u pb and th pb dating of apatite by la icpms abstract apatite is a common u and th bearing accessory mineral in igneous and metamorphic rocks and a minor but widespread detrital component in clastic sedimentary rocks u pb and th pb dating of apatite has potential application in sedimentary provenance studies as it likely represents first cycle detritus compared to the polycyclic behavior of zircon however low u th and radiogenic pb concentrations elevated common pb and the lack of a u th pb apatite standard remain significant challenges in dating apatite by la icpms and consequently in developing the chronometer as a provenance tool this study has determined u pb and th pb ages for seven well known apatite occurrences durango emerald lake kovdor mineville mud tank otter lake and slyudyanka by la icpms analytical procedures involved rastering a 10 m spot over a 40 40 m square to a depth of 10 m using a geolas 193 nm arf excimer laser coupled to a thermo elementxr single collector icpms these raster conditions minimized laser induced inter element fractionation which was corrected for using the back calculated intercept of the time resolved signal a tl u bi np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias external standards plesovice and 91500 zircon nist srm 610 and 612 silicate glasses and stdp5 phosphate glass along with kovdor apatite were analyzed to monitor u pb th pb u th and pb pb ratios common pb correction employed the 207pb method and also a 208pb correction method for samples with low th u the 207pb and 208pb corrections employed either the initial pb isotopic composition or the stacey and kramers model and propagated conservative uncertainties in the initial pb isotopic composition common pb correction using the stacey and kramers 1975 model employed an initial pb isotopic composition calculated from either the estimated u pb age of the sample or an iterative approach the age difference between these two methods is typically less than 2 suggesting that the iterative approach works well for samples where there are no constraints on the initial pb composition such as a detrital sample no 204pb correction was undertaken because of low 204pb counts on single collector instruments and 204pb interference by 204hg in the argon gas supply age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common pb corrected ages a tera wasserburg concordia intercept age and a tera wasserburg concordia intercept age anchored through common pb the samples in general yield ages consistent at the 2 level with independent estimates of the u pb apatite age which demonstrates the suitability of the analytical protocol employed weighted mean age uncertainties are as low as 1 2 for u and or th rich palaeozoic neoproterozoic samples the uncertainty on the youngest sample the cenozoic 31 44 ma durango apatite ranges from 3 7 7 6 according to the common pb correction method employed the accurate and relatively precise common pb corrected ages demonstrate the u pb and th pb apatite chronometers are suitable as sedimentary provenance tools the kovdor carbonatite apatite is recommended as a potential u pb and th pb apatite standard as it yields precise and reproducible 207pb corrected 232th 208pb and common pb anchored tera wasserburg concordia intercept ages

flow variability at the continental shelf break of the mackenzie shelf in the beaufort sea observations from four yearlong current meter deployments made in 1987 1988 near the shelf break in the canadian beaufort sea are analyzed by statistical and spectral methods to characterize the structure and variability vertical and horizontal of the velocity field and to compare measurements obtained during summer ice free and winter ice covered conditions three main frequency bands are defined low frequencies 0 01 0 07 cpd intermediate or synoptic scale frequencies 0 07 0 7 cpd and high frequencies 0 7 cpd including tides and inertial currents within this division about 65 of the kinetic energy is in the low frequency band 15 in the intermediate band and 20 is in the high frequency band the latter is dominated by tidal motions low frequency variability is well correlated both vertically and horizontally along the shelf for separation distances exceeding 200 km variability in this band appears to be related to wind forcing and topographic wave propagation over large horizontal scales low frequency variability is highest during october and november in association with the occurrence of intense autumn storms and lowest during periods of ice cover due to wind shielding and increased frictional damping by ice cover intermediate scale motions have significant correlation in the vertical but poor correlation in the horizontal motions in this frequency band appear to be associated with mesoscale eddies advected by the mean flow there is also evidence of local generation of intermediate frequency current fluctuations by storms in late autumn and again an apparent damping during winter periods of ice cover finally high frequency motions show significant peaks in diurnal and semidiurnal tidal bands which are well correlated horizontally and vertically however other high frequency motions in this band show no significant correlation in either the vertical or horizontal direction there is no clear evidence in the current meter records of coupling between high frequency motions and direct atmospheric forcing

glacial and syntectonic sedimentation the upper proterozoic kingston peak formation southern panamint range eastern california a sedimentological stratigraphic study of the upper proterozoic kingston peak formation in the southern panamint range shows that it was deposited under glacial conditions with contemporaneous volcanism and tectonic activity evidence for glaciation rests primarily upon 1 the homogeneity thickness and lateral extent of two diamictite units 2 the facies association of the diamictite and 3 presence of striated stones and dropstones within the formation elsewhere in the death valley area in the panamint range pillowed basalt interbedded with diamictite demonstrates synchronous subaqueous volcanism lower kingston peak units rest on a variable substrate and locally overlap faults indicating tectonism prior to deposition tectonism during kingston peak deposition is inferred from abrupt thickness changes and buried faults sedimentation was chiefly on a submerged continental platform and locally terrestrial during a period of incipient rifting two ice advances are recorded with associated sea level fluctuations the formation thickens northward from 40 to about 1 200 m over 40 km initial sediments were fine grained and in basins a few kilometres across nearby islands provided coarse debris overlying sandstone and conglomerate indicate regression predominantly massive diamictite as much as 450 m thick and interpreted as lodgment till or glacioma rine sediment records the first ice advance a northward increase in diamictite thickness decrease in clast size and facies change from diamictite to argillite and graywacke suggest a southern source overlying laminated limestone marks a transgression succeeding interbedded sandy limestone thick bedded graywacke and parallel laminated siltstone and sandstone double in thickness over a few kilometres demonstrating local subsidence and renewed terrigenous input trough cross laminated arkosic sandstone and conglomerate overlain by predominantly massive diamictite as much as 190 m thick with a locally erosive base represent glaciofluvial deposits and lodgment till and record the second ice advance

upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

the cryogenian record in the southern kingston range california the thickest death valley succession in the hunt for a gssp abstract the kingston peak formation of the death valley area california allows valuable insight into both regional cordilleran stratigraphy and the number of glacial cycles preserved in the cryogenian record in the kingston range the eponymous strata have been previously interpreted to record both sturtian and marinoan pan glacial events in the context of a search for a global boundary stratotype section and point gssp for the cryogenian we provide the first detailed description of the thickest diamictite bearing interval in the western usa two clast poor muddy diamictite intervals within the succession one at the base and one near the top have been used to support sturtian and marinoan events previously however new data from the southern part of the kingston range suggest that the upper diamictite interval is genetically related to underlying strata the deposits are interpreted as glaciogenic debris flow deposits which probably represent the proximal tract of a subaqueous fan medial to distal portions of this fan are dominated by turbidites which were transported down a consistent se oriented palaeoslope lowermost beds of the upper diamictite interval are intercalated with graded sandstones and sandy matrix supported conglomerates the graded beds turbidites and matrix supported conglomerates debrites testify to a subaqueous setting with the compositionally and texturally distinct diamictites indicating a glacial origin

cap carbonate platform facies model noonday formation se california the neoproterozoic outcrop belt of the death valley region california preserves an oblique cross section of the noonday formation a mixed carbonate siliciclastic platform that hosts distinctive basal ediacaran cap carbonate affiliated sedimentary structures stromatolite textures and 13 c carb values the noonday platform encompasses two depositional sequences that reveal two cycles of relative sea level change within strata conventionally considered to record a single rapid postglacial sea level rise in updip localities facies of the first depositional sequence record the transition from a carbonate ramp to a stromatolite bearing tubestone textured reef rimmed platform downdip localities seaward of the reefal escarpment variably preserve a thin and condensed onlapping foreslope wedge base level fall exposed the reef crest to karstic dissolution and propagated submarine incised valleys into the seaward margin of the reef overlying strata record the backfilling of a submarine incised valley and reestablishment of a back stepping carbonate dominated ramp prior to a second subaerial exposure event that defines the contact between the noonday and johnnie formations we address the relative contributions of syndepositional tectonism and recovery from low latitude deglaciation in dictating noonday platform architecture and the intra noonday formation sequence boundary noonday formation deposition coincided with extension of the laurentian margin during disaggregation of the rodinian supercontinent within this framework previous work has suggested that the intra noonday formation sequence boundary records growth faulting that reinforced differential topography uplifting reef rimmed horsts exposing the reef crest to karstic dissolution and downdropping grabens however we trace the intra noonday formation sequence boundary seaward of the reef crest and demonstrate that for a time wave base was situated downdip of the reef escarpment on putatively downdropped fault blocks thus if the noonday margin were undergoing extension then the creation of the intra noonday formation sequence boundary required a concomitant decrease in accommodation due perhaps to postglacial isostatic uplift attendant with low latitude deglaciation we speculate that noonday formation sequence architecture records 1 immediate deglacial flooding 2 shoaling and exposure due to isostatic rebound induced by either a hiatus in meltwater flux or rapid ice sheet collapse against a background of global deglaciation and 3 resumed flooding following complete deglaciation as rift related tectonism could amplify or counter glacial isostasy inferences of the amplitude of local postglacial sea level change will require robust estimates of syndepositional extension across the noonday margin

a new high resolution unstructured grid finite volume arctic ocean model ao fvcom an application for tidal studies 1 a spherical coordinate version of the unstructured grid 3 d fvcom finite volume coastal ocean model has been applied to the arctic ocean to simulate tides with a horizontal resolution ranging from 1 km in the near coastal areas to 15 km in the deep ocean by accurately resolving the irregular coastlines and bathymetry in the arctic ocean coastal regions this model reproduces the diurnal k1 and o1 and semidiurnal m2 and s2 tidal wave dynamics and captures the complex tidal structure along the coast particularly in the narrow straits of the canadian archipelago the simulated tidal parameters harmonic constituents of sea surface elevation and currents agree well with the available observational data high resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves which are quite energetic along the greenland siberia and spitsbergen continental slope and shelf break areas water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation the comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the arctic ocean particularly in the canadian archipelago

rock magnetic signature of gas hydrates in accretionary prism sediments sediments from two ocean drilling program leg 146 sites from the cascadia margin of western north america have magnetic properties indicating diagenesis of magnetic minerals associated with the presence of gas hydrates two indices combining coercivity remanence and susceptibility parameters djh jrs js hcr hc and ds jrs k hcr when combined with thermo magnetic data can be diagnostic of these changes at site 892 ds values are distinctly higher and more scattered above the bottom simulating seismic reflector bsr which marks the base of the hydrate stability zone within the hydrate stability zone at site 892 djh shows two trends an increase from about 50 mbsf to the bsr at 73 mbsf corresponding to an expected increase in hydrate concentration near the bsr and a second increase upwards from 50 mbsf to peak values at less than 21 mbsf associated with hydrate recovered in cores above 19 mbsf at site 889 890 djh increases downhole to about 285 mbsf substantially below the bsr at 225 mbsf high djh sediments within a low cl zone at this site have magnetic mineralogies which are dominated by fine grained magnetic sulfides whereas sediments from above and below this zone are characterised by magnetite magnetic sulfide mixes this trend at site 889 890 is consistent with an interpretation based on pore water geochemistry low cl and bottom water temperature that a fossil gas hydrate zone extended downwards to about 295 mbsf during the last glacial the observed changes in magnetic properties can be attributed to steps in the reduction series from magnetite through sd greigite to pyrite or to overgrowth of sd greigite to md size diagenetic growth of magnetic iron sulfides greigite and or pyrrhotite has been reported in other accretionary wedge sediments thermal demagnetization of multi component isothermal remanent magnetization mirm indicates the presence of a low coercivity magnetic mineral with an unblocking temperature tub between 310 and 350 c high jrs k ratios suggest that the low coercivity low unblocking temperature mineral is predominantly greigite rather than pyrrhotite a low to medium coercivity mineral with tub ca 580 c magnetite is also present in varying amounts hydrate apparently controls the presence of greigite by incorporating h2s shown to be present as a hydrate phase together with methane in hydrate recovered at site 892 release of h2s below the base of the hydrate layer allows overgrowth of greigite grains to md size or the conversion of some of the greigite to pyrite

intrusion of warm bering chukchi waters onto the shelf in the western beaufort sea 1 wind driven changes in the path of warm bering chukchi waters carried by the alaska coastal current acc through barrow canyon during late summer are described from high resolution hydrography acoustic doppler current profiler measured currents and satellite measured sea surface temperature imagery acquired from mid august to mid september 2005 2007 near barrow alaska numerical simulations are used to provide a multidecadal context for these observational data four generalized wind regimes and associated circulation states are identified when winds are from the east or east southeast the acc jet tends to be relatively strong and flows adjacent to the shelf break along the southern flank of barrow canyon these easterly winds drive inner shelf currents northwestward along the alaskan beaufort coast where they oppose significant eastward intrusions of warm water from barrow canyon onto the shelf because these easterly winds promote sea level set down over the beaufort shelf and upwelling along the beaufort slope the acc jet necessarily becomes weaker broader and displaced seaward from the beaufort shelf break upon exiting barrow canyon winds from the northeast promote separation of the acc from the southern flank of barrow canyon and establish an up canyon current along the southern flank that is fed in part by waters from the western beaufort shelf when winds are weak or from the southwest warm bering chukchi waters from barrow canyon intrude onto the western beaufort shelf

glaciers flows and fans origins of a neoproterozoic diamictite in the saratoga hills death valley california abstract the kingston peak formation of death valley california provides an exceptional archive of cryogenian glaciation and concomitant rifting of rodinia in the saratoga hills an 800 m thick succession of diamictite dominated strata is exposed allowing lithofacies and clast compositions to be studied in detail and for the relative influence of glacial versus slope processes on sedimentation to be critically assessed for the first time two detailed sections 400 m apart allow four facies associations to be established 1 thinly laminated argillaceous sandstone interpreted as low density turbidites 2 laminated deformed and brecciated limestone interpreted as carbonate sourced turbidites 3 bedded massive diamictite interpreted as glacially fed debrite and 4 interbedded mudstone sandstone and diamictite interpreted as stratified diamictite deposited via ice rafted debris and passing gradually into turbidites separated by intensely deformed intervals bedded massive diamictite is dominant in the succession and shows a gradual up section transition into interbedded mudstone sandstone and diamictite this succession is interpreted to record a waning glacial influence from glacially sourced debris flows to stratified diamictite strongly influenced by ice rafted debris clasts in the diamictite include carbonate siliciclastic intraclasts granite diabase gneiss and quartzite clast presence profiles suggest that in spite of the comparable along strike facies profiles between the two logs clast content is significantly different within the same stratigraphic unit this finding suggests that clast content is of little use in aiding correlation and lithostratigraphic subdivision of the kingston peak formation the differences in clast compositions is envisaged to be due to complex drainage network examinations of the sedimentary structures and stacking pattern of the lithofacies complex drainage network and localized deformation features of fa4 all support deposition as part of a trough mouth fan system

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

properties of the atlantic derived halocline waters over the laptev sea continental margin evidence from 2002 to 2009 1 a series of transects carried out in 2002 2009 across the laptev sea continental margin show consistent cross slope differences of the lower halocline water lhw over the slope the lhw core is on average warmer and saltier by 0 39 c and 0 26 practical salinity unit respectively relative to the off slope lhw underlying atlantic water aw thermohaline properties exhibit an opposite pattern it is colder and fresher over the slope and warmer and saltier off the slope although on slope and off slope lhws have different formation histories our results suggest that an important part of the heat and salt lost from the aw is gained by the overlying lhw over the continental slope area this implies the role of enhanced vertical mixing over the sloping topography which contributes to the difference between the on and off slope lhw properties the distribution of chemical tracers dissolved oxygen and nutrients provides further evidence supporting this interpretation and additionally suggests that the lhw may also be influenced by water from the outer shelf

a pseudo thellier relative palaeointensity record and rock magnetic and geochemical parameters in relation to climate during the last 276 kyr in the azores region summary in the pseudo thellier method for relative palaeointensity determinations tauxe et al 1995 the slope of the nrm intensity left after af demagnetization versus arm intensity gained at the same peak field is used as a palaeointensity measure we tested this method on a marine core from the azores spanning the last 276 kyr we compared the pseudo thellier palaeointensity record with the conventional record obtained earlier by lehman et al 1996 who normalized nrm by sirm the two records show similar features intensity lows with deviating palaeomagnetic directions at 40 45 ka and at 180 190 ka the first interval is associated with the laschamps excursion while the 180 190 ka low represents the iceland basin excursion channell et al 1997 the pseudo thellier method in combination with a jackknife resampling scheme provides error estimates on the palaeointensity spectral analysis of the rock magnetic parameters and the palaeointensity estimates shows orbitally forced periods particularly 23 kyr for climatic precession this suggests that palaeointensity is still slightly contaminated by climate fuzzy c means cluster analysis of rock magnetic and geochemical parameters yields a seven cluster model of predominantly calcareous clusters and detrital clusters the clusters show a strong correlation with climate for example samples from detrital clusters predominantly appear during rapid warming although both the pseudo thellier palaeointensity m a and fuzzy clusters show climatic influences we have not been able to find an unambiguous connection between the clusters and m a

a key source area and constraints on entrainment for basin scale sediment transport by arctic sea ice combining field measurements remote sensing and numerical modelling a key site for ice entrainment and basinwide dispersal of sediments by sea ice has been identified near the new siberian islands the total ice bound sediment export of 18 5 x 10 6 t for an entrainment event documented in 1994 95 is of the same order of magnitude as annual sediment supply to the deep sea sector of the eurasian arctic and the greenland sea satellite imagery and ancillary data indicate that ice advection from this source may play an important role in sedimentation downstream in the transpolar drift

1 08 ga diabase sills in the pahrump group california implications for development of the cordilleran miogeocline u pb baddeleyite ages of 1087 3 and 1069 3 ma for twodiabase sills that intrude the crystal spring formation of the pahrump group southeastern california provide a minimum estimate for the depositional age of the crystal spring formation the new ages high light the potential range in deposition ages for the pahrump group from 1087 ma to possibly as young as 600 ma for kingston peak glaciogenic sediments consequently there probably are significant disconformities within the pahrump group that separate unrelated tectonically distinct episodes of basin subsidence the crystal spring and beck spring formations are considered to be platform cover rocks preserved as a result of block faulting during deposition of the upper kingston peak formation the age of the pahrump sills is in excellent agreement with the age of sills that intrude the apache group central arizona and the unkar group grand canyon and supports earlier correlations of those units

seasonal variability of atlantic water on the continental slope of the laptev sea during 2002 2004 abstract 2002 04 observations carried out on the laptev sea continental slope as part of the nansen and amundsen basins observational system nabos project are used to study variations of the intermediate 150 800 m atlantic water aw layer of the arctic ocean at the mooring site aw exhibits seasonal changes with higher lower temperature and salinity in winter summer this variability is attributed to the shift of the aw core toward the slope in winter and away from the slope in summer seasonal variation of wind is among the possible factors governing seasonal changes of the aw layer

seasonal variation of upwelling in the alaskan beaufort sea impact of sea ice cover 1 data from a mooring array deployed from august 2002 to september 2004 are used to characterize differences in upwelling near the shelf break in the alaskan beaufort sea due to varying sea ice conditions the record is divided into three ice seasons open water partial ice and full ice the basic response is the same in each of the seasons roughly 8 h after the onset of easterly winds the shelf break jet reverses followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break pacific winter water and warm at depth atlantic water the secondary circulation at the outer shelf is to first order consistent with a two dimensional ekman balance of offshore flow in the upper layer and onshore flow at depth there are however important seasonal differences in the upwelling overall the response is strongest in the partial ice season and weakest in the full ice season it is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack ice as the strength of the wind forcing was comparable over the three seasons an eof based upwelling index is constructed using information about the primary flow secondary flow and hydrography the ability to predict upwelling using the wind record alone is explored which demonstrates that 90 of easterly wind events exceeding 9 5 m s 1 drive significant upwelling during certain periods the ice cover on the shelf became landfast which altered the upwelling and circulation patterns near the shelf break

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

fuzzy c means cluster analysis of early diagenetic effects on natural remanent magnetisation acquisition in a 1 1 myr piston core from the central mediterranean abstract the influence of early diagenesis on the natural remanent magnetisation nrm in sediments from the calabrian ridge central mediterranean is analysed with the help of fuzzy c means fcm cluster analysis and non linear mapping nlm the sediments are variably coloured white beige purplish greenish and grey layers occur with occasionally intercalated sapropels the nrm acquired depends on both depositional conditions and diagenetic processes to describe these fcm was performed with in arm caco3 ba mn and s as variables an eight cluster model was derived with the clusters belonging to two categories one expressing mainly diagenetic processes i e dissolution and precipitation and the other expressing mainly depositional conditions the impact of diagenesis on nrm acquisition is profound and not restricted to the close vicinity of the anoxic sapropelitic layers as a consequence the influence of diagenetic processes on the nrm should be thoroughly assessed when selecting samples e g for the determination of the relative palaeointensity of the geomagnetic field application of multivariate classification techniques appears to be useful because it links rock magnetic parameters to the geochemical environment in the present piston core three short reversed geomagnetic events in the brunhes chron are preserved and indeed occur in clusters expressing no or minor diagenesis the recording of the blake event however has been prevented by later precipitation of magnetite in the corresponding interval

thermal alteration of pyrite to pyrrhotite during earthquakes new evidence of seismic slip in the rock record seismic slip zones convey important information on earthquake energy dissipation and rupture processes however geological records of earthquakes along exhumed faults remain scarce they can be traced with a variety of methods that establish the frictional heating of seismic slip although each has certain assets and disadvantages here we describe a mineral magnetic method to identify seismic slip along with its peak temperature through examination of magnetic mineral assemblages within a fault zone in deep sea sediments cored from the japan trench one of the seismically most active regions around japan during the integrated ocean drilling program expedition 343 the japan trench fast drilling project fault zone sediments and adjacent host sediments were analyzed mineral magnetically supplemented by scanning electron microscope observations with associated energy dispersive x ray spectroscopy analyses the presence of the magnetic mineral pyrrhotite appears to be restricted to three fault zones occurring at 697 720 and 801 m below sea floor in the frontal prism sediments while it is absent in the adjacent host sediments elevated temperatures and coseismic hot fluids as a consequence of frictional heating during earthquake rupture induced partial reaction of preexisting pyrite to pyrrhotite the presence of pyrrhotite in combination with pyrite to pyrrhotite reaction kinetics constrains the peak temperature to between 640 and 800 c the integrated mineral magnetic microscopic and kinetic approach adopted here is a useful tool to identify seismic slip along faults without frictional melt and establish the associated maximum temperature

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

an integrated paleomagnetic rock magnetic and geochemical study of the marcellus shale in the valley and ridge province in pennsylvania and west virginia an integrated paleomagnetic rock magnetic and diagenetic study of the devonian marcellus subgroup from threefolds in the valley and ridge province in pennsylvania and west virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization crm with south southeast declinations and shallow negative inclinations residing in pyrrhotite and a crm with more southerly declinations and shallow positive inclinations residing in magnetite rock magnetic results confirm the presence of pyrrhotite and magnetite tilt tests indicate that pyrrhotite and magnetite crms are syntilting to posttilting and paleopoles for both crms are similar and plot on the permian part of the apparent polar wander path for north america the marcellus subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation the magnetite and pyrrhotite crms formed in the permian probably due to burial diagenetic processes and not orogenic fluids the base of the unit contains the highest total organic content toc values and highest magnetic intensities both of which decrease up section this connection between toc and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis the pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir the similar permian crm ages may be explained by thrusting which resulted in rapid burial of the marcellus subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite respectively

grenville age a type and related magmatism in southern laurentia texas and new mexico u s a abstract large grenville age plutons are known to be present in the 1340 1370 ma basement in texas and eastern new mexico but their distribution and compositional ranges are poorly known new u pb zircon dates shrimp rg stanford university on subsurface samples have identified widespread presence of compositionally diverse grenville age 1070 1110 ma plutonic rocks in the texas panhandle core from a 175 m thick sill like gabbroic intrusion yielded a date of 1081 8 3 ma in situ differentiation of this tholeiitic magma led to a 7 fold increase in incompatible element concentrations as ree patterns remained essentially flat trace element data suggest an e morb like source to the south alkali feldspar granite with a type affinities was recovered from drill core from the abilene gravity minimum near albany texas it yielded a date of 1078 23 ma similar to undeformed post orogenic granites in the llano uplift further west an anorthosite xenolith from the eocene three sisters intrusion in el paso texas yielded a date of 1068 30 ma which is within error of the 1110 19 ma age determined for the main stage of the nearby a type red bluff granitic suite xenoliths from potrillo maar volcano in the center of the southern rio grande rift include monzonitic xenoliths with granulitic texture which yielded dates of 1072 ma in contrast potrillo maar xenoliths with igneous textures yielded u pb dates of 27 ma development of the granulitic texture is interpreted to reflect granulite facies metamorphism during tertiary time 26 27 ma on the basis of age zoning and u concentrations in the zircon crystals our results show that grenville age magmatism in the texas and new mexico subsurface was widespread and was coeval with syn and post deformation granites in the llano uplift of central texas the compositions of dated samples suggest that mafic magmas were broadly tholeiitic in character and that granitic magmas were a type these magmatic affinities are thought to be associated with crustal extension rather than with subduction moreover the presence of anorthosite xenoliths in the el paso kilbourne hole region the broadly tholeiitic character of mafic rocks and the a type nature of the granitic rocks are broadly similar to amcg anorthosite mangerite charnockite granite suites present in the grenville province of eastern laurentia

the arctic circumpolar boundary current we present high resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the siberian and alaskan shelves in the arctic ocean thus far the arctic circumpolar boundary current acbc has been seen as comprising two branches the fram strait and barents sea branches fsb and bsb respectively here we describe a new third branch the arctic shelf break branch asbb we show that the forcing mechanism for the asbb is a combination of buoyancy loss and non local wind creating high pressure upstream in the barents sea the potential vorticity influx through the st anna trough dictates the cyclonic direction of flow of the asbb which is the most energetic large scale circulation structure in the arctic ocean it plays a substantial role in transporting arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum the simulations show the continuity of the fsb all the way around the arctic shelves and the uninterrupted asbb between the st anna trough and the western fram strait the bsb flows continuously along the siberian shelf as far as the chukchi plateau where it partly diverges from the continental slope into the ocean interior the alaskan shelf break current asc is the analog of the asbb in the canadian arctic the asc is forced by the local winds and high upstream pressure in bering strait caused by the drop in sea surface height between the pacific and arctic oceans

kara sea freshwater dispersion and export in the late 1990s 1 a regional coupled ice ocean model for the kara sea forced with boundary conditions from a large scale north atlantic arctic ocean model is used to study dispersion and export of freshwater from ob and yenisei rivers toward the arctic ocean and the laptev sea for the period 1996 2001 the years 1998 and 1999 were characterized by a strong positive sea level pressure slp anomaly in the siberian part of the arctic ocean owing to prevailing northeasterly winds the slp anomaly caused a blocking situation which suppressed the otherwise eastward freshwater export to the arctic ocean and laptev sea this reversal of the prevailing circulation scheme led to a dramatic freshening of the kara sea through accumulation of low saline river water in the central and western parts additionally the kara strait inflow from the barents sea which presents the main source for saline atlantic derived water was reduced and partly even reversed the suppressed freshwater export during winter 1998 1999 recovered in the following winter 1999 2000 when a significant pulse of low saline surface water left toward the laptev sea the variability of the river discharge plays a minor role for the investigated period because the interannual variability of runoff rates is generally too low to explain the observed hydrographic changes the results underline the importance of local shelf sea processes for the variability of the freshwater export from the arctic shelves to the central arctic ocean

authigenic or detrital origin of pyrrhotite in sediments resolving a paleomagnetic conundrum monoclinic pyrrhotite fe7s8 is widely claimed to carry magnetizations acquired during early diagenesis in anoxic sedimentary environments in contrast geochemical literature indicates that pyrrhotite formation is extremely slow below 180 c which makes it a highly unlikely carrier of early diagenetic remanences in sediments this view is confirmed by the occurrence of late diagenetic fe7s8 in ancient sediments and the general lack of fe7s8 in modern sediments horng et al c s horng m torii k s shea s j kao inconsistent magnetic polarities between greigite and pyrrhotite magnetite bearing marine sediments from the tsailiao chi section southwestern taiwan earth planet sci lett 164 1998 467 481 documented the presence of fe7s8 that carries a magnetic signal indistinguishable from that of detrital magnetite in pleistocene marine sediments from taiwan we tested the possibility that the fe7s8 could have a detrital origin by conducting a source to sink study and found fe7s8 in metamorphic rocks of the taiwan central range and in material eroded from these rocks in the transportation pathway and in the depositional sink this confirms that the fe7s8 has a detrital origin rapid transportation from source to sink e g by typhoon associated flood events probably assists preservation of the fe7s8 which might otherwise oxidize during transportation the widespread occurrence of exhumed metamorphic rocks in orogenic belts around the world makes them a likely source of fe7s8 in marginal sedimentary basins detrital fe7s8 should therefore be more routinely considered to be responsible for paleomagnetic records when it is present in sediments with partial metamorphic provenance

strong remanent magnetization in pyrrhotite a structurally controlled example from the paleoproterozoic tanami orogenic gold province northern australia abstract rocks associated with an orogenic gold system in the paleoproterozoic granites tanami inlier of northern australia exhibit strong natural remanent magnetism identifiable in regional aeromagnetic data petrographical analysis indicates the two dominant magnetic minerals in the rocks of this region are multidomain magnetite and monoclinic pyrrhotite chemical analysis using an electron microprobe has determined that the magnetite and pyrrhotite are stoichiometrically pure without significant elemental substitution alternating field demagnetization curie temperature and hysteresis analysis indicates that the remanently magnetized phase is monoclinic pyrrhotite with low magnetic susceptibility in contrast multidomain magnetites lack remanence and have high magnetic susceptibilities pyrrhotite is preserved in the rock mass along with other sulfide minerals as millimeter scale veins parallel to regionally developed penetrative mylonitic shear bands c planes formed during sulfide remobilization in the waning cooling stages of hydrothermal au deposition in contrast magnetite grains exhibit porphyroblastic textures consistent with formation during prograde to peak metamorphism indicating formation prior to pyrrhotite earlier in the orogenic cycle because of the low curie temperature ca 325 c of pyrrhotite it is therefore likely that remanent magnetization effects observed in aeromagnetic images of the tanami inlier are associated with structures intimately related to the late stages of au mineralization during retrograde greenschist metamorphism after the peak thermal point of the orogenic cycle

barotropic and baroclinic tidal currents on the mackenzie shelf break in the southeastern beaufort sea 1 tidal currents near the outer shelf break of the mackenzie shelf in the southern beaufort sea were examined using year long 1987 1988 current measurements from the upper 35 m and lower 150 m layers at four sites along the southeast ss1 northeast ss2 north central ss3 and northwest ss4 perimeter of the shelf at all stations semidiurnal currents were dominant and upper layer currents were approximately double those observed in the lower layer maximum m2 currents were observed above the sharp northeastern corner of the mackenzie shelf 6 0 7 5 cm s 1 while in the mackenzie canyon they were negligible diurnal currents were weaker and depth uniform maximum k1 currents 1 5 3 0 cm s 1 were found in the eastern part of the shelf diurnal and lower layer semidiurnal currents were in good agreement with those computed numerically by kowalik and proshutinsky 1994 indicating that these currents are essentially barotropic in contrast upper layer semidiurnal currents were mainly baroclinic about 74 of the total energy of semidiurnal currents was associated with baroclinic coherent phase locked tidal currents while barotropic 12 baroclinic incoherent 7 and inertial 7 components are the remaining semidiurnal currents in this area high baroclinic generation coefficients the ratio of locally generated baroclinic waves to barotropic waves for stations ss2 and ss3 about 7 0 8 0 in comparison with 0 3 for ss1 and ss4 located near the northeastern mackenzie shelf identify this region as a probable generation source of intensive internal tidal waves which become then locally resonantly trapped between the shelf and the critical latitudes

late precambrian tectonism in the kingston range southern california speculation on the early history of the cordilleran geosyncline of north america has relied in part on interpretation of the tectonic setting of the precambrian pahrump group recent mapping in the kingston range resulted in new data to aid our speculation specifically precambrian tectonic events involving folding and later low angle normal faulting affected the crystal spring formation beck spring dolomite and lower part of the kingston peak formation unconformably overlying these units is a relatively undeformed conglomerate diamictite occurs both above and below the unconformity hence cordilleran wide correlations of the kingston peak formation based on diamictite require reassessment the nature of boundaries localized deformation and outcrop distribution of the pahrump group suggest that these rocks may be preserved in transtensional basins associated with strike slip faulting possibly occurring during development of the late precambrian continental margin

the alkali element and boron geochemistry of the escanaba trough sediment hosted hydrothermal system a suite of conjugate pore fluid and sediment samples were collected during leg 169 of the odp from within the clastic sedimentary sequences which host massive sulphides at central hill escanaba trough odp site 1038 we report the alkali element and boron and li and b isotope data for these samples relative to a reference site site 1037 located outside the zone of high heat flow pore fluids from site 1038 show a wide variation in cl 300 800 mm and have far higher concentrations of li up to 6 2 mm b up to 9 7 mm cs up to 5 0 m and rb up to 97 m we show that the pore fluids are derived from hydrothermal circulation that has extended into the basement oceanic crust with input of the alkali elements and b as the rising hydrothermal fluids interact geochemically with the overlying clastic sediments there is however no marked depletion of these elements in the conjugate sediments suggesting that there has been advective transport of fluids away from the primary hydrothermal reaction site this is supported by modelling of the li and b isotope systematics of the pore fluids which shows that they record extensive formation of secondary minerals during cooling of the fluids from 350 to 20 c precipitation of metal rich sulphides would have occurred prior to the formation of these minerals thus the pore fluid li and b isotope data can place important constraints on the locus of sulphide deposition beneath the seafloor at escanaba

a grenville age layered intrusion in the subsurface of west texas petrology petrography and possible tectonic setting the nellie intrusion is a thick more than 4420 m mafic to ultramafic layered intrusion with a radiometric age of 1163 ma rock types change abruptly with stratigraphic height and include norite pyroxenite gabbronorite hornblende gabbro gabbro anorthosite harzburgite and lherzolite norite is most abundant but gabbro and hornblende gabbro are locally abundant rare olivine rich layers are also present the general order of crystallization was olivine orthopyroxene plagioclase clinopyroxene and hornblende mg s expressed as 100 mg mg fe range from 76 3 to 85 8 for olivine 56 7 to 84 9 for orthopyroxene 62 5 to 90 3 for clinopyroxene and 52 4 to 82 8 for amphibole mg s vary with height and display abrupt reversals which indicate open system addition of new mafic magma eleven cyclic units were identified on the basis of evidence for injection of basaltic magma these can be grouped into three megacyclic units the abundance of orthopyroxene and mineral compositional evidence for

the canada basin 1989 1995 upstream events and far field effects of the barents sea 1 the effects of upstream events on southern canada basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995 these events included atlantic layer warming relocation of the atlantic pacific water mass boundary and increased ventilation of boundary current waters early signals of change in the canada basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream differences in physical and geochemical properties nutrients oxygen 129i and cfcs were observed between 150 and 1600 m of the water column by 1995 the boundary between pacific and atlantic origin water was shallower and atlantic origin water occupied more of the canada basin water column atlantic origin lower halocline water was colder and more ventilated fram strait branch water was colder fresher and more ventilated and barents sea branch water was warmer fresher more ventilated and occupied a larger volume of the water column than in previous years water mass analysis showed that the composition of atlantic origin water in the canada basin in 1995 included 20 more water from the barents sea two related events upstream appear to be the source of this change an atmospheric regime shift in 1989 that increased cyclonic circulation a transition unprecedented within the latter half of the 20th century in magnitude geographic reach and apparent oceanographic impacts and a large volume of dense water flowed from the barents sea to the arctic ocean between 1988 and 1989 these two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the canada basin at depths 1000 m

discharge of hydrothermal fluids through sediment at the escanaba trough gorda ridge odp leg 169 assessing the effects on the rock magnetic signal an integrated rock magnetic and multivariate statistical analysis of a suite of sediment samples recovered from odp sites 1037 and 1038 leg 169 escanaba trough gorda ridge spreading center ne pacific ocean has been carried out to assess the use of the sediment magnetic signal as a tracer of post depositional alteration related to the discharge of hydrothermal fluids through these sediments the uppermost above 40 mbsf section of three separate holes holes 1037 b 1038 i and 1038 g was sampled previous sedimentological and geochemical studies indicated that these holes represent a transect from unaltered to strongly hydrothermally influenced sediments analysis of nrm arm anisotropy of magnetic susceptibility ams hysteresis parameters and low temperature magnetic properties suggest increasing alteration of the magnetic minerals with increasing circulation of hydrothermal circulation of fluids fuzzy c means clustering combined with non linear mapping yields a more elaborate picture because similar alteration groupings at different holes can be compared at hole 1037 b a sedimentary reference site drilled away from the area of high heat flow the rock magnetic signal is a sensitive record of changes in detrital inputs magnetite and some monoclinic pyrrhotite are detected the detrital magnetic signal is still apparent at intermediate hole 1038 i but cluster analysis detects an increasing hydrothermal influence on the magnetomineralogy in the lower part of the hole strong hydrothermal alteration at hole 1038 g results in a complete loss of the detrital diagenetic magnetic signal which is replaced by a much weaker hydrothermal signal composed of monoclinic pyrrhotite and pyrite the alteration of the magnetic signal is not restricted to the uppermost few meters of the sediment column and the magnetic properties of the sediment can be used to trace even minor alterations of marine sediments related to the lateral and vertical advection of hydrothermal fluids which may easily be overlooked by more traditional methods fl 2000 elsevier science b v all rights reserved

deep sea sedimentary record of the late wisconsin cataclysmic floods from the columbia river new results from ocean drilling program site 1037 and u s geological survey high resolution seismic reflection profiles confirm the great thickness fast deposition rate distant source and convolute path of turbidites that fill the escanaba trough the rift valley of the southernmost segment of the gorda ridge accelerator mass spectrometry 14 c measurements provide the first direct dating of the escanaba trough turbidites demonstrating an average deposition rate faster than 10 m k y between 32 and 11 ka and as fast as 15 m k y during the oxygen isotope stage 2 lowstand in the upper 60 m of sediment the petrology of turbidite sand beds which are as much as 12 m thick show that the dominant source for the turbidites is from the columbia river which is more than 800 km to the north rather than from the much closer rivers of northern california new high resolution seismic reflection profiles show that except for areas of very recent volcanism the entire escanaba trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at site 1037b the ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest quaternary jokulhlaups from glacial lake missoula the age and source characteristics suggest that these megaturbidite beds in escanaba trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the lake missoula floods entered the sea

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

magnetic characterization of holocene sedimentation in the south atlantic surface sediment samples representative for the tropical and subtropical south atlantic 15 n to 40 s were investigated by isothermal magnetic methods to delineate magnetic mineral distribution patterns and to identify their predominant holocene climatic and oceanographic controls individual parameters reveal distinct yet frequently overlapping regional sedimentation characteristics a probabilistic fuzzy c means cluster analysis was applied to five concentration independent magnetic properties assessing magnetite to hematite ratios and diagnostic of bulk and fine particle magnetite grain size and coercivity spectra the resultant 10 cluster structures establish an oceanwide magnetic sediment classification scheme tracing the major terrigenous eolian and fluvial fluxes authigenic biogenic magnetite accumulation in high productivity areas transport by ocean current systems and effects of bottom water velocity on depositional regimes distinct dissimilarities in magnetic mineral inventories between the eastern and western basins of the south atlantic reflect prominent contrasts of both oceanic and continental influences

u th pb rb sr and ar ar mineral and whole rock isotopic systematics in a metamorphosed granitic terrane southeastern california mesozoic structural domes are developed in an older proterozoic crystalline basement of granitic to granodioritic foliate metaplutonic rocks in the halloran hills southeastern california isotopic analyses of whole rocks and mineral separates from these rocks by u th pb rb sr and ar ar techniques yield a complex pattern of discordance that is the result of a fairly simple geologic history individual mineral isotopic systems have variably equilibrated with each other in response to mesozoic regional metamorphism and locally to later heating during mesozoic batholith emplacement discordant u th pb zircon data indicate that the granitic core rocks are 1 710 ma and that one dioritic phase may be slightly older rb sr whole rock model dates scatter about 1 700 ma rb sr amphibole whole rock and u th pb amphibole dates are also proterozoic potassium feldspars retain a 207 pb 206 pb signature of their proterozoic age ar ar amphibole spectra from the flank of the main dome reveal disturbed dates of 1 450 ma to 1 100 ma and the dates become younger toward the structurally deeper core of the dome all remaining isotopic determinations yield mesozoic or younger dates for mineral whole rock systems rb sr whole rock apatite feldspar biotite analyses show nonequilibration of strontium isotopes with resultant mineral pair dates from 4 foliate plutonic rocks ranging from 200 to 50 ma no single metamorphic age is indicated by the rb sr data rb sr whole rock biotite dates are consistently younger than any other determinations and may be reduced by weathering or gain of nonradiogenic strontium from ground water u pb sphene and apatite analyses from rocks that yield 1 710 ma zircon dates are nearly concordant at 140 ma an amphibole from the structurally deepest rocks of the main dome that yield 140 to 150 ma u pb sphene dates has an ar ar plateau date of 144 ma the u pb sphene and ar ar amphibole analyses are believed to be the best age estimate for the end of the highest temperature phase of regional metamorphism th pb sphene and apatite dates and ar ar biotite dates cluster at 90 5 ma as a consequence of regional cooling during late cretaceous time following extensive mesozoic plutonism in the region at 97 to 90 ma we interpret the discordant mineral date patterns to have resulted from metamorphism of 1 700 ma plutonic rocks during the jurassic 140 50 ma and subsequent uplift and cooling to 200 c at about 90 ma on the basis of this study the isotope dating systems ranked in decreasing order of resistance to resetting are u th pb zircon concordia intercept rb sr whole rock rb sr amphibole u th pb amphibole pb pb whole rock ar ar amphibole rb sr sphene u pb sphene and apatite rb sr plagioclase potassium feldspar apatite th pb sphene and apatite ar ar biotite u pb feldspars rb sr biotite

the neoproterozoic noonday formation death valley region california the neoproterozoic cambrian succession in the death valley region of the southwestern united states is among the best exposed and easily accessible in the world the largest single exposure of these strata occurs in the panamint range on the west side of death valley and it although variably metamorphosed contains the most complete sections of the noonday formation cap carbonate sequence new geological mapping measured sections and high resolution carbon isotope data for the noonday formation in this range enable establishment of a unified stratigraphy across the death valley region that consists of three units from the base upward they include the sentinel peak member of light gray massive to laminated fine dolostone locally containing vugs and tubes variably filled with micrite spar or quartz and rarely galena and varying from 2 to 200 m in thickness the radcliff member composed of feldspathic shale and sandstone and thin bedded limestone 0 200 m thick and the newly defined mahogany flats member of gray commonly stromatolitic thin to medium bedded fine dolostone that is 200 m thick at its type locality carbon isotopic trends in the panamint range match to within 1 2 reproducibility those known for the equivalent nonmetamorphosed strata in the eastern death valley sections a composite section of the noonday formation displays a chemostratigraphic profile with values near 3 through the cap dolostone of the sentinel peak member a decline to 6 in the lower part of the radcliff member followed by a recovery to near 0 and subsequent decline toward 2 in the remainder of the radcliff units and lower mahogany flats member and then a return to positive values 4 through the remainder of the mahogany flats member this pattern matches the ediacaran cap carbonate in namibia remarkably well and assuming our carbon isotopic correlations are correct it indicates that noonday deposition occurred at the beginning of the ediacaran period and that the immediately underlying wildrose diamictite of the kingston peak formation probably represents the younger cryogenian marinoan glacial episode

origin of the sedimentary magnetic record at ocean drilling program sites on the owen ridge western arabian sea the 3 2 m y whole core magnetic susceptibility record obtained during ocean drilling program leg 117 from the owen ridge in the western arabian sea represents one of the most convincing demonstrations of the ability of rock magnetic measurements to yield paleoceanographically significant information the salient features of this record are that 1 it correlates strongly with variations in the concentration and flux of eolian dust 2 it is driven strongly at earth orbital periodicities and 3 there is a significant change in the spectral character at 2 4 m y which may reflect the effect of the initiation of major northern hemisphere glaciation on aridity cycles within the eolian source areas in view of its potential paleoclimatic significance we have examined the origin of the rock magnetic signal from the owen ridge in more detail we find that despite the strong relationship throughout the record between magnetic susceptibility and percent terrigenous content there has been significant postdepositional alteration of the magnetic minerals via the process of reductive diagenesis we ascribe two steplike shifts in magnetic properties in the uppermost part of the section to this process the first occurs at about 1 5 m depth and is characterized by a loss of fine grained ferrimagnetic material the second stepshift in magnetic properties occurs at a depth of 6 8 m and is characterized by changes in rock magnetic parameters which indicate significant loss of both low coercivity magnetite and high coercivity hematite and or goethite magnetic mineral components scanning electron microscope and energy dispersive xray analyses show that the bulk of the coarse grained strongly magnetic fraction is detrital titanomagnetite and that there is a significant reduction in the fe ti ratio of these grains across the lower diagenetic front this suggests that titanomagnetite grains with higher ti contents may be more resistant to the process of reductive diagenesis and this may provide a mechanism for the relative stability of the ferrimagnetic fraction below the second diagenetic front

wind forced upwelling and internal kelvin wave generation in mackenzie canyon beaufort sea low frequency current temperature and salinity variations over the shelf break in the southeastern beaufort sea mackenzie shelf are examined to determine the response of seasonally ice free waters to wind forcing and the role of submarine canyons in upwelling events and shelf circulation upwelling events were found to be statistically correlated to northeasterly winds which transport surface waters offshore and draw up water from deeper layers the response to alongshore wind stress is significantly amplified in mackenzie canyon where isopycnal displacements of over 400 m are observed such displacements are then observed to propagate eastward at a phase velocity near 0 6 m s 1 the canyon is thus a site of intense upwelling while the collapse of displaced isopycnals subsequent to cessation of wind forcing creates a disturbance propagating northeast along shelf as a free internal kelvin wave

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

remagnetization and chemical alteration of sedimentary rocks remagnetization is a common phenomenon in rocks and developing a greater understanding of its mechanisms has several benefits acquisition of a secondary magnetization is usually tangible evidence of a diagenetic or thermal event which can be dated using palaeomagnetic techniques this is important because the timing of diagenetic and thermal events is commonly difficult to determine remagnetization can also obscure primary magnetizations and a better understanding of remagnetization could improve our ability to uncover primary magnetizations many chemical remagnetization mechanisms have been proposed including those associated with chemical alteration by a number of different fluids e g orogenic weathering mineralizing hydrocarbons and burial diagenetic processes e g clay diagenesis maturation of organic matter this book contains case studies and review articles that focus on remagnetization chemical remagnetization mechanisms and magnetic changes associated with chemical alteration by hydrocarbons

storm induced upwelling of high pco2 waters onto the continental shelf of the western arctic ocean and implications for carbonate mineral saturation states 1 the carbon system of the western arctic ocean is undergoing a rapid transition as sea ice extent and thickness decline these processes are dynamically forcing the region with unknown consequences for co2 fluxes and carbonate mineral saturation states particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors in october 2011 persistent wind driven upwelling occurred in open water along the continental shelf of the beaufort sea in the western arctic ocean during this time cold 32 4 halocline water supersaturated with respect to atmospheric co2 pco2 550 atm and undersaturated in aragonite aragonite 1 0 was transported onto the beaufort shelf a single 10 day event led to the outgassing of 0 18 0 54 tg c and caused aragonite undersaturations throughout the water column over the shelf if we assume a conservative estimate of four such upwelling events each year then the annual flux to the atmosphere would be 0 72 2 16 tg c which is approximately the total annual sink of co2 in the beaufort sea from primary production although a natural process these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region and could have significant impacts on regional carbon budgets as sea ice retreat continues and storms increase in frequency and intensity further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable

wind driven shelf basin exchange on an arctic shelf the joint roles of ice cover extent and shelf break bathymetry 1 the efficiency of shelf basin exchange sbe in polar regions during summer is strongly moderated by the location of the ice edge relative to underlying topography numerical model calculations suggest that upwelling favorable winds generate very little sbe so long as the ice edge remains shoreward of the shelf break but an abrupt onset of shelf break upwelling takes place when the ice edge retreats beyond the shelf break a climatology 1968 2000 of ice conditions from the canadian shelf of the beaufort sea shows large interannual variability in ice edge extent and duration of ice free conditions in summer similarly available hydrographic data reflect a corresponding variability in water mass properties under scenarios of climate warming associated with greenhouse gas build up both the extent and duration of summer melt back are predicted to increase and this may have dramatic impacts on sbe and biological productivity

cyclostratigraphy and rock magnetic investigation of the nrm signal in late miocene palustrine alluvial deposits of the librilla section se spain 1 we constructed a high resolution time frame for the cyclic continental palustrine alluvial section of librilla se spain which covers the onset of the messinian salinity crisis in the marine realm the section was dated earlier by garces et al 1998 using magnetostratigraphy we resampled part of the section that contained a reversed overprint in detail to refine the magnetostratigraphy and to investigate the behavior of the natural remanent magnetization nrm signal the detailed sampling yielded a better constrained position of the upper reversal of chron c3an 1n by counting the number of cycles in c3an 1n and taking into account the duration of this chron we were able to show that the basic sedimentary cycles in librilla reflect climatic precession subsequently the sedimentary pattern was tuned to the summer insolation curve providing a high resolution time two intervals of complex nrm behavior were identified showing normal and reversed overprints the reversed overprints seemed to be restricted mainly to gray palustrine layers the analysis of coercivity components revealed no difference between samples with overprints or real nrm directions we performed fuzzy c means cluster analysis on a geochemical data set to link magnetic behavior to geochemical proxies resulting in a three cluster model that roughly describes lithology remarkably all the samples with a normal overprint belong to one particular cluster the reversed overprints however do not show any relation to the cluster partition we favor the explanation of garces et al 1998 that the reversed overprint would be related to the messinian salinity crisis

geochemistry and petrogenesis of proterozoic diabase in the southern death valley region of california diabase sills and dikes of proterozoic age intrude crystalline basement and the overlying crystal spring formation in the southern death valley region of california despite pervasive deuteric alteration analyses of relict plagioclase an66 45 titaniferous augite and ilmenite permit the calculation of initial crystallization temperatures of 1 165 25 c for plagioclase and 1 110 25 c for augite with an oxygen fugacity of 10 11 atm the early crystallization of plagioclase is consistent with the generally subophitic texture of the diabase

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

a neoproterozoic ice advance sequence sperry wash california the kingston peak formation is an archetypal cryogenian succession that crops out across the death valley region of eastern california above pre glacial strata kp1 two distinct glacial phases have been recognized and are interpreted to be allied to the panglacial sturtian kp2 and kp3 and marinoan kp4 icehouse events the thickest and most extensive unit kp3 forms the entire exposed section at sperry wash at this locality ice distal turbidites are succeeded in turn by ice medial and ice proximal facies comprising a spectrum of ice rafted debris bearing turbidites debrites and shales these are overlain by ice marginal grounding line fan deposits interbedded with glacitectonically deformed heterolithics supporting local advance to an ice contact position the succession records accumulation within a glacier fed subaqueous shelf wherein the clear progradational signature is driven by ice advance towards the south east evolution of the subaqueous complex is five fold comprising i ice distal outwash ii build out of ice medial depositional lobes iii ice proximal deposition and increased calving iv resumed ice margin advance and v growth of ice contact grounding line fan this sequence is unique in the death valley region for recording the first evidence of advance to ice marginal and ice contact settings thereby enabling the location of the glacier terminus to be documented for the first time

zircon saturation in lunar basalts and granites the saturation surface for zircon in late stage lunar basalts and granites has been determined over the temperature range1400 1070 c the saturation surface in the basalt shows a strong temperature dependence from 1400 to 1200 c below 1200 the saturation surface turns down sharply and becomes nearly temperature independent the saturation surface in the granitic composition is similar to the basaltic composition although less zr is required for saturation at 1100 c 9000 ppm zr and 5000 ppm zr are required for zircon saturation in the basalt and granite respectively if a magma with chondritic zr content is assumed then zircon saturation would not be reached until 99 96 99 92 crystallization this precludes zircon crystallization playing a major role in the trace element evolution of lunar magmas

tracking provenance change during the late miocene in the eastern mediterranean using geochemical and environmental magnetic parameters 1 marls of the metochia section gavdos greece have been analyzed using geochemistry environmental magnetism and diffuse reflectance spectrometry to study late miocene paleoenvironmental changes in the eastern mediterranean region fuzzy c means cluster analysis fcm combined with nonlinear mapping nlm has been performed on a multiparameter data set to identify and characterize terrigenous source areas from north africa and the aegean margin the parameters included in the fcm were selected on the basis of their univariate characteristics and their ability to trace input changes from regional source areas the hard isothermal remanent magnetization hirm calculated on a carbonate free basis and the ti al ratio are used to distinguish aeolian dust and transport mechanisms of material originating from north africa mass accumulation rates of al and ni are employed to represent the input of terrigenous material originating from the aegean region caco3 calculated from ca abundance provides information concerning marine productivity and mn al is used to trace reductive diagenesis in the marls after performing the fcm and nlm analysis a four cluster solution has the greatest stability and describes paleoenvironmental changes in both the african and european source areas the cluster solution clearly reveals the change from input dominated by terrigenous material in the lower parts of the metochia section to marine input at the top of the section but also reveals changes in paleoenvironmental conditions in north africa from arid to more humid conditions at 8 2 ma

atmospheric driven state transfer of shore fast ice in the northeastern kara sea received 9 september 2004 revised 19 april 2005 accepted 2 june 2005 published 21 september 2005 1 frequencies of observed occurrences of shore fast ice in the northeastern kara sea for each month during 1953 1990 reveal a multimodality of shore fast ice extent in late winter and spring the fast ice extent exhibits mainly three different configurations modes associated with the regional topography of coasts and islands these modes show fast ice areas equal to approximately 98 6 122 6 and 136 8 1000 km 2 analysis of the time series of fast ice extent shows that favorable conditions for expansion of fast ice seaward in winter and spring are met if the atmospheric circulation over the northeastern kara sea is controlled by the arctic high resulting in offshore winds and a significant up to 6 c decrease of the monthly mean surface air temperature in contrast the penetration of the icelandic low into the kara sea accompanied by arctic cyclones coming from the west is responsible for the partial breakup and decrease of fast ice extent in winter or spring

wind driven transport pathways for eurasian arctic river discharge distributions of temperature salinity and barium in near surface waters depth 50 m of the laptev sea and adjacent areas of the arctic ocean are presented for the summers of 1993 1995 and 1996 the tracer data indicate that while fluvial discharge was largely confined to the shelf region of the laptev sea in the summer of 1993 surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the laptev sea in the summers of 1995 and 1996 these distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central arctic basins from the laptev sea when southerly to southeasterly wind conditions prevail river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas these waters can then enter the interior arctic ocean via upper layer flow in the vicinity of the lomonosov ridge under other wind conditions river waters are steered primarily along the inner laptev shelf and into the east siberian sea as part of the predominantly eastward coastal current system these waters then appear to cross the shelf and enter the interior arctic ocean via upper layer flow aligned roughly along the mendeleyev ridge the extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle

cross shelf transport of warm and saline water in response to sea ice drift on the laptev sea shelf 1 oceanographic moorings and conductivity temperature depth ctd surveys from september 2009 to september 2010 are used to describe recent changes in the laptev sea hydrography and to highlight wind and ice driven surface ekman transport as the mechanism to translate these changes from the outer to the inner shelf bottom waters in february 2010 moored oceanographic instruments recorded a sudden increase in temperature 0 8 c and salinity 3 near the bottom of the inner laptev sea shelf such warm and saline waters had not been previously observed on the inner shelf in winter they likely originated from the basin and were first observed during a summer 2009 ctd survey in the northwestern shelf break region subsequently spreading east and shoreward across the laptev sea shelf the changes were introduced to the mooring site by the first of a series of bottom intensified flow events with velocities reaching 20 cm s 1 topographically guided along a relic submarine river valley each of the flow events coincided with negative pressure anomalies at the mooring site and offshore directed upwelling favorable winds and ice drift we suggest that the observations to first order resemble a simplified two dimensional two layered ocean where offshore surface ekman transport is compensated for by a barotropic shoreward response flow near the bottom in this paper we use one of the first comprehensive long term laptev sea datasets to highlight ice ocean atmosphere interactions in early and late winter and discuss the role of freshwater stratification and ice mobility on under ice circulation on the laptev sea shelf

two diamictites two cap carbonates two δ13c excursions two rifts the neoproterozoic kingston peak formation death valley california stratigraphic mapping of the neoproterozoic glaciogenic kingston peak formation death valley california provides evidence for two temporally discrete extensional deformation episodes these episodes are bracketed by the sourdough limestone and noonday dolomite the facies characteristics and 13 c data ranging between 2 15 and 2 56 and 1 88 and 4 86 respectively of which make them equivalent to sturtian and varangian age cap carbonates respectively this constrains the two extensional episodes along the southwestern margin of laurentia to ca 700 ma and ca 600 ma these observations and data show that the field evidence for mid neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest neoproterozoic breakup are both correct thus neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m y or more confining rifting to within the kingston peak formation thereby places the younger proterozoic rocks of the southwestern great basin in the rift to drift tectonic phase

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

a diamictite dichotomy glacial conveyor belts and olistostromes in the neoproterozoic of death valley california usa multiple intercalations of glacially derived and slope derived diamictites testify to the drawbacks of correlating neoproterozoic diamictites more widely but shed new light on the close interrelationship of these processes in the cryogenian world in the neoproterozoic of death valley california usa rifting of rodinia occurred concomitantly with a major glacial event that deposited the kingston peak formation a new sedimentologic investigation of this formation in the silurian hills demonstrates for the first time that some diamictites are ultimately of glacial origin abundant dropstone textures occur in interstratified heterolithic deposits with clasts of identical composition gneiss schist granite metabasite quartzite to those of boulder bearing diamictites suggesting a common source the glacial conveyor belt in stark contrast megaclast bearing diamictites yielding clasts of carbonate and siliciclastic preglacial strata as much as 100 m across are interpreted as olistostromes the occurrence of syn sedimentary faults within the succession allows glacial versus slope derived material to be distinguished for the first time

transport processes in the kara sea field data from late summer cruises in 1993 1996 and results from a rotating laboratory model study are used to infer transport routes for contaminants in the kara sea on the western siberian coast the data show a circulation pattern that differs significantly from published concepts and contains a richer structure both the inflowing coastal water from the west and the modified atlantic water from the barents sea and the arctic ocean in the north affect the water properties of the east novaya zemlya trough through mixing intrusion and possible transformation during winter convection much of the current structure can be explained as a result of topographical steering of the throughflows weak summer winds of variable direction affect only the upper layer whereas persistent strong winds may affect long term circulation patterns and transports the main outflow routes are north to the santa anna trough and northeast to the voronin trough the outflowing surface water and ice to the north are expected to join the inflowing polar water from the arctic ocean that forms the persey current into the barents sea deeper outflows are expected to follow the continental slope to the east in the arctic ocean the laboratory model has been validated to earlier current measurements to the north and south of novaya zemlya and shows several of the features observed in the newer field measurements this suggests that the dynamic similitude and boundary forcing of the model are good two notable exceptions are the westward transport of drifting buoys to the north of novaya zemlya and the late winter hydrography to the north of the ob and yenisey estuaries both are probably due to persistent winds the conclusions from the measured and modeled currents are supported by measurements of 137cs in the seawater and sediments

connections among ice runoff and atmospheric forcing in the beaufort gyre during sheba thin ice and freshening of the arctic ocean surface in the beaufort sea led to speculation that perennial sea ice was disappearing mcphee et al 1998 since 1987 we have collected salinity 18o and ba profiles near the initial sheba site and in 1997 we ran a section out to sheba resolving fresh water into runoff and ice melt we found a large background of mackenzie river water with exceptional amounts in 1997 explaining much of the freshening at sheba ice melt went through a dramatic 4 6 m jump in the early 1990s coinciding with the atmospheric pressure field and sea ice circulation becoming more cyclonic the increase in sea ice melt appears to be a thermal and mechanical response to a circulation regime shift should atmospheric circulation revert to the more anticyclonic mode ice conditions can also be expected to revert although not necessarily to previous conditions

mechanisms of pacific summer water variability in the arctic s central canada basin pacific water flows northward through bering strait and penetrates the arctic ocean halocline throughout the canadian basin sector of the arctic in summer pacific summer water psw is modified by surface buoyancy fluxes and mixing as it crosses the shallow chukchi sea before entering the deep ocean measurements from ice tethered profilers moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the psw component of the halocline in the central canada basin with increasing trends in integrated heat and freshwater content a consequence of psw layer thickening as well as layer freshening and warming it is shown here how properties in the chukchi sea in summer control the temperature salinity properties of psw in the interior by subduction at isopycnals that outcrop in the chukchi sea results of an ocean model forced by idealized winds provide support to the mechanism of surface ocean ekman transport convergence maintaining psw ventilation of the halocline

precambrian olistoliths masquerading as sills from death valley california olistolith production and magmatism are processes commonly associated with extensional tectonic settings such as rift basins we present a cautionary exemplar from one such precambrian basin in which we reinterpret metabasite bodies previously documented as sills to be olistoliths we nevertheless demonstrate that on the basis of field observation alone the previous but erroneous sill interpretation is parsimonious indeed it is only by using isotopic age and compositional analysis that the true identities of these metabasite olistoliths are revealed we present new data from metabasites and metasedimentary strata of the kingston peak formation cryogenian and crystal spring formation mesoproterozoic of death valley usa these include field observations u pb apatite ages u pb zircon ages detrital and igneous and whole rock geochemistry these data also provide a new maximum age for the base of the pahrump group and suggest that the crystal spring diabase was more tholeiitic than previously thought similar sill olistolith misinterpretations may have occurred elsewhere potentially producing erroneous age and tectonic setting interpretations of surrounding strata this is particularly relevant in precambrian rocks where fossil age constraints are rare this is illustrated herein using a potential example from the neoproterozoic literature of the lufilian belt africa we caution others against precambrian olistoliths masquerading as sills supplementary material details of a meta igneous boulder from p12 of the silurian hills la icp ms and whole rock geochemistry methods and standards and u pb apatite and zircon isotopic data including standards and selected cathodoluminescence images are available at https doi org 10 6084 m9 figshare c 3990639

the siberian coastal current a wind and buoyancy forced arctic coastal current we describe circulation and mixing in the siberian coastal current scc using fall shipboard measurements collected between 1992 and 1995 in the western chukchi sea the scc forced by winds siberian river outflows and ice melt flows eastward from the east siberian sea it is bounded offshore by a broad 60 km front separating cold dilute siberian coastal water from warmer saltier bering sea water the alongshore flow is incoherent because the current contains energetic eddies and squirts probably generated by frontal baroclinic instabilities these enhance horizontal mixing and weaken the cross shore density gradient along the scc path eventually the scc converges with the northward flow from bering strait whereupon it deflects offshore and mixes with that inflow deflection occurs where the alongshore pressure gradient vanishes that location varies on synoptic and seasonal timescales because this gradient depends on the winds buoyancy fluxes and the sea level difference between the pacific and arctic oceans deflection usually occurs on the chukchi shelf but the scc occasionally flows southward through bering strait such events are short lived 1 10 days and occur mainly in fall and winter under northerly winds scc transport is likely small 0 1 sv but its dilute waters could substantially freshen the bering strait inflow and affect the disposition of pacific waters in the arctic ocean arctic river outflows should preferentially form surface advected fronts rather than bottom advected fronts because vertical mixing energy is low on arctic shelves surface advected fronts are more susceptible to upwelling winds and for the scc the pressure gradient between the pacific and arctic oceans than bottom advected fronts the scc never developed in fall 1995 because of anomalously steady upwelling winds the western chukchi shelf could have formed upper halocline source water in the winter of 1995 1996

the contiguous panarctic riverine coastal domain a unifying concept the riverine coastal domain rcd is a narrow 15 km shallow 10 m contiguous feature that is primarily forced driven by an aggregate of continental runoff sources and which extends clockwise 10 103 km around northern north america we hypothesize that a similar feature extends around northern eurasia the rcd carries a terrestrial signal that affects light nutrient and carbon regimes and provides a coastal pathway for the dispersal and migration of marine biota the physical and biogeochemical variables within the rcd yield a contiguous gradient of environmental conditions along and across the panarctic coastal zone the rcd acts as the initial connector between terrestrial and marine ecosystems and may become even more prominent as terrestrial runoff permafrost thawing and local ice melt are assumed to increase in the near future climate

neoproterozoic ice sheets and olistoliths multiple glacial cycles in the kingston peak formation california the kingston peak formation is a diamictite bearing succession that crops out in the death valley region california usa an exceptionally thick 1 5 km outcrop belt in its type area the kingston range provides clear insights into the dynamics of mid cryogenian sturtian ice sheets in laurentia seven detailed logs allow the lateral and vertical distribution of facies associations to be assessed we recognize 1 diamictite facies association ice proximal glacigenic debris flows 2 lonestone bearing facies association ice marginal hemipelagic deposits and low density gravity flows with iceberg rafting 3 pebble to boulder conglomerate facies association ice proximal cogenetic glacigenic debris flows and high density turbidites 4 megaclast facies association olistostrome and hemipelagic sediments subject to ice rafting and 5 interbedded heterolithics facies association low density turbidites and hemipelagic deposits the stratigraphic motif allows three glacial cycles to be inferred across the range ice minimum conditions interrupting the kingston peak succession are associated with the development of an olistostrome complex succeeded by a thick accumulation of boulder conglomerates deposited during ice readvance the data testify to a strong glacial influence on sedimentation within this ancient subaqueous succession and to highly dynamic ice sheet behaviour with clear glacial cycles during the sturtian glaciation

magnetic mineral diagenesis in suboxic sediments at bettis site w n ne pacific ocean the effects of iron diagenesis on paleomagnetism and rock magnetism were examined in suboxic sediments from bettis site w n in the ne pacific ocean as part of the oxidative decomposition of organic matter ultrafine grained authigenic magnetites are produced immediately above the iron reduction zone this zone is commonly observed in deep sea sediments as a prominent color change from brown to greenish grey the magnetite authigenesis is evidenced by systematic increases in natural magnetic intensities and stabilities and by comparable shifts in other rock magnetic properties the magnetites are composed of relatively pure fe3o4 and fall within a restricted size range of 0 06 0 12 m which is nominally single domain some of these finest grained magnetites are rapidly destroyed during burial upon entering the zone of iron reduction leaving a relatively coarser population magnetite dissolution appears to continue with depth according to a first order surface area reaction process when at steady state iron reduction is independent of sulfide formation in these sediments because solid sulfur profiles show no increase at depth and most of the sulfur occurs as barite despite a well constrained carbonate stratigraphy comparisons of paleomagnetic directions between nearby cores show little agreement suggesting that the directions are composed of a complex mixture of remanences acquired at different depths subsurface magnetic peaks may represent paleoredox markers preserved by non steady state redox conditions caused by climatically induced variations in organic matter flux and sedimentation rates

kugmallit valley as a conduit for cross shelf exchange on the mackenzie shelf in the beaufort sea 1 kugmallit valley spans the midsection of a transect across the mackenzie shelf of the beaufort sea its greatest relief is 20 m and its width is 20 km using a yearlong record of ice drift ocean current temperature and salinity acquired near the center of the valley we describe a pattern of flow that is correlated with wind stress and ice motion and discuss its similarity to flow within larger submarine canyons that cut through the shelf break as in such canyons there is enhanced cross shelf transport within kugmallit valley during upwelling favorable surface stress the data also document the down valley flow of dense water from a flaw lead

integration of diverse physical property models subsurface zonation and petrophysical parameter estimation based on fuzzy c means cluster analyses inversions of an individual geophysical data set can be highly nonunique and it is generally difficult to determine petrophysical parameters from geophysical data we show that both issues can be addressed by adopting a statistical multiparameter approach that requires the acquisition processing and separate inversion of two or more types of geophysical data to combine information contained in the physical property models that result from inverting the individual data sets and to estimate the spatial distribution of petrophysical parameters in regions where they are known at only a few locations we demonstrate the potential of the fuzzy c means fcm clustering technique after testing this new approach on synthetic data we apply it to limited crosshole georadar crosshole seismic gamma log and slug test data acquired within a shallow alluvial aquifer the derived multiparameter model effectively outlines the major sedimentary units observed in numerous boreholes and provides plausible estimates

a late diagenetic syn folding magnetization carried by pyrrhotite implications for paleomagnetic studies from magnetic iron sulphide bearing sediments paleomagnetic rock magnetic and sedimentary micro textural data from an early miocene mudstone sequence exposed in okhta river sakhalin russia indicate the presence of pyrrhotite and magnetite at different stratigraphic levels sites that contain only magnetite have a reversed polarity characteristic remanent magnetization chrm with a low coercivity overprint which coincides with the present day geomagnetic field direction pyrrhotite bearing sites have stable normal polarity chrms that are significantly different from the present day field direction after correction for bedding tilt the chrm data fail a reversals test however the normal polarity pyrrhotite chrm directions become antipodal to the tilt corrected magnetite chrm directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40 partial unfolding these data suggest that the pyrrhotite magnetization was acquired during folding and after lock in of the magnetite remanences electron microscope observations of polished sections indicate that fluid associated halos surround iron sulphide nodules pyrrhotite is present in randomly oriented laths in and around the nodules and the nodules do not appear to have been deformed by sediment compaction this observation is consistent with a late diagenetic origin of pyrrhotite documentation of a late diagenetic magnetization in pyrrhotite bearing sediments here and in recent studies of greigite bearing sediments suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn depositional magnetization

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

the arctic circumpolar boundary current abstract the main water transformations in the arctic mediterranean take place in the boundary current of atlantic water which crosses the greenland scotland ridge from the north atlantic into the eastern norwegian sea it enters and flows around the arctic ocean before it exits the arctic mediterranean as the east greenland current primarily through denmark strait on route it experiences numerous branchings and mergings by examining how the properties of this circumpolar boundary current evolve it is possible to identify and describe the processes causing the water mass transformations in the arctic mediterranean it is also possible to follow the arctic ocean deep waters as they spread into the nordic seas and eventually provide 40 of the overflow water supplying the north atlantic deep water