metre scale cycles in shallow water carbonate successions milankovitch and stochastic origins metre scale cycles are a common feature in precambrian and phanerozoic shallow water carbonate successions and astronomically forced changes in sea level milankovitch cycles may have been an important driver controlling their deposition nevertheless the degree to which potentially low amplitude astronomically paced sea level oscillations may have controlled carbonate accumulation in deep time is unclear in this study a stochastic model of carbonate accumulation demonstrates how metre scale exposure bound sequences can be generated under conditions of random sea level change these sequences have characteristic durations close to milankovitch cycles despite the absence of any astronomical control on their formation metre scale sequences with sub milankovitch millennial scale durations can also be generated by the model potentially shedding light on the origin of sub milankovitch sequences such as those recorded on the middle triassic latemar platform of northern italy sensitivity tests demonstrate how shallow water carbonates may be very sensitive to weak i e low amplitude astronomically forced sea level oscillations notably strong statistical evidence p 0 01 for astronomical cycles can be preserved in modelled successions even when astronomical forcing contributes 1 of the sea level variance on million year timescales taken together metre scale cycles with milankovitch scale durations in ancient carbonate successions may reveal very little about the amplitude or even the existence of astronomical forcing as a sea level driver

tests of australian aerial radiometric data for use in petroleum reconnaissance recon exploration pty ltd has successfully completed initial testing of a new method for processing and interpretation of agso s australian geological survey organization formerly bureau of mineral resources aerial gamma ray spectrometer data for petroleum exploration in the canning basin western australia and the otway basin victoria count rate data for potassium and uranium were normalized to the thorium count rate for each sample to suppress unwanted effects of variations in surface lithology or soil type soil moisture vegetation cover and counting geometry the canning basin test area included five producing oil fields all except one clearly exhibit significant and characteristic radiometric anomalies which include negative normalized potassium and more positive normalized uranium values the otway basin test areas included ppl 1 commercial gas production which is associated with a group of significant radiometric anomalies similar to those in the canning basin these results are similar t

quantifying lateral heterogeneities in fluvio deltaic sediments using three dimensional reflection seismic data offshore gulf of mexico scale invariant statistics and strong anisotropy in rock properties are documented from well log and three dimensional seismic data in pleistocene fluvial and deltaic deposits in the eugene island 330 field gulf of mexico systematic quantification of lateral lithologic heterogeneity within a stratigraphic framework using reflection seismic data reveals that fluvial and deltaic depositional systems exhibit statistical behavior related to stratigraphic fabric well log and seismic data profiles show a decay in power spectra with wavenumber k according to k with between 1 and 2 3 vertical and horizontal well log data exhibit power law scaling behavior with between 1 and 2 horizontal seismic horizon slices were extracted from within fluvial and deltaic deposits seismic data from fluvial and deltaic deposits exhibit distinct differences in variance and each depositional system reveals directional anisotropy in one dimensional seismic data profiles from the fluvial deposit reveal anisotropy along depositional strike 1 1 and dip 2 2 the higher correlation observed in the direction of stratigraphic dip for the fluvial deposit may reflect the depositional fabric associated with channel systems correlation parameters obtained in specific depositional environments can potentially be used to quantify rock fabric and provide constraints in the modeling of sedimentary processes

exxon global cycle chart an event for every occasion the basic premise of the recent exxon cycle chart that there exists a globally correlatable suite of third order eustatic cycles remains unproven many of the tests of this premise are based on circular reasoning the implied precision of the exxon global cycle chart is not supportable because it is greater than that of the best available chronostratigraphic techniques such as those used to construct the global standard time scale correlations of new stratigraphic sections with the exxon chart will almost always succeed because there are so many exxon sequence boundary events from which to choose this is demonstrated by the use of four synthetic sections constructed from tables of random numbers a minimum of 77 successful correlations of random events with the exxon chart was achieved the existing cycle chart represents an amalgam of regional and local tectonic events and probably also includes unrecognized miscorrelations it is of questionable value as an independent standard of geologic time

low altitude aeromagnetic reconnaissance for petroleum in the arctic national wildlife refuge alaska variations in the earth s magnetic field arising from local concentrations of shallow subsurface magnetite were mapped in the arctic national wildlife refuge and elsewhere in northern alaska the anomalies were delineated with a magnetic horizontal gradiometer mounted on a low flying 300 ft or 90 m above ground fixed wing airplane limited data from stable carbon isotope and remanent magnetism measurements of rock cores from the cape simpson region strongly suggest that the magnetic anomalies result from the chemical reduction of iron oxides in the presence of seeping hydrocarbons the magnetic contrast between sedimentary rocks of normally low magnetic susceptibility and those locally enriched with this epigenetic magnetite results in distinctive high wavenumber and low amplitude total field anomalies magnetometers extended from each wing tip and in a tail stinger permit calculation of the resultant horizontal gradient vector relative to the flight path this calculation allows more meaningful interp

opal ct in chert beneath the toe of the tohoku margin and its influence on the seismic aseismic transition in subduction zones thick accumulation of chert is a ubiquitous feature of old oceanic plates at convergent margins in this study we investigate chert fragments recovered by the integrated ocean drilling program expedition 343 at the japan trench where the 2011 tohoku oki earthquake mw 9 0 occurred this sample provides a unique opportunity to investigate in situ chert diagenesis at an active subduction margin and its influence on the kinematics of megathrust faulting our mineralogical analyses revealed that the chert is characterized by hydrous opal ct and may therefore be highly deformable via pressure solution creep and readily accommodate shear strain between the converging plates at driving stresses of kilopascal order as chert diagenesis advances any further deformation requires stresses of 100 mpa given the increasing transport distances for solutes as represented in cherts on land the chert diagenesis is thus related to the mechanical transition from a weakly to strongly coupled plate interface at this margin

a study of the relationship between hydrocarbon migration and the precipitation of authigenic magnetic minerals in the triassic chugwater formation southern montana to test the hypothesis that hydrocarbons can cause the precipitation of authigenic magnetite hydrocarbon saturated bleached and unaltered samples of the chugwater red beds were examined using petrographic rock magnetic and paleomagnetic techniques samples were collected from the crest of red dome in carbon county montana where the chugwater is saturated with hydrocarbons and bleached around fractures the fractures formed during laramide deformation and provided conduits for oil migration the red beds contain triassic and rotated triassic magnetizations which reside in hematite the magnetization of the oil saturated sandstones predominantly resides in magnetite and there is some rock magnetic evidence for pyrrhotite the intensity of the natural remanent magnetization nrm in these sands is at least an order of magnitude less than that observed in the red beds a stable magnetic direction could not be isolated from the oil saturated sandstones petrographic studies indicate that both detrital and authigenic magnetite are present in the oil saturated sandstones the bleached specimens possess intermediate magnetic characteristics and contain abundant secondary authigenic specular hematite these specimens contain an early tertiary magnetization that resides in the authigenic hematite the chemical conditions created by the hydrocarbons caused the dissolution of the hematite which uncovered and relatively enhanced the magnetization residing in detrital magnetite it is also likely that hydrocarbons caused the precipitation of some authigenic magnetite and pyrrhotite the early tertiary magnetization in the bleached sandstones is interpreted to be of chemical origin and a byproduct of hydrocarbon migration at red dome the magnetization was probably acquired when the dissolved iron from the red beds precipitated as specular hematite the results of this study have implications for understanding hydrocarbon induced diagenesis and remagnetization mechanisms and for aeromagnetic hydrocarbon exploration

magnetic data processing for hydrocarbon exploration in the pannonian basin yugoslavia because magnetic minerals may directly indicate the presence of oil and gas deposits magnetic methods are applied to hydrocarbon exploration in oil bearing sedimentary basins the basic problem in applying these methods is the isolation of weak magnetic anomalies sourced by low concentrations of the magnetic minerals present these weak anomalies are often masked by much stronger magnetic anomalies caused by underlying magnetic rocks and or by rocks in the basin sediments weak local anomalies can efficiently be isolated by applying selective 1 d digital frequency filters the method of filtering has been checked by data obtained using simple models of magnetic sources and using a model representative of the local geology in our study area in the southern pannonian basin yugoslavia the magnetic field frequency content was analyzed by applying the power spectral density estimation using the maximum entropy method the digital filters were designed using the window function method the best results were

association between magnetic susceptibilities and hydrocarbon deposits in the barinas apure basin venezuela we have measured the magnetic susceptibility of 5425 drill cuttings coming from 20 oil wells distributed in eight fields of the petroliferous barinas apure basin barinas venezuela seeking evidence of magnetic anomalies associated with the presence of hydrocarbon deposits the rock samples are located between the near earth s surface and the basement s top approximately 4000 m in the magnetic susceptibility profiles we observed high magnetic susceptibilities at the top of the sedimentary units corresponding to reservoir and source rocks of oil producing wells whereas in the case of nonproducing wells we observed low magnetic susceptibilities a basic statistical analysis of the magnetic susceptibility measurements shows a significant difference between the mean values across producing and nonproducing wells at the correspondent oilrelated formations with a ratio of 4 1 of producing to nonproducing wells in the producing wells we have found a relation between the magnitudes of the magnetic susceptibility and the age of the formation the larger the magnetic susceptibility the younger the geological stratum the age and depth of the formations where the cuts were obtained exclude the presence of cultural human origin contamination of the samples suggesting the evidence of authigenic origin of the magnetic minerals due to the reductive effect of hydrocarbons in rocks

comparison between petroleum hydrocarbon concentrations and magnetic properties in chennai coastal sediments bay of bengal india abstract petroleum hydrocarbon concentrations phc of surface sediments along the chennai coast india were measured by uv fluorescence uvf spectroscopy and the results are expressed in terms of chrysene equivalents the concentration of phc in sediment varies widely from 1 88 ppm to 39 76 ppm as compared to the baseline 1 88 ppm with higher values obtained in the northern part of the study area the highest magnetic susceptibility 96 8 10 8 m 3 kg 1 value was determined from the chennai harbour area the magnetic parameters show that the chennai coastal sediments are dominated by ferrimagnetic minerals the positive correlation r 2 0 86 p arm and sirm covary with the petroleum hydrocarbon concentration suggesting that large amounts of magnetic minerals originate from anthropogenic activities it is evident that using magnetic measurements may be considered a simple rapid cheap and non destructive method to determine petroleum hydrocarbon concentrations in coastal sediments furthermore this technique may be applied to petroleum exploration studies magnetic susceptibility measurements in sediments have been proposed as complementary or alternative means of exploration and assessment of hydrocarbon reservoirs

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

power spectrum of sea level change over fifteen decades of frequency 1 the power spectrum of relative sea level change has been estimated over more than 15 orders of magnitude in frequency from a frequency of 1 591 ma to a frequency of 1 5 s although there are still regions of the spectrum where data sampling and duration do not allow the power to be calculated most notably between periods of 100 1000 years the general shape of the spectrum is that in which the power depends on the square of the reciprocal frequency apart from periods between 1 and 100 years where the power spectrum falls off less steeply with increasing frequency a spectrum in which power depends on reciprocal frequency squared is the same spectrum as that calculated from a random walk signal of finite length there are some causes that have defined frequencies such as those associated with tides and the milankovitch cycles of the ice ages but there is also a continuum of relative sea level change that requires other causes the implications of this are discussed in the light of global change and heating of the lithosphere from the bottom

climatic and tectonic sea level gauge for midcontinent pennsylvanian cyclothems new sedimentological determinations suggest that pennsylvanian sea level change ranged from as little as 40 m to as much as 160 m depending on which model establishes the deepest water facies of a midcontinent cyclothem average sedimentological estimates of sea level change for models of heckel and gerhard are 96 4 m and 86 0 m respectively in the midcontinent tectonic subsidence contributed 5 to 20 of the total pennsylvanian sea level change in platform areas and basin depocenters additional change in sea level was controlled by short term glacial eustasy nearly 70 of sea level change and long term climate change nearly 15 of sea level change these findings suggest that away from orogenic belts climatic change is the principal driving mechanism controlling sea level change whereas within orogenic belts climate becomes more subordinate to tectonic processes that influenced pennsylvanian sea level change even though indicators of climatic change reportedly are preserved

analysis of light hydrocarbons in soil gases lost river region west virginia relation to stratigraphy and geological structures analyses of 471 near surface soil gas samples for light hydrocarbons c1 c4 c2l c3l and h2 from the lost river gas field in hardy county west virginia reveal sites or clusters of sites containing anomalously high concentrations of light hydrocarbon gases which occur directly over the faulted eastern limb of the whip cove anticline compositional changes in the soil gases data clearly define major changes in the maturity and locations of potential source beds grids placed on botanically defined anomalies confirm a possible correlation between these two independent indicators statistical analysis shows that samples from 45 sites contain anomalously large concentrations of light hydrocarbons in the soil gas constituents large concentrations coupled with high saturate to olefin ratios further confirms that this active seepage is near macroseep levels variations in soil gas compositional trends separate the soil gas data into two domains with oilier compositions to the west and gassier compositions to the east although the composition of the shallow soil gases above the lost river gas field are oilier than the reservoir gases they occur directly over the eastern faulted limb of the producing anticlinal structure suggesting that the dry gases from the oriskany reservoir are probably mixed with oilier gases from organic rich strata among devonian shales the eastern anomalies are much gassier and are very similar to the oriskany gases produced by the lost river gas field the eastern anomalies directly overlie near vertical beds of devonian and older age formations that are likely conduits for deeper mature thermal gases

origin of the pennsylvanian coal bearing cyclothems of north america past controversy about the tectonic or eustatic origin of pennsylvanian cyclothems is resolved by regional basin subsidence analysis global paleoclimate paleogeography and plate tectonic evolution differences between marine carbonate kansas type cyclothems of the northern midcontinent and nonmarine clastic appalachian type cyclothems of the eastern united states are controlled by laterally changing flexural deformation during plate accretion into a supercontinent coupled with superposed glacial eustasy kansas type cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of north american margins these cycles are eustatic characterized by a periodicity comparable to milankovitch orbital parameters appalachian type cyclothems accumulated in response to episodic thrust loading during plate collisions that developed a series of flexurally deformed wide and shallow resurgent foreland basins this resurgent foreland basin evolution during paleozoic time increased crustal rigidity in the appalachians thus yoking the appalachian and illinois basins during pennsylvanian time with each thrust load foreland basin deepening favored transgressive cyclothem facies which changed to a regressive facies because sediment yield increased as denudation rates increased off uplifted orogens illinois type cyclothems are intermediate between the two end member processes of flexural tectonics and glacial eustasy characterizing appalachian type and kansas type cyclothems respectively thus the pennsylvanian coal bearing cyclothems of north america owe their origin to the remarkable coincidence of supercontinent development concomitant glaciation and eustatic sea level change and associated episodic thrust loading and foreland basin subsidence of small magnitude on progressively more rigid crust

fluid transport properties in sediments and their role in large slip near the surface of the plate boundary fault in the japan trench abstract fluid transport properties such as permeability and porosity are significant parameters that affect earthquake generation we measured the transport properties of shallow sediments sampled around the plate boundary near the japan trench during iodp expedition 343 at confining pressures up to 40 mpa the permeabilities of samples from the shallow plate boundary fault were very low at 10 20 m 2 equivalent to a hydraulic diffusivity of 10 10 m 2 s 1 permeability and porosity in the core of the fault zone at the plate boundary were lower than those in the immediately overlying sediments and the surrounding intact sediment suggesting that the plate boundary fault can act as a barrier for fluid flow low permeability and high pore compressibility in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating even when the initial shear stress is low our investigation supports the hypothesis that thermal pressurization on the fault plane helped facilitate the extremely large slip in the shallow part of the subduction zone during the tohoku earthquake as the fault zone has a lower permeability than the surrounding sediments and a higher clay content pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust which does not affect pore pressure at depth in the fault zone although there are many possible mechanisms of fault weakening thermal pressurization can act relatively efficiently as slip begins even at shallow depths therefore our results support the role of thermal pressurization in shallow slip during the tohoku earthquake

observed relation of soil magnetic susceptibility and soil gas hydrocarbon analyses to subsurface hydrocarbon accumulations magnetic susceptibility ms studies on soils over 19 oil and gas fields showed anomalously large amounts of diagenetic magnetic minerals in shallow depth samples in about 89 of the cases tested soil ms anomalies were compared with soil gas hydrocarbon ghc anomalies over 12 oil and gas fields including several stratigraphic traps and one gas storage reservoir samples were collected along the same profiles six examples are presented with detailed data listings our goal is to test the utility of soil magnetic susceptibility and soil gas hydrocarbons as petroleum prospecting methods we emphasize statistical evaluation of anomalies and their empirical correlation with producing areas and leads identified by other geochemical geological or geophysical data for direct comparison of anomaly strengths data are expressed statistically in terms of the appropriate background mean and standard deviation soil ms and soil ghc data complement each other providing better guidance to productive areas than either data set alone when used in an integrated exploration program their combined positive evidence of hydrocarbon presence under prospects could result in fewer dry holes than when drilling with structural information only

integration of geologic geochemical and geophysical data of the cement oil field oklahoma using spatial array processing geologic geochemical and geophysical measurements were made at the cement oil field oklahoma test site using airborne and spaceborne sensors coupled with ground based data collection the data collected include 1 airborne gamma ray spectrometry 214bi 208tl 40k and total intensity channels 2 low altitude aeromagnetic profiles 3 precision gravity measurements 4 images from the landsat multispectral scanner mss systems and u 2 photography and 5 geologic and topographic maps in order to reduce analyze display and correlate the information it was necessary to transform the data from vector space to raster space a two dimensional image array with fixed resolution and array dimension with the data in array form spatial array processing techniques were applied to 1 correct geometrically the data for proper registration 2 perform areal interpolation and smoothing 3 display the data as images and 4 perform integration and correlation studies each data set was transforme

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

origin of magnetization in the phosphoria formation at sheep mountain wyoming a possible relationship with hydrocarbons hydrocarbon impregnated fenestral dolomites of the phosphoria formation were sampled on both flanks of sheep mountain anticline wyoming demagnetization results indicate one dominant component that is either synfolding laramide in age or predates folding cretaceous in age thermal demagnetization yields stable decay to temperatures between 500 c and 550 c and rock magnetic experiments suggest that the magnetization is dominated by a low coercivity component magnetic extracts contain spheres 15 diameter as well as other authigenic forms energy dispersive analysis demonstrates that fe is the only detectable element present in the spheres and x ray diffraction analysis indicates that magnetite is present in the extracts the spheres are interpreted to be authigenic magnetite the magnetization is interpreted as a chemical remanent magnetization crm residing in this authigenic magnetite chemical conditions created by the hydrocarbons may have caused precipitation of the authigenic magnetite and acquisition of the associated crm

evidence for a relationship between hydrocarbons and authigenic magnetite establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to 1 elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite 2 developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods and 3 evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool the direct association of hydrocarbon migration and the precipitation of authigenic magnetite has however not been established in this paper we report palaeomagnetic rock magnetic petrographic and geochemical results of a study of samples from permian spelebthems and gilsonite found in the ordovician arbuckle group in southern oklahoma the results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic magnetite

a shallow strong patch model for the 2011 great tohoku oki earthquake a numerical simulation 1 a numerical simulation is conducted for understanding the mechanics of the 2011 great tohoku oki earthquake mw 9 0 which widely broke the plate interface at the pacific plate subducting beneath northern honshu tohoku japan in the model frictional stress on the plate interface is assumed to obey a rate and state dependent friction law a strong patch asperity with higher effective normal stress and a large value of characteristic slip distance is assumed at a shallower part of the plate interface this strong patch controls the occurrence of great earthquakes that broke the entire seismogenic plate interface with recurrence intervals of several hundred years the present model explains large coseismic slip at a shallower part of the 2011 great earthquake and accumulation of slip deficit at deeper parts where smaller m7 class earthquakes repeatedly occurred before the great earthquake

lava flows are fractals we have conducted a preliminary investigation of the fractal nature of the plan view shapes of lava flows in hawaii based on field measurements and aerial photographs as well as in idaho and the galapagos islands using aerial photographs only our results indicate that the shapes of lava flow margins are fractals in other words lava flow shape is scale invariant at least within the range of scale measured 0 5m to 2 4km this observation has important implications for understanding the fluid dynamics of lava flows it suggests that nonlinear forces are operating in them because nonlinear systems frequently produce fractals furthermore a a and pahoehoe flows can be distinguished by their fractal dimensions d the majority of the a a flows we measured have d between 1 05 and 1 09 whereas the pahoehoe flows generally have higher d 1 14 1 23 we have extended our analysis to other planetary bodies by measuring flows from orbital images of venus mars and the moon all are fractal and have d consistent with the range of terrestrial a a and pahoehoe values combining the terrestrial and extraterrestrial data the fractal nature of lava flow outlines holds for over five orders of magnitude in scale 0 5m to 60km

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

combining gps and repeating earthquakes for a high resolution analysis of subduction zone coupling abstract increasingly complex spatiotemporal patterns of subduction zone coupling are being revealed by geodetic and seismic observations understanding the mechanisms which control it is useful for improving seismic hazard assessments gps and characteristically repeating earthquakes cres are complementary datasets for monitoring aseismic slip here both of them are combined to estimate the rate and distribution of creep on the northeast japan subduction zone between 21 march 1996 and 24 september 2003 we find that the majority of the upper part at 0 30 km depth remains locked there are three regions creeping at 7 8 cm yr distributed along strike at 40 70 km depth we observe that these creeping regions occur in areas of low effective pressure and reduced porosity which are inferred from vp and vs velocities moreover an area of high clay content and high effective pressure coincides with the rupture area of the tohoku oki earthquake we discuss these results in the context of potential mechanisms governing creep in northeast japan our results highlight the benefits of combining gps and cres for advancing our understanding of the seismic cycle in subduction zones

correlating biodegradation to magnetization in oil bearing sedimentary rocks abstract a relationship between hydrocarbons and their magnetic signatures has previously been alluded to but this is the first study to combine extensive geochemical and magnetic data of hydrocarbon associated samples we report a detailed study that identifies a connection between magnetic mineralogy and oil biodegradation within oil bearing sedimentary units from colombia canada indonesia and the uk geochemical data reveal that all the oil samples are derived from mature type ii kerogens deposited in oxygen poor environments biodegradation is evident to some extent in all samples and leads to a decrease in oil quality through the bacterially mediated conversion of aliphatic hydrocarbons to polar constituents the percentage of oil components and the biodegradation state of the samples were compared to the magnetic susceptibility and magnetic mineralogy a distinct decrease in magnetic susceptibility is correlated to decreasing oil quality and the amount of extractable organic matter present further magnetic characterization revealed that the high quality oils are dominated by pseudo single domain grains of magnetite and the lower quality oils by larger pseudo single domain to multidomain grains of magnetite and hematite hence with decreasing oil quality there is a progressive dominance of multidomain magnetite as well as the appearance of hematite it is concluded that biodegradation is a dual process firstly aliphatic hydrocarbons are removed thereby reducing oil quality and secondly magnetic signatures are both created and destroyed this complex relationship may explain why controversy has plagued previous attempts to resolve the connection between magnetics and hydrocarbon deposits these findings reinforce the importance of bacteria within petroleum systems as well as providing a platform for the use of magnetization as a possible exploration tool to identify subsurface reservoirs and a novel proxy of hydrocarbon migration

chemical and microbial processes causing anomalous magnetization in environments affected by hydrocarbon seepage aero magnetic anomalies have been reported from several commercial hydrocarbon accumulations however the processes responsible for such anomalies are relatively poorly understood this paper conceptually discusses chemical and microbiological processes involved in generating anomalous magnetization related to hydrocarbon accumulations including hydrocarbon seepage environments based on thermodynamic criteria and microbiologic activity the formation and destruction of magnetic mineral assemblages can be predicted under the influence of hydrocarbons magnetite and pyrrhotite are the most important magnetic minerals formed and the most abundant magnetic mineral destroyed is hematite hence the invasion of hydrocarbons may result in positive absent or negative magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending upon the amounts of authigenic magnetite and pyrrhotite formed relative to the amounts of hematite destroyed magnetism may be generated al

multifractal and white noise evolutionary dynamics in jurassic cretaceous ammonoidea for more than a decade there has been interdisciplinary debate on whether fossil origination and extinction time series show evidence of self organized criticality soc or some other more complex hierarchical structure analyses of a new data set of jurassic and cretaceous ammonoid genera demonstrate that these taxonomic subgroups do not reproduce the patterns seen in larger data sets that pool disparate taxa rather originations and extinctions in these ammonoids show no evidence of soc limited evidence for a hierarchical multifractal pattern and at least within the suborder ammonitina evidence consistent with a white noise signal although a white noise pattern has been identified previously in an ammonoid family diversity time series the significance of such a result for ammonoid genus originations and extinctions is discussed here for the first time this white noise pattern indicates that processes acting on short time scales less than a few million years dominate the ammonitina origination and extinction records producing a nonhierarchical diversity dynamic because origination events in one interval do not appear to trigger originations in subsequent intervals ammonite evolutionary radiations were likely to be extremely rapid and driven by physical rather than biological opportunities for diversification

are topographic data sets fractal the scale invariant properties of fractal sets make them attractive models for topographic profiles because those profiles are the end product of a complex system of physical processes operating over many spatial scales if topographic data sets are fractal their power spectra will be well represented by lines in log log space with slopess such that 3 s 1 the power spectra from a digital elevation model 30 meter sample spacing of the sierra nevada batholith and from seabeam center beam depths 425 meter sample spacing along a flowline in the south atlantic are curved straight sections in the spectra can be identified but the slopes of those sections are strongly dependent upon the particulars of the data analysis fractal geometry must be used with caution in the discussion of topographic data sets

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

pore pressure distribution along plate interface that causes a shallow asperity of the 2011 great tohoku oki earthquake 1 kato and yoshida 2011 conducted a numerical simulation for understanding the mechanics of the 2011 tohoku oki earthquake in this model a strong asperity with higher effective normal stress was assumed at a shallower part of the plate interface this shallow strong asperity controls the occurrence cycle of great earthquakes the present paper discusses pore pressure distribution along the interface at the pacific plate subducting beneath northern honshu tohoku japan assuming that the permeability is exponentially dependent on effective stress and that the proportional constant drops to a lower value at a critical effective stress due to pore collapse we obtained nearly hydrostatic pore pressure at a shallow part and nearly lithostatic pressure at a deep part of the plate interface assuming a different permeability model in which increase of confining pressure has a larger effect than decrease of pore pressure we obtained similar results such pore pressure distributions provide a possible generation mechanism for a shallow strong asperity

melting and seismic structure beneath the northeast japan arc transportation of h2o associated with subduction of the pacific plate beneath the northeast japan arc is modeled to predict distribution of aqueous solution and melt and the consequent p wave velocity structure the observed velocity structure coincides well with the model for equilibrium transport of h2o most of h2o subducted is brought down to 150 200 km depth along the slab then the aqueous fluid generated ascends to initiate melting which explains the low velocity regions 6 reduction observed beneath the backarc rather than beneath the volcanic front if equilibrium transport of h2o occurs initiation of melting beneath the backarc with deep subduction of h2o is likely to be the case also for other subduction zones with slabs older than several tens of m y cold enough to stabilize serpentine to a great depth

deposition of magnetic pyrrhotite during alteration of crude oil and reduction of sulfate abstract crude oil seepage is widespread in carbonate cap rock and in overlying sediments of the damon mound salt dome brazoria county texas scanning electron microscopy of calcite lined cavities provides insight to the latest stage of mineral deposition in this salt dome environment solid crude oil residues and microbes occur in association with surface minerals such as gypsum and barite deposition of pyrrhotite pyrite marcasite sphalerite and elemental sulfur is attributed to microbial sulfate reduction and deposition of aragonite and calcite is related to microbial oxidation of crude oil hydrocarbons the c1 c4 hydrocarbons in pyrrhotite bearing cap rock samples are a biodegraded residue derived from crude oil higher molecular weight crude oil components in cap rock are altered by water washing and to a lesser extent by biodegradation hydrocarbon compositions could be explained by limited aerobic biodegradation but a component of anaerobic biodegradation cannot be excluded some damon mound samples are highly magnetic because of abundant ferrimagnetic pyrrhotite this study provides new evidence of a link between crude oil migration microbial activity and diagenetic magnetic anomalies in rocks

combined geological and surface geochemical methods discovered agaritta and brady creek fields concho county texas from december 1987 to march 1991 25 prospects in the lower king sand upper pennsylvanian cisco play in concho county texas were tested by several operators they used combinations of subsurface geology reconnaissance airborne gas sensing surface radiometrics soil magnetic susceptibility and soil gas hydrocarbon measurements to define prospects six new king sand discoveries or extensions and three deeper goen discoveries resulted in a 36 exploratory success rate the total exploration and development cost was approximately 0 67 bbl of proven producing oil reserves final locations for the discovery wells on each of the nine successful prospects were selected primarily on the basis of combined subsurface geology and surface geochemical data as examples we present information about the discovery of brady creek and agaritta fields agaritta field is one of the two largest of the new field discoveries with estimated proven producing recoverable reserves of 6 million bbl of oil its discovery was based on a combination of 1 regional subsurface geologic projection 2 airborne hydrocarbon sensing 3 interstitial soil gas hydrocarbon data 4 soil magnetic susceptibility measurements and 5 surface potassium and uranium concentrations measured by gamma ray spectrometry

data processing and recognition of seepage and microseepage anomalies of acid extractable hydrocarbons in the south slope of the dongying depression eastern china abstract the successful use of near surface anomalous signals exhibited in all petroliferous basins must lead to great development in petroleum exploration the elementary equations and methods for objective and accurate separation of anomalous signals from background signals are the most critical requirements in these surface geochemical surveys therefore we have worked up a series of fundamental equations and methods for eliminating surface interference and influences of geological conditions on anomaly intensities and recognizing multi type anomalies of uni and multi variates by using statistics fractal geometry wavelet analysis and artificial neural networks these equations illustrate that the threshold i e the boundary between background and micro seepage anomalies is determined by means standard deviations and prior probabilities of background and micro seepage anomalies when multi normality is met and that the traditional equation for the threshold background mean plus one or two standard deviations is not correct in the face of many new equations and methods it is important how to comprehensively use them to resolve the problems in geochemical surveys a geochemical survey in the south slope of the dongying depression eastern china provides a good opportunity to address this issue the anomalies obtained with the traditional equation do not reflect oil gas fields this study reveals three problems in the previous data processing and anomaly recognition 1 the surface interference caused by the variation of soil composition was not identified and removed 2 the influence of caprock thickness on anomaly intensities was not revealed and eliminated and 3 the micro seepage related to oil gas pools and seepage related to faults anomalies were not separated and correctly recognized furthermore the interaction of these problems makes the data processing and anomaly recognition more difficult to ensure effective elimination of the surface interference and caprock thickness influence and correct recognition of uni variate anomalies we iteratively applied the wavelet analysis based methods to eliminate the surface interference and caprock thickness influence and statistical methods with new fundamental equations to recognize uni variate anomalies of seepage and microseepage and then multi variate anomalies of seepage and microseepage were recognized with our fundamental equations and the corresponding methods in the results the seepage anomalies display a string bead shaped pattern and are distributed along faults and the micro seepage anomalies are ring shaped and coincide with oil gas pools sandbodies or traps therefore reprocessing of geochemical data with our fundamental equations and methods combined in an iterative manner can resolve the complicated problems in data processing and anomaly recognition and thus greatly improve the predictive capability of surface geochemical survey

glacial eustatic sea level curve for early late pennsylvanian sequence in north central texas and biostratigraphic correlation with curve for midcontinent north america at least 30 transgressive regressive cycles of deposition are recognized from the upper desmoinesian east mountain shale to the mid virgilian wayland shale in north central texas maximum regressive deposits are typically paleosol mudstones and fluvial sand stones maximum transgressive deposits are typically widespread ammonoid bearing conodont rich dark phosphatic shales in more major cycles and persistent fossiliferous shales or limestones overlying terrestrial deposits in more minor cycles delta complexes dominate the regressive sequences of many cycles using biostratigraphic criteria of first last sole or acme occurrence of ammonoid conodont and fusulinid taxa we correlate 17 cycles in the texas sequence directly with 17 glacial eustatic cycles of similar magnitude in the northern midcontinent this correlation suggests that glacial eustacy was the basic control over the cyclic sequence in texas that tectonic masking of the eustatic signal by nearby orogenic movement in texas was negligible and that delta shifting though conspicuous was only a secondary control over the cyclicity there minor cycles recognized between the correlated cycles also match well enough between texas and the midcontinent to further discount potential tectonic or deltaic masking of glacial eustatic cyclicity this strengthens the likelihood of correlating glacial eustatic events across larger parts of north america and perhaps with other parts of the world

glacier fed sandstone sheets in the weller coal measures permian allan hills antarctica abstract the upper member of the weller coal measures permian at allan hills victoria land antarctica consists of repetitive coal layers separated by sheetlike bodies of predominantly sandstone and subordinate siltstone and conglomerate all of fluvial origin investigation of the lowermost inter coal sheet wc1 reveals abrupt planar basal contacts persistent upward fining and a strong westward palaeocurrent trend three lithofacies are recognized in the wc1 sheet a small scale cross bedded pebbly sandstone which occupies most of the basal portions of the sheet b large scale cross bedded medium coarse sandstone confined to a linear ne sw belt overlying or locally replacing facies a and c siltstone and rippled fine grained sandstone which drapes and overlaps facies a and b and contains glossopteris leaves and vertebraria root traces facies distribution patterns indicate the wc1 body initiated as an abrupt sheetlike incursion of coarse sediment over a low lying mire facies a followed by entrenchment and confinement of flow as the sheet extended distally facies b facies c represents low energy floodplain sedimentation co existing with and later succeeding facies b as deposition evolved toward abandonment and eventual renewal of peat deposition relatively rapid deposition of the sandstone sheet is implied by the lack of any significant hiatus markers outsized clasts up to 45 cm in diameter one observed to display prominent striations occur sporadically throughout the wc1 including within siltstone beds of facies c these are inferred to be ice rafted deposits which together with other evidence suggest meltwater influence possibly glacial on sediment transport and deposition preliminary examination of other sandstone sheets in the upper weller indicates attributes similar to the wc1 including abrupt bases upward fining character and predominantly westward palaeocurrent patterns the allan hills exposures are believed to represent a succession of low lying mire complexes interrupted by abrupt but infrequent incursions of coarse sediment possibly by extreme meltwater floods

pennsylvanian cyclothems methods of distinguishing tectonically induced changes in sea level from climatically induced changes analysis of tectonic subsidence permits calculation of the magnitude of tectonic processes and associated climatic effects which controlled changes in sea level during deposition of pennsylvanian cyclothems far field tectonic effects in response to regional orogenic movements influenced pennsylvanian sea level change in the midcontinent of north america and the illinois basin organization of virgilian and missourian midcontinent cyclothems into fourfold to fivefold bundles shows that sea level changes in midcontinent platform areas were influenced partly by milankovitch orbital parameters whereas desmoinesian sea level change apparently was influenced more strongly by tectonic subsidence sea level change associated with cyclothems in the central appalachian basin and the asturias basin of spain were controlled mostly by foreland basin subsidence and later strike slip faulting methods developed herein permit calculation of magnitudes of both tectonic and glacio eustatic components of sea level change influencing pennsylvanian cyclothem deposition and may be applicable to other cyclic sequences

magnetotactic bacteria and single domain magnetite in hemipelagic sediments remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time scale study geomagnetic reversals and secular variation and measure the rates of seafloor spreading although these sediments may contain different magnetic minerals magnetite is the most commonly observed and magnetically stable phase and its size shape and post depositional fate affect the magnetic remanence of the sediments biogenic magnetites are single domain with a high natural magnetic remanence nrm and have been suggested as a significant source of magnetic remanence in marine sediments we have studied surface sediments from the santa barbara basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra fine grained single domain magnetite using a novel extraction technique transmission electron microscopy and squid magnetometry we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments

thrust fault nucleation due to heterogeneous bedding plane slip evidence from an ohio coal mine abstract shales often form the roof and floor rocks of coal mines in the appalachian basin from a geologic perspective these mines offer outstanding 3d exposures of fresh rocks otherwise only accessible via boreholes or heavily weathered surface outcrops and present an excellent opportunity to directly observe pristine in situ natural fractures in shale in carroll county ohio small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal shale contacts are steepest causing ground instability we hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state resulting in localized thrust fault development using borehole and in mine survey data we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations our modeling results suggest that inherited non planarity of contact surfaces influenced the nucleation of secondary faults simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures for mining purposes recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards

the impact of climate change tectonism and hydrology on the formation of carboniferous tropical intermontane mires the springhill coalfield cumberland basin nova scotia abstract both climate and tectonism are influential in determining basin and mire hydrology in the rapidly subsiding intermontane basins of euramerica which formed in response to the variscan hercynian alleghenian orogeny however the record of climate change has been muted and may therefore go unrecognized the complex interplay of climate and tectonism in a tropical continental setting is recorded in the 4 km thick westphalian a b fill of the cumberland basin thick peat accumulation was favoured at the southern basin margin where rheotrophic forested mires 4 9 km wide flourished between basin axis rivers and coalesced alluvial fans derived from the cobequid highlands as a result of their geomorphic setting the thicker coals 4 3 m exhibit distinct areal zones piedmont inner mire and riverine evidence that the forest swamps were nourished both by rainfall and by groundwater discharge from alluvial fans includes the stratigraphic affinity of thick coals and basin margin conglomerates interfingering of distal fan sheetflood and mire deposits petrographic evidence of elevated ph partial gelification of tissues and predominance of the arboreous lycopsids lepidodendron and paralycopodites whereas such groundwater supply is crucial to maintenance of modern wetlands in drier periods a subhumid climate is implied coals at joggins further removed from groundwater discharge at the basin margin are less well developed a 600 m thick coal window within the fining and reddening upward basin fill sequence at springhill is inferred to represent a coincidence of optimal groundwater supply and net subsidence the ultimate decline of peat accumulation in the basin may reflect decrease in catchment area and fan size and loss of rainshadow as the cobequid massif was denuded and the basin filled the coal window ca 6 9 10 5 yr is punctuated by non marine cyclothems of coal grey sideritic mudrock and multistorey sandstone that share similar time frames with astronomic cycles of axial precession ca 1 4 10 4 yr the stress of related climate change is inferred to have caused peat accumulation to fall into disequilibrium with sediment flux and basin subsidence the late quaternary history of certain african mires illustrates the dramatic impact of climate change especially temperature and seasonality and orographic effects on tropical continental peat accumulation aspects of the groundwater recharge model may be applicable to the westphalian stephanian intermontane mires of spain and mesozoic coal basins of northern china

sedimentary cyclicity in the marine pliocene pleistocene of the wanganui basin new zealand sequence stratigraphic motifs characteristic of the past 2 5 m y earth s climatic history since 2 5 ma has been controlled by milankovitch variations in the planetary orbit comprising alternate periods of glaciation and interglaciation with a dominant frequency of 41 000 yr concomitantly eustatic sea level has fluctuated 70 to 130 m causing rapid transgressions and regressions of the shoreline across the world s continental shelves the resulting sedimentary record is cyclothemic each cyclothem corresponding to a single climate and sea level cycle the wanganui basin new zealand contains a 2 km thick almost complete composite record since isotope stage 100 ca 2 5 ma in the form of 47 superposed cyclothems of shelf origin each cyclothem corresponds to an unconformity bound stratigraphic sequence and typically contains a transgressive systems tract sometimes a mid cycle shell bed a highstand systems tract and sometimes a regressive systems tract no advantage accrues from using transgressive regressive units rather than cyclothems and or sequences in description of the succession six basic sequence motifs represent deposition in locations between the shoreline and offshore shelf i e the hawera birdgrove turakina seafield castlecliff and rangitikei motifs a seventh the nukumaru motif which includes dominant coquina limestone represents deposition in shallow water areas of reduced terrigenous sediment on the flank of the basin the sequence motifs represented in any section change systematically in sympathy with basin scale changes in subsidence and sediment supply in contrast with the 41000 year length of individual glacioeustatic sequences these basin wide tectonic cycles have a periodicity of many hundreds of thousands to a few million years i e that of third or fourth order sequences of the exxon type this coupled with the restriction of strongly cyclothemic sediments to geological periods of known glacio eustasy permiancarboniferous pliocene pleistocene suggests that tectonic subsidence cycles rather than glacio eustasy are the driving forces behind the development of the third and fourth order unconformity bound sequences that are reported to occur throughout the stratigraphic record

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

a statistical and graphical workflow for the analysis of magnetic susceptibility data from drill cuttings in a hydrocarbon exploration setting abstractwe have analyzed the magnetic susceptibility measurements for more than 5000 samples of drill cuttings from oil gas wells in the venezuelan oil fields to facilitate information extraction and improve data presentation including the determination of threshold values used in hydrocarbon exploration the values for each well typically ranged over several orders of magnitude we have developed a new scale called the magnetization contrast magnitude scale m based on a logarithmic transformation of to better represent the data collectively the m data appear to be influenced by more than one process source resulting in skewed bimodal distributions with a significant degree of overlap between the individual modes each mode or subpopulation of the m data could be modeled with a lognormal distribution we have determined that a method based on normal probability plots could be used to decompose the observed bimodal distributions into their individual components and to obtain initial estim

magnetic forward models of cement oil field oklahoma based on rock magnetic geochemical and petrologic constraints magnetic forward models of the cement oil field oklahoma were generated to assess the possibility that ferrimagnetic pyrrhotite related to hydrocarbon seepage in the upper 1 km of permian strata contributes to aeromagnetic anomalies at cement six bodies having different magnetizations were constructed for the magnetic models based on geology and on petrologic and geochemical results supplemented by rock magnetic measurements of shallow core and outcrop samples the column of rock through which hydrocarbons have passed is divided into three sulfide zones on the basis of pyrrhotite content and the column is capped by a 30 m thick zone that contains ferric oxide minerals formed mainly from oxidized pyrite red beds unaffected by sulfidization as well as a zone of rock depleted in hematite but lacking sulfide surround sulfidic zones the synthetic magnetic profiles are controlled mainly by pyrrhotite bearing strata at depths of 200 500 m the magnetizations of these bodies are calculated from 1 pet

relationship between magnetic anomalies and hydrocarbon microseepage above the jingbian gas field ordos basin china in this study soil magnetic measurements susceptibility and hysteretic parameters and soil hydrocarbon analyses were conducted on samples from three profiles profiles i and ii run across and profile iii runs parallel to the trend of the jingbian gas field in the ordos basin central china to determine the relationship between the magnetic anomalies e g volume specific magnetic susceptibility k and the hydrocarbon seepage environments the results document a strong correlation between magnetic susceptibility and soil gas hydrocarbon concentration furthermore the spatial distribution of k and hydrocarbon anomalies correlate with those of the gas field in addition magnetic minerals in the soils with higher susceptibility are predominantly magnetite with little or no substitution of titanium compared to that of samples with lower susceptibility 7 105 si international unit of susceptibility these results provide strong evidences for the formation of highly magnetic minerals in close association with hydrocarbon seepage recognition of such seepage induced magnetic anomalies can be used to facilitate the exploration for oil and gas in china and elsewhere

causes and spatial distribution of anomalous magnetization in hydrocarbon seepage environments in diagenetic environments containing hydrocarbons the most important magnetic minerals formed appear to be magnetite and pyrrhotite whereas the most important magnetic mineral dissolved or replaced is hematite hence hydrocarbon seepage and migration may result in positive absent or negative anomalous magnetization magnetic contrasts relative to the total magnetization prior to hydrocarbon invasion depending on the amounts of magnetite and pyrrhotite formed relative to the amounts of hematite destroyed where anomalous magnetization is formed by hydrocarbon seepage the magnetic contrasts are located in relatively reducing geochemical plumes such plumes are located above leaking subsurface hydrocarbon accumulations if buoyancy is the predominant driving force for hydrocarbons commonly however migration of the escaping hydrocarbons is dominated by advection hydrocarbon seepage therefore may be vertical or may have any direction other than vertical depending on the position of the leaking hydrocarbon accumulation in the prevailing flow system and on the distribution of high permeability pathways such as carrier beds and faults in these cases magnetic contrasts are deflected or displaced and they are not likely to be vertically above the hydrocarbon source anomalous magnetization magnetic contrasts has been documented from some hydrocarbon seepage environments and can be used for hydrocarbon exploration in association with other surface exploration methods similar magnetic contrasts should also be detectable in core and could be used for evaluation of subsurface proximity to hydrocarbon traps the magnitude and spatial distribution of such magnetic contrasts whether at the surface or in the subsurface depend on geochemical microbial geophysical sedimentologic and hydrogeologic processes these factors must be taken into consideration in aeromagnetic and ground based prospecting for hydrocarbons in particular the use of anomalous magnetization as an exploration tool should always be accompanied by a hydrogeologic study the results of this study suggest that magnetic contrasts could also be used in environmental studies for example to detect hydrocarbons leaking from storage tanks or waste disposal sites on the other hand magnetic contrasts may be generated also by natural and anthropogenic processes that have no genetic relationships to hydrocarbons consequently anomalous magnetization may or may not be genetically related to natural or anthropogenic hydrocarbon accumulations

remote sensing detection of heavy oil through spectral enhancement techniques in the western slope zone of songliao basin china landsat 7 enhanced thematic mapper plus etm imagery was used to identify anomalous areas caused by hydrocarbon leakage in fula erji in the western slope of songliao basin china three image enhancement techniques including principal component analysis pca band ratioing and false color composition fcc were used based on the spectral characteristics of hydrocarbon induced minerals and the eigenvectors of pca the best four principal components pcs 1345 pc3 the third component of the pca on bands 1 3 4 and 5 1357 pc3 3457 pc4 and 123457 pc4 were selected for fcc combined with band ratios of 3 1 4 3 and 7 5 according to the tonal characteristics of the surface near wells and their visual expression four fcc images were acquired for hydrocarbon induced area delineation the result indicates that anomalies are expressed as a faint tone blob and are mostly located in the holocene sediments an analysis of two cross sections traversing the identified anomalies suggests that they are closely related to the anomalous area interpreted from the four fcc images field data of magnetic susceptibility and delta carbonate are consistent with the distribution of the tonal anomalies and suggest a positive spatial association between the identified anomalous area and the hydrocarbon leakage environment

borehole magnetostratigraphy absolute age dating and correlation of sedimentary rocks with examples from the paris basin france total and cea have conceived and developed two new logging tools which allow continuous precise and accurate in situ magnetic measurements within weakly magnetized sedimentary rocks encountered in uncased industry drilled wells the combination of these magnetic measurements permits for the first time continuous determination of natural remanent magnetization nrm polarities occurring in the logged section the resulting well magnetostratigraphic sequence wms which may be recognized from well to well magnetostratigraphic correlations may also be correlative to a geomagnetic polarity time scale gpts or reference magneto stratigraphic scale rms given adequate dating tie points and lack of noticeable remagnetizations application of this method to the upper jurassic formation in four wells of the paris basin has yielded promising results for both stratigraphic and near absolute age correlations as well as determination of facies diachronisms the comparison of results obtained from magnetic measurements and from sequence stratigraphy analysis shows that third order sequence boundaries may be correlative to geomagnetic reversals but may also be diachronous in wells 80 km or less apart the potential of borehole magnetic measurements as presented in this paper is still under investigation however these encouraging initial results show that this new investigating and dating method could be of great help in the analysis of subsurface stratigraphy by extending the concepts of magnetostratigraphy from the outcrops and laboratory directly into borehole logging

application of sequence and genetic stratigraphic concepts to carboniferous coal bearing strata an example from the black warrior basin usa carboniferous strata provide an excellent example on which to test the application of genetic stratigraphic and sequence stratigraphic concepts both approaches are employed in the evaluation of the coal bearing strata of the black warrior basin south eastern usa bounding hiatal surfaces have been recognized in the succession of rock that includes the mary lee coal zone within the framework of genetic stratigraphy one genetic sequence has been identified comprised of offlap progradational and aggradational facies and onlap aggradational and transgressive facies components seven parasequence sets have been delimited according to the concepts of sequence stratigraphy these have been ascribed to transgressive highstand and shelf margin systems tracts the identification of components of these contrasting frameworks provide the basis for evaluating other carboniferous strata

slip weakening models of the 2011 tohoku oki earthquake and constraints on stress drop and fracture energy we present 2d dynamic rupture models of the 2011 tohoku oki earthquake based on linear slip weakening friction we use different types of available observations to constrain our model parameters the distribution of stress drop is determined by the final slip distribution from slip inversions as three groups of along dip slip distribution are suggested by different slip inversions we present three slip weakening models in each model we assume uniform critical slip distance eastward from the hypocenter but several asperities with smaller critical slip distance westward from the hypocenter the values of critical slip distance are constrained by the ratio of deep to shallow high frequency slip rate power inferred from back projection source imaging our slip weakening models are consistent with the final slip slip rate rupture velocity and high frequency power ratio inferred for this earthquake the average static stress drop calculated from the models is in the range of 4 5 7 mpa though large spatial variations of static stress drop exist to prevent high frequency radiation in the region eastward from the hypocenter the fracture energy needed there is in the order of 10 mj m2 and the average up dip rupture speed cannot exceed 2 km s the radiation efficiency calculated from our models is higher than that inferred from seismic data suggesting the role of additional dissipation processes we find that the structure of the subduction wedge contributes significantly to the up dip rupture propagation and the resulting large slip at shallow depth

surface geochemical exploration for hydrocarbons in the area of prospective structures of the lublin trough eastern poland abstract the search for crude oil and natural gas deposits is dominated by expensive seismic methods however less expensive and faster surface methods are available which may improve the effectiveness of petroleum exploration one of these methods is the surface geochemical survey the objective of this method is to detect record and analyse the trace amounts of hydrocarbons in soil gas samples our paper presents the results of such research carried out over the prospective structures of the lublin trough in the eastern poland three hundred fifty five soil gas samples were collected from 1 2 m depth below the surface which were analysed by gas chromatographic analysis for their molecular composition sampling sites were arranged along 5 sampling lines with 200 m spacing maximum concentrations of ch4 total alkanes c2 c4 total alkenes c2 c4 h2 co2 and o2 detected in our samples were 0 16 vol 0 95 ppm 6 79 ppm 0 37 vol 5 01 vol and 21 6 vol respectively the results demonstrate that alkanes recorded in the soil gas which are heavier than methane originated from the deeper hydrocarbon accumulations these components migrated to the near surface zone due to their active microseepage along the tectonic discontinuities and cracks in the overburden weak correlation of h2 and co2 with alkanes were found which precludes the application of both components as additional prospective indicators in the study area diverse activity of partial oxidation of alkanes to alkenes perhaps due to different rate of microseepage of hydrocarbons has been determined using the c2h6 c2h4 c2 c2 ratio the presence of numerous tectonic dislocations intensifies the microseepage and increases the amplitudes of geochemical anomalies recorded at the surface normalization of concentrations of methane total alkanes c2 c4 and total alkenes c2 c4 with their of background values which were calculated for separate subsets of c2 c2 ratio values significantly reducing the ranges and the amplitudes of hydrocarbons anomalies it allowed for modification of the anomalous pattern due to diverse activity of partial oxidation of alkanes to alkenes statistical analysis of c2h6 c3h8 c2 c3 ratio values showed that in the study area accumulations of gas condensate and dry gas dominate with the strongest surface geochemical signals the surface geochemical results were integrated with the structural map of the top of devonian formations as well as we when displayed as trend integrated with geological cross sections the surface alkane anomalies generally occur along the major nw se trending chain of structural uplifts located between abramow glinnik and nasutow this zone is most prospective and indicates the highest petroleum potential changes in normalized concentrations of total alkanes c2 c4 allowed the identification of 9 anomalous zones indicating the presence of deep hydrocarbon sources the no 2 anomaly which was localized at the intersection of the b b and the e e sampling lines seems to be the most prospective the accumulations of dry gas or gas condensate likely occur in the anticline formed by devonian and or carboniferous strata this zone should be opened for confirmation by drilling the geochemical lead should now be integrated with all available geological seismic data for prospect development our study demonstrates that the results of surface geochemical surveys combined with the results of geological studies and geophysical surveys provide a valuable source of comprehensive information about the explored area

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

identifying hierarchical spatial patterns within paleocommunities an example from the upper pennsylvanian ames limestone of the appalachian basin abstract identifying ecological mechanisms that produce hierarchically arrayed spatial variation in community structure can be difficult in the fossil record due to conflation of spatial and temporal patterns however this difficulty can be mediated by minimizing the temporal duration of deposition within the unit examined in this study the fauna of the upper pennsylvanian ames limestone conemaugh group was analyzed to explore whether ames paleocommunities exhibited hierarchical structure in a spatial dimension this widespread carbonate unit was deposited during the maximum flooding interval of a glacio eustatically influenced fifth order sea level cycle and preserved taxa are contemporaneous within only a few thousand years paleocommunity structure and variability was assessed at multiple spatial scales using samples collected from seven outcrops of the ames limestone throughout southeastern ohio which form a northeast to southwest trending transect parallel to the paleoshoreline abundance data were collected using quadrat sampling for brachiopods bivalves gastropods bryozoa corals crinoids echinoids trilobites and foraminifera paleocommunity structure was analyzed via cluster ordination guild and abundance analyses at multiple spatial scales within a single locality among localities and within the total study area to provide insight on geographic partitioning of paleocommunity variation multiple levels of paleocommunity organization were recovered within the ames fauna all levels exhibited spatial partitioning but the inferred proximate controls shifted from abiotic environmental controls at higher hierarchical levels to biotic controls at the lowest level at the highest level differentiation into a northern and southern regional paleocommunity was controlled primarily by substrate consistency and habitat heterogeneity related to variation in fluvial input within the basin local paleocommunity differentiation reflects biotic responses to topographic and environmental conditions that were geographically distributed within the region whereas within outcrop variation was due largely to biotic feedback mechanisms

climatically driven cyclicity and peat formation in fluvial setting of the moscovian early kasimovian cracow sandstone series upper silesia poland abstract the approximately 1200 m thick cracow sandstone series middle early late pennsylvanian in the polish part of the upper silesian coal basin consists of 25 70 m thick fining up and laterally widespread fluvial cycles the cycles are marked by alternating sheet like sandstone bodies overlain by much thinner intervals dominated by mudstone and coal these two member cycles record the alternation of a sand dominated fluvial braidplain and floodplain dominated fluvial system with channels confined to narrow belts the lateral persistence internal architecture and isochronous alternations suggest an allogenic origin for the cycles possibly related to climate this interpretation is supported by a three stage evolution of pedogenic processes operating on floodplain deposits beginning with the formation of vertisols followed later by gleying and finally termination by a histosol peat formation such a succession of paleosols indicates a climatic shift from highly seasonal vertisol to humid climate coal with the most seasonal part of the cycle likely represented by the sheet like sandbody the mechanistic link between climate and the cyclic pattern of strata is explained as climatically driven variations in clastic supply which was highest during periods of prominent seasonality short term climatic oscillations generating cyclic patterns in the cracow sandstone series are superimposed on a long term climatic shift towards increased seasonality near the middle late pennsylvanian boundary this is evidenced by the termination of peat formation in the upper silesian basin as well as in some other coeval basins of the equatorial pangea and is interpreted to represent a potentially regional climatic event

paleomagnetism of paleozoic asphaltic deposits in southern oklahoma usa paleomagnetic measurements on asphaltic samples from two formations in southern oklahoma have been performed a bioclastic unit from the boggy formation known as the buckhorn asphalt exhibited a stable characteristic remanent moment rm after a f demagnetization between 5 20 mt we infer from our data that very fine possibly authigenic magnetite like that shown to have a genetic relationship with the migration through rocks of hydrocarbons elmore et al 1987 is the primary rm carrier in these samples the tilt corrected paleopole for the buckhorn asphalt 121 9 e 43 5n p 1 3 m 2 3 falls on the early permian apparent polar wander path for north america of irving and irving 1982 using a 30 ma window 270 280 ma because the boggy form ation containing the buckhorn asphalt was depos ited during the late pennsylvanian desmoinesian we interpret the data to indicate magnetization during minor uplift in the early permian of the arbuckle mountain region the rm appears to have been acquired at this time probably as the result of magnetite production facilitated by the introduction time of sulfate reducing bacteria

a fractal analysis of quaternary cenozoic mesozoic and late pennsylvanian sea level changes sea level changes are related to both climatic variations and tectonic movements the fractal dimensions of several sea level curves were compared to a modern climatic fractal dimension of 1 26 established for annual precipitation records a similar fractal dimension 1 22 based on 18o 16o in deep sea sediments has been suggested to characterize climatic change during the past 2 m y our analysis indicates that sea level changes over the past 150 000 to 250 000 years also exhibit comparable fractal dimensions sea level changes for periods longer than about 30 m y are found to produce fractal dimensions closer to unity and missourian late pennsylvanian sea level changes yield a fractal dimension of 1 41 the fact that these sea level curves all possess fractal dimensions less than 1 5 indicates that sea level changes exhibit nonperiodic long run persistence the different fractal dimensions calculated for the various time periods could be the result of a characteristic overprinting of the sediment record by prevailing processes during deposition for example during the quaternary glacio eustatic sea level changes correlate well with the present climatic signature during the missourian however mechanisms such as plate reorganization may have dominated resulting in a significantly different fractal dimension

geochemical relationships of late paleozoic carbon rich shales of the midcontinent usa a compendium of results advocating changeable geochemical conditions abstract previous studies have shown that pennsylvanian black shales of the midcontinent us possess a more complex geochemical history than was once thought vine and tourtelot econ geol 65 1970 253 and coveney and glascock appl geochem 4 1989 347 note that the widespread nature of metalliferous pennsylvanian black shales and the diverse geological environments across the midwestern us pose the likelihood that metals contained in the black shales are of complex origins detailed geochemical and statistical representations using characteristics of numerous black shale members have shown that water depth may not have been uniformly deep as previously inferred by numerous workers earlier suggestions that these black shales were associated exclusively with anoxic depositional conditions have been challenged by a more realistic theory of multifaceted fluctuating environmental conditions a wide range of major and trace element concentrations combined with widely varying characteristics and diverse types of organic matter indicate the presence of fluctuating geochemical settings the presumption is that numerous associated chemical reactions occurred syngenetically one geochemical index degree of pyritization dop suggests a dysaerobic to aerobic setting for many of the shales whereas some other geochemical proxies i e v v ni indicate punctuated episodes of bottom water anoxia schieber abstr programs geol soc am 33 6 2001 a102 notes that in some black shales pyrite enrichment due to intermittent organic reworking explains the high dop values once thought to equate with extreme euxinic depositional conditions it seems likely therefore that even during apparent euxinic periods as indicated by bulk geochemistry oxygen deprived events were apparently short lived the seemingly euxinic fingerprint as shown by geochemical characteristics may result through time averaging abstr programs geol soc am 33 6 2001 a102 of intermittent euxinic events providing a misleading indication of dominant euxinic conditions thus detailed microstratigraphic sampling is necessary to delineate short punctuated occurrences of intermittent sub oxic episodes the midcontinent pennsylvanian shales may reflect a complex array of bottom water oxygenation variations and water depth fluctuations in response to climatic and localized events hatch j r and leventhal j s 1992 relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas usa in meyers p a pratt l m nagy b eds geochemistry of metalliferous black shales chem geol 99 65 82 complicated by post depositional events appl geochem 4 1989 347 this research examines the previous exclusively anoxic origin for midcontinent pennsylvanian black shales from a geochemical perspective and offers an alternative supported by detailed statistical presentations with the hypothesis that events of anoxia were punctuated by short lived dysaerobic or even near oxic events

source of anomalous magnetization in area of hydrocarbon potential petrologic evidence from jurassic preuss sandstone wyoming idaho thrust belt the jurassic preuss sandstone which crops out in the central part of the wyoming idaho thrust belt on trend with a hydrocarbon producing region to the south has been previously identified as the source of anomalous magnetization in the area elsewhere anomalous magnetization in sedimentary rocks near hydrocarbon accumulations has been attributed to hydrocarbon engendered magnetic minerals but magnetization of the preuss is controlled by detrital magnetite evidence of a detrital origin for magnetite includes 1 concentration of magnetite grains along laminations containing other heavy minerals 2 the presence of exsolved ilmenite hematite and spinel in the magnetite grains and 3 titanium contents typical of igneous derived magnetite that detrital magnetite is responsible for the anomalous magnetization in the preuss is further indicated by the systematic eastward decrease in magnetite abundance corresponding to a similar eastward decrease in magnetic susceptibility and remanent magnetization of the unit petrologic and vitrinite reflectance studies indicate a complex low temperature 150 c or 302 f diagenetic history for the preuss nevertheless preservation of detrital magnetite the presence of diagenetically early ferric oxide minerals and the absence of sulfide minerals all indicate that the preuss has not experienced sulfidic reducing conditions common in areas of hydrocarbon seepage the marine carbon isotopic composition of calcite that cements most preuss sandstones dgr13c values ranging from 2 47 to 1 48 pmil is evidence that carbonate diagenesis also was not influenced by hydrocarbons the results of this multidisciplinary study of the preuss underscore the importance of similar studies when evaluating the sources of aeromagnetic anomalies in areas of hydrocarbon potential

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

predictions of oil or gas potential by near surface geochemistry recent advances in surface geochemical prospecting have enabled age old seep detection technology to be used to determine the gas versus oil character of a potential fairway extensive field work has demonstrated that the chemical compositions of near surface hydrocarbon soil gases measured by flame ionization gas chromatography are largely determined by the hydrocarbons in nearby underlying reservoirs by using compositions and ratios of the light hydrocarbons methane ethane propane and butane one may predict whether oil or gas is more likely to be discovered in the prospect area near surface hydrocarbons are best represented by normalized histograms of composition data these histograms are strongly correlative with those of reservoir gas and with compositions o gas from shows recorded in downhole mud logging this correspondence with the actual formation gases suggests that the upward migration of reservoired light hydrocarbons into near surface soils represents a viable mechanism allowing surface geochemical exploration to be utilized for regional hydrocarbon evaluations geochemical profiles over known production areas are shown for the sacramento and san joaquin basins in california and for the utah wyoming overthrust belt geochemical predictions were documented by subsequent drilling near the pineview field in utah the data imply that the pineview field should extend westward into an area containing a dry hole in addition a new gas discovery on the intersection of a landsat lineament and a large methane anomaly was made 6 5 km 4 mi northeast of the pineview field by amoco in 1981 most of the geochemical examples reported show direct anomalies over known fields however seeps can be laterally displaced in certain geologic settings in addition geochemical investigations indicate that seep magnitudes depend on tectonic activity to aid gas migration along faults and fractures which appear to provide the major migration pathways this fault association suggests that diffusion is of secondary importance geochemical prospecting must be used with caution and only in conjunction with geologic and geophysical tools because the location and shape of many geochemical anomalies are governed more by the local tectonic structure of the region than by the position and shape of the actual deposit regional groundwater flow is less significant thus geochemical prospecting when used alone cannot predict whether a particular soil gas anomaly is associated with a commercial deposit it can only be used to verify the presence of petroleum hydrocarbons and to predict whether gas or oil is likely to occur in a potential structure geochemical prospecting yields excellent regional evaluations of hydrocarbon potential

temporal change of interplate coupling in northeastern japan during 1995 2002 estimated from continuous gps observations summary temporal change of deformation in northeastern japan is clarified by continuous global positioning system gps observations from 1995 april to 2002 march the observed gps velocity is approximately parallel to the direction of plate convergence on east and west plate boundaries of northeastern japan and shows post seismic transient deformation around source regions of the mw 7 8 1993 hokkaido nansei oki and the mw 7 7 1994 sanriku haruka oki earthquakes we interpret the source of the observed deformation as contemporary interplate coupling on the east subducting boundary to the pacific plate and the west collision boundary to the amurian plate using elastic dislocation theory we inverted horizontal and vertical velocities of 212 gps stations to estimate interplate coupling on both boundaries the estimated coupling during 1995 2002 is spatially heterogeneous however it is temporally almost constant except for the region around the 1993 and 1994 earthquakes after slip of the 1994 earthquake occurred over the coseismic rupture area and its downdip extension on the plate boundary for 0 3 1 3 yr after the earthquake after slip continued only in the downdip extension for later periods and decayed with time weak coupling was recovered in the eastern part of the coseismic rupture area 3 3 yr after the earthquake interplate coupling on the pacific plate was strong in two regions miyagi oki and tokachi oki the west plate boundary is tightly coupled except for the source areas of three large earthquakes that occurred in 1964 1983 and 1993 the apparent decoupling of the source areas of these earthquakes implies long term post seismic deformation as a result of viscoelastic relaxation in the subseismogenic lithosphere

sedimentary cycles and paleogeography of the dnieper donets basin during the late visean serpukhovian based on multiscale analysis of well logs abstract an integrated approach combining the available geological geophysical information was employed to construct a series of paleogeographic maps of the northwestern part of the dnieper donets basin ddb during the late visean serpukhovian early carboniferous the major source of information consists of well log data the basin fill shows a pattern of stacked transgressive regressive units of different order correlations on the scale of the basin are based on biostratigraphy seismics cyclostratigraphic subdivisions and correlations of the successions throughout the basin the cyclicity has a multifold character short shallowing upward transgressive regressive t r cycles characterized by the presence of hydrocarbons productive horizons cover a time span of the order of 500 ka long cycles include 4 to 6 short t r cycles they seem to be correlatable to western europe and probably to north america the long cycles form part of higher order stacking patterns indicative of still longer cycles considering the variable thickness of the cycles throughout the basin tectonics must have influenced the character of the series in addition to glacio eustatic sea level fluctuations the paleogeographical development of the basin shows axial deposition during the late visean likely related to late stage rifting related subsidence of a central graben followed by basin wide subsidence related to thermal subsidence during the serpukhovian

occurrence of secondary magnetite within biodegraded oil samples of solid bitumen from the thornton quarry illinois and the cynthia quarry mississippi were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from re magnetized paleozoic carbonate units from other localities organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil the occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in our samples we infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons the discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration

relation of thorium normalized surface and aerial radiometric data to subsurface petroleum accumulations a new exploration method has been developed using surface and aerial gamma ray spectral measurements in prospecting for petroleum in stratigraphic and structural traps formerly troublesome lithologic and environmental variables are suppressed by correcting potassium and uranium readings using a new process of thorium normalization normalized potassium shows characteristic low concentrations above petroleum deposits normalized uranium shows higher values than normalized potassium over petroleum and generally lower values elsewhere we attribute these anomalies to effects of microbial consumption of microseeping light hydrocarbons studies of national uranium resource evaluation nure program aerial gamma ray spectral data covering portions of six states have shown characteristic normalized potassium and uranium anomalies above 72 7 percent of 706 oil and gas fields additionally an average of 27 similar untested anomalies were found for each 1000 square mi 2600 square km covered similar aerial ga

rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal bearing sediments offshore shimokita peninsula japan iodp site c0020 sediments recovered at integrated ocean drilling program iodp site c0020 in a forearc basin offshore shimokita peninsula japan include numerous coal beds 0 3 7 m thick that are associated with a transition from a terrestrial to marine depositional environment within the primary coal bearing unit 2 km depth below seafloor there are sharp increases in magnetic susceptibility in close proximity to the coal beds superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence we investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record using isothermal remanent magnetization irm thermal demagnetization anhysteretic remanent magnetization arm iron speciation and iron isotopes magnetic mineral assemblages in all samples are dominated by very low coercivity minerals with unblocking temperatures between 350 580 c that are interpreted to be magnetite samples with lower unblocking temperatures 300 400 c higher arm higher frequency dependence and isotopically heavy 56fe across a range of lithologies in the coal bearing unit between 1925 1995 mbsf indicate the presence of fine grained authigenic magnetite we suggest that iron reducing bacteria facilitated the production of fine grained magnetite within the coal bearing unit during burial and interaction with pore waters the coal peat acted as a source of electron donors during burial mediated by humic acids to supply iron reducing bacteria in the surrounding siliciclastic sediments these results indicate that coal bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time within the subsequent deep biosphere