismic profiles of the shoreface and inner shelf located two mudbanks updrift of the previous eastern limit in french guiana 210 pb geochronology shows that these two banks are migrating to the northwest over a relict mud surface in 5 20 m water depth the mudbanks are 3 4 m thick and are translating over a modern shoreface mud wedge deposited by previous mudbank passage in

an introduction to the geological significance of sediment transport and accumulation on the amazon continental shelf in order to understand the formative processes and resulting stratigraphy on the amazon shelf and adjacent shoreline of amapa geological investigations were undertaken as part of a multidisciplinary amazon shelf sediment study amasseds the design of the study provided results of a multifaceted nature integrated with observations in other disciplines focused on sedimentary processes representative of fluctuating conditions on several time scales and broadly distributed on the shelf including regions not investigated in the past on short time scales most muddy sediment is transported northwest of the river mouth from there it moves seaward as fluid mud to cause rapid accumulation of foreset beds and moves northwestward to prograde the northernmost amapa shoreline and to supply sediment to the guianas fluid muds cover the shelf as far northward as 3 5 n and allow strong tides to propagate to shore where tidal currents cause most of the amapa shoreline to undergo erosion today averaged over decades and centuries about half of the amazon sediment discharge accumulates on the adjacent shelf and another significant fraction one sixth leads to accretion of the northernmost amapa shoreline and northwestward bypassing of sediment the remaining sediment is hypothesized to be trapped in deltaplain deposits of the lower amazon river system the foreset region and shoreline represent the two common loci of sediment accumulation that alternate their predominance on time scales of millennia and lead to a two stage progradation of coastal plain and subaqueous deltaic deposits this muddy regressive sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions future research in the study area should address important considerations that were delineated by the present study including mechanisms of shoreline accretion the holocene history recorded in topset and coastal plain strata the role in local sedimentation played by the large shoal extending from cabo norte and the entrapment of amazon sediment by the delta plain

comparative hypsometric analysis of earth and venus the comparison between earth and venus global hypsometric distributions is reinvestigated on the basis of the high resolution data provided by the recent magellan global topographic coverage of venus surface and the detailed etopo 5 topographic database for the earth s surface the study of the cumulative hypsometric curve for both planets reveals that there exists a domain of elevation for which the relationship between the elevation and the square root of cumulative area percentage is linear this domain covers about 80 of the mapped venusian surface and nearly all the terrestrial oceanic surface 55 of the earth s surface and corresponds to an elevation range of about 2000 m for both planets proposing the upper threshold elevation of this domain as a common geophysical reference level it is shown that the terrestrial oceanic peak and the venusian peak coincide very closely in addition the terrestrial and venusian hypsometric distributions for elevations lower than this reference level are quite similar in their amplitude modal distribution and pronounced symmetry the correspondence of the venusian peak with the terrestrial oceanic peak is a striking feature but it does not necessarily imply the occurrence of plate tectonics on venus the present observation is consistent with the existence of a similar thermal isostasy acting at the planetary scale it places an upper bound at 90 10 km for the modal thermal lithosphcric thickness of venus if the venus mantle thermal conditions are earth like this estimate is reduced if hotter conditions occur

radarclinometry of the sand seas of africa s namibia and saturn s moon titan abstract radarclinometry is a powerful technique for estimating heights of landforms in synthetic aperture radar sar images of planetary surfaces in particular it has been used to estimate heights of dunes in the sand seas of saturn s moon titan lorenz r d and 39 colleagues 2006 science 312 724 727 in this work we verify the technique by comparing dune heights derived from radarclinometry to known topography of dune fields in the namib sand sea of western africa we compared results from three different image grid spacings and found that 350 m pixel the same spacing at which the cassini radar data was processed is sufficient to determine dune height for dunes of similar morphometry to those of the namib sand sea at this grid spacing height estimates derived from radarclinometry are largely representative of though may underestimate by as much as 30 or overestimate by as much as 40 true dune height applying the technique to three regions on titan we estimate dune heights of 45 180 m and dune spacings of 2 3 3 3 km obtaining accurate heights of titan s dunes will help to constrain the total organic inventory on titan

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

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

the topography of iapetus leading side abstract we have used cassini stereo images to study the topography of iapetus leading side a terrain model derived at resolutions of 4 8 km reveals that iapetus has substantial topography with heights in the range of 10 km to 13 km much more than observed on the other middle sized satellites of saturn so far most of the topography is older than 4 ga neukum g wagner r denk t porco c c 2005 lunar planet sci xxxvi abstract 2034 which implies that iapetus must have had a thick lithosphere early in its history to support this topography models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50 100 km iapetus prominent equatorial ridge porco c c and 34 colleagues 2005 science 307 1237 1242 reaches widths of 70 km and heights of up to 13 km from their base within the modeled area the morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant ip w h 2006 geophys res lett 33 doi 10 1029 2005gl025386 l16203 the transition from simple to complex central peak craters on iapetus occurs at diameters of 11 3 km the central peaks have pronounced conical shapes with flanking slopes of typically 11 and heights that can rise above the surrounding plains crater depths seem to be systematically lower on iapetus than on similarly sized rhea which if true may be related to more pronounced crater wall slumping which widens the craters on iapetus than on rhea there are seven large impact basins with complex morphologies including central peak massifs and terraced walls the largest one reaches 800 km in diameter and has rim topography of up to 10 km generally no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors which is inferred from crater depth to diameter measurements in particular a 400 km basin shows up domed floor topography which is suggestive of viscous relaxation a model of complex crater formation with a viscoplastic bingham rheology melosh h j 1989 impact cratering oxford univ press new york of the impact shocked icy material provides an estimate of the effective cohesion viscosity at 0 04 0 01 mpa 0 6 0 2 gpa s the local distribution of bright and dark material on the surface of iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components but frost deposits are possible as well

global tectonic and climatic control of mean elevation of continents and phanerozoic sea level change abstract mean elevation of all continents as well as mean elevation of individual continents should be at the fundamental level controlled by the global tectonic and climatic systems i propose a first order model considering the interplay of the two factors in controlling mean elevation of continents the model is able to account for the positive correlation between the present day mean elevation and area of individual continents except for antarctica furthermore it can also explain the low sea level during the times of supercontinents finally the model is used to evaluate the variation of continental crust thickness with time

isotopic signatures of organic matter in sediments of the continental shelf facing the orinoco delta possible contribution of organic carbon from savannas abstract the 87 sr 13 c and 15 n isotopic signatures of organic matter in sediments from the continental shelf facing the orinoco delta were measured to determine the contribution of sediments transported from the amazon river by the coastal guayana current and the sediments transported by the orinoco river box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the orinoco delta were analyzed carbon and nitrogen concentrations decreased with depth under water on the shelf and were strongly correlated indicating homogeneity of organic matter composition phosphorus content was also associated to organic matter in most samples but some of them revealed deposition of p enriched sediments the 87 sr 86 sr ratios showed a strong continental signature averaging 0 7117 therefore limiting the possible carbon and nitrogen sources associated with these sediments to c3 trees c4 grasses or freshwater phytoplankton the 13 c values were relatively high averaging 21 above values reported for sediments on the amapa shelf and the amazon river in brazil average 13 c values did not differ significantly among transects high 13 c values point to the influence of organic matter transported from the c4 plants dominated savannas in the northern fringe of the orinoco river 15 n values were positive and averaged 5 being within the range of values measured in the marajo island amazon river and the estuary of the para river the 15 n values differed significantly among transects 4 9 5 2 lowest values corresponding to the northernmost transect near the coast of trinidad and the highest values corresponding to the transect located at the southernmost position

stratigraphic evidence of changes in amazon shelf sedimentation during the late holocene abstract late holocene sedimentation on the amazon shelf was investigated using a combination of seismic sedimentological and geochronological methods piston cores collected in the subaqueous delta region during a multidisciplinary amazon shelf sediment study amasseds penetrated a regionally traceable 1 25 10 4 km 2 seismic discontinuity which corresponds to a dense relict mud reflector overlain by acoustically transparent sediment distinct offsets in profiles of wet bulk density p wave velocity and 210 pb activity are noted in cores at the reflector horizon unconformity signifying a past change in sedimentation conditions on the shelf bulk sediment 14 c dating indicates net depositional conditions for the subaqueous delta from 1800 yr b p to 700 yr b p and a net erosional phase from about 700 yr b p to 100 yr ago sedimentological evidence of the erosional phase includes lag deposits and burrows present at the unconformity surface in piston cores the deposits above and below the unconformity are similar with respect to grain size parameters and sedimentary structures suggesting that environmental conditions during the two depositional periods were similar according to 14 c dates of coastal deposits the shoreline of amapa state brazil served as a major depocenter of amazon mud during the erosional phase on the shelf 210 pb geochronology indicates that the most recent phase of sediment accumulation in the study area commenced about 100 yr ago resulting in rapid progradation of topset deposits and burial of relict strata in the present environment oceanographic and meteorologic processes cause along shelf variations in sediment dispersal and depositional patterns and about 1400 km 2 of the erosional relict deposits are still exposed at the seabed the short time scales over which amazon shelf strata respond to changes in the physical environment preclude the influence of relative sea level cyclicity on recent sedimentation patterns during the late holocene sedimentation and strata formation on the amazon shelf are linked to fluvial oceanographic and meteorologic processes that affect sediment supply deposition and erosion

the detrital record of cretaceous to pliocene sandstones across the ne south american margin the cretaceous to pliocene erosional history of the ne south american margin depicts the increasing influence of the uplifting caribbean mountain belt petrographic analyses of 59 cretaceous to late pliocene sandstone samples derived from across the islands of trinidad and barbados demonstrate systematic mineralogical changes whereby early cretaceous arkosic arenites gave way to mature quartz arenites by the late cretaceous and caribbean mountain derived lithic rich arenites during the neogene changes in the framework compositions are accompanied by changes in textural attributes with caribbean mountain detritus being notably finer grained than cratonic input silica cements predominate in quartzose sandstones and sericitic and clay cements within litharenites the changing mineralogical compositions record the gradual deformation of the northern south american passive margin and initiation of the andean caribbean mountain foreland basin system with incipient orogenic detritus evident from the latest eocene and unambiguous orogenic input by the late oligocene the preponderance of finer grain sizes within deltaic pliocene sandstones records the later fill of an established foredeep with sediments sourced primarily from erosion of the andean hinterland these interpretations agree with heavy mineral compositional changes and the timing of uplift from geo and thermo chronological data across the margin supplementary material qualitative descriptions sample coordinates and raw point counts are available at https doi org 10 6084 m9 figshare c 3659381

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

late holocene flooding history of a tropical river in western india in response to southwest monsoon fluctuations a multi proxy study from lower narmada valley abstract a multi proxy study on the sediments from lower narmada valley western india records large flooding events and high sediment influx linked to southwest monsoon variations during late holocene on the basis of proxy data and chronology of preserved sediments three major environmental perturbations at 1809 1487 and 1187 cal bp have been identified that corroborate well with the regional fluctuations in southwest monsoon variability a phase of dominant marine influence between 2185 and 1809 cal bp is inferred based on the presence of marine palynomorphs mangrove pollen and amorphous organic matter and is coincident with the phase of weak monsoon in the region a transition from marine marsh environment to a phase of high fluvial influx occurred around 1809 cal bp the fluvial influence is inferred based on the replacement of amorphous organic matter with structured organic matter presence of fresh water algae decrease in the 13c values and dominance of kaolinite clay the fluvial regime stabilized between 1487 and 1187 cal bp as recorded in the overbank sediments palynomorphs and geochemical indices and sedimentation occurred under a highly oxidizing and high energy condition with long distance transport of sediments the later incision of the sediment sequence which post dates 1187 cal bp can be attributed to enhanced precipitation the response of the lower narmada valley to short term southwest monsoon fluctuations is manifest in the shifting deposition environments and a major role of terrestrial sediment influx variability is surmised leading to relative sea level variations in this part of the indian subcontinent a temporal and process based interplay between flooding periods and sediment discharge in river systems and tidal conditions is suggested for the tropical estuarine environments

shapes of the saturnian icy satellites and their significance the sizes and shapes of six icy saturnian satellites have been measured from cassini imaging science subsystem iss data employing limb coordinates and stereogrammetric control points mimas enceladus tethys dione and rhea are well described by triaxial ellipsoids iapetus is best represented by an oblate spheroid all satellites appear to have approached relaxed equilibrium shapes at some point in their evolution but all support at least 300 m of global wavelength topography the shape of enceladus is most consistent with a homogeneous interior if enceladus is differentiated its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and or an irregularly shaped core iapetus supports a fossil bulge of over 30 km and provides a benchmark for impact modification of shapes after global relaxation satellites such as mimas that have smoother limbs than iapetus and are expected to have higher impact rates must have relaxed after the shape of iapetus was frozen

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

global drainage patterns and the origins of topographic relief on earth mars and titan rivers have eroded the topography of mars titan and earth creating diverse landscapes however the dominant processes that generated topography on titan and to some extent on early mars are not well known we analyzed drainage patterns on all three bodies and found that large drainages which record interactions between deformation and erosional modification conform much better to long wavelength topography on titan and mars than on earth we use a numerical landscape evolution model to demonstrate that short wavelength deformation causes drainage directions to diverge from long wavelength topography as observed on earth we attribute the observed differences to ancient long wavelength topography on mars recent or ongoing generation of long wavelength relief on titan and the creation of short wavelength relief by plate tectonics on earth

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

multifractal topography of several planetary bodies in the solar system abstract topography is the expression of both internal and external processes of a planetary body thus hypsometry the study of topography is a way to decipher the dynamics of a planet for that purpose the statistics of height and slopes may be described by different tools at local and global scale we propose here to use the multifractalapproach to describe fields of topography this theory encompasses height and slopes and other statistical moments of the field taking into account the scale invariance contrary to the widely used fractalformalism multifractals are able to describe the intermittency of the topography field as we commonly observe a juxtaposition of rough and smooth topographies at a given scale the multifractal framework seems to be appropriate for hypsometric studies here we analyze the data at global scale of the earth mars mercury and the moon and find that the statistics are in good agreement with the multifractaltheory for scale larger than 10 km surprisingly the analysis shows that all bodies have the same fractal behavior for scale smaller than 10 km we hypothesize that dynamic topography of the mantle may be the explanation at large scale whereas the smaller scale behavior may be related to elastic thickness

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

correlation of paleotectonic fracture and microfracture orientations in cores with seismic anisotropy at cajon pass drill hole southern california fractures and microfractures in oriented cores from the cajon pass drill hole southern california have strong preferred orientations there are two major sets of extensional fractures and microfractures that have northwest and northeast strikes and vertical dips relative and absolute densities of both sets vary greatly within a single core the regional tectonic history implies that these fractures and microfractures probably formed before late miocene pliocene vertical seismic profiling experiments in the drill hole show shear wave splitting with polarization directions parallel to the fracture and microfracture orientations the measured seismic anisotropy is due to these inherited deformation fabrics and does not appear to be caused by the current local stress field

surface albedo spectral properties of geologically interesting areas on titan we investigate the nature and possible formation processes of three areas on titan s surface which have been suggested as geologically interesting hotei regio tui regio and sotra patera we also reanalyze the spectral characteristics of the huygens landing site we apply a statistical principal component analysis pca and a radiative transfer rt method on the visual and infrared mapping spectrometer datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared we have been able to exploit only a subset of the currently available hotei regio data which are in general not optimal in terms of geometry for an analysis with a plane parallel rt code our inferred surface albedos present generally higher values from 1 to 2 m and lower ones at 0 94 and in the 2 6 5 m region the regions of interest rois within hotei regio tui regio and sotra patera are always significantly brighter than the surrounding areas the largest variations are found longward of 2 m and mainly at 5 m this higher surface albedo with respect to the surrounding area and in general the fact that the spectral behavior is different for each of these areas is probably indicative of diverse chemical compositions and origins we compare the spectral albedos with some suggested surface candidates on titan such as h2o co2 and ch4 ices as well as tholin and discuss possible chemical composition variations as well as other interpretations

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

sources of organic carbon in the portuguese continental shelf sediments during the holocene period organic c oc and total n tn concentrations and stable isotope ratios 13 c in muddy deposit sediments of the northern and southern portuguese continental shelf were used to identify sources of fine sized organic matter 63 m during the holocene period sedimentary columns off the guadiana core crida 05 tagus core md 992332 and douro core ksgx 57 estuaries are characterised by elemental and isotopic values that reflect distinct sources of organic matter oc tn and 13 c ranging respectively from 8 5 to 21 and from 22 4 to 27 intense supplies to the guadiana continental shelf of fine terrigenous particles during the younger dryas event are closely linked with higher oc tn values and lower 13 c ratios during the postglacial transgression phase an increasing contribution of marine supplies up to 80 occurred higher 13 c up to 22 4 values and low oc tn ratios down to 8 5 are found as the sea level approaches the current one the upper holocene records emphasize the return to enhanced terrestrial supplies except for the little climatic optimum between the 11th and 15th centuries ad this climatic event is especially obvious in the three cores as a return to marine production and a decrease in terrestrial sediment supply to the continental shelf the return to a cooling event the little ice age between the 15th and 19th centuries ad is mirrored by decreased terrigenous supplies in core ksgx 57 gradually increasing sedimentation in estuaries as well as formation of coastal dune fields have been hypothesized on the basis of increasing 13 c and decreasing oc tn and oc tn values

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

cross channel mixing and its effect on sedimentation in the orinoco river at high discharge cross channel mixing of water in the orinoco river main stem requires several days and up to 500 km of downriver transit for completion during mixing substantial amounts of 0 063 mm sediment are lost from suspension the water closest to the left bank appears to lose the most probably by deposition onto the floodplain this occurs in two ways first sediment laden left bank tributaries draining the andes such as the apure deposit sediment in distributary systems following impoundment by the orinoco backwater second when sediment laden waters from the andes actually join the orinoco the slow nature of cross channel mixing causes the water and sediment to be confined more to the left side of the channel significant sediment loss or storage probably occurs only near flood stage since sedimentation occurs preferentially on the left andean foreland basin bank the orinoco remains stably situated on the border of the foreland basin with the guayana shield

geology and hydrocarbon accumulations columbus basin offshore trinidad the columbus basin situated on the eastern shelf of trinidad lies at the eastern extremity of a belt of severe deformation along the northern boundary of south america that has been affected by compressional and wrench tectonics in pliocene pleistocene time two major structural trends are present in the columbus basin a series of east northeast trending anticlines and north northwest oriented normal faults the basin was filled during late miocene to holocene time with sediments deposited by an ancestral orinoco river draining a hinterland to the southwest the pliocene pleistocene section which contains the hydrocarbon accumulations in the columbus basin was deposited in three coarsening upward sedimentary sequences followed by a late pleistocene transgressive sequ nce traps for hydrocarbon accumulation were formed by an easterly trending pliocene pleistocene wrench system with associated east northeast oriented anticlines combined with north northwest oriented normal faults oil was sourced in the late miocene lower cruse formation whereas gas was derived both from pliocene pleistocene pro delta shales and as a late high temperature phase of lower cruse hydrocarbon generation the north northwest faults formed migration conduits from the oil source rock to pliocene pleistocene reservoirs the temporal relationship of faulting to oil generation is a major factor affecting the distribution of oil and gas the size of hydrocarbon accumulations is limited to some extent by a lack of an effective hydrocarbon seal particularly in the western half of th basin

holocene evolution of the western orinoco delta venezuela the pristine nature of the orinoco delta of eastern venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta remote sensing images shallow cores and radiocarbon dating of organic remains form the basis for describing deltaic environments and interpreting the holocene history of the delta the orinoco delta can be subdivided into two major sectors the southeast sector is dominated by the rio grande the principal distributary and complex networks of anastomosing fluvial and tidal channels the abundance of siliciclastic deposits suggests that fluvial processes such as overbank flooding strongly influence this part of the delta in contrast the northwest sector is represented by few major distributaries and overbank sedimentation is less widespread relative to the southeast sector peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km 2 in area northwest directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast mapping of surface sediments vegetation and major landforms identified four principal geomorphic systems within the western delta plain 1 distributary channels 2 interdistributary flood basins 3 fluvial marine transitional environments and 4 marine influenced coastal environments coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20 30 km during the late holocene sea level highstand progradation has been accomplished by a combination of distributary avulsion and mudcape progradation this style of deltaic progradation differs markedly from other deltas such as the mississippi where distributary avulsion leads to coastal land loss rather than shoreline progradation the key difference is that the orinoco delta coastal zone receives prodigious amounts of sediment from northwest moving littoral currents that transport sediment from as far away as the amazon system 1600 km late holocene progradation of the delta has decreased delta plain gradients increased water levels and minimized overbank flooding and siliciclastic sedimentation in the northwest sector these conditions coupled with large amounts of direct precipitation have led to widespread peat accumulation in interdistributary basins because peat forming environments cover up to 5000 km 2 of the delta plain the orinoco may be an excellent analogue for interpreting ancient deltaic peat deposits

statistics of mars topography from the mars orbiter laser altimeter slopes correlations and physical models data obtained recently by the mars orbiter laser altimeter mola were used to study the statistical properties of the topography and slopes on mars we find that the hemispheric dichotomy manifested as an elevation difference can be described by long baseline tilts but in places is expressed as steeper slopes the bimodal hypsometry of elevations on mars becomes unimodal when referenced to the center of figure contrary to the earth for which the bimodality is retained however ruling out a model in which the elevation difference is expressed in a narrow equatorial topographic step cannot be done by the hypsometry alone mars slope distribution is longer tailed than those of earth and venus indicating a lower efficiency of planation processes relative to relief building tectonics and volcanics we define and compute global maps of statistical estimators including the interquartile scale rms and median slope and characteristic decorrelation length of the surface a correspondence between these parameters and geologic units on mars is inferred surface smoothness is distinctive in the vast northern hemisphere plains where slopes are typically 0 5 amazonis planitia exhibits a variation in topography of 1 m over 35 km baselines the region of hematite mineralization in sinus meridiani is also smooth with median slopes lower than 0 4 but does not form a closed basin the shallower long wavelength portion of the lowlands topographic power spectrum relative to the highlands can be accounted for by a simple model of sedimentation such as might be expected at an ocean s floor the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths among their application these mola derived roughness measurements can help characterize sites for landing missions

mountain torque and its influence on the atmospheric angular momentum on titan abstract the impact of titan s large scale topography and surface roughness on the atmospheric angular momentum budget is investigated by the cologne titan general circulation model that is run with and without topography constrained by cassini on seasonal timescales the angular momentum exchange is dominated by the friction torque which oscillates semi annually topography gives rise to a large diurnal and small seasonal mountain torque the diurnal mountain torque is caused by surface pressure variations associated with saturn s tide but has no net effect on the atmospheric angular momentum the seasonal mountain torque is mainly contributed by low latitude mountains that are hit by easterly surface winds the seasonal mountain torque causes a net transfer of angular momentum from the surface to the atmosphere which is counterbalanced by an opposite angular momentum transfer by the friction torque the atmospheric angular momentum is larger if topography is included

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

mapping the zonal structure of titan s northern polar vortex abstract saturn exhibits an obliquity of 26 7 such that the largest moon titan experiences seasonal variations including the formation of a polar vortex in the winter hemisphere titan s polar vortex is characterised by cold stratospheric temperatures due to the lack of insolation over the winter pole and an increase in trace gas abundance as a result of complex organic chemistry in the upper atmosphere combined with polar subsidence meridional variations in temperature and gas abundance across the vortex have previously been investigated but there has not yet been any in depth study of the zonal variations in the temperature or composition of the northern vortex here we present the first comprehensive two dimensional seasonal mapping of titan s northern winter vortex using 18 nadir mapping sequences observed by the composite infrared spectrometer cirs instrument on board cassini we investigate the evolution of the vortex over almost half a titan year from late winter through to mid summer ls 326 86 2007 2017 we find the stratospheric symmetry axis to be tilted from the solid body rotation axis by around 3 5 although our results for the azimuthal orientation of the tilt are inconclusive we find that the northern vortex appears to remain zonally uniform in both temperature and composition at all times a comparison with vortices observed on earth mars and venus shows that large scale wave mechanisms that are important on other terrestrial planets are not as significant in titan s atmosphere this allows the northern vortex to be more symmetrical and persist longer throughout the annual cycle compared to other terrestrial planets

size and shape of saturn s moon titan cassini observations show that saturn s moon titan is slightly oblate a fourth order spherical harmonic expansion yields north polar south polar and mean equatorial radii of 2574 32 0 05 kilometers km 2574 36 0 03 km and 2574 91 0 11 km respectively its mean radius is 2574 73 0 09 km titan s shape approximates a hydrostatic synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to saturn than titan presently does titan s lack of high relief implies that most but not all of the surface features observed with the cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation titan s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

suspended sediments of the modern amazon and orinoco rivers abstract the amazon and orinoco rivers are massive transcontinental conveyance systems for suspended sediment they derive about 90 of their sediment from the andes that support their western headwaters transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the atlantic at their points of maximum suspended sediment discharge the amazon transports an average of 1100 1300 10 6 tons per year and the orinoco transports about 150 10 6 tons per year relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization increased storage and reduced transport of sediment in the middle orinoco during periods of peak water discharge and storage of suspended sediment in the lower amazon during rising discharge and resuspension during falling discharge spatial distributions of suspended sediment in cross sections of both rivers are typically heterogeneous not only in the vertical sense but also in the lateral the cross channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete considerable fine grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion

analysis and interpretation of cassini titan radar altimeter echoes abstract the cassini spacecraft has acquired 25 radar altimeter elevation profiles along titan s surface as of april 2008 and we have analyzed 18 of these for which there are currently reconstructed ephemeris data altimeter measurements were collected at spatial footprint sizes from 6 60 km along ground tracks of length 400 3600 km the elevation profiles yield topographic information at this resolution with a statistical height accuracy of 35 50 m and kilometer scale errors several times greater the data exhibit significant variations in terrain from flat regions with little topographic expression to very rugged titanscapes the bandwidth of the transmitted waveform admits vertical resolution of the terrain height to 35 m at each observed location on the surface variations in antenna pointing and changes in surface statistics cause the range compressed radar echoes to exhibit strong systematic and time variable biases of hundreds of meters in delay it is necessary to correct the received echoes for these changes and we have derived correction algorithms such that the derived echo profiles are accurate at the 100 m level for off nadir pointing errors of 0 3 and 0 6 for leading edge and echo centroid estimators respectively the leading edge of the echo yields the elevation of the highest points on the surface which we take to be the peaks of any terrain variation the mean value of the echo delay is more representative of the mean elevation so that the difference of these values gives an estimate of any local mountain heights finding locations where these values diverge indicates higher relief terrain elevation features are readily seen in the height profiles several of the passes show mountains of several hundred m altitude spread over 10 s or even 100 s of km in spatial extent so that slopes are very small large expanses of sub 100 m topography are commonplace on titan so it is rather smooth in many locations other areas exhibit more relief although the overall observed variation in surface height on any pass is less than about 1 km some elevation features correspond to observed changes in brightness in cassini infrared images but many do not correspondence between the imaging sar ground tracks and the altimeter paths is limited so that identifying elevation changes with higher resolution sar features is premature at present

mountains on titan observed by cassini radar abstract the cassini titan radar mapper has observed elevated blocks and ridge forming block chains on saturn s moon titan demonstrating high topography we term mountains summit flanks measured from the t3 february 2005 and t8 october 2005 flybys have a mean maximum slope of 37 and total elevations up to 1930 m as derived from a shape from shading model corrected for the probable effects of image resolution mountain peak morphologies and surrounding diffuse blankets give evidence that erosion has acted upon these features perhaps in the form of fluvial runoff possible formation mechanisms for these mountains include crustal compressional tectonism and upthrusting of blocks extensional tectonism and formation of horst and graben deposition as blocks of impact ejecta or dissection and erosion of a preexisting layer of material all above processes may be at work given the diversity of geology evident across titan s surface comparisons of mountain and blanket volumes and erosion rate estimates for titan provide a typical mountain age as young as 20 100 million years

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

fluvial features on titan insights from morphology and modeling fluvial features on titan have been identified in synthetic aperture radar sar data taken during spacecraft flybys by the cassini titan radar mapper radar and in descent imager spectral radiometer disr images taken during descent of the huygens probe to the surface interpretations using terrestrial analogs and process mechanics extend our perspective on fluvial geomorphology to another world and offer insight into their formative processes at the landscape scale the varied morphologies of titan s fluvial networks imply a variety of mechanical controls including structural influence on channelized flows at the reach scale the various morphologies of individual fluvial features implying a broad range of fluvial processes suggest that paleo flows did not occupy the entire observed width of the features disr images provide a spatially limited view of uplands dissected by valley networks also likely formed by overland flows which are not visible in lower resolution sar data this high resolution snapshot suggests that some fluvial features observed in sar data may be river valleys rather than channels and that uplands elsewhere on titan may also have fine scale fluvial dissection that is not resolved in sar data radar bright terrain with crenulated bright and dark bands is hypothesized here to be a signature of fine scale fluvial dissection fluvial deposition is inferred to occur in braided channels in paleo lake basins and on sar dark plains and disr images at the surface indicate the presence of fluvial sediment flow sufficient to move sediment is inferred from observations and modeling of atmospheric processes which support the inference from surface morphology of precipitation fed fluvial processes with material properties appropriate for titan terrestrial hydraulic equations are applicable to flow on titan for fully turbulent flow and rough boundaries for low reynolds number flow over smooth boundaries however knowledge of fluid kinematic viscosity is necessary sediment movement and bed form development should occur at lower bed shear stress on titan than on earth scaling bedrock erosion however is hampered by uncertainties regarding titan material properties overall observations of titan point to a world pervasively influenced by fluvial processes for which appropriate terrestrial analogs and formulations may provide insight

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques