first archaeomagnetic secular variation curve for the iberian peninsula comparison with other data from western europe and with global geomagnetic field models 1 a first secular variation sv curve for the iberian peninsula was computed by hierarchical bayesian method using a total of 134 archaeomagnetic directions with ages ranging from 775 to 1959 a d a general agreement is observed between the iberian curve and the french and german sv curves although some interesting differences were found such as the occurrence of lower inclinations between the 11th and 14th centuries in the iberian curve the analysis of these three reference curves indicates that sv in western europe is characterized by three major directional changes at 125 200 and 1350 a d it is suggested that these cusps are regional features of the geomagnetic field the iberian curve has been compared with the predictions of the jackson calsk7k 2 and hongre global models despite large differences recognized between these models even for the dipolar terms they predict reasonably well the iberian archaeomagnetic sv

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

archaeomagnetism of burnt cherts and hearths from middle palaeolithic amud cave israel tools for reconstructing site formation processes and occupation history abstract apart from magnetostratigraphy archaeomagnetism is rarely used in middle and late pleistocene sites here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from amud cave israel 68 55 ka two types of materials common in levantine middle palaeolithic cave sites both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction for cemented hearths or intensity palaeointensity for chert at the time of the last burning or shortly after we test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the holocene we show that divergent palaeointensities can help identify diachronic burning events suggesting different activity patterns in two areas of the cave additionally we used palaeomagnetic directional vectors to distinguish between a well preserved hearth and one that had been mixed prior to cementation using rock magnetic investigations we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 c the palaeomagnetic results are in agreement with results of previous studies at amud cave obtained by other independent methods this study shows that palaeomagnetic methods can serve as a powerful tool in the study of palaeolithic sites

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

origin chronology and environmental significance of holocene aeolian and alluvial sands at blue mountain falkland islands extensive and thick sand accumulations containing organic rich horizons at blue mountain falkland islands are most probably derived from weathering of local bedrock under late pleistocene periglacial conditions weathering and subsequent deflation produced several shallow basins that are now occupied by lakes sand morphology sedimentary structures and site characteristics indicate that the sand deposits are predominantly aeolian although some alluvial sands are also present deflation occurred either before the lakes existed or at times of lower lake levels sixteen 14c dates from organic rich horizons show that some sand accumulated in the early holocene or late pleistocene but that most is of mid to late holocene age landscape stability instability phases were not synchronous between sites and cannot be explained by the regional trends of holocene climate change a period of significantly lower lake levels and major aeolian erosion at c 5000 4500 bp is proposed but is not supported by regio

stone run block stream formation in the falkland islands over several cold stages deduced from cosmogenic isotope 10be and 26al surface exposure dating cosmogenic isotope 10be and 26al surface exposure dating has been applied to valley axis and hillslope stone runs relict periglacial block streams and their source outcrops in the falkland islands south atlantic the data indicate that stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product of the last glacial maximum the samples range in apparent 10be age from 42k to 731k yr bp but some of these are minima the results indicate that valley axis stone runs may be up to 700 800k yr old have simple exposure histories and are composite landforms that developed over several cold stages analyses of some hillslope and outcrop samples also demonstrate simple exposure histories with 10be ages from 42k to 658k yr bp in contrast isotopic ratios from other hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding the samples range in 10be age from 59k to 569k yr bp and these are regarded as minimum age estimates larger stone runs may be older than smaller runs and there is a possibility that stone runs older than 800k yr exist in other parts of the falklands the assertion that glaciation in the falklands was restricted to the highest uplands is supported by the data and the potential for age determination of other boulder strewn and bedrock landforms using cosmogenic isotope analysis in order to extend the geochronology of quaternary events and processes is noted

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

archaeomagnetic secular variation in the uk during the past 4000 years and its application to archaeomagnetic dating this paper examines the limitations and deficiencies of the current british archaeomagnetic calibration curve and applies several mathematical approaches in an attempt to produce an improved secular variation curve for the uk for use in archaeomagnetic dating the dataset compiled is the most complete available in the uk incorporating published results phd theses and unpublished laboratory reports it comprises 620 archaeomagnetic directional data and 238 direct observations of the geomagnetic field and includes all relevant information available about the site the archaeomagnetic direction and the archaeological age a thorough examination of the data was performed to assess their quality and reliability various techniques were employed in order to use the data to construct a secular variation sv record moving window with averaging and median as well as bayesian statistical modelling the sv reference curve obtained for the past 4000 years is very similar to that from france most differences occurring during the early medieval period or dark ages two examples of dating of archaeological structures medieval and pre roman are presented based on the new sv curve for the uk and the implications for archaeomagnetic dating are discussed

ductile opening mode fracture by pore growth and coalescence during combustion alteration of siliceous mudstone opening mode fractures with blunt tips and large maximum apertures are characteristic of clinker that formed by combustion alteration of siliceous mudstone these fractures are inferred to result from pore growth and coalescence with initially circular pores inherited from the diatomaceous protolith circular pores grow preferentially in an en echelon arrangement and coalesce to elongate pores and blunt tipped fractures by thinning and rupture of bridges between pores coalescence of overlapping en echelon pores causes fracture propagation in a zig zag path that is considered indicative of significant inelastic deformation outside the immediate vicinity of the fracture tips this process of fracture formation by void growth and coalescence is inferred to result from solution mass transfer and possible bulk melt movement during partial melting of clinker chemical mass transfer provides a mechanism for extensive inelastic deformation in the surrounding host rock concurrent with fracturing that is considered characteristic of ductile fracture the preferred elongation of coalescing pores and local rupture of pore bridges is explained by a tensile sintering stress due to the thermodynamic tendency of the system for energy minimization of solid and liquid surfaces it is suggested that ductile fracture processes that are accompanied by extensive inelastic deformation lead to opening mode fractures with large apertures in a variety of crustal settings including metamorphic and magmatic systems as well as in reactive diagenetic environments thus affecting fracture controlled transfer of heat and mass and the rheology of the earth s crust

is it possible to identify temporal differences among combustion features in middle palaeolithic palimpsests the archaeomagnetic evidence a case study from level o at the abric romani rock shelter capellades spain abstract archaeomagnetic dating is probably one of the most known applications of magnetic methods to archaeology but there are others still underutilized and of particular interest to palaeolithic archaeology here we report a novel application of archaeomagnetism as a technique to determine temporal diachronies among combustion features from the same surface within palaeolithic palimpsests the approach is based on the subtle directional changes of the earth s magnetic field through time secular variation sv and on the ability of burned materials to record such variations under certain conditions three middle palaeolithic hearths from level o ca 55 ka bp at the abric romani rock shelter ne spain were archaeomagnetically investigated the studied surface black homogeneous carbonaceous facies recorded the magnetic enhancement produced by fire with a tenfold increase in concentration dependent magnetic parameters in the uppermost centimetre with respect to its unburned or deeper counterparts pseudo single domain psd ti low titanomagnetite was identified as the main remanence carrier the irreversibility of thermomagnetic curves suggests that these samples did not undergo enough high temperatures as to record a full thermoremanence trm additionally the occasional occurrence of maghaemitized magnetite is interpreted as an indication of a thermochemical remanent magnetization tcrm making these samples unsuitable for absolute palaeointensity determinations two well defined 95

fluctuation of the earth s magnetic field elements in mexico revealed by archive documents since 1587 abstract historical documents archives and old photographic collections allowed to analyze 877 direct geomagnetic measurement data obtained by sailors including pirates united states coast and geodetic survey and national astronomical observatory since 1587 the updated catalogue includes 844 values of magnetic declination 495 of inclination 467 of the horizontal intensity component h and 455 of the vertical intensity component z all data were relocated to mexico city through the pole conversion method in order to build a reference secular variation curve for mexico and surrounding area using bootstrap method to mitigate the effect of outliers and estimate the probability of density functions the directional variation patterns obtained in this investigation were compared to the curves retrieved from sha dif 14k gufm1and igrf 12 models while vadm fluctuations were confronted to similar quality determinations from other localities worldwide as well as archaeomagnetic curves from mesoamerica

late quaternary glacial history of george vi sound area west antarctica during the last glacial maximum in west antarctica separate ice caps developed on alexander island and on palmer land became confluent in george vi sound and discharged northward from latitude 72 s radiocarbon 32 000 yr and amino acid approximately 120 000 yr age determinations on shell fragments hiatella solida found in basal till suggest a wisconsin age for the glaciation that incorporated them the pattern of ice flow differed from that deduced for this area in the climap reconstruction following the maximum stage there was a stadial event when outlet valley glaciers flowed from smaller ice caps into george vi sound more widespread recession permitted the george vi ice shelf to deposit palmer land erratics on eastern alexander island before isostatic recovery raised them to final elevations of about 82 m the ice shelf may have been absent at about 6500 yr b p when large barnacles bathylasma corolliforme were living in the sound small glaciers readvanced to form at least two terminal moraines before the ice shelf re formed and incorporated the barnacle shells into its moraine on alexander island the shells gave a 14c age corrected for antarctic conditions of about 6500 yr b p and an amino acid ratio consistent with a holocene age valley glaciers readvanced over the ice shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice cored moraines probably during the little ice age such oscillations may represent a climatic control not yet observed in the dry valleys of victoria land the only other part of antarctica studied in detail for glacier fluctuations

evidence for a younger dryas glacial advance in the andes of northwestern venezuela abstract deposits of push moraine outwash and glaciolacustrine sediments recovered from two areas in the northwestern venezuelan andes document the latest pleistocene advance of merida ice underlying peats provide maximum ages on till and outwash evidently emplaced during the younger dryas yd climatic event one example recovered from the humboldt massif where the farthest extent of yd ice buried peat in the surface of late glacial till provides a within glacier advance age of 12 4 ka cal bp the peat lies on moraine deposited during a stillstand event when the humboldt glacier retreated to the area of lago verde at 4000 m a s l approximately 0 5 km upvalley toward lago suero yd till buries peat deposited in glaciolacustrine sediments of presumed late glacial age farther north in the mucunuque mucubaji catchment of the eastern cordillera a push moraine of possible yd age buries older till of late glacial age 0 2 km upvalley outwash of yd age buries glaciolacustrine peat and organic rich alluvial sediment dated to 13 7 and 13 3 ka cal bp the latest merida advance documented here is approximately synchronous with the yd cold event of europe and the north atlantic region ca 11 6 12 7 ka cal bp the yd event in both areas of the northwestern venezuelan andes nearly reestablished earlier late glacial ice positions and termination appears to have been abrupt the valleys in both areas were evacuated of yd ice without emplacement of recessional moraines as during the main deglaciation at the humboldt site equilibrium line altitudes ela s for the late glacial were about 50 m lower than during the inferred yd in the mucunuque mucubaji catchment ela s for the late glacial 3900 m a s l are difficult to establish given the absence of lateral moraines

three archaeomagnetic applications of archaeological interest to the study of burnt anthropogenic cave sediments abstract recent archaeomagnetic studies carried out on mid to late holocene burnt anthropogenic cave sediments have shown that under certain conditions these materials are suitable geomagnetic field recorders archaeomagnetic analyses carried out on these contexts constitute a rich source of information not only for geophysical purposes in terms of reconstructing the variation of earth s magnetic field in the past but also from the archaeological point of view for example by archaeomagnetic dating here we report three different archaeomagnetic applications to the study of burnt cave sediments i archaeomagnetic dating ii determining palaeotemperatures and iii assessing post depositional processes the first case study is a dating attempt carried out on a late holocene bronze age burnt level from el mirador cave burgos spain using the directional european secular variation curve several dating intervals were obtained for the last burning of this combustion feature considering the archaeological evidence and the independent radiometric 14 c dating available the possible ages obtained are discussed this is the first archaeomagnetic dating obtained in these contexts so far the second case study is an application of the method to determine the last heating temperatures reached by the carbonaceous facies of these fires stepwise thermal demagnetization of oriented samples can be used to quantitatively estimate heating temperatures an intermediate normal polarity component interpreted as a partial thermo remanence ptrm with maximum unblocking temperatures of 400 450 c was systematically identified revealing the last heating temperatures experienced by this facies these temperatures were confirmed with partial thermomagnetic curve experiments finally archaeomagnetic analyses on a partially bioturbated burning event were performed in order to evaluate until what spatial extent the burnt sediments were affected by post depositional mechanical alteration processes for each case study the archaeological implications are discussed highlighting the potential of archaeomagnetic methods to retrieve archaeological information

a new approach to the problem of tektite genesis abstract variations in the major cation ratios in the micro tektites of each of the different strewn fields were studied with the help of niggli parameters there is a high degree of variability in almost each individual strewn field which however is not random invariably as sio 2 increases the proportion of alumina and the alkalies among the cations increases that of mgo feo total iron as feo and cao decreases simultaneously k 2 o na 2 o increases while mgo feo decreases this is entirely analogous to magmatic differentiations and is incompatible with an explanation by mechanical mixing of sedimentary parent rocks the picture can best be explained by partial melting in analogy to fulgurites and combustion ultrametamorphic glasses in some strewn fields e g javaites georgiaites bediasites all tektites formed from the same set of parent rocks in these fields each cation parameter when plotted against silica follow a linear slightly curved path with a very small scatter simple type in others e g moldavites philippinites australites some or all cation parameters show a strong scatter which sometimes almost obliterates the differentiation trends these complex diagrams can be reduced to 2 5 diagrams lineages of the simple type each reflecting a different combination of parent rocks most lineages again show the influence of partial melting differentiation if the chemical variations of tektites are caused by partial melting the silica poor end of each variation diagram case of total melting and not the average composition corresponds to the parent rock combination involved thus neglecting losses by evaporation which are minor the chemical compositions of 25 starting materials were established all except one of these can very closely be matched by a combination in appropriate proportions of only two of the most common sedimentary rocks the only group which cannot be duplicated by a combination of any two sedimentary rocks are the bottle green microtektites

new archaeomagnetic directions from portugal and evolution of the geomagnetic field in iberia from late bronze age to roman times abstract this study presents new archaeomagnetic results from 33 combustion structures kilns and hearths from the archaeological sites of castelinho crestelos olival poco da barca and fonte do milho in ne portugal the age of the investigated structures ranges from 1210 bc to 200 ad according to calibrated radiocarbon dating thermoluminescence dating and archaeological constraints stepwise thermal and alternating field demagnetization isolate a single stable characteristic remanence component with very well defined directions rock magnetic analyses suggest low ti titanomagnetite maghemite as the main magnetic carrier of the remanence mean directions are well grouped in most structures the effect of thermoremanent anisotropy on mean directions has been evaluated and was found to be important inclination increases of between 2 and 13 after applying the anisotropy correction at specimen level this highlights the requirement of evaluating this effect on the directions of small and flattened thin kilns and hearths the 31 new directional data improve both the temporal and spatial distribution of the iberian archaeomagnetic dataset from late bronze age to roman times finally a new directional palaeosecular variation curve for iberia for the last twelve centuries bc is proposed the curve has been computed using the bootstrap method and includes data coming from sites within 900 km of madrid the new palaeodirectional secular variation curve for iberia is consistent with the western european palaeosecular variation curve and with the prediction of regional european models

rock magnetic analyses as a tool to investigate archaeological fired sediments a case study of mirador cave sierra de atapuerca spain summary here we report a detailed mineral magnetic study of neolithic burnt levels in the mirador cave sierra de atapuerca burgos spain to reconstruct the burning history and to investigate their suitability for archaeomagnetic purposes as a consequence of the ancient burning a characteristic facies sequence was developed along the holocene stratigraphy from top to bottom it includes i 2 10 cm ash layers ii 2 cm underlying rubefied layers and iii clay mainly unburnt and of variable thickness in some cases a thermally altered facies 2 6 cm with a heterogeneous texture was identified facies tf usually between rubefactions and the unburnt levels 126 oriented samples from 4 units mir12 15 18 and 21 and a 2 m section all comprised between units mir21 6380 40 14c bp and mir9 5090 40 14c bp were analysed with rock magnetic methods in addition bulk sediment from each facies that comprise the neolithic sequence was investigated measurements included stepwise alternating field and thermal demagnetization of natural remanent magnetization nrm viscosity experiments determination of the anisotropy of the magnetic susceptibility ams the susceptibility frequency dependence at room temperature and determination of the temperature dependence of the susceptibility additional experiments consisted in the determination of the behaviour of anhysteretic and isothermal irm remanences magnetic hysteresis loops first order reversal curve diagrams and thermal demagnetization of three axial irm it appeared that the facies all show a fairly similar magnetic mineralogy and grain size dominated by low titanium magnetite that is often partially maghaemitized main differences constitute the amount of superparamagnetic particles that is higher in unburnt strata concurring with a less well defined nrm behaviour the magnetic mineral concentration is notably higher in ashes this homogeneity strongly suggests that similar sources and burial conditions prevailed during neolithic times agreeing with archaeological observations and favoured by rapid burial conditions very limited alterations have been deduced ams data revealed the absence of fluid flow in the ash lenses sampled demagnetization revealed a stable single nrm component in ashes a single or two component nrm in rubefactions and less stable multicomponent behaviour in clays in ashes magnetic minerals are likely secondary in origin formed by low temperature oxidization soon after burning although this thermochemical nature of the nrm invalidates the use of these sediments for palaeointensity studies archaeomagnetic directional data can be successfully obtained because the burning and oxidation are closely confined in time

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

updated iberian archeomagnetic catalogue new full vector paleosecular variation curve for the last three millennia authors acknowledge the spanish ministry of economy cgl2014 54112 r and cgl2017 87015 p projects bes 2015 074575 and bes 2016 077257 grants the spanish ministry of education fpu14 02422 grant and the autonomous community of madrid through the european youth employment initiative pej15 amb ai 0203 m g p and m r acknowledge the ramon y cajal program and the cgl2015 63888 r project of the spanish ministry of economy and competitiveness financial support was also given by the pics international program for scientific cooperation cnrs france and csic spain

identifying potentially active volcanoes in the andes radiometric evidence for late pleistocene early holocene eruptions at volcan imbabura ecuador abstract recent eruptions from volcanoes with no previously known historical activity in chile and indonesia have raised the importance of the early identification of potentially active centers for the purpose of hazard assessment here we bring radiometric evidence 14 c 39ar 40ar of previously unrecognized but significant magmatic activity at partly eroded imbabura volcano ecuador in late pleistocene to early holocene times on whose perimeter live more than 300 000 persons following an effusive stage from 50 to 30 ka with the emplacement of andesitic lava flows on different flanks of its edifice the activity became explosive with the generation of andesitic block and ash flows on its eastern side beginning at 35 ka cal bp subsequently a flank collapse associated with a volcanic blast occurred on the volcano s sw flank at 30 ka cal bp the resulting debris avalanche and blast breccias cover an area now heavily populated around san pablo lake and its source was later concealed by successive dome building episodes at huarmi which produced 2 8 km3 of silicic andesite renewed dome activity at the edifice s taita summit occurred at 17 ka cal bp and continued intermittently into early holocene times as indicated by pyroclastic flow deposits overlying a palaeosoil dated at 9 ka cal bp in summary this study reveals an eruptive behavior characterized by a low recurrence rate but with quite large eruptions a pattern which is also observed at other silicic volcanoes of ecuador s western cordillera it is now imperative to reconsider the origin and source of the many tephra layers catalogued in holocene lacustrine sediments in the imbabura area tephra and lava volume estimates for imbabura volcano converted to dense rock equivalent values yield a minimum magmatic output rate of 0 13 km3 ka in the past 35 000 years which argues for sustained magma production for this volcano in recent geological times the imbabura example thus raises the question of how to improve population preparedness for volcanoes with infrequent eruptions and how to guide authorities decisions concerning the development of urban areas and infrastructures near presently inactive but potentially highly dangerous volcanoes

a preliminary secular variation reference curve for archaeomagnetic dating in austria the construction of a secular variation sv reference curve for a region for which little or no archaeomagnetic directions are available is presented here a sv curve is illustrated for austria centred on radstadt 47 38 n 13 45 e and based on data from sites in other countries less than 500 km away the published data were selected on site characteristics of n 3 and k 50 and dated within 400 yr this yielded 170 directions from which a sv curve was derived using bayesian techniques the obtained reference curve represents the past 2300 yr new data mainly from austria substantiate this curve and confirm the validity of the techniques employed which can therefore be applied for similar situations another test has been made using the german reference curve for dating the austrian archaeological sites here a systematic shift to older times in the order 30 110 yr occurs

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

late cenozoic glacial history of the ross embayment antarctica abstract the ross ice drainage system comprises about 25 per cent of the surface area of the antarctic ice sheet its fluctuations during the late quaternary have been determined in two ways from analyses of three deep ice cores extracted at byrd west antarctica and at vostok and dome circe east antarctica and from the distribution stratigraphy and chronology of glacial drifts in the transantarctic mountains the ice core studies give time series records for the last 160 ka that correspond well with the marine isotope record and clearly show glacial interglacial stadial and interstadial intervals they also suggest that during glaciation maxima the polar plateau was characterised by an accumulation rate 50 per cent lower and temperature 7 9 c lower than present values glacial geological studies reveal a hiatus in the drift record between older miocene early pleistocene glacial sediments and drifts of the last two glaciations isotope stages 6 and 2 there are two leading but contradictory interpretations of the older drift sirius formation one is based primarily on biological data and favours partial deglaciation of antarctica in the pliocene early pleistocene followed by regrowth of the east antarctic ice sheet to dimensions larger than now and then substantial uplift of the transantarctic mountains the other is founded on glacial geological observations and implies a larger than present ice sheet over antarctica during the miocene and only 200 m of uplift subsequently for the late quaternary reconstructed ice surface profiles based on detailed mapping and dating of drift sheets show that large outlet glaciers from the east antarctic polar plateau became about 1000 m thicker during glaciation maxima while the plateau ice barely thickened at all this is attributed to extensive northward migration of the ice grounding line in the ross embayment as global sea level fell dates obtained from the drift sheets confirm that glaciers in the ross embayment area reached maximal limits at 190 160 ka bp and at 23 14 ka bp recession from the last glaciation maximum was underway by 13 ka bp and was complete by ca 6 ka bp alpine glaciers terminating in dry valleys fluctuate asynchronously with the ross embayment glaciers they retreat during glacial maxima when they become starved of accumulation and readvance during warmer intervals because of their dependence on grounding line position glacier fluctuations in much of antarctica are primarily led by sea level changes controlled by ice sheets in the northern hemisphere

evidence for a cosmogenic origin of fired glaciofluvial beds in the northwestern andes correlation with experimentally heated quartz and feldspar abstract fired sediment considered equivalent to the black mat impact of 12 9 ka has been located and analyzed in the andes of northwestern venezuela the black mat refers to possible fallout from the encke comet airburst presumed to have occurred over the laurentide ice sheet the impact spreading ejecta over large portions of north america and europe making it an interhemispheric event of considerable magnitude these possible equivalent beds in the northern andes first considered to result from a lightning induced conflagration adjacent to the retreating late wisconsinan merida glaciation ice are now known to have undergone intense heating upon impact to a temperature much higher than what would occur in a wet first stage successional tundra analyses carried out by sem and fesem in se and bse modes show massive micro disruption on grain surfaces fractures diminishing with depth toward grain interiors and c welded onto quartz and plagioclase minerals bubbles on some grains possibly the result of exclusion of water of crystallization are seen on some samples principally quartz the presence of copious monazite in the carbonaceous coatings is considered part of the incoming ejecta as it is not a common indicator mineral in the local lithology analysis by sem and fesem of quartz and plagioclase subjected experimentally to temperatures ranging from 500 to 900 c shows that intense heating affects resident mineralogies to differing extents with grain disruption more prevalent along cleavage planes deep into grain interiors the intergrowth of carbonaceous black mat material with thermally disrupted and fragmented quartz and feldspar a welded patina of 100 400 nm thickness could only occur with temperatures in excess of 900 c the event interpreted here to be of cosmogenic origin

a new bathymetric compilation highlighting extensive paleo ice sheet drainage on the continental shelf south georgia sub antarctica a grid derived from a new compilation of marine echo sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around south georgia at an unprecedented level of detail the grid is the first continuous bathymetric data set covering south georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution large and previously undescribed glacially eroded troughs linked to south georgia s modern day fjords radiate from the island marking the former pathways of large outlet glaciers and ice streams a tectonic or geological influence is apparent for the major troughs where glaciers have exploited structural weaknesses on the continental block bed forms lining the troughs give some first insights into glacial dynamics within the troughs suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates on the outer shelf and within the troughs large ridges and banks are also common interpreted as terminal lateral and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation a small trough mouth fan has developed at the mouth of at least one of the cross shelf troughs demonstrating a focused sediment delivery to the margin slides and slide scars are also present on parts of the margin showing that margin stability perhaps also related to glaciation has been an important factor in depositional processes on the continental slope implications of the new observations are that ice sheets have been more extensive on south georgia than any previous studies have reported their age may date back to late miocene times and evolution of the shelf system has probably involved numerous late cenozoic glacial episodes however relatively fresh seafloor geomorphology coupled with evidence from other maritime antarctic islands heard island and kerguelen island indicating extensive glaciation at the last glacial maximum raises the possibility that the extent of sub antarctic glaciation for the last glacial period has until now been underestimated

oxygen isotope δ18o evidence of holocene hydrological changes at signy island maritime antarctica a record of holocene hydrological changes has been produced from variations in oxygen isotope composition delta 18 o preserved in freshwater lake sediments from maritime antarctica small amounts 5 of authigenic carbonate have been extracted from a non marl sediment core from sombre lake signy island 60 degrees 43 s 45 degrees 38 w oxygen isotope and particle size analysis provide a sensitive record of hydrological events in the lake arising from local and regional climate phenomena the climate affects delta o 18 through snowpack volume and glacier activity in the catchment lakewater temperatures the input versus evaporation balance and the duration of seasonal lake ice cover the most depleted negative delta o 18 values are associated with influxes of meltwater at times of glacier advance or retreat enriched positive delta o 18 values occur during more arid warmer conditions with longer periods of open water in summer this isotope record can be used to determine century scale to decadal variability in air circulation and moisture origin strong similarities with other holocene proxy records from the weddell sea and antarctic peninsula region are apparent including the mid holocene climate optimum followed by the neoglacial and most recently late twentieth century climatic warming the oxygen isotope record from sombre lake illustrates the importance of remote islands in contributing to our understanding of teleconnections in atmospheric and oceanographic circulation sea ice extent air temperatures and precipitation in the southern ocean

glacial marine sedimentation and quaternary glacial history of marguerite bay antarctic peninsula abstract marguerite bay situated between the subpolar glacial regime of the northern antarctic peninsula and the polar glacial regime of west antarctica is ideally located to test various models of glacial and glacial marine sedimentation and specific scenarios of late wisconsin ice sheet expansion piston cores and single channel seismic reflection data were collected during the deep freeze 85 and 86 expeditions to determine the late quaternary history of the area seismic data in the bay show a rugged seafloor with numerous deep troughs and a very thin layer of sediment over crystalline basement or older sediments glacial erosion is important in modifying existing features although the ultimate repository of the eroded material is not known it is not found within the bay the piston cores are topped by diatomaceous muds which are underlain by terrigenous muds and muddy gravels that imply deposition beneath an ice shelf basal tills were penetrated at three sites reflecting deposition by a grounded marine ice sheet a reconstruction of the glacial history of marguerite bay since the last glacial maximum shows grounded ice filling the bay in late wisconsin time rising sea level caused an uncoupling of the ice sheet and slow retreat of an ice shelf throughout the holocene

late pleistocene sediments and environmental change at plaza creek falkland islands south atlantic late pleistocene organic rich sediments exposed in coastal bluffs near the head of plaza creek east falkland have yielded conventional and ams 14c dates of between 36 and 28 ka bp and possess a pollen spectrum dominated by grasses indicating a vegetation assemblage similar to that of the present day although some sample dates are anomalous and contamination by non contemporaneous carbon cannot be ruled out entirely the age estimates are consistent with evidence and dates from antarctica south america and the amphi north atlantic for climate shifts to interstadial conditions at around that time the organic rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting grain size characteristics suggest that these sediments may have been emplaced by solifluction shallow translational landsliding and surface wash in at least five mass wasting episodes some of the mass wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka bp at san carlos east falkland and with periods of cirque and valley glaciation identified in the uplands of the falkland islands the similarity between late pleistocene interstadial holocene and present day pollen assemblages and the lack of vegetation change within these periods is characteristic of most cool temperate southern ocean islands and may reflect the lack of sensitivity of the vegetation to climate change and or a lack of climate variability for the time intervals covered 1998 john wiley sons ltd

directional changes of the geomagnetic field in west africa insights from the metallurgical site of korsimoro abstract this work shows the first archeomagnetic directions from western africa measured on 32 iron smelting kilns dated between 650 and 1800 ad the archeological excavation of the vast metallurgical site of korsimoro established the existence of four distinct iron smelting techniques the time frame of each technique could be clearly determined with radiocarbon dating many of the kilns investigated in this study could also be dated individually with residual charcoals found in their inside the results indicate that the inclination of the field changed gradually from shallow normal to shallow reversed during 800 to 1300 ad and then went back to shallow normal around 1600 1700 ad the declination was instead stable around 10 e between 800 and 1400 ad thereafter it started changing towards north this trend correlates well with available secular variation curves from the balkan and from spain and indicates that the field variation in west africa was similar to the one in europe

geomagnetic field variations in western europe from 1500bc to 200ad part i directional secular variation curve abstract to improve the geomagnetic field secular variation curve svc of western europe during protohistoric times archaeomagnetic directions of 39 archaeological kilns or hearths from france were investigated the dating of each archaeological structure was established with archaeological or chronometric methods thirty seven of these structures are dated from the first millennium bc one from the end of the second millennium bc and the last one from the fourth millennium bc thermomagnetic curves unblocking temperatures and coercivities suggest that the main carrier of the remanent magnetization is a ti poor titanomagnetite archaeodirections were obtained by alternating field and thermal demagnetizations on almost 900 specimens the anisotropy tensor of thermoremanent magnetization was determined for 35 structures and 22 mean archaeodirections were corrected for anisotropy the new archaeodirections are very consistent with previously published data a new directional svc was built using bivariate statistics with selected western europe data located within 1000 km of paris selection criteria include the number of samples the dating reliability and the accuracy of the mean archaeodirection resulting secular variation between 1500bc and 0ad mainly shows large changes in declination while inclinations are bracketed between 65 and 75 the declinations show a strong maximum with values 30 35 around 800 750bc followed by a sharp decrease to values around 0 at 500bc and close to 7 around 250bc the main features of the secular variation from 1500bc to 0ad appear to be a dominant westward drift and two major changes around 800 and 250bc compared to the global and regional geomagnetic models the new reference data are better fitted by arch3k cst 1 and scha dif 3k than by arch3k 1 and cals3k 4 models the strong variation of the archaeodirection between 1000 and 500bc makes archaeomagnetism very useful for dating purposes

archaeomagnetic secular variation in germany during the past 2500 years summary the german archaeomagnetic data set was supplemented with 35 new directions from ger man sites mainly dating from the past 3000 yr together with archaeomagnetic data from the neighbouring countries of germany a database of 166 reliable archaeomagnetic directions has been compiled for the reference area which is defined by a 500 km radius circle around gottingen the retrieved directions come from well dated archaeological structures and about 40 per cent of the dating relay on natural science methods such as radiocarbon thermolumines cence dendrochronology dating or historical documents from this data set a secular variation sv reference curve has been calculated using a bivariate algorithm which fits a natural cubic spline based on roughness penalty to declination inclination and time simultaneously the error tube surrounding this curve was obtained from bayesian modelling of the experimental errors which can also take stratigraphic information into account the obtained sv reference curve for the past 2500 yr is similar to that from france but also significant differences are seen comparison of the curves does not show a simple westward drift of the sv pattern the german reference curve allows archaeomagnetic dating in the reference area and extends this dating technique to sites situated in middle europe

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

late pleistocene and holocene landscape evolution and environmental change in the lake sulivan area falkland islands south atlantic abstract late pleistocene and holocene landscape evolution around lake sulivan falkland islands south atlantic is assessed using morphological stratigraphical palaeoecological and 14c dating evidence data indicate a complex landscape history involving frost related activity ventifact development growth and degradation of peat terrain expansion and contraction of lakes and the development stabilisation and subsequent reworking of alluvial and aeolian sand bodies late pleistocene cold conditions favoured production of sandy diamicts on hillslopes and ventifacts on outcrops and blockfield clasts lateglacial climatic amelioration was marked by early growth of peat ca 16 500 cal yr bp since then peat accumulation changes in lake areas and depths and alluvial and or aeolian sand deposition have been recurring and dominant features of landscape change which throughout the late pleistocene and early holocene may have been a response to near synchronous climatic fluctuations along the south america antarctica axis marked landscape changes around lake sulivan coincided with intervals of glacier readvance in south america and south georgia at ca 3200 1900 and 700 100 cal yr bp with lower lake levels and aeolian sand transport from exposed lakebeds and shorelines implying greater aridity in the falklands than at present

new directional archeomagnetic data of burned cave sediments from switzerland and geomagnetic field variations in central europe this paper presents new directional archeomagnetic data from nine meso neolithic fireplaces sampled in a cave shelter at arconciel in western switzerland rock magnetic measurements indicate a homogenous magnetic mineralogy in all fireplaces with magnetite as the main magnetic carrier the remanent magnetization is stable and generally shows one characteristic directional component nine new directions which were obtained from arconciel are combined with 356 other archeomagnetic data from a circular area with a radius of 700 km around this site to obtain a penalized least square spline fit for the past 9000 yr we found in general good agreement with other local compilations such as the balkan curve the regional scha dif 8k model and with lake sediments from uk fennoscandia and switzerland nevertheless a time lag of several centuries is observed for a declination maximum between the archeomagnetic spline fit and the other european data records around 5900 bc this time lag is also observed in the swiss lake sediment record therefore we interpret this shift as a local feature of the earth s magnetic field

new high precision full vector archaeomagnetic data from a roman kiln in merida spain abstract this study presents new high precision age and full vector archaeomagnetic data from a kiln excavated in the roman archaeological site of mitreo s house merida badajoz spain the age of the kiln was obtained by the stratigraphic method and by the ceramological study of the italic and sigillata pottery found with a very precise age date of 55 15 years ad rock magnetic experiments pointed towards magnetite as the main carrier of remanence and highly reversible thermomagnetic curves suggested that the studied samples were suitable for archaeoeointensity determinations paleomagnetic experiments including thermal and stepwise alternating field demagnetization yielded the following mean direction for the kiln declination d 0 6 inclination i 54 0 k 481 95 2 5 archaeointensityexperiments with the thellier coe protocol on 28 samples yielded successful determinations in 27 cases anisotropy factors between 0 90 and 1 04 were obtained from anisotropy of thermoremanent magnetization atrm experiments a mean anisotropy corrected archaeointensity value f 56 3 5 5 t was obtained the geomagnetic model sha dif 14 k was used for an archaeomagnetic dating yielding a chronological interval between 40 bce and 150 ce this low age resolution when compared with the pottery based age data is related to the behavior of the geomagnetic field in the iberian peninsula during the roman period which does not allow to differentiate well between results corresponding to those centuries however it is also related to the fact that the iberian archaeomagnetic dataset in the analysed time range is highly scattered a high quality full vector data with a very precise age have been obtained which contribute to improve the iberian secular variation curve and geomagnetic databases

millennial scale climate changes on south georgia southern ocean abstract the location of south georgia 54 s 36 w makes it a suitable site for the study of the climatic connections between temperate and polar environments in the southern hemisphere because the mass balance of the small cirque glaciers on south georgia primarily responds to changes in summer temperature they can provide records of changes in the south atlantic ocean and atmospheric circulation we use grey scale density weight loss on ignition and grain size analyses to show that the proportion of glacially eroded sediments to organic sediments in block lake was highly variable during the last 7400 cal yr b p we expect that the glacial signal is clearly detectable above noise originating from nonglacial processes and assume that an increase in glacigenic sediment deposition in block lake has followed holocene glacier advances we interpret proglacial lake sediment sequences in terms of summer climate warming and cooling events prominent millennial scale features include cooling events between 7200 and 7000 5200 and 4400 and 2400 and 1600 cal yr b p and after 1000 cal yr b p comparison with other terrestrial and marine records reveals that the south georgian record captures all the important changes in southern hemisphere holocene climate our results reveal a tentative coupling between climate changes in the south atlantic and north atlantic because the documented temperature changes on south georgia are anti phased to those in the north atlantic

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

a geochemical approach to constraining the formation of glassy fallout debris from nuclear tests glassy nuclear fallout debris from near surface nuclear tests is fundamentally reprocessed earth material a geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation an improved understanding of fallout formation is of interest both for its potential to guide post detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high energy natural events such as meteorite impacts and lightning strikes this study presents a large major element compositional dataset for glasses within aerodynamic fallout from the trinity nuclear test trinitite and a geochemically based analysis of the glass compositional trends silica rich and alkali rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains quartz and alkali feldspar respectively from the test site sediment the volumetrically dominant glass phase called the camgfe glass shows extreme major element compositional variability compositional trends in the camgfe glass are most consistent with formation through volatility controlled condensation from compositionally heterogeneous plasma radioactivity occurs only in camgfe glass indicating that co condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite camgfe trinitite glasses overlap compositionally with basalts rhyolites fulgurites tektites and microtektites but display greater compositional diversity than all of these naturally formed glasses indeed the most refractory camgfe glasses compositionally resemble early solar system condensates specifically cais

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

glaciomarine sedimentation and its paleoclimatic implications on the antarctic peninsula shelf over the last 15 000 years abstract analyses of sedimentological geochemical and micropaleontological parameters from radiocarbon dated sediment cores retrieved from the antarctic peninsula s western continental shelf reveal a detailed paleoclimatic and or paleoceanographic history over the last 15 000 radiocarbon years deglaciation of the outer shelf off anvers island commenced prior to at least 15 000 yr bp marked by the deposition of distal glaciomarine diamicton facies 2 beneath a floating ice shelf and lasted for 3800 years with increasing diatom abundance and total organic carbon toc over time a return to colder conditions occurred between 12 800 and 11 600 yr bp with a drop in toc content and diatom abundance which is coincident with the younger dryas event in the north atlantic region at this time an abrupt increase in percentage sea ice taxa as well as in the ratio of fragilariopsis curta fragilariopsis cylindrus thalassiosira antarctica suggests renewed ice shelf advance in contrast the inner shelf was deglaciated somewhat later about 11 000 yr bp that is 3000 years after the outer shelf prior to 11 000 yr bp deposition of proximal glaciomarine diamicton facies 1 close to the grounding line under a floating ice shelf and or persistent sea ice may have occurred on the inner shelf after this date deposition of distal glaciomarine diamicton facies 2 followed a climatic optimum is recognized between 6000 and 2500 yr bp coinciding with a mid holocene climatic optimum from several other antarctic sites e g the palmer deep during this time as the glacial system receded from the shelf greatly enhanced primary productivity occurred in open marine conditions resulting in the deposition of diatomaceous mud facies 3 and causing post depositional dissolution of calcareous benthic and planktonic foraminifers in sediment around 2500 yr bp the onset of the neoglacial diatomaceous sandy mud facies 4 characterized by a decrease in toc and diatom abundance reflects the formation of more extensive and seasonally persistent sea ice as evidenced by an increase in percentage of sea ice taxa and in the ratio of f curta f cylindrus t antarctica our results provide evidence of climatic change on the antarctic peninsula s western shelf that helps to refine the existence and timing of late pleistocene and holocene millennial scale climatic events in the southern hemisphere

iceberg scours pits and pockmarks in the north falkland basin abstract glaciation in the southern hemisphere is limited by the availability of land from which to seed ice sheets the extents of the antarctic patagonian and new zealand ice sheets at the last glacial maximum lgm are relatively well known although the rates and styles of their retreat after the lgm are poorly constrained particularly in antarctica offshore records of glaciation are relatively sparse in the southern hemisphere despite the potential ocean climate insights that can be gained from records of glaciation that are preserved offshore in this study we document the occurrence of iceberg scours and accompanying pits within the north falkland basin c 50 s and discuss their origin the cross sectional shapes of scours are u to v shaped and occur in present day water depths of 280 to 460 m individual scours are up to 38 km long 1 km wide and up to 10 m deep the scours are observed as erosional linear to curvilinear depressions showing only one point of contact between the iceberg and seafloor often with raised berms composed of excavated material identified either side of the main depression undulating width of scours is interpreted as an effect of rotation of the iceberg keel during scour excavation the elongate morphology of the scours differentiates them from asymmetrical pits interpreted to represent iceberg impact pits and symmetrical pockmarks interpreted to form due to fluid expulsion in cross section the differentiation is highly interpretative but the 3d bathymetric expression is unequivocal the sinusoidal character of the scours suggests the interaction between local tidal currents and the east falkland malvinas currents in the north falkland basin at the time of formation offshore and onshore landscape analysis is used to determine potential sources of icebergs and suggests that they were most likely sourced from the antarctic peninsula these results inform our understanding of southern hemisphere ocean climate interactions during the last glacial cycle and suggest that the east falklands malvinas current a key current in the southern hemisphere bringing cold low salinity antarctic derived waters into the south atlantic was in operation during the last glacial cycle the accumulation of icebergs west of the falkland islands would also result in further cooling from fresh meltwater perturbations enhancing the development of a potential ice bridge along the argentinian coast

late glacial and holocene glacier fluctuations and environmental change on south georgia southern ocean south georgia provides a terrestrial record of postglacial environmental change from a largely oceanic zone of the earth the record is representative of the southern westerlies and provides a link between antarctica and the temperate zones of southern south america evidence from glacial geomorphology slope stratigraphy and analyses of environmental indicators in peat and lake cores is used to interpret this record wastage of the full glacial ice cap was interrupted by a late glacial stade of the outlet and valley glaciers before ca 10 000 yr b p plant growth had begun at low altitude 50 m on the sheltered lee side northeast coast within the late glacial moraine limits by 9700 yr b p environmental conditions on slopes above 80 m probably were too rigorous for a stable vegetation cover until ca 6400 yr b p this was followed by a period from 5600 to 4800 yr b p when conditions were warmer than at present by up to 0 6 c periods of climatic cooling occurred at ca 4800 3800 yr b p ca 3400 1800 yr b p and within the last 1400 yr the most extensive holocene advance of south georgia glaciers culminated just before 2200 yr b p these holocene temperature changes of between 0 5 and 1 0 c are comparable in scale and timing to those identified from recent analyses of vostok ice cores from the antarctic ice sheet

a method for correcting geographically separated remanence directions for the purpose of archaeomagnetic dating summary spatial variations in the geomagnetic field must be taken into account if secular variation master curves and directional magnetic dates are to be optimized two methods for relocating remanence vectors have been proposed and in this paper their relative accuracies are compared using a numerical model based on the present day field a method which converts archaeomagnetic directions via a virtual geomagnetic pole is shown to be the more efficient transformation for an archaeomagnetic region the size of the british isles 900 km radius the maximum error in relocating vectors to a central location is predicted to be of the order of 1 2

a matlab tool for archaeomagnetic dating a matlab tool for archaeomagnetic dating has been developed in this work well dated palaeosecular variation curves psvcs can be used to date archaeological artefacts with unknown ages the archaeomagnetic direction declination and or inclination and the archaeointensity obtained from the archaeological artefact are compared with a master psvc in addition historical lava flows with controversial ages can be dated using this methodology the dating process follows the descriptions given by lanos 2004 which is based on the combination of temporal probability density functions of the three geomagnetic field elements here we develop an interactive tool in matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic or lava flow data with a master psvc the master psvcs included with the matlab tool are the different european bayesian curves and those generated using both regional and global geomagnetic field models a case study using all the psvcs available in europe and some undated archaeomagnetic data has been carried out to analyze how the different psvcs affect the dating process in addition the dating uncertainty and the relocation error have been analyzed in the european region results show that some regional bayesian psvcs and the regional scha dif 3k archaeomagnetic model are the best choices to obtain an accurate date in europe moreover when it is available the full geomagnetic field vector must be used for archaeomagnetic dating

modeling the growth and decay of the antarctic peninsula ice sheet a model of the growth and decay of the antarctic peninsula ice sheet during the last glacial interglacial cycle is used to identify the main controls on ice sheet behavior using as input glaciological assumptions derived by w f budd and i n smith 1982 annals of glaciology 3 4249 bedrock topography isostatic compensation and mass balance relationships the model is driven by sea level change over the last 40 000 yr in association with assumed changes in the rate of melting beneath ice shelves an ice sheet dome over 3 5 km thick grows on the offshore shelf and straits west of the antarctic peninsula and reaches a maximum at 18 000 yr b p collapse begins at 14 000 yr b p but becomes rapid and continuous after 10 000 yr b p the present stable ice cover is achieved at 6500 yr b p ice growth and decay are characterized by thresholds which separate periods of steady state from periods of rapid transition the thresholds usually relate to topography tests show that ice sheet behavior is most sensitive to sea level change basal marine melting and accumulation and is less sensitive to isostasy spatial variation in accumulation calving rates and ice flow parameterization tests of the model against field evidence show good agreement in places as well as discrepancies which require further work o

regional modeling of the geomagnetic field in europe from 6000 to 1000 b c we have developed a first low degree regional geomagnetic model for the european continent valid for the period 6000 1000 b c from a selected compilation of sedimentary and archeomagnetic data the scha dif 8k model this model provides information about both direction declination and inclination and intensity of the earth s magnetic field by connecting it with our previous model scha dif 3k valid from 1000 b c to 1900 a d and the igrf we furnish continuous geomagnetic field information for the last 8000 years in europe it has been developed using the revised spherical cap harmonic analysis in 2 dimensions technique r scha2d and using the norm of the earth s magnetic field to constrain the inversion problem the size of the cap is 22 and the maximum degree of the expansion is 2 the linearization problem was solved by using the truncated taylor s series applied to the expressions representing the relationship between the declination inclination and intensity data and the cartesian components of the geomagnetic field we used the geocentric axial dipole gad field as our initial or reference field for time we used the classical sliding overlapping window method the size of the window was set to 100 years shifted by 50 years we compared the model s prediction with the input data with the global cals7k 2 model and with new independent data the regional model shows a better fit to the input and to the independent data than the global model especially in terms of intensity and agrees with the virtual axial dipole moment given by other studies for the last 8000 years the european geomagnetic field has recorded rapid changes or archeomagnetic jerks the average field for the last 8000 years in europe is indistinguishable from the gad field

first directional european palaeosecular variation curve for the neolithic based on archaeomagnetic data neolithic cha1colithic and bronze age anthropogenic cave sediments from three caves from northern spain have been palaeomagnetically investigated 662 oriented specimens corresponding to 39 burning events ash carbonaceous couplets from the three sites with an average of 16 samples per fire were collected 26 new archaeomagnetic directions have been obtained for the time period ranging from 5500 to 2000 yr ca bc these results represent the oldest archaeomagnetic directions obtained from burnt archaeological materials throughout all western europe magnetisation is carried by pseudo singie domain low coercivity ferromagnetic minerals magnetite magnetite with no significant isomorphous substitution and or maghaemite rock magnetic experiments indicate a thermoremanent origin of the magnetisation although a thermochemical magnetisation cannot be excluded combination of the new data presented here and the recent updated bulgarian database allows us to propose the first european palaeosecular variation psv curve for the neolithic a bootstrap method was applied for the curve construction using penalised cubic b splines in time the new palaeosecular variation curve is well constrained from 6000 bc to 3700 bc the period with the highest density of data showing a declination maximum around 4700 bc and a minimum in inclination at 4300 bc which are not recorded by the recent global calslok 1 b and regional scha dif 8k models due to the use of lake sediment data dating resolution by using the proposed psv curve oscillates from approximately 30 yr to 200 yr for the period 6000 to 1000 yr bc reaching similar resolution as radiocarbon dating considering the good preservation age control and widespread occurrence of burnt archaeological materials across southern europe they represent a new source of data for geomagnetic field modelling as well as for archaeomagnetic dating

late quaternary ice surface fluctuations of hatherton glacier transantarctic mountains abstract former longitudinal profiles of hatherton glacier an outlet through the transantarctic mountains constrain nearby polar plateau elevations and ice shelf grounding in the southwestern ross embayment four gravel drift sheets of late quaternary age beside hatherton glacier are from youngest to oldest hatherton britannia i britannia ii and danum the hatherton drift limit is uniformly 20 to 70 m above the present ice surface the britannia ii drift limit is within 100 m of the present surface of uppermost hatherton glacier but is 450 m above middle hatherton glacier extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present ross ice shelf the britannia i drift limit is parallel to but 50 100 m below britannia ii drift the danum drift limit is parallel to but 50 100 m above the britannia ii profile from correlation with drifts near mcmurdo sound and from local 14 c dates we assign an early holocene age to hatherton drift a late wisconsin age to britannia drifts and an age of marine isotope stage 6 to danum drift by our age model the upper reaches of hatherton glacier and presumably the adjacent polar plateau have not exceeded their current elevations by more than 100 150 m during the last two complete global glacial interglacial cycles whereas the middle and lower reaches of hatherton glacier have thickened considerably during the last two global glaciations late wisconsin and marine isotope stage 6 the effect of ice shelf grounding probably was the major control of these changes of hatherton glacier holocene ice surface lowering probably represents the last pulse of grounding line recession in the southwestern ross embayment

fluctuations of the south patagonian ice field during the last glaciation and the holocene mapping along a transect from the southeastern margin of the south patagonian ice field in torres del paine national park chile to the limits of fresh moraines of the last glacial cycle indentified eight glacier advances the four younger ones have been dated by dendrochronology tephrochronology and radiocarbon dating although the bases of 10 m deep bogs were sampled close limiting radiocarbon dates were not obtained because bog formation in this rain shadow area appears not to have commenced until ca 12000 yr ago the outermost little ice age moraine formed during the seventeenth century and three inner ones were deposited around ad 1805 1845 and after 1890 densely vegetated older moraines contiguous with little ice age deposits are possibly of late holocene age tephra from the eruption of reclus volcano at ca 11 880 yr bp was incorporated by a readvance that deposited large multiple moraines 10 16 km from the modern ice front the oldest basal peat found inside the moraine has been dated to ca 9200 yr bp these bracketing dates indicate that some eastern outlet glaciers of the ice field advanced at a time when some western tidewater outlet glaciers terminated inside their modern limits this questions the view of j h mercer and other that patagonian glaciers did not readvance during the late glacial interval a stadial event also occurred when the glaciers were some 18 20 km from their modern positions and is closely dated to ca 11880 yr bp because reclus pumice flushed down glacier forms thick upper beds in outwash deltas deposited in proglacial lakes the four older moraines pre date the late glacial eruption of reclus but are not dated closely comparison of their spatial extent with well dated moraines in the chilean lakes region suggests that they may mark advances culminating at ca 14000 yr bp ca 20000 yr bp and earlier

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

magnetic properties of k t and e o microspherules origin by combustion abstract magnetic spherules and spheroids are found in association with ir anomalies at the cretaceous tertiary k t boundary and near to the eocene oligocene e o boundary detailed magnetic analyses have been performed on these particles and on bulk k t boundary clay from marine and continental sections coercivity spectra and blocking and curie temperatures of the spheroids and k t boundary clays have been determined and natural remanence and susceptibility measured for the bulk clay and associated strata marine k t boundary clays are strongly magnetic with remanent coercivities similar to those of the spheroids in contrast the continental clays are diamagnetic except for the thin overlying impact layer which contains abundant paramagnetic jarosite along with shocked quartz and feldspar the morphologies mineralogies and magnetic properties of the k t magnetic spheroids are closely analogous to magnetic fly ash spherules this similarity may be related to the presence of carbonaceous soot particles in some marine k t boundary clays and the recent identification of plerospheres and cenospheres in continental boundary clay in contrast tektites and microtektites differ from the k t magnetic spherules in a number of fundamental ways the late eocene particles are magnetically distinct from the k t spheroids both in their coercivity and thermal spectra inaa results on upper cretaceous combustible shales indicate that the anomalous abundances of certain chalcophile and lithophile elements at the k t boundary may be explained in terms of the natural combustion of bituminous sediments

combustion metamorphism of bituminous sediments and the formation of melts of granitic and sedimentary composition during combustion metamorphism i e the heating of sediments rich in organic matter by spontaneous subsurface combustion temperatures obtained are frequently high enough to cause partial or total melting of the original rocks these melts are of particular geochemical interest because at lower temperatures their composition closely simulates that of granitic and at higher temperatures that of common sedimentary rocks at the california localities studied here the parent rocks are mainly bituminous mudstones with smaller amounts of diatomites and phosphorites and lesser dolomites limestones shales and cherts it is estimated that rock melting started below 1000 c the first partial melts correspond to a melt fraction of about 5 have a constant composition which is controlled by the eutectic of the dominant mudstones and are undistinguishable in major and trace element composition from common s type granites compared with the original rocks these melts are enriched in sio2 al2o3 k2o na2o as well as in ta hf zr th and ree and are depleted in all other elements studied the only difference between these low temperature melts and granitic ones is their oxygen isotope composition which is that of the sedimentary parent rocks these melts intruded the country rocks as sills and dikes and cooled to glassy rocks simulating obsidians as temperatures rose the melts changed composition and left the magmatic field at the highest temperatures in excess of 1650 c their composition equals that of the original sediments from which they are derived except for volatile components such as h2o and co2 these melts formed intrusive bodies mainly stocks up to several kilometers across on cooling these melts formed fine grained but holocrystalline rocks the dominant minerals of which are cristobalite and tridymite calcic plagioclase cordierite wollastonite gehlenite andradite and apatite where the parent rocks included phosphorites two immiscible melts formed an emulsion in which droplets of apatitic composition are surrounded by a silicate melt almost devoid of p2o5

assessing post depositional processes in archaeological cave fires through the analysis of archaeomagnetic vectors abstract this paper presents a methodological application of archaeomagnetism and rock magnetism as a tool to evaluate post depositional mechanical alterations in archaeological cave fires most taphonomic and post depositional studies on anthropogenic sediments have mainly focused on the diagenetic alterations that these contexts undergo from a geochemical point of view however physical alterations are still largely assessed from mere macroscopic observations of the burnt facies comprising these fires this paper compares the archaeomagnetic directions recorded in the ashes of two holocene fires from the mirador cave sierra de atapuerca burgos spain one apparently well preserved and the other clearly bioturbated vector analyses of archaeomagnetic directions together with the study of magnetic properties combined with field macroscopic observations can provide a powerful tool to assess when a fire is actually in situ the anisotropy of magnetic susceptibility ams in both fires exhibits a dominant sedimentary fabric produced by compaction and also exhibits differences between the areas mechanically disturbed within these fires from those which are not the following set of magnetic features was identified when an archaeological fire preserves its primary position i univectoral and high intensity nrm orthogonal demagnetisation diagrams in ashes ii koenigsberger q n ratio values higher than unity indicative of an undisturbed thermo remanence trm or a partial thermoremanence p trm and iii a good clustering of characteristic directions defining an statistically representative mean archaeomagnetic direction the concurrence of these observations can be used as criterion to determine when an archaeological cave fire is physically in situ thus allowing a correct interpretation of the archaeological record

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

late quaternary ice surface fluctuations of beardmore glacier transantarctic mountains abstract former longitudinal profiles of beardmore glacier an outlet through the transantarctic mountains constrain polar plateau elevations near the center of antarctica and ice shelf grouding in the southern ross embayment three gravel drift sheets of late quaternary age occur alongside beardmore glacier plunket drift the youngest is parallel to and 7 30 m above the present ice surface the upper limit of beardmore drift intermediate in age is within 35 40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth the upper limit of meyer drift the oldest is parallel to and 30 50 m above beardmore drift from correlation with numerically dated drifts farther north we assign an early holocene age to plunket drift a late wisconsin age to beardmore drift and an age of marine isotope stage 6 to meyer drift by our age model beardmore glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by beardmore and meyer drifts most likely grounded ice in the southern ross embayment caused such thickening of beardmore glacier almost to the polar plateau a concomitant decline in precipitation is implied by ice cap retreat on the nearby dominion range and is consistent with little change of upper beardmore glacier ice shelf grounding most likely resulted from lowered sea level and or basal melting lower than present precipitation was probably caused by colder air temperatures and more distant open water the plunket profile records holocene ice surface lowering from increased surface ablation decreased ice flow or grounding line recession

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

stone runs in the falkland islands periglacial or tropical abstract stone runs is the falklands vernacular term for openwork boulder accumulations which include extensive blockstreams like the famous darwin stone river and associated features such as stone stripes since the early 20th century they have been interpreted as the product of a suite of periglacial processes including frost wedging gelifluction frost heave frost sorting and snowmelt runoff following a literature review the results of recent field investigations of the valley floor blockstreams of east falkland are presented access to the internal structure of these forms provides evidence for the existence of a three fold profile with clear vertical size gradation presenting striking similarities with an inverted weathering profile micromorphological analyses sem xrd thin sections and grain size analyses lead to the hypothesis of an alternative model of stone run formation it is suggested that the material forming the stone run profile lato sensu including the superficial pavement is not of periglacial origin but derives directly from the stripping and accumulation downslope of a regolith possibly tertiary in age and formed under subtropical or temperate conditions the valley floor stone runs should therefore be considered as complex polygenetic landforms that may have formed according to a six stage scenario including in situ chemical weathering regolith stripping by mass movements soil formation further regolith stripping downslope accumulation and matrix washing out all phases possibly achieved by the early quaternary periglacial reworking of the stone run material would have operated at a final stage i e during quaternary cold stages with boulder bioweathering and limonite staining operating during the temperate intervals including the present one the suggested antiquity of the falklands blockstreams is in accordance with caine s pioneer interpretation of tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from scandinavia and north america

reconstruction of the pre merida glaciation northwestern venezuelan andes abstract valley glaciers have been well studied in the northwestern venezuelan andes over the last 20 year period but most reconstructions have been limited to the last glacial maximum lgm analyses have been confined to the mapping of moraine positions and the detailed analysis of pedostratigraphic sequences reaching back through the middle to the early wisconsinan weichselian glaciation using bedding macrofeatures fabric analysis magnetic azimuths with mirror images clast inclination and microtextural evidence much has been learned about the lithology source of ice growth of an ice cap in the eastern cordillera and weathered state of surface paleosols analysis of two sections of pre merida age the only two such sections known in the sierra de santa domingo eastern cordillera provides new information on lithology source of the ice and weathered state of sediment of pre merida age the fabric in these sections is used to deduce the build up of valley ice in the lower el caballo valley from an ice cap similar to one that developed later in early merida time 90 ka to 65 ka the presence of weathered tills in both sections suggests two glaciations perhaps correlative with the illinoian and kansan glaciations of north america the weathered state of tills and outwash in both sections is assessed on the basis of geochemical inaa and mineral composition xrd and microtextural evidence determined by sem eds

late holocene glacier reconstruction reveals retreat behind present limits and two stage little ice age on subantarctic south georgia observational data show that climate in the southern ocean region is rapidly changing however past the instrumental period our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records alpine glaciers present on many southern ocean islands may provide such data because changes in their mass balance extent and erosion rates often mark a response to climate shifts rock flour the fine grained fraction of the glacial erosion process is suspended in meltwater streams and transferred into the sediments of downstream lakes continuously recording glacier variations here we utilize this relationship to present a reconstruction of the late holocene glacier history of subantarctic south georgia using sediments from the glacier fed middle hamberg lake to fingerprint a glacial erosion size signal we used titanium counts validated against changes in sediment density and grain size allowing a continuous reconstruction of glacier variations over the past similar to 1250 years together with local moraine evidence and supporting evidence from other southern hemisphere glaciers on new zealand and in patagonia our findings reveal a series of consecutively diminishing late holocene advances in addition to a glacier maximum before 1250 cal a bp these include a twostage litle ice age with advances around 300 and 120 cal a bp in line with evidence from southern patagonia in addition we present evidence for an unreported retreat behind present limits around 500 cal bp

quaternary glaciations in the southern ocean and antarctic peninsula area abstract there are three main difficulties in constructing detailed time series for late quaternary glacier fluctuations in the southern ocean sub antarctic region sea level control on ice extent differential tectonics and lack of material for radiometric dating south of 60 s the glacial equilibrium line altitude is low enough for glaciers to expand without a decrease in temperature if sea level falls thus most tidewater glaciers in this region are not reliable indicators of small scale fluctuations in climate tectonic uplift during the quaternary may explain why the falkland islands did not develop most of their glacial and nivoglacial features until the last glaciation the south shetland islands have a unique assemblage of raised marine features in the sub antarctic possibly because the crustal block overlies a zone of magmatism and may respond sensitively to isostatic changes imposed by fluctuating ice masses despite the lack of vegetation some radiometric dates have been obtained from peat seaweed and fossil remains of marine shells and bones associated with glacial and raised beach deposits together with relative weathering criteria and drift distribution these suggestthat glaciers in the southern ocean and sub antarctic region have fluctuated synchronously with glaciers elsewhere in the southern hemisphere during the last 100 ka the last glaciation maximum culminated after 26 ka bp and glacier advances are inferred for the late glacial intervals 15 14 ka and 12 10 ka bp and the neoglacial interval last 5 ka

origin of moldavites abstract moldavites are supposed to be products of the ries impact but neither has the source material been identified in the ries area nor is the mode of moldavite glass formation sufficiently clear it is the purpose of this investigation to elucidate both problems by means of new chemical data fifty nine moldavites from 20 localities in bohemia and moravia and 30 samples of middle miocene sediments from the ries were analyzed for major oxides x ray fluorescence 30 trace elements neutron activation water content infrared spectroscopy and 18 o 16 o ratios microprobe analysis shows that moldavites are composed of thin laminae of optically and chemically somewhat different glasses bent and curled in three dimensions indicating the confluence of primary melt units under conditions of laminar flow the moldavites cannot be derived from crystalline basement rocks and mesozoic sediments involved in the ries impact the only lithology from which moldavites could have been formed is middle miocene sands which formed a thin veneer in the ries area at the time of the impact moldavites and these middle miocene sands are compositionally similar but not identical which indicates that moldavite formation from sands involved chemical fractionation enrichments and depletions of individual elements in moldavites can not be explained by fractional vaporization this was confirmed also by melting experiments with sand samples moreover the negligible water content in moldavites and the scarcity of vesicles excludes the formation of moldavite melt by simple fusion of sands for individual elements the distribution ratios q concentration in moldavites concentration in sands and ionic radii r are significantly correlated q 2 21r 1 18 it is inferred that at the encounter of the impactor with the ground surficial sands were transformed by high pressures and temperatures into a plasma like vapor in the expanding and ascending vapor droplets of a liquid phase condensed consisting of a framework of interconnected si al o4 tetrahedra which selectively incorporated cations to compensate its negative charge the uptake of cations was controlled by the ionic radius because ions fit better into the interstices of the liquid framework the larger they are the primary melt droplets separated from residual vapor and coalesced to moldavite bodies the lower o content of moldavites 11 5 as compared to dry sands 16 is explained by an admixture meteoric water o 10 which filled the pore space

holocene glacier fluctuations and environmental changes in subantarctic south georgia inferred from a sediment record from a coastal inlet the subantarctic island of south georgia provides terrestrial and coastal marine records of climate variability which are crucial for the understanding of the drivers of holocene climate changes in the subantarctic region here we investigate a sediment core co1305 from a coastal inlet on south georgia using elemental lipid biomarker diatom and stable isotope data to infer changes in environmental conditions and to constrain the timing of late glacial and holocene glacier fluctuations because of the scarcity of terrestrial macrofossils and the presence of redeposited and relict organic matter in the sediments age control for the record was obtained by compound specific radiocarbon dating of mostly marine derived n c 16 fatty acids a basal till layer recovered in little jason lagoon was likely deposited during an advance of local glaciers during the antarctic cold reversal after glacier retreat an oligotrophic lake occupied the site which transitioned to a marine inlet around 8 0 0 9 ka because of relative sea level rise from 7 0 0 6 to 4 0 0 4 ka reduced vegetation coverage in the catchment as well as high siliciclastic input and deposition of ice rafted debris indicates glacier advances in the terrestrial catchment and likely in the adjacent fjord a second less extensive period of glacier advances occurred in the late holocene after 1 8 0 3 ka