applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

effective tension shear relationships in extensional fissure swarms axial rift zone of northeastern iceland abstract the geometry of fracture systems in selected areas of the active krafla fissure swarm mid atlantic ridge northeastern iceland is analysed based on geodetic analysis of the present day topography at the top of holocene basaltic lava flows which fill the axial rift zone the deformation of this initially horizontal surface can be reconstructed extensional deformation is localised at all scales and block tilting though present remains minor using simple models of the surface expression of normal faults the geometrical characteristics of the topographic features related to active deformation during tectonic volcanic events are quantitatively analysed at crustal depths of about 1 km normal faults are present and have an average 70 dip comparison with the dip data of older normal faults observed in the uplifted and eroded shoulders of the rift zone at palaeodepths of 1 2 km indicates that this dip determination is valid comparisons between the local case study and structural analyses of active fissure swarms on a larger scale suggest that normal faulting plays a major role in the middle section of the thin newly formed brittle crust of the rift zone in the axial oceanic rift zone of ne iceland the extensional deformation in the upper crust is dominated by horizontal tension and shear of normal sense their relative importance depending on depth absolute tension dominates in the uppermost several hundred metres of the crust resulting in the development of fissure swarms effective tension plays an important role at a deeper level 2 5 km because of the presence of magmatic fluid pressure from magma chambers which feed dyke injections at crustal depths of about 1 km normal shear prevails along fault planes which dip 60 75 this importance of normal shear at moderate depth between upper and lower crustal levels where tension prevails is pointed out within the extensional context of rifting these variations of tectonic behaviour with depth are controlled by both the lithostatic pressure and the effective tension induced by the presence of magmatic fluid pressure

high heat flux on ancient mars evidence from rift flank uplift at coracis fossae 1 we have identified flexural uplift at the flanks of the coracis fossae rift valley modeling the topography the elastic thickness is constrained to 10 3 12 5 km the corresponding mechanical thickness and thermal gradient are 15 19 km and 27 33 k km 1 respectively the time of rifting is dated by evaluating the crater size frequency distribution of key surface units related to the rifting thus the heat flux between 3 5 and 3 9 ga is calculated to be 54 66 mw m 2 furthermore the stresses supported by the rift bounding faults are estimated to be below 5 mpa we speculate that this weakness may be connected to the presence of water below the surface

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

interior layered deposits within a perched basin southern coprates chasma mars evidence for their formation alteration and erosion a basina like area containing three interior layer deposits ilds on the southern margin of coprates chasma was studied we interpret the area as an ancestral basin and demonstrate that ild deposition postdates the formation of the current wall rock slopes the geometry of the ild and the wall rock spurs form a catchment area between each ild and the plateau to the south erosional remnants of extensive ash or dust layers deposited on the plateau south of valles marineris also crop out on the southern plateau of coprates chasma a mass balance calculation suggests that the volume of each ild is compatible with the volume of the ash or dust that would have been deposited within each catchment area we propose that the ilds likely formed by episodically washing such aerially deposited material down from chasma walls rifting of the iusa melasa coprates graben opened the enclosed basin and removed any standing water faults within the ilds are compatible with this chasm opening sulfates are associated with the ilds and lighta toned material on the basin floor we suggest that they result from water alteration of preexisting deposits though the timing of that alteration may predate or postdate the breaching of the basin scours within one ild are similar to terrestrial glacial scours during a period of high obliquity ice would accumulate in this region hence we argue the scours are martian glacial scours a late deposited layer marks the end of the active local geological history between 100 my and 1 gy

valles marineris tectonic and volcanic history inferred from dikes in eastern coprates chasma magmatic dikes have been proposed to have weakened and fractured the crust allowing the formation of valles marineris hence dikes were studied in the region of eastern coprates chasma in an area that includes a major transition between hesperian aged volcanic deposits in the western walls and pristine noachian crust in the eastern walls over a hundred dikes were identified dike widths are 13 m on average estimation of magma eruption rates are comparable with previous estimates for hesperian lava flows on mars 105 to 106 m3 s 1 dikes dips range from 55 to 90 orientations record two distinct main tectonic stress fields 90 and 70 different from the chasmata dikes striking 90 are only observed at elevations below 1500 m dikes striking 70 are observed at elevation below 0 m and are therefore considered older however linear features are also observed on the late noachian early hesperian surrounding plateaus and could be related to the 70 dike group in the western part of our study area dikes 10 of the total amount of dikes mapped strike 110 sub parallel to valles marineris and suggests a relationship between dike emplacement and graben formation the presence of pre existing faults in the two directions 90 and 70 could explain the shape of eastern valles marineris and chaotic terrains which have a different general orientation than the valles marineris main rift our results suggest a complex relationship between dike emplacement and the formation of valles marineris

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

morphology stratigraphy and mineralogical composition of a layered formation covering the plateaus around valles marineris mars implications for its geological history an extensive layered formation covers the high plateaus around valles marineris mapping based on hirise ctx and hrsc images reveals these layered deposits lds crop out north of tithonium chasma south of ius chasma around west candor chasma and southwest of juventae chasma and ganges chasma the estimated area covered by lds is not vert similar42 300 km2 they consist of a series of alternating light and dark beds a 100 m in total thickness that is covered by a dark unconsolidated mantle possibly resulting from their erosion their stratigraphic relationships with the plateaus and the valles marineris chasmata indicate that the lds were deposited during the early to late hesperian and possibly later depending on the region before the end of the backwasting of the walls near juventae chasma and probably before louros valles sapping near ius chasma their large spatial coverage and their location mainly on highly elevated plateaus lead us to conclude that lds correspond to airfall dust and or volcanic ash the surface of lds is characterized by various morphological features including lobate ejecta and pedestal craters polygonal fractures valleys and sinuous ridges and a pitted surface which are all consistent with liquid water and or water ice filling the pores of lds lds were episodically eroded by fluvial processes and were possibly modified by sublimation processes considering that lds correspond to dust and or ash possibly mixed with ice particles in the past lds may be compared to dissected mantle terrains currently observed in mid to high latitudes on mars which correspond to a mantle of mixed dust and ice that is partially or totally dissected by sublimation the analysis of crism and omega hyperspectral data indicates that the basal layer of lds near ganges chasma exhibits spectra with absorption bands at not vert similar1 4 m and not vert similar1 9 m and a large deep band between not vert similar2 21 and not vert similar2 26 m that are consistent with previous spectral analysis in other regions of lds we interpret these spectral characteristics as an enrichment of lds in opaline silica or by al phyllosilicate rich layers being overlain by hydroxylated ferric sulfate rich layers these alteration minerals are consistent with the aqueous alteration of lds at low temperatures

crustal failure on icy moons from a strong tidal encounter abstract close tidal encounters among large planetesimals and moons should have been more common than grazing or normal impacts using a mass spring model within an n body simulation we simulate the deformation of the surface of an elastic spherical body caused by a close parabolic tidal encounter with a body that has similar mass as that of the primary body such an encounter can induce sufficient stress on the surface to cause brittle failure of an icy crust and simulated fractures can extend a large fraction of the radius of body strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons such as dione tethys ariel and charon

hematite bearing materials surrounding candor mensa in candor chasma mars implications for hematite origin and post emplacement modification abstract the valles marineris canyon system on mars is of enduring scientific interest in part due to the presence of interior mounds that contain extensive layering and water altered minerals such as crystalline gray hematite and hydrated sulfates the presence of hematite and hydrated sulfate minerals is important because their host rock lithologies provide information about past environments that may have supported liquid water and may have been habitable this work further defines the association and relationship between hematite bearing materials and low albedo presumably aeolian deposits and layered materials identifies physical characteristics that are strongly correlated with the presence of hematite and refines hypotheses for the origin and post emplacement modification including transport of these hematite bearing and associated materials there are only three regions surrounding candor mensa where hematite has been identified even though morphologic properties are similar throughout the entire mensa three possible explanations for why hematite is only exposed in these regions include 1 the topographic structure of the mensa walls concentrates hematite at the base of the layered deposits influencing the ability to detect hematite from orbit 2 the presence of differing amounts of dark mantling material and hematite free erosional sediment 3 the potential fracturing of the mensa and the influence of these structures on fluid flow and subsequent digenesis the observations of hematite bearing materials in this work support the hypothesis that hematite is eroding from a unit in the candor mensa interior layered deposits ild and is being concentrated as a lag deposit adjacent to the lower layers of candor mensa and at the base in the form of dark aeolian material due to the similar geologic context associated with hematite bearing and ild materials throughout the valles marineris canyon system the insight gained from studying these materials surrounding candor mensa can likely be applicable to similar layered deposits throughout valles marineris

using rock eval 6 pyrolysis for tracking fossil organic carbon in modern environments implications for the roles of erosion and weathering this work relates to the debate on the fossil organic carbon foc input in modern environments and its possible implication for the carbon cycle and suggests the use of rock eval 6 pyrolysis as a relevant tool for tracking foc in such environments considering that such a delivery is mainly due to supergene processes affecting the continental surface we studied organic matter in different reservoirs such as bedrocks alterites soils and rivers in two experimental catchments at draix alpes de haute provence france samples were subjected to geochemical rock eval 6 pyrolysis investigations and artificial bacterial degradations after comparing the geochemical fingerprint of samples geochemical markers of foc were defined and tracked in the different reservoirs our results confirm the contribution of foc in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of foc during its exchange between these pools in addition the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter fom bedrock to river fluxes controlled by gully erosion are characterized by a qualitative and quantitative preservation of fom bedrock to alterite fluxes governed by chemical weathering are characterized by foc mineralization without qualitative changes in deeper alterites alterite to soils fluxes controlled by bio chemical weathering are characterized by strong foc mineralization and qualitative changes of fom thus weathering and erosional processes induce different fom evolution and affect the fate of foc towards the global carbon cycle in this study gully erosion would involve maintenance of an ancient sink for the global carbon cycle while bio chemical processes provide a source of co2 finally this study suggests that rock eval 6 pyrolysis can be considered as a relevant tool for tracking foc in modern environments copyright 2006 john wiley sons ltd

the formation of valles marineris 1 tectonic architecture and the relative roles of extension and subsidence 1 the formation of the valles marineris troughs on mars is widely held to involve some combination of horizontal extension and vertical subsidence or collapse but the specific tectonic mechanism is poorly understood this study uses boundary element models of valles marineris formation to evaluate a range of fault dip angles for two end member models of trough formation simple extensional tectonism and extension together with vertical accommodation at the base of the lithosphere representing either viscous lower crustal flow or some other form of deep seated collapse the models are constrained by the lack of footwall uplift on the plateau surface outside the troughs and the lack of significant tectonic failure of the plateau in response to the stress changes induced by valles marineris formation the results demonstrate that trough formation by extensional tectonism alone generates large surface uplifts in the surrounding plateau and enormous stresses in the lithosphere in conflict with the observations the only mechanism that is compatible with both the observed topography and the limitations imposed by the finite strength of the lithosphere is trough formation through displacement along steeply dipping to subvertical border faults together with vertical accommodation at the base of the subsiding fault block fault dips are constrained to be greater than or equal to 85 leading to a ratio of vertical subsidence to horizontal extension exceeding 5 7 and a maximum extension of less than 4 6 km these results confirm earlier studies suggesting that trough formation involved a substantial component of vertical subsidence or collapse with only modest amounts of total extension

strike slip faulting of ridged plains near valles marineris mars the surface of mars shows abundant evidence of extensional and contractional deformation in the form of normal faults grabens and wrinkle ridges 1 3 in contrast strike slip faults have been considered to be extremely rare or absent on mars4 5 this view is based on the lack of significant lateral offset of pre existing markers such as craters across suspected faults thus mars is believed to have evolved without plate tectonics or other large scale lateral motions of the lithosphere6 however careful study of viking orbiter images is revealing that strike slip faults may be present on mars7 here i identify and document several well preserved examples of martian strike slip faults and examine their relationships to wrinkle ridges the strike slip faulting predates or overlaps periods of wrinkle ridge growth south east of valles marineris and some wrinkle ridges may have nucleated and grown as a result of strike slip displacements along the echelon fault arrays lateral displacements of several kilometres inferred along these arrays may be related to tectonism in tharsis

reassessing rock mass properties and slope instability triggering conditions in valles marineris mars the rock walls of the valles marineris valleys vm in the equatorial area of mars exhibit several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume questions arise as to forces at play and rock strength in the stability of the walls of vm in this work we address the stability analysis of the walls of vm by considering the strength of the materials of the walls and the causes of landslides using finite element calculations and the limit analysis upper bound method we explore the range of cohesion and friction angle values associated with realistic failure geometries and compare predictions with the more classical culmann s translational failure model our analysis is based both on synthetic simplified slope profiles and on the real shape of the walls of vm taken from the mola topographic data validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre and post failure profiles the estimated failure surface geometry and ridge crest retreat this offers a link between rock mass properties slope geometry and volume of the observed failure represented in dimensionless charts the role of groundwater flow and seismic action on the decrease of slope stability is also estimated pseudo static seismic analyses provide another set of dimensionless charts and show that low seismicity events induced by meteoroid impacts consistent with the size of craters could be a cause for some of the observed landslides if poor rock properties for vm are assumed analyses suggest that rock mass properties are more similar to their earth equivalents with respect to what has been previously supposed

topography of valles marineris implications for erosional and structural history compilation of a simplified geologic geomorphic map onto digital terrain models of the valles marineris permitted an evaluation of elevations in the vicinity of the troughs and the calculation of depth of troughs below surrounding plateaus thickness of deposits inside the troughs volumes of void spaces above geologic geomorphic units and volumes of deposits the central troughs north ophir north and central candor and north melas chasmata lie as much as 11 km below the adjacent plateaus in ophir and candor chasmata interior layered deposits reach 8 km in elevation if the deposits are lacustrine and if all troughs were interconnected lake waters standing 8 km high would have spilled out of coprates chasma onto the surrounding plateaus having surface elevations of only 4 5 km in this case interior deposits above about 4 km in the central troughs would not be lacustrine they could be volcanic on the other hand the troughs may not have been interconnected at the time of interior deposit emplacement they may have formed isolated ancestral basins the existence of such basins is supported by independent structural and stratigraphic evidence the ancestral basins may have eventually merged perhaps through renewed faulting to form northern subsidiary troughs in ophir and candor chasmata and the coprates north melas ius graben system the peripheral troughs are only 2 5 km deep shallower than the central troughs they may have formed from a combination of erosional collapse and structural activity chaotic terrain is seen in the peripheral troughs near a common contour level of about 4 km on the adjacent plateaus which supports the idea of release of water under artesian pressure from confined aquifers the layered deposits in the peripheral troughs may have formed in isolated depressions that harbored lakes and predated the formation of the deep outflow channels if these layered deposits are of volcanic origin they may have been emplaced beneath ice in the manner of table mountains areal and volumetric computations show that erosion widened the troughs by about one third and that deposits occupy one sixth of the interior space even though the volume eroded is larger than the volume deposited topographic and geologic considerations imply that material eroded from trough walls was probably part of the interior layered deposits but not their sole source additional material may have come from subterranean piping from reworking of local disintegration products on the floors such as chaotic materials or from eolian influx but overall it is likely that the additional material is volcanic and that it forms mostly the upper more diversely bedded layers of the interior deposits

the light toned stratified sedimentary rock exposures in western juventae chasma mars in context abstract juventae chasma an isolated depression northeast of the valles marineris trough system hosts four mounds of light toned layered materials these are erosional remnants interpreted to consist of sedimentary rocks the geological setting of juventae chasma is a complex amalgamation of terrains and surfaces of different morphologies ages and structures most previous published studies assumed or interpreted that the light toned mound forming materials were deposited in the chasm after it opened or began to open here we use detailed observations of the geologic setting the nature of chasm wall rocks and the distribution and nature of the contacts of the light toned materials with adjacent geologic materials to argue that the light toned mounds in juventae chasma are more likely remnants of light toned materials that existed in the subsurface before the chasm opened up the rock cut by the chasm was not a monolithic unit e g lava flows and might have included both light toned and dark toned sedimentary rocks bearing a range of diagenetic properties the light toned materials were deposited as clasts precipitates or both within craters or depressions that were filled buried lithified and then exposed when juventae chasma formed because the sedimentary rock types and stratal package properties differ from one mound to the next the buried craters or depressions could have existed at different times and provide sedimentary records of different environments that existed at different times during the planet s early history noachian period upon exposure these materials as well as chasm wall rocks and chaotic terrain blocks underwent differential erosion as a function of rock physical properties to produce the geomorphic expressions observed today

stability of rock slopes in valles marineris mars 1 new slope measurements from the mars orbiter laser altimeter mola in conjunction with the rock mass rating system rmr permit inversions of slope height and angle from wallrock and interior deposits within valles marineris troughs for strength and lithology wallrock 50 rmr 65 is stronger than interior deposits 30 rmr 55 these values are consistent with layered igneous rock beneath wallrock slopes with interior deposits consistent with partially indurated sedimentary or volcaniclastic rocks larger volumes of landslide debris relative to terrestrial slides are related to the reduced martian gravity seismicity along trough bounding normal faults likely triggered the landslides in the adjacent wallrock the weaker interior deposits are located sufficiently far from a border fault and on its hangingwall to have remained stable during the seismogenic faulting in valles marineris

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

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

modern foraminifera δ13c and bulk geochemistry of central oregon tidal marshes and their application in paleoseismology we assessed the utility of 13c and bulk geochemistry total organic content and c n to reconstruct relative sea level changes on the cascadia subduction zone through comparison with an established sea level indicator benthic foraminifera four modern transects collected from three tidal environments at siletz bay oregon usa produced three elevation dependent groups in both the foraminiferal and 13c bulk geochemistry datasets foraminiferal samples from the tidal flat and low marsh are identified by miliammina fusca abundances of 45 middle and high marsh by m fusca abundances of 25 the 13c values from the groups defined with 13c bulk geochemistry analyses decrease with an increasing elevation 24 1 1 7 in the tidal flat and low marsh 27 3 1 4 in the middle and high marsh and 29 6 0 8 in the highest marsh samples we applied the modern foraminiferal and 13c distributions to a core that contained a stratigraphic contact marking the great cascadia earthquake of ad 1700 both techniques gave similar values for coseismic subsidence across the contact 0 88 0 39 m and 0 71 0 56 m suggesting that 13c has potential for identifying amounts of relative sea level change due to tectonics

amazonian volcanism inside valles marineris on mars the giant trough system of valles marineris is one of the most spectacular landforms on mars yet its origin is still unclear although often referred to as a rift it also shows some characteristics that are indicative of collapse processes for decades one of the major open questions was whether volcanism was active inside the valles marineris here we present evidence for a volcanic field on the floor of the deepest trough of valles marineris coprates chasma more than 130 individual edifices resemble scoria and tuff cones and are associated with units that are interpreted as lava flows crater counts indicate that the volcanic field was emplaced sometime between 0 4 ga and 0 2 ga the spatial distribution of the cones displays a control by trough parallel subsurface structures suggesting magma ascent in feeder dikes along trough bounding normal faults spectral data reveal an opaline silica rich unit associated with at least one of the cones indicative of hydrothermal processes our results point to magma water interaction an environment of astrobiological interest perhaps associated with late stage activity in the evolution of valles marineris and suggest that the floor of coprates chasma is promising target for the in situ exploration of mars

strike slip faults on mars observations and implications for global tectonics and geodynamics 1 the tectonic evolution of mars has been driven primarily by the interaction of tharsis induced loading stresses with a uniform contractional stress field leading to global assemblages of graben and wrinkle ridges until recently strike slip faults have appeared to be largely absent from the tectonic record we here present evidence for a new set of noachian to early hesperian strike slip faults southwest of tharsis the best preserved fault in the newly mapped set has a length of 200 km and measured lateral offset of 5 9 km we use the locations of both previously mapped and newly identified strike slip faults to investigate the tectonic and geodynamic evolution of mars we model the tectonic evolution of the planet in response to the evolving balance between the loading and contractional stresses finding widespread regions in which strike slip faulting was favored the observed tectonic history is consistent with a scenario in which loading induced stresses peaked early in mars history followed by the growth of contractional stresses leading to a shift in the preferred locus of strike slip faulting from regions southwest of tharsis in the noachian to early hesperian to northwest of tharsis in the early amazonian the contractional strain history inferred from the ages and locations of the strike slip faults is consistent with the strains calculated from models of the thermal evolution of mars in which the gradual secular cooling of the planet over time was augmented by plume induced contraction during tharsis formation in the noachian

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

recent seismicity in valles marineris mars insights from young faults landslides boulder falls and possible mud volcanoes abstract current seismicity of mars is poorly known geodynamic models and analysis of surface faults indicate that mars could be seismically active globally particularly within the tharsis region however published geologic constraints on such activity are sparse in this study we use geomorphologic observations and crater size frequency age determinations gleaned from high resolution orbiter data to demonstrate that the valles marineris region is recently seismo tectonically active the chasmata shows evidence of reactivated dip slip faults that cross cut the chasmata walls and floors and indicates up to 1 2 km total vertical displacement along the trough bounding faults more than 16000 boulder fall occurrences with pristine trails are observed throughout the chasmata wall with an average slope of 25 degrees the boulder falls are interpreted to have been triggered by recent seismic shaking from the shallow marsquakes occurring along the chasmata faults possibly in the last thousands of years synthetic ground motion models indicate several m w 4 6 marsquakes at shallow depths 1 6 km are required to produce these canyon wide boulder falls in addition the presence of many young landslides 22 790 ma proximal to the reactivated trough bounding faults and formation of thousands of possible mud volcanic cones throughout the chasmata floor all suggest marsquake triggered shaking in the past tens to hundreds of million years corresponding to late to middle amazonian epochs we estimate formation of 20 m to 1 3 km diameter fresh impact craters around the chasmata had negligible contribution to the recent seismicity therefore valles marineris tectonism is an important source of marsquakes that may be readily detectable by the upcoming insight seismometers

tracking sedimentation from the historic a d 2011 mississippi river flood in the deltaic wetlands of louisiana usa management and restoration of the mississippi river deltaic plain southern united states and associated wetlands require a quantitative understanding of sediment delivery during large flood events past and present here we investigate the sedimentary fingerprint of the 2011 mississippi river flood across the louisiana coast atchafalaya delta terrebonne barataria and mississippi river delta basins to assess spatial patterns of sedimentation and to identify key indicators of sediment provenance the sediment deposited in wetlands during the 2011 flood was distinguished from earlier deposits based on biological characteristics primarily absence of plant roots and increased presence of centric planktonic diatoms indicative of riverine origin by comparison the lithological bulk density organic matter content and grain size and chemical stable carbon isotopes of bulk organic matter properties of flood sediments were nearly identical to the underlying deposit flood sediment deposition was greatest in wetlands near the atchafalaya and mississippi rivers and accounted for a substantial portion 37 to 85 of the annual accretion measured at nearby monitoring stations the amount of sediment delivered to those basins 1 1 1 6 g cm 2 was comparable to that reported previously for hurricane sedimentation along the louisiana coast 0 8 2 1 g cm 2 our findings not only provide insight into how large scale river floods influence wetland sedimentation they lay the groundwork for identifying previous flood events in the stratigraphic record

geomorphic study of fluvial landforms on the northern valles marineris plateau mars 1 fluvial landforms are observed on the plateau near echus chasma and other locations on the valles marineris plateau using high resolution 10 to 50 m pixel mars express images and topography branching valleys have a 20 to 100 m deep v shape profile typical of fluvial processes their incision occurred in a thin 150 m and weak dark unit that overlies the plateau basement the valleys are distributed close to watershed boundaries as expected for overland flows and different from pure glacial or hydrothermal processes the 2d geometry of valley networks show drainage densities reaching 1 3 km 1 that indicate a strong 2d extension stage that usually requires a minimum of thousands of years as established from terrestrial examples however the 3d valley geometry shows a limited incision and a lack of concavity suggesting a limited development in time millions of years of evolution are unlikely many outlets connect to the heads of canyons of echus chasma that might involve sapping processes these canyons might have formed coevally with shallow valleys their difference in geometry is a consequence of the difference in lithology which induced a difference in the erosion capacity and an enhanced infiltration conducing to sapping valleys are submitted to modification by aeolian processes sometimes leading to the formation of inverted channels as observed more broadly through the region these landforms formed late in the early mars history and might be considered as examples of episodic fluvial events due to short term climate changes and or regional fluvial activity after the noachian

organic carbon sources and transformations in mangrove sediments a rock eval pyrolysis approach abstract a rock eval pyrolysis study was carried out on sedimentary cores and leaf and woody tissue of vascular plant species from the mangroves of french guiana these forests develop on moving mudbanks and have a lifetime limited to few decades before being eroded our main purpose was to complete the understanding of carbon cycling in this specific environment using a method that allows monitoring the depth evolution of sources and transformation of organic matter om within a tight depth span leaf and woody tissue showed clearly distinct rock eval parameters however these parameters strongly varied with om decomposition rapidly limiting their efficiency as mangrove plant tracers the decrease in values of tps2 pyrolysis temperature corresponding to the maximum release of hydrocarbons with depth clearly showed a line between a pedogenetic layer enriched in autochthonous om and marine sediments enriched in allochthonous om this allochthonous om originated from the particulate discharge of the amazon river which is partly deflected northwestwards by the current of the guianas within the soil layer decay processes induced a strong dehydrogenation and slight oxidation of om the two processes occurring simultaneously the deeper layers were characterized by a very strong increase in oico2 quantity of pyrolysed co2 relative to total organic carbon beneath both the young and the senescent forests this trend resulted rather from an increasing content of authigenic carbonate than from increasing concentration of oxidized allochthonous debris carbonate can form as a result of the more anoxic conditions prevailing in buried layers vs the upper suboxic ones beneath the senescent mangrove a greater increase in oico2 probably reflected greater carbonate precipitation resulting from the decomposition of higher amounts of om

derivation of lowland riparian wetland deposit architecture using geophysical image analysis and interface detection for groundwater surface water interactions to be understood in complex wetland settings the architecture of the underlying deposits requires investigation at a spatial resolution sufficient to characterize significant hydraulic pathways discrete intrusive sampling using conventional approaches provides insufficient sample density and can be difficult to deploy on soft ground here a noninvasive geophysical imaging approach combining three dimensional electrical resistivity tomography ert and the novel application of gradient and isosurface based edge detectors is considered as a means of illuminating wetland deposit architecture the performance of three edge detectors were compared and evaluated against ground truth data using a lowland riparian wetland demonstration site isosurface based methods correlated well with intrusive data and were useful for defining the geometries of key geological interfaces i e peat gravels and gravels chalk the use of gradient detectors approach was unsuccessful indicating that the assumption that the steepest resistivity gradient coincides with the associated geological interface can be incorrect these findings are relevant to the application of this approach in settings with a broadly layered geology with strata of contrasting resistivities in addition ert revealed substantial structures in the gravels related to the depositional environment i e braided fluvial system and a complex distribution of low permeability putty chalk at the bedrock surface with implications for preferential flow and variable exchange between river and groundwater systems these results demonstrate that a combined approach using ert and edge detectors can provide valuable information to support targeted monitoring and inform hydrological modeling of wetlands

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

underlying structural control of small scale faults and fractures in west candor chasma mars 1 orientations of small scale faults and fractures within the interior layered deposits of west candor chasma were measured to investigate what information about the geologic history of valles marineris they can contribute deformational features were separated into six categories based on morphology and their orientations were analyzed the elevations at which the deformational features formed are recorded as a proxy for stratigraphic level deformational features occur over a continuous range of elevations and display regionally consistent preferred orientations indicating their formation was controlled by a regional stress regime the two most abundant preferred orientations of 35 and 110 are approximately parallel to the chasma walls and the inferred underlying normal faults the alignment of three populations of small faults at 140 consistent with the morphology of release faults indicates a large scale fault underlying the southeastern border of ceti mensa the preferred orientations imply these small scale deformational features formed from a continuation of the same imposed stresses responsible for the formation of valles marineris indicating these stresses existed past the formation of the interior layered deposits the origins of a fourth preferred orientation of 70 is less clear but suggests the study area has undergone at least two periods of deformation

revealing the temporal dynamics of subsurface temperature in a wetland using time lapse geophysics summary there is growing recognition of the need to understand the subsurface hydrological mechanisms within wetlands given their potentially significant role in the hydrological and biogeochemical function of catchments as well as their effects on the wetland habitat itself conventional subsurface hydrological sampling and monitoring techniques are often limited in such environments because of the invasive nature of such approaches and the sensitivity of the environment in this study we use ground penetrating radar gpr and electrical resistivity tomography ert to characterise the stratigraphy at a small riparian wetland site then through time lapse ert measurements over a 12 month period we demonstrate how changes in resistivity may provide additional value about localised recharge we compare direct measurements of water table depth and pore fluid electrical conductivity and temperature with subsurface resistivity derived from the ert measurements and reveal that temporal fluctuations in temperature of the subsurface dominates the change in resistivity over the monitored period from this we use the ert images of resistivity to estimate spatio temporal changes in subsurface temperature and thus infer localised zones of groundwater recharge due to suppressed seasonal variation in temperature although we focus here on one 2 d vertical profile through the wetland the results highlight the potential value of non invasive time lapse geoelectrical surveys for mapping 3 d thermal patterns within a wetland environment

the formation of the south tharsis ridge belt basin and range style extension on early mars the south tharsis ridge belt strb is located along the northeastern edge of terra sirenum and partially surrounds the southwestern part of tharsis in an arc it consists of 29 large ridges separated by distances 130 to 260 km with average relief of 1 5 km above the surrounding plains because the strb is among the oldest tectonic features associated both spatially and developmentally with tharsis it may provide key information on the early evolution of tharsis and possibly pre tharsis processes earlier studies concluded that the ridges formed through compressional tectonism however the shape size and separation of the ridges support the interpretation that the strb resembles the extensional basin and range province on earth both regions are characterized by series of parallel mountain ranges separated by broad valleys in this study we evaluate both extensional and compressional hypotheses for the origin of the ridges using evidence from topography deformed craters crustal thickness models and strain modeling though neither interpretation explains all aspects of the ridges the topography of the ridges and crustal thinning associated with the western part of the ridge belt support an extensional origin strain models predict that basin and range style wide rifting would be expected for early martian conditions this extension may have been initiated by plume induced uplift in the early stages of tharsis formation but the large amount of extensional strain inferred in the western strb must have been accommodated by compression elsewhere possibly in the heavily deformed craters of western terra sirenum

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

crustal spreading due to dikes and faults in southwest iceland abstract a 30 km long profile extending from 3 million year old pleistocene rocks to the holocene rocks of the rift zone in southwest iceland is dissected by 443 dikes and 156 normal faults nearly all the dikes are basaltic with an average strike of n26 e which is subparallel to the trend of fractures in the nearby rift zone their average dip is 69 and average thickness 1 37 m both values much lower than averages for regional tertiary dike swarms in iceland many dikes are seen to change into sills the great majority of the faults are pure dip slip with an average throw of 10 2 m their average strike n37 e is different from the average strike of the dikes in this area and the fractures in the nearby rift zone their average dip is 75 2 which is somewhat steeper than in the tertiary areas but the dips are less in the interbedded sedimentary layers than in the lava flows growth faults are very rare in the area and most of the faults appear to have completed their growth in less than 10 000 years in subsections crustal dilation due to dikes is 0 4 3 7 that due to faults is 0 6 5 3 and that due to both dikes and faults is 1 04 6 44 in these subsections average fault spacing is one fault per 170 563 m spacing decreases toward the active rift zone it is concluded that in typical fissure swarms of the rift zone the dilation at the surface is almost entirely due to extensional fractures and gaping vertical normal faults in the depth range of a couple of hundred metres to perhaps 1 km the non vertical faults contribute most to the dilation at deeper crustal levels however dilation due to dikes becomes dominant

modelling the effects of climate change and its uncertainty on uk chalk groundwater resources from an ensemble of global climate model projections projections of climate for the 2080s from an ensemble of global climate models gcms run under a medium high a2 emissions scenario are used to simulate changes in groundwater resources of a chalk aquifer in central southern england few studies that have investigated the impacts of climate change on groundwater resources have addressed uncertainty in this paper the uncertainty associated with use of a suite of gcm outputs in catchment scale impact studies is quantified a range of predictions is obtained by applying precipitation and temperature change factors derived from thirteen gcms to a distributed recharge model and a groundwater flow model of the chalk aquifer of the marlborough and berkshire downs and south west chilterns in the uk the ensemble average suggests there will be a 4 9 reduction in annual potential groundwater recharge across the study area although this is not statistically significant at the 95 confidence level the spread of results for simulated changes in annual potential groundwater recharge range from a 26 decrease to a 31 increase by the 2080s with ten predicting a decrease and three an increase whilst annual recharge is not found to change significantly the multi model results suggest that the seasonal variation in the groundwater resource will be greater with higher recharge rates during a reduced period of time in winter the spread of predictions for changes in river baseflow at the bottom of the largest river sub catchment is from 16 to 33 in march and from 68 to 56 in october the effects of climate change are shown to depend significantly on the type of land use it is concluded that further research is required to quantify the effect of different vegetation types on chalk covered by different thicknesses of soil and their response to a changing climate

igneous dikes on mars revealed by mars orbiter laser altimeter topography the origin of martian grabens has remained controversial for decades given the nonuniqueness of graben morphology and conflicting interpretations of dike induced or faultingbased formation processes we use measurements from the mars orbiter laser altimeter to identify the characteristic topographic signature at the surface of an igneous dike beneath a martian graben our results suggest that this subtle but diagnostic signature can be used to test competing interpretations of the formation of grabens and associated fissures and collapse depressions

an isotopic biogeochemical assessment of shifts in organic matter input to holocene sediments from mud lake florida abstract a molecular and isotopic study of sediment cores from a sinkhole lake mud lake florida usa was performed in order to relate documented changes in the regional terrestrial vegetation and water table over the last 5500 years to molecular and isotopic proxies for biological sources of organic matter to the lake sediments temporal shifts in the source of organic matter to the sediment as determined by the stable carbon isotope composition of bulk organic matter and biomarkers correspond with previously defined regional scale transitions in forest ecosystems quercus to pinus at 5500 14 c yr bp and taxodium expansion at 2500 14 c yr bp and coincident increases in the floridan water table the 13 c values for total sedimentary organic carbon showed a shift from terrestrial and aquatic macrophyte sources 27 8 in sediments dated at 5400 14 c yr bp within the basal peat to a cyanobacterial dominated sapropel 18 1 at the surface a comparison of the 13 c values of bulk sediment and biomarkers representative of cyanobacterial and algal input e g 7 and 8 methylheptadecane and the n alkane c 17 indicates that the present shallow lake was fully developed by 2400 14 c yr bp differences among the 13 c values of specific biomarkers derived from vascular plants c 29 and c 31 n alkanes and cuo lignin oxidation products and from cyanobacteria and algae are nearly equivalent in magnitude to the shift recorded in 13 c of toc indicating their effective use as source proxies in this system

three dimensional models of deformation near strike slip faults we use three dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike slip faults deformation of the brittle upper crust in the vicinity of strike slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle the driving motion is represented by displacement that is spectied on the bottom of a 15km thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults which we term the shear zone stress free basal boundary conditions are specified within the shear zone the basal driving displacement is either pure strike slip or strike slip with a small oblique component and the geometry of the fault system includes a single fault several parallel faults and overlapping en echelon faults we examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults in models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude i c1 j l c i rl l b blhi aill i srizcxi ld 3 rr ij i n flail 3il i dilitiiiat df ti ijtluii clicili c i i zor tz a j t s ii acmes strong fault lnnlds havs lnore luc tlixd dxz a ac tip of tne faults and the deformation is partly distributed outside the fault zone the dimensions of large basins along strike slip faults such as the rukwa and dead sea basins and the absence of uplift around pull apart basins fit models with weak faults better than models with strong faults our models also suggest that the length to width ratio of pull apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested we show that pure strike slip motion can produce tectonic features such as elongate half grabens along a single fault rotated blocks at the ends of parallel faults or extension perpendicular to overlapping en echelon faults which can be misinterprete d to indicate a regional component of extension zones of subsidence or uplift can become wider than expected for transform plate boundaries when a minor component of oblique motion is added to a system of parallel strike slip faults

mars reconnaissance orbiter radio science gravity investigation 1 the objectives of the mars reconnaissance orbiter mro radio science gravity investigation are to improve knowledge of the static structure and characterize the temporal variability of the martian gravitational field relevant to the planet s internal dynamics the structure and dynamics of the atmosphere and the orbital evolution of spacecraft at mars the investigation will utilize range rate and range measurements from x band and when available ka band tracking systems of the mro spacecraft mro will enable a considerable improvement in the spatial resolution and quality of mars global gravity field the low orbital periapsis of mro 255 km will yield gravity maps suitable for study of regional 102 km structure of the crust and lithosphere the addition of tracking data from the mars global surveyor and mars odyssey spacecraft also currently orbiting mars will be useful in decorrelating errors in spherical harmonic coefficients of the gravity field that will improve the quality of the static field studies of the low degree gravity field combined with measurements of rotational dynamics will permit insight about the structure of mars deep interior changes in the low degree spherical harmonic coefficients of the martian gravity field and in polar mass anomalies will be used to track the seasonal cycle of co2 exchange with the surface measurements of spacecraft drag will be used to estimate density variations in the atmosphere relevant to weather patterns and aerobraking of future spacecraft tracking observations will also be used to improve the ephemeris of mars and the masses of the martian moons

formation and growth of normal faults at the divergent plate boundary in iceland the divergent plate boundary in iceland is characterized by 40 80 km long and 5 10 km wide swarms of tension fractures 102 m long and normal faults 103 m long the upper part of the crust is mainly composed of lava flows with abundant columnar joints that are mostly perpendicular to the lava contacts the lava flows are horizontal at the surface of the rift zone but become tilted at the rate of 1 for every 150 m depth in the crust at the surface of the rift zone the joints are vertical and parallel to the vertical principal stress because of tilting of the lava pile the columnar joints become oblique to this stress hence becoming potential shear fractures and form echelon sets at greater depths in the crust theoretical considerations suggest that normal faults start to nucleate on sets of en echelon columnar joints and or large scale tension fractures at crustal depths of 0 5 1 5 km the width depth must be the smallest controlling dimension of many faults nevertheless there is a positive linear relation r 0 91 between maximum throw and length of the holocene faults if the faults grow as self similar structures the throw length relationship can be explained by a similar relation between fault length and width

equatorial glaciations on mars revealed by gravitational collapse of valles marineris wallslopes abstract martian global climate models that account for evidence of past glaciations reported in tropical to mid latitude regions of mars predict accumulation of water ice in valles marineris during past periods of high obliquity observational evidence for such glaciations is given here topographic basement ridges of tectonic origin are common in valles marineris and display sackung features an assemblage of tectonic patterns that are diagnostic of deep seated gravitational slope deformation this deformation is most easily explained by paraglacial ridge failure subsequent to ridge wall debuttressing and decohesion following the retreat of glaciers this interpretation is supported by extensive bibliographic analysis of sackung triggers on earth by morphological evidence of subglacial erosion of the lower parts of valles marineris wallslopes of periglacial erosion of their upper parts and by the presence of various types of glacial landforms on the floors of valles marineris troughs the age of these equatorial glaciations is found to be older than 1 4 gy and younger than 3 5 gy

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

hydrodynamics of floodplain wetlands in a chalk catchment the river lambourn uk variations in floodplain channel water levels and valley floor groundwater levels measured in piezometers and boreholes are examined at selected points along the course of the river lambourn a chalk river in southern england a local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river s perennial profile variations in hydraulic gradient between local borehole levels and or floodplain channel water levels are described for three sites in the seasonal section of the channel at bockhampton east garston and west shefford the results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain however as the floodplain widens and the alluvial gravel aquifer increases in size the gravel aquifer accounts for a substantial down valley component of groundwater flow with a diffuse vertical water flux in the lower catchment the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water table variability providing a stable hydrological regime for valley bottom wetlands catchment controls upon the local valley bottom wetland regime are demonstrated with the application of a simple groundwater model developed using modflow the model is used to simulate groundwater discharge to the river in the upper and lower catchment in addition to the water level regime at selected points in the valley bottom in the lower catchment the results demonstrate the importance of taking catchment scale water flow into account when managing isolated wetlands in a permeable catchment

tepexpan palaeoindian site basin of mexico multi proxy evidence for environmental change during the late pleistocene late holocene the tepexpan palaeoindian skeleton was discovered in 1947 close to the former lake texcoco margin in the basin of mexico the find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation here we report new ams radiocarbon dates associated with the sedimentary succession at tepexpan with ages between 19 110 90 and 612 22 14c years bp and a new uranium series date for the skeleton with an age of 4700 200 years bp that indicates a mid holocene age the sedimentary succession was studied in detail using stable isotopes diatoms organic geochemistry and tephrochronology the multi proxy evidence suggests large changes around the margins of lake texcoco in terms of the balance between aquatic and terrestrial plants c3 and c4 plants saline alkaline and freshwater conditions volcanic activity marginal reworking of lake sediments and input from the drainage basin through the late pleistocene late holocene these changes had large impacts on the prehistoric human populations living by the lake shores since the late pleistocene in the basin of mexico

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

stepped fans and facies equivalent phyllosilicates in coprates catena mars stepped fan deposits and phyllosilicate mineralogies are relatively common features on mars but have not previously been found in association with each other both of these features are widely accepted to be the result of aqueous processes but the assumed role and nature of any water varies in this study we have investigated two stepped fan deposits in coprates catena mars which have a genetic link to light toned material that is rich in fe mg phyllosilicate phases although of different sizes and in separate but adjacent trough like depressions we identify similar features at these stepped fans and phyllosilicates that are indicative of similar formation conditions and processes our observations of the overall geomorphology mineralogy and chronology of these features are consistent with a two stage formation process whereby deposition in the troughs first occurs into shallow standing water or playas forming fluvial or alluvial fans that terminate in delta deposits and interfinger with interpreted lacustrine facies with a later period of deposition under sub aerial conditions forming alluvial fan deposits we suggest that the distinctive stepped appearance of these fans is the result of aeolian erosion and is not a primary depositional feature this combined formation framework for stepped fans and phyllosilicates can also explain other similar features on mars and adds to the growing evidence of fluvial activity in the equatorial region of mars during the hesperian and amazonian

long term holocene groundwater fluctuations in a chalk catchment evidence from rock eval pyrolysis of riparian peats he depositional history of peat dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change however in chalkland valleys seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen and there is a need for alternative investigative techniques the method of rock eval pyrolysis can track changes in organic matter source and degradation potentially relating to historic changes in vegetation cover this is the first rock eval on cores from a groundwater dependent riparian chalk valley wetland combined with radiocarbon dating the dating showed that the cores represented approximately 4000 years of depositional history changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species relating to periods of climate wetness these climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest europe however the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment nonetheless this study suggests that rock eval pyrolysis is a useful and cost effective tool that can provide evidence for long term holocene groundwater fluctuations

craters in the vicinity of valles marineris region mars chronological implications to the graben and pits activities abstract graben and pits are features closely associated with the valles marineris vm region on mars earlier studies indicated that they are likely precursors for the vm trough formation and thus they may assist in our understanding of how long the trough formation prevailed in the vicinity of vm this study aims to understand how the graben and pit formation varied chronologically and spatially within a 100 km vicinity of the vm region we examined 1516 craters and found 48 craters that are superposed cross cut by graben pits and troughs or vice versa with adequate ejecta or floor area for dating tithonium region graben and troughs cross cut the craters around 3 7 ga in the ophir region pits are formed on or post 3 92 ga at different elevations and have variable depths pital crater in the ophir region interestingly hosts 1 a broad catena 14 km wide crosscutting its ne rim likely formed on or post to 2 61 ga which inferred to be one tenth to the adjoining candor chasma width of vm 2 lobe like deposits associated with the catena emplaced over the pital ejecta formed around 1 14 ga and 3 2 km wide pit superposed the lobe that reveals pit activity plausibly prolonged during mid amazonian overall our results likely point towards the contribution of graben and pits in the modification development of peripheral areas of vm up to at least mid amazonian thus this study substantiated that the period and extent of graben and pit activities varied around the vm region

radon in chalk streams spatial and temporal variation of groundwater sources in the pang and lambourn catchments uk summary variations in dissolved 222 rn radon concentrations in rivers and groundwater are observed in the cretaceous chalk catchments of the pang and lambourn stream radon concentrations and flow data were used to model radon inputs to rivers from groundwater with the modelled radon input concentrations c i varying between 0 2 bq l 1 and 3 8 bq l 1 consistent with measured groundwater values groundwater in both catchments was found to have higher and more variable radon concentrations 2 12 bq l 1 in the near surface weathered horizons compared to a consistent 1 bq l 1 from the solid chalk the variations in c i can be related to flow generation pathways and hydrological events in the lambourn the radon budget is controlled by diffuse groundwater inputs supporting the hypothesis that the alluvial aquifer plays a greater role during periods of high accretion the pang is more complex than the lambourn having a combination of diffuse and point source inputs with spring inputs dominating both flow and radon signatures in the lower part of the catchment significant temporal and spatial variations were determined for c i in both catchments reflecting their differing geologies and flow regimes one use of radon in hydrology is the determination of groundwater discharges to rivers but the observed variations in c i mean this approach may not be appropriate to all situations and that changes in source need further evaluation nonetheless radon is shown to be a useful tracer of flow paths and processes within these catchments

regional climate change from peat stratigraphy for the mid to late holocene in central ireland at the millennial scale bog surface wetness bsw records show a clear holocene climate event stratigraphy with major phases comparable with other regional climate proxies such as chironomid inferred temperature records moving towards the centennial scale however and towards the limits of chronological certainty within the records regional differences are apparent which likely reflect the more heterogeneous precipitation patterns which occur on shorter timescales the bsw data presented in this paper are reconstructed from testate amoebae assemblages from central ireland and are compared with other regional records the results suggest that this region is in phase with the north of ireland in terms of timings and durations of climate change but the comparisons are less clear with a stacked and tuned record from northern britain that shows an apparent offset compared to the irish records this may reflect variations in past regional precipitation or be a function of the tuning and stacking process the broad phases of comparison between the irish records and the extension of the central irish record back to 6000 cal bp allow comparisons with low frequency temperature reconstructions from chironomids which also show a broad level of correlation with cooler temperatures relating to wetter bsw at centennial to millennial timescales

one million cubic kilometers of fossil ice in valles marineris relicts of a 3 5 gy old glacial landsystem along the martian equator abstract self consistent landform assemblages suggest that valles marineris the giant valley system that stretches along the martian equator was entirely glaciated during late noachian to early hesperian times and still contains huge volumes of fossil ice some of these glacial landform assemblages are illustrated here with representative examples selected in three regions ius chasma central candor chasma and the junction between coprates chasma and capri chasma a morphological boundary separating an upper spur and gully morphology from a smooth basal escarpment has been spectacularly preserved along valley walls throughout valles marineris the boundary winds around topographic obstacles and displays long wavelength variations in elevation it is associated with lateral benches hanging valleys and truncated spurs comparisons with terrestrial analogs indicate that it is most reasonably interpreted as a glacial trimline chasma floors are covered by various kinds of terrains including hummocky terrains platy terrains lateral banks layered benches and a draping mantle landforms in these terrains and their spatial relationship with the interpreted trimline suggest that they correspond to various disintegration stages of an ancient glacial fill currently protected by a superficial cover of ablation till altogether these landforms and terrains compose a full glacial landsystem with wet based glaciers that were able to flow and slide over their beds it was most probably fed by ice accumulating at low elevations directly from the atmosphere onto valley floors and walls with only minor contributions from tributary glaciers flowing down from higher elevations similar fossil glacial landsystems dating back from the early martian history are to be expected in many other low latitude troughs such as chasmata chaos valleys impact craters and other basins

faceted spurs at normal fault scarps insights from numerical modeling 1 we present a combined surface processes and tectonic model which allows us to determine the climatic and tectonic parameters that control the development of faceted spurs at normal fault scarps sensitivity tests to climatic parameter values are performed for a given precipitation rate when hillslope diffusion is high and channel bedrock is highly resistant to erosion the scarp is smooth and undissected when instead the bedrock is easily eroded and diffusion is limited numerous channels develop and the scarp becomes deeply incised between these two end member states diffusion and incision compete to produce a range of scarp morphologies including faceted spurs the sensitivity tests allow us to determine a dimensionless ratio of erosion f for which faceted spurs can develop this study evidences a strong dependence of facet slope angle on throw rate for throw rates between 0 4 and 0 7 mm a facet height is also shown to be a linear function of fault throw rate model performance is tested on the wasatch fault utah using topographic geologic and seismologic data a monte carlo inversion on the topography of a portion of the weber segment shows that the 5 ma long development of this scarp has been dominated by a low effective precipitation rate 1 1 m a and a moderate diffusion coefficient 0 13 m2 a results demonstrate the ability of our model to estimate normal fault throw rates from the height of triangular facets and to retrieve the average long term diffusion and incision parameters that prevailed during scarp evolution using an accurate 2 d misfit criterion

correction to localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution 1 in the paper localized gravity topography admittance and correlation spectra on mars implications for regional and global evolution by patrick j mcgovern sean c solomon david e smith maria t zuber mark simons mark a wieczorek roger j phillips gregory a neumann oded aharonson and james w head journal of geophysical research 107 e12 5136 doi 10 1029 2002je001854 2002 the thickness of the lithosphere and lithospheric heat flow for a number of regions of mars and as functions of time were inferred on the basis of gravity topography admittance spectra observed admittances derived from spherical harmonic expansions localized with the scheme of simons et al 1997 were compared with those predicted from models for the flexural response to lithospheric loading e g turcotte et al 1981 gravity was calculated according to the finite amplitude scheme of wieczorek and phillips 1998 estimates for the thickness of the elastic lithosphere te at the time of loading for each region were converted to equivalent thermal gradient dt dz and heat flux q by means of an elastic plastic stressenvelope formalism mcnutt 1984 here we describe a correction required in the calculation of the modeled gravity anomalies we report new estimates of te load density rl dt dz and q from corrected model admittances and we discuss the implications of the new results 2 the source of the required correction is a difference in reference radius values as defined by mcgovern et al 2002 the planetary shape was taken to equal the radius from the center of mass of mars to the martian surface expressed as a spherical harmonic expansion and referenced to the mean equatorial radius req 3396 km

floodplain environmental change during the younger dryas and holocene in northwest europe insights from the lower kennet valley south central england abstract many lowland rivers across northwest europe exhibit broadly similar behavioural responses to glacial interglacial transitions and landscape development difficulties exist in assessing these largely because the evidence from many rivers remains limited and fragmentary here we address this issue in the context of the river kennet a tributary of the thames since c 13 000 cal bp some similarities with other rivers are present suggesting that regional climatic shifts are important controls the kennet differs from the regional pattern in a number of ways the rate of response to sudden climatic change particularly at the start of the holocene and also mid holocene forest clearance appears very high this may reflect abrupt shifts between two catchment scale hydrological states arising from contemporary climates land use change and geology stadial hydrology is dominated by nival regimes with limited winter infiltration and high spring and summer runoff under an interglacial climate infiltration is more significant the probable absence of permafrost in the catchment means that a lag between the two states due to its gradual decay is unlikely palaeoecology supported by radiocarbon dates suggests that at the very start of the holocene a dramatic episode of fine sediment deposition across most of the valley floor occurred lasting 500 1000 years a phase of peat accumulation followed as mineral sediment supply declined a further shift led to tufa deposition initially in small pools then across the whole floodplain area with the river flowing through channels cut in tufa and experiencing repeated avulsion major floods leaving large gravel bars that still form positive relief features on the floodplain followed mid holocene floodplain stability prehistoric deforestation is likely to be the cause of this flooding inducing a major environmental shift with significantly increased surface runoff since the bronze age predominantly fine sediments were deposited along the valley with apparently stable channels and vertical floodplain accretion associated with soil erosion and less catastrophic flooding the kennet demonstrates that while a general pattern of river behaviour over time within a region may be identifiable individual rivers are likely to diverge from this consequently it is essential to understand catchment controls particularly the relative significance of surface and subsurface hydrology

a high resolution late glacial to holocene record of environmental change in the mediterranean from lake ohrid macedonia albania lake ohrid macedonia albania is the oldest extant lake in europe and exhibits an outstanding degree of endemic biodiversity here we provide new high resolution stable isotope and geochemical data from a 10 m core co1262 through the late glacial to holocene and discuss past climate and lake hydrology tic 13ccalcite 18ocalcite as well as the terrestrial and aquatic vegetation response to climate toc toc n 13corganic rock eval pyrolysis the data identifies 3 main zones 1 the late glacial holocene transition represented by low tic and toc contents 2 the early to mid holocene characterised by high toc and increasing toc n and 3 the late holocene present which shows a marked decrease in tic and toc in general an overall trend of increasing 18ocalcite from 9 ka to present suggests progressive aridification through the holocene consistent with previous records from lake ohrid and the wider mediterranean region several proxies show commensurate excursions that imply the impact of short term climate oscillations such as the 8 2 ka event and the little ice age this is the best dated and highest resolution archive of past late glacial and holocene climate from lake ohrid and confirms the overriding influence of the north atlantic in the north eastern mediterranean the data presented set the context for the international continental scientific drilling program scientific collaboration on past speciation conditions in lake ohrid project cores recovered in spring summer 2013 potentially dating back into the lower pleistocene and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history

toward understanding the history and mechanisms of martian faulting the contribution of gravitational potential energy 1 current stress solutions for mars match the long wavelength signal of present day topography and gravity but fail to match many surface faults including the normal faults in northern claritas fossae north to tantalus and alba fossae a deviatoric stress field associated with horizontal gradients of gravitational potential energy gpe provides an excellent fit as measured by objective functions to many of the normal faults in the western martian hemisphere as well as wrinkle ridges circumferential to tharsis 70 of the faults have a misfit 0 1 the fit of faults to the gpe derived stress field reflects the thermal state of the planet at the times of faulting and suggests that at such times elastic thicknesses and membrane stresses were small and topography was supported by buoyancy forces

testing the use of microfossils to reconstruct great earthquakes at cascadia coastal stratigraphy from the pacific northwest of the united states contains evidence of sudden subsidence during ruptures of the cascadia subduction zone transfer functions empirical relationships between assemblages and elevation can convert microfossil data into coastal subsidence estimates coseismic deformation models use the subsidence values to constrain earthquake magnitudes to test the response of foraminifera the accuracy of the transfer function method and the presence of a pre seismic signal we simulated a great earthquake near coos bay oregon by transplanting a bed of modern high salt marsh sediment into the tidal flat an elevation change that mimics a coseismic subsidence of 0 64 m the transplanted bed was quickly buried by mud after 12 mo and 5 yr we sampled it for foraminifera reconstruction of the simulated coseismic subsidence using our transfer function was 0 61 m nearly identical to the actual elevation change our transplant experiment and additional analyses spanning the a d 1700 earthquake contact at the nearby coquille river 15 km to the south show that sediment mixing may explain assemblage changes previously interpreted as evidence of pre seismic land level change in cascadia and elsewhere