kinematic constraints on thrust belt curvature from syndeformational magnetizations in the lagos del valle syncline in the cantabrian arc spain a detailed paleomagnetic study in a single first order refolded syncline in the western hinge zone of the variscan foreland fold and thrust belt of northern spain was carried out to constrain the tectonic deformation of the cantabrian arc results show a complex pattern of structural deformation and acquisition of at least two secondary syntectonic magnetizations on the basis of local and regional fold tests we document an early permian b component that postdates earlier f1 westphalian and stephanian thrusting and folding and a late carboniferous to earliest permian c component that is synfolding acquired during fl the b component only resides in the carbonates and is carried by magnetite the c component is carried by magnetite in the gray carbonates and by hematite in the red beds both b and c components reveal significant vertical axis rotations that indicate that an originally cylindrical lagos del valle syncline was refolded f2 about a vertical axis after acquisition of the b component magnetization the pattern of rotations suggests that the entire cantabrian arc may have originated as a much more linear fold and thrust belt which was later modified by significant oroclinal bending with relative rotations totaling at least 120 the temporal distribution of remagnetization and deformation also suggests a protracted variscan orogeny in the area lasting from at least the late carboniferous into the permian

active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

carbonate deposition pyramid lake subbasin nevada 1 sequence of formation and elevational distribution of carbonate deposits tufas abstract during the late quarternary the elevation of terrace cutting and carbonate deposition in the pyramid lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins sill elevations are 1177 1183 m mud lake slough sill 1207 m emerson pass sill and 1265 m darwin pass sill carbonate deposition was favored by 1 hydrologic closure 2 proximity to a source of calcium 3 elevated water temperature and 4 a solid substrate the thickness and aspect of tufa are a function oflake level dynamics relatively thin sheets and pendant sheets were deposited during a rising or falling lake the upper parts of thick reef form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the carson desert subbasin the lower parts of the reef form tufas are thinner and their outer surface has a vertical aspect indicating that the lower part formed in a receding lake the thickest and most complete sequences of tufa are mounds that border the pyramid lake shore the tops of the tallest mounds reach the elevation of the darwin pass sill and many mounds have been eroded to the elevations of the mud lake slough sill of the emerson pass sill the sequence of tufa formation from oldest to youngest displayed in these mounds is 1 a beachrock containing carbonate cemented volcanic cobbles 2 broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa 3 large cylindrical tubular tufas capped by 4 coatings of old dense tufas and 5 several generations of old branching tufa commonly associated with thin platy tufas and coatings of thinolitic tufa 6 young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge 7 a transitional thinolite to branching tufa 8 two or more layers of young branching tufa 9 a 0 5 cm thick layer of fine grained dolomite 10 a 2 cm thick layer of young dense laminated tufa 11 a 0 1 cm thick layer of encrusting tufa that was covered by a beach deposit and 12 a 1 0 cm thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds the elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations it seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of lake lahontan it is hypothesized that the thinolitic tufa ikaite formed in the near freezing hypolimnion and the braching tufa calcite formed in the seasonally warmer epiliminion of the lake

greenland snow accumulation estimates from satellite radar scatterometer data data collected by the c band ers 2 wind scatterometer escat the ku band adeos 1 nasa scatterometer nscat and the ku band seawinds on quikscat qscat satellite instruments are used to illustrate spatiotemporal variability in snow accumulation on the greenland ice sheet microwave radar backscatter images of greenland are derived using the scatterometer image reconstruction sir method at 3 day intervals over the periods 1991 1998 and 1996 1997 for escat and nscat respectively the backscatter coefficient normalized to 40 incidence a and gradient in backscatter b in the range 20 60 are compared with historical snow accumulation data and recent measurements made in the program for arctic regional climate assessment parca shallow snow pits empirical relationships derived from these comparisons reveal different exponential relationships between c and ku band a values and dry snow zone mean annual accumulation q frequency difference images between overlapping scatterometer images suggest that c band data are more sensitive to snow layering and buried inhomogeneities whereas ku band data are more sensitive to volume scattering from recently accumulated snow direct comparisons between nscat b values and in situ q measurements show a linear relationship between ln q and b with a negative rank correlation of r 0 8 the root mean square residual in fitting regression line equation ln q 3 08 17 83b to the data is 0 05 m snow water equivalent this simple ku band empirical relationship is exploited to investigate decadal changes in dry snow zone accumulation between seasat 1978 and nscat 1996 additional comparisons between nscat and recent qscat 1999 data reveal significant upslope shifts in the dry snow line along the southwestern flank of the ice sheet recent acceleration in the increase in intensity of scattering is observed in the percolation zone suggesting increased melting between 2000 and 3000 m elevation in the southern half of the ice sheet

kinematics of orocline tightening in the core of an arc paleomagnetic analysis of the ponga unit cantabrian arc northern spain 1 paleomagnetic and structural analyses of the western european variscan belt wevb suggest that the most viable kinematic model for variscan deformation in northern iberia is oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases e w in the late carboniferous and n s in the permian both in present day coordinates which resulted in the refolding about steeply plunging axes of initially north south trending thrusts and folds in the hinge zone and oroclinal tightening due to vertical axis rotation of the belt s limbs however the orocline model has yet to be critically tested in the wevb s core this study reports new paleomagnetic rock magnetic and structural data from the inner core of the wevb in order to test opposing kinematic models for the well documented fault and fold interference structures formed by late stage variscan deformation and to better understand the overall development of the wevb arc map scale structural features within the wevb core have a highly sinuous geometry characterized by transverse and thrust parallel fold systems formed by fault bend folding over footwall ramps the intersections of these two fold systems produce steeply plunging interference folds which are best exposed in the ponga thrust unit a total of 67 paleomagnetic sites were collected in the barcaliente formation of the ponga unit with emphasis placed on detailed spatial coverage of individual structural domains a multicomponent paleomagnetic remanence was measured which is interpreted to be composed of two components a low unblocking temperature recent viscous magnetization and a high unblocking temperature ancient magnetization that was acquired in the latest stephanian to early permian after initial d1 thrusting and folding bur prior to major secondary rotation rock magnetic experiments show that the characteristic remanence magnetization is carried by secondary authigenic pseudosingle domain magnetite these paleomagnetic results are used to determine the kinematics and geometry of postmagnetization deformation by restoring in situ magnetic vectors back to a defined reference direction on the basis of the restored ponga unit geometry the steeply plunging interference folds found in the wevb core are best described by a combination of secondary buckling of frontal ramp parallel hanging wall anticlines and modification of d1 lateral oblique ramps as frontal ramps during late stage north south shortening this combination of structural modification of the inner core of the wevb was necessary to accommodate oroclinal bending during the final amalgamation of pangea in the late paleozoic

late pleistocene to present lake level fluctuations at pyramid and winnemucca lakes nevada usa a new lake level curve for pyramid and winnemucca lakes nevada is presented that indicates that after the 15 500 cal yr bp lake lahontan high stand 1338 m lake level fell to an elevation below 1200 m before rising to 1230 m at the 12 000 cal yr bp younger dryas high stand lake level then fell to 1155 m by 10 500 cal yr bp followed by a rise to 1200 m around 8000 cal yr bp during the mid holocene levels were relatively low 1155 m before rising to moderate levels 1190 1195 m during the neopluvial period 4800 3400 cal yr bp lake level again plunged to about 1155 m during the late holocene dry period 2800 1900 cal yr bp before rising to about 1190 m by 1200 cal yr bp levels have since fluctuated within the elevation range of about 1170 1182 m except for the last 100 yr of managed river discharge when they dropped to as low as 1153 m late holocene lake level changes correspond to volume changes between 25 and 55 km 3 and surface area changes between 450 and 900 km 2 these lake state changes probably encompass the hydrologic variability possible under current climate boundary conditions

analysis of variscan dynamics early bending of the cantabria asturias arc northern spain calcite twinning analysis in the cantabria asturias arc caa of northern spain provides a basis for evaluating conditions of variscan stress and constrains the arc s structural evolution twinning typically occurs during earliest layer parallel shortening offering the ability to define early conditions of regional stress results from the somiedo correcilla region are of two kinds early maximum compressive stress oriented layer parallel and at high angles to bedding strike d1c1 and later twin producing compression oriented sub parallel to strike d2c1 when all d1 compressions are rotated into a uniform east west reference orientation a quite linear north south trending fold thrust belt results showing a slight deflection of the southern zone to the south southeast north south directed d2c1 compression was recorded prior to bending of the belt calcite twinning data elucidate earliest structural conditions that could not be obtained by other means whereas the kinematics of arc tightening during d2 is constrained by paleomagnetism a large and perhaps protracted d2c1 is suggested by our results as manifested by approximately 50 arc tightening prior to acquisition of paleomagnetic remagnetizations throughout the caa early east west compression d1c1 likely resulted from the ebro aquitaine massif docking to laurussia whereas the north directed collision of africa d2c1 produced clockwise bending in the northern zone radial folding in the hinge and rotation of thrusts in the southern zone fl 2000 elsevier science b v all rights reserved

the formation of an orocline by multiphase deformation a paleomagnetic investigation of the cantabria asturias arc northern spain the variscan orogeny in the cantabria asturias arc caa of northern spain represents a multiphase deformation history associated with pangea s amalgamation to determine the timing and kinematic history of deformation a paleomagnetic investigation was carried out on devonian limestones in three structural domains of the caa s hinge zone two characteristic remagnetizations in the caa are distinguished an early permian b component that postdates initial westphalian stephanian aged folding f1 and f2 and a late carboniferous c component that postdates f1 deformation both the b and c magnetizations experienced a later f3 folding phase the kinematics and geometry of post magnetization deformation are determined by bringing measured magnetic directions into agreement with reference directions these structural corrections also allow separation of deformation events in time we conclude that generally east west trending but variably plunging fold axes characterize f3 folding in the hinge zone of the caa this post magnetization deformation involved significant amounts of tilting and sub vertical axis rotation which together produced clockwise rotation in the north of the arc and counterclockwise rotation in the south of the arc to form the horseshoe shaped orocline that is observed today f3 fold axes change from near vertical to moderately inclined between and within structural domains due to the structural fabric imposed by f1 and f2 based on calculated f3 fold properties we can reconstruct pre existing f1 and f2 structural geometries of the hinge zones this analysis shows that f1 and f2 structures are the result of late carboniferous deformation as part of the same east west but temporally discrete compression regimes on the other hand f3 is controlled by permian north south

surface melting on antarctic peninsula ice shelves detected by passive microwave sensors a 13 year time series of spaceborne passive microwave radiance measurements over the antarctic peninsula ice shelves reveals a systematic increase in the duration of the summer melt season combined with data from meteorological stations on the antarctic peninsula the annual motion and long term trends of the 0 c isotherm can be monitored

thin skinned tectonics in the ponga region cantabrian zone nw spain the variscan thrust and associated fold structures of the ponga region cantabrian zone nw spain are interpreted in terms of thin skinned tectonics with a dominant eastward transport direction

mega fold interference patterns in the beishan orogen nw china created by change in plate configuration during permo triassic termination of the altaids abstract kilometer size fold interference patterns in the beishan orogenic collage boc in the southernmost altaids formed by fold superimposition in fossiliferous permian sedimentary rocks first phase f 1 upright and almost north trending folds were refolded by e to ene trending f 2 folds whose axial planes and axes are vertical or subvertical from east to west there is a regional change in style of interference patterns from lobate cuspate to crescent to mushroom shape this variation is accompanied by a westward decrease in the f 2 interlimb angle and related to a higher percentage of coarse grained clastic rocks suggesting a dependence of the f 2 deformation on lithology axial planar slaty cleavages are well developed in f 1 and poorly developed in f 2 folds the superposed folds mainly underwent flexural slip and flexural flow folding to give rise to the lobate cuspate pattern and to the crescent pattern caused by flattening and flexural flow folding where the sediments were unconsolidated and enriched in fluids the two folding events are interpreted to result from a major change in plate configuration that caused the inversion of an inter arc basin during the final amalgamation of the boc in the latest permian to early to mid triassic the two folding events bracketed between a maximum detrital zircon age of

calving and ice shelf break up processes investigated by proxy antarctic tabular iceberg evolution during northward drift using a combination of satellite sensors field measurements and satellite uplinked in situ observing stations we examine the evolution of several large icebergs drifting east of the antarctic peninsula towards south georgia island three styles of calving are observed during drift rift calvings edge wasting and rapid disintegration rift calvings exploit large pre existing fractures generated in the shelf environment and can occur at any stage of drift edge wasting is calving of the iceberg perimeter by numerous small edge parallel sliver shaped icebergs preserving the general shape of the main iceberg as it shrinks this process is observed only in areas north of the sea ice edge rapid disintegration where numerous small calvings occur in rapid succession is consistently associated with indications of surface melt saturation surface lakes firn pit ponding freeboard measurements by icesat indicate substantial increases in ice thinning rates north of the sea ice edge from 30 m a 1 but surface densification is shown to be an important correction 2 m freeboard loss before the firn saturates edge wasting of icebergs in warm surface water sea ice free 1 8 c implies a mechanism based on waterline erosion rapid disintegration larsen b style break up is likely due to the effects of surface or saturated firn water acting on pre existing crevasses or on wave or tidally induced fractures changes in microwave backscatter of iceberg firn as icebergs drift into warmer climate and experience increased surface melt suggest a means of predicting when floating ice plates are evolving towards disintegration

correlating deformation in variscan nw iberia using porphyroblasts implications for the ibero armorican arc abstract 3 d microstructural analysis of 30 porphyroblastic samples from the variscan orogen in nw iberia has revealed four sets of inclusion trails with distinctive geographic trends and relative timing the chronological and orientational consistency of these microstructures provides a reference frame for the correlation of macroscopic structural successions the two younger inclusion trail sets correlate with the main map scale structures of middle to upper carboniferous age whereas the two older sets correspond to mesoscopic structures preserved locally in low strain pods and dating back as far as 365 ma upper devonian inclusion trail orientations appear uninfluenced by a major orocline in the study area ibero armorican arc outlined by late stage folds and thrusts with variable trends it is proposed that the orocline developed by wnw ese trending transpression superposed on originally n s to ne sw trending structures during a late stage of the orogeny upper carboniferous domains of low or zero strain e g porphyroblasts are inferred to have maintained relatively constant orientations in the zone of transpression presumably due to deformation partitioning effects consequently they preserve a succession of pre orocline structural trends the collected microstructural data also indicate moderate preferred vertical and horizontal orientations of inclusion trails in the analysed samples as reported earlier in other variscan regions this probably witnesses a dynamic equilibrium between tectonic forces and gravity during four periods of differently oriented crustal shortening that generated the four recognised sets of inclusion trails

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

three dimensional geometry and interference of fault bend folds examples from the ponga unit variscan belt nw spain abstract examples of the three dimensional geometry and interference patterns between fault bend folds occur in the ponga unit of the variscan cantabrian foreland thrust and fold belt of nw spain the ponga unit consists of several e directed thrust sheets with a cumulative displacement of 93 km which were emplaced during upper westphalian stephanian time two major lateral ramps developed in the basal thrust of the ponga unit reaching 15 and 20 km in length respectively and some 3 km in height lateral structures are also common within the hangingwall thrust sheets the three dimensional staircase trajectories of thrust faults together with the tectonic superposition of thrust sheets has produced a complex interference pattern of fault related folds most map scale folds formed as fault bend folds related to interference between frontal and lateral ramps fold geometry and size varies depending on the geometry and size of the associated thrust ramp and flat the axial traces are grouped into lateral and frontal sets which are sub parallel or sub perpendicular to the tectonic transport direction respectively corner folds form with plunging axes at the intersections of frontal and lateral ramps and generally link pairs of frontal lateral folds they have relatively short axial traces that are oblique to the tectonic transport direction fold plunge varies due to the superposition of lateral and frontal structures of a thrust fault and also depends on the geometry of subsequent thrusts in the footwall the final geometry of frontal folds in the ponga unit are not only the result of the bending mechanism but have been modified by simple shear parallel to the emplacement direction major lateral structures have been reactivated as reverse faults and are locally overturned due to post emplacement north south compression

crustal structure of the external variscides in northwest spain from deep seismic reflection profiling abstract recent deep crustal seismic reflection profiling escicantabrica 1 provides a detailed image of the external parts of the variscan belt in northwest spain these seismic data together with surface geological information provide constraints on the crustal structure of the foreland thrust and fold belt cantabrian zone and the transition to the hinterland areas narcea antiform area the image in the cantabrian zone includes strong inclined reflections in the upper 5 s that correspond to mappable paleozoic rocks at the surface which have been deformed by thrusting and folding during the carboniferous some of the major thrust faults imaged show a ramp flat geometry at depth and merge into a highly reflective band between 5 and 6 s that corresponds to the cantabrian zone detachment the precambrian basement is almost transparent underneath the cantabrian zone detachment there are a few subhorizontal discontinuous reflections at 11 s that may correspond to the reflection moho at the transition to the hinterland the seismic profile includes short inclined reflections grouped in several reflective bands in the upper 6 s these correspond to the narcea antiform which comprises at the surface a stack of thrust sheets containing precambrian rocks the narcea antiform is placed above a crustal scale ramp imaged by strong w dipping reflections between 6 and 9 s these reflections merge upwards into the cantabrian zone detachment at 6 s and downwards into a reflective lower crustal zone located between 9 and 12 s these midcrustal reflectors are interpreted as a major variscan shear zone that marks the transition between the thin skinned tectonics of the external areas and the thick skinned tectonics of the hinterland areas the lower crust is highly reflective below the narcea antiform area and reflectivity fades out to the east beneath the foreland thrust and fold belt the different seismic responses at middle and lower crustal levels in the foreland and hinterland areas suggest that variscan tectonics strongly affected deep crustal levels in the hinterland areas whereas they remained undeformed beneath the foreland

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

analysis of kilometric scale superposed folding in the central coal basin cantabrian zone nw spain abstract the carboniferous paralic sequence of the central coal basin cantabrian zone hercynian nw spain contains an outstanding example of kilometric scale superposed folding that allows comparison with previous experimental models first generation folds have a n s trend and mainly constitute a fold train of fault propagation folds in which an increase of interlimb angle and an increase in the dip of the axial plane is observed from west to east a second folding phase gave rise to two types of upright roughly e w oriented superposed folds the superposed folds generated in general by buckling but their trend and situation are controlled by lateral ramps of the previous thrusts in many cases superposed folds of the first type are the most common and have developed on the limbs of previous folds without folding their axial surfaces they occur in zones and usually have kilometre scale hinge lines with syngenetic curved traces these folds present wavelengths distinctly smaller than those of the previous folds the second type of superposed folds affect both the limbs and axial planes of the previous folds these second type folds are in some cases smaller than previous folds and have developed on closed early folds but in other cases they are large wavelength folds related to the tightening of lateral ramps of the thrusts

comparison of microwave backscatter anisotropy parameterizations of the antarctic ice sheet using ascat the c band eumetsat advanced scatterometer ascat was launched in 2007 and provides backscatter measurements with excellent azimuth and incidence angle diversity in polar regions c band backscatter measurements can be used to retrieve near surface snow firn properties such as grain size and accumulation rate however the antarctic ice sheet ais exhibits strong microwave backscatter anisotropy as a function of both incidence and azimuth angles and this anisotropy must be well understood before such physical parameter retrieval can be accurately performed this paper presents a detailed comparison of several different parameterizations of both the azimuth and the incidence anisotropy parameterizations used here result in residuals similar to the radiometric performance of ascat indicating accurate characterization of the anisotropy the analysis of these parameterizations provides an insight into the physical mechanisms taking place near the surface of the ais 30 day composite maps of several parameters are presented and discussed in the context of near surface glaciology this anisotropy characterization will form the basis of a technique for extraction of physical parameters of the ais

patterns of fold interference influence of early fold shapes abstract model experiments were specifically designed to test the effect of different profile shapes of early folds on refolding patterns comparison of natural examples with experimental results and analogy with engineering information on buckling of fold shapes suggest that when layers are mechanically active during refolding the profile shape of the early folds markedly affects the patterns of fold interference open rounded folds tend to refold to form dome and basin patterns of interference whereas isoclinal folds tend to refold by folding their axial plane forming type 2 patterns of interference hence the dimensions and shape of the profile of the early folds control the preferred buckling mode during refolding

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

enhanced resolution reconstruction of ascat backscatter measurements a wind scatterometer measures the normalized radar cross section of the earth s surface in order to estimate the ocean near surface wind each measurement is the weighted integral of over an area so samples of are filtered by a measurement spatial response function srf enhanced resolution data may be produced from measurements and their associated srf using image reconstruction algorithms these enhancedresolution data products are useful for land and ice studies in addition to high resolution ocean wind retrieval the spatial resolution and noise may be improved by combining data for multiple passes trading off temporal resolution for spatial resolution in this paper we consider the production of enhanced resolution image reconstruction from the advanced scatterometer ascat on the metop satellites for land and ice regions two previously introduced image reconstruction algorithms the weighted average ave and scatterometer image reconstruction sir are applied to ascat data as well as a conventional gridding method we select optimum values of the reconstruction parameters for ascat the imaging algorithms are compared and evaluated as quantified by the spatial resolution pixel mean and variance and pixel correlation of the produced images the effective spatial resolution of the ave and sir reconstructed images is on the order of 15 to 20 km an improvement over the nominal spatial resolution of 25 and 50 km for the spatially averaged swath oriented ascat l1b products

hinge migration as a mechanism of superimposed folding abstract paraffin wax analogue modelling of superimposed folding shows how early fold shape and orientation determine fold axis orientation type of interference pattern and mechanism of superposed folding during two successive deformations the behaviour depends on the angle between the first and second compression directions i when they are perpendicular to each other classic superposed folding with either domes and basins or folds with vertical axes develop depending on whether the earlier folds were open or closed ii when the two compression directions are oblique the earlier folds rotate the degree of rotation depends on the angle between the first folds and the later compression direction and is proportional to the amount of strain the orientations of the new folds are close to those of the earlier open folds the final deformation pattern consists of domains where the orientations of the axes depend on whether the early folds were previously either open or closed many early folds are reused to become later folds by the mechanism of hinge migration these results are consistent with the pattern of superimposed folding observed in the devoluy structure of the french alps they show that simply by studying the directions of fold axes in areas of superposed folding it is not possible to define compression directions moreover there is the possibility that superposed folding may go unnoticed if hinge migration has occurred

crescent like large scale structures in the external zones of the western gibraltar arc betic rif orogenic wedge the external wedge of the gibraltar arc orogenic system western mediterranean is a natural case of a fold and thrust salient although at the scale of the arc a swing of the structural trend can be observed the presence of closed crescent like structures some of them more than 25 km long and scattered over an area of 3500 km 2 characterize the gibraltar arc external wedge this feature makes it very different from a classical arc shaped fold and thrust belt detailed structural maps of representative crescent like structures are presented synorogenic sediments reveal that they probably formed during a short time interval most probably during a single shortening event the crescent like structures are localized in front of a recess formed by the internal zones that acted as backstop this backstop shape and a viscous substrate essentially triassic evaporites below the fold and thrust external wedge constrain the experimental setting of an analogue model in which we were able to reproduce structures that developed originally with a highly non cylindrical shape during a single straight convergence moreover the tectonic transport directions along the thrusts are broadly comparable in the natural case and the model

paleothermicity in the central asturian coal basin north spain this research shows for the first time maps of vitrinite reflectances and paleotemperatures from the central asturian coal basin north spain which is a carboniferous pennsylvanian basin mainly of moscovian age vitrinite reflectance values decrease from north to south whereas volatile matter distribution increases from south to north vitrinite reflectance and volatile matter parameters indicate a coal rank ranging from high volatile bituminous coal in the north to semianthracite and anthracite in the south rock eval data show that the organic matter of this basin is type iii kerogen with a maturation ranging from oil to gas window paleotemperatures were calculated by diverse methods using vitrinite reflectance data for different durations of heating and rock eval results the calculated paleotemperatures and vertical paleotemperature gradients decrease from south to north the thermal gradient variation in the central asturian coal basin points to the influence of at least two heating events that affected the organic matter the first associated with a regular geothermal gradient operating over a long period of time and the second linked to a southern granitic event of short duration estimated by tectonic data the short thermal event was located at the end of sedimentation late moscovian and late westphalian d and after folding but before the overthrusting during the asturian tectonic phase located before the early kasimovian cantabrian and stephanian deposits finally a simulation of paleotemperatures around the granitic pluton was calculated and compared to maps of paleotemperatures obtained by various methods these maps refer to an initial depth of one or two km in accordance with the selected methods that are compatible with local erosion this approach was preferred in order to explain the metamorphism of coal rather than the hypothesis of hydrothermal fluid flow proposed for other foreland basins this regional thermal anomaly could be important for future coalbed methane assessment

conical folding in the core of an orocline a geometric analysis from the cantabrian arc variscan belt of nw iberia abstract the cantabrian arc of the variscan belt has been recently defined as a true orocline constraining kinematics and deformation timing this curved sector of the orogenic belt is characterized by two different fold sets 1 one runs parallel to the outcrops of the main thrusts and describes a horseshoe shape concave towards the east and 2 another is radial to the arc a detailed geometric study of the fold interference patterns in the cantabrian arc revealed the conical nature of the folds belonging to the radial set these conical folds developed with different geometrical characteristics semi apical angles and axis attitudes depending on the initial orientation and geometry of the folded surfaces they are interpreted to result from a vertical axis rotation during oroclinal buckling of the variscan belt in nw iberia this study of conical folds in the cantabrian arc highlights that conical folds in curved orogenic arcs are a powerful tool for establishing the sequence of tectonic events because interference patterns due to vertical axis secondary differential rotations provide unique geometrical characteristics observed in the cantabrian arc that can be extrapolated to other oroclines

dating north america s oldest petroglyphs winnemucca lake subbasin nevada abstract on the west side of the winnemucca lake subbasin nevada distinctive deeply carved meter scale petroglyphs are closely spaced forming panels on boulder sized surfaces of a partially collapsed tufa mound the large complex motifs at this side are formed by deeply carved lines and cupules a carbonate crust deposited between 10 200 and 9800 calibrated years b p ka coats petroglyphs at the base of the mound between elevations of 1202 and 1206 m petroglyphs above the carbonate crust are carved into a branching form of carbonate that dates to 14 8 ka radiocarbon dates on a multiple layered algal tufa on the east side of the basin which formed at an elevation of 1205 m as well as a sediment core based total inorganic carbon record for the period 17 0 9 5 ka indicate that water level in the winnemucca lake subbasin was constrained by spill over the emerson pass sill 1207 m for most of the time between 12 9 0 3 and 9 2 ka these and other data indicate that the lake in the winnemucca lake subbasin fell beneath its spill point between 14 8 and 13 2 ka and also between 11 3 and 10 5 ka or between 11 5 and 11 1 ka exposing the base of the collapsed tufa mound to petroglyph carving the tufa based 14 c record supports decreased lake levels between 14 8 13 2 ka and 11 3 10 5 ka native american artifacts found in the lahontan basin date to the latter time interval this does not rule out the possibility that petroglyph carving occurred between 14 8 and 13 2 ka when pyramid lake was relatively shallow and winnemucca lake had desiccated

fold interference structures the influence of layer competence contrast using the geometrical properties of curved surfaces it can be predicted that the geometries of natural refolded folds should differ from the well known forms resulting from superposed shear folds if the sequence undergoing folding contains competent horizons the simple dome and basin patterns expected from kinematic considerations are incompatible with constant bed length folding isometric deformation isometric deformation requires that a flat sheet folds to give a surface consisting of points of zero gaussian curvature like for example the surfaces of cylindrical and conical folds we suggest that the coaptation folds recently recognized by stauffer 1988 are topologically necessary crumples on the flanks of domes and basins rather than bends at the intersection of two oblique intersecting folds and should be known as curvature accommodation folds

melt detection in antarctic ice shelves using scatterometers and microwave radiometers ku band dual polarization radar backscatter measurements from the seawinds on quikscat scatterometer are used to determine periods of surface freeze and melt in the antarctic ice shelves the normalized horizontal polarization radar backscatter sigmao and backscatter polarization ratio are used in maximum likelihood estimation of the ice state this method is used to infer the daily ice surface conditions for 25 study locations located on the ronne ross larsen amery shackleton and other ice shelves the temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period criteria for determining the dates of melt onset and freeze up for each austral summer are presented validation of the ice state and melt onset date estimates is performed by analyzing the corresponding brightness temperature tb measurements from special sensor microwave imager ssm i radiometers quikscat sigmao measurements from 1999 to 2003 are analyzed and found to be effective in determining periods of melt in antarctic ice sheets at high temporal and spatial resolutions these estimates can be used in studies of the climatic effects of the seasonal and interannual melting of the antarctic ice sheets

kinematic constraints on buckling a lithospheric scale orocline along the northern margin of gondwana a geologic synthesis abstract the paleozoic variscan orogeny was a large scale collisional event involving amalgamation of multiple continents and micro continents existing data suggests oroclinal buckling of an originally near linear convergent margin during the last stages of variscan deformation in the late paleozoic closure of the rheic ocean resulted in e w shortening present day coordinates in the carboniferous producing a near linear n s trending east verging belt subsequent n s shortening near the carb permian boundary resulted in oroclinal buckling this late stage orogenic event remains an enigmatic part of final pangea amalgamation the present day arc curvature of the variscan has inspired many tectonic models with little agreement between them while there is general consensus that two separate phases of deformation occurred various models consider that curvature was caused by dextral transpression around a gondwana indentor strike slip wrench tectonics or a change in tectonic transport direction due to changing stress fields more recent models explain the curvature as an orocline with potentially two opposite facing bends caused by secondary rotations deciphering the kinematic history of curved orogens is difficult and requires establishment of two deformation phases an initial compressive phase that forms a relatively linear belt and a second phase that causes vertical axis rotation of the orogenic limbs historically the most robust technique to accurately quantify vertical axis rotation in curved orogens is paleomagnetic analysis but recently other types of data including fracture geochemical petrologic paleo current and calcite twin data have been used to corroborate secondary buckling a review of existing and new variscan data from iberia is presented that argues for secondary buckling of an originally linear orogenic system together these data constrain oroclinal buckling of the cantabrian orocline to have occurred in about 10 ma during the latest carboniferous which agrees well with recent geodynamical models and structural data that relate oroclinal buckling with lithospheric delamination in the variscan

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

antarctic surface melting dynamics enhanced perspectives from radar scatterometer data 1 antarctic ice sheet surface melting can regionally influence ice shelf stability mass balance and glacier dynamics in addition to modulating near surface physical and chemical properties over wide areas here we investigate variability in surface melting from 1999 to 2009 using radar backscatter time series from the seawinds scatterometer aboard the quikscat satellite these daily continent wide observations are explored in concert with in situ meteorological records to validate a threshold based melt detection method radar backscatter decreases during melting are significantly correlated with in situ positive degree days as well as meltwater production determined from energy balance modeling at neumayer station east antarctica these results support the use of scatterometer data as a diagnostic indicator of melt intensity i e the relative liquid water production during melting greater spatial and temporal melting detected relative to previous passive microwave based studies is attributed to a higher sensitivity of the scatterometer instrument continental melt intensity variability can be explained in part by the dynamics of the southern annular mode and the southern oscillation index and extreme melting events across the ross ice shelf region may be associated with el nino conditions furthermore we find that the antarctic peninsula accounts for only 20 of antarctic melt extent but greater than 50 of the total antarctic melt intensity over most areas annual melt duration and intensity are proportional however regional and localized distinctions exist where the melt intensity metric provides greater insight into melting dynamics than previously obtainable with other remote sensing techniques

modes of superposed buckling in single layers controlled by initial tightness of early folds in a series of experiments with soft test models superposed buckling folds were produced in a competent layer resting on a slab of incompetent painter s putty the angle between the hinge lines of the first set of cylindrical folds f1 and the direction of the second compression p2 was varied in the different experiments the experiments showed that with an increase in the initial tightness of f1 there was a transition from one mode of superposed buckling to another when the interlimb angle of f1 was very large the superposed deformation gave rise to a dome and basin pattern the first mode of superposed buckling the second mode with small f2 folds riding over larger f1 folds developed when the initial interlimb angle ranged roughly between 135 and 90 the third mode was observed when the f1 interlimb angle was less than about 90 but the fold was not very tight in the third mode a set of non plane non cylindrical folds developed however the sinuous hinge line of the non cylindrical structure was newly created by replacing the old f1 hinge when f1 was very tight or isoclinal the fourth mode of superposed buckling led to the development of non plane non cylindrical folds without concomitant hinge replacement

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

the onset of spring melt in first year ice regions of the arctic as determined from scanning multichannel microwave radiometer data for 1979 and 1980 sea ice ablation is an important physical process affecting the global climate system during the arctic melt season rapid changes occur in both sea ice surface conditions and the extent of ice these changes alter the albedo and vary the surface energy budget understanding variations in arctic sea ice is critical for global climate studies this paper investigates the spring onset of melt in the arctic seasonal sea ice zone through analysis of melt signatures derived from nimbus 7 scanning multichannel microwave radiometer data satellite derived melt signatures determined by 18 and 37 ghz vertical brightness temperatures are associated with the initial melt of the snow pack on the sea ice surface sea ice melt events vary spatially and temporally within the arctic basin the melt signature is observed first in the chukchi sea and the kara and barents seas as melting progresses the melt signature moves westward from the chukchi sea and eastward from the kara and barents seas to the laptev sea region the initial location of the melt signal also varies with year in 1979 the melt signature occurs first in the chukchi sea and in 1980 in the kara sea the date for the initial melt varies between 1979 and 1980 by an average of 7 10 days with a maximum of 25 days in the chukchi sea region monitoring the occurrence of melt signatures can be used as an indicator of climate variability in the arctic s seasonal sea ice zones

paleomagnetic results in support of a model for the origin of the asturian arc abstract paleomagnetic directions have been determined at 17 cambrian and 28 carboniferous limestone sites distributed along the asturian arc of the hercynian fold belt in northwestern spain the stable vectors are carried by hematite in all cases and also by magnetite in some grey carboniferous limestones a secondary component of magnetization is usually removed well below 400 c and the higher temperature component is taken to be the characteristic direction the structure at each site was carefully evaluated in order to make optimum local tectonic corrections in addition the data must be corrected for rotations about a vertical axis to allow for a phase of radial folding superimposed on earlier structures the corrected paleomagnetic declinations are found to vary systematically along the arc of the fold belt consequently paleomagnetic data from the asturian arc should not be included in compilations used for the construction of a paleozoic apparent polar wander path the paleomagnetic data allow us to distinguish between different tectonic models for the evolution of the asturian arc a two stage model for the development of the present curvature is favored part of the curvature appears to be primary preceding the hercynian deformation the first stage of the model involved rotations of thrust sheets during their emplacement producing a more tightly curved arc than the original form in a second stage the development of radial folds further tightened the curvature of the arc both stages result in clockwise rotations in the north and anticlockwise rotations in the south

the influence of initial fold geometry on type 1 and type 2 interference patterns an experimental approach abstract experiments on superposed folding were performed in a plane strain pure shear rig using paraffin wax as an analogue for rocks a series of pre formed cylindrical folds were refolded with the compression direction acting parallel to the initial fold hinge direction the intermediate axis perpendicular to the first fold axial plane and the extension direction parallel to the first fold axial plane and perpendicular to its axis type 1 interference geometry roundness tightness and amplitude were varied to investigate the influence of first fold geometry on the interference patterns experimental folding of an initially planar layer oriented parallel to the first fold envelope provides a reference geometry for comparison the results suggest that hinge roundness has less influence on the interference pattern than other factors close initial folds refold into type 2 interference patterns which become even more pronounced as the tightness increases open folds produce type 1 interference patterns folds with the same interlimb angle and the same roundness produce different interference patterns depending on relative amplitude folds with relatively large amplitude are refolded into type 2 patterns whereas folds with small amplitude give clear dome and basin structures in a second set of experiments the compression direction also acted parallel to the first fold hinge but the orientations of the intermediate and extension axes were interchanged the interference patterns obtained are very similar to those in type 1 interference geometry suggesting that the major factor in determining whether type 1 or type 2 interference patterns develop is the initial fold geometry and not the kinematics of the second deformation

carbonate deposition pyramid lake subbasin nevada 3 the use of 87sr values in carbonate deposits tufas to determine the hydrologic state of paleolake systems abstract sierran rivers that discharge to the lahontan basin have much lower 4 5 87sr values than the humboldt river which drains northeastern nevada the 87sr values of tufas deposited during the last lake cycle were used to determine when humboldt derived sr entered the pyramid lake subbasin prior to 15 000 yr b p the humboldt river flowed to the smoke creek black rock desert subbasin during the recession of lake lahontan the humboldt river diverted to the carson desert subbasin this study has demonstrated that 87sr can be used to determine drainage histories of multi basin lake systems if the 87sr values of rivers that discharge to the basins are sufficiently different

paleoindian rock art establishing the antiquity of great basin carved abstract petroglyphs in the northern great basin one of the principal ways that researchers date archaeological sites is by using temporally diagnostic projectile points as index fossils however this practice has not been widely employed to date rock art sites we use this approach here to test the hypothesis that the great basin carved abstract gbca petroglyph style found in the northern great basin was produced by paleoindians using frequencies of projectile points at 55 gbca sites we demonstrate that paleoindian points are significantly overrepresented there relative to their occurrence on the general landscape providing evidence that great basin populations produced rock art sometime during the terminal pleistocene early holocene tp eh 12 500 8000 radiocarbon years ago additionally we examine several environmental variables at gbca sites and propose a model of paleoindian land use in the northern great basin that highlights seasonal visits to uplands to procure geophytes i e root crops

insights from a synthesis of old and new climate proxy data from the pyramid and winnemucca lake basins for the period 48 to 11 5 cal ka abstract a synthesis of old and new paleoclimatic data from the pyramid and winnemucca lake basins indicates that between 48 0 and 11 5 103 calibrated years bp hereafter ka the climate of the western great basin was to a degree linked with the climate of the north atlantic paleomagnetic secular variation psv records from pyramid lake core plc08 1 were tied to the gisp2 ice core record via psv matches to north atlantic sediment cores whose isotopic and or carbonate records could be linked to the gisp2 18o record relatively dry intervals in the western great basin were associated with cold heinrich events and relatively wet intervals were associated with warm dansgaard oeschger do oscillations the association of western great basin dry events with north atlantic cold events and vice versa switched sometime after the laurentide ice sheet lis reached its maximum extent for example the lahontan highstand which culminated at 15 5 ka and a period of elevated lake level between 13 1 and 11 7 ka were associated with cold north atlantic conditions the latter period with the youngest dryas event relatively dry periods were associated with the bolling and allerod warm events a large percentage of the lis may have been lost to the north atlantic during heinrich events 1 and 2 and may have resulted in the repositioning of the polar jet stream over north america the trego hot springs wono carson sink and marble bluff tephras found in core plc08 1 have been assigned gisp2 calendar ages of respectively 29 9 33 7 34 1 and 43 2 ka given its unique trace element chemistry the carson sink bed is the same as wilson creek ash 15 in the mono lake basin this implies that the mono lake magnetic excursion occurred at approximately 34 ka and it is not the laschamp magnetic excursion the entrance of the first americans into the northern great basin is dated to approximately 14 4 ka a time when the climate was relatively dry evidence for human occupation of the great basin is lacking for the next 1100 years y i e the oldest western stemmed point site in the great basin dates to 13 3 ka two hypotheses are suggested for this cultural hiatus 1 the climate had deteriorated to the point that people vacated the great basin or 2 people moved to basin bottom wetlands that persisted during the dry period and then the subsequent younger dryas wet event erased the archaeological evidence deposited around the low elevation wetland sites

earliest art in the americas incised image of a proboscidean on a mineralized extinct animal bone from vero beach florida abstract a fragmented fossil bone incised with the figure of a proboscidean was recently found at vero beach florida near the location where late pleistocene fauna and human bones were recovered from 1913 to 1916 this engraving may represent the oldest and only existing example of terminal pleistocene art depicting a proboscidean in the americas because of the uniqueness rarity and potential antiquity of this specimen caution demanded that a variety of tests be used in an attempt to verify its authenticity the mineralized bone was identified as mammoth mastodon or giant sloth rare earth element analysis was consistent with the fossil bone being ancient and originating at or near the old vero site 8 ir 9 forensic analysis suggests the markings on the bone are not recent optical microscopy results show no discontinuity in coloration between the carved grooves and the surrounding material indicating that both surfaces aged simultaneously scanning electron microscopy sem revealed that the edges of the inscription are worn and show no signs of being incised recently or that the grooves were made with metal tools in addition the backscattered sem images suggest there is no discontinuity in the distribution of light and heavy elements between the scribed region and the surrounding bone indicating that both surfaces aged in the same environment this is very different from an intentional mark made on the bone for comparison energy dispersive x ray spectroscopy edxs shows that the surface contains significant amounts of calcium phosphorus oxygen and carbon typical of a mineralized bone surface examination of a cast and mold of the incised bone by reflectance transformation imaging rti also provided no evidence that the engraving was made recently all of these results are consistent with the mammoth engraving being authentic

superposed buckle folding in the eastern iberian chain spain abstract the aliaga area eastern iberian chain shows large scale examples of buckle superposition developed during tertiary folding in most cases ene trending folds overprint earlier nnw sse trending ones the resulting structures are mapped analysed and genetically classified by comparison with analogue models described by several authors the following types are found standard type 1 1a dome and basin structure 1b unequal wavelength overprinted folds modified type 1 1c t shaped joined folds 1d t shaped abutting folds 1e l shaped folds 1f snake like folds standard type 2 2a non cylindrical buckling of earlier axial surfaces involving hinge replacement different superposed sets of flexural slip striations record successive folding episodes in snake like folds and hinge replacement in the case of type 2a superpositions types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90 respectively which fits the results of analogue modelling and theoretical analysis by previous authors types 1b and 1d are associated with higher w1 w2 wavelength ratios than types 1a and 1c other controlling factors are viscosity contrast and erosion processes specifically erosion of competent limestone beds in the hinge zone of a nnw sse trending anticline allowed the near vertical eastern limb to be refolded into snake like folds

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis