effects of lateral friction on the structural evolution of fold and thrust belts insights from sandbox experiments with implications for the origin of landward vergent thrust wedges in cascadia various factors are inferred to influence the structural evolution of fold and thrust belts or thrust wedges but the effects of lateral friction such as that exerted by the opposite block of a strike slip fault in nature or by sidewalls in analogue models have rarely been given sufficient attention and hence are still far from being fully understood up to now seaward vergent and dually vergent thrust wedges have been satisfactorily explained by the classic coulomb wedge theory and can be well reproduced in analogue and numerical models in contrast landward vergent thrust wedges which are uncommon in nature e g those occurring in the cascadia subduction zone have not yet been adequately explained by the classic coulomb wedge theory and can only be reproduced in a few analogue models under particular conditions in order to look closer at the effects of lateral friction on the structural evolution of fold and thrust belts and to explore the origin of landward vergent thrust wedges we conducted a series of sandbox models under different conditions of lateral friction and various ratios of initial average lateral frictional stress to basal shear stress s d results of our models revealed that in the presence of a weak or ductile basal decollement the direction of lateral friction can dictate not only the deformation propagation direction and the surface slope direction but also the structural vergence of fold and thrust belts fold and thrust belts normally show a structural vergence in the same direction as the direction of lateral friction but a deformation propagation direction and surface slope direction opposite to the direction of lateral friction according to the results of models and the relationships between structural vergence and lateral friction direction occurring both in cascadia and the analogue models we propose that an extremely high s d ratio due to an extremely weak basal decollement and landward directed lateral friction exerted by the opposite blocks of basement involved strike slip faults are probably the two key factors responsible for the origin of landward vergent thrust wedges in cascadia this work illustrates that effects of lateral friction should be properly taken into account both in the kinematic analysis and designs of models to simulate fold and thrust belts in the presence of weak or ductile basal decollements

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

lineated valley fill lvf and lobate debris aprons lda in the deuteronilus mensae northern dichotomy boundary region mars constraints on the extent age and episodicity of amazonian glacial events abstract in order to assess the nature degradational processes and history of the dichotomy boundary on mars we conducted a detailed morphological analysis of a 70 000 km 2 region of its northern portion north central deuteronilus mensae south of lyot in the vicinity of sinton crater this region is characterized by the distinctive sinuous 2 km high plateau scarp boundary outlying massifs to the north and extensive fretted valleys dissecting the plateau to the south these features represent the first order modification and retreat of the dichotomy boundary and are further modified by processes that form lineated valley fill lvf in the fretted valleys and lobate debris aprons lda along the dichotomy scarp and surrounding the outlying massifs we use new high resolution image and topography data to examine the nature and origin of lvf and lda and to investigate the climatic and accompanying degradational history of the escarpment on the basis of our analysis we conclude that 1 lvf and lda deposits within the study region are comprised of the same material show integrated flow patterns and originate as debris covered valley glaciers a significant amount of ice hundreds of meters is likely to remain today beneath a thin cover of sublimation till 2 there is depositional evidence to suggest glacial highstands at least 800 m above the present level implying previous conditions in which the distribution of ice was much more widespread this is supported by similar deposits within many other areas across the dichotomy boundary 3 the timing of the most recent large scale activity of the lda lvf in this area is about 100 500 million years ago similar to ages reported elsewhere along the dichotomy boundary 4 there is evidence for a secondary but significantly limited phase of glaciation the deposits of which are limited to the vicinity of the alcoves similar later phases have also been reported elsewhere along the dichotomy boundary 5 modification of the fretted valleys of the dichotomy boundary has been substantial locally but we find no evidence that the amazonian glacial epochs caused retreat of the dichotomy boundary of the scale of tens to hundreds of kilometers our findings support the results of an analysis just to the east of the study region and of studies carried out elsewhere along the dichotomy boundary that find further evidence for the remnants of debris covered glaciers and extensive valley glacial land systems

concentric crater fill in the northern mid latitudes of mars formation processes and relationships to similar landforms of glacial origin abstract hypotheses accounting for the formation of concentric crater fill ccf on mars range from ice free processes e g aeolian fill to ice assisted talus creep to debris covered glaciers based on analysis of new ctx and hirise data we find that concentric crater fill ccf is a significant component of amazonian aged glacial landsystems on mars we present mapping results documenting the nature and extent of ccf along the martian dichotomy boundary over 30 to 90 e latitude and 20 80 n longitude on the basis of morphological analysis we classify ccf landforms into classic ccf and low definition ccf classic ccf is most typical in the middle latitudes of the analysis area 30 50 n while a range of degradation processes results in the presence of low definition ccf landforms at higher and lower latitudes we evaluate formation mechanisms for ccf on the basis of morphological and topographic analyses and interpret the landforms to be relict debris covered glaciers rather than ice mobilized talus or aeolian units we examine filled crater depth diameter ratios and conclude that in many locations hundreds of meters of ice may still be present under desiccated surficial debris this conclusion is consistent with the abundance of ring mold craters on ccf surfaces that suggest the presence of near surface ice analysis of breached craters and distal glacial deposits suggests that in some locations ccf related ice was once several hundred meters higher than its current level and has sublimated significantly during the most recent amazonian crater counts on ejecta blankets of filled and unfilled craters suggests that ccf formed most recently between 60 and 300 ma consistent with the formation ages of other martian debris covered glacial landforms such as lineated valley fill lvf and lobate debris aprons lda morphological analysis of ccf in the vicinity of lvf and lda suggests that ccf is a part of an integrated lvf lda ccf glacial landsystem instances of morphological continuity between ccf lvf and lda are abundant the presence of formerly more abundant ccf ice coupled with the integration of ccf into lvf and lda suggests the possibility that ccf represents one component of the significant amazonian mid latitude glaciation s on mars

do young martian ray craters have ages consistent with the crater count system abstract mcewen et al mcewen a s preblich b s turtle e p artemieva n a golombek m p hurst m kirk r l burr d m christensen p 2005 icarus 176 351 381 developed a useful test for the internal consistency of crater count chronometry systems they argued that certain multi kilometer fresh looking martian craters with prominent rays should be the youngest or near youngest craters in their size range the mcewen et al test is that the ages determined from crater densities of the smallest superimposed craters typically diameter d 5 20 m should thus be comparable to the expected formation intervals of the host primary mcewen et al concluded from moc data that crater chronometry failed this test by factors of 700 2000 we apply hirise and other imagery to eight different young craters in order to re evaluate their arguments we use existing crater chronology systems as well as the reported observed production rate of 16 m craters malin m c edgett k posiolova l mccolley s noe dobrea e 2006 science 314 1573 1557 hartmann w k quantin c mangold n 2007 icarus 186 11 23 kreslavsky 2007 seventh international conference on mars 3325 every case passes the mcewen et al test we conclude that the huge inconsistencies suggested by mcewen et al are spurious many of these craters show evidence of impact into ice rich material and appear to have ice flow features and sublimation pits on their floors as production rate data improve decameter scale craters will provide a valuable way of dating these young martian geological formations and the processes that modify them

geomorphic signatures of glacial activity in the alba patera volcanic province implications for recent frost accumulation on mars 1 glacial periglacial landforms lying within impact craters on mars have led to the identification of two mechanisms for their formation 1 intermittent deposition of atmospherically emplaced snow ice during past spin axis orbital conditions and 2 flow of debris covered ice rich deposits the maximum presence of the young ice snow rich features thermal contraction crack polygons gullies arcuate ridges and lobate debris tongues was observed on the pole facing slope indicating that this slope was the preferred site for ice snow accumulation during the last 10 ma in this study we investigated 30 craters lying in the alba patera volcanic province in the latitudinal bands between 45 n and 32 4 n morphological comparison of the younger ice snow rich features in these craters led us to conclude that glacial periglacial features in alba patera are mainly present within pole facing slopes of craters lying within 45 n 39 n the craters lying within 40 2 n 40 n did not show any glacial periglacial features we suggest that the formation of these young ice snow rich features follows the same orientation trends as those of other older 10 ma glacial features debris covered ice snow rich large deposits at the base of the crater wall in the region the present work has revealed that the onset of physical processes that result in the formation of glacial periglacial landforms is also dependent on the changes in elevation ranges of the investigated craters in alba patera our results confirm past inferences for accumulation of ice snow on mars and suggest that the period of ice snow accumulation activity in alba patera occurred throughout the amazonian and lasted until the recent past i e 2 1 0 4 ma

dynamics of ice ages on mars mars experiences much greater fluctuations in exposure to sunlight than the earth does because of larger variations in astronomical factors such as the tilt of its axis relative to the orbital plane climate change is accordingly more intense on mars than on earth norbert schorghofer has now developed a climate model that accounts for the advance and retreat of the subsurface martian ice sheets over forty major ice ages and five million years this explains the present distribution of subsurface ice on mars in addition lessons learned from the long and relatively simple martian ice age stratigraphy should help when it comes to interpreting the more complicated events here on earth numerical simulation and modelling of the retreat and growth of ground ice on mars demonstrates how the subsurface ice sheets could have evolved and ended up in the state we see them today and also reveals that 40 major ice ages occurred on mars over the past 5 million years unlike earth where astronomical climate forcing is comparatively small mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale1 2 3 4 5 6 the geographic extent of the subsurface ice found poleward of approximately 60 latitude on both hemispheres of mars7 8 9 coincides with the areas where ice is stable7 10 11 however the tilt of mars rotation axis obliquity changed considerably in the past several million years earlier work3 12 has shown that regions of ice stability which are defined by temperature and atmospheric humidity differed in the recent past from today s and subsurface ice is expected to retreat quickly when unstable11 12 13 here i explain how the subsurface ice sheets could have evolved to the state in which we see them today simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years today this gives rise to pore ice at mid latitudes and a three layered depth distribution in the high latitudes of from top to bottom a dry layer pore ice and a massive ice sheet combined these layers provide enough ice to be compatible with existing neutron and gamma ray measurements7 8 9

does the holton tan mechanism explain how the quasi biennial oscillation modulates the arctic polar vortex idealized experiments with the whole atmosphere community climate model waccm are used to explore the mechanism s whereby the stratospheric quasi biennial oscillation qbo modulates the northernhemispherewintertimestratosphericpolarvortex overall theeffectofthecriticallineemphasized in the holton tan mechanism is less important than the effect of the mean meridional circulation associated with qbo winds for the polar response to the qbo more specifically the introduction of easterly winds at the equator near 50 hpa 1 causes enhanced synoptic scale eliassen palm flux epf convergence in the subtropics from 150 to 50 hpa which leads to the subtropical critical line moving poleward in the lower stratosphere and2 createsabarriertoplanetarywavepropagationfromsubpolarlatitudestomidlatitudesin the middle andupper stratosphere e g less equatorwardepf near 508n whichleads to enhancedplanetary wave convergence in the polar vortex region these two effects are mechanistically distinct while the former is relatedtothesubtropicalcriticalline thelatterisduetothemeanmeridionalcirculationofthe qbo allof these effects are consistent with linear theory although the evolution of the entire wind distribution is only quasi linear because induced zonal wind changes cause the wave driving to shift and thereby positively feed back on the zonal wind changes finally downward propagation of the qbo in the equatorial stratosphere upper stratospheric equatorial zonal wind and changes in the tropospheric circulation appear to be less important than lower stratospheric easterlies for the polar stratospheric response overall an easterly qbo wind anomaly in the lower stratosphere leads to a weakened stratospheric polar vortex in agreement with previous studies although not because of changes in the subtropical critical line

control of clay mineral stratigraphy by selective transport in late pleistocene holocene sediments of northern cascadia basin juan de fuca abyssal plain implications for studies of clay mineral provenance abstract previous investigations duncan and others 1970 stokke and carson 1974 of cascadia basin clay mineralogy indicate a general trend in which montmorillonoids smectites 17 a are enriched relative to illite 10 a and chlorite 7 a in holocene lutites whereas illite and chlorite dominate in late pleistocene deposits the apparent crystallinity of all clay mineral groups declines from pleistocene to holocene russell 1967 there exist however numerous local exceptions to these general patterns which are not readily explained by the previous works fifteen samples from 5 cores in northern cascadia basin and juan de fuca abyssal plain were fractionated into 6 size classes semi quantitative determinations of clay mineralogy and crystallinity were made on each of the 90 subsamples the results indicate a definite size dependency in clay mineralogy and crystallinity which is consistent both areally and temporally discriminant function analysis indicates that clay mineralogy and crystallinity of some individual size fractions are statistically distinct but that the stratigraphic units late holocene early holocene and late pleistocene are not statistically discernible textural variations within and between holocene and pleistocene parallel sediment clay mineral changes and mineralogy can be predicted on the basis of clay min ral size dependency and grain size distribution it is inferred that the stratigraphic textural mineralogic variations result from selective transport and deposition and not from contrasting source areas or weathering conditions as had previously been suggested duncan and others 1970 stokke and carson 1974 future investigations of clay mineral provenance dispersal or correlation in any area should be based upon data which has been corrected for the effects of clay mineral size dependency

linear volcanic features at alba patera mars probable spatter ridges a number of extensive linear constructional features occur on the north and east flanks of alba patera they are found in a 150 km wide zone and comprise aligned ridge elements that are locally associated with short volcanic flows they are among the youngest volcanic features in the region and are believed to be martian analogs of terrestrial spatter ridges on the basis of measurements made on viking images it appears that active volcanic fissures on mars were larger than their terrestrial counterparts

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

distribution and orientation of northern hemisphere gullies on mars from the evaluation of hrsc and moc na data abstract martian gullies show morphologic characteristics that indicate the presence of a flowing liquid during their formation process however the current climate in the northern hemisphere of mars does not allow the existence of substantial amounts of liquid water and therefore an assessment of the regional distribution and characteristics of gullies is required in order to understand the most recent climatic development of mars we examined high resolution stereo camera hrsc and mars orbiter camera narrow angle moc na data covering the northern hemisphere in order to determine the distribution geological setting and orientation of gullied slopes we used these results to test the consistency of formation models proposed in earlier works and to define the climate dependence gully orientations were analyzed only at impact crater walls because craters have an azimuthally uniform distribution of slopes this is ideal when investigating the influence of insolation on the distribution and development of landforms we examined 230 hrsc and 21 000 moc na images and identified more than 2200 gullies on hrsc and more than 3100 gullies in moc na data both surveys show the highest densities of gullies between 35 n and 55 n and a shift of gully orientation at 40 n from pole facing slopes to slopes facing the equator orientation trends as well as the latitudinal distribution of identified gullies strongly support the view of gully formation caused by insolation climatic conditions this result suggests that formation mechanisms based on the assumption of atmospheric water ice deposition proposed in earlier work are more likely than processes related to groundwater flow further support for a theory related to deposition is gained through observation of the high occurrence of gullies at isolated knobs and hills which cannot be associated with formation models based upon groundwater flow

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

landward vergence and oblique structural trends in the oregon margin accretionary prism implications and effect on fluid flow abstract the central oregon margin spans a regional transition in accretionary structures from seaward verging in the south to landward verging in the north new multichannel seismic mcs data image both landward and seaward vergent provinces along the central and northern oregon margin landward vergence is characterized by a deep decollement with deformation distributed across a broad lower continental slope in a coherent structural style in the landward vergent area virtually all 4 km of incoming trench sediments overthrust the preceding thrust sheet forming fault bend folds and a distinctive ridge trough morphology this style of landward vergence is not explained by existing models in contrast seaward vergence correlates with a shallower decollement approximately 1 4 km above the oceanic crust and a more intense style of deformation within a narrower slope initial thickening of the trench sediments occurs across a well developed protothrust zone the frontal thrust forms a ramp anticline that is cut by a prominent backthrust previously observed seafloor vent sites in both regions correlate with thrusts that exhibit high amplitude reversed polarity reflections suggestive of enhanced porosity along the faults potential fluid sources and migration paths are strongly influenced by changes in the level of the decollement and vergence along the margin abrupt changes in structural style occur both along strike and updip and are bounded by two sets of oblique slip faults three nw striking left lateral faults are imaged in both mcs and seabeam data plunging anticlines developed along the nw striking faults are venting fluids and were previously interpreted as mud volcanoes the deformation front is locally disrupted where these faults intersect the prism but they appear to have limited influence on the structural evolution of the prism in contrast the ne striking right lateral faults are confined to the deforming sediments of the upper plate these faults interact with the thrusts within the prism forming a rhomboidal pattern of three dimensional deformation

shortening of analogue models with contractive substrata insights into the origin of purely landward vergent thrusting wedge along the cascadia subduction zone and the deformation evolution of himalayan tibetan orogen abstract origin of certain uncommon fold and thrust belts such as the purely landward vergent rearward vergent thrusting wedge along the cascadia subduction zone and the wide flat toped himalayan tibetan orogen were proposed to be closely related to their ductile substrata results of a series of sandbox models with contractive substrata of various contracting velocities and different contracting directions designed to study the influences of horizontal contraction of ductile substrata on deformation evolution and structural style of fold and thrust belts show that purely rearward vergent thrusting wedges can be reproduced under the condition of syn directionally horizontal contraction of the ductile substrata without other requirements of forward dipping backstops landward dipping detachments and strong wedges relative to weak bases therefore syn directionally horizontal contraction of the ductile substrata can be considered an important cause for the formation of purely landward vergent thrusting wedge along the cascadia subduction zone our modeling results together with the results of some other previous physical and numerical models reinforce the opinion that the deformation evolution of the himalayan tibetan orogen were likely governed by its weak lower crust and suggest that the north and south edges of the himalayan tibetan orogen may have undergone almost synchronous cenozoic deformation evolution owing to the existence of weak lower crust it is also proposed that 1 development of thrusts in the himalayan tibetan orogen may not necessarily occur in a frontward sequence 2 much later uplift deduced from cenozoic sedimentary records in the basins along the northeastern margin of the himalayan tibetan orogen does not necessarily imply much later initiation of uplift and deformation at the northeastern margin of the orogen

release of mineral bound water prior to subduction tied to shallow seismogenic slip off sumatra plate boundary fault rupture during the 2004 sumatra andaman subduction earthquake extended closer to the trench than expected increasing earthquake and tsunami size international ocean discovery program expedition 362 sampled incoming sediments offshore northern sumatra revealing recent release of fresh water within the deep sediments thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial induced temperature increases in the past 9 million years complete dehydration of silicates is expected before plate subduction contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction shallow slip offshore sumatra appears driven by diagenetic strengthening of deeply buried fault forming sediments contrasting with weakening proposed for the shallow tohoku oki 2011 rupture but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records

effect of clay content and mineralogy on frictional sliding behavior of simulated gouges binary and ternary mixtures of quartz illite and montmorillonite 1 we investigated the frictional sliding behavior of simulated quartz clay gouges under stress conditions relevant to seismogenic depths conventional triaxial compression tests were conducted at 40 mpa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz montmorillonite and illite in all cases frictional strengths of mixtures fall between the end members of pure quartz strongest and clay weakest the overall trend was a decrease in strength with increasing clay content in the illite quartz mixture the trend was nearly linear while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers two micromechanical models were used to analyze the critical clay fractions for the two regime transitions on the basis of clay porosity and packing of the quartz grains the transition from regime 1 high strength to 2 intermediate strength is associated with the shift from a stress supporting framework of quartz grains to a clay matrix embedded with disperse quartz grains manifested by the development of p foliation and reduction in riedel shear angle the transition from regime 2 intermediate strength to 3 low strength is attributed to the development of shear localization in the clay matrix occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects

sources and dispersal patterns of clay minerals in surface sediments from the continental shelf areas off alaska the three mineral suites were recognized in the gulf of alaska the glaciomarine sediments of fjords and the eastern shelf consist typically of the primary phyllosilicates micas and chlorites derived locally from argillite graywacke and metavolcanics under conditions of mild chemical weathering more glycol expandable clay minerals gecm in the north gulf substantiate clay supply to that region primarily from the yakataga and poul creek formations and to a lesser extent from the copper river the northern gulf clay mineral suite is transported to central prince william sound and northeast kodiak shelf by the alaska coastal current in the western gulf clay minerals adjacent to the alaska peninsula are derived principally from the susitna river via cook inlet whereas those of the outer shelf presumably have their provenance in kodiak island and the katmai ash submarine deposit in the southeast bering sea a progressive northwestward decrease in gecm from 65 to 11 is caused by a gradually decreased sediment export from the alaska peninsula and the aleutians with a possible minor increase in illite from the kuskokwin river the yukon river is the predominant clay source for the north bering sea as signified by an abrupt increase in that area of gecm 20 to 35 and of kaolinite chlorite ratios clay mineralogy indicates that the central chukchi sea is the major repository of the yukon clays suggesting that clay mineral stratigraphic studies have implications for interpretation of the quaternary paleogeography of beringia in the beaufort sea nearshore influence of different fluvial inputs and their dispersals by currents are sharply defined the lack of a definite pattern to the distribution of clay minerals in the outer continental shelf may be due to haphazard transport of clays by ice rafting and or reworking and redistribution of sediments resulting from ice gouging of the sea substrate movement of sediment to the west in the alaskan portion of the inner shelf of beaufort sea is evident an apparent seaward increase in illite gecm ratio in the colville delta is tentatively ascribed to regeneration of degraded illite micas by k fixation in saline waters an isolated area of sediment rich in expandable clay minerals in the central beaufort shelf presumably is relict

polygenic eruptions on alba patera mars a combination of photogeologic mapping analysis of viking orbiter thermal inertia data and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano alba patera numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non juvenile water from unconsolidated flank deposits using the thermal inertia measurements we estimate the particle size of these deposits to be 3 10 m which together with theoretical modelling of the disperison of explosively derived volcanic materials leads us to conclude that the flank deposits on alba patera are low relief pyroclastic flows the recognition of numerous late stage summit and sub terminal lava flows thus makes alba patera a unique martian volcano that is transitional between the older pyroclastic dominated highland paterae and the more recent effusive central vent volcanoes such as the tharsis montes

accretion and recent deformation of sediments along the northern cascadia subduction zone new multichannel seismic reflection profiles acoustic imagery and swath bathymetric data from the vancouver island continental margin reveal the surface morphology cross sectional geometry and deformation style of this part of the cascadia accretionary prism the incoming 3 to 5 km thick sediment section fails most commonly along landward dipping thrusts that penetrate to or very close to the top of the underlying oceanic crust the faults are listric with approximately circular cross sections and hanging wall sediments are back tilted in a planar manner high near lithostatic pore pressures in the deeper part of the section are inferred from the flattening of the faults near the decollement and from the long distances over which the decollement has propagated seaward the faults dip more steeply at 40 45 near the surface where pleistocene turbidites are displaced similar folds have developed where the turbidites are particularly thick 4 km and near hydrostatic pore pressures are inferred to occur in the turbidite part of the section an increase in pore pressure with depth is expected as a consequence of sedimentation and tectonic loading particularly because the deeper hemipelagic sediments are probably far less permeable than are the overlying turbidites the top of the downgoing juan de fuca plate which defines the base of the accreted sedimentary wedge beneath the margin is well imaged in the new seismic reflection profiles and is further defined by land reflection data seismic refraction and earthquake hypocenters the landward dipping continental backstop to the prism is also well located if these constraints are used for the geometry of the accretionary prism a general balance is found between the present prism volume and the estimated total sediment supply over the approximately 42 m y accretion history this result along with the observation that deformation front faults penetrate most or all of the sediment section suggests that little or no sediment has been subducted since initiation of the present phase of subduction in the eocene application of the critically tapered wedge model of davis and others to the observed prism geometry suggests that high average pore pressures occur in the prism particularly the seawardmost part beneath the lower slope beneath the continental shelf the dip of the subducting slab increases to greater than 11 a dip that according to the critically tapered wedge model is too steep to allow upward growth of an accretionary prism this provides a simple explanation for ongoing subsidence of the tofino sedimentary basin over the older part of the accretionary complex to the southeast the juan de fuca plate dips much more gently beneath the olympic peninsula of northern washington allowing the accretionary prism to grow upward well above sea level to form the olympic mountains

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

fluid history related to the early eocene middle miocene convergent system of the northern apennines italy constraints from structural and isotopic studies 1 the late eocene middle miocene erosive plate boundary between the european and the adriatic plates is exhumed in the northern apennines of italy the fossil fault zone is 500 m thick and the outcropping portion exposes the first 5 km of its depth at this plate boundary basal and frontal tectonic erosion incorporated unlithified fluid rich sediments into the fault zone the deformation and nature of the material along the plate boundary define a fossil subduction channel here we couple a detailed structural analysis of the apennine subduction channel focusing in particular on calcite veins with a stable isotope analysis to characterize the fluid regime along an active subduction channel the 13c and 18o composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upward along the subduction channel in addition to locally derived fluid components dewatering of subducting turbidites contributes significantly only in the shallowest part of the channel structural observations indicate fluid flow along and across the subduction channel at deep levels fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs filled with implosion breccias at intermediate levels deformation is still cyclic and associated with repeated crack and seal events at the shallowest levels deformation occurred while portions of the subducting material were still unlithified here the deformation was quasicontinuous without associated vein development both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak fault with a vertical maximum principal stress

interseismic uplift rates for western oregon and along strike variation in locking on the cascadia subduction zone 1 we quantify the spatial pattern of uplift rate in western oregon and northernmost california using tidal and leveling records to better understand the pattern of interseismic locking on the cascadia subduction zone we extend relative sea level time series of the six primary noaa tide gauges to include all observations from 1925 to 2006 previously unidentified bench mark instability biases portions of tidal records by 1 6 mm a 1 before correction we determine precise relative uplift rates at the six tidal sites with an adjustment that includes rates of differenced time series as additional constraints our analysis of national geodetic survey leveling data between tide gauges corrects errors in 1941 leveling and 184 secondary ties double the number of highest quality uplift rate estimates relative uplift rates from leveling are adjusted to the tidal rates accounting for uncertainties in both data types tidal and leveling uplift rates agree within error for all but one of the coastal segments where we infer systematic leveling error affects the 1988 line uplift rates are made absolute using an interval and location specific geocentric sea level rise rate of 2 3 0 2 mm a 1 total propagated one sigma errors for the absolute uplift rates of bench marks are 0 4 mm a 1 along strike changes in uplift rate near 45 n and 42 8 n require two distinct changes in locking depth as inferred from elastic dislocation modeling the along strike changes in locking on this portion of the cascadia subduction zone interface correlate to the western and southern extent of the mafic siletzia block in the fore arc

negative polarity seismic reflections along faults of the oregon accretionary prism indicators of overpressuring either thrusting of higher over lower impedance sediment or reduction of impedance locally in the fault zone can produce negative polarity reflections along the protothrusts and the frontal thrust of the oregon accretionary prism the vertical displacement of protothrusts averages only 27 m is uncorrelated to the occurrence of polarity reversals and is insufficient to generate the impedance contrasts associated with the negative polarity reflections the negative polarity reflections from the protothrusts are probably due to localized impedance reduction in the fault zone waveform modeling of these negative polarity reflections indicates they develop due to a single interface with negative impedance contrast this seismic signal could be produced by a fault zone with a sharp upper boundary with low impedance fault material and a transition down section to sediment of higher impedance an impedance inversion due to the 1 km throw on the frontal thrust could create the observed negative polarity reflections interval velocities do not decrease across the frontal thrust but core scale velocity measurements indicate a velocity decrease in the frontal thrust therefore the negative polarity reflections are apparently produced by a localized decrease in impedance waveform modeling of frontal thrust reflections suggests the low impedance interval is about 20 m thick with discrete upper and lower boundaries moderately dipping faults are an efficient path for fluid expulsion across the turbidites with low equivalent vertical permeability fluid migration from the over pressured section up the faults can locally reduce the velocity sufficiently to cause the negative polarity reflections

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

gasa impact crater mars very young gullies formed from impact into latitude dependent mantle and debris covered glacier deposits abstract the mode of formation of gullies on mars very young erosional depositional landforms consisting of an alcove channel and fan is one of the most enigmatic problems in martian geomorphology major questions center on their ages geographic and stratigraphic associations relation to recent ice ages and if formed by flowing water the sources of the water to cause the observed erosion deposition gasa 35 72 s 129 45 e a very fresh 7 km diameter impact crater and its environment offer a unique opportunity to explore these questions we show that gasa crater formed during the most recent glacial epoch 2 1 0 4 ma producing secondary crater clusters on top of the latitude dependent mantle ldm interpreted to be a layered ice dust rich deposit emplaced during this glacial epoch high resolution images of a pre gasa impact crater 100 km northeast of gasa reveal that portions of the secondary crater covered ldm have been removed from pole facing slopes in crater interiors near gasa gullies are preferentially located in these areas and channels feeding alcoves and fans can be seen to emerge from the eroding ldm layers to produce multiple generations of channel incision and fan lobes we interpret these data to mean that these gullies formed extremely recently in the post gasa impact time period by melting of the ice rich ldm stratigraphic and topographic relationships are interpreted to mean that under favorable illumination geometry steep pole facing slopes and insolation conditions melting of the debris covered ice rich mantle took place in multiple stages most likely related to variations in spin axis orbital conditions closer to gasa in the interior of the 18 km diameter ldm covered host crater in which gasa formed the pole facing slopes display two generations of gullies early somewhat degraded gullies have been modified by proximity to gasa ejecta emplacement and later fresh appearing gullies are clearly superposed cross cut the earlier phase and show multiple channels and fans interpreted to be derived from continued melting of the ldm on steep pole facing slopes thus we conclude that melting of the ice rich ldm is a major source of gully activity both pre gasa crater and post gasa crater formation the lack of obscuration of gasa secondary clusters formed on top of the ldm is interpreted to mean that the gasa impact occurred following emplacement of the last significant ldm layers at these low latitudes and thus near the end of the ice ages this interpretation is corroborated by the lack of ldm within gasa however gasa crater contains a robustly developed set of gullies on its steep pole facing slopes unlike other very young post ldm craters in the region how can the gullies inside gasa form in the absence of an ice rich ldm that is interpreted to be the source of water for the other adjacent and partly contemporaneous gullies analysis of the interior floor and walls of the host crater suggest that prior to the gasa impact the pole facing walls and floor were occupied by remnant debris covered glaciers formed earlier in the amazonian which are relatively common in crater interiors in this latitude band we suggest that the gasa impact cratering event penetrated into the southern portion of this debris covered glacier emplaced ejecta on top of the debris layer covering the ice and caused extensive melting of the buried ice and flow of water and debris slurries on the host crater floor inside gasa the impact crater rim crest and wall intersected the debris covered glacier deposits around the northern pole facing part of the gasa interior we interpret this exposure of ice rich debris covered glacial material in the crater wall to be the source of meltwater that formed the very well developed gullies along the northern pole facing slopes of gasa crater

clay mineralogy of a glacially dominated subarctic continental shelf northeastern gulf of alaska abstract glaciation is the single most important process responsible for contributing sediment to the northeastern gulf of alaska continental shelf over 75 percent of the northeastern gulf s drainage basin is presently ice covered or only recently has emerged from beneath holocene glacial ice many glaciers terminate in rivers that drain into the gulf or terminate in tidewater bays this study examines the mineralogy of the northeastern gulf of alaska continental shelf clay minerals in light of the glacially dominant nature of the area analyses of 110 bottom samples from the gulf of alaska continental shelf between icy point and prince william sound show an average clay mineral assemblage of 61 percent kaolinite chlorite 37 percent illite and 2 percent smectite over most of the shelf deviations from the average composition are generally 10 percent one significant exception is an area south of the copper river where illite content is as high as 65 percent and kaolinite chlorite ranges from 35 to 48 percent suspended sediment and bottom samples collected in successive years from the copper river the largest sediment source to the gulf have variations in clay mineralogy suggesting that different tributaries and hence different source areas control the composition of the river s mineralogy during different years upper river sources are rich in kaolinite chlorite whereas illite rich sediment is introduced in the lower 100 km transportation of sediment south of the copper river across the shelf and into prince william sound is documented by a decrease in illite from a continental shelf point source south of the river s mouth in addition to modern fluvial input a second source of the modern shelf sediment appears to be the glacially derived miocene to quaternary yakataga formation older formations such as the poul creek and katalla formations show fewer compositional similarities to nearby shelf sediment

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

strike parallel variations in clay minerals and fault vergence in the cascadia subduction zone clay minerals probably affect the zonation of mechanical properties within a thick unit of abyssal plain deposits as they enter the cascadia subduction zone landward vergent thrust faults develop above a deeper decollement because smectite rich mudrocks within that corridor release more water during clay dehydration which in turn elevates pore pressure and reduces basal shear stress relative to wedge strength conversely di lution of smectite by illite and chlorite increases the frictional coefficient and fluid over pressure should drop where smectite dehydration is volumetrically reduced thus thrust faults within chlorite rich segments of the margin are seaward vergent

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

periglacial mass wasting landforms on mars suggestive of transient liquid water in the recent past insights from solifluction lobes on svalbard abstract on earth periglacial solifluction is a slow mass wasting process related to freeze thaw activity we compare the morphology of small scale lobate features on mars to solifluction lobes in svalbard to constrain their processes of formation the analysis is based on high resolution satellite imagery of mars hirise 25 cm pxl aerial images of svalbard with a similar spatial resolution hrsc ax 20 cm pxl acquired through an air campaign in summer 2008 and ground truth obtained during two summer expeditions in 2009 and 2011 on svalbard we present a detailed study of two crater environments on mars displaying two types of lobate forms characterized as sorted clast banked and non sorted lobes on both svalbard and mars such lobes typically occur as clusters of overlapping risers lobe fronts pointing to differential velocities in the soil the martian small scale lobes have well defined arcuate risers and lobe treads surface lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m riser height is estimated to be approximately 1 5 m the lobes on mars share the plan view morphology of solifluction lobes on svalbard and their morphometry is within the range of values of terrestrial solifluction lobes the lobes are distinct from permafrost creep landforms such as rock glaciers we show the results of a survey of 53 hirise images covering latitudes between 59 n and 81 n similar to svalbard the studied lobate features on mars occur in close spatial proximity to gullies and thermal contraction polygons the widespread distribution of the lobate forms in the northern hemisphere and their close association to ground ice and gullies are best explained by mass wasting processes related to frost creep gelifluction and or plug like flow this suggests a protracted process thousand to several thousands of years of freeze thaw activity at the northern high latitudes on mars age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years

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

preservation of late amazonian mars ice and water related deposits in a unique crater environment in noachis terra age relationships between lobate debris tongues and gullies abstract the amazonian period of mars has been described as static cold and dry recent analysis of high resolution imagery of equatorial and mid latitude regions has revealed an array of young landforms produced in association with ice and liquid water because near surface ice in these regions is currently unstable these ice and water related landforms suggest one or more episodes of martian climate change during the amazonian here we report on the origin and evolution of valley systems within a degraded crater in noachis terra asimov crater the valleys have produced a unique environment in which to study the geomorphic signals of amazonian climate change new high resolution images reveal hesperian aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris via mass wasting for the surrounding annular valleys the occurrence of steep slopes 20 relatively narrow sheltered valleys and a source of debris have provided favorable conditions for the preservation of shallow ice deposits detailed mapping reveals morphological evidence for viscous ice flow in the form of several lobate debris tongues ldt superimposed on ldt are a series of fresh appearing gullies with typical alcove channel and fan morphologies the shift from ice rich viscous flow formation to gully erosion is best explained as a shift in martian climate from one compatible with excess snowfall and flow of ice rich deposits to one consistent with minor snow and gully formation available dating suggests that the climate transition occurred 8 ma prior to the formation of other small scale ice rich flow features identified elsewhere on mars that have been interpreted to have formed during the most recent phases of high obliquity taken together these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

non coulomb wedges wrong way thrusting and natural hazards in cascadia landward vergence in accretionary wedges is an uncommon phenomenon not readily explained by classical mohr coulomb critical wedge theory predominantly landward vergent thrust faults are observed along the cascadia convergent margin from 45 n to 48 n we present depth migrated multichannel seismic images of the internal structure of the accretionary wedge offshore washington collected during the orwell project in 1996 these reveal a high p wave velocity 4 km s basal layer that thickens landward and serves as a decollement for a series of overlying landward vergent thrust faults analog modeling using a ductile basal layer consisting of silicone putty produces an array of trenchward propagating landward vergent thrusts and offers a plausible mechanical model for the evolution of these structures the rheological properties of a basal calcareous mudstone layer offshore cascadia are discussed in relation to the mechanics of landward vergence and to rapid loading due to the prograding nitinat and astoria deep sea fans a viscoelastic layer beneath the accretionary wedge is considered to be capable of rupturing during great interplate earthquakes and thus represents an increased risk for both the maximum size of such an event and for the generation of tsunamis

links between sediment consolidation and cascadia megathrust slip behaviour at sediment rich subduction zones megathrust slip behaviour and forearc deformation are tightly linked to the physical properties and in situ stresses within underthrust and accreted sediments yet the role of sediment consolidation at the onset of subduction in controlling the downdip evolution and along strike variation in megathrust fault properties and accretionary wedge structure is poorly known here we use controlled source seismic data combined with ocean drilling data to constrain the sediment consolidation and in situ stress state near the deformation front of the cascadia subduction zone offshore washington where the megathrust is inferred to be strongly locked we find over consolidated sediments near the deformation front that are incorporated into a strong outer wedge with little sediment subducted these conditions are favourable for strain accumulation on the megathrust and potential earthquake rupture close to the trench in contrast offshore central oregon a thick under consolidated sediment sequence is subducting and is probably associated with elevated pore fluid pressures on the megathrust in a region where reduced locking is inferred our results suggest that the consolidation state of the sediments near the deformation front is a key factor contributing to megathrust slip behaviour and its along strike variation and it may also have a significant role in the deformation style of the accretionary wedge consolidated sediments in the cascadia subduction zone may create conditions favourable for megathrust earthquake ruptures over long distances and close to the trench according to analyses of seismic velocity of sediments from the region less consolidated sediments instead may promote aseismic slip of the plate boundary