modes of origin and genetic pathways of peloids within the duwi formation late cretaceous in eastern and western deserts of egypt a petrologic perspective abstract peloids are considered as major constituents of modern and ancient sedimentary rocks although their origins and pathways of formation are not yet comprehensively understood based on field and petrologic investigations peloids have been recorded in the duwi formation late cretaceous in both eastern and western deserts of egypt the duwi formation represents the first onset of fully marine conditions in egypt accompanying the major late cretaceous marine transgression it comprises a heterogeneous suite of shallow marine sediments phosphorites oyster limestones shales glauconites and dolomite according to the hosted rock peloids are classified into two types peloids in phosphorites and peloids in limestones which are characterized by different shapes and sizes systematic study indicates that peloids resulted from the interplay between physico chemical and microbial processes accordingly the more important modes of origin are peloids derived from coprolites by micritization of bivalve shells fragmentation and abrasion of intraclasts by phosphomicritization of bone fragments peloids derived from internal molds intraskeletal and interskeletal peloids nucleated peloids and peloids within matrices the size and morphology of the studied peloids are mainly controlled by the parent material

the belize margin revisited 1 holocene marine facies belize is best known for its 260 km long barrier reef and associated lagoon reef shoals but also exhibits a complete transition from near shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and in addition has three of the very few occurrences of caribbean atolls published holocene facies relationships on the belize shelf have been semi quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon this contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf supplemented by additional information to produce a modified factor analysis facies distribution for the entire shelf the resulting nine facies are extended seaward to include previously published analysis of sediment on the three belize off shelf atolls resulting in a total of 11 facies in addition the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that in places the distribution pattern clearly indicates a barrier platform source of lagoon deposited carbonate mud dunham s limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments

modeling of suction distributions in an unsaturated heterogeneous residual soil slope the formation of residual soil of grade v and grade vi due to tropical weathering process introduces small hydraulic heterogeneities in the soil mantle which greatly alter the suction distribution during rainfall infiltration and hence the stability of the residual soil slopes this paper presents field evidences of suction distributions in a heterogeneous residual soil slope several modeling approaches were attempted to simulate the observation by considering the presence of thin layer of grade vi the variation in the hydraulic conductivity of grade v layer as well as the effect of evaporation the soil hydraulic heterogeneity in grade v layer was modeled by adopting continuum method in which the residual soil was subdivided into three zones of average hydraulic conductivities the analysis results show that the presence of thin layer of grade vi residual soil and the relict discontinuities in grade v soil must be considered in the analysis as these features introduced permeability disparity and thus a natural capillary barrier effect that limited the downward movement of infiltrated rainwater even during the exceptionally wet condition the results also show that the inclusion of evaporation effect provided a better prediction to the suction distributions during wet condition than dry condition

landsliding in partially saturated materials 1 rainfall induced landslides are pervasive in hillslope environments around the world and among the most costly and deadly natural hazards however capturing their occurrence with scientific instrumentation in a natural setting is extremely rare the prevailing thinking on landslide initiation particularly for those landslides that occur under intense precipitation is that the failure surface is saturated and has positive pore water pressures acting on it most analytic methods used for landslide hazard assessment are based on the above perception and assume that the failure surface is located beneath a water table by monitoring the pore water and soil suction response to rainfall we observed shallow landslide occurrence under partially saturated conditions for the first time in a natural setting we show that the partially saturated shallow landslide at this site is predictable using measured soil suction and water content and a novel unified effective stress concept for partially saturated earth materials

a review of the nature and origin of limestone microporosity abstract limestone microporosity is ubiquitous and extensively developed in most phanerozoic limestones from an economic perspective microporosity is important because it contributes substantially to the carbonate pore system which can host significant volumes of water and hydrocarbons therefore determining the presence and distribution of limestone micropores is necessary for accurate hydrocarbon estimations reservoir characterization and fluid flow simulations from an academic standpoint microporosity is important because its genesis is intimately linked with the mineralogical stabilization of metastable sediments a fundamental process in carbonate diagenesis many types of micropores contribute to what has been referred to as microporosity but the vast majority is hosted among low magnesium calcite lmc microcrystals that are present in limestone matrix and allochems geochemical textural and mineralogical data from natural settings and laboratory experiments indicate that lmc microcrystals are diagenetic in origin more specifically these data support a diagenetic model of mineralogical stabilization that involves dissolution of precursor sediments dominated by aragonite and high magnesium calcite hmc minerals and precipitation of lmc microcrystal cements the stabilization process is inferred to take place in the meteoric marine and burial diagenetic realms although it has not been directly observed carbon and oxygen isotopes as well as trace element data suggest that lmc microcrystals form during burial diagenesis in marine like fluids evidence suggests that porosity is not generated during this dissolution precipitation process but rather inherited from the precursor sediments the final arrangement of the micropores in a limestone however depends on the precise diagenetic pathway lmc microcrystals exhibit a range of microcrystalline textures that are classified on the basis of crystal morphology and size the three main textural classes granular framework fitted mosaic and clustered have been recognized across a wide range of ages depositional settings burial depths and precursor types and are characterized by distinct petrophysical properties such as porosity permeability and pore throat size observations from modern sediments also support the hypothesis that lmc microcrystals develop from aragonite and hmc dominated lime mud the origin of lime mud has been extensively studied but still highly debated of particular interest to the discussion of microporosity are proposed secular variations in the dominant mineralogy of carbonate sediments through the phanerozoic microporous limestones comprised of lmc microcrystals are equally abundant during times of aragonite seas and calcite seas which suggests that no special mineral precursor is required microporous textures are also observed in deep marine chalks where micropores are hosted between chalk constituents unlike shallow marine limestones deep marine sediments start out as mostly lmc therefore mineralogical stabilization is not a significant process in chalk diagenesis

construction model and paleogeographic distribution of late pennsylvanian phylloid algal microbial reefs a case study in eastern inner mongolia north china abstract the gzhelian late pennsylvanian reefs of the amushan formation in eastern inner mongolia north china were formed by filamentous microbes and phylloid algae loosely accumulated prostrate phylloid algae provided substrates for growth of filamentous microbes to construct a rigid reef framework filamentous microbes grew parallel to the surfaces of phylloid algae forming micritic encrustations subsequent developed stage of the filamentous microbes growing perpendicularly to the phylloid algae surfaces produced the peloid a aggregations concentrated areas of peloids of a type the remaining spaces in the phylloid algal microbial frameworks were filled by microbes that grew perpendicularly to the phylloid algae surfaces generating peloid b aggregations concentrated areas of peloids of b type microbial sediment with various proportions of phylloid algae is a significant character of the gzhelian buildups in the subtropical north china north china buildups have similar reef building organisms to the typical tethyan buildups but have a different construction model as such the subtropical north china buildups are considered as a sub type of the tropical tethyan buildups

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

vertical and lateral collapse of tharsis tholus mars tharsis tholus a more than 3 9 ga old composite shield volcano to the east of the major tharsis montes has experienced a complex history of growth and destruction on the basis of new high resolution images we analysed the morphology as well as the tectonic structures of the tharsis tholus volcano in detail from morphological data cross cutting relations of the surface structures and crater modelling ages we propose a chronostratigraphy for the volcano tectonic history of tharsis tholus the strongly faulted volcano reveals two large scale landslide events followed by two subsequent shield re growth phases between 3 8 and 1 7 ga and two caldera collapses tharsis tholus was also affected by regional extensional tectonics between 1 7 ga and 0 4 ga recorded by sub parallel sets of ne trending graben structures the steep and up to 5 4 km high landslide scarps on tharsis tholus suggest deep faulting of the edifice in order to confirm this hypothesis we used analogue sand box models in which we demonstrated that gravitational flank movement on top of weak basal substrata may have produced the deformation structures as observed on tharsis tholus c 2011 elsevier b v all rights reserved

composition and genesis of temperate shallow marine carbonate muds spencer gulf south australia abstract the origin of carbonate muds grain sizes 63 m in shallow nontropical marine environments is poorly documented coarse grained carbonates often characterize coastal temperate seafloors but many such deposits also have abundant carbonate muds spencer gulf a large shallow embayment along the southern australian margin 60 m water depth contains mixtures of carbonate gravels sands and muds with muds constituting up to 84 volumetrically benthic environments include dense seagrass meadows sand barrens and rhodolith pavements where bivalves benthic foraminifera coralline algae and bryozoans dominate heterozoan carbonate assemblages mud grain morphologies were investigated using scanning electron microscopy leading to the conclusion that muds are predominantly composed of skeletal fragments bivalves benthic foraminifera ascidians echinoderms and coralline algae interpreted to have formed due to breakdown of rigid material via maceration x ray diffraction analysis confirms that these muds contain combinations of intermediate mg calcite low mg calcite and aragonite with concentrations varying among locations according to skeletal grain types spencer gulf muds differ in mineralogy and composition from those of classic models of tropical and deep water carbonate mud deposition unlike shallow water tropical carbonate muds these temperate muds are not dominated by aragonite and there is no evidence of carbonate precipitation from seawater pelagic organisms contribute only trivial amounts to these deposits in contrast to deep water muds

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

marine and meteoric diagenesis of pleistocene carbonates from a nearshore submarine terrace oahu hawaii abstract the nearshore slope of oahu consists of a shallowly dipping shelf extending from the shoreline out to the 20 m contour where there is a sharp break in slope down to 30 m limestones recovered in a series of short cores taken from this nearshore terrace are typical of shallow marine reef environments and comprise either a branching coral or massive coral facies the composition as well as shoreward zonation of facies suggests that the terrace represents an in situ fossil reef complex th u ages of in situ corals are all pleistocene and suggest that the bulk of the feature formed during marine oxygen isotope stage 7 later accretion along the seaward front of the terrace occurred during marine oxygen isotope substages 5a and or 5c deposition during these interglacial highstands has not previously been documented in the sea level record on oahu although the diagenetic record in the cored samples is incomplete three periods of diagenesis are identified early shallow marine meteoric and post meteoric shallow marine early shallow marine diagenesis includes cementation by aragonite and mg calcite in an active marine phreatic zone and predominantly micritization in a stagnant marine phreatic zone meteoric processes occurred in the vadose zone and include precipitation of calcite needle fibers meniscus cements micritic networks neomorphism and dissolution all limestones are now in an active marine phreatic zone evidence of post meteoric shallow marine diagenesis is found in last generation mg calcite cements and internal sediments occurring directly on limestone substrates that have otherwise been stabilized to calcite the present seafloor is undergoing extensive biological and physical erosion no holocene limestones were recovered petrographic and geochemical signatures of subaerial exposure and meteoric diagenesis are recognized within the upper several centimeters of all cores thus the present seafloor in the study area is a flooded pleistocene subaerial exposure surface

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

how wide is a road the association of roads and mass wasting in a forested montane environment a spatial data base of 1609 landslides was analysed using a geographic information system to determine landslide frequency in relation to highways a 126 km long transportation network in a 201km 2 area of humid tropical mountainous forested terrain in puerto rico was used in conjunction with a series of 20 buffer disturbance zones varying from 5 to 400 m in length measured perpendicular to the highways average landslide frequency in the study area at distances greater than 85 m from roads was about six landslides per square kilometre at distances of 85 m or less on either side of a highway landslide frequency was about 30 landslides per square kilometre on average this elevated disturbance rate affected 330 m 2 km 2 a 1 within the 170 m swath the mass wasting rate outside of the disturbance zone affected 40 m 2 km 2 a 1 these results indicate that the rate of mass wasting disturbance is increased from five to eight times in a 170 m wide swath along road corridors the lateral extent of the environmental impact of roads in the study area is greater than is commonly perceived the approach described herein demonstrates a simple method to assess the spatial association of mass wasting with highways 1997 by john wiley sons ltd

analysis of a retrogressive landslide in glaciolacustrine varved clay abstract the largest landslides in estonia are associated with glaciolacustrine varved clays one of the recent slope failures audru landslide was chosen for detailed investigation landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events the first stage of audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body the influence of the various modeling parameters on the overall slope stability was also investigated

upper devonian frasnian stromatactis bearing mud mounds western alberta canada reef framework dominated by peloidal microcrystalline calcite

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

structural architecture of the 1980 mount st helens collapse an analysis of the rosenquist photo sequence using digital image correlation the collapse of mount st helens united states on 18 may 1980 is one of the only incidents of its kind that was visually witnessed and instrumentally recorded previous analyses determined that the northern flank of the mountain failed which resulted in a rockslide and disintegrated during its mobilization to form a blocky facies and hummocky terrain in the downslope region gary rosenquist9s iconic photographs of the initial 18 may collapse were here analyzed by using a modern photogrammetric method to track portions of the moving flank across the photographs in the sequence thirty years after the 1980 mount st helens rockslide the digital image correlation technique enabled a precise investigation of the associated displacement vectors and strain a listric basal detachment and several associated faults at the lateral edge of the rockslide were identified in addition the heterogeneous movements and a number of shear zones were detected within the sliding block which had previously been assumed to be cohesive the results of my study demonstrate the value of using optical images for strain analyses of active volcanoes even decades after recording

the 2004 2005 etna eruption implications for flank deformation and structural behaviour of the volcano the development of the 2004 2005 eruption at etna italy is investigated by means of field surveys to define the current structural state of the volcano in 2004 2005 a fracture swarm associated with three effusive vents propagated downslope from the se summit crater towards the se such a scenario is commonly observed at etna as a pressure increase within the central conduits induces the lateral propagation of most of the dikes downslope nevertheless some unusual features of this eruption slower propagation of fractures lack of explosive activity and seismicity oblique shear along the fractures suggest a more complex triggering mechanism a detailed review of the recent activity at etna enables us to better define this possible mechanism in fact the nw se trending fractures formed in 2004 2005 constitute the southeastern continuation of a n s trending fracture system which started to develop in early 1998 to the east of the summit craters the overall 1998 2005 deformation pattern therefore forms an arcuate feature whose geometry and kinematics are consistent with the head of a shallow flank deformation on the e summit of etna similar deformation patterns have also been observed in analogue models of deforming volcanic cones in this framework the 2004 2005 eruption was possibly induced by a dike resulting from the intersection of this incipient fracture system with the se crater a significant acceleration of this flank deformation may be induced by any magmatic involvement the central conduit of the volcano is presently open constantly buffering any increase in magmatic pressure and any hazardous consequence can be expected to be limited a more hazardous scenario may be considered with a partial or total closing of the central conduit in this case magmatic overpressure within the central conduit may enhance the collapse of the upper eastern flank triggering an explosive eruption associated with a landslide reaching the eastern lower slope of the volcano

twenty ninth canadian geotechnical colloquium the role of advanced numerical methods and geotechnical field measurements in understanding complex deep seated rock slope failure mechanisms the underlying complexity associated with deep seated rock slope stability problems usually restricts their treatment to phenomenological studies that are largely descriptive and qualitative quant

long term dynamics of rockslides and damage propagation inferred from mechanical modeling 1 long term observations of large active rockslides show accelerating deformation over many thousands of years since the last deglaciation the effect of deglaciation on slope stability is however poorly understood due to 1 limited long term observations and 2 a complex interaction between glacier retreat and hydrogeological mechanical and morphological processes to assess the sensitivity of rockslide dynamics to these different processes a model of progressive damage through intact rock mass is developed in this study based on the finite element method this model uses time to failure laws based on rock laboratory creep experiments it is able to reproduce progressive damage localization along shear bands associated with strain rate acceleration as observed during tertiary creep the model reproduces the different phases of deformation associated with morphologies typical of large rockslides this model is thus suitable for simulating the dynamics of large rockslides and the transition from initiation to rapid sliding the sensitivity of rockslide kinematics and morphology to different mechanical properties is analyzed this analysis shows that the time evolution of the rockslide can be inferred with the knowledge of only one time parameter independent of the knowledge of the mechanical properties of the rock mass this parameter is here chosen as the time when the summit slope displacement has reached 10 m a parameter that can be estimated with cosmogenic dating the model is then used to study the effects of deglaciation on the valley flank stability and the formation of large rockslides this study shows that the deglaciation velocity can affect the morphology of the rockslide with the shear band of the rockslide emerging at higher elevation as the velocity decreases we also show that the response to the deglaciation can last several thousands of years after the glacier retreat

landslide subsurface slip geometry inferred from 3 d surface displacement fields the stability of many large landslides is determined in part by deformation along buried often inaccessible slip surfaces factors such as infiltrating rainfall on the slip surface lead to stability changes yet characterizing the depth and shape of this slip surface is challenging here we examine the hypothesis that the subsurface slip geometry can be constrained by ground surface displacements in concert with two mechanically distinct forward models we estimate a 3 d ground displacement field for the slow moving cleveland corral landslide in california using repeat terrestrial laser scanner data we test the efficacy of two models to estimate slip depth and slip magnitude of the slide a 2 d balanced cross section method and an elastic dislocation model the estimated slip surface depth using both methods matches in situ observations from shear rods installed in the slide within the 0 45 m misfit indicating that these are valuable approaches for investigating landslide geometry and slip behavior

a comparative study of modern carbonate mud in reefs and carbonate platforms mostly biogenic some precipitated abstract carbonate mud from reefs and carbonate platforms in six locations of the atlantic indian and pacific oceans belize bahamas florida the maldives french polynesia great barrier reef was systematically and quantitatively analyzed with regard to texture composition mineralogy and geochemistry mud composition shows considerable variability however the data supports the contention that these muds are largely derived from the breakdown of skeletal grains and codiacean algae only mud from the bahamas and northern belize areas which are characterized by common whitings is interpreted to be mainly inorganically precipitated three grain size fractions 63 20 m 20 4 m

numerical models of translational landslide rupture surface growth we analyze the initiation and enlargement of the rupture surface of translational landslides as a fracture phenomenon using a two dimensional boundary element method both processes are governed largely by the stress field and the pre existing planes of weakness in a slope near the ground surface the most compressive stress becomes either parallel or perpendicular to the slope depending on the topography and regional stresses the shear stress available to drive slope parallel sliding in a uniform slope thus is small and therefore pre existing weaknesses are required in many cases for sliding stresses in a uniform slope favor the initiation of sliding near the slope base sliding can progress upslope from there in retrogressive fashion most slopes are not uniform and notches in a slope will concentrate stresses and generally promote sliding there as the region of sliding at depth enlarges the stress concentration near the edge of the area of slip will tend to rise stress concentrations can become sufficient to open fractures above and below a basal slide plane in keeping with observations if one tip of a slide plane intersects the ground surface then stresses near the other tip can increase markedly as can slip our analyses show that slope parallel sliding along a plane at depth will cause downslope extension in the upslope half of a slide mass and shortening in the downslope half consistent with observations displacement profiles that could be interpreted as rotational can result from sliding along such a plane however careful analysis of surface deformation can be used to understand sliding at depth

recent sedimentary facies of isolated carbonate platforms belize yucatan system central america abstract distribution of recent sedimentary facies is significantly different in four closely spaced isolated carbonate platforms off the coasts of belize and yucatan se mexico these differences are largely controlled by variations in submarine topography which are likely the result of differential subsidence and karstification from platform to platform a variety of depositional styles and patterns is found in platform interiors that developed during the same holocene sea level rise composition and texture of surface sediment samples were used to define four major sediment types and to distinguish nine depositional environments within the platforms facies maps are based on analysis of 454 sediment samples and high resolution satellite imagery glovers reef is characterized by a circular facies distribution the nearly continuous reef margin is composed of a coral red coralline algae halimeda grainstone mixed nonskeletal peloidal skeletal wackestones and packstones are present in shallow lagoon parts 5 m water depth behind the margin the deep interior from 5 to 18 m water depth is characterized by mollusk foram halimeda wackestones with over 860 patch reefs of coral red algae halimeda mollusk packstones lighthouse reef also has a coral grainstone and coral red algae halimeda grainstone rim but the facies distribution in the interior is strongly asymmetrical the 8 m deep eastern lagoon is floored by mollusk foram halimeda wackestones and packstones the 3 m deep western lagoon has the mixed peloidal skeletal wackestone to grainstone facies a linear trend of coalescing patch reefs and skeletal grainstone facies separates the two lagoons banco chinchorro is similar to lighthouse reef inasmuch as facies distribution patterns of the interior are strongly asymmetrical mollusk foram halimeda wackestones grainstones are present in eastern lagoon areas whereas shallow 5 m western parts of the lagoon are composed of mixed peloidal skeletal grainstones packstones and wackestones most of turneffe islands is protected on the east by lighthouse reef accordingly turneffe has a narrower reef and skeletal grainstone rim than the other two platforms restricted interior lagoons are up to 8 m deep and are enclosed by wide mangrove rims and surface sediments dominated by halimeda rich wackestone rich in organic matter coral patch reefs are absent in contrast the unprotected northernmost part of turneffe has a wide reef and grainstone rim and the open lagoon area consists of mollusk foram halimeda wackestones packstones with abundant patch reefs

the mechanics of deep seated landslides results are presented of a sequence of laboratory tests undertaken to elucidate the behaviour of deep seated landslides in deep seated failures deformation has been reported at depths of up to 250 m in the movement zone owing to the weight of the overburden and the surrounding stress environment conventional soil mechanics cannot be used to explain effectively associations between the landslip activity and the deformation mechanisms operating within the moving mass a series of experiments has been undertaken on london clay using a high pressure servohydraulically controlled triaxial deformation system to replicate the stresses acting at the base of a large deep seated landslide a number of tests were undertaken the most significant focusing on the transition between ductile and brittle behaviour although sediments usually behave in a brittle manner at low effective stresses common to many geomorphological studies and in a ductile manner at high effective stresses the results presented here identify for the first time in mudrocks a transitional phase of behaviour in which creep like movement will manifest itself at the base of a deep seated landslide as the growth of microcracks the microcracks may eventually coalesce to form a shear surface a consequence of which is likely to be sudden failure the results thus have important implications in the understanding of movement mechanisms in large deep seated failures rates of displacement and how they may change through time 1997 by john wiley sons ltd

mechanical models of the 1975 kalapana hawaii earthquake and tsunami abstract our objective is to produce a mechanically realistic model for the 1975 kalapana event that explains the overall deformation and geological evolution of the south flank of kilauea and reproduces most known earthquake and tsunami observations to do this we present a new structural interpretation of geological data from kilauea along with modeling of the tsunami using recent seismic analyses in so doing we hypothesize an offshore north facing normal fault that we call the kalapana fault because of its limited onshore expression near kalapana we argue that several different interpretations of seismic data are simultaneously true each coinciding with a specific geological structure we perform a direct numerical simulation of the 1975 kalapana tsunami and we report results for the near field and the far field simultaneously our interpretation of geological structures provides sufficient constraints to derive three tsunami sources the kalapana fault a slump and a thrust fault these three tsunami sources are mechanically coupled according to our model of kilauea evolution although their contributions to tsunami generation remain relatively distinct slump displacement predicts a small shear stress beneath kilauea volcano we find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations repeated earthquakes like the 1975 kalapana event will produce extension and subsidence in the upper flank of kilauea as well as compression and uplift of the toe region accompanied by limited slump movement these deformations appear to stabilize kilauea and make catastrophic failure of the volcano flank less likely at this time

depositional environments and diagenesis of the kuldhar and keera dome carbonates late bathonian early callovian of western india abstract this paper describes 11 microfacies types in late bathonian early callovian carbonates of the kuldhar member of the jaisalmer formation rajasthan and the keera golden oolite member of the chari formation kachchh mainland western india the different microfacies associations reported in this study reflect an ideal shallowing upward sequence representing a system of bioclastic bars developed on the lower ramp evolving into an oolitic bar to bank system separating restricted lagoonal from lower ramp environment four main types of cements i e bladed fibrous syntaxial overgrowth and blocky cement characterized in a few cases by ferroan calcite and anhydrite ii occur in these carbonates the study also reveals that chemical compaction followed the two phases of early mechanical compaction that largely governed porosity of these limestones however micritization and neomorphism also contributed significantly in this respect diagenetic signatures in these carbonates suggest that marine phreatic and fresh water phreatic environments dominated but deep burial diagenesis also played its role in shaping these rocks the early and late diagenetic changes have been controlled by the depositional facies evolving in a basin riddled with rifting in an extensional tectonic regime forcing regional scale sea level fluctuations

why blind thrust faults do not propagate to the earth s surface numerical modeling of coseismic deformation associated with thrust related anticlines high fault tip stress concentrations are associated with coseismic slip on blind thrust faults and suggest that these structures should readily propagate to the earth s surface seismic profiles of blind thrust related earthquakes reveal diffuse zones of aftershocks surrounding the fault tip which are attributed to inelastic deformation such as flexural slip or extensional fracturing the complex interaction between blind thrust faults and secondary structures may control the evolution of blind thrust systems the influence of bedding plane slip on fault propagation is simulated with numerical models using the boundary element method we use two parameters to estimate the tendency for thrust fault propagation 1 the mode ii stress intensity factor and 2 the maximum coulomb stress near the fault tip calculations from both analyses suggest that shallow thrust faults may exhibit an increased tendency to propagate as a result of interaction with the earth s surface and slip along bedding planes above the fault tip and a decreased tendency to propagate due to slip along bedding planes at or below the fault tip our results demonstrate that the magnitude and style of inelastic deformation in active fault systems control fault propagation

micritized skeletal grains in northern belize lagoon a major source of mg calcite mud abstract lime mud in northern belize lagoon is composed predominantly of silt size cryptocrystalline grains and clay size clumps both of which consist of anhedral equant crystals less than 0 5 m in size this mud is 70 90 mg calcite containing 9 10 mole mgco3 detailed petrographic morphologic and mineralogic analyses suggest that the cryptocrystalline grains are micritized skeletal grains and that the mud formed by abrasion and bioerosion of these altered grains micritization of skeletal grains occurred primarily by recrystallization of original skeletal carbonate laths prisms and blades of mg calcite aragonite and calcite to equant crystals of micritic mg calcite with additional alteration by micritic infilling of microborings and skeletal cavities because of d fferences between crystal morphologies and mineralogies of original skeletal components and their micritized counterparts mud produced by diminution of micritized grains is distinct from that produced by skeletal breakdown the abundance of cryptocrystalline grains in the bahamas and other shallow carbonate environments suggests that micritized grains are potentially an important source of lime mud that has not previously been identified

lithified and unlithified mg calcite precipitates in tropical reef environments abstract push cores from the branching coral framework of lagoonal reefs in belize and panama indicate that the micritic mg calcite in the unlithified mud matrix is similar in composition to the well documented submarine lithified micritic crusts and infillings found in open reef framework the sediment matrix of the lagoonal framework contains significant concentrations of 12 to 13 mole mgco3 calcite that shows almost no signs of skeletal origins as indicated by a fairly consistent mineralogy and independent distribution patterns in sand silt and clay size fractions its sedimentological and mineralogical similarity to cemented micritic crusts and infillings suggests that the precipitation of micritic mg calcite is widespread in tropical reef waters and becomes lithified when precipitated in open frameworks but remains unlithified when trapped in impermeable lagoonal muddy sediments

valley shape influence on deformation mechanisms of rock slopes stress distribution in mountainous areas is influenced by local morphology valley morphology and the relationship between main and tributary valleys strongly depend on geological characteristics and evolution they may control the evolution of slope instabilities especially when interacting with pervasive structural features we performed parametric three dimensional 3d numerical modelling of simplified slope geometries with variable slope angle from 218 to 358 length combining different orientations for different slope sectors and changing attitude of pervasive planes of anisotropy foliation schistosity bedding data used in the 3d models are the initial slope geometry rock mass properties and internal anisotropy we assumed mohr coulomb behaviour with the presence of ubiquitous joints and different piezometric levels the model results show that plastic deformation initiates near the highest ridge just after deglaciation commences a shear zone develops and propagates toward the toe of the slope and its shape is strongly controlled by slope geometry anisotropy and in situ stresses the thickness of the failing mass for model slope reliefs up to 3200 m increases from 50 mto some hundreds of metres during glacier retreat and it depends on geometry of slopes anisotropy and in situ stresses results are compared to examples of deep seated slope deformations from the alps which helps in the interpretation of such phenomena and in the understanding of their influence on valley evolution

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

progressive failure of sheeted rock slopes the 2009 2010 rhombus wall rock falls in yosemite valley california usa progressive rock fall failures in natural rock slopes are common in many environments but often elude detailed quantitative documentation and analysis here we present high resolution photography video and laser scanning data that document spatial and temporal patterns of a 15 month long sequence of at least 14 rock falls from the rhombus wall a sheeted granitic cliff in yosemite valley california the rock fall sequence began on 26 august 2009 with a small failure at the tip of an overhanging rock slab several hours later a series of five rock falls totaling 736 m3 progressed upward along a sheeting joint behind the overhanging slab over the next 3 weeks audible cracking occurred on the rhombus wall suggesting crack propagation while visual monitoring revealed opening of a sheeting joint adjacent to the previous failure surface on 14 september 2009 a 110 m3 slab detached along this sheeting joint additional rock falls between 30 august and 20 november 2010 totaling 187 m3 radiated outward from the initial failure area along cliff sub parallel sheeting joints we suggest that these progressive failures might have been related to stress redistributions accompanying propagation of sheeting joints behind the cliff face mechanical analyses indicate that tensile stresses should occur perpendicular to the cliff face and open sheeting joints and that sheeting joints should propagate parallel to a cliff face from areas of stress concentrations the analyses also account for how sheeting joints can propagate to lengths many times greater than their depths behind cliff faces we posit that as a region of failure spreads across a cliff face stress concentrations along its margin will spread with it promoting further crack propagation and rock falls published in 2012 this article is a us government work and is in the public domain in the usa

fiber bundle model for multiscale modeling of hydromechanical triggering of shallow landslides 1 sudden and rapid mass movements associated with landslides and snow avalanches present a hazard to life and infrastructure yet their predictions and triggering mechanisms remain poorly understood statistical methods and correlative studies have been used to produce landslide or avalanche susceptibility maps often with limited physical basis mechanistic approaches based on factor of safety computation seldom represent the progressive transition from local failure events to a landslide and in general do not include heterogeneities associated with land cover or with subsurface material properties and hydrologic pathways focusing on rainfall induced shallow landslides we propose the use of the fiber bundle model fbm a generic yet powerful and adaptable model used in modeling fatigue and fracture of complex and disordered materials the primary strength of the fbm is its ability to represent the progressive failure of cracks and shear zones and the ruptures of highly heterogeneous bonding elements that are present in soils at all scales the model also provides a natural framework for interpretation of acoustic emission signatures from failing slopes which may form the basis of a monitoring and warning system

fracture mechanical models of dry slab avalanche release experimental evidence shows that snow is a pressure sensitive dilatant strain softening material in slow constant rate shear deformation when strain softening initiates in a weak layer underneath a snow slab avalanche release is hypothesized to be possible with or without additional loading specifically two cases are discussed 1 a shear crack like disturbance can initiate after formation of a slip surface in the weak layer and traverse the layer by a self propagating progressive failure with or even without loading and 2 a self propagating shear instability can develop when a region of the weak layer is driven past peak shear strength by loading for these cases the implied fracture sequence fracture geometry time scale of release and temperature effects are discussed and shown to be consistent with the known facts of dry slab avalanche release

use of longitudinal strain in identifying driving and resisting elements of landslides observations of deformation at the surfaces of landslides in utah and hawaii indicate that the upslope parts of the land slides have stretched and the downslope parts have shortened parallel with the direction of movement the maximum displacement of each landslide occurs in a relatively undeformed zone between the zones of shortening and stretching the pattern of deformation at the surface of these landslides may be useful in analyzing their mechanics by helping to constrain the longitudinal forces in limit equilibrium stability analysis we used earth pressure calculations to determine the range of possible longitudinal forces per unit width for active failure in the zone of stretching and for passive failure in the zone of shortening of one of the hawaiian landslides longitudinal forces computed by stability analysis assuming homogeneous strength exceeded the possible forces in much of the upslope half of the landslide consequently we assumed inhomogeneous strength and adjusted shear strength parameters at each segment of the slip surface until the longitudinal forces computed by stability analysis agreed with those computed by earth pressure theory and the factor of safety approached unity the distribution of longitudinal forces computed for inhomogeneous strength indicated that the boundary between driving and resisting elements of the landslide is near the thickest part of the slide in agreement with a simple formula for the location of the boundary

composite micrite envelopes in the lagoon of abu dhabi and their application for the recognition of ancient firm to hardgrounds abstract micrite envelopes are common early diagenetic features in marine carbonates throughout the phanerozoic this paper documents a continuum of sub recent constructive and destructive composite micrite envelopes and discusses their application for the recognition of ancient marine firm to hardgrounds in the modern subtropical carbonate depositional environment of the abu dhabi coastal lagoon micrite envelopes are actively forming and are directly assigned to a range of processes and depositional environments i in the outer high energy lagoon bioclasts and ooids typically contain empty microendolithic borings ii in the unconsolidated sediments of the inner to middle lagoon destructive micrite envelopes yield fragments of their host grains that result from boring etching activity and are bound and covered by biofilms iii constructive envelopes are formed by high mg calcite micrite cements and coat destructive envelopes in the inner to middle lagoon or may nucleate on aragonite needle cements in the outer lagoon micrite cements that form constructive envelopes are typical early marine diagenetic features and are among the main fabrics of firm to hardgrounds calcitic skeletal grains such as benthic foraminifera and coralline red algae are less affected by microbioeroders compared to aragonitic ooids gastropods and bivalves high mg calcite constructive envelopes have a higher preservation potential relative to aragonite host particles and aragonite cements hence the presence and recognition of constructive micrite envelopes in the rock record may be instrumental to identifying ancient aragonitic as well as unconventional firm to hardgrounds that may otherwise be difficult to recognise

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

stepped settlement a possible mechanism for translational landslides abstract translational landslides are a unique type of landslide that often causes disastrous consequences during their concealment based on the latest study and survey results we discussed the cause of translational landslides and built a corresponding model then the reliability of the genetic mechanism was validated via case studies the results showed that higher water levels increase the total stress thus leading to stepped settlement of the bedrock the alternate assemblage of hard and soft layers causes large quantities of tension fissures and considerable settlement this enormous settlement produces larger gravitational potential energies and impact energies and leads to the generation of pull rift troughs in addition a large number of landslides occurred with relatively moderate amounts of rainfall the increasing total stress on the sill caused by the reservoir water level and the heavy rainfall represents the spatiotemporal difference in the stepped settlement of bedrock which is one of the main reasons for atypical landslides therefore analyses of the failure mechanism and safety evaluations of translational landslides in reservoir areas should focus on their special engineering geological information such as the sliding bed with distributed soft and hard strata

origin of micropores in late jurassic oxfordian micrites of the eastern paris basin france porous micritic facies either primary chalks or resulting from secondary destructive micritization can constitute important hydrocarbon or water reservoirs characterization of reservoir properties and the understanding of factors which controlled the distribution of porosity are of primary interest to evaluate the prospective reserves middle and late oxfordian limestones of the eastern paris basin show several horizons with porosities higher than 20 the porosity is mainly microporous and located either within secondary micritized grains or in the micritic matrix using sem cathodoluminescence as well as confocal microscopy stable oxygen and carbon isotope ratios and petrophysical measurements a scenario for the evolution of the micropores is proposed lime mudstones to packstones constitute the majority of the high porosity facies hpfs inner lagoonal deposits are more micritized and thus more porous than grainstones and facies rich in leiolitic oncoids and echinoid clasts are less impacted by micritization micritization was responsible for an increase of the intragranular porosity in most grain types during both eogenesis and shallow burial mineralogical stabilization dissolved aragonitic particles and allowed precipitation of calcite rhombs this process was probably enhanced below surfaces of subaerial exposure during burial ostwald ripening allowed the growth of larger micrite crystals at the expense of smaller ones during early berriasian and late aptian recharges of deep aquifers when the northern margin of the basin was exposed overgrowths on micrite crystals were more important in intervals strongly affected by chemical compaction which favored oversaturation of waters with respect to calcite in low porosity horizons lpfs the dense micritic texture of oncoids and the monocrystalline architecture of echinoid clasts prevented an intense micritization while the strong chemical compaction enhanced poronecrosis telogenetic fracturing created new fluid pathways that favored inputs of meteoric fluid in porous micrite and allowed the continuation of ostwald ripening during cenozoic times as a whole mesogenetic inputs of waters undersaturated with respect to calcite in deep aquifers during exposure of basin margins are a more efficient process than early subaerial exposure for enhancing aggrading neomorphism and appearance of microporous micrites initial mineralogical heterogeneities also impact the intensity of chemical compaction and thus the stratigraphical distribution of microporous limestones

smoothness priors modeling of seafloor bathymetric data multibeam bathymetric data is modeled from a bayesian smoothness priors framework smoothness priors is a penalized likelihood nonparametric linear regression form of modeling and the bathymetry data are modeled one beam at a time the method is applied to data previously analyzed in goff and jordan 1988 and gilbert and malinverno 1988 the results contrast nonparametric and parametric modeling dispute the almost conventional removal of deterministic components prior to stochastic modeling and reveal new evidence about mid ocean ridge spreading processes

landslide deformation monitoring with alos palsar imagery a d insar geomorphological interpretation method the objective of this work is to propose a geomorphologically guided method for the interpretation of l band alos palsar interferograms created by differential interferometric synthetic aperture radar d insar the interferograms are used to estimate the deformation pattern of two rapid and large landslides poche la valette south east france the wrapped and unwrapped phase values are interpreted for different movement types rotational translational and complex sliding and two ranges of surface displacement rates kinematic sub units are detected for both landslides and zones affected by enlargement or retrogression are identified the insar derived displacement rates are consistent with ground based measurements and with remote estimates of the displacement from c band and x band satellite sar sensors the results demonstrate the potential of l band alos palsar imagery for the monitoring of active landslides with important changes in the soil surface state and covered by vegetation

coseismic landsliding during the mw 7 1 darfield canterbury earthquake implications for paleoseismic studies of landslides abstract the head scarp of the harper hills landslide consists of ground cracks with vertical displacement and extension that opened during the 2010 darfield canterbury mw 7 1 earthquake the geomorphology of the cracks regional geology and ground penetrating radar indicate that the landslide formed by bedding controlled translation and joint controlled toppling and suggest incipient deep seated movement crack depth and displacement along the head scarp vary along the ridge maximum values are located where the head scarp is closest to the local ridge line increased seismic shaking due to topographic and geometric amplification of seismic waves is suggested as an explanation for this relationship an excavation across the head scarp revealed no evidence of prior slip events over a time period that is likely to exceed the return period 1000 2500 years of peak ground accelerations experienced at this location in the darfield earthquake we suggest that specific seismologic attributes of the darfield earthquake may have influenced the location of landsliding in this instance studies of paleo landslides must consider crack preservation potential as well as complex source site effects that may complicate estimates of acceleration return periods from the subsurface investigation of individual landslide head scarps

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

geometry and kinematics of a landslide surface in tertiary clays from the duero basin spain abstract the penalba roto translational landslide is one of the large landslides that can be observed in the central area of the duero basin spain its present morphology is a semicircular shaped depression in which more than 6 m of vertical movement have been measured the erosion of the banks of the duero river affecting the slope of the penalba hill has incised vertical cliffs where a slip surface outcrops and can be observed currently the incision level of the duero river is located 22 m below this surface the slip surface on the translational zone within a large roto translational landslide developed within the duenas facies in a single bed with a high pi 39 0 47 8 and lower carbonate contents would have behaved as low shear strength surfaces r 18 21 8 at penalba the slip surface and the deformation structures related to it have been exceptionally well preserved the structures observed are similar to those usually described in shear zones of tectonic origin an s c fabric related to progressive simple shear and c planes called extensional crenulation cleavage these similarities suggest that analogous kinematic processes would have taken place in completely different geodynamic environments in the present work we have adopted a structural geological kinematic approach to explain the development of the features in this roto translational landslide

the origin of carbonate mud in isolated carbonate platforms of belize central america carbonate mud from three small isolated carbonate platforms of belize central america is largely a product of the breakdown of skeletal grains the composition of the 63 20 and 20 4 m fractions of 37 samples was determined by point counting under sem composition of the 4 m fraction was assessed qualitatively under sem the 63 4 m fractions are dominated by fragments of mollusks the codiacean alga halimeda and other skeletal types about one third of the particles in the 63 4 m fractions remained unidentified probably due to obliteration of diagnostic features by early recrystallization processes such as micritization nanograins 1 m and short 3 5 m aragonite needles are most common in the 4 m fraction these grains are interpreted to be largely fragments of codiacean algae halimeda penicillus the 20 4 and 4 m sediment fractions are composed of 80 and 75 aragonite on average respectively trace element composition of strontium averages 7 900 ppm in the 20 4 m fraction and in codiacean algae samples and 5 600 ppm in the 4 m fraction geochemical trace element data also argue against inorganic aragonite precipitation within the water column and favor a skeletal origin the lower strontium contents in the 4 m fraction as compared with the 20 4 m fraction may also be a consequence of early recrystallization processes

differential early diagenetic low mg calcite cementation and rhythmic hardground development in campanian maastrichtian chalk abstract the campanian maastrichtian limestones in the south of the netherlands are well sorted fine grained mudstones and silt to fine sand sized bioclastic grainstones these limestones show a distinct lithological cyclicity manifested by fining upward grain size cycles with calcite cemented layers or hardgrounds capping each cycle in the lower part of the succession the cyclicity is further enhanced by nodular chert layers these fining upward cycles are caused by fair weather or storm wave related energy fluctuations and consequently changing rates of deposition differences in composition and texture and differences in the degree of early diagenesis cemented layers and hardgrounds are the result of differential early marine calcite cementation in these limestones early calcite cementation cannot be explained by the supply of cementing materials from saturated seawater an alternative model for early marine calcite cementation is proposed in which early calcite cementation occurred within the sediment at some distance below the seafloor as a result of organic matter degradation and internal redistribution of bioclastic carbonate bacterial organic matter degradation caused dissolution of relatively unstable high mg calcite and or aragonite in the oxic zone followed by precipitation of calcite cement as a consequence of bacterial iron reduction duringperiods with a lower sedimentation rate any significant early cementation and replacement of high mg calcite occurred when younger oxic burrows dissected older burrowed sediment with a more advanced stage of organic matter degradation in particular iron reduction cementation also occurred when redox boundaries repeatedly moved through the same layers during periods with low nett sedimentation and increased storm activity and erosion the differences in the degree of early diagenetic calcite cementation were further enhanced during paleocene karstification and development of secondary porosity by dissolution of remaining unstable carbonate grains and by associated meteoric water calcite cementation

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation

a characterization of the spectral density of residual ocean floor topography ocean floor topography can be characterized as a signal related to lithospheric cooling and a residual the residual can be further modeled by comparing the shape of its power spectrum with that of a fractal process power spectra of seabeam profiles along a flowline in the south atlantic are calculated the data are resampled pre whitened by first differencing tapered with a hanning window and passed to an fft the effects of the pre whitening are removed and the spectra are smoothed the spectra of ocean floor topographic residuals are curved power increases less rapidly with increasing wavelength at wavelengths greater than several 10 s of kilometers and straight at shorter wavelengths

investigating controls on boron isotope ratios in shallow marine carbonates abstract the boron isotope ph proxy has been widely used to reconstruct past ocean ph values in both planktic foraminifera and corals species specific calibrations are required in order to reconstruct absolute values of ph due to the prevalence of so called vital effects physiological modification of the primary environmental signals by the calcifying organisms shallow marine abiotic carbonate e g ooids and cements could conceivably avoid any such calibration requirement and therefore provide a potentially useful archive for reconstructions in deep pre cenozoic time however shallow marine abiotic carbonates could also be affected by local shifts in ph caused by microbial photosynthesis and respiration something that has up to now not been fully tested in this study we present boron isotope measurements from shallow modern marine carbonates from the bahama bank and belize to investigate the potential of using shallow water carbonates as ph archives and to explore the role of microbial processes in driving nominally abiogenic carbonate deposition for bahama bank samples our boron based ph estimates derived from a range of carbonate types i e ooids peloids hardground cements carbonate mud stromatolitic micrite and calcified filament micrite are higher than the estimated modern mean annual seawater ph values for this region furthermore the majority 73 of our marine carbonate based ph estimates fall out of the range of the estimated pre industrial seawater ph values for this region in shallow sediment cores we did not observe a correlation between measured pore water ph and boron derived ph estimates suggesting boron isotope variability is a depositional rather than early diagenetic signal for belize reef cements conversely the ph estimates are lower than likely in situ seawater ph at the time of cement formation this study indicates the potential for complications when using shallow marine non skeletal carbonates as marine ph archives in addition variability in 11b based ph estimates provides additional support for the idea that photosynthetic co2 uptake plays a significant role in driving carbonate precipitation in a wide range of shallow water carbonates