lithic raw material units based on magnetic properties a blind test with armenian obsidian and application to the middle palaeolithic site of lusakert cave 1 classification of lithic artifacts raw materials based on macroscopic attributes e g color luster texture has been used to pull apart knapping episodes in palimpsest assemblages by attempting to identify artifacts produced through the reduction of an individual nodule these classes are termed raw material units rmus in the old world and minimum analytical nodules in the new world rmus are most readily defined for lithic artifacts in areas with distinctive cherts and other siliceous raw materials allowing pieces from different nodules to be recognized visually opportunities to apply rmus however are strongly limited at sites where lithic material visual diversity is low the magnetic properties of obsidian which result from the presence of microscopic iron oxide mineral grains vary spatially throughout a flow consequently obsidian from different portions of a source i e different outcrops or quarries can vary in magnetic properties this raises the possibility that magnetic based rmus mrmus for obsidian artifacts could be effective to distinguish individual scatters from multiple production episodes and offer insights into spatial patterning within a site or specific occupation periods first we assess the potential of mrmus using obsidian pebbles from gutansar volcano in armenia second we evaluate the validity of this approach based on a double blind test involving an experimental assemblage of gutansar obsidian flakes cluster analysis can successfully discern flakes from obsidian specimens containing high concentrations of iron oxides obsidian with more magnetic material has more opportunities for that material to vary in unique ways e g grain size morphology physical arrangement finally we apply the mrmu approach to obsidian artifacts from the middle palaeolithic site of lusakert cave 1 in armenia and compare the results to traditional rmu studies at contemporaneous sites in europe in particular we seek but do not find differences between retouch flakes which reflect rejuvenation of tools and the other small debris which reflect other reduction activities this result likely reflects the local landscape specifically the abundance of obsidian and thus little pressure to curate and retouch tools as this approach is applied to additional sites such findings will play a central role in regional assessments about the nature and timing of the middle to upper palaeolithic transition and the relationship or lack thereof between technological behaviors and presumed population dynamics

a model of the western laurentide ice sheet using observations of glacial isostatic adjustment we present the results of a new numerical model of the late glacial western laurentide ice sheet constrained by observations of glacial isostatic adjustment gia including relative sea level ind

formation of large beaches in an area of rapid differential isostatic rebound the three outlet control of lake agassiz abstract shorelines in basins undergoing differential isostatic rebound do not remain geographically fixed for long periods and are either transgressive or regressive during regression a relatively uniform blanket of shoreface sediment may be deposited but unless regression is slow or punctuated by periods of lake level equilibrium large beaches do not form in contrast along transgressive shorelines which migrate upslope large morphostratigraphic features commonly are maintained along the lake s margin these may subsequently be stranded when lake level declines beaches around isostatically rebounding proglacial lakes are commonly considered to have formed during a period of lake regression punctuated by abrupt drops in lake level however in basins that are differentially rebounding large beaches cannot form this way and only periods of transgressing waters allow enough time for large beaches to form and define a continuous shoreline around the basin with this in mind some of the largest and most extensive beaches in the glacial lake agassiz basin the norcross tintah and upper campbell constructed between 10 4 and 9 4 ka 14 c yr bp are reinterpreted as strandlines that were formed by transgression each of these three transgressions followed lower lake phases and resulted from in sequence differential isostatic rebound of the eastern outlet rebound and ice damming of the northwestern outlet and rebound of the northwestern outlet each of these transgressions ended when lake level reached the southern outlet stranding the norcross tintah and upper campbell beaches about 10 2 9 9 and 9 4 ka 14 c yr bp respectively

sourcing geochemically identical obsidian multiscalar magnetic variations in the gutansar volcanic complex and implications for palaeolithic research in armenia abstract in obsidian rich armenia one of the most archaeologically significant obsidian resources is the gutansar volcanic complex gvc numerous palaeolithic sites across armenia consist of little more than deposits of obsidian tools and debris and within the hrazdan gorge the vast majority of artifacts is crafted from gvc obsidian for example about 93 of the lithic assemblages from the lower palaeolithic site of nor geghi 1 and the middle palaeolithic site of lusakert cave 1 are gvc obsidian although erupted from multiple volcanic centers gvc obsidians are geochemically identical and cover an area more than 70 km2 for studies seeking to reconstruct movements of palaeolithic hunter gatherers throughout the local landscape the expansive gvc is problematic geochemically identical obsidians dominate the foraging territories of sites within and near the complex here we explore the potential of obsidian magnetic properties to reveal hitherto unobservable patterns in gvc obsidian utilization with the ultimate goal of elucidating palaeolithic behavioral patterns our results show that magnetic properties vary over multiple scales within the gvc allowing obsidian sourcing to become multiscalar these measurements are rapid inexpensive and entirely nondestructive for small artifacts measuring a few basic magnetic properties enables us to distinguish geochemically identical obsidians from three eruptive centers and potentially to attribute artifacts to specific quarrying sites recognize changes in provisioning strategy and estimate a minimum number of cores represented by a lithic scatter

a reconstruction of moorhead and emerson phase environments along the eastern margin of glacial lake agassiz rainy river basin northwestern ontario mapping of quaternary geology in the rainy river lowland northwestern ontario resulted in discovery of several fossil bearing localities organic remains are associated with both the moorhead and

environment and collapse eastern anatolian obsidians at urkesh tell mozan syria and the third millennium mesopotamian urban crisis the early to middle bronze age transition in northern mesopotamia has received great attention for the apparent concurrence of aridification deurbanisation and the end of the akkadian empire around 2200 bce our understanding of the crisis has been almost exclusively shaped by ceramics demography and subsistence exchange and the associated social networks have been largely neglected here we report our sourcing results for 97 obsidian artefacts from urkesh a large urban settlement inhabited throughout the crisis before the crisis six obsidian sources located in eastern anatolia are represented among the artefacts such a diversity of eastern anatolian obsidians at one site is hitherto unknown in mesopotamia it implies urkesh was a cosmopolitan city with diverse visitors or visitors with diverse itineraries during this crisis however obsidians came from only two of the closest sources two to three centuries passed before varied obsidians reappeared even when an obsidian source reappears the raw material seems to have come from a different collection spot we discuss the likely exchange mechanisms and related social networks responsible for the arrival of obsidians at urkesh and how they might have changed in response to climatic perturbations and regional government collapse

mapping and measuring lake agassiz strandlines in north dakota and manitoba using lidar dem data comparing techniques revising correlations and interpreting anomalous isostatic rebound gradients based on light detection and ranging lidar digital elevation model dem data at 1 m spatial resolution lake agassiz strandlines were mapped and their elevations determined in northeastern north dakota and southern manitoba two different techniques for determining strandline elevations from lidar imagery are compared one based on measuring the crests of constructional beaches and the other using the elevation of slope breaks along the shorelines defined by shadows on the lidar hillshade map our measurements on lake agassiz strandlines show that previous correlations of younger strandlines around the pembina delta accepted for more than a century are incorrect the gladstone ojata and emerado strandlines south of the delta are offset by 10 m from their namesakes to the north and so are equivalent to the ojata emerado and hillsboro strandlines respectively furthermore anomalously low gradients for the ojata and emerado strandlines around the pembina delta are interpreted as resulting from postdepositional compaction of underlying fine sediment elevations on the isostatically rebounded strandlines confirm that older higher ones have steeper northward rising elevations and that gradients on those strandlines can be used as proxies for relative age

questioning the age of the moorhead phase in the glacial lake agassiz basin abstract the stratigraphy of sites within the lake agassiz basin that constrain the timing of the onset of the moorhead low water phase is reexamined stratigraphic interpretation of the oldest date 10 960 14 c yr bp from cross bedded sand of the ojata beach is questioned particularly in light of demonstrated long distance transport and reworking of older organic material from elsewhere in the basin a maximum onset age for the moorhead phase is suggested from a 10 675 60 14 c yr bp age from wood in gravel from the base of the southern outlet whereas radiocarbon dates from in situ peat indicate a later minimum onset age of 10 340 100 14 c bp

pleistocene volcanism and the geomorphological record of the hrazdan valley central armenia linking landscape dynamics and the palaeolithic record abstract the southern caucasus lies at the intersection of africa the levant and eurasia and is thus a region of considerable interest in the study of pleistocene hominin population dynamics and behaviour while palaeolithic archaeological sites in the region such as dmanisi and nor geghi 1 attest to such palaeogeographic significance a greater understanding of the chronology and nature of climatic and geomorphic changes in the region is needed to fully understand hominin settlement dynamics the hrazdan river valley central armenia has the potential to offer such insights given its rich palaeolithic record and complex history of pleistocene infill as a result of alluvial lacustrine aeolian and volcanic processes we therefore present a stratigraphic framework for basin infill and hominin activity during the pleistocene based on extensive geomorphological and geological mapping published chronometric results 40ar 39ar and k ar and archaeological survey we demonstrate that the onset of pleistocene volcanism in the gegham range to the immediate east of the hrazdan valley occurred around 700 ka bp after which there were several phases of effusive eruption lasting until 200 ka interbedded with lava emplaced by these eruptions are alluvial and lacustrine sequences some with evidence of pedogenesis and several of which have yielded palaeolithic artefacts taken together these sequences suggest a cyclical model of infill whereby lava flow along the valley resulted in the blockage of the palaeo hrazdan river and lake formation in the lea of the lava dams breaching of these dams resulted in a shift to predominately fluvial deposition and the consequent development of floodplain soils hominin populations exploited the floodplains at times when the last of these phases coincided with interglacial and interstadial climates but they also occupied the surrounding valley sides during the same warm humid phases

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

late collision rhyolitic volcanism in the north eastern part of the armenian highland abstract plio pleistocene acidic volcanism of the northeastern part of the armenian highland is related to a continental collision zone as a result of convergence between eurasia and arabia lithosphere plates the development of volcanism is divided into three stages of 10 17 4 5 7 5 and 0 1 2 8 ma a crustal origin model is proposed to explain the geochemical and petrogenetic aspects of the acidic volcanism formation spatially separated ba rich and rb rich geochemical types of rhyolites were revealed indicating more evolved and primitive rhyolitic magma types respectively the variation interval of the primary 87sr 86sr ratio was found to be from 0 70438 to 0 70636 age and lateral variation of geochemical and isotopic parameters were determined by differences of initial substrates and degrees of their partial melting the mechanisms of rhyolitic magma evolution were the remelting of heterogeneous sialitic materials and low pressure fractional crystallization in isolated magmatic chambers these facts confirm the model of crustal anatexis origin of the eutectic melts the eutectic rhyolitic magma was generated by an open system melting in the presence of deep horizon mobile k rb fluids initiated by mantle resources

the magnetic sourcing of obsidian samples from mediterranean and near eastern sources abstract the magnetic properties of obsidians are examined for their potential in sourcing obsidian artifacts the three simplest to determine magnetic parameters initial intensity of magnetization saturation magnetization and low field susceptibility are found to be effective discriminants of many mediterranean central european and near eastern sources although the between source precision is not as good as geochemical analyses of minor and rare earth elements the technique demonstrated the existence of new sources that were subsequently confirmed by minor element analyses unfortunately some key sources do not appear to be readily distinguishable on these three simple magnetic parameters alone although more sophisticated magnetic analyses may prove diagnostic despite this it would appear that effective discrimination can be made in many cases occasionally with more precision than minor element analyses this technique therefore offers as a minimum a preliminary sourcing tool for use in many areas of the world thus reducing the number of expensive geochemical analyses furthermore its very low cost non destructive nature and speed open the possibility of quantitative evaluation of trade routes based on obsidian distributions particularly as versions of the equipment are now suitable for use in the field

from flow to quarry magnetic properties of obsidian and changing the scale of archaeological sourcing abstract previous studies have endeavored to use petrophysical traits of obsidian particularly its magnetic properties as an alternative to conventional geochemical sourcing one of the greatest successes in archaeological science magnetic approaches however have not seen widespread application due to their mixed successes in a time when geochemical analyses can be conducted non destructively in the field and in a minute or two magnetic measurements of obsidian must offer novel archaeological insights to be worthwhile not merely act as a less successful version of geochemistry to this end we report the findings of our large scale study of obsidian magnetism which includes 734 geological obsidian specimens and 97 artifacts measured for six simple magnetic parameters based on our results we propose rather than using magnetic properties to source artifacts to a particular obsidian flow inter flow sourcing these properties are best used to differentiate quarrying sites within an individual flow intra flow sourcing our results also demonstrate that certain magnetic properties are highly affected by ancient knappers material selection criteria furthermore depending on the spatial scales of variation which likely vary from flow to flow we envision several potential applications of this approach including integration into minimum analytical nodule analysis mana magnetic data appear to shift the scale of obsidian sourcing from flows to quarries and in turn enable new insights into raw material procurement strategies group mobility lithic technology and the organization of space and production

macusani obsidian from southern peru a characterization of its elemental composition with a demonstration of its ancient use transparent obsidian artifacts have been reported for the northern lake titicaca basin based on instrumental neutron activation analysis inaa of these artifacts a distinct chemical group was identified yet the location of the source of transparent obsidian in the southern andes remained unreported in the archaeological literature this paper reports on the chemical composition and geographic location of a source of transparent obsidian from the macusani region of peru through the use of inaa and portable x ray fluorescence pxrf we demonstrate that macusani obsidian or macusanite comprises at least two chemical groups one of these groups was used for making artifacts during the archaic period artifacts made of this obsidian were found more than 120 km from the source and yet one third of the obsidian artifacts encountered at macusani were from the non local source of chivay which is 215 km to the southwest

tongan and samoan volcanic glass pxrf analysis and implications for constructs of ancestral polynesian society a provenance study of volcanic glass specimens from 12 archaeological sites in the kingdom of tonga is carried out employing pxrf portable x ray fluorescence analysis to accomplish this volcanic glass samples from previously identified sources in northern tonga and the adjacent islands of samoa are analyzed results indicate inter island voyaging and interaction over a 600 km linear distance along the tongan island chain from first lapita settlement ca 2900 bp throughout later prehistory tongan volcanic glass however is not found in samoa and with the exception of one late prehistoric specimen samoan volcanic glass is not present in tonga this distribution challenges current concepts of an integrated ancestral society and homeland common to tonga and samoa from the lapita period onward

late pleistocene palaeoenvironments of the southern lake agassiz basin usa macroscopic plant remains pollen insect and mollusc fossils recovered from a cut bank on the red river in north dakota usa provide evidence that an extensive wetland occupied the southern basin of lake agassiz from 10 230 to 9900 14 c yr bp marsh dwelling plants and inver tebrates had colonised the surface of a prograding delta during the low water moorhead phase of lake agassiz a species of salix willow was abundant along distributary channels and stands of populus tremuloides aspen ulmus sp elm betula sp birch and picea sp spruce grew on the better drained sand bars and beach ridges most of the species of plants insects and molluscs represented as fossils are within their existing geographic ranges based on a few species with more northerly distributions mean summer temperature may have been about 1 2 c lower than the pre sent day no change in species composition occurred in the transition from the younger dryas to preboreal at the time that the wetland existed lake agassiz was draining either eastward to the north atlantic ocean or northwestward to the arctic ocean the wetland was drowned during the emerson phase transgression that resulted in meltwater draining southward to the gulf of mexico after 9900 14 c yr bp copyright 2005 john wiley sons ltd

factors controlling reservoir properties and hydrocarbon accumulation of the eocene lacustrine beach bar sandstones in the dongying depression bohai bay basin china abstract lacustrine beach bar sandstone reservoirs are economical important exploration targets in the dongying depression bohai bay basin the factors that controls reservoir quality and hydrocarbon accumulation in lacustrine beach bar sandstones were systematically investigated through an integrated petrographic petrophysical and diagenesis analysis the reservoir properties of the beach bar sandstones are mainly affected by compaction carbonate cementation and dissolution significant negative relationships exist between both the porosity and permeability and the volume of carbonate cement carbonate cement is mainly distributed along the sandstone mudstone contacts sandstones with thicknesses less than 1 m are generally tightly cemented to form zones with low petrophysical properties the material source of the carbonate cement in the tightly cemented zone was highly likely from the interbedded mudstone content of carbonate cements in the center of the thick sandstones is low whereas compaction is the dominant diagenetic process with some dissolution there is a positive correlation between the petrophysical properties of the beach bar sandstones and the content of kaolinite the petrophysical properties have an inverse correlation with the contents of illite and illite smectite mixed layer clays reservoir petrophysical property largely controls hydrocarbon accumulation in the beach bar sandstones compared with non oil bearing sandstones oil bearing sandstones have higher porosity and a larger pore throat size sandstones with a porosity of less than 8 5 and or low permeability of less than 1 02 10 3 m2 are mostly incapable of accumulating oil

chronology of glacial lake agassiz meltwater routed to the gulf of mexico abstract sediment cores with new radiocarbon dates from the southern outlet of glacial lake agassiz indicate that meltwater delivery to the mississippi valley was disrupted at 10 800 14 c yr b p and the outlet was abandoned by 9400 14 c yr b p these findings confirm the timing of generally accepted terminations of the lockhart and emerson phases of lake agassiz additionally the radiocarbon chronology indicates that the spillway was fully formed by 10 800 14 c yr b p and that the occupancy in late emerson time was likely short lived with minimal spillway erosion

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

the tintah campbell gap and implications for glacial lake agassiz drainage during the younger dryas cold interval abstract reconstructions of glacial lake agassiz paleogeography and drainage have been an important contribution to formulating a hypothesis in which glacial lake agassiz drainage to the atlantic ocean initiated the younger dryas cold interval this study evaluates the lake level and outlet history of lake agassiz as recorded by strandlines visible on lidar digital elevation models from north dakota and minnesota the former lake levels are warped due to glacial isostatic adjustment older levels have experienced more uplift and therefore have more curvature the strandline data establish that the moorhead lowstand of lake agassiz was bracketed by the strongly diverging campbell and tintah lake levels which creates a vertical gap between the former lake levels this gap exists due to a lake level drop of 90 m when the laurentide ice sheet retreat opened a lower outlet which must have been a northwest outlet to the arctic ocean by applying an exponential decay rebound model this event dates to 12 180 480 cal yr bp post dating the beginning of the younger dryas at 12 900 cal yr bp eastern drainage outlets to the atlantic ocean through the laurentian great lakes that were contemporaneous with the onset of the younger dryas cannot be ruled out but if these outlets existed their duration of occupation was short lived and not characterized by significant drawdown events within glacial lake agassiz

moving sources a preliminary study of volcanic glass artifact distributions in northeast china using pxrf recent studies have highlighted the long distance transport of obsidian from the paektusan tianchi or baitoushan in chinese volcano on the border between china and north korea to eastern russia and korea but little is known about the role of the local population in the production and movement or exchange of this important raw material this paper addresses this data lacuna by presenting sourcing results of 440 artifacts from 18 late paleolithic sites located in northeast china a portable xrf enabled rapid non destructive characterization of samples the results show that although paektusan obsidian was widely transported throughout northeast asia material from at least three other sources was also used in particular we highlight the significance of basaltic glass artifacts with the same geochemistry as sources found in the primorye region of far east russia in sites from northeast china this result indicates a two way movement of volcanic glass artifacts between primorye and the northeast of china rather than a unidirectional long distance exchange system originating from paektusan volcano

beach ridge development and lake level variation in southern lake michigan abstract the most accurate source of information on lake level fluctuations in the great lakes is the historical record from lake level gauges although it can be semiquantitatively extended back into the late 1700 s the historical record is too short to recognize long term patterns of lake level behavior to extend the historical record information must be obtained from the great lakes geologic record such information includes the elevation and age of geomorphic features and stratigraphic sequences one of the longest geologic records of late holocene lake level variation is preserved in a beach ridge complex along the southern shore of lake michigan called the toleston beach this strandplain contains over 150 beach ridges that arc across northwestern indiana and fan out into northeastern illinois each ridge was formed during the fall from a high lake level and the elevation of the foreshore deposits in each ridge provides information on the upper physical limit of lake level over the past 4000 years three scales of quasi periodic lake level variation were determined by radiocarbon dating basal peats of wetlands between the ridges and by measuring the elevation of foreshore swash deposits within ridges these three scales are 1 a short term and small scale fluctuation of 25 to 35 years with a range of about 0 5 to 0 6 m 2 an intermediate term and meso scale fluctuation of 140 to 160 years and a range of about 0 8 to 0 9 m and 3 a long term and large scale fluctuation of 500 to 600 years and a range of 1 8 to 3 7 m the short term and intermediate term fluctuations are reflected in the historical record an increase in the rate of shoreline progradation from east to west across indiana s shoreline causes differential preservation of the lake level fluctuations that is groups of four to six ridges in the western part of the strandplain that formed in response to the small scale fluctuations combine eastward into single ridges and groups of ridges representing the meso scale fluctuations the large scale fluctuations produced the most dramatic response in the western part of the toleston beach here following each high stand individual spits prograded southward off of a bedrock headland the successive spit extensions created several small lakes landward of the spits and started the 20 km eastward stream mouth deflection of the grand calumet river across indiana s western lakeshore

paleotopographic reconstructions of the eastern outlets of glacial lake agassiz paleotopographic reconstructions of the eastern outlets of glacial lake agassiz provide a foundation for understanding the complex manner in which terrain morphology controlled the routing of overflow through the eastern outlets during the lake s nipigon phase ca 9400 8000 14 c years bp and for understanding the causes of outlet driven declines in lake level during that period although flow paths across the divide between the agassiz and nipigon basins were numerous eastward releases from lake agassiz to glacial lake kelvin modern lake nipigon were channeled downslope into a relatively small number of major channels that included the valleys of modern kopka river ottertooth creek vale creek whitesand river pikitigushi river and little jackfish river from lake kelvin these waters overflowed into the superior basin the numerous lowerings in lake level between stages of the nipigon phase controlled by topography and the position of the retreating southern margin of the laurentide ice sheet had magnitudes of between 8 and 58 m although some of these drawdowns may have occurred as multiple individual events that could have been as small as several metres the total volumes of water released in association with these drops were as great as 8100 km 3 and for all nipigon stages were probably between about 140 and 250 km 3 per metre of lowering the topographic reconstructions demonstrate that lake agassiz occupied the area of glacial lake nakina located northeast of modern lake nipigon by the the pas stage ca 8000 14 c years bp and that lake agassiz drainage through the nipigon

ten seconds in the field rapid armenian obsidian sourcing with portable xrf to inform excavations and surveys armenia has one of the most obsidian rich natural and cultural landscapes in the world and the lithic assemblages of numerous palaeolithic sites are predominantly if not entirely composed of obsidian recent excavations at the middle palaeolithic cave of lusakert 1 recovered on average 470 obsidian artifacts daily after sourcing more than 1700 artifacts using portable xrf pxrf in our field house our team sought to shift pxrf based obsidian sourcing into the field itself believing that the geological origins of artifacts would be useful information to have on site during an excavation or survey despite increasing use of portable instruments previous studies have principally focused on collections in museums and other archives and as a result obsidian sourcing has remained embedded in post excavation studies one critical factor in the uptake of obsidian sourcing in the field is the time needed to measure each artifact frequently 2 6 min in previous studies here we report our two methods of obsidian sourcing including source matching done automatically by the pxrf instrument s onboard software in only 10 s our tests with armenian geological specimens and palaeolithic artifacts demonstrate the high efficacy of our two methods which are sufficiently fast to become syncopated with our excavation and survey activities by reducing measurement times from a mode of 300 s in recent studies to just 10 s here we show how and why to shift pxrf based obsidian sourcing from the context of white lab coats to that of muddy boots

lateral variations near the core mantle boundary differential travel times between s and sks ts sks and skks and sks tskks sks along with amplitude behavior have been used to study lateral variations at the core mantle boundary the data were recorded by the world wide seismographic station network wwssn and the canadian seismograph network csn from source regions in south america and the fiji tonga area a core mantle boundary region traversed by sks and s beneath the mid pacific from the fiji tonga area to north american stations shows the most anomalous behavior in ts sks sks and s are anomalously separated by up to 8 seconds in addition to ts sks anomalies sks and skks are anomalously separated by 2 to 3 seconds a model fitting ts sks for this anomalous region requires one or more of the following 1 up to 5 increase in the top 300 km of outer core velocity 2 a large scale high vs region 2 increase in the lower mantle ne of tonga 3 lateral variations in d shear wave velocities of up to 3 however 1 above predicts a decrease in tskks sks contradicting the observations this suggests that 2 and 3 are more likely explanations in modeling this data set

northwest outlet channels of lake agassiz isostatic tilting and a migrating continental drainage divide saskatchewan canada lake cores obtained from the northwest outlet of glacial lake agassiz in northwest saskatchewan canada provide a minimum date for the cessation of the flood from the northwest outlet and a chronology for abandonment of mid holocene channels that presently straddle the mackenzie and churchill drainage divide the stratigraphy of a vibracore taken from long lake consists of a lower pebble gravel fining to massive sand silty clay and then fibrous peat wood fragments from the base of the clay yielded an accelerator mass spectrometry ams date of 9120 bp because the lake is scour in origin and is in the head of the spillway the date is considered to be a minimum estimate for cessation of the flood from the northwest outlet at the beginning of the emerson phase a vibracore taken at haas lake in an abandoned channel surrounded by muskeg with no influent streams consists of 0 8 m of stratified pebble gravel containing abundant shell and wood fragments overlain by 1 62 m of gyttja with a sharp conformable lower contact ams dates range from 5590 bp from the topmost gravel to 3080 bp within the gyttja the gravel is interpreted as fluvial recording a river draining wasekamio lake north into the clearwater river across the present day drainage divide today a drop of 2 m occurs from wasekamio lake southeast to lac ile a la crosse along 150 km of lake basins parallel to the cree lake moraine the dates from haas lake suggest that before 5200 bp the drainage divide was about 100 km further southeast implying that during the emerson phase lake level was controlled by a sill near flatstone lake at about 430 m instead of between wasekamio lake and the clearwater river as was previously proposed holocene differential isostatic uplift caused the flow reversal in the upper churchill basin anastomosed channels at the mouth of rivers flowing north into lakes indicate that uplift is still active in the area today

glacial lake agassiz its northwest maximum extent and outlet in saskatchewan emerson phase abstract six different lines of evidence support the hypothesis that glacial lake agassiz expanded an additional 70 000 km2 over that previously mapped in northwestern saskatchewan and that the lake discharged out the northwestern clearwater outlet then through glacial lake mcconnell and mackenzie river to the arctic ocean elevations of formerly unmapped 1 strandlines and 2 glaciolacustrine sediments between the previously mapped northwest limit of lake agassiz and the clearwater lower athabasca spillway indicate that water extended 170 km farther northwest recently mapped strandlines at elevations up to 60 m above the previously mapped extent of lake agassiz can be traced along 3 isobases to the mouth of the spillway based upon 4 six radiocarbon dates recovered from spillway flood deposits in the athabasca river valley and its late pleistocene delta the 5 clearwater spillway was cut at 9 9 ka bp this date is synchronous with the initiation of the emerson phase 9 9 ka bp in the southern lake agassiz basin and 6 coincides with the position of the laurentide ice sheet at the cree lake moraine 10 ka bp along the northern margin of the lake following closure of the eastern outlets at the onset of the emerson phase lake agassiz transgressed toward the northwest into the deglaciated and isostatically depressed glacial foreland in the churchill river valley to an elevation of 490 m the pre flood elevation of the churchill mackenzie drainage divide at the head of the clearwater lower athabasca spillway the beaver river moraine an earthen drainage divide was breached resulting in lowering lake agassiz 52 m to a stable elevation at 438 m the lake discharged 21 000 km3 of water into the arctic ocean that raised global sea level by 6 cm

megaflooding associated with glacial lake agassiz abstract significant baseline and episodic megaflooding from glacial lake agassiz was routed to the south east and north coasts of north america over the lake s nearly 6000 year history the five phases of lake level change were controlled by which outlet was active which in turn was controlled by ice margin position and glacioisostatic adjustment the southern outlet is the oldest and best understood outlet while successively younger outlets are progressively less understood eastern drainage synchronous with the younger dryas chronozone had been assumed by most studies but a spillway to accommodate the 90 m drop in lake level is yet to be described with the south and east outlets unable to accommodate the necessary lake level drawdown the northwest outlet has become the default outlet with arctic ocean core data supporting it however extant terrestrial data from the continent only provides data for a large flood from the fort mcmurray area closer to the end of the younger dryas coinciding with the timing of the preboreal oscillation the challenge remains to find agreement between the marine and terrestrial records uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the lake consisting of large spillways large boulders and in places giant current ripples composed of boulders flood discharge estimates into and out of the lake range from 0 04 to 1 sv with final subglacial drainage into the tyrell sea estimated at 5 sv sufficient to raise global sea level by 0 18 m and initiate the 8 2 ka stadial

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

characterization of pebble fabrics in modern terrestrial glacigenic sediments pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers where sedimentary processes can be observed or inferred with relatively little ambiguity over 100 samples from contemporary environments illustrate fabrics characterizing melt out till deformed and undeformed lodgement till sediment flow deposits and ice slope colluvium lodgement till fabric variability is related to the two layer structure of these sediments a structureless friable upper layer with low shear strength and high consolidation coefficient overlying a very compact material of horizontal platy structure fabric strength assessed by eigenvalue analysis is weaker and pebble dip is more dispersed in the upper structureless horizon stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon alternatively upper horizon fabrics may be characteristic of all recently deposited lodgement tills with stronger fabrics developing at depth by dewatering and consolidation there is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt out tills through undeformed and deformed lodgement tills to sediment flow deposits and ice slope colluvium there is however considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some quaternary glacial sediments relatively strong fabrics characteristic of melt out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments

a cost surface model of volcanic glass quarrying and exchange in hawai i abstract the spatial distribution of artifacts from the pu u wa awa a volcanic glass source north kona district hawai i island shows a pattern of direct access by those living in the immediately vicinity of the source with subsequent down the line exchange most quarrying and exchanges likely occurred within a single day s travel from sites where artifacts were deposited the exception to this is the discovery of non local direct access evident in assemblages from the extreme southern end of hawai i island these visits may have involved voyages by canoe while people did not often travel far for volcanic glass they nonetheless appear to have had unfettered accessed to source material and freely conducted inter community exchanges this implies volcanic glass was treated as a common pooled resource and the existence of informal exchange relationships

freshwater outbursts to the oceans from glacial lake agassiz and their role in climate change during the last deglaciation abstract lake agassiz was the largest lake in north america during the last deglaciation as the laurentide ice sheet lis retreated large volumes of water stored in this proglacial lake were episodically released into the oceans these waters were variably routed to the gulf of mexico arctic ocean north atlantic ocean and hudson bay during this period the three largest cooling events in the northern hemisphere closely followed 4 of the 5 largest outbursts from lake agassiz 1 the younger dryas which was preceded by a release of 9500 km 3 2 the preboreal oscillation preceded by releases of 9300 km 3 and 5900 km 3 and 3 the 8 2 ka cold event preceded by a 163 000 km 3 outburst these are respectively fluxes of 0 30 sv 0 29 sv 0 19 sv and 5 2 sv if released in 1 year because the influx of freshwater reaching the north atlantic ocean can inhibit thermohaline circulation partly depending on whether the ocean was in a glacial interglacial or transitional mode of circulation we believe that at least these large outbursts from lake agassiz may have provided the triggers for changes in ocean circulation and in turn for widespread climate change

characterization of new zealand obsidian using pxrf abstract new zealand has some of the most active areas of rhyolitic volcanism in the world and this has produced numerous obsidian sources in the northern half of the north island in total archaeologists have recognized 27 named locations from which obsidian can be obtained scattered across 4 geological source regions shortly after colonization in the late 13th century ad polynesian settlers began transporting this material some thousands of kilometers throughout the country and across the sea in small quantities to distant neighbors in the kermadecs and chatham islands although considerable research has been conducted on obsidian sourcing in new zealand the complexity of geochemical source discrimination and the lack of a practical method of non destructive geochemical analysis has hindered progress we present the results of our use of pxrf to provide geochemical data on new zealand obsidian sources and to compare the use of discriminant analysis and classification tree analysis to discriminate among sources and attribute archaeological samples to sources our research suggests that classification tree analysis is superior to discriminant analysis in sourcing studies a large case study using an important settlement phase site s11 20 from the auckland region demonstrates the utility of the methods and the results support a model of high degrees of mobility and interaction during the early settlement of new zealand

glacial lake agassiz the northwestern outlet and paleoflood valley morphology and sediment in the fort mcmurray region of alberta indicate that a catastrophic flood discharged down the lower clearwater and athabasca river valleys 9900 yr b p geomorphic and chronologic evidence suggests that glacial lake agassiz emerson phase was the probable water source as the flood incised a drainage divide located near the alberta saskatchewan border the level of glacial lake agassiz decreased by 46 m discharged 2 4 x 106 m3 s for at least 78 days and stabilized at 438 m above sea level in the lake wasekamio area at that time water entered the arctic ocean via glacial lake mcconnell and the mackenzie river rather than the gulf of mexico via the mississippi river as previously thought such a large influx of fresh water 8 6 km3 h into the arctic at the close of the last glaciation may have had an abrupt major influence on northern climate

age determinations for glacial lake agassiz shorelines west of fargo north dakota usa understanding the evolution of lake agassiz is vital to developing a comprehensive late quaternary history of central north america although many of the geomorphic features of the lake are well known current reconstructions pri marily depend upon relative ages of landforms here we report new optically stimulated luminescence osl ages on a flight of strandlines located 140 km north of the southern outlet strandline ages at this location range from 14 3 0 2 to 10 0 0 2 ka cal spanning 4000 years of lake history using geomorphic relationships and osl age control it is pro posed that the herman through tintah strandlines developed over a period of 1000 years followed by a hiatus of strandline development until the campbell strandline developed at 10 3 0 2 ka cal there is agreement between our new osl dates and osl and radiocarbon ages from geomorphically correlative landforms elsewhere in the lake basin the use of high reso lution lidar imagery greatly aids localized mapping of shoreline features additional site specific field work and osl ages are necessary to further evaluate strandline tracing across the basin resume il est essentiel de comprendre l evolution du lac agassiz pour avoir un historique complet du quaternaire tardif du centre de l amerique du nord bien que plusieurs des caracteristiques geomorphologiques du lac soient bien connues les reconstructions actuelles sont surtout determinees par l ge relatif des formes de terrain dans cet article nous donnons de nouveaux ges determines par luminescence stimulee optiquement osl a d anciennes lignes de plage situees a 140 km au nord de l exutoire sud les ges des anciennes lignes de plage a cet endroit varient entre 14 3 0 2 et 10 0 0 2 ka cal soit 4000 ans d histoire du lac base sur des relations geomorphologiques et le controle de l ge par osl il est propose que les anciennes lignes de plage herman a tintah se soient developpees durant une periode de moins de 1000 ans une periode sans developpement de lignes de plage aurait suivi jusqu au developpement de la ligne de plage campbell vers 10 3 0 2 ka cal il y a concordance entre nos nouvelles dates osl et les ges determines par osl et par radiocar bone sur des formes de terrain correlees par geomorphologie ailleurs dans le bassin du lac l utilisation d imagerie lidar a haute resolution a grandement aide la cartographie locale des caracteristiques des lignes de rivage d autres travaux speci fiques au site et d autres ges osl sont necessaires pour continuer a tracer les anciennes lignes de plage a travers le bassin traduit par la redaction

non destructive pxrf analysis of museum curated obsidian from the near east abstract non destructive pxrf has the potential to expand sample populations of archaeological provenancing studies by facilitating access to museum collections of artefacts in this study we use museum curated obsidian for the sites of tell brak mersin yumuktepe and tell arpachiyah and geological obsidian samples from central turkey to demonstrate that non destructive pxrf is comparable to other techniques in differentiating between near eastern obsidian sources secondly we use multivariate analysis to evaluate whether non destructive pxrf is sufficiently accurate and precise to enable comparison with legacy datasets from previous analysis using pixe and icp ms multivariate analyses show that instrumental offsets between the results from pxrf and other analytic techniques are less than source to source variation typical for most anatolian obsidian outcrops and pxrf identified geochemical groups are directly comparable to legacy datasets non destructive pxrf analysis indicates that during the chalcolithic east gollu dag and nenezi dag continued to be the major sources of obsidian to communities in central anatolia and the bingol range and mountains surrounding lake van supplied sites east of the levant variations in the analysed assemblages suggest a number of obsidian exchange networks existed during this period

postglacial history and paleoecology of wampum manitoba a former lagoon in the lake agassiz basin a small paleolagoon along the margin of the glacial lake agassiz basin near wampum manitoba 130 km southeast of winnipeg contains an unusually thick and continuous sequence of late glacial and holocene organic sediment cores at 17 sites through this sequence provide insight into the fluctuations of the level of lake agassiz the timing of the construction of the lake9s most extensive strandline the upper campbell beach and the paleoecology of this area during the past 10 000 14 c yr the history of this area is established from 26 new ams radiocarbon dates siliceous microfossils plant macrofossils mineralogy sediment characteristics and stratigraphic relationships following deglaciation at wampum about 11 14 c ka deposition of largely unfossiliferous silty clay with occasional ice rafted clasts represents relatively deep water conditions in lake agassiz overlying this is a spatially and temporally variable mixture of silt sand peat gyttja and marl containing an allochthonous assemblage of siliceous microfossils and plant macrofossils with a wide range of radiocarbon dates these sediments were deposited in an embayment of lake agassiz mainly in shallow quiet waters as the lake transgressed about 10 ka over the moorhead low water phase surface between about 9 7 and 9 3 ka the wampum embayment was progressively isolated from lake agassiz by growth of the upper campbell spit resulting in the formation of a lagoon organic rich deposits on the lakeward side of the lagoon were buried 9 3 9 4 ka by sand and gravel of the spit and a thin overwash of sand marks this event throughout the lagoon at about this time lake agassiz fell below the upper campbell beach level subsequent accumulation at wampum consists mainly of algal gyttja during the early holocene and marl during the middle holocene only minor fluctuations in hydrological conditions occurred except for slightly warmer and drier conditions between 6 2 and 4 0 14 c ka these stable shallow water conditions may be due partly to persistent groundwater contributions to the site progressive encroachment of rooted aquatics led to present day fen conditions peat accumulation across the basin began by about 4 0 ka

testing the accuracy of portable x ray fluorescence to study aztec and colonial obsidian supply at xaltocan mexico abstract this article demonstrates the accuracy of non destructive portable x ray fluorescence p xrf for the study of obsidian in central mexico obsidian sources were identified for a sample of 103 artifacts from the site of xaltocan which spanned the rise and fall of the aztec empire and the first centuries of spanish colonial rule ad 900 1700 sources were assigned by comparing p xrf measurements with previously published source data and were verified using the standard techniques of laboratory xrf l xrf and instrumental neutron activation analysis inaa additional tests of potentially confounding factors show that neither length of read time presence of surface residue nor incomplete detector coverage due to small artifact size compromised our ability to attribute sources to artifacts concave surfaces did decrease the accuracy of readings because of the greater distance between the artifact and the detector our results provide new insight into the stability of supply networks and markets well into the colonial period as well as the homogenizing tendencies of the aztec market system

using lidar digital elevation model data to map lake agassiz beaches measure their isostatically induced gradients and estimate their ages abstract high resolution lidar digital elevation model dem data were used to create dem mosaics and hillshade maps of a large region in north dakota for better defining and measuring the strandlines of glacial lake agassiz although many of the strandlines in this region had been identified and named more than a century ago by warren upham lidar images clearly reveal their complexity and identify additional small and low relief ridges not previously mapped the elevations of the crests of six well developed strandlines the campbell mccauleyville lower blanchard emerado upper ojata and lower ojata beaches were measured for each of these strandlines north south gradients were calculated which were produced by differential isostatic rebound the steepest gradient is on the uppermost campbell beach in the sequence and the gradient on each beach below is progressively lower confirming that these beaches were deposited in sequence from oldest to youngest as the level of lake agassiz declined because there were no anomalous beach gradients in this sequence the ojata beach formed after 9400 14 c 10 630 cal bp which is when the higher elevation campbell beach was deposited rather than at 10 000 14 c 11 480 cal years ago as some have suggested because of the age of organics below the ojata beach those organics and the subaerial surface on which they lie survived the moorhead transgression to the campbell beach and the ojata beach must have been deposited over the older organic unit later as lake level regressed a simple extrapolation model was used to estimate the ages of beaches in the sequence

assessing the applicability of portable x ray fluorescence spectrometry for obsidian provenance research in the maya lowlands recent innovations in portable energy dispersive x ray fluorescence pxrf spectrometry have increased its utility for the geochemical characterization of obsidian artifacts for archaeological provenance research however concerns over the utility of pxrf instrumental analyses have been raised focused on the validity and reliability of the geochemical data produced here we adopt the framework of richard hughes on reliability validity and scale in obsidian sourcing research 1998 whereby reliability addresses instrument stability and issues of measurement while validity pertains to an instrument s ability to discern geochemical source provenance this is done in order to test the utility of pxrf instruments for archaeological provenance research k means cluster analysis was used to test the accuracy of pxrf through statistical comparison of data acquired via laboratory and portable energy dispersive xrf instruments multivariate analysis was employed to demonstrate obsidian source representation at two classic maya archaeological sites in southern belize uxbenka and ek xux and to test the validity of data obtained from a pxrf instrument in answering archaeological research questions pertaining to regional interactions between lowland maya polities results suggest that portable xrf instruments produce internally consistent results however data acquired from a pxrf instrument are not statistically equivalent to other xrf instruments this is to say that while pxrf is not a reliable technique it is valid for questions pertaining to geochemical source representation

strandline analysis in the southern basin of glacial lake agassiz minnesota and north and south dakota usa glacial lake agassiz a large pleistocene lake left behind strandlines at multiple elevations within its basin prior researchers have used these strandlines to identify four relatively stable water level stages but tracing them over long distances is often problematic in this study the elevation of the tintah strandline is returned to its original designation and a newly interpreted stable lake level at 1020 1030 ft 311 314 m is referred to as the upham level based on a concentration of ridges and a spit at that elevation cores from strandline and lagoon complexes from the milnor to tintah beaches reveal a decreasing thickness of strandline sediment associated with shorter aggregate length strandlines this relationship is most likely controlled by sediment starvation greater water level fluctuations and shallower water beaches near the head of the southern outlet spillway indicate that shoreline occupation at the lower campbell level was either very short lived or strandline development was hampered by shallow water the modern day sill elevation between the southern outlet spillway and the lake basin is found to be 3 km south of white rock minnesota at an elevation of 974 ft 297 m all but the campbell strandlines at the southern outlet are interpreted as the result of a regression driven by incision of the southern outlet spillway

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

the chronology climate and confusion of the moorhead phase of glacial lake agassiz new results from the ojata beach north dakota usa rapid drainage of glacial lake agassiz to the north atlantic ocean has been implicated as a triggering mechanism for the younger dryas yd cold event 13 11 6 ka cal a key component to this hypothesis is the interpretation that the ojata beach of lake agassiz in north dakota usa formed during a regression of the lake at the beginning of the yd this paper reviews the chronological data for the lowwater moorhead phase presents new radiocarbon and optically stimulated luminescence osl ages for the ojata beach and utilizes plant and insect macrofossils to reconstruct the paleoenvironmental conditions during the moorhead phase in eastern north dakota the integrated analysis of the geochronologic data emphasizes the need to distinguish between in situ and reworked plant macrofossils new ages obtained stratigraphically below the ojata beach sediments and reinterpreted chronologic data for the moorhead phase suggest that contrary to previous interpretations the ojata beach is a record of transgression of the lake in the later part of the yd and the oldest in situ minimum age for the moorhead phase is 10 47775 ka 14 c bp paleoenvironmental analysis indicates that a

testing northwest drainage from lake agassiz using extant ice margin and strandline data extant data on shorelines and ice margins in the glacial lake agassiz basin defines the limits of lake agassiz through deglacial time the ice sheet margin had not retreated far enough northwards by the beginning or end of the younger dryas chronozone for the lake to drain northwest however once lake agassiz reached the campbell beach stage at 10 800 10 300 cal bp then projections of lake agassiz strandlines were higher than the topography allowing for the first possible pathway to the northwest this relationship is used to reject the recent assertion that there was northwest drainage from lake agassiz at the beginning and end of the younger dryas chronozone

magnetite grain size analysis and sourcing of mediterranean obsidians abstract the potential of magnetic grain size variations as an obsidian source characteristic is investigated using geological and archaeological obsidians from five islands of the mediterranean sea lipari sardinia palmarola pantelleria melos four parameters are used magnetic and anhysteretic a susceptibilities saturation isothermal remanent magnetizations at room sirm 293 and liquid nitrogen sirm 77 temperature the ratio s t sirm 77 sirm 293 which depends on the superparamagnetic grains relative abundance varies little in each individual site with the exception of lipari which is characterized by large variations and the highest content of superparamagnetic grains the a vs plot king et al 1982 shows some within site dispersion of the samples but the ratio q a a which is strongly influenced by the single domain grains content is characteristic for each site the combined use of the king and q a vs s t plots discriminates the samples from most of the sites and suggests that the grain size analysis is a promising approach in sourcing obsidian archaeological artefacts moreover the measurements of the four parameters used are simple quick and feasible with no or little damage to archaeological finds

validity of off the shelf handheld portable xrf for sourcing near eastern obsidian chip debris handheld portable xrf hhpxrf has received considerable recent attention in archaeology especially for obsidian sourcing published studies largely suggest a high potential for success hhpxrf though has been met with debate and scepticism concerns fall into three categories 1 low accuracy and precision 2 data correction schemes and calibration and 3 ignorance of fundamental xrf issues such as specimen size limits and morphology effects the result is that archaeological interpretations in hhpxrf based studies are cast into doubt should interpretations be believed if authors did not follow the perceived best practices to address such questions the validity of hhpxrf for near eastern obsidian sourcing was tested under deliberately sub optimal conditions irregular obsidian debitage near the minimum size limits was sourced with a success rate of 94 based on a rank matches to 100 based on a and b rank matches even under conditions chosen to mimic off the shelf operation

initial source evaluation of archaeological obsidian from the kuril islands of the russian far east using portable xrf obsidian artifacts recently have been recovered from 18 archaeological sites on eight islands across the kuril island archipelago in the north pacific ocean suggesting a wide ranging distribution of obsidian throughout the island chain over the last 2 500 years although there are no geologic sources of obsidian in the kurils that are known to have been used prehistorically sources exist in hokkaido japan and kamchatka russia the southern and northern geographic regions respectively from which obsidian may have entered the kuril islands this paper reports on the initial sourcing attempt of kuril islands obsidian through the analysis of 131 obsidian artifacts data from this research were generated through the application of portable xrf technology and are used to address research questions concerning prehis toric mobility exchange and social networking in the kuril islands

isostatic rebound in the northwestern part of the lake agassiz basin isobase changes and overflow abstract based on new gps elevation data on the upper and lower campbell strandlines in the northwestern part of the glacial lake agassiz basin the trend of isobases representing differential glacio isostatic rebound in that region is shown to bend and assume a nearly west east orientation this differs from the northwest southeast orientation to the southeast of the study area which others had projected into the northwestern corner of the lake agassiz basin this means that there was more isostatic depression than previously thought north of 53 n the difference in slopes on reconstructed water planes of the upper and lower campbell beaches is less with these isobases which better reflects the short period of time between their formation it is likely that the change in orientation of isobases reflects the presence of a thick keewatin ice center to the north our revised west east isobase reconstruction indicates that when the lake was at the campbell beach levels 9900 9400 14c b p lake agassiz overflowed across the paleo divide at wycherley lake saskatchewan which controlled flow through the northwestern outlet of lake agassiz during part of its history overflow would not have occurred through the wycherley lake channels at this time using the old isobase projections

the hysteresis properties of multidomain magnetite and titanomagnetite titanomaghemite in mid ocean ridge basalts abstract hysteresis measurements have been carried out on a suite of ocean floor basalts with ages ranging from quaternary to cretaceous approximately linear yet separate relationships between coercivity bc and the ratio of saturation remanence saturation magnetization mrs ms are observed for massive doleritic basalts with low ti magnetite and for pillow basalts with multi domain titanomagnetites with x 0 6 even when the morb has undergone low temperature oxidation resulting in titanomaghemite the parameters are still distinguishable although offset from the trend for unoxidized multidomain titanomagnetite the parameters for these iron oxides with different titanium content reveal contrasting trends that can be explained by the different saturation magnetizations of the mineral types this plot provides a previously underutilized and non destructive method to detect the presence of low titanium magnetite in igneous rocks notably morb

preboreal oscillation caused by a glacial lake agassiz flood the preboreal oscillation pbo has been attributed to increased meltwater but the source of the meltwater and causative mechanism of the pbo has remained elusive here we attribute the source to a massive meltwater discharge event from an abrupt drainage of glacial lake agassiz canada via the mackenzie river into the arctic ocean a maximum volume of 21 000 km 3 was discharged over a 1 5 3 yr period with a peakdischarge of 0 500 sverdrups sv equivalent to a 6 m rise in the arctic ocean or 0 062 m rise in global sea level the flood occurred at about 11 335 cal yr bp and was followed by a b0 042 sv flow until 10 750 cal yr bp when the southern outlet of lake agassiz reopened and diverted drainage to the mississippi river system we estimate that only 2 4 of the flood water would have frozen into sea ice within the beaufort region but coupled with increased river ice production during winter and thicker pack ice growth throughout the arctic ocean a thicker longer lasting and more extensive packice may have been flushed through fram strait the thicker and more extensive packice and freshened sea surface may have triggered the pbo by increasing albedo and generating a low salinity anomaly upon melting in the north atlantic thus decreasing the formation of north atlantic deep water r 2002 elsevier science ltd all rights reserved

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume