sub ice topography and meteorite finds near the allan hills and the near western ice field victoria land antarctica we have investigated the glaciological causes of large meteorite concentrations on blue ice fields west and southwest of the allan hills in antarctica a sub ice topography map for the area was prepared from data of a radio echo sounding survey the map reveals a mesa type paleosurface it was formed prior to and modified by glacial processes during the initial stage of glaciation of antarctica ice flow toward mawson glacier north of the allan hills is largely confined to a n s trending depression between the allan hills ice field and the near western ice field blue ice at the margins of the ice stream flows over the mesas on both sides of this depression meteorites entrained in blue ice are uncovered by sublimation and ablation we present arguments showing that currently almost all of the blue ice flowing into the allan hills ice field is sublimated leaving meteorites on the ice surface we present evidence that windblown meteorites are trapped by snow bridges across crevasses resulting in a near surface meteorite concentration near the ice ridges of the allan hills ice field nevertheless most meteorites are exposed for only a short period of time to the atmosphere before they are blown by the wind across the ice toward the western foot of the allan hills from where they are slowly carried northward to mawson glacier and the ross sea

seismicity induced by wastewater injection in washington county ohio influence of preexisting structure regional stress regime and well operations recent seismicity in washington county ohio has been suggested to be induced by wastewater disposal operations despite injection 2 km above the precambrian basement we investigated the relationships between disposal well locations and operational histories spatio temporal patterns of seismicity enhanced by waveform correlation and mapped subsurface structures we also analyzed proxies for in situ stress conditions to evaluate existing principal stress orientations and magnitudes double difference relocations of small ml 2 1 seismicity revealed linear clusters defining a ne sw orientation that parallels the trend of small amplitude folds in upper paleozoic rocks within 1 2 km of the injection well hypocenter depths of 3 1 to 4 3 km indicate seismicity occurred along faults below the silurian injection interval in lower paleozoic strata and precambrian crystalline basement similar folds faults imaged in nearby seismic reflection lines were associated with basement involved fault systems that cut the injection interval targeted by the injection well providing permeability pathways for fluid pressure increases that initiated slip interpreted faults were also optimally oriented in the regional stress field for reactivation due to injection related decreases in effective stress well completion records suggest that during the recorded seismicity the long run 1 well was injecting disposal fluids close to or above the fracture pressure of the targeted silurian injection interval a comparison of observed seismicity rates and monthly injection records from the disposal well also indicate a close correspondence between earthquake frequency and injection rate taken together these results provide a physical framework for understanding why wastewater disposal operations induced the washington county seismic sequence

martin brasier s contribution to the palaeobiology of the ediacaran cambrian transition martin brasier s work spanned almost the entire geological column but the origin of animals and the nature of the cambrian explosion were areas of particular interest to him martin adopted a holistic approach to the study of these topics that considered the interplay between multiple geological and biological phenomena and he sought to interpret the fossil record within the broad context of geological biogeochemical and ecological changes in the earth system here we summarize martin s main contributions to this area of research and assess the impact of his findings on the development of this field karl popper would have said that palaeontology is not real science because you can t go out and sample it i think absolutely the opposite i think this is actually where science is it s trying to guess what lies over the hill and map terra incognita when people come in and colonize that s just technology martin brasier 2013 excerpt from a phone interview in moor 2016

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

skeletal faunas of the lower cambrian yu anshan formation eastern yunnan china metazoan diversity and community structure during the cambrian age 3 abstract the lower cambrian stage 3 yu anshan formation in yunnan province south china hosts the chengjiang lagerstatte an exceptional window on the cambrian explosion however skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates here we characterize a new assemblage of small shelly fossils from the maotianshan shale member of the yu anshan formation the assemblage consists of univalved mollusc hyolith and brachiopod shells trilobite and bradoriid carapaces chancelloriid sclerites sponge spicules and echinoderm ossicles combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies we performed quantitative comparisons of the genus level taxonomic diversity and modes of life and nutrition of four mutually equivalent early cambrian age 3 paleocommunities 1 skeletal faunas of the inner shelf 2 predominantly soft bodied faunas of the intra shelf basin 3 archaeocyathan faunas of the carbonate shelf and 4 sponge dominated faunas of the slope to basin areas the taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat ecospace ranges though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats the present integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the cambrian explosion than do investigations based on single communities

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

cephalopod ancestry and ecology of the hyolith allatheca degeeri s l in the cambrian evolutionary radiation abstract pyritized elongate conical conchs of allatheca degeeri s l are common in dysoxic dark gray mudstone intervals in the early cambrian upper terreneuvian series 2 boundary interval cuslett formation at keels eastern newfoundland wave oriented horizontal specimens are most abundant in this cool water high latitude off shore shelf facies of the early palaeozoic avalon microcontinent based on conch morphology shell microstructure and the operculum the species is an orthothecid hyolith comparison with the sizes of the early shells of planktic gastropods indicates a non planktic life mode of a degeeri s l hatchlings although buoyancy calculations show that small juveniles with septate conchs to ca 17 mm long could have been nektic planktic if smaller a degeeri s l individuals had a non benthic mode of life they and pseudoconodonts were the oldest skeletalized pelagic nektic animals in the cambrian evolutionary radiation most a degeeri s l conchs at keels are horizontally embedded and show a bimodal wave determined orientation but about 10 of the large conchs are vertically embedded with their aperture down as larger shells were not neutrally buoyant the vertical orientations of about 10 of the conchs suggests an infaunal likely detritivore life mode suggestive of a scaphopod available morphologic and taphonomic evidence suggests that the vertically embedded conchs are in situ remains of dead benthic animals that colonized the bottom in better oxygenated intervals based on the current knowledge of early palaeozoic hyolith and cephalopod larval and adult morphologies existing hypotheses of a planktic origin of cephalopods from hyolith ancestors are evaluated and no evidence for such an evolutionary relationship is concluded to exist

interpreting ancient ice in a shallow ice core from the south yamato antarctica blue ice area using flow modeling and compositional matching to deep ice cores 1 we explore methods of dating a 101 m ice core from a bare ice ablation area in the yamato mountains dronning maud land east antarctica there are two unknowns the age of the ice at the surface and the age spanned by the core the ice crystal growth rate was used to estimate the age span of the core at about 5 kyr co2 ch4 and n2o data on the core were compared with well dated records from deep cores leading to two plausible matches both within isotope stage c detailed comparison of high resolution dep records from this core and the dome fuji core support the 55 61 kyr bp fit best oxygen isotope values in the core were then used to constrain the source elevation of the snow in the core and hence the velocities in a simple flow line model we inverted the ice core surface age age span and origin site and their confidence intervals in a sensitivity study of flow model parameter space the flow line model predicts good matches to the core by reducing glacial flow rates to 70 of present day accumulation rates by 45 with 10 confidence intervals the modeled surface age for the whole meteorite field yields maximum surface ages of about 90 kyr which is consistent with known but poorly constrained tephra dating meteorite terrestrial ages and the frequency of meteorite discoveries this approach can be used quite generally to link deep ice cores to surface outcrops on blue ice fields

epica dome c record of glacial and interglacial intensities abstract climate models show strong links between antarctic and global temperature both in future and in glacial climate simulations past antarctic temperatures can be estimated from measurements of water stable isotopes along the epica dome c ice core over the past 800 000 years here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile the consistency between stable isotope derived temperature and other environmental and climatic proxies measured along the edc ice core is analysed at the orbital scale and compared with estimates of global ice volume mis 2 12 and 16 appear as the strongest glacial maxima while mis 5 5 and 11 appear as the warmest interglacial maxima the links between edc temperature global temperature local and global radiative forcings are analysed we show i a strong but changing link between edc temperature and greenhouse gas global radiative forcing in the first and second part of the record ii a large residual signature of obliquity in edc temperature with a 5 ky lag iii the exceptional character of temperature variations within interglacial periods focusing on mis 5 5 the warmest interglacial of edc record we show that orbitally forced coupled climate models only simulate a precession induced shift of the antarctic seasonal cycle of temperature while they do capture annually persistent greenland warmth models fail to capture the warming indicated by antarctic ice core d we suggest that the model data mismatch may result from the lack of feedbacks between ice sheets and climate including both local antarctic effects due to changes in ice sheet topography and global effects due to meltwater thermohaline circulation interplays an mis 5 5 sensitivity study conducted with interactive greenland melt indeed induces a slight antarctic warming we suggest that interglacial edc optima are caused by transient heat transport redistribution comparable with glacial north south seesaw abrupt climatic changes

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

ice motion and mass balance at the allan hills blue ice area antarctica with implications for paleoclimate reconstructions we present a new surface balance and ice motion dataset derived from high precision gps measurements from a network of steel poles within three icefields of the allan hills blue ice area antarctica the surveys were conducted over a 14 year time period ice flow velocities and massbalance estimates for the main icefield mif are consistent with those from pre gps era measurements but have much smaller uncertainties the current study also extends these measurements through the near western icefield nwif to the eastern edge of the mid western icefield mwif the new dataset includes for the first time well constrained evidence of upward motion within the allan hills mif indicating that old ice should be present at the surface these data and terrestrial meteorite ages suggest that paleoclimate reconstructions using the surface record within the allan hills mif could potentially extend the ice core based record beyond the 800 000 years currently available in the epica

the succession of small shelly fossils especially conoidal microfossils from english precambrian cambrian boundary beds small shelly fossils especially conoidal microfossils have potential for biostratigraphic correlation of precambrian cambrian boundary rocks where evolutionary successions of taxa can be recognized a succession of hyoliths brachiopods and species of sunnaginia torellella eccentrotheca and rhombocorniculum can be recognized in the home farm member of nuneaton and or the comley limestone of shropshire england revised ranges of taxa are given and sunnaginia neoimbricata n sp s parva n sp s angulata n sp eccentrotheca grandis n sp and several new records are described from nuneaton and comley the similarity in the sequence of small shelly fossils in england and siberia indicates that a correlation can be achieved between the two areas it is suggested that the lower tommotian to lower atdabanian correlates with the hartshill formation of nuneaton of which the condensed home farm member spans the mid tommotian to lowest atdabanian while the upper atdabanian to lower botomian correlates with the condensed comley limestone of shropshire

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

microfossils and precambrian cambrian boundary stratigraphy at maldeota lesser himalaya an assemblage of problematical microfossils of precambrian cambrian boundary age is redescribed from the chert phosphorite member at the base of the lower tal formation of maldeota in the lesser himalaya of india this assemblage has previously been ascribed to various ages from precambrian to cretaceous but is held by us to contain maldeotaia bandalica protohertzina anabarica group trumpet shaped elements acicular elements a b conotheca sp ovalitheca cf multicostata allathecid sp a barbitositheca ansata hexangulaconularia cf formosa coleoloides aff typicalis hyolithellus aff insolitus h cf isiticus h vladimirovae spirellus shankari and olivooides multisulcatus these compare closely with assemblages found above the base of the first anabarites trisulcatus protohertzina anabarica zone in china and in the second pseudorthotheca costata zone of southern kazakhstan the stratigraphic setting of the krol tal succession is reviewed and several similarities are noted between the precambrian cambrian boundary successions of lesser himalaya in india and of yunnan and sichuan in southwest china indicating that correlation between them is possible at several levels

timing and temperature of decollement on hydrocarbon source rock beds in cyclic lacustrine successions abstract the generation of hydrocarbons causes lubrication of source rock bedding planes which can enhance deformation during basin subsidence and subsequent tectonic events deformation includes decollement i e gravitational sliding of rocks above the lubricated horizon in cyclic sequences such as occur in many lacustrine basins decollement is generally restricted to the organic rich beds of the cycle case studies in lacustrine successions in the devonian orcadian basin scotland and the triassic jurassic hartford deerfield basin usa show that movement of material associated with the decollement surface occurred in the current down dip direction these extensional basins experienced rapid subsidence and a high heat flow such that hydrocarbon generation and therefore decollement occurred early in the basin histories during extension half graben rotation ensured that the beds were dipping during hydrocarbon generation facilitating decollement inversion of the orcadian basin reactivated decollement surfaces involving thrust motion in some cases minerals precipitated in tension cavities associated with decollement yield fluid inclusion homogenization temperatures in the ranges 96 139 c and 85 96 c for the orcadian and hartford deerfield basins respectively these data are consistent with burial into the oil window at depths of between 1 5 and 2 0 km

joint initiation in bedded clastic rocks abstract two general types of sedimentary structures serve as initiation points ip for cross fold joints in siltstone beds of the ithaca formation appalachian plateau new york planar bed boundaries and geometrically complex features such as bedforms trace fossils and soft sediment deformation structures the relative abundance of each ip type varies with the stratigraphic position of the jointed body when they are mechanically isolated by thicker shales siltstone bodies have a higher percentage of ip associated with complex features this association supports the hypothesis that sedimentary structures serve to concentrate stress thus becoming preferred sites for primary joint initiation secondary joint initiation occurs at planar bed boundaries through interaction with pre existing joints in adjacent siltstone beds that are mechanically coupled to form composite joints the propagation path of joints passing through planar bed boundaries of composite joints can be traced backward to primary ip at complex sedimentary structures modeling suggests that when beds are mechanically coupled the modest joint tip stress concentration across a shale layer e g

climate archives from 90 to 250 ka in horizontal and vertical ice cores from the allan hills blue ice area antarctica abstract terrestrial meteorite ages indicate that some ice at the allan hills blue ice area ah bia may be as old as 2 2 ma as such ice from the ah bia could potentially be used to extend the ice core record of paleoclimate beyond 800 ka we collected samples from 5 to 10 cm depth along a 5 km transect through the main icefield and drilled a 225 m ice core s27 at the midpoint of the transect to develop the climate archive of the ah bia stable water isotope measurements d of the surface chips and of ice core s27 yield comparable signals indicating that the climate record has not been significantly altered in the surface ice measurements of 40 ar atm and 18 o atm taken from ice core s27 and eight additional shallow ice cores constrain the age of the ice to approximately 90 250 ka our findings provide a framework around which future investigations of potentially older ice in the ah bia could be based

lower cambrian anabaritids from south china anabaritids are a distinctive group of early skeletal fossils with tri radially symmetrical tubes they occur in the earliest cambrian deposits and seem to be especially characteristic of the tommotian strata and putative pre tommotian units e g manykay horizon a detailed redescription of anabarites rotundus qian from near kuanchuanpu shaanxi province emphasizes the degree of morphological variation new data on shell composition suggest a bilayered structure the outer unit composed of fibres parallel to growth lines overlying a distinctive inner lamella with a chevron ultrastructure tentative evidence for anabaritids possibly being operculate is presented the putative operculum being a simple convex disc more poorly preserved anabaritids from the yangtze gorges hubei province and meishucun yunnan province are referred to a trisulcatus all these chinese occurrences of anabaritids are consistent with a lower tommotian age of the associated faunas but reliable and precise correlations with other precambrian cambrian boundary sections remain inconclusive

cold glaciers erode and deposit evidence from allan hills antarctica here we report previously undescribed features of erosion and deposition by a cold polar glacier a recent study challenged the assumption that cold glaciers neither slide nor abrade their beds but no geological evidence was offered the features we describe include abrasion marks subglacial deposits glaciotectonically deformed substrate isolated blocks ice cored debris mounds and boulder trains all products of a recent cold ice advance and retreat mapping these features elsewhere in antarctica will document recent shifts in the east antarctic ice sheet margin providing new insight on regional mass balance changes

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

deformation conditions for fracturing in the middle devonian sequence of the central appalachians during the late paleozoic alleghenian orogeny in the central appalachians fluid inclusion microthermometry and oxygen and carbon stable isotope analysis vein minerals from the middle devonian shale section show that fluid conditions pressure temperature and composition are constantly changing during deformation and vary spatially across the fold thrust belt the earliest fractures in the region formed prior to folding early during the alleghenian orogeny as the rocks were buried into the oil generation window they contain minerals that contain degraded hydrocarbon inclusions and basinal brine inclusions during multiple vein reopening events later mineral stages contain increasingly more mature hydrocarbon fluids late quartz mineralization is pervasive and typically contains the high temperature brine inclusions the vein opening history is related to changes in fluid connectivity associated with 1 burial by over thrusting and or syntectonic depositional loading and or 2 folding during uplift and erosion initial fracture formation and fluid trapping depths range from 3 5 km 2 2 mi in the plateau province and along the appalachian structural front to 4 5 to 5 0 km 2 8 to 3 1 mi in the valley and ridge province late stage fracturing and fracture reopening is related to the maximum syntectonic burial which varies from about 4 km 2 5 mi in the plateau to over 11 km 6 8 mi in the valley and ridge fractures in the valley and ridge and western pennsylvania plateau provinces cannot be categorized into the simple and classification model burial history modeling indicates that fractures forming within and near the end of the oil window were nnw and nw striking not ene striking fractures

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

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

applications of twin analysis to studying meteorite impact structures abstract this paper describes a technique twin analysis of dolomite and calcite which was used to estimate the level of erosion of an impact crater if the age of impact is known the level of erosion gives the amount of sediments present at that time the estimate of the level of erosion and the presence or absence of tectonic strains in calcite constrains the age of impact this technique might also be useful in identifying deeply eroded impact structures twin analysis gives the greatest shortening direction e 1 tilt corrected e 1 directions converge at or above the present day surface if a shallow gas explosion or meteorite impact explains the structure rather than a deep gas or cryptovolcanic explosion the energy density recorded by twinning distinguishes an impact from a shallow gas explosion for structures 100 m diameter at serpent mound a well established impact structure e 1 directions converge at 1400 390 m 95 confidence interval of the mean above the present day structure and the sample closest to the center of the structure records an energy density of 1 7 10 7 j m 3 these results are consistent with previous studies showing that serpent mound is an impact e g r w carlton c koeberl m t baranoski g a schumacker discovery of microscopic evidence for shock metamorphism at the serpent mound structure south central ohio confirmation of an origin by impact earth and planet sci lett 162 1998 177 185 the level of erosion and other data suggests that serpent mound formed between 290 and 256 ma and was originally 8 5 to 11 km in diameter dolomite twinning is not observed at serpent mound suggesting that this technique may only be useful for studying larger more deeply eroded structures

deep radiostratigraphy of the east antarctic plateau connecting the dome c and vostok ice core sites several airborne radar sounding surveys are used to trace internal reflections around the european project for ice coring in antarctica dome c and vostok ice core sites thirteen reflections spanning the last two glacial cycles are traced within 200 km of dome c a promising region for million year old ice using the university of texas institute for geophysics high capacity radar sounder this provides a dated stratigraphy to 2318 m depth at dome c reflection age uncertainties are calculated from the radar range precision and signal to noise ratio of the internal reflections the radar stratigraphy matches well with the multichannel coherent radar depth sounder mcords radar stratigraphy obtained independently we show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar related age uncertainty of approximately 1 3 1 2 that of the ice cores reflections are extended along the byrd totten glacier divide using university of texas technical university of denmark and mcords surveys however core to core connection is impeded by pervasive aeolian terranes and lake vostok s influence on reflection geometry poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas we demonstrate that while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances careful survey planning is necessary to extend ice core chronologies to distant regions of the east antarctic ice sheet

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

palaeoecology of the archaeocyathan reefs from the lower cambrian harkless formation southern nevada western united states and carbon isotopic evidence for their demise abstract archaeocyath sponges the first group of reef building organisms have a globally distributed albeit restricted stratigraphic occurrence archaeocyathan reefs are well known from the western united states particularly in units like the montenegro poleta and harkless formations of the white inyo ranges and esmeralda county nevada while it is recognized that these organisms disappear at some time above the last occurrence of their reefs in the harkless formation the precise timing of their disappearance is unknown here we show that the last archaeocyathan reefs in the upper harkless formation near gold point nevada are overlain by 20 60 m of interbedded siltstone and carbonate that preserve a negative carbon isotopic excursion consistent with the aece event archaeocyath extinction carbon excursion point counts of reef thin sections and analysis of acid insoluble residues of reef and reef adjacent samples illustrate that these last reefs also harbor previously undescribed diversity and abundance of animals living in and among the reefs including an array of small shelly fossil taxa we confirm previous work that the reefs of the early cambrian were ecologically diverse and functioned in many ways like reefs of the later paleozoic even just prior to their global demise in the late early cambrian and that the extinction of archaeocyaths is recorded in strata of the harkless formation

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

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

atmospheric composition 1 million years ago from blue ice in the allan hills antarctica here we present direct measurements of atmospheric composition and antarctic climate from the mid pleistocene 1 ma from ice cores drilled in the allan hills blue ice area antarctica the 1 ma ice is dated from the deficit in 40ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12 m section at the base of a 126 m ice core the 1 ma ice appears to represent most of the amplitude of contemporaneous climate cycles and co2 and ch4 concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion ppb respectively these concentrations together with measured d of the ice are at the warm end of the field for glacial interglacial cycles of the last 800 ky and span only about one half of the range the highest co2 values in the 1 ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka the lowest co2 values are 30 ppm higher than during any glacial period between 450 and 800 ka this study shows that the coupling of antarctic temperature and atmospheric co2 extended into the mid pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in antarctic blue ice areas

microstructures of bedding parallel faults under multistage deformation examples from the southeast basin of france abstract we conducted a microstructural analysis of bedding parallel faults bpfs in mesozoic clay rich layers of the southeast basin of france various microstructures are recognized in thin sections under a petrographic microscope and by cathodoluminescence the microscale observations are combined with outcrop observations from previous studies to provide insight into the origin of the bpfs and their evolution during successive phases of deformation in a basin that had a polyphase tectonic history the bpfs slipped while normal faults were formed during the oligocene extension then another phase of slip occurred later during the basin inversion these two phases of deformation are expressed by recurrent crack seal veins pull apart veins and stylolites in addition calcite veins with an elongate blocky morphology suggest an opening normal to bedding before the reactivation the bpfs initiated in clay layers that were shallow dipping such conditions may appear mechanically unfavourable for an opening normal to bedding or a shearing parallel to bedding we suggest that the role of rock anisotropy is critical this study furthermore demonstrates that bpfs can be long lived brittle structures that may record successive tectonic events

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

microfossils and small shelly fossils from the lower cambrian hyolithes limestone at nuneaton english midlands the lower cambrian sequence at nuneaton is outlined with attention to the 2 m thick home farm member including the hyolithes limestone and its faunal succession at the type locality woodlands quarry hartshill there follows the first modern description and illustration of microfossils and small shelly fossils from this member of thirty two species covered here twenty are described and illustrated from nuneaton for the first time and eight of these are new records the varied fauna includes phosphatic and calcareous microproblematica especially coleoloides typicalis protoconodonts agglutinated foraminifera cap shaped mollusks primitive bivalves hyoliths inarticulate brachiopods and sponges the fauna has affinity with fossils in the top tommotian to lower atdabanian rocks from siberia and china from the baltic area and the belt from southwest newfoundland to massachusetts modified journal abstract

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

characterization of the seismically imaged tuscarora fold system and implications for layer parallel shortening in the pennsylvania salient abstract the tuscarora fold system tfs is located in the pennsylvania salient in the foreland of the valley and ridge province the tfs is imaged in high quality 3d seismic data and comprises a system of small scale folds within relatively flat lying lower silurian tuscarora formation strata we characterize the tfs structures and infer layer parallel shortening lps directions and magnitudes associated with deformation during the alleghany orogeny previously reported lps data in our study area are from shallow devonian and carboniferous strata based on outcrop and core analyses above the shallowest of three major detachments recognized in the region seismic data allows us to characterize lps at depth in strata beneath the shallow detachment our lps data orientations and inferred magnitudes are consistent with the shallow data leading us to surmise that lps during alleghanian deformation fanned around the salient and was distributed throughout the stratigraphic section and not isolated to strata above the shallow detachment we propose that a nw se oriented alleghanian maximum principal stress was perturbed by deep structure associated with the non linear margin of laurentia resulting in fanning of shortening directions within the salient

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

magnetic fabric in amphibolized eclogites and serpentinized ultramafites in the marianske lazně complex bohemian massif czech republic product of exhumation driven retrogression abstract the largest body of metabasic rocks in the bohemian massif the marianske lazn complex mlc represents an early paleozoic ophiolite complex which experienced poly metamorphic evolution with an early high pressure amphibolite followed by eclogite and subsequent amphibolite facies overprint this study aims to investigate the fabric relationships among the rock bodies and to analyze the deformation recrystallization history of the mlc using the anisotropy of magnetic susceptibility ams magnetic susceptibility of the mlc rocks varies according to the presence of para and ferromagnetic minerals as well as according to the primary lithologies in weakly magnetic rocks km the results of ams indicate that the orientation of magnetic minerals in most rocks is related to the last exhumation and retrogression event that occurred in amphibolite facies conditions however there are some well preserved eclogites possessing the magnetic fabrics that are at least partially related to prograde or peak pt conditions during metamorphism in addition massive metagabbros that suffered only weak deformation partially preserve the intrusive magnetic fabrics

on the mid pleistocene transition to 100 kyr glacial cycles and the asymmetry between glaciation and deglaciation times 1 a mechanism is proposed for the mid pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations the same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41 kyr oscillations prior to the transition these features arise naturally within the framework of the sea ice switch glacial cycle mechanism of gildor and tziperman 2000 as a result of the gradual cooling of the deep ocean during the pleistocene this cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets it is this latter change that leads to the activation of the sea ice switch and therefore to the initiation of the 100 kyr oscillations the gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods this proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid pleistocene gradual cooling of the deep ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 1620 global change climate dynamics 3309 1640 global change remote sensing 4267 oceanography general paleoceanography keywords climate dynamics glacial cycles mid pleistocene transition 100 kyr 41 kyr

deep ice cores the need for going back in time abstract after the success of epica the european project for ice coring in antarctica which at dome c east antarctica has provided access to climate and environmental records covering the last 800 ka thousands of years the ice core community is now engaged in the challenge to obtain older records obtaining a 1 5 million year ma record of climate and greenhouse gases is one of the priorities of the international partnerships in ice core sciences ipics largely motivated by the yet unexplained shift in climate cyclicity around the mid pleistocene transition mpt around 1 2 ma ago from epica results and recently published articles we further examine how such a 1 5 ma old ice core will help and is indeed indispensable to depict and understand this transition

mechanisms controlling rupture shape during subcritical growth of joints in layered rocks during joint propagation the orientation of plume lines on joint faces allows for mapping the path taken by the crack tip line during rupture growth rupture shapes in layered clastic sediments of the devonian catskill delta finger lakes district new york indicate joint growth through three stages where velocity of the tip line v tl varies as a function of the crack tip stress intensity k i the initial stage of growth is characterized by a rupture of approximately circular or elliptical shape that expands from an initiation fl aw with a velocity v tl in some cases primary growth involves self correction where an elliptical rupture redistributes the crack tip stress so that the rupture returns to a more stable circular shape the crack tip line eventually propagates to a bedding interface where properties of either a plastic or a noncohesive bedding interface cause v tl 0 along a portion of the tip line the onset of secondary growth occurs when the rupture tip line intersects both bedding interfaces and splits into two discontinuous segments that propagate synchronously as a single coherent rupture nonuniform nonsystematic v tl eventually interferes with the rupture s ability to grow coherently and thus leads to the transition to tertiary growth characterized by the detachment of the coherent rupture into one or more independently propagating noncoherent tip lines throughout all three stages of rupture growth the k i dependent v tl points to subcritical propagation variation from a smooth to rough plume morphology is consistent with propagation through region i of the subcritical regime with a transition at v tl 10 5 m sec rupture velocity may enter region ii of the subcritical regime but such a broad range of k i must be crossed to reach region iii and quasistatic behavior at the critical stress intensity k ic that region ii acts as a barrier through which few joints pass thus greatly limiting the number of postcritical joints in the catskill delta if not in the crust of the earth

mini thief zones subcentimeter sedimentary features enhance fracture connectivity in shales this study examines the influences on fluid flow within a shale outcrop where the networks of two distinct paleoflow episodes have been recorded by calcite filled veins and green alteration halos such direct visualization of flow networks is relatively rare and provides valuable information of fluid flow behavior between core and seismic scale detailed field mapping fracture data and sedimentary logging were used over a 270 m2 2910 ft2 area to characterize the paleo fluid flow networks in the shale distal remnants of turbidite flow deposits are present within the shale as very thin 1 10 mm 0 04 0 4 in fine grained sandstone bands the shale is cut by a series of conjugate faults and an associated fracture network all at a scale smaller than seismic detection thresholds the flow episodes used fluid flow networks consisting of subgroups of both the fractures and the thin turbidites the first fluid flow episode network was mainly comprised of thin turbidites and shear fractures whereas the network of the second fluid flow episode was primarily small joints opening mode fractures connecting the turbidites the distribution of turbidite thicknesses follows a negative exponential trend which reflects the distribution of thicker turbidites recorded in previous studies fracture density varies on either side of faults and is highest in an area between closely spaced faults better predictions of hydraulic properties of sedimentary structural networks for resource evaluation can be informed from such outcrop subseismic scale characterization these relationships between the subseismic features could be applied when populating discrete fracture networks models for example to investigate such sedimentary structural flow networks in exploration settings

late pleistocene and early holocene change in the weddell sea a new climate record from the patriot hills ellsworth mountains west antarctica the transition from the late pleistocene to the holocene 30 000 5000 years ago was a period of considerable climate variability which has been associated with changes in deep water formation and the intensity of the meridional overturning circulation although numerous records exist across the north atlantic region few antarctic ice core records have been obtained from the south here we exploit the potential of upwelling ancient ice so called blue ice areas bias from the patriot hills in the ellsworth mountains to derive the first deuterium isotope record d from continental antarctica south of the weddell sea gas analysis and glaciological considerations provide a first relative chronology inferred temperature trends from the patriot hills bia and snow pit suggest changing climate influences during the transition between the last glacial period and holocene under modern conditions the interplay between the antarctic high pressure system and the southern annular mode appears to play a significant role in controlling katabatic wind flow over the site while the bia record suggests that greater sea ice extent during the last glacial period was a major control our results demonstrate the considerable potential of the patriot hills site for reconstructing past climate change in the south atlantic region

fluid evolution in fracturing black shales appalachian basin opening mode veins in cores drilled from the mudrocks overlying and underlying the major silurian salt decollement in the appalachian plateau tioga and lawrence counties pennsylvania have mineralogic and isotopic compositions generally matching those of their host mudrocks suggesting opening and filling amid little cross stratal fluid motion calcite and most trace minerals probably entered the veins via dissolution reprecipitation from nearby host rock consistent with this interpretation are the observations that 1 trace minerals within the veins including quartz pyrite and dolomite are invariably also present within the layers hosting the veins with vein cement minerals generally reflecting the abundance and solubility of minerals in the host rock and 2 carbon and oxygen isotopic compositions of vein filling calcite are similar to those of calcite within the host rock with vein filling 18o slightly depleted and 13c slightly enriched modeling the fluid isotopic evolution assuming vein opening and filling amid immobile connate formation water accounts for these minor but systematic differences which are attributable to increasing temperature and hydrocarbon maturation an exception to the above trend is barite which despite its low solubility is systematically enriched in veins with respect to the host rock it is unclear whether barite precipitation resulted from the influx of external fluids perhaps deriving from silurian salt or from barium mobilized at depth from local clays or organic material

dating the cambrian purley shale formation midland microcraton england zircons from a bentonite near the base of the purley shale formation in the nuneaton area warwickshire yield a 206pb 238u age of 517 22 0 31 ma based on the fauna of small shelly fossils and the brachiopod micromitra phillipsii in the underlying home farm member of the hartshill sandstone formation trilobite fragments that are questionably referred to callavia from the basal purley shale formation and the presence of trilobites diagnostic of the sabulosa biozone 66 m above the base of the purley shale formation the bentonite likely dates an horizon within cambrian stage 3 at about the level of the fallotaspis or basal callavia biozone this is consistent with bentonite ages from other localities in southern britain which constrain the age of the lower and uppermost parts of cambrian stage 3 the new date provides additional chronological control on the earliest occurrence of trilobites in the midland microcraton a date for the marine transgression at the base of the purley shale formation and is the first radiometric age from the cambrian succession of warwickshire

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

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

deformation history of the roanoke recess appalachians usa the evolution of the roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments because it may or may not have behaved like an adjacent salient and recess because while many salients have been investigated few recesses have and because the role of blind thrusts is unclear to gain insight into these controversies we estimated shortening directions shortening magnitudes and relative timing in the recess from map scale folds outcrop scale stylolites and grain scale solution structures and twins the key results from combining these new data with previous work are as follows 1 the deformation history around the roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from n directed to almost w directed 2 consequently the roanoke recess did not deform in the symmetrical manner of the adjacent pennsylvania salient nor with the two step history of the kingston recess further to the north in the appalachians 3 the timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

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

fractal interrelationships between topography and structure fractal interrelationships between topography and structure are investigated in two areas of the north american central appalachian mountains one in the intensely deformed valley and ridge province and the other in the relatively undeformed foreland area of the appalachian plateau province in the valley and ridge province the fractal dimensions of topographic and structural relief vary systematically along the strike of major folds following a second order polynominal trend cross correlation of the fractal dimensions of topography to structure indicates that there is a significant positive correlation between the two fractal analysis of topography in the relatively undeformed foreland area of the appalachian plateau revealed no significant variation in the fractal characteristics of topography across the study area consistent with the lack of near surface structure however fractal analysis of deeper structures beneath the plateau area undertaken using reflection seismic data revealed step wise increases in fractal dimension from the deeply buried precambrian basement to the near surface these vertical changes in fractal dimension can be related to the tectonic history of the area taken together these studies indicate that fractal analysis provides a means to quantify and compare the influence of near surface structure on topographic development and lateral and vertical structural variability fractal analysis provides a means to characterize the systematic changes in the complex patterns formed by topography and structure and the interrelationships between them similarity in their fractal characteristics implies similarity in the relative amplitude and abundance of different wavelength features in the topographic or structural profile 1998 john wiley sons ltd

characterization and development of subsurface fractures observed in the marcellus formation appalachian plateau north central pennsylvania we report on subsurface deformation features measured from recently acquired core and image logs from the marcellus formation in north central pennsylvania supplemented with data collected from valley and ridge outcrop the subsurface data are from an area that bridges a gap in existing published data between outcrop in the valley and ridge province of pennsylvania and the relatively undeformed outcrop exposed on the appalachian plateau of new york we find one distinct set of vertical veins that strike orthogonal to appalachian plateau fold axes and an associated set of low angle reverse faults and stylolites that strike parallel to fold axes as the trend of the fold axes changes around the pennsylvania salient the trend of associated mesostructures changes to maintain kinematic compatibility with the shortening direction change along the salient these structures are interpreted to support a single although possibly protracted strain event during alleghanian deformation as opposed to multiple events previously interpreted to occur in different regions and stratigraphic levels within the fold belt the veins are associated with clusters of bedding plane slip surfaces which are found at distinct mechanical stratigraphic positions where the competence contrast between shale and stiff limestone units is greatest we interpret this association to indicate that bed parallel shear within detachment zones provides the sufficient driving force required to nucleate vertical veins and the decoupling of beds accommodates extension orthogonal to the shortening direction although these veins are oriented orthogonal to the present day maximum principal horizontal stress they remain propped open by crystalline cements homogenization temperatures of fluid inclusions trapped in the veins combined with one dimensional burial and thermal history models suggest that the pervasive vein set formed during the late pennsylvanian permian during the alleghanian orogeny

dating antarctic blue ice areas using a novel ice flow model 1 we present a new type of flow model suitable for antarctic blue ice areas with application to dating ice for paleoclimate purposes the volume conserving model uses field data for surface velocities mass balance and ice thickness along a flow line with parameterized variation of ice rheology with depth to produce particle trajectories and isochrones the model is tested on the contrasting allan hills near western ice field and the scharffenbergbotnen blue ice fields in antarctica by comparing predicted ages with ages inferred from meteorites and 14c data during the glacial periods ice surface velocities at the allan hills must have been 25 less and accumulation rates 50 less than present day values in order to match meteorite ages in contrast scharffenbergbotnen velocities have probably been fairly constant over time due to the atypical valley where it resides

modelling northern hemisphere ice volume over the last 3 ma the northern hemisphere ice sheet volumes over the last 3 ma were simulated using the lln 2 d model the forcings were both insolation and co2 concentration different atmospheric co2 scenarios were used because of a lack of co2 reconstruction over this remote past with constant co2 concentrations the simulated ice volume does not show any gradual increase as recorded in the marine sediments moreover its spectrum changes according to the chosen value of co2 when co2 is fixed at 220 ppmv the simulated ice volume is dominated by the similar to 100 ka period if a pre industrial co2 concentration of 280 ppmv is used the simulation is dominated by the similar to 41 ka period by using a linearly decreasing co2 concentration going from 320 ppmv at 3 ma bp to 200 ppmv at present the simulated changes in the power spectrum are in agreement with those obtained from the sedimentary records roughly before 1 ma bp the dominating period is similar to 41 ka afterwards the similar to 100 ka period becomes dominant this transition is accompanied by a gradual increase of the ice volume potential mechanisms for this transition are discussed using cyclic co2 fluctuations over the last 0 6 ma does not change significantly the spectral characteristics of the simulated ice volume but amplifies the amplitude of its variations c 1998 elsevier science ltd all rights reserved

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

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

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

expression of the bipolar see saw in antarctic climate records during the last deglaciation ice core records of climate from greenland and antarctica show asynchronous temperature variations on millennial timescales during the last glacial period 1 the warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres a pattern attributed to the thermal bipolar see saw 2 however a record from the ross sea sector of east antarctica has been suggested to be synchronous with northern hemisphere climate change 3 here we present a temperature record from the talos dome ice core also located in the ross sea sector we compare our record with ice core analyses from greenland based on methane synchronization 4 and find clearly asynchronous temperature changes during the deglaciation we also find distinct differences in antarctic records pointing to differences in the climate evolution of the indo pacific and atlantic sectors of antarctica in the atlantic sector we find that the rate of warming slowed between 16 000 and 14 500 years ago parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over greenland in addition our chronology supports the hypothesis that the cooling of the antarctic cold reversal is synchronous with the bolling allerod warming in the northern hemisphere 14 700 years ago 5 the period from about 8 to 25kyr before present bp includes the climate transition from the last glacial to the holocene as documented from polar ice cores and other climate archives the pattern of climate changes throughout this transition is different between antarctica and the surrounding southern ocean and the northern hemisphere the steady antarctic deglacial warming reaches a first maximum antarctic isotopic maximum aim1 ref 1 followedbyaninterruptiontowardscoolerconditionsduring the antarctic cold reversal acr conversely greenland records show two rapid warming phases at the onset of the dansgaard oeschger 1 do1 event bllingaller dinterstadial b a andthe

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

assessing the continuity of the blue ice climate record at patriot hills horseshoe valley west antarctica we use high resolution ground penetrating radar gpr to assess the continuity of the blue ice area bia horizontal climate record at patriot hills horseshoe valley west antarctica the sequence contains three pronounced changes in deuterium isotopic values at 18 cal ka 12 cal ka and 8 cal ka gpr surveys along the climate sequence reveal continuous conformable dipping isochrones separated by two unconformities in the isochrone layers which correlate with the two older deuterium shifts we interpret these incursions as discontinuities in the sequence rather than direct measures of climate change ice sheet models and internal layer continuity index plots suggest that the unconformities represent periods of erosion occurring as the former ice surface was scoured by katabatic winds in front of mountains at the head of horseshoe valley this study demonstrates the importance of high resolution gpr surveys for investigating both paleo flow dynamics and interpreting bia climate records