orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

practical equivalent continuum characterization of jointed rock masses a simple practical method to characterize the strength and stiffness of jointed rock masses is presented in this paper the empirical relations for the strength and stiffness of rock masses have been arrived based on the statistical analysis of a large amount of experimental data which are used for representing the jointed rock mass as an equivalent continuum the effect of joints in the rock mass is taken into account by a joint factor these obtained relations are incorporated in a non linear fem code to represent the equivalent continuum analysis the equivalent continuum model has been validated against experimental results for jointed rock masses with different joint fabric and joint orientation and also with the results from explicit modeling of joints using fem the developed model has also been applied to calculate the deformation around a large power station cavern in rhyolite rock at 200 m depth

stochastic analysis of strength and deformability of fractured rocks using multi fracture system realizations this thesis presents a systematic numerical modeling framework to simulate the stress deformation and coupled stress deformation flow processes by performing uniaxial and biaxial compressive tests on fractured rock models with considering the effects of different loading conditions different loading directions anisotropy and coupled hydro mechanical processes for evaluating strength and deformability behavior of fractured rocks by using code udec of discrete element method dem a series of numerical experiments were conducted on discrete fracture network models dfn at an established representative elementary volume rev based on realistic geometrical and mechanical data of fracture systems from field mapping at sellafield uk the results were used to estimate the equivalent young s modulus and poisson s ratio and to fit the mohr coulomb and hoek brown failure criteria represented by equivalent material properties defining these two criteria the results demonstrate that strength and deformation parameters of fractured rocks are dependent on confining pressures loading directions water pressure and mechanical and hydraulic boundary conditions fractured rocks behave nonlinearly represented by their elasto plastic behavior with a strain hardening trend fluid flow analysis in fractured rocks under hydro mechanical loading conditions show an important impact of water pressure on the strength and deformability parameters of fractured rocks due to the effective stress phenomenon but the values of stress and strength reduction may or may not equal to the magnitude of water pressure due to the influence of fracture system complexity stochastic analysis indicates that the strength and deformation properties of fractured rocks have ranges of values instead of fixed values hence such analyses should be considered especially in cases where there is significant scatter in the rock and fracture parameters these scientific achievements can improve our understanding of fractured rocks hydro mechanical behavior and are useful for the design of large scale in situ experiments with large volumes of fractured rocks considering coupled stress deformation flow processes in engineering practice

north polar region of mars topography of circumpolar deposits from mars orbiter laser altimeter mola data and evidence for asymmetric retreat of the polar cap we have used high resolution mars orbiter laser altimeter mola data to analyze the topography morphology stratigraphy and geologic history of the martian north circumpolar deposits the present polar deposits are offset about toward 0 w from the rotational pole an arc of irregular topography concentric to olympia planitia and the cap consists of polar material remnants depressions which we interpret to be kettles frost covered and residual ice filled craters and frost patches olympia planitia originally thought to be a flat sand covered plain is characterized by a convex upward topography contiguous with the polar cap we interpret olympia planitia to represent a now dune covered extension of the polar materials together olympia planitia and the outlying deposits delineate a former extent of the polar cap topographic data have clarified relationships among the circumpolar deposits contributors to these deposits include local volcanics fluvial and aqueous sediments from outflow channels and a possible standing body of water pyroclastic ash sublimation lag from the olympia lobe and eolian reworked materials significant events in the history of the region include 1 formation of the northern lowlands 2 emplacement of volcanic plains fluvial and aqueous sedimentation and subsequent desiccation forming polygonal patterns which in part underlie the present polar layered deposits 3 formation of the polar cap composed primarily of layered deposits 4 asymmetric retreat of the olympia lobe resulting in sublimation lag deposits polar remnants and kettles and 5 continued collection and reworking of sediments by eolian processes the cause of the asymmetrical retreat of the olympia lobe is unknown

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

a constitutive model for the deformation of a rock mass containing sets of ubiquitous joints abstract as part of the rock mass the discontinuities inherently affect the strength and the deformational behavior of rock mass existing models can either handle the pre or post peak deformation of intact rock or joints alone however a model which can determine the failure mode and simulate the complete pre and post deformation of rock mass with multi sets of joints is not yet available this study focusses on rock mass with multi sets of ubiquitous joints and establishes a mathematic model and an associated numerical implementation accounting for the anisotropy in strength and deformation induced by the existence of joints accordingly an approach incorporating the existing models or methods to enable simulation of the complete deformation of rock mass is proposed in addition to the pre and post peak deformation characteristics for intact rock the pre peak deformation of joint such as the closure shear and dilatancy effect as well as its post peak deformation such as the reduction on roughness have also been taken into account a series of comparisons validates that the proposed model is capable of presenting the joint induced anisotropy in strength and deformation of rock mass determining the possible failure modes and reasonably simulating the complete stress strain relationship as well

stratigraphic relationships within martian polar cap deposits abstract deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits while erosion of equator facing slopes of layered terrain expose these layers banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole facing trough walls these deposits unconformably overlap onto adjacent layered terrain stripping of layers occurs in areas of strong multidirectional wind forming striped terrain local wind scour has also produced steep scarps with crescentic planform often associated with dune fields positioned immediately downwind unconformities are common within layered deposits in areas of complex topography at the north pole these indicate that episodes of deposition of 5 10 layers alternate with slight erosion of pole facing trough walls troughs that strike north south alternate between erosional widening and deepening and depositional infilling creating multiple unconformities troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and locally by erosional deepening troughs may migrate poleward replacing the relief increase by depositional infilling when they near the poles

onset and migration of spiral troughs on mars revealed by orbital radar the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years a pinwheel array of deep troughs has been one of the most perplexing features of the north polar layered deposits on mars many ideas have been put forward about how it formed but there is as yet no consensus here penetrating radar has been used to rule out erosional cutting as a mechanism for the formation of the array instead it is concluded that the troughs are largely depositional in origin and have migrated to the poles and upwards in elevation over the past two million years or so the landscape of the north polar layered deposits of mars npld is dominated by a pinwheel array of enigmatic spiral troughs1 the troughs have intrigued planetary scientists since the mariner 9 spacecraft returned the first close up image in 1972 but conclusive evidence of their origin has remained elusive debate continues regarding all aspects of the troughs including the possibility that they have migrated2 3 4 5 their age in relation to the current npld surface6 and whether they are fundamentally erosional6 7 or constructional2 4 features the troughs are probably related to climatic processes2 8 yet the nature of this relationship has remained a mystery previous data characterizing only the exposed nlpd surface were insufficient to test these hypotheses here we show that the central spiral troughs initiated after deposition of three quarters of the npld quickly reached a stable morphology and migrated approximately 65 kilometres poleward and 600 metres in altitude over the past two million years or so our radar stratigraphy rules out hypotheses of erosional incision post dating deposition6 7 9 10 and instead largely validates an early hypothesis for constructional trough migration2 3 4 5 with wind transport and atmospheric deposition as dominant processes these results provide hard constraints for palaeo climate models and a new context for evaluating imagery spectral data and now radar sounding data the better to understand the link between orbital parameters and climate the role of climate in shaping the polar ice of mars and eventually the age of the polar deposits themselves8 11 12 13

three dimensional structure and origin of a 1 8 km thick ice dome within korolev crater mars korolev is an 80 km diameter impact crater located at 72 7 n 164 5 e containing a large domed deposit perennial water ice is thought to be currently unstable there however using a 3 d analysis of the dome s internal radar stratigraphy we estimate that korolev s central mound contains between 1400 and 3500 km3 of water ice that is up to 1 8 km thick furthermore the stratigraphic structure of this ice dome is strikingly similar to the north polar layered deposits npld on planum boreum approximately 600 km to the north additionally our stratigraphic analysis suggests that korolev ice was not previously part of a once larger polar ice sheet but rather it was deposited locally we conclude that korolev crater s ice likely deposited during the same climate regime as planum boreum s npld but independently this implies that the incorporation of circumpolar ice deposits such as korolev may prove useful in reconstructing a unique mars polar climate history

geology and insolation driven climatic history of amazonian north polar materials on mars a wealth of image and topographic data from the mars global surveyor and mars odyssey missions has been combined in a detailed geological map of the north polar region of mars one intriguing finding is a cycle of ice deposition similar in duration to a 1 470 year climate cycle of unknown origin on earth if both are externally driven a mechanism that affects both planets such as variation in solar luminosity must be involved mariner 9 and viking spacecraft images revealed that the polar regions of mars like those of earth record the planet s climate history however fundamental uncertainties regarding the materials features ages and processes constituting the geologic record remained1 2 3 4 5 6 recently acquired mars orbiter laser altimeter data7 and mars orbiter camera high resolution images8 from the mars global surveyor spacecraft and moderately high resolution thermal emission imaging system visible images9 from the mars odyssey spacecraft permit more comprehensive geologic and climatic analyses10 11 12 13 14 15 16 17 here i map and show the history of geologic materials and features in the north polar region that span the amazonian period 3 0 gyr ago to present 18 19 erosion and redeposition of putative circumpolar mud volcano deposits15 formed by eruption of liquefied fine grained material led to the formation of an early amazonian polar plateau consisting of dark layered materials crater ejecta superposed on pedestals indicate that a thin mantle was present during most of the amazonian suggesting generally higher obliquity and insolation conditions at the poles than at present brighter polar layered deposits rest unconformably on the dark layers and formed mainly during lower obliquity over the past 4 5 myr ref 20 finally the uppermost layers post date the latest downtrend in obliquity 20 000 years ago20

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

dolomitization of the leduc formation upper devonian southern rimbey meadowbrook reef trend alberta abstract upper devonian leduc carbonate buildups along the southern part of the rimbey meadowbrook reef trend in alberta buried at depths of 2300 3500 m have been extensively dolomitized dolomitization occurred first by pervasive replacement and later by minor cementation in general replacement dolomites are composed of fabric destructive fine to medium 60 250 m planar subhedral to anhedral crystals replacement dolomitization postdates submarine cementation and deposition of shales and carbonates from the overlying ireton formation and overlaps stylolitization it predates dolomite cementation that is interpreted to have originated from hydrothermal fluids in a shallow burial environment prior to basin tilting this combined with the d18o mean 4 5 0 4 pdb and 87sr 86sr mean 0 70853 values in the replacement dolomites suggests that replacement dolomitization occurred also prior to basin tilting probably during the antler orogeny in the subsurface at a temperature of about 45 c and a depth of about 500 m from slightly modified late devonian seawater two generations of dolomite cements postdate replacement dolomites a coarse and planar e s cement dolomite c1 and a later coarser nonplanar cement dolomite c2 dolomite c1 has oxygen mean d18o 4 73 pdb and strontium mean 87sr 86sr 0 70855 isotopic compositions similar to replacement dolomites these similarities combined with the local association of dolomite c1 with stylolites suggest that some dolomite c1 precipitated from fluids whose composition reflects pressure solution of the preexisting replacement dolomites the composition of fluid inclusions in dolomite c1 mean th 117 c mean salinity 19 wt acl equivalent indicates that most dolomite c1 precipitated from warm hydrothermal brines little variation in fluid inclusion homogenization temperatures occur with burial depth suggesting that dolomite c1 precipitated prior to basin tilting and may be related to antler orogenic events dolomite c2 postdates dolomite c1 is relatively more depleted in 18o mean d18o 9 06 pdb and has a more radiogenic 87sr 86sr ratio 0 71087 preliminary fluid inclusion data from the crimson field suggest precipitation temperatures of about 150 c thus dolomite c2 originated from fluids of higher temperatures and different composition than do omite c1 the petrographic paragenetic and geochemical characteristics of replacement dolomites in this study are similar to those of other leduc buildups along the reef trend and of other devonian dolostones of western canada supporting a model of large scale basinwide fluid flow the pervasive distribution of replacement dolomites along the rimbey meadowbrook reef trend and the similar petrographic and geochemical character of dolomites from both the leduc and cooking lake formations is consistent with the hypothesis that the underlying cooking lake platform acted as a subsurface conduit system for the dolomitizing fluids a potential regional fluid source may have been formation fluids including residual evaporite brines expelled tectonically during the antler orogeny

effect of discontinuity orientation and confinement on the strength of jointed anisotropic rocks abstract we have investigated the effects of discontinuity dip and dip direction difference on rock mass strength together with an assessment of how the degree of anisotropy varies with changes of the confining pressures this assessment was made possible through introduction of a dimensionless anisotropy effect parameter numerous studies have been conducted on the effect of dip variation so far but none of them have paid attention to the dip direction difference of joints on the strength response of the rocks to begin with we investigate the behavior of anisotropic specimens with regard to confining pressure and the jointing inclinations in order to assess the failure mechanism then we proceed to study the effects of discontinuities dip direction difference on the rock mass strength through testing artificial plaster specimens the samples were tested under triaxial conditions subjected to different confining pressures we present the details of the investigations tables of the evaluated test results and the empirical equation deduced during the course of this research

the stochastic assessment of strength and deformability characteristics for a pyroclastic rock mass abstract a practical procedure is described for implementing probabilistic determination of rock mass strength and deformability properties of a pyroclastic rock medium in order to carry out this procedure the discontinuity properties of rock mass are collected in the field and laboratory studies are conducted on the intact rock samples the appropriate statistical distributions are fitted on the available data by using the chi square goodness of fit technique for the estimation of strength and deformability of rock mass input parameters of the generalized hoek brown empirical equations are replaced by previously defined probability density functions after running monte carlo simulations potential ranges of the strength and deformability values of the investigated rock mass are accomplished the simulation results suggest that it is promising to represent the random characters of rock mass mechanical properties when used with proper empirical or analytical relationships

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

stabilization of early formed dolomite a tale of divergence from two mississippian dolomites abstract several large hydrocarbon accumulations in alberta canada are hosted in dolomitized successions of stacked thin sabkha capped cycles of visean age porosity is micro intercrystalline and occurs in dolomitized restricted subtidal and intertidal muds that have their fine primary fabric preserved two such fields are here considered that illustrate divergent and contrasting modes of dolomite stabilization despite initial similarities in facies and textures the dolomite in the upper debolt formation of the dunvegan field nw alberta forms planar e or microsucrosic fabrics with crystals in the 1 20 m range the dolomite is non ferroan ca rich average of 58 mol caco 3 and poorly ordered its stable isotopic signatures range from 0 12 to 3 4 vpdb for 18 o mean 1 3 and 0 9 to 4 3 vpdb for 13 c mean 2 6 the average radiogenic 87 sr 86 sr ratio for this dolomite is 0 7077 both sets of values are consistent with dolomite precipitation from mississippian marine or modified marine evaporated seawater these parameters are strongly reminiscent of holocene protodolomites and hence suggestive of a sabkha dolomitization process shallow seepage reflux or evaporitive pumping this dolomite with its high associated porosity average of 15 and up to 38 relatively unaltered mineralogical and chemical signatures both preserved despite 4 km of burial depth suggests a very unique set of relatively non reactive physico chemical conditions during burial likely a closed system in contrast the dolomite from the mount head formation of the shell waterton field sw alberta has undergone measurable neomorphic alteration in several stages in deeper burial environments open system such alteration has affected its crystal size range 18 o ranges between 1 5 in the least altered dolomite and 13 2 vpdb 13 c ranges from 3 9 to 1 5 vpdb and 87 sr 86 sr ranges from 0 7078 to 0 7090 the dolomite has retained a degree of non stoichiometry with an average ca content of 55 mol caco 3 the mount head dolomites clearly indicate ongoing reactivity between the rocks and basinal fluids during burial and are in this respect representative of the norm for dolostones in the western canada sedimentary basin

empirical methods to estimate the strength of jointed rock masses abstract the ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil and mining engineering structures in rocks in the field it is extremely difficult to stress a rock mass to its ultimate failure stress consequently the field tests are performed up to a certain predefined stress level it is shown in this study that the results of these tests can be used to arrive at the ultimate strength of the rock mass a large number of uniaxial compressive strength ucs tests were conducted on the specimens of jointed block mass having various combinations of orientations and different levels of interlocking of joints four dominating modes of failure were observed the strength and the tangent elastic modulus values of the mass for a specific failure mode when plotted on the deere miller classification chart are found to follow an empirical straight line indicating strong correlation between them using the gradient of this empirical line correlations have thus been suggested to assess the ultimate strength of the jointed rock mass the findings of the study have been verified by applying it to estimate the ultimate rock mass strength of nine rock types from few dam sites in the lower himalayas the ultimate strength obtained by the present methodology is compared with that obtained through the q classification system it is concluded that reasonably good estimates on field strength of jointed rocks are possible by using the correlations suggested in this study

integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits mars abstract shallow radar sharad on board nasa s mars reconnaissance orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits npld of mars radar reflections are hypothesized to originate from the same material interfaces that result in visible layering as a first step towards verifying this assumption this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an npld outcrop to understand subsurface structures and reflector geometry reflector surfaces have been gridded in three dimensions taking into account the influence of surface slopes to obtain accurate subsurface geometries these geometries reveal reflector dips that are consistent with optical layer slopes distance elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography verifying that reflectors represent paleosurfaces of the deposit statistical and frequency domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers direct elevation comparisons between individual reflectors and discrete optical layers while necessary for a one to one correlation are complicated by variations in subsurface structure that exist between the outcrop and the sharad observations as inferred from subsurface mapping although these complications have prevented a unique correlation a genetic link between radar reflectors and visible layers has been confirmed validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy furthermore the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations

host rock dolomitization and secondary porosity development in the upper devonian cairn formation of the fairholme carbonate complex south west alberta canadian rockies diagenesis and geochemical modelling the upper devonian carbonate reefs in west central alberta are important petroleum reservoirs that are well known for their extensive secondary porosity an outcrop analogue study indicates that an early matrix selective dolomitization event occurred which is characterized by a major late devonian sea water component with increased salinity because of evaporation it is interpreted that the matrix replacive dolomite formed during the famennian as the result of a combination of both seepage and latent reflux dolomitization although an additional type or overprinting of later immediate burial dolomitization cannot be excluded formation of the moulds is attributed mainly to the dissolution of undolomitized fossil cores most typically stromatoporoids geochemical modelling indicates that carboxylic acid fluids have the highest potential for dissolving residual calcite in this case geochemical models consistent with this analysis and interpretations can reproduce the secondary porosite and suggest a viable dolomitization process for the localities studied

evidence for subsurface water ice in korolev crater mars abstract following the work of kieffer and titus 2001 icarus 154 162 180 we present results of thermal ir observations of korolev crater located at 73 latitude in the martian northern polar region similar to techniques employed by titus et al 2003 science 299 1048 1050 we use infrared images from the thermal emission imaging system themis aboard mars odyssey to identify several regions within the crater basin with distinct thermal properties that correlate with topography the themis results show these regions exhibit temperature variations spatially within the crater and throughout the martian year in addition to the variations identified in the themis observations mars global surveyor thermal emission spectrometer tes observations show differences in albedo and temperature of these regions on both daily and seasonal cycles modeling annual temperature variations of the surface we use tes observations to examine the thermal properties of these regions this analysis reveals the crater interior deposits are likely thick layers several meters of high thermal inertia material water ice or extremely ice rich regolith spatial variations of the physical properties of these regions are likely due to topography and possibly variations in the subsurface material itself the nature of these deposits may help constrain polar processes as well as provide context for the polar lander mission phoenix

cooling in rifting sequences during increasing burial depth due to heat flow decrease two case histories are presented to give evidences for sediment cooling during increasing burial depth due to heat flow decrease at the end of crustal stretching in extensional settings the first refers to the lower cretaceous succession accumulated in a strongly subsiding trough within the sirt basin libya the second relates to the mesozoic succession of the lombardian basin nw italy formed during late triassic early jurassic rifting of the northern margin of the adriatic microplate in both cases heat flow decreasing at the end of crustal stretching overbalanced the thermal effect of increasing burial depth causing a net cooling of rocks these examples provide an alternative to exhumation for explaining cooling events recorded by rifting sedimentary sequences

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

internal structure of planum boreum from mars advanced radar for subsurface and ionospheric sounding data 1 an investigation of the internal structure of the ice rich planum boreum pb deposit at the north pole of mars is presented using 178 orbits of mars advanced radar for subsurface and ionospheric sounding data for each radargram bright laterally extensive surface and subsurface reflectors are identified and the time delay between them is converted to unit thicknesses using a real dielectric constant of 3 results include maps of unit thickness for pb and its two constituent units the stratigraphically older basal unit bu and the stratigraphically younger north polar layered deposits npld maps of the individual units surface elevation are also provided estimates of water ice volume in each unit are 1 3 0 2 106 km3 in pb 7 8 1 2 105 km3 in the npld and 4 5 1 0 105 km3 in the bu no lithospheric deflection is apparent under pb in agreement with previous findings for only the gemina lingula lobe which suggests that a thick elastic lithosphere has existed at the north pole of mars since before the emplacement of the bu the extent of bu material in the olympia planum lobe of pb is directly detected providing a more accurate map of bu extent than previously available from imagery and topography a problematic area for mapping the bu extent and thickness is in the distal portion of the 290 e 300 e region where marsis data show no subsurface reflectors even though the bu is inferred to be present from other lines of evidence

climate driven deposition of water ice and the formation of mounds in craters in mars north polar region this paper explores the origins and evolution of ice rich interior mounds found within craters of the north polar region of mars we present a systematic study of impact craters above 65 n and identify 18 craters that have interior mounds at least 11 of these mounds are composed of water ice and geometric similarities suggest that dune covered mounds may also have a water ice core the mounds are found in the deeper craters in the north polar area and we suggest that these form a specific microclimate favorable for mound initiation and growth it is likely that at least seven of the mounds have evolved as individual outliers rather than conterminous with the main polar cap our observations suggest that the mounds are built up by atmospheric deposition similar to that of the north polar layered deposits using a combination of remote sensing techniques enabling topographic spectral radar and image data analyses we have documented the morphology composition and stratigraphy of selected mounds we advance and test four hypotheses for formation of these mounds artesian outpouring from a deep aquifer hydrothermal activation of ground ice remnants of a more extensive polar cap and atmospheric deposition on ice caps in meteorologically isolated locations we propose that during periods when the perihelion was located in northern summer most recently 10 25 ka before present the microclimate in these craters retarded the sublimation of co2 and water ice in northern spring thus creating a cold trap for volatiles released as the seasonal cap retreated this created a thick enough deposit of water ice to withstand sublimation over the summer and initiate a positive feedback leading to mound building mounds without complete dune cover may be in dynamic equilibrium with the ambient climate and show evidence of both present day and past periods of erosion and aggradation we conclude that the water ice mounds formed in deep impact craters in mars north polar region may contain sensitive records of past polar climate that may enhance our understanding of the co2 h2o system in the polar regions

the spiral troughs of mars as cyclic steps we combine observations of stratigraphy morphology and atmospheric processes to relate the spiral troughs on mars polar layered deposits to a class of features known as cyclic steps cyclic steps are quasi stable repeating and upstream migrating bed forms that have been studied in terrestrial and submarine environments the repeating pattern is bounded by hydraulic jumps which act to stabilize the form we use radar stratigraphy from the shallow radar instrument on mars reconnaissance orbiter to examine trough evolution and constrain lateral transport we examine visible images from the thermal emission imaging system and observe low altitude clouds that we interpret to be the result of katabatic jumps i e the aeolian counterpart of hydraulic jumps in open channel flow we then devise a theoretical framework for understanding the origin of the spiral troughs that agree with 10 criteria that should be explained for any scenario to satisfactorily model the spiral troughs finally we use froude and geometrical analysis to estimate the rate of upstream migration caused by katabatic winds for the spiral troughs

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

north polar region craterforms on mars geometric characteristics from the mars orbiter laser altimeter abstract this study focuses on topographic characterization of ice associated north polar region impact craters and several enigmatic polar craterforms using new information from the mars orbiter laser altimeter mola an instrument aboard the mars global surveyor mgs orbiter we find that for ice associated craters the topography reveals several surprising results not previously apparent from orbital images alone first geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80 of reconstructed preerosion levels second craters associated with ice also demonstrate unique cavity geometries relative to their nonpolar counterparts finally in some cases ice associated impact features are anomalously deep on the basis of depths modeled from the best available scaling laws we suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of mars has occurred subsequent stripping has exhumed the features leaving behind cavity infill deposits and a few of these display topographic levels above the surrounding preimpact surface in at least one case cavity interior deposits show layering with a typical thickness of 10 m suggesting episodic deposition and ablation of materials as in the polar layered terrain in addition to ice associated craters we investigated the topography of several enigmatic polar craterforms in particular a few craterforms within 150 km of the permanent north polar cap appear to resemble simple effusive lava shield volcanoes found on earth their geometric properties cannot be reconciled with previous suggestions that they were manifestations of martian hydromagmatic processes i e maar volcanism mola s initial measurements of impact craters and other craterforms in the north polar latitudes of mars support the concept of a geologically recent surface with evidence of effusive volcanism and enhanced sedimentation in addition the measured impact crater depths for ice associated craters suggest at least a few cases of enhanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains

fluid rock interactions associated with regional tectonics and basin evolution an integrated approach consisting of fracture analysis petrography carbon oxygen and strontium isotope analyses as well as fluid inclusion micro thermometry led to a better understanding of the evolution of fluid rock interactions and diagenesis of the upper permian to upper triassic carbonates of the united arab emirates the deposited carbonates were first marked by extensive early dolomitization during progressive burial the carbonates were affected by dolomite recrystallization as well as precipitation of vug and fracture filling dolomite quartz and calcite cements after considerable burial during the middle cretaceous sub vertical north south oriented fractures f1 were cemented by dolomite derived from mesosaline to hypersaline fluids upon the late cretaceous maximum burial and ophiolite obduction sub vertical east west fractures f2 were cemented by dolomite dc2 and saddle dolomite ds derived from hot highly saline fluids then minor quartz cement has precipitated in fractures from hydrothermal brines fluid inclusion analyses of the various diagenetic phases imply the involvement of increasingly hot 200 degrees c saline brines 20 to 23 nacl eq through one dimensional burial history numerical modelling the maximum temperatures reached by the studied rocks are estimated to be in the range of 160 to 200 degrees c tectonically driven flux of hot fluids and associated diagenetic products are interpreted to have initiated during the late cretaceous maximum burial and lasted until the oligocene miocene compressional tectonics and related uplift the circulation of such hydrothermal brines led to partial dissolution of dolomites dc2 and ds and to precipitation of hydrothermal calcite c1 in new mainly oriented north south f3 and pre existing reactivated fractures the integration of the obtained data confirms that the diagenetic evolution was controlled primarily by the interplay of the burial thermal evolution of the basin and the regional tectonic history hence this contribution highlights the impacts of regional tectonics and basin history on diagenetic processes which may subsequently affect reservoir properties

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

recent ice rich deposits formed at high latitudes on mars by sublimation of unstable equatorial ice during low obliquity observations from the gamma ray spectrometer instrument suite on the mars odyssey spacecraft have been interpreted as indicating the presence of vast reservoirs of near surface ice in high latitudes of both martian hemispheres1 2 3 4 5 ice concentrations are estimated to range from 70 per cent at 60 latitude to 100 per cent near the poles possibly overlain by a few centimetres of ice free material in most places4 this result is supported by morphological evidence of metres thick layered deposits that are rich in water ice6 7 8 9 and periglacial like features10 11 found only at high latitudes diffusive exchange of water between the pore space of the regolith and the atmosphere has been proposed to explain this distribution12 but such a degree of concentration is difficult to accommodate with such processes9 13 14 alternatively there are suggestions that ice rich deposits form by transport of ice from polar reservoirs and direct redeposition in high latitudes during periods of higher obliquity9 13 but these results have been difficult to reproduce with other models here we propose instead that during periods of low obliquity less than 25 high latitude ice deposits form in both hemispheres by direct deposition of ice as a result of sublimation from an equatorial ice reservoir that formed earlier during a prolonged high obliquity excursion using the ice accumulation rates estimated from global climate model simulations we show that over the past ten million years large variations of mars obliquity have allowed the formation of such metres thick sedimentary layered deposits in high latitude and polar regions

planum boreum basal unit topography mars irregularities and insights from sharad shallow radar investigations of planum boreum mars basal unit bu deposit have revealed multiple reentrants morphologic irregularities and thickness trends that differ from those of the overlying north polar layered deposits we present detailed subsurface maps for these features and offer explanation for genesis of the deposit s morphologic asymmetry expressed in different erosional characteristics between 0 e 180 e and 180 e 360 e additionally this work revealed a depression in the basal unit that may have provided a site for spiral trough initiation interpretations of the findings suggest that antecedent bu topography has a marked impact on modern morphology and that aeolian forces have been the dominant driver of polar deposit accumulation since at least the end of rupes unit emplacement we find no results requiring explanation beyond common martian surface processes including aeolian erosion and impact armoring to add to the detailed morphologic study of the bu we mapped the variability of the bu radar reflection character combining generalized katabatic wind flow with the radar mapping results suggests that rupes unit material sourced the younger cavi we present clear evidence that while compositionally distinct from the overlying layered deposits the bu and its morphology are intimately linked to the morphology of the north polar layered deposits combining geologic evidence with paleoclimate modeling the deposits contain evidence for a long history of aeolian emplacement and modification

reassessing the 2006 guerrero slow slip event mexico implications for large earthquakes in the guerrero gap in guerrero mexico slow slip events have been observed in a seismic gap where no earthquakes have occurred since 1911 a rupture of the entire gap today could result in a mw 8 2 8 4 earthquake however it remains unclear how slow slip events change the stress field in the guerrero seismic region and what their implications are for devastating earthquakes most earlier studies have relied on a sparse network of global navigation satellite systems measurements here we show that interferometric synthetic aperture radar can be used to improve the spatial resolution we find that slip due to the 2006 slow slip event enters the seismogenic zone and the guerrero gap with 5 cm slip reaching depths as shallow as 12 km we show that slow slip is correlated with a highly coupled region and estimate that slow slip events have decreased the total accumulated moment since the end of the 2001 2002 slow slip event 4 7 years by 50 nevertheless even accounting for slow slip the moment deficit in the guerrero gap increases each year by mw 6 8 the guerrero gap therefore still has the potential for a large earthquake with a slip deficit equivalent to mw 8 15 accumulated over the last century correlation between the slow slip region and nonvolcanic tremor and between slow slip and an ultraslow velocity layer supports the hypothesis of a common source potentially related to high pore pressures

calcitization dedolomitization of jurassic dolostones lebanon results from petrographic and sequential geochemical analyses calcitized jurassic dolostones from central mount lebanon kesrouane formation are discussed utilizing petrographic mineralogical and geochemical data in particular two sequential extraction methods for both major trace elements and stable isotope analyses provide results that support and refine conventional bulk analyses data the new data demonstrate that the major dedolomitization phase of the investigated jurassic carbonates occurred as a result of the migration of karst related meteoric waters characterized by soil derived carbon and estimated 18ov smow composition between 7 2 and 3 4 into previously dolomitized horizons within the limestone rock during the final uplift and emergence of mount lebanon after palaeogene time the study demonstrates that in this case the mechanisms of dedolomitization and their resulting fabrics are controlled primarily by the texture of the original dolomite rock pervasively dolomitized rocks where the micritic matrix is entirely dolomitized show calcitization mainly through dissolution precipitation by contrast the rock textures that still include a considerable amount of limey micritic matrix spared from dolomitization are more prone to mole per mole and mimic replacement of the dolomite crystals by calcite

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

sequence of thrusting and origin of culminations in the northern and central oman mountains abstract detailed mapping and structural analysis of three large scale culminations sumeini and asjudi half windows and haybi hawasina window in the oman mountains shows a considerably more complex history of deformation than a simple foreland or downward sequence of thrust development early thrusting processes tended to create a regular stacking order of imbricate slices and major thrust sheets complying with the rules of thrust propagation assembled progressively downwards and forwards in the direction of translation out of sequence thrusts can also be demonstrated in places by truncation of footwall structures folds imbricate slices etc gross strain differences between thrust sheets downward facing structures in footwall units and elimination of thrust sheets beneath late stage thrusts frequently cut up section through the previously assembled stack putting previously younger lower thrust sheets over previously older higher ones many of the culminations in the northern and central oman mountains were formed by ramping associated with this late stage leap frog rethrusting event

assessment of rock mass strength for underground excavations abstract when the stability of underground openings is assessed one must concern with local and global failure modes local failures may take place as long as rock blocks are kinematically movable into openings while global failure modes are associated with the stress state and the strength of rock mass surrounding openings this fact is always confused in underground rock engineering first the authors briefly describe several approaches how to assess the strength of rock masses together with some new proposals for underground excavations then the estimations by these methods are compared with each other as well as with experimental data finally the validity of these methods are discussed and some recommendations are made for practical applications

orbital radar imagery and atmospheric modeling reveal an aeolian origin for abalos mensa mars 1 icy deposits surrounding planum boreum mars contain crucial information for deciphering paleoclimate and past geologic processes at the martian north pole one such deposit abalos mensa is an enigmatic wedge of material located near the 1 km high rupes tenuis its unique location and lobate morphology have fostered formation hypotheses that assume either fluvial or aeolian erosion of a once larger ice deposit the aeolian scenario posed previously requires impact shielding of ancient basal unit material to provide an erosional remnant which seeds later deposition while the fluvial hypotheses invoke cryovolcanism beneath the younger north polar layered deposits npld and associated outflow to erode the adjacent chasmata here we combine newly available radar sounding data high resolution imagery digital elevation models and atmospheric modeling to examine internal structure and infer both the mechanisms for and timing of abalos mensa formation from this integrative approach we conclude that abalos mensa formed as a distinct feature via atmospheric deposition following erosion of rupes tenuis and grew concurrently with the rest of planum boreum as the npld accumulated the required processes are consistent with those observed today no exotic phenomena cryovolcanism fluvial activity or impact shielding appear necessary to explain the formation of abalos mensa

a subsurface depocenter in the south polar layered deposits of mars the south polar layered deposits spld are one of the largest water ice reservoirs on mars and their accumulation is driven by variations in the climate primarily controlled by orbital forcings patterns of subsurface layering in the spld provide important information about past atmospheric dust content periods of substantial erosion and variations in local or regional deposition here we analyze the spld using shallow radar sharad sounder data to gain a unique perspective on the interior structure of the deposits and to determine what subsurface layers indicate about the preserved climate history sharad data reveal a major deviation from the gently domical layering typical of the spld a subsurface elongate dome the dome most likely formed due to variations in the accumulation of ice and snow across the cap with a higher rate occurring in this region over a prolonged period this spld depositional center provides an important marker of south polar climate patterns

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

stratigraphic architecture and fracture controlled dolomitization of the cretaceous khami and bangestan groups an outcrop case study zagros mountains iran this work has been carried out as part of a joint study between norsk hydro now statoil and nioc national iranian oil company

empirical estimation of rock mass modulus the deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations field tests to determine this parameter directly are time consuming expensive and the reliability of the results of these tests is sometimes questionable consequently several authors have proposed empirical relationships for estimating the value of rock mass deformation modulus on the basis of classification schemes these relationships are reviewed and their limitations are discussed based on data from a large number of in situ measurements from china and taiwan a new relationship based upon a sigmoid function is proposed the properties of the intact rock as well as the effects of disturbance due to blast damage and or stress relaxation are also included in this new relationship