an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

appalachian stress study 1 a detailed description of in situ stress variations in devonian shales of the appalachian plateau we describe an experiment to measure variations in the state of stress within a horizontally bedded devonian shale sandstone limestone sequence in western new york a total of 75 stress measurements were made in three wells a kilometer or so apart using a wireline supported hydraulic fracturing system the stress profiles indicate that a major drop in horizontal stress level occurs in the generally massive shales this drop occurs principally across the lowermost member of a group of sand beds and corresponds to an offset in sh and sh of 3 5 and 9 mpa respectively above the sands thrust regime conditions prevail although the amount by which sh exceeds sv is undetermined since instantaneous shut in pressures isips were clipped at the level of sv due to fracture rotation below the sands the regime is strike slip with both horizontal stresses showing lateral uniformity despite substantial variations in topography the magnitude of sh in the sand beds themselves and a lower limestone remains at least as great as sv despite the decline in shale stress hence stress contrasts between these beds and neighboring shales become pronounced with depth the contrast in sh and sh between the lowermost sand and the immediately underlying shale is at least 6 and 14 5 mpa respectively sh levels in the lower strike slip regime are about 1 75 times greater than sh and are less than the value required to initiate slippage on favourably oriented frictional interfaces for the upper thrust regime and the sand and limestone beds however the inferred lower bound on sh is close to the slippage threshold for a coulomb friction coefficient of 0 6 the orientation of sh is ene with a standard deviation of 20 fracture traces were usually splayed occasionally spanning 30 of well bore no systematic correlation between mean orientation and lithology is evident significantly different orientations were obtained for adjacent tests in which almost identical islps were observed suggesting that the fractures quickly reorient themselves to propagate normal to the least principal stress direction similarly vertical traces were observed in those tests where isips apparently reflect sv suggesting that rotation to horizontal was rapid

the concept of joint saturation and its application two of the major joint driving mechanisms are joint normal stretching and poroelastic shrinkage and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing respectively regardless of joint driving mechanism joint infilling is a nonhomogeneous poisson process in the presence of stress shadows through probability modeling we show that in all cases joint spacing is best fit with gamma distributions the shape parameter of the best fit gamma distribution to joint spacing data is a quantitative means to assess the extent of saturation which is represented in a new parameter the joint saturation ratio jsr to test the utility of jsr we call upon published structural bending joint data elk basin lilstock and rives plate bending experiment the shape parameters for these well developed structural bending joints are equal to around three corresponding to a jsr of approximately 30p using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas prone devonian sections of the appalachian basin we find that natural hydraulic fractures differ in two aspects from structural bending joints first the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections second the joint saturation of natural hydraulic fractures is generally lower than in well developed structural bending joints thus the jsr is a means to distinguish the joint driving mechanism and to represent joint saturation level independent of bed thickness effects it can be used to distinguish natural fractures from drilling induced fractures and to improve the fracture network modeling

jointing within the outer arc of a forebulge at the onset of the alleghanian orogeny the oldest joint set in devonian rocks of western new york state has an atypical ns strike and predates regionally more abundant nw striking and ene striking joints driven by hydrocarbon related fluid decompression the ns joints originated in higher modulus diagenetic carbonate and were driven initially by a different mechanism either joint normal stretching and or thermoelastic contraction the origin of these joints in higher modulus carbonate concretions indicates the presence of a tensile stress produced by uniform regional extensional strain upper devonian shale hosting the ns joints crops out in that area of the appalachian basin where a morrowan erosional unconformity marks the region of maximum upward lithospheric flexure of an early alleghanian forebulge the ns strike of these early joints points to a forebulge stretching axis oriented approximately east west and associated in time and space with crustal loading that drove both the northfieldian orogeny and the underplating of the bronson hill anticlinorium in new england ultimately subsidence of the morrowan forebulge buried the upper devonian shale succession to the oil window during the latter part of the alleghanian tectonic cycle resulting in the propagation of fluid driven nw and ene trending joints in black shale

u pb geochronologic constraints on paleoproterozoic orogenesis in the northwestern makkovik province labrador canada a 45 km wide shear zone bounded segment of the northwestern makkovik province labrador is underlain by archean gneisses derived from the adjacent nain craton this lithotectonic block kaipokok domain was reworked at high metamorphic grade overthrust by supracrustal sequences lower aillik and moran lake groups and intruded by granitoid plutons during the paleoproterozoic initial amphibolite facies reworking of the kaipokok domain at 1896 6 ma is indicated by u pb ages of metamorphic zircon from a foliated kikkertavak metadiabase dyke this is one of the oldest paleoproterozoic tectonic events dated thus far in northeast laurentia and may be linked with ca 1890 ma plutonism documented elsewhere in the kaipokok domain intrusion of granitoid plutons at 1877 5 and in the kaipokok bay area postdates early thick and thin skinned thrusting possibly east to northeast directed that involved lower aillik group strata u pb titanite ages of 1866 1847 ma in part record a metamorphic event that fo

former carboniferous overburden in the northern appalachian basin a reconstruction based on vitrinite reflectance abstract elevated vitrinite reflectance values have been observed in the upper devonian west falls group of the northern new york appalachian basin in new york lopatin modeling suggests that the high thermal maturity of these and associated strata was caused by the presence of a devonian and carboniferous overburden that has subsequently been eroded from the northern appalachian basin devonian overburden reconstructed from extrapolation of stratigraphic data thickens from west 0 4 km to east 2 0 km across the field area in contrast carboniferous overburden reconstructed by lopatin modeling thins from west 2 0 3 4 km to east 0 7 1 2 km the inferred geometry of a northeasterly thinning wedge of sediment is compatible with the existing distribution of late paleozoic sediments in the appalachian basin and suggests the northern part of the basin experienced only moderate subsidence during carboniferous time

chemical and isotopic evidence for hydrogeochemical processes occurring in the lincolnshire limestone over 150 groundwater samples from the lincolnshire limestone have been analysed for ph major ions and 13c ratios where possible field eh and iodide concentrations were measured and methane concentrations were determined for 12 samples stable isotope ratios were determined for soil and rock carbonate samples a system of zonation allows the division of hydrogeochemical processes occurring in the aquifer the use of hydrochemical and isotope data in modelling exercises enables the re evaluation and possible enhancement of the understanding of hydrogeochemical processes the carbonate chemistry of outcrop groundwaters is explained by calcite saturation being achieved under open system conditions in the soil zone 13c ratios in the range 15 99 to 10 57 may be generated from a stoichiometric reaction with possible additional partial and or simultaneous exchange with soil co2 or carbonate the isotopic composition of soil carbonate shows the effects of precipitation from soil waters the incongruent dissolution of primary depositional limestone carbonate results in increasing magnesium and strontium concentrations and increasing 13c ratios for the groundwaters with flow down the hydraulic gradient as a result of incongruent dissolution secondary calcite may be precipitated onto fissure surfaces significant nitrate and sulphate reduction in non saline groundwaters is not supported by the results of hydrochemical and isotope modelling exercises however sulphate reduction and methane fermentation may be affecting the isotopic and chemical compositions of saline groundwaters sodium calcium ion exchange leads to limited calcite dissolution deep in the aquifer but the evolution of these groundwaters is confused by the uncertain effects of oxidation of organic carbon and mixing with a saline end member solution

burwell domain of the palaeoproterozoic torngat orogen northeastern canada tilted cross section of a magmatic are caught between a rock and a hard place

post alleghanian unroofing history of the appalachian basin pennsylvania from apatite fission track analysis and thermal models results of apatite fission track analyses on 29 ordovician through permian sandstones from the appalachian basin in pennsylvania are presented ages range from 111 17 to 184 10 ma mean track lengths of 10 71 0 29 to 13 10 0 17 m with unimodal negatively skewed length distributions are indicative of slow cooling the data separate into two groups on an age versus mean length plot the younger group 111 144 ma is found in the structural depressions of the anthracite basin and the broad top basin and adjacent appalachian plateau the older group 144 184 ma is found in the structurally higher southwestern appalachian plateau and juniata culmination and adjacent central plateau fission track data suggest that the basin cooled slowly after the alleghanian orogeny with culminations cooling earlier than depressions cooling histories modeled from apatite fission track data with maximum temperatures constrained by vitrinite reflectance indicate cooling beginning soon after the alleghanian orogeny except in the juniata culmination which apparently experienced synorogenic cooling and unroofing during formation of the underlying duplex model cooling histories and available geologic information indicate that the foreland basin did not experience mesozoic reheating unroofing histories were modeled from fission track cooling histories using heat flow estimates and burial depths derived from vitrinite reflectance profiles the models suggest that the unroofing history of the appalachian basin in pennsylvania can be divided into three episodes an initial episode of relatively rapid cooling and unroofing late permian early jurassic is attributed to flexural rebound of the foreland in response to erosional removal of alleghanian topographic load initial unroofing rates are higher in eastern pennsylvania than in the west consistent with a flexural model an episode of little to no unroofing middle jurassic late oligocene began contemporaneously with the inception of drift at the atlantic continental margin at this time unloading of the orogen was replaced by subsidence and sedimentation on the new margin without flexural rebound the driving force for unroofing of the basin was removed and unroofing slowed greatly an episode of rapid unroofing over the full width of the basin occurred from the miocene to the present although the driving mechanism for unroofing at this time has not been identified it is consistent with increased sedimentation rates in the middle atlantic offshore basins for the same period

geopressured jurassic reservoirs in the viking graben modelling and geological significance abstract formation pressure data from jurassic and triassic reservoirs of 192 wells 68 in the norwegian sector 124 in the uk sector in the viking graben have been analysed several different pressure regimes are distinguished an open system consists of hydropressured reservoirs adjacent to the east shetland platform in the west and the horda platform in the east a restricted system consists of moderately geopressured reservoirs overpressure typically lower than 1500 psi located at greater distance from the platforms and is interpreted to be in partial pressure communication with the open system through lateral or vertical pressure drainage a closed system consists of geopressured reservoirs practically isolated from the open system in this system formation pressure is assumed to be representative of the various overpressuring mechanisms active locally pressure data analysis suggests that pore pressure is mainly controlled by rapid loading aquathermal pressuring oil generation and possibly by shale dewatering above the depth for the onset of gas generation formation overpressure typically in the range 1500 2500 psi gas generation is interpreted to constitute a major overpressuring mechanism below that depth formation overpressure higher than 2500 3000 psi in the former case a pore pressure gradient approximately 50 higher than the hydrostatic gradient is estimated in the latter case a much more drastic overpressure increase with depth is suggested this model also applies to the norwegian central graben where only a limited number of wells tested jurassic reservoirs despite unavoidable simplification and approximation this model is believed to provide a better understanding of the areal distribution of geopressured jurassic reservoirs in the viking and central grabens it may be used to impose constraints on hydrocarbon migration models and for prediction of porosity preservation in relation to reservoir overpressuring

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

decompression reactions and p t conditions in high grade rocks northern labrador p t t paths from individual samples and implications for early proterozoic tectonic evolution

mechanisms of natural fracturing in a sedimentary basin mechanisms of natural fracture generation in a sedimentary basin may be studied by the use of physical properties of sedimentary rocks and of pore fluid pressure the physical properties of rocks such as poisson s ratio and young s modulus under laboratory conditions are available but only a few of these are reported under subsurface conditions in this paper in situ values of poisson s ratio derived from analysis of artificial hydrofracturing data in the gulf coast are used for estimating horizontal stresses in both hydrostatically and abnormally pressured zones there in a tectonically relaxed basin such as the gulf coast the horizontal stress can be a function of vertical overburden stress fluid pressure and poisson s ratio the horizontal stress increases with depth in the hydrostatic pressure zone but is abnormally low in the abnormally pressured zone fracture pressure and its gradient given as a sum of least horizontal stress and fluid pressure is however not abnormally low in the abnormally pressured zone because the fluid pressure there is abnormally high this paper describes the in situ fracture pressure gradient estimated for the gulf coast area on the basis of models of vertical fluid charging through an aquifer and a fault system during continuous burial the depth at which the charged fluid pressure gradient exceeds the fracture gradient or the point of natural hydrofracturing is estimated after an erosional event the most significant decline of fracture pressure gradient is expected in the uppermost part of the original abnormal pressure zone hydrofracturing there could occur if an effective fluid is charging from deep to shallow through an aquifer or a fault system if the erosion continues to a point at which approximately two thirds of the total sediment thickness is removed the horizontal stress may become almost zero if such a stress condition is developed the sedimentary rocks become greatly relaxed possibly causing fractures

is there a genetic relationship between selected regional joints and contemporary stress within the lithosphere of north america on the appalachian plateau of new york ene striking joints parallel the mid continent contemporary stress field and do not correlate with other structures joints within ohio indiana michigan and west virginia also parallel the mid continent maximum horizontal compression as indicated by hydraulic fracture measurements in northern indiana where the contemporary stress field deviates significantly from the orientation of the mid continent stress the attitude of the joints deviates accordingly in addition to joints structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid continent stress field from this i conclude that these joints are mode i cracks whose orientation corresponds to the contemporary tectonic stress field in itself the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults and folds

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

multi stage zircon and monazite growth revealed by depth profiling and in situ u pb geochronology resolving the paleoproterozoic tectonics of the trans hudson orogen on southeastern baffin island canada abstract understanding the growth and recrystallization of zircon and monazite during regional metamorphism is important for identifying the nature and timescales of tectonic processes in continental crust we present extensive in situ u pb monazite geochronology and u pb zircon depth profiling analyses from the mid crust exposed on southeastern baffin island canada in the internal zone of the paleoproterozoic trans hudson orogen in situ la icp ms u pb monazite dating on ten metasedimentary rocks totalling 300 analyses from different paleodepths reveals a dominant ca 1860 1820 ma monazite population that records regional mid amphibolite to granulite facies metamorphism with coeval fabric development subordinate monazite with ages between ca 1800 1750 ma are interpreted to have formed through dissolution reprecipitation the sims u pb depth profiling technique allowed dating of ca 1861 1833 ma zircon rims and less abundant ca 1800 1764 ma zircon rims that would be unresolvable using conventional spot dating trace element depth profiling via la icp ms shows that zircon rims typically have lower th u values higher hf contents and different ree compositions than zircon interiors zircon rim compositions are highly variable with no apparent link to u pb age and are interpreted as the combined result of metamorphic zircon growth and dissolution reprecipitation our data demonstrate that the timing of peak metamorphism is recorded by both monazite and zircon and that they are both sensitive to u pb age resetting at lower temperatures during late orogenic tectonism regional mid amphibolite to granulite facies metamorphism and east directed crustal shortening are bracketed between ca 1860 1820 ma these events are interpreted to result from the accretion of cratonic blocks in the internal zone of the trans hudson orogen the integrated geochronological approach on regionally distributed samples enabled us to document ca 1800 1750 ma monazite domains and zircon rims which we interpret to result from the terminal collision with the lower plate superior craton followed by late to post orogenic tectonothermal activity that continued for at least 70 myr after thermal peak this prolonged history is characteristic of the northeastern trans hudson orogen and implies that orogenic collapse may not be a hallmark of all hot thickened orogens

the value of iodide as a parameter in the chemical characterisation of groundwaters abstract brackish and saline groundwaters can severely constrain the use of fresh groundwaters their chemical characterisation is important in understanding the hydraulic conditions controlling their presence in an aquifer major ions are frequently of limited value but minor ions can be used iodide in groundwater is particularly significant in many environments due to the presence of soluble iodine in aquifer matrix materials iodide is found in groundwaters in parts of the english chalk aquifer in concentrations higher than are present in modern seawater its presence is considered as a indication of groundwater residence and is of use in the characterisation of fresh as well as saline waters under certain circumstances modern seawater intrusion into aquifers along english estuaries produces groundwaters which are easily identified due to iodide enrichment from estuarine muds in other environments iodide concentrations are of value in distinguishing between groundwaters in limestones and shaly gypsiferous rocks as shown by a study in qatar while in an alluvial aquifer study in peru iodide has been used to identify groundwaters entering the aquifer from adjacent granodiorites

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

the morphology of a saline groundwater body its investigation description and possible explanation in many countries knowledge concerning the occurrence and behaviour of saline groundwaters is becoming even more vital as water resource and waste disposal projects become more sophisticated this paper outlines the approach adopted in and the result obtained from a study of saline water occurrence in an important united kingdom aquifer saline groundwater of concentration up to at least 100 g l 1 cl occurs as a layer of variable thickness below fresh groundwater in the permo triassic sandstones of the lower mersey basin of northwestern england as part of a general water resources study a detailed investigation of the morphology of the saline water body was undertaken using modern and historical chemical data surface geophysics borehole geophysics open hole depth sampling and borehole core porewater analysis it was found that cl concentrations at all sites show a pattern of steady increase to depths of at least 320 m the surface of the saline water body has a considerable topographic variation saline water occurs at highest elevations below the roughly east west trending mersey valley where it approaches ground level but declines in elevation both to the north and south in the north the saline interface meets the rising base of the sandstone sequence at a depth of around 280 m evidence from chemical and viscous flow analogue studies suggests that this ridged topography can be explained in terms of flushing and regional upconing in response to low groundwater heads in the mersey valley

upb geochronology of the northern torngat orogen labrador canada a record of palaeoproterozoic magmatism and deformation abstract the palaeoproterozoic torngat orogen located in northeastern quebec and northern labrador canada records the sinistral transpressional collision of the western margin of the archaean nain province and the eastern margin of the rae province u pb age determinations are presented for twelve samples from the northern part of the orogen and used to evaluate models for its tectonic evolution voluminous granitoid plutonic rocks which in part intrude gneisses interpreted as the northern extension of the nain province and are possibly related to subduction below it have zircon ages of 1910 2 ma 1895 3 ma 1891 2 ma 1890 2 ma 1869 3 2 ma and 1864 2 ma suggesting at least 45 m y of convergence between the rae and nain provinces granulite facies conditions may have existed in the northern part of the area at 1 84 ga these plutonic rocks as well as tonalitic gneisses of the nain province were reworked at amphibolite facies conditions within a north south corridor referred to as the komaktorvik zone zircon age determinations of two granitic veins which were intruded synchronously with ongoing deformation in the komaktorvik zone are 1789 2 ma and 1719 2 ma suggesting that deformation within the zone may have lasted for up to 70 m y metamorphic titanite from samples within the komaktorvik zone have ages of 1776 4 ma 1774 4 ma 1767 4 ma 1710 4 ma and 1632 4 ma and support the interpretation of long lived deformation in the komaktorvik zone palaeoproterozoic subduction beneath the nain province has not been widely recognized in southern parts of the orogen suggesting that a distinct tectonic regime existed in the study area

differentiation of palaeomarine and modern seawater intruded salinities in coastal groundwaters of karaikal and tanjavur india based on inorganic chemistry organic biomarker fingerprints and radiocarbon dating abstract hydrosalinity evolution is examined in the karaikal and tanjavur coastal aquifers situated about 300 km south of madras tamil nadu india ancient and modern sources of solutes in groundwaters have been differentiated using hydro geochemical data environmental radioisotope dates and organic biomarkers results from different techniques show consistently that the pliocene aquifer possesses characteristic palmitoleic and oleic acid biomarkers apparent 14 c ages of more than 20 000 years and high i cl ratio the modern marine estuarine intruded groundwaters in the alluvial aquifer display relatively younger apparent 14 c ages modern to 3000 years enriched potassium ion low i cl ratio and contain vaccenic and hopanoic acid biomarkers and they also tend to display transient changes in chemical characteristics these results have practical importance with regard to identifying and controlling seawater intrusion in coastal areas

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

top seal development in the shale dominated upper devonian catskill delta complex western new york state the preferential generation of vertical natural hydraulic fractures at the contact of the upper devonian hanover gray shale and overlying dunkirk black shale of the catskill delta complex western new york state suggests that the latter served as a hydraulic top seal to formation fluids migrating upward from deeper in the sediment pile petrophysical properties and small scale textural characteristics of these siliceous fine grained rocks confirm the crucial role of depositional environment and sequence stratigraphic position of a shale lithotype in determining its sealing capacity the especially high sealing capacity of the basal interval of the dunkirk shale inferred early high stand systems tract hst strata reflects the anoxic depositional environment of these deposits that favored the preservation of their abundant organic matter and finely laminated depositional texture the absence of bioturbation enabled the undisrupted sediment notably carbonaceous clay rich laminae to undergo rapid mechanical compaction platy grain reorientation and porosity reduction compaction induced squeezing of ductile organic matter into void spaces further reduced pore throat diameters immediately underlying heavily bioturbated deposits of the organic lean hanover shale inferred upper hst or low stand wedge sediments accumulated in a dysoxic depositional environment disruption of layering and homogenization of sediment by burrowing organisms produced a more porous and permeable microfabric through which formation fluids moved only to be arrested by the high capillary entry pressures at the base of the dunkirk shale natural hydraulic fractures some of which propagated into the dunkirk shale formed when fluid pressure at the top of the hanover shale reached the fracture gradient the high sealing capacity of the basal dunkirk shale was probably enhanced by its finely laminated nature and the generation of biogenic methane both of which contributed to the formation of a near impermeable gas capillary seal

joint interaction with embedded concretions joint loading configurations inferred from propagation paths abstract the interaction between propagating joints and embedded concretions in a devonian black shale near seneca lake ny permits identification of the loading configurations responsible for two joint sets of different ages striking at nearly the same orientation the earlier set consists of systematic joints cut by later alleghanian joints of the appalachian plateau the later set consists of non systematic curving cross joints that abut these same alleghanian joints field evidence shows that concretions functioned as stiff inclusions in a compliant black shale as a consequence of this elastic contrast local perturbations in the remote stress field persisted around the concretions during burial tectonic deformation and exhumation these stress perturbations influenced joint propagation paths of both joint sets our conclusions about loading configurations are based on finite element modeling of the effect of the local stress perturbation on concretion modified joint propagation modeling shows that the local stress perturbation from a thermoelastic loading was responsible for deflecting cross joints away from concretions in a curved propagation path near the concretion this load configuration also led to arrest of cross joints before they penetrated the shale concretion interface at greater distances from the concretion the propagation path of cross joints was controlled by the contemporary tectonic stress field the interface between concretions and the surrounding shale was strongly bonded as indicated by the crossing of the interface by some of the systematic ene joints higher compressive stress levels within the concretions relative to the shale suppressed joint development in the concretion causing the arrest of those joints once they had driven across the interface and a short distance into the concretion numerical modeling shows that interface penetration by the systematic ene joints is consistent with a fluid load the same loading configuration postulated for the subsequent alleghanian joints the traces of the systematic ene joints align on opposite sides of concretions rather than curving toward the concretion as predicted by two dimensional models of the fluid load co planar traces are indicative of large planar joints propagating in plane around the concretion making it energetically inefficient for the crack front to curve as it enters the local stress perturbation near the concretion a fluid load for the systematic ene joints came from high pore pressure during the pre alleghanian stages of burial of the devonian catskill delta complex

hydrogeochemical analysis of salinization processes in the coastal aquifer of oropesa castellon spain the coastal aquifer of oropesa is affected by salinization processes undoubtedly associated with intense groundwater exploitation for agriculture supply the aquifer corresponds geologically to a tectonic depression with plioquaternary fill hydrogeologically this aquifer is detrital with intergranular porosity which receives substantial recharge from adjacent mesozoic aquifers contact with the sea in addition to the presence of cultivated soil requiring extreme exploitation of groundwater frequently give rise to processes of seawater intrusion the present research is an attempt to understand the saltwater intrusion in this aquifer using hydrochemical analyses of the behavior of certain minor ions that could help in the characterization process in the case of the oropesa sector groundwater salinization does not appear to be attributable solely to the intrusion of seawater but there are also anomalies related largely to the geology of the sector and its surroundings the type of recharge the hydrodynamic conditions in the specific area etc

an integrated assessment of a type euxinic deposit evidence for multiple controls on black shale deposition in the middle devonian oatka creek formation an integrated lithologic paleontologic and multi proxy geochemical study of the middle devonian oatka creek formation a black shale in the northern appalachian basin indicates that a number of different factors contributed to organic carbon rich black shale deposition conditions leading to this organic rich sedimentary deposit were ultimately controlled by a relative sealevel rise dominantly eustatic but with possible contributions from local tectonics which cut off the supply of carbonate to the basin geochemical proxy evidence such as mo ti fe ti corg spy and 34spy suggests that as sealevel continued to rise after the carbonate supply was cut off a threshold was crossed at which point conditions in the basin shifted from dominantly anoxic to dominantly euxinic anoxic sulfidic bottom waters concurrent with the shift to dominantly euxinic conditions the supply of siliciclastic sediments was cut off resulting in a condensed horizon as evidenced by the elemental ratios of si al and k fe mg and the relative concentration of eolian silt as determined petrographically and from scanning electron microscopy sediment starvation in the basin appears to have facilitated the biogeochemical re cycling of c n and p specifically the elemental ratios of c n and p and the stable carbon isotope composition of organic matter suggest that the preferential regeneration of p under anoxic conditions and of n during the oxic phase of oxic anoxic oscillation led to enhanced primary production in surface waters thereby maintaining euxinic conditions in the bottom waters through respiration of settling organic matter finally it is observed that though conditions in the basin seem to have remained consistently anoxic sulfidic for some time after the initial shift to euxinic conditions a progressive increase in siliciclastic sedimentation led to a corresponding decrease in the enrichment of various redox related elements illustrating the overriding control that sedimentation can have on geochemical proxy records

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

early jointing in coal and black shale evidence for an appalachian wide stress field as a prelude to the alleghanian orogeny early ene striking joints present coordinates within both pennsylvanian coal and devonian black shale of the central and southern appalachians reflect an approximately rectilinear stress field with a dimension 1500 km this appalachian wide stress field awsf dates from the time of joint propagation when both the coal and shale were buried to the oil window during the 10 15 m y period straddling the pennsylvanian permian boundary the awsf was generated during the final assembly of pangea as a consequence of plate boundary tractions arising from late stage oblique convergence where maximum horizontal stress s h of the awsf was parallel to the direction of closure between gondwana and laurentia after closure the awsf persisted during dextral slip of peri gondwanan microcontinents when sh appears to have crosscut plate scale trans current faults at around 30 sup o following 10 m y of dextral slip during tightening of gondwana against laurentia the awsf was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline shaped alleghanian map pattern seen today

upper mantle and crustal fragments in the ithaca kimberlites xenocrysts and xenoliths from three ithaca kimberlite localities are consistent with derivation from mantle depths of less than 150 km mantle mineral assemblages reconstructed from xenocrysts and rare 2 4 mineral fragments include spinel and garnet peridotites and garnet pyroxenites the cr rich garnets pyroxenes and spinels and the subcalcic diopsides commonly found in mantle xenoliths from other kimberlites are apparently absent secondary pargasitic amphibole attributed to mantle metasomatism is found associated with pyrope garnet al rich pyroxenes and spinels suggest that al spinel lherzolites of the type commonly found in alkali basalts but rarely found in kimberlites occur some of the spinels are the most aluminous ever reported from kimberlites these al spinel lherzolites suggest either a fossil high geothermal gradient or a very undepleted mantle in the ithaca region fragments of presumed crustal origin include a suite of mg rich minerals which may belong to a granulite carbonate assembl

revisiting the hubbert rubey pore pressure model for overthrust faulting inferences from bedding parallel detachment surfaces within middle devonian gas shale the appalachian basin usa abstract both bedding parallel slickensides and cleavage duplexes are forms of mesoscopic scale detachment faulting populating black marcellus and geneseo burket and intervening gray mahantango shales of the middle devonian a section known for abnormal pore pressure below the appalachian plateau the abundance and the orientation of slickensides and cleavage duplexes in the more organic rich black shale relative to gray shale suggests that maturation related abnormal pore pressure facilitates detachment a mesoscopic manifestation of the hubbert rubey pore pressure model for overthrust faulting the former are discrete slip surfaces whereas the latter consists of nested anastomosing slip surfaces either cutting through bedding or on disrupted bedding surfaces stacked as mesoscopic versions of thrust duplexes cleavage duplexes are between a few cm and over 1 m thick with their hanging walls commonly transported toward the appalachian foreland regardless of local limb dip cleavage duplexes are most common near the stratigraphic maximum flooding surface the organic rich section most prone to develop maturation related pore pressure in the middle devonian gas shales bedding parallel slickensides are somewhat more evenly distributed in the black shale but also found in overlying gray shale in both black and gray shales slickensides are more abundant on the limbs of folds an indication of pore pressure related flexural slip folding on the macroscopic scale the pine mountain block of the southern appalachian mountains was enabled by a basal detachment cutting along the upper devonian chattanooga black shale which has a thermal maturity sufficient for the generation of abnormal pore pressure the pine mountain block is a large scale overthrust showing little evidence of collapse of the hinterland side a credible example of a pore pressure aided overthrust fault block of the type envisioned by the hubbert rubey model

joints and decollement zones in middle devonian shales evidence for multiple deformation events in the central appalachian plateau fractures in oriented middle devonian shale cores from the appalachian plateau province provide evidence for multiple deformation events associated with the alleghanian orogeny post orogenic stress relaxation and neotectonic stresses the orientation distribution and mineral paragenesis of these fractures are used to establish the timing regional extent and stress orientation of each deformation event during the alleghanian orogeny the middle devonian shale section was a regional decollement zone in the central appalachian plateau province the decollement extends from the appalachian structural front to northwestern pennsylvania and east central ohio it is defined by abundant joints veins and slick ensided fractures localized within multiple zones of organic rich brown and black shale these zones are distributed over tens to hundreds of meters of the middle devonian shale section the shale cores record a continuous counterclockwise rotation of the maximum compressive stress direction in the west central appalachians during the alleghanian orogeny three stages are recognized 68 refs 10 figs 3 tabs

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

the role of soil organic matter in the geochemical cycling of chloride and bromide abstract chloride to bromide ratios were determined for rainfall in western australia and groundwaters and surface waters from a number of catchments in western australia victoria and queensland the ratio in rainfall though showing a large short term scatter on average reflected the ratio in ocean water groundwaters and surface waters often showed characteristic differences in cl br presumably associated with the cycling of bromide through soil organic matter to prove this association it is shown that in the leachate of saturated small columns of soil the cl br ratio is governed by chloride and bromide released from decomposing organic matter on leaching the columns of soil the cl br weight ratio decreased rapidly from a high 300 reflecting rainfall to a low 10 reflecting the ratio of chlorine to bromine bound to soil organic matter

natural fractures in shale a review and new observations natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low porosity and low permeability shale host rock many shale outcrops cores and image logs contain fractures or fracture traces and microseismic event patterns associated with hydraulic fracture stimulation have been ascribed to natural fracture reactivation here we review previous work and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization orientation and size patterns a wide range of shales have a common suite of types and configurations of fractures those at high angle to bedding faults bed parallel fractures early compacted fractures and fractures associated with concretions these fractures differ markedly in their prevalence and arrangement within each shale play however constituting different fracture stratigraphies differences that depend on interface and mechanical properties governed by depositional diagenetic and structural setting several mechanisms may act independently or in combination to cause fracture growth including differential compaction local and regional stress changes associated with tectonic events strain accommodation around large structures catagenesis and uplift fracture systems in shales are heterogeneous they can enhance or detract from producibility augment or reduce rock strength and the propensity to interact with hydraulic fracture stimulation burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated the role of microfractures in production from shale is currently poorly understood yet potentially critical we identify a need for further work in this field and on the role of natural fractures generally

pancake joints in utica gas shale mechanisms for lifting overburden during exhumation abstract the flat creek member of the utica formation along canajoharie creek south of canajoharie ny is populated with unmineralized pancake joints a term for horizontal bed parallel partings each pancake joint propagated outward from a central initiation point with radial growth in excess of 0 5 m in some instances propagation arrests with out of plane growth displaying either a tilt characteristic of an arrest line or bifurcation into a complex set of cylindrical splays or hackles a rough surface morphology relative to vertical fractures i e joints and veins in the flat creek coupled with bifurcation at arrest are the manifestation of an accelerating crack tip reaching critical growth at the shear wave velocity of the shale the lack of mineralization and containment between vertical fractures are consistent with propagation during exhumation one driving mechanism for a late propagation event could be axial splitting which places pancake joints in a class of brittle fracture that includes sheeting joints the high speed propagation is a manifestation of the rapid release of fracture energy characteristic of sheeting joints however we also consider a second driving mechanism natural hydraulic fracturing in the appalachian basin high pore pressure is maintained in gas shale at depths less than 50 of the original overburden if abnormal pore pressure is maintained for 300 my or more it is present when exhumation carries the shale upward through the crossover depth where the least stress becomes vertical if pore pressure exceeds the vertical stress then pore pressure will lift overburden a possible mechanism for maintaining pore pressure during exhumation to shallow depths is a poroelastic phenomenon known as skemption s behavior we posit that pancake joints differ from common sheeting joints because of the additional contribution from abnormal pore pressure as a driving mechanism that allows for deeper propagation depth

finite element analysis of the stress distribution around a pressurized crack in a layered elastic medium implications for the spacing of fluid driven joints in bedded sedimentary rock bedding perpendicular joints confined to individual beds in interbedded sedimentary rocks commonly exhibit spacings which are proportional to the thickness of the jointed bed and which vary according to lithology or structural position the mechanical explanation for this relationship is well understood when the joints are driven by far field crack normal tensile stresses but poorly understood for cracks driven by elevated fluid pressures where the crack driving stress is the difference between the crack normal compression and the fluid pressure in the crack through a series of finite element numerical models we investigate how various parameters influence the driving stress distribution around pressurized cracks in layered media and thereby identify factors influencing the spacing of fluid driven joints for the situation we modeled we observe that 1 crack driving stress is reduced in the vicinity of pressurized joints and that the extent of the stress reduction depends on the contrast in elastic properties between the layers and 2 crack driving stress distribution depends on the ambient pore pressure during jointing these results indicate the spacing of fluid driven joints should depend on lithology and pore pressure

crustal scale flexural slip folding during late tectonic amplification of an orogenic boundary perturbation in the paleoproterozoic torngat orogen northeastern canada large variations in metamorphic grade over short distances disparate orientations and diverse kinematics of contemporaneous structures and a previously unexplained 90 counterclockwise bend in the orogenic boundary of the amphibolite to granulite facies northern segment of the paleoproterozoic torngat orogen are shown to be the result of multiple tectonic events acting upon an orogenic boundary perturbation the perturbation was initiated when a promontory on the nain province margin composed of a 1910 1885 ma continental magmatic arc burwell domain indented the rae province hinterland during the onset of collisional orogeny at ca 1870 ma dn 1 sinistral transpression at ca 1845 1822 ma dn 2 caused formation of the orogen parallel abloviak shear zone and oblique burial of the nain province margin beneath a tilted section of the hot buoyant magmatic arc reactivation of the orogen at ca 1798 1770 ma dn 3 involved crustal scale flexural slip folding of the perturbation and simultaneous exh

geology of the devonian black shales of the appalachian basin abstract black shales of devonian age in the appalachian basin are a unique rock sequence the high content of organic matter which imparts the characteristic lithology has for years attracted considerable interest in the shales as a possible source of energy the recent energy shortage prompted the u s department of energy through the eastern gas shales project of the morgantown energy technology center to underwrite a research program to determine the geologic geochemical and structural characteristics of the devonian black shales in order to enhance the recovery of gas from the shales geologic studies by federal and state agencies and academic institutions produced a regional stratigraphic network that correlates the 15 ft black shale sequence in tennessee with 3000 ft of interbedded black and gray shales in central new york these studies correlate the classic devonian black shale sequence in new york with the ohio shale of ohio and kentucky and the chattanooga shale of tennessee and southwestern virginia biostratigraphic and lithostratigraphic markers in conjunction with gamma ray logs facilitated long range correlations within the appalachian basin basinwide correlations including the subsurface rocks provided a basis for determining the areal distribution and thickness of the important black shale units the organic carbon content of the dark shales generally increases from east to west across the basin and is sufficient to qualify as a hydrocarbon source rock significant structural features that involve the black shale and their hydrocarbon potential are the rome trough kentucky river and irvine paint creek fault zone and regional decollements and ramp zones

curving cross joints and the lithospheric stress field in eastern north america cross joints are late formed nonsystematic fractures that extend across intervals between systematic joints traces of such cross joints are seen on bedding plane surfaces of devonian catskill clastic sedimentary rocks of the appalachian plateau of western new york state where the maximum horizontal principal stress s h is oriented n65 e as indicated by in situ stress measurements between pairs of closely spaced systematic joints traces of cross joints are commonly planar and orthogonal to the preexisting joints however in the mid region between some widely spaced systematic joints in western new york cross joints strike parallel to the s h of the present lithospheric stress field but then curve to abut the preexisting joints at right angles a curving trace reflects a local perturbation of the regional stress field in the vicinity of preexisting joints and the perpendicular termination indicates that the preexisting joints were open depending on their age the strike of the mid region of curving cross joints denotes the orientation of either the neotectonic stress field or its tertiary predecessor in the north american lithosphere

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

the southeastern churchill province synthesis of a paleoproterozoic transpressional orogen the paleoproterozoic southeastern churchill province secp is located in the northeastern canadian shield of labrador and quebec the secp formed through the oblique collisions of the archean nain and superior cratons with a third intervening archean block the core zone the belt has a tripartite structure comprising the torngat orogen to formed by nain craton core zone collision in the east the core zone in the centre and the new quebec orogen nqo formed by superior craton core zone collision in the west the secp thus records transpressional development on the flanks of the superior and nain cratons as they indented northwards to form the larger trans hudson nagssugtoqidian orogenic belt to the north principal stages of tectonic development were 1 2 2 2 1 ga crustal rifting of nain and superior cratons 2 ca 1 9 ga subduction under eastern nain craton 3 ca 1 87 1 85 ga collision of nain craton and core zone to form the to 4 1 845 1 820 ga sinistral transpression in the to and subduction under the western core zone and 5 1 82 1 77 ga collision of superior craton and core zone to form the nqo in association with dextral transpression crustal scale cross sections of the secp have been developed from reflection and refraction seismic data the western part of the nqo is dominantly west vergent and associated with an imbricate thick skinned thrust stack that ramps from the base of the crust the core zone is characterized by a 35 40 km thick crust and pervasive east dipping fabrics related to westerly thrusting the to is a narrow doubly vergent belt associated with a 48 km thick crust that forms a crustal root with a moho relief of 12 km the root is interpreted to result from attempted subduction of the core zone under the nain craton possibly as a result of mid crustal wedging by the nain craton the to was the site of intense convergence that resulted in excision of juvenile crust possibly including tectonic removal of the axial magmatic arc as a result the middle to lower levels of the secp consist largely of refractory archean lithosphere this may account for the lack of widespread post collisional plutonism in the secp and the preservation of the to root

recognizing and quantifying expulsion of oil from the woodford formation and age equivalent rocks in oklahoma and arkansas accumulations of oil in fractures stylolites burrows sandstone lenses and chert nodules deeply embedded within organic rich mature oil source beds of late devonian early mississippian age are considered prima facie evidence of internal migration and expulsion most oil migrated internally and was expelled as a separate phase within a given section in which chert and black shale are interbedded contain the same type of organic matter and have reached the same level of thermal maturity black shales typically contain less hydrocarbons per weight percent toc than cherts the observed differences represent the amount of oil expelled from the black shales and range from 10 to 15 mg g toc for total bitumen 7 to 8 mg g toc for saturated hydrocarbons and 11 mg g toc for volatile hydrocarbons approximately 27 33 of the oil generated in these source rocks was calculated to have been expelled in the main oil producing region of central and southern oklahoma 22 billion bbl of bitumen and 16 billion bbl of saturated hydrocarbons were estimated to have been expelled from the woodford formation relatively efficient separate phase oil expulsion may be characteristic of very rich oil source rocks like those reported here such rocks would reach effective oil saturation and begin to expel oil as a separate phase at a relatively early stage of generation timing and efficiency of oil expulsion must then be influenced by the concentration and type of organic matter in the source rock because these factors determine the volume of oil generated and hence the time when a source rock becomes oil saturated

fractures in mudrocks advances in constraining timing and understanding mechanisms abstract recent advances in fracture timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks methods to constrain fracture timing in mudrocks include i field evidence including crosscutting relationships and evidence of compaction ii petrographic evidence including signs of soft sediment deformation and diagnostic mineral assemblages or textures iii stable isotopic evidence iv thermometric dating using burial history modelling and v radiometric age dating in this contribution we briefly review each method with salient examples from the literature many documented examples of mudrock hosted fractures formed during early burial a non intuitive finding that demands a re assessment of our assumptions about what types of materials can develop opening mode fractures in general the style and distribution of fractures varies dramatically based on fracture timing highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms including the role of fluid flow

kilometer scale upward migration of hydrocarbons in geopressured sediments by buoyancy driven propagation of methane filled fractures several lines of evidence support kilometer scale upward migration of fluids in the gulf of mexico basin discharge of hypersaline brines at the sea floor long term natural hydrocarbon seeps and microseeps gas chimneys lead zinc mineralization in salt dome cap rocks and allochthonous brines in cenozoic sediments we explore the hypothesis that upward fluid transport in geopressured sediments is caused by buoyancy driven propagation of isolated methane filled fractures in other words instead of fluid migrating along a fixed network of interconnected pores or fractures fluid enclosed within an isolated fracture is transported upward by hydrofracturing the mechanically weak geopressured sediments thus the fluid filled fracture propagates upward through the sediments hydrofracture is driven by the pressure difference buoyancy between the enclosed methane and the surrounding sediments our results show that methane filled fractures with half lengths of a few meters should propagate upward through geopressured sediments with velocities of hundreds of meters per year or higher as methane filled fractures increase in volume and decrease in density with decreasing confining pressure they develop the potential to entrain and transport more than 1000 kg m3 of oil or brine methane filled fractures should propagate to the surface unless they are trapped beneath a layer that has high fracture toughness such as salt or are absorbed when they intersect a permeable 10 md sand layer

calculated volume and pressure changes during the thermal cracking of oil to gas in reservoirs 1 the rising temperature that accompanies increasing burial depth converts oil in a reservoir into thermal gas a consideration of hydrogen balance during this cracking shows that approximately 3000 cubic ft 85 cubic meters of gas at standard temperature and pressure is generated from each barrel of oil in addition a graphitic residue is precipitated if the volume relationships among oil thermal gas and the graphitic residue are combined with data for gas solubility in pore water and gas nonideality z factor then pressure can be calculated for any degree of thermal cracking these calculations show that in an effectively isolated system pressures would become very high and could considerably exceed the rock load so that fracturing must occur causing pressure b eed off and loss of gas the lithostatic gradient 1 0 psi ft or 22 6 kpa m is reached after only about 1 0 of the oil is cracked if the reservoir system remains open i e at hydrostatic pressure and is initially filled with oil that is subsequently cracked to gas then roughly 75 of the gas will be lost or the reservoir volume must effectively increase in size for example by moving the gas water contact downward

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

chemical kinetic model of hydrocarbon generation expulsion and destruction applied to the maracaibo basin venezuela this paper describes the development and application of a compositional chemical model of hydrocarbon generation expulsion and destruction for the cretaceous la luna formation source rock of the maracaibo basin venezuela applications include both laboratory and geological settings laboratory pyrolysis experiments were used to study bulk oil generation expulsion and associated changes in composition of the kerogen extractable organic matter and expelled and unexpelled hydrocarbons the laboratory experiments were also used to determine kinetic parameters to quantitatively describe organic reactions via a computer model that also includes simulation of pressure driven primary expulsion over widely varying conditions we show that the chemical model accurately sim lates the experimental results thermal history models for wells in the maracaibo basin were used to simulate hydrocarbon generation and pore pressure development in the la luna formation and expulsion into nearby cretaceous reservoirs results of the modeling indicate that both compaction disequilibrium and organic maturation play important roles in the development of excess pore pressure in the la luna formation the model simulation of the variation of indicators such as rock eval parameters and extract and oil compositions shows generally good agreement with measurements from remaining kerogen oils and extracts recovered from the la luna formation and from nearby cretaceous reservoirs

groundwater chemistry in southeast suffolk u k and its relation to quaternary geology abstract east anglia has a complex pleistocene geological history having been affected both by major changes in the level of the adjacent north sea and by glacial processes the resulting geology has a profound effect on the distribution of water chemistry in the chalk aquifer which underlies the pleistocene deposits a detailed study of the chemistry of the chalk groundwater including strontium fluoride and iodide as well as major elements has shown that this chemistry results from three phases of saline intrusion early pleistocene to modern and at least two periods of freshwater flushing climatic changes and erosional history were important in controlling flushing periods

lithotectonic elements and tectonic evolution of torngat orogen saglek fiord northern labrador a cross section of the eastern part of the early proterozoic torngat orogen is exposed along saglek fiord in northern labrador it shows the transition from a foreland through a frontal zone to the internal zone of the orogen the latter being composed of two lithologically distinct terranes that are part of abloviak shear zone a crustal scale transcurrent shear zone with a sinistral sense of displacement one of these terranes is parautochthonous with respect to the foreland the other is allochthonous and interpreted as being separated from the parautochthon by a cryptic suture ramah group an early proterozoic supracrustal sequence that lies unconformably on archean gneisses in the foreland can be traced across the frontal zone but does not occur in abloviak shear zone in the saglek area tectonic evolution of torngat orogen involved crustal thickening to approximately double normal thickness with transcurrent shearing of the thickened crust taking place during peak metamorphic conditions synmetam

horizontal slip along alleghanian joints of the appalachian plateau evidence showing that mild penetrative strain does little to change the pristine appearance of early joints abstract some alleghanian joints in black shales of the geneseo and middlesex formations of the catskill delta complex finger lakes district new york slipped horizontally up to 8 cm horizontal slip is measured by the offset of ene striking joints alleghanian joints striking 330 350 display a right lateral slip with an average value of 1 9 cm while joints striking 004 010 slip in the left lateral sense with an average value of 1 3 cm the maximum horizontal stress sh driving this slip falls between 350 and 004 the orientation of local alleghanian layer parallel shortening as indicated by both disjunctive and pencil cleavage by commonality of orientation we infer that slip on alleghanian joints is driven contemporaneously with layer parallel shortening if so the offset ene striking joints predate the alleghanian stress field these observations mean that both pre alleghanian and early alleghanian joints persist through a period of penetrative strain

an analysis of horizontal microcracking during catagenesis example from the catskill delta complex horizontal bitumen filled microcracks are common within clay laminae of the finely laminated organic carbon rich shale in the lower half of the heavily jointed upper devonian dunkirk shale western new york state such cracks are not found higher in the dunkirk shale where moderate bioturbation resulted in a relatively porous and permeable microfabric horizontal microcracks in a hydrocarbon source rock that carries regional vertical joints indicating a horizontal least principal stress owe their presence to material properties of the fractured shale and the magnitude and orientation of the crack driving stress during kerogen maturation three material properties favored the horizontal initiation of microcracks in the dunkirk shale 1 the abundance of flat kerogen grains oriented parallel to layering 2 a marked strength anisotropy in large part caused by the laminated nature of the rock and 3 the tight strongly oriented planar clay grain fabric produced by gravitational compaction of flocculated clay at shallow burial depth the latter was especially important to sustaining elevated pore pressure the crack driving stress which was generated by the conversion of kerogen to bitumen poroelastic deformation of the low permeability laminated shale pressurized by catagenesis perhaps enhanced by compaction disequilibrium prior to kerogen conversion elevated the in situ horizontal stress in excess of the vertical stress which remained constant during pore pressure buildup thereby favoring the propagation of microcracks in the horizontal plane

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

isotope palaeohydrology and the prediction of long term repository behaviour there are considerable well recognized difficulties involved in the investigation of very low permeability rocks by conventional measurements of water potentials and spatial distribution of hydrological parameters such as permeability and effective porosity therefore most studies of predictive behaviour are based on models which when unconstrained by data are often worse than no model at all geochemistry and environmental isotope geochemistry are techniques well suited for hydrological investigations of potential sites of nuclear waste isolation and for constraining predictive models stable isotopes constitutive of the water molecule 2h and 18o may give information on the origin of the water especially 2h which is practically uninvolved in isotope exchange with rock forming minerals variations in stable isotope contents can be related to palaeohydrological and palaeoclimatic conditions whereas 3h is indicative of recent recharge the 13c content of dissolved carbon is related to its origin s and the 14c activity gives a time scale however the initial carbon isotope contents can be modified by various diagenetic effects such as precipitation dissolution of secondary calcite and oxidation of reduced carbon the heavy isotope content of the total dissolved inorganic carbon tdic cannot be interpreted without a detailed knowledge of the carbon chemistry and of the mineralogy and isotope contents of secondary carbonates species of dissolved organic carbon doc with high molecular weights hmw can generally be attributed to soil derived compounds their 14c content may be measured by ams accelerator mass spectrometry thus providing an estimate of the time elapsed since recharge took place chlorine 36 is an interesting potential tool for dating old ground waters because of its long half life 301 kyr and its hydrophilic behaviour it can be also produced in situ in significant amount if the rocks are rich some tens of ppm in u and th in such cases this time dependent build up provides a more systematic radiochronometer of ci residence time in the rock than the decay of cosmic input 36ci provided no cl is leached from the rock the isotopic composition of aqueous sulphur compounds depends on their origin and on their diagenetic evolution the redox reactions of so2 4 reduction or of s2 oxidation are marked by strong isotope effects especially when generated by bacteria sulphate reduction by organic matter is a potential source of dissolved inorganic carbon and may thus interfere with 14c age interpretations after discussion of the possible age and origin of waters and solutes some scenarios of evolution of local and regional palaeohydrological conditions are proposed examples are given with special emphasis on detailed results from the fennoscanian shield stripa project and from northern switzerland

loading configurations and driving mechanisms for joints based on the griffith energy balance concept abstract using the griffith energy balance concept to model joint propagation in the brittle crust two laboratory loading configurations serve as appropriate analogs for in situ conditions the dead weight load and the fixed grips load the distinction between these loading configurations is based largely on whether or not a loaded boundary moves as a joint grows during displacement of a loaded boundary the energy necessary for joint propagation comes from work by the dead weight i e a remote stress when the loaded boundary remains stationary as if held by rigid grips the energy for joint propagation develops upon release of elastic strain energy within the rock mass these two generic loading configurations serve as models for four common natural loading configurations a joint normal load a thermoelastic load a fluid load and an axial load each loading configuration triggers a different joint driving mechanism each of which is the release of energy through elastic strain and or work the four mechanisms for energy release are joint normal stretching elastic contraction poroelastic contraction under either a constant fluid drive or fluid decompression and axial shortening respectively geological circumstances favoring each of the joint driving mechanisms are as follows the release of work under joint normal stretching occurs whenever layer parallel extension keeps pace with slow or subcritical joint propagation under fixed grips a substantial crack normal tensile stress can accumulate by thermoelastic contraction until joint propagation is driven by the release of elastic strain energy within the earth the rate of joint propagation dictates which of these two driving mechanisms operates with faster propagation driven by release of strain energy like a dead weight load acting to separate the joint walls pore fluid exerts a traction on the interior of some joints joint propagation under fluid loading may be driven by a release of elastic strain energy and or work by the pore fluid during poroelastic contraction again propagation velocity dictates the driving mechanism with critical to supercritical joint propagation accompanying fluid decompression and subcritical crack propagation taking place under a constant fluid drive during axial shortening a jointing process called axial splitting may occur following wing crack growth from an initial crack tilted relative to the maximum compressive stress here the joint driving mechanism may be either the work of a remote stress i e a dead weight or the release of elastic strain energy i e fixed grips

formation of regional cross fold joints in the northern appalachian plateau abstract fold axis parallel elongation associated with the development of arcuate fold and thrust belts is proposed as a causal mechanism for syn orogenic cross fold joints such a mechanism can be coupled with other joint propagation models providing a widely applicable resolution to the enigmatic origin of regional systematic joints the fold axis parallel elongation model is compatible with kinematic indicators as recorded by a sequence of cross fold joints and related deformational fabrics in the central and northern appalachian plateau modeling of an arcuate tectonic boundary subjected to normal compressive loading demonstrates that tangential tensile stress can be large enough to initiate cross fold joints on the convex side of the tectonic boundary simulated stress trajectories from boundary element modeling bear a strong resemblance to the stress trajectories inferred from the regional cross fold joint patterns in the central and northern appalachian plateau modeling also displays a cratonward decrease in both the tangential stress and the tangential strain such a decrease is consistent with the deformation styles observed in the central and northern appalachian plateau

late paleozoic deformation of the cratonic carbonate cover of eastern north america paleozoic carbonates that cover the eastern half of the north american craton preserved a bedding parallel shortening fabric up to 800 km away from the appalachian ouachita orogenic front as recorded by mechanical twins in calcite a strain fabric is present in 29 of 31 samples from three traverse within the flat lying cratonic cover sequence jasper arkansas to minneapolis bluefield west virginia to madison wisconsin and albany new york to hamilton ontario twinning is found only in paleozoic carbonates and is absent in cretaceous limestones in the two southernmost traverses the orientation of the principal shortening axis e1 is perpendicular to the thrust front and parallel to the thrusting direction of the southern appalachians and the ouachitas the magnitude of calcite shortening strain 6 and the calculated differential stress 90 mpa decrease exponentially away from the orogenic front until twinning is absent the northernmost traverse shows greater complexity probably because of its location in the bend of the appalachian trend the authors conclude that the regional strain fabric preserved in the cratonic cover sequence of eastern north american was produced by late paleozoic orogenic stresses of the appalachian ouachita orogeny and that compressive stresses were transmitted over distances greater than 1200 km awaymore from the active plate margin less

iodine in major danish aquifers iodine in groundwater can have direct importance for human dietary iodine intake in areas where drinking water is of groundwater origin as in denmark knowledge on the sources and processes for the varying iodine concentrations in groundwater is of utmost importance for understanding the variation in iodine intake of the population via drinking water the aim of this study was to characterize groundwater with elevated iodine concentrations and to investigate the sources and processes controlling natural iodine speciation and concentration at four study sites in denmark with postglacial sandy quaternary sandy and cretaceous limestone aquifers analyses included iodide i iodate io3 total iodine ti major ions and stable h and o isotopes dissolved organic iodine doi was calculated by subtracting i and io 3 from ti a diagram of stable 18o and 2h isotopes in danish groundwater was compiled in order to interpret the groundwater iodine geochemistry groundwater had ti concentrations from 5 to 14 500 g l iodine speciation reflected the prevailing neutral to alkaline and reduced conditions at the investigated sites with domination of i and doi correlated with dissolved organic carbon we found three different explanations for elevated ti concentrations at the four danish sites 1 leaching from soil enriched in iodine due to atmospheric deposition and proximity to the sea 2 influence from the marine origin of the aquifer sediment due to desorption of iodine from iodine enriched organic matter or minerals and 3 influence from residual saline water due to upward advective or and diffusive transport of iodine

correlation between abnormal pore pressure and tectonic jointing in the devonian catskill delta using the preferred orientation of chlorite we measured vertical compaction in 53 samples from the devonian catskill delta in central new york state the marine part of this delta contains three levels based on different amounts of vertical compaction these levels correspond roughly to 1 black shales at the base 2 prodelta turbidites and 3 a cap of shallow water sediments including abundant storm washed shell hashes deposited within the wave base the cap is normally compacted whereas the lower two levels are undercompacted tectonic cross fold joints that propagated during the late paleozoic alleghanian orogeny are restricted to the deeper undercompacted levels of the catskill delta whereas unloading cross fold joints pervade the cap the correlation between undercompaction and the distribution of tectonic joints indicates that abnormal fluid pressure was a key mechanism during the propagation of these joints

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

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

tracking the burial and tectonic history of devonian shale of the appalachian basin by analysis of joint intersection style the most pervasive systematic joints hosted by devonian black shale of the appalachian plateau include east northeast joints and younger northwest striking cross fold joints both sets were driven exclusively by fluid pressure generated as a consequence of hydrocarbon related maturation supplemented by subsequent tectonic compaction during the alleghanian tectonic cycle in the more deeply buried proximal region of the catskill delta joints of both sets cross cut however in stratigraphically equivalent black shale of the distal shallower region of the delta to the west 25 of the joint intersections are crosscutting whereas 75 of the intersections are defined by east northeast joints curving into and abutting cross fold joints east northeast joints in the distal shale propagated early but were neither as long nor as pervasive as similarly oriented joints in the more deeply buried proximal delta deposits however these same joints are much better developed more closely spaced stratigraphically lower in the distal shale succession where essentially all intersections are crosscutting it is likely that relatively high contact stress an effective stress on east northeast joints in the more deeply buried parts of the delta enabled the unimpeded transmission of elastic stress concentration at the tip of cross fold joints across the older joints in the distal delta exhumation of the devonian shale sequence following establishment of the contemporary stress field in middle tertiary time to within 1 km of the earth s surface resulted in renewed propagation of east northeast joints the propagation path of the reactivated joints curved into and terminated against cross fold joints at angles of 60 90 the curving to termination intersection style is a manifestation of crack tip stress field blunting as a consequence of slippage along the interface of cross fold joints enabled by exhumation induced relaxation of contact stress on these latter joints it is noteworthy that the orientation of the densely formed east northeast joints parallel to the maximum horizontal stress direction of the contemporary lithospheric stress field likely imparts a meaningful permeability anisotropy to these hydrocarbon source rocks

denitrification in a major limestone aquifer abstract the chalk aquifer of eastern central england is seriously affected by nitrates leached from agricultural land and like many similar aquifers its future as a potable resource must depend considerably on the nature and rates of denitrification the regional distribution of nitrate supports a viewpoint based on thermodynamic criteria that denitrification is actively occurring and that the problem will be short lived more detailed considerations based on major ion and environmental isotope data however indicate that denitrification is not significant and that the apparent lowering of nitrate concentration from 10 to 1 no 3 n in the apparent direction of flow is due primarily to mixing between waters of different origins presence of reduced nitrogen species is possible evidence of denitrification in some older waters 4000 yr b p it is concluded that denitrification can not be relied upon to reduce elevated concentrations of nitrate in modern recharge waters

isotope data on the age and genesis of layered basic ultrabasic intrusions in the kola peninsula and northern karelia northeastern baltic shield abstract new u pb zircon ages and sm nd data are presented for layered basic ultrabasic intrusions of the kola peninsula and northern karelia in the northeastern part of the baltic shield all ages are in the range between 2 5 and 2 4 ga but there appear to exist three phases of intrusion thus the monchegorsk intrusion and the fedorovy pansky massif have ages between 2493 and 2470 ma the kivakka and lukkulaisvaara massifs of the olanga group of intrusions between 2445 and 2435 ma while the imandra lopolith is 2396 7 ma old a narrow range of negative nd t values between 2 3 and 1 2 suggests formation by partial melting of a semi homogeneous enriched mantle source

fracking in tight shales what is it what does it accomplish and what are its consequences fracking is a popular term referring to hydraulic fracturing when it is used to extract hydrocarbons we distinguish between low volume traditional fracking and the high volume modern fracking used to recover large volumes of hydrocarbons from shales shales are fine grained rocks with low granular permeabilities during the formation of oil and gas large fluid pressures are generated these pressures result in natural fracking and the resulting fracture permeability allows oil and gas to escape reducing the fluid pressures these fractures may subsequently be sealed by mineral deposition resulting in tight shale formations the objective of modern fracking is to reopen these fractures and or create new fractures on a wide range of scales modern fracking has had a major impact on the availability of oil and gas globally however there are serious environmental objections to modern fracking which should be weighed carefully against its benefits

natural iodine 129 as an environmental tracer abstract iodine 129 t 1 2 16 my is a naturally occurring tracer which can be used to study hydrologic and geologic processes on time scales up to 100 my the pre bomb atmospheric ratio 129 i i should have been constant in time and space and is the starting value in ground water recharge subsequent ratio changes in ground water should be determined by isotope contributions from three sources recharge water iodine leached from the formation and in situ uranium fission the mathematical expression of these time dependent processes forms the basis for dating and tracing applications the expected behavior of natural 129i in ground water is compared to results from field studies ground water samples from the great artesian basin australia provide an estimate of the atmospheric equilibrium ratio 6 10 13 down gradient changes in water up to 1 my old suggest that subsurface production can be significant the usefulness of 129i as an indicator of brine source and age is verified in brines collected in and around louisiana salt domes the method leads to ages of 7 and 9 my for two brine pockets trapped within jurassic salt and 32 to 40 my for oil field brines in miocene sands adjacent to the domes the results demonstrate the capability of tandem accelerator mass spectrometry to measure as few as 107 atoms of 129i in 10 mg i with 10 precision although such atom sensitivity can be achieved otherwise the accelerator technique is necessary to measure naturally low pre 1945 cosmogenic isotope ratios

uranium series isotopes in the groundwater of the permo triassic sandstone aquifer lower mersey basin u k abstract an investigation of u and th series isotopes in rock and groundwater samples from a permo triassic sandstone aquifer of northwest england is described the groundwaters sampled range in age and composition from fresh and modern to highly saline and ancient with at least two sources of salinity highest u and th concentrations are present in the mudrock beds within the sandstone sequences the 234u 238u and 226ra 230th rock activity ratios suggest that saline waters were once much more extensive throughout the aquifer and have been flushed by several volumes of fresh groundwater since the last glaciation uranium contents and activity ratios confirm that the isotope signatures observed in most of the sampled groundwaters are not the result of simple conservative mixing relations between high u saline waters and low u fresh groundwaters but that the isotopic content of the matrix the matrix mineralogy and fabric the redox conditions the salinity and possibly the carbonate chemistry are all important petrographic studies have demonstrated the multiphase nature of the sandstones and although the isotopic signatures are consistent with the origins of the sampled water as concluded from other hydrochemical and hydrogeological data quantitative modelling of the processes involved is limited by lack of details of u bearing phases pore architecture and the chemistry of u in high ionic strength solutions however ra concentrations are controlled by sorption processes and ra is shown to be mobilised under saline conditions the mechanisms of rn release from the aquifer matrix are reviewed and a rn release factor of 0 11 is calculated this value is believed to be inappropriate as a measure of the recoil supply of the longer lived rn precursors in the u decay series

salinization properties of a shallow groundwater in a coastal reclaimed area yeonggwang korea the need for more agricultural or residential land has encouraged reclamation at the coastal areas of korea since 1200 ad approximately the groundwaters of these reclaimed areas could be expected to reveal hydrogeochemical properties different from those of areas directly affected by seawater intrusion the purpose of this study therefore was to examine the salinization of shallow groundwater in a coastal reclaimed area and to identify the effect of land reclamation on groundwater quality major cations and anions iodide total organic carbon d 18o and 13c were measured to assist the hydrogeochemical analysis chloride d and 18o data clearly show that the na cl type water results from mixing of groundwater with seawater in particular the d and 18o of ca mg cl no3 type groundwaters are close to the meteoric water line but na cl type waters enriched in chloride are 18o enriched with respect to the meteoric water line meanwhile carbon isotopic data and i cl ratios strongly suggest that there are various sources of salinity the 13c values of na cl type groundwaters are generally similar to those of ca mg cl no3 type waters which are depleted in 13c with respect to seawater i cl ratios of na cl type groundwater are 10 100 times higher than that of seawater because the reclamation has incorporated a large amount of organic matter it provides optimum conditions for the occurrence of redox processes in the groundwater system therefore the salinization of groundwater in the study area seems to be controlled not only by saltwater intrusion but also by other effects such as those caused by residual salts and organic matter in the reclaimed sediments

a magmatic sheet origin for thin metagabbroic anorthosite units in the fishog subdomain of the southern central gneiss belt grenville province ontario thin tens of metres wide by tens of kilometres long sheets of metagabbroic anorthosite are a common and intriguing feature of the central gneiss belt cgb southwestern grenville province their

models of convergent boundary tectonics implications for the interpretation of lithoprobe data physical models of convergent boundary processes can provide insights into compressional orogens such as those studied by lithoprobe we summarize the qualitative tectonic style of a series of mode

hydrogeochemical effects of groundwater mining of the sierra de crevillente aquifer alicante spain the groundwater mining of the crevillente aquifer southeastern spain has resulted in the progressive deterioration of water quality with particularly significant increases in chloride sulfate and sodium the possibility of a vertical hydrochemical zoning is deduced that would require examining the importance of the geometry and lithology evaporitic materials in the salinization process the time of water rock contact residence time and dilution by infiltration of rainwater also influences the hydrogeochemistry of the aquifer the hydrochemical data are useful in defining the conceptual model of the aquifer completely karstified with relative homogeneity

fringe cracks key structures for the interpretation of the progressive alleghanian deformation of the appalachian plateau vertical joints in devonian clastic sedimentary rocks of the finger lakes area of new york state are ornamented with arrays of fringe cracks that reveal the complex deformational history of the appalachian plateau detachment sheet during the alleghanian orogeny three types of fringe cracks were mapped gradual twist hackles abrupt twist hackles and kinks gradual twist hackles are curviplanar en echelon fringe cracks that propagate with an overall vertical direction within the bed hosting the parent crack and are found in all clastic lithologies of the detachment sheet abrupt twist hackles propagate as planar features in thick shale beds above or below the siltstone beds hosting parent joints kinks propagate horizontally as planar surfaces from the tips of parent joints in siltstone beds the breakdown of the parent joint into either gradual or abrupt twist hackles depends on the orientation and magnitude of the remote stress field internal fluid pressure and the elastic properties of the bed the twist angle of gradual twist hackles is larger in coarser clastic beds indicating that stress and internal pressure are more important parameters than elastic properties in controlling breakdown assuming that the vertical stress axis s v equals 78 mpa at 3 km burial depth the difference in twist angle between sandstone and shale beds is used to estimate the maximum horizontal stress difference in the shale beds as s h s h 2 5 mpa when s h s h 12 mpa in sandstone beds the twist angle of the fringe cracks and the abutting relationships of parent joints give an indication of the overall change in stress field orientation within the detachment sheet during alleghanian tectonics these parent joints indicate a regional clockwise stress rotation of alleghanian age concordant with the twist angle of fringe cracks throughout the western part of the study area a counterclockwise twist angle in the eastern portion indicates a local stress attributed to drag where no salt was available to detach the eastern edge of the plateau sheet the clockwise change in stress orientation is consistent with the rotation in stress orientation found in the anthracite belt of the pennsylvania valley and ridge but is opposite to the sense of rotation in the southwestern portion of the detachment sheet western pennsylvania and west virginia the two regional rotation domains are separated by the juniata culmination

precise u pb baddeleyite ages of mafic dykes and intrusions in southern west greenland and implications for a possible reconstruction with the superior craton the archaean block of southern greenland constitutes the core of the north atlantic craton nac and is host to a large number of precambrian mafic intrusions and dyke swarms many of which are regionally extensive but poorly dated for southern west greenland we present a u pb zircon age of 2990 13 ma for the amikoq mafic ultramafic layered intrusion fiskefjord area and four baddeleyite u pb ages of precambrian dolerite dykes specifically a dyke located se of ameralik fjord is dated at 2499 2 ma similar to a previously reported ar 40 ar 39 age of a dyke in the kangamiut area for these and related intrusions of ca 2 5 ga age in southern west greenland we propose the name kilaarsarfik dykes three wnw trending dykes of the md3 swarm yield ages of 2050 2 ma 2041 3 ma and 2029 3 ma a similar u pb baddeleyite age of 2045 2 ma is also presented for a se trending dolerite iglusuataliksuak dyke in the nain province the rifted western block of the nac in labrador we speculate that the md3 dykes and age equivalent nne trending kangamiut dykes of southern west greenland together with the iglusuataliksuak dyke after closure of the labrador sea represent components of a single areally extensive radiating swarm that signaled the arrival of a mantle plume centred on what is presently the western margin of the north atlantic craton comparison of the magmatic barcodes from the nain and greenland portions of the north atlantic craton with the established record from the north eastern superior craton shows matches at 2500 ma 2214 ma 2050 2030 ma and 1960 1950 ma we use these new age constraints together with orientations of the dyke swarms to offer a preliminary reconstruction of the north atlantic craton near the north eastern margin of the superior craton during the latest archaean and early palaeoproterozoic possibly with the core zone craton of eastern canada intervening c 2010 elsevier b v all rights reserved less

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective