late precambrian u pb ages for the brookville gneiss southern new brunswick tonalitic orthogneiss from the brookville gneiss in southern new brunswick has an igneous protolith age of 605 pm 3 ma based on u pb dating of zircon metamorphic titanite from the same sample gives a minimum age of 564 pm 6 ma for upper amphibolite facies metamorphism of the unit based on u pb analyses of single detrital zircons a maximum sedimentary protolith age of about 641 ma is suggested for associated paragneiss these ages indicate that the igneous protolith of the orthogneiss was at most 35 ma younger than the sedimentary rocks it intruded and that the brookville gneiss is younger than the green head group to which it was previously considered basement both orthogneiss and paragneiss in the brookville gneiss contain proterozoic and archean detrital zircon grains suggesting an old heterogeneous continental source we conclude that the brookville gneiss does not represent the basement to the avalon terrane

40ar 39ar dating in the lochaber mulgrave area northern mainland nova scotia implications for timing of regional metamorphism and sediment provenance in the late devonian early carboniferous horton group 40ar 39ar dating of whole rock samples and muscovite separates using age spectrum analysis and of single muscovite grains using total fusion analysis yields new insights into the timing of regional metamorphism and sediment provenance in the late devonian early carboniferous horton group in the lochaber mulgrave area of nova scotia the time of regional metamorphism is constrained to ca 340 335 ma by whole rock spectra from well cleaved slate and shale samples from the lowermost clam harbour river and overlying tracadie road formations of the horton group this ca 340 335 ma event may have been the result of burial and deformation of the horton group by older volcanic and sedimentary rocks of the guysborough group which were overthrust from the south as the result of development of a positive flower structure at a restraining bend along the cobequid chedabucto fault system the boundary between the meguma and avalon terranes detrital muscovite ages of ca 410 380 and ca 500 ma were obtained from

minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

orogenesis and basin development u pb detrital zircon age constraints on evolution of the late paleozoic st marys basin central mainland nova scotia abstract the st marys basin along the southern flank of the composite late paleozoic magdalen basin in the canadian appalachians and along the avalon meguma terrane boundary contains late devonian early carboniferous continental clastic rocks of the horton group that were deposited in fluvial and lacustrine environments after the peak of the acadian orogeny shrimp ii geological survey of canada data on approximately 100 detrital zircons from three samples of horton group rocks from the st marys basin show that most of the zircons have been involved in a multistage history recycled from clastic rocks in the adjacent meguma and avalonian terranes although there is a minor contribution from early silurian 411 ma and late devonian suites ca 380 370 ma neoproterozoic ca 700 550 ma and paleoproterozoic ca 2 0 2 2 ga zircon populations predominate with a minor contribution from ca 1 0 1 2 and 1 8 ga zircons published u pb single zircon analyses on clastic sedimentary rocks indicate th

shallow landslide hazard assessment using a physically based model and digital elevation data a model for the analysis of topographic influence on shallow landslide initiation is applied to an experimental mountain basin where high resolution digital elevation data are available the cordon catchment 5 km2 located in northern italy the model delineates those areas most prone to shallow landsliding due to surface topographic effects on hydrologic response the model is composed of two parts a steady state model for shallow sub surface runoff and an infinite slope coulomb failure model which assumes that the soil is cohesionless at failure an inventory of landslide scars is used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions the model reproduces the observed distribution of landslide locations in a consistent way although spatial variations in soil strength and transmissivity which are not accounted for in the model influence specific distribution of landslide areas within regions of similar topographic control

the missing rheic ocean magmatic arcs provenance analysis of late paleozoic sedimentary clastic rocks of sw iberia abstract early carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the rheic suture in sw iberia were studied for provenance analysis an enigmatic feature of this suture which resulted from closure of the rheic ocean with the amalgamation of pangea in the late carboniferous is that there are no recognizable mid to late devonian subduction related magmatic rocks which should have been generated during the process of subduction on either side of it u pb la icp ms geochronology of detrital zircons from early carboniferous turbidites in the vicinity of the rheic suture in sw iberia where it separates the ossa morena zone with gondwana continental basement to the north from the south portuguese zone with unknown meguma continental basement to the south reveals the abundance of mid to late devonian 51 81 and early carboniferous 13 25 ages the cabrela and mertola turbidites of the ossa morena and south portuguese zones respectively are largely devoid of older zircons differing from the age spectra of detrital zircons in the oldest late devonian strata in the underlying south portuguese zone which contain abundant cambrian and neoproterozoic ages mid to late devonian zircons in the cabrela formation age cluster at c 391 ma eifelian givetian transition and mertola formation age clusters at c 369 ma and at c 387 ma famennian and givetian respectively are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement the terrane capable of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely removed by erosion in sw iberia given that closure of the rheic ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the rheic suture we suggest 1 the source of the zircons in the sw iberia basins was a short lived rheic ocean magmatic arc and 2 given the lack of older zircons in the sw iberia basins this short lived arc was probably developed in an intra oceanic environment

influence of subsurface flow by lidar dems and physical soil strength considering a simple hydrologic concept for shallow landslide instability mapping abstract high resolution dems and physical soil strength among other factors have significant effects on the shallow landslide instability mapping subsurface flow in soil mantle normally is assumed by slope parallel flow based on resolution of dems and measuring soil strength which is affected by subsurface flow within the soil mantle is difficult in both the field and the laboratory thus the aims of this study are to investigate the effect of subsurface flow by high resolution lidar dems and the effect of physical soil strength attributes on shallow landslide instability mapping respectively in this study two dems with 1 m and 5 m resolutions were used and physical soil strength was calibrated using a simple subsurface hydrological concept with lidar and field survey data in order to quantify the influence of soil strength on shallow landslide instability mapping to this end various field surveys were performed at woomyeon mountain seoul republic of korea where shallow landslides occurred in 2012 the physical shallow landslide stability shalstab model were applied the modified success rate msr method were applied to assess the predicted results in the first series of simulations using the two dems and experimentally derived soil strength values relatively low msr values of 0 42 0 468 for the 1 m dem and 0 42 0 47 for the 5 m dem were recorded in the second series of simulations using soil strength calibrated using a simple theoretical approach the msr for the 1 m dem was 0 78 0 823 and the msr for the 5 m dem was 0 723 0 80 these results indicated that soil strength had a more important role in shallow landslide instability mapping than assuming subsurface flow by topographic resolution therefore it may be useful to apply field collected soil strength data using hydrological concepts to improve the accuracy of predictive models based on high resolution surface data

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

model test study on the hydrological mechanisms and early warning thresholds for loess fill slope failure induced by rainfall abstract under rainfall conditions the characteristics of hydraulic changes related to the failure evolution of fill slopes are critical to the early warning of slope failure in this study a series of model tests are carried out on loess fill slopes with different slope types the matric suction volumetric moisture content pore water pressure and deformation of the slope are monitored in real time during the rainfall process meanwhile the development of cracks and the failure modes of the slope are analyzed and then the early warning strategy of fill slope failure induced by rainfall is studied the results show that loess landslides induced by rainfall exhibit a hysteresis however the volumetric water content and the matrix suction respond earlier than the pore water pressure the slope failure is produced when the volumetric water content and the matrix suction are respectively at their maximum and minimum values the evolution mechanism of cracks on the slope starts when tensile cracks are first generated near the leading edge surface and then extend backwards in the next stage shear fracture is produced near the flanking of the slope and finally the trailing edge produces a transfixion tensile crack from the top to toe of the fill slope which not only provides the advantage of an infiltration channel to control the hydrological process but also evolves into the trailing edge boundary of each failure of fill slope with the increase of rainfall duration the filling slope presents different failure characteristics revealing the hydraulic behavior of a partially saturated slope in addition combined with the infinite slope stability analysis in mohr coulomb soil the matrix suction and volumetric water content thresholds of the fill slopes with different slope angle are determined the early warning threshold model for rainfall induced slope instability is proposed and a new framework of early warning is provided

the provenance of middle jurassic sandstones in the scotian basin petrographic evidence of passive margin tectonics the tectonic and geomorphological evolution of the scotian margin and its hinterland is poorly known between late triassic rifting and the early cretaceous progradation of major deltas this study determined sedimentary provenance of middle jurassic mohican formation sandstones from three wells using heavy minerals and mineral chemistry indicator minerals such as xenotime altered ilmenite and varietal types of garnet and tourmaline are similar to those in hauterivian barremian sandstones in the western scotian basin which are almost exclusively derived from the meguma terrane the wells adjacent to the canso ridge have more zircon and less ilmenite indicating a greater contribution of polycyclic reworking but with an ultimate source in the meguma terrane zircon and ilmenite were likely derived in part from carboniferous sandstones in eastern mainland nova scotia and cape breton island any river drainage from the inboard terranes of the appalachians either was diverted through the fundy basin or entered the easternmost scotian basin where the mohican formation is 5 5 km thick along the linear continuation of the southwest grand banks transform such sediment did not reach the canso ridge suggesting that the cobequid chedabucto fault zone in orpheus graben was not a significant physiographic feature this tectonically controlled paleogeography in the middle jurassic is quite different from that during active rifting in the late triassic early jurassic middle jurassic quiescence was followed in the tithonian early cretaceous by renewed tectonic uplift associated with rifting of grand banks from iberia and labrador from greenland

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

internal soil moisture and piezometric responses to rainfall induced shallow slope failures summary better knowledge regarding internal soil moisture and piezometric responses in the process of rainfall induced shallow slope failures is the key to an effective prediction of the landslide and or debris flow initiation to this end internal soil moisture and piezometric response of 0 7 m deep 1 5 m wide 1 7 m high and 3 94 m long semi infinite sandy slopes rested on a bi linear impermeable bedrock were explored using a chute test facility with artificial rainfall applications the internal response time defined by the inflection point of the soil moisture and piezometric response curves obtained along the soil bedrock interface were closely related to some critical failure states such as the slope toe failure and extensive slope failures it was also found that the response times obtained at the point of abrupt bedrock slope decrease can be used as indicators for the initiation of rainfall induced shallow slope failures an investigation of spatial distributions of soil water content or degrees of saturation s r in the slope at critical failure states shows that the 0 2 m below surface zone remains unsaturated with s r 40 60 regardless of their distances from the toe and the rainfall intensity non uniform distributions of or s r along the soil bedrock interface at critical failure states were always associated with near saturation states s r 80 100 around the point of bedrock slope change or around the transient toe upstream of the slumped mass induced by the retrogressive failure of the slope these observations suggest the important role of the interflow along the soil bedrock interface and the high soil water content or high porewater pressure around the point of bedrock slope deflection in the rainfall induced failure of sandy slopes consisting of shallow impermeable bedrocks the present study proposes an internal response time criterion to substantiate the prediction of rainfall induced shallow slope failures it is believed that the internal response time reflects the overall characteristics of a slope under rainfall infiltration and can be as useful as the conventional meteorology based threshold times the internal response time theory can be generalized via numerical modeling of slope hydrology slope geology and slope stability in the future

effects of midlatitude westerlies on the paleoproductivity at the agulhas bank slope during the penultimate glacial cycle evidence from coccolith sr ca ratios modern primary productivity on the agulhas bank off south africa has been proposed to be linked to the midlatitude westerlies a paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics accordingly we produced a coccolith sr ca based paleoproductivity record from core md96 2080 agulhas bank slope during the penultimate glacial interglacial cycle deriving the productivity signal from sr ca requires a correction for a temperature effect here constrained using mg ca sea surface temperatures from the foraminifer globigerina bulloides from core md96 2080 phases of depressed productivity coincided with periods of stratification in the same core indicated by high relative abundances of the coccolithophore florisphaera profunda and with low relative abundances of the upwelling indicator g bulloides in the nearby cape basin these observations collectively suggest that productivity was regulated by upwelling throughout this region we infer that as in the present periods of low productivity result from a more northerly position of the westerlies potentially accompanied by subtropical front displacements and blockage of upwelling promoting easterlies productivity minima also coincide with periods of increased ice rafted detritus ird deposition on the agulhas plateau which also indicates extreme northward positions of the westerlies the influence of the westerlies appears to be obliquity conditioned as productivity minima and ird maxima occur during low obliquity intervals the dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the south indian gyre that likewise respond sensitively to a poleward contraction of the westerlies

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

sediment sources and dispersion as revealed by single grain 40ar 39ar ages of detrital muscovite from carboniferous and cretaceous rocks in mainland nova scotiageological survey of canada contribution 20090289 single grain ages of detrital muscovite from 15 sand stone samples from the lower carboniferous horton group and the lower cretaceous chaswood formation of central nova scotia were used to infer the nature of the early carboniferous unroofing of the meguma terrane and the reworking of carboniferous rocks in the early cretaceous in the western windsor basin a sample from the oldest horton group rocks yielded ages principally between ca 400 and 380 ma suggesting that most of the muscovite present came from the metamorphic rocks of the meguma terrane but was variably reset by the intrusion of the south mountain batholith at ca 380 ma other samples in this part of the basin show partial post depositional resetting younger horton group metamorphic rocks in the eastern windsor basin contain many grains with ages of ca 370 360 ma suggesting derivation from the central core of the south mountain batholith or the musquodoboit pluton horton group sandstones from the western part of the st marys basin co

the major ion composition of cenozoic seawater the past 36 million years from fluid inclusions in marine halite fluid inclusions from ten cenozoic eocene miocene marine halites are used to quantify the major ion composition mg2 ca2 k na so42 and cl of seawater over the past 36 my criteria used to determine a seawater origin of the halites include 1 stratigraphic sedimentologic and paleontologic observations 2 br in halite 3 34s of sulfate minerals 4 87sr 86sr of carbonates and sulfates and 5 fluid inclusion brine compositions and evaporation paths which must overlap from geographically separated basins of the same age to confirm a global seawater chemical signal changes in the major ion chemistry of cenozoic seawater record the end of a systematic long term 150 my shift from the ca2 rich mg2 and so42 poor seawater of the mesozoic cacl2 seas to the mgso4 seas with higher mg2 and so42 ca2 of the cenozoic the major ion composition of cenozoic seawater is calculated for the eocene oligocene 36 34 ma serravallian tortonian 13 5 11 8 ma and the messinian 6 5 ma assuming chlorinity 565 mmolal salinity and the k concentration 11 mmolal are constant and the same as in modern seawater fluid inclusions from cenozoic marine halites show that the concentrations of mg2 and so42 have increased in seawater over the past 36 my and the concentration of ca2 has decreased mg2 concentrations increased from 36 mmolal in eocene oligocene seawater 36 34 ma to 55 mmolal in modern seawater the mg2 ca2 ratio of seawater has risen from 2 3 at the end of the eocene to 3 4 and 4 0 respectively at 13 5 to 11 8 ma and 6 to 5 ma and to 5 in modern seawater eocene oligocene seawater 36 34 ma has estimated ranges of so42 14 23 mmolal and ca2 11 20 mmolal if the ca2 so42 product is assumed to be the same as in modern seawater 300 mmolal2 eocene oligocene seawater had ca2 16 mmolal and so42 19 mmolal the same estimates of ca2 and so42 for serravallian tortonian seawater 13 5 11 8 ma are so42 19 27 mmolal and ca2 8 16 mmolal and so42 24 mmolal and ca2 13 mmolal if the ca2 so42 product is equal to that in modern seawater messinian seawater has an estimated range of so42 21 29 mmolal and ca2 7 15 mmolal with so42 26 mmolal and ca2 12 mmolal assuming the ca2 so42 product is equal to that in modern seawater regardless of the estimation procedure so42 shows progressively increasing concentrations from 36 ma to the present values which are the highest of the cenozoic

the provenance of jurassic and lower cretaceous clastic sediments offshore southwestern nova scotia jurassic and cretaceous sandstones in the shelburne subbasin and fundy basin offshore nova scotia are poorly known but are of current interest for petroleum exploration the goal of this study is to determine the provenance of sandstones and shales which will contribute to a better understanding of regional tectonics and paleogeography in the study area mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells using scanning electron microscopy and an electron microprobe whole rock geochemical composition of shales was used to test the hypotheses regarding provenance of mesozoic clastic sedimentary rocks in the sw scotian basin lower jurassic clastic sedimentary rocks in the fundy basin contain magnetite biotite and chlorite suggesting local supply from the north mountain basalt and meguma terrane whereas pyrope and anthophyllite suggest small supply from distant sources in the sw scotian basin detrital minerals lithic clasts and shale geochemistry from middle jurassic to early cretaceous indicate a predominant meguma terrane source and transport by local rivers rare spinel and garnet grains of meta ultramafic rocks only in the middle jurassic at the mohawk b 93 well suggest minor supply from the rising labrador rift via the same river that transported distant sediments to the fundy basin lower cretaceous sandstones from the mohican i 100 well contain minor garnet spinel and tourmaline from meta ultramafic rocks characteristic of sediment supplied to the central scotian basin at that time the dominant meguma terrane provenance precludes thick deep water sandstones in the eastern part of the shelburne subbasin but the evidence of middle jurassic distant river supply through the fundy basin is encouraging for deep water reservoir quality in the western part

calcium isotope fractionation during coccolith formation in emiliania huxleyi independence of growth and calcification rate 1 recently calcium isotope fractionation in the coccolithophore emiliania huxleyi was shown to exhibit a significant temperature dependency an important subsequent question in this context is whether the observed fractionation patterns are caused by temperature itself or related growth rate changes in order to separate growth and calcification rate effects from direct temperature effects batch culture experiments with the coccolithophore e huxleyi were conducted under varying light intensities despite large changes in cellular growth and calcification rates calcium isotope fractionation remained constant independence of calcium isotope fractionation on growth and calcification was also obtained in two additional sets of experiments in which growth rates changed in response to varying calcium concentration and seawater salinity these experiments also showed no direct effects of calcium concentration and salinity on calcium isotope fractionation values for calcium isotope fractionation of e huxleyi coccoliths fell within a range of 1 0 to 1 6 1000 ln confirming earlier results this range is similar to that observed in several foraminiferal species and coccolith oozes suggesting a rather homogeneous calcium isotopic composition in marine biogenic calcite our data further show that the calcium isotope fractionation does not change with changing isotopic composition of seawater this is a basic requirement for reconstructing the calcium isotopic composition of the ocean over time

u pb geochronological constraints on precambrian stratified units in the avalon composite terrane of nova scotia canada tectonic implications concordant u pb ages of detrital zircons in several proterozoic units in the avalon composite terrane of nova scotia along with previously published data indicate that deposition of low and high grade stratified units in the cobequid highlands gamble brook formation and central cape breton island variously assigned to the george river group or george river metamorphic suite and the bras d or gneiss started after 977 ma extended through a period of volcanic activity between 694 and 637 ma and ended before the 629 612 600 ma volcanic activity associated with deposition of the georgeville and jeffers groups in the antigonish and cobequid highlands and the east bay hills and coxheath groups in southern cape breton island these age data along with u pb analyses of metamorphic and igneous zircon and monazite also constrain three late proterozoic tectonothermal events i oblique sinistral ductile shear deformation and greenschist amphibolite facies metamorphism probably occurred between 694 an

provenance and paleodrainage patterns of upper jurassic and lower cretaceous synrift sandstones in the flemish pass basin offshore newfoundland east coast of canada upper jurassic to lower cretaceous synrift sandstones from two industry exploratory wells in the flemish pass basin were studied for provenance using heavy mineral proxies these sandstones were deposited during the north atlantic rifting stage at which time rifting intensified between iberia and the grand banks several heavy mineral methods were used including in situ u pb geochronology and morphological and chemical analysis of detrital zircons chemical discrimination of detrital tourmalines and heavy mineral ratios clastic bed load material entering the northern flemish pass basin during the tithonian to berriasian was connected to transport systems reaching west as far as 400 to 500 km 249 311 mi source areas to the west included igneous rocks and associated cover sequences of the avalon zone as well as the magmatic rocks metasedimentary rocks and associated cover sequences present in the central mobile belt the eastward directed input of bed load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin with deteriorating reservoir grade toward the east given the regional extent of drainage systems it is likely that similar constraints apply to equivalent sandstones in the adjacent east orphan basin by the valanginian barremian paleodrainage orientations had switched and bed load material began to enter the flemish pass basin from more proximal areas to the southeast with the avalon zone basement overall no evidence exists to support sediment sourcing from the iberian margin or the flemish cap galicia bank continental fragment to the east and material from these areas is instead interpreted to have been shed into the incipient atlantic ocean or bay of biscay also no evidence exists to support sourcing from grenville basement farther to the west implying that a drainage divide may have existed somewhere between central and western newfoundland west of which material was presumably being transported to the south or southwest

correlation of unsaturated soil and dielectric property for monitoring of subsurface characteristics development of unsaturated dielectric mixing models and its application the behavior due to rainfall infiltrating the ground plays a role in landslides groundwater recharge and various other ground responses most of these geotechnical behaviors have a correlation between soil pore space and soil volumetric water content in the unsaturated and saturated soil porous media therefore the soil porosity associated with soil pores and the distribution of volumetric water content are significantly important hydrological characteristics in the case of shallow slope failure such as landslide the infiltration activity due to the connectivity of soil pore spaces in a porous media is induced slope failure may be attributed to the effect of a wetting front with the slope due to liquid infiltration which changes the volumetric water content soil matric suction and shear strength of the slope this study was performed with an unsaturated injection test using a frequency domain reflectometry fdr dielectric device which measures the dielectric constant of unsaturated soil and the study then proposed the unsaturated dielectric mixing models to calculate soil porosity and effective porosity of unsaturated soils from the experimental results the ratio of effective porosity to porosity of soils are measured in a range of 70 85 these experimental results show a decrease of about 5 10 for unsaturated soil compared to the ratio of effective porosity to porosity of saturated soil the infiltration passages of tracer material are restricted within the pore connectivity in the unsaturated soil which is caused by dead pores in the soil using the fdr device and the unsaturated dielectric mixing models we can consider the acquisition of physical properties to detect the infiltration activity the response of the dielectric constant along with the injected tracer and hydrological parameters for the unsaturated soil porous media

birth and demise of the rheic ocean magmatic arc s combined u pb and hf isotope analyses in detrital zircon from sw iberia siliciclastic strata paleozoic continental reconstructions indicate that subduction of rheic oceanic lithosphere led to collision between laurussia and gondwana which was a major event in the formation of the ouachita appalachian variscan orogenic belt and the amalgamation of pangea however arc systems which record rheic ocean subduction are poorly preserved the preservation of devonian detrital zircon in late devonian early carboniferous siliciclastic rocks of sw iberia rather than arc related igneous rocks indicates that direct evidence of the arc system may have been largely destroyed by erosion here we report in situ detrital zircon u pb isotopic analyses of late devonian early carboniferous siliciclastic rocks from the pulo do lobo zone which is a reworked late paleozoic suture zone located between laurussia and gondwana detrital zircon age spectra from the pulo do lobo zone frasnian formations show striking similarities revealing a wide range of ages dominated by neoproterozoic and paleoproterozoic grains sourced from rocks typical of peri gondwanan terranes such as avalonia the meguma terrane and the ossa morena zone pulo do lobo rocks also include representative populations of mesoproterozoic and early silurian zircons that are typical of avalonia and the meguma terrane which are absent in the ossa morena zone the famennian tournaisian formations from the pulo do lobo zone however contain more abundant middle late devonian zircon indicating the contribution from a previously unrecognized source probably related to the rheic ocean magmatic arc s the middle late devonian to early carboniferous zircon ages from the siliciclastic rocks of sw iberia south portuguese pulo do lobo and ossa morena zones have a wide range in ehft values 8 2 to 8 3 indicating the likely crystallization from magmas formed in a convergent setting the missing rheic ocean arc was probably built on a meguma avalonia type basement we propose for the pulo do lobo zone that the frasnian sedimentation occurred through the opening of a back arc basin formed along the laurussian active margin during rheic ocean subduction as has been recently proposed for the rhenohercynian zone in central europe detrital zircon ages in the frasnian siliciclastic rocks indicate provenance in the meguma terrane avalonia and devonian rheic ocean arc s as a result of back arc basin inversion the frasnian formations underwent deformation metamorphism and denudation and were unconformably overlain by famennian to visean siliciclastic strata including the phyllite quartzite formation of the south portuguese zone the latest devonian early carboniferous detritus were probably shed to the pulo do lobo zone represa and santa iria formations by recycling of devonian siliciclastic rocks from the south portuguese zone meguma terrane and from a new distinct source with baltica laurentia derivation preserved in the horta da torre formation and alajar melange

ten years of debris flow monitoring in the moscardo torrent italian alps abstract field data on debris flows are of utmost importance for improving knowledge of these hazardous phenomena and for the development of attenuation measures in alpine basins debris flows generally occur with a frequency high enough to create serious risk to human settlements and transportation routes but too low to justify monitoring activity capable of providing enough data in a sufficiently short time the moscardo torrent a small stream in the eastern italian alps is an exception to this general situation since it displays a high frequency of debris flows commonly at least one event per year in 1989 this torrent was instrumented and the results of the following 10 years 1989 1998 of debris flow monitoring are presented with an analysis of collected data the equipment installed allowed measurement of rainfall flow stage and ground vibrations caused by debris flows other important debris flow variables that is mean front velocity peak discharge and flowing volume were estimated from instrumental records video pictures have proved to be useful for the visual interpretation of debris flow waves and have made it possible to estimate the surface velocity of debris flows recorded data are compared with other experimental data sets collected and documented worldwide advantages and shortcomings of different types of sensors are discussed with relevance both for research monitoring purposes and for possible use in debris flow warning systems

40ar 39ar white mica ages reveal neoproterozoic paleozoic provenance and an alleghanian overprint in coeval upper ordovician lower devonian rocks of meguma and avalonia abstract 40ar 39ar analyses ir single grain total fusion of white micas from upper ordovician lower devonian sedimentary strata in the meguma annapolis section and avalon arisaig section terranes of the canadian appalachians complement recent detrital zircon studies by providing constraints on local source areas and identifying the age of low temperature a remarkable outcome of the study is that many muscovite ages are significantly younger than the depositional age of the strata they do not record the middle late devonian age of acadian folding or adjacent intrusions but instead preserve a precise age of 322 6 2 1 ma 16 analyses although the sections sampled display no discernable evidence for carboniferous tectonism these ages are coeval with documented alleghanian deformation in both avalonian and meguma terrane rocks and we interpret them to reflect distributed fluid flow coeval with dextral shear along the avalon meguma terrane boundary

diagenesis to metamorphism transition in an episutural basin the late paleozoic st mary s basin nova scotia canada the late devonian early carboniferous st mary s basin in the canadian appalachians consists of horton group fluviatile and lacustrine clastic rocks the basin occurs along the boundary between the avalon and meguma ter ranes and developed during coeval dextral shear along that boundary x ray diffraction reveals that the rocks contain ubiq uitous quartz k white mica and albite illite smectite mixed layers and chlorite are very common and na k mica kaolinite chlorite smectite mixed layers k feldspar berthierine and rutile occur in some samples crystal chemical pa rameters of white mica indicate the pressure and temperature of mineral growth and discriminate between diagenetic an chizone and low grade metamorphic processes kubler index values measured in the 5 a u peak and the presence of chlorite mica stacks are indicative of high anchizone epizone grades with a crystallinity crystal size and number of de fects that increases towards the chedabucto fault which defines the northern margin of the basin kubler index values measured in the 10 a u peak indicate that a late fluid rich event could have produced the observed illite smectite mixed layers the overall clay mineral content and the b cell dimension of the k white micas are typical of postdepositional evo lution in extensional sedimentary basins with high heat flow 35 8c km taken together our data record two superposed events related to deformation along the basin margins and coeval regional fluid flow in which retrograde reactions at tem perature t 300 8c regional syntheses indicate that this fluid flow may have occurred during epi sodes of late carboniferous dextral shear along the avalon meguma terrane boundary

late devonian palinspastic reconstruction of the avalon meguma terrane boundary implications for terrane accretion and basin development in the appalachian orogen abstract a late devonian early carboniferous palinspastic reconstruction of atlantic canada restoring subsequent motion along the avalon meguma terrane boundary and other major faults facilitates re examination of the spatial distribution of important accretionary and post accretionary events in the northern appalachian orogen the reconstruction suggests a genetic relationship between 415 and 360 ma tectonothermal activity in both these terranes and the collision between laurentia and gondwana in a zone of anomalously intense shortening opposite the st lawrence promontory in the appalachian orogen erosional products of this collision are an order of magnitude greater than the thin ca 1 km veneer of latest devonian early carboniferous clastic rocks that were deposited in intermontane basins across the orogen this missing detritus may be found in the thick deposits of the catskill clastic wedge in the central appalachians

crustal xenoliths in triassic lamprophyre dykes in western morocco tectonic implications for the rheic ocean suture dykes of calc alkaline lamprophyre cutting granite of the hercynian jebilet massif of the moroccan meseta western morocco contain crustal xenoliths the xenoliths range in composition from mafic cognate cumulates and upper crustal granitic rocks through gneisses to middle crustal felsic granulites shrimp u th pb zircon analyses of these rocks indicate that the dykes were likely intruded during middle triassic times similar 235 ma whereas the xenoliths contain zircons with concordant carboniferous early permian neoproterozoic and palaeoproterozoic ages 280 328 ma c 540 615 ma 700 ma and similar 2000 ma the 280 328 ma ages appear to record synchronous intrusive and high grade up to granulite facies variscan metamorphic events suggesting that high grade metamorphism may have facilitated the s type granitic magmatism on the other hand the similar 540 615 ma 700 ma and 2000 ma ages correspond with pan african and eburnian orogenic events recorded in the west african craton in a triassic reconstruction morocco is juxtaposed against nova scotia canada and some have proposed that the basement of the easternmost terrane meguma terrane is a piece of the west african craton however lower crustal xenoliths from devonian dykes similar 370 ma cutting the meguma terrane have yielded late devonian neo and mesoproterozoic ages 378 ma 575 629 ma similar 880 1050 ma and similar 1530 ma the presence of similar 1 ga ages suggests that the basement of the meguma terrane is avalonian rather than west african implying that in a pangean reconstruction the rheic ocean suture between nw africa and maritime canada coincides with the atlantic ocean

u pb dating of single detrital zircon grains from mesozoic sandstone in the beipiao basin in the eastern yan liao orogenic belt china provenance and correlation of tectonic evolution single grain u pb ages of sediments from the beipiao basin northeast china were conducted to determine the evolution of basin provenance zircons from a sandstone in the upper triassic laohugou formation yield a wide range of ages and according to their u pb ages fall into four groups 209 3 4 0 304 2 4 9 1565 5 71 2154 50 2400 35 2499 9 2512 11 2557 74 ma these ages indicate that the zircons were principally derived from late archean proterozoic and late paleozoic plutonic rocks intrusions in the mongolian accretion belt and the northern margin of the north china block ncb were probably the main source of the sediments in the basin but the easterly liaodong block also provided minor detrital material with lower u pb ages during the late triassic most of the u pb ages from zircons collected from a sandstone in the lower jurassic beipiao formation range from 194 3 2 9 to 233 8 4 2 ma reflecting the major sediment source during the early jurassic zircons derived from late indosinian plutonic rocks increased which suggests that the detritus was supplied mainly from the interior of the yan liao orogenic belt especially from the liaodong block late indosinian zircons 200 230 ma were eroded and deposited in the lower jurassic beipiao formation and this implies that intensive tectonic activation and uplift of the yan liao orogenic belt in the mesozoic commenced in the late indosinian c 2005 elsevier ltd all rights reserved

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

late palaeozoic formation and development of the st marys basin mainland nova scotia canada a prolonged record of intracontinental strike slip deformation during the assembly of pangaea

the analysis of rainfall induced slope failures at iva valley area of enugu state nigeria this paper analyses the dominant mechanisms of slope failures and identifies potential obstacles to landslide hazard reduction at the iva valley area enugu nigeria the landscape is replete with landslide scars and gullies of varied sizes and the slope deposits comprise unconsolidated friable sands inter bedded with thin units of montmorillonitic claystone forty three landslide events were identified in the study area with most being shallow short run out movements with slip surface depth 2 m the study found the landslides mainly occur in the beginning of rainy season characterized by short duration high intensity rainfall an integrated approach comprising field mapping laboratory tests and numerical analyses reveals that the barren nature of the slopes prior to the outset of rainy season high rainfall intensity erosion overgrazing soil characteristics and the site s unique lithologic sequence are the main causes of instability shearing tests under several conditions showed that the soils strongly strain soften until low steady state strength is achieved a computer code based on this strength reduction technique used input parameters obtained from the field and laboratory studies to simulate a landslide with similar structure travel distance and distribution area it is noted that urbanization has gradually increased the vulnerability of the society s poor to landslide hazards as they now erect unplanned residence tents and blocks on the slopes this work is part of a regional study aimed at finding ways of protecting the vulnerable by generating data that could be used to build future landslide susceptibility map

applications of single grain zircon evaporation analyses to detrital grain studies and age discrimination in igneous suites abstract 207 pb 206 pb ages determined by evaporation of single zircon grains from rocks of the new england appalachians in the usa permit an assessment of the applicability of this method to rocks that have been strongly disturbed by orogenesis tests conducted on highly metamorphosed and deformed orthogneisses of known protolith age whose u pb upper intercept zircon ages obtained through isotope dilution methods show profound post crystallization discordance demonstrate that the evaporation method is successful in recovering protolith ages uncertainties are 10 15 my for rocks of paleozoic age or older preliminary results suggest that the method is particularly useful for provenance studies of sedimentary rocks and in the discrimination among groups of rocks that are known to differ in age but are otherwise difficult to separate on the basis of field or petrographic characteristics 207 pb 206 pb ages of detrital zircon grains from two metasedimentary units from opposite sides of the new england appalachians reveal the distinct provenances of these rocks the missisquoi formation in southeastern vermont usa is comprised in part of detritus derived from the 1 0 1 2 ga grenvillian province of laurentia whereas this component is conspicuously absent from the plainfield formation in easternmost connecticut the detrital zircon age data suggest that the missisquoi formation accumulated peripheral to the laurentian craton during the early paleozoic whereas the plainfield formation detritus was supplied by non laurentian ossibly west african sources during the late proterozoic or early paleozoic in southern vermont the evaporation method successfully distinguishes between two groups of augen gneisses with ages of 960 ma and 1120 ma which were first recognized through isotope dilution methods collectively these results indicate that the dating of single zircon grains by the evaporation method can be widely exploited in the study of complexly deformed and strongly metamorphosed rocks

probing the composition of unexposed basement south portuguese zone southern iberia implications for the connections between the appalachian and variscan orogens geochemistry and sm nd and u pb magmatic zircon isotope data from a postcollisional batholith that crosscuts the allochthonous south portuguese zone spz of southern iberia suggest that the base

palaeoclimatic signals recognized by chemometric treatment of molecular stratigraphic data abstract the high resolution stratigraphy of various marker compounds has been studied using gc hplc and gc ms in a 13 m gravity core recovered from the kane gap region eastern equatorial atlantic which provides a record of the glacial interglacial episodes over the last million years downhole variations in many presumed source specific components are observed e g in n alkanes from terrigenous land plants and dinosterol from dinoflagellates which may be due to perturbations or cyclicities resulting from climatic change fluctuations in the unsaturation of alkenones attributable to variations in water temperatures show correlations with the glacial interglacial cycles recorded in the 18 o values for planktonic foraminifera thereby providing a potential organic geochemical measure of past climates these molecular abundance data can be linked to the palaeotemperature record following computer treatments using principal component and spectral analyses molecular stratigraphy shows promise as a new chemostratigraphical tool where other means of stratigraphy fail for example through calcium carbonate dissolution

40ar 39ar dating of ribbon textured veins and wall rock material from meguma lode gold deposits nova scotia implications for timing and duration of vein formation in slate belt hosted vein gold deposits results of 15 40ar 39ar age spectra for whole rock argillite samples collected from within and adjacent to veins from eight meguma gold districts in the meguma terrane of southern nova scotia are presented the samples give excellent plateau ages i e concordance of plateaux correlation and integrated ages that range from ca 379 to ca 403 ma and there is no apparent correlation of age with bulk rock composition k2o al2o3 or sampling localities in addition apparent ages for samples from a district are similar within analytical error except for one deposit and there is no difference for samples from within ribbon textured veins versus samples collected outside of the gold districts i e in areas free of quartz veining the results of this work compare well to previous whole rock 40ar 39ar dating of meguma group samples and we concur with previous workers that the range in dates i e 380 410 ma reflects diachronous cooling of the area through the intracrystalline retention temperature fo

influence of rainfall induced wetting on the stability of slopes in weathered soils abstract shallow failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall these failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration this paper reports trends of rainfall induced wetting band depth in two types of weathered soils that are commonly found in korea both theoretical and numerical analyses for wetting band depth are presented based on the soil water characteristic curve obtained using filter paper as well as tensiometer tests it is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils theoretical analysis based on modified green and ampt model tends to underestimate the wetting band depth for typical korean weathered soils it was also deduced that for korean weathered soils the factor of safety drops rapidly once the wetting band depth of 1 2 m reached

analysis of physical testing of rainfall induced soil slope failures rainfall is a significant factor that triggers slope failures around the world this paper reports a series of physical tests which were conducted to simulate rain induced slope failures the experiments dealt with two scenarios including 1 rainwater infiltration into the slope and 2 slope failures induced by artificial rainfall with different initial conditions slope deformation and slope failures were observed and possible mechanisms were interpreted based on the experimental results the results confirm the hypothesis that pore water pressure and water content in a loose soil slope change rapidly and that water infiltration into cracks in the slope has a great impact on landslide development the observed slope failures can be divided into three types overall sliding failure partial sliding failure and flow slide the effect of slope gradient rainfall intensity and distribution of initial suction on the slope deformation and failure process are also summarized for possible applications under the similar conditions

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

a warning system for rainfall induced shallow failures abstract it is widely recognised that soil slips and debris flows are triggered by short intense storms owing its geologic geomorphologic and climatic settings the piedmont region nw italy is highly prone to the occurrence of this kind of landslides in the last two centuries in fact a total of 105 severe meteoric events which triggered shallow failures occurred and of these 18 events took place from 1990 to 2002 a fair number of rainfall thresholds have been proposed in the literature defined both on empirical or on physical bases empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides while physical thresholds are based on numerical models that consider the relation between rainfall pore pressure and slope stability the main objective of this paper is the identification of the empirical triggering thresholds for the piedmont region four meteoric events were selected and analysed november 4 5 1994 july 7 8 1996 april 27 30 2000 october 13 16 2000 because they supply a wide range of variation for both rainfall parameters duration intensity cumulative rainfalls and the number of induced landslides in the intensity duration plot the critical limit is described by the equation i 19d 0 50 where i rainfall intensity expressed in mm h and d rainfall duration expressed in hours such a limit is traced to envelop 90 of the points on the graph in the ni d diagram the triggering thresholds are given by the equations ni 0 76d 0 33 and ni 4 62d 0 79 where ni normalised intensity with respect to the annual precipitation map expressed in mm h pma 100 in the article the different meaning of these thresholds is discussed finally the diagram ni ncr is proposed the triggering threshold is given by the expression ni 0 09ln ncr 0 54 where ncr is the normalised cumulative critical rainfall mm pma 100 the application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide prone areas is discussed in detail an operating procedure which is presently being verified and tested in the studied area is described

controls over δ 44 40 ca and sr ca variations in coccoliths new perspectives from laboratory cultures and cellular models coccoliths comprise a major fraction of the global carbonate sink therefore changes in coccolithophores ca isotopic fractionation could affect seawater ca isotopic composition affecting interpretations of the global ca cycle and related changes in seawater chemistry and climate despite this a quantitative interpretation of coccolith ca isotopic fractionation and a clear understanding of the mechanisms driving it are not yet available here we address this gap in knowledge by developing a simple model casri co to track coccolith ca isotopic fractionation during cellular ca uptake and allocation to calcification we then apply it to published and new 44 40ca and sr ca data of cultured coccolithophores of the species emiliania huxleyi and gephyrocapsa oceanica we identify changes in calcification rates ca retention efficiency and solvation desolvation rates as major drivers of the ca isotopic fractionation and sr ca variations observed in cultures higher calcification rates higher ca retention efficiencies and lower solvation desolvation rates increase both coccolith ca isotopic fractionation and sr ca coccolith ca isotopic fractionation is most sensitive to changes in solvation desolvation rates changes in ca retention efficiency may be a major driver of coccolith sr ca variations in cultures we suggest that substantial changes in the water structure strength caused by past changes in temperature could have induced significant changes in coccolithophores ca isotopic fractionation potentially having some influence on seawater ca isotopic composition we also suggest a potential effect on ca isotopic fractionation via modification of the solvation environment through cellular exudates a hypothesis that remains to be tested

disintegration of aggregates and coccospheres in sediment trap samples abstract a method for non destructive disaggregation of coccoliths contained in fecal pellets marine snow and on coccospheres is described it consists of repeated chemical oxidation of organic material with naclo and h2o2 combined with brief periods of ultrasonification

a time space based approach for mapping rainfall induced shallow landslide hazard a rainfall induced shallow landslide is a major hazard in mountainous terrain but a time space based approach is still an unsettled issue for mapping rainfall induced shallow landslide hazards rain induces a rise of the groundwater level and an increase in pore water pressure that results in slope failures in this study an integrated infinite slope analysis model has been developed to evaluate the influence of infiltration on surficial stability of slopes by the limit equilibrium method based on this new integrated infinite slope analysis model a time space based approach has been implemented to map the distributed landslide hazard in a gis geographic information systems and to evaluate the shallow slope failure induced by a particular rainfall event that accounts for the rainfall intensity and duration the case study results in a comprehensive time space landslide hazard map that illustrates the change of the safety factor and the depth of the wetting front over time

varietal heavy mineral analysis of sediment provenance lower cretaceous scotian basin eastern canada abstract the origin of a major increase in sand supply in the early cretaceous of the scotian basin offshore eastern canada has been investigated by analysis of heavy mineral varieties the chemistry of detrital minerals from the scotian basin was compared with that of minerals from potential source rocks sampled from older sedimentary successions river sands and glacial tills on land heavy mineral varieties were established based on 1000 high quality electron microprobe emp analyses and used to classify heavy mineral types by mineral liberation analysis mla which uses a rapid scanning electron microscope particle analyser heavy mineral varieties were compared between the cretaceous quartz arenites and subarkoses and samples from potential source areas different chemical varieties of the same mineral group have different grain size distributions so that their relative modal abundances may be influenced by hydraulic sorting but modal abundance of different varieties of tourmaline garnet and spinel provides useful information widely used provenance sensitive mineral ratios are difficult to interpret because of the abundance of polycyclic sources comparisons of the shape parameters of the individual mineral types are also useful for provenance identification aspect ratio in elongate grains such as tourmaline and zircon is a measure of polycyclic reworking but is influenced by the initial shapes of minerals from different source rocks uniformity of varietal heavy minerals over a large area and stratigraphic range and the covariance of spinel and zircon with quite different crystalline sources indicate predominance of polycyclic sources to the central scotian basin probably principally from carboniferous and lower paleozoic sandstones in part sourced from western newfoundland ophiolites heavy mineral varieties in the west scotian basin can be closely matched to sources in the adjacent meguma terrane of the appalachians all the data show that the sands of the scotian basin were derived from reworking of crystalline basement of the appalachian orogen and its paleozoic sandstone cover uplifted during rifting of iberia from the grand banks there is no evidence of a significant supply of sand to the scotian basin from a proto st lawrence river

suggestion of a method for landslide early warning using the change in the volumetric water content gradient due to rainfall infiltration an early warning system can be an effective measure to reduce the damage caused by landslides by facilitating the timely evacuation of residents from a landslide prone area early detection of landslide triggering across a broad range of natural terrain types can be accomplished by monitoring rainfall and the physical property changes of soils in real time or near real time this study involved the installation of a real time monitoring system to observe physical property changes in soils in a valley during rainfall events this monitoring included the measurement of volumetric water content which was compared with the results of laboratory flume tests to identify landslide indicators in the soils the response of volumetric water content to rainfall events is more immediate than that of pore water pressure and volumetric water content retains its maximum value for some time before slope failure therefore an alternative method for landslide monitoring can be based on the observation of volumetric water content and its changes over time at shallow soil depths although no landslide occurred the field monitoring results showed a directly proportional relationship between the effective cumulative rainfall and the gradient of volumetric water content per unit time t t max this preliminary study thus related slope failure to the volumetric water content gradient as a function of rainfall laboratory results showed that a high amount of rainfall and a high gradient of volumetric water content could induce slope failure based on these results it is possible to suggest a threshold value of the volumetric water content gradient demarcating the conditions for slope stability and slope failure this threshold can thus serve as the basis of an early warning system for landslides considering both rainfall and soil properties

middle to late paleozoic acadian orogeny in the northern appalachians a laramide style plume modified orogeny the laramide orogeny of the western united states is proposed as a modern analogue for the silurian devonian acadian orogeny and subsequent diachronous voluminous short lived magmatism and basin formation in the northern appalachians shallowing of the benioff zone accounts for several enigmatic features associated with plate convergence in the northern appalachians including 1 wenlockian ludlovian termination of arc related magmatism in the avalon terrane followed by a period of relative magmatic quiescence from 395 to 380 ma and 2 diachronous migration of the acadian deformation front from ca 415 ma in the southeast to ca 370 ma in the northwest extending more than 600 km into the continental interior the flattening of the subduction zone is attributed to overriding of a plume by the convergent margin which may explain 1 the abrupt termination of magmatic quiescence by 380 370 ma and voluminous felsic magmatism and production of plume related lamprophyres in the southeast meguma terrane as the plume thermally eroded the oceanic lithosphere causing melting of the lower crust 2 late devonian regional high temperature low pressure metamorphism in the meguma terrane related to the thermal anomalies above a plume 3 synchronous devonian emplacement of meguma gold deposits and associated siderophile elements possibly derived from fluid circulation above an ascending plume 4 rapid late devonian uplift and erosion of as much as 10 km due to dynamic uplift over a plume 5 migration of magmatism to the north avalon terrane cobequid highlands so that plume related carboniferous magmatism occurred in and around the carboniferous permian maritimes basin 6 the high density lens at the base of the crust beneath the maritimes basin the product of plume derived underplated mafic rocks and 7 a subsidence mechanism for formation of the maritimes basin by cooling of a decapitated plume head

toward better paleocarbonate ion reconstructions new insights regarding the caco3 size index 1 the reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the caco3 cycle to the decrease in atmospheric co2 content during glacial time such reconstructions have been challenging because each of the existing paleo co32 indices has serious limitations in this study we reexamine the broecker clark caco3 size index by analyzing the 20 m 20 to 38 m and 38 to 63 m fractions in sediments from the ontong java plateau and the ceara rise scanning electron microscope analyses demonstrate that the less than 20 m caco3 is dominated by coccoliths and the greater than 20 m caco3 is dominated by foraminifera our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera referenced to a core top sample from 2 31 km depth in a core top sample from 4 04 km depth on the ontong java plateau 70 of the foraminifera caco3 was dissolved as opposed to only 7 of the coccolith caco3 we found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 m in size and thus the broecker clark size index is not a measure of the extent of fragmentation rather it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths on the basis of these results we propose a new dissolution index which involves the ratio of dissolution susceptible foraminifera caco3 to total caco3

40ar 39ar ages of detrital muscovite within lower cambrian and carboniferous clastic sequences in northern nova scotia and southern new brunswick implications for provenance regions detrital muscovite from lowermost cambrian sequences exposed in the avalon composite terrane in nova scotia and new brunswick record 40ar 39ar plateau ages of ca 625 600 ma these are interpreted to date times of cooling in source areas the regional distribution of coarse grained detrital muscovite in lower cambrian rocks of avalonian overstep sequences suggests a source region of dimensions considerably larger than any presently exposed in appalachian segments of the avalon composite terrane late proterozoic tectonic reconstructions locate the avalon composite terrane adjacent to northwestern south america thereby suggesting a possible source within late proterozoic panafrican brasiliano orogens detrital muscovite from clastic sequences of the proximally derived lower carboniferous tournaisian horton group and the more distal upper carboniferous westphalian d stephanian pictou group in nova scotia records 40ar 39ar spectra that define plateau ages of ca 390 380 ma horton group and and ca 370 ma pictou group finer grained fractions from samples of the horton group display more internally discordant age spectra defining total gas ages of ca 397 395 ma a provenance for the finer muscovite may be found in southern nova scotia where cambrian ordovician turbidites of the meguma group display a regionally developed micaceous cleavage of this age the ca 390 380 ma detrital muscovites probably were derived from granite stocks presently exposed in proximal areas of northernmost cape breton island a more distal source for the ca 370 ma detrital muscovites in the pictou group is suggested by its original extensive distribution although a local possibly recycled source may also have been present the presence of only 400 370 ma detrital muscovite suggests a rapidly exhumed orogenic source with characteristics similar to those of crystalline rocks presently exposed in the cape breton highlands and or the meguma terrane

regionalization of rainfall thresholds an aid to landslide hazard evaluation rainfall soil properties and morphology are major factors controlling shallow landsliding a series of meteorological events that triggered soil slips in northern italy were studied to define rainfall thresholds and to evaluate a possible regionalization soil properties triggering rainfall and local lithological and morphometrical settings of different sites were used as input to an infiltration model the approach allows the recognition of several triggering conditions in the piedmont pre alpine and alpine regions this suggests the need for different rainfall thresholds with respect to those derived with other methods intensity versus rainfall duration relationships become particularly important when related to soil permeability and thickness and demonstrate the role of antecedent precipitation events with exceptional water discharge from obstructed road culverts reveal the role played by anthropic structures in triggering such phenomena different approaches to slope stability analysis are shown taking into account bedrock lithology topography seepage and local saturation conditions

identification of soil redistribution using 137cs for characterizing landslide prone areas a case study in sarno quindici italy debris flows are among the most hazardous and unpredictable processes whose hazard evaluation requires an understanding of the processes that govern sediment supply sediment bulking flow volume and deposition in line with this challenge we estimate the net soil redistribution rates in an area characterized by recurrent instability phenomena using 137cs as a tracer for monitoring soil dynamics an extension of this method by applying it to the case of major landslides is addressed specifically surveys of soil 137cs content at sites in the pizzo d alvano massif italy where a set of particularly damaging landslides occurred on 5 6 may 1998 are reported being this region prone to debris flows two zero order basins are examined one of which experienced a landslide event in that basin deposition is observed whereas the other shows a net loss of soil these results appear to be relevant particularly because the rate of hollow filling could be correlated with the magnitude and or frequency of debris flow occurrence or with some measure of the hazard presented by individual gullies

age of detrital zircon and titanite in the meguma group southern nova scotia canada clues to the origin of the meguma terrane abstract precise u pb isotopic analysis of seventeen selected high quality laboratory abraded zircon single grains seven multigrain fractions of similar material and four paramagnetic titanite fractions record the ages of the various detrital grain types from two turbidite samples collected from the top and about 5 km below the top of the goldenville formation of the meguma group the results show that the source of both sediments contained 600 ma and 2000 ma old volcanic plutonic components whereas a third 3000 ma old component occurs exclusively in the upper sample and the youngest zircons and titanite are found in the lower sample lead lead ages of bulk fractions at 2300 ma and two nearly concordant single grains at 2040 ma and 2140 ma upper sample together with 2157 ma bulk fraction and 2060 ma and 2080 ma single grain fractions lower sample indicate that the 2000 ma component dominates the pink purple euhedral grain types detrital titanite gives ages of 605 ma upper sample and 552 ma lower sample with the latter sample containing a minor 1975 ma component colourless zircons record this same age difference the lower sample contained the youngest concordant single zircon grain 566 ma and 580 605 ma bulk grain fraction even though two concordant single grains have ages of 632 and 643 ma estimated bulk fraction ages for certain zircon grain types from the upper sample fall in the range of 605 to 675 ma these data suggest that while the youngest rocks in the source region were removed by erosion during the early stages of deposition of the goldenville formation the oldest source rocks were not unroofed until later in the depositional history the 566 8 ma age of the youngest concordant zircon from the stratigraphically lower sample provides a maximum age for the deposition of this grain with the base of the cambrian placed between 545 and 530 ma the goldenville formation may straddle the precambrian cambrian boundary graptolites from the immediately overlying halifax formation are of early ordovician tremadocian age the lower sample contains spherical zircons that may have been derived from mafic granulite with an estimated age of 2000 2200 ma with this one possible exception all of the zircons analyzed appear to be igneous in origin and all are relatively euhedral indicating that rocks of the ages referred to above probably outcrop in the source area anomalous discordance patterns imply that part of the 2960 ma area was metamorphosed by the 2000 ma event and that both the 2960 and 2000 ma regions were metamorphosed during the 600 ma event the complete lack of detritus with ages between 680 and 2040 ma virtually eliminates a northern north american or baltic shield provenance however the available data are not sufficient to distinguish between a west african or guyana shield source