upper miocene magnetic stratigraphy at odp site 1092 sub antarctic south atlantic recognition of cryptochrons in c5n 2n summary u channel samples from odp site 1092 in the sub antarctic south atlantic ocean provide an interpretable magnetic stratigraphy from 1 95 to 3 6 ma and from 5 9 to 13 5 ma although the interpretation is unclear within the gilbert chron c3 the record represents one of the more complete upper miocene polarity stratigraphies from the south atlantic eight polarity subchrons that are not included in the standard polarity timescale are identified polarity subchron c4r 2r contains a normal polarity interval that has also been identified in sediments from odp leg 138 three short subchrons are recorded within c4n 2n c5r 3r and c5aar the record of c5n 2n contains four short reverse polarity subchrons of durations estimated to be 3 6 kyr

southern ocean frontal system changes precede antarctic ice sheet growth during the middle miocene abstract the middle miocene climate approximately 14 ma ago was characterized by the glaciation of antarctica deep ocean cooling and variations in the global carbon cycle although the southern ocean underwent significant oceanographic changes there is limited information on their spatial extent and timing however such knowledge is crucial for understanding the role of the southern ocean and the antarctic circumpolar current acc for antarctic glaciation and the coupling between the ocean and continental climate we have reconstructed surface temperatures and seawater oxygen isotopes at ocean drilling program odp site 1092 in the polar frontal zone of the atlantic sector of the southern ocean from foraminiferal oxygen isotopes 18 o and magnesium to calcium ratios mg ca sea surface cooling by 4 c and freshening indicated by the 1 reduction of seawater 18 o 18 o sw at 14 2 ma precede the major step in antarctic ice sheet growth at 13 8 13 9 ma this pattern qualitatively mirrors previous findings from the pacific sector and we interpret the surface hydrographic changes to reflect the circum antarctic northward shift of the southern ocean fronts and specifically at site 1092 the passage of the subantarctic front the magnitude of change in reconstructed 18 o sw requires a 18 o sw salinity gradient significantly higher than the modern value 0 52 and it possibly exceeded 1 1 this implies the polar frontal zone was influenced by freshwater derived from antarctica which in turn confirms higher than modern continental precipitation the latter has previously been suggested to have contributed to antarctic glaciation

possible crustal contamination of midcontinent rift igneous rocks examples from the mineral lake intrusions wisconsin interlayered mafic telsic intrusions from the mineral lake intrusive complex in northwest wisconsin reflect the typical bimodal basalt rhyolite compositional pattern of the midcontinent rift flood

the skaergaard layered series part vi excluded trace elements in contrast to the smooth trends of major elements and mineral principal minerals of the skaergaard layered series my purpose here is to examine the corresponding excluded compositions the excluded trace elements in the skaergaard layered series have an irregular distribution that does not conform to the elements and their relations to progressive differentiation of the skaergaard magma the principal conclusion that normal trends of rayleigh type fractionation their concentrations are about constant or even decline through the lower and middle will emerge is that the trends of enrichment of these elements differ markedly from those of the major elezones before increasing sharply to reach maximum concentrations 100 200 m above the sandwich horizon as in the case of ments possibly because their distribution was affected by a build up and eventual exsolution of volatile comincluded elements the relative concentrations of excluded elements in coexisting phases deviate widely from those predicted by exponents in the magma it will also be shown that the observed partition coefficients differ widely from those perimentally determined partition coefficients under presumed magmatic conditions this is seen most clearly in the immiscible predicted from experimental studies several earlier studies addressed various aspects of the melanogranophyres and conjugate ferrogabbros although the major elements conform to the experimentally determined relations for skaergaard trace elements haskin and his co workers haskin haskin 1968 paster et al 1974 were the first immiscible liquids the trace elements do not they follow a totally independent trend the abrupt increase in the concentrations of to attempt to reconcile the distribution of excluded trace elements with earlier interpretations of trace element excluded elements in the upper part of the intrusion could plausibly be attributed to an addition of new magma or to a density inversion behavior during crystallization and differentiation of the layered series other previous work has been sumthat resulted in upward migration of a late liquid or fluid but these possibilities are inconsistent with the compositional and spatial marized by wager brown 1968 and more recently by mcbirney 1996 1998a relations of the upper parts of the intrusion although a late residual liquid certainly migrated upward the most likely explanation for the structural form of the intrusion and its principal units illustrated in simplified form in fig 1 have already the observed distribution of excluded elements is that the partition coefficients were altered by volatile components which gradually been described at length mcbirney 1989 1995 1996 boudreau mcbirney 1997 mcbirney nicolas 1997 increased during the early stages of crystallization then began to exsolve near the top of the middle zone sonnenthal mcbirney 1998 and need not be repeated apart from minor differences noted in the appendix the distribution and selection of samples as well as the methods by which they have been analyzed are essentially the same as those described in part v of this

alkalic to transitional ferrogabbro magma associated with paleohelikian anorthositic plutons in the flowers river area southeastern nain igneous complex labrador fine grained gabbroic chilled margins and crosscutting dikes are associated in space and time with three ca 1400 ma anorthositic plutons in the flowers river area southeastern nain igneous complex both the anorthositic and gabbroic rocks have distinctive compositions compared to rocks of similar age and lithology elsewhere in northcentral labrador the anorthositic rocks contain olivine and augite rather than orthopyroxene and fe ti oxides apatite and orthoclase are unusually abundant cumulus plagioclase is abnormally enriched in incompatible elements most of the gabbroic rocks are uniform in composition although the effects of contamination and fractionation are evident in some places they define a transitional to alkalic ferrogabbro magma that is strongly enriched in k p and incompatible trace elements the chemical characteristics of the ferrogabbro magma imply derivation from enriched mantle or involvement of a significant crustal component a parent daughter relationship between the ferrogabbro magma and anorthositic rocks is suggested by their compositional similarities and the fact that the gabbroic chilled margins and plagioclase rich pluton interiors appear to be completely gradational in composition and texture

do critical stresses for incipient motion and erosion really exist the concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed observational definitions of incipient motion are many and not entirely compatible some laboratory flume observations of sediment movement suggest that no true threshold exists current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time mean velocities a combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept

geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part ii ree and the trapped liquid fraction rare earth elements in bulk cumulates and in separated minerals plagioclase apatite ca poor and ca rich pyroxenes ilmenite and magnetite from the bjerkreim sokndal layered intrusion rogaland anorthosite province sw norway are investigated to better define the proportion of trapped liquid and its influence on bulk cumulate composition in leuconoritic rocks made up of plagioclase ca poor pyroxene ilmenite fmagnetite folivine where apatite is an intercumulus phase even a small fraction of trapped liquid significantly affects the ree pattern of the bulk cumulate together with cumulus minerals proportion and composition contrastingly in gabbronoritic cumulates characterized by the presence of cumulus ca rich pyroxene and apatite cumulus apatite buffers the ree content la sm and eu eu vs p2o5 variations in leuconorites display mixing trends between a pure adcumulate and the composition of the trapped liquid assumed to be similar to the parental magma assessment of the trapped liquid fraction in leuconorites ranges from 2 to 25 and is systematically higher in the north eastern part of the intrusion the likely reason for this wide range of tlf is different cooling rates in different parts of the intrusion depending on the distance to the gneissic margins the ree patterns of liquids in equilibrium with primitive cumulates are calculated with mass balance equations major elements modelling duchesne j c charlier b 2005 geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos 83 299 254 permits calculation of the ree content of melt in equilibrium with gabbronorites partition coefficients for ree between cumulus minerals and a jotunitic liquid are then calculated calculated liquids from the most primitive cumulates are similar to a primitive jotunite representing the parental magma of the intrusion taking into account the trapped liquid fraction calculated from the p2o5 content consistent results demonstrate the reliability of liquid compositions calculated from bulk cumulates and confirm the hypothesis that the trapped liquid has crystallized as a closed system without subsequent mobility of ree in a migrating interstitial liquid d 2005 elsevier b v all rights reserved

magma dynamics at the base of an evolving mafic magma chamber incompatible element evidence from the partridge river intrusion duluth complex minnesota usa abstract a characteristic feature of the partridge river intrusion of the keweenawan duluth complex is the approximately fivefold to ninefold increase in the concentrations of incompatible elements in the lower zone compared with cumulates stratigraphically higher the concentrations of incompatible elements decrease from the lower zone upward to steady state values which is ascribed to variations in the proportions of trapped liquid rather than variable degrees of fractional crystallization of a single parental magma the calculated average composition of trapped liquid using our algorithm is similar to typical keweenawan low alumina high ti p basalts associated with the duluth complex but is different from the leading edge ferrodioritic liquid quenched in the chilled margin of the intrusion this difference suggests that the chilled margin does not represent the original parental magma composition from which the whole intrusion solidified and that the enrichment of incompatible elements may be related to the local flotation of magmatic suspensions to test the latter hypothesis numerically we have used heat mass transfer models assuming a sheet like magma chamber to calculate the parameters of the model that best reproduce the observed distribution of incompatible elements in a mush zone at the base of the partridge river intrusion the results indicate that a mush zone enriched in the incompatible elements is produced if the velocity of movement of the lower solidification front into the magma body was less than the floating velocity of the bulk crystal mush the dynamic parameters that best reproduce the observed distribution of incompatible elements include a magma emplacement pressure of 2 kbar critical crystallinities of 50 68 in the mush zone from which the liquid is being expelled and an emplacement temperature of 1160 c for the initial magma

infiltration on sloping terrain and its role on runoff generation and slope stability abstract a modified green and ampt model is formulated to quantify infiltration on sloping terrain underlain by homogeneous soil wetted by surficial water application this paper s theory for quantifying infiltration relies on the mathematical statement of the coupled partial differential equations pdes governing infiltration and runoff these pdes are solved by employing an explicit finite difference numerical method that yields the infiltration the infiltration rate the depth to the wetting front the rate of runoff and the depth of runoff everywhere on the slope during external wetting data inputs consist of a water application rate or the rainfall hyetograph of a storm of arbitrary duration soil hydraulic characteristics and antecedent moisture and the slope s hydraulic and geometric characteristics the presented theory predicts the effect an advancing wetting front has on slope stability with respect to translational sliding this paper s theory also develops the 1d pde governing suspended sediment transport and slope degradation caused by runoff influenced by infiltration three examples illustrate the application of the developed theory to calculate infiltration and runoff on a slope and their role on the stability of cohesive and cohesionless soils forming sloping terrain

the effects of vegetative ash on infiltration capacity sediment transport and the generation of progressively bulked debris flows abstract through the alteration of the physical characteristics of a landscape such as the destruction of vegetation and the formation of a hydrophobic layer a fire can dramatically amplify erosion rates on the basis of field observations it has been proposed that the deposition of a layer of ash on the ground surface can enhance the erosion of mountainous terrain by surface runoff and might even be a necessary condition for the generation of progressively bulked debris flows in this study a flume was constructed to investigate the role of ash in increasing both the volume and the transport capacity of runoff the experiments demonstrated that the presence of ash on the soil surface reduces the ability of flowing water to infiltrate this effect is even greater when the ash has been pre wetted in addition the ability of ash slurries to infiltrate decreases with increasing ash concentration the results also indicate that the transport capacity of runoff is enhanced by the incorporation of ash into the flow because of the increased fluid density however the addition of ash reduces the boundary reynolds number such that at high ash concentrations and with fine grained sediment sediment transport declines as the flow becomes hydraulically smooth the experimental results were also used to evaluate the ability of steep flow fronts a common characteristic of debris flows and flash floods to increase sediment transport rates finally it is proposed that ash slurries may evolve into progressively bulked debris flows through a positive feedback between fluid density transport capacity and erosivity

the effects of fire and water repellency on infiltration and runoff under mediterranean type forest abstract an investigation is being made into the relationship between forest fire and hillslope hydrology in the selva region of catalonia over a three year period at sites with a known fire history the major sites are on granite granodiorite or on sediments derived from these rocks at locations between santa christina d aro and santa coloma de farnes it appears that there is a general relationship between the type of organic profile found in a forest and the impact of fire in terms of loss of organic matter soil erosion hillslope hydrology and on the regeneration of the forest this paper summarises the results of about 150 rainfall simulation experiments and presents an overview of work carried out so far a major conclusion is that runoff processes are discontinuous and spatially structured due mainly to the effects of water repellency as a result of surface properties macropores hydrophobic behaviour and swelling four types of infiltration curve can be recognised at many locations infiltration increases with time during the early part of an experiment reaches a maximum value after about 30 minutes therupon subsequently decreasing this type of relationship can not be modelled with standard infiltration equations illustrations are given of sections through both burnt and unburnt soils to show how the hydrophobic effect influences water penetration it can be seen that infiltration patterns are similar for both burnt and unburnt soils and that micropores filled with organic matter are very important in conducting water through a water repellent surface layer the hydrophobic layer traps water in the bc horizon and prevents evaporation and loss by upwards capillary movement although the hydrophobic effects mean that small areas sometimes have a high runoff coefficient on larger areas there are many macropores and shrubs beneath which the soil is permeable and these trap runoff generated on the water repellent areas the main effect of fire is to illiminate the storage of water in the organic horizons several cm at first infiltration rates remain high but later these decrease as there is a reduction in porosity the sites having a moder type profile have better water retention properties more organic matter that survives the fire and a faster rate of vegetation recovery sites with a mor type profile can be degraded and erode if they are subject to disturbance the study provides another example of how on seemingly uniform slopes hydrological processes are structured by interactions with vegetation the patterns produced by these interactions survive the effects of fire

the distinction between geomagnetic excursions and reversals summary two recent studies of the geomagnetic eld in the last 1 myr have found 14 excursions large changes in direction lasting 5 10 kyr each six of which are established as global phenomena by correlation between diierent sites the older picture of the geomagnetic eld enjoying long periods of stable polarity may not therefore be correct instead the eld appears to suier many dramatic changes in direction and concomitant reduction in intensity for 10 20 per cent of the time during excursions the eld may reverse in the liquid outer core which has timescales of 500 yr or less but not in the solid inner core where the eld must change by diiusion with a timescale of 3 kyr this timescale is consistent with the remarkably uniform duration of well dated excursions the disparity of dynamical timescales between the inner and outer cores a factor of 10 is consistent with the 10 excursions between full reversals

porous sidewall and sloping floor crystallization experiments using a reactive mush implications for the self channelization of residual melts in cumulates abstract tank crystallization experiments with aqueous solutions were used to explore interactions between a buoyant residual fluid and a porous cumulate at a sloping floor and a vertical wall the fluid flow path in a non reactive mush glass beads was used as a control for a vertical non reactive mush the rise of the buoyant solute depleted fluid was confined within it fluid flow paths were curved in the case of a sloping mushy floor with the upper part of the mush being principally a plume discharge zone and the lower part being a recharge zone more realistic reactive mushes were created by supercooling a nh 4 cl solution cooling against a vertical surface produced an initial mat of dendrites that were subsequently overgrown by a vertically grooved dendrite structure the grooves contained upwardly flowing residual melt while the ridges extended beyond the buoyant boundary layer into the thermally convecting solute rich part of the tank with time the grooves were covered over by a dendrite mat but remained as open channels within the mush focussing and accelerating the upflow of residual melt a buoyant boundary layer on the outside of the mush was not observed in the experiment with a sloping floor a thin mat of homogeneous mush was succeeded by a more organized deposit characterized by chimneys residual melt escaped as plumes through the chimneys chimneys formed because buoyant residual melt dissolved the mush as it rose and warmed chimney spacing increased and the number of chimneys decreased as the mush thickened dissection of the mush showed that individual chimney channels were inclined upslope so that melt residual from crystallization at the foot of the slope emerged from chimneys near the top of the slope formation of channels in cumulates would greatly increase fractionation efficiency by increasing the effective volume from which residual melts could be extracted and by increasing the rate at which residual melts could be transferred to the upper part of the chamber

spatial structures of stream and hillslope drainage networks following gully erosion after wildfire the drainage networks of catchment areas burned by wildfire were analysed at several scales the smallest scale 1 1000 m2 representative of hillslopes and the small scale 1000 m2 to 1 km2 representative of small catchments were characterized by the analysis of field measurements the large scale 1 1000 km2 representative of perennial stream networks was derived from a 30 m digital elevation model and analysed by computer analysis scaling laws used to describe large scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region the hillslope drainage network appears to have a second order effect that reduces the number of order 1 and order 2 streams predicted by the large scale channel structure this network comprises two spatial patterns of rills with width to depth ratios typically less than 10 one pattern is parallel rills draining nearly planar hillslope surfaces and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head the magnitude of this critical area depends on infiltration hillslope roughness and critical shear stress for erosion of sediment all of which can be substantially altered by wildfire order 1 and 2 streams were found to constitute the interface region which is altered by a disturbance like wildfire from subtle unchannelized drainages in unburned catchments to incised drainages these drainages are characterized by gullies also with width to depth ratios typically less than 10 in burned catchments the regions hillslope interface and channel had different drainage network structures to collect and transfer water and sediment copyright 2005 john wiley sons ltd

is earth s magnetic field reversing abstract earth s dipole field has been diminishing in strength since the first systematic observations of field intensity were made in the mid nineteenth century this has led to speculation that the geomagnetic field might now be in the early stages of a reversal in the longer term context of paleomagnetic observations it is found that for the current reversal rate and expected statistical variability in polarity interval length an interval as long as the ongoing 0 78 myr brunhes polarity interval is to be expected with a probability of less than 0 15 and the preferred probability estimates range from 0 06 to 0 08 these rather low odds might be used to infer that the next reversal is overdue but the assessment is limited by the statistical treatment of reversals as point processes recent paleofield observations combined with insights derived from field modeling and numerical geodynamo simulations suggest that a reversal is not imminent the current value of the dipole moment remains high compared with the average throughout the ongoing 0 78 myr brunhes polarity interval the present rate of change in earth s dipole strength is not anomalous compared with rates of change for the past 7 kyr furthermore there is evidence that the field has been stronger on average during the brunhes than for the past 160 ma and that high average field values are associated with longer polarity chrons there is no evidence from recent millennial scale time varying paleofield models to indicate that the field is entering a polarity transition nevertheless it remains a reasonable supposition that the magnetic field will eventually reverse even though the time scale is unpredictable a more immediate concern is that ongoing secular variation in the magnetic field may be expected to moderate the current high dipole strength on centennial to millennial time scales it would not be surprising if it dropped substantially returning closer to the average without necessarily reversing this could have important consequences for space weather and also highlights the need for improved understanding of the impact of geomagnetic field strength on the production rates of cosmogenic isotopes that are used to estimate past solar variability

marine magnetic anomalies evidence that tiny wiggles represent short period geomagnetic polarity intervals since the 1960 s the geomagnetic polarity time scale which is based on marine magnetic anomalies has become fundamentally important in geochronology despite the importance of marine magnetic anomaly records there has been longstanding uncertainty about the meaning of the smallest anomalies observed in these records small amplitude short wavelength anomalies are frequently observed in marine magnetic anomaly records across fast spreading oceanic crust s 50 mm yr the origin of these small scale anomalies referred to as tiny wiggles has remained controversial over the last 30 years tiny wiggles have been interpreted to represent either short period polarity intervals or largescale fluctuations in the ancient field intensity we present palaeomagnetic evidence from a sedimentary record from the north pacific ocean which demonstrates that two short but clearly resolvable polarity zones in addition to a probable geomagnetic excursion occur within chron c5n 2n 9 92 10 95 ma where three tiny wiggles have been reported on marine magnetic anomaly profiles relative palaeointensity data indicate that the field collapsed prior to and during the reversals and during the excursion but that it recovered to higher field intensities within the polarity intervals before collapsing to low values at the succeeding polarity transition this indicates that some tiny wiggles represent real short period geomagnetic polarity intervals while others may represent geomagnetic excursions the existence of such short polarity intervals confirms the predictions of statistical analyses of geomagnetic reversal frequency and indicates that tiny wiggles represent the maximum resolution of geomagnetic polarity intervals in marine magnetic anomaly records fl 2000 elsevier science b v all rights reserved

orbital driven environmental changes recorded at odp site 959 eastern equatorial atlantic from the late miocene to the early pleistocene palaeorecords from tropical environments are important to explore the linkages between precipitation atmospheric circulation and orbital forcing in this study new high resolution xrf data from odp site 959 3 37 n 2 44 w have been used to investigate the relationship between palaeoenvironmental changes in west africa and sedimentation in the tropical east atlantic ocean iron intensity data have been used to build a 91 m composite depth record that has been astronomically tuned allowing the development of a detailed age model from 6 2 to 1 8 ma based on this new stratigraphy we studied the variations of ti al ti ca and al si ratios proxies for aeolian versus fluvial supply as dust indicator and fine versus coarse grain size respectively we discuss sedimentation patterns at odp site 959 associated with the environmental changes from the late miocene until the early pleistocene during the interval corresponding to the earlier stages of the messinian salinity crisis our proxy records indicate enhanced run off from the west african continent and major supply of fine material at odp site 959 suggesting a stronger monsoon and increased precipitation during eccentricity minima a long term decrease of river supply is documented after 5 4 ma until the end of the pliocene from the increased values and variability of ti al and ti ca ratios we suggest that after 3 5 ma dust started to reach the study site probably as a result of the southward shift of the intertropical convergence zone during winter between 3 2 and 2 9 ma odp site 959 ti ca ratios exhibit three maxima corresponding to eccentricity maxima similarly to other dust records of northern africa this suggests continent wide aridity or larger climate variability during that interval eccentricity forcing 405 and 100 kyr and precession frequencies are found in the entire studied interval the variations of ti al ratio suggest stronger seasonality between 5 8 and 5 5 ma and after 3 2 ma

geologic versus wildfire controls on hillslope processes and debris flow initiation in the green river canyons of dinosaur national monument abstract as in many areas of high relief debris flows are an important process linkage between hillslopes and the green river in the canyons of the eastern uinta mountains yet the physical conditions that lead to debris flow initiation are unknown a recent episode of enhanced debris flow and wildfire activity provided an opportunity to examine the geomorphic impact of fire and the processes by which weathered bedrock is transported to the green river field investigations and analysis of elevation and precipitation data were undertaken in 15 catchments with recent debris flows to determine how surficial geology wildfire topography bedrock strength and meteorology influence hillslope processes the recent debris flows were triggered by intense summer rainstorms the dominant debris flow initiation mechanism the firehose effect occurred when overland flow generated on bedrock hillslopes cascaded down steep cliffs onto colluvium causing failure sixty percent of the debris flows occurred in unburned catchments however 15 of the burned catchments in the study area produced debris flows over the study period whereas only 7 of the unburned catchments did thus fire was not the primary driver of debris flows but fire related events did contribute to the increased debris flow activity the geomorphic impact of wildfire in the eastern uinta mountains is not as great as in transport limited settings with regolith mantled hillslopes the strong rocks and dry climate of the study area cause hillslopes to be very steep and weathering limited with high runoff ratios and a dearth of regolith as a result there is little vegetation and thus we hypothesize that burning does little to change hillslope processes the suite of hillslope processes in the eastern uintas are like those documented in the similarly dry grand canyon but differ from other locations in the western u s where wildfire is a primary control on debris flow processes

illuminating wildfire erosion and deposition patterns with repeat terrestrial lidar erosion following a wildfire is much greater than background erosion in forests because of wildfire induced changes to soil erodibility and water infiltration while many previous studies have documented post wildfire erosion with point and small plot scale measurements the spatial distribution of post fire erosion patterns at the watershed scale remains largely unexplored in this study lidar surveys were collected periodically in a small first order drainage basin over a period of 2 years following a wildfire the study site was relatively steep with slopes ranging from 17 to 30 during the study period several different types of rain storms occurred on the site including low intensity frontal storms 2 4 mm h 1 and high intensity convective thunderstorms 79 mm h 1 these storms were the dominant drivers of erosion erosion resulting from dry ravel and debris flows was notably absent at the site successive lidar surveys were subtracted from one another to obtain digital maps of topographic change between surveys the results show an evolution in geomorphic response such that the erosional response after rain storms was strongly influenced by the previous erosional events and pre fire site morphology hillslope and channel roughness increased over time and the watershed armored as coarse cobbles and boulders were exposed the erosional response was spatially nonuniform shallow erosion from hillslopes 87 of the study area contributed 3 times more sediment volume than erosion from convergent areas 13 of the study area however the total normalized erosion depth volume area was highest in convergent areas from a detailed understanding of the spatial locations of erosion we made inferences regarding the processes driving erosion it appears that hillslope erosion is controlled by rain splash for detachment and overland flow for transport and quasi channelized erosion with the sites of highest erosion corresponding to locations with the lowest roughness by contrast in convergent areas we found erosion caused by overland flow soil erosion was locally interrupted by immobile objects such as boulders bedrock or tree trunks resulting in a patchy erosion network with increasing roughness over time

testing astronomically tuned age models astrochronology is fundamental to many paleoclimate studies but a standard statistical test has yet to be established for validating stand alone astronomically tuned time scales those lacking detailed independent time control against their astronomical insolation tuning curves shackleton et al 1995 proposed that the modulation of precession s amplitude by eccentricity can be used as an independent test for the successful tuning of paleoclimate data subsequent studies have demonstrated that eccentricity like amplitude modulation can be artificially generated in random data following astronomical tuning here we introduce a new statistical approach that circumvents the problem of introducing amplitude modulations during tuning and data processing thereby allowing the use of amplitude modulations for astronomical time scale evaluation the method is based upon the use of the hilbert transform to calculate instantaneous amplitude following application of a wide band precession filter and subsequent low pass filtering of the instantaneous amplitude to extract potential eccentricity modulations statistical significance of the results is evaluated using phase randomized surrogates that preserve the power spectrum structure of the data but have randomized amplitude modulations application of the new testing algorithm to two astronomically tuned data sets demonstrates the efficacy of the technique and confirms the presence of astronomical signals additionally it is demonstrated that a minimal tuning approach using at maximum one precession cycle per 100 kyr eccentricity cycle does not introduce systematic frequency modulations even when a narrow band pass filter is applied allowing direct comparison of data amplitudes and orbital eccentricity

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

scale effects on the estimation of erosion thresholds through a distributed and physically based hydrological model abstract slope incision and subsequent development of rills gullies and channels are responsible for significant soil losses and are often irreversible with very high restoration costs particularly in semiarid environments the location of potential areas of erosion where these processes occur is vital to land management and conservation the study of the relationship between the local slope s and the drainage area a through the geomorphological relationship s a b combined with hydrologic simulation models has proved to be appropriate for the identification and characterisation of potential areas of incision especially when it takes into account the spatial distribution of soil properties and the evolution of hydrological processes however physical properties of soil digital elevation models dems and flow algorithms used may affect the results this study employs a distributed physically based hydrological model to evaluate the infiltration runoff relationships and their influence on selecting critical area from three dems with different resolutions the results show a significant scale effect on flow distribution and the location of threshold points on slopes the results obtained from a 30 m dem significantly differ from those obtained from 10 and 5 m dems because the former was unable to capture the spatial variability of geomorphic processes the selected set of critical points shows high s a correlations for different values of critical shear stress the physical model confirmed the dominance of surface runoff in the study site and was validated from field identification of erosion risk areas although for incision areas

experimental study of a kiglapait marginal rock and implications for trace element partitioning in layered intrusions abstract experiments on a chilled marginal rock from the kiglapait intrusion labrador have been performed in order to constrain the partitioning behaviour of major and trace elements during formation of kiglapait lower zone lz cumulates at 0 1 mpa and f o 2 close to fmq the liquidus is bracketed between 1225 and 1212 c and the only liquidus phases are plagioclase an 73 74 and olivine fo 82 85 in contrast lz troctolites contain fo 67 5 olivine and an 63 4 plagioclase plagioclase melt partition coefficients d s for li ti rb sr y zr ba la and eu determined by ion microprobe analysis of run products are similar to those for other basaltic systems but differ systematically from apparent d s calculated from bulk analyses of lz plagioclases and modelled liquid compositions obtained by summation the discrepancies in d s and phase compositions are inconsistent with diffusion controlled boundary layer growth crystallisation of trapped intercumulus liquid is quantitatively plausible however a the volume of liquid required to reconcile experimental and model d s 20 1 is larger than that estimated from observed proportions of intercumulus phases 11 2 and b this mechanism alone cannot reduce x an in lz plagioclases due to very slow al si interdiffusion the discrepancy between experiment and model is best resolved if the parental melt to lz cumulates was more evolved higher fe mg na ca ree and alkalis lower sr than the summed bulk composition in accord with a recent revision of the kiglapait fe mg based on olivine compositions

trace element variations in olivine from the eastern deeps intrusion at voisey s bay labrador as a monitor of assimilation and sulfide saturation processes ni cu co sulfide mineralization in the mesoproterozoic voisey s bay intrusion is spatially and genetically associated with magmatic breccia zones within an extensive dike system and in particular with the entry point of this system into a larger intrusion eastern deeps intrusion the massive sulfide and breccia bearing inner basal margin of this upper intrusion is enveloped by weakly mineralized variable textured troctolite that progressively decreases in sulfide content contains fewer paragneiss fragments and eventually grades into a largely sulfide barren homogeneous plagioclase and olivine meso cumulate termed normal troctolite toward the top of the intrusion olivine from the troctolite lithologies the mineralized basal breccia sequence and the uppermost olivine gabbro in the eastern deeps intrusion was analyzed with secondary ion mass spectrometry sims we present multitrace element data including petrogenetically important elements v cr mn co ni zn sr and y which indicate that four petrological processes important to ore formation are recorded by the compositional diversity of olivine the heterogeneous ni co fo contents of olivine in the eastern deeps intrusion co ni ratios in olivine gabbro 0 18 1 1 normal troctolite 0 07 0 26 variable textured troctolite 0 11 0 29 basal breccia sequence 0 20 0 34 are due to variable modification of original compositions by reequilibration with trapped silicate and sulfide liquids the abrupt changes of fe fo79 fo66 and ni 2 500 to 80 ppm contents and some trace elements up to 1 5x more sr up to 3x more y than average normal troctolite olivine in olivine from intervals in the barren upper normal troctolite indicate that olivine crystallized from separate pulses of magma with variable degrees of differentiation the severe ni depletion of one troctolite melt batch 10 ppm ni vs 290 ppm ni for average normal troctolite magma is likely a result of sulfide saturation and segregation either in a deeper staging chamber or in the conduit prior or contemporary to olivine precipitation and emplacement the gradational increase of fe from fo80 to fo62 mn from 4 000 to 10 000 ppm and zn from 400 to 620 ppm in olivine from the weakly mineralized and contaminated lower part of the variable textured troctolite downward into the massive sulfide bearing and strongly contaminated basal breccia sequence is consistent with olivine fractionation from an increasingly country rock contaminated sulfide saturated silicate magma olivine here crystallized prior to or contemporaneously with the segregation of an immiscible sulfide liquid olivine grains that are enclosed by sulfide display homogeneous forsterite contents fo62 with pronounced intragrain trace element zonation mn ni co zn diffusion profiles mn ni indicate a relatively short immersion time 1 000 years of these olivine grains in sulfide liquid which likely resulted in the partial retention of ni in the olivine olivine in the vicinity of massive sulfides in the eastern deeps intrusion from variable textured troctolite to basal breccia sequence has a distinct minor and trace element signature v cr mn co ni zn compared to olivine from the barren troctolite and olivine gabbro a multiple regression analysis using these data yields an index that describes the relative vertical proximity of olivine to massive sulfides in conjunction with the stratigraphic context of the host lithology this information could potentially be used as a vector toward massive sulfide mineralization in the eastern deeps intrusion and also support ni exploration in other olivine bearing mafic intrusions with similar style of sulfide mineralization

dimensionless erosion laws for cohesive sediment abstracta method of achieving a dimensionless collapse of erosion rate data for cohesive sediments is proposed and shown to work well for data collected in flume erosion tests on mixtures of sand and mud silt plus clay sized particles for a wide range of mud fraction the data collapse corresponds to a dimensional erosion law of the form e c m where e is erosion rate is shear stress c is the threshold shear stress for erosion to occur and m 7 4 this result contrasts with the commonly assumed linear erosion law e kd c where kd is a measure of how easily sediment is eroded the data collapse prompts a re examination of the way that results of the hole erosion test het and jet erosion test jet are customarily analyzed and also calls into question the meaningfulness not only of proposed empirical relationships between kd and c but also of the erodibility parameter kd itself fuller comparison of flume erosion data with hole erosion and jet erosion data will require revised analyses o

the effects of wildfire on the sediment yield of a coastal california watershed the occurrence of two wildfi res separated by 31 yr in the chaparral dominated arroyo seco watershed 293 km 2 of california provides a unique opportunity to evaluate the effects of wildfi re on suspended sediment yield here we compile discharge and suspended sediment sampling data from before and after the fi res and show that the effects of the postfi re responses differed markedly the 1977 marble cone wildfi re was followed by an exceptionally wet winter which resulted in concentrations and fl uxes of both fi ne and coarse suspended sediment that were 35 times greater than average sediment yield during the 1978 water year was 11 000 t km 2 yr we suggest that the combined 1977 1978 fi re and fl ood had a recurrence interval of greater than 1000 yr in contrast the 2008 basin complex wildfi re was followed by a drier than normal year and although suspended sediment fl uxes and concentrations were signifi cantly elevated compared to those expected for unburned conditions the sediment yield during the 2009 water year was less than 1 of the post marble cone wildfi re yield after the fi rst postfi re winters sediment concentrations and yield decreased with time toward prefi re relationships and continued to have signifi cant rainfall dependence we hypothesize that the differences in sediment yield were related to precipitationenhanced hillslope erosion processes such as rilling and mass movements the millennialscale effects of wildfi re on sediment yield were explored further using monte carlo simulations and these analyses suggest that infrequent wildfi res followed by flincrease long term suspended sediment fl markedly thus we suggest that the current approach of estimating sediment yield from sediment rating curves and discharge data without including periodic perturbations from wildfi res may grossly underestimate actual sediment yields

a morphometric analysis of gullies scoured by post fire progressively bulked debris flows in southwest montana usa in the fall of 2001 an intense thunderstorm in southwest montana triggered many debris flows in the burned area of sleeping child creek in most instances the debris flows cut deep gullies into previously unchannelized colluvial hollows and deposited large volumes of sediment onto the valley floor the presence of rill networks above the gullies as well as the absence of landslide features indicate that the gullies were scoured by progressively bulked debris flows a process in which dilute surface runoff becomes increasingly more laden with sediment until it transforms into a debris flow in this contribution we present a morphometric analysis of six of the gullies to better understand this relatively understudied process we find that the locations of the rill heads and gully heads conform to slope area thresholds that are characteristic of erosion by overland flow our data also suggest that the volumes of the debris flows increase exponentially with normalized drainage area thus lending support to an assumption used in a recently proposed debris flow incision law finally the debris flow fans have been relatively unaltered since deposition suggesting that the valley may be currently aggrading while the hillslopes are being denuded

miocene diatom biostratigraphy at odp sites 689 690 1088 1092 atlantic sector of the southern ocean abstract four odp sites located between 64 s and 41 s in the eastern atlantic sector of the southern ocean were investigated to refine the miocene diatom biostratigraphic zonation tied to the geomagnetic chronology the miocene diatom stratigraphy from two sites located on maud rise odp leg 113 is revised considering the progress in diatom biostratigraphic research diatom taxonomy and magnetostratigraphic age assignment during the past 10 years a new diatom zonation was erected for site 1092 odp leg 177 located on meteor rise integrating a magnetostratigraphic interpretation of the shipboard data this zonation was also applied to site 1088 odp leg 177 located on astrid ridge the study is focused to middle and upper miocene sequences it reveals latitudinal differentiations in stratigraphic species ranges and species occurrence pattern that are related to latitudinal differences in surface water masses reflecting the climatic development of the antarctic cryosphere considering the latitudinal differences two stratigraphic zonations are proposed that are applicable to the northern and southern zone of the southern ocean respectively the southern southern ocean miocene diatom biostratigraphic zonation consists of 16 zones in which 11 represent new or modified zones the northern biostratigraphic zonation contains 10 diatom zones allowing a stratigraphic resolution in the range of 0 2 2 myr this paper also includes the taxonomic transfer of seven miocene diatom taxa from genus nitzschia hassal to fragilariopsis hustedt

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

confirmation of a late miocene subchron c4n 2n 1r from the eastern qaidam basin in the ne tibetan plateau

sediment availability on burned hillslopes 1 erodibility describes the inherent resistance of soil to erosion hillslope erosion models typically consider erodibility to be constant with depth this may not be the case after wildfire because erodibility is partly determined by the availability of noncohesive soil and ash at the surface this study quantifies erodibility of burned soils using methods that explicitly capture variations in soil properties with depth flume experiments on intact cores from three sites in western united states showed that erodibility of fire affected soil was highest at the soil surface and declined exponentially within the top 20 mm of the soil profile with root density and soil depth accounting for 62 of the variation variation in erodibility with depth resulted in transient sediment flux during erosion experiments on bounded field plots material that contributed to transient flux was conceptualized as a layer of noncohesive material of variable depth dnc this depth was related to shear strength measurements and sampled spatially to obtain the probability distribution of noncohesive material as a function of depth below the surface after wildfire in southeast australia the initial dnc ranged from 7 5 to 9 1 mm which equated to 97 117 mg ha 1 of noncohesive material the depth decreased exponentially with time since wildfire to 0 4 mm or 5 mg ha 1 after 3 years of recovery the results are organized into a framework for modeling fire effects on erodibility as a function of the production and depletion of the noncohesive layer overlying a cohesive layer

the nature of a cryptochron from a paleomagnetic study of chron c4r 2r recorded in sediments off the antarctic peninsula abstract the magnetostratigraphy from ocean drilling program odp site 1095 off the pacific margin of the antarctic peninsula contains an extra normal polarity event that occurs near the base of chron 4r 2r 8 072 8 699 ma which we interpret to be cryptochron c4r 2r 1 owing to the relatively high sedimentation rates about 90 m m y this event is particularly well recorded at the site spanning 4 99 m of the stratigraphic section this allows the characteristics of the cryptochron to be investigated in greater detail than possible from marine magnetic anomalies where it was originally identified or from other sedimentary sections in which it has been recorded at much lower resolution our observations suggest that the cryptochron is a full geomagnetic reversal in which both the direction and paleointensity attain levels similar to that of other normal polarity chrons at the site based on its position within chron 4r 2r the cryptochron started at 8 622 ma and terminated 56 k y later at 8 566 ma at the transition zones bounding the cryptochron the paleointensity collapses to near zero but recovers within a few thousand years our results as well as paleomagnetic observations from other thick sedimentary units indicate that cryptochrons are not always purely paleointensity variations instead they are a record of short term geomagnetic variability that includes short geomagnetic reversals excursions intervals of high paleosecular variation and paleointensity lows all of which are part of a vector field that varies in both strength and direction over time

initiation of motion in overland flow this article reports the results of an experimental study concerning the initial movement of sediment in overland flow experiments were carried out in a small flume using water and quartz materials of various grain sizes the comparison of our experimental results with classic criteria showed that the shields curve and the criterion of yang can also be used for turbulent overland flow generally higher shear stresses are necessary to provoke bed instability under laminar flow conditions especially at higher shear velocity particle reynolds numbers a relative roughness effect also exists in laminar flow contrary to the observations by savat on fixed beds laminar flow does not show an uncommon selectivity when loose homogeneous beds are considered

critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires received 26 february 2004 revised 15 september 2004 accepted 5 november 2004 published 22 january 2005 1 increased erosion is a well known response after wildfire to predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles as this soil property is temperature dependent a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required in this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures 40 550 c for 1 hour results were obtained for four replicates of soils derived from three different types of parent material granitic bedrock sandstone and volcanic tuffs in general the relation between critical shear stress and temperature can be separated into three different temperature ranges 275 c which are similar to those for water repellency and temperature the critical shear stress was most variable 1 0 2 0 n m 2 for temperatures 2 0 n m 2 between 175 and 275 c and was essentially constant 0 5 0 8 n m 2 f or temperatures 275 c the changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire

reequilibration of olivine with trapped liquid in the duluth complex minnesota a 525 m long drill core ddh 221 through the partridge river intrusion in northeastern minnesota consists of mesocumulates and or orthocumulates of troctolite olivine gabbro and olivine gabbronorite the cumulus olivine whose composition fo 31 to fo 71 is a function of the amount of intercumulus liquid followed an equilibrium crystallization path with this liquid estimates of the primary magmatic compositions of the olivine are fo 57 to fo 79 none of the olivine in the drill core samples has retained an original cumulus composition i e one that was in equilibrium with the parental magma the plagioclase is strongly zoned and the cumulus cores an 59 to an 73 are thought to record crystallization from the parental magma

contrasting petrological and geochemical relationships in the voisey s bay and mushuau intrusions labrador canada implications for ore genesis new data on the voisey s bay and mushuau intrusions indicate that the two bodies which were formerly grouped as the reid brook complex differ markedly in age petrology geochemistry and the scale of known mineralization u pb dating of baddeleyite and zircon has revealed that the mushuau intrusion has an age of 1 313 ga which is 20 m y younger than the 1 333 ga voisey s bay intrusion the voisey s bay intrusion is host to the 124 million tons ni cu co sulfide deposit reserves resources mineralization occurs at the base of an upper subchamber the eastern deeps subchamber and in a conduit that connects the eastern deeps to a lower subchamber the reid brook subchamber the mineralization is associated with a basal breccia that contains abundant reacted inclusions of paragneiss within the eastern deeps the basal mineralization is overlain by a varied textured troctolite that contains variable amounts of disseminated sulfide and gneiss inclusions by comparison only minor amounts of sulfide mineralization have been observed within the mushuau intrusion the mushuau intrusion comprises a layered unit that has been intruded by a stellate textured troctolite along its contact with footwall orthogneiss the layered unit consists dominantly of melatroctolite at the margin with leucotroctolite toward the center and olivine gabbro at the core the cumulates of the mushuau intrusion are richer in olivine and thus have higher mgo contents than those of the voisey s bay intrusion notwithstanding this olivines in the melatroctolite inclusions of the voisey s bay intrusion which are thought to represent disrupted cumulus layers contain up to 81 mole percent forsterite whereas those in the melatroctolite of the mushuau intrusion contain no more than 70 mole percent forsterite nickel depletion in olivine is more pronounced in the voisey s bay intrusion than in the mushuau intrusion our data indicate that the parental magmas of both intrusions were broadly basaltic mgo 8 1 wt and that the magma of the mushuau intrusion was more evolved than that of the voisey s bay intrusion yet still capable of forming olivine rich cumulates the troctolites of the voisey s bay intrusion have ce yb 22 to 27 whereas most troctolites of the mushuau intrusion have ce yb 12 to 17 the rocks of the mushuau intrusion are simple mixtures of mantle derived magma and local orthogneiss whereas the rocks of the voisey s bay intrusion are formed by multiple stages of crustal contamination including an early stage of contamination at lower midcrustal level and a late stage of contamination by tasiuyak paragneiss at upper crustal level the assimilation of the sulfide bearing tasiuyak paragneiss by magma at voisey s bay may have promoted initial sulfide saturation and or increased sulfide oversaturation thus contributing to the segregation of large amounts of sulfide liquid from magma continuing flow of magma through a dynamic conduit system at voisey s bay has caused the local accumulation of sulfide of sufficient size and grade to constitute mineable reserves

sediment and hydrological response to vegetation recovery following wildfire on hillslopes and the hollow of a small watershed summary wildfire can cause dynamically spatial and temporal variations of hydrology and sedimentation from forested environments the largest wildfire historically recorded in south korea burned 23 484 ha of forest land in april 2000 in 2001 systems to monitor post fire runoff and sediment were installed at the outlet of a small watershed and at seven plots on hillslopes of different vegetation condition the hillslope and catchment responses were monitored for five years post fire the watershed was divided into four sites including terrace sodding ts pine planting and fast recovery pf pine planting and slow recovery ps and hollow h according to treatment methods and topographical characteristic the ts site showed the fastest vegetation recovery among the sites and the greatest reduction of soil erosion with time elapsed after wildfire sediment yield from the watershed as well as from plots depended strongly on rainfall erosivity index while the runoff coefficient showed the highest correlation with rainfall amount the sediment response rate had the strongest correlation with a vegetation index characterizing vegetation structure litter and root the hollow mostly acted as a depositional zone but only contributed to erosion when it was disturbed by the treatment applications following the fire or during heavy rain following landslide activity in the catchment these results indicate that gently sloping hollow areas with rapidly recovering vegetation have the potential to reduce the flood and sediment risk however heavy and extreme rainfall events during the study produced excessive sediment by catastrophic debris flow and landslide processes even on vegetated hillslopes the study suggests that the boundary condition for whether i rain is heavy or extreme ii surface condition is bare and iii terrain has a deposition zone should be considered in order to evaluate sediment yields from burnt catchments

simulation of primary phase relations and mineral compositions in the partridge river intrusion duluth complex minnesota implications for the parent magma composition in order to describe the composition and crystallinity of the initial parental magma of the partridge river intrusion of the keweenawan duluth complex and thereby understand the mode of emplacement and solidification of the intrusion we have applied a numerical simulation technique called geochemical thermometry frenkel et al 1988 the parental magma was a low alumina high ti p olivine tholeiite similar to typical keweenawan low alumina high ti p basalts associated with the duluth complex and from the nearby portage lake area of the lake superior region the parental magma was emplaced as a crystal liquid suspension followed by chilling of an evolved leading edge ferrodioritic liquid in the basal zone of the intrusion the conditions of emplacement at the present crustal location were 1 150 c 2 kbar and fo2 slightly above the wustite magnetite wm buffer the main differentiation process after emplacement was the sorting and redistribution of plagioclase and olivine crystals on a local scale accompanied by less efficient convection and minor settling of olivine calculated crystallization sequence for the parental magma is olivine plagioclase 1 240 c olivine plagioclase magnetite 1 146 c wm 0 5 olivine plagioclase magnetite augite 1 140 c wm 0 5 the calculated compositions of the cumulus olivine and plagioclase in equilibrium with the parent magma at 1 150 c are fo66 7 1 1 and an64 5 2 5 respectively and are similar to the estimated average composition of primary olivine fo69 1 2 8 and the average composition of plagioclase core an66 3 2 8 measured in drill core samples through the intrusion chalokwu and grant 1987

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

differentiation of the cuthbert lake ultramafic dikes and related mafic dikes in the cuthbert lake region of north central manitoba northeasterly trending ultramafic mafic dikes part of the molson dike swarm show a range of composition from gabbro to olivine hornblende pyroxenite to hornblende peridotite the major dike which is ultramafic in composition is 60 m thick olivine and chromian spinel were the earliest cumulus phases formed in a subcrustal magma chamber before the emplacement of the dikes orthopyroxene and clinopyroxene were formed following emplacement at about 1120 c plagioclase and hornblende were the latest phases to crystallize from the intercumulus melt mineralogical and chemical variations across the major dike are interpreted to have resulted from flow differentiation of multiple injections of magma carrying suspended olivine crystals olivine phenocrysts changed their compositions from about fo87 to values ranging from fo80to fo73 as a function of the amount of intercumulus melt the composition of this melt is estimated to have been basaltic a mafic dike about 10 m thick and occurring about 20 m away from the main ultramafic dike is believed to have been formed from magmas that were tapped from an upper layer overlying the olivine rich zone in a subcrustal magma chamber separation must have occurred when clinopyroxene and plagioclase appeared on the liquidus

the parent magmas of the cumulate eucrites a mass balance approach the cumulate eucrite meteorites are gabbros that are related to the eucrite basalt meteorites the eucrite basalts are relatively primitive nearly flat ree patterns with la approx 8 30 x ci but the parent magmas of the cumulate eucrites have been inferred as extremely evolved la to greater than 100 x ci this inference has been based on mineral magma partitioning and on mass balance considering the cumulate eucrites as adcumulates of plagioclase pigeonite only both approaches have been criticized as inappropriate here mass balance including magma equilibrium pigeonite equilibrium plagiociase is used to test a simple model for the cumulate eucrites that they formed from known eucritic magma types that they consisted only of magma crystals in chemical equilibrium with the magma and that they were closed to chemical exchange after the accumulation of crystals this model is tested for major and rare earth elements ree the cumulate eucrites serra de mage and moore county are consistent in both ree and major elements with formation by this simple model from a eucrite magma with a composition similar to the nuevo laredo meteorite serra de mage as 14 magma 47 5 pigeonite and 38 5 plagioclase moore county as 35 magma 37 5 pigeonite and 27 5 plagioclase these results are insensitive to the choice of mineral magma partition coefficients results for the moama cumulate eucrite are strongly dependent on choice of partition coefficients for one reasonable choice moama s composition can be modeled as 4 nuevo laredo magma 60 pigeonite and 36 plagioclase selection of parent magma composition relies heavily on major elements the ree cannot uniquely indicate a parent magma among the eucrite basalts the major element composition of y 791195 can be fit adequately as a simple cumulate from any basaltic eucrite composition however y 791195 has lree abundances and la lu too low to be accommodated within the model using any basaltic eucrite composition and any reasonable partition coefficients postcumulus loss of incompatible elements seems possible it is intriguing that serra de mage moore county and moama are consistent with the same parental magma could they be from the same igneous body on the eucrite parent asteroid 4 vesta

multi element variations in olivine as geochemical signatures of ni cu sulfide mineralization in mafic magma systems examples from voisey s bay and pants lake intrusions labrador canada olivine from the olivine gabbro to troctolite intrusions at voisey s bay and at pants lake labrador was analyzed for multiple elements ca sc mg si ti v cr mn fe co ni cu zn sr y and zr with secondary ion mass spectrometry sims both intrusions have similar lithologies and petrographic characteristics and are approximately coeval 1 34 and 1 32 ga respectively members of the mesoproterozoic nain plutonic suite the voisey s bay intrusion hosts a producing economic ni cu sulfide deposit whereas the pants lake intrusion displays evidence of ni cu sulfide mineralization but to date a viable ore deposit has not been discovered olivine from both barren and mineralized lithologies was analyzed to assess the potential of the olivine composition for providing a record of silicate melt evolution and sulfide saturation related to formation of a massive sulfide deposit two detailed transects were sampled using five diamond drill holes that laterally approach the basal massive sulfide in the eastern deeps portion of the voisey s bay intrusion from the barren central part olivine displays distinct trace element distributions that vary coherently with host lithology and proximity to sulfide mineralization in particular olivine shows an increase in fe fo80 to fo60 mn 2500 to 5000 ppm and zn 280 to 700 ppm generally coupled with a decrease in ni 1600 to 900 ppm co 270 to 190 ppm and cr 110 to 45 ppm from barren troctolite normal troctolite nt and weakly mineralized troctolite variable textured troctolite vtt towards the heavily mineralized brecciated basal succession basal breccia sequence bbs the enrichment in fe mn zn is most pronounced in samples that laterally approach but do not directly intersect the massive sulfide deposit at the base of the intrusion particularly in samples from the lower variable textured troctolite and the basal breccia olivine from gabbro lithologies within the basal gabbro bg and upper gabbro ug of the pants lake intrusion is fairly homogeneous fo60 4300 ppm mn 460 ppm zn 340 ppm ni 50 ppm cr with a more evolved composition 2100 ppm ca 20 ppm sc 300 ppm ti 4 ppm y than the average olivine of the voisey s bay intrusion 570 ppm ca 6 ppm sc 65 ppm ti 0 3 ppm y pants lake olivine also commonly lacks the mutually mn zn rich signature of olivine from the basal breccia at voisey s bay that is characteristic of contamination of the parent magma by country rock gneiss and there reflects a close proximity to massive sulfides in conjunction with petrographic observation and the stratigraphic context a multiple element v cr mn fe co ni zn regression can be applied to calculate a lateral proximity of olivine to massive sulfide mineralization in the eastern deeps part of the voisey s bay intrusion over a distance exceeding 150 m the compositional variations in olivine from the economic voisey s bay intrusion bimodal and primitive and the mainly barren pants lake intrusion homogeneous and evolved provide potential as a regional scale mineralogical fertility indicator for mafic intrusions with comparable types of sulfide mineralization

deciphering magmatic and metasomatic processes recorded by fluid inclusions and apatite within the cu ni pge sulfide mineralized bathtub intrusion of the duluth complex ne minnesota usa

odp site 1092 revised composite depth section has implications for upper miocene cryptochrons summary an upper miocene magnetic polarity stratigraphy has been developed for the c3r to c5abn interval of odp site 1092 from the sub antarctic south atlantic evans channell 2003 new data from x ray fluorescence xrf scanning of half cores has led to development of a revised composite depth section for the site this has implications for the magnetostratigraphic interpretation using the shipboard derived composite section four subchrons were identified within the normal polarity zone correlative to c5n 2n the revised composite section results in subchrons c5n 2n 2 and c5n 2n 3 of evans channell 2003 becoming a single subchron recorded in two overlapping cores the revised number of polarity subchrons within c5n 2n is now three rather than four which is consistent with the number of cryptochrons recognized in marine oceanic anomaly data

post wildfire erosion response in two geologic terrains in the western usa abstract volumes of eroded sediment after wildfires vary substantially throughout different geologic terrains across the western united states these volumes are difficult to compare because they represent the response to rainstorms and runoff with different characteristics however by measuring the erosion response as the erodibility efficiency of water to detach and transport sediment on hillslopes and in channels the erosion response from different geologic terrains can be compared specifically the erodibility efficiency is the percentage of the total available stream power expended to detach remobilize or transport a mass of sediment erodibility efficiencies were calculated for the i initial detachment and for the ii remobilization and transport of sediment on the hillslopes and in the channels after wildfire in two different geological terrains the initial detachment efficiencies for the main channel and tributary channel in the granitic terrain were 10 9 and 5 4 and were similar to those for the volcanic terrain which were 5 5 and 1 1 no initial detachment efficiency could be measured for the hillslopes in the granitic terrain because hillslope measurements were started after the first major rainstorm the initial detachment efficiency in the volcanic terrain was 1 3 0 41 the average remobilization and transport efficiencies associated with flash floods in the channels also were similar in the granitic 0 18 0 57 and volcanic 0 11 0 41 terrains on the hillslope the remobilization and transport efficiency was greater in the volcanic terrain 2 4 than in the granitic terrain 0 65 however this may reflect the reduced sediment availability after the first major rainstorm 30 min maximum rainfall intensity 90 mm h 1 in the granitic terrain while easily erodible fine colluvium remained on the hillslope after the first rainstorm 30 min maximum rainfall intensity 7 2 mm h 1 in the volcanic terrain the erosion response in channels and on hillslopes of the granitic and volcanic terrains was similar when compared using erodibility efficiencies

the cumulate paradigm reconsidered the cumulate terminology outlined by wager and coworkers provided a logical system for describing the textures of the rocks of layered intrusions but recent work shows that this model fails to accommodate all the processes responsible for the petrographic features of coarse grained rocks textures of adcumulates and orthocumulates in the skaergaard intrusion cannot be correlated with concentrations of incompatible elements representing trapped liquid compaction and open system percolative processes have altered their textures modes and even bulk compositions although a rock may be a cumulate in the absence of other evidence it can be misleading to refer to it in terms of the cumulate nomenclature

source of tiny wiggles in chron c5 a comparison of sedimentary relative intensity and marine magnetic anomalies 1 in addition to the well established pattern of polarity reversals short wavelength fluctuations are often present in both sea surface data tiny wiggles and near bottom anomaly data while a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations independent evidence from another geomagnetic recording medium such as deep sea sediments is required to determine the true nature of the tiny wiggles we present such independent evidence in the form of sedimentary relative paleointensity from chron c5 we make the first comparison between a sedimentary relative paleointensity record odp site 887 at 54 n 148 w and deep tow marine magnetic anomaly data 43 n 131 w bowers et al 2001 for chron c5 the sediment cores are densely sampled at 2 5 kyr resolution the inclination record shows no evidence for reverse intervals within the 1 myr long normal chron c5n 2n rock magnetic measurements suggest that the primary magnetic carrier is pseudo single domain magnetite we choose a partial anhysteretic magnetization parm as our preferred normalizer and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization we then compare the results of this model with the stacked deep tow anomaly records the two records show a significant degree of correlation suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations an analysis of our sampling density suggests that if any reverse intervals exist at this site they are likely to be 5 kyr in duration furthermore we suggest that reverse intervals during chron c5n 2n documented in other locations are unlikely to be global

evidence for the trapped liquid shift effect in the mount ayliff intrusion south africa postcumulus trapped liquid shift in layered complexes produces cumulate minerals with more fractionated compositions than the original primary phases this effect is shown by olivine compositions from the base of the mount ayliff intrusion where varying proportions of olivine to interstitial liquid produce a suite of rocks which define a tight linear trend on a binary whole rock plot of mgo versus feo extrapolation of this trend constrains the composition of the primary cumulus olivine to the range fo84 86 whereas olivine actually present have compositions fo77 83 the magnitude of the discrepancy between the theoretical and observed olivine compositions correlates directly with the weight fraction of interstitial liquid these observations are quantitatively predicted by the trapped liquid shift model they also argue against significant migration of residual liquid trapped liquid shift is documented over a vertical interval of 60 m it occurred in rocks lying only 1 m above the basal contact of the intrusion and hence must be a comparatively rapid process

constraining the relative importance of raindrop and flow driven sediment transport mechanisms in postwildfire environments and implications for recovery time scales national geographic society proposal002929 2009 0046 1 national science foundation 02 39749 09 34131 u s geological survey usgs landslide hazards program

open magma chamber processes in the formation of the permian baima mafic ultramafic layered intrusion sw china abstract the baima mafic ultramafic layered intrusion of the 260 ma emeishan large igneous province elip hosts the second largest fe ti v oxide deposit in the panxi region sw china it is a 1600 m thick layered body intruded by slightly younger syenitic and granitic plutons the intrusion includes the lower and upper zones troctolite and olivine pyroxenite of the lower zone contains conformable oxide ore layers whereas the upper zone consists of olivine gabbro and gabbro with abundant apatite in the higher level the crystallization order of the silicates in the baima intrusion is olivine plagioclase clinopyroxene fe ti oxides titanomagnetite and ilmenite crystallized after olivine and possibly plagioclase the oxide ores in the lower zone show slightly lree enriched patterns with la yb n values between 2 0 and 6 4 and positive eu anomalies eu eu of 1 0 to 2 7 in contrast olivine gabbros in the lower zone display stronger lree enrichments la ybn 7 7 14 0 and positive eu anomalies eu eu 2 8 3 3 gabbros in the upper zone have ree profiles characterized by intermediate lree enrichments with la yb n values of 3 2 to 11 2 and positive eu anomalies of 2 1 to 3 0 primitive mantle normalized trace element patterns are characterized by negative la ce th sm and positive nb ta ba and ti anomalies in oxide ores and negative th u zr hf and positive ba sr and ti anomalies in olivine gabbro and gabbro fo of olivine and an of plagioclase remain roughly constant from 0 to 90 m in the lower zone indicating that the magma chamber was continuously filled by compositionally similar magmas during the initial stage three magma replenishments occurred afterwards in the upper part of the lower zone and the upper zone based on compositional reversals of plagioclase olivine and sr isotope mass balance calculations show that the baima parental magma can produce all oxide ores under closed system conditions a wide range of an values of plagioclase within thin sections and disequilibrium sr isotopic compositions of plagioclase both along the stratigraphic profile 87sr 86sri 0 70312 0 70510 and within thin sections indicate convection and co accumulation of cumulus plagioclase that had crystallized from different magmas we propose that the 1600m thick baima intrusion formed in an open and isotopically heterogeneous magma chamber that was periodically recharged by compositionally similar or more primitive magmas in each replenishment cycle the magma underwent progressive crustal contamination and fractional crystallization convection and sorting of crystals based on density differences result in igneous layering characterized by intervals of oxide ores troctolite and olivine gabbro

post fire hillslope debris flows evidence of a distinct erosion process abstract after wildfire a hitherto unexplained erosion process that some authors have called miniature debris flows on hillslopes and that leave behind levee lined rills has been observed in some regions of the world despite the unusual proposition of debris flow on planar hillslopes the process has not received much attention the objectives of this study were to 1 accumulate observational evidence of hillslope debris flows hdf as we have defined the process to 2 understand their initiation process by conducting runoff experiments on hillslopes to 3 propose a conceptual model of hdf and to 4 contrast and classify hdf relative to other erosion and transport processes in the post wildfire hillslope domain hdf have been observed at relatively steep slope gradients 0 4 0 8 on a variety of geologies and after fire of at least moderate severity and consist of a lobe of gravel to cobble sized material 0 2 1 m wide that is pushed by runoff damming up behind it during initiation runoff moved individual particles that accumulated a small distance downslope until the accumulation of grains failed and formed the granular lobe of the hdf hdf are a threshold process and runoff rates of 0 5 l s 1 2 l s 1 were required for their initiation during the experiments the conceptual model highlights hdf as a geomorphic process distinct from channel debris flows because they occur on planar unconfined hillslopes rather than confined channels hdf can erode very coarse non cohesive surface soil which distinguishes them from rill erosion that have suspended and bedload transport on a matrix of slope and grain size hdf are enveloped between purely gravity driven dry ravel and mostly runoff driven bedload transport in rills

an astronomical polarity timescale for the late middle miocene based on cyclic continental sequences 1 we present an astronomically tuned polarity timescale for the late middle miocene based on a cyclic shallow lacustrine mudflat succession exposed in the orera composite section ocs calatayud basin ne spain spectral analysis and band pass filtering of high resolution carbonate and color reflectance records in the depth domain reveal cyclic changes with different cycle lengths which correspond to lithological alternations observed in the field an initial age model was constructed by calibrating the ocs magnetostratigraphy to the geomagnetic polarity timescale of cande and kent 1995 subsequent spectral analysis of the proxy records in the time domain reveals periodicities close to 23 41 and 400 kyr and to a lesser extent 100 kyr supporting an astronomical origin for the sedimentary cyclicity in the ocs we established a new age model based on the astronomical calibration of the ocs to the laskar et al 1993 la93 solution by tuning the cycles to the astronomical target curves cross spectral analysis results of the tuned time series followed by band pass filtering reveal a remarkably good and in phase relation with precession and with obliquity despite a presumed uncertainty of 20 40 kyr in the tuning in some short intervals our tuning provides astronomical ages for sedimentary cycles and subsequently for polarity reversals in the interval between 12 9 and 10 6 ma comparison with cande and kent shows that the ocs polarity reversal ages are older by 80 kyr this age discrepancy decreases with increasing age to 50 60 kyr index terms 1035 geochemistry geochronology 1520 geomagnetism and paleomagnetism magnetostratigraphy 8105 tectonophysics continental margins and sedimentary basins 9335 information related to geographic region europe 9604 information related to geologic time cenozoic keywords geochronology magnetostratigraphy cyclostratigraphy astronomical timescale orbital forcing miocene

detachment and transportation of loose sediments by raindrop splash summary laboratory experiments on sediments ejected by splash consisted of two parts quantities ejected and mean projected distances were measured since the splash tray was 100 cm long and 20 cm wide and since both measurements were made on a receiving screen of one square metre it was obvious that only part of the translocated sediment was caught it was subject to serious doubt that the measured distances were representative for all sediment translocated if it is stated that the ejected sediment is distributed according to an exponential function around any point of impact located on the tray and if by definition tray and rainfall are perfectly homogeneous the ratio of the true to the measured distance and the ratio of the caught to the translocated sediment are only a function of the exponent of the real function the apparent distance being also a function of this exponent is thus the only factor needed to solve the two questions hence all empirical data were transformed into true data

prediction of spatially explicit rainfall intensity duration thresholds for post fire debris flow generation in the western united states abstract early warning of post fire debris flow occurrence during intense rainfall has traditionally relied upon a library of regionally specific empirical rainfall intensity duration thresholds development of this library and the calculation of rainfall intensity duration thresholds often require several years of monitoring local rainfall and hydrologic response to rainstorms a time consuming approach where results are often only applicable to the specific region where data were collected here we present a new fully predictive approach that utilizes rainfall hydrologic response and readily available geospatial data to predict rainfall intensity duration thresholds for debris flow generation in recently burned locations in the western united states unlike the traditional approach to defining regional thresholds from historical data the proposed methodology permits the direct calculation of rainfall intensity duration thresholds for areas where no such data exist the thresholds calculated by this method are demonstrated to provide predictions that are of similar accuracy and in some cases outperform previously published regional intensity duration thresholds the method also provides improved predictions of debris flow likelihood which can be incorporated into existing approaches for post fire debris flow hazard assessment our results also provide guidance for the operational expansion of post fire debris flow early warning systems in areas where empirically defined regional rainfall intensity duration thresholds do not currently exist