p wave anisotropy stress and crack distribution at coso geothermal field california a new inversion method for p wave anisotropy wu and lees 1999a has been applied to high precision microseismic traveltime data collected at coso geothermal region california direction dependent p wave velocity and thus its perturbation are represented by a symmetric positive definite matrix a instead of a scalar the resulting anisotropy distribution is used to estimate variations in crack density stress distribution and permeability within the producing geothermal field a circular dome like structure is observed at the southwestern part of the geothermal region southwest of sugarloaf mountain using a linear stress bulk modulus relationship deviatoric stress is estimated to be 3 6 mpa at geothermal production depths 1 2 km assuming all the anisotropy is related to stress the stress field is compressional nne ssw and dilational wnw ese coinciding with a previous independent study using earthquake focal mechanisms following a theory on flat elliptic cracks residual crack density estimated from p anisotropy is 0 0078 assuming crack aspect ratios 1 60 and is 0 041 when crack aspect ratios are close to 1 60 residual crack orientation distribution is related to velocity anisotropy on the basis of anisotropic part of crack density distribution function the anisotropic part of permeability distribution may be calculated by a statistical approach via simple parallel fluid flow along cracks

postorogenic denudation along the late paleozoic ouachita trend south central united states of america magnitude and timing constraints from apatite fission track data the magnitude and timing of synorogenic and postorogenic denudation along fold and thrust belts and their associated foreland basins of interest because of both tectonic and economic implications is generally poorly constrained along the late paleozoic ouachita trend a thin veneer of cretaceous strata is preserved above a low relief erosional surface that beveled the ouachita orogen and adjacent foreland areas this regional erosion surface provides a valuable constraint for interpreting new and previously published apatite fission track aft data obtained from exposed structural highs along the ouachita trend marathon llano arbuckle and benton uplifts aft data from sampled localities within the deformation belt marathon and benton uplifts exhibit younger ages and generally longer mean lengths than data from localities on the foreland side of the deformation front llano and arbuckle uplifts this observation suggests that erosion of the orogen rather than its extensional collapse was the primary mechanism responsible for flexural isostatic unloading of the foreland crust in addition all samples show evidence for mild reheating following their pre cretaceous cooling history specifically the lack of a significant population of 14 5 m tracks in all samples appears to require residence at temperatures of 55 5 c after development of the sub cretaceous erosional surface this implies that 1000 m of cretaceous paleogene strata were deposited across the entire ouachita frontal trend and subsequently removed during later tertiary time this tertiary denudation is interpreted to reflect the interplay between regional denudation and isostatic compensation in response to slow 10 m m y epeirogenic uplift of the southern midcontinent and a long term drop 200 m in eustatic sealevel during this time

apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

apatite fission track thermochronology of the southern appalachian basin maryland west virginia and virginia apatite fission track apparent ages 246 pm 37 to 95 pm 18 ma for 26 samples of upper devonian hampshire and chemung formations and middle devonian age tioga ash bed from the southern appalachian basin of maryland virginia and west virginia along with confined track length distributions for 13 of these samples suggest that uplift was contemporaneous with triassic jurassic extension along the atlantic continental margin uplift as measured by apatite fission track analysis began earliest in the northwestern section on the cumberland plateau at sim225 pm 25 ma this area probably required the least amount of erosional unroofing 3 1 km samples from the valley and ridge province of northern west virginia virginia and maryland yield progressively younger apatite fission track apparent ages to the east ranging from 163 pm 10 to 95 pm 18 ma this is consistent with deeper burial in the eastern appalachian basin as indicated by increasing cai indices and geodynamic modeling t

factors controlling prolific gas production from low permeability sandstone reservoirs implications for resource assessment prospect development and risk analysis low permeability reservoirs from the greater green river basin of southwest wyoming are not part of a continuous type gas accumulation or a basin center gas system in which productivity is dependent on the development of enigmatic sweet spots instead gas fields in this basin occur in low permeability poor quality reservoir rocks in conventional traps we examined all significant gas fields in the greater green river basin and conclude that they all occur in conventional structural stratigraphic or combination traps we illustrate this by examining several large gas fields in the greater green river basin and suggest that observations derived from the greater green river basin provide insight to low permeability gas charged sandstones in other basins we present evidence that the basin is neither regionally gas saturated nor is it near irreducible water saturation water production is both common and widespread low permeability reservoirs have unique petrophysical properties and failure to fully understand these attributes has led to a misunderstanding of fluid distributions in the subsurface an understanding of multiphase effective permeability to gas as a function of both varying water saturation and overburden stress is required to fully appreciate the controls on gas field distribution as well as the controls on individual well and reservoir performance low permeability gas systems such as those found in the greater green river basin do not require a paradigm shift in terms of hydrocarbon systems as some have advocated we conclude that low permeability gas systems similar to those found in the greater green river basin should be evaluated in a manner similar to and consistent with conventional hydrocarbon systems to date resource assessments in the greater green river basin have assumed a widespread continuous type resource distribution failure to recognize some of the fundamental elements of low permeability reservoirs has led to an underappreciation of the risks associated with exploration and development investment decisions in these settings and likely a significant overestimation of available resource levels

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

the hydrocarbon trap distribution patterns of the simple dip area of a continental basin a case study from the western slope of the songliao basin china simple dip areas of continental sedimentary basins feature stratal overlap gentle changes in slope uniform dip angles and minimal fault development locating hydrocarbon traps in these environments therefore presents a difficult challenge this paper analyzes reservoir sand body and hydrocarbon trap development and their distributions within the gently dipping western area of the songliao basin and discusses the determinants influencing the distribution of reservoir sand bodies and oil and gas bearing zones sand bodies within the simple east dipping western basin margin exhibit thin singular layering extensive planar distribution and frequent interbedding with mudstone layers in the homoclinal slope areas that lack significant fault development sand bodies served as important hydrocarbon migration pathways spatial shifts in the paleosedimentary system caused by basin subsidence and late stage tectonism can help constrain the search for hydrocarbon traps the spatial patterns of the depositional system influenced the distribution of different types of traps southerly prograding delta lobes were subsequently tilted to the east creating sand bodies that form up dip wedge out lithologic stratigraphic traps along their western edge some of the delta lobes are folded or cut by faults along their peripheral edges making structural traps and combination traps the primary types in this region the delta lobes in the western provenance system however dip in a direction parallel to that of sediment supply most subaqueous distributary channel sand bodies are continuous into the western source area and lack seal conditions lenticular lithologic traps are therefore found only along the outer edges of delta lobes and the adjacent shallow lacustrine environments

permeability anisotropy and its relations with porous medium structure 1 the complete permeability tensor of 18 porous rock cores was determined by means of x ray tomography monitoring during the displacement of a salty tracer to study the effect of the pore space geometry on the anisotropy of permeability we compared the three dimensional shape of the invasion front with the x ray porosity maps obtained before injection the samples clean and shale bearing sandstones limestones and volcanic rocks belong to a broad variety of granulometry and pore space geometry their porosity ranges from 12 to 57 and their permeability ranges from 1 5 10 14 to 4 10 12 m2 for sandstones the permeability anisotropy is well correlated with the presence of bedding for volcanic rocks it is clearly related to the orientation of vesicles or cracks however for limestones no evident link between the geometry of the porous network and the permeability anisotropy appears probably because of the influence of the nonconnected porosity that does not contribute to the hydraulic transport this systematic work evidences the ability and the limitations of the tracer method to characterize the anisotropy of permeability in the laboratory in a simple and rapid way

geochronology of the monteregian hills alkaline igneous province quebec three distinct groups of alkaline rocks can be recognized on the basis of silica content in the monteregian hills quebec strongly undersaturated slightly undersaturated to critically saturated and oversaturated the first two groups were derived from basanite and alkali picrite magmas respectively and yield distinct ages of intrusion clustered about 118 ma and 136 ma the age data are not readily explained by the translation of the north american plate across a fixed mantle hotspot but because the alkali picrite magmas were derived from greater mantle depths than the basanite magmas the data do suggest an upward migration of the zone of melting this change in the depth of melting may be a response to the upward transport of a metasomatic fluid perhaps with a coupled rise in mantle isotherms

relationship of p wave seismic attributes azimuthal anisotropy and commercial gas pay in 3 d p wave multiazimuth data rulison field piceance basin colorado this case history is one of three field projects funded by the us department of energy as part of its ongoing research effort aimed to expand current levels of drilling and production efficiency in naturally fractured tight gas reservoirs the original stated goal for the 3 d p wave seismic survey was to evaluate and map fracture azimuth and relative fracture density throughout a naturally fractured gas reservoir interval at rulison field this interval is the cretaceous mesaverde approximately 2500 ft 760 m of lenticular sands silts and shales three dimensional full azimuth p wave data were acquired for the evaluation of azimuthal anisotropy and the relationship of the anisotropy to commercial pay in the target interval the methodology is based on the evaluation of two restricted azimuth orthogonal source receiver azimuth 3 d p wave volumes aligned with the natural principal axes of the azimuthal anisotropy as estimated from velocity analysis of multiazimuth prestack gathers the dix interval

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

the deliberate search for the stratigraphic trap twenty four years have elapsed since the publication of halbouty s aapg memoir of 1982 the deliberate search for the subtle trap since then the technologies employed in hydrocarbon exploration have become extraordinarily sophisticated yet current exploration for stratigraphic traps is to some extent restricted to areas where seismic data simplifies exploration by allowing direct inference of fluid fill and reservoir development this special publication draws upon contributions that examine current industry perceptions of stratigraphic trap exploration and the technologies tools and philosophies employed in such exploration given the changing industry environment this book contains a collection of papers examining a number of themes related to exploration for stratigraphic traps ranging from play and risk assessment through regional assessments of stratigraphic trapping potential specific exploration programmes targeted at stratigraphic traps to specific working traps and plays where stratigraphic trapping is prevalent

a new geometrical model for non linear fluid flow through rough fractures summary fractures in rock mass are the main flow paths and introduce as a most important attribute in rock mass hydraulic behavior the non linear fluid flow through rock fractures was studied in this paper computational domain of an artificial three dimensional fracture is generated and used for cfd simulations both laminar and turbulent flow simulations were performed for a wide range of flow rates also a new non linear fluid flow formulation was developed on the basis of some geometrical and kinematical assumptions for fracture and fluid flow respectively based on comparison between simulation results and developed formulation a new geometrical model has been proposed for non linear fluid flow through rough fractures which suggests a polynomial expression like forchheimer law to describe the dependence of pressure drop on flow rate finally this model has been evaluated with experimental results of a fracture with different geometries the results show that the predicted pressure drop for turbulent flow simulation was roughly 3 17 more than those for laminar one at the reynolds number of 4 5 89 5 respectively moreover a good accuracy was found between the proposed model and turbulent flow simulation results these findings may prove useful for computational studies of flows through real rock fractures or inclusions in simulators for large scale flow in fractured rocks

the relationship of the degree of interconnection to permeability in fracture networks the problem of determining the permeability of a rock mass containing a system of finite fractures is highly dependent on both the degree of interconnection between fractures and the heterogeneity of individual fracture characteristics this paper examines how degree of interconnection affects both magnitude and nature of the fracture permeability the interconnection between given fracture sets is a complex function of 1 fracture density i e the number of fractures per unit volume and 2 the fracture extent or size unfortunately neither the density nor the extent of fractures is easily determined from borehole data however fracture frequency can be directly measured in a borehole because it is simply the number of fractures intersected per unit length of the borehole the frequency is a measure of the product of fracture density and size because the probability of a fracture intersecting a borehole is proportional to this product the effect of the degree of interconnection was investigated by numerically simulating flow in fracture networks where fracture size and density varied inversely while the product of these two parameters was held fixed directional permeabilities of a number of such networks were determined and the hydraulic behavior of each fracture system was compared to that of an ideal porous medium the permeability of the rock matrix between the fractures was assumed to be low enough to be negligible the results show that as fracture length increases the degree of interconnection increases thus for a given fracture frequency as measured in a borehole the permeability of the system increases as fracture length is increased and density is proportionally decreased also fracture systems with shorter but more dense fractures behave less like porous media than do systems with longer but less dense fractures knowledge of fracture frequency and orientation alone is inadequate when determining permeability or deciding the important question of whether a given system behaves like a porous medium for many cases where these parameters can be measured in the borehole it is critical to know fracture length in order to predict the degree of fracture network interconnection however for certain cases where fractures are larger than some critical size it may not be necessary to know fracture lengths exactly

an experimental study of single and two phase fluid flow through fractured granite specimens triaxial tests on the two phase flow of air and water through fractured granite specimens were performed to discover whether the two phase fluid flow within rock fractures was laminar or turbulent the two phase flow characterization was carried out based on the macroscopic two phase steady state flow model and the homogeneous steady state flow model rock specimens with a single natural fracture joint roughness coefficient jrc 10 were tested using two phase high pressure triaxial rig experimental results show that the estimated reynolds numbers for various inlet fluid pressures are well below 1000 the findings of this study reveal that both single and two phase flow through rock fractures jrc 10 can be characterized as laminar flows at moderate inlet fluid pressures however for single phase air flow an increase in inlet air pressures may result in the formation of turbulent flow

fracture detection using crosshole surveys and reverse vertical seismic profiles at the conoco borehole test facility oklahoma summary shear waves in combined crosshole surveys chss and reverse vertical seismic profiles rvsps at the conoco borehole test facility oklahoma are analysed to examine the relationship between shear wave propagation and natural fracture systems the surveys cover a range of azimuths and angles of incidence and give the possibility of studying fracture induced azimuthal anisotropy in some detail the data display several features characteristic of seismic anisotropy shear wave splitting displaying substantial time delays up to 7 ms for source geophone distances of less than 50 m suggest large fracture densities estimates of fast shear wave polarizations and time delays confirm the n75de 10d fracture strike deduced from other geological and hydrological observations analyses of chs data including modelling with synthetic seismograms suggest that at least the dominant fracture set is rotated by 20d from the vertical one of the most important results of this study is the positive identification of guided waves propagating between wells along interfaces with sufficient velocity constrast in chs profiles it appears that combinations of chss and rvsps offer unique possibilities in evaluating fracture parameters at shallow depths this could be important for the study of fluid flow at shallow depths in hydrological investigations

the thermal history of the new york basement determined from 40ar 39ar k feldspar studies constraints on the thermochronologic evolution of the new york crystalline basement are mainly restricted to the high temperature early cooling history following 1 1 ga grenville metamorphism u pb methods and the late cooling history fission track methods the thermal history for the one billion years between these intervals is herein assessed using 40ar 39ar hornblende muscovite biotite and k feldspar thermochronology hornblende preferred ages suggest cooling below 450 500 c between ca 900 and 950 ma total gas ages of biotites range from 746 1060 ma and their age spectra complexity is probably related to younger thermal events and or excess argon a single muscovite analysis yields a preferred age of 854 ma argon isotope analyses of k feldspar provide a quantitative evaluation of the thermal history between 175 and 350 c multi diffusion domain thermochronology on highly variable k feldspar results yield internally consistent thermal histories and along with geologic constraints suggest thermal maxima of 275 350 c at ca 700 470 450 and 300 ma combining all of the k feldspar analyses provides an internally consistent thermal history for the region and allows for the following inferences reheating at 700 ma associated with late precambrian rifting during the formation of the iapetus ocean apparently affected the entire adirondack region with the highest temperatures occurring in the eastern part of new york local reheating in the ordovician is inferred to have affected the eastern adirondack mountains and probably resulted from the combined effects of burial during the early paleozoic emplacement of taconic thrust sheets and migration of hot fluids along normal faults during the taconic orogeny high paleotemperatures for the devonian section of eastern new york are related to maximum burial of the basement during the carboniferous at ca 300 ma

anisotropic structure beneath central java from local earthquake tomography 1 in this study we present the new tomographic code anita which provides 3 d anisotropic p and isotropic s velocity distribution based on p and s traveltimes from local seismicity for the p anisotropic model we determine four parameters for each parameterization cell this represents an orthorhombic anisotropy with one predefined direction oriented vertically three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0 60 and 120 and one is a perturbation along the vertical axis the nonlinear iterative inversion procedure is similar to that used in the lotos code we have implemented this algorithm for the updated data set of central java part of which was previously used for the isotropic inversion it was obtained that the crustal and uppermost mantle velocity structure beneath central java is strongly anisotropic with 7 10 of maximal difference between slow and fast velocity in different directions in the forearc area between southern coast and volcanoes the structure of both isotropic and anisotropic structure is strongly heterogeneous variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust beneath volcanoes we observe faster velocities in vertical direction which is probably an indicator for vertically oriented structures channels dykes in the crust beneath the middle part of central java north to merapi and lawu volcanoes we observe a large and very intense anomaly with a velocity decrease of up to 30 and 35 for p and s models respectively inside this anomaly e w orientation of fast velocity takes place probably caused by regional extension stress regime in a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and or penetration of quasi horizontal lenses with molten magma in the mantle trench parallel anisotropy is observed throughout the study area such anisotropy in the slab entrained corner flow may be due to presence of b type olivine having predominant axis parallel to the shear direction which appears in conditions of high water or and melting content

the 40ar 39ar laser analysis of k feldspar constraints on the uplift history of the grenville province in ontario and new york 1 a comprehensive geochronologic database describes a period of late extension across the metasedimentary belt mb of the grenville province in northeastern north america because extension continued through much of the young unroofing history of the region these data do not bracket the timing of final extension across all shear zones and do not constrain the timing of final juxtaposition of terranes analysis of k feldspar in the mb by the 40ar 39ar method can give information on the very latest perturbations in the area since k feldspars have multiple low closure temperatures ranging from about 150 to 300 c these multiple diffusion domains require temperature time modeling to fully interpret argon release spectra this modeling requires precise knowledge of the temperature of degassing of each step which usually requires the use of a resistance furnace for sample analysis we establish a first order relationship between laser power and temperature which can be used for multidiffusion domain modeling of k feldspars comparison of samples analyzed by both methods reveals virtually no difference between the systems supporting the validity of k feldspar analyses by laser step heating our data suggest that using the laser for k feldspars can give results that are geologically reasonable precise and easier to collect in this case these data are then applied to the cooling history of the north american grenville province our k feldspar analyses show that the latest extensional motion along shear zones in the mb is after 900 ma and the region is uplifting as a uniform block by 780 ma

mesozoic cenozoic unroofing of the southern appalachian basin apatite fission track evidence from middle pennsylvanian sandstones apatite fission track ages 137 pm 8 to 92 pm 7 ma and mean etchable track lengths 12 1 pm 1 8 to 12 9 pm 1 3 mu m are reported for 10 sandstones from the breathitt formation middle pennsylvanian at the northern end of the pine mountain overthrust in kentucky and virginia because all of the apatite fission track ages are 150 200 m y younger than the depositional age fission tracks that formed in the detrital apatite prior to deposition have been totally annealed thus maximum temperatures attained by these samples exceeded 110 pm 20 circ c the length distribution of etchable horizontally confined fission tracks precludes rapid 10 c m y cooling through the zone of partial annealing 60 125 c assuming a geothermal gradient of 25 pm 5 circ c km and a mean surface temperature of 15 c sandstones at the northern end of the pine mountain overthrust underwent slow erosional unroofing of 4 pm 1 km since the early cretaceous average rate of 28 pm 6 m m y the age t

backstacking apatite fission track stratigraphy a method for resolving the erosional and isostatic rebound components of tectonic uplift histories measuring tectonic uplift of the mean surface of earth using thermochronological data to document uplift histories is often plagued by confusion arising from the independent nature of the thermal and sea level frames of reference the technique of backstacking apatite fission track stratigraphy differentiates between vertical movement of rocks toward earth9s surface due to erosional or tectonic denudation and tectonic uplift of earth9s surface apatite fission track analysis can also be used to identify episodes of erosion where no other evidence for the erosional event exists in addition to providing information about the timing magnitude and geographic distribution of erosion

mesozoic evolution of nw africa implications for the central atlantic ocean dynamics the central atlantic ocean opened during the early jurassic and represents the oldest portion of the atlantic ocean although the american margin has been well studied the onshore evolution of its african counterpart is poorly understood we investigated the evolution of a c 1300 km transect across the reguibat shield morocco mauritania algeria in the northern west african craton using low temperature thermochronology fourteen samples were dated using apatite fission track analysis nine of these samples were also dated using u th sm he analysis fission track ages range from 118 10 to 497 61 ma with mean track lengths between 11 2 0 4 and 12 5 0 2 m u th sm he single grain ages range from 32 3 to 396 32 ma through forward and inverse thermal modelling we demonstrate that the craton underwent kilometre scale exhumation between the early middle jurassic and the late cretaceous based on our new results published data on nw africa and data from the conjugate eastern north american passive margin we show that this post rift early middle jurassic to early cretaceous exhumation affected both margins to a similar areal extent and simultaneously transient mantle dynamic support is suggested to account for the major erosional phase recorded on both margins supplementary material the method for thermal modelling the thermal modelling for all samples and the relationship between apatite chemistry and u th he ages are available at https doi org 10 6084 m9 figshare c 3770918

presence of a long term lithospheric thermal anomaly evidence from apatite fission track analysis in northern new england abstract apatite fission track aft ages from 56 samples of paleozoic and mesozoic crystalline rocks in new hampshire northeastern vermont and western maine range from 70 to 140 ma and reflect widespread early to late cretaceous cooling the regional aft age distributions determined in this study suggest that reactivation of preexisting orogen parallel faults and the presence of a long lived thermal anomaly in the lithospheric mantle controlled the late unroofing history of this part of the northern appalachians a northeast trending zone of young dominantly late cretaceous aft ages 70 118 ma extends from southwestern new hampshire through the central white mountain region and continues into northern new hampshire northeastern vermont and western maine providing evidence for regional nw se extension and cooling at this time significantly older aft ages 125 140 ma in the region bounded by the bill little ammonoosuc and northey hill faults in northwestern new hampshire suggest a normal sense r

bullwinkle a unique 3 d experiment in the spring of 1988 shell offshore inc acquired two orthogonal three dimensional 3 d surveys at prospect bullwinkle located in the green canyon area of the gulf of mexico to aid the development program which began later that year two surveys were acquired because of the complexity of the salt structures in the vicinity of the prospect the independent acquisition and processing of two surveys shot perpendicular to each other provided a unique data set for checking the quality and accuracy of standard 3 d techniques the high development cost of this deep water 410 m turbidite field supported the acquisition of two 3 d data sets to provide a valuable redundancy for stratigraphic interpretation this large scale 3 d experiment has been analyzed in terms of interpretive impact detailed comparisons of the seismic images away from the salt complex show good agreement between the two surveys and verify the relative accuracy and repeatability of the acquisition processing and interpretation techniq

evidence for differential unroofing in the adirondack mountains new york state determined by apatite fission track thermochronology abstract apatite fission track ages of 168 83 ma for 39 samples of proterozoic crystalline rocks three samples of cambrian potsdam sandstone and one cretaceous lamprophyre dike from the adirondack mountains in new york state indicate that unroofing in this region occurred from late jurassic through early cretaceous samples from the high peaks section of the adirondack massif yielded the oldest apatite fission track ages 168 135 ma indicating that it was exhumed first unroofing along the northern northwestern and southwestern margins of the adirondacks began slightly later as shown by younger apatite fission track ages 146 114 ma determined for these rocks this delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the high peaks apatite fission track ages for samples from the southeastern adirondacks are distinctly younger 112 83 ma than those determined for the rest of the adirondack region these younger apatite fission track ages are from a sec

distribution of maximum burial temperatures across northern appalachian basin and implications for carboniferous sedimentation patterns clay mineral diagenesis and apatite fission track age data indicate that the maximum burial temperatures to which the middle devonian tioga metabentonite was exposed rise abruptly from low values in western new york state to higher values in the east the highest temperatures which approach 175 sup 0 c were reached just west of syracuse neither the pattern nor the magnitude of burial temperatures can be explained solely by burial of the metabentonite beneath upper devonian sediments although spatial variations in the geothermal gradient could have produced the observed pattern of burial temperatures it is more likely that carboniferous sediments no longer preserved in the area were responsible for the indicated burial the inferred presence of thick carboniferous sequences in western new york state suggests that the allegheny orogeny had a stronger influence on sedimentation in the northern appalachian basin than has been previously recognized 25 references 2 figures 2 tables

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

mesozoic fault reactivation along the st lawrence rift system eastern canada thermochronologic evidence from apatite fission track dating the st lawrence rift system is an active fault zone where reactivation of late proterozoic iapetus related faults is believed to occur it forms both a ne sw trending half graben and nw se trending grabens that link and include the ottawa bonnechere and saguenay river grabens both interpreted as aulacogens the rift faults locally preserve kinematic evidence for normal sense displacement the lack of isotopic chronological constraints and the absence of strata younger than the ordovician make it difficult to determine the timing of fault increments field relations in the quebec city charlevoix and saguenay river regions suggest faulting event s younger than the devonian age charlevoix crater we determined apatite fission track aft ages for grenvillian basement rocks from the hanging wall and footwall of typical rift faults at different locations of the st lawrence and saguenay river fault systems along the st lawrence rift system the footwall rocks of major faults yielded late triassic early jurassic aft ages ranging from 235 28 ma to 184 22 ma the hanging wall samples yielded older ages between 443 44 ma and 279 28 ma along the nw trending saguenay river fault system that are consistent with triassic early jurassic normal faulting at ca 250 200 ma based on hefty inverse models of fission track length distributions younger late jurassic aft ages ranging from 152 17 ma to 149 14 ma in the hanging wall of the ne sw trending st lawrence fault system suggest the occurrence of localized faulting increments during the late jurassic the latter aft age discontinuities are interpreted as the result of normal faulting at ca 250 200 ma followed by tectonic inversion evidence for the reactivation and inversion of preexisting normal faults during or after jurassic time is also found in the mesozoic rift related basins of the atlantic coast the nw se trending compressive stress field currently documented along the st lawrence river is consistent with tectonic inversion along the st lawrence rift system this study provides geochronological support for atlantic rift related extensional deformation followed by compressional deformation in the interior of the canadian shield more than 500 km west of the axis of the mesozoic atlantic rift basins

modelling the elastic and hydraulic properties of fractured rocks abstract it is now commonly accepted that the earth s upper crust is permeated by discontinuities such as joints fractures and cracks in addition artificial fractures are usually created in low permeability reservoirs so that petroleum can be produced economically these discontinuties play a significant part in oil production and geothermal exploitation there is therefore great interest in using seismic measurements to characterize the discontinuities in reservoir rocks a model has been developed to relate the effective elastic properties of rocks containing aligned fractures or joints to their hydraulic properties at various pressures the model is considerably different from the earlier hertzian contact models because in addition to the deformation of asperities in contact due to compression the deformation of void surfaces has also been taken into account when evaluating the specific stiffness of fractures numerical results show that indentation of the void surfaces is the major factor affecting the evaluation of joint stiffness indicating that the previous hertzian contact models underestimate joint compliances the theory has been used to model the velocities and permeabilities measured on carefully fractured rock samples at various confining pressures very good fits between the predicted and measured results have been found

t matrix approach to shale acoustics summary the t matrix approach of quantum scattering theory is used here to place many long wavelength equivalent medium approximations for porous composites polycrystals and cracked media on a common footing and to indicate their limitations but also to derive some new results based on two point statistics in this way we have obtained an insight into the difficult problem of elastic inclusions at finite concentrations which is of foremost relevance when estimating the effective material parameters of porous cracked shales involving stacks of more or less horizontally aligned clay platelets mixed together with more rounded silt minerals and with fluid filling the spaces a rather involved perturbative analysis of the effects of interactions between or structural correlations among the various inclusions minerals and cavities making up a real shale of hexagonal symmetry was performed in an attempt to obtain a better match between theoretical predictions based on a combination of coherent and optical potential approximations and experimental results recovered from ultrasonic wave speeds for the effective elastic stiffness tensor for the particular data set considered in this study the t matrix approach was able to match the data better than the approach of hornby et al but the match was not completely satisfactory further progress in theoretical shale modelling may come from a better knowledge of the elastic properties of pure clay minerals a more detailed knowledge of the microstructure of shales the incorporation of constraints obtained from comparisons between theoretical predictions and experimental results as well as a continuing development of the t matrix approach numerical results also for the effect of bedding parallel microcracks on the elasticity of such a real shale have value in illustrating the importance of taking into account the effects of spatial distribution when trying to deal with non dilute mixtures of highly contrasting material properties

conodont u th he thermochronology initial results potential and problems abstract we performed he diffusion experiments and u th he age determinations on conodonts from a variety of locations to explore the potential of conodont u th he thermochronology to constrain thermal and exhumation histories of some sedimentary rock dominated terrains based on two diffusion experiments and age results from some specimens he diffusion in conodont elements appears to be similar to that in durango apatite fragments of similar size and closure temperatures are approximately 60 70 c for cooling rates of 10 c m y u th he ages of conodonts from some locations yield reproducible ages consistent with regional thermal history constraints and in at least two cases require a closure temperature lower than 80 c other samples however yield irreproducible ages and in one case yield ages much younger than expected based on regional geologic considerations these irreproducible samples show inverse correlations between parent nuclides and age consistent with late stage open system u th behavior

mesozoic hotspot epeirogeny in eastern north america geologic data especially conodont paleotemperatures imply that southeastern canada and new england have been elevated at least 4 km relative to the central appalachian region apatite fission track ages suggest that the uplift and consequent erosion occurred in cretaceous early tertiary time consistent with the formation of a broad swell as north america moved northwestward over the great meteor hotspot

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

time temperature burial significance of devonian anthracite implies former great 6 5 km depth of burial of catskill mountains new york specimens of coalified plant debris in tully correlative strata of the gilboa formation uppermost middle devonian within the eastern catskill mountains of new york state have been converted to anthracite having a vitrinite reflectance of 2 5 this implies a level of organic metamorphism lom of 16 the specimens are about 350 m y old if 200 m y is taken as the duration of the time of exposure to the maximum geothermal temperature then the lom of 16 and other thermal indicators imply a maximum temperature of 190 sup 0 c using a geothermal gradient of 26 sup 0 c km sup 1 17 sup 0 f 1 000 ft sup 1 a former depth of burial of 6 5 km is implied such former deep burial is not usually inferred for the catskills but it is consistent with the idea that the thick about 6 4 km or 21 000 ft carboniferous strata of northeastern pennsylvania formerly extended northeast far enough to bury the catskills the lack of metamorphism of the paleozoic strata lying about 4 5 km beneath the tully correlative rocks and exposed in the adjacent hudson valley places low limits on the former geothermal gradient this supports the concept of great depth of former burial of the catskills for example 6 5 km of former burialmore and a geothermal gradient of 26 sup 0 c km sup 1 imply a temperature of 307 sup 0 c for the base of the paleozoic by contrast only 1 km of former burial requires a geothermal gradient of 170 sup 0 c km sup 1 which would have subjected the base of the paleozoic to a temperature of 955 sup 0 gamma which is far higher than the 600 to 650 sup 0 c recently inferred for the acadian age metamorphism of the taconic allochthon in southwestern massachusetts and adjoining areas less

permeability estimation from velocity anisotropy in fractured rock cracks in a rock mass subjected to a uniaxial stress will be preferentially closed depending on the angle between the fracture normal vectors and the direction of the applied stress if the prestress fracture orientation distribution is isotropic the effective elastic properties of such a material after application of the stress are then transversely isotropic due to the overall alignment of the cracks still open velocity measurements in multiple directions are used to invert for the probability density function describing orientations of crack normals in such a rock this is accomplished by expanding the crack orientation distribution function into generalized spherical harmonics the coefficients in this expansion are functions of the crack density and the crack aspect ratio distribution the information on fracture distribution obtained from the velocity inversion allows an estimation of the anisotropic permeability of the fractured rock system permeability estimates are based on the number of cracks open of each aspect ratio and the contribution of a given crack is weighted by the cosine of the angle between the crack and the direction of the applied pressure gradient this approach yields a prediction of permeability as a function of the angle from the uniaxial stress axis the inversion for crack orientation is applied to ultrasonic velocity measurements on barre granite and permeability predictions for this sample are presented the inversion results are good and reproduce velocity measurements well and the permeability predictions show some of the expected trends initial comparisons of the predictions with available permeability data however show deviations suggesting that further information on partial crack closure and connectivity of cracks should be included into the permeability model

thermal history of michigan basin and southern canadian shield from apatite fission track analysis apatite fission track ages and confined length distributions were collected from 38 basement outcrop and 5 basement drillcore samples in order to reconstruct the phanerozoic thermal history of the michigan basin and southern canadian shield the apatite data indicate two periods of thermal activity in the region triassic heating cooling that affected the basin and adjacent shield and cretaceous or post cretaceous heating cooling that primarily affected the basin the magnitude timing and cause of cretaceous thermal activity cannot be identified with the present data model calculations suggest that some of the shield samples and probably all of the basin samples were heated to temperatures of at least 90c just prior to relatively rapid cooling in the triassic available stratigraphic and geochemical constraints suggest that these elevated temperatures were the result of burial by an additional 2 5 km of late paleozoic probably pennsylvanian and permian sediments it is likely that the basin was buried during the alleghenian orogeny as observed for the adjacent appalachian basin

hydraulic properties of 3d rough walled fractures during shearing an experimental study abstract this study experimentally analyzed the influence of shear processes on nonlinear flow behavior through 3d rough walled rock fractures a high precision apparatus was developed to perform stress dependent fluid flow tests of fractured rocks then water flow tests on rough walled fractures with different mechanical displacements were conducted at each shear level the hydraulic pressure ranged from 0 to 0 6 mpa and the normal load varied from 7 to 35 kn the results show that i the relationship between the volumetric flow rate and hydraulic gradient of rough walled fractures can be well fit using forchheimer s law notably both the linear and nonlinear coefficients in forchheimer s law decrease during shearing ii a sixth order polynomial function is used to evaluate the transmissivity based on the reynolds number of fractures during shearing the transmissivity exhibits a decreasing trend as the reynolds number increases and an increasing trend as the shear displacement increases iii the critical hydraulic gradient critical reynolds number and equivalent hydraulic aperture of the rock fractures all increase as the shear displacement increases when the shear displacement varies from 0 to 15 mm the critical hydraulic gradient ranges from 0 3 to 2 2 for a normal load of 7 kn and increases to 1 8 8 6 for a normal load of 35 kn and iv the forchheimer law results are evaluated by plotting the normalized transmissivity of the fractures during shearing against the reynolds number an increase in the normal load shifts the fitted curves downward additionally the forchheimer coefficient decreases with the shear displacement but increases with the applied normal load

40ar 39ar ages for plutons of the monteregian hills quebec evidence for a single episode of cretaceous magmatism 40ar 39ar data for biotite and amphibole from six plutonic complexes of the monteregian petrographic province in quebec canada are presented generally uncomplicated and concordant incremental heating spectra are observed although there is evidence for minor excess 40ar at several localities biotites and amphiboles are concordant consistent with rapid cooling of the high level complexes ages for different phases of individual complexes are analytically indistinguishable and suggest that the various principal lithologies are cogenetic the 40ar 39ar ages of six monteregian complexes st hilaire rougemont johnson shefford brome megantic all fall within the very restricted range of 124 1 m y it is suggested that all of the monteregian plutons with the exception of oka were formed within a short interval 1 2 m y during the cretaceous consistent with paleomagmetic results the new ages along with geochemical characteristics support derivation of the alkaline magmas by a fixed mantle hot spot which also produced broadly similar complexes in new england and the chain of new england seamounts

west of shetland revisited the search for stratigraphic traps the west of shetland area has scope for the stratigraphic entrapment of hydrocarbons at various jurassic to palaeogene stratigraphic levels mapping and identification of such traps requires a fundamental understanding of the regional geology the study of analogues and source kitchens and a thorough approach to trap validation since 1982 47 exploration wells have been positioned on paleocene prospects with a significant stratigraphic component but few have found hydrocarbons many failing as a result of poor trap definition and overconfidence in the predictive use of amplitude anomalies hydrocarbon sourcing of many of the failed prospects was also poorly constrained few amplitude related stratigraphic features could be tied with confidence to a viable source kitchen the presence of a regional seal is a prerequisite ingredient for a successful paleocene play many remaining undrilled subtle prospects rely on a stratigraphic trapping component and high quality 3d seismic data are seen as an essential search tool examples of undrilled prospects are presented from the paleocene of the northern faroe shetland basin and the mesozoic of the east solan basin and corona ridge

regional scale mid jurassic to late cretaceous unroofing from the adirondack mountains through central new england based on apatite fission track and u th he thermochronology abstract apatite fission track aft ages of 178 to 70 ma for 108 samples from the adirondack mountains and eastern new york state vermont western massachusetts and connecticut and western new hampshire indicate that widespread unroofing occurred throughout the region during the middle jurassic to late cretaceous additionally u th he ages of 167 to 85 ma were determined on nine of those samples and support cooling rates of 1 8 2 2 c m yr from 100 to 65 c during the middle jurassic to late cretaceous assuming a geothermal gradient of 25 c km unroofing rates for the region were estimated to be on average 0 07 0 08 km m yr the aft age discontinuities between the high peaks region and the fault dissected southeastern adirondack mountains and along the ammonoosuc fault in the connecticut river valley between vermont and new hampshire suggest differential unroofing that may have been accommodated by fault reactivation syn post late cretaceous time after the youngest aft ages 82 and 70 ma resp

hydromechanical properties and alteration of natural fracture surfaces in the soultz granite bas rhin france natural fractures are characterized by rough surfaces and complex fluid flows a large distribution of apertures residual voids within their walls and the presence of contact points in situ normal loads produce heterogeneous flows channeling the resulting permeabilities porosities or fluid rock exchange surfaces cannot be realistically modeled by parallel and smooth plate models four natural fractures are sampled at different depths and degrees of alteration in the soultz sandstone and granite eps1 drillhole soultz sous forets bas rhin france the fracture surfaces are measured with mechanical profilometry and maps of asperity heights xyz resulting local apertures xye are then calculated a statistical study of the surface profiles xz show that the fractures are more or less rough and tortuous according to the types of alteration altered samples are characterized by smoother surfaces of fractures such differences imply that i the average fracture aperture is not representative for the whole fracture and that ii the different local apertures should be integrated in hydraulic and mechanical models a hydraulic model finite difference calculations of fluid flow taking into account the elastic closure hertz contact theory of fractures with depth is used maps of contact points and relative local loads within the fracture planes are compared to flow maps they show different channeling of fluid flows strongly altered fractures are characterized by homogeneous fluxes despite the presence of numerous contact zones during the closure of fracture by contrast fresh fractures develop increasing fluid flow channels with depth fracture closure increasing normal stress does not systematically increase the channeling of fluid flow there is evidence for a general smoothing out of the irregularities of the fracture walls due to precipitation of secondary minerals indicating that the cubic law can be commonly valid also at great crustal depth but this validity depends on the degree of fracture alteration mineralogical and geochemical observations thus should be taken into account to perform more accurate permeability calculations and models of fluid circulation in fracture networks d 2002 elsevier science b v all rights reserved

uplift rate of adirondack anorthosite measured by fission track analysis of apatite the uplift history of the adirondack anorthosite has been clarified by analyzing apatite using the fission track method ages ranged from 86 to 147 m y on samples collected over an elevation difference of 11 560 m in the anorthosite massif an uplift rate of about 0 03 mm yr is obtained for the 61 m y interval from 86 to 147 m y ago on the basis of the correlation between fission track age and elevation the calculated value for the uplift rate during the past 86 m y is 0 05 mm yr a mesozoic hotspot epeirogeny is not required to explain the uplift rates based on apatite fission track data

sensitivity of three component 3d finite difference elastic seismic modeling to inclusion parameters in hti and tti media with high inclusion density parameters associated with the presence of inclusions cracks or vugs significantly influence seismic responses the t matrix method is used to define approximate anisotropic effective elastic stiffness tensors for media with inclusions this allows 3d three component eighth order staggered grid finite difference modeling to simulate the seismic responses of anisotropic media with high inclusion density various aspect ratios spatial distributions and orientations of inclusions and fluid content the model parameters are chosen to represent aligned inclusions ranging from vertical cracks to vugs in a carbonate reservoir encased in clastics the magnitude of anisotropy increases with increasing inclusion density for p and s waves cracks in a high velocity carbonate reduce the stiffnesses and correspondingvelocities this results in smaller contrasts with the surrounding lower stiffness clastics and hence smaller reflection coefficients s wave splitting and the anisotropy of vp vs are clearly

uplift of the tug hill plateau in northern new york state the tug hill plateau is a roughly elliptical shaped area located in northern new york state that rises above the adjacent landscape and is underlain predominantly by middle to upper ordovician strata its elevated character is inter preted as a passive response to the tectonic uplift of the adjacent precambrian basement located to the east and northeast of the plateau uplift of the basement is also inferred to have resulted in the strata on the plateau and in the topographi cally lower terrain to the north dipping gently towards the southwest tilting of the plateau was probably facilitated by ro tation along the newly recognized regionally extensive black river fault which separates the plateau from the uplifted basement and marks the plateau s east northeastern limit the northern limit of the plateau accentuated by a pronounced escarpment is aligned with the northeast trending carthage colton shear zone a major precambrian tectonic boundary uplift of the adirondack highlands and tug hill plateau relative to their counterparts northwest of the shear zone is be lieved to have been enabled by reactivation of the carthage colton shear zone resume le plateau de tug hill est un secteur a forme plutot elliptique situedans le nord de l etat de new york il est plus haut que le paysage avoisinant et il repose surtout sur des strates datant de l ordovicien moyen asuperieur son ca ractere eleveest interpretecomme une reponse passive au soulevement tectonique du socle precambrien adjacent situea l est et au nord est du plateau le soulevement du socle aurait aussi fait que les strates sur le plateau et dans le terrain to pographiquement plus bas vers le nord pendent doucement vers le sud ouest l inclinaison du plateau a probablement ete facilitee par une rotation le long de l extension regionale recemment reconnue de la faille de black river laquelle separe le plateau du socle souleveet marque la limite est nord est du plateau la limite nord du plateau accentuee par un escar pement abrupt est alignee avec la zone de cisaillement carthage colton atendance nord est laquelle forme une impor tante limite tectonique du precambrien le soulevement des terres hautes des adirondack et du plateau de tug hill par rapport aleurs contreparties au nord ouest de la zone de cisaillement aurait eteaidepar une reactivation de la zone de ci saillement carthage colton traduit par la redaction

exhumation of the dahinggan mountains ne china from the late mesozoic to the cenozoic new evidence from fission track thermochronology abstract zircon and apatite fission track ft analyses were used to reveal the exhumation of phanerozoic granitoid intrusions in the dahinggan mountains northeastern china zircon ft ages ranging from 84 5 to 97 8 ma and apatite ft ages from 47 3 to 67 4 ma with mean track lengths between 12 3 2 3 and 13 3 2 2 m respectively were obtained for the phanerozoic granitoids sampled along a south south west to north north east transect across the dahinggan mountains three cooling stages from the late mesozoic to the cenozoic have been identified in the studied region based on ft results and modeling stage one was a rapid cooling period from the closure temperature of zircon ft to the high temperature part of the apatite ft partial annealing zone 210 110 c during 90 57 ma stage two was a relatively slow cooling period 110 60 c occurred between 57 ma and 20 ma suggesting that the granitoids had been exhumed to depths of 1 2 km the final stage was a cooling period 60 20 c occurred since the miocene which bring studied samples to the earth s surface at an accelerated exhumation rate the estimated maximum exhumation is 5 km assuming a steady state geothermal gradient of 35 c km our results indicate that this exhumation is possibly led by the pacific plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling

early cretaceous uplift and erosion of the northern appalachian basin new york based on apatite fission track analysis abstract the thermal history of outcropping devonian sediments of the northern appalachian basin new york has been investigated using fission track analysis of detrital apatites from 57 sandstone samples based on lengths and apparent age measurements using fission tracks in apatite it is concluded that lower devonian sediments presently at the surface in the catskill region were cooled rapidly from temperatures higher than about 110 c during early cretaceous times 120 140 ma ago in the western part of new york wellsville buffalo data from late devonian sediments are consistent with cooling at the same time as that identified for the catskill region but from lower temperatures in the range of approximately 80 110 c the maximum temperature these sediments experienced since deposition for a pre uplift paleogeothermal gradient of 25 35 c km the confined track length data indicates uplift and erosion of 2 3 km for western new york and greater than 3 4 km for the catskill region a differential uplift pattern which is consistent with the historical stratigraphic data from the region this conclusion is at variance with earlier interpretations put forth by others rapid broad scale uplift and erosion of the scale identified imply that large volumes of sediment could have been supplied from the northern appalachian basin during the early cretaceous this timing for the dominant post devonian cooling phase in the basin is not accounted for by recent models of the tectonic evolution of the appalachian orogen but is compatible with the change from carbonate to siliciclastic deposition in the atlantic coastal plain it is suggested that this style of broad regional uplift without significant deformation is characteristic of a tectonic regime associated with and subsequent to continental rifting apatite fission track analysis is shown to be a basic tool in providing fundamental limits for thermal history assessment in regional tectonic problems

hidden cretaceous basins in nova scotia early cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of nova scotia are preserved in narrow half grabens obscured by glacial drift the chaswood formation sediments can be subdivided into three members upper and lower members dominated by cyclical sand mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin ferruginous oxisols are common in the fine grained facies of the upper and lower members seismic data indicate that chaswood formation strata in the elmsvale basin are deformed into steeply dipping faults and fault related folds rutherford road fault zone an aptian albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the late cretaceous and tertiary that truncates the chaswood formation exhumation of a thick cover of mesozoic sediment 1 2 km is needed to account for the preservation of chaswood formation outliers after 80 ma of erosion the half grabens that host the chaswood formation were formed in the mesozoic and were antecedent to the present day structurally controlled lowlands

the effects on seismic waves of interconnected nearly aligned cracks summary transfer of fluid between connected cracks may occur during the passage of seismic waves such fluid flow can be modelled using an extension of effective medium theory hudson et al 1996 and is effected via non compliant pores the flow is governed by a parameter representing the relaxation time of pressure equalization between cracks however if the cracks are fully aligned and have the same aspect ratio the theory produces the unexpected result that at low frequencies the cracks are effectively isolated and at high frequencies they are fully drained the artificial restriction of the model to perfectly aligned cracks of identical aspect ratio is seen to be the cause of this result by reworking the model to allow the crack orientation and aspect ratios to vary we see that a more realistic model has the usual properties in which the cracks are isolated at high frequencies and undrained at low frequencies we have chosen the distributions of aspect ratios to be in agreement with observation hay et al 1988 thomsen s parameters thomsen 1986 and the attenuation coefficients are seen to be frequency dependent via the non dimensional parameter

isotopic constraints on emplacement age of anorthositic rocks of the marcy masiff adirondack mts new york the igneous emplacement age of anorthositic rocks comprising the marcy massif have been constrained by fixing minimum and maximum ages for their intrusion minimum ages have been fixed by a u pb dating of cores of air abraded zircons from the anorthosite 1113 ma b u pb dating of baddeleyite within the anorthosite 1087 ma c u pb dating of baddeleyite from an olivine metagabbro crosscutting marcy massif anorthosite 1109 ma d u pb zircon dating of jotunitic rocks crosscutting the marcy anorthosite massif 1143 pm 31 ma maximum emplacement ages are based upon a sheets of anorthositic rock crosscutting mangeritic charnockitic gneiss dated by u pb zircon at 1125 pm 10 ma 1134 pm 4 ma and 1135 pm 43 ma and b anorthosite related pyroxenite dikes crosscutting mangerite that contains xenoliths of identical pyroxenite these results constrain emplacement of the marcy anorthosite to 1113 1138 ma with the most probable age in the interval 1125 1135 ma this time of in

age progressive volcanism in the new england seamounts and the opening of the central atlantic ocean radiometric ages k ar and oar 39ar methods have been determined on dredged volcanic rocks from seven of the new england seamounts a prominent northwest southeast trend ing volcanic lineament in the northwestern atlantic ocean the oar 39ar total fusion and increnental heating ages show an increase in seamount construction age from southeast to northwest that is consistent with northwestward motion of the north american plate over a new england hot spot between 103 and 82 ma a linear volcano migration rate of 4 7 cm yr fits the seamount age distribution these ages fall within a longer age progression from the corner seamounts 70 to 75 ma at the eastern end of the new england seamounts to the youngest phase of volcanism in the white mountain igneous province new england 100 to 124 ma the new england hot spot estimated from the new radio metric ages and motion of north america in the hot spot reference frame to be near 28on 33ow probably generated a short line of mid to late tertiary age seamounts on the african plate but appears to be presently inactive the hot spot reference frame is used to calculate the motion of the north american plate away from the african plate from early cretaceous time to the present rominent magnetic anomalies recorded in the central atlantic seafloor give the positions of the spreading ridge for a bange of known ages hot spots that now underlie the african plate in the eastern central atlantic new england canary madeira cape verde azores could have produced cretaceous seamount and island chains on the north american plate during the early opening of the central atlantic each of these hot spots has been overridden by spreading ridges at pre dictable times some of these hot spot crossings are expressed as geochemical anomalies in the oceanic crust now far removed from spreading ridges

unified pipe network method for simulation of water flow in fractured porous rock abstract rock masses are often conceptualized as dual permeability media containing fractures or fracture networks with high permeability and porous matrix that is less permeable in order to overcome the difficulties in simulating fluid flow in a highly discontinuous dual permeability medium an effective unified pipe network method is developed which discretizes the dual permeability rock mass into a virtual pipe network system it includes fracture pipe networks and matrix pipe networks they are constructed separately based on equivalent flow models in a representative area or volume by taking the advantage of the orthogonality of the mesh partition numerical examples of fluid flow in 2 d and 3 d domain including porous media and fractured porous media are presented to demonstrate the accuracy robustness and effectiveness of the proposed unified pipe network method results show that the developed method has good performance even with highly distorted mesh water recharge into the fractured rock mass with complex fracture network is studied it has been found in this case that the effect of aperture change on the water recharge rate is more significant in the early stage compared to the fracture density change

coupled hydromechanical modeling of rock fractures under normal stress in this paper a nonlinear poromechanical model is developed for a single rock fracture under normal stress the fracture is represented by a set of voids and the progressive fracture displacement

the deliberate search for the stratigraphic trap an introduction this special publication draws upon contributions to a similarly titled conference the deliberate search for the stratigraphic trap where are we now held at the geological society in london during 2004 observations in this introductory paper have been drawn from the authors experience talks given at the conference and papers within this volume specifically it is noted that by analogy to basins which are perceived to be mature for structural traps stratigraphic traps can have substantial remaining potential additionally current exploration for stratigraphic traps seems rather restricted to areas where seismic data allow the direct assessment of fluid fill and reservoir development it is argued that the industry is probably not doing enough to learn from established stratigraphic traps to guide future exploration for such traps looking forward it is suggested that the industry faces two key challenges firstly the use of all available data to assess fluid type and reservoir presence in areas of unfavourable rock physics and secondly the development of sufficiently sophisticated predictive models of stratigraphic trap development

the northern appalachian anomaly a modern asthenospheric upwelling the northern appalachian anomaly naa is an intense laterally localized 400km diameter low velocity anomaly centered in the asthenosphere beneath southern new england its maximum shear velocity contrast at 200km depth is about 10 and its compressional to shear velocity perturbation ratio is about unity values compatible with it being a modern thermal anomaly although centered close to the track of the great meteor hot spot it is not elongated parallel to it and does not crosscut the cratonic margin in contrast to previous explanations we argue that the naa s spatial association with the hot spot track is coincidental and that it is caused by small scale upwelling associated with an eddy in the asthenospheric flow field at the continental margin that the naa is just one of several low velocity features along the eastern margin of north america suggests that this process may be globally ubiquitous

u pb zircon geochronology of the adirondack mountains and implications for their geologic evolution u pb zircon studies of metamorphosed igneous rocks in the adirondack mountains have yielded preliminary ages within the range 1420 990 ma several geochronologically and geochemically distinct episodes of igneous intrusion and at least one pre granulite facies dynamothermal metamorphic event are documented this information is consistent with recent field and geochronological studies throughout the grenville province and suggests that a complex sequence of events occurred in the adirondack mountains prior to the widespread deformation and metamorphism commonly attributed to the approximately 1100 1000 ma ottawan phase of the grenvillian orogenic cycle