neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

a seismic study of deep geological structure in the bristol channel area sw britain summary results from eight seismic refraction lines 35 90 km long in the bristol channel area are presented the data mostly land recordings of marine shots have been interpreted mainly by ray tracing and time term modelling upper layer velocities through palaeozoic rocks usually fall within the range 4 8 5 2 km s 1 below the carboniferous limestone with a normal velocity of 5 1 5 2 kms 1 the old red sandstone with a velocity of 4 7 4 8 kms 1 acts as a low velocity layer as do parts of the underlying lower palaeozoic succession in the central south wales bristol channel area and the mendips a 5 4 5 5 km s 1 refractor is correlated with a horizon at or near the top of the lower palaeozoic succession under the whole area except for north devon a 6 0 6 2 km s 1 basal refractor has been located and is correlated with precambrian crystalline basement rocks in general this refractor deepens southwards from a series of basement highs which existed before the major movements of the variscan orogeny in south wales resulting in a southerly thickening of the pre upper carboniferous supra basement sequence in north devon a 6 2 km s 1 refractor at shallow depth interpreted as a horizon in the devonian or lower palaeozoic succession overlies a deep reflector that may represent the precambrian crystalline basement

contribution of deep seismic profiling to the knowledge of the lower crust in france and neighbouring areas abstract in france and neighbouring areas the crust is essentially formed of segments of the variscan orogen 380 300 ma and older formations cratonic basins began to form in the permian but extensive subsidence only occurred from the lias in basins such as the paris and aquitaine basins and also along the margin of the alpine tethys ocean the pyrenees and alps range eventually formed during the tertiary as a result of the collision between the european and african continental plates large grabens were also rifted in the rhine and rhone valleys deep seismic profiles show remarkable features common to the crust of the whole area although it underwent such a complicated geological history the most striking feature is the occurrence of conspicuous flat reflections densely distributed in the lower part of the crust below a comparatively transparent upper crust these reflections hereafter called laminations have been found to occur on most profiles within a large area covering western europe although they vary in depth thickness and energy dipping reflections have frequently been observed in the upper crust some of them extend across the lower crust and even penetrate into the upper mantle they may be reasonably interpreted as variscan compressional features by correlation with surface geology and comparison with similar features found in deep seismic profiles from other regions the origin of the flat laminations which generally lie in the lower part of the crust is more controversial this paper attempts to use the well known geological history of the region to place some constraints on the hypotheses which may be advanced to explain the formation of these laminations these features may be explained by the following tectonothermal events 1 1 compression which prevailed during the variscan orogeny may have formed the laminations as a result of delamination and shearing near the bottom of the crust associated with melting intrusion and metamorphism during the different stages of the crustal evolution 2 2 the thermal equilibration of the upper mantle which occurred in the permian at the end of the variscan orogeny may have caused metamorphism and magmatism in the overlying crust 3 3 a regional thermal event which might be associated with subordinate extension occurred during the rifting of the alpine tethys and the initiation of mesozoic cratonic basins in late triassic middle jurassic times it may also have caused metamorphism and magmatism in the lower crust while the first model implies conservation of the crust material the other two suggest that the crust mantle transition has been somewhat uplifted since the end of the variscan orogeny the latter hypothesis is one way to explain the undeniable occurrence of seismic events below the present moho reflection the above three models are not mutually exclusive and all these phenomena may well have affected the crust to some extent however the data at hand are still insufficient to determine what parts tectonic and nontectonic processes have played in the creation of the laminations in the lower crust and the moho further experiments are needed to check these hypotheses

major geodynamic processes studied from the ecors deep seismic profiles in france and adjacent areas abstract for more than five years the french ecors project has obtained deep seismic profiles across major structural features that are related to the variscan alpine and pyrenean belts as well as the permo mesozoic subsidence in the celtic sea the english channel and the bay of biscay profiles across the orogenic belts show striking similarities such as the flexure of the down going plate and the geometry of the frontal detachment and related thrusts and nappes whatever the age of the belt however straight dipping reflections cutting through large sections of the crust seem to be common in the variscan belt and are interpreted as late features in its tectonic history the tertiary alpine and pyrenean belts show extensive crustal thickening and crust mantle imbrication while the layered lower crust and its bottom are flat beneath the late palaeozoic variscan belt this is interpreted as a late equilibration of the crust mantle boundary which involved deep metamorphism in the crust and occurred between the permian and the middle jurassic the permo jurassic basins reveal an unattenuated lower crust while both the upper and lower crusts are thinned beneath the cretaceous tertiary ones observation does not support the current models of basin formation and nowhere does extension appear to have played a major role in subsidence the lower crust of the permo jurassic basins may have been reworked and equilibrated after their rifting

in situ calcium carbonate dissolution in the pacific ocean over the past several years researchers have been working to synthesize the woce jgofs global co2 survey data to better understand carbon cycling processes in the oceans the pacific ocean data set has over 35 000 sample locations with at least two carbon parameters oxygen nutrients cfc tracers and hydrographic parameters in this paper we estimate the in situ caco3 dissolution rates in the pacific ocean water column calcium carbonate dissolution rates ranging from 0 01 1 1 mmol kg1 yr1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon in the north pacific intermediate water between 400 and 800 m caco3 dissolution rates are more than 7 times faster than observed in middle and deep water depths average 0 051 mmol kg1 yr1 the total amount of caco3 that is dissolved within the pacific is determined by integrating excess alkalinity throughout the water column the total inventory of caco3 added by particle dissolution in the pacific ocean north of 40s is 157 pg c this amounts to an average dissolution rate of approximately 0 31 pg c yr1 this estimate is approximately 74 of the export production of caco3 estimated for the pacific ocean these estimates should be considered tomore be upper limits for in situ carbonate dissolution in the pacific ocean since a portion of the alkalinity increase results from inputs from sediments less

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

initiation and evolution of the valencia trough western mediterranean constraints from deep seismic profiling and subsidence analysis abstract the structure and evolution of the valencia trough western mediterranean a neogene basin bordered in the north by prominent oligocene early miocene grabens in the catalan coastal ranges and to the south by the early miocene thrust sheets of the betic belt is investigated through a deep seismic reflection profile shot across the basin this profile shows that extensional features related to the rifting are concentrated in the catalan valencian domain in the north whereas in the south the betic balearic domain shows little extensional structures and no clear thrusting the smooth quite symmetrical moho uplift seems to cross cut strong se dipping reflectors which are clearly visible below the moho in the central basin deep seismic data tied on wells and industrial lines are used to establish a regional depth section which is backstripped and along which the history of tectonic subsidence is investigated assuming local isostasy we find out that observed tectonic subsidence shows a classical exponential decay for the period 0 15 2 ma consistently with observed moho attenuation even to the south where a foreland type mechanism of subsidence is not recognized little subsidence is found for the period 25 2 20 ma we also indicate that some brittle basement readjustement must have occurred around 15 2 ma and that the heat flow although variable is not inconsistent with theoretical model of uniform lithosphere attenuation we therefore propose that the development of the valencia trough occurred in two rifting stages the first the oligo miocene west european rifting event had minor effects in the deep basin and affected mostly the catalan margin the second serravallian in age 15 2 10 2 ma is responsible for present day moho uplift and explains the post mid miocene basin development this second rifting is coeval with the opening of the tyrrhenian basin its significance at the west of the western mediterranean remains to be investigated

high pressure metamorphism in the early variscan subduction complex of the sw iberian massif abstract several units exposed in the boundary area of the ossa morena zone omz and the south portuguese zone spz preserve petrographic and thermobarometric evidence for an early metamorphic episode m1 developed under a high p low to intermediate t gradient related to early variscan subduction in the sw iberian massif in the omz these are the cubito moura unit p min 9 2 kbar and t 395 45 c blueschists from its basal melange p min 12 4 kbar and t 310 11 c and the underlying fuenteheridos group p 10 9 0 4 kbar and t 449 31 c the equivalent units in the spz are the la minilla formation p 8 7 0 4 kbar and t 388 16 c and the lawsonite pseudomorphs bearing pulo do lobo formation all these units formed part of an approximately ne verging orogenic wedge present coordinates developed by the accretion of subducted slabs of the outermost margin of gondwana and other elements of the rheic ocean realm from at least the middle devonian to the lowermost tournaisian high pressure rocks were subsequently emplaced on more internal zones of the omz that only experienced a younger high t low to intermediate p metamorphism m2 this high t event was coeval with magmatic activity from the uppermost devonian to the middle mississippian probably as a consequence of transtensional lithospheric thinning and or delamination of the lower crust and mantle lithosphere of the gondwana margin pre late devonian synorogenic sedimentation in forearc and back arc basins of the subduction complex evolved to a late devonian middle mississippian foreland basin system in early collisional stages finally a new middle late mississippian fold and thrust belt with opposite sw vergence and new foreland basins developed during late collisional stages

three dimensional gravity and magnetic modelling of the irish sector of the ne atlantic margin abstract a new 3d lithospheric model has been constructed using high resolution gravity data from the irish national seabed survey the sedimentary component of the model incorporated density variations due to laterally varying overcompaction associated with cenozoic denudation after optimisation based on gravity inversion regional crustal thickness variations were defined which are in reasonable agreement with the results of wide angle seismic experiments high crustal extension factors 5 characterise the deeper parts of the rockall and porcupine basins and in places the model indicates extreme stretching 10 beneath these basins this could be because of instability in the gravity inversion although other recent investigations have independently suggested similarly high extension factors in contrast the hatton basin is characterised by an apparent extension factor of about 2 the modelling resolves a pattern of ne to nne trending local mesozoic basins on the margins of the rockall trough helping to delineate structures that were previously only sparsely sampled by seismic surveys it appears possible that rifts with similar trends underlie the volcanic rocks which obscure the deeper parts of the hatton basin the linear trends of the basins to the south and east of ireland are interpreted to have been inherited from a basement fabric that was initially established during the late precambrian assembly of this basement and subsequently subjected to caledonian and variscan reactivation magnetic modelling indicates that the variations in the thickness of the crystalline crust predicted by the gravity models can explain the regional magnetic anomaly patterns over the rockall and porcupine basins but that significant additional magnetic material probably igneous rocks of both palaeogene and cretaceous ages is required to explain the anomalies in the hatton basin region the magnetic signature of the rockall basin is distinctly different to that over the basement of similar apparent thickness formed during mid cretaceous c34n opening of the ocean basin to the south this is an impediment to hypotheses that invoke mid cretaceous sea floor spreading rather than intracontinental rifting to explain the development of the basin the exception is in the extreme south of the basin where the volcanism associated with the barra volcanic ridges combined with indications of relatively strong lithosphere could be evidence of incipient ocean opening

large variscan overthrusts beneath the paris basin the ecors project is devoted to the deep geophysical investigation of the continental and oceanic crust in france through the study of fundamental problems such as the formation of basins mountain belts and continental margins the first of the profiles completed is the nord de la france which is mainly devoted to the survey of the major units of the northern hercynian belt and of the deep crust below the mesozoic paris basin the deep geophysical investigations undertaken on this profile have led tothe acquisition of diverse information such as vibroseismic wide angle reflection refraction and magnetotelluric data the main results presented here show evidence of large overthrusts in the variscan chain which is currently buried beneath the thin mesozoic cover of the paris basin they show a differentiation of structural units in the upper crust their link with the lower crust and the depth and geometry of the moho they also give rise to some speculations regarding the nature of various gravimetric and magnetic anomalies such as the large anomalie magnetique du bassin de paris ambp

emplacement of lobate sheet flows with hyaloclastites onto soft sediment the erquy neoproterozoic lava pile armorican massif france abstract the neoproterozoic volcano sedimentary succession of the heussaye headland erquy belongs to the cadomian block located in the north east of the armorican massif france the volcanism dated at approximately 608 7 ma zircon u pb data occurred in a back arc basin this site exhibits a noteworthy verticalized pile of moderately metamorphosed greenschist facies basaltic andesite flows of arc back arc tholeiite affinity alternating with metasedimentary layers sandstones and siltstones a large range of volcanic facies characteristic of an underwater soft substrate environment can be continuously studied for over than 200 m parallel to the flow edges they include pillow lavas lava lobes fluidal peperites and sediment matrix hyaloclastites the presence of parallel lava lobes in a sector where one lava flow is capped by a variably thick hyaloclastite carapace together with the occurrence of asymmetric turbiditic folds in interbedded metasedimentary layers suggests the existence of an easterly facing gentle paleoslope the sudden thinning of this hyaloclastite carapace in two spots located approximately 60 m from each other is attributed to the synvolcanic activity of two conjugate normal paleofaults this hypothesis is supported by the observation of a hyaloclastite accumulation in one of the two spots close to a strike slip fault which may have been extensional at the time of the volcanism water entered the lava flow along the faults resulting in an interstitial network of hyaloclastites by quench fragmentation in the upper part of the hanging wall block all these observations are consistent with a model of lava emplacement along a subaqueous slope resulting from synmagmatic extensional faulting in a marginal basin context

shallow depth caco3 dissolution evidence from excess calcium in the south china sea and its export to the pacific ocean national basic research program of china 973 program 2009cb421201 2009cb421206 national science foundation of china nsfc 40821063 90711005 south china sea institute of oceanology the chinese academy of sciences

the climatic significance of late ordovician early silurian black shales the ordovician silurian transition approximate to 455 430ma is characterized by repeated climatic perturbations concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales the relationship between the climatic evolution and the oceanic redox cycles however remains largely debated here using an ocean atmosphere general circulation model accounting for ocean biogeochemistry mitgcm we investigate the mechanisms responsible for the burial of organic carbon immediately before during and right after the latest ordovician hirnantian 445 444ma glacial peak our results are compared with recent sedimentological and geochemical data we show that the late katian time slice approximate to 445ma typified by the deposition of black shales at tropical latitudes represents an unperturbed oceanic state with regional organic carbon burial driven by the surface primary productivity during the hirnantian our experiments predict a global oxygenation event in agreement with the disappearance of the black shales in the sedimentary record this suggests that deep water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater in the context of the post hirnantian deglaciation does not sustain over sufficiently long geological periods to cause the rhuddanian approximate to 444ma oceanic anoxic event input of nutrients to the ocean through increased continental weathering and the leaching of newly exposed glaciogenic sediments may instead constitute the dominant control on the spread of anoxia in the early silurian

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

the observations of faulting in westerly granite under triaxial compression by x ray ct scan abstract observations of the spatial development of cracks in granite undergoing triaxial compression provide new insights into the proces of fault formation dry intact westerly granite samples were loaded under confining pressure of 100 mpa and the progress of fault formation was controlled by maintaining the increment of circumferential displacement at a constant rate the samples were unloaded when they experienced stress drops and were successfully recovered without severe crushing a stereo microscope was used to observe the spatial pattern of cracks on the sample surfaces and an x ray ct scanning system was used to non destructively image the sample interiors microscope observations show that several fault like linear cracks developed on the surfaces of all the samples and have an angle of about 30 degrees to the maximum compression axis this suggests that fault nucleation began just after peak stress the x ray ct images show that a fault like linear crack grew inward toward the sample interior as axial stress decreased it is concluded that the fault nucleated locally on the sample surface just after peak stress and developed into an apparent fault by the plateau stage of the complete stress strain relationship

crustal structure of the goban spur continental margin northeast atlantic from deep seismic reflection profiling deep reflection data across the uk continental margin are used to test theories concerning the origin of a pervasive reflective fabric in the lower continental crust seen on many deep reflection profiles worldwide the origin of the reflections is at present little understood but clearly represents an important crustal process the western approaches margin wam line was designed to determine the behaviour of the lower crustal reflections in crust which has undergone significant extension the wam profile across the continental shelf is characterized by bright continuous lower crustal reflections some of which reach 30 km in length and have minimum reflection coefficients of 0 1 deep water multiples in the area of the continental slope partially obscure reflections from the lower crust but detailed analyses show that reflectors are present in the lower crust on the continental slope adjacent to the continent ocean boundary the lower crust on the wam profile is well imaged and free of noise and multiples this very thin crust exhibits the same reflectivity pattern as is observed on the continental shelf i e the upper half of the crust is blank and the lower half contains sub horizontal reflections the lower crustal reflections adjacent to the continent ocean boundary are less continuous than the reflections seen on the shelf and are interpreted as being the remnants after extension of the lower crustal reflectors observed on the continental shelf the lower crustal reflectors are thus interpreted to pre date the extensional episode that led to the opening of the atlantic the preservation of thinned sections of both transparent upper crust and reflective lower crust adjacent to the continent ocean boundary suggests that extension by pure shear was the mechanism by which the crust was thinned in the goban spur area

cocorp and the continental crust this is a speculative paper on the continental crust a major frontier of modern earth science seismic reflection profiling data from the cocorp project coupled with other kinds of geophysical and geological observations suggest some fresh perspectives on the crust for example there is evidence for great differences within the basement at a single site and from one cocorp site to another a simple layered model is surely not an adequate representation of the crust in most areas there is however the puzzling and rather common occurrence of limited zones of parallel though not always flat layered features at various depths in certain parts of the crust are the corresponding rocks metasedimentary or igneous or both there are transparent zones from which little or no coherent reflected seismic energy is detected are the corresponding rocks intrusions or highly deformed metasediments can degree of deformation suggest whether rocks were deformed in the hanging wall or footwall of a thrust there is evidence for large scale thrusting and related features that emphasizes the great importance of the wilson cycle to continental tectonics and that raises the possibility that water and rocks of sedimentary origin are trapped deep in the crust by the thrusting process and remain there for long periods with a variety of possible rheological and petrological consequences in some places the modern moho and adjacent rocks may correspond to parts of former oceanic or continental margin sections that have been emplaced at depth as a result of thrusting the widely held concept of the moho as a consistent boundary that is everywhere similar and that always separates the same kinds of rocks may be a major barrier to further progress in understanding the continental crust

seismic signature and tectonic cross section of the variscan crust in western france deep seismic reflection profiling ecors program vertical and wide angle survey coupled with field and subsurface geology are used to propose a complete nne ssw section of the variscan belt in western france from belgium to southern brittany on this 800 km long profile which probably crosses two paleozoic sutures the variscan belt appears as a broad fanlike orogen characterized by large 100 km northward and southward overthrusts with polyphase deformation and metamorphism the central part of the belt central armorican zone suffered a simpler dextral shearing parallel to the strike of the belt with only green schist metamorphism deep reflection profiling shows that all the large thrusts visible at the surface root deeply in the lower crust or even crosscut the moho in the same way all the large strike slip faults parallel to the belt appear at depth as narrow discontinuities which crosscut the whole crust and in some cases the moho the seismically well layered crust develops essentially at depth in the most deformed and metamorphic internal parts of the belt in contrast with the relatively transparent brabant foreland basement which escaped the variscan deformation the moho appears as a relatively flat boundary at an average depth of 35 km with different characters it is sharp and strongly reflective both by wide angle and vertical seismics below the internal thrust zones much less distinct in the central armorican zone and only defined by low frequency signals at wide angle below the brabant foreland all these characteristics led us to consider the layering of the lower crust and the moho itself as initially tectonometamorphic features essentially produced by shearing and crust mantle decollement during the variscan stacking of the crust by intracontinental lithospheric subduction

deep seismic reflection survey across the variscan front of southern england in 1979 the institute of geological sciences commissioned two lines of seismic reflection profile a technique which has proved successful1 for studying crystalline basement the survey was sited to cross the concealed variscan front in southern england with recording time extended to 12 s two way time twt similar profiles in adjacent parts of europe have suggested that the variscan front is characterized by major thrust zones extending to considerable depths2 3 our profiles reported here show good primary reflections to 6 s twt and give new detail on the nature of variscan deformation in southern england zones of differing reflection character are evident a northern zone of low northerly apparent dips a central zone of poor reflector quality and a southern zone of steeper dips to the sse the southern zone is presumed to represent deformed variscan basement including several minor thrust planes and a proposed major thrust zone analogous to similar structures in europe impersistent reflections between 9 and 10 s twt could possibly relate to the moho

the deep structure of the ardennes variscan thrust belt from structural and ecors seismic data abstract a new crustal tectonic model is proposed for the ardennes external variscides of northern france belgium on the basis of original microtectonic data further complemented by revised ecors deep seismic information this model is illustrated by both restored and balanced crustal sections that clearly emphasize the direct control exerted by pre existing extensional structures on the collision related processes of variscan deformation indeed the deep structure of the ardennes belt appears as a continental accretionary prism that thickens south towards the hinterland above a staircase type basal thrust innermost crustal shortening is here assigned to a deeply rooted foreland directed ramp thrust system soled at depth by a thick ductile decoupling shear zone actually imaged at about 20 km depth on the ecors section this thrust system is bounded upwards by a shallow infra devonian roof thrust to account for the present day high structural position of the rocroi cambrian inlier as well as for its internal superimposed ductile fabrics major uplift of a previously sheared crust is assumed to have occurred along a frontal ramp which nucleated on an early s dipping extensional fault the rocroi fault according to the ecors data the hanging wall of the rocroi fault has been translated about 40 km northwards along the dinant infra devonian shallow decollement this estimate is quite consistent with the 40 stratal shortening undergone at its front by the devonian detached cover whose thin skinned fold thrust structures also reflect the direct influence of early devonian normal faulting basin inversion tectonics are clearly expressed along the frontal thrust zone where the thin condroz basement sheet is now interpreted as resulting from slicing of the dinant decollement through the footwall of a major lower devonian extensional fault scarp that separated the namur shallow shelf from the dinant downthrowing basin the present thrust model also implies that the dinant decollement extends as a blind thrust beneath the slightly detached namur carboniferous coalfield and that the midi frontal ramp only represents a minor out of sequence thrust reactivating a rotated basement cover contact

crustal evolutionary model for the variscides of ireland and wales from swat seismic data the swat seismic reflection profiles recently acquired across the celtic sea demonstrate that the crust which underlies the munster and pembroke variscan foldbelts contains extensive south dipping reflections interpreted as hercynian foreland directed ramp thrusts largely involving the pre devonian basement these large scale crustal ramps developed without any intervening flat lying decollement levels and are thought to have originated in a deep infra crustal decoupling zone not imaged on the swat profiles because it lies within the present day layered lower crust at approximately 25 km depth the pre existing extensional basinal pattern is assumed to have highly influenced the geometry of these deeply rooted thrusts and in particular that of the frontal ramp which emerges along a discontinuous n100 trending thrust zone located above the faulted extensional margin of the munster pembroke and mendips devonian basins shortening of the irish and welsh external zones is hence assigned to dominantly crustal stacking achieved along steep ramps dying out upwards and giving way to mainly undisrupted folds in the thick overlying devonian infill in addition a shallow thin skinned fold thrust system developed above an intra namurian master decollement still preserved in the footwall of the frontal ramp where it either stays blind ireland or emerges pembroke above a dominantly wrench faulted caledonian basement compiling swat seismic data and structural geology leads to a crustal evolutionary model for the irish and south welsh external variscides from a devonian basin template to a final deformation pattern

superimposed variscan caledonian and proterozoic features inferred from deep seismic profiles recorded between southern ireland southwestern britain and western france abstract from southern ireland to the northern bay of biscay subduction was active from the proterozoic to the late palaeozoic they led to the cadomian caledonian and variscan collisions features characterizing these three orogenies have been crossed by the winch swat wam and bay of biscay deep seismic profiles recorded by the birps and ecors groups in the celtic sea the variscan front is characterized by a s dipping ramp rising directly from the middle crust with much less northward flattening than shown by the front in the northern france and west germany profiles south of the variscan front other s dipping reflections occur above a possible deep detachment the lizard ophiolitic suture marks s dipping events traversing the entire crust and the present moho in the english channel several sets of prominent n dipping reflections occurring in the celtic sea and south irish sea are interpreted as caledonian features running parallel to the caledonian iapetus suture and the pattern of folds and faults recognized in wales and southeastern ireland proterozoic s dipping subduction is recorded by geological data in northern wales and the english channel related crustal structures correspond to deep seismic events cutting across the lower crust and the moho and show the same apparent dip as the variscan features parallelism between dips and or strikes of structural features with different ages suggests a tectonic heritage the crust thus appears to be characterized by n and s dipping features which cut across large parts of it and may be assigned to variscan caledonian or candomian thrusts or shear zones the lower part of the crust shows a band of high amplitude subhorizontal reflections and a flat moho reflection which seem to have overprinted the above mentioned dipping features in a later period the lack of evidence of any shallow detachment in the caledonian and variscan belts together with the presence of dipping crustal thrust like features suggest that the region may have reached the very latest collisional stage the end of both of these orogenies

assessment of the engineering behavior of ultramafic and mafic rocks using chemical indices geochemistry is of great importance for the interpretation of the geomechanical quality of rock materials used in various construction applications this paper investigates the interrelationships between selected chemical indices and various engineering parameters of ultramafic and mafic rocks from the vourinos pindos koziakas and othrys ophiolite complexes northern and central greece the significance of these indices for the engineering assessment of ophiolitic aggregates is strongly demonstrated based on statistical analysis of the experimental results the studied lithologies include dunites olivine rich harzburgites typical harzburgites plagioclase bearing lherzolites troctolites diorites and dolerites which show various degrees of alteration and tectonic deformation the effect of alteration on rock strength and particularly the relationships between specific chemical indices and the engineering parameters are determined using simple regression analysis the results designate that the wpi index is the most appropriate for the assessment of the engineering behavior of ultramafic lithologies while the loi index seems to provide a general estimation of the strength properties of mafic rocks

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

mixing and remineralization in waters detrained from the surface into subantarctic mode water and antarctic intermediate water in the southeastern pacific a hydrographic data set collected in the region and season of subantarctic mode water and antarctic intermediate water samw and aaiw formation in the southeastern pacific allows us to estimate the preformed properties of surface water detrained into these water masses from deep mixed layers north of the subantarctic front and antarctic surface water south of the front using 10 measured seawater properties we estimate the fractions of samw aaiw that originate as surface source waters as well as fractions that mix into these water masses from subtropical thermocline water above and upper circumpolar deep water below the subducted samw aaiw ages associated with the detrained surface water and remineralization and dissolution rates and ratios the mixing patterns imply that cabbeling can account for 0 005 0 03 kg m 3 of additional density in aaiw and 0 0 02 kg m 3 in samw we estimate a shallow depth 300 700 m above the aragonite saturation horizon calcium carbonate dissolution rate of 0 4 0 2 mol caco3 kg 1 yr 1 a phosphate remineralization rate of 0 031 0 009 mol p kg 1 yr 1 and remineralization ratios of p n o2 corg of 1 15 5 0 6 143 10 104 22 for samw aaiw our shallow depth calcium carbonate dissolution rate is comparable to previous estimates for our region our o2 p ratio is smaller than many global averages our model suggests neglecting diapycnal mixing of preformed phosphate has likely biased previous estimates of o2 p and corg p high but that the corg p ratio bias may have been counteracted by a second bias in previous studies from neglecting anthropogenic carbon gradients

possible overestimation of shallow depth calcium carbonate dissolution in the ocean 1 we argue that diagnostics of excess dissolved calcium carbonate ta above the saturation horizon cannot be unambiguously interpreted in terms of local in situ dissolution we examine a three dimensional numerical model of global ocean circulation and biogeochemistry with explicit representation of the formation and dissolution of calcium carbonate in particular dissolution is only allowed to occur below the saturation horizon the model qualitatively captures the observed basin and global scale patterns of alkalinity and ta as well as the relationship between ta and chlorofluorocarbon age in the thermocline the existence of ta above the saturation horizon in the model can only be explained in terms of transport subsequent to dissolution the model study does not rule out the possibility of shallow depth calcium carbonate dissolution but suggests that dissolution rates derived from tracer observations have not adequately accounted for the influence of transport

the seismic reflection character of the continental mohorovicic discontinuity the continental mohorovicic discontinuity is most often interpreted as a step function velocity boundary however on deep crustal seismic reflection profiles reflections at depths where refraction data places the moho have laminated character and are laterally discontinuous these observations on continental reflection data point to a model of the moho that has thin layered rather than block structure previous workers who have synthetically generated seismic responses from various crust mantle boundary models have shown that thin layered models of alternating high and low velocity generate responses that best emulate observed moho arrivals geologic interpretations of the thin layering include relatively undeformed metasediments cumulate layering tectonic banding and lenses of partial melt to obtain more direct geologic evidence a synthetic seismogram is generated from geologic cross sections of the ivrea verbano zone an exposed section through the lower crust and upper mantle the synthetic shows laminations similar to those observed on reflection data without more direct evidence no single geologic interpretation of the moho is reasonable indeed the moho may be a laterally variable boundary its composition and structure dependent upon the geologic history of the overlying crust

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

the deep structure of northern england and the iapetus suture zone from birps deep seismic reflection profiles the nec deep seismic reflection profile images structures in the lower crust which represent the iapetus suture zone beneath southern scotland and northern england on the basis of reflectivity characteristics of the lower crust and reflection moho we recognize four different crustal zones which correspond to four crustal terrane types midland valley zone a a sub continental subduction complex zone b lake district zone c and midland platform zone d the junctions between each of these zones are interpreted as being tectonic a and b originate from the northern continental margin of the iapetus ocean and are separated from c and d which are derived from a southern continent by strong northerly dipping reflections between approximately 15 and 30 km deep in the crust the structure responsible for these reflections does not displace the reflection moho north of the ab cd junction the base of zone b and base of the reflective crust is marked by a pair of parallel reflectors persistent for a horizontal length of about 55 km these reflectors are interpreted as the top and bottom of a slice of remnant oceanic crust at their northerly limit the deepest of the two parallel reflectors transects the moho to a depth of 6 7 km into the uppermost mantle we suggest that their termination delimits the northerly extent of a decollement or shear zone at the present continental moho the shear zone was active during the late stages of caledonian collision when mantle originally from beneath the southern continent underthrust old and newly created crust of the collision zone

on the variations of geo engineering properties of dunites and diorites related to weathering geo engineering properties of rocks including discontinuity properties physical and mechanical properties and crack propagation under axial loads are affected by weathering all of these rock properties have an impact on various scales on engineering applications therefore weathering related variations on rocks and rock masses are of great importance in this study dunites and diorites are compared from the view of weathering related geo engineering property variations both on field and on laboratory scales the studies were initiated in the field by measuring the discontinuity properties including spacing aperture fill material roughness and schmidt hammer rebound tests mineralogical and petrographic investigations were performed on thin sections gathered from different weathering grades the quantitative petrographic studies were concentrated on the micropetrographic index and the quantification of microcracks at this stage of the study a new method to quantify microcracks was proposed basic physical and mechanical properties e g specific gravity dry and saturated unit weights water absorption effective porosity p wave velocity uniaxial compressive strength and slake durability index test were also investigated on samples of all of the weathering grades where the sample preparation was available the data obtained from the field studies suggest that dunite discontinuity spacing decreases from 577 to 1 cm and ranges from 487 to 1 cm for diorite schmidt hammer rebound test values shv in the field were only obtained for fresh slightly weathered and moderately weathered grades shv values range from 54 to 41 for dunite and 63 to 32 for diorite the quantitative microcrack data obtained during the petrographic studies indicated that microcracks for diorite increase with increasing weathering but a decrease was observed for dunite which was related to the formation of serpentine minerals with weathering furthermore with increasing weathering the changes in the physical properties of dunite specimens exhibit a wider range than in the diorite specimens unconfined compressive test results for the rocks showed similar decreasing trends with weathering but the dunite specimen started to slake by the highly weathered stage where the diorite exhibited a considerable slaking by the completely weathered stage this research concludes that the micropetrographic index and quantitative microfracture data provide useful input to recognize the weathering grades of studied rocks it is also emphasized that serpentinization is the distinct process for dunite weathering and has a high impact on the weathering process influencing physical and mechanical properties considerably however the increase of micro and macrocracks is the dominant distinctive feature for diorite weathering

crustal structure of the celtic sea and western approaches from gravity data and deep seismic profiles constraints on the formation of continental basins a free air anomaly map of the celtic sea and the western approaches is presented including all available marine gravimetric data and bouguer anomalies on land n60 features are predominant in the area they correspond to the n60 so called caledonian grain which played a major role in the variscan orogeny and in the formation of the permo triassic sedimentary basins the fundamental new point which comes out from this gravimetric map is the existence of a closely spaced pattern of n105 features which we regard as late carboniferous transpressional structures in the eastern pan of the celtic sea thrusts are in the same n105 direction west of 6 w longitude however folds and thrusts trend preferentially in a n60 direction following the older grain there the n105 lineaments may be regarded as dextral shear structures with a possible compressive component the hercynian shortening of the celtic sea domain located between the variscan front and the lizard suture resulted from the displacement along the n160 direction of the two adjacent rigid domains north of the variscan front the n105 and n135 features were possibly active in more recent times then both the n60 and n105 trends controlled the formation of permo triassic basins the n105 directions being transfer faults two dimensional gravity modelling of the swat profiles in the celtic sea shows that the base of the reflective lower crust may be associated with the moho discontinuity everywhere in the celtic sea except below the saint george s channel basin the lower crust does not change significantly in depth and thickness beneath the permo triassic basins none of the available models simply satisfies such conditions they all require at least a modification of the geometry of the lower crust after the formation of the celtic sea basins nevertheless if the simple shear model can be ruled out mainly from structural arguments the uniform stretching and to a lesser degree the thermomechanical models seem to be more relevant models however two additional conditions are necessary 1 the preservation of crustal seismic features formed before the creation of basins must be explained and 2 a significant portion of the volume of the stretched lower crust about 40 of this volume for the north celtic sea basin must be added below or perhaps partly above the lower crust by lateral flow of the crust or at the expense of the upper mantle

a novel determination of calcite dissolution kinetics in seawater we present a novel determination of the dissolution kinetics of inorganic calcite in seawater we dissolved 13 c labeled calcite in unlabeled seawater and traced the evolving 13 c composition of the fluid over time to establish dissolution rates this method provides sensitive determinations of dissolution rate which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals we have determined dissolution rates for two different abiotic calcite materials and three different grain sizes near equilibrium dissolution rates are highly nonlinear and are well normalized by geometric surface area giving an empirical dissolution rate dependence on saturation state of rate g cm 2 day 7 2 0 6 10 4 1 3 9 0 1 this result substantiates the non linear response of calcite dissolution to undersaturation the bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms implying a criticality in the calcite seawater system finally our new rate determination has implications for modeling of pelagic and seafloor dissolution nonlinear dissolution kinetics in a simple 1 d lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth and also confirm the importance of respiration driven dissolution in setting the shape of the calcite lysocline

calcium carbonate budget in the atlantic ocean based on water column inorganic carbon chemistry 1 recent independent lines of evidence suggest that the dissolution of calcium carbonate caco3 particles is substantial in the upper ocean above the calcite 100 saturation horizon this shallow water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic caco3 at shallow water depths here we use more than 20 000 sets of carbon measurements in conjunction with cfc and 14c data from the woce jgofs oaces global co2 survey to estimate in situ dissolution rates of caco3 in the atlantic ocean a dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface the in situ caco3 dissolution increases rapidly at the aragonite 100 saturation horizon estimated dissolution rates north of 40on are generally higher than the rates to the south which is partly attributable to the production of exported caco3 being higher in the north atlantic than in the south atlantic as more caco3 particles move down the water column more particles are available for in situ dissolution the total water column caco3 dissolution rate in the atlantic ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5 6 1012 mol c yr 1 from caco3 rich sediments the resulting water column dissolution rate of caco3 for the atlantic ocean is approximately 11 1 1012 mol c yr 1 this corresponds to about 31 of a recent estimate 35 8 1012 mol c yr 1 of net caco3 production by lee 2001 for the same area our calculation using a large amount of high quality water column alkalinity data provides the first basin scale estimate of the caco3 budget for the atlantic ocean

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

inorganic carbon in the indian ocean distribution and dissolution processes 1 this study uses nearly 25 000 carbon measurements from the woce jgofs global co2 survey to examine the distribution of dissolved inorganic carbon dic and total alkalinity ta in the indian ocean shallow and intermediate distributions of inorganic carbon do not strictly follow temperature and salinity because of differing surface gradients and vertical biological processes that work to modify the circulation derived features anthropogenic co2 has increased the shallow dic by as much as 3 decreasing the vertical dic gradient deep ocean dic and ta increase toward the north because of the decomposition and dissolution of organic and inorganic particles calcite saturation depths range from 2900 3900 m with the deepest saturation depth in the central indian ocean variations of aragonite saturation depth 200 1400 m are similar to calcite but the deepest saturations are in the southwestern indian ocean the shallowest aragonite saturation depths are found in the bay of bengal in the northern arabian sea and bay of bengal the current aragonite saturations are 100 and 200 m shallower respectively than in preindustrial times estimates of carbonate dissolution rates on isopycnal surfaces range from 0 017 to 0 083 mol kg 1 yr 1 in deep waters upper water column dissolution rates range from 0 to 0 73 mol kg 1 yr 1 with a local maximum occurring in intermediate waters just below the aragonite saturation horizon dissolution is also generally higher north of the chemical front at 10 20 s there is some evidence for significant sedimentary sources in the northern indian ocean

fracturing process of granite inferred from measurements of spatial and temporal variations in velocity during triaxial deformations fracturing in fine grained homogeneous granite during triaxial deformation was investigated by measuring the spatial and temporal variations of elastic wave velocities velocities along 20 ray paths were measured with 12 piezoelectric transducers attached to a sample under confining pressures up to 400 mpa systematic velocity differences observed among the 20 paths apparently indicate the formation of a dilatant region near the surface of a sample the damaged region formed near the surface due to asymmetric development of dilatancy seemed to play an important role in controlling ultimate failure no evidence of the formation of a crack concentration zone adjacent to the ultimate fracture plane could be found before failure insofar as could be estimated from the velocity variations of elastic waves propagating along its plane however a highly concentrated region of cracks in which the fracture nucleated was generated in the damaged region at stresses of more than 97 99 of the ultimate strength in all the specimens based on tomographic images computed using an algebraic reconstruction technique the elastic waves were strongly affected by the damaged region even under the high confining pressures at which cracks are considered to close

characterization of granite matrix porosity and pore space geometry by in situ and laboratory methods summary most available studies of interconnected matrix porosity of crystalline rocks are based on laboratory investigations that is work on samples that have undergone stress relaxation and were affected by drilling and sample preparation the extrapolation of the results to in situ conditions is therefore associated with considerable uncertainty and this was the motivation to conduct the in situ connected porosity experiment at the grimsel test site central swiss alps an acrylic resin doped with fluorescent agents was used to impregnate the microporous granitic matrix in situ around an injection borehole and samples were obtained by overcoring the 3 d structure of the porespace represented by microcracks was studied by u stage fluorescence microscopy petrophysical methods including the determination of porosity permeability and p wave velocity were also applied investigations were conducted both on samples that were impregnated in situ and on non impregnated samples so that natural features could be distinguished from artefacts the investigated deformed granites display complex microcrack populations representing a polyphase deformation at varying conditions the crack population is dominated by open cleavage cracks in mica and grain boundary cracks the porosity of non impregnated samples lies slightly above 1 per cent which is 2 2 5 times higher than the in situ porosity obtained for impregnated samples measurements of seismic velocities vp on spherical rock samples as a function of confining pressure spatial direction and water saturation for both non impregnated and impregnated samples provide further constraints on the distinction between natural and induced crack types the main conclusions are that 1 an interconnected network of microcracks exists in the whole granitic matrix irrespective of the distance to ductile and brittle shear zones and 2 conventional laboratory methods overestimate the matrix porosity calculations of contaminant transport through fractured media often rely on matrix diffusion as a retardation mechanism

coalescence of fractures under shear stresses in experiments a series of uniaxial compression tests were performed on gypsum specimens with preexisting fractures to study the failure mechanism of fractures and rock bridges in fractured rock masses the coalescence mechanism of two parallel and offset fractures was investigated by monitoring the process of fracture initiation and propagation with a video camera the tests showed that two inclined parallel fractures can coalesce by shear failure and or tensile failure under a uniaxial load the coalescence path and mechanism mainly depend on the relative position of the two fractures for instance when the two fractures are coplanar or slightly offset coalescence is generated by shear failure when they are overlapping in the loading direction coalescence is generated by mixed shear and tensile failure two types of preexisting fractures one without initial surface contact and hence frictionless and another with surface contact and friction were used to study the influence of fracture contact conditions on the coalescence path and load it was found that coalescence of fractures with surface contact and friction requires loads as much as 35 higher than that for coalescence of fractures without contact and friction a stress analysis was conducted in this study to explain the different coalescence mechanisms the analytical work indicated that different fracture geometries produce significantly different stress fields in the rock bridge area and hence result in different failure modes

a new estimate of the caco3 to organic carbon export ratio 1 we use an ocean biogeochemical transport box model of the top 100 m of the water column to estimate the caco3 to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate we find a global average molar export ratio of 0 06 0 03 this is substantially smaller than earlier estimates of 0 25 on which a majority of ocean biogeochemical models had based their parameterization of caco3 production contrary to the pattern of coccolithophore blooms determined from satellite observations which show high latitude predominance we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres our results suggest a dominant contribution to global calcification by low latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods

deep seismic reflection and refraction profiling along the aquitaine shelf bay of biscay summary the 300 km ecors bay of biscay profile was carried out along the aquitaine shelf and comprised a complete set of experiments including zero offset and 7 5 km constant offset vertical seismic reflection and six expanding spread profiles large offset recordings were fundamental for the definition of the layered lower crust and the moho while esps provided decisive complementary information for the geological interpretation these data show a strong variation in crustal thickness from about 20 km beneath the rifted parentis basin a failed arm of the oceanic bay of biscay up to 35 km to the north below the armorican shelf in the hercynian domain and to the south below the cantabria shelf in the vicinity of the pyrenean deformation front the results have important implications for the behaviour of the crust during the formation of rifted sedimentary basins and during continental collision

dissolution affected coccolithophore fluxes in the central greenland sea 1994 1995 coccolithophore fluxes were investigated by sediment trap studies in the central greenland sea from 1994 to 1995 the trap mooring comprised traps at 300 900 and 2100 m water depths with 19 trapping intervals 10 28 days this site was characterised by a very strong seasonality in coccolithophore fluxes the seasonal flux signal was most pronounced in the shallow trap with high fluxes only during two trapping intervals in september and early october 1994 max coccolithophore flux 12 x 10 6 ind m 2 d 1 no or only very low fluxes were recorded during most of the investigated time interval in the deeper traps high fluxes occurred over a longer time interval than in the upper traps from late august to november 1994 the dominant species 90 was coccolithus pelagicus f pelagicus only very few other species including emiliania huxleyi 7 occasionally occurred the coccolithophore settling assemblages of the investigated traps were strongly influenced by dissolution the dissolution impact probably diminished diversity and sharpened seasonality in fluxes dissolution was prominent in near surface waters of the east greenland current but not in bottom waters however maximum fluxes were of the same magnitude as previously reported fluxes from the nearby norwegian sea and higher than in the southern greenland sea in contrast to the other sites resuspension seemed to be of minor importance total annual coccolithophore fluxes differed significantly in the norwegian greenland seas reflecting the local oceanographic signature of coccolithophore production

fracture process zone in granite a microstructural analysis shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip we investigated the crack microstructures along experimentally formed shear fractures from four granite samples uniaxial compression tests five transects across a macroscopic fracture were inspected optically in transmitted light five hundred thirty two photomicrographs were taken from seven study areas along each transect we determined length width density and orientation of open cracks and their assignment to intra transgranular or grain boundary cracks crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip the highest crack densities correlate with the maximum number of acoustic emissions most cracks enclose a small angle 0 20 with the macroscopic shear fracture intragranular cracks are more abundant than transgranular and grain boundary cracks the number of transgranular cracks increases towards the macroscopic shear fracture but the number of grain boundary cracks decreases the decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault fracture process zone widths range from 2 1 0 8 mm ag51r to 5 6 1 9 mm ag18r the ratio of process zone width to fault length is approximately 0 04 0 07 this observation agrees with observations from natural fault zones the fracture surface energy ranges from 0 2 to 1 2 j this corresponds to 10 of the total strain energy

on ocean transport diagnostics the idealized age tracer and the age spectrum abstract the idealized age tracer is commonly used to diagnose transport in ocean models and to help interpret ocean measurements in most studies only the steady state distribution the result of many centuries of model integration has been presented and analyzed however in principle the transient solution provides more information about the transport here it is shown that this information can be readily interpreted in terms of the ventilation histories of water masses a simple relationship is derived valid for stationary transport between the transient evolution id r t of the idealized age tracer and the age spectrum g r t the distribution of times t since a water mass was last ventilated namely g r t tt id r t implications of the relationship are discussed and the relationship is illustrated with an idealized model

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

relationship between density compressive strength tensile strength and aggregate properties of andesites from hungary aggregate properties and strength parameters of four andesites from two operating hungarian quarries of nogradkovesd one lithotype and gyongyossolymos three lithotypes are presented in this paper air dry water saturated and freeze thaw subjected specimens were tested on core drilled cylindrical specimens and the aggregate properties were also determined from the remaining part of the drilled rock blocks tensile strength values rapidly decreased from air dry to water saturated and finally to freeze thaw subjected specimens linear relationships between air dry and water saturated bulk densities and between ucs and modulus of elasticity were found micro fabric influences strength and aggregate parameters of studied andesites fine porphyritic andesite has the highest ucs and tensile strength and the best micro deval results while coarser porphyritic andesite has lower strength and aggregate parameters test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks a good exponential correlation was found between micro deval and ucs values of this paper and previously published data sets but there was no indication that micro deval values correlate well with los angeles values

engineering properties of a low grade metamorphic limestone abstract a particular type of limestone in singapore is studied in this paper seventeen uniaxial compressive strength ucs tests and seventeen brazilian tensile strength bts tests are conducted from a comprehensive petrographical study the generally high ucs and bts values are found to be attributed to the respective mineralogy and texture as a result of the prevalence of low grade metamorphism altered grain boundaries resulted from pressure solution are observed wavy suture contacts between interlocking and interpenetrating grains are common signs of subsequent precipitation cementation processes are recognized which reduce the primary porosity and enhance the packing of the rock on the other hand with the aid of a high speed video capturing technology during the loading tests exceptional low strengths obtained in certain specimens can be accounted for an analysis of the high speed videos reveals that the early crack initiation is often favored along calcite veins mudstone stringers fossil fragments and hair line cracks etc which appear to be local zones of weakness we also attempt to correlate the presence of heterogeneities in the rocks with the specimen failure mode under uniaxial compression in summary the results presented in this technical note fill in an existing gap of the engineering geology literature of singapore with respect to limestone the novelty of our research approach which integrates the microscopic study and the high speed video imaging technique is demonstrated to account for the large strength variation of the study limestone

digital features of main constituents in granite during crack initiation and propagation abstract the purpose of this study is to investigate the digital features of various constituents on granite specimen in the crack initiation and propagation process the test video image photographed during laboratory uniaxial compression test and digital image processing techniques were used to conduct this study the video image was first converted into the format easily recognized in programming a multiple object tracking technique was then developed to detect the locations of the individual cracks at any time the initiation of each crack was determined by the occurring instant of the bounding box including the cracks the length width and area of each crack at any time were thereafter recorded the relation of the propagation process with digital features of the constituents in various locations was furthermore investigated it shows that two cracks propagated respectively along the vertical and horizontal directions as uniaxial compression test was performed a limit box technique can be used to determinate the initiation instants of the multi cracks on the specimen surfaces during propagation the width of the cracks increased quickly just after initiation and then fluctuated around a magnitude until the completely failure of the specimen the constituents near the crack would split as the crack initiated the shape features of biotites feldspar and quartz changed in different manners during crack s initiation and propagation the technique presented herein may be referable in investigating the failure mechanism of rock materials

traces of caledonian and proterozoic crustal features in deep seismic profiles recorded between france and the british isles abstract the area between france and the british isles has undergone three major orogenies since proterozoic times the cadomian monian late proterozoic caledonian late silurian early devonian and variscan devonian carboniferous this paper shows that crustal structures related to the first two orogenies can be recognized in deep seismic profiles in the english channel the celtic sea and the irish sea in the northernmost area remarkable north dipping reflections in the deep crust of the celtic and irish seas may be correlated with surface structures and interpreted as caledonian south verging thrusts parallel to the lapetus suture these features occur as far south as the cornubian ridge cornwall within the northern segment of the variscan north verging thrust belt the latter is characterized by south dipping reflections interpreted as variscan thrusts caledonian thrusts were probably re activated by the variscan compression evidence of caledonian thin skinned detachment cannot be recognized in the seismic profiles it is possible that either detachment structures were strongly deformed and obliterated by late caledonian thrusting or that detachment may never existed caledonian shortening was probably dominated by deep rooted crustal thrusts as a result of the overall obliquity of the collision caledonian thrusts are regarded as very late features formed when the crust between the colliding continents was already relatively thick they are distributed throughout the southern caledonides including the lapetus suture area deep south dipping reflections in the lower crust in the southern irish sea and the english channel may be related to the cadomian monian orogenic event the cadomian caledonian and variscan features have probably been re activated a number of times

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

relationships among mechanical physical and petrographic properties of siwalik sandstones central nepal sub himalayas abstract mechanical and physical characteristics of rocks generally depend on their composition and texture because they are reflective of their environments during sedimentation diagenesis and weathering in each location to understand this relationships between mechanical and physical indices and composition and texture have been analyzed using several rock samples obtained from mio pleistocene sandstone sequence of the siwalik group widely distributed in foothills of the nepal himalayas sandstones are quartzo feldspathic to quartzo lithic and quartzo feldspathilithic cement matrix and void vary from 6 to 41 0 to 18 and 1 to 12 respectively ferroan calcitic and siliceous cements are the dominant cements and their ratio to total cement varies from 0 2 to 1 0 packing density of sandstones ranges from 59 to 95 clasts are loosely to closely packed and are weakly to strongly bonded by cement results of correlation analyses show that sandstones strongly depend on several indices that is percent void strong cement over total cement strong over weak contacts concavo convex contacts and packing density most of which are measured on thin sections contrarily they depend little on grain size shape mineralogical maturity index and the other petrographic indices increased interlocking and strong cementing with reduced void tends to possess high densities low porosity and offer good resistance against deformation therefore proportion of strong cement over total cement void content strong over weak contacts grain to void contact concavo convex contact and packing density are meaningful indices considering the sandstones of the siwalik group based on the multiple regression correlation analyses and then stepwise multiple regression analysis some regression equations with significant explanatory indices are indicated for estimating mechanical and physical properties in other words such relationships may be useful in estimating mechanical and physical properties using the significant petrographic indices

tectono stratigraphy and evolution of the mesozoic pindos ophiolite and related units northwestern greece the northwest pindos mountains expose mesozoic and tertiary thrust sheets which include the jurassic pindos ophiolite composed of ultramafic and mafic oceanic crustal rocks the tectono stratigraphy of these units is i mainly ultramafic ophiolitic thrust sheet and basal metamorphic sole dramala complex and loumnitsa unit ii late cretaceous platformal limestones orliakas group iii dismembered intrusive and extrusive ophiolitic rocks aspropotamos complex iv tectonic melange and olistostromes dominated by triassic jurassic volcanic and sedimtntary rocks avdella melange v coherent thrust sheets of late jurassic late cretaceous deep water sediments dio dendra group vi early tertiary flysch pindos flysch immobile trace element studies indicate that triassic and jurassic extrusives of the volcanic sedimentary melange formed mainly at within plate and or mid ocean ridge settings by contrast structurally overlying ophiolitic extrusives include boninitic volcanics and island arc tholeiites of supra subduction zone origin initial ophiolite displacement c 165 ma is recorded in metamorphic sole formation including basal peridotite mylonite amphibolites and greenschists the sole rocks have morb and wpb chemical affinities in our favoured model the pindos ophiolite formed above a mid jurassic westerly dipping intra oceanic subduction zone accompanied by accretion to form melange followed by collision and emplacement with the pelagonian margin final suturing of the pindos ocean however did not take place until early tertiary times

shear strain localization from the upper mantle to the middle crust of the kohistan arc pakistan shear structures from mantle to middle crust levels of the kohistan palaeo island arc in pakistan are described pre himalayan ductile shear zones show a wide variety in size and shape and developed from gabbro subsolidus to amphibolite facies conditions their lithological context and geological history give insights into mechanisms that initiate shear strain localization factors that control stabilization of deformation in shear zones and flow properties at the mantle crust transition shear strain localization began within compositional gradients gabbros were more prone to localization into anastomosing patterns than diorites and granites which show more homogeneous strain shear strain localization during cooling led to less numerous but longer and thicker shear zones viscous heating within shear zones resulted in melt production and segregation in deformation structures and seems to have taken part in the plutonic history of the arc using kohistan as an example we suggest that the plutonic lower crust of arcs is strongly affected by subhorizontal synmagmatic shear zones probably consistent with the bulk flow direction of the subduction zone these features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision

correlation of mineralogical and textural characteristics with engineering properties of selected granitic rocks from turkey abstract granitic rocks show a variety of engineering properties that may affect quarrying operations tunneling mining slope stability and the use of rock as a construction material the physical and mechanical properties are a function of the mineralogical and textural characteristics of the rock the purpose of this study is to apply correlation analysis to investigate the relationships between petrographical and engineering properties of granitic rocks a variety of granitic rock samples from different parts of turkey were subjected to petrographic studies the same samples were then tested to determine specific gravity dry and saturated unit weight water absorption effective and total porosity sonic velocity schmidt hardness point load strength index uniaxial compressive strength tensile strength and modulus of elasticity the relationships between these properties and the petrographical characteristics are described by simple regression analyses the study revealed that the influence of the textural characteristics on the engineering properties appears to be more important than the mineralogy it also determined that the types of contacts grain mineral shape and size significantly influence the engineering properties of the granitic rocks

in situ calibration of mg ca ratio in planktonic foraminiferal shell using time series sediment trap a case study of intense dissolution artifact in the south china sea this study examines mg ca temperature equations through the use of planktonic foraminifers collected from continuous time series sediment traps at four water depths in the south china sea this deployment provides an opportunity to refine partial dissolution artifacts and to identify responses of shell chemistry to changes in ambient seawater conditions paired mg ca and 18o measurements on shells are strongly correlated with seasonal variability in terms of temperature at specific habitat depths however partial dissolution can significantly alter mg ca ratios even at depths well above the calcite lysocline or carbonate compensation depth of the three species studied neogloboquadrina dutertrei is the most sensitive species to dissolution relative to the other surface dwelling species globigerinoides ruber and globigerinoides sacculifer differences between the mg derived temperature equation here and those from previously established core top or sediment trap calibrations can be attributed to various degrees of dissolution and lateral advection thus highlighting the need for in situ empirical calibration for different ocean basins

crustal thinning on the aquitaine shelf bay of biscay from deep seismic data in recent years an increasing amount of new scientific data on the structure and nature of the whole continental crust has been acquired from deep seismic profiling the bay of biscay profile was recorded in 1984 at sea along the aquitaine platform for the french ecors group in association with hispanoil it collected a unique set of two ship multi channel seismic data with constant offset and expanded spread profiles in a complex geological area the data are of very good quality and contain clear moho and lower crust reflections as seen under most parts of western europe where similar experiments have been conducted1 4 this profile provided for the first time the most convincing evidence for an anomalously thin crust below a rifted basin the parentis basin which is directly connected to the oceanic area of the bay of biscay it gives new constraints for understanding the formation of extensional sedimentary basins

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

major crustal reflectors beneath sw england strong wide angle reflection events were detected during a crustal seismic experiment carried out in sw britain in 1979 three crustal reflectors have been identified referred to as rl r2 and r3 rl lies at a depth of about 8 km and appears to be restricted to the interior of the granite batholith underlying sw england the nature of this reflector is unknown r2 is a mid crustal reflector lying at a depth of 10 15 km and interpreted as rising gradually northwards it coincides locally with the base of the granite as predicted by gravity modeling but extends well beyond the northern limit of the granite body it is suggested that r2 may represent a major thrust of late variscan age r3 is the deepest reflector identified and lies at a depth of 27 30 km r3 is interpreted as the base of the crust and its computed depth is in close agreement with the local depth to the moho derived from an earlier seismic experiment in sw britain

deep events in u k south western approaches summary apparently planar dipping events are observed in seismic data off south west britain within otherwise essentially transparent upper and middle crust these are believed to represent variscan thrusts some of which were re activated during the post carboniferous phase of extension that affected the southern u k they can be seen in two extensive commercial seismic surveys recorded to 6 s two way time twt and where laterally persistent they have been mapped to reveal their essentially planar nature commonly these dipping events are associated with deeper near horizontal or gently convex upwards events with which they often appear to converge where real these are thought to indicate a complex fault system or possibly the top of the reflective lower crust the thrusts are seen over the whole area except where granite is known to occur and commonly exert a major control on the position and subsequent deformation of overlying sedimentary basins

relating estimates of caco3 production export and dissolution in the water column to measurements of caco3 rain into sediment traps and dissolution on the sea floor a revised global carbonate budget 1 the global caco3 budget is constrained by new estimates of standing stocks fluxes through the water column and dissolution in the water column and on the sea floor previous estimates of carbonate production and export are indistinguishable within a large range of values 0 4 1 8 gt pic yr 1 globally excess alkalinity ta and water mass tracers indicate dissolution of 1 0 gt pic yr 1 between 200 and 1500 m suggesting production and export must at least equal this amount most water column dissolution occurs at high latitudes and alkalinity fluxes from outer shelf and upper slope sediments 100 1500 m only support 5 10 of the ta inventory below 2000 m the sinking flux of pic 0 6 gt pic yr 1 is consistent with the rate of sea floor dissolution 0 4 gt pic yr 1 plus burial 0 1 gt pic yr 1 this rain rate constrains the export value to 1 6 gt pic yr 1 satellite based estimates of standing stocks of caco3 indicate a decrease equatorward which is opposite in trend to sediment trap fluxes this observation may be explained by an equatorward decrease in sinking particle dissolution systematic changes in pic residence time with latitude or satellite retrieval problems globally averaged euphotic zone standing stock 5 4 mmol m 2 and export estimates indicate pic residence times of 5 18 days

crystallographic orientation of microcracks in quartz and inferred deformation processes a study on gneisses from the german continental deep drilling project ktb abstract this study was carried out on four gneiss samples from the german continental deep drilling project ktb taken at depths between 556 and 8633 m the crystallographic orientation of microcracks in quartz was determined by a combination of the electron channelling pattern method ecp and u stage microscopy the distinct preferred crystallographic orientations of various crack generations point to different processes of crack initiation and propagation which partly seem to be depth dependent for older healed cracks a crystalplastic initiation due to dislocation pile up and related lattice distortion is indicated by cracking normal to prominent slip directions which are a at lower or c at comparatively higher temperatures in contrast younger open cracks preferentially formed on crystallographic planes with low surface energy rhombs and prisms which is interpreted in terms of pure elastic crack mechanisms because of the thermoelastic anisotropy of quartz internal stresses resulting from thermal contraction during cooling may be the main driving force for the initiation or further propagation of cracks parallel to the c axis crack propagation preferentially affects grains with crystal lattices and operating crack mechanisms being in a direction appropriate to the applied external tectonic stresses this selective cracking explains why cracks also show constant orientations with respect to geographic directions up to regional dimensions

physical properties of indus ophiolites from kashmir himalaya abstract the indus suture rocks from the dras sanko kargil regions have been studied for their petrography chemical and physical properties seismic velocities as a function of pressure up to 10 kbar are obtained on different rock types of the ophiolite assemblage such as spilite metabasalt schist dunite peridotite pyroxenite serpentinite metagreywacke and associated granodiorite empirical relations of density versus velocity density versus porosity the results of anisotropy due to multidirectional measurements of velocity data of static strength and dynamic moduli and regression analysis of stress strain data are presented they exhibited low anisotropy and high strength the exceptions being those that are serpentinized the metamorphism of the regional rocks the consequent hydrothermal alteration the degree of serpentinization in the ultramafics and the groundmass to phenocryst ratio amongst the metabasics are found to influence the physical properties thermal studies yielded the results of the increase in expansion of the decrease in density and the dependence of on the porphyritic mineral content the absence of a definite sequential association as well as a lack of metamorphic contact in the area between the ultramafics and metavolcanics and the differing compatible nature in the pressure velocity modelling results the ultramafics gabbros dykes being compatible with the oceanic rocks and ophiolites while the metavolcanics are incompatible suggest the dismembered nature of the indus ophiolites

geophysical images of the deep crust the iapetus suture the iapetus suture arguably the most fundamental lineament of british and irish structure has been previously identified on the birps winch deep seismic reflection profiles offshore as a nw dipping feature new depth migrated interpretations of these and other reflection data show good correlation of structure for 100 km along strike in the northern irish sea towards magnetotelluric stations onshore in the north of england and southern uplands of scotland three different methods of inverting data from these sites all reveal a thin nw dipping slab of high conductivity a contour map of the suture trace dipping at 15 25 nw can be constructed down to and through the moho at 28 km depth this map suggests crustal stretching below the solway basin the mylonitic suture zone is characterized by good seismic reflection layering high conductivity presumably fluid produced and a steep increase of p wave velocity over the few kilometres of its width crustal refraction experiments lispb and cssp provide useful velocities but locally misleading structure so that the combination of the seismic reflection and geoelectric methods may be the most powerful means of determining deep crustal structure with a good degree of both vertical and lateral resolution

elastic moduli evolution and accompanying stress changes with increasing crack damage implications for stress changes around fault zones and volcanoes during deformation summary the elastic moduli of rock in areas susceptible to crack damage such as within fault zones or volcanic edifices can be subject to large modifications knowledge of how elastic moduli may vary in such situations is important for both the reliable modelling of volcano deformation and stability and for linear and non linear elastic crack models for earthquake rupture furthermore it has previously been shown that changes in elastic moduli can induce changes in the stress field surrounding faults here we report both uniaxial experimental measurements of changes in elastic moduli during increasing amplitude cyclic stressing experiments on a range of different rock types basalts sandstones and granite and the results of modelled stress modifications the trend in elastic moduli evolution with increasing damage was remarkably similar for each rock type with the exception of essentially crack free intrusive basalt that exhibited very minor changes in general young s modulus decreased by between 11 and 32 per cent and poisson s ratio increased by between 72 and 600 per cent over the total sequence of loading cycles these changes are attributed to an increasing level of anisotropic crack damage within the samples our results also show that acoustic emission ae output during any loading cycle only commenced when new crack damage was generated this corresponded to the level of stress where ae ceased during the unloading portion of the previous cycle using the multilayer elastic model of faulkner et al we demonstrate that the damage induced changes in elastic moduli also result in significant decreases in differential stress increases in mean stress and rotation of the applied greatest principal stress relative to the orientation of the mechanical layering the similar trend in the evolution of the elastic moduli of all the rocks tested suggests that stress modification in the damage zone of faults might take the same form regardless of the lithology through which the fault runs these observations are discussed in terms of their applicability to both fault zones and deformation at volcanoes

calcium carbonate dissolution in the upper 1000 m of the eastern north atlantic recent analyses suggest that considerable caco3 dissolution may occur in the upper water column of the ocean 1500 m this study uses the distribution of particulate calcium from high resolution suspended matter sampling along the climate variability and predictability co2 repeat hydrography a16n transect in 2003 to estimate caco3 dissolution in the top 1000 m of the north atlantic dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces water masses were found to be undersaturated with respect to aragonite at intermediate depths 400 1000 m in the eastern tropical north atlantic the caco3 dissolution rate in this region is estimated to be 0 9 mmol caco3 m 2 d 1 indicating this region is a hotspot for upper water column caco3 dissolution compared to the atlantic basin as a whole dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower 0 2 mmol caco3 m 2 d 1 and are comparable to previous estimates of caco3 dissolution flux for the atlantic ocean the magnitude of upper water column dissolution rates compared to measured surface ocean caco3 standing stocks suggests that biologically mediated caco3 dissolution may be occurring in the top 1000 m of the atlantic

the influence of alteration on the engineering properties of dolerites the examples from the pindos and vourinos ophiolites northern greece abstract the influence of alteration on the physico mechanical properties of dolerites from the pindos and vourinos ophiolites northern greece is investigated quantitative petrographic analysis shows that the samples display various percentages of secondary minerals two new micropetrographic indices are calculated from the results of petrographic modal analysis for the engineering assessment of dolerites the micropetrographic strength index i ps and the replacement index i rep the samples are also tested to determine water absorption apparent density total porosity sand equivalent uniaxial compressive strength los angeles abrasion value aggregate impact value aggregate abrasion value and polished stone value the influence of alteration on the rock quality and especially the relationships between the proposed micropetrographic indices and the engineering parameters are determined using regression analysis and the derived equations were verified by the t test and the f test the relationships between the i ps and i rep indices and the engineering properties show that alteration products generally result in mechanically weaker rocks however the results of the physico mechanical tests indicate that dolerites retain their strength and durability due to the low proportions of soft minerals and microcracks along with the preservation of their igneous textures the polishing resistance is the only engineering parameter that is positively affected by alteration processes as expressed by the i ps index particularly the replacement of the primary mafic minerals by secondary minerals expressed by the i rep index can enhance the polishing resistance of dolerites when used in the wearing surface of a road the results also indicate strong positive correlations between the chlorite content and the water absorption and total porosity values

a deep seismic reflection profile over a caledonian granite in central england in 1980 a short deep reflection profile undertaken jointly by the university of leicester and the institute of geological sciences crossed a buried caledonian granite to the south west of melton mowbray in leicestershire little structure is seen in the section between the top of the granite at 0 25 s two way time stwt and a zone of very strong sub horizontal reflections at 6 s twt a further reflection zone is identified at 7 2s twt below which there are a series of strong but impersistent reflections to the full reording time of 12 s twt the data indicate that the granite must be relatively homogeneous and underlain by several marked sub horizontal boundaries at mid to lower crustal levels this suggests that during emplacement either the granite must have had little effect on the lower crust sampled by the profile or the lower crust was mobile enough to have developed layering since the granite was emplaced during the caledonian orogeny

ultrasonic and x ray computed tomography characterization of progressive fracture damage in low porous carbonate rocks abstract this paper studies the fracturing process in low porous rocks during uniaxial compressive tests considering the original defects and the new mechanical cracks in the material for this purpose five different kinds of rocks have been chosen with carbonate mineralogy and low porosity lower than 2 the characterization of the fracture damage is carried out using three different techniques ultrasounds mercury porosimetry and x ray computed tomography the proposed methodology allows quantifying the evolution of the porous system as well as studying the location of new cracks in the rock samples intercrystalline porosity the smallest pores with pore radius

global calcite cycling constrained by sediment preservation controls 1 we assess the global balance of calcite export through the water column and burial in sediments as it varies regionally we first drive a comprehensive 1 d model for sediment calcite preservation with globally gridded field observations and satellite based syntheses we then reformulate this model into a simpler five parameter box model and combine it with algorithms for surface calcite export and water column dissolution for a single expression for the vertical calcite balance the resulting metamodel is optimized to fit the observed distributions of calcite burial flux we quantify the degree to which calcite export saturation state organic carbon respiration and lithogenic sedimentation modulate the burial of calcite we find that 46 of burial and 88 of dissolution occurs in sediments overlain by undersaturated bottom water with sediment calcite burial strongly modulated by surface export relative to organic carbon export we find surface calcite export skewed geographically toward relatively warm oligotrophic areas dominated by small prokaryotic phytoplankton we assess century scale projected impacts of warming and acidification on calcite export finding high sensitive to inferred saturation state controls with respect to long term glacial cycling our analysis supports the hypothesis that strong glacial abyssal stratification drives the lysocline toward much closer correspondence with the saturation horizon our analysis suggests that over the transition from interglacial to glacial ocean a resulting 0 029 pgc a 1decrease in deep atlantic indian and southern ocean calcite burial leads to slow increase in ocean alkalinity until pacific mid depth calcite burial increases to compensate

microcracks in ultrabasic rocks under uniaxial compressive stress the initiation and propagation of microcracks under stress are highly dependent upon the mineralogical and textural characteristics of the various lithotypes detailed observation and quantification of microcracks before and after uniaxial compression test were conducted a fresh olivine rich harzburgite and a serpentinized dunite were analyzed collected from the pindos and vourinos ophiolites northern greece respectively in order to compare their microcrack patterns quantitative analysis indicated that during uniaxial compression the intragranular microcracks which are the dominating crack type are gradually transformed or organized into transgranular cracks some of the newly formed transgranular cracks may also be a result of the growth of existing grain boundary cracks the new intragranular microcracks in the olivine rich harzburgite are oriented predominantly parallel to the compressive stress direction while those in the serpentinized dunite show a scattered orientation presumably due to the mesh texture of this rock type the new transgranular cracks of both peridotites tend to be subparallel to the compressive stress direction however many of them show a random orientation due to the fact that they have been formed as a result of the propagation of grain boundary cracks the occurrence of the soft serpentine along fracture surfaces of olivine when it is in assemblage with orthopyroxene tends to absorb the applied stress hampering the development of microcracks in olivine on the other hand in serpentinized peridotites the microcracks are enhanced in olivine because it is surrounded by large amounts of the much softer and flexible serpentine microcracks are usually formed along the cleavage planes of orthopyroxene porphyroclasts indicating that such crystallographic preferred orientations act as planes of weakness controlling the direction of the crack paths cr spinel grains likely comprise locations of initiation of microcracks due to their very hard nature and different mechanical behaviour relative to the surrounding silicate phases knowledge of the mineralogical and textural characteristics may assist in the prediction of potential development of failure surfaces of an ultrabasic rock in service

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea