new silurian and devonian palaeomagnetic results from the hexi corridor terrane northwest china and their tectonic implications summary a total of 239 orientated drill core samples from 23 sites were collected for palaeomagnetic study from silurian and devonian red beds marlaceous sandstone and limestone rocks in the eastern part of the hexi corridor southwest ningxia north china the characteristic high temperature component resides in both haematite and magnetite it clusters around a northwesterly and shallow to moderate downward direction and its antipode after tilt correction the primary origin of this characteristic remanent magnetization chrm is ascertained by positive fold and reversal tests at the 95 per cent confidence level the corresponding palaeopoles at 339 0 e 60 1 n with a 95 11 2 silurian and 336 0 e 56 0 n with a 95 9 2 devonian imply that the north china block ncb had a low palaeolatitude of around 15 n in the northern hemisphere during the silurian devonian period comparison with the early middle ordovician palaeopole of the ncb suggests that the ncb moved rapidly northwards by 30 8 10 9 to cross the palaeo equator during the early middle ordovician to silurian in combination with the palaeobiogeographical data from ningxia our palaeomagnetic results suggest that the ncb was located close to australia during the late devonian

silurian and devonian paleomagnetic poles from north china and implications for gondwana abstract we have obtained paleomagnetic results from silurian and devonian rocks on the western margin of the north china block ncb ages which previously were thought to be unrepresented throughout north china high unblocking temperature components of magnetization isolated from both the silurian and devonian strata pass fold and reversal tests suggesting that they are primary remanence the corresponding paleopoles at 228 4 e 26 2 n silurian and 228 7 e 34 2 n devonian imply low paleolatitude positions of north china during the middle paleozoic probably adjacent to east gondwana

fish from the upper devonian of the shan thai terrane indicate proximity to east gondwana and south china terranes we report the first discovery of abundant devonian vertebrates from thailand an unusual form of coronodontid shark tooth with six equal sized cusps occurs only in the upper devonian of thailand shan thai terrane and south china and a new species of phoebodus is reported that occurs elsewhere only in south china and australia east gondwana terrane the occurrence of the chondrichthyan harpagodens thrinacodus ferox turner 1982 in the late devonian of thailand australia and south china predates the appearance of this species in euramerica early carboniferous these data suggest late devonian proximity of the shan thai south china and east gondwana terranes and is in accord with recent paleomagnetic data

ice sheet load cycling and fluid underpressures in the eastern michigan basin ontario canada strong fluid underpressures have been detected in paleozoic strata in the eastern michigan basin with hydraulic heads reaching 400 m below land surface 4 mpa underpressure and 200 m below sea level in strata where unusually low permeabilities 10 20 10 23 m2 were measured in situ multiple glaciations including three with as much as 3 km of ice cover at the site in the last 120 ka suggest a causal link with the underpressures we examined this possibility using a one dimensional groundwater flow model incorporating mechanical loading from both ice weight and lithospheric flexure because hydrologic and mechanical changes during glaciation are not well characterized and subsurface properties are imperfectly known the model was used inversely to estimate flexural loads and loosely constrained permeabilities by matching observed pressures acceptable matches were obtained for a surprisingly wide range of scenarios with permeabilities close to measured values and plausible flexural loads matches were not obtained when too many parameters were preselected or when permeabilities were constrained to be significantly larger than measured values in successful model runs groundwater expulsion under glacial mechanical loads caused the underpressuring and flexural loads were important if aquifer and sub glacial pressures were significantly elevated during glaciation simulated fluid pressures in the low permeability strata fluctuated by 30 40 mpa during glacial cycles but resulted in advective transport of only tens of meters or less although other mechanisms cannot be ruled out we conclude that glacial mechanical forcing of a water saturated system can explain the observed underpressures

late paleozoic polar wander path for the tarim platform and its tectonic significance abstract stepwise thermal and a f demagnetizations have been carried out on 518 samples 47 sites from the sishichang section across the akesu area in the tarim basin the results lead to a discussion on some problems concerning the tectonic history of the tarim platform and adjacent blocks during the late paleozoic from the late carboniferous until the early permian the tarim platform collided with the kazakhstan block siberian platform and russian platform no large displacements have occurred between these blocks since the mesozoic however the permian pole position of the tarim platform obviously differs from that for the sino korea platform the difference in paleolatitude between the tarim and sino korea platforms in the permian was about 10 their orientations were also different the paleomagnetic result is in contrast to the geologically accepted idea that the two platforms in question occur as a whole in the late paleozoic

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

glacially induced hydromechanical coupling in shale may have caused underpressured water in the eastern michigan basin despite the possible presence of gas phase methane

seasonal and interannual particle export in an african rift valley lake a 5 yr record from lake malawi southern east africa a time sequencing sediment trap was deployed at 300 350 m in lake malawi east africa from 1987 to 1992 to measure particulate export to the deep anoxic hypolimnion in the northern and central lake regions the monthly settling particulate samples provide a data set of seasonal and interannual export fluxes of organic carbon biogenic opal calcium carbonate and lithogenic material maximum total particle fluxes 50 400 mg m 2 d 1 occurred primarily during the dry windy season april through october when algal productivity is high because of wind induced upwelling of nutrient enriched metalimnion and hypolimnion waters peak flux particulates contained an abundance of aulacoseira and stephanodiscus diatom valves and chains the total particle mass flux during the wet austral summer months november through march was consistently one to three orders of magnitude less than that measured during the dry months and consisted of mineral shards terrestrial plant debris and scattered diatom tests the 5 yr trap data provide support for the claim that the light dark lamination couplets abundant in northern and central lake cores reflect seasonal delivery to the sediments of diatom rich particulates during the windy months and diatom poor material during the wet season however interannual and spatial variability in upwelling and productivity patterns as well as el nino southern oscillation enso related rainfall and drought cycles appears to exert a strong influence over the magnitude and geochemical composition of particle export to the deep hypolimnion of lake malawi

axial flow hydraulic pulse testing of an argillaceous limestone lindsay limestone is an argillaceous limestone encountered in southern ontario canada the lindsay formation is regarded as a suitable geologic medium for the construction of a deep geologic repository for storing low to intermediate level nuclear waste the lindsay limestone is a nodular argillaceous rock with very low permeability requiring the use of hydraulic pulse tests for the measurement of its permeability characteristics the paper describes the triaxial testing facility the theoretical basis for the test and the procedures used to analyze the experimental results for estimating the permeability of the lindsay limestone the results are compared with the data available in the literature

hydrochronology of a proposed deep geological repository for low and intermediate level nuclear waste in southern ontario from u pb dating of secondary minerals response to silurian and cretaceous events u pb ages have been measured on secondary dolomite and silica cements in cambrian sandstone at the base of an 840 m thick sub horizontally bedded sedimentary sequence beneath the bruce nuclear site

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

the source and evolution of paleofluids responsible for secondary minerals in low permeability ordovician limestones of the michigan basin abstract in this study we report on the source and evolution of fluids associated with secondary vein and replacement minerals in low permeability carbonate units in the michigan basin this petrogenetic information was collected using thermometric data from fluid inclusions combined with c o and sr isotope data and focuses on mm or cm wide vein and vug minerals from ordovician limestones of the trenton and black river groups and cambrian sandstones in sw ontario canada primary fluid inclusions in dolomite represent fluid stage i and have the highest trapping temperatures ttrap in the sedimentary succession between 88 and 128 c primary inclusions in calcite stage ii and celestine and anhydrite stage iii represent the final stages of secondary mineral formation and have ttrap values of 54 78 c all three stages of vein minerals formed from brines with salinities of 31 37 wt cacl2 nacl eq that were saturated in halite and methane gas at the time of mineral growth three subsequent stages of secondary fluid inclusions were observed in the samples stages iv vi however no secondary vein minerals formed during these stages and they are interpreted as re mobilization and or minor fluid ingress along grain boundaries and micro fractures notably stage iv secondary inclusions are gas undersaturated with salinities of 32 34 wt cacl2 nacl eq and minimum ttrap values of 57 106 c and are interpreted to have formed during a late devonian mississippian regional heating event secondary minerals from the cambrian units and the shadow lake formation have 13c values of 6 1 to 2 5 vpdb 18o values of 14 6 to 24 2 vsmow and 87sr 86sr of 0 70975 0 71043 relative shifts of approximately 2 to 3 in 13c 4 in 18o and 0 002 in 87sr 86sr are observed upward across the boundary between the cambrian shadow lake units and the overlying gull river formation samples from the gull river and coboconk formations and the trenton group kirkfield sherman fall and cobourg formations have 13c values of 1 0 to 1 9 18o values of 18 9 to 28 1 and 87sr 86sr values of 0 70790 0 70990 the combined microthermometric and isotopic data for secondary minerals in the cambrian shadow lake units suggest they formed from hydrothermal brine with a geochemical signature obtained by interaction with the underlying precambrian shield or shield derived minerals in the cambrian sandstones previous u pb dating of vein calcite and rb sr dating of secondary k feldspar from the region suggests that brine ingress occurred during the late ordovician silurian the o and sr isotope variability in vein samples from the gull river and coboconk formations is interpreted as localized mixing of 18o enriched connate fluids with hydrothermal brine in comparison isotopic data for the trenton group indicate secondary mineral formation from connate fluids sourced from 18o enriched evolved seawater and or modified hydrothermal brine that experienced fluid rock interaction during transit through the underlying stratigraphy

analysis and interpretation of borehole hydraulic tests in deep boreholes principles model development and applications a review of the literature on hydraulic testing and interpretive methods particularly in low permeability media indicates a need for a comprehensive hydraulic testing interpretive capability physical limitations on boreholes such as caving and erosion during continued drilling as well as the high costs associated with deep hole rigs and testing equipment often necessitate testing under nonideal conditions with respect to antecedent pressures and temperatures in these situations which are common in the high level nuclear waste programs throughout the world the interpretive requirements include the ability to quantitatively account for thermally induced pressure responses and borehole pressure history resulting in a time dependent pressure profile around the borehole as well as equipment compliance effects in low permeability intervals a numerical model was developed to provide the capability to handle these antecedent conditions sensitivity studies and practical applications are provided to illustrate the importance of thermal effects and antecedent pressure history it is demonstrated theoretically and with examples from the swiss nationale genossenschaft fur die lagerung radioaktiver abfalle regional hydrogeologic characterization program that pressure changes expressed as hydraulic head of the order of tens to hundreds of meters can result from 1 to 2 c temperature variations during shut in packer isolated tests in low permeability formations misinterpreted formation pressures and hydraulic conductivity can also result from inaccurate antecedent pressure history interpretation of representative formation properties and pressures requires that antecedent pressure information and test period temperature data be included as an integral part of the hydraulic test analyses

hydrology and hydraulic properties of a bedded evaporite formation the permian salado formation in the delaware basin of new mexico is an extensively studied evaporite deposit because it is the host formation for the waste isolation pilot plant a repository for transuranic wastes geologic and hydrologic studies of the salado conducted since the mid 1970 s have led to the development of a conceptual model of the hydrogeology of the formation that involves far field permeability in anhydrite layers and at least some impure halite layers pure halite layers and some impure halite layers may not possess an interconnected pore network adequate to provide permeability pore pressures are probably very close to lithostatic pressure in the near field around an excavation dilation creep and shear have created and or enhanced permeability and decreased pore pressure whether flow occurs in the far field under natural gradients or only after some threshold gradient is reached is unknown if far field flow does occur mean pore velocities are probably on the order of a meter per hundreds of thousands to tens of millions of years flow dimensions inferred from most hydraulic test responses are subradial which is believed to reflect channeling of flow through fracture networks or portions of fractures that occupy a diminishing proportion of the radially available space or through percolation networks that are not saturated fully interconnected this is probably related to the directional nature of the permeability created or enhanced by excavation effects inferred values of permeability cannot be separated from their associated flow dimensions therefore numerical models of flow and transport should include heterogeneity that is structured to provide the same flow dimensions as are observed in hydraulic tests modeling of the salado formation around the wipp repository should also include coupling between hydraulic properties and the evolving stress field because hydraulic properties change as the stress field changes

a conventional straddle sliding packer system as a borehole extensometer monitoring shear displacement of a fault during an injection test abstract a constant head step injection test using a conventional straddle packer system was performed for a normal fault in siliceous mudstone the test applied a new method whereby axial displacements of isolated test sections in a borehole during injection are monitored by measuring the pressures of sliding packers and the pore pressure in the test section the measured pressures and axial displacement and the injection flow rate were used to estimate the hydraulic aperture shear displacement normal compliance normal stress shear stiffness and hydraulic dilation angle of the fault during the test the injection successfully yielded a large shear displacement during normal faulting of up to 13 3 49 5 mm including the estimation error which left residual shear displacement of 2 8 10 4 mm after a remarkable shear slip event the shear stiffness during faulting is estimated to be 2 3 107 to 8 4 107 pa m 1 considering the estimation error which is consistent with empirically predicted values based on previous studies the hydraulic dilation angle was inferred to be effectively zero as the residual shear displacement did not leave any increase in hydraulic aperture the experimental method applied here does not require specialized equipment and could aid in the investigation of the hydromechanical behavior of subsurface fractures or aquifers

a systematized drillstem test a solution of the well response to a drillstem test dst is presented the advantages of a dst over conventional slug tests are discussed a systematized procedure of a dst is proposed where a slug test is terminated in the midpoint of the flow period and the subsequent shut in data are recorded and analyzed this method requires a downhole shut in device and a pressure transducer which is no more than the conventional deep well slug testing as opposed to slug tests which are ineffective when a skin is present more accurate estimate of formation permeability can be made using a dst premature termination also shortens the test duration considerably because in most cases no more information is gained by completing a slug test to the end the author recommends that conventional slug tests be replaced by the premature termination technique

new cambrian and ordovician paleomagnetic poles for the north china block and their paleogeographic implications multicomponent magnetization has been revealed in several cambrian and ordovician sedimentary units from localities in hebei and shandong provinces of the north china block ncb a well defined component with lower unblocking temperature is characterized by northerly declination and moderate to steep inclination with both polarities and postdates the late cretaceous folding the pole position derived from the overprinted directions is close to both the cretaceous pole for the ncb as well as the present north pole the overprint is not a simple thermal remanent magnetization but is probably a chemical remanent magnetization imposed at moderately elevated temperature during the major episode of regional deformation in the late mesozoic the higher unblocking temperature characteristic components pass reversal baked contact and fold tests and are internally consistent with rocks of different lithologies from widely distributed localities moreover the data exhibit an overall similarity in the magnetic polarity pattern in the stratigraphic sequence at sampled localities hence the high unblocking temperature characteristic component was probably acquired at or near the time of deposition the cambrian and ordovician paleopoles are somewhat different from the other coeval poles for the ncb which are based on much less data and do not pass as many reliability tests but all imply that the ncb was in the equatorial zone in the early paleozoic

early paleozoic paleomagnetic poles from the western part of the north china block and their implications abstract we collected 917 oriented drill core samples 124 sites from 22 units spanning the early cambrian to middle ordovician formations of the north china block ncb to construct an apparent polar wander path apwp of the early paleozoic for the ncb sampling areas are located in the helanshan tongchuan hancheng and yuncheng luliang regions along the margin of the ordos basin characteristic remanent magnetizations for five periods between the cambrian and ordovician are isolated from 281 samples by careful demagnetization directions cluster around northwesterly direction with upward shallow inclination and its antipode after tilt correction reliability of these five directions is ascertained through positive fold and reversal tests the five cambrian and ordovician paleopoles plot in the present atlantic ocean which is consistent with previously reported paleomagnetic poles a newly constructed apwp between the cambrian and ordovician indicates that the ncb was located in the southern hemisphere around 15 s during cambro ordovician time motion of the ncb between the early and middle cambrian comprised a counterclockwise rotation of 22 3 7 0 and a northward latitudinal displacement of 7 2 6 8 combining the paleobiogeographic and paleoclimatic data with the paleomagnetic implies that the ncb was probably located in east gondwana in the early cambrian and may have separated from gondwana in post early cambrian time the ncb is also inferred to have been located close to siberia and north america during the middle ordovician

on conducting the modified slug test in tight formations the method introduced by bredehoeft and papadopulos 1980 for conducting a modified slug test in tight formations does not assure the condition of approximate equilibrium necessary at the start of the test in addition compressibility in the shut in well can be significantly larger than the compressibility of water which bredehoeft and papadopulos indicate should be used in the calculations errors that may result from using the original test procedure are discussed and a modified procedure and testing arrangement are presented

low temperature behavior of single domain through multidomain magnetite abstract we have investigated the low temperature behavior of a suite of grown synthetic and natural magnetites that span single domain sd and multidomain md behavior synthetic samples had been grown in the laboratory either in an aqueous medium or in glass natural samples included sd magnetites occurring in plagioclase and truly md magnetites in the form of large octahedra in all experiments a sample was first given a saturation remanence at room temperature next moment was measured continuously during cooling and warming between 230 k and 60 k similar to results reported earlier by other workers magnetic memory is large in sd samples whereas truly md samples are almost completely demagnetized by cycling between room temperature and 60 k pseudo single domain samples exhibit behavior that is intermediate with respect to that of the sd and truly md states when data from this study are combined with data obtained by hartstra 10 from sized natural magnetites it is found that the percentage of total remanence that survives cycling between room temperature and 60 k decreases linearly with the logarithm of grain size and thus with increasing number of domains this relation suggests that memory can provide a reasonable estimate of grain size in those magnetite bearing rocks for which these samples provide good analogues remarkably some of the large natural octahedra provide a magnified view of md response to low temperatures and thus reveal two surprising and intriguing types of behavior first below approximately 180 k these octahedra demagnetize through a series of large barkhausen jumps second near 117 k these same octahedra exhibit a wild zone where magnetic moment executes large random excursions we interpret these two phenomena as direct evidence for the unpinning and irreversible displacement of domain walls in response to the drop in coercivity and possibly the broadening of domain walls as temperatures drop toward the isotropic point one implication of this behavior is that cooling to progressively lower temperatures could provide an effective method for stepwise removal of paleomagnetic components carried by md grains even without passage through the isotropic point of magnetite

geostatistics based regional characterization of groundwater chemistry in a sedimentary rock area with faulted setting sophisticated modeling of a hydrogeological structure and the environment are crucial for underground construction this study characterizes hydrochemical properties of groundwater in a sedimentary rock area clarifying their spatial distribution and correlation with geologic structure and interpreting the groundwater source and chemical evolution water samples geological columns and well logs to 1 km depth were taken at 10 sites in horonobe of northern japan toward the objectives a 3d model of cl concentration was produced in conjunction with resistivity logging data through kriging estimation and sequential gaussian cosimulation variography shows that the dip of the main omagari fault is a control on the spatial correlation structure of cl concentration the 3d model shows that this fault and its auxiliary constitute a clear boundary between high and low saline waters and that cl concentrations tend to change in accord with sedimentary layer structures the integration of stable isotope analysis suggests that deep saline water with heavy d and 18o originated from fossilized seawater whereas shallow freshwater with light values is of meteoric water origin dilute saline water in the deep part of study area is partially attributable to dehydration of silica minerals vertical and lateral groundwater flows are estimated to prevail near the omagari fault and be general in other zones respectively difference in the depth of transition zones may be caused by the dominant flow among downward ascending and lateral consequently geostatistical techniques and data integration are useful to depict regional groundwater systems with a data set of water investigation limited by quantity and location

molecular and isotopic evaluation of the maturation history of the organic matter in an ordovician aquiclude michigan basin evidence for late diagenetic biodegradation abstract previous characterization of a low permeability 10 16 kh 10 12 m s 1 and high salinity 5 m of cl 10 seawater salinity aquiclude in upper ordovician aged sediments situated on the eastern flank of the michigan basin where a deep geological repository for low and intermediate level nuclear waste is proposed suggested a microbial origin for ch4 and co2 based on their stable isotope values ch4 is believed to have been produced and trapped during the paleozoic in a relatively discrete and high organic matter om horizon at the shale carbonate transition to further investigate the efficiency of confinement of this aquiclude here we present detailed isotopic and geochemical stratigraphic profiles of om and biomarkers with the objective of understanding the origin of ch4 and its relative timing of confinement classical diagnostic ratios of polycyclic aromatic hydrocarbons relative abundances of hopanes and degraded hopanes coupled to dual compound specific isotopic analysis of n alkanes as well as 13c analysis on different fractions of om were measured a partitioning of the ordovician sedimentary succession into two systems is observed with an upper system that is self sourced and confined hosting the microbially derived ch4 with evidence of late diagenetic om biodegradation and a lower system that reveals later secondary oil migration which has overprinted the organic geochemical record we propose a conceptual model that would explain the generation and preservation of this paleo bioreactor over time using the maturation history reconstruction derived from this dataset this work not only provides essential field empirical evidence of a relationship between methanogenesis and late diagenetic biodegradation but also shows the power of dual compound specific isotope analyses in deciphering between different maturation processes affecting om in natural subsurface settings

geochemical evolution and residence time of porewater in low permeability rocks of the michigan basin southwest ontario abstract drill cores collected from an 860 m thick paleozoic cambrian to devonian sedimentary sequence of the michigan basin in southwest ontario canada were used to develop vertical profiles of natural tracers in porewater from the sedimentary sequence and build a conceptual model regarding processes and timing of solute migration in this paper the conceptual model is quantitatively assessed with numerical simulations of diffusion dominated solute transport cl and 18o the conceptual model suggests that the tracer profiles result from mixing between a deep shield brine with isotopic characteristics consistent with water rock interaction over a long period of geologic time ordovician seawater at intermediate depth and an overlying hypersaline brine formed by evaporation of seawater in a restricted basin during the silurian between the peak of basin consolidation at 300 ma bp and the pleistocene 2 6 ma bp salinity and isotopic concentration gradients are thought to have driven mixing dominantly by diffusion water isotope data indicate that in the pleistocene melt water infiltrated to a maximum depth of 330 m in the silurian salina formation likely in response to transient glacial loading and elevated sub glacial hydraulic pressures also in the pleistocene over pressured conditions in deep regions of the basin drove high salinity brine eastward in the basal cambrian aquifer interrupting pre existing tracer diffusion profiles a base case set of boundary and initial conditions provides a good fit between simulated and measured tracer profiles but requires effective diffusion coefficients de in the ordovician limestones that are lower than the average values obtained in laboratory measurements by as much as a factor of 10 the base case values are still within the overall range of measured values at the formation scale relatively low in situ de values are attributed to the intermittent occurrence of gas and liquid hydrocarbons in the ordovician carbonate units and the effect of lithostatic confining pressure neither of which are accounted for in the laboratory measurements but both would have the effect of decreasing de for aqueous solutes the numerical model is most sensitive to the formation specific de values and geologically reasonable variations in initial and boundary conditions have a relatively small influence on the results additional simulations indicate that hydraulic disturbance and ingress of meltwater during the pleistocene can explain second order features observed in the measured tracer profiles this work provides supporting evidence for previous research indicating that the porewater residence time in the ordovician sequence approaches the age of the rocks

hydraulic testing of low permeability silurian and ordovician strata michigan basin southwestern ontario summary straddle packer hydraulic testing was performed in 31 silurian intervals and 66 ordovician intervals in six deep boreholes at the bruce nuclear site located near tiverton ontario as part of site characterization activities for a proposed deep geologic repository dgr for low and intermediate level radioactive waste the straddle packer assembly incorporated a hydraulic piston to initiate in situ pulse tests within low hydraulic conductivity horizontal hydraulic conductivities of the silurian test intervals range from approximately 4e 14 to 4e 8 m s the average horizontal hydraulic conductivities of the ordovician intervals range from 2e 16 to 2e 10 m s the lower member of the cobourg formation the proposed host formation of the dgr between 660 and 688 meters below ground surface was found to have a horizontal hydraulic conductivity of 4e 15 to 3e 14 m s the formation pressures inferred from the hydraulic testing confirmed by long term monitoring show that the upper ordovician and middle ordovician trenton group are significantly underpressured relative to a density compensated hydrostatic condition and relative to the overlying silurian strata and underlying black river group and cambrian strata these underpressures could not persist if hydraulic conductivities were not as low as those measured

diagenetic evolution of a sedimentary system michigan basin insights from petrography and s isotope micro analysis of pyrite abstract the study presents a detailed investigation of s isotope systematics of pyrite from cambrian ordovician sedimentary rocks along the eastern flank of the michigan basin ontario canada whole rock and secondary ion mass spectrometry sims pyrite analyses of 34s 32s were undertaken in association with a detailed petrographic investigation of the different crystal morphologies to better constrain the diagenetic history of the sedimentary rocks by informing about the processes of pyrite formation the broad range of sims isotopic data i e 37 1