external dose rate determinations for esr dating at bau de l aubesier provence france abstract at bau de l aubesier provence france mousterian artefacts and human teeth occur in inhomogeneous lumpy sedimentary deposits that include bone and tooth fragments due to uranium u uptake by the bones and teeth the external dose rate experienced by the teeth has changed over time such changes must be considered when calculating thermoluminescence tl ages for burnt flint artefacts or electron spin resonance esr ages for the teeth therein here we assess the external dose rates using three methods in situ tl dosimetry gives the modern dose rate whereas volumetrically averaged geochemical analysis is used to estimate time averaged dose rates that consider u uptake by u rich sedimentary components blackwell and blickstein 2000 quarternary international 68 71 329 343 in esr isochron analysis blackwell and schwarcz 1993 applied radiation and isotopes 44 243 252 multiple subsamples with variable u concentrations measure the external dose rate experienced by the tooth regardless of reworking but do depend on the uptake model assumed the methods each suggest significantly different dose rates tl dosimetry for two combustion horizons measured external dose rates at 0 143 0 012 mgray y in layer iv and 0 184 0 016 mgray y in layer h geochemical analysis when volumetrically averaged to account for the influence from different sedimentary components indicates external dose rates ranging from as low as 0 094 0 024 mgray y assuming ru for u rich sedimentary components to a maximum of 0 251 0 048 mgray y assuming eu for the u rich components isochron analyses suggest more variable dose rates ranging from a minimum of 0 009 0 040 mgray y lu in the lower layers to a high of 1 103 0 160 mgray y eu in layer h1 three isochrons indicated that the teeth had experienced u leaching or a second uptake event which would affect the accuracy of the dose rate determinations for those teeth other teeth may have experienced similar processes quaternary researchers who want reliable dates in the age ranges for esr or tl must carefully consider both the nature of the sediment especially u rich bone fragments and its geometric arrangement around the samples to be dated corresponding results using more than one analytic method may be required for a reasonable confidence level

niobium uranium evidence for early formation of the continental crust niobium uranium ratios in greenstone belt basalts and gabbros indicate that parts of the late archean mantle beneath western australia underwent a level of melt extraction resulting in formation of the continental crust comparable to that seen in the present mantle the implication is either that i the amount of continental crust that formed before 2 7 x 10 9 years ago was much greater than generally thought or ii crustal growth occurred by severe depletion of small volumes of the mantle rather than by moderate depletion of a large volume of mantle

the theory and application of dem gassmann rock physics model for complex carbonate reservoirs the storage spaces of carbonate reservoirs in the tarim basin are dominated by secondary pore porosity such as dissolution caves holes and cracks song et al 2001 research has shown that pore shapes can significantly influence the velocities of elastic waves eshelby 1957 kuster and toksoz 1974 xu and white 1995 yan et al 2002 sun et al 2004 empirical vp vs relationships such as castagna s 1985 mudrock line han s relations 1986 and greenberg castagna s 1992 relationship that ignore the effect of pore geometry are not applicable to carbonates xu and white 1995 wang et al 2009 cheng and toksoz 1979 imaged various pore space structures using sem and proposed a pore aspect ratio spectrum that can be used to explain velocity prediction han 2004 measured velocities of 52 different carbonate rocks indicating that caves influence seismic velocities due to high rigidity while micropores or cracks significantly decrease velocities of rocks due to the low rigidity regarding

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

considering sedimentary u uptake in external dose rate determinations for esr and luminescent dating abstract at many archaeological sites including bau de l aubesier la quina and la chaise de vouthon artefacts teeth and bones occur in heterogeneous lumpy sedimentary deposits that include bone and tooth fragments due to uranium u uptake by the bones and teeth in the adjacent sediment the external dose rate experienced by teeth bones or the sediment itself will have changed over time such changes must be considered when calculating dose dependent ages whether thermoluminescent tl age for burnt flint artefacts optically stimulated luminescent osl or radioluminescent rl ages for sediment or electron spin resonance esr ages for the teeth therein u uptake or loss in the sedimentary bone and tooth fragments can be modelled in the same manner as u uptake or loss in the dated teeth compared to dose rates derived from single bulk sedimentary geochemical analyses volumetrically averaged sedimentary dose rates at bau de l aubesier show significant differences depending on the model adopted for the u uptake in order to calculate the dosimetric contribution from the sedimentary components that had absorbed u

mapping stress and structurally controlled crustal shear velocity anisotropy in california we present shear velocity anisotropy data from crustal earthquakes in california and demonstrate that it is often possible to discriminate structural anisotropy polarization of the shear waves along the fabric of major active faults from stress induced anisotropy polarization parallel to the maximum horizontal compressive stress stress directions from seismic stations located near but not on the san andreas fault indicate that the maximum horizontal compressive stress is at a high angle to the strike of the fault in contrast seismic stations located directly on one of the major faults indicate that shear deformation has significantly altered the elastic properties of the crust inducing shear wave polarizations parallel to the fault plane

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

fractured reservoir delineation using multicomponent seismic data the characteristic seismic response to an aligned fracture system is shear wave splitting where the polarizations time delays and amplitudes of the split shear waves are related to the orientation and intensity of the fracture system this offers the possibility of delineating fractured reservoirs and optimizing the development of the reservoirs using shear wave data however such applications require carefully controlled amplitude processing to recover properly and preserve the reflections from the target zone here an approach to this problem is suggested and is illustrated with field data the proposed amplitude processing sequence contains a combination of conventional and specific shear wave processing procedures assuming a four component recording the split shear waves can be simulated by an effective eigensystem and a linear transform technique can be used to separate the recorded vector wavefield into two principal scalar wavefields representing the fast and slow split shear waves conventional scalar processing methods designed for processing p waves including noise reduction and stacking procedures may be adapted to process the separated scalar wavefields an overburden operator is then derived from and applied to the post stacked scalar wavefields a four component seismic survey with three horizontal wells drilled nearby was selected to illustrate the processing sequence the field data show that vectormore wavefield decomposition and overburden correction are essential for recovering the reflection amplitude information in the target zone the variations in oil production in the three horizontal wells can be correlated with the variations in shear wave time delays and amplitudes and with the variations in the azimuth angle between the horizontal well and the shear wave polarization dim spots in amplitude variations can be correlated with local fracture swarms encountered by the horizontal wells less

the lithoprobe abitibi grenville transect two billion years of crust formation and recycling in the precambrian shield of canada we summarize the results of lithoprobe studies in the neoarchean southeastern superior province and the mesoproterozoic grenville province in the southeastern precambrian shield of canada through two composite cross sections based on seismic reflection data which define dramatically different styles of crust formation and tectonic accretion in the neoarchean and mesoproterozoic in the neoarchean the structures at the surface are steep with discontinuous and flatter structures at depth much of the crust appears to be juvenile and the predominant process of crustal growth is inferred to have been subduction accretion of primitive crust in a prograding arc system in the mesoproterozoic surface structures are shallow and the seismic character of the crust is continuous over the entire cross section archean parautochthonous rocks and reworked archean crust comprise a very significant proportion of the preserved crust in the mesoproterozoic and provided the backstop to the grenvillian orogeny result

archean plate tectonics constraints and inferences the earth has been cooling since archean time the higher temperatures beneath archean ridges resulted in more partial melting which extended down to greater depths than at present the archean oceanic crust was much thicker 20 km than modern crust 5 km this inference is compatible with previous ideas of suspected oceanic crust the thicker oceanic crust in the archean tended to resist subduction similar to modern aseismic ridges but could not prevent it short lived episodes of intra arc spreading followed by cordilleran type compression may have produced archean greenstone belts archean meta tonalites represent a significant part of the continental crust and were probably produced by melting of the subducted slab which was favored by the higher mantle temperatures

deep crustal mineral assemblages and potential for crustal rocks below the moho in the scottish caledonides summary the scottish caledonian lower crust is strongly seismically reflective beneath the moho at about 30km very few reflections are seen on seismic records with the exception of a strong reflector at about 50km depth the rocks between the moho and this strong reflector have been interpreted as crustal but with mantle velocities and densities we report tests of this in which the densities and seismic velocities of likely crustal precursors are assessed through determination of the stable mineral assemblages along geotherms appropriate to the region likely crustal precursors were selected from suites of exhumed deep crustal rocks and deep crustal xenoliths and from a variety of basaltic rocks mineral assemblages were estimated using a variant of the lowest free energy search procedure of wood 1987 with account taken of nonideal mixing in solid solutions geotherms were calculated from the heatdow heatproduction relationship for the scottish caledonides using the methods of pollack chapman 1977 seismic velocities were estimated from empirical density velocity relationships and from the velocities of individual mineral species weighted for modal proportions

growth and differentiation of the continental crust declining radiogenic heat production since the archaean has resulted in a secular evolution from a regime of numerous fast moving small thin torsionally weak plates to the present regime of larger thicker torsionally stronger plates moving at an average rate of less than one sixth of the archaean rate this has been accompanied by episodic changes in geological effects by 2500 ma b p about 85 of the present crustal mass had grown by the addition and amalgamation of mafic and calc alkaline rocks in oceanic arcs at an average rate of 11 17 pg a during the early proterozoic the first large cratons were stabilized and locally thickened and differentiated the proterozoic was an era of little continental growth falling average sea level and intracontinental deformation by 700 ma b p cratons had become much more stable marginal accretionary terrians had begun to develop with an average phanerozoic growth rate of 1 64 pg a and blueschists and ophiolites sensu stricto witness the advent of the extant plate tectonic regime

water saturation effects on elastic wave attenuation in porous rocks with aligned fractures summary elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing of the earth s structure and to hydrocarbon reservoir characterization in particular we investigated the effect of partial water saturation on attenuation in fractured rocks in the laboratory by conducting ultrasonic pulse echo measurements on synthetic silicacemented sandstones with aligned penny shaped voids fracture density of 0 0298 0 0077 chosen to simulate the effect of natural fractures in the earth according to theoretical models our results show for the first time contrasting variations in the attenuation q 1 o fp and s

lithoprobe crustal reflection cross section of the southern canadian cordillera 1 foreland thrust and fold belt to fraser river fault seismic reflection data from the south central canadian cordillera covering the interval from the easternmost metamorphic core complexes near arrow lakes to the fraser river fault system along the fraser river reveal a highly reflective and complex crust the base of the crustal reflectivity interpreted as the reflection moho is clearly delineated by a continuous sharp boundary that is essentially planar and slopes uniformly over a distance of 250 km from about 12 0 s in the east to about 10 5 s in the west this virtual lack of relief at the base of the crust contrasts sharply with surface structures that involve 25 km or more of structural relief some of these surface structures can be readily correlated to structures that are outlined by the reflection data and that can be followed into the middle and lower crust even though part of this area was subjected to large amounts of eocene extension the crust is not divisible into transparent upper and reflective lower layers as it is in parts of the u s cordillera three structural culminations the monashee complex the vernon antiform and the central nicola horst are interpreted on the basis of the reflection configuration and the surface geological relationships to have formed initially during jurassic to eocene compression and then to have been modified and exposed during early and middle eocene extension an example of a compressional structure observed on the profiles is the monashee decollement which can be traced from the surface westward into the lower crust extension is manifested along a variety of normal faults including the regionally extensive low angle okanagan valley eagle river fault system moderately dipping faults such as the columbia river and slocan lake faults and high angle faults such as the quilchena creek and coldwater faults both jurassic to eocene compressional shear zones and early to middle eocene extensional shear zones are listric into the lower crust or moho under the intermontane belt

how feasible was subduction in the archean as the asthenospheric mantle rises at oceanic spreading centres it undergoes partial melting producing oceanic crust and depleted mantle both of which have lower intrinsic density than the asthenospheric mantle from which they were derived with a warmer asthenosphere in the archean these effects are enhanced leading to the possibility that subduction was no longer feasible i investigate the density of the oceanic crust and underlying mantle for a mantle with temperatures 200 c higher than today using models of the chemistry of melting and the mineralogy of the ensuing rocks for the melting model used crustal thicknesses are 21 km and the depth to which the mantle is partially melted is 114 km compared with 7 and 54 km for a comparable model of modern earth two thermal evolution models for archean oceanic lithosphere are examined one assumes twice the heat flow into the base of the plates which severely restricts the depths to which the plates can cool with age a second assumes the plates c

esr dating of tooth enamel comparison with 230th234u speleothem dates at la chaise de vouthon charente france abstract one way to assess a new dating method s reliability is by comparing its results with those from well established independent techniques a controlled test of the electron spin resonance esr dating method as it is currently being applied to teeth was attempted for the time range 100 250 ka beyond that of 14 c at the archaeological site of la chaise de vouthon charente france although absent in modern enamel a single esr signal with g 2 0018 in fossil tooth enamel hydroxyapatite increases in amplitude with increasing irradiation doses esr ages are derived from the ratio of the ad the radiation dose needed to produce the observed esr signal relative to the natural environmental dose rate ed experienced by the tooth after deposition since the age depends on the uranium u uptake history assumed three ages are calculated assuming 1 early u uptake eu 2 continuous linear uptake lu 3 recent uptake ru generally the lu age agrees best with known ages determined by other methods although the ru model is better for some teeth esr dating assumes that the fossil has not suffered recrystallization or significant diagenetic alteration in the preliminary test three teeth were dated in bourgeois delaunay a bovid molar associated with palaeolithic artefacts was collected from layers dated at 101 12 to 114 7 ka by 230 th 234 u dating of the over and underlying stalagmitic floors from suard two equus teeth were collected from beneath a stalagmitic floor dating 112 12 ka esr dating teeth significantly underestimated the true age for the teeth the mean esr ages range from 37 to 94 ka with standard errors of 2 6 ka and good replicability although more teeth at la chaise need to be tested to ascertain that the underestimation does not result from random variation commonly seen among teeth within one unit the consistent underestimation suggests a fault in one of the assumptions underlying the dating method the most obvious source of error lies in the difficulty in modelling the external dose only u leaching not incorrectly modelled u uptake would cause the underestimation diagenetic alteration may also cause anomalous fading thermal instability variation in k or esr signal suppression more study into the effects of diagenesis alteration on enamel esr signals is needed as is a reevaluation of the mean signal life and efficiency for several more enamel samples

characteristics of anisotropy and dispersion in cracked medium abstract in upper crustal conditions where effective pressure is not high enough to close them all rocks contain cracks understanding the effect of cracks on both the elastic anisotropy and the elastic waves frequency dependence dispersion is of major interest to underground storage monitoring reservoir monitoring and fault mechanics the challenge is to extract from geophysical data the maximum information with a minimal number of assumptions and model parameters this is possible if reference data exist at the laboratory scale and if extrapolation from laboratory to field scale is not biased in order to check that investigating few basic idealized cases can provide useful guidelines let us consider an isotropic rock matrix and assume that dispersion is the result of squirt flow in this paper we will not consider crack to pore but rather focus on crack to crack squirt flow three basic cracks configurations are quantitatively investigated for which the elastic symmetry is transverse isotropy ti our aim is to check if from first principles high frequency laboratory data can be used for field data interpretation in these three cases the first case is that of identical cracks aligned in the same direction a sufficiently strong deviatoric stress field in a given plane is expected to induce such a distribution at the field scale 1 2 3 we show that it results in a maximum anisotropy but with virtually no dispersion because there is no dispersion high frequency data obtained in the laboratory mhz ultrasonic range are directly applicable to field data hz to khz range interpretation thomsen parameters provide then a direct proxy for crack density a second case is that of identical cracks with random orientations isotropic distribution such a situation could exist at the field scale if cracks result from the superposition of several independent tectonic episodes associated with different directions of principal stresses in that case 1 2 3 this configuration could also result from thermal cracking in an initially isotropic metamorphic rock obviously there is no overall anisotropy then but we show that dispersion may be large due to dispersion ultrasonic laboratory data are not directly applicable to field data interpretation unless the medium is dry a third intermediate case is that of cracks randomly distributed in zone with a given axis the corresponding symmetry is that of a so called axi symmetric triaxial test which in fact is biaxial it is of interest because it represents a classical laboratory experiment situation it can also exist at the field scale if one principal stress is much larger than both others 1 2

freeboard revisited continental growth crustal thickness change and earth s thermal efficiency abstract the rate of growth of earth s continental crust is commonly estimated from the age distribution of present continental crust and from the geochemistry of ancient mantle derived lavas in this paper i assess the rate of growth from relationships between the volume and thickness of continental crust the thickness of the continental crust is governed by its total volume and by the relative buoyancy of the continental and oceanic lithospheres the buoyancy of the oceanic lithosphere is governed by the amount of melting at mid oceanic ridges and the mean age of the ocean floor which are functions of the mantle temperature and its relationship to global heat loss thus the relationship between continental crustal thickness continental crustal volume and mantle temperature may be specified provided the functional dependence of global heat loss on mantle temperature is known using this relationship i investigate the implications of crustal growth models for changes in continental crustal thickness over time if archean continental crustal volumes had been the same as or similar to modern ones continental crustal thicknesses would have been significantly greater than today this would be reflected in subsequently deeply eroded archean terrains and is inconsistent with the geological record sigmoidal growth models in which significant crustal growth occurred during the proterozoic also require several kilometers of erosion for strong dependence of heat loss on mantle temperature but permit nearly constant continental crustal thicknesses through time if the dependence is weak with more precise information on the erosion of archean terrains it will be possible to constrain both crustal growth models and the nature of the functional dependence of heat loss on mantle temperature

modeling elastic properties in carbonate rocks carbonate limestone and dolomite reservoirs account for approximately 50 of oil and gas production worldwide however seismic responses in carbonate rocks are poorly understood in addition dhi ranking and avo classification systems developed for clastic rocks are unlikely to be applicable to carbonate rocks an accurate and physically sound carbonate rock physics model is needed to address these technical issues

velocities of compressional and shear waves in limestones carbonate rocks are important hydrocarbon reservoir rocks with complex textures and petrophysical properties porosity and permeability mainly resulting from various diagenetic processes compaction dissolution precipitation cementation etc these complexities make prediction of reservoir characteristics e g porosity and permeability from their seismic properties very difficult to explore the relationship between the seismic petrophysical and geological properties ultrasonic compressional and shear wave velocity measurements were made under a simulated in situ condition of pressure 50 mpa hydrostatic effective pressure at frequencies of approximately 0 85 mhz and 0 7 mhz respectively using a pulse echo method the measurements were made both in vacuum dry and fully saturated conditions in oolitic limestones of the great oolite formation of southern england some of the rocks were fully saturated with oil the acoustic measurements were supplemented by porosity and permeability measurements petrological and pore geometry studies of resin impregnated polished thin sections x ray diffraction analyses and scanning electron microscope studies to investigate submicroscopic textures and micropores it is shown that the compressional and shear wave velocities vp and vs respectively decrease with increasing porosity and that vp decreases approximately twice as fast as vs the systematic differences in pore structures e g the aspect ratio of the limestones produce large residuals in the velocity versus porosity relationship it is demonstrated that the velocity versus porosity relationship can be improved by removing the pore structure dependent variations from the residuals the introduction of water into the pore space decreases the shear moduli of the rocks by about 2 gpa suggesting that there exists a fluid matrix interaction at grain contacts which reduces the rigidity the predicted biot gassmann velocity values are greater than the measured velocity values due to the rock fluid interaction this is not accounted for in the biot gassmann velocity models and velocity dispersion due to a local flow mechanism the velocities predicted by the raymer and time average relationships overestimated the measured velocities even more than the biot model

current challenges to esr dating abstract electron spin resonance dating is applicable to a wide range of materials found at quaternary sites and which can generally be assured to exhibit zero signals at the time to be dated t 0 local inhomogeneity in external dose rates may contribute to dispersion in apparent dates but average dates may still be good estimates of site ages testing of u uptake models by u series measurements shows that both early and continuous uptake can occur possibly even in the same site problems of signal lifetime determination and diagenesis are reviewed

continent elevation mountains and erosion freeboard implications 1 to the simplest approximation earth s continental crust is a floating aggregate on the planet s surface that is first attracted to subduction zones and upon arrival thickened by mountain building then producing some extension thickened regions are thinned again by erosion a comparison between 65 ma and the present shows that the modern state is significantly more mountainous an estimated average continental elevation increase relative to average ocean floor depth of about 54 m and sea level decrease relative to the ocean floor of about 102 m add up to a 156 m increase of continent elevation over sea level since 65 ma both are affected most strongly by the roughly 1 7 continent surface area decrease caused by cenozoic mountain building this includes contributions from erosion volumes of sediments in deltas and submarine fans indicate an average thickness of 371 m deposited globally in the ocean basins since 65 ma this relatively large change of continent area over a short span of earth history has significant consequences extrapolating if continent area change exceeded 5 in the past either severe erosion or flooded continents occurred if continent elevation freeboard remains at the present value of a few hundred meters the past continent ocean area ratio might have been quite different depending on earlier volumes of continental crust and water we conclude that along with the ages of ocean basins continental crustal thickening exerts a first order control on the global sea level over hundreds of million years

on some controversial issues in rock physics we examine some basic issues in elasticity of reservoir rocks that are of central importance for the hydro carbon exploration and production technologies serious misconceptions appear to persist in these areas and they may lead to dubious guidelines for log editing synthetic forward modeling avo and 4d studies our motivation here is to clarify some of these issues we also identify challenges in relating the elastic properties of rocks to their microstructure they concern irregular shapes of cracks and pores and their proper quantitative characterization

precambrian continental freeboard and geological evolution a time perspective abstract continental crustal growth rates crustal volumes thicknesses and continental freeboard are considered to be intimately related however none are easy to quantify least of all in the precambrian additionally crustal volumes thicknesses and isostasy are related to changing mantle heat and the concomitant variation in thickness of ocean crust another set of variables would be the interaction of plate tectonics and the onset of plate tectonics a contentious issue in itself and mantle plumes superplumes further complication is provided by the ranges of freeboard elevations and eustatic sea level changes overlapping in scale and sharing common genetic causes the constant freeboard model suggests that the net results of the interaction of this complex set of variables has been that continental elevation relative to sea level has remained essentially similar on a global average basis over much of geological time assuming an essentially constant ocean volume since c 3 8 ga application of this model to the precambrian geological record suggests that sigmoidal crustal growth rate models are probably the most reliable a conundrum of the constant freeboard model would be that freeboard would tend to become lowered towards mean sea level for any specific craton over time this freeboard equilibrium would be interrupted for a particular craton by active geodynamic processes resulting from the interplay of plate tectonics and mantle thermal instabilities in this paper we test the validity of this thesis of alternating approximate freeboard equilibrium and active geodynamics by examining the volcano sedimentary record of a number of cratons kaapvaal singhbhum and pilbara for the singhbhum craton and bearing in mind its poor chronological data base freeboard equilibrium appears to have prevailed until c 2 1 ga but for kaapvaal and pilbara until c 1 8 ga the geodynamic processes largely outweighed the tendency towards equilibrium except for c 200 my from c 2 6 to 2 4 ga when global sea level appears to have remained high and transgression was the norm we thus tentatively add the plate tectonic cycle and mantle thermal processes to the already complex association of concepts controlling continental freeboard over time

global tectonic and climatic control of mean elevation of continents and phanerozoic sea level change abstract mean elevation of all continents as well as mean elevation of individual continents should be at the fundamental level controlled by the global tectonic and climatic systems i propose a first order model considering the interplay of the two factors in controlling mean elevation of continents the model is able to account for the positive correlation between the present day mean elevation and area of individual continents except for antarctica furthermore it can also explain the low sea level during the times of supercontinents finally the model is used to evaluate the variation of continental crust thickness with time

3 5 billion years of reshaped moho southern africa abstract according to some previous studies archean continental crust is on global average apparently thinner than proterozoic crust subsequently the validity of this statement has been questioned to provide an additional perspective on this issue we present analyses of moho signatures derived from recent seismic data along swaths 2000 km in length across southern africa and its flanking ocean the imaged crust has a near continuous age range between ca 0 1 and 3 7 billion years and the seismic data allow direct comparison of moho depths between adjacent archean proterozoic and phanerozoic crust we find no simple secular change in depth to moho over this time period in contrast there is significant variation in depth to moho beneath both archean and proterozoic crust archean crust of southern africa displays as much crustal diversity in thickness as the adjacent proterozoic crust the moho beneath all crustal provinces that we have analysed has been severely altered by tectono metamorphic and igneous processes in many cases more than once and cannot provide unequivocal data for geodynamic models dealing with secular changes in continental crust formation these results and conclusions are similar to those documented along ca 2000 km swaths across the canadian shield recorded by lithoprobe tying the age and character of the precambrian crust of southern africa to their depth diversities is clearly related to manifold processes of tectono thermal surgery subsequent to their origin the details of which are still to be resolved as they are in most precambrian terranes reconstructing pristine moho of the early earth therefore remains a formidable challenge in south africa better knowledge of fossilised archean crustal sections turned on edge such as at the vredefort impact crater for the continental crust and from the barberton greenstone belt for oceanic crust is needed to characterize potential pristine archean moho transitions

studying chert with electron spin resonance abstract archaeologists generally want to know how old their artifacts are and from where they came electron spin resonance esr is a tool for studying chert using radiation induced signals analogous to those used for thermoluminescence tl and optically stimulated luminescence osl dating as a dating technique it is well established for tooth enamel and shells and initial studies suggest it may be possible to date quartz sediments for this study however it is presently applicable only to heated chert work on samples from numerous sources has confirmed that heating chert is a complex process and both the duration and temperature of heating must fall within certain ranges in order to obtain datable samples both old world and new world material has been dated looking at these samples has also shown that variability among sources may permit proveniencing

esr in the 21st century from buried valleys and deserts to the deep ocean and tectonic uplift abstract electron spin resonance esr dating can date many materials including hydroxyapatite in enamel and some fish scales aragonite and calcite in corals molluscs some travertine and calcrete and quartz from ash fluvial deposits and some flint dating studies using these materials have numerous potential applications in many varied quaternary settings esr dating uses signals resulting from trapped charges created by radiation in crystalline solids ages are calculated by comparing the accumulated radiation dose in the dating sample with the internal and external radiation dose rates produced by natural radiation in and around the sample and produced by cosmic radiation when compared to other dating techniques age agreement has been excellent for teeth corals molluscs and quartz recent improvements have included using a more complex modelling technique to calculate the cosmic dose rates and more detailed modelling techniques for dealing with variable external dose rates methods in development include using quartz from buried fluvial valleys to date geomorphic surfaces and using the signals in barnacles and benthic foraminifera for dating fossils or their associated sediment new chronometer applications recently developed include using coral and mollusc dates to build sealevel curves and to monitor volcanic activity and tectonic uplift using tooth and mollusc dates to assess water availability in deserts and using isochron data to assess u uptake processes into teeth when coupled with other geochemical and geomorphological techniques esr can provide the chronometric control to build paleoclimatic and other paleoenvironmental records many other applications are possible from heating studies for artefacts to dating sulphates and other minerals on distant planets

experimental study on the effects of fractures on elastic wave propagation in synthetic layered rocks abstractfractures greatly increase the difficulty of oil and gas exploration and development in reservoirs consisting of interlayered carbonates and shales and increase the uncertainty of highly efficient development the presence of fractures or layered media is also widely known to affect the elastic properties of rocks the combined effects of fractures and layered media are still unknown we have investigated the effects of fracture structure on wave propagation in interlayered carbonate and shale rocks using physical models based on wave theory and the similarity principle we have designed and built two sets of layered physical models with randomly embedded predesigned vertically aligned fractures according to the control variate principle we have measured the p and s wave velocities and attenuation and analyzed the effects of fracture porosity and aspect ratio ar on velocity attenuation and power spectral dimension of the p and s waves the experimental results indicated that under condition

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

confirmation of a near 400 ka age for the yabrudian industry at tabun cave israel abstract the important lower and middle palaeolithic site of tabun has been previously dated using esr u series and tl esr ages throughout the site are substantially younger than tl dates although these methods have been shown to agree at other sites in israel and elsewhere all previous esr dates have been obtained on museum specimens using only attached sediments for dosimetry here we report the first esr and u series analyses of a tooth found in situ in an area equivalent to the lowest part of layer ed we obtain a combined esr u series age of 387 49 36ka in good agreement with a tl age of 340 33 ka for similar levels and substantially older than an esr u series age using attached or nearby sediment for dosimetry we conclude that the most likely explanation for the previous shorter esr chronology was the use of inappropriate gamma dose rates based on sediments attached to teeth

p and s wave anisotropy of a synthetic sandstone with controlled crack geometryl1 a method is reported for the production of synthetic porous sandstones containing cracks of known dimensions and geometry with respect to the matrix a synthetic sandstone was manufactured from sand cemented with an epoxy glue the cracks of known geometry were introduced into the material in the manufacturing stage by emplacing thin metallic discs in the sand epoxy matrix these discs were chemically leached out of the consolidated porous sandstone acoustic anisotropy and shear wave splitting were observed in the synthetic sandstones for the dry sample the observed angular dependence of the p and s wave velocities at 100 khz compares well qualitatively with the theoretical models of hudson and of thomsen quantitatively however the experimental data fits hudson s model better for the case of a saturated sample the experimental results are in excellent agreement with thomsen s model hudson s model on the other hand predicts a different angular dependence for p waves this demonstrates that the concept of fluid transfer between cracks and the ambient porosity can be a significant process the results reported here are from the first successful experiment in which the theoretical models were tested on a porous material containing a known crack geometry

a case for late archaean continental emergence from thermal evolution models and hypsometry abstract the secular cooling of the earth s mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans in the oceanic bathymetry and in the area of emerged continental crust the evolution of these variables is of fundamental importance to the geochemical coupling of mantle continental crust atmosphere and ocean to explore this further we developed a model that evaluates the area of emerged continental crust as a function of mantle temperature continental area and hypsometry in this paper we investigate the continental freeboard predicted using different models for the cooling of the earth we show that constancy of the continental freeboard 200 m is possible throughout the history of the planet as long as the potential temperature of the upper mantle was never more than 110 210 c hotter than present such numbers imply either a very limited cooling of the planet or most likely a change in continental freeboard since the archaean during the archaean a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere thus limiting crustal thickening due to mountain building processes and the maximum elevation in the earth s topography rey p f coltice n neoarchean strengthening of the lithosphere and the coupling of the earth s geochemical reservoirs geology 36 635 638 2008 taking this into account we show that the continents were mostly flooded until the end of the archaean and that only 2 3 of the earth s area consisted of emerged continental crust by around 2 5 ga these results are consistent with widespread archaean submarine continental flood basalts and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from 2 5 ga the progressive emergence of the continents as shown by our models from the late archaean onward had major implications for the earth s environment particularly by contributing to the rise of atmospheric oxygen and to the geochemical coupling between the earth s deep and surface reservoirs

how shear wave properties relate to rock fractures simple cases shear wave data analysis despite its ambiguities is probably the most direct and sensitive method available for deducing rock fracture properties from remote measurements deducing fracture properties from the data requires understanding the relationships of shear wave s wave particle motions and velocities to fracture orientations and strengths the purpose of this article is to help the nonspecialist gain such understanding

dimensions of continents and oceans water has carved a perfect cistern abstract the ocean basins have almost exactly the correct surface area and average depth to hold earth s water this study asserts that three processes are responsible for this first the crust is thickened by lateral compression from mountain formation second earth s continental crust is leveled by erosion third due to the efficiency of erosion the average elevation is a few hundred meters above sea level a theoretical fluid model suggested partly by laboratory experiments includes an ocean of specified depth the resulting continents are tabular that is their elevation view is rectangular the surface lies above sea level contributing to a well known double maximum in earth s elevation corresponding to continents and ocean basins next a simple hydrostatic balance between continent and ocean gives average depth and area of present oceans and continents within 33 further calculations with a suitable correction to fit present earth cover a wide range of possible crust volumes for earlier earth with the present water volume ocean area always exceeds 25 of the globe for all possible water volumes average continental crust thickness always exceeds 23 4 km this may explain why cratons have thicknesses comparable to younger crust so that they are found on earth s surface today therefore mountain building and erosion have enabled water to carve its own cistern in the form of the accumulated ocean basins the wide range of areas and depths of oceans and continents found here can constrain models of early earth similar calculations can be done for earthlike planets as well

transtensional deformation of montserrat revealed by shear wave splitting here we investigate seismic anisotropy of the upper crust in the vicinity of soufriere hills volcano using shear wave splitting sws analysis from volcano tectonic vt events soufriere hills which is located on the island of montserrat in the lesser antilles became active in 1995 and has been erupting ever since with five major phases of extrusive activity we use data recorded on a network of seismometers between 1996 and 2007 partially spanning three extrusive phases shear wave splitting in the crust is often assumed to be controlled either by structural features or by stress aligned cracks in such a case the polarization of the fast shear wave would align parallel to the strike of the structure or to the maximum compressive stress direction previous studies analyzing sws in the region using regional earthquakes observed temporal variations in which were interpreted as being caused by stress perturbations associated with pressurization of a dyke our analysis which uses much shallower sources and thus only samples the anisotropy of the upper few kilometres of the crust shows no clear temporal variation however temporal effects cannot be ruled out as large fluctuations in the rate of vt events over the course of the study period as well as changes in the seismic network configuration make it difficult to assess average delay times of approximately 0 2 s similar in magnitude to those reported for much deeper slab events suggest that the bulk of the anisotropy is in the shallow crust we observe clear spatial variations in anisotropy which we believe are consistent with structurally controlled anisotropy resulting from a left lateral transtensional array of faults which crosses the volcanic complex

experiment study of pore structure effects on velocities in synthetic carbonate rocks abstractcarbonate rocks have a complex pore structure show strong heterogeneity and have a wide range of velocities that lead to more complicated velocity porosity relationships compared with sandstones we designed and prepared 72 carbonate synthetic cores with known pore structures according to the control variate principle we measured the p and s wave velocities of these cores by an ultrasonic pulse transmission method analyzed the effects of the pore aspect ratio ar and pore size d on velocities and compared the experimental results with predictions of effective medium theories emts the matrix of our synthetic cores was consolidated mixture of carbonate cuttings and epoxy we randomly imbedded predesigned penny shaped silicone disks or expandable polystyrene balls into the matrix during the core preparation process to simulate secondary pores the experimental results indicated that han s empirical linear velocity porosity relation was a good prediction for cores with only interparticle por

full wavefield modeling and reverse time migration of laser ultrasound data a feasibility study abstractlaser ultrasound lu data acquired on cylindrical core samples effectively probe the physical properties of geologic materials although most lu analyses focus on estimating and inverting traveltimes of direct arrivals it is important to recognize that lu data sets can have rich wavefield coda and can now be acquired with a sufficient spatial density to enable the application of exploration seismic full wavefield techniques such as reverse time migration rtm and potentially full waveform inversion fwi we have developed a feasibility study that examines the applicability of 2d acoustic forward modeling and 2d rtm analyses on laboratory lu data acquired on cylindrical polymer samples forward modeled waveforms from our numerical tests matched the kinematics of the lu body waves measured through homogeneous samples as well as the scattered wavefield generated by fractures induced in an otherwise homogeneous medium the scattered wavefield is then used in an rtm scheme to directly image mill

relationships among compressional wave attenuation porosity clay content and permeability in sandstones anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves understanding the causes of compressional wave attenuation is important in the acquisition processing and interpretation of high resolution seismic data and in deducing the physical properties of rocks from seismic data we have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 mpa equivalent to a depth of burial of about 1 5 km in a frequency range from 0 5 to 1 5 mhz the compressional wave measurements were made using a pulse echo method in which the sample 5 cm diameter 1 8 cm to 3 5 cm long was sandwiched between perspex lucite buffer rods inside the high pressure rig the attenuation of the sample was estimated from the logarithmic spectral ratio of the signals corrected for beam spreading reflected from the top and base of the sample the results show that for these samples compressio

quantification of pore structure and its effect on sonic velocity and permeability in carbonates carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude traditional pore type classifications describe these pore structures but are inadequate for correlations to the rock s physical properties we introduce a digital image analysis dia method that produces quantitative pore space parameters which can be linked to physical properties in carbonates in particular sonic velocity and permeability the dia parameters derived from thin sections capture two dimensional pore size domsize roundness aspect ratio ar and pore network complexity poa comparing these dia parameters to porosity permeability and p wave velocity shows that in addition to porosity the combined effect of microporosity the pore network complexity and pore size of the macropores is most influential for the acoustic behavior combining these parameters with porosity improves the coefficient of determination r2 velocity estimates from 0 542 to 0 840 the analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small complicated pores estimates of permeability from porosity alone are very ineffective r2 0 143 but can be improved when pore geometry information poa r2 0 415 and domsize r2 0 383 are incorporated furthermore results from the correlation of dia parameters to acoustic data reveal that 1 intergrain and or intercrystalline and separate vug porosity cannot always be separated using sonic logs 2 p wave velocity is not solely controlled by the percentage of spherical porosity and 3 quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates

observations of fluid dependent shear wave splitting in synthetic porous rocks with aligned penny shaped fractures p and s wave velocity and attenuation coefficients accurate to 0 3 and 0 2 db cm respectively were measured in synthetic porous rocks with aligned penny shaped fractures using the laboratory ultrasonic pulse echo method shear wave splitting was observed by rotating the s wave transducer and noting the maximum and minimum velocities relative to the fracture direction a block of synthetic porous rock of fracture density 0 0201 0 0068 and fracture size 3 6 0 38 mm measured from image analysis of x ray ct scans was sub sampled into three 20 30 mm long 50 mm diameter core plugs oriented at 0 45 and 90 to the fracture normal transversely isotropic symmetry axis full waveform data were collected over the frequency range 500 1000 khz for both water and glycerin saturated cores to observe the effect of pore fluid viscosity at 1 cp and 100 cp respectively the shear wave splitting observed in the 90 core was 2 15 0 02 for water saturated and 2 39 0 02 for glycerin saturated in agreement with the theory that suggests that the percentage splitting should be 100 times the fracture density and independent of the saturating fluid in the 45 core by contrast splitting was 0 00 0 02 for water saturation and 0 77 0 02 for glycerin saturation this dependence on fracture orientation and pore fluid viscosity is consistent with the poro visco elastic theory for aligned meso scale fractures in porous rocks the results suggest the possible use of shear or converted wave data to discriminate between fluids on the basis of viscosity variations

implications of melting for stabilisation of the lithosphere and heat loss in the archaean abstract the increased depth and volume of melting induced in a higher temperature archaean mantle controls the stability of the lithosphere heat loss rates and the thickness of the oceanic crust the relationship between density distributions in oceanic lithosphere and the depth of melting at spreading centres is investigated by calculating the mineral proportions and densities of residual mantle depleted by extraction of melt fractions the density changes related to compositional gradients are comparable to those produced by thermal effects for lithosphere formed from a mantle which is 200 c or more hotter than modern upper mantle if archaean continental crust formed initially above oceanic lithosphere the compositional density gradients may be sufficient to preserve a thick archaean continental lithosphere within which the archaean age diamonds are preserved the amount of heat advected by melts at mid ocean ridges today is small but heat advected by melting becomes proportionally more important as higher mantle temperatures lead to a greater volume of melt and as the rate of production of oceanic plates increases archaean tectonics could have been dominated by spreading rates 2 3 times greater than now and with mantle temperatures between ca 1600 c and 1800 c at the depth of the solidus mid ocean ridge melting would produce a relatively thick but light refractory lithosphere on which continents could form protected from copious volcanism and high mantle temperatures

ultrasonic velocities of north sea chalk samples influence of porosity fluid content and texture we have studied 56 unfractured chalk samples of the upper cretaceous tor formation of the dan south arne and gorm fields danish north sea the samples have porosities of between 14 and 45 and calcite content of over 95 the ultrasonic compressional and shear wave velocities vp and vs for dry and water saturated samples were measured at up to 75 bar confining hydrostatic pressure corresponding to effective stress in the reservoir the porosity is the main control of the ultrasonic velocities and therefore of the elastic moduli the elastic moduli are slightly higher for samples from the south arne field than from the dan field for identical porosities this difference may be due to textural differences between the chalk at the two locations because we observe that large grains i e filled microfossils and fossil fragments that occur more frequently in samples from the dan field have a porosity reducing effect and that samples rich in large grains have a relatively low porosity for a given p wave modulus the clay content in the samples is low and is mainly represented by either kaolinite or smectite samples with smectite have a lower p wave modulus than samples with kaolinite at equal porosity we find that ultrasonic vp and vs of dry chalk samples can be satisfactorily estimated with gassmann s relationships from data for water saturated samples a pronounced difference between the vp vs ratios for dry and water saturated chalk samples indicates promising results for seismic amplitude versus offset analyses