convection with internal heat sources and thermal turbulence in the earth s mantle summary the influence of internal heat sources on mantle convection is investigated using numerical calculations of 2 d thermal convection in an infinite prandtl number incompressible fluid the geometry is a cylindrical annulus with inner and outer radii in proportion to the whole mantle time dependent calculations are made starting from random initial conditions with rayleigh numbers rat based on boundary temperature difference and ra based on internal heat production in the range 1dsrats lo7 and osra 524rat at fixed rat increasing ra results in transitions in flow structure from steady cells to a pattern of stationary cells with time variable amplitude and finally to thermally turbulent convection with a non stationary cell count for rat 10 and ra rat approximately the travelling plumes disrupt the large scale circulation producing turbulent convection at ra lo7 the flow is fully developed thermal turbulence and for ra 0 consists of a rapidly fluctuating irregular flow driven by transient rising and sinking sheets of buoyant fluid large fluctuations in total kinetic energy occur in this regime with periodicities ranging from 40 to 1400myr the transition to thermal turbulence occurs in these calculations at rayleigh numbers well below the value estimated for subsolidus convection in the mantle suggesting thermally turbulent convection may occur in the mantle a consequence of internal heat sources thermal turbulence offers an explanation for long term fluctuations in the rate of subduction sea floor spreading and global volcanic activity

a nonlinear rheology model for mid ocean ridge axis topography this paper describes a mechanical model of the mid ocean ridge axis based on a nonlinear rheology the oceanic lithosphere is modeled as a strongly temperature dependent power law material with the byerlee s friction law describing the brittle behavior of the upper oceanic lithosphere we examined two simple models a mantle only model predicted an axial rift valley 1 2 km deep and 10 15 km wide at slow half rates of 5 25 mm yr which is in fair agreement with observations however the rift valley did not completely vanish at fast spreading rates even though its width and relief became much smaller thus the mantle only model failed to explain the observed transition in axial topography with spreading rate by including a uniform thickness oceanic crust with theological properties different from the mantle our second model produced the first order variation of axial topography with spreading rate a pronounced rift valley with 1 2 km relief at slow rates a smaller relief 500 m rift valley at intermediate rates and no rift valley at fast rates there are two additional results of the nonlinear rheology model which are distinctively different from the previous uniform viscosity mantle models first horizontal velocity at the seafloor changes sharply in a very narrow zone at the ridge axis i e the stresses are concentrated in a very narrow zone for the nonlinear rheology this conclusion is remarkably independent of the boundary conditions at the seafloor second the computed width of the axial plastic failure zone decreases with spreading rate a result very different from that of a uniform viscosity model this is caused by the strong temperature dependence of the power law rheology and the fact that the temperature of the oceanic lithosphere depends greatly on the spreading rate beyond some distance from the ridge axis the brittle plate roughly the region above the 750 c isotherm deforms very little both the horizontal strain rate 11 and the maximum shear strain rate max are less than 10 17 s 1 which is in good agreement with the 10 18 s 1 average for oceanic brittle plate deformation inferred from seismic moment data within the ductile region area beneath the 750 c isotherm the strain rates are in the range of 10 14 10 16 s 1 except within a narrow band near the ridge axis where higher strain rates are located we found that the thermal structure of the oceanic lithosphere is not very sensitive to the details of the mantle flow pattern or the rheology but is very sensitive to the cooling by hydrothermal circulation near the ridge axis axial structure is also influenced by factors other than the spreading rate within the range of slow and intermediate rates our calculations show that the size of an axial rift valley decreases with an increase in either the thickness of the oceanic crust or the mantle temperature in other words a thinner crust or a cooler mantle temperature will produce a more pronounced rift valley in the vicinity of hotspots the absence of an axial rift valley even at slow spreading rates such as the reykjanes ridge can be well explained by the anomalously thicker crust and higher mantle temperatures in contrast at the australian antarctic discordance a deeper than normal section of an intermediate spreading ridge has very rough topography not present on the adjacent sections of the ridge this can be explained by our model as due to an anomalously low mantle temperature as has been suggested or perhaps also due to a thinner oceanic crust

time dependent convection in the earth s mantle abstract the range of rayleigh numbers accessible to 2 dimensional numerical models of mantle convection has been increased by almost two orders of magnitude through the use of high resolution numerical grids with up to 200 intervals in each of the horizontal and vertical directions the range of rayleigh numbers studied is believed to encompass conditions which would have existed in a hot archaean mantle although the models are highly idealized in that they neglect the compressibility and variations of viscosity in the earth s mantle they suggest that during the archaean and earlier boundary layer instabilities developed more frequently than at present and did so with a scale and separation comparable to the thickness of the thin thermal boundary layers rather than to the depth of the convecting layer itself the rising and sinking plumes which develop from these instabilities drive transient flows which nevertheless have a horizontal scale comparable to the depth of the convecting layer thus although surface motions during the archaean may have been more variable than at present in terms of speed and direction they might have occurred on a horizontal scale which is similar to that of present day plate motion the numerical models indicate that motions at the upper surface of time dependent convection cells are 1 predominantly controlled by transient sinking plumes and 2 converge directly towards the source region of the sinking plumes on the other hand rising plumes have a more diffuse influence on the upper surface and surface divergence does not always occur immediately above a rising plume if oceanic plates on earth constitute the upper surface of mantle wide convection cells the more pronounced geophysical signature of subduction zones compared to oceanic ridges may be simply due to the fact that buoyancy is most concentrated at the earth s surface in the form of sinking plumes the total surface heat flow is found to fluctuate significantly in the time dependent convection models since estimates of the present day heat loss from the earth s interior are at best instantaneous measurements it is possible that these estimates are not representative in a time averaged sense of the present thermal state of the planetary interior

evaluating the sulfur isotopic composition of biodegraded petroleum the case of the western canada sedimentary basin abstract the sulfur isotopic composition 34s of petroleum is believed to be affected mainly by sulfur incorporation reactions into the sedimentary organic matter during the early diagenesis however secondary processes could affect the original 34s of oil under the effect of thermal maturity or of the microbial activity of biodegraded reservoirs in this study the different processes that may affect the 34s of in reservoir oils were assessed based on the sulfur content and isotopes of a series of oil and core samples coming from various reservoirs of the lower cretaceous mannville group western canada sedimentary basin wcsb based on the molecular study these samples appear to have reached various levels of maturity and biodegradation ranging from 0 to 6 5 on the biodegradation scale of peters and moldowan in addition mixing of organic matter coming from different source rocks was identified based on the comparison with extensive correlation studies performed in the wcsb investigation of the 34s shows a trend that seems a priori correlated to the level of biodegradation however a careful interpretation of molecular and sulfur isotope data leads to the conclusion that the observed 34s variations have rather to be ascribed to contributions of oils generated by various source rocks alternatively variations of 34s could neither be related to maturity differences nor to kinetic effects during organic sulfur compounds biodegradation in the case of some specific core samples showing a common origin based on biomarker study 34s variations might not be related to different sources but to secondary sulfur incorporation exchange processes occurring within the reservoir these processes would involve reduced sulfur species from bacterial sulfate reduction formed in situ or migrated into mannville reservoirs this hypothesis is supported by laboratory experiments showing sulfur exchange incorporation under plausible conditions for shallow reservoirs

some geodynamical effects of anisotropic viscosity summary rheological anisotropy in the mantle may arise from various causes the most important are the preferred orientation of single crystals and the orientation of streaks of eclogitic material in a marble cake mantle in both cases the orientation can be achieved by the flow kinematics and in steady state convection the planes of easy slip will eventually be orientated parallel to the stream lines the dynamic equations for a 2 d incompressible anisotropic viscous fluid are derived and some geodynamic consequences are studied a difference of the order 10 100 between shear and normal viscosity is considered post glacial rebound would be affected by the mechanical properties in deeper parts of the mantle the observed uplift history near the ice margin has been taken as argument against strong viscosity stratification in the mantle it is shown here that with strong viscous anisotropy at least in the upper mantle the uplift history is compatible with a significant increase in viscosity between upper and lower mantle the topographic and geoid signal can show a spatial offset from a generating mass anomaly in the mantle this may provide the opportunity for in situ observation of anisotropic flow properties in the mantle in numerical case studies of steady state convection streamline orientated anisotropy is considered at high rayleigh number for bottom heated convection the formation of velocity boundary layers is observed with no flow in the stagnant core of the convection cell with internal heating or strong pressure and temperature dependence of viscosity this is no longer found but in the latter case anisotropy enhances the channelling of flow into lowviscosity regions e g hot rising plumes a few experiments have been performed for time dependent convection the results suggest that the onset of time dependent boundary layer instabilities may be somewhat retarded but would not be strongly suppressed by anisotropy strong time dependence may destroy any large scale coherence in the orientation of anisotropy and thus render the mantle to appear viscously isotropic

finite element modeling of lateral viscosity heterogeneities and post glacial rebound abstract the existence of lateral viscosity heterogeneities of a few orders of magnitude in the earth mantle has recently been proposed by several authors although classical post glacial rebound models are consistent with a rather uniform structure tomographic results reveal the presence of lateral heterogeneities in seismic velocities within the mantle which can be correlated with temperature and viscosity variations our aim is to analyze the uplift in deglaciated areas using a realistic horizontal viscosity profile of the mantle in order to determine the influence of such models on global mantle viscosity evaluation since analytical models cannot handle lateral heterogeneities we used a finite element numerical approach the code is a version of tecton program melosh and raefsky 1983 suitable for treating the axisymmetric case and modified to take isostatic compensation of the surface load into account we found that the average mantle viscosity values deviate from the canonical value of 1021 pa s when lateral variations are taken into consideration the displacement in the center is controlled by the average viscosity underlying the load for long wavelengths heterogeneities of two orders of magnitude the estimated average viscosity may differ by a factor 7 from the results obtained using radial models for stronger variation of four orders of magnitude the deviation is a factor of 30 although such strong viscosity seems to be inconsistent with the data difficulties in data fitting are also encountered for smaller variations when short wavelengths are considered when the interplay of vertical and lateral stratification is considered we find that average viscosities in the upper and lower mantle depend on the magnitude and pattern of the heterogeneities in each layer in particular strong lateral viscosity contrasts in the upper mantle can overlie a uniform lower mantle

time dependent convection with non newtonian viscosity we have used a numerical model of bottom heated two dimensional convection in boxes of aspect ratios 2 5 and 4 0 to study the differences in time dependent convection between newtonian and stress dependent viscosity the onset of time dependence due to boundary layer instability is found at approximately the same effective rayleigh number for both rheologies however with increasing rayleigh number the temporal and spatial fluctuations in the flow field become much more pronounced with non newtonian rheology also the tendency for breakup of long cells into smaller ones is stronger the presence of stress dependent rheology can cause long wavelength lateral viscosity variations up to an order of magnitude this result could have strong implications for the interpretation of mantle viscosity from postglacial rebound

the effects of upper mantle lateral heterogeneities on postglacial rebound we have investigated the potentially important effects arising from lateral heterogeneities on postglacial uplifts time dependent solutions for maxwell rheology with lateral variations in the upper mantle are obtained by finite element techniques in cylindrical geometry the displacements in the central portion of the ice sheet are not at all influenced by these lateral variations whereas the uplifts near the edge of the ice load are extremely sensitive to lateral heterogeneities in the upper mantle for ice sheets characteristic of the laurentide ice sheet deformations around the peripheral bulge can still be affected by an asthenosphere as far as twenty five degrees away the continental lithosphere under the former ice load would appear to be thicker with the presence of a neighboring asthenosphere recent estimates of the north american plate thickness would exceed 250 km under these circumstances

formation of immature asphalt from organic rich carbonate rocks i geochemical correlation abstract the formation of low maturity asphaltic oils immature asphalts from carbonate source rocks was investigated the senonian bituminous rocks sbr in israel are organic rich carbonate rocks that were deposited in a high productivity environment and they are part of a sedimentary sequence that also contains cherts and phosphorites the sbr were studied in different basins and the samples are from outcrops and three deep drillholes the bitumen contents of the rocks are exceptionally high up to 700 mg g c org and immature asphalts are found to be associated with them geochemical analysis indicates that the bitumens are indigenous to the host sbr and the associated asphalts are bitumens that have migrated a short distance with negligible chemical fractionation the high heteroatom content of the kerogens up to 30 in the sbr is suggested as a possible cause of the generation of asphaltic oils in an early stage of maturation

convectively induced transition in mantle rheological behavior mantle flow occurs through both linear and nonlinear creep mechanisms and the style of convection is strongly influenced by the dominant creep mechanism in a composite rheology we show here by numerical modelling of convection with a composite flow law that the nonlinear strain rate dependence of mantle rheology would dominate over the linear newtonian portion for sufficiently vigorous convection such as might have prevailed in the early earth this rheological transition occurs at a rayleigh number value which increases dramatically with higher values of the activation energy for activation energy values for dislocation and diffusion creep of about 100 and 70 kj mole respectively we find a transition between rayleigh numbers 106 and 107 corresponding values of the transition stress agree with estimates for the lower mantle from empirical data for perovskite analogue these results suggest that early in the earth s thermal history a transition would have taken place from a primarily non newtonian flow to a newtonian temperature dependent style of mantle convection with a high activation energy greater than 125 kj mole the mantle would have been in a newtonian regime throughout most of its thermal history

secondary convection and the growth of the oceanic lithosphere abstract this paper presents a study of the evolution of the oceanic lithosphere from a thermomechanical approach we have investigated the finite amplitude development of secondary convection cells beneath the oceanic plates by means of the single mode mean field equations and the fully 2 dimensional convection equations using finite element techniques both newtonian and non newtonian rheologies with highly temperature and pressure dependences and an activation energy of 100 kcal mol 1 have been employed the temperature at the base of the convecting medium governs the final thickness of the lithosphere the mean interior temperature varies only slightly during the temporal evolution non newtonian rheology has the tendency to induce oscillatory time dependent behavior of the flow heat flow topography and gravity are influenced by secondary convection in two ways small scale perturbations with wavelengths of around 600 km arise from the lateral thermal differences between the uprising and descending convective limbs large scale features are also produced as a consequence of lithospheric growth the calculated quantities of the heat flow topography and gravity associated with small scale convection are typically in the range of o hfu o 102m and o 10 mgal the horizontal mean temperature profiles from the convection model are used to calculate long wavelength geophysical observables as a function of age convective processes are found to reduce the rate of lithospheric thickening predictions from our model can fit well the observed data of heat flow ocean floor topography and geoid offsets along fracture zones the last data base exhibiting the most sensitivity to thermal perturbations below the lithosphere our calculations show that the oceanic lithosphere is able to grow continuously up to o 109 y long past the flattening of the seafloor we report here that the thickness of a thermally equilibrated lithosphere could reach 250 km which lies within the appropriate range of values for the continental lithosphere as inferred from studies in seismology flexure observations and secular polar motions

observational hints for a plume fed suboceanic asthenosphere and its role in mantle convection an asthenosphere layer which is entirely fed from below by plumes and which loses equal mass by accretion to the overlying oceanic lithosphere and at subduction zones may play a critical role in shaping the form of mantle convection in this study we discuss geochemical seismic and geoid depth evidence for lateral flow within this type of asthenosphere in particular we suggest that there are large scale layered horizontal flow structures that connect upward plume input beneath hotspots to near ridge regions of increased asthenosphere accretion into the growing oceanic lithosphere lateral asthenosphere flow is also shaped by oceanic subduction zones with a partial return flow from trenches and by deep continental roots that are migrating barriers to asthenosphere flow this alternative paradigm offers relatively simple explanations for several puzzles about mantle convection for example the low mantle heat flow beneath continents it also offers an explanation for why mid ocean ridges appear to be passive features that migrate with little geochemical or morphological change with respect to the lower mantle and seem to be uncoupled from large scale mantle flow while in contrast trenches appear to be strongly coupled to mantle thick regions of fast colder seismic velocity anomalies we also discuss several implications of this paradigm that should be testable in future studies such as the prediction of cogenetic off axis seamount volcanism that is created between an off axis hotspot and its neighboring ridge axis

numerical studies of non newtonian mantle convection abstract numerical model computations have been carried out to determine how the stress dependence of non newtonian viscosity affects the flow structure of thermal convection the viscosity laws have been chosen in accordance with present knowledge of upper mantle rheology based on the diffusion and dislocation creep laws of olivine the results show that there are important differences between the structures of newtonian and non newtonian convection while the newtonian models are insufficient in some respects the non newtonian solutions can explain the characteristics of the real mantle flow however this may require a faster plastic deformation than power law dislocation creep at least in the high stress regions of the mantle e g at the active plate margins

hydrocarbon potential of dead sea rift valley the dead sea rift is one of the world s unique geologic and topographic features whose petroleum potential has not yet been evaluated the sector of the dead sea is an asymmetric graben 20 km 12 mi from rim to rim and over 120 km 75 mi long the total throw from the west rim where the upper cretaceous crops out to the deeper portion of the grabens is more than 8 km 26 200 ft throw on the eastern side is considerably greater as the valley wall is largely precambrian the level of the dead sea is 400 m 1300 ft the lowest place on earth asphalt blocks floating from the dead sea along with asphalt and heavy oil seeps in the valley have been known since biblical times these are suggestive of leaks from deeper accumulations although some exploration drilling has been done no test has yet reached objectives in the deeper sunken block where the miocene is figured to be at a depth of at least 7 km 23 000 ft

convection and lithospheric strength in dione an icy satellite of saturn abstract finite element numerical simulations for the structure of convection cells within a self gravitating boussinesq fluid sphere with variable viscosity are used to determine temperature distribution stream functions velocities and intensities of the stresses within dione an icy satellite of saturn a non newtonian i e stress dependent viscosity is considered but the numerical simulation according to u r christensen 1984a geophys j r astron soc 77 343 384 is carried out knowing that the properties of power law convection can be closely simulated by newtonian flow with a reduced value of the activation enthalpy the initial temperature profile has been determined taking into account the amount of energy trapped as heat during the accumulation process and the other energy source is the radioactivity of the long lived isotopes the obtained results seem to show a long duration endogenic activity in agreement with the geological observations the intensities of the stress are able to fracture the icy crust both in extensional and in compressional regimes the thickness of the mechanical lithosphere evolves in a way determined by the complex interplay of the lithospheric temperature gradient and the strain rate

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

the thermal signature of subducted lithospheric slabs at the core mantle boundary abstract we study the thermal structure around a cold deformable lithospheric slab as it sinks to the core mantle boundary and migrates along it we present analytical results for the steady thermal structure established by a steady but spatially varying motion the analysis gives a time like criterion for the thermal signature of a cold slab to persist by the time that the slab moves along the core mantle boundary the model is used to assess the feasibility of a purely thermal origin for some of the observed seismic reflectors near the core mantle boundary calculations of the time like criterion show that the dynamical conditions in our model namely the velocity and the thickness of the descending slab are hard to reconcile with observations of subduction and seismic features seismic reflections and refractions from anomalously fast regions above the core mantle boundary could be explained as thermal slabs if the thickness of the slab at subduction was larger than 200 km or somewhat less if the slab did not split at the core mantle boundary a simple thermal model also predicts from mineral physics a certain correlation between s and p wave velocity anomalies which is not observed however a purely thermal origin cannot be ruled out if the slab is buckling this process could be in agreement with the observations the amplitude of the seismic anomalies the vertical extent of high gradient zones and the p versus s comparisons chemical heterogeneities and phase transformations remain alternative or complementary explanations

hard turbulent thermal convection and thermal evolution of the mantle this article summarizes the results of hard turbulent convection obtained in laboratory experiments and numerical simulations its applications to mantle convection are illustrated by two dimensional numerical solutions to 1 newtonian 2 non newtonian convection and 3 newtonian convection with multiple phase transitions in newtonian mantle convection the transition from soft to hard turbulence is marked by the appearance of disconnected plumes spectral analysis of the time series of the nusselt number reveals the presence of a spectral scaling subrange for hard turbulence but not for soft turbulence in hard turbulence there is correspondence between the spectra in frequency and wavenumber domains the slope of the seismic wave spectra measured from seismology suggests that the mantle convection today is strongly time dependent the transition to hard turbulence takes place at much lower nusselt numbers for non newtonian than for newtonian rheology for the mantle this would have important ramifications non newtonian plumes behave quite differently from newtonian ones in that large curvatures are developed in their trajectories in the hard turbulent regime mantle convection with phase transitions tends to become more layered with increasing rayleigh numbers the style of mantle convection might have changed from a layered to a more whole mantle type of flow with time catastrophic overturns associated with strong gravitational instabilities in the transition zone could be responsible for superplume events

molecular archaeology export of dead sea asphalt to canaan and egypt in the chalcolithic early bronze age 4th 3rd millennium bc abstract nine archaeological bitumens from excavations in canaan sinai and egypt tel irani ein zik palmahim tel arad jerusalem ein besor site h sheik awad and maadi dated 3900 2200 bc and two natural asphalts of the dead sea area ein gedi floating blocks and nahal heimar have been compared using the following geochemical techniques chloroform extraction and gc and gc ms analyses of c15 alkanes and c15 aromatics isotopic analysis 13c and d on chloroform extracts and asphaltenes and rock eval pyrolysis of the insoluble organic residue all samples are genetically related and are different from other archaeological bitumens from syria and iraq tel irani archaeological bitumen was found to be identical to the floating block asphalts of the dead sea other archaeological bitumens were recognized as having been weathered and biodegraded to various degrees at archaeological sites in the course of the millennia they are regarded as counterparts of floating block asphalts altered by aging this study is the first evidence of the trade and export of raw bitumens from the dead sea area within canaan and to egyptian trading centers on the mainland route to egypt between 3900 and 2200 bc prior to the extensive utilization of bitumen for mummification in ancient egypt

asphalts oils and bituminous rocks from the dead sea area a geochemical correlation study oils and asphalts gilsonite from the dead sea area israel were characterized by bulk composition specific c15 hydrocarbons n alkanes isoprenoids steranes triterpanes and aromatics including sulfur compounds and light hydrocarbons c2 to c8 molecular range these indicators complemented by literature data sulfur content sulfur isotope composition and distribution of petroporphyrins define the oils and asphalts as belonging to a single geochemical province the geochemical characteristics suggest a source material of bacterially reworked algae and a source rock poor in clay minerals probably a calcareous rock calcareous bituminous rocks of the campanian maestrichtian ghareb formation are exposed on the margin of the dead sea graben on downwarped blocks and they probably extend under the thick graben fill the agreement of the geochemical indicators suggests that these bituminous rocks are a potential source of the asphalts and oils in the dead sea area differences between the various types of hydrocarbon occurrences are due to a combination of several effects such as variations in source material the thermal history of the different downwarped blocks water washing and biodegradation the distribution characteristics of hydrocarbons c6 to c35 and c2 to c8 is sensitive to biodegradation and or water washing the aromatic fractions except very soluble compounds like benzene toluene etc are less affected by these processes and record the variability due to source and possibly thermal history the interpretation of the triterpane and sterane distribution corroborates that of other hydrocarbons with respect to maturation and type of source rock differences in maturation are pronounced the bituminous rocks and asphalts are immature and the oils are derived from source rocks in an initial stage of petroleum generation

the influence of facies and depositional environment on the occurrence and distribution of carbazoles and benzocarbazoles in crude oils a case study from the gulf of suez egypt abstract two major hinge zones separate the gulf of suez gos of egypt into three tectonic sub provinces namely the northern central and southern sectors based on bulk and molecular parameters the crude oils from the gos can be subdivided into three groups according to their geographical origin from the three sectors the geochemical characteristics of the oils are consistent with inferred depositional environments of anoxic marine carbonate facies in the central sector compared to a more oxic environment that has received an increased proportion of clastic input in the southern sector while the northern is intermediate in character most of the oils cover a relatively narrow maturity range 0 86 0 98 r c in the peak oil window the biomarker parameter ts ts tm is controlled by variations of facies and depositional environment but not by maturity concentrations of pyrrolic nitrogen compounds in the gos crude oils are in general relatively low but show a large range of variability in crude oils of the northern sector a strong predominance of c 4 and c 5 carbazoles over the lower homologues is observed towards the south the relative abundance of carbazole and the methylcarbazoles increases successively variations within the methylcarbazoles and c 2 carbazoles are rather small and therefore are not useful for a straightforward classification of oil families however atypical patterns in some of the oils particularly from the northern sector give evidence for contributions from yet unidentified local sources which might not be of general importance in the gos petroleum province benzo b carbazole is near or even below detection limit in the gos crude oils the benzocarbazole a a c ratio shows a consistently positive correlation with api gravity pr ph and ts ts tm and a negative correlation with the sulphur content based on these observations it is inferred that facies and depositional environment of the relevant source rocks are the major factors influencing the benzocarbazole distributions in the central sector of the gos in which oils are predominantly sourced from carbonates deposited under strongly reducing conditions a a c values are mainly below 0 5 in the southern sector where source rocks were deposited under less reducing conditions and received significant clastic input as well as in the northern sector the a a c values are mainly above 0 5

the relationship between plate velocity and trench viscosity in newtonian and power law subduction calculations convection with a newtonian temperature dependent rheology leads to little or no surface velocity unless zones of weakness are introduced plate like features are observed in calculations both with newtonian rheology employing imposed weak zones and with power law non newtonian rheology where high stresses at the trench reduce the effective viscosity since deformation at subduction zones involves faulting both of these parameterizations should be treated with some skepticism it is important to understand how the parameterizations affect the model results we study the relationship between trench viscosity and plate velocity using a newtonian rheology by varying the viscosity at the trench the plate velocity is a function of the trench viscosity for fixed rayleigh number and plate slab viscosity slab velocities for non newtonian rheology calculations are significantly different from slab velocities from newtonian rheology calculations at the same effective rayleigh number both models give reasonable strain rates for the slab when compared with estimates of seismic strain rate non newtonian rheology eliminates the need for imposed weak zones and provides a self consistent fluid dynamical mechanism for subduction in numerical convection models

biological markers in bitumens and pyrolyzates of upper cretaceous bituminous chalks from the ghareb formation israel abstract the sterane and triterpane distributions of three bituminous chalks from the upper cretaceous ghareb formation israel were investigated both in the original extractable bitumens and in extracts obtained after pyrolysis of whole rock and isolated kerogen samples at 450 c pyrolysis was performed in a closed system under hydrous whole rock and anhydrous conditions isolated kerogens the carbon number distributions of steranes and triterpanes differ significantly between original bitumen and pyrolyzates unlike the bitumens in which diasteranes were not detected the anhydrous pyrolyzates contain small amounts of diasteranes the presence of water during pyrolysis leads to an increase of sterane isomerization the abundant formation of diasteranes and an increase of the 18 h trisnorneohopane 17 h trisnorhopane ratio sterane isomerization maturation parameters show a closer match between original bitumen and pyrolyzates after pyrolysis in a closed system when compared with an open system

mantle convection with internal heating and pressure dependent thermal expansivity recent laboratory work 1 suggests that the thermal expansivity of the mantle decreases strongly with pressure determines the buoyancy of plumes and the rate at which plumes lose their thermal signature as they rise and so may be expected to have a strong influence on the temperature and velocity structure of the mantle numerical simulations were conducted on convection in an internally heated compressible mantle including constant and pressure dependent and thermal conductivityk they show that a pressure dependent allows the existence of thermal plumes rising from the core mantle boundary cmb however the plumes are weak and dissipate higher in the mantle

biological marker characteristics of oils and asphalts from carbonate source rocks in a rapidly subsiding graben dead sea israel abstract a detailed gc ms study of biological marker compounds in the saturated and aromatic hydrocarbon fractions of oils and asphalts from the dead sea area israel provided decisive information to the solution of a long lasting controversy by showing that the asphalts are products of early generation in an immature stage from the same type of carbonate source rock which generated more mature oils the asphalts are not biodegraded residues of the oils oils from six different wells and asphalts from wells outcrops and a floating block from the dead sea all have very similar sterane and triterpane patterns they all lack rearranged steranes diasteranes indicating a carbonate source matrix and compare reasonably well with a sample of upper cretaceous bituminous chalk from nebi musa the main difference between the oils and the asphalts is a significantly higher triaromatic to mono plus triaromatic steroid hydrocarbon ratio in the former this is explained as a result of rapid subsidence and heating of their source rock close to the deep parts of the dead sea graben the oils thus were generated in the more deeply buried source rock blocks under the graben fill whereas the asphalts either originate from an immature source rock section closer to the graben rims or represent an earlier phase of generation and expulsion this study also provides general information on the evolution of biological markers in carbonate source rocks low activation energy processes like isomerisation of steranes appear to occur much faster at low temperatures than in shales the high sulfur content and less cross linking of the biogenic organic matter into a complex kerogen structure are suggested to be responsible for this care should be taken when using only sterane isomerisation to assess the maturity of hydrocarbons from carbonate rocks and of carbonate derived oils

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

the impacts of mantle phase transitions and the iron spin crossover in ferropericlase on convective mixing is the evidence for compositional convection definitive new results from a yin yang overset grid based control volume model high resolution seismic tomographic images from several subduction zones provide evidence for the inhibition of the downwelling of subducting slabs at the level of the 660 km depth seismic discontinuity furthermore the inference of old 140 myr sinking slabs below fossil subduction zones in the lower mantle has yet to be explained we employ a control volume methodology to develop a new anelastically compressible model of three dimensional thermal convection in the mantle of a terrestrial planet that fully incorporates the influence of large variations in material properties the model also incorporates the influence of 1 multiple solid solid pressure induced phase transitions 2 transformational superplasticity at 660 km depth and 3 the high spin low spin iron spin transition in ferropericlase at midmantle pressures the message passing interface parallelized code is successfully tested against previously published benchmark results the high resolution control volume models exhibit the same degree of radial layering as previously shown to be characteristic of otherwise identical 2 d axisymmetric spherical models the layering is enhanced by the presence of moderate transformational superplasticity and in the presence of the spin crossover in ferropericlase stagnation of cold downwellings occurs in the range of spin crossover depths 1700 km although this electronic spin transition has been suggested to be invisible seismically recent high pressure ab initio calculations suggest it to have a clear signature in body wave velocities which could provide an isochemical explanation of a seismological signature involving the onset of decorrelation between vp and vs that has come to be interpreted as requiring compositional layering

effects of depth variations in creep laws on the formation of plates in mantle dynamics we have studied the influences of depth varying rheologies on the structure of mantle convection and the near surface flow fields upwelling flows crossing the upper lower mantle boundary become considerably thinner and faster streamlines are concentrated near the surface and other plate like characteristics are enhanced by this type of rheological stratification in which the averaged effective viscosity of the upper mantle is about two orders of magnitude lower than that of the lower mantle the presence of a lithosphere with a higher non linear dependence in the flow law further promotes plate like behavior plate like character of the top boundary layer is encouraged by a decreasing depth dependent viscosity in the non newtonian upper mantle and by greater convective vigor

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

plume formation in the d double prime layer and the roughness of the core mantle boundary numerical simulations of the formation of thermal plumes in the d layer at the base of the earth s mantle show that plumes are initiated by coalescence of small scale convective instabilities within the low viscosity region immediately above the core mantle boundary cmb these instabilities support topographic roughness on the cmb having horizontal scales of 20 50 km and provide a source for scattered p waves seen as precursors to the phases pkikp and pkkp the calculated structure of fully developed plumes emerging from d consists of 5 50 cm yr 1 flow confined to 50 100 km thick vertical conduits with strongly temperature dependent viscosity plumes exhibit time dependent behaviour including upward propagating solitary conduit waves which may contribute to episodicity in hotspot volcanism

an eulerian technique for thermomechanical modeling of lithospheric extension a two dimensional eulerian spline function finite element method for modeling the coupled thermomechanical processes which control lithospheric extension is presented the model domain comprises a cross section through the lithosphere and part of the asthenosphere material may enter or leave through the bottom and side boundaries on the side boundary a fixed velocity or a fixed force condition can be applied highly nonlinear and thermally activated creep laws are used for the brittle and ductile rheologies of the lithosphere compositional differences between crust and mantle are described by a continuous function which is advected and which affects density rheology and heat production an approximate topography is calculated from the normal stress at a free slip surface boundary a set of sample case studies is presented which highlights the capabilities and possible applications of the method it also serves to study the influence of numerical parameters and of conceptual assumptions in various nontrivial applications the examples comprise narrow rifting continuing into the stage of seafloor spreading formation of a wide basin formation of a metamorphic core complex and impact of a mantle plume onto the bottom of the lithosphere in the last case the entire upper mantle is modeled and the instability of a thermal bottom boundary layer gives rise to a diapiric mantle plume the main weakness of the eulerian approach as compared to the lagrangian technique was found to be the effective blurring of material discontinuities like the moho this is of little consequence in pure shear deformation but when strong simple shear occurs it impairs the resolution the main advantage of the eulerian technique is that very large deformation poses no problem as it does for the lagrangian method the new approach is especially suited to study processes where strong differential flow occurs in part of the modeled system a further possible advantage of the method is its efficiency in terms of computer time

in search of an ice history that is consistent with composite rheology in glacial isostatic adjustment modelling abstract global reconstructions of the earth s quaternary ice sheet history such as ice 6g assume that mantle rheology is linear and earth properties are laterally homogeneous however these assumptions are unrealistic because high temperature pressure creep experiments show that both linear and non linear creep laws operate simultaneously in the mantle also surface geology and seismic tomography show that mantle properties vary laterally this study uses the coupled laplace finite element method to find an ice model that is consistent with an earth model with composite rheology where both linear and non linear creep laws operate simultaneously in the mantle and the effective viscosity is laterally heterogeneous we use the ice 6g ice model as initial load on a composite rheology earth model and iteratively improve both the ice and earth model parameters until they fit observations of glacial isostatic adjustment or gia relative sea level and land uplift rate well simultaneously we thereby focus on north america and northern europe our best combination model called ice c m c also fits gravity rate of change data in both areas this finding removes the obstacle in using composite rheology in gia studies since previous work found it impossible for composite rheology to fit both relative sea level and land uplift rate data simultaneously it shows that composite rheology is clearly an alternative to linear rheology in future gia studies the ice c model is at the last glacial maximum lgm position from 26 ka bp thousand years before present to 19 ka bp which implies that composite rheology also supports the timing of lgm proposed by clark et al 2009 the model is found to be significantly thicker in the center of rebound in fennoscandia than ice 6g from the lgm to about 8 ka bp but significantly thinner around the fennoscandian coastline from lgm to about 12 ka bp these changes in the lower boundary conditions in northern europe may affect the reconstruction of past climate there regional differences in ice thickness between ice c and ice 6g are also found in laurentia during lgm there are negligible differences in total ice volume between ice c and ice 6g thus it remains questionable if a composite rheology may help in solving the missing ice problem ice c is also consistent with meltwater pulses 1a and 1b mantle viscosities and creep parameters of earth model m c are consistent with previous findings from gia modeling and microphysics experiments

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

a community benchmark for subduction zone modeling we have developed a suite of benchmarks to facilitate the comparison of numerical models for the dynamics and thermal structure of subduction zones the benchmark cases are based on a thermomechanical approach in which the slab is prescribed kinematically and the wedge flow is computed dynamically we propose various cases to investigate the influence of boundary conditions and rheology on wedge flow and resulting thermal structure a comparison between the codes suggest that accurate modeling of the thermal field requires a good implementation of the velocity discontinuity along the seismogenic zone and high resolution in the thermal boundary layers a minor modification to the boundary conditions of the wedge flow is also necessary to avoid a pressure singularity that exists in analytical solutions of the cornerflow model

pulsating diapiric flows consequences of vertical variations in mantle creep laws abstract recent laboratory work has suggested that the rheology of the lower mantle may be newtonian we have studied the time dependent dynamics of plumes interacting with a rheological interface separating an upper non newtonian mantle and a newtonian lower mantle pulsating diapiric structures with fast time scales are promoted by the interaction of the rising plumes with this rheological boundary surface heat flow signals are discernible as pulses which remain relatively stationary they correlate well with the localized upwellings just below the surface the presence of a mobile lithosphere from increasing the non newtonian power law index helps to produce a large scale circulation in the upper mantle which draws large hot patches away from nearby upwellings in our calculations the resultant averaged effective viscosity of the non newtonian upper mantle is about two orders of magnitude lower than that of the newtonian lower mantle a viscously stratified newtonian model produces more incoherent and broad scale diapiric structures and is less efficient for generating sharply varying time dependent thermal signatures

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

rise of deep diapirs diapiric ascent is often assumed to occur in a mantle with a viscosity of order 10 21 p the value estimated from glacial rebound studies segregation of melt from residual crystals en route is then a necessary consequence of the slow ascent velocity the temperatures and stresses associated with diapirs however are much greater than those involved in glacier unloading and the controlling viscosity is therefore relatively low high stresses may also result from the volume change associated with the partial melting process itself stress and temperature feedback considerably increase the velocity of ascent of a deep diapir and this may allow the melt and the residual crystals to rise together without separating the material delivered to shallow mantle magma chambers may therefore be similar in composition to the deeper source region this reopens the possibility that a deep eclogite layer 200 km depth may be the source region for mid ocean ridge basalts

geochemical study of some cretaceous rocks from kuwait comparison with oils from cretaceous and jurassic reservoirs abstract a set of 18 cretaceous rock samples from wells drilled in the raudhatain and minagish oil fields and 10 oil samples from cretaceous reservoirs raudhatain bahra burgan and minagish oil fields were characterized using geochemical methods including compound specific carbon isotope analyses of n alkanes and isoprenoids in addition one oil miqua from the jurassic marat formation of the great burgan oil field was included in the study despite having high organic carbon content in some samples the burgan and zubair formations and the ratawi shale member of albian to valanginian age are not source rocks for the oils for several reasons but primarily due to lack of correlation of molecular and isotope chemistry as well as a humic organic matter type these results are consistent with the corresponding depositional conditions for these rocks which are deltaic estuarine in the burgan formation and littoral deltaic in the zubair formation the minagish and sulaiy formations of late jurassic to cretaceous age appear to be potential source rock candidates based on their molecular and bulk isotope geochemistry detailed isotopic analysis using individual normal and isoprenoid c 15 alkanes did not provide a good correlation between these possible source rocks and the oils however one sample from the sulaiy formation was found to be comparable to the oils the oils belong to the same genetic family and were expelled from a source rock with a dominant carbonate lithology e g the sulaiy minagish formations these formations contain sulphur rich amorphous kerogen as observed in recent shallow marine shelf deposits the miqua oil which accumulated in the jurassic marat formation reservoir does not differ from the other oils in terms of genetic characteristics this oil is the deepest and most mature of the set maturity assessment has not been possible using well known parameters based on steranes terpanes or methylphenanthrenes however sulphur bearing aromatics comprised of alkylated bt and dbt show important variations parameters based on alkylated bt and dbt have been applied successfully as tools to evaluate maturity changes oil maturity was determined to be middle oil window but has been found not to be related directly to the present depth of the reservoir however it has been established that within the same oil field oil maturity increases with reservoir depth evaluation of these maturity characteristics may be related to major chronological events especially major tectonic movements that have enabled oil to fill different reservoirs successively the reconstruction of the most important phases i e genesis and migration through active faults will provide guidelines to understand the present day maturity pattern of these oils

natural and artificial maturation of biological markers in a toarcian shale from northern germany steroid and terpenoid biological marker evolution was studied in a maturity sequence of lias toarcian shales and adjacent strata from three shallow boreholes in the hils syncline northern germany excellent facies control within the study area ensures the comparability of the organic matter type among the stratigraphically equivalent samples of the natural maturation series in the early hydrocarbon generation stage 0 68 r0 a strong facies dependence of some sterane and hopane isomerisation values was found within the same borehole at only a few metres depth difference the extent of sterane isomerisation at c 14 and c 17 was close to 80 in the toarcian shale and between about 55 and 65 in the adjacent dogger and lias sediments similar differences were observed for the 17 h hopane moretane and 22 29 30 trisnor 18 h neohopane 22 29 30 trisnor 17 h hopane ratios whereas the 20s 20s 20r sterane isomerisation ratio did not show this difference the observed differences mostly disappear by the end of the main oil generation phase 0 88 ro where several reactions appear to have reached completion hydrous pyrolysis experiments by variations of time and temperature were used to simulate the natural evolution of the biological markers results for sterane isomerisation in the high temperature range were compared to those published by mackenzie and mckenzie geol mag 120 417 470 1983 for natural sediments kinetic data derived for this reaction from the hydrous pyrolysis results alone or from the combination of hydrous pyrolysis and natural data sets differ markedly from those determined by mackenzie and mckenzie 1983 the hydrous pyrolysis data alone yield an activation energy for sterane isomerisation at c 20 of 131 kj mol the combined data of 170 kj mol the frequency factors are in the 105 108 s 1 range the significance of the data is discussed in detail

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

rheological transition in mantle convection with a composite temperature dependent non newtonian and newtonian rheology numerical simulations of mantle convection with a composite temperature dependent newtonian and non newtonian creep law have revealed a transition in the dominant creep mechanism with the increasing vigour of convection newtonian creep is found to dominate in the low rayleigh number regime with sufficiently high effective rayleigh number the overall creep mechanism in the convective flow becomes non newtonian the transitional rayleigh number increases strongly with the activation energy these results would suggest a scenario that in the early epochs of earth the flow in the mantle would have been governed by non newtonian rheology and would have exhibited both strong spatial and temporal fluctuations with time the flow mechanism would behave like a newtonian fluid and would have a different time dependent character in time dependent newtonian dominated flows there are still localized features with distinctly non newtonian character our analysis of the relative contributions to the lateral viscosity field supports the idea that the inference of the nature of lateral viscosity heterogeneities by seismic tomography may be strongly contaminated by the dominant non newtonian contributions to the total lateral viscosity field

the effect of porosity on the strength of quartz aggregates experimentally deformed in the dislocation creep regime abstract the presence of porosity results in significant although transient strengthening of quartz aggregates experimentally deformed in the dislocation creep regime experiments were conducted on four quartz aggregates with porosities of

plate tectonics and aspherical earth structure the importance of poloidal toroidal coupling we derive poloidal flow internal loading green functions for incompressible fluid models of the mantle consisting either of a single constant viscosity spherical shell or of two adjacent spherical shells having different viscosities from the green function we obtain kernels connecting the surface divergence the geoid and the surface topography fields to the lateral density heterogeneity inferred on the basis of the application of seismic tomographic imaging techniques and with these kernels we argue that both the surface divergence and geoid fields consisting of harmonic degrees 2 5 may be reasonably fit with only a factor of 8 viscosity increase at a depth of 1200 km we point out however that the coupling from poloidal to toroidal flow which is required to understand surface velocity spectra may allow these observations to be understood in terms of a viscosity increase at depth which is smaller than required by nonhydrostatic geoid data in the context of pure poloidal models using the observed kinetic energy in the surface plate motions as a constraint allows us to infer a value for the steady state upper mantle viscosity of 2 0 0 5 1021 pa s we comment on the implication of the difference between this number and the somewhat lower value 1 1021 pa s which has been derived on the basis of analyses of signatures of the glacial isostatic adjustment process

quartz deformation across interlayered monomineralic and polymineralic rocks a comparative analysis abstract given the increased availability of ebsd and fabric analyzer facilities quartz microstructural and cpo analysis have become tools of the trade for studies investigating crustal tectonics therefore improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes we contribute to this understanding by comparing quartz deformation between monomineralic rocks which have simple compositions and polymineralic rocks which are more complex and representative of the crust mylonite quartzites and gneisses of the main central thrust nw himalaya are used for comparison under similar deformation conditions quartz inside monomineralic rocks forms well developed cpos and dynamically recrystallized microstructures typical of grain size insensitive gsi creep mechanisms quartz inside polymineralic rocks by contrast exhibits weak cpos and fine grained microstructures commonly interpreted as grain size sensitive creep but also exhibits lattice distortions e g undulose extinction sub grain boundaries associated with gsi creep we postulate that intrinsic factors such as interphase boundaries cause these ambiguous results the lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and cpos for rapid diagnoses of their rheology and broader tectonic significance

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

vanadium nickel and sulfur in crude oils and source rocks and their relationship with biomarkers implications for the origin of crude oils in venezuelan basins abstract this work presents a study of vanadium nickel and sulfur concentrations and biomarkers in a suite of crude oils and source rocks from three venezuelan basins maracaibo and eastern basins and barinas sub basin crude oils range from unaltered to altered by biodegradation and source rocks are characterized by having different kerogen types type ii iii or iv and maturity levels early mature to post mature vanadium nickel and sulfur concentrations v ni or v v ni and saturate biomarkers were used to classify the oils and source rocks based on inferred paleo redox environment lithology and maturity of the source rock oils are classified into five groups based on v ni ratios they appear to be related to variations in the paleo redox environment from suboxic dysoxic to anoxic suboxic of source rocks with variable lithological composition and organic matter input regardless of their maturity or biodegradation level these five groups are also classified based on biomarkers related to maturity organic matter type paleo redox environment and source rock lithology in source rocks vanadium nickel and sulfur concentrations together with v ni or v v ni ratios provide information about the paleo redox environment and are related to lithology regardless of their maturity these results also indicate variable paleo redox conditions during the sedimentation of venezuelan source rocks all this suggests that while the main source rocks in venezuelan basins are well established there are still uncertainties regarding their lateral and vertical variations in organic and inorganic facies and paleo redox conditions the presence of other source rocks contributing to the accumulation of hydrocarbons in the venezuela basins is also a possibility

formation of immature asphalt from organic rich carbonate rocks ii correlation of maturation indicators the present study focuses on some discrepancies among maturation indicators of the senonian bituminous rocks sbr in israel these rocks are mainly carbonates that were deposited under reducing conditions and contain heteroatom rich organic matter that has been severely reworked by bacteria in two cases heavy asphaltic oils are associated with the sbr and a genetic relation between them has been established whereas the time temperature index tti 3 and vitrinite reflectance r0 0 3 0 4 indicate early stage maturation the bitumen content up to 700 mg g corg 1 and the asphaltic oils imply an oil generation zone in the sbr other indicators such as isomerization of hopanes and steranes and cpi values indicate even higher maturation levels the discrepancies between these maturation indicators are explained by the different kinetic parameters of the maturation processes in the various constituents of the organic matter