mechanics of upward propagation of cover collapse sinkholes cover collapse sinkholes occur by failure of the walls of a soil void above cavernous bedrock i examine conditions for failure in compression by crack propagation and coalescence and for failure by sloughing in which pore water pressure produces a net tension perpendicular to the wall of the void compressive failure without relaxation of stress does not explain observed long term stability of thick soils nor failures in thin residual soils if stress relaxation occurs with compressive failure soil voids tend to stabilize and sinkholes are not predicted sloughing failure is not predicted for steady state pore pressure fields even for a perched water table at the surface over a drained void transient pore pressure conditions that could produce sloughing may result from 1 rapid drawdown causing soil consolidation and transient high pore pressure gradients 2 approach of a wetting front in unsaturated soil with high permeability behind the front 3 dissolution of air from bubbles in the soil and exsolution near the void producing a low permeability zone near the void

prediction of undrained sinkhole collapse sinkholes are surface depressions or shafts resulting from the collapse of a submerged cavity in soil the cavities that lead to sinkholes form as a result of underlying geology in limestone areas or as a result of human activity such as mining or leakage from a sewer the formation of sinkholes is often sudden and can lead to extensive damage and loss of life especially in urban areas much of the literature on the subject of sinkhole formation is empirical in nature often being associated with specific locations this paper presents the results of a study using numerical modeling of the undrained stability of the submerged cavities that lead to sinkhole formation finite element limit analysis techniques using programs developed at the university of newcastle are used to obtain upper and lower bound values of a suitable load parameter which bracket the exact solution the results are compared to analytical solutions both from literature and derived independently

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

stable carbon isotope signatures preserved in authigenic gibbsite from a forested granitic regolith panola mt georgia usa six samples selected from a weathering profile developed on a granite in the panola mountain research watershed in the georgia piedmont were studied for their stable carbon isotopic properties the purpose was to understand the relationship between the stable carbon isotopic composition of the organic matter pool and the preservation of carbon in the authigenic soil minerals the method for yielding carbon from authigenic phases is based on that of yapp and

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

origin and distribution of carbon dioxide in the unsaturated zone of the southern high plains of texas partial pressures of co2 o2 n2 and ar were monitored at two locations in the ogallala aquifer system on the southern high plains of texas samples were collected monthly during parts of 1980 1981 from nine depths ranging from 0 6 to 36 meters below land surface pco2 was observed to be greater at depth than in the active soil zone and thus appears to contradict the normal process in which co2 is generated in the soil zone and diffuses upward to the atmosphere and downward to the water table the 13c of the co2 gas was quite uniform and averaged 17 9 per mil po2 declined with depth suggesting in situ generation of co2 by the oxidation of carbon several hypotheses were considered to explain the origin of the co2 at depth it was concluded that the most probable hypothesis was that dissolved and particulate organic carbon introduced by recharging water was oxidized to co2 by the aerobic microbial community that utilized oxygen diffusing in from the atmosphere this hypothesis is consistent with the co2 concentration profile calculated production profile of co2 13c values of co2 gas caliche soil humic acid fraction and dissolved carbonate in groundwater the abundance of co2 its concentration profile and its probable origin provide information for evaluating the observed complex sequence of caliche dissolution and precipitation known to occur in the aquifer

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

stable carbon isotope budget of co2 in a wet modern soil as inferred from fe co3 oh in pedogenic goethite possible role of calcite dissolution abstract 13c values of the fe co3 oh component in pedogenic goethites from a young soil developed on the eocene weches formation in east texas increase from approximately 13 or 14 at depths of 31 64 cm to values around 6 to 4 at depths greater than 122 cm this spatial distribution of 13c values suggests that dissolution of precursor fossiliferous marine calcite still present at deeper levels in the soil has contributed significantly to the isotopic budget of co2 in this soil a local isotopic material balance was calculated for the soil co2 at each sample depth using a calcite 13c value of 1 an organic matter 13c value of 25 and the measured 13c value of the fe co3 oh component in each sample although there is presently no calcite in the upper 120 cm of the profile the calculated apparent contribution of co2 from a calcite source ranges from 16 to 45 at these shallow depths below 120 cm dissolution of calcite appears to contribute more than 50 of the co2 in the soil gas similar results might be expected in other wet goethite bearing soils that contain relict calcite and thus have not achieved the highly leached characteristics of laterites such as those in the amazon basin models of the soil co2 budget in such systems may need to consider both oxidation of organic matter and dissolution of carbonate minerals as in situ sources of carbon isotope variation in co2 the variation with depth of the 13c values of the fe co3 oh component suggests an ongoing process of goethite dissolution and reprecipitation in the active aerobic soil zone if so the extremely low solubility of goethite in oxidizing environments suggests that this dissolution process is probably biologically mediated dissolution and reprecipitation of goethite in an aerobic soil would favor the recording of steady state soil co2 13c patterns preservation of such information in ancient soils would probably depend upon burial and consequent removal from the biologically active soil zone

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

new faults v fault reactivation implications for fault cohesion fluid flow and copper mineralization mount gordon fault zone mount isa district australia fluid flow leading to mineralization can occur both on newly formed faults and on faults that are reactivated subsequent to their initial formation conventional models of fault reactivation propose that under high pore fluid pressures misorientated faults may reactivate due to low fault cohesion timing and orientation data for a mineralized palaeo to mesoproterozoic terrain mount gordon fault zone mgfz indicate that multiple successive new orientations of predominantly strike slip faults developed between 1590 and c 1500 ma requiring that during the younger deformations some earlier formed faults were too cohesive and or had insufficient pore fluid pressures or other potential fault weakening effects to induce reshear low pore fluid pressures were probably not to blame for failed reactivation on all older faults because some young faults did form or reactivate due to high pore fluid pressures as evidenced by jigsaw fit dilatant breccias hypogene copper mineralization in veins and breccia infill and subvertical tensile quartz veins aligned subparallel to 1 the assumption that old faults consistently have little or no cohesion appears to be incorrect in this terrain many older faults display prominent quartz veins along their length which may explain this conclusion furthermore faults with high cohesion may have acted as barriers and compartments so that intersections between them and newly formed faults host mineralization not because of reactivation but because of interaction between new faults and cohesive materials defined either by fault precipitates or rock juxtaposition together these results and observations provide new simple tools to stimulate copper exploration within the region and in fault hosted terrains

finite strains within recumbent folds of the kishorn nappe northwest scotland abstract this study is based on the torridonian and cambro ordovician rocks of the kishorn nappe on the isle of skye and the adjacent mainland of scotland grain shape fabric skolithos pipe shape analysis and palaeomagnetic techniques have been used to give an indication of the strain distribution and possible mechanisms involved in the generation of the recumbent folds within the kishorn nappe results indicate that recumbent folding has occurred without internal deformation

application of matrix analysis in delineating sinkhole risk areas along highway i 70 near frederick maryland sinkhole collapse in the area of maryland interstate 70 i 70 and nearby roadways south of frederick maryland has been posing a threat to the safety of the highway operation as well as other structures the occurrence of sinkholes is associated with intensive land development however the geological conditions that have been developing over the past 200 million years in the frederick valley control the locations of the sinkholes within an area of approximately 8 km 2 138 sinkholes are recorded and their spatial distribution is irregular but clustered the clustering indicates the existence of an interaction between the sinkholes the point pattern of sinkholes is considered to be a sample of a gibbsian point process from which the hard core strauss model is developed the radius of influence is calculated for the recorded sinkholes which are most likely to occur within 30 m of an existing sinkhole the stochastic analysis of the existing sinkholes is biased toward the areas with intensive land use this bias is adjusted by considering 1 topography 2 proximity to topographic depressions 3 interpreted rock formation 4 soil type 5 geophysical anomalies 6 proximity to geologic structures and 7 thickness of overburden based on the properties of each factor a scoring system is developed and the average relative risk score for individual 30 m segments of the study area is calculated the areas designated by higher risk levels would have greater risk of a sinkhole collapse than the areas designated by lower risk levels this risk assessment approach can be updated as more information becomes available

the carbon isotope geochemistry of goethite α feooh in ironstone of the upper ordovician neda formation wisconsin usa implications for early paleozoic continental environments carbon isotope exchange experiments and data from natural samples in a state of isotopic disequilibrium indicate that the apparent fe co3 oh component in natural goethites is a closed system these results support the solid solution model for fe co3 oh in goethite the carbon isotope geochemistry of the oolitic neda formation ironstone at occurrences in wisconsin and iowa is consistent with goethite formation in a late ordovician subaerial weathering environment 13c values of the fe co3 oh component in neda formation goethite indicate that organic matter was being oxidized to produce co2 in the ancient weathering profile the 13c value of this organic matter was about 27 at depths greater than about 20 cm the partial pressure of co2 in the late ordovician weathering profile was 5 6 times larger than the pco2 of the earth s atmosphere at that time this high soil co2 partial pressure and its origin in the oxidation of organic matter suggest that there was substantial biological activity on continental land surfaces prior to the widespread colonization by vascular plants it indicates a possible role for biological activity in the chemical weathering of continents in the early paleozoic

the transition from the passive to active continental margin a case study of brittle fractures in the miocene loshui sandstone on the hengchun peninsula southern taiwan 1 in the hengchun peninsula southern taiwan the miocene loshui sandstone of deep sea fan facies provides an opportunity and challenge to investigate the brittle deformation history of an emerging accretionary prism a survey of brittle fractures was carried out along the coastline the brittle fractures include joints of various sets a few faults and veins the intricacy of joints lies in the large number of joint sets that often vary not only from one site to another site but in bed thickness at a given site as well and in the complicated abutting relationships between the joint sets in order to investigate the joint sequence we define a full spectrum of possible systematic joint sets and develop an algorithm to determine the shortest joint sequence from the observed abutting relationships little difference between the shortest joint sequences for the southern and northern parts of the study transect attests to the evolution of overall uniform stress throughout the area that is responsible for these various systematic newly formed or reactivated joint sets the fracture sequence derived reveals a complicated stress evolution during the transition from the passive to active continental margin

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

application of younging tables to the construction of relative deformation histories 1 fracture systems abstract for a collection of age relationships there are several possible histories younging tables provide a simple and direct method with which all valid deformation histories can be identified the application of this technique to fracture systems is illustrated using two case studies these examples demonstrate how unobserved relationships synchronous structures and fractures that appear in more than one stage of a deformation history can be dealt with using younging tables suggestions are made for the presentation of relative deformation histories that highlight ambiguities and convey a visual impression of the confidence that may be placed on a particular history application of the approach to the analysis of grain fragmentation has identified a range of multi stage deformation histories all of these histories involve to a greater or lesser extent the operation of extension fractures shear fractures linked shear fractures and extension fractures and several sets of synchronous extension fractures analysis of an exposed fracture system using younging tables has raised the possibility of the simultaneous growth of two sets of orthogonal extension fractures with the implication that the scale of stress homogeneity may be only a few metres

climate model sensitivity to atmospheric co2 levels in the early middle paleogene this study examines the sensitivity of the slab ocean version of the national center for atmospheric research climate system model with revised eocene geography orography and vegetation to changing carbon dioxide co2 levels we compare model results with temperature proxies from the geologic record for the early middle paleogene we ran three modeling experiments with co2 levels at 500 1000 and 2000 ppm and all with atmospheric methane levels of 3 5 ppm surface temperatures in the two higher co2 scenarios are warmer than those of the 500 ppm scenario the largest warming with increasing co2 occurred in the high latitudes particularly in the northern hemisphere during the wintertime compared to the 500 ppm case arctic wintertime temperatures increased by 10 c for the 1000 ppm scenario and 20 c for the 2000 ppm scenario the 1000 and 2000 ppm scenarios produced mean annual and cold month mean temperatures in mid and high latitudes that are much more compatible with the climate interpretations from eocene flora especially for data from the southern hemisphere tropical sea surface temperatures ssts in the 2000 ppm scenario however are still 4 c higher than the warmest temperatures inferred from proxy data the better match between temperatures in the high co2 modeling scenario and high latitude climate interpretations is consistent with the idea that the co2 levels during the eocene were high at least 3 4 times the pre industrial value of 280 ppm but the discrepancies in the tropics suggest that sst estimates from proxies are too low or that the models lack some tropical cooling mechanism that was important at this time

mixing of co 2 in surficial environments as recorded by the concentration and δ 13 c values of the fe co 3 oh component in goethite measured values of mol fraction x and 13c in the fe co3 oh component of 49 samples of goethite feooh from a wide variety of environments range from 0 0015 to 0 0182 and from 21 7 to 3 3 respectively the distribution of 13c values appears to be bimodal 13c values are 12 for marine hydrothermal goethites and continental goethites crystallized as secondary minerals in host rocks with the exception of a young soil drr 13c is 14 for pedogenic oolitic and bog ore goethites values of x and temperature determined for pedogenic goethite can be combined with the modern global relation between soil respiration q and average annual temperature to estimate diffusion coefficients ds for steady state fickian diffusion of co2 in soils although there is considerable scatter in the relationship between q and t an illustrative calculation for a characteristic depth of 0 20 m yields calculated values of ds that range from about 0 002 to 0 011 cm2 s among seven goethite bearing soils steady state diffusive transport of co2 in soils with one in situ source of co2 oxidation of organic matter yields a soil co2 mixing equation for two isotopically distinct co2 components oxidized organic matter and atmospheric co2 with pedogenic goethite as a proxy for the soil co2 the positive slope of this two component mixing equation can be used for determinations of co2 pressures in the earth s atmosphere if however dissolution of carbonates is concurrent with goethite crystallization the mixing equation at z z becomes three component with a negative slope that precludes estimates of atmospheric pco2 an example is the drr soil in which in situ low ph dissolution of relict marine invertebrate fossils produced a negative mixing slope and goethite 13c values that range from 14 2 to 4 1 these results indicate that only goethites which crystallized in carbonate free soils highly leached or formed on initially carbonate poor rocks should be used to deduce ancient atmospheric co2 pressures addition of co2 from dissolution of carbonates also appears to explain the range of 13c values of most of the secondary continental goethites presumably formed in saturated groundwater systems however some of the variation of x and 13c of the fe co3 oh component in these goethites may be a consequence of variations in ambient ph this possible dependence on ph seems to be manifested in a suite of goethites pseudomorphed after pyrite in a marine limestone

apparent gibbsite growth ages for regolith in the georgia piedmont abstract carbon bound in gibbsite collected from a residual weathering profile developed on a paleozoic granite in the georgia piedmont was examined for its 14 c content and found to be geologically young the study site located at the panola mountain research watershed has developed a granite saprolite soil regolith in which 14 c gibbsite model ages deep within the profile c horizon average about 8000 years near the surface a and b horizon 14 c gibbsite model ages range from 2100 to 4200 years quartz has acquired 26 al and 10 be inventories suggesting a near surface residence time of at least 90 000 years this age disparity supports the notion that secondary minerals undergo significant recrystallization as weathering fronts propagate into the landscape combining the results of 14 c 26 al and 10 be analyses offers the potential to assess differential rates of chemical weathering and continental denudation to understand better the links between rates of silicate rock weathering climate and soil residence times

construction and systematic assessment of relative deformation histories abstract the systematics of deformation histories have been investigated using basic combinatorial mathematics using this approach the number of deformation histories and the number of relationships associated with a given number of structures can be calculated the range of possible deformation histories can also be determined using this information the ambiguous nature of all deformation histories is examined together with the impact of unobserved relationships the number of possible deformation histories that are compatible with a collection of age relationships is used as a crude measure of confidence in those histories a procedure is described for the construction of deformation histories that is systematic repeatable and rapid and within which ambiguities can be easily recognised

deformation in a complex crustal scale shear zone errabiddy shear zone western australia detailed mapping of four areas representing different geological units with varying formation histories within the crustal scale errabiddy shear zone shows an apparently simple temporal progression from foliation and mineral lineation development to folding nd then to brittle deformation across the shear zone however in detail the structural evolution of the shear zone shows considerable complexity the dominant foliation throughout the shear zone was formed in the upper greenschist to amphibolite facies during the 2000 1960 ma glenburgh orogeny which involved the accretion of the archaean to palaeoproterozoic glenburgh terrane onto the archaean yilgarn craton and the subsequent formation of the errabiddy shear zone

stability charts for the collapse of residual soil in karst collapse of the residual soil over bedrock cavities often occurs during construction in karst terrain particularly when the thickness of the residuum is reduced during excavation even if an estimate of the strength of the residual soil is known uncertainty with respect to the size geometry of the subterranean voids makes a detailed analysis difficult and straightforward methods to check the stability are needed in this study numerical analyses were performed to develop a stability chart expressed in terms of a dimensionless stability number and the geometry of a potential void in the residual soil the stability charts include the effect of friction angle and are also developed to allow the investigation of the effect of the inverted strength profile typically observed in karst terrain such stability numbers may be useful to estimate the stability of a given site based on the expected thickness of the soil overburden and the likely range of anticipated soil void diameters

scale dependence strain compatibility and heterogeneity of three dimensional deformation during mountain building a discussion plate motion at convergent margins causes crustal shortening and orogenic thickening relative motion that is oblique to the plate margins is an inevitable consequence of plate kinematics on a sphere and results in non coaxial three dimensional deformation that cannot be approximated to simple shear models of mountain building that include a smoothly varying component of pure shear shortening allow strain compatibility to be maintained by deforming the upper free surface of the earth without disrupting the material continuum however such models do not reflect accurately the nature of deformation in many areas of high strain in the upper crust which are characterized by interconnected arrays of kinematically linked faults that can be active on several scales of magnitude simultaneously as brittle deformation increases the coherence of the material continuum is highly reduced in such situations strain compatibility is maintained by partitioning the deformation amongst structures of varying kinematic significance over a wide range of scales and not by smooth variations in strain magnitude acting on a single scale across a material continuum there is a marked tendency for such partitioned domains to be oriented parallel or sub parallel to the orogenic grain alignment of domains in this way represents a strong structural anisotropy which acts as a highly significant boundary condition that controls deformation at subordinate scales finite strain observed within an individual domain at a given scale need not therefore display the same magnitude or orientation as bulk finite strain at the plate scale and consequently data must be collected from as large an area as possible to relate outcrop scale structures to global scale tectonics

concentration of carbon dioxide in the late cretaceous atmosphere stable carbon isotope data from late cretaceous maastrichtian palaeosols in india are used to estimate the concentration of carbon dioxide in the late cretaceous atmosphere we show that the maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of co 2 this value agrees with an independently modeled value of co 2 in the late cretaceous atmosphere a low concentration of the greenhouse gas carbon dioxide in the maastrichtian atmosphere relative to concentrations in the earlier cretaceous is consistent with palaeotemperature information from terrestrial plant and marine fossils which suggest that the global climate cooled toward the end of the cretaceous period

the effects of deformation induced microstructures on intragrain 40ar 39ar ages in potassium feldspar a combination of forescattered scanning electron microscopy and both ultraviolet uv laser and cycle stepped heating 40 ar 39 ar dating techniques have been applied to a single deformed grain of potassium feldspar to investigate the relationship between microstructure and 40 ar 39 ar isotope systematics the form and distribution of deformation induced microstructures have been mapped by using intragrain variations in lattice orientation these variations are related to thin section and regional structural data to provide a well constrained deformation history for the feldspar grain thirty uv laser 40 ar 39 ar analyses show age variations that correlate with the internal microstructure stepped heating data provide further evidence of this relationship our approach allows the recognition of different ar reservoirs within the deformed feldspar and identifies microstructural controls on ar migration such a relationship has important implications for the understanding and interpretation of 40 ar 39 ar geochronological data and the subsequent use of such data to constrain the temperature vs time evolution of deformed rocks

carbon dioxide in the paleozoic atmosphere evidence from carbon isotope compositions of pedogenic carbonate stable carbon isotope compositions of pedogenic carbonate occurring in three clay rich vertic paleosols within paleozoic red bed successions in central pennsylvania provide a record of past pedogenic environments and can be used to estimate co sub 2 pressure p sub co sub 2 of the paleozoic atmosphere the delta sup 13 c values of carbonate nodules from paleosols in the deltaic lower bloomsburg formation upper silurian reflect the contribution of carbon from marine groundwater or fossils coupled with low biological activity the delta sup 13 c values of carbonate rhizocretions from stratigraphically high paleosols in the bloomsburg formation and in the alluvial catskill upper devonian and mauch chunk upper mississippian formations suggest an extensive c sub 3 flora and significant contribution of atmospheric co sub 2 paleozoic atmospheric co sub 2 levels inferred from delta sup 13 c of pedogenic carbonate are significantly higher than present levels

linking the wasatchian bridgerian boundary to the cenozoic global climate optimum new magnetostratigraphic and isotopic results from south pass wyoming new paleomagnetic and stable isotopic results from the northeastern margin of the greater green river basin south pass wyoming provide a refined geochronological context for the wasatchian bridgerian land mammal age boundary and suggest the existence of large amplitude milankovich scale carbon and oxygen isotopic oscillations in this area during the early eocene analysis of 55 paleomagnetic sites through a 310 m section of wasatch green river and bridger formations indicates several reversals that can be correlated to the geomagnetic polarity time scale using radiometric age constraints this correlation places the wasatchian bridgerian boundary in chron c23r at about 52 ma approximately two million years older than previous estimates this new correlation suggests that the mammalian turnover which characterizes the wasatchian bridgerian boundary is coincident with the onset of the cenozoic global climate optimum the warmest interval of the entire cenozoic intrabasinal magnetostratigraphic correlation supports earlier claims that community composition and biostratigraphic datums of basinmargin faunas can differ significantly from coeval basin center faunas oxygen and carbon isotopic composition of paleosol carbonates show in phase cyclic variations on the order of 6 and 3 5 respectively based on the preferred magnetostratigraphic correlation the four best defined cycles represent 397 thousand years indicating potential forcing by variations in orbital eccentricity oxygen isotopic variations may be tracking wet dry cycles amplified by adjacent changes in levels of paleolake gosuite carbon isotopic variations may be tracking the vegetative response to these climate variations alternative interpretations involve cyclic changes in pedogenesis driving correlated variations in isotopic inheritance from parent paleozoic carbonate material and the possibility that c4 plants existed in marginal habitats earlier in geological time than previously thought q 2001 elsevier science b v all rights reserved

structural analysis of a newly emerged accretionary prism along the jinlun taimali coast southeastern taiwan from subduction to arc continent collision abstract in southern taiwan the initial collision of the luzon volcanic arc with the passive continental margin of china results in the emergence of an accretionary prism of predominantly turbidites in composition thus providing an appropriate place to study the temporal and spatial variation of deformation during the transition of subduction to arc continent collision field surveys have recently been carried out in slightly metamorphosed rocks along the well exposed jinlun taimali coast in southeastern taiwan three folding phases are identified in the area the first phase is characterized by gently dipping but widely distributed phyllitic cleavage s 1 the second phase is represented by sparsely distributed crenulation cleavage s 2 that folded the phyllitic cleavage the third phase is characterized by e w trending antiforms f 3 that involved both types of pre existing cleavages restoration of such an antiform in the north using a method proposed in this paper reveals that phyllitic cleavage in the overturned beds dips gently towards the southeast or east southeast before the antiform in relation to the first phase thrusting or folding under regional ese wnw compression from the first to third phase the maximum horizontal compression underwent an about 90 anticlockwise rotation from ese wnw to e w or ne sw to n s and the deformation depth seems to decrease drastically in terms of the decreasing proportion of pervasive deformation all these variations are attributed to the oblique arc continent collision that exhumed the whole accretionary prism and induced a local stress perturbation in southeastern taiwan

a case study of the reliability of multielectrode earth resistivity testing for geotechnical investigations in karst terrains abstract the thinly mantled karst areas of northeastern pennsylvania have been associated with a number of structural failures caused by sinkholes geotechnical investigations in these areas have primarily relied upon intrusive probe tests either through borings or air track drillings the silty clay soils overlying the carbonate bedrock have limited the use of nonintrusive ground penetrating radar and electromagnetic methods however multielectrode earth resistivity testing may be a suitable method for locating subsurface features associated with sinkhole formation in these areas the case study presented in this paper concerns a site in northampton county where sinkholes have been occurring at an accelerated rate due to the influence of construction the bedrock at the site is located between 1 m and approximately 10 m below the surface the soil is primarily a silty clay seventy resistivity lines using a variety of electrode and line spacings were conducted at the site using the data obtained from the earth resistivity tests 17 borings were located to assess the accuracy of the resistivity results comparisons between boring and resistivity results demonstrate that the resistivity tests provide good information concerning the depth to the irregular surface of the bedrock however use of the test to locate subsurface anomalies associated with sinkhole formation and to determine their size will require additional research the paper presents the results of the study and provides recommendations for geotechnical investigation in silty clay soils overlying shallow carbonate bedrock

designing foundations around sinkholes there is an increasing awareness among developers and owners of the need to conduct subsurface exploration studies before planning a project the use of geophysical methods in subsurface exploration has been established to be valuable in locating sinkhole activity and suggesting pro active measures however the value of geophysical exploration to supplement geotechnical investigation has not yet been stressed primarily out of cost concerns ground penetrating radar and electrical resistivity tests which were used to determine void spaces below proposed buildings are gaining wider acceptance as a result of information obtained from geophysical tests foundation designs were modified to use post tensioned mats or to include grouting an improved grouting technique that controls the volume of grout being pumped is also discussed this paper is an attempt to document some case studies which resulted in making design improvements to mitigate the effects of known sub surface solution activity these case studies illustrate the use of geophysical exploration methods in adding value to the engineered design

rock mass collapse mechanism of concealed karst cave beneath deep tunnel abstract local collapse of the surrounding rock often occurs during tunnel construction in a karst area particularly when the rock pillar between the tunnel and the karst cave is very thin the collapse of the surrounding rock in tunnel construction is sudden and may lead to great economic loss or even loss of life to predict the collapse of rock mass where a tunnel is excavated above a karst cave an analytical expression of the collapse surface is derived from variational calculation in the framework of the upper bound theorem based on the analytical solution the shape of the collapse surface is plotted to investigate the effects of rock parameters on the collapse surface of the rock mass where a karst cave exists beneath a tunnel according to the changing law of the collapse surface varying with the distance between tunnel and cave the computational formula of the minimum safety thickness for preventing the collapse of rock pillar is derived to evaluate the validity of the proposed method in this paper we compared the analytical solution with numerical solution the comparison result indicates the analytical solution matches up with the numerical solution very well which suggests that the analytical approach proposed in this paper is valid

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

silicate weathering machine at work rock magnetic data from the late paleocene early eocene cicogna section italy we describe a scenario of climate forcing on sedimentation recorded in the late paleocene early eocene cicogna marine section from the belluno basin ne italy previously published magneto biostratigraphic data revealed that the 81 m cicogna section extends from chron c25r to chron c23r spanning the np7 np8 np12 nannofossil zones 52 2 56 6 ma using previously published rock magnetic data augmented by data from this study we describe and thoroughly discuss a pronounced increase of hematite relative to maghemite or magnetite between 54 9 and 54 6 ma immediately above the paleocene eocene boundary followed by a second long term increasing trend from 54 ma up to 52 2 ma in the early eocene this hematite is essentially of detrital origin insofar as it is associated with a strong shallow bias of paleomagnetic inclinations and is interpreted to have formed on land by the weathering of fe bearing silicates and other primary minerals we speculate that the warm and humid climate typical of the paleocene eocene thermal maximum petm 54 9 ma as well as of the warming trend leading to the early eocene climatic optimum eeco 52 50 ma enhanced continental weathering of silicate rocks with the consequent production transport and sedimentation of detrital hematite grains this hypothesis is confirmed by a statistical correlation between the rock magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature our temporal coupling between oxidation state of sedimentary magnetic phases and global climate is therefore consistent with the existence in the paleocene eocene of the silicate weathering negative feedback mechanism for the long term stabilization of the earth s surface temperature

orthogonal fracture systems at the limits of thrusting an example from southwestern wales abstract a well developed orthogonal vein system is located in the autochthonous foreland just beyond the limits of variscan thrusting in southwestern wales the two vein sets trend 200 and 290 perpendicular and parallel respectively to variscan structures the veins contain stretched quartz fibers indicating horizontal extensions of between 0 3 and 2 5 the 200 set has greater extension with a distinctive morphology including shorter more curvilinear fractures that have components of normal offset vein intersections are simple indicating episodic growth by alternating regional propagation of each set during propagation maximum compression was subvertical and the horizontal principal stresses switched direction with the alternation of set growth the system formed during waning variscan compression when the directions of horizontal principal stresses were still controlled by the tectonic compression the differential stress may have been greater during propagation of the 200 set this example indicates that orthogonal fracture systems in forelands beyond thrusting 1 are initiated by fracturing parallel to tectonic compression 2 form in a few stages that are controlled by changes in regional stress and 3 form during waning tectonic compression that controls fracture orientations

goethite calcite and organic matter from permian and triassic soils carbon isotopes and co2 concentrations abstract pedogenic goethites in each of two early permian paleosols appear to record mixing of two isotopically distinct co2 components atmospheric co2 and co2 from in situ oxidation of organic matter the 13c values measured for the fe co3 oh component in solid solution in these permian goethites are 13 5 for the lower leonardian 283 ma bp paleosol mcgoeth and 13 9 for the upper leonardian 270 ma bp paleosol sap these goethites contain the most 13c rich fe co3 oh measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned co2 components 13c measured for 43 organic matter samples in the lower leonardian waggoner ranch fm has an average value of 20 3 1 1 1s the average value yields a calculated early permian atmospheric p co 2 value of about 1 pal but the scatter in the measured 13c values of organic matter permits a calculated maximum p co 2 of 11 pal pal present atmospheric level measured values of the mole fraction of fe co3 oh in mcgoeth and sap correspond to soil co2 concentrations in the early permian paleosol profiles of 54 000 and 50 000 ppmv respectively such high soil co2 concentrations are similar to modern soils in warm wet environments the average 13c values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with mcgoeth waggoner ranch fm range from 6 5 to 4 4 with a mean 13c value for all profiles of 5 4 thus the value of 13c between the pedogenic calcite data set and mcgoeth is 8 1 0 9 which is in reasonable accord with the value of 7 7 expected if atmospheric p co 2 and organic matter 13c values were the same for both paleosol types furthermore the atmospheric p co 2 calculated for the early permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 pal with a maximum calculated atmospheric p co 2 permitted by one standard deviation of the organic matter 13c value of 5 pal if however measured average 13c values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13c depleted labile organic compounds calculated permian atmospheric p co 2 using these 13c enriched organic values would underestimate the actual atmospheric p co 2 using either goethite or calcite this is the first stratigraphically constrained intrabasinal study to compare ancient atmospheric co2 concentrations calculated from pedogenic goethite and calcite these results demonstrate that the two different proxies record the same information about atmospheric co2 the fe co3 oh component in pedogenic goethite from a triassic paleosol in utah is significantly enriched in 13c relative to fe co3 oh in goethites from soils in which there are mixtures of two isotopic co2 components field relationships and the 13c value 1 9 of the triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct co2 components at the time of goethite crystallization the three components were probably atmospheric co2 co2 from in situ oxidation of organic matter and co2 from in situ dissolution of preexisting calcite although mixing of three isotopically distinct co2 components as recorded by fe co3 oh in goethite has been described in modern soil this is the first example from a documented paleosol its preservation affirms the need for careful case by case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric p co 2

conditions of vein formation in the southern appalachian foreland constraints from vein geometries and fluid inclusions abstract the nolichucky shale in the whiteoak mountain thrust sheet of the southern appalachian foreland contains four coeval bed normal calcite vein sets that trended 015 055 090 and 320 before thrusting the pretectonic veins were displaced by syn tectonic bed parallel slickensided calcite veins during local alleghanian thrusting fluid inclusion thermometry indicates precipitation of both bed normal and bed parallel veins from nacl cacl2 brines 27 wt nacl equiv salinity at 80 110 c for bed normal veins and 110 c for bed parallel veins these temperatures correspond to burial depths of 2 4 3 6 km which were attained after the middle mississippian these pressure corrected homogenization temperatures are comparable to time temperature indicators such as cai and illite crystallinity and indicate that inclusions were trapped near maximum burial conditions and were not deformed after trapping this conclusion is supported by the absence of petrographic evidence for inclusion failure and a worst case mechanical analysis that indicates a lack of brittle deformation to inclusions after trapping the four coeval bed normal vein sets could not be formed by one simple stress field nor by the development of a single structure but required the interaction of at least two stress components or structures it is proposed that the interaction of the alleghanian and ouachita orogenic stress components beyond the limits of thrusting produced the sets as coeval alleghanian orthogonal 055 320 and ouchita sub orthogonal 015 090 mode i fractures

fe co3 oh in goethite from a mid latitude north american oxisol estimate of atmospheric co2 concentration in the early eocene climatic optimum abstract measured mole fractions x and 13c values of the fe co3 oh component in pedogenic goethite from a mid latitude oxisol of early eocene age 52 ma b p range from 0 0014 to 0 0064 and 20 1 to 15 4 respectively these values of x imply that concentrations of co2 gas in the paleosol were 7400 to 34 000 ppm 13c and 1 x are correlated and define a linear soil co2 diffusive mixing line with a positive slope such positive slopes are characteristic of mixing of two isotopically distinct co2 endmembers atmospheric co2 and co2 from oxidation of soil organic matter from the intercept of the mixing line it is calculated that the 13c value of organic matter in the ancient soil was 28 0 the magnitude of the slope implies an early eocene atmospheric co2 concentration of 2700 ppm a simple model for forest soils suggests that a canopy effect may cause atmospheric co2 concentrations deduced from pedogenic minerals to underestimate the actual concentrations of atmospheric co2 if a significant forest canopy were present at the time of formation of pedogenic goethite in the ione fm the concentration of 2700 ppm calculated for atmospheric co2 could be slightly low but the underestimate is expected to be