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

anisotropy of electrical conductivity record of initial strain at the toe of the nankai accretionary wedge an approach based on march s theory is applied to measurements of the anisotropy of electrical conductivity on samples and is used to quantify initial strain at the toe of the nankai accretionary wedge a quantitative determination of strain is possible from simple assumptions passive reorientation offlat pores forming the porous network and existence of a linear relationship between fabric tensor and electrical conductivity tensor we show that this simple model correctly accounts for the increase of anisotropy with compaction at a reference site located in the trench ocean drilling program drill site 1173 at the toe of the accretionary wedge site1174 development of anisotropy in the horizontal plane and concurrent reduction of vertical plane anisotropy are observed this can be explained by 12 horizontal ductile shortening occurring after decollement initiation but before slip on imbricate thrust faults anisotropy in the underthrust sequence is correctly described by vertical compaction consistent with decoupled stress states across the decollement at site 1174 the magnitude of ductile strain implies at least 75m slip on the decollement ductile shortening is associated with porosity loss implying partly drained conditions above the decollement

appalachian stress study 3 regional scale stress variations and their relation to structure and contemporary tectonics using commercial hydrofracture data to supplement published stress data we map regional variations in least horizontal stress magnitude sh and orientation within the paleozoic sediments of the appalachian plateau systematic trends revealed by the data are examined for correlations with structure the study area includes a prominent salt detachment and tectonic history the dominant stress component present at all depths including basement throughout the region is ene oriented compression and is most likely of tectonic origin no deviations from this rule are found that are statistically significant near surface 600 m stresses are consistently greater than the overburden with strike slip regime conditions prevailing below however where the salina salt beds are present thrust regime conditions extend deeper reaching the salt in most places where data are available limited to where the salt is shallower than 1 5 km at the salt a discontinuity in the trend of sh with depth marks the abrupt transition to the underlying strike slip regime characterized by least stress ratios i e rh sh sv in the range 0 5 0 7 and extending to basement the comparatively high stress found above the salt may reflect a difference between the strain histories of the overlying and underlying sections facilitated by mechanical decoupling by the salt and perhaps includes a component of stress remnant from nw oriented alleghanian shortening of the upper section the lower subsalt stress regime extends beyond the eastern salt margin and displays remarkable uniformity over distances of hundreds of kilometers this is particularly evident across ohio where an rh value of 0 6 0 05 appears valid down to basement north of ohio values increase markedly whereas to the south of the salt pinch out in west virginia and eastern kentucky values as low as 0 35 are found in devonian shales at 1 1 5 km depth although values deeper in the section may be higher the northward increasing trend can be reasonably well modeled as the effect of persisting lithospheric flexure due to the pleistocene ice sheet however flexure was much greater in the past and as devonian shales in south ohio west virginia are currently only marginally stable a modest increase over the present flexure would be expected to cause shear failure this suggests that the very low stress in the shales of south ohio west virginia is of different origin and more recent than the pleistocene

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

a comparison of the strain of crinoid columnals with that of their enclosing silty and shaly matrix on the appalachian plateau new york abstract a pole figure goniometer was used to measure the preferred orientation of the basal planes of chlorite in 87 samples from the upper devonian clastic rocks of the appalachian plateau new york interpretation of the preferred orientation according to the theory of march yields an estimate of how much an element of the sediment has changed shape since deposition this deformation can be interpreted according to three distinct models for the strain history all begin with compaction followed by one of three types of tectonic strain 1 a plane strain that conserves bedding plane area by compensating for horizontal shortening with horizontal elongation at right angles 2 one that uniaxially shortens a horizontal line normal to the fold axes without compensating elongation and 3 a plane strain again which conserves the area in the vertical plane containing a shortened horizontal direction by stretching it vertically for lack of suitable names we will simply call the three total strains type b u and v from the initials of the distinguishing features of their tectonic increment the horizontal strain components estimated from preferred orientation are compared at a number of localities with those implicit in the principal horizontal diameters of the elliptical outlines of deformed crinoid columnals found on bedding planes expressed for constant bedding plane area or type b total strain the strain in the direction of greatest elongation measured by preferred orientation was found to range from no recorded strain to 0 19 with a median of 0 04 as a rule however the more intensive strains were recorded in shales with a fine grained phyllosilicate content exceeding 85 by volume in which the mean was 0 07 deformed crinoid columnals in the same set of samples have elongations parallel to their long axes that range from 0 04 to 0 10 with a median and average of 0 07 the discrepancy between the two sets of strain measures at least in the coarser and more permeable rock types may either be real and caused by easier flushing of dissolved ions or may be caused by imperfect strain recording in coarse matrix materials

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

effects of variations in fault slip rate on sequence stratigraphy in fan deltas insights from numerical modeling results from a newly developed numerical model incorporating tectonic subsidence eustasy and sedimentation are presented for rift basin settings in particular we simulate contemporaneous fan delta deposition subsidence and eustatic sea level variations to investigate the three dimensional nature of depositional sequences in the hanging wall of a normal fault a random walk algorithm is used for sediment delivery from source to shoreline together with a nonlinear three dimensional diffusion equation for sediment movement on steep delta foresets three sediment sources are modeled they are located along strike in areas of low medium and high subsidence rates of hanging wall subsidence eustatic sea level variation and sediment supply are derived from studies of active extensional basins the resulting stratigraphy contains three fan deltas with distinct morphologies and internal stacking patterns sequence boundaries and offlap forced regression are restricted to areas of low subsidence toward the fault tip aggradationally stacked deltaic wedges are along strike where subsidence rates are high near the fault center the simulated geometries compare well to natural examples and highlight along strike sequence variability and the importance of local controls in such settings

sediment supply as a control on the variability of sequences an example from the late namurian of northern england currently variations in accommodation space are seen as the major control on facies stacking patterns and stratal geometries this paper emphasizes the importance of the sediment supply variable through the use of a regional stratal surface based interpretation of the late namurian stratigraphy of northern england late highstand palaeogeographies and stacking pattern variations highlight spatial and temporal variations in sediment supply which promote the contemporaneous development of prograda tional aggradational and retrogradational stacking patterns this questions the derivation of relative sea level curves from specific stacking patterns and highlights the potential for miscorrelation in areas with major sediment supply variations

appalachian stress study 2 analysis of devonian shale core some implications for the nature of contemporary stress variations and alleghanian deformation in devonian rocks detailed stress measurements in three boreholes penetrating horizontally bedded devonian silt stones sandstones and limestones above a prominent salt decollement in the appalachian plateau of western new york have revealed variations in horizontal stress magnitudes which correlate with lithologic and stratigraphic units in all wells high differential stress levels up to 20 mpa were found in shales of very high clay content contrary to the proposition that such materials have negligible long term strength elastic modulus data show that stiffer beds generally host higher stress levels and suggest that sand shale stress contrasts result in large part from elastic shortening of the section in response to regional ene compression no correlation between stress and poisson s ratio was found however a major systematic drop in stress level within the generally massive shales which occurs across a group of sand beds near the base of the rhinestreet formation appears to be of different origin the stress offset corresponds to the top of a section which we conclude on the basis of local and regional total strain data derived from chlorite fabric measurements once hosted abnormally high pore pressures the total strain data also suggest the entire section above the salt has been uniformly shortened during alleghanian compression to explain the stress discontinuity two kinematic patterns for alleghanian deformation of the devonian section are proposed both involving abnormal pore pressure development in the sub rhinestreet section in response to limited drainage of fluid drainage of this paleo overpressure is the best available explanation of the stress offset although an additional remnant stress component must also be present to satisfy the stress data precisely

the role of lithological layering and pore pressure on fluid induced microseismicity the success of hydraulic fracturing treatments is often judged by the shape and size of the resulting microseismic cloud however it is challenging to predict the anticipated microseismic cloud prior to treatment we use geomechanical modeling to predict the distribution of the microseismicity prior to the hydraulic fracture treatment we analyze the likelihood of tensile and shear failure due to 1 d variations in local stresses and rock strengths induced by layering and pore pressure for two field cases the deviation in the local stresses from the regional stress field is induced by vertical variations in stiffness this promotes failure of the stronger layers instead of the weaker ones since the stronger layers can become essentially load bearing the simulations and field studies show that 1 microseismic events tend to locate preferentially where layers reach tensile failure due to fluid injection and the number of events tends to decrease in layers that do not reach tensile failure 2 shear initiation can occur in different layers from those failing in tension thereby creating additional fluid migration paths and 3 reactivation of preexisting fractures may occur due to fluid migration even if their orientations are unfavorable numerical modeling is a significant aid in understanding the interplay of regional and local stresses and associated in situ failure due to variations in rock strength pore pressure and stiffnesses in a wider perspective it gives fundamental insights into the understanding of earthquakes and fault localization the mechanisms of fracture development and the role of fractures on fluid circulation and on the in situ stress field

foliation development and refraction in metamorphic rocks reactivation of earlier foliations and decrenulation due to shifting patterns of deformation partitioning reactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation its role has generally been insufficiently emphasized because evidence is best preserved where por phyroblasts which contain inclusion trails are present reactivation occurs when progressive shearing operating in a synthetic anastomosing fashion parallel to the axial planes of folds changes to a combination of coarse and fine scale zones of progressive shearing some of which operate antithetically relative to the bulk shear on a fold limb reactivation of earlier foliations occurs in these latter zones reactivation decrenulates pre existing or just formed crenulations generating shearing along the decrenulated or rotated pre existing foliation planes partitioning of deformation within these foliation planes such that phyl losilicates and or graphite take up progressive shearing strain and other minerals accom modate progressive shortening strain causes dissolution of these other minerals this results in concentration of the phyllosilicates in a simi lar but more penetrative manner to the for mation of a differentiated crenulation cleavage except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds reactivation can generate bedding parallel schistosity in multideformed and meta morphosed terrains without associated folds heterogeneous reactivation of bedding gen erates rootless intrafolial folds with sigmoidal axial planes from formerly through going struc tures reactivation causes rotation or refrac tion of axial plane foliations forming in the same deformation event causing reactivation in those beds or zones in which an earlier foli ation has been reactivated and results in destruction of the originally axial plane foli ation at high strains reactivation also provides a simple explanation for the apparently wrong sense but normally observed rotation of gar net porphyroblasts whereby the external foli ation has undergone rotation due to antithetic shear on the reactivated foliation alter natively the rotation of the external foliation can be due to its reactivation in a subsequent deformation event porphyroblasts with inclusion trails com monly preserve evidence of reactivation of earl ier foliations and therefore can be used to ident ify the presence of a deformation that has not been recognized by normal geometric methods because of penetrative reactivation reac tivation often reverses the asymmetry between pre existing foliations and bedding on one limb of a later fold leading to problems in the geo metric analysis of an area when the location of early fold hinges is essential the stretching lineation in a reactivated foliation can be rad ically reoriented potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events other aspects of reac tivation however can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized for example d grown porphyroblasts may be dis solved against reactivated s and hence appear to have grown syn d

strike variability of clastic depositional systems does it matter for sequence stratigraphic analysis current sequence stratigraphic models are two dimensional in nature and predict variability in depositional dip sections strike and dip variability of sediment supply to clastic depositional systems causes significant changes to sequence architecture so that contrasting yet coeval stacking patterns result these changes ultimately affect prediction potential based on fixed systems tract stacking patterns and relation to relative sea level curves identification of key surfaces in sequences rather than stacking patterns is the most reliable indicator of relative sea level history

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 role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

proterozoic tectonic evolution of the picuris mountains northern new mexico the gross structure of the picuris range defined by the buckled and imbricated km thick ortega formation quartzite is that of a tight synclinorium bounded by limb parallel ductile shear zones folds are moderately inclined horizontal and are locally refolded cleavage transected and cut by ductile faults three boundaries separate lithostratigraphic successions 1 the south dipping pilar shear zone which separates the glenwoody formation from overlying hondo group shows both reverse and normal motion 2 the plomo fault is a south dipping ductile reverse fault which separates the hondo group from the structurally overlying but older vadito group and 3 the north striking picuris pecos fault which truncates both of the other boundaries separates supracrustal rocks from an eastern plutonic terrane granitoids 1680 1450 ma intrude vadito group rocks only the first two boundaries do not juxtapose different tectonometamorphic terranes even though they are major shear zones although the p

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

origin of thick first cycle quartz arenite successions evidence from the 1 7 ga ortega group northern new mexico abstract the 1700 ma old ortega group in northern new mexico represents a 1000 m thick succession of metamorphosed quartz arenites and subordinate pelites published ages of detrital zircon grains from the ortega group indicate that the sediments were derived mainly from 1760 1700 ma old volcano plutonic basement rocks and not from the archean wyoming province to the north evidence for recycling within the ortega group also is lacking consequently the ortega group quartz arenites are considered to be first cycle sediments the compositional and textural maturity of these sandstones is attributed to intense chemical and mechanical weathering abnormally high al contents of pelites within the ortega group imply intense chemical weathering in the provenance similar to present day low relief tropical regions quartz arenites in the ortega group were deposited exclusively within a shallow marine shelf environment influenced by tide storm and wave processes prolonged sediment transport especially on the tide dominated inner shelf in conjunction with inferred gradual subsidence optimized mechanical destruction of labile grains and rounding of quartz grains although the maturity of sediments in the ortega group can be accounted for the mode of origin of 850 m of quartz arenites remains enigmatic thick quartz arenite sequences of global distribution in the phanerozoic coincide with first order eustatic sea level rises world wide occurrences of 1700 ma old thick quartz arenite shelf successions suggest that the ortega group may have accumulated in response to a similar major eustatic sea level rise

rheological characterization of a sedimentary formation from a stress profile inversion summary detailed stress measurements have been carried out within a sedimentary sequence composed of a hard clay formation laying horizontally between two limestone units in the eastern paris basin france orientations of the minor and major horizontal principal stresses are found to be in good agreement with the direction of major shortening that prevailed during the last tectonic stage however their magnitudes exhibit an intriguing evolution with depth while the magnitude of the maximum horizontal stress slowly but regularly increases with depth the magnitude of the minimum horizontal one is larger in the hard clay formation than in the surrounding limestone units contrary to expectation from simple elastic considerations an analytical calculation demonstrates that the genesis of the current stress state may be reproduced by taking into account horizontal strains in two different directions and simulating erosion of part of the overburden with a viscoelastic model for the hard clay and an elastic behaviour for the limestone however the elastic constants that are derived for the limestone in order to fit the measured stress field correspond to a material that is more deformable and has a lower poisson s ratio than predicted by laboratory tests this discrepancy may be explained by a slow long term deformation process in the limestone possibly associated with pressure solution

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

the correlation between low tectonic stress and the appalachian basin quiet zone abstract in order to assess the nature of the appalachian basin quiet zone abqz a region of low seismic activity a minimum horizontal stress profile from sonic logs was calibrated using hydraulic fracture stress measurements in a well from mckean county pa the calibrated minimum horizontal stress profile that best fits with the hydraulic fracture stress data was established using an extended eaton s model that treats rock as a transverse isotropic material with a vertical symmetry axis tiv to achieve a best fit several assumptions are introduced 1 a constant tectonically induced elastic strain of ehmax 3 3 10 4 2 an anisotropic velocity model annie approximation for shales and 3 a bimodal pore pressure distribution with abnormally high pore pressure in the marcellus gas shale other calibration methods assume an isotropic medium a constant tectonic strain gradient corresponding to zero stress at ground surface or constraints from sidewall core data to estimate stiffness constants by testing four calibration methods we find that stress profiles are affected by multiple factors including the ratio of maximum tectonically induced elastic strain over minimum tectonic strain pore pressure in the marcellus biot s coefficients and elastic properties sensitivity analysis was conducted to analyze the influence of these parameters our stress profile is most influenced by pore pressure and tectonically induced elastic strain while other factors had much smaller effects tectonically included strain in the abqz is insufficient to achieve the critical stress necessary to induce frictional slip on favorably oriented faults in the sedimentary cover which presumably speaks to the lack of earthquakes in the basement of the abqz however induced earthquakes from deep disposal wells suggest that basement at the edge of the abqz may be decoupled from the sedimentary cover in which case the cover has relaxed through a time dependent deformation mechanism such as pressure solution creep

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

subsurface geology of the warfield structures in southwestern west virginia implications for tectonic deformation and hydrocarbon exploration in the central appalachian basin data from over 6000 wells and five multichannel reflection seismic lines were used to constrain the subsurface geometry of the warfield structures in southwestern west virginia within the central appalachian basin based on their vertical differences in geometry and structural styles we divided the warfield structures into shallow above the devonian onondaga limestone intermediate between the devonian onondaga limestone and the silurian tuscarora sandstone and deep below the ordovician trenton horizon structural levels shallow structures are related to the alleghanian deformation above the major detachment horizon of the devonian shales and consist of the warfield anticline with a 91 5 m closure and southeast dipping monoclines which aided the northwest migrati n and entrapment of oil and gas at the intermediate level the closure of the warfield anticline is lost because the alleghanian deformation is obscured below the major detachment of the devonian shales which explains the reduced production from the devonian and silurian reservoirs deep structures are characterized by an asymmetric half graben within a continental rift system known as the rome trough in which a thick sequence of sedimentary rocks exists to provide sources for overlying reservoirs although stratigraphic traps may be associated with thickness and facies changes the deep level is structurally unfavorable for trapping hydrocarbons based on changes we found in map trend we divided the warfield structures into a middle segment and southern and northern bends the middl segment is parallel to the new york alabama lineament a northeast trending magnetic gradient the southern and the northern bends are linked to the 38th parallel lineament a west trending fault system and the burning springs mann mountain lineament a north trending magnetic gradient respectively we propose a wedge tectonic model to explain 1 northern and southern bends of the warfield structures and hydrocarbon distribution in the subsurface of southwestern west virginia 2 vertical changes in geometry and structural style from the deeply buried half graben to the overlying asymmetric anticline and 3 geometric and kinematic relationship among the warfield structures the 38th parallel and the burning springs mann mountain lineaments

present day stress states underneath the kumano basin to 2 km below seafloor based on borehole wall failures at iodp site c0002 nankai accretionary wedge we constrain the state of stress to 2 km below seafloor in the nankai accretionary prism at the integrated ocean drilling program iodp site c0002f southwest japan based on borehole wall failures and rock strengths the logging while drilling resistivity images from 872 5 to 2005 5 meters below seafloor show that drilling mud control in riser drilling worked properly to minimize borehole wall failures available breakouts indicate a consistent maximum compression orientation subparallel to the subducting plate margin breakout analysis with drill logs suggests that breakouts occurred only when borehole pressure was slightly lowered and time lag between hole cutting and image logging was several hours this indicates that the observed breakouts are not immediate stress induced failure but brought up into shape gradually with time due to other mechanisms laboratory investigations on deformation and failure of the cores suggest that the time delayed breakout might be a result of progressive rock spall out in borehole wall damage zones that occur at a stress level close to failure condition we constrain stress magnitudes assuming that the stress state is sufficient to bring about the damage zones at the borehole wall an integrated method utilizing breakouts drilling induced tensile fractures and a leak off test suggests that the stress states are on the boundary between strike slip faulting and normal faulting stress regimes and somewhat variable depending on depth the stress magnitudes in the accretionary wedge appear to be controlled by frictional strength of the rock such that the differential stresses are constrained by the laboratory determined frictional coefficients this article is protected by copyright all rights reserved

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

in situ stress amplification due to geological factors in tunnels the case of pajares tunnels spain geological and geomechanical anisotropies can significantly increase the magnitude of in situ stress in a rock mass excavated for tunnelling purposes four tunnels for the new high speed railway lines in pajares in the cantabrian mountains n spain were analysed and significant deformations was found to have occurred in forty specific zones of these tunnels during excavation requiring much more support than envisaged before construction local factors influencing in situ stress have been identified in these zones of the tunnels related to geological structures of high compressive tectonic stress regimes including thrust faults folds with steep flank dip orwith geomechanical anisotropies in contact zones between rock formations of different strengths amethodological procedurewas applied to four tunnels to assess the influence of the geological anisotropies on the insitu stress magnitudes this procedure is based on the analysis of tunnel deformations and the support pressure needed to stabilise the excavations affected by geological anisotropies the increase of in situ stress due to local factors is expressed by the stress amplification factor saf defined by the ratio between the k h v local value estimated in a particular rock mass tunnel zone and the mean k h v regional value representative of the whole rock mass tunnel kregional was estimated from hydrofracture tests and from the tsi index klocal was calculated from the back analysis of the support pressure required to stabilise the deformed tunnel zones saf values for the forty specific tunnel zones ranged from 1 1 to 2 5 this significant increase in the magnitude of in situ stress emphasises the influence of geological and geomechanical anisotropies in tunnel stability and support design the results provide a quantitative approach for assessing structural stresses in rock masses for tunnelling excavations

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

relation between seismic source parameters and mechanical properties of rocks a case study this study attempts to determine the relation between source parameters and mechanical properties of the rock matrix in which the microseismic events occur for this purpose accurate geological mechanical and seismological data were acquired on a gas field experiencing induced seismicity due to its reservoir pressure drop more than 30 deep boreholes depth greater than 4 km are concentrated in a 10 10 5 km volume providing core samples for both geological and mechanical assessment in this study we focus on induced seismic events recorded by the local seismic network over a three year long period characteristics of the seismic sources were obtained using spectral analysis and a dynamic model of failure results point out correlation between physical parameters of the seismic sources and the geomechanical properties of the rocks involved maximal static stress drops are found to be associated with the mechanical strength of the geological strata where the rupture occurs the fracture size using a circular model of failure is also found to be dependent on the geomechanical setting it is found that the size of the seismic fractures is dependent on the layer thickness and the prefracturation of the medium both factors influencing the extension of preexisting discontinuities the parameters of the seismic sources also show important changes when the gas reservoir is reached the reservoir unit experienced a 45 mpa pore fluid pressure drop over a period of 20 years

the role of pore water circulation during the deformation of foreland fold and thrust belts volume loss strain accompanying pressure solution of calcite occurred within both the umbria marches apennines of italy and the appalachian mountains of western new york data from strain markers show that volume loss strain was greater within the shallow portions of the apennines than within the appalachians within the deeper portions of both fold and thrust belts strain was nearly volume constant calcite solubility data suggest that downward circulation of meteoric water is necessary for the 35 volume loss strain of the limestones within the apennines strain at a depth of about 1 km was volume constant and is interpretated as indicative of restricted pore fluid circulation in the appalachians calcite comprises less than 1 of the clastic rocks and a 10 volume loss of this calcite may occur during circulation of connate or dehydration water derived from dewatering of the shales but in an environment that restricts the circulation of meteoric water here the volume of calcite removed 0 1 of the total rock is so small that circulation of meteoric water is not necessary for strain by pressure solution

loading paths to joint propagation during a tectonic cycle an example from the appalachian plateau u s a abstract based on the timing of joint propagation during the history of burial lithification deformation and denudation of clastic rocks within sedimentary basins four types of joints may be distinguished tectonic hydraulic unloading and release tectonic and hydraulic joints form at depth prior to uplift in response to abnormal fluid pressures whereas unloading and release joints form near the surface in response to thermal elastic contraction accompanying erosion and uplift tectonic joints are distinguished from hydraulic joints in that tectonic compaction is a mechanism for achieving abnormal pore pressures leading to the propagation of the former whereas compaction by overburden loading leads to the abnormal pore pressures in the latter case the orientation of unloading joints is controlled by either a residual or contemporary tectonic stress whereas the orientation of release joints is controlled by a rock fabric examples of some of these joints are found within the devonian catskill delta of the appalachian plateau new york during the alleghanian orogeny tectonic joints cross fold joints formed under abnormal pore pressure as indicated by the observation that joints propagated in the siltstones before they developed in shales and by the cross cutting relationships of folds cleavage and joints this sequence is compatible with oil company hydraulic fracture data which show that the least principal stress within sandstone layers is less than that in the intercalated shale layers plumose structures indicate that the joints within siltstones propagated as discontinuous rupture events each of which affected less than a meter of bed length the discontinuous rupturing is compatible with models for natural hydraulic fracturing release joints strike joints post date the alleghanian orogeny as indicated by abutting relationships within the deeper parts of the devonian clastic section unloading joints are orthogonal to the contemporary tectonic stress field

orogeny and stratigraphy numerical models of the paleozoic in the eastern interior of north america a computer model is used to estimate patterns of lithospheric deformation caused by obduction and removal of loads within orogenic belts regions of lithospheric downwarp become sedimentary depocenters and regions of lithospheric upwarp suffer erosion by following the deposition and erosion of sedimentary packages through a number of model time steps it is possible to calculate a synthetic stratigraphy for a given study area this model is applied to the post early ordovician stratigraphy of the eastern interior region of north america the loading that drives lithospheric deformation is associated with the development of the appalachian and ouachita orogens and the independent development of the michigan and illinois intracratonic basins model results are shown to be consistent with presently observed stratigraphy lithology and cumulative erosion and are then used to estimate the configuration of given sediment packages at discrete intervals following their deposition these estimates are presented in the form of isopach maps stratigraphic cross sections and time stratigraphic diagrams as a function of time over the last 470 ma by tracking the burial and erosion history of sedimentary units we are able to establish a cause and effect relationship between particular tectonic events and the extent of preservation of sedimentary units in particular we suggest that the pennsylvanian permian alleghanian orogeny produced major sediment cover over much of the study area

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

quantitative comparison of microfabric and magnetic fabric in black shales from the appalachian plateau western pennsylvania u s a abstract anisotropy of magnetic susceptibility ams has been shown to be a good proxy for crystallographic preferred orientation texture however it is not clear in detail how different factors e g modal composition and preferred orientation define the total ams in a rock black shale samples from a drill core on the appalachian plateau in western pennsylvania were analyzed with respect to their microfabric as determined by texture and microstructure and ams low and high field ams which was measured at room temperature reveals that the ams of the samples is dominated by the para and diamagnetic phases synchrotron diffraction was applied to determine the texture of all relevant mineral phases incorporated in the samples muscovite and chlorite pole figures show single maxima perpendicular to the foliation reflecting dominant flattening strain from these textures and the modal compositions ams models were calculated using the intrinsic magnetic anisotropy of the single crystals the modeled and measured ams are comparable in terms of their principal directions and shapes of the anisotropy ellipsoid for the dominantly paramagnetic samples with the maximum susceptibility axes oriented subhorizontal to the ne sw both textures and ams indicate that the samples have undergone largely bedding compaction with a weak tectonic overprint linked to the alleghenian orogeny our results suggest that the microfabric and the magnetic fabrics on the plateau 200 km away from the allegheny front detect the tectonic shortening the ams modeling demonstrates how the contribution of the intrinsic ams of each mineral controls the ams of the whole rock

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

compaction fabrics of pelites experimental consolidation of kaolinite and implications for analysis of strain in slate abstract compaction of clay and shale results in large reductions in volume as pore water is expelled preferred orientation of the platy minerals increases with compaction strain and loss of porosity according to the march owens model this relationship has been studied quantitatively by experimentally consolidating kaolinite clay from slurries and analyzing the resulting fabrics with the x ray pole figure goniometer and scanning electron microscope sem initial porosity corresponds to the onset of the strain recorded by the preferred orientation and the values of 0 78 for dispersed slurries and 0 76 for flocculated slurries reflect the electrostatic forces between the clay platelets initial porosities of recently deposited fine silt and clay are in the range of 0 60 0 90 and are a function of grain size and mineralogy loss of this initial porosity has a large effect on the subsequent development of slaty cleavage matrix methods were used to model deformation paths for slates in the welsh slate belt preferred orientation of mica and ellipsoidal shapes of reduction spots were simulated for one locality by loss of a 0 60 initial porosity a 6 tilt of the beds and horizontal shortening involving plane strain strain determinations for shales and slates should include the large reduction in volume

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

determination of march strain from phyllosilicate preferred orientation a semi numerical method abstract the tensor for the strain in a fine grained phyllosilicate rich rock can be estimated according to the march theory an extended march equation with seven coefficients relates march strain in a rock to the angular density distribution function adf of the basal planes of its phyllosilicates the adf is mapped from 420 intensity measurements by an automatic x ray pole figure goniometer in the transmission mode five of the coefficients are the independent components of the constant volume strain tensor the two additional coefficients pertain to x ray goniometry the strain tensor and the adf share principal directions by theory by visually determining these directions from the fabric diagram and expressing the extended march equation in reference coordinates coinciding with the principal directions the seven coefficients in the equation are reduced to four applying the levenberg marquardt routine we calculate the remaining four coefficients by a best fit of the adf to the march equation in principal coordinates as an example the strain in a slate from north wales was measured by this method as 0 77 0 05 0 30 0 04 0 57 0 00 which is compatible with the results from the direct measurement of ellipsoidal strain indicators 0 80 0 31 0 57 this is an improvement over earlier estimates on the same sample by means of a graphic approximation 0 81 0 38 0 60 the stability and uniqueness of the solution was tested by convergences starting from a wide range of guess values and its sensitivity to bad estimates of principal direction by test calculations starting from two misalignments of different severity

influence of poroelastic behavior on the magnitude of minimum horizontal stress sh in overpressured parts of sedimentary basins in many sedimentary basins of the world the minimum hori zontal stress s h is greater in overpressured zones than in normally pressured zones at equivalent depths a common explanation is that the frictional slip on listric normal faults keeps the difference between vertical stress s v and s h within certain bounds and the difference is smaller under lower effective stress i e higher pore pressure p p however in the overpressured parts of the central north sea graben united kingdom and the sable subbasin of the scotian shelf canada conventional friction envelopes underestimate the magnitude of s h these data instead indicate that s h increases at a rate proportional to but less than the rate of increase of p p a condition consistent with a p p induced deformation of the rock called poroelastic behavior this paper argues that whereas friction may govern s h in normally pressured basins poroelastic behavior is responsible for the unusually high s h in the overpres sured parts of these same basins data on the p p and s h gradients from these basins suggest that s h p p 0 7

basin sedimentation and the growth of prograding deltas a theoretical model is developed for the infilling of a basin by the progradation of a delta the model simulates four mechanisms for the transfer of sediment from the land to the sea 1 bed load dumping along the delta front 2 hemipelagic sedimentation under the seaward flowing river plume 3 proximal slope bypassing by turbidity currents and 4 the combined effects of both short term wave and tidal action and long term creep and small slides downslope diffusion of the accreting sediment mass the general model is of relatively low precision useful for predicting basin infilling on time scales greater than a few hundred years the river plume portion of the model can predict sedimentation on time scales of less than a year and is designed to reflect the dynamics of a free two dimensional buoyant jet that transports a composite size population of suspended particles the general model allows the prediction of lithologies changing with time and space the model has been used to simulate infilling processes for knight and bute inlets two grabenlike fjord basins along the coast of british columbia model simulations of delta progradation over the last 10 000 years favorably predicted the modern seafloor bathymetry and sediment accumulation rates to within a factor of 2 of measured 210pb 137cs and sediment trap rates

primary and tectonic fabric intensities in mudrocks abstract in this paper we present a summary of quantitative measurements of the preferred orientation of phyllosilicate grains in a variety of tectonically weakly deformed to undeformed fine grained pelitic rocks we also briefly examine a small amount of data on clay fabrics in deep sea cores and compare them to fabrics in deformed equivalents from the mariposa formation and calaveras complex sierra nevada california the measured fabric ellipsoids support the following conclusions 1 a bedding parallel foliation forms in pelitic rocks during compaction that in our samples is associated with shortening between 3 and 74 2 the amount of compaction is in part controlled by the quartz feldspar content interbedded sandy layers undergo little to no compaction and do not develop bedding parallel foliations and 3 it is impossible to determine precisely the amounts of compaction horizontal shortening and later tectonic strain in deformed samples because of the variability of initial compactions our data and results presented by others indicate that strain paths in pelitic rocks always include early compaction followed by an episode of simultaneous compaction and plane strain in accretionary wedges and by a variety of other types of strain in other settings

correlation between magnetic anisotropy and fabric for devonian shales on the appalachian plateau the magnetic anisotropy of devonian black shale samples was measured from two cores drilled in the appalachian plateau the mineralogy of the shales is predominantly clay with small quantities of quartz and minor amounts of opaques and chlorite magnetite is the predominant ferromagnetic mineral present in the samples the magnetic fabric was measured at both room temperature and liquid nitrogen temperature and is dominated by a well defined bedding vertical compaction and a lesser defined magnetic lineation measurements of the anisotropy of magnetic susceptibility ams at liquid nitrogen temperature which enhances the paramagnetic contribution in the rock showed a strong increase in both the bulk susceptibility and susceptibility differences this increase suggests that the ams is controlled by the paramagnetic minerals particularly the clays and chlorite strain was measured from the orientation of basal planes of the chlorite crystals by texture goniometry good correlations have been found 1 between the orientation of the magnetic lineation and the long axes of the chlorite crystals and 2 between the degree of magnetic foliation and the amount of vertical compaction the magnetic lineation also agrees well with the direction of seismic anisotropy over the plateau the anisotropy of the anhysteretic remanence which expresses the anisotropy due to the ferromagnetic component in the rocks shows a weaker correlation with the amount of vertical compaction a weak magnetic lineation suggests that the magnetite grains were aligned during a deformation phase which post dates the main alleghanian orogeny the magnetic anisotropy of the devonian shales mirrors the compaction and tectonic fabric on the appalachian plateau

geophysical log responses and their correlation with bed to bed stress contrasts in paleozoic rocks appalachian plateau new york a 1 km profile of in situ stress and geophysical log data was acquired in the wilkins well to study the relationship between rock properties and in situ stress contrasts the wilkins well penetrates devonian clastic rocks on the appalachian plateau near the town of south canisteo new york open hole hydraulic fracture stress measurements were made in stratigraphic sequences where geophysical logs indicated significant bed to bed variations in elastic and lithologic properties analysis of stress magnitudes and interval averaged geophysical data shows that principal horizontal stress magnitudes correlate directly with elastic stiffness and inversely with clay content a similar relation is found for older paleozoic strata penetrated by a well at auburn new york correlations between stress magnitude and geophysical properties observed in the wilkins and auburn wells provide strong evidence that bed to bed stress variations arise from a uniform ene wsw directed strain acting on beds of different young s modulus rather than from variations in rock shear strength because of their high young s modulus sandstones siltstones and limestones in the northern appalachian basin are likely to be stronger barriers to hydraulic fracture propagation than shales porosity logs in the wilkins well show that the large decrease in horizontal stress found at the base of the rhine street formation occurs where shales are less compacted the correlation with undercompaction is consistent with a paleo overpressure drainage mechanism as the cause for the stress decrease

structural analysis and stratigraphic problems of precambrian rocks of the picuris range new mexico precambrian metasedimentary and amphibolite rocks of the picuris range have formerly been divided into the ortega group and the overlying vadito group we present the results of a structural analysis of a small area straddling the contact between these two groups younging criteria and structural facing relationships show that the vadito group as formerly defined together with the piedra lumbre formation of the ortega group is an overturned sequence in fault contact with the remainder of the ortega group the relative ages of the two groups are unknown and their determination depends on interpretation of regional structure and structural history we define four possible structural models each of which would favor but not require reverse slip on the boundary fault suggesting that the vadito group is probably in part or entirely older than the ortega group possible models for development of the observed geometry are 1 rotational fault in major second generation folds 2 a folded and faulted angular unconformity between the two groups 3 major refolding of an earlier nappe like structure and 4 minor refolding and faulting of major first generation folds

three dimensional numerical modeling of coarse grained clastic deposition in sedimentary basins a three dimensional numerical model of clastic deposition in sedimentary basins is used to investigate the development of coarse grained deltas in response to relative sea level changes the model incorporates fully three dimensional sediment delivery and deposition together with incised channel formation and slope failure a combined random walk steepest descent algorithm is used to simulate sediment delivery from a drainage basin outlet to the depositional shoreline together with a nonlinear three dimensional diffusion equation for modeling slope dependent sediment erosion transport and deposition when sediment channels transport pathways are out of a specified grade advective erosion occurs thereby increasing the total sediment supply delivered to the basin multiple sediment sources into a basin can be simulated together with tectonic subsidence and eustatic sea level changes the model results presented display many of the key features observed in both modern and ancient coarse grained deltas during periods of slowly changing and high relative sea level highstands a broad delta front progrades approximately radially away from the sediment source conversely incised channels are developed during rapid falls of relative sea level leading to localized deposition of deltaic lobes at the mouths of these channels the incised channels initiate at the exposed delta front and propagate backward toward the sediment source the rate of growth of incised channels is shown to be an important control on delta morphology sediment distribution and lowstand lobe size and location lobes are particularly well developed during periods of slowly changing low relative sea level lowstands periods of rapid rise of relative sea level lead to flooding and infilling of incised channel systems and a rapid landward shift in deposition transgressions incised channels and delta lobes are best developed in a model where tectonic subsidence is similar to that expected for hanging wall sourced deltas in extensional half graben settings in contrast both channels and lobes are less well developed in a model where tectonic subsidence is similar to that expected for footwall sourced deltas in such settings many of the features developed in the models are by their nature three dimensional and two dimensional analysis of the model results can lead to erroneous interpretations of the causes of along strike variability these aspects of sequence variability have important implications for the application of the sequence stratigraphic methodology to many sedimentary basins