magnetic susceptibility anomalies of lithosphere beneath eastern europe and the middle east standard inversion methods for inverting aeromagnetic anomalies into magnetic susceptibility contrast in the crust are based on the assumption that the core field is constant over the region considered this assumption however does not hold over regions of a few thousand kilometer extent an inversion technique is developed which takes into account the variations in the core field both in direction and in intensity it can also take into account the surface topography of a magnetic layer within the lithosphere the technique is applied to a scalar magnetic anomaly map of eastern europe and the middle east derived from the magnetometer satellite magsat data the magnetic susceptibility contrast map thus obtained delineates the major tectonic features of the region small scale precambrian shields are characterized by high magnetic susceptibility the alpine himalayan belt has a distinct magnetic signature the collision zones are low susceptibility regions whereas the continental plates within the b

application of satellite magnetic anomaly data to curie isotherm mapping a boundary condition on temperature at depth in the continental crust can in principle be obtained by mapping of the curie isotherm where it forms the base of the magnetic crust an approach to mapping magnetic crustal thickness using satellite magnetic anomaly data is described because magnetic crustal thickness is small with respect to satellite altitude inversion of the anomaly data yields magnetization models expressing regional variations in the vertical integral of magnetization this parameter is inversely correlated with regional heat flow in the western united states suggesting that areas of low apparent magnetization are areas of thin magnetic crust resulting from a shallow curie isotherm for a simple model of a uniformly magnetized magnetic crust or intra crustal layer curie depth is linearly related to apparent magnetization if the relation can be calibrated by two or more curie depth estimates regional apparent curie isotherm configuration can be mapped in an alternative approach a family of curie depth models can be computed using assumed magnetization values in each case the curie depth configuration is used as a boundary condition in a thermal model that model is selected which gives a heat flow distribution best fitting observations conductive heat flow models for a traverse across the rio grande rift using a finite element technique and for a map grid using a one dimensional thermal model approximation are given as examples

chronology of the late weichselian glaciation in the bohemian forest in central europe abstract a glacial chronology based on in situ produced 10 be surface exposure dating of moraines in the bohemian forest central europe was established eleven exposure ages obtained for moraine boulders in the prasilske lake and laka lake valleys czech republic were complemented by 10 be ages from kleiner arbersee germany recalculated according to recently calibrated production rates in the northern hemisphere the glacial phases in the bohemian forest occurred during the last glacial maximum around 24 1 2 5 23 6 2 4 21 8 2 0 and 19 5 2 1 ka following phases of local glaciation occurred during the northern hemisphere deglaciation period around 16 ka and 14 ka the last indicated phase may correlate with older dryas the glacial chronology of the bohemian forest is in agreement with local glaciation chronologies in the giant mts krkonose mts and the eastern alps

cosmogenic nuclides and the dating of lateglacial and early holocene glacier variations the alpine perspective abstract based on cosmogenic 10 be data from four sites in the alps we discuss geological uncertainties associated with the dating of former cirque and small valley glacier margins at the early lateglacial gschnitz site trins austria a 3000 yr spread in 10 be exposure ages points to prolonged boulder instability three out of seven ages are not included in the mean age calculation which yielded 15 400 1000 yr indistinguishable from the oldest boulder age of 16 130 1040 yr as a result of the distinctive morphology at julier pass switzerland site we are able to exposure date the early 12 300 1300 yr and the late 11 300 600 yr egesen stadial glacier advances younger dryas equivalent not just final retreat at the kromer site austria 10 be exposure ages from five clast supported boulders are indistinguishable within the analytical uncertainties mean age 8400 500 yr in addition to moraine age key factors that may lead to too young ages include degree of matrix vs clast support of the boulders post depositional periglacial activity and tree coverage at the nagelisgratli bedrock site near grimsel pass switzerland exposure ages of 10 760 11 720 yr are consistent with early holocene cirque glacier retreat and underline the marked lack of nuclide inheritance in bedrock exposures in the alps

geophysical interpretation of the magnetic anomalies of china derived from magsat data the ambiguities about geophysical implications based on the correlation of scalar magnetic anomalies and geological features were investigated a method was developed to convert scalar magnetic anomalies into a map of the lateral variations of magnetic susceptibility of the lithosphere this map is directly correlated with the causative sources the method is based on spherical harmonic analysis of lateral variations seen on the scalar magnetic anomaly map and those of the lithospheric magnetic susceptibility the harmonic coefficients are related through the fundamental causality relationship governing a magnetized body and its associated scalar magnetic anomaly the main features of the resulting magnetic susceptibility anomalies are outlined

spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion abstract to facilitate geologic interpretation of satellite elevation potential field data analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation a powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion linear transformations of the equivalent source field lead to corresponding geoidal anomalies pseudo anomalies vector anomaly components spatial derivatives continuations and differential magnetic pole reductions a number of examples using 1 averaged surface free air gravity anomalies and pogo satellite magnetometer data for the united states mexico and central america illustrate the capabilities of the method

from valley to marginal glaciation in alpine type relief lateglacial glacier advances in the piec stawow polskich roztoka valley high tatra mountains poland abstract the piec stawow polskich roztoka valley in the high tatras western carpathians features typical alpine type relief with a deeply incised glacial trough and large compound trough head cirque the prominent hypsographic maximum in the valley 1680 2000 m along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms specifically the most recent lateglacial advances the valley has been intensively studied before in the context of glacial chronology in this paper we re establish the post last glacial maximum lgm glacial chronology of the valley via detailed geomorphologic mapping equilibrium line altitude ela reconstruction and schmidt hammer sh dating along with a critical review of previously published cosmogenic exposure age data 36 cl and lacustrine sediment chronology our results indicate that the first four of the five distinguished lateglacial stages roztoka i iii pusta i occurred before the bolling allerod b a interstadial thus virtually the entire valley became deglaciated in course of the oldest dryas cold phase a distinct reorganization of deglacial patterns from valley type to marginal type occurred before b a warming when the ela increased above the valley hypsographic maximum concentrated at the cirque bottom elevation it shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing this points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions we infer that glaciers vanished in the tatra mountains during the b a interstadial later a renewed advance during the younger dryas pusta ii formed a nearly continuous festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls furthermore we discus some paleoenvironmental significance of the geomorphological record in the valley as well the applicability of sh dating in constructing glacial chronology

analysis of magsat magnetic contrasts across africa and south america abstract comparisons of magsat magnetic contrasts and geology across the mesozoic assembly of africa and south america provide new insight into the interpretation of the long wavelength magnetic anomalies near the present continental margins across continental africa and south america the magsat magnetic contrasts can be correlated with geologic provinces formed before the mesozoic separation of the continents on the continents areas affected by significant mesozoic hotspot tectonism display negative magnetic contrasts suggesting a causative relationship between hotspot tectonism and the origin of the observed magnetic contrasts the magnetic characteristics of a portion of the lower crust in these areas appear to have been significantly altered during the mesozoic hotspot epeirogeny by analogy with the processes of continental rifting it is suggested that the magnetic mineralogy of the intruded lower crust may be dominated by weakly to non magnetic titanomagnetites oceanic magnetic contrast comparisons show that the positions of magnetic anomaly highs over the rio grande walvis ridge system of the south atlantic are consistent with the interpretation of their evolution over the walvis hotspot however only the parts of these ridges that were formed during the cretaceous normal polarity geomagnetic epoch bear strong magnetic contrasts remanent magnetization thus appears to be an important contributor toward the magsat magnetic anomalies of these features

timing and climatic drivers for glaciation across semi arid western himalayan tibetan orogen abstract mapping and forty seven new 10 be ages help define the timing of glaciation in the ladakh and pangong ranges in northwest india five new local glacial stages are defined for the ladakh range from oldest to youngest these include the ladakh 4 glacial stage at 81 20 ka the ladakh 3 glacial stage not dated the ladakh 2 glacial stage at 22 3 ka the ladakh 1 glacial stage not dated and the ladakh cirque glacial stage at 1 8 0 4 ka three local glacial stages are defined for the pangong range which include the pangong 2 glacial stage at 85 15 ka the pangong 1 glacial stage at 40 3 ka and the pangong cirque glacial stage at 0 4 0 3 ka the new 10 be ages are combined with 645 recalculated 10 be ages from previous studies to develop the first regional framework of glaciation across the dryland regions of the greater himalaya transhimalaya pamir and tian shan at the western end of the himalayan tibetan orogen nineteen regional glacial stages are recognized that are termed semi arid western himalayan tibetan stages swhts these include swhts 9 at 311 32 ka swhts 7 at 234 44 ka tentative swhts 6 at 146 18 ka swhts 5e at 121 11 ka swhts 5a at 80 5 ka swhts 5a at 72 8 ka swhts 4 at 61 5 ka swhts 3 at 46 4 ka swhts 2f at 30 3 ka swhts 2e at 20 2 ka swhts 2d at 16 9 0 7 ka swhts 2c at 14 9 0 8 ka swhts 2b at 13 9 0 5 ka swhts 2a at 12 2 0 8 ka swhts 1e at 8 8 0 3 ka tentative swhts 1d at 6 9 0 2 ka tentative swhts 1c at 3 8 0 6 ka swhts 1b at 1 7 0 2 ka and swhts 1a at 0 4 0 1 ka regional glacial stages older than 21 ka are broadly correlated with strong monsoons swhts that are 21 ka or younger have smaller uncertainties and broadly correlate with global ice volume given by marine oxygen isotope stages and northern hemisphere climatic events oldest dryas older dryas younger dryas roman humid period and little ice age

improved moraine age interpretations through explicit matching of geomorphic process models to cosmogenic nuclide measurements from single landforms abstract the statistical distributions of cosmogenic nuclide measurements from moraine boulders contain previously unused information on moraine ages and they help determine whether moraine degradation or inheritance is more important on individual moraines here we present a method for extracting this information by fitting geomorphic process models to observed exposure ages from single moraines we also apply this method to 94 10 be apparent exposure ages from 11 moraines reported in four published studies our models represent 10 be accumulation in boulders that are exhumed over time by slope processes moraine degradation and the delivery of boulders with preexisting 10 be inventories to moraines inheritance for now we neglect boulder erosion and snow cover which are likely second order processes given a highly scattered data set we establish which model yields the better fit to the data and estimate the age of the moraine from the better model fit the process represented by the better fitting model is probably responsible for most of the scatter among the apparent ages our methods should help resolve controversies in exposure dating we reexamine the conclusions from two published studies based on our model fits

tl dating of partially bleached sediments by the regeneration method abstract thermoluminescence dating of sediments in the warsaw laboratory is based on blue to green emission the partial bleach regeneration method is proposed for dating sediments which have not been completely bleached at the time of burial correct tl ages are reported for sediments covering organic deposits of the eemian interglacial and also for glacial sediments of wurm and riss age we obtained good results for dating till using the partial bleach regeneration method the tl zeroing in till is explained by the rubbing or compression of grains beneath the glacier and by the freeze thaw activity occurring during glacial transport and deglaciation

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

the influence of aspect and altitude on the size shape and spatial distribution of glacial cirques in the high tatras slovakia poland the shape of glacial cirques is generally considered to result from the combined actions of climate topography and geology the goal of this article was to determine the dependence of cirque morphology on mesoclimatic conditions defined by altitude and aspect in the highest part of the carpathians the high tatras the morphology of each of 116 analyzed cirques was described using a set of 12 morphometric characteristics the relationships between the obtained data were evaluated using simple and multivariate statistical methods the results indicate that cirques in the high tatras are scale specific landforms with allometric development their occurrence increases with altitude but their size decreases the shape of the cirques is determined by altitude only to a small extent with the exception of an increase in the degree of incision with altitude the spatial distribution of cirques is negatively influenced by incoming solar radiation and positively influenced by moisture sources which came mainly from the nw to n during the cold phases of the pleistocene for this reason north facing cirques have proportionally stronger representation and are more incised with steep slopes thus cirques have proportionally stronger representation on the northern slopes and represent more developed glacial erosion landforms than those on the southern slopes although some relationships were detected between cirque morphology and mesoclimatic factors such as altitude and aspect a general discriminant analysis showed that these environmental factors did not explain variations in cirque morphology with sufficient cogency

10be exposure age chronology of the last glaciation in the krkonose mountains central europe abstract a new chronology of the last glaciation is established for the krkonose giant mountains central europe based on in situ produced 10be in moraine boulders exposure ages and schmidt hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the last glacial maximum lgm large moraines at the outlet of the snowy cirques niezne kotly and in the middle part of the upa ob i d l trough were deposited around 21 ka while a series of smaller moraines above the lgm deposits represent readvances that occurred no later than 18 1 0 6 ka 15 7 0 5 ka 13 5 0 5 ka and 12 9 0 7 ka an exposure age of 13 8 0 4 ka obtained for protalus ramparts at the foot of the upska jama cirque headwall indicates that glaciers advanced only in north to east facing cirques during the lateglacial the last glacier fluctuation was synchronous with the younger dryas cold event the timing of local glacier advances during the last glacial episode correlates with the late weichselian glacier phases in the alps and in the bavarian bohemian forest

deglaciation constraints in the parâng mountains southern romania using surface exposure dating cosmogenic nuclide surface exposure ages have been widely used to constrain glacial chronologies in the european regions this paper brings new evidence that the romanian carpathians sheltered mountain glaciers in their upper valleys and cirques until the end of the last glaciation twenty four 10be surface exposure ages were obtained from boulders on moraine crests in the central area of the par ng mountains southern carpathians exposure ages were used to constrain the timing of the deglaciation events during the late glacial the lowest boulders yielded an age of 13 0 1 1 1766 m and final deglaciation occurred at 10 2 0 9 ka 2055 m timing of the late glacial events and complete deglaciation reported in this study are consistent with and confirm previously reported ages of deglaciation within the carpathian and surrounding european region

size specific steady state accumulation area ratio an improvement for equilibrium line estimation of small palaeoglaciers abstract characteristic distribution of the steady state accumulation area ratio aar0 of valley and corrie glaciers was investigated in a global dataset comprised of 46 glaciers there is a positive relationship between aar0 and glacier area with smaller glaciers having lower values of aar0 compared with larger glaciers the relationship between glacier area s and steady state aar of studied glaciers can be optimally described by a logarithmic regression equation this relationship is thought to be a globally valid approximation if the size of the glacier is not smaller than 10 1 km2 in the case of palaeoglaciers an aar0 value of 0 44 0 07 is best applied on glaciers with areas in the range 0 1 1 km2 0 54 0 07 for glaciers covering areas between 1 and 4 km2 and 0 64 0 04 for glaciers larger than 4 km2 this assumes insignificant debris cover for the investigated palaeoglaciers the proposed size specific aar0 values take into account the geometric hypsometric properties of palaeo glaciers the results have major importance for palaeoglaciological reconstructions in many regions of former marginal niche glaciation characterized by small former glaciers

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

pogo and pangaea abstract long wavelength magnetic anomalies of crustal origin derived from the pogo and magsat satellite data often display a strong continuity across the now rifted continental margins when the continents are reassembled into pangaea these anomalies predate the breakup of the supercontinent and represent major blocks whose crustal properties are broadly similar even though those blocks are no longer contiguous

cosmogenic exposure dating of late pleistocene moraine stabilization in alaska seventy three new 1 0 be 2 6 al ages from 57 moraine boulders and 2 tors together with 43 previously published cosmogenic exposure ages from 41 moraine boulders allow us to critique the use of cosmogenic exposure ce dating of moraine boulders in alaska boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls boulder surface bedrock erosion rate can be roughly constrained and leads to a range in moraine stabilization ages snow cover history is difficult to constrain but its effect is thought to be minor for the tall boulders sampled despite these complications the ce ages provide important new information regarding the timing of the last and penultimate glaciations in alaska three penultimate moraines yielded ce ages that overlap with marine isotope stage mis 4 early mis 3 45 65 ka rather than mis 6 ca 140 ka based on a combination of our new ce chronologies and existing 1 4 c ages from six study areas glaciers retreated from their local late wisconsin maxima ca 24 27 ka kokrines hills west interior alaska ca 24 26 ka northeastern brooks range ne alaska ca 21 23 ka yukon tanana upland east interior alaska ca 22 ka ahklun mountains sw alaska ca 20 ka western alaska range central alaska ca 16 18 ka chuilnuk mountains sw alaska overall glacier retreat was concurrent with the peak of the last global glacial maximum probably in response to limited moisture availability

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

10 be exposure age chronology of the last glaciation of the rohacska valley in the western tatra mountains central europe abstract 10 be exposure ages from moraines and bedrock sites in the rohacska valley provide chronology of the last glaciation in the largest valley of the western tatra mts the western carpathians the minimum apparent exposure age of 19 4 2 1 ka obtained for the oldest sampled boulder and the mean age of 18 0 0 8 ka calculated for the terminal moraine indicate that the oldest preserved moraine was probably deposited at the time of the global last glacial maximum lgm the age of this moraine coincides with the termination of the maximum glacier expansion in other central european ranges including the adjacent high tatra mts and the alps the equilibrium line altitude ela of the lgm glacier in the rohacska valley estimated at 1400 1410 m a s l was 50 80 m lower than in the eastern part of the range indicating a positive ela gradient from west to east among the north facing glaciers in the tatra mts lateglacial glacier expansion occurred no later than 13 4 0 5 ka and 11 9 0 5 ka as indicated by the mean exposure ages calculated for re advance moraines this timing is consistent with the exposure age chronology of the last lateglacial re advance in the high tatra mts alps and lower mountain ranges in central europe the ela in the rohacska valley estimated at 1690 1770 m a s l in this period was located 130 300 m lower than in the north facing valleys in the high tatra mts 10 be exposure ages obtained for a rock glacier constrains the timing of this landform stabilization in the salatinska valley and provides the first chronological evidence for the lateglacial activity of rock glaciers in the carpathians

delineation of canadian sedimentary basins from magsat data abstract a crustal scalar magnetic anomaly map of canada and the northern united states is derived using data collected from the magsat satellite the anomalies are correlated to geological features basins associated with failed arms of old rifts have high magnetic anomalies the rocky mountains the appalachian mountains the suture zone of the grenville province modern hotspots and ocean ridges have low magnetic anomalies

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

expression of the younger dryas cold event in the carpathian mountains ukraine past glacial activity in the ukrainian carpathian mountains is characterized by cirques glacial valleys and moraine ridges at altitudes between 1350 and 1850 m a s l although the geomorphology of this area was extensively studied the deposition time of these glacial forms and specifically the moraines was never determined we surveyed and mapped the geomorphology of the pozhezhevs ka glacial valley which is part of the charnogora ridge we used surface exposure dating and developed a data base of this area using remote sensing and geographic information system to understand the timing and nature of glacial event in the eastern carpathian mountains well developed continuous lateral frontal moraines cross the valley floor at 1400 m a s l ten sandstone boulders were sampled from one of these to determine the deposition time of the moraine samples were prepared at the glasgow university cosmogenic nuclide laboratory and analyzed at the suerc ams laboratory surface exposure ages were calculated using the cronus earth online 10be exposure age calculator our exposure ages for nine samples ukr 2 to ukr 10 range from 11 0 0 4 10be ka to 14 5 0 5 10be ka one sample ukr 1 produced no current and thus no exposure age is available the mean deposition time for the moraine ranges from 12 4 0 3 to 12 9 0 3 10be ka depending on choice of surface erosion and snow cover these results provide the first direct indication using surface exposure dating of a possible glacier response in the ukrainian carpathian mountains to a cold event contemporary with the younger dryas yd together with exposure ages from other mountain ranges across europe the new data provide direct chronological evidence for a widespread expression of the yd cold event outside the main ice margin limits left by the former scandinavian ice sheet

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

timing of glacier advances and climate in the high tatra mountains western carpathians during the last glacial maximum during the last glacial maximum lgm long valley glaciers developed on the northern and southern sides of the high tatra mountains poland and slovakia chlorine 36 exposure dating of moraine boulders suggests two major phases of moraine stabilization at 26 21 ka lgm i maximum and at 18 ka lgm ii the dates suggest a significantly earlier maximum advance on the southern side of the range reconstructing the geometry of four glaciers in the sucha woda panszczyca mlynicka and velicka valleys allowed determining their equilibrium line altitudes elas at 1460 1460 1650 and 1700 m asl respectively based on a positive degree day model the mass balance and climatic parameter anomaly temperature and precipitation has been constrained for lgm i advance modeling results indicate slightly different conditions between northern and southern slopes the n s ela gradient finds confirmation in slightly higher temperature at least 1 c or lower precipitation 15 on the south facing glaciers during lgm i the precipitation distribution over the high tatra mountains indicates potentially different lgm atmospheric circulation than at the present day with reduced northwesterly inflow and increased southerly and westerly inflows of moist air masses

minimal crustal magnetizations from satellite data abstract the minimum amplitude crustal magnetization needed to explain magsat vector anomaly data is found using harmonic splines as basis functions shure et al 1982 phys earth planet inter 28 215 229 and choosing a subset of the original basis parker and shure 1982 geophys res lett 9 812 815 to represent magnetization we suggest the optimum model of this type is obtained by associating representers only with north and vertically downwards data points given the larger uncertainties associated with east component magsat data following parker et al 1987 rev geophys 25 17 40 we find a model minimizing the r m s volume integral of magnetization over the magnetized lithosphere the numerical effort involved in producing a regional or continental scale model with given horizontal spatial detail with our method is less than that for an equivalent source dipole model when the magnetization is not assumed induced approximately equal to that for an induced magnetization equivalent dipole model and considerably less than that for a spherical harmonic apparent susceptibility model the method is demonstrated by producing a solution for two regions the contiguous usa for comparison with previously published models and africa and its continental margins magnetization models fit the data slightly worse than those of the downward continued anomaly field at the earth s surface comparison of our component of magnetization for the usa in the direction of the core field with the induced magnetization equivalent dipole model of mayhew 1984 earth planet sci lett 71 290 296 is very good as expected for magnetization either induced by or frozen remanently in an approximately dipole field either parallel or antiparallel to the current rotation axis the east component of magnetization is much smaller than the north and vertically downwards components we make no assumptions about the relative contributions of remanent and induced magnetization and the resulting models have a substantial remanent component however our models suffer from the severe non uniqueness common to all magnetization models whereby magnetization in a uniform susceptibility and thickness shell concentric with the earth s centre owing to any internal magnetic field that is then switched off generates no external magnetic field

constraints on the late quaternary glaciations in tibet from cosmogenic exposure ages of moraine surfaces abstract this contribution provides new constraints on the timing of tibetan glacial recessions recorded by the abandonment of moraines we present cosmogenic radionuclide 10 be inventories at 17 sites in southern and western tibet 32 crests 249 samples and infer the range of permissible emplacement ages based on these analyses individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10 be abundance we consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages 1 erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age and 2 erosion progressively exposes large boulders with little prior exposure and so the oldest sample age records the minimum moraine emplacement age we found that depending on the scenario chosen the moraine emplacement age can vary by 50 for 100 ka old samples we consider two scaling models for estimating the production rates of 10 be in tibet which has an important although lesser effect on inferred moraine ages while the data presented herein effectively increase the database of sample exposure ages from tibet by 20 we find that uncertainties related to the interpretation of the 10 be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies a reanalysis of published data from moraines throughout tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the tibetan moraine age database thus when viewed in a similar way with other samples collected from this area uncertainties within moraine exposure ages obscure attribution of tibetan glacial advances to temperature minima or precipitation maxima our work suggests that more reliable chronologies of tibetan glaciations will come from improvements in production rate models for this portion of the world as well as a better understanding of the processes that form and modify these geomorphic surfaces

an interpretation of magnetic signatures of aulacogens and cratons in africa and south america abstract magnetic susceptibility anomalies associated with the lithosphere in africa and south america show that the lithosphere underlying sedimentary basins within aulacogens which originated during the rupture of the gondwana continent have lower magnetic susceptibility than the lithosphere underlying the cratons this can be explained by the demagnetization effects of high temperature asthenospheric material possibly intruded into the aulacogens during the rupture thermal evolution of different intrusion models implies that a thermal demagnetization may last for about 300 ma b there is no close relationship between the early subsidence rate of a basin and the magnetization of the underlying lithosphere c surface heat flow anomalies do not necessarily correlate with the magnetic susceptibility anomalies and d once an intrusion of more magnetic material cools to the ambient temperature the total magnetic susceptibility of the lithosphere may increase high magnetic susceptibilities associated with sedimentary basins over old crustal rifts can be explained by this phenomenon

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

paleoclimatic implications based on equilibrium line altitude depressions of reconstructed younger dryas and holocene cirque glaciers in inner nordfjord western norway abstract relative to a present cirque glacier in innner nordfjord western norway equilibrium line altitude ela depressions for reconstructed cirque glaciers formed during the younger dryas 11 000 10 000 yr b p the erdalen event 9100 200 yr b p and the little ice age mid 18th century are calculated by the use of accumulation area ratio aar and compared to the corresponding values for plateau glaciers the temperature precipitation ela tp ela as reflected by plateau glaciers gives considerably larger ela depressions than use of the temperature precipitation wind ela tpw ela for cirque glaciers ela depressions during the younger dryas erdalen event and the little ice age thus strongly indicate that cirque glaciers are much more sensitive to changes in winter precipitation than plateau glaciers the difference in ela depressions of contemporaneous plateau and cirque glaciers during the younger dryas erdalen event and the little ice age suggests that winter precipitation was reduced to 59 7 71 6 and 88 7 compared to present values taken into account the reduced winter precipitation the corresponding mean ablation season temperature depressions were probably 4 3 0 3 3 0 0 2 0 3 and 1 4 0 3 0 2 c respectively

a satellite magnetic model of northeastern south american aulacogens magnetic modeling of the amazon river and takatu aulacogens in northeastern south america illustrate the utility of satellite magnetic data in characterizing the properties and structure of the lithosphere specifically reduction of preliminary magsat scalar magnetic anomaly data to an equivalent condition of vertical polarization shows a general correlation between magnetic anomaly minima and the amazon river and takatu aulacogens surface gravity data demonstrate a correlative positive anomaly spherical earth modeling of the magnetic data indicates a less magnetic crust associated with the aulacogens which is compatible with previous studies over the mississippi river aulacogen and rio grande rift in north america

petrologic model of the northern mississippi embayment based on satellite magnetic and ground based geophysical data abstract a petrologic model of the northern mississippi embayment derived from gravity seismic and rift data is evaluated by converting the model to a magnetization model which is compared with satellite magnetic anomaly models a magnetization contrast of approximately 0 54 a m determined from the petrologic model of the embayment compares favorably to values of 0 62 a m and 0 45 a m from a magsat united states apparent magnetization contrast map and a published pogo magnetization contrast model respectively the petrologic model suggests that the magnetic anomaly low associated with the mississippi embayment may be largely due to the intrusion under non oxidizing conditions of low curie temperature gabbroic material at the base of the crust of the embayment near surface mafic plutons bordering the mississippi valley graben appear from aeromagnetic data to have higher magnetizations than the deeper gabbroic material however it is impossible to ascertain if this is due to compositional differences or similar material at shallower lower temperature depths these results indicate that variations in the curie temperatures of intrusions accompanying rifting may account for a large part of the wide range of magnetic anomalies associated with presently inactive rifts with normal heat flow

regional magnetic and gravity anomalies of south america preliminary satellite scalar magnetic anomaly data magsat reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of south and central america are compared to major tectonic features a number of correlations are observed but these must be generalized because of the preliminary nature of the geophysical data and the inherent petrophysical variations within tectonic features statistical analysis of the magnetic data reveals that south and central america are more magnetic and magnetically more variable than adjacent marine areas more obvious correlations exist between magnetic anomalies and tectonic elements of the continents than in the case of oceanic areas no obvious correlations occur between the tectonic features of the atlantic ocean including the mid atlantic ridge and magnetic anomalies the continental shields generally are more magnetic than adjacent basins oceans and orogenic belts in contrast the major aulacogens are characterized by negative magnetic anomalies positive free air gravity anomalies are related to the andean foldbelt but the relationship of this feature to magnetic anomalies is much less obvious however along the west coast of south america the magnetic anomalies of the pacific ocean are separated from those of the eastern platforms by north to northwest trending anomalies south of the equator along the foldbelt gravity maxima are related to magnetic minima a relationship analogous to the situation observed in the rocky mountain cordillera north of the equator in columbia gravity and magnetic maxima roughly correlate along the foldbelt

detecting uniaxial single domain grains with a modified irm technique summary mid ocean ridge basalt morb specimens have often been found to have high ratios of saturation remanence to saturation magnetization mrs ms this has been attributed either to dominant cubic anisotropy or to insufficient saturating field leading to overestimation of mrs ms of a dominantly uniaxial single domain usd assemblage to resolve this debate we develop an independent technique to detect usd assemblages the experimental protocol involves subjecting the specimen to bidirectional impulse fields at each step the experiment is similar to the conventional isothermal remanent magnetization irm acquisition experiment but the field is applied twice in antiparallel directions we define a new parameter irat as the ratio of the remanences at each field step and show it to have characteristic behaviour for the two assemblages irat 1 at all field steps for usd and 1 with a strong field dependence for multi axial single domain msd grains we verified the theoretical predictions experimentally with representative usd and msd specimens experiments with morbs gave low irats for specimens having high mrs ms this argues for a dominant msd assemblage in the morbs possibly cubic in nature although undersaturation of the samples can indeed be a contributing factor to the exceptionally high mrs ms this study shows that the nature of the assemblage cannot be dominantly usd