experimental investigations on the thermal conductivity characteristics of beishan granitic rocks for china s hlw disposal abstract crystalline rocks are potential host rock types for the construction of high level radioactive waste hlw repositories a better understanding of thermal conductivity of rocks is essential to safe evaluation and engineering optimization of a hlw disposal system in the rock at depth in the present study experimental investigations on the thermal conductivity characteristics of 47 pairs of granitic rock specimens were conducted using the transient plane source tps method the specimens were collected from borehole cores in the beishan area which is being considered as the most potential candidate area for china s hlw repository to evaluate geological nature of the rocks mineralogical compositions of the rocks were identified and porosity of the specimens was measured the thermal conductivities of the specimens under dry and water saturated conditions were determined and the effect of water saturation on the thermal conductivity was investigated in addition the influence of temperature and axial compression stress on the thermal conductivity of dry specimens was studied the results revealed that the thermal conductivity of tested rocks was dependent on water saturation temperature and compression stress based on the obtained data some models considering porosity were established for describing the thermal conductivity characteristics of the tested rocks furthermore when the rocks have a similar porosity the quartz content dominates the thermal conductivity and there exists an obvious increase of the thermal conductivity with increasing quartz content the test results constitute the first systematic measurements on the beishan granitic rocks and can further be used for the development of thermal models for predicting thermal response near the underground excavations for hlw disposal

calculations on the thermal conditions around a salt diapir temperature modeling around the vejrum salt structure in denmark shows that the heat flow near the top is twice the regional heat flow the temperature in the vicinity of the top of the diapir is thus anomalously high overlying permeable formations could therefore be attractive for geothermal energy exploitation a negative temperature anomaly of 20 c is calculated around the root of the salt body comparisons between calculated and measured temperatures are used to test the model it is shown that measurements of heat flow or temperature gradients in wells penetrating the region of groundwater circulation could be used in identification of salt diapirs

geomagnetic field intensity and reversals during the past four million years a long and continuous record of the geomagnetic field intensity shows that intensity variations are dominated by two modes major episodes of field regeneration prevail on timescales of a few thousand years immediately after most reversals whereas stable polarity states are characterized by a slow 0 5 myr relaxation process reversals can be seen as the consequence of a progressive degradation of the dipole field

orbital modulation of the earth s magnetic field intensity more than 20 years ago on the basis of data from a pacific sediment core it was suggested that geomagnetic field intensity may vary with the earth s orbital obliquity centred on a period of 41 kyr as a result of the effect of obliquity on precessional forces in the earth s core1 it had also been proposed that precession plays an important role in the energy budget of the earth s geodynamo2 but subsequent analyses indicated that the energy available from precession is at least an order of magnitude less than that required to drive the geodynamo3 here however we report a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two north atlantic sites which shows significant power both at orbital eccentricity 100 kyr and obliquity 41 kyr the eccentricity power is also present in bulk magnetic properties such as susceptibility and is therefore attributable to lithological variations controlled by eccentricity driven climate change the obliquity power however is not apparent in bulk magnetic properties and seems to be a property of the geomagnetic field itself thus providing evidence for the orbital forcing of geomagnetic field intensity

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

recent evolution of a bahamian ooid shoal effects of hurricane andrew hurricane andrew a category 4 hurricane having wind velocities of 240 km hr passed north of joulters cays bahamas in a westerly direction on august 23 1992 we documented three sedimentary facies in a 2 7 km 2 study area dominated by mobile ooid sands before the hurricane using aerial photographs surface observations and shallow coring the shoal crest at this locality had aggrading and northward prograding parallel to depositional strike washover bars composed of cross bedded well sorted ooid sands burrowed poorly sorted ooid sands were present seaward of the washover bars whereas poorly sorted ooids and mud occupied a stabilized area bankward of the actively migrating shoal and local areas between washover bars on the crest of the shoal the shoal was crosscut by tidal channels and older washover bars were being dissected by tidal currents although hurricane andrew profoundly changed surface features within the study area its effects will probably be only partly preserved the hurricane eroded washover bars and transported sediment seaward leaving a nearly flat shoal crest overlain by a laterally continuous decimeter thick lens of well sorted ooid sand that thins seaward and bankward post hurricane tidal currents deposited a centimeter thick discontinuous layer of carbonate mud over this lens of well sorted ooid sand and transported ooids seaward off the shoal the well sorted ooid sand layer will most likely be reworked when an actively migrating shoal crest is reestablished although some of this storm deposit may be preserved on the shoal crest where the ooid sand layer was deposited in areas of normally less agitated conditions ooids may also be preserved in finer grained sediments seaward of the shoal as suggested by previous studies mud deposits on the shoal crest may be preserved where buried beneath reestablished washover bars although some of this mud will be removed by reworking during diurnal tides

apparent correlation of palaeomagnetic intensity and climatic records in deep sea sediments most reports of a correlation between pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic nrm intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment critical assessment of relevant data presented here and elsewhere1 2 from deep sea sediment cores shows that a pronounced dependence of nrm intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid as sediment composition often reflects varying depositional conditions induced by climatic change the significance of correlations proposed between pleistocene palaeomagnetism and climatic indicators in deep sea sediments may be less dramatic than sometimes supposed

geomagnetic dipole strength and reversal rate over the past two million years independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1 2 and thus provide information regarding the processes governing the geodynamo so far this procedure has been limited to the past 800 000 years 800 kyr ref 3 which does not include any geomagnetic reversals here we present a composite curve that shows the evolution of the dipole moment during the past two million years this reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas which were used for calibration we show that at least during this period the time averaged field was higher during periods without reversals but the amplitude of the short term oscillations remained the same as a consequence few intervals of very low intensity and thus fewer instabilities are expected during periods with a strong average dipole moment whereas more excursions and reversals are expected during periods of weak field intensity we also observe that the axial dipole begins to decay 60 80 kyr before reversals but rebuilds itself in the opposite direction in only a few thousand years

thermal properties and thermal structure in the deep water coalbed basin off the shimokita peninsula japan abstract heat transport properties are significant parameters that affect geothermal processes in deep sedimentary basins we measured the thermal properties of deep sediment core samples to a depth of approximately 2500 m below sea floor mbsf whereas most previous studies have only presented data 1 k 1 and calcite cemented sandstone siltstone exhibits the highest conductivity of approximately 3 wm 1 k 1 the other thermal properties are also influenced by the porosity and lithological contrast the correlation between thermal conductivity and porosity is explained by the mixed law model of the geometric mean the one dimensional temperature depth profile at site c0020 estimated from measured thermal conductivity reveals a regression of the thermal gradient with depth and the surface heat flow of 30 mwm 2 which is consistent with the heat flow data near this site was evaluated the obtained results suggest that the linear geothermal gradient estimated from the average thermal conductivity value at shallow sediment materials could overestimate the temperature at greater depths and underestimate the heat flow

the thermal conductivity for granite with various water contents the thermal conductivities of granite were measured under different conditions of porosity and water content to investigate the effects of the porosity and water content on the thermal conductivity for the dry samples the thermal conductivities range from 2 12 w mk for the rocks with a high porosity to 3 12 w mk for the ones with a low porosity water sorbed samples have greater thermal conductivities than dry samples of the same granite the thermal conductivities range from 2 99 w mk for granites with a high porosity to 3 62 w mk for ones with a low porosity under saturated condition

role of salt in restraining the maturation of subsalt source rocks abstract the presence of salt within a sedimentary basin can potentially modify its temperature distribution and history in particular the positive thermal anomaly associated with the top of salt domes has attracted considerable attention in the past the role of the lesser appreciated negative thermal anomaly associated with the base of salt domes in modifying the maturation history of subsalt source rocks is explored the finite element method was used to model the transient and steady state conductive temperature perturbations induced by salt layers domes and pillows the results indicate that the modification of the thermal regime due to evolving salt domes may significantly affect the maturation level of source rocks in the vicinity of the domes modelling the temperature structure of various salt structures has shown that in general the refraction of heat flow induces a dipole shaped temperature anomaly a positive anomaly located towards the top of the salt structure and a negative anomaly located towards its base these dipole anomalies can be strongly asymmetrical the degree of asymmetry depending on the shape of the salt structure and the proximity of the top of the salt structure to the surface of the basin however when the salt structure reaches the surface the dipole shaped temperature anomaly collapses to a monopole below the salt structure all sediments independent of their depth and lithology are colder relative to a section with no salt similarly salt domes that reach the surface very efficiently drain the heat from below and from the side of the dome these negative thermal anomalies may extend for a considerable depth beneath the base of the salt dome and may reach values of 85 c locally because of the large contrast in thermal conductivity between the highly porous sediments and salt at lower temperatures the efficiency of a salt dome to channel heat increases the closer the salt dome is to the surface these results indicate that deep sedimentary basins containing salt are more prospective than basins without salt and or salt diapirism in addition to the structural traps associated with salt tectonics salt domes and tongues connected to their source dissipate heat more efficiently and thus keep deeper regions of the basin relatively colder and potentially within the oil window for a longer time this cooling effect is maximized when the top of the salt dome remains close to the surface of the sedimentary basin for a significant period of time and may be especially important for continental margins such as brazil and offshore west africa where most of the source rocks lie beneath extensive evaporite deposits in contrast it was found that for the gulf of mexico basin pre and early tertiary salt diapirism and sheet emplacement may have caused significant delays in the maturation of subsalt source rocks in the deeper regions of the gulf basin but the maturation is likely to be relatively insensitive to the late miocene pliocene stage of salt mobilization because the time interval has been too short

thermal conductivity and radiogenic heat production of sedimentary and magmatic rocks in the northeast german basin thermal rock properties were determined for the northeast german basin a subbasin of the southern permian basin in europe the new thermal data provide new aspects for the determination of heat flow and for hydrocarbon and geothermal resource evaluation in the basin thermal conductivity was measured on drill core samples using the optical scanning method values for permian and pre permian clastic rocks are variable 2 3 4 8 w m k because of different depositional environments compaction and cementation reflected in lithology permian carboniferous igneous rocks show lowest thermal conductivity in basalts 2 2 w m k and highest 3 1 w m k in granitoids anisotropy of thermal conductivity in all rocks is low formation thermal conductivity was determined by upscaling the values determined for single lithotypes radiogenic heat production was determined on drill cores for the upper paleozoic sediments and igneous rocks for the younger formations without sample control a well log approach was used the heat production of sedimentary rocks is lowest 0 4 w m3 in the permian zechstein salt and anhydrite and highest 2 1 w m3 in the permian rotliegende clastic rocks heat production of the permian carboniferous rhyolites and granitoids is on the order of 2 6 3 8 w m3 and heat production of andesites and basaltoids is on the order of 0 9 1 9 and 0 1 0 7 w m3 respectively the contribution to surface heat flow by these up to 2 km 1 2 mi thick igneous complexes amounts to 7 mw m2 at a maximum on the same order is the total heat budget provided by the supra permian sedimentary succession in the basin

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

geomagnetic moment instability between 0 6 and 1 3 ma from cosmonuclide evidence 1 the reliability of paleomagnetic records as proxies of the geomagnetic field intensity is still a matter of controversy since volcanic materials hardly provide continuous records and marine sediments are suspected to carry a remanence biased by post depositional realignments and or by overprints such long standing debate emphasizes the need for the development of methods independent from paleomagnetism to decipher geomagnetic intensity variations high resolution measurements of authigenic 10be 9be along with a detailed sedimentary record of directional and relative paleointensity variations evidence over the 0 6 1 3 ma time interval frequent and recurrent excursions or short events in the late matuyama and the early brunhes epochs among which two brunhes matuyama reversal precursors and an intra jaramillo excursion the results of this study confirm the idea of a highly unstable geomagnetic field as suggested by paleomagnetic evidences

wavelet analysis of relative geomagnetic paleointensity at odp site 983 abstract we performed spectral analysis of the record of relative geomagnetic paleointensity obtained at odp site 983 covering the time interval 0 1 1 ma the results confirm the presence of significant power at frequencies corresponding to the earth orbital parameters eccentricity obliquity precession the construction of the evolutionary spectrum allowed us to establish the non stationarity of the signal at those frequencies the subsequent use of wavelet techniques made it possible to demarcate the time intervals over which orbital frequencies are present in the record for those intervals the paleointensity record shows some coherency with the isothermal remanent magnetization normalizer of the natural remanent magnetization and the ratio anhysteretic remanent magnetization k these results suggest that the orbital frequencies embedded in the paleointensity record are the expression of lithologic variations and probably not a characteristic of the geodynamo itself extracting filtering these wavelet components from the site 983 paleointensity record indicates however that this secondary overprint is of sufficiently low level that it has a minor effect on the overall character of the record

lack of impact of hurricane michelle on tidal flats andros island bahamas integrated remote sensing and field observations abstract major storms commonly are cited as important geomorphic and sedimentologic agents and their significance is perhaps most emphatically noted in interpretations of modern and ancient tidal flats the purpose of this study was to assess the impact of hurricane michelle on the carbonate tidal flats of andros island bahamas by coupling remote sensing data and field observations although regional modis remote sensing data reveal that the passage of hurricane michelle suspended sediments across the shallow bank integrating ultra high resolution remote sensing data with field observations demonstrates that the hurricane had almost no impact on the andros island tidal flats this lack of impact is surprising because the storm still had hurricane force winds as it passed immediately over some of the focal areas with this hurricane storm strength and intra storm interval were probably not limiting factors instead several influences combined to minimize the storm s impact on both sedimentation and erosion including the low level of water on the bank resulting from ebb tides and in the northwestern area from offshore storm winds and the short duration of the storm resulting from its high forward velocity given the apparent prevalence of widespread storm effects on ancient tidal flats but the spatially limited major geomorphic impacts of storms on many modern systems we suggest that the geologic evolution and preservation of ancient tidal flat successions may have been shaped by mega storms that simply cannot form in the present global climate nonetheless understanding tidal flat dynamics and changes on human timescales will require continued monitoring and assessment of low impact storms such as michelle as well the more sensational hurricanes that produce widespread death destruction and deposition

blackriveran carbonates from the subsurface of the lake simcoe area southern ontario stratigraphy and sedimentology of a low energy carbonate ramp the lowest upper ordovician blackriveran strata in the lake simcoe area represent the base of a major transgressive sequence of peritidal carbonates and siliciclastics from detailed petrographic

geomagnetic dipole moment and 10be production rate intercalibration from authigenic 10be 9be for the last 1 3 ma 1 a synthesis of authigenic 10be 9be ratio records constructed from sedimentary sequences deposited over the last 300 ka in the north east atlantic and over the 500 1300 ka bp interval in the west equatorial pacific ocean is compared with proxies of the geomagnetic moment variations over the same time intervals these proxies consist in 1 relative paleointensity records obtained from the same sediments 2 a seafloor magnetization record derived from magnetic anomalies and 3 an absolute virtual dipole moment vdm record constructed from an updated database of absolute paleointensities the authigenic 10be 9be ratio records document the occurrence of the paleomagnetic events excursions and reversals reported for these time intervals by paleomagnetic studies reconstructions of 10be 9be derived magnetic moment records based on theoretical and empirical relationships between 10be 9be ratio and absolute vdm allow establishing 10be derived vdm records that exhibit the same overall structures as the geomagnetic proxy records

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

amplitude and frequency modulations of the earth s obliquity for the last million years the variability of the earth s obliquity is a result of the deviation of the obliquity from its main component at 41 kyr and is generated by amplitude and frequency modulation for the last million years the amplitude modulation of the obliquity explains 8 of the obliquity s total variance and the frequency modulation explains 10 3 the spectra of both the amplitude and frequency modulations display significant power at 171 and 97 kyr the contribution of these two modulations to the variance of the insolation is evaluated at 65 degreesn in june the amplitude modulation of the obliquity explains 1 3 of the variance of the insolation and the frequency modulation explains 1 6 it is shown that the obliquity s frequency modulation is physically questionable and could only be meaningful for its components at 41 54 and 29 kyr taken separately

topographic and sea level controls on oolite microbialite coralgal reef sequences the terminal carbonate complex of southeast spain the terminal carbonate complex of southeast spain is a miocene messinian unit of oolite microbialite and coralgal reefs deposited in association with glacioeustasy and evaporitic drawdown the relationship between paleotopography and sea level history is useful for prediction of microbialite and oolite reservoir facies in the subsurface four sequences record sea level change with minimum amplitudes of 32 77 m 105 253 ft sequences commonly have local basal stromatolites overlain by local thrombolites ooid grainstone volcaniclastic rich planar bedded ooid grainstone and fenestral ooid grainstone at low substrate positions thrombolite boundstones are thicker and laterally more continuous than at higher positions at intermediate substrate positions relative to sea level history sequences have a build and fill architecture characterized by a relief building phase and a relief filling phase with thin sequences draping paleotopography microbialites dominate during the relative sea level rises and build topographic relief oolites dominate during the relative sea level falls and fill topographic relief at higher substrate positions close to highstand sequences thicken and yield stratigraphic character that is inconsistent with a build and fill model apparently the build and fill model requires an intermediate elevation substrate position and nonoptimal carbonate productivity during rapid sea level change sequences progressively show increasing diversity and more normal marine organisms possibly caused by decreasing aridity lithofacies of the la molata area show evidence of more restricted conditions compared to the la rellana ricardillo area lithofacies likely because la molata was in an embayment these results show that distribution of oolite microbialite and reef facies are predictable given known interaction among sea level paleotopography of the depositional surface substrate and coastline configuration

geomagnetic moment variation and paleomagnetic excursions since 400 kyr bp a stacked record from sedimentary sequences of the portuguese margin abstract a paleomagnetic study was performed in clayey carbonate sedimentary sequences deposited during the last 400 kyr on the portuguese margin northeast atlantic ocean declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction the normalized intensity documents a series of relative paleointensity rpi lows recognized in other reference records three directional anomalies occurring during rpi lows chronologically correspond to the laschamp excursion 42 kyr bp the blake event 115 122 kyr bp and the icelandic basin excursion 190 kyr bp a fourth directional anomaly recorded at 290 kyr bp during another rpi low defines the portuguese margin excursion four non excursional rpi lows are recorded at the ages of the jamaica pringle falls mamaku calabrian ridge 1 and levantine excursions the rpi record is characterized by a periodicity of 100 kyr paleointensity lows often coinciding with the end of interglacial stages this record sets the basis of the construction of an authigenic 10be 9be record from the same sedimentary sequences carcaillet et al this issue

form function and feedbacks in a tidally dominated ooid shoal bahamas although the general aspects of oolitic depositional systems are well documented seascape scale 10 3 10 6 m 2 patterns of oolitic shoals and the details of processes acting on them are not well understood or quantified to begin to fill this basic gap in understanding this paper describes the morphology and hydrodynamics of lily bank a modern tidally dominated bahamian ooid shoal in this study integrating remote sensing imagery with quantitative geo located bathymetrical hydrological and granulometric data in a geographic information system documents geomorphic and sedimentological patterns and facilitates interpreting these patterns in the context of the processes operating in this system the results of these analyses reveal that parabolic bars up to several kilometres in wavelength and several metres in height form a common morphologic motif although there is considerable variation on that general theme the seascape scale configuration of bars and superimposed sedimentary structures is closely linked to spatial patterns of tidal movements and includes the presence of mutually evasive flood and ebb channels sedimentologically bars are neither homogenous nor random bodies instead granulometric parameters such as sorting and percentage mud vary systematically as shaped by hydro geomorphic controls the best sorted coarsest ooids are on bar crests whereas the finest grains are found in the lower energy deeper interior and flanking regions in short results clearly document hydrodynamic bathymetrical influences on these ooid shoals and their granulometry linkages akin to siliciclastic analogues sedimentological hydrodynamic and geomorphic observations are consistent with a conceptual model for the formation of parabolic bars in which initial irregularities in nonparabolic bars are enhanced through their effect of focusing flow constricted flow leads to higher flow velocities tidal flow velocity asymmetries differential net sediment transport and growth of bathymetrical highs this bathymetrical divergence creates separate paths for flood and ebb tides facilitating emergence of better developed parabolic forms the resultant parabolic geometries and component bedforms appear to be either in dynamic equilibrium with both ebb and flood tide flows or evolving toward that state in exploring patterns and processes within carbonate shoals this study illustrates some of the first documented insights on quantitative details of morphology and dynamics and in the links between geomorphic framework and grain size and sorting in an oolitic carbonate system assuming a

hurricane deposits on carbonate platforms a case study of hurricane irma deposits on little ambergris cay turks and caicos islands the study of modern hurricane deposits is useful in both identifying ancient hurricane deposits in the rock record and predicting patterns of deposition and erosion produced by future storm events hurricane deposits on carbonate platforms have been studied less frequently than have been those along continental coasts here we present observations of the characteristics of deposition and scour caused by hurricane irma on little ambergris cay a small uninhabited island located near the southeastern edge of the caicos platform in the turks and caicos islands hurricane irma passed directly over little ambergris cay on 7 september 2017 as a category 5 hurricane we described and sampled multiple types of hurricane deposits and determined that the washover fans were the best sedimentological records for hurricane conditions as they were subject to very little reworking over time we compared different model predictions of storm tide and wave height with eyewitness reports and distributions of scour examining the washover fans allowed for the construction of a conceptual model for hurricane deposits formed in a high energy storm event on a carbonate platform characteristics of the washover fans were their small size the lack of sedimentary structures and very well sorted sediment the size and distribution of carbonate boulders eroded and transported by the storm are consistent with depth averaged flow velocities in the range of 1 5 5 3 m s the strength of the storm and the low lying topography distinct features of a carbonate platform setting contributed to high levels of sediment bypass and high flow velocities resulting in small unstructured deposits

determination of thermal conductivity for deep boreholes two methods for thermal conductivity determinations on rock cores and fragments were tested on a suite of samples from the kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb superdeep drill hole in germany they were also compared with estimates of thermal conductivity using the mineral composition of the rock and physical well logs and with in situ thermal conductivity measurements laboratory methods provide reasonably precise determinations of the thermal conductivities of both solid core 5 and drill cuttings 10 at room temperature and pressure the most common methods presently used for crystalline rocks are the steady state divided bar db technique and the transient half space line source ls sample preparation and measurement times are comparable for the db and ls with sample preparation being more time consuming on average for isotropic rocks there is little to choose from between the two methods which both give reliable values of conductivity in the vertical direction the ls is easier to set up and use in field laboratory situations which renders it the preferred method for field reconnaissance the gneissic crystalline rocks penetrated by the ktb boreholes typically have anisotropy of the order of 10 20 the db provides unambiguous values of conductivity in a given direction so its use is preferable for obtaining both principal conductivities and the vertical component anisotropy can be estimated using ls measurements in many different directions but the potential for large random errors is much greater than with the more straightforward db approach for deep research wells the difficulties of extrapolating laboratory results to in situ conditions particularly temperature present additional obstacles to determining heat flow laboratory measurements of water saturated samples under in situ conditions combined with in situ measurements and judicious use of calculations based on mineralogy and well log derived physical properties can aid in the accurate characterization of thermal conductivity in deep wells the application of different methods helped to link variations of heat flow with depth in the ktb hole to the anisotropy of thermal conductivity or thermal refraction and thus allowed the calculation of background heat flux in this geologically complex area

estimation of thermal conductivity from the mineral composition influence of fabric and anisotropy measured values of thermal conductivity from crystalline rocks are compared with values calculated from the mineral content using the layered model first thermal conductivity is estimated using data based on quasi isotropic mixtures of fragments or powder second the approach is applied on core data considering the anisotropy of some rock forming minerals the numerical value of estimated thermal conductivity is controlled by the quartz content sheet silicates control anisotropy and fabric in gneisses and their thermal consequences if imformation about the fabric of the rock is available the anisotropy of minerals can be considered in a layered model and this improves the estimation of thermal conductivity from mineral contents

rapid high resolution 14c chronology of ooids abstract ooids are small spherical to ellipsoidal grains composed of concentric layers of caco 3 that could potentially serve as biogeochemical records of the environments in which they grew such records however must be placed in the proper temporal context therefore we developed a novel acidification system and employed an accelerator mass spectrometer ams with a gas accepting ion source to obtain radiocarbon 14 c chronologies extending radially through ooids within one 8 h workday the method was applied to ooids from highborne cay bahamas and shark bay australia yielding reproducible 14 c chronologies as well as constraints on the rates and durations of ooid growth and independent estimates of local 14 c reservoir ages

mantle heat flow and geotherms for the main geologic domains in morocco thermal and deep seismic soundings data are used to study the dependence between the compressional pn velocity and the surface heat flow or the temperature at the moho discontinuity in morocco this correlation indicates a significant decrease in pn velocity where high heat flow and moho temperature are observed this result is consistent with respect to other regions of the world crustal heat generation models and geotherms are constructed for the major moroccan geological domains extending from the precambrian units in the south to the alpine units in the north the crustal contribution in surface heat flow is on average 35 mwm 2 with high values of 41 42 mwm 2 in the western and eastern meseta where hercynian granite intrusions could enrich the crust in radioactive heat sources high mantle heat flow values are obtained beneath the alboran neogene basin 62 mwm 2 the rif 47 mwm 2 the middle atlas 41 mwm 2 and the south atlantic margin 40 mwm 2 where the crust is thinned by an extensional tectonic regime despite their similar formation context the intra continental belts of the middle and the high atlas show different geothermal field components a lithospheric heating process in the middle atlas could be the result of a plio quaternary basaltic volcanism finally the precambrian basement of the anti atlas like all the west african shield is a stable domain showing the lowest subsurface temperatures

a wavelet investigation of possible orbital influences on past geomagnetic field intensity 1 a number of sedimentary records of relative paleointensity have been reported to contain modes of variability that could have been driven by changes in the earth s orbital or climatic state proposed relationships are often based on visual correlation in the time domain or the presence of peaks in relative paleointensity frequency spectra close to those of the orbital components when discussing hypothesized connections it is not common for the phase relationship between paleointensity and orbital change to be addressed so a true mechanistic link cannot be confirmed the existence of a direct link between records of paleointensity and orbital climatic variation is tested using the cross wavelet transform and squared wavelet coherence it is found that while all the records show common power at certain periods the geomagnetic and orbital variations do not exhibit a consistent phase relationship suggesting there is no direct physical link between them this interpretation is supported by a lack of significant correlation in the time frequency plane between the studied records as measured by the squared wavelet coherence

anisotropy of elastic moduli p wave velocities and thermal conductivities of asan gneiss boryeong shale and yeoncheon schist in korea abstract this paper presents the anisotropic characteristics of the elastic moduli p wave velocities and thermal conductivities of three types of anisotropic rocks i e asan gneiss boryeong shale and yeoncheon schist occurring in korea the experiments were conducted on rock samples that show clear evidence of transverse isotropy cylindrical core samples with different anisotropy angles were prepared by coring at 15 degree intervals from the transversely isotropic plane using the laboratory directional coring system established for this study elastic moduli p wave velocities and thermal conductivities were determined along the sample axis for different anisotropy angles the anisotropy ratio is defined as the ratio of the properties parallel to the transversely isotropic plane to those perpendicular to the plane and the anisotropy ratios for the thermal conductivities k 90 k 0 of asan gneiss boryeong shale and yeoncheon schist were 1 4 2 1 and 2 5 respectively the p wave velocity anisotropy ratios v p 90 v p 0 for asan gneiss boryeong shale and yeoncheon schist were 1 2 1 5 and 2 3 respectively the elastic moduli p wave velocities and thermal conductivities that were obtained were compared with theoretical predictions by mean prediction error mpe the correlations between the measured properties were evidently correlated with some minor scatter in the data the degree of anisotropy measured in this study suggests that ignoring anisotropy in rock properties may mislead to erroneous results the application of tensorial transformation evaluations revealed that the three types of rocks chosen for this study can be modeled effectively by a transversely isotropic model

a surprising asymmetric paleothermal anomaly around el gordo diapir la popa basin mexico thirty seven mudstone samples were collected from the uppermost lower mudstone member of the potrerillos formation in el gordo minibasin within la popa basin mexico the unit is exposed in a circular pattern at the earth s surface and is intersected by el gordo diapir in the northeast part of the minibasin vitrinite reflectance ro results show that samples along the eastern side of the minibasin i e south of the diapir are mostly thermally immature to low maturity ro ranges from 0 53 to 0 64 vitrinite values along the southern western and northwestern part of the minibasin range between 0 67 and 0 85 values of ro immediately northwest of the diapir are the highest reaching a maximum of 1 44 the results are consistent with two different possibilities 1 that the diapir plunges to the northwest or 2 that a focused high temperature heat flow existed along just the northwest margin of the diapir if the plunging diapir interpretation is correct then the thermally immature area south of the diapir was in a subsalt position and the high maturity area northwest of the diapir was in a suprasalt position prior to tertiary uplift and erosion if a presumed salt source at depth to the northwest of el gordo also fed el papalote diapir which is located just to the north of el gordo diapir then the tabular halokinetic sequences that are found only along the east side of el papalote may be subsalt features however if the diapir is subvertical and the high maturity values northwest of the diapir are caused by prolonged high temperature fluid flow along just the northwestern margin of the diapir then both of these scenarios are in disagreement with previously published numerical models this disagreement arises because the models predict that thermal anomalies will extend outward from a diapir a distance roughly 1 5 times the radius of the diapir but the results reported here show that the anomalous values on one side of the diapir are about two times the radius whereas they are as much as five times the radius on the other side of the diapir the results indicate that strata adjacent to salt margins may experience significantly different heat histories adjacent to different margins of diapirs that result in strikingly different diagenetic histories even at the same depth

geomagnetic field intensity excursions reversals and the 41 000 yr obliquity signal abstract the possibility that precession provides power to the geodynamo has been tested by comparing variations in field intensity and the occurrence of excursions and reversals with the obliquity signal the strongest minima in the paleomagnetic intensity records for the past 800 000 yr correlate with obliquity minima the distribution of the length of polarity intervals less than 100 000 yr peaks between 30 and 40 000 yr i e marginally shorter than the obliquity period reversals preferentially occur when the average amplitude of the obliquity signal is low the most recent reversals occur close to the point of inflection during the decrease from the maximum of the obliquity signal these results suggest that precession provides some power to the geodynamo

thermal conductivity anisotropy of metasedimentary and igneous rocks 1 thermal conductivity anisotropy was determined for three sets of metasedimentary and igneous rocks from central utah usa most conductivity measurements were made in transient mode with a half space line source instrument oriented in two orthogonal directions on a flat face cut perpendicular to bedding one orientation of the probe yields thermal conductivity parallel to bedding kpar directly the other orientation of the probe measures a product of conductivities parallel and perpendicular to bedding from which the perpendicular conductivity kperp is calculated some direct measurements of kpar and kperp were made on oriented cylindrical discs using a conventional divided bar device in steady state mode anisotropy is defined as kpar kperp precambrian argillites from big cottonwood canyon have anisotropy values from 0 8 to 2 1 with corresponding conductivity perpendicular to bedding of 2 0 to 6 2 w m 1 k 1 anisotropy values for price canyon sedimentary samples are less than 1 2 with a mean of 1 04 although thermal conductivity perpendicular to bedding for the samples varied from 1 3 to 5 0 w m 1 k 1 the granitic rocks were found to be essentially isotropic with thermal conductivity perpendicular to bedding having a range of 2 2 to 3 2 w m 1 k 1 and a mean of 2 68 w m 1 k 1 the results confirm the observation by deming 1994 that anisotropy is negligible for rocks having kperp greater than 4 0 w m 1 k 1 and generally increases for low conductivity metamorphic and clay rich rocks there is little evidence however for his suggestion that thermal conductivity anisotropy of all rocks increases systematically to about 2 5 for low thermal conductivity rocks

a high resolution authigenic 10be 9be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the portuguese margin a high resolution study of authigenic be isotopes 10be and 9be combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the portuguese margin n e atlantic covering the past 300 ka in order to assess relationships between geomagnetic moment variations and 10be production rate variations a carefull examination of the various ways of taking into account environmental disturbing effects on the authigenic 10be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10be 9be ratio eight intervals of significant authigenic 10be 9be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions some being already admitted others being proposed as new geomagnetic features since contrarily to sedimentary magnetic remanence the authigenic 10be 9be records dipole moment variations without significant acquisition delay it provides better constraints on their timing comparison of 10be 9be and benthic 18o records from the same cores suggests that dipole moment lows preferentially occured during or at the end of interglacial episodes with a quasi period of 100 ka

extraction of non continuous orbital frequencies from noisy insolation data and from palaeoproxy records of geomagnetic intensity using the phase of continuous wavelet transforms the presence or absence of orbital frequencies in the palaeomagnetic field spectrum is the subject of intense discussions while palaeoclimatic variations i e glacial interglacial alternation periods are known to be governed by insolation variations via orbital frequencies the link between such frequencies and the geomagnetic field maintenance processes convection and rotation in the fluid metallic core remains unclear the study of frequency behaviour of long time series proxy records requires a robust and linear time frequency method with local and scale analysis properties for these reasons we use algorithms based on complex continuous wavelet theory and the stationary phase method first developed in acoustics in the years 1988 1991 for extracting frequency and amplitude modulation laws of arbitrary signals from the phase of their wavelet transform this method is robust in the presence of noise and does not require restrictive conditions on the energy of signals after introducing the basis of the method with some illustrations on periodic signals we show the efficiency of our algorithms on a synthetic insolation signal milankovitch cycles by extracting the main three orbital frequencies precession obliquity and eccentricity then we show its robustness in the presence of a high level of noise finally we apply this method to various proxy records of i past climate variations 18o ii the past geomagnetic field intensity variations recorded by ocean sediments and iii along the deep seafloor basalts and iv variations of the production of cosmogenic nuclide 10be 9be our results confirm the presence of orbital frequencies in all these palaeoproxy records and suggest an orbital forcing of geomagnetic field variations via geodynamo processes

evaluation of rock anisotropy using 3d x ray computed tomography abstract the anisotropic nature of fabric and internal structures plays a significant role in fluid flow heat transfer and geomechanical behavior in rock the existence and orientation of anisotropy in various rocks have been evaluated using laboratory experiments and image analyses to characterize anisotropic pore networks micro fractures mineralogy grain fabric and stiffness from micro to macro scales we present an assessment of anisotropy in rock by systematic and planar clustering of three dimensional x ray attenuation values and associated statistical analysis on the basis that x ray ct numbers directly represent the internal density of the mineral fabric in the rock mass variation in voxel values across the slicing plane for a given orientation enables identification of the unique orientation of anisotropy in rock the proposed concept is validated using a 3d virtual structure and is applied to four different rock types the sensitivity of anisotropic features and the image noise effect are further explored to highlight the robustness of the proposed method for evaluating the anisotropy of rock fabrics

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico ii structure the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope

radiogenic heat production of crustal rocks an assessment based on geochemical data a survey of the geochemical literature and unpublished data has resulted in the classification of u th and k concentrations by rock type over 2500 data entries have been compiled permitting calculation of their radiogenic heat production in the igneous rocks mean heat production ranges from highs of 12 20 heat production units hpu wm 3 in some peralkaline intrusives through 4 hpu in acidic 2 in intermediate and 1 in basic rocks to a low of 0 3 hpu in ultramafic rocks siliceous clastic rocks generally have greater heat production 2 to 4 hpu than do chemical sedimentary rocks including the carbonates 0 4 to 2 hpu the heat production of metamorphic rocks generally depends on the radioelement contents of their igneous and sedimentary predecessors modified by metamorphic processes based on estimates of the proportion of the continental crust that specific rock types occupy the weighted mean radiogenic heat production of the upper continental crust estimated from this data base is 3 hpu

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

thermophysical properties of the po basin rocks summary we present an analysis on thermal properties density and porosity of clastic chemical biochemical and intrasedimentary volcanic rocks collected from petroleum exploration wells of the po basin northern italy moreover we investigate the applicability of the hashin shtrikman s model for a mineral aggregate in combination with the zimmerman s model that takes pore shape into account to calculate the bulk thermal conductivity in case of macroscopically isotropic rocks deviations between predicted and measured values range from 2 2 per cent to 6 9 per cent and significantly decrease if a proper pore aspect ratio is chosen regarding the volumetric heat capacity approximate estimates were obtained by means of a weighted average of the volumetric heat capacity of the mineral grains and that of the pore filling water the differences between the computed and measured values range from 6 2 per cent to 4 9 per cent and on average the computed volumetric heat capacity is lower by 1 6 per cent the water loss during compaction and the temperature increase with depth are main factors controlling thermal properties an anisotropy effect occurs in the case of rocks rich in sheet silicates due to rotation of these minerals the vertical thermal conductivity of sheet silicates decreases exponentially with burial depth from 2 13 w m 1 k 1 at the surface to 0 52 w m 1 k 1 at 4 5 km the laboratory data allow the formulation of compaction curves

geomagnetic paleointensity variation with a 100 kyr quasi period abstract we analyzed records of geomagnetic field intensity paleointensity during the last 700 kyr in five sediment cores from a wide region of the pacific ocean a global paleointensity variation with a 100 kyr quasi period was successfully extracted using the wavelet transform because the variation does not correlate with that of magnetic properties of the sediments it originated from a change in the geomagnetic field the 100 kyr quasi period of the geomagnetic field is close to the timescales of eccentricity one of the earth s orbital elements and of the glacial interglacial cycle of the late quaternary paleoclimate in particular there is a correlation between the variations of the geomagnetic field intensity and climate with an 18 kyr time lag while the geodynamo has widely been thought to be a self sustained system our results support the possibility of an external energy supply of the variation through orbital forcing or climate change

major controlling factors on hydrocarbon generation and leakage in south atlantic conjugate margins a comparative study of colorado orange campos and lower congo basins abstract we present a supra regional comparative study of the major internal and external factors controlling source rock sr maturation and hydrocarbon hc generation and leakage in two pairs of conjugate margins across the south atlantic the brazil campos basin angola lower congo basin margins located in the central segment and the argentina colorado basin south africa orange basin in the southern segment our approach is based on the analysis and integration of borehole data 1d numerical modeling 2d seismic reflection data and published reports coupling of modeling results sedimentation rate calculation and seal bypass system analysis reveal that 1 oil window is reached by syn rift srs in the southern segment during the early to late cretaceous when thermal subsidence is still active while in the central segment they reach it in late cretaceous neogene during a salt remobilization phase and 2 early hc generation from post rift srs in the southern segment and from all srs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates the latter seems to be associated with the andes uplift history for the western south atlantic basins campos and colorado and to a possibly climate driven response for the eastern south atlantic basins orange and lower congo additionally we observe that the effect of volcanism on sr maturation in the southern segment is very local the comparison of cretaceous mass transport deposit mtd episodes with hc peak of generation and paleo leakage indicators in the southern segment revealed the possible causal effect that hc generation and leakage have over mtd development interestingly paleogene leakage indicators which were identified in the argentina south africa conjugate margins occur contemporaneously to low sedimentation rate periods nonetheless present day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal failure events linked to eustatic sea level drops

the influence of salt domes on paleotemperature distributions a characteristic of salt domes is that an enhanced heat flux is associated with them due to the contrast in thermal conductivity between rock salt and typical sedimentary formations we present a simple analytical model of heat flow in the vicinity of an isolated salt dome with numerical evaluations for some sample cases in addition to an enhanced surface heat flow these models show that on the upper flanks of a salt dome a temperature higher than the regional trend is predicted thus enhancing hydrocarbon maturation at these depths on the lower flanks a temperature lower than the regional trend is predicted thus inhibiting overmaturation the magnitude of this temperature anomaly depends upon the position of the measurement point both vertical and radial relative to the salt dome roughly speaking it is confined to within one salt dome radius of the salt sediment interface the magnitude of the anomaly can be quite large for typical salt domes these basic ideas are corroborated by observing downhole measurements from a salt dome in the gulf of mexico the good agreement allows us to bracket the height of that particular dome at between 9 000 and 15 000 m and also permits us to determine that the total sediment thickness overlying the basal salt is between 13 200 and 19 200 m at the location of the salt dome these results indicate that the presence of a salt dome can have a significant impact on the subsurface temperature distribution and hence on the thermochemical maturation of any source rocks or hydrocarbon accumulations in close proximity to the salt dome in addition to providing trapping structures a salt dome also provides an enhanced environment for hydrocarbon maturation on its upper flanks and for inhibiting overmaturation on its lower flanks such effects should be included when evaluating the hydrocarbon potential of a salt dome province

geomagnetic intensity variations over the past 780 kyr obtained from near seafloor magnetic anomalies knowledge of past variations in the intensity of the earth s magnetic field provides an important constraint on models of the geodynamo a record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences but a long term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust here we show that near seafloor magnetic anomalies recorded over the southern east pacific rise are well correlated with independent estimates of geomagnetic intensity during the past 780 kyr moreover the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well documented dipole intensity pattern for the past 50 kyr a comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ages of surficial lava flows in this region the record of geomagnetic intensity preserved in the oceanic crust should provide a higher time resolution record of crustal accretion processes at mid ocean ridges than has previously been obtainable

thermal conductivity from core and well log data abstract the relationships between thermal conductivity and other petrophysical properties have been analysed for a borehole drilled in a tertiary flysch sequence we establish equations that permit us to predict rock thermal conductivity from logging data a regression analysis of thermal conductivity bulk density and sonic velocity yields thermal conductivity with an average accuracy of better than 0 2 w m k 1 as a second step logging data are used to compute a lithological depth profile which in turn is used to calculate a thermal conductivity profile from a comparison of the conductivity depth profile and the laboratory data it can be concluded that thermal conductivity can be computed with an accuracy of less than 0 3 w m k 1 from conventional wireline data the comparison of two different models shows that this approach can be practical even if old and incomplete logging data are used the results can be used to infer thermal conductivity for boreholes without appropriate core data that are drilled in a similar geological setting

localization of self potential sources in volcano electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano 1 this study concerns the fluid flow circulation associated with magmatic intrusion during volcanic eruptions from electrical tomography studies the objective is to localize and characterize the sources responsible for electrical disturbances during a time evolution survey between 1993 and 1999 of an active volcano the piton de la fournaise we have applied a dipolar probability tomography and a multi scale analysis on synthetic and experimental sp data we show the advantage of the complex continuous wavelet transform which allows to obtain directional information from the phase without a priori information on sources in both cases we point out a translation of potential sources through the upper depths during periods preceding a volcanic eruption around specific faults or structural features the set of parameters obtained vertical and horizontal localization multipolar degree and inclination could be taken into account as criteria to define volcanic precursors

gas exsolution during fluid migration and its relation to overpressure and petroleum accumulation abstract petroleum systems in the tertiary sections of the gulf of mexico and niger delta among other basins are characterized by the close association between petroleum accumulation and over pressure although overpressure is generated mainly by compaction disequilibrium of the low permeability sediments exsolution of gases from water and petroleum during migration over great vertical distance may create overpressure or modify the existing overpressure in this paper the author combined relative permeability data and petroleum phase behavior modelling to explain and predict the presence of an overpressure and petroleum baffle due to gas exsolution generalized isoperm diagrams for oil gas and water phases in sandy and silty shaly sediments were created based on published data aqueous solubility of methane and carbon dioxide as a function of temperature pressure and salinity is summarized based on literature data phase diagrams of petroleum with a wide range of composition api gravity and gor were produced using phase behavior software with calibration using field data these tools were integrated to model overpressure and petroleum phase variations in two oil gas fields in the gulf of mexico the pressure gradients in these fields are likely modified by gas exsolution from the petroleum which migrated and accumulated within and below the pressure transition zone ptz petroleum trapped within ptz tends to be fractionated whereas that accumulated below ptz tends to be single phase with high api gravity these results provide a model which explains both the effect of gas exsolution on ptz and the occurrence of different types of petroleum in these fields these tools may be integrated with geological and seismic data to assess more accurately the economic value of petroleum accumulations in petroleum systems governed by overpressure and petroleum phase separation and fractionation

thermal evolution and maturation of lower paleozoic source rocks in the tarim basin northwest china the tarim basin is one of the richest basins in oil and gas resources in china the cambrian and middle upper ordovician strata are the most important source rocks previous early paleozoic thermal histories have led to varied hypotheses on the evolution of the lower paleozoic source rocks causing a significant impact on petroleum exploration in the basin a new paleozoic thermal history of the tarim basin was reconstructed in this article using the integrated thermal indicators of apatite and zircon uranium thorium helium ages apatite fission tracks and equivalent vitrinite reflectance data the modeled results indicate that different parts of the basin experienced widely differing early paleozoic thermal gradient evolution the eastern and central regions of the basin experienced a decreasing thermal gradient evolution from 37 to 39c km during the cambrian and ordovician to 35 to 36c km in the silurian whereas the northwestern region of the basin had an increasing early paleozoic thermal gradient evolution from 28 to 32c km in the cambrian to 30 to 34c km in the ordovician and silurian the lower cambrian thermal gradient resulted from the higher thermal conductivity of the 800 to 1000 m 2625 to 3280 ft thickness of gypsum and salt in the cambrian strata the basin experienced an intracratonic phase during the late paleozoic and a foreland basin phase during the mesozoic and cenozoic with the thermal gradient decreasing to the present day value of 20 to 25c km the sensitivity of thermal modeling by the best fit method is less than 5 in our study and the differences of the early paleozoic thermal gradient evolution in different regions of the basin may result in differential maturation of lower paleozoic source rocks the maturity histories of the source rocks modeled based on the new thermal histories indicate that the lower paleozoic source rocks in most areas of the basin matured rapidly and reached the late mature to dry gas stage during the paleozoic but experienced slower maturation during the mesozoic and cenozoic these new data on the paleozoic thermal history and lower paleozoic source rock maturity histories of the tarim basin provide new insights to guide oil and gas exploration of the basin

delineating and quantifying depositional facies patterns in carbonate reservoirs insight from modern analogs modern carbonate settings have long been used as analogs for interpreting various environments of deposition in subsurface data sets based on well log and core data and have provided examples of how these environments can be interrelated within a larger context this study focuses on carbonate sands in the exuma islands part of the great bahama bank to show how modern settings can be better used for reservoir analogs by emphasizing visualization and quantification techniques that conceptually delineate aspects of potential grainstone reservoir distribution and heterogeneity along the windward margin of the exumas the association of tidal deltas channels and islands forms an exploration scale linear belt of mostly ooid sand approximately 5 10 km 3 1 6 mi wide and 170 km 106 mi long paralleling the platform margin but set back from the platform edge the distribution of carbonate sands in the exumas was assessed with a digital elevation model and satellite imagery by selecting different water depth intervals parts of the sand belt were highlighted for visual analysis and extracted for measurements of size and shape for example 37 of the sand belt comprises shallowest sands in which the largest areas greater than 100 000 m2 1 07 million ft2 are highly sinuous and maintain connectivity the sand belt was also subdivided into various depositional settings flood tidal delta lobes comprise 85 of the sand belt tidal channels and islands add further heterogeneity to the sand belt channels average about 3 km 1 8 mi in length and have regular but locally variable spacing a representative island shows how the syndepositional topography of holocene ridges develops complexly around antecedent pleistocene topography

paleoclimatic context of geomagnetic dipole lows and excursions in the brunhes clue for an orbital influence on the geodynamo the hypothesis of an influence of the astronomical precession on the geodynamo energy budget was recently reappraised by theoreticians paleomagnetic indications of such an influence remain controversial because reconstructions of paleointensity variations from sediments are suspected to be contaminated by lithological paleoclimatically induced influences three sets of complementary indicators are however available 1 records of the direction of magnetization in sediments 2 records of magnetic anomalies of the deep sea floor basalts and 3 records of production variations of cosmogenic isotopes from sediment and ice cores these records confirm the genuine geomagnetic origin of paleointensity lows and their narrow link with excursions or short reversals recorded in various materials and often dated by radiometric methods the analysis of these time series and their comparison with 18o records of the paleoclimate suggest that such globally recorded geomagnetic dipole lows have preferentially occurred in the context of interglacial or transitional paleoclimates at the time of low or decreasing obliquity the dominant periods extracted with the complex continuous wavelet transform technique range from 40 to 125 ka further suggesting a link with orbital parameters these results encourage future efforts of research to improve the precision the resolution and the dating of the time series of geomagnetic dipole low in order to better decipher orbital signatures and understand their origin an important implication of this topic is that the next geomagnetic dipole low should be related with the present interglacial

a diagenetic rock physics approach for siliciclastics this study presents a new heuristic approach that includes temperature in rock physics modelling temperature is the most important factor for chemical compaction and hence velocity evolution in the chemical compaction domain given brine saturated rocks the modelling is dependent on only three input parameters lithology vsh porosity and temperature the simplicity of the approach and the ability to model all stages of diagenesis in sands and shales make this strategy suitable in early exploration settings where little information is available due to fundamental differences in sands and shales one sand model and one shale model are proposed both temperature dependent the models are calibrated to local sands and shales and then used to predict scenarios not observed in the data set it is further demonstrated how the models can be used to guide seismic interpretation when interpreting shale sand reflections at different diagenetic stages finally the suggested models are also used to predict

geomagnetic 100 kyr variation excited by a change in the earth s orbital eccentricity 1 geomagnetic secular variations on a time scale of 10 100 kyr have important implications regarding the energy source of the geomagnetic field some high quality paleomagnetic records from marine sediment cores show quasi periodic variations having a time scale close to that of the earth s orbital eccentricity we analyzed a paleomagnetic record of core md982185 from the equatorial pacific and the earth s eccentricity for the last 2 2 m y utilizing wavelet analysis variations in the geomagnetic vertical component were synchronous with those in the first derivative of the eccentricity implying that the geomagnetic variations are excited by changes in the eccentricity

the deep thermal field of the glueckstadt graben with this paper we assess the present day conductive thermal field of the glueckstadt graben in nw germany that is characterized by large salt walls and diapirs structuring the graben fill we use a finite element method to calculate the 3d steady state conductive thermal field based on a lithosphere scale 3d structural model that resolves the first order structural characteristics of the graben and its underlying lithosphere model predictions are validated against measured temperatures in six deep wells our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the glueckstadt graben however the local temperatures may result from the superposed effects of different controlling factors especially the upper sedimentary part of the model exhibits huge lateral temperature variations which correlate spatially with the shape of the thermally highly conductive permian salt layer variations in thickness and geometry of the salt cause two major effects which provoke considerable lateral temperature variations for a given depth 1 the chimney effect causes more efficient heat transport within salt diapirs as a consequence positive thermal anomalies develop in the upper part and above salt structures where the latter are covered by much less conductive sediments in contrast negative thermal anomalies are noticeable underneath salt structures 2 the thermal blanketing effect is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present the latter effect leads to both local and regional thermal anomalies locally this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments for the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust finally the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere asthenosphere boundary defining the regional variations of the overall geothermal gradient we find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells whereas the steady state conductive approach appears not to be valid for the sixth well

the geomagnetic dipole moment variation between 250 and 800 ka bp reconstructed from the authigenic 10be 9be signature in west equatorial pacific sediments the authigenic 10 be 9 be ratio proxy of the cosmogenic radionuclide 10 be production rate in the atmosphere was measured in sediments deposited in the west equatorial pacific gulf of papua 10 25 s 146 15 e in order to reconstruct the geomagnetic dipole moment variations in the 250 800 ka time interval independently from paleomagnetic methods the pelagic clayey carbonate muds continuously deposited between marine isotope stages 8 and 20 were subsampled every 10 cm the 10 be production rate record reconstructed for the 250 800 ka interval is described and compared over the same time interval with global paleomagnetic stacks sint 2000 and piso 1500 the highlighted cosmogenic 10 be overproductions appear to be triggered by the series of geomagnetic dipole lows gdl that have occurred since the brunhes matuyama reversal calibration using absolute values of the geomagnetic dipole moment drawn from a paleomagnetic database produces a new record of the dipole moment variations over the 250 800 ka time interval the timing and amplitude of the gdl succession revealed by such records will contribute to improving knowledge of the geodynamo rhythms and rate of changes at millennial to million year scales

milankovitch climatic signals in lower triassic olenekian peritidal carbonate successions nanpanjiang basin south china abstract meter scale peritidal carbonate strata from an isolated platform in the nanpanjiang basin of south china were tested for the presence of periodic or quasi periodic climatic signals these signals provide information on factors controlling cyclic sedimentation in the equatorial eastern tethys during the early triassic greenhouse period parasequences are composed of shallowing upward successions of subtidal facies including skeletal packstone and grainstone calcimicrobial boundstone and oolitic packstone and grainstone intertidal laminated lutite and ribbon rock and rare supratidal microbial laminite parasequence stacking patterns display three orders of cyclicity suggesting hierarchical stratigraphic relationships gamma analysis of kominz and bond earth planet sci lett 48 1990 233 244 was used to estimate facies dependent thickness time conversion factors i e s and to construct tuned and untuned time series for two stratigraphic sections spectra of these time series indicate the presence of quasi periodic signals with prominent short eccentricity 94 9 131 2 kyr short obliquity 35 8 kyr and long precessional index 21 2 kyr peaks and minor long eccentricity 412 9 kyr long obliquity 45 3 kyr short precessional index 17 7 kyr and constructional tone 9 7 kyr peaks when calibrated on the tuned spectra thus milankovitch climatic forcing probably greatly influenced sedimentation the calibration indicates that the subtidal facies has a sedimentation rate of 24 6 30 7 cm kyr and the intertidal supratidal facies has a rate of 2 7 6 0 cm kyr the estimated duration of deposition of the two sections is 1139 1423 kyr and corresponds to a stratigraphic completeness of 32 92 the completeness is much greater than that of icehouse stratigraphic records we speculate that variations in carbonate productivity and environmental conditions driven by milankovitch climatic forcing combined with low amplitude sea level fluctuations were likely major controls on cyclic sedimentation furthermore evolutional spectra of the two sections show that dominant milankovitch climatic forcings varied from short eccentricity obliquity to long precessional index during the course of sedimentation some spectral differences between the two sections suggest variations in depositional recording mechanisms of milankovitch climatic signals between platform interior and windward platform margin

thermal properties of sedimentary rocks in the tarim basin northwestern china thermal properties of rocks are essential parameters for investigating the geothermal regime of sedimentary basins and they are also important factors in assessments of hydrocarbon and geothermal energy resources the tarim basin the largest basin located in the north of the tibetan plateau northwestern china has great hydrocarbon resource potential and is an ongoing target for industry exploration however the thermal properties of sedimentary rocks within the basin are yet to be systematically investigated at a basin scale thereby limiting our understanding of the thermal regime in the basin here we collected 101 samples of sedimentary rocks and measured their thermal properties our results show that the ranges and means of thermal conductivity radiogenic heat production and specific heat capacity are 1 08 5 35 w mk 2 52 0 99 w mk 0 03 3 24 w m3 1 24 0 87 w m3 and 0 75 1 10 kj kg c 0 87 0 07 kj kg c respectively volumetric heat capacity and thermal diffusivity at the temperature of 40 c range from 1 61 to 2 79 mj m3 k 2 26 0 25 mj m3 k and 0 44 2 95 10 6 m2 s 1 12 0 53 10 6 m2 s respectively the thermal properties vary considerably for different lithologies even within the same lithotype indicating that thermal properties alone cannot be used to distinguish lithology thermal conductivity increases with increased burial depth density and stratigraphic age suggesting the dominant influence is porosity variation on thermal conductivity furthermore a strong contrast in the thermal properties of rock salt and other sedimentary rocks perturbs the geothermal pattern which should be taken into consideration when performing basin modeling

characterization of the sedimentary thermal regime along the corsair growth fault zone texas continental shelf using corrected bottomhole temperatures temperatures of deep 3 km 1 8 mi sediments along the corsair growth fault zone in the texas continental shelf are elevated relative to those off the fault zone this observation is based on a compilation of nearly 400 bottomhole temperatures bhts obtained from about 230 wells widely distributed across the continental shelf the bhts have been individually corrected for the thermal disturbance associated with drill fluid circulation the isotherm of 140 c 284 f derived from the corrected bhts shows more or less continuous peaks along the fault zone thermal gradients in the depth range of 3 to 5 km 1 8 to 3 1 mi shows higher values along the fault zone than off the fault zone these trends are similar to the previous observations made along the wilcox growth fault zone in the texas coastal plain previous studies suggest that the faults of the wilcox system serve as the conduits for hot fluids expelled from deep overpressured sediments a similar mechanism may explain the elevated temperatures along the corsair fault zone

3 d seismic endoscopy multiscale analysis and dynamic azimuthal filtering of borehole waves summary we previously proposed a method of seismic endoscopy and a related prototype tool to acquire directional information and to produce three dimensional 3 d seismic images in a cylindrical volume surrounding a borehole with an investigation radius of several metres basic imaging algorithms were developed where the azimuthal move out amo process is combined to a timescale method to refocus directional information and analyse the surrounding medium further processing tools however were necessary for separating the various types of waves recorded the present paper describes a multiscale and dynamic azimuthal filtering to separate the far field waves from borehole or tube waves generated by the pipe we call this filter stoneley move out smo because it characterizes stoneley waves associated with the tube it is then possible to reconstruct details of the far field by an inverse wavelet transform the comparison with classical methods such as the covariance method is discussed applications on noisy synthetic and experimental data are presented

geothermal characteristics of the vorotilovo deep borehole drilled into the puchezh katunk impact structure abstract the vorotilovo borehole 5374 m in depth was drilled in 1989 1992 in the central part of the large puchezh katunk impact structure which is located in the east european platform lat 57 1 n long 43 6 e the geothermal studies of the borehole section were based on the temperature logging of the entire borehole 1992 1995 on the thermal conductivity measurements for more than 3700 air dry and fluid saturated core samples under normal p t conditions and for 473 samples at a temperature up to 100 c the rock anisotropy was taken into account in these measurements significant local vertical variations 20 30 even within short depth intervals of 100 200 m and a regular increase of conductivity from 0 8 1 2 w m 1 k 1 to 2 5 3 0 w m 1 k 1 with depth were established it was shown that conductivity variations are closely related to the grade of shock thermal metamorphism the thermal conductivity of metamorphic rocks from the basement of the vorotilovo uplift appeared to be substantially lower up to 40 than the conductivity of similar archaean rocks from ukrainian and baltic shields which we have investigated previously after the drilling had been completed the thermal regime of the rock massif was restored significantly faster than was inferred from previous theoretical considerations by september 1995 it was generally stabilized substantial vertical variations were recorded for all geothermal characteristics the section can be subdivided into three segments with distinct heat flow densities the interval down to 1200 m with the least heat flow density 22 31 mw m 2 i e 50 60 of the highest value the 1200 1900 m interval 34 42 mw m 2 i e 75 85 of the highest value and the 1900 5300 m interval with the highest density 40 56 mw m 2 appreciable local variations of the heat flow density obviously are caused by the refraction of heat flow at structural elements of the massif the character of mutual change of geothermal parameters in certain intervals testifies to the non steady thermal regime and fluid filtration the value of terrestrial heat flow density for the drilling site was estimated as 52 58 mw m 2 calculations show that in the depth range of 400 2000 m the effect of palaeoclimate causes a reduction of heat flow density of approximately 25 this cannot exhaustively account of the recorded vertical variation of heat flow density and allows us to suppose an effect of mass transfer or non steady thermal regime in the upper part of the section

isolating climatic and paleomagnetic imbricated signals in two marine cores using principal component analysis high resolution measurements of climatic and magnetic parameters have been performed on two cores from the eastern china sea and the western caroline basin on both cores magnetic parameters show a strong imprint of climatic changes but the absence of relationship between the inclination and the bulk density indicates that the directional changes do not depend on lithology a weak 100 ka cycle is present in the china sea inclination variations but this period is not in phase with the orbital eccentricity and thus not relevant all normalization parameters yielded similar estimates of relative paleointensity rpi but we have noticed the persistence of climatic components in the signal principal component analysis pca applied to different parameters related to climate lithology and paleointensity has allowed to extract a clean magnetic signal that we refer as principal component of paleointensity pcp which is in better agreement with the sint 2000 composite curve and provides a reliable record of relative paleointensity the presence of climatic frequencies in rpis most likely reflects the influence of lithology on the response of magnetization to field intensity we suggest that pca analysis can be very useful to approach these problems not only can the calculation separate overlapping climatic and magnetic signals but it indicates what confidence should be given to the data incidentally the present results emphasize the importance of carrying out detailed paleoclimatic analyses along with paleointensity studies

estimation of the thermal conductivity anisotropy of rock with application to the determination of terrestrial heat flow a moderately large data set of mostly sedimentary and metamorphic rocks compiled from the literature shows an inverse correlation between thermal conductivity anisotropy and thermal conductivity perpendicular to bedding the empirical relationship can be represented by a simple two component end member mixing model one end member is anisotropic x z 2 5 and has a relatively low thermal conductivity perpendicular to bedding z 1 w m k the other end member is isotropic and has a relatively high thermal conductivity perpendicular to bedding 4 w m k the proposed model may be used to derive a correction for anisotropic effects observed during thermal conductivity measurements on mixtures of randomly oriented aggregates although the accuracy and reliability of a universal correction procedure remain to be determined the proposed correction scheme should enhance our ability to estimate accurately heat flow in sedimentary basins where generally only borehole cuttings are available for thermal conductivity measurements

subsurface thermal conductivity assessment in calabria southern italy a regional case study determining the suitability of a local area at a regional or local scale for the geothermal application of low enthalpy systems requires the knowledge of rock thermal conductivity values to evaluate the possibility of low enthalpy heat exchange a digital cartographic tool is also needed to synthesize the thermal properties of the underground this tool should be easily accessible and upgradeable and thus suitable for territorial planning and environmental control in order to address these key issues a methodological approach was developed within the framework of the national vigor project dedicated to evaluating the geothermal potential in southern italy in this paper the region of calabria was selected as a case study around 70 samples that were representative of the main geological formations were collected from all over the area thermal property tests were carried out both in dry and wet conditions using a thermal device in accordance with the modified transient plane source method the thermal conductivity values were then compared with data from the international literature in order to consider the influence of the entire stratigraphic sequence on the thermal conductivity parameters a geostatistical analysis of the available lithostratigraphic data was performed using the matlab toolbox modalstrata specially developed for this purpose a comprehensive geothermal subsurface characterization of calabria was thus obtained

on the origin of the 100 kyr cycles in the astronomical forcing 1 investigations during the last 25 years have demonstrated that the astronomically related 19 23 and 41 kyr quasiperiodicities actually occur in long records of the quaternary climate however the same investigations also identified the largest climatic cycle as being about 100 kyr long as the 100 kyr variations in standing insolation due to eccentricity change are too small they cannot be the direct cause of the ice ages this is the reason why most of the modeling studies attempting to explain the relation between the astronomical forcing and climatic change have focused on this 100 kyr cycle in this paper we will show the astronomical origin of the periods at about 100 kyr that characterize the long term variations of eccentricity of its first derivative of the frequency modulation of obliquity and of the inclination of the earth s orbit on the invariable plane of reference five independent values are found between 95 and 107 kyr and a wavelet signature is suggested to test the possible relationships between the astronomical and climatic variables proxy records from deep sea cores and european programme for ice coring in antarctica ice core and modeling results from the louvain la neuve two dimensional model are used for illustration