geomorphic relations among glacial lake algonquin and the munising and grand marais moraines in eastern upper michigan usa abstract data obtained from ground penetrating radar gpr optically stimulated luminescence osl dating and geostatistical reconstructions of lake algonquin water planes indicate that high standing outwash aprons flanking the munising moraine s southern margin in eastern upper michigan terminate as large coalescing gilbert type ice contact deltas graded to the main level of lake algonquin nearly 30 km of gpr imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation in time these deltas aggraded to the main lake algonquin level as the ice margin stabilized an osl date of 12 5 1 1 ka on a nearby beach ridge associated with the main algonquin shoreline is consistent with this interpretation these new data coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta indicate that lake algonquin was falling as delta deposition waned eventually reaching a level concordant with the lower orillia level before final abandonment large regionally extensive heads of outwash marking the crest of the munising moraine are graded to the upper margins of these deltas and by inference must also correlate with main lake algonquin and the associated two rivers deglaciation ca 13 12 5 ka the deltas in turn are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group lake algonquin shoreline because these aforementioned heads of outwash part of drexler and others grand marais moraine correlate with the marquette moraine farther west they likely date to the marquette advance ca 11 5 ka thus landforms related to two rivers and to marquette glaciations appear to comingle across the study area in the absence of extensive exposures and datable materials our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of michigan

joint inversions of seismic and geodynamic data for models of three dimensional mantle heterogeneity the seismic models of three dimensional 3 d mantle heterogeneity may be interpreted in terms of the density perturbations which drive mantle flow and thus provide important predictions of flow related observables such as the nonhydrostatic geoid the current models of global scale shear velocity heterogeneity provide reasonably good fits to the long wavelength nonhydrostatic geoid data 60 70 variance reductions but rather poor fits to the corresponding free air gravity anomalies 30 40 variance reductions this major difference is due to two factors 1 the very different amplitude spectrum of the gravity anomalies which is nearly flat for degrees l 3 the largest mismatch between the pattern of predicted and observed gravity anomalies is in the southern hemisphere this observation suggests that one reason for the poor overall match between the two fields may be that the global seismic data are not resolving sufficiently well the heterogeneity in the southern hemisphere portion of the deep mantle in contrast the gravity data provide accurate and geographically uniform constraints on the vertically integrated heterogeneity in the mantle we therefore perform a series of experiments in which we simultaneously invert a large set of seismic data which includes long period waveforms ss s and scs s differential travel times and normal mode structure coefficients and the long wavelength gravity anomaly data we thus determine whether it is possible to derive new 3 d heterogeneity models which satisfy both data sets the gravity anomaly data are interpreted in the context of spherically symmetric viscous flow models of the mantle in these inversion experiments we test several radial viscosity and ln ln profiles and thereby assess their plausibility the joint seismic geodynamic inversions reveal that it is indeed possible to greatly improve the fit to the free air gravity anomalies with variance reductions of 80 90 readily accessible while preserving the fit to the seismic data this improvement is achieved with some adjustment to the heterogeneity in the depth range 1500 2500 km where the seismic data constraints appear to be weakest the joint inversions also reveal new structures in the southern hemisphere portion of the lower mantle which apparently are not resolved by the seismic data alone

deformation in the lowermost mantle beneath australia from observations and models of seismic anisotropy observations of seismic anisotropy near the core mantle boundary may yield constraints on patterns of lowermost mantle flow we examine seismic anisotropy in the lowermost mantle beneath australia bounded by the african and pacific large low shear velocity provinces we combined measurements of differential splitting of sks skks and s scs phases sampling our study region over a range of azimuths using data from ten long running seismic stations observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle we identified two sub regions for which we have robust measurements of d associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations we tested a variety of elastic tensors and orientations including single crystal elasticity of lowermost mantle minerals bridgmanite post perovskite and ferropericlase tensors based on texture modeling in post perovskite aggregates elasticity predicted from deformation experiments on polycrystalline mgo aggregates and tensors that approximate the shape preferred orientation of partial melt we find that post perovskite scenarios are more consistently able to reproduce the observations beneath new zealand the observations suggest a nearly horizontal 100 axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models our modeling results further suggest dominant slip on the 010 plane in post perovskite aggregates provide a good fit to the data but the solution is non unique our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow

late quaternary temporal and event classifications great lakes region north america abstract several temporal and event classifications are used for the quaternary glacial and interglacial record in the great lakes region of north america although based on contrasting principles the classifications as practiced are similar to one another in most respects and they differ little from the classification proposed by chamberlin a century ago all are based on stratigraphic units having time transgressive boundaries thus the associated time spans and events are diachronous where application of geochronologic classification based on isochronous boundaries is not practical or useful we advocate the use of diachronic principles to establish local and regional temporal and event classifications diachronic and event classifications based on such principles are proposed herein for the great lakes region well established names including wisconsin sangamon and illinois are used at the episode or glaciation interglaciation rank without significant redefinition the hudson episode interglaciation is introduced for postglacial time the current interglacial interval the wisconsin episode is divided into the ontario elgin and michigan subepisodes in the eastern and northern parts of the great lakes region and into the athens and michigan subepisodes in the southern and western parts of the great lakes region

the northern limits of glacial lake algonquin in upper michigan abstract a number of ancient shorelines formed by late pleistocene proglacial lakes have been found in eastern upper michigan these shorelines delimit several water planes the uppermost of which is correlated with the main lake algonquin stage this correlation is based on the continuity of the highest water plane with main algonquin shorelines in wisconsin and ontario the strength of the shoreline features its altitudinal relationship with lower water planes and a reinterpretation of radiocarbon dates from the sault ste maria area the isobases of this water plane have a bearing of s75 e at the time of the maximum extent of lake algonquin ca 10 600 yr b p its northern ice limited border lay along the munising moraine the northernmost of the two main morainic systems of eastern upper michigan this interpretation lends support to the idea of a period of slow deglaciation from ca 11 000 to 10 000 yr b p an ice lobe occupied the central lake superior basin until early holocene time radiocarbon dates on wood found beneath till or outwash at several sites indicate a minor ice readvance from the central lake superior basin ca 10 000 yr b p if true this would have prevented the development of the post duluth series of glacial lakes in the western lake superior basin until ca 9900 yr b p well after the end of the main lake algonquin stage

variable azimuthal anisotropy in earth s lowermost mantle a persistent reversal in the expected polarity of the initiation of vertically polarized shear waves that graze the d layer the layer at the boundary between the outer core and the lower mantle of earth in some regions starts at the arrival time of horizontally polarized shear waves full waveform modeling of the split shear waves for paths beneath the caribbean requires azimuthal anisotropy at the base of the mantle models with laterally coherent patterns of transverse isotropy with the hexagonal symmetry axis of the mineral phases tilted from the vertical by as much as 20 are consistent with the data small scale convection cells within the mantle above the d layer may cause the observed variations by inducing laterally variable crystallographic or shape preferred orientation in minerals in the d layer

phase transition in mgsio 3 perovskite in the earth s lower mantle a new polymorph of mgsio3 more stable than the pbnm perovskite phase has been identified by first principles computations it has the cairo3 structure with cmcm symmetry and consists of sio3 layers intercalated by eightfoldcoordinated mg ions high temperature calculations within the quasiharmonic approximation give a volume change of f1 5 and a clapeyron slope of f7 5f0 3 mpa k at f2750 k and f125 gpa these pressure temperature p t conditions are close to those in which a phase transition in mgsio3 perovskite has been observed by in situ angle dispersive x ray diffraction measurements this transition appears to be associated with the du discontinuity d 2004 elsevier b v all rights reserved

the effect of temperature on the seismic anisotropy of the perovskite and post perovskite polymorphs of mgsio3 using elastic constants determined by ab initio molecular dynamics over a range of temperatures we show that the seismic anisotropy of mgsio3 perovskite is significantly temperature dependent at 90 gpa the direction of greatest shear wave splitting changes from 001 at 0 k to 010 at 3500 k in addition there is no shear wave splitting in the 100 direction at 0 k but a significant amount of splitting is exhibited at 3500 k we have also calculated the first set of high temperature elastic constants of the new post perovskite phase by ab initio molecular dynamics methods we find that in contrast to mgsio3 perovskite temperature has little effect on the acoustic anisotropy of this phase we determine ln vs ln vp for the post perovskite phase and find it to be very low about 0 9 this may be an important parameter for mapping out the post perovskite phase in the lowermost mantle

high pressure elastic anisotropy of mgsio3 perovskite and geophysical implications using plane wave pseudopotential method within the local density approximation lda we calculate single crystal elastic constants cij of orthorhombic mgsio3 perovskite generally accepted to be the major component of the lower mantle as a function of pressure up to 150 gpa our results are in excellent agreement with experimental data at zero pressure and compare favorably with other pseudopotential predictions over the pressure regime studied here we use our elastic constants to calculate anisotropy of seismic wave velocities as a function of pressure depth mgsio3 perovskite is shown to be highly anisotropic in all portions of the lower mantle and the nature of anisotropy changes significantly with depth the absence of significant seismic anisotropy in most of the lower mantle suggests that mgsio3 perovskite assumes nearly random orientation in most of this region anisotropy at the topmost lower mantle suggested by some studies can be attributed to the preferred orientation of perovskite however anisotropy in the d layer is difficult to be attributed to preferred orientation of perovskite some other mechanisms including the presence of the aligned melt pockets and or lattice preferred orientation of magnesiowustite are needed

paleowind 11 000 bp directions derived from lake spits in northern michigan we report on the characteristics of several previously unstudied late pleistocene spits in northern lower michigan each spit developed as strong waves eroded a headland or island within the main and or later stages of glacial lake algonquin most have ese to wnw orientations with prominent recurved hooks at their ends some are as long as 20 km sedimentologically the spits contain thick several meters or more sequences of sand and well rounded gravel we suggest that summertime winds during the spits formation 11 800 to 10 500 bp were both very strong and dominantly from the e and se based on the following data 1 their ese source or head of the spit to wnw orientation 2 the presence of steep wave cut bluffs on the east sides of the islands and headlands and 3 spit locations on the northeastern shore of michigan s lower peninsula coupled with their absence on the northwestern shore just 100 km away wind direction data provided by these spits agree with paleoclimatic models that suggest that the laurentide ice sheet had developed a strong anticyclonic circulation the near lack of archeological sites from this time period in the northern lower peninsula which was surrounded by lake algonquin at that time supports the notion that the climate of northern lower michigan was inhospitably cold and very windy in the late pleistocene

deformation and texture development in cairo3 post perovskite phase up to 6 gpa and 1300 k at near ambient conditions cairo3 is isostructural with the high pressure polymorph mgsio3 post perovskite ppv mgsio3 ppv is thought to be a major phase in the earth s lowermost mantle cairo3 can thus serve as an analog for studying deformation of the ppv phase under conditions achievable with a multi anvil deformation apparatus here we study the rheologic behavior of cairo3 ppv at a variety of pressure and temperature conditions from 2 gpa to 6 gpa and 300 k to 1300 k and various strain rates sintered polycrystalline cairo3 ppv cylindrical in shape was deformed in the d dia multi anvil press in several shortening cycles up to 20 axial strain at each temperature and pressure shortening cycles were followed by lengthening back to 0 strain quantitative texture information was obtained using in situ synchrotron x ray diffraction and the rietveld method to analyze images in all cases we find that 010 lattice planes align perpendicular to the compression direction upon shortening and that there is little change in texture with temperature or pressure this texture pattern is consistent with slip on 010 100 the texture observed here is different from that produced in room temperature diamond anvil cell dac experiments on mggeo3 and mgsio3 ppv which both display textures of 100 and 110 lattice planes at high angles to the compression direction this implies that cairo3 ppv may not be a good analog for the plastic behavior of mgsio3 ppv 2008 elsevier b v all rights reserved

glacial isostatic deformation of the great lakes region tilting of ancient shorelines of the great lakes region has been studied for more than a century nevertheless fundamental disagreements exist among both glacial geologists trying to understand the chronology of lake events geophysicists investigating the causes of tilting and glaciologists attempting to reconstruct ice sheet thickness along the southern perimeter of the laurentide ice sheet fundamental to many of these studies is the belief that the southern part of the great lakes region has been geodynamically stable for at least the past 11 000 yr results of our numerical model of the glacio isostatic process for a spherical layered self gravitating viscoelastic earth suggest constraints upon earth models shoreline chronologies and ice sheet thickness as a test of the model predictions were compared to observations of outlet chronology and isobases of both ancient shorelines and modern tilting indicated by lake level gauges earth models with a uniform viscosity mantle resulted in the best fit to observed shorelines earth models with a low viscosity asthenosphere or a high viscosity lower mantle do not predict deformation consistent with known outlet chronologies an ice sheet with thickness of 2 000 m over the region results in an excessive amount of tilting in most instances whereas a much thinner ice sheet 700 m although in better agreement with the data generally resulted in underestimates none of the results suggests stability in the southern great lakes region at any time predictions indicate instead that submergence of ancient shorelines has complicated the record there

a holocene history of dune mediated landscape change along the southeastern shore of lake superior abstract causal links that connect holocene high stands of lake superior with dune building stream damming and diversion and reservoir impoundment and infilling are inferred from a multidisciplinary investigation of a small watershed along the se shore of lake superior radiocarbon ages of wood fragments from in place stumps and soil o horizons recovered from the bottom of 300 ha grand sable lake suggest that the near shore inland lake was formed during multiple episodes of late holocene dune damming of ancestral sable creek forest drownings at 3000 1530 and 300 cal years bp are highly correlated with local soil burial events that occurred during high stands of lake superior during these and earlier events sable creek was diverted onto eastward graded late pleistocene meltwater terraces ground penetrating radar gpr reveals the early holocene valley of sable creek now filled and its constituent sedimentary structures near planar paleosols identified with gpr suggest two repeating modes of landscape evolution mediated by levels of lake superior high lake stands drove stream damming reservoir impoundment and eolian infilling of impoundments falling lake superior levels brought decreased sand supply to dune dams and lowered stream base level these latter factors promoted stream piracy breaching of dune dams and aerial exposure and forestation of infilled lakebeds the bathymetry of grand sable lake suggests that its shoreline configuration and depth varied in response to events of dune damming and subsequent dam breaching the interrelated late holocene events apparent in this study area suggest that variations in lake level have imposed complex hydrologic and geomorphic signatures on upper great lakes coasts

in situ observations of phase transition between perovskite and cairo 3 type phase in mgsio 3 and pyrolitic mantle composition abstract in situ observations of the perovskite cairo3 phase transition in mgsio3 and in pyrolitic compositions were carried out using a laser heated diamond anvil cell interfaced with a synchrotron radiation source for pure mgsio3 the phase boundary between the orthorhombic mg perovskite and cairo3 type phases in the temperature range of 1300 3100 k was determined to be p gpa 130 3 0 0070 0 0030 t 2500 k using platinum as a pressure calibrant we confirmed that the cairo3 type phase remained stable up to pressures of at least 156 gpa and temperatures of 2600 k the consistency of our results with previous theoretical calculations leads us to conclude that the 2700 km seismic discontinuity at the bottom of the lower mantle can be attributed to a phase transition to the cairo3 type phase the phase change from an orthorhombic mg perovskite to a cairo3 type bearing assemblage in a pyrolitic mantle composition was also observed at p 125 gpa which corresponds to the same mantle depth as the seismic discontinuity the phase boundary between the orthorhombic mg perovskite and cairo3 type bearing assemblage was determined to be p gpa 124 4 0 008 0 005 t 2500 k using gold as a pressure calibrant this transition boundary indicates that the temperature at a depth of 2700 km is about 2600 k and the adiabatic temperature gradient in the lower mantle is estimated to be 0 31 k km the partition coefficients and the effect of some elements on the phase equilibrium between the orthorhombic mgsio3 perovskite and cairo3 type mgsio3 were estimated from ab initio calculations our experimental and theoretical results indicate that the d layer consists of a cairo3 type bearing assemblage which is likely to have significant effect on the chemical and thermal evolution of the earth s mantle

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

temperature profile in the lowermost mantle from seismological and mineral physics joint modeling the internal structure of the core mantle boundary cmb region of the earth plays a crucial role in controlling the dynamics and evolution of our planet we have developed a comprehensive model based on the radial variations of shear velocity in the d layer the base of the lower mantle and the high p t elastic properties of major candidate minerals including the effects of post perovskite phase changes this modeling shows a temperature profile in the lowermost mantle with a cmb temperature of 3 800 200 k which suggests that lateral temperature variations of 200 300 k can explain much of the large velocity heterogeneity observed in d a single crossing phase transition model was found to be more favorable in reproducing the observed seismic wave velocity structure than a double crossing phase transition model

reinterpretation of a portion of the munising moraine in northern michigan field relationships between topography and surficial sediments indicate that the 25 km long segment of the munising moraine south of grand marais in michigan9s northern peninsula is not composed of till as suggested or implied by others but consists of a series of heads of outwash and related stagnation landforms topographic and limited subsurface data support the interpretation that mean drift thickness in the segment is at least 10 to 20 m these relationships show that the feature does not have a bedrock core and is not a classical end moraine instead deglaciation was characterized by stagnation zone retreat with glaciofluvial deposition at three successive ice marginal positions defined by closely spaced morphosequences

fabric development in mg fe o during large strain shear deformation implications for seismic anisotropy in earth s lower mantle abstract large strain shear deformation experiments were performed on mg 1 x fe x o x 0 25 1 0 one of the important minerals in earth s lower mantle deformation experiments were made on coarse grained 15 20 m grain size hot pressed aggregates at conditions of t t m 0 46 0 65 t temperature t m melting temperature and 0 4 10 3 to 0 9 10 3 differential stress shear modulus up to the shear strain of 7 8 under these conditions deformation occurs by dislocation creep the microstructural development in mg fe o is found to be sluggish and the complete dynamic recrystallization and nearly steady state fabric lattice preferred orientation are achieved only after shear strains of 4 at nearly steady state mg fe o shows strong fabrics characterized by the 1 1 0 axes being parallel to the shear direction and the poles of the 1 0 0 planes and to a lesser extent the poles of the 1 1 1 planes normal to the shear plane the seismic anisotropy corresponding to the deformation fabrics in mg fe o was calculated the nature of anisotropy corresponding to a given flow geometry changes significantly with strain as a result of fabric evolution anisotropy changes also with depth pressure due to the large variation of elastic anisotropy of mg fe o with depth seismic anisotropy caused by the deformation fabric of mg fe o is very weak in the shallow lower mantle v sh v sv anisotropy assuming that mg fe o occupies 20 volume fraction of the lower mantle and little shear wave splitting of vertically travelling waves a result that is consistent with the seismological observations in the d layer of the circum pacific regions thus the deformation fabric of mg fe o is a vital candidate of the cause of seismic anisotropy in these regions anisotropy caused by the lattice preferred orientation of mg fe o has a distinct azimuthal anisotropy with a strong 4 term azimuth the direction of propagation of the fastest slowest sh or p wave is parallel perpendicular to the flow direction and the slowest fastest sh or p wave is at 45 from these two directions

the postperovskite transition the discovery of the postperovskite ppv transition has profound impact on our understanding of the core mantle boundary cmb region unlike perovskite pv the ppv phase has a layered structure of the sio6 octahedra which may lead to a large contrast in some properties with pv recent studies have proposed unusual properties of ppv such as a large positive clapeyron slope a large sensitivity of the transition depth to iron a decrease in bulk sound speed at the transition and a development of significant lattice preferred orientation many of the proposed properties can provide explanations for the intriguing seismic observations at the cmb region yet significant discrepancies still exist however rapid developments in mineral physics will continue to improve our knowledge on the changes across the ppv transition

paleoenvironmental and geomorphic significance of bluff top dunes along the au sable river in northeastern lower michigan usa abstract we report on the age and evolution of five well developed parabolic dunes that are perched on high 40 m bluffs along the southern lip of the au sable river valley in northeastern lower michigan u s a these dunes are located on west northwest facing exposures and mantle the jackpines delta which formed when the glacial au sable river system deposited sands and gravels into glacial lake warren in the huron basin sometime between 15 1 and 14 7 ka lake level subsequently fell 35 m as the ice margin retreated northward during the twocreekan interstadial this regression resulted in abandonment of the jackpines delta and incision of the associated surface by the ancestral au sable river lake level subsequently rose 50 m during the algonquin transgression which likely promoted valley widening through channel migration eight samples were collected for osl age determination of the dunes and yielded ages that suggest dune formation occurred mostly between 13 5 ka and 13 ka this result coupled with the landscape position of the dunes i e south side of river west northwest facing bluffs suggests that the dunes largely formed 1 during the algonquin transgression when bluffs were eroded by stream channel migration and 2 by west northwesterly winds that transported eolian sands from exposed bluff faces to the adjacent valley edge this study contributes to the understanding of perched dune formation in the great lakes region and further supports models indicating that westerly winds prevailed within 150 km of the ice margin during the late pleistocene it also demonstrates that interior dunes in this region formed in similar environmental settings to interior dunes in northern europe and suggests that local factors rather than specific climate intervals should also be considered as they relate to dune evolution

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

maximum flood regionalization in large basins study case of the alto sao francisco region minas gerais brazil this paper describes a regionalization method based on the tcev two component extreme value distribution function and its application to annual maximum flood series for the sao francisco river in minas gerais state brazil this statistical model is equivalent to the product of two exponentials both representing a poisson process the first corresponding to the most frequent floods and the second to the rare floods the theoretical aspects of the model and the regionalization method are briefly presented the study region is a 50 870 km2 river basin located in the southeast region of brazil characterized by a tropical climate in applying the technique two homogeneous regions were identified dividing the basin into southern and northern parts with respect to the annual maximum floods to validate the tcev regionalization model a stream gauge with a short of maximum floods that was not used in the fitting procedure was selected the tcev regionalized model fitted well showing that the method can be used for prediction across the entire basin copyright 2009 john wiley sons ltd

early holocene dune activity linked with final destruction of glacial lake minong eastern upper michigan usa abstract the early holocene final drainage of glacial lake minong is documented by 21 osl ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern upper michigan we employ a simple model wherein lake level decline exposes unvegetated littoral sediment to deflation resulting in dune building dunes formed subsequent to lake level decline prior to stabilization by vegetation and provide minimum ages for lake level decline optical ages range from 10 3 to 7 7 ka 15 ages on dunes adjacent to the lowest lake minong shoreline suggest final water level decline 9 1 ka the clustering of optical ages from vertically separated dunes on both sides of the nadoway gros cap barrier around 8 8 ka and a basal radiocarbon date behind the barrier 8120 40 14 c yr bp 9 1 cal ka bp support the hypothesis that the barrier was breached and the final lake level drop to the houghton low occurred coincident with 1 high meltwater flux into the superior basin and 2 an abrupt negative shift in oxygen isotope values in lake huron

on the resolution of density within the earth roughly 30 years have passed since the last publication of a linear resolution calculation of density inside the earth since that time the data set of free oscillation degnerate frequencies has been completely re estimated taking into account the biassing effects of splitting and coupling due to 3d structure this paper presents a new resolution analysis based on the new data and focuses on two particular issues 1 the density jump at the inner core boundary which is important in discussions of the maintenance of the geodynamo and 2 a possible density excess in the lowermost mantle which might be indicative of a hot abyssal layer we find that the density jump at the inner core boundary is 0 82 0 18 mg m 3 which is significantly larger than previously thought we also find little support for an excess density in the lowermost mantle though an increase

kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central lower michigan usa abstract in association with an undergraduate honors seminar at michigan state university we studied two small kame deltas in north central lower michigan these recently identified deltas provide clear evidence for a previously unknown proglacial lake glacial lake roscommon in this large basin located in an interlobate upland our first goal was to document and characterize the geomorphology of these deltas because both deltas are tied to ice contact ridges that mark the former position of the retreating ice margin within the lake our second goal was to establish the age of one of the deltas thereby constraining the timing of ice retreat in this part of michigan for which little information currently exists both deltas are composed of well sorted fine and medium sands with little gravel and have broad nearly flat surfaces and comparatively steep fronts samples taken from the upper 1 5 m of the deltas show little spatial variation in texture aside from a general fining toward their outer margins gullies on the outer margins of both deltas probably postdate the formation of the deltas proper we suggest that they formed by runoff during a permafrost period subsequent to lake drawdown we named the ice lobe that once covered this area the mackinac lobe because it had likely advanced into the region across the mackinac straits area five of six optically stimulated luminescence osl ages from one of the deltas had minimal scatter and were within 1000 years of one another with a mean age of 23 1 0 4 ka these ages suggest that the mackinac lobe had started to retreat from the region considerably earlier than previously thought even while ice was near its maximum extent in illinois and indiana and the remainder of michigan was ice covered this early retreat which appears to coincide with a short lived warm period indicated from the greenland ice core formed an opening that was at least occasionally flooded thick and deep fine textured deposits which underlie much of the region probably date to this time our work provides the first evidence of this extremely early ice retreat from central lower michigan occurring almost 4000 years before the southern margin of the ice saginaw lobe had started its retreat from the state

ground penetrating radar investigation of a lake bonneville deita provo level brigham city utah field experiments carried out in the brigham sand and gravel company pit near brigham city utah show an impressive similarity between observed gravelly deltaic foreset facies in highwall exposures and inclined reflections detected by ground penetrating radar gpr beneath the pit floor the radar indicates additional inclined strata more than 30 m deep in a test to compare different antenna frequencies 50 100 and 200 mhz using a 400 v transmitter 50 mhz antennas are capable of detecting gravel facies in excess of 30 m whereas signal loss for the 100 and 200 mhz antennas occurs below 23 and 17 m respectively though providing higher resolution

high resolution 3 d s velocity structure in the d region at the western margin of the pacific llsvp evidence for small scale plumes and paleoslabs abstract although previous tomographic studies found a large low s velocity province llsvp in the lowermost mantle beneath the pacific due to a lack of resolution it remains unclear whether the llsvp consists of clusters of small scale low velocity anomalies or large scale anomalies we recently deployed a seismic array in thailand which provides a dataset with wide azimuthal coverage at the western pacific llsvp we analyze the new dataset using waveform inversion and find high velocity anomalies extending vertically to a height of 400 km above the core mantle boundary cmb beneath the philippine sea and small scale low velocity patches with a diameter of 300 km at the cmb beneath new guinea the locations of the high velocity anomalies are consistent with the past izanagi plate subduction boundary and the low velocity anomalies can be interpreted as a small scale plume cluster hence we conclude that vertical flow upwelling plumes and downwelling of slabs is dominant in the lowermost mantle beneath the western pacific region

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

a new paradigm for earth s core mantle boundary understanding the boundary between earth9s rock mantle and the molten core is one of the key challenges in geoscience in his perspective garnero discusses recent geophysical discoveries that are forcing the adoption of a new paradigm for studying the core mantle boundary long thought to be a simple division between solid silicate rock and liquid iron alloy the core mantle boundary is now emerging as an active complex and heterogeneous region of earth9s interior

can we resolve 3d density heterogeneity in the lower mantle we reexamine the possibility of resolving 3d density structure in the mantle by performing test inversions using a dataset of well constrained degree 2 splitting coefficients we show that degree 2 in vs and vp can be resolved and confirm that dlnvs dlnvp 2 5 at depths 2000km indicating a chemical component to large scale heterogeneity models with positively correlated with vs in the deepest mantle fit the data at least as well as those in which density and velocities are anti correlated however some rough bounds on dln dlnvs can be inferred models obtained from geodynamic considerations are acceptable in contrast to models with large negative 0 6 dln dlnvs throughout the lower mantle the most robust feature is a marked increase in dln dlnvs at the top of the lower mantle reaching a maximum around 1500 km

mgsio3 postperovskite at d conditions the postperovskite transition in mgsio3 at conditions similar to those expected at the d discontinuity of earth s lower mantle offers a paradigm for interpreting the properties of this region despite consistent experimental and theoretical predictions of this phase transformation the complexity of the d region raises questions about its geophysical significance here we report the thermoelastic properties of cmcm postperovskite at appropriate conditions and evidences of its presence in the lowermost mantle these are i the jumps in shear and longitudinal velocities similar to those observed in certain places of the d discontinuity and ii the anticorrelation between shear and bulk velocity anomalies as detected within the d region in addition the increase in shear modulus across the phase transition provides a possible explanation for the reported discrepancy between the calculated shear modulus of postperovskite free aggregates and the seismological counterpart in the lowermost mantle

lowermost mantle flow at the eastern edge of the african large low shear velocity province abstract observations of seismic anisotropy in the lowermost mantle are plentiful but their interpretation in terms of mantle flow remains challenging here we interrogate the anisotropic structure of the lowermost mantle beneath the afar region just outside the edge of the african large low shear velocity province using a combination of shear wave splitting techniques applied to phases propagating at five distinct raypath orientations we then model the resulting data set by testing various candidate mechanisms for anisotropy the observations are best fit by a model that invokes the lattice preferred orientation lpo of post perovskite with the 100 crystallographic axis oriented either nearly vertically or highly obliquely to the horizontal plane plausible corresponding mantle flow scenarios involve a significant vertical flow component which suggests that the african large low shear velocity province edge may deflect ambient mantle flow upwards or may be associated with a sheet like upwelling

anisotropy as cause for polarity reversals of d reflections recordings of seismic events that sample the deep mantle can test different hypotheses of mantle processes and composition seismic reflections from structures in the d region the bottom 200 400 km of the earth s mantle can provide information on the velocity contrasts in this region by studying the waveforms and polarities of the d reflections in p and s waves we can potentially distinguish between different explanations for the observed structures such as phase transitions mineral texture or thermal anomalies here we use source receiver combinations that contain reflections from d in two different regions that are both characterised by fast seismic velocities in tomographic models beneath the caribbean a positive s velocity contrast but negative p wave velocity contrast across the d reflector has been reported previously consistent with a model of a phase change in mgsio3 in the second fast velocity region eurasia we detect positive p and s wave velocity contrasts in two orthogonal paths crossing in the lowermost mantle indicating a different scenario for d a path that crosses this region in 45 to the other two great circle paths shows evidence for a negative p velocity contrast one explanation to reconcile observations in both regions is a phase transition from perovskite to post perovskite with a fraction of 12 preferred crystal alignment in the post perovskite phase depending on the travel direction of the waves with respect to the flow direction in the lower mantle positive or negative velocity jumps can be expected other anisotropic models are considered but cannot fully explain the range of observations we find in the data c 2011 elsevier b v all rights reserved

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept