on the application of simple rift basin models to the south polar region of enceladus 1 the south polar terrain spt of saturn s moon enceladus is a mysteriously active region that exhibits intriguing tectonic signatures and widespread fracturing the central region of the nearly circular spt is depressed into the surface by a few hundred meters and bounded by a ring of cliffs roughly 1 km high in this study we investigate whether this depression and surrounding mountainous uplift is consistent with the morphology of terrestrial rift basins and the possibility that the spt could have formed during a tectonic event analogous to those of such rift basins on earth using three mechanical models of basin formation we compare our predicted topography of the spt with observed topography of the region the first of three models we consider assumes crustal stretching by factor b and predicts a basin depth of roughly 600 m closely matching previously published estimates of the depth at the spt models of extension and compression assuming an elastic response in the ice crust predict best fit mountain uplift of roughly 1820 m and 1130 m respectively our preferred model suggests that the icy shell in the spt has been stretched but the extension is partially balanced by compression along the edges of the basin leading to the uplift of the mountains along the boundary thereby implying that the spt may have a tectonic origin analogous to that of a terrestrial basin

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

rheology of the earth s mantle a historical review abstract historical development of our understanding of rheological properties of the earth s mantle is reviewed rheological properties of the earth s mantle control most of the important geological processes such as the style of mantle convection e g stagnant lid versus plate tectonics and the nature of thermal evolution however inferring the rheological properties of the earth s mantle is challenging because of the presence of multiple mechanisms of deformation that have different dependence on time scale strain rate stress levels and other parameters through the integration of a broad range of observations including the elastic stiffness from tidal deformation and the viscosity from the concept of isostasy a gross picture of rheological stratification of the earth s mantle a strong lithosphere a weak asthenosphere and a strong layer below was proposed in the mid 19th century however not only the physical basis for such a model was weak due to the lack of proper understanding of some materials science issues such as the interplay between elastic and viscous deformation but also the lack of understanding of temperature depth relation associated with convection prevented our understanding of the rheological structure of the earth s interior major progress occurred in the first half of the 20th century in our understanding of the atomistic mechanisms of plastic deformation in solids and much of the theoretical framework on the plastic deformation of solids was established by late 1960s those developments provided a basis for scaling analyses that are critical to the applications of laboratory results to the earth s interior major progress in laboratory studies on rheological properties occurred in the mid 1960s to the early 1970s in griggs lab using a new type of solid medium high pressure deformation apparatus to pressure 2 gpa and temperature 1600 k the basic concepts such as the water weakening non linear rheology and deformation induced lattice preferred orientation were identified by their studies however large uncertainties in the stress measurements with this type of apparatus were recognized in the late 1970s and high resolution experimental studies using synthetic samples were initiated in paterson s lab in the mid 1980s using a high resolution gas medium deformation apparatus however experimental studies with such a gas medium deformation apparatus can be conducted only at low pressures

normalized undrained shear strength of clay shales this paper examines the possibility of normalizing the undrained shear strength behavior of clay shales shales are formed in sedimentary basins by diagenetic processes which turn young clay sediments into compacted and lithified shales cementation at grain contacts affects many properties of shales including the apparent preconsolidation and shear strength based on a study of 25 different types of materials the normalized undrained shear strength of clay shales was found to correlate satisfactorily with overconsolidation ratio following the shansep stress history and normalized soil engineering properties normalization procedure for clays the normalized undrained shear strength correlation appears valid regardless of the cause of the apparent preconsolidation correlations of the apparent preconsolidation stress with unconfined compressive strength and compressional wave velocity are proposed to predict the normalized undrained shear strength of clay shales

decalcification and residual shear strength reduction in fuller s earth clay analyses of borehole samples at 1 m intervals through the fuller s earth succession at bath reveal an inverse correlation between calcite content and atterberg limits the calcareous component of t

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

identification of cementation in overconsolidated clays the note describes the application of the generalized compressibility equations for normally and overconsolidated clays presented by nagraj srinivasa murthy 1986 based on physico chemical principles the ideas are used in a new combination as a method of identifying possible particle cementation in overconsolidation clays examination of the present method indicates that errors due to cementation of overconsolidated soils are likely the note recommends the inclusion of a step which compares the shear strength of the soil sample to that predicted for that soil based on physico chemical principles the derived sensitivity can be used to avoid cemented soils being inadvertently analyzed as uncemented overconsolidated soils

viscosity of the earth direct and indirect estimates of the variation of viscosity with depth in the mantle indicate that a low viscosity layer exists in the upper mantle a viscosity varying with depth can be used to reconcile the various estimates of relaxation times if the seismic anelasticity can be used as a guide the average viscosity of the lower mantle is about 10 23 p combined with previous estimates of the upper mantle viscosity this gives a relaxation time of about 3000 years for the non equilibrium bulge of the earth this is close to the time from the last ice age but is much less than the 10 7 years required if the non equilibrium bulge is due to the changing rate of rotation which requires an average mantle viscosity of 10 26 p if the latter value is correct the activation volume for creep is much larger than for anelasticity or the effect of a phase change in the upper mantle is more effective in suppressing creep than attenuation the response of a layered viscous sphere to a surface load is calculated for a wide range of parameters including the above range of estimates for lower mantle viscosity these results can be used to estimate the decay time or the isostatic time scale for various sized features

mineralogy chemistry and physical properties interrelationships of some sensitive clays from eastern canada this paper describes the use of quantitative mineralogy and specific surface area in interpreting the index properties of clayey soils from nine sites in eastern canada samples representative of t

the bayesian probabilistic prediction of strong earthquakes in the hellenic arc abstract the bayesian probability theory in conjunction with the poisson process model is used to develop a bayesian discrete distribution to estimate or predict the inter arrival times tj for strong earthquakes in the hellenic arc the bayesian posterior probabilities may be computed from the relationship p t r m t r e t r 1 e t r j 1 m t j e t j 1 e t j where p t r m is the conditional probability of the event tr given that an earthquake of magnitude m has occurred the bayesian discrete analysis is performed first by using the poisson process to determine the prior probability distribution for tj and the likelihood function we can imagine the random earthquake experiment involved in the application of bayes theorem to earthquake prediction to be a two stage experiment the first stage was initiated a long time ago when the real time arrival dates of strong earthquakes were first recorded the second stage was initiated in 1935 when the earthquake magnitude scale was introduced by richter 1935 in southern california richter probably never thought that this measure of the earthquake magnitude then will be an experiment designed to give us information about the outcome of the earthquake inter arrival times the first stage the earthquake data analyzed in this study have been taken from the earthquake catalog for the hellenic arc prepared by ambraseys 1981 the discrete bayesian analysis suggests determining the most likely outcomes for the length of earthquake inter arrival times by using some maximum values of the final bayesian probabilities the following inferences concerning future strong earthquake occurrences in the hellenic arc area may be drawn 1 1 our western northwestern zone is a seismic region which approximately coincides with the region studied by wyss and baer therefore we agree with the geographic location of the expected earthquake forecasted by wyss and baer 1981 2 2 using probability theory bayes theorem poisson process we concluded that a period of strong earthquake activity is expected to occur in the same geographic location during the decade 1992 2002 this conclusion supports ambraseys conclusion however it should be noted that our conclusion indicates that the period of strong earthquake activity will occur anyway a decade later than predicted by wyss and baer

four seismogenic environments in eastern canada abstract although the seismogenic environments in eastern canada have some common features the respective seismotectonic environments are influenced by local features the seismotectonic environment in four seismogenic regions are described in order to illustrate how local features are reacting with the ambient plate tectonic stress a common feature to modify the nature of the seismic activity the charlevoix earthquakes are occurring along steeply dipping planes formed during the opening of lapetus ocean in the proterozoic perturbed by a meteor impact during the paleozoic and reactivated by the opening of the present day atlantic ocean in the mesozoic theoretical curves of maximum shear stress versus depth based on a wet upper crust and a wet quartz rheology in the lower crust for which the heat flow is 1 0 hfu 42 mw m2 can account for the depth distribution of earthquakes in this region potential trigger mechanisms are gravitationally induced stress water infiltration and vertical shear strain changes approximately 3 10 8 yr due to post glacial rebound the unusually deep focus 29 km of the m 5 9 saguenay earthquake of 1988 could be due in part to the lower heat flow in this region as compared with that in the charlevoix region which is about 70 km to the east the miramichi earthquake sequence is occurring on conjugate faults within an intrusion at depths shallower than 10 km theoretical curves of maximum shear stress versus depth based on a wet quartz rheology in the lower crust for which the heat flow is 1 5 hfu can account for this depth distribution the steep gradient in the vertical ground movement rate 5 10 8 yr in the epicentral area which is probably due to post glacial rebound is a potential trigger mechanism for favorably oriented faults the normal fault seismic regime along northeastern baffin island can be explained by a combination of topography and post glacial rebound which can generate horizontal extensional stresses capable of overcoming the ambient compressional plate tectonic stress post glacial rebound stress can act as a trigger mechanism for the ne dipping faults in this region in the grand banks region there is seismic evidence indicating that the slump that caused the destructive tsunami also generated the strong seismic m 7 2 signals but double couple solutions that satisfy certain criteria are not ruled out the absence of surface faulting especially in the epicentral regions of large earthquakes is not properly understood but several possibilities are near surface layering that could mask the underlying fault offsets and a spatiotemporal variation in the ambient plate tectonic stress field as knowledge of the causative factors of eastern canada earthquakes and also the data base for empirical earthquake scaling relations increase an overview of the seismotectonics of these mid plate earthquakes should be enhanced

thermal evolution of the earth abstract models to study the thermal evolution of the earth have been developed based on a calculation of finite amplitude thermal convection in an incompressible and viscous mantle with temperature and pressure dependent physical parameters the lateral dependences of the variables are resolved through their spherical harmonic representations while the radial and time dependences are calculated using numerical procedures the major emphasis of this paper is to illustrate the effects of different factors on the thermal evolution of the earth rather than to present a definite earth model the main conclusions achieved in this study are 1 1 a significant portion of the present day temperature in the mantle and surface heat flux is due to initial heat of the earth resulting from accretion and core formation 2 2 since the effective rayleigh number of the earth s mantle is high solid state convection is found to be sufficiently efficient to maintain an almost adiabatic temperature gradient within the convecting region while large temperature gradients exist across the thermal boundary layers core mantle boundary and below the lithosphere 3 3 the convection is oscillatory with avalanche type properties this is due to the slow development of instability in the thermal boundary layer near the surface which causes the episodic behavior the periods of the oscillations are about 50 250 m y the oscillation in the mantle also induces periodic features in the surface heat flux and the thickness of the lithosphere mantle viscosity structure plays an important role in the cooling rate and nature of oscillations 4 4 the mobility of the lithosphere is an important factor controlling the thermal state of the earth s interior a mobile lithosphere will cool the interior faster

viscoelastic membrane tectonics the theory of membrane tectonics proposed by turcotte and oxburgh 1973 to explain intraplate tensional features and earthquakes and developed by turcotte 1974 for an elastic lithospheric membrane is extended to the case of a viscoelastic lithosphere such an extension may be expected to seriously modify the theory since for all lithospheric viscosities except the very highest the time scale for viscous relaxation is comparable to the time scale for changes in plate curvature it is found that for most viscosities considered the membrane stresses generated by changes in plate curvature do not exceed 10 bars we conclude that either the effective viscosity of the lithosphere is much higher than indicated by most studies or membrane tectonic stresses play a secondary role in the generation of intraplate features and earthquakes

towards a general model of quick clay development abstract within the clear definition of a quick clay as being a soil which has a sensitivity greater than 30 and a remoulded strength less than 0 5 kpa a general model for quick clay development is presented based on the influences of various material properties and natural processes on the sensitivity and remoulded strength the influences are separated according to depositional requirements and post depositional factors and according to whether the influence is to increase the undisturbed strength or to decrease the remoulded strength depositional factors are the requirements for a flocculated structure and the dominance of low activity minerals post depositional factors are cementation and slow load increase which increase the undisturbed strength and little consolidation leaching and dispersants which decrease the remoulded strength the application of the model to marine brackish water and freshwater sediments is discussed

viscosity of the lower mantle as inferred from rotational data until recently most estimates of the deep mantle viscosity were based on analyses of postglacial uplifts and there were no serious estimates of the sensitivity of the derived viscosity solutions to variations of the input parameters such as those associated with the surface loading in this paper the viscosity of the lower mantle is arrived at by making comparisons of the observed secular motions of the earth s rotation axis with theoretical results from a layered viscoelastic rotating earth which has been subjected to glacial forcing our model consisting of an elastic lithosphere a two layer adiabatically stratified viscoelastic mantle and an inviscid core is essentially analytical and this makes it economically feasible to use as an aid in conducting an extensive sensitivity analysis of the lower mantle viscosity from changes in the parameters connected with the deglaciation phenomenon both sets of rotational data polar wander and nontidal deceleration of the length of the day have been employed to constrain the viscosity structure on the basis of this type of investigation the viscosity of the lower mantle is found invariably to be larger than that of the upper mantle and lies between 1 and 4 1022 p our results which just rely on the second degree harmonic of the strain field also lead to a determination of an upper bound to the thickness of the globally averaged lithosphere this value ranging between 130 and 190 km suggests that strong lateral heterogeneities between oceanic and continental plates may extend a few hundred kilometers into the upper mantle

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

some aspects of viscous stress relaxation and intraplate seismicity abstract considerable evidence suggests that the lithosphere has a maxwellian rheology with an effective viscosity of 1026 poise or less in a maxwellian lithosphere viscous stress dissipation limits the maximum attainable stresses due to mechanisms providing a constant stress buildup to a value max given by the product of stress buildup rate c and viscous relaxation time max c where is the ratio of viscosity to rigidity the effectiveness of several intraplate stress building mechanisms in a maxwellian lithosphere was analysed with the following results 1 1 the maximum stress produced by the latitudinal drift of lithospheric plates is 27 bars or less 2 2 the maximum stress produced by the cooling of uplifted eroded regions is 90 bars or less 3 3 lithospheric flexure due to isostatic rebound causes maximum stresses of 68 bars or less for the appalachian rebound and approximately 150 bars for the laurentide rebound it is concluded that none of the mechanisms considered are likely to cause earthquakes if the mechanical strength of the lithosphere is on the order of 1 kb if the strength of the lithosphere is on the order of 100 bars then intraplate earthquakes may result from the laurentide deglaciation as well as from the cooling of uplifted eroded regions but if the lithospheric viscosity is on the order of 1025 poise then only the laurentide deglaciation may produce adequate stresses the fact that a stress buildup rate of 74 bars 200 yrs along the san andreas fault generates earthquakes requires a minimum lithospheric viscosity on the order of 1022 poise

lithofacies of lower palaeozoic deep marine sediments in the isle of man a new map and stratigraphic model of the manx group

mineralogy and geochemistry of neoproterozoic siliceous manganese formations from ntui betamba cameroon pan african fold belt implications for mineral exploration the siliceous manganese formations from ntui betamba area have been studied with the aim to constrain their mineralogy geochemistry and genesis neoproterozoic manganese bearing rocks at ntui betamba include garnet galaxite bearing quartzite and galaxite bearing quartzite that besides a characteristic quartz spessartine garnet and galaxite mnal2o4 assemblage comprises also graphite and rutile galaxite crystals show chemical zoning from core to rim due to the change in composition from galaxite to cryptomelane bulk rock geochemistry reveals that the studied rocks are characterized by high sio2 content 52 83 wt they are enriched in fe2o3 and al2o3 and display mn fe ratio of 1 2 mno concentrations are high in galaxite bearing quartzite 16 wt and moderate 8 03 wt in garnet galaxite bearing quartzite the transition trace metal co cu and ni contents are lower with co and cu markedly depleted relative to ni and variable contents of zn the ree pattern of garnet galaxite bearing quartzite shows ce positive anomaly similar to the hydrogenous sediment but differs from the later with strong eu negative anomaly and the lack of weak positive anomaly in yb whereas the galaxite bearing quartzite is characterized by the lack of ce anomaly and the weak eu negative anomaly both rocks show hree content close to that of hydrothermal sediment and exhibit flat hree trend the high contents of silica iron and aluminum together with the co zn ratios 0 3 and the contrasting behavior of ree suggest that the studied manganese bearing rocks are of sedimentary origin probably derived from a mixed hydrothermal hydrogenous source the high content of mn bearing minerals in these rocks represents indicators of concealed or buried mineralization and could be used as exploration guide

some geophysical implications of the satellite determined geogravity field summary possible locations for the sources of the low degree gravity harmonics are examined in the context of the interrelationships of the geogravity field with the geomagnetic field and its drifting and non drifting parts as well as certain other geophysical controls the available evidence does not support the westward drift of the gravity field the hypothesis that the upper mantle is the most probable location for a bulk of the mass anomalies which produce the low degree gravity harmonics seems to be most acceptable at this stage of our knowledge a bulk of the mass anomalies is believed to be generated by lateral compositional and thermal variations in the asthenosphere these variations also seem to be responsible for a major part of the observed correlation between the geogravity field and the geomagnetic secular variations by dint of their property of affecting both the density and electrical conductivity of materials lateral heterogeneities of the asthenosphere seem to be closely associated with relative motions in the asthenosphere and seem to play an important role in the tectonic model which explains continental drift as a result of sea floor spreading

geochemistry of ferromanganoan metasediments from the island of andros cycladic blueschist belt greece abstract on the island of andros cycladic blueschist belt metamorphosed ferromanganoan sediments occur in widespread lateral distribution they form concordant layers and lenses within a uniform sequence of quartz rich metapelitic schists which can be derived from pelagic siliceous mudstones three main types of ferromanganoan metasediments were geochemically investigated 1 piemontite spessartine and piemontite quartzites psq containing braunite rich lenses 2 spessartine quartzites sq and 3 napyroxene quartzites npxq textural and geochemical evidence leads to the conclusion that psq is derived from a mn nodule bearing sediment consisting of a mixture of terrigenous illitic clay with biogenic radiolarian ooze compared to recent nodule bearing sediments psq is markedly enriched in cu pb sr and as we assume that these elements were mobilized during diagenesis and or early metamorphism from the sedimentary column and were subsequently concentrated in minerals like piemontite ardennite and braunite under highly oxidizing conditions in contrast to psq sq and npxq are derived from parent sediments rich in smectite sq shows a higher al fe ratio in rock composition than npxq and may change into npxq by a decreasing content of spessartine while sq is chemically equivalent to a montmorillonitic clay mn 2 na almost spessartine free npxq can be derived from fe rich nontronitic clay na mn 2 required for the formation of sq was probably mobilized from adjacent mn nodule bearing sediments psq

upper crustal stresses and vertical stress migration in eastern canada diversified phenomena are contributing to our knowledge of various aspects of the stress field and the origin of the crustal stresses in eastern canada both in situ stress measurements to 2100 m and earthquake fault plane solutions in the upper crust 5 20 km indicate that the maximum horizontal stress is greater than the vertical absence of earthquakes in the lower crust 20 km implies a comparatively lower deviatoric horizontal stress in this layer stress directions as determined from both in situ measurements and earthquake fault plane solutions indicate an overprint confined to the ene octant which correlates with the direction predicted by modeling of plate tectonic stresses thus spreading mid atlantic ridge stress is considered to be one of the important contributors to the stress field in eastern canada viscoelastic relaxation of this stress is considered to enhance the deviatoric stress level in the upper crust while simultaneously reducing that in the lower crust the crust acts as a stress guide within which stresses in the upper crust that are lost through brittle failure i e earthquake stress drop can be replenished from the lower crust moreover the directionality predicted by modeling of spreading mid atlantic ridge stress is maintained incomplete postglacial rebound also contributes to deviatoric compression other possible contributors to the upper crustal stress field are basal drag and membrane stress but the relative contributions from these sources are not properly understood

physical chemical and mineralogical properties of mexico city sediments a geotechnical perspective discussion the authors paper presents interesting results from mineralogical tests conducted on the sediments beneath mexico city from the title it could be inferred that the paper would lend some quantitative insight into the reasons for the dis tinctive geotechnical behaviour of the mexico city sediments valuable profiles of the mineralogy index tests shear wave velocity grain size distribution and a cone penetration test log are provided however it appears that no attempt has been made to quantitatively link the observed fascinating behaviours with the presented data if any such links exist rather it is stated that results from the present study sug gest that the exceptional properties of mexico city sediments i e very high water content and plasticity low shear wave velocity and remarkable elastic behaviour are associated with the presence of amorphous material coating the particles the authors attribute considerable importance to amorphous materials i e noncrystalline oxides of various minerals principally iron aluminum and silicon in the formation of the mexican sediments and their observed behaviours yet the processes by which the amorphous material content is determined segalen 1968 are chemically aggressive bentley 1980 quigley 1980 torrance 1995 and could also strip away any carbonate minerals that represent up to 30 of the mexico city soil mineralogy the sediments within zone 4 are noted to exhibit considerably different behaviours than those in zones above or below of the mineralogical index property and grain size data presented it is the differences in calcite cation exchange capacity and organic matter which are most characteristic of zone 4 when compared with other zones it is of interest to compare the mexico city sediments with illitic sensitive clays in canada the united states and norway and published data from fucino italy the discussers have found interesting correlations between the carbonate content and vertical effective yield stress preconsolidation pressure of glacially derived fine grained soils of new york state and southern ontario boone and lutenegger 1997 burghignoli et al 1991 concluded that carbonates play a role in the observed initial shear modulus shear wave velocity and undrained shear strength of the italian clay and that the influence of carbonate bonding was likely obliterated by the large strains involved in penetra tion testing the sedimentary environment and typical index and mineralogical properties of some of these soils are compared in table 1 several differences are striking namely 1 the scandinavian and north american soils were deposited relatively rapidly during retreat of the ice sheets in the last ice age from approximately 11 000 years before present whereas those of italy and mexico city are reported to have been deposited over a significantly longer period of time from approximately 64 000 and 600 000 years before present respectively i e sedimentation rates were likely half an order of magnitude or more slower for the italian and mexican deposits 2 both the fucino and mexico city lacustrine basins were without an outlet for the majority of the inferred sedimentation period what role might dissolved salts or other minerals within the water body or in the pore water have on the final structure and behaviour of the sediments despite many years of research into the effects of salinity on the formation and resultant behaviour of natural sediments related issues were not discussed in the paper

landslides in weakly cemented glaciolacustrine sediments morkill river valley british columbia slopes in weakly cemented glaciolacustrine sediments in the morkill river valley in the canadian rocky mountains stand at up to 70 based on field and laboratory observations it appears that a contributing factor to insta bility is the softening of the soils by frost action and the leaching of calcite cement field density profiles demon strated increased density and carbonate content with an increase in depth laboratory tests of carbonate content indicated a positive correlation between calcium carbonate and density in the glaciolacustrine sediments the relation ship was strongest in sands in which leaching and dissolution were important components of softening in clays frost action was the dominant component of softening freeze thaw tests showed a 50 decrease in strength after one cycle of freeze and thaw in the silts and clays

deformational and stratigraphic influences on mineralization in se ireland the evidence that has accumulated to date to support the thesis that deformational and stratigraphic controls are reflected in the occurrence and siting of metal deposits in se ireland is evaluated in the case of an important tungsten deposit stratigraphic influences can be seen in the geochemical and mineralogical development of wallrocks prior to crystallization of granite hosted mineralization tourmalinites confined to a definable stratigraphic interval are associated with pegmatite hosted lithium deposits though the stratigraphic control is important the tungsten and lithium deposits are in addition confined to the trace of a major deformation zone

models of crustal deformation this review is principally concerned with theoretical models of crustal deformation developed during this quadrennium observational data as well as topics in lithospheric flexure and isostasy are covered in companion reviews in this volume progress has been made toward constructing both new inelastic and inhomogeneous elastic models of earthquake induced crustal deformation most of the inelastic models involve dislocations or green s functions in an elastic or anelastic lithosphere which overlies a maxwell viscoelastic asthenosphere

geologic control on soil composition and properties lake ojibway clay plain matagami quebec varved clays deposited in proglacial lake ojibway at matagami quebec were derived from two source areas carbonate deficient precambrian crystalline igneous rocks from new quebec to the east and

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

on the paucity of amorphous minerals in the sensitive postglacial marine clays the abundance and role of amorphous minerals in the sensitive marine clays of eastern canada has been a subject of investigation since 1974 unfortunately the segalen selective extraction procedure alternating hcl and naoh which was used in most of the experiments is very aggressive by attacking both oxide minerals which were presumed to be amorphous and crystalline phyllosilicates its use led to major overestimates of the possible amorphous mineral content less aggressive selective extraction procedures indicate that less than 1 of the sensitive champlain sea sediments is oxide minerals and mossbauer spectroscopy has detected only crystalline iron oxides which are probably of detrital origin the amount of amorphous oxide minerals is at most a small fraction of 1 crystalline iron oxides in the concentrations naturally present have been demonstrated to influence the rheology of the sensitive marine clays but it seems improbable that the very small amounts of amorphous minerals that m

carbonates and cementation of glacially derived cohesive soils in new york state and southern ontario cet article presente des resultats se rapportant a la teneur en carbonate de silts et d argiles naturels en fonction de la profondeur de l emplacement geographique et de l origine geologique on etudie aussi l influence de cette teneur en carbonate sur le comportement geotechnique l effet sur la pression de preconsolidation apparente est illustre en detail pour l un des sites etudies la repartition des carbonates a l interieur des varves d un depot glacio lacustre est egalement presentee pour demontrer la variabilite potentielle de la cimentation naturelle des sols les donnees en provenance de quinze sites etayent les relations proposees entre teneur en carbonate et pression de preconsolidation apparente

geologic origin effects on mineralogy index properties and fabric of a fine grained carbonatic deposit abstract this paper addresses the relationship between geological history and depositional environment and the characteristics of natural soils based on an experimental study conducted on a soft fine grained lacustrine carbonatic deposit formed about 22 000 bp during the wisconsin glaciation in the southwestern part of the state of indiana usa the carbonatic soil layer characterized in this study is approximately 4 m thick and is formed by the repetition of thin sublayers of two different soils with distinct composition and engineering properties the differences in index properties between these two soils and their relationship to the mineral composition derived from x ray diffraction xrd analyses are discussed in detail scanning electron microscopy sem is used to describe the microstructure of the two soils including the morphology of select minerals pyrite and calcite and the biological intrusions present in one of them these observations combined with a detailed study of the local geology lead to hypothesize that different source materials and sedimentary environments alternated during the formation process of the deposit

tectonic setting and regional significance of the port aux basques gneiss sw newfoundland the port aux basques gneiss of southwest newfoundland comprises three paragneiss and schist assemblages the grand bay and port aux basques complexes and the harbour le cou group they are intruded by large volumes of basic sheets and coeval middle ordovician granitoids the margaree and kelby cove orthogneiss which also cut a tectonic slice of earlier ultrabasic to basic rocks within the grand bay complex the big barachois assemblage the grand bay and port aux basques complexes are juxtaposed by the late silurian isle aux morts fault zone against the harbour le cou group to the east which dominantly comprises sillimanite and garnet bearing pyritiferous metasediments with amphibolitic intrusions and meta pillow basalts in its lower stratigraphic units geochemical studies have shown that metabasites of the grand bay complex port aux basques complex margaree and kelby cove orthogneiss comprise fractionated and crustally contaminated morb like and within plate tholeiites suggestive of an ensialic okinawa type back arc basin these have comparable characteristics to metabasites in the harbour le cou group and suggest that these units comprise remnants of an extensive mid ordovician marginal basin developed within a promontory on the peri gondwanan continental margin in contrast the big barachois assemblage in part comprises a distinct suite of pre mid ordovician island arc tholeiites

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

state of stress in the oceanic lithosphere in response to loading summary flexure studies of the oceanic lithosphere constrained by bathymetry and gravity data suggest that the lithosphere behaves elastically over geological time scales for loads to be supported however large bending stresses approaching 10 kb in some cases are required at the top and bottom of the elastic plate these stress differences can be significantly reduced by introducing more complex rheologies we propose a model of layered lithosphere consisting of a purely elastic upper layer a transition zone with viscosity varying with depth and a perfectly plastic lower layer the transition layer is grossly centred at the bottom of the elastic plate such a model results in a noticeable reduction of stress differences reaching 60 per cent for flow laws representing creep mechanisms in olivine when applied to a number of seamount loads this model leads to maximum stress differences which do not exceed 1 2kb the approach used in this study allows us to follow stress relaxation over time taking account of the thermal cooling of the lithosphere we show that the elastic thickness of the lithosphere is stabilized after a given time while the time required for stabilization is found to be of the order 5 6 per cent of the age of the lithosphere at the date of loading

microstructure and cementation of two carbonatic fine grained soils this paper presents an investigation of the microstructure and cementation of two carbonatic fine grained soils obtained from a deposit of lacustrine origin formed during the wisconsin glaciation

stress and relaxation time in the viscoelastic lithosphere inferred from the outer topographic rise the deformation of a thin viscoelastic plate is usually analyzed by use of an equation that is derived with an artificial assumption of the poisson s ratio equal to 1 2 it is shown in this paper that a simple treatment applicable to an arbitrary value of poisson s ratio is possible by introducing a new variable that represents the pressure gradient between the top and bottom of the plate in this treatment a one dimensional stationary deformation of moving plate is given by a simple analytic equation this equation is used to analyze the bathymetry of the outer topographic rise seaward of the deep sea trenches the analysis reveals that the lithosphere in the western pacific trenches is subject to an extensional horizontal force of 100 mpa or greater the horizontal force may be much less or even compressive in the eastern pacific trenches to prevent horizontal force and bending stress from being extraordinarily large the maxwell relaxation time of the plate must be 1 m y or shorter and the effective viscosity must be 1024 pa s or less

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

mantle stratification and long term polar wander there is accumulating evidence1 2 that the average location of the earth s magnetic pole has moved relative to the deep mantle over the past 200 myr this phenomenon of true polar wander may be caused by the advance and retreat of ice sheets3 or by mass redistribution in the earth s interior due to changes in the pattern of mantle convection4 5 new analyses1 2 6 of polar wander data show a significant shift of the pole in the late cretaceous but this period is thought to have been too warm for glaciation to have occurred thus most of the true polar wander must be due to mass movements in the mantle here we show by analysing the appropriate equations for polar wander that both viscosity and chemical stratification in the mantle are important in determining the rate of polar wander the dynamical effects of chemical stratification and high viscosity 1023 poise in the lower mantle are to decrease polar wander speed to a level consistent with the averaged velocities inferred from palaeomagnetic data whole mantle convection models without non adiabatic density jumps at 670 km depth and with viscosities less than 1023 p would produce wandering rates in excess of 5 per myr

geological setting and genesis of coticules spessartine metapelites in the lower ordovician of the stavelot massif belgium the lower ordovician in the caledonian stavelot massif belgium contains a coticule member probably arenig in age composed of red hematite rich shales alternating with thin yellowish coticule beds these coticules are fine grained highly manganiferous metamorphic rocks mainly composed of spessartine garnet mica and quartz similar rocks of about the same age occur in several localities along the appalachian and caledonian fold belts the belgian coticules are thought to have originated from marly sediments which had been deposited rapidly probably by density currents and in which caco 3 had been diagenetically replaced by mnco 3 during metamorphism spessartine garnets were formed from this mnco 3 and mica manganese and iron are thought to have originated from volcanic exhalative processes

factors affecting at rest lateral stress in artificially cemented sands this paper presents the results of a laboratory study on the at rest lateral stress and ko of two artificially cemented sands a modified oedometer ring was used to measure the lateral stress of cemented and uncemented sands test materials were no 3 ottawa sand and a marine sand with portland cement the specimens were prepared using the method of undercompaction to minimize the influence of specimen preparation on test results the cement contents were 0 0 5 1 0 2 0 4 0 and 8 0 by the weight of dry sand the water content of the specimens was 4 of the weight of dry sand and cement when the sands were cured under zero confining pressure the test results indicated the following the at rest lateral stress in cemented sands decreases significantly with increasing cement content the relationship between the vertical and at rest lateral stress is nonlinear and the value of ko increases with increasing vertical stress and the lateral stress decreases with sand density and curing period when the s

thermomechanical properties of deep argillaceous formations abstract a difficulty in the interpretation of mechanical and thermo mechanical tests on specimens drawn from large argillaceous formations is the strong inhomogeneity of void ratio clay minerals and carbonates content in this paper a relationship is developed to link strength and the maximum preconsolidation stress to the initial void ratio and carbonate content compressibility is also correlated to carbonates thermal strains in drained and undrained conditions for a spanish a belgian and an italian natural clay are compared in the elastic state strains are comparable while in the plastic range thermal strains are highest for the belgian clay lower in the spanish cemented clay and lowest in the italian clay very stiff and cemented

leda clay from deep boreholes at hawkesbury ontario part i geology and geotechnique the geologic and geotechnical characteristics of thick soft champlain sea clay deposits at hawkesbury ontario are presented in this paper a second paper will deal with the mineralogy and geochemistry of the same deposits a westerly clay plain at 50 m and an easterly plain at 75 m elevation occur in the area preconsolidation pressure versus depth curves obtained for clays from both deposits show marked preconsolidation near the top and bottom drainage boundaries and nearly normally consolidated conditions at the centre this suggests that both sites were loaded by sandy fluvial deltaic sediments that were eroded 70 years after deposition an ancestral meander of the ottawa river being responsible for the erosion on the lower clay plain two stratigraphic schemes compatible with the p versus depth profiles are presented for the lower elevation clay plain these schemes suggest erosion of 21 m of deltaic sands a value generally confirmed by field studies of deltaic sand terraces to the west the se

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

efficient early global relaxation of asteroid vesta abstract the asteroid vesta is a differentiated planetesimal from the accretion phase of solar system formation although its present day shape is dominated by a non hydrostatic fossil equatorial bulge and two large mostly unrelaxed impact basins vesta may have been able to approach hydrostatic equilibrium during a brief early period of intense interior heating we use a finite element viscoplastic flow model coupled to a 1d conductive cooling model to calculate the expected rate of relaxation throughout vesta s early history we find that given sufficient non hydrostaticity the early elastic lithosphere of vesta experienced extensive brittle failure due to self gravity thereby allowing relaxation to a more hydrostatic figure soon after its accretion vesta reached a closely hydrostatic figure with 40 200 my after formation depending on the assumed depth of megaregolith the veneneia and rheasilvia giant impacts which generated most non hydrostatic topography must have therefore occurred 40 200 my after formation based on crater retention ages topography and relation to known impact generated features we identify a large region in the northern hemisphere that likely represents relic hydrostatic terrain from early vesta the long wavelength figure of this terrain suggests that before the two late giant impacts vesta had a rotation period of 5 02 h 6 3 faster than present while its spin axis was offset by 3 0 from that of the present the evolution of vesta s figure shows that the hydrostaticity of small bodies depends strongly on its age and specific impact history and that a single body may embody both hydrostatic and non hydrostatic terrains and epochs

the coefficient of earth pressure at rest laboratory experiments on undisturbed specimens of a large number of soft clay deposits as well as previous measurements on clays and granular soils were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest k0 i after sedimentation primary consolidation ii during secondary compression aging iii after active or passive preshearing away from the laterally constrained condition iv during a decrease in effective vertical stress and v during an increase in effective vertical stress in the recompression or compression range in terms of the slope of the effective horizontal versus effective vertical stress path the behavior of k0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition the jaky equation provides in terms of the angle of internal friction a good estimate of k0 of sedimented normally consolidated young clays and granular soils as well as of of presheared clays and sands

the interior structure of ceres as revealed by surface topography abstract ceres the largest body in the asteroid belt 940 km diameter provides a unique opportunity to study the interior structure of a volatile rich dwarf planet variations in a planetary body s subsurface rheology and density affect the rate of topographic relaxation preferential attenuation of long wavelength topography 150 km on ceres suggests that the viscosity of its crust decreases with increasing depth we present finite element fe geodynamical simulations of ceres to identify the internal structures and compositions that best reproduce its topography as observed by the nasa dawn mission we infer that ceres has a mechanically strong crust with maximum effective viscosity 10 25 pa s combined with density constraints this rheology suggests a crustal composition of carbonates or phyllosilicates water ice and at least 30 volume percent vol low density high strength phases most consistent with salt and or clathrate hydrates the inference of these crustal materials supports the past existence of a global ocean consistent with the observed surface composition meanwhile we infer that the uppermost 60 km of the silicate rich mantle is mechanically weak with viscosity 21 pa s suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes

geo engineering properties of eemian peats from radzymin central poland in the light of static cone penetration and dilatometer tests abstract the paper presents the results of field studies testing the reaction of eemian peats on the mechanical effect of standard measurement tools cpt cptu marchetti dilatometer based on the collected undisturbed samples macroscopic observations were made and sem observations were conducted to identify the microstructural features a fibrous structure and advanced diagenetic changes have been noted in the studied peats despite their relatively young age these may have resulted from an exceedingly strong structural reinforcement which causes that the studied sediments cannot be treated as low bearing soils diagenetic processes caused farfetched changes of the mechanical properties which is reflected e g in classification normograms standardized diagrams may lead to false conclusions the presented studies of organic soils are an example of strong influence of structural features and diagenetic phenomena on the results obtained for native soils at the same time they imply particular caution in the interpretation of the substratum properties based only on the commonly used in situ tests the values and variability of the collected parameters have been presented as frequency distributions additionally the apparent character of the properties of preconsolidation parameters ocr has been shown

quartz spessartine metasediments coticules and their protoliths in north wales thin beds and small pods of quartz spessartine metasediments coticules occur in pelites of the gamlan formation cambrian of the harlech dome the original microfabric of these sediments has been largely destroyed by recrystallization under low greenschist facies conditions the quartz spessartine pods occur throughout the pelites and appear to have formed by the metamorphism of diagenetic mn carbonate concretions the thin beds of quartz spessartine rock appear to have formed by the metamorphism of a protolith which was deposited rapidly and repeatedly over a wide area although there is no direct evidence of the nature of this protolith the presence of altered mn carbonate rich tuff beds in anchizonal mudstones of similar age in the st tudwal s peninsula suggests that the bedded quartz spessartine rocks are in fact metamorphosed mn carbonate rich tuff units both the bedded and podiform quartz spessartine metasediments appear to have formed by reaction between clay minerals and mn carbonates of earlier diagenetic origin