abrupt global ocean anoxia during the late ordovician early silurian detected using uranium isotopes of marine carbonates widespread marine anoxia is hypothesized as the trigger for the second pulse of the late ordovician hirnantian mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters we test the anoxia hypothesis using 238u values of marine limestones as a global seawater redox proxy the 238u trends at anticosti island canada document an abrupt late hirnantian 0 3 negative shift continuing through the early silurian indicating more reducing seawater conditions the lack of observed anoxic facies and no covariance among 238u values and other local redox proxies suggests that the 238u trends represent a global ocean redox record the hirnantian ocean anoxic event hoae onset is coincident with the extinction pulse indicating its importance in triggering it anoxia initiated during high sea levels before peak hirnantian glaciation and continued into the subsequent lowstand and early silurian deglacial eustatic rise implying that major climatic and eustatic changes had little effect on global ocean redox conditions the hoae occurred during a global 13c positive excursion but lasted longer indicating that controls on the c budget were partially decoupled from global ocean redox trends u cycle modeling suggests that there was a 15 increase in anoxic seafloor area and 80 of seawater u was sequestered into anoxic sediments during the hoae unlike other ocean anoxic events oae the hoae occurred during peak and waning icehouse conditions rather than during greenhouse climates we interpret that anoxia was driven by global cooling which reorganized thermohaline circulation decreased deep ocean ventilation enhanced nutrient fluxes stimulated productivity which lead to expanded oxygen minimum zones

arenigian early ordovician sea level history and the response of conodont communities western newfoundland four cluster analyses were performed which recognized 17 conodont communities in the arenigian lower ordovician of western newfoundland the analyses include 69 598 identifiable conodont specimens recovered from 153 conodont bearing samples from four stratigraphical sections representing the environmental settings of the platform upper proximal slope lower proximal slope and distal slope the distribution of conodont communities along the platform to slope environmental gradient shows that sea level changes simultaneously affected the development and replacement of the conodont communities in the different facies the pattern of change in conodont communities allows an interpretation of sea level change that is correlated precisely into the detailed graptolite biozonation a gradual transgression lasted most of tetragraptus approximatus zone time which was followed by a brief regression a transgression regression cycle occurred in the t akzharensis zone time a major transgression caused a highst

conodonts as biostratigraphic tools for redefinition and correlation of the cambrian ordovician boundary the cambrian ordovician boundary is recognized at different horizons on various continents by utilizing several fossil groups conodonts are abundant diverse and less provincial and facies controlled than other fossils in this interval many species are widespread and some are cosmopolitan strata representing the cambrian ordovician boundary interval from asia australia and north america can be correlated easily when those strata are from cratonal or shelf environments strata from slope facies have fewer conodonts fewer taxa and taxa may have different ranges compared with cratonal and shelf facies it may be easier to correlate intercontinentally within cratonal shelf facies than to correlate intracontinentally from cratonal shelf facies to slope facies a new hierarchical arrangement of conodont interval zones and subzones is proposed for western north america these include the proconodontus tenuiserratus zone the p posterocostatus zone new the p muelleri zone new the eoconodontus zone new with eoconodontus notchpeakensis and cambrooistodus minutus subzones the cordylodus proavus zone emended with hirsutodontus hirsutus fryxellodontus inornatus and clavohamulus elongatus subzones the cordylodus intermedius zone new with hirsutodontus simplex and clavohamulus hintzei subzones the cordylodus lindstromi zone new and cordylodus angulatus zone new the boundary point for the base of the ordovician system will be chosen so as to coincide with a correlatable conodont zonal boundary other fossil groups will support correlation of this boundary point three alternative horizons are being considered the base of the cordylodus proavus zone is the most distinctive but is regarded by some as older than is appropriate for the base of the ordovician the base of the cordylodus intermedius zone is recognizable by faunal changes in several evolutionary lineages at a level that is slightly younger than the presently recognized boundary in australia north america and parts of asia but slightly older than the base of the tremadoc series of europe the base of the c lindstromi zone can be recognized in most areas by the lowest occurrence of the nominate species which is of questioned taxonomic validity and uncertain biostratigraphic utility this horizon is closest to the base of the tremadoc series of europe choice of a stratotype section has been narrowed to the cow head group in newfoundland eastern canada and to the fengshan and yehli formations in jilin province northeastern china the cow head group was deposited on and near the base of the continental slope erosion by debrisslide breccias resulted in a significant hiatus near the boundary interval in the broom point sections a condition contrary to guidelines for choice of boundary sections this may be less of a problem in other sections such as green point the dayangcha section in china was deposited on the outer part of a continental shelf and has acritarchs conodonts graptolites and trilobites additional study of the china section is needed to document fully the ranges of critical conodont taxa

geoelectric field measurements on a planetary scale oceanographic and geophysical applications the characteristics of an initial year of electric field measurements obtained from a long 3900 krn unpowered submarine cable extending from point arena california to hanauma bay hawaii are reported the power spectrum estimated from the cable time series is similar to that from seafloor point electric field sensors at frequencies above 1 cpd but differs at lower frequencies by decreasing monotonically down to at least 0 02 cpd the multiple squared coherence between the cable data and three component geomagnetic fluctuations measured at fresno ca is high t2 0 9 from 1 0 0 09 cpd then declines slowly with decreasing frequency maps of the squared coherence between the cable voltage and the sur face air pressure wind stress and wind stress curl derived from the fleet numerical oceanography center product over the entire eastern north pacific show no significant relationships at frequencies above 0 05 cpd but strong nonlocal coherence with the wind stress curl forcing obtains at lower frequencies taken together these observations support a transition from high frequency dominance by external sources to low frequency dominance by oceanic motional sources at 0 05 0 1 cpd a considerably smaller value than has previously been observed with point electric field sensors on the ocean bottom the difference is caused by horizontal averaging of the short spatial scale motional component over the long submarine cable

study of tidal periodicities using a transatlantic telecommunications cable we report the results of determinations of tidal periods from spectral analysis of the voltage induced across an unpowered length of the tat 7 telecommunications cable in the north atlantic ocean over an approximately 19 day interval particularly prominent spectral components are observed at several frequencies including those identified as corresponding to the diurnal declination luni solar k1 semi diurnal principal solar s2 semidiurnal principal lunar m2 and monthly lunar mm components in addition a large amplitude spectral component of high statistical significance was observed at a frequency of 3 0051 cpd approximately one third the sidereal day this component does not appear to be related to the solar component s3 and possibly corresponds to a declination luni solar k3 frequency although the amplitude is very much larger than that which might be expected other common lunar tides appear to be a minor component of the data such cable data can be used for studies and refinement on a global scale of large scale tidal ocean and ionosphere models

discrete element modeling of subglacial sediment deformation 1 the discrete element method dem is used in this study to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm based glaciers complementary to analog experiments the numerical approach allows a detailed analysis of the material dynamics and the shear zone development during progressive shear strain the geometry of the heterogeneous stress network is visible in the form of force carrying grain bridges and adjacent volumetrically dominant inactive zones we demonstrate how the shear zone thickness and dilation depend on the level of normal overburden stress and we show how high normal stress can mobilize material to great depths the particle rotational axes tend to align with progressive shear strain with rotations both along and reverse to the shear direction the results from successive laboratory ring shear experiments on simple granular materials are compared to results from similar numerical experiments the simulated dem material and all tested laboratory materials deform by an elastoplastic rheology under the applied effective normal stress these results demonstrate that the dem is a viable alternative to continuum models for small scale analysis of sediment deformation it can be used to simulate the macromechanical behavior of simple granular sediments and it provides an opportunity to study how microstructures in subglacial sediments are formed during progressive shear strain

high resolution strontium isotope stratigraphy across the cambrian ordovician transition we have analyzed 214 fossil apatite samples from nine stratigraphic sections worldwide that cover the lower cambrian to lower ordovician for their strontium isotope ratios of these samples 180 from six sections that cover the cambrian ordovician transition 5 ma reveal how the extent of isotopic alteration can differ greatly according to lithology and sample type from three limestone sections 126 euconodont samples yield the most consistent 87sr 86sr ratios and are used in this article to constrain seawater 87sr 86sr across the cambrian ordovician boundary by contrast protoconodonts paraconodonts and inarticulate brachiopods are far less likely to retain a primary 87sr 86sr signature and appear to be of only limited value for chemostratigraphy seawater 87sr 86sr fell from maximum values for the phanerozoic of more than 0 7092 during the early late cambrian to 0 7090 by the earliest ordovician high resolution sampling has permitted the recognition of sinusoidal variations with a wavelength on the order of 1 ma that are superimposed on the overall fall in 87sr 86sr these variations may be caused by high order cycles in seawater 87sr 86sr or diagenetic alteration

large scale electric field measurements on the earth s surface a review there exist only a few reported measurements of quasi stationary near dc electric potentials over very large spatial scales hundreds of kilometers or more on the earth s surface such measurements have typically been made using unpowered submarine telecommunications cables the measurements pose unique experimental challenges and require careful procedures to avoid data contamination by electrode contact potentials and local ground currents in addition there are possible interpretational problems from pervasive poorly understood low frequency electric fields induced by ocean water motion through the earth s stationary magnetic field nevertheless estimates of the magnitude of the electric field computed from large scale potential difference measurements made principally to date in the pacific ocean can be used to place a limit on the size of the toroidal magnetic field at the core mantle boundary under certain conditions on the earth s electrical conductivity profile thus large scale electric potential measurements can serve as an adjunct probe of the earth s dynamo process in addition to measurements of the poloidal magnetic field and its secular changes made at and above the surface of the earth a review of all of these data suggests that the toroidal and poloidal magnetic fields at the top of the core are comparable in magnitude

carbon isotope stratigraphy of the uppermost cambrian in eastern laurentia implications for global correlation the 13 c profile from an interval of the martin point section in western newfoundland canada spans the upper furongian uppermost cambrian the interval 90 m is a part of the green point formation of the cow head group and consists of the martin point lower and the broom point upper members it is formed of slope marine carbonates alternating with shales rhythmites and conglomeratic interbeds the preservation of the investigated micritic carbonates was meticulously evaluated by multiple petrographic and geochemical screening tools the 13 c and 18 o values 0 5 0 8 vpdb and 7 1 0 3 vpdb respectively exhibit insignificant correlation r 2 0 002 and similarly the correlation of 13 c values with their sr and mn counterparts which supports the preservation of at least near primary 13 c signatures that can be utilized to construct a reliable high resolution carbon isotope profile for global correlations the 13 c profile exhibits two main negative excursions a lower broad excursion 3 that reaches its maximum at 70 m below the martin point broom point members boundary and an upper narrow excursion 2 5 immediately below the same boundary the lower excursion can be correlated with the global latest furongian herb event toce which is also recognized in the c isotope profile of the gssp boundary section at green point whereas the upper excursion matches with that of the cambrian ordovician boundary in the same section the peak of the herb 13 c excursion is correlated with positive shifts on the th u and ni profiles redox and productivity proxies

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

hydraulic properties of subglacial sediment determined from the mechanical response of water filled boreholes freezing of water filled boreholes drives water into the subglacial bed and the associated pressure effects yield information about subglacial hydraulic properties a numerical model describing the mechanical response of an unconnected borehole and the bed beneath it to this freezing forcing was developed using a nonlinear transient visco elastic ice flow law and an approximate model of top down freezing the resulting system of equations was solved using the method of lines results agreed well with analytic solutions when parameters were correctly chosen forward modelling of pressure records from three 1992 boreholes and three from other years indicated that the till underlying trapridge glacier has a hydraulic conductivity of 1 35 7 0 10 9 m s 1 the model was also used to investigate the response of a borehole to sudden pressure changes the response is very fast compared to pressure sensor sampling rates thus the true basal signal is essentially unaffected by the presence of the borehole except during the initial freeze in

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

impact of climate variability on the tidal oceanic magnetic signal a model based sensitivity study esa s satellite magnetometer mission swarm is supposed to lower the limit of observability for oceanic processes while periodic magnetic signals from ocean tides are already detectable in satellite magnetometer observations changes in the general ocean circulation are yet too small or irregular for a successful separation an approach is presented that utilizes the good detectability of tidal magnetic signals to detect changes in the oceanic electric conductivity distribution ocean circulation tides and the resultant magnetic fields are calculated with a global general ocean circulation model coupled to a 3 d electromagnetic induction model for the decay of the meridional overturning circulation as an example the impact of climate variability on tidal oceanic magnetic signals is demonstrated total overturning decay results in anomalies of up to 0 7 nt in the radial magnetic m2 signal at sea level the anomalies are spatially heterogeneous and reach in extended areas 30 or more of the unperturbed tidal magnetic signal the anomalies should be detectable in long time series from magnetometers on land or at the ocean bottom the anomalies at satellite height 430 km reach 0 1 nt and pose a challenge for the precision of the swarm mission climate variability induced deviations in the tide system e g tidal velocities and phases are negligible changes in tidal magnetic fields are dominated by changes in seawater salinity and temperature therefore it is concluded that observations of tidal magnetic signals could be used as a tool to detect respective state changes in the ocean

impact of oceanic warming on electromagnetic oceanic tidal signals a cmip5 climate model based sensitivity study in contrast to ocean circulation signals ocean tides are already well detectable by electromagnetic measurements oceanic electric conductivities from the coupled model intercomparison project phase 5 cmip5 climate simulations are combined with tidal currents of m2 and o1 to estimate electromagnetic tidal signals and their sensitivity to global warming ninety four years of global warming leads to differences of 0 3 nt in tidal magnetic amplitudes and 0 1 mv km in the tidal electric amplitudes at sea level locally the climate induced changes can be much higher e g 1 nt in the north atlantic in general all studied electromagnetic tidal amplitudes show large scale climate induced anomalies that are strongest in the northern hemisphere and amount to 30 of their actual values consequently changes in oceanic electromagnetic tidal amplitudes should be detectable in electromagnetic records electric and magnetic signals as well as tides of different frequencies contain complementary regional information

middle ordovician late dapingian darriwilian conodonts from the cow head group and lower head formation western newfoundland canada1this article is one of a series of papers published in cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology middle ordovician late dapingian darriwilian conodonts from the shallow bay and green point formations cow head group and the lower head formation are recorded from three sections in gros morne national park the collection was investigated to clarify local age relationships between the uppermost part of the cow head group and the interbedded to overlying sediments of the lower head formation conodonts from st pauls inlet north section indicate a middle dapingian age for the upper lower bed 13 latest dapingian to early darriwilian age for the upper bed 13 an early darriwilian dw 1 age for the top beds or bed 15 of the shallow bay formation at lower head and the lower head formation is referred to the darriwilian the uppermost part of the lower bed 13 contains periodon hankensis n sp gothodus sp a and diaphorodus delicatus followed by periodon macrodentatus ansella longicuspica erraticodon n sp a and spinodus wardi n sp in the lowermost part of upper bed 13 the fauna with p macrod

tempo of earliest ordovician graptolite faunal succession conodont based correlations from the tremadocian of quebec successive tremadocian planktic dendroid graptolite assemblages from continental slope sequences in quebec can be correlated with north american platform biozonations on the basis of conodonts anisograptid bearing assemblage 2 middle tremadocian matane faunas are associated with early ordovician rossodus manitouensis zone new designation conodonts younger middle tremadocian faunas with adelograptids assemblage 3 are no younger than the rossodus manitouensis zone key dendroid evolutionary immigration events take place within the lower conodont fauna b interval rooted dendroids near cap des rosiers quebec and in eastern new york state occur with lower fauna b conodonts and the trilobites pareuloma and borthaspidella however the earliest tremadocian and earliest ordovician dendroid immigration event represented by the local lowest occurrence of faunas with dictyonema flabelliforme s l at localities in western newfoundland eastern new york state norway and eastern china also lies with

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

electromagnetic study of the atlantic continental margin using a section of a transatlantic cable the induction of currents in an approximately 1200 km length of the tat 7 transatlantic telecommunications cable by geomagnetic field fluctuations is studied analyses of the induced voltage drop across the essentially geomagnetically east west oriented cable and of magnetic field data obtained at field sites at the cable head tuckerton new jersey and in new hampshire show a very high correlation over a wide frequency range between the induced currents in the cable and the east west magnetic field fluctuations the observations do not correspond to the classical ocean coast effects discussed in the literature the results of the analyses suggest that there are telluric currents flowing in an approximately north south direction off the east coast of the united states the electrical current flow could be primarily confined in the ocean water or channeled in a conductivity structure within the earth s crust and upper mantle if the latter situation exists as may be likely because of the wide range of frequencies over which the effect is seen then the region of the induced current flow could be related to the east coast magnetic anomaly ecma in this case these results would indicate that in addition to being a static magnetic anomaly the ecma is a structure with significant electrical characteristics such as higher conductivity

geoelectric power spectra over oceanic distances we present initial results of simultaneous measurements of the geoelectric potential as measured across two long cable routes in the pacific guam to philippines and california to hawaii separated by 6h in local time and 30 o in latitude over the fre quency range 10 5 to 1 67 x 10 3 hz the power levels tend to be enhanced near local noon along the two routes especially during geomagnetic quiet intervals during the seven days analyzed geoelectric power levels up to 104 mv km 2 km were measured on a geomagnetically disturbed day the power levels at the longest periods 17m to 150m are gen erally found to be largest along the route at lower geomagnetic latitudes guam to philippines when comparisons are made at equivalent local times in con trast the power levels for periods in the hydromagnetic wave region periods 5m tend to be larger at all local times for the higher geomagnetic latitude route the nightside geoelectric power levels along the higher lati tude route tend to increase with increasing geomagnetic activity

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

lower ordovician scolecodonts from the cow head group western newfoundland a scolecodont polychaete jaw fauna from the latest tremadoc and arenig strata of the cow head group includes some of the earliest representatives of these fossils in the world no biostratigraphically useful changes seem to occur within the interval although rapid diversification follows their appearance in the latest tremadoc insufficient data were recovered to permit conclusions regarding ecological control of assemblages in early paleozoic down slope environments

geomagnetic induction on a transatlantic communications cable the phenomenon of geomagnetically induced currents in long conductors has been recognized since the mid nineteenth century when the use of the telegraph became prevalent in north america and europe1 powering systems of telegraph and telephone cables are now engineered to eliminate large current surges although the occasional significant geomagnetic disturbance such as those produced by the february 19582 august 19723 flare events can still be a problem however induced voltages can be used with complementary geophysical and geological data to deduce features of the earth s crust and upper mantle13 14 improved scientific understanding of mag netospheric phenomena means that the geomagnetic induction process in long conductors and thus in the earth are better understood for example the cable outage problem associated with the august 1972 geomagnetic storm interval was qualitatively attributed not to the line currents associated with normal auroral current systems but rather to the significant enhanced currents flowing on the magnetosphere boundary at the time of an extreme compression of this boundary in greatly enhanced solar wind conditions3 we have measured the geomagnetic induction phenomenon on modern day long cables to get better assessments of the induced currents in various types of geomagnetic variations our initial work was concerned with induction in the transatlantic telecommunications cable no 6 tat 6 which is laid between green hill rhode island 41 4 n 71 7 w geographic and st hilaire de riez france 46 7 n 1 9 w 4 we concentrate quantitatively here on induction by the solar induced quiet day currents sq in the ionosphere and find that calculated values agree well with observed values of sq

radiolarian diversity changes during the late cambrian early ordovician transition as recorded in the cow head group of newfoundland canada abstract upper cambrian to lower ordovician pelagic carbonate rocks of the cow head group in western newfoundland canada were sampled for the study of their radiolarian fauna well preserved and diverse faunal assemblages were obtained from a number of levels of the shallow bay and green point formations three different assemblages including a total of five families eight genera and 20 species are recognized in three different sections situated on a palaeobathymetric profile the various recognized assemblages are compared with previous studies conducted on the cow head group they improve considerably our understanding of the pattern of changes in radiolarian diversity during the cambrian ordovician transition the radiolarian biotic record of western newfoundland unveils a two step faunal change across the cambrian ordovician transitional interval one situated at the base of the uppermost cambrian stage 10 and the second at a poorly constrained interval situated towards the top of the same stage 10 these biotic changes consist of genus level selective extinctions as well as within clade species faunal turnover i e echidnina paleospiculum decrease of species abundance species extinction and within clade episodes of species diversification i e protoentactinia parechidnina

carbon isotope δ13ccarb heterogeneity in deep water cambro ordovician carbonates western newfoundland abstract carbonates of western newfoundland span the cambro ordovician interval and preserve a record of slope basinal deposition in the cow head group near cow head this unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at cow head peninsula these conglomerates although prevalent throughout the section vary in thickness and abundance stratigraphically and record both local disruption and large scale episodic sedimentation events microfacies drilled for carbon isotope 13 c carb analysis of conglomerates reveal isotopic heterogeneity within individual samples in some cases more than 1 while this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample permil level variability was observed both between individual clasts in a sample between different parts of the same matrix and between a clast and its surrounding matrix no associated variation in 18 o carb or trace element distributions exists to suggest that this 13 c carb variability is the result of later stage meteoric diagenesis the 13 c carb variability suggests multiple sources of dissolved inorganic carbon dic associated with carbonate precipitation for phases within these individual samples these data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment water interface swi are either contributing to or controlling 13 c carb values in cambrian carbonates perhaps more so than at other intervals in earth history

induction of currents in long submarine cables by natural phenomena the influence of induced currents on long submarine cables has been observed for nearly a century the currents originate from time variations in the magnetic field of external origin magnetospheric atmospheric tides and earth and ocean tides steady earth currents of internal origin have also been proposed as a possible source the induced currents will depend upon the length depth and geomagnetic location of the cables present understanding of the phenomena is reviewed also discussed are potential scientific problems which might be addressed with data from such long cables and possible limitations on the information obtained such problems include studies of 1 the deep conductivity structure of the earth 2 telluric currents flowing in mid oceanic ridges 3 the spatial extent of external source fields and 4 a possible role of electromagnetic eddy currents in fluctuations of the earth s spin rate

comparative lower middle ordovician conodont oxygen isotope palaeothermometry of the argentine precordillera and laurentian margins abstract stratigraphic palaeontologic and palaeomagnetic data support a hypothesis that argues for the argentine precordillera rifting from the southwestern margin of laurentia in low latitudes during the cambrian migrating across the iapetus ocean colliding with the gondwanan margin in the late middle ordovician and receiving glaciogenic sediments in the late ordovician an alternative model proposes that the precordillera originated as a low latitude segment of gondwana migrated southward through major transform faulting toward high latitudes in the late middle ordovician to reach its present position in the devonian new conodont oxygen isotope compositions 18ophos have been determined by ion microprobe shrimp ii using samples from both the precordillera and laurentia marathon area of texas wilcox pass in alberta and western newfoundland significantly the 18o values of conodonts from all four widely separated areas show a consistent pattern of a cyclic but overall increasing trend in 18o ca 16 to 18 hence ocean cooling through the early and middle ordovician an apparent change occurs at the basal late ordovician where 18o values obtained from conodonts in the uppermost sample from the precordillera are significantly higher 1 5 than those from laurentia albeit from a single sample this higher value implies significantly cooler conditions as would be anticipated with a southerly poleward migration of the precordillera irrespective of either hypothesis the virtual absence of conodont bearing carbonates in most of the precordilleran upper ordovician precluded analysis of younger samples when combined with existing macrofaunal and palaeomagnetic data the oxygen isotope data would tend to favour the model of a drift of the precordillera from tropical to higher latitudes during the ordovician however further studies are needed to determine unequivocally whether the precordillera originated from southern laurentia ouachita embayment these new oxygen isotope values provide the best and regionally most consistent data through the early middle ordovician

a semi global reference model for electrical conductivity in the mid mantle beneath the north pacific region 1 one dimensional electrical conductivity structure in the mid mantle of the one fourth of the earth beneath the north pacific ocean was obtained by a semi global electromagnetic induction study electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account as a most preferred model a smooth conductivity depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km

in situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems continuous subglacial measurements of turbidity and electrical conductivity two indicators of basal water quality can be used to help characterize subglacial drainage systems these indicators of water quality yield information that complements that provided by water pressure measurements quantitative attributes of subglacial drainage systems such as water velocity and subglacial residence time as well as qualitative behaviour for example spatial and temporal variations in system morphology can be deduced using water quality measurements interpretation is complicated by the many potential influences on turbidity and electrical conductivity but when these complications are appreciated a richer interpretation results to demonstrate the utility of basal water quality measurements observations from trapridge glacier yukon territory canada were examined the data reveal complex behaviour of the drainage system but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system the measurement and interpretation methods described and demonstrated are applicable to other glaciers as such they should prove useful for characterizing different subglacial drainage configurations and behaviours thereby improving our general understanding of the hydrology and dynamics of wet based glaciers

conodonts from the cambrian ordovician boundary interval in the southeast margin of the sichuan basin china abstract conodonts from the cambrian ordovician transition at the liangcun section in xishui county guizhou and at the huangcao section in wulong county chongqing are examined for the first time both sections are located at the southeast margin of the sichuan basin a total of 1367 specimens were recovered representing 30 species and 15 genera based on the ranges of conodonts generalized from these two sections and another six sections previously studied in the same region three conodont zones cordylodus proavus monocostodus sevierensis and cordylodus angulatus zones are recognized the index species of the cambrian ordovician boundary at the global stratotype section and point gssp iapetognathus fluctivagus and its substitute in china iapetognathus jilinensis are not observed in the study sections therefore it is impossible to determine the cambrian ordovician boundary exactly however it probably lies within the lower part of m sevierensis zone the upper part of the loushanguan group correlating with the gssp in canada and the dayangcha section in china chronological sequences of the fad first appearance datum of c angulatus chosonodina herfurthi and rossodus manitouensis are not obvious in the study so the c angulatus zone here is correlated with zones defined by c angulatus ch herfurthi and r manitouensis in the lower yangtze platform

terminal cambrian and lowest ordovician succession of mexican west gondwana biotas and sequence stratigraphy of the tinu formation the tinu formation of oaxaca state is the only fossiliferous lower palaeozoic unit between the laurentian platform in northwest mexico and gondwanan successions in andean south america the tinu traditionally has been referred to the lower ordovician tremadoc and regarded as having a provincially mixed fauna with laurentian avalonian and gondwanan elements bio and lithostratigraphic re evaluation demonstrates that the tinu is a gondwanan passive margin succession it includes a lower thin to 16 m condensed uppermost cambrian yudachica member new the yudachica nonconformably overlies middle proterozoic basement as a result of very high late late cambrian eustatic levels the yudachica changes from storm dominated but slightly dysoxic shelf facies fossil hash limestone and shale in the south to an upper slope facies with debris flows 50 km to the north three biostratigraphically distinct depositional sequences comprise the yudachica the yudachica has gondwanan aspect trilobites with low diversity conodonts characteristic of unrestricted marine temperate facies the upper tinu or rio salinas member new is a lower ordovician tremadoc depositional sequence that records strong early but not earliest tremadoc eustatic rise marked by graptolite and olenid bearing dysoxic mudstones higher strata shoal upward into shell hash limestones and proximal tempestite sandstones with upper lower tremadocian unrestricted marine temperate conodonts new taxa include orminskia rexroadae landing gen et sp nov from the cordylodus andresi zone this euconodont is related to hyaline coniform genera best known from ordovician tropical platform successions cornuodus clarkei landing sp nov resembles the coeval upper lower tremadoc tropical species scalpellodus longipinnatus ji barnes

new conodont records of the los sombreros formation cambrian ordovician from the western precordillera argentina biostratigraphic and palaeoenvironmental implications

magnetic and electric fields produced in the sea during geomagnetic disturbances to understand geomagnetic effects on systems with long conductors it is necessary to know the electric field those systems experience for surface conductors such as power systems and pipelines this can easily be calculated from the magnetic field variations at the surface using the surface impedance of the earth however for calculating the electric fields in pipelines and submarine cables at the seafloor it is necessary to take account of the attenuating effect of the conducting seawater assuming that the fields are vertically propagating plane waves we derive the transfer functions between the electric and magnetic fields at the seafloor and the magnetic field variations at the sea surface these transfer functions are then used with surface magnetic field data to determine the power spectra of the seafloor magnetic and electric fields in a shallow sea depth 100 m and in the deep ocean depth 5 km for different values of the kp magnetic activity index for the period range considered 2 min to 3 hrs the spectral characteristics of the seafloor magnetic and electric fields for a 100 m deep sea are very similar to those of the surface fields for the deep ocean the seafloor spectra show a faster decrease in spectral density with increasing frequency compared to the surface fields the results obtained are shown to be consistent with seafloor observations assessment of the seafloor electric fields produced by different levels of geomagnetic activity can be useful in the design of the power feed equipment for submarine cables and cathodic protection for undersea pipelines

new uppermost cambrian u pb date from avalonian wales and age of the cambrian ordovician boundary a crystal rich volcaniclastic sandstone in the lower peltura scarabaeoideszone at ogof ddu near criccieth north wales yields a u pb zircon age of 491 1 ma this late late cambrian date indicates a remarkably young age for the cambrian ordovician boundary whose age must be less than 491 ma hence the revised duration of the post placentian trilobite bearing cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by ordovician graptolites and mesozoic ammonites

estimation of subglacial hydraulic properties from induced changes in basal water pressure a theoretical framework for borehole response tests in this paper we develop a theoretical model describing water motion in a coupled borehole subglacial flow system the theory applies to basal drainage systems having multiple and extensive interconnected flow paths within this domain it encompasses a broad range of flow regimes from laminar darcian flow in a thick permeable unit to turbulent sheet flow in a very thin layer important terms in the model are highlighted by recasting the problem in dimensionless form the non dimensional formulation indicates that there are four free parameters in the coupled system these parameters characterize skin friction in the borehole and diffusion transmissivity and turbulent transport in the subglacial flow layer dimensionless results show that under most circumstances the effects of skin friction in the borehole are negligible diffusion transmissivity and especially turbulent transport in the basal layer are found to influence subglacial water flow strongly we use our model to predict fluctuations of borehole water levels that result from different types of disturbances we show how this framework can be used to estimate subglacial hydraulic properties by comparing model results with data collected during field experiments on trapridge glacier yukon territory canada in 1989 and 1990

the proposed cambrian ordovician global boundary stratotype and point gssp in western newfoundland canada sections exposing the cambrian ordovician boundary interval at broom point in western newfoundland have been proposed earlier for a global systemic boundary stratotype these lie within the cow head group a late middle cambrian to early middle ordovician allochthonous unit of limestone shale and conglomerate deposited at the toe of the ancient continental slope and on the adjacent continental rise several recent studies have further investigated the stratigraphy sedimentology and palaeontology of the cow head group and others are under way on magnetostratigraphy and chemostratigraphy these aspects are reviewed for six key boundary sections representing proximal to distal facies cow head ledge broom point south broom point north st pauls inlet quarry martin point and green point in particular new data are presented from 260 conodont samples that yielded 15500 conodonts this intense sampling has allowed the discrimination of minor hiatuses in the proximal to intermediate facies where conglomerates have eroded and cannibalized underlying strata new conodont data from broom point north have lowered the base of the c lindstromi zone into unit 74 conglomerates thereby making this section unsuitable as a boundary stratotype new collections from green point have yielded abundant conodonts and over 9400 conodonts have been recovered from 77 samples the conodont graptolite and trilobite biostratigraphy through the boundary interval is documented allowing accurate correlation between sections and more precisely revealing small hiatuses in the proximal and intermediate facies the sequence of conodont zones is eoconodontus notchpeakensis cordylodus proavus c caboti c intermedius c lindstromi and c angulatus these can be correlated with trilobite zones established from both in situ and clast faunas from the proximal to intermediate facies and with graptolite assemblages of cooper 1979 especially in the intermediate to distal facies three new species of cordylodus are described c andresi c hastatus and c tortus and the full apparatus of iapetognathus preaengensis is illustrated the criteria for selecting a global boundary stratotype and point gssp are reviewed in terms of the cow head sections the green point section is shown to meet and largely surpass the prerequisites required of a stratotype the green point section is proposed to be the global boundary stratotype with the base of the ordovician system defined at the base of unit 23 which is the base of the broom point member green point formation at a level coincident with the base of the cordylodus lindstromi zone in addition to an abundant and superbly preserved conodont fauna this section preserves the best sequence of earliest planktic graptolites through a 40 m interval the first nematophorous graptolites of assemblage 1 occur in unit 25 6 9 m above the base of the c lindstromi zone this level can be readily correlated into the proximal facies where both deep and shallow water trilobites in situ and in clasts respectively show the base of the c lindstromi zone to lie within the symphysurina brevispicata trilobite subzone

black box modeling of the subglacial water system measurements of water pressure beneath trapridge glacier yukon territory canada yield the following generalizations about subglacial conditions in the studied region 1 even over short distances the subglacial water system is highly heterogeneous 2 the subglacial water system consists of at least two distinct components which we refer to as the connected and unconnected water systems 3 regions of the glacier bed can switch back and forth from being part of the connected or part of the unconnected water system 4 large spatial pressure gradients can exist within the unconnected water system and between the connected and unconnected systems 5 rapid pressure variations can occur in the unconnected water system 6 pressure variations in the unconnected water system do not match those in the connected system and can in fact be strongly anticorrelated with pressure variations in the connected system if the water pressure variations in the connected system are viewed as a forcing and those in the unconnected system as a response to this forcing the input output relation between forcing and response can be efficiently represented as a low order nonlinear ordinary differential equation the response of the unconnected system to forcing from the connected system is governed by time constants having approximate magnitudes of 1 7 hours and 7 4 hours that we believe are associated with process rates for substrate compression and pore water diffusion respectively

transatlantic earth potential variations during the march 1989 magnetic storms measurements of the cable power supply voltage at the north american end of the fiber optic transatlantic telecommunications cable tat 8 during the march 1989 magnetic storm has provided a measure of the large scale changes in the total earth potential across the atlantic during the storm interval east west potential changes as large as 700 volts 0 12 volts km peak to peak were observed with many smaller amplitude variations also seen the largest variations in earth potential occurred during an extended interval of a very intense eastward electrojet as measured by a magnetometer at the north american terminus of the cable the eastward electrojet current probably exceeded 106 amps the design of the tat 8 cable power feed equipment is sufficiently conservative that even such unusually large earth potentials as those measured during this storm were not a threat to the integrity of the communications system

cambrian ordovician conodonts from slump deposits of the argentine precordillera new insights into its passive margin development fil voldman gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet cordoba centro de investigaciones en ciencias de la tierra universidad nacional de cordoba facultad de ciencias exactas fisicas y naturales centro de investigaciones en ciencias de la tierra argentina

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

redox conditions across the cambrian ordovician boundary elemental and isotopic signatures retained in the gssp carbonates the final publication is available at elsevier via https doi org 10 1016 j palaeo 2015 09 014 2015 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes