chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

millennial scale changes in sea surface temperature and ocean circulation in the northeast pacific 10 60 kyr bp 1 a new centennial scale mg ca temperature record from the california margin odp site 1017e reveals large millennial scale oscillations between 10 to 60 kyr this record indicates that sea surface temperature on the california margin warmed rapidly on the deglacial by 7 4 0 8 c and was preceded by a pre bolling temperature oscillation of 2 6 1 2 c millennial scale events of the last glacial episode were marked by sea surface temperature oscillations of between 3 and 7 c on the california margin and interstadials were associated with an increase in surface water salinity the data are consistent with evidence for a glacial southward shift in the polar jet stream and concomitant strengthening of the relatively cold fresh california current during stadial events the data also support previous hypotheses suggesting a tight coupling between the north atlantic and northeast pacific response to climate instability of the last glacial episode

on the 1470 year pacing of dansgaard oeschger warm events 1 the oxygen isotope record from the greenland ice sheet project 2 gisp2 ice core was reanalyzed in the frequency and time domains the prominent 1470 year spectral peak which has been associated with the occurrence of dansgaard oeschger interstadial events is solely caused by dansgaard oeschger events 5 6 and 7 this result emphasizes the nonstationary character of the oxygen isotope time series nevertheless a fundamental pacing period of 1470 years seems to control the timing of the onset of the dansgaard oeschger events a trapezoidal time series model is introduced which provides a template for the pacing of the dansgaard oeschger events statistical analysis indicates only a 3 probability that the number of matches between observed and template derived onsets of dansgaard oeschger events between 13 and 46 kyr b p resulted by chance during this interval the spacing of the dansgaard oeschger onsets varied by 20 around the fundamental 1470 year period and multiples thereof the pacing seems unaffected by variations in the strength of north atlantic deep water formation suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period

quaternary events in the elkwater lake area of southeastern alberta new data necessitate revisions in the quaternary chronology of the elkwater lake area relicts of post middle miocene preglacial erosion surfaces descend to the north and south from the middle miocene depositional surface on the cypress hills plateau both sets of surfaces are marked by oxidized weathering zones locally culminating in relicts of preglacial paleosols both surfaces are overlain by a loess replete with cryogenic imprints deposition of this loess with cryogenic imprints shortly predates arrival of the green lake glacier at its terminus the green lake end moraine marks the maximum extent of laurentide ice in this area features previously attributed to the older elkwater glacier can be explained with reference to proglacial meltwater action associated with the green lake glacier the concept of elkwater drift is no longer valid younger loesses called upper loess mantle nonglaciated terrain and the green lake end moraine and began accumulating just before glacier peak tephra was deposited

late quaternary events in the lethbridge area alberta new observations in the lethbridge area permit a more complete reconstruction of the landscape history in late wisconsinan and holocene time the plain of glacial lake macleod the lethbridge moraine and the plain of glacial lake lethbridge became exposed in that order and in quick succession almost immediately thereafter a discontinuous mantle of loess began to accumulate on those surfaces the presence of glacier peak layer g or manyberries tephra near the base of the loess indicates these events occurred just before 11 200 bp the similarity of this chronology to that established for the older green lake end moraine in the cypress hills region and the fact that the younger buffalo lake moraine was formed before 11 000 bp indicate that deglaciation of southern alberta proceeded very rapidly the oldest buried paleosol observed near lethbridge began to form shortly after 11 200 bp subsequently and throughout the holocene intervals of loess deposition alternated with soil forming intervals at least

origin of a postglacial kettle fill sequence near georgetown ontario stratigraphic relationships radiocarbon dating and pollen and plant macrofossil analyses establish the origin and developmental history of a kettle near georgetown ontario the early inorganic s

precise u pb ages and geochemistry of palaeoproterozoic mafic dykes from southern west greenland linking the north atlantic and the dharwar cratons palaeoproterozoic magmatism throughout the north atlantic craton nac has produced dyke swarms of diverse orientations and emplacement ages in southern west greenland previously identified swarms include the ca 2500 ma kilarsaarfik dykes ca 2215 ma boninitic norite bn dykes and the abundant ca 2040 ma kangamiut and coeval 2050 2030 ma md3 dykes additional insight into the distribution of swarms is provided by new baddeleyite u pb id tims dates interpreted as emplacement ages for six dykes the geochemistry for a total of 42 samples on 40 dykes including the dated dykes provides some constraints on their petrogenesis two e w trending dykes yield ages of 2365 2 ma and 2374 4 ma representing a hitherto unknown magmatic event we propose the name graedefjord dykes for dykes of this age in southern west greenland one ne sw trending dyke is dated at 2209 5 ma close to a previously published 2214 10 ma age for a n s trending dyke member of bn dykes three dykes yield md3 ages of 2053 2 ma e w trending 2049 6 ma n s trending and 2042 2 ma wnw ese trending ca 2 21 ga old and predominantly ne se and nne sse trending dolerites some of which are high al basalts were derived from a relatively depleted mantle and injected during a boninite dolerite magmatic event together with nearby bn dykes derived from a harzburgitic yet highly lree and lile enriched subcontinental lithospheric mantle sclm ca 2 05 ga kangamiut md3 dolerites were derived from a similar ambient asthenospheric mantle and subsequently experienced crustal assimilation during fractional crystallisation the ca 2370 ma dykes in the nac are coeval with the dharwar giant dyke swarm of the dharwar craton dc and based on this unique age match it is proposed that the dharwar and nac were neighbours in the palaeoproterozoic furthermore both blocks share 222 2 21 ga dykes and matching the trends of 2 2 2 1 and 2 37 ga swarms between the two blocks allows several plausible reconstructions c 2012 published by elsevier b v

metasomatic mantle source and crustal contamination for the formation of the neoproterozoic mafic dike swarm in the northern yangtze block south china abstract in the huangling region of the northern yangtze block south china the 820 ma huangling felsic pluton was intruded by 800 ma mafic dikes these dikes are composed of fine to medium grained diabase porphyritic diabase and olivine gabbro quartz xenocrysts occur locally in the olivine gabbro the rocks are alkaline to sub alkaline in composition and have sio2 ranging from 43 3 to 57 2 wt mgo from 3 7 to 9 2 wt and total alkali from 3 0 to 7 3 wt they exhibit lree enrichment la yb n 3 3 28 5 with slightly negative eu anomalies eu eu 0 6 1 0 their primitive mantle normalized trace element patterns are characterized by enrichment of large ion lithophile elements rb ba th and u depletion of high field strength elements nb ta zr and hf and positive pb and negative ti anomalies they have relatively high initial 87sr 86sr ratios ranging from 0 7052 to 0 7080 and variably negative end t values from 4 2 to 10 9 the rocks have a large range of whole rock ehf values 0 35 to 11 34 and a relatively narrow range of pb isotope ratios 206pb 204pb 16 96 to 17 97 207pb 204pb 15 41 to 15 58 and 208pb 204pb 38 08 to 39 66 initial 87sr 86sr ratios correlate negatively with 206pb 204pb ratios whereas 143nd 144nd and 208pb 204pb ratios and ehf values correlate positively with 206pb 204pb ratios these features are indicative of an em2 source region suggesting a lithospheric mantle source modified by subducted components during the neoproterozoic the quartz xenocrysts and linear isotopic variations indicate strong crustal contamination during magma emplacement the energy constrained assimilation and fractional crystallization ec afc modeling calculations reveal that the parental magmas were contaminated by continental crust including archaean amphibolites granitic gneisses metasedimentary rocks and granitic rocks the mafic dikes are 20 myrs younger than the huangling felsic pluton which was produced by partial melting of a thickened continental crust suggesting that the mafic dikes were a consequence of post orogenic extension the huangling region may have originally been located at the centre of the yangtze block the possible heat source for the generation of the huangling felsic pluton and mafic dikes was asthenospheric wedging resulting from oceanic slab subduction beneath the northern margin of the yangtze block this conclusion rules out the possibility that the yangtze block was located in the central part of the rodinia supercontinent the block was more likely situated along the margin of rodinia

geochemical constraints on the late stage evolution of basaltic magma as revealed by composite dikes within the kangâmiut dike swarm west greenland abstract the kang miut dike swarm in west greenland contains numerous composite dikes with mafic margins and andesitic centers internal chilled margins show that the andesitic centers intruded into the middle of the mafic dikes major element systematics indicate that the fractionation of olivine clinopyroxene plagioclase and fe ti oxides drove the evolution of the kang miut parental magma during its transition from mafic to andesitic compositions incompatible trace elements show a marked relative decrease in middle and heavy rare earth elements ree between the mafic margins and the andesitic centers the decrease in the ree is not explicable by olivine clinopyroxene plagioclase and fe ti oxide fractionation or by the fractionation of the accessory phases apatite zircon or garnet rb sr and sm nd isotopes from margin and center pairs from these composite dikes are nearly identical indicating that crustal contamination had little to no affect on their evolution trace element modeling utilizing the mixing of evolved kang miut magmas and low degree melts derived from partial melting of garnet lherzolite produce excellent fits with the trace element patterns for the andesitic centers these models suggest that the late stage evolution of the kang miut dikes included input of mantle melts produced during the end stages of rifting

the california current system during the last 136 000 years response of the north pacific high to precessional forcing abstract alkenone sea surface temperature sst records were generated from the ocean drilling program s odp sites 1014 and 1016 to examine the response of the california current system to global climate change during the last 136 ka the temperature differences between these sites sstnep sstodp1014 sstodp1016 reflected the intensity of the california current and varied between 0 4 and 6 1 c a high sstnep weaker california current was found for late marine isotope stage mis 2 and early mis 5e while a low sstnep stronger california current was detected for mid mis 5e and mis 1 spectral analysis indicated that this variation pattern dominated 23 precession and 30 ka periods comparison of the sstnep and sst based on data from core md01 2421 at the japan margin revealed anti phase variation the high sstnep weakening of the california current corresponded to the low sst at the japan margin the southward displacement of the nw pacific subarctic boundary and vice versa this variation was synchronous with a model prediction of the tropical el nino southern oscillation behavior these findings suggest that the intensity of the north pacific high varied in response to precessional forcing and also that the response has been linked with the changes of tropical ocean atmosphere interactions

evidence from the rare earth element record of mantle melting for cooling of the tertiary iceland plume widespread flood basalt volcanism and continental rifting in the northeast atlantic in the early tertiary period 55 myr ago have been linked to the mantle plume now residing beneath iceland1 2 3 4 5 although much is known about the present day iceland plume6 7 8 9 its thermal structure composition and position in the early tertiary period remain unresolved estimates of its temperature for example range from 1 600 c in some plume models3 to 1 500 c based on the volume and composition of basaltic crust10 11 12 several recent studies4 have emphasized similarities in the thermal and chemical structure of the tertiary and present day plumes to argue for stability of the mantle anomaly whereas others12 13 relate variations in basalt volumes and compositions to changes in plume flux moreover some authors1 2 13 have assumed that the plume was rift centred for its entire history whereas others argue that it became ridge centred only after plate separation14 15 here we report compositional data for 6 000 metres of flood basalts erupted in east greenland close to the inferred plume axis that we use to constrain the tertiary plume structure rare earth element systematics place limits on the pressures and extents of mantle melting and show that the mantle was initially moderately hot 1 500 c but that its temperature declined during flood volcanism these observations are difficult to reconcile with current plume head models and call for important lithospheric control5 10 16 17 18 on actively upwelling mantle along the rifted margin

the scourie dyke suite petrogenesis and geochemical nature of the proterozoic sub continental mantle the petrogenesis of bronzite picrite olivine gabbro norite and quartz tholeiite dykes which make up the 2 39 b y scourie dyke swarm cutting the archaean lewisian gneisses of n w scotland is interpreted on the basis of their major and trace element geochemistry most of the dykes bear primary amphibole and or phlogopite and with one exception are all hypersthene or quartz normative apart from one tholeiite dyke which shows relative light rare earth element depletion all the dykes show enrichment in light rare earths and large ion lithophile elements they do not however show an equivalent enrichment in other incompatible high field strength ions such as nb and ta and in this respect resemble island arc and calc alkaline basalts the different dyke types have distinctive rare earth patterns and other trace element ratios which are maintained over a range of major element compositions

an 18 000 year palynological record from the southern alberta segment of the classical wisconsinan ice free corridor radiocarbon dates of 18 300 380 years bp gsc 2668 and 18 400 1090 years bp gsc 2670 on moss fragments from the clay near the base of a core from chalmers bog alberta indicate that the classical wisconsinan ice free corridor was in existence in the foothills of southern alberta by this time palynological studies show sparse herbaceous tundra like vegetation probably prevailed at this time in the area surrounding the small lake formed in the abandoned glacial spillway later shrubs became more prominent to form a shrub tundra environment sometime before 8220 years bp gsc 2851 trees began to invade the area and the pinus contorta dominated coniferous forest extant in the area today began to form bog and fen vegetation invaded the shallow lake basin about this time as well to form the bog that occupies the basin to the present day

the application of radiocarbon age estimates to the dating of glacial sequences an example from the miami sublobe ohio u s a abstract despite the importance of dating glacial sequences little evidence has been available to highlight the stratigraphic issues associated with the interpretation of age analysis a compilation of radiocarbon data from the miami sublobe of the laurentide ice sheet provides a large enough data set more than 133 dates to identify at least two sources of error sample and unit variability and transportation problems analysis of different samples from the same stratigraphic level commonly differ by more than the reported one sigma error and 2 000 year differences do occur glacial entrainment and transportation emplace older organic material over younger in situ materials and this effect may also give age errors in the data set of up to 2 000 years at a minimum multiple radiocarbon ages from a sequence of units are necessary to assign a reliable age to events within a glacial sequence however representing multiple ages poses its own problems a graphical representation that combines the probability of each sample appears to be one solution

mantle temperature anomalies along the past and paleoaxes of the galapagos spreading center as inferred from gravity analyses to better understand the effects of hot spots on mid ocean ridge thermal structure we investigate the subsurface density structure of the galapagos spreading center and nearby lithosphere using shipboard gravity and bathymetry data we obtain maps of mantle bouguer anomalies mba by removing from the free air gravity the attractions of seafloor topography and a 6 km thick model crust comparison of observed and theoretical mba profiles along isochrons for ages 0 0 7 7 ma suggests that seafloor topography is isostatically compensated by mass anomalies primarily in the upper 100 km of the mantle this result is consistent with the notion that seafloor topography along the galapagos spreading center is supported by lateral changes of crustal thickness and upper mantle density both of which are controlled by temperatures in the upper mantle where decompression melting occurs along the ridge axis the mba decreases from the east and west toward the galapagos hot spot by 90 mgal reaching a minimum nearest the hot spot at 91 w seafloor topography mirrors the mba along axis increasing by 1 1 km toward the hot spot these variations in mba and bathymetry can be explained by crustal thickening and mantle density variations resulting from a gradual axial temperature increase of 50 25 c toward the hot spot the predicted crustal thickening of 2 4 km nearest the hot spot accounts for 70 75 of the along axis mba and bathymetry anomalies mantle density variations account for the rest of the anomalies from the crustal isochron of age 7 7 ma to the present day axis the along isochron amplitudes of mba decrease from 150 to 90 mgal the corresponding along isochron bathymetry anomalies decrease from 1 7 to 1 1 km these observations along the paleoaxes of the galapagos spreading center indicate that the axial temperature anomaly was 70 hotter in the past 86 25 c and has steadily decreased to 50 25 c as the ridge axis migrated away from the galapagos hot spot these along isochron temperature anomalies however have remained well below that estimated for the hot spot itself 200 c indicating that the lateral temperature gradient between the hot spot and the ridge axis has remained 10 20 times greater than that along the ridge axis over the past 7 7 m y

petrogenetic relationship between palaeoproterozoic tholeiitic dykes and associated high mg noritic dykes labrador canada abstract trace element and sr nd isotopic studies of the palaeoproterozoic 2235 ma kikkertavak dyke swarm in labrador provide information on early sub continental lithosphere development there are three distinct chemical dyke types two are tholeiitic the third of high mg norite composition petrogenetically it is not possible to relate any of the chemical groups one to another by simple fractional crystallisation processes nor can they be derived by contaminating asthenospheric magmas with local crustal components from their sr nd isotopic characteristics in relation to their rare earth and multielement patterns it is clear that significant heterogeneity existed in the source regions of the dyke magmas at the time they were generated and that the mantle processes responsible can be linked with the phase of crustal growth in the region at 3 0 ga modelling suggests that the observed compositions can be accounted for by lower lithosphere asthenosphere mantle sources which have been variably depleted by previous episodes of basalt magma extraction and then re enriched by a lamproitic melt component and possibly by progressive infiltration of melts from a subducted sediment or subduction component high mg noritic dykes are relatively common worldwide in the palaeoproterozoic and are often broadly coeval with tholeiitic dykes but are much less common in younger dyke suites most have compositions which require a refractory major element composition coupled with significant re enrichment in incompatible lithophile elements recent models for cyclic mantle overturns with related deep mantle plumes begin to provide the right thermal and compositional environment beneath immature lithosphere which can generate the dyke types observed

mid wisconsin sediment record from baldwin lake reveals hemispheric climate dynamics southern ca usa abstract recently acquired cores from baldwin lake southern california document the first regional terrestrial based evidence for glacial period millennial to orbital scale climate variability eight ams 14c dates on a 14 m core from the lake s present day depocenter provide initial age control over the interval from 20 000 to 48 000 years before present bp a linear age model extends the record to a minimum age of 65 000 years bp a combination of lithologic description and one cm contiguous sedimentological analyses indicates significant changes in the dominant type of depositional environment over the length of the record at millennial to orbital time scales as a first order interpretation the dominant sedimentary environments alternate between permanent and ephemeral lake systems orbital scale forcing includes long term winter summer insolation variability and its modulation of winter storm tracks and the north american monsoon respectively millennial scale variability is attributed to extra tropical ocean atmosphere dynamics akin to historical interdecadal pacific climate variability in addition there is notable correspondence to the independently dated greenland ice core record gisp 2 at millennial to orbital time scales suggesting that baldwin lake contains in addition to its local regional record a hemispheric record of climate change similar to owens pyramid and summer lake of central and northwestern north america an initial comparison to gisp2 18o ice indicates that north atlantic interstadials correlate to permanent lake environments in coastal southwestern north america these results present a notable conflict with the proposed super enso phenomenon in the western tropical pacific these results also highlight the necessity for acquiring additional high resolution glacial period records for resolving questions of spatial temporal phasing of late quaternary climates

pleistocene stratigraphy of the saskatoon area saskatchewan canada an update pleistocene deposits in the saskatoon area are divided into the sutherland and saskatoon groups the sutherland group is divided into the mennon dundurn and warman formations and the saskatoon group is divided into the floral and battleford formations the floral formation is subdivided into the lower till the riddell member and the upper till each formation is composed of a sequence of deposits including basal proglacial sediment till upper proglacial sediment and nonglacial sediment each formation is defined primarily on the basis of carbonate content and stratigraphic position of its till and commonly it is bounded by weathered zones and or nonglacial sediments the sutherland group is pre illinoian in age and the lower till of the floral formation is illinoian in age the riddell member between the lower and upper tills of the floral formation is late rancholabrean probably sangamon in age radiocarbon ages of sediments lying between the upper till of the floral formation early wis

regionalized models for the thermal evolution of the earth abstract traditional models for the heat loss in oceanic and continental regions are combined into a regionalized model for the thermal evolution of the earth the need for regionalization is obvious when one considers that the mantle loses 3 to 4 times as much heat per unit area in oceanic regions than in continental areas the present day rate of heat loss together with a geochemical estimate of the concentration of heat producing elements in the earth fixes the response time of the thermally convecting mantle the response time in turn can be used to select the most reasonable representation for mantle convection in terms of the sensitivity of viscosity on temperature and layering versus mantle wide circulation present geochemical estimates of the bulk composition of the earth are most easily reconciled with the observed heat flow if the mantle is layered and its rheology is slightly less temperature dependent than generally assumed the layered system can produce sufficiently high temperatures to explain the high magnesian komatiites of the archean one difficulty with the models is that they predict widespread melting at shallow depth in the early stages of earth history but do not address how such melting affects and alters the heat transfer mechanisms

atmospheric circulation during holocene lake stands in the mojave desert evidence of regional climate change it is commonly thought that the climate conditions that supported lakes over a period of years in the mojave desert in southern california only existed before 8 000 yr bp and that the environment has been arid since1 2 here we look at a drill core in the silver lake playa at the terminus of the mojave river and find holocene lake deposits which indicate that shallow lakes existed for at least a few decades these deposits were radiocarbon dated at 3620 70 and 390 90 yr bp corresponding to the early neo glacial and the little ice age respectively3 to identify the conditions necessary to produce these holocene lake events we have examined the modern climate and hydrological patterns that produce ephemeral lakes in this usually arid watershed available data indicate that there is a link between anomalous winter atmospheric conditions over the north pacific and mojave river floods that produced ephemeral lakes in the silver lake playa and that the mojave river filters out small to medium floods and allows only the extreme floods to reach the terminal playa and leave a record of the anomalous conditions we suggest that the late holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods

tertiary fluvial gravels and evolution of the western canadian prairie landscape abstract the early tertiary of western canada and northern united states was marked by a change from compressional to extensional tectonics the result was regional uplift and magmatic events the uplift resulted in a major unconformity and deposition of extensive regional sheets of gravel and sand of which only isolated remnants remain these units are the eocene to miocene cypress hills formation the miocene wood mountain formation miocene flaxville formation and preglacial souris river gravels all four stratigraphic units consist of gravel and sand with lesser amounts of clay the formations were largely deposited as laterally continuous sheets of braided river gravels with some occurrences of meandering river sedimentation the sediment was deposited several hundred kilometres downstream of their source areas paleocurrent data for the cypress hills and wood mountain formations indicate that regional paleoslope dipped towards the north northeast the modern prairie landscape of western canada began to evolve with the deposition of these gravels during the eocene with creation of a basin wide unconformity followed by deposition of an extensive braidplain system that was subsequently uplifted incised and molded into its present form

paleoproterozoic mafic dike swarms of northeast laurentia products of plumes or ambient mantle abstract the occurrence of mafic dike swarms in archean and paleoproterozoic terranes is often cited as evidence for mantle plume activity associated with abnormally high mantle potential temperatures t p quantitative modeling of rare earth element ree abundances for the 2 04 ga kang miut dike swarm in west greenland and comparisons among other paleoproterozoic dike swarms in northeast laurentia indicates that the conditions for mantle melt generation were similar beneath much of laurentia and only ca 120 c hotter than present day ambient mantle t p ca 1300 c these thermal conditions correspond closely to estimates of ambient mantle potential temperatures during the paleoproterozoic era based on secular cooling models and continental freeboard constraints thus the geochemistry of most paleoproterozoic dikes of northeast laurentia can be accounted for by partial melting of upwelling mantle accompanying passive rifting and do not necessitate plume activity ambient mantle conditions during the paleoproterozoic t p ca 1420 c are similar to those inferred for the paleogene volcanic rift margins of the north atlantic igneous province where the rate of crustal production associated with early oceanic spreading was two to three times higher than at the modern ridge likewise rifting under ambient mantle conditions in the precambrian could have resulted in similar rates of crustal productivity and thus contributed significantly to continental growth

landscape evolution and human occupation during the archaic period on the northern plains recent archaeological excavations at a deeply stratified site in northwest calgary alberta have uncovered four occupation layers spanning the interval from 8000 to 2000 bp depending on the dating one accepts for the holocene thermal maximum two or more of these occupations occurred during this interval of aridity this site thus provides a record of human occupation during the archaic middle prehistoric i period in the calgary area more importantly the site occurs in an upland setting apparently far removed from reliable sources of water and normal environments of deposition yet the cultural deposits occur in sediments which extend 2 m below surface and include five sedimentary units as well as a minimum of three pedogenic units this paper presents the results of geoarchaeological research on the changing landscape for the site and notes the implications of these changes for the study of archaic manifestations on the northern plains

a reconstruction of holocene geomorphology and climate western cypress hills alberta and saskatchewan received january 28 1990 revision accepted july 18 1990 the cypress hills of southwestern saskatchewan and southeastern alberta are a key area for quaternary research because the permanent lakes and coniferous forest are sources of proxy paleoenvironmental data generally not available on the surrounding northern great plains in this paper the holocene paleoclimate of the western cypress hills is reconstructed from the pollen and organic matter contents of a 9 6 m sediment core from harris lake saskatchewan this climatic history is considerably longer than others from the semiarid interior plains of canada chronological control consists of a basal conventional radiocarbon date of 9120

depositional and tectonic setting of the miocene wood mountain formation southern saskatchewan coarse gravels of the miocene wood mountain formation that cap the wood mountain upland in southern saskatchewan are an erosional remant of a much more expansive sheet of gravel and sand the formation consists of gravel and sand deposited as a thin sheet on a regional planation surface that extends approximately along strike for at least 160 km this sheet with a maximum thickness of 31 m is the deposit of low sinuosity braided river channels that flowed to the north northeast the wood mountain formation represents an initial episode of erosion followed by low accommodation deposition where the net aggradation rate was likely low the sediments of the wood mountain formation are associated with change in tectonic style in western north america from one of compression to one of extension the gravels were deposited above a regional erosion surface associated with isostatic uplift of the central montana uplift

late wisconsinan and holocene history of southwestern saskatchewan the late wisconsinan laurentide ice sheet reached the limit of glaciation along the north facing slope of the unglaciated part of the cypress hills nunatak but elsewhere around the cypress hills and wood mountain uplands of southwestern saskatchewan it did not reach the limit of glaciation an interval of deglaciation was followed by a readvance of the ice sheet about 15 ka to a position near the late wisconsinan limit and was marked by strong flow of keewatin ice from the north and weaker flow of hudson ice from the northeast final deglaciation resulted in the formation of glacial lakes around the cypress hills nunatak a network of ice marginal and subglacial trenches presently occupied by the frenchman valley and its tributaries was formed when these lakes drained along over and under ice towards the western part of the wood mountain upland to the east the main trench joined an ancestral part of frenchman valley along the ice free southern slopes of wood mountain upland meltwater from the ic

stratigraphy of the north cliff section wellsch valley site saskatchewan eight separate till sheets are displayed at the north cliff which is part of the wellsch valley site in saskatchewan those tills are differentiated by using physical characteristics particle size clay and primary mineralogy and sediment chemistry grain size tends to fine downward in the section and a significant increase in the mean 4 centre of gravity indicates that some weathering occurred after deposition of the tills within the clay mineral suites smectite tends to dominate in all eight tills indicating that the paleoclimate was generally as dry as the present day climate only till number 4 counting from the bottom contains halloysite this halloysite may have been entrained from a preweathered surface by the glacier or it may have formed in situ following deposition among the primary minerals quartz dominates throughout the section whereas plagioclases are least abundant in tills 4 and 5 possibly as a result of postdepositional weathering element composition shows only minor changes for cu pb zn co and ni whereas mo increases upward in the section cr remains uniform in tills 1 2 3 7 and 8 but increases slightly in tills 4 6 and mn increases downward possibly as a response to fluctuating amounts of groundwater till 4 forms the best stratigraphic marker in the sequence because of its high mn content and the presence of halloysite but till 5 also contains distinctive features in its element composition the clay composition of the surface soil which has formed in the top till since the departure of the last glacier resembles that found in the underlying tills whereas quartz and plagioclase are present in lesser amounts these properties reflect both weathering in a semiarid climate and the presence of preweathered material from earlier paleosols

u pb baddeleyite ages for the scourie dyke swarm scotland evidence for two distinct intrusion events precise and accurate radiometric ages for continental mafic dyke swarms are a prerequisite for global correlation of mafic magmatic events calibration of apparent polar wander paths and deciphering mechanisms of dyke emplacement precambrian dyke swarms such as the scourie dyke swarm in north west scotland are invaluable time markers so that a precise and accurate knowledge of their emplacement age is critical when unravelling the complex geological evolution of many terrains precise dating is often difficult however because magma interaction with country rock and subsequent metamorphic events can severely perturb some isotopic systems recent advances in u pb geochronology1 3 combined with the discovery that some mafic dykes contain trace amounts of uranium bearing minerals such as baddeleyite zro2 and or zircon have made it possible to obtain u pb ages for these rocks with a precision typically on the order of 1 2 myr4 5 some of the first detailed u pb studies of precambrian mafic dyke swarms5 6 have shown that large volumes of mafic magma 100 000 km3 were emplaced into the continental crust in surprisingly short periods of time 2 myr here we report the results from a u pb study of three members of the scourie dyke swarm and find at least two periods of dyke emplacement at 2 418 and 1 992 myr bp we speculate on a potential global correlation of early proterozoic mafic magmatism and hence on the origin of dyke swarms

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

atmospheric re organization during marine isotope stage 3 over the north american continent sedimentological and mineralogical evidence from the gulf of mexico abstract mineralogical and sedimentological records from the gulf of mexico gom reveal major changes in the terrigenous particles provenance during the marine isotopic stage 3 mis3 that likely resulted from modifications of the environmental conditions including glacial activity and precipitation distribution over the north american continent the southeastern margin of the laurentide ice sheet lis was active throughout the entire mis3 whereas the southwestern margin contributed to short term meltwater events only during late mis3 some of the major mineralogical changes cannot be attributed to glacial activity but rather result from the changes in precipitation distribution combining sedimentological records from the gom with previously published climate related archives from the north american continent allows the reconstruction of two main schematic patterns of moisture inflow and precipitation distribution that may have prevailed during mis3 meltwater discharges contribute to modifying the lis configuration and the gom hydrological properties ultimately affecting large scale oceanic circulation and may have influenced atmospheric re organizations although the insolation variation rate appears to be the main driver of the system

nongeocentric axial dipole field behavior during the mono lake excursion a new record of the mono lake excursion mle is reported from the summer lake basin of oregon usa sediment magnetic properties indicate magnetite as the magnetization carrier and imply suitability of the sediments as accurate recorders of the magnetic field including relative paleointensity rpi variations the magnitudes and phases of the declination inclination and rpi components of the new record correlate well with other coeval but lower resolution records from western north america including records from the wilson creek formation exposed around mono lake the virtual geomagnetic pole vgp path of the new record is similar to that from another high resolution record of the mle from ocean drilling program odp site 919 in the irminger basin between iceland and greenland but different from the vgp path for the laschamp excursion le including that found lower in the odp 919 core thus the prominent excursion recorded at mono lake california is not the le but rather one that is several thousands of years younger the mle vgp path contains clusters the locations of which coincide with nonaxial dipole features found in the holocene geomagnetic field the clusters are occupied in the same time progression by vgps from summer lake and the irminger basin but the phase of occupation is offset a behavior that suggests time transgressive decay and return of the principal field components at the beginning and end of the mle respectively leaving the nonaxial dipole features associated with the clusters dominant during the excursion

a holocene soil geomorphic record from the ham site near frontier southwestern saskatchewan the soil geomorphic evolution of a hillslope in hummocky moraine terrain in one of the most arid parts of the palliser triangle is reconstructed from ca 12 600 bp to the present a transect from a moraine plateau into an internally drained basin provided evidence for seven postglacial landscape cycles each cycle includes a phase of land surface instability marked by erosional and depositional imprints and a phase of stability marked by pedologic imprints five cycles of slope wash dominated erosion left behind four superposed downslope thickening and downslope fining sediment mantles and were followed by two eolian cycles each of which left behind a loess mantle that accumulated from a local loess dispersal system accumulation of long range calcareous dust coincided with each of these loess cycles the five complete buried soil catenas and the surficial catena have systematic textural differentiation reflecting the preceding geomorphic regimen and color differentiation reflecting the soil draina

the excess temperature of plumes rising from the core mantle boundary we study the rise of conduit type thermal plumes from the core mantle boundary cmb in a simplified numerical model viscosity is a strong function of temperature and pressure assuming that all plumes start with the same excess temperature at the cmb we find that their temperature in the upper mantle is controlled by the plume flux and is insensitive to variations in viscosity or other material parameters or to the kind of flow law newtonian or non linear the reduction of excess temperature with height is stronger for weaker plumes plumes with a buoyancy flux of less than 1000 kg s should have cooled so much that they would not melt beneath old lithosphere the existence of such hot spots possibly indicates that not all plumes rise from the cmb

effects of sand supply on the morphodynamics and stratigraphy of active parabolic dunes bigstick sand hills southwestern saskatchewangeological survey of canada contribution 20060654 sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings in this study aerial photographs ground penetrating radar gpr and stratigraphic analysis d

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

sand water flows on cold climate eolian dunes environmental analogs for the eolian rock record and martian sand dunes abstract sand water flows were observed on the slopes of cold climate eolian dunes in southwestern saskatchewan canada during episodes of intense thawing in the winters of 2004 and 2005 meltwater produced flows with varying grain water contents on slopes of active blowout hollows and parabolic dunes the sand water flows emplaced small structureless lobate and tongue shaped deposits and alluvial fans the greatest concentration of deposits occurred on south facing slopes which frequently thaw in winter from intense insolation transport modes ranged from high density viscous slurry flows to lowdensity hyperconcentrated flows the triggering cause of these flows is high pore water pressure that develops in thawed nearsurface sand due to impeded infiltration by frozen sand with pore ice at depth these observations broaden the environmental context of sand water flows on dunes and contribute to interpretations of these deposits in the eolian rock record and to recent alluvial features observed on martian sand dunes

postglacial vegetation and climate in the northwestern great plains of montana abstract two pollen records from the northern great plains of montana portray vegetational and climatic changes during the last 12 200 yr in a region where few other data are available a 6 4 m core from guardipee lake east of the rocky mountains in the area formerly covered by the two medicine glacial lobe contains the glacier peak g and mt st helens jy volcanic ashes pollen percentage data are dominated by pinus poaceae artemisia and chenopodiaceae amaranthaceae high nonarboreal percentages and small amounts of juniperus alnus salix and populus pollen in sediments deposited between ca 12 200 and ca 9300 yr b p suggest a temperate grassland with shrubs growing locally in mesic settings after ca 9300 yr b p an increase in chenopodiaceae amaranthaceae pollen and a concomitant decline in artemisia indicate the development of more xerophytic grassland and the beginning of the altithermal period the lake probably was intermittently dry thoughout the holocene a high sedimentation rate and the presence of cereal taxa characterize the last ca 100 yr of euroamerican settlement lost lake at the northern margin of the highwood mountains yielded a 16 94 m core with no volcanic ashes that spans the last 9400 yr high amounts of chenopodiaceae amaranthaceae artemisia and poaceae pollen from ca 9400 to ca 6000 yr b p suggest the presence of xeric grassland and a climate drier than at present after ca 6000 yr b p chenopodiaceae amaranthaceae values declined and artemisia poaceae pinus picea salix alnus and betula increased the inferred spread of shrubs in wet habitats at this time and the expansion of forest in nearby mountain ranges indicate the end of the altithermal period and the onset of cooler moister conditions

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

comparison of four methods to calculate aeolian sediment transport threshold from field data implications for transport prediction and discussion of method evolution abstract aeolian sediment transport threshold is commonly defined as the minimum wind speed or shear stress required for wind driven sediment transport accurate and consistent quantification of this threshold is essential because it is an input variable in models used to predict wind erosion dune activity and dust emissions the majority of threshold quantification has been performed with analogs analytical models or wind tunnels however in the past few decades field based approaches to threshold parameterization have become more common although several methods of calculating transport threshold from field data are available their comparability is unknown to address this issue we collected high resolution sediment transport and wind measurements 1 hz on an active sand dune for 11 days and compared four different methods of calculating threshold i time fraction equivalence method tfem ii gaussian time fraction equivalence method gtfem iii instantaneous method and iv regression method time paired measurements from the two most widely used methods tfem and gtfem were strongly correlated r 0 977 however correlations between other methods varied from r 0 861 to r 0 261 to demonstrate the implications of using different threshold calculation methods we predicted mass transport which ranged from 63 6 instantaneous method to 126 6 kg per crosswind meter regression method this inconsistency suggests that the threshold calculation method could have an appreciable impact on transport predictions threshold values are similarly inconsistent when the measurement interval is modified as such we do not recommend comparing any measured threshold with another we discuss several strategies that may mitigate the impact of this issue such as clarification of semantics and method standardization we also discuss several criticisms of field based threshold measurements and re conceptualizations that could allow investigators to develop a better understanding of field based measurements overall results from this study could allow future investigators to improve threshold and transport predictions

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

age of the frenchman valley and associated drift south of the cypress hills saskatchewan canada frenchman valley extends about 340 km from the cypress hills saskatchewan to its confluence with the milk river in montana in one area the valley is 3 km wide and it was 180 m deep prior to deposition of as much as 80 m of landslide debris channel sand and gravel and alluvial and colluvial deposits six radiocarbon ages ranging from 3440 to 11 460 bp suggest the frenchman valley is wisconsinan the frenchman valley could not have formed in its side hill position if late wisconsinan ice had not been present south at the cypress hills

metamorphism denudation and sea level in the archean and cooling of the earth abstract over long enough time scales an antagonistic balance acting between tectonics uplift and rifting and the sedimentary cycle erosion and deposition probably keeps continental surfaces close to sea level we argue that this balance constitutes the primary mechanism for keeping long term continental freeboard constant by regulating the continental thickness an important implication is that the long term uplift or down warp history of ancient continental segments provides direct information on secular changes in the isostasy of the adjacent ocean basins through time the amount of uplift can be estimated from the regional metamorphic grade the burial pressures at present exposure of ten undisturbed archean granite greenstone segments are estimated to be 1 5 0 5 kb from this we infer a maximum long term uplift and erosion of 5 2 km for stable continent since 3 0 ga implying a mean continental thickness of 46 km at the time of crustal stabilization for a constant mean ocean depth isostasy requires a palaeo oceanic crust 14 2 km thick in the middle archean alternatively if little continent existed then the oceans would have been shallower and the palaeo oceanic crust 21 2 km thick assuming plate spreading did occur in the archean potential temperatures in the shallow mantle at 3 ga were 90 30 c or 170 20 c for no continent hotter than those prevailing today these temperatures translate into time averaged cooling rates for the shallow mantle of 57 c ga 1 and are comparable to estimates of the present day cooling rate for the whole earth the low burial pressures are a strong argument against the existence of catastrophic mantle flush events in the geological past which have been predicted by some mantle convection models taken together these constraints suggest a plume related geological setting i e oceanic plateau like flood basalt for the initial stage of greenstone belt evolution

early proterozoic mafic dykes in the north atlantic and baltic cratons field setting and chemistry of distinctive dyke swarms

application of till pebble lithology to the differentiation of glacial lobes in southern alberta variations in the pebble composition of surface till in southern alberta indicate the presence of three contemporaneous lobes in the last continental glacier the ice lobe domains have similar pebble associations and differ only in the frequency of occurrence of rock constituents a large part of the percentage variability within each domain is caused by irregular entrainment of locally derived stones which dilutes pebble contents and results in a lithology substantially different from the provenance composition the study has shown that the regional trends are preserved and can be recognized in the locally modified lithologies but the latter have to be isolated and evaluated differently from the regular provenance lithologies the common diluting agent in the area is fluvial gravel that is widespread on erosional bedrock surfaces and in preglacial valleys because the gravel is generally coarse pebble fractions of larger size are more affected by local dilution than are successively finer fractions q

climatic and hydrologic oscillations in the owens lake basin and adjacent sierra nevada california oxygen isotope and total inorganic carbon values of cored sediments from the owens lake basin california indicate that owens lake overflowed most of the time between 52 500 and 12 500 carbon 14 14 c years before present b p owens lake desiccated during or after heinrich event h1 and was hydrologically closed during heinrich event h2 the magnetic susceptibility and organic carbon content of cored sediments indicate that about 19 sierra nevada glaciations occurred between 52 500 and 23 500 14 c years b p most of the glacial advances were accompanied by decreases in the amount of discharge reaching owens lake comparison of the timing of glaciation with the lithic record of north atlantic core v23 81 indicates that the number of mountain glacial cycles and the number of north atlantic lithic events were about equal between 39 000 and 23 500 14 c years b p

spatial and temporal patterns of aeolian sediment transport on an inland parabolic dune bigstick sand hills saskatchewan canada abstract topographic changes from erosion pins and on site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation stabilized inland prairie dune field over two years the sediment budget calculated from digital elevation models shows that the total volume of erosion 9890 m 3 is greater than the amount of deposition 6990 m 3 indicating a net loss of 2900 m 3 of sediment or 29 of eroded sediment from the dune sediment erosion occurred mainly on the stoss slope 3600 m 3 36 of eroded sediment but also on the south 2100 m 3 21 and north sides of the dune head 1700 m 3 17 the blowouts along the arms 1740 m 3 18 and the crest 650 m 3 7 erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit 100 m 3 1 thus the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes 5500 m 3 80 coinciding with the southeasterly resultant transport direction for november 2004 05 the net loss of about 2900 m 3 29 may be attributed to sediment carried in suspension over and beyond the dune correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions e g vegetation cover ground freezing moisture buffer the relative importance of temperature and precipitation on rates of sediment transport conversely wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions seasonal effects produce a complex interaction between wind climate and surface conditions this leads to a dynamic range of threshold velocities which in turn causes spatial and temporal variations in transport limiting and supply limiting conditions collectively these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid to high latitude inland settings

a re examination of the three most prominent holocene tephra deposits in western canada bridge river mount st helens yn and mazama abstract volcanic ash deposits tephra in western canada are instrumental in providing independent chronologic control for many archaeological and paleoenvironmental sites in alberta tephra are a key chronologic tool in a region where radiocarbon dates are often unreliable because of the prevalence of carbonate rich bedrock and other old carbon sources such as coal however many studies using tephra for age control particularly archaeological projects identify tephra simply through field characteristics or light microscopy in both alberta and british columbia many radiocarbon dates that were used to date key tephra deposits were bulk conventional ages on peat and lake sediments which are not always reliable these factors have led to uncertainty in the age and number of bridge river and mount st helens msh set y tephra present in the region and incomplete distribution maps new major element geochemical analyses from archaeological and sedimentary sites across south central alberta complemented by new analyses of tephra from british columbia and saskatchewan refine the distribution of the bridge river msh yn and mazama tephra new geochemical data radiocarbon dates and a detailed overview of proximal msh set y stratigraphy and geochemistry show that only one msh layer yn is present in this region rather than two msh set y tephra as previously suggested additionally re assessment of age data combined with new geochemical analyses confirm that there is also only one bridge river tephra a bayesian modelled age estimate is determined for msh yn based on new ams dates on the tephra and vetted existing conventional ages providing a revised age estimate for msh yn of 3805 3535 cal bp mean of 3660 cal bp

morphodynamics and climate controls of two aeolian blowouts on the northern great plains canada blowouts are the most regionally pervasive active aeolian landform on the northern great plains of north america this study reports a long term investigation into the morphological development of two adjacent blowouts in a continental dune field the blowouts were monitored for a decade in the bigstick sand hills of southwestern saskatchewan canada topographic changes were determined from dense arrays of erosion pins in each blowout 1 per 4 m2 n 171 and 1 per 16 m2 n 150 pin measurements were made 16 times between may 1994 and may 2004 over the decade both blowouts expanded and more than doubled in volume differences in form flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin and the smaller blowout to erode by more than a metre a negative feedback effect was triggered when the larger blowout reached a critical size around 1994 60 m 36 m 8 1 m length width height when sediment was no longer eroded from the deflation basin a positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability sediment is more readily available throughout the year on south facing slopes which receive greater insolation than north facing slopes and are often drier and more frequently thawed in this cold climate environment comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level nevertheless the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station i the amount of precipitation ii the transport capacity of the wind and iii transporting winds from a directional wedge between 180 and 330 taken altogether the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings copyright 2006 john wiley sons ltd

terrain controls on depressional soil distribution in a hummocky morainal landscape in hummocky morainal landscapes soil distribution in well drained landscape positions tends to follow a consistent pattern soils in depressions however are more difficult to predict reliably this study had two objectives 1 to determine the parent material and landscape properties controlling the formation of the different depressional soils and 2 to use these controls to identify quantitative terrain based predictors of soil type in depressions only two terrain attributes specific dispersal area sda and elevation relative to open water bodies were required to distinguish three main soil groups gley recharge non gley recharge and discharge soils specific dispersal area is the downslope area draining flow from a given grid cell gley recharge soils occur primarily at points with sda of less than 2 m2 m 1 regardless of elevation within a given site because most of the runoff flowing to a point with very low sda values will pond or infiltrate vertically rather than flow downslope non gley recharge soils and discharge soils both occur at points with sda of greater than 2 m2 m 1 the majority of the non gley recharge soils occur above 5 m elevation relative to an open water body and the majority of the discharge soils occur below 5 m elevation relative to an open water body reflecting the importance of solute cycling in the development of discharge conditions buried and depositional soils could not be predicted from current terrain attributes because their profile characteristics were derived from the paleosurface

flood frequency of the mojave river and the formation of late holocene playa lakes southern california usa perennial lakes lasting several decades occupied silver lake playa the terminus of the mojave river as recently as 390 90 and 3620 70 bp flood routings from the mojave river headwaters to its terminal playa and water balance calculations for the resulting lakes indicate that floods comparable in magnitude to the largest floods in the modern record must occur almost annually to generate and maintain perennial lakes in contrast the modern floods of this magnitude have recurrence intervals greater than 18 years such an increase in flood frequency is required even if lake evaporation is reduced by as much as 50 modern extreme floods of the mojave river are related to meridional atmospheric circulation and a southeastward shift in the winter low pressure center over the north pacific ocean causing vigorous storms over the headwaters in the san bernardino mountains of southern california this winter pattern probably occurred more frequently to induce the large number of storms and floods needed

stratigraphy and correlation of the glacial deposits on the montana plains till units representing at least three pre illinoian continental glaciations at least one illinoian glaciation and a late wisconsin glaciation have been identified on the montana plains early wisconsin or middle wisconsin till units have not been identified the southernmost limit of late wisconsin glaciation is in montana more than 170 km south of the lethbridge moraine in alberta canada figs 1 and 2 an interpretation that the lethbridge moraine is the limit of late wisconsin glaciation stalker 1977 1980 1983b stalker and harrison 1977 rutter 1980 1981 jackson 1983 is incompatible with stratigraphic and morphologic evidence from montana

directly dated mis 3 lake level record from lake manix mojave desert california usa abstract an outcrop based lake level curve constrained by 70 calibrated 14 c ages on anodonta shells indicates at least 8 highstands between 45 and 25 cal ka bp within 10 m of the 543 m upper threshold of lake manix in the mojave desert of southern california correlations of manix highstands with ice marine and speleothem records suggest that at least the youngest three highstands coincide with dansgaard oeschger d o stadials and heinrich events 3 and 4 the lake level record is consistent with results from speleothem studies in the southwest that indicate cool wet conditions during d o stadials notably highstands between 43 and 25 ka apparently occurred at times of generally low levels of pluvial lakes farther north as interpreted from core based proxies mojave lakes may have been supported by tropical moisture sources during oxygen isotope stage 3 perhaps controlled by southerly deflection of pacific storm tracks due to weakening of the sea surface temperature gradient in response to north atlantic climate perturbations

diamict fill in sub glacial channels poplar river strip mine southern saskatchewan abstract the poplar river coal mine is within a marginal zone of the laurentide ice sheet where it bordered the unglaciated flaxville plain along the international boundary drift and bedrock relationships seen in the mine wall suggest a diamict was emplaced by subglacial processes not previously documented elsewhere in the glaciated parts of the canadian interior plains region the mine trench 5 km long 200 m wide 35 m deep exposed a massive clay diamict more than 20 m thick emplaced within channel like excavations cut into late tertiary gravel and sand contacts outline a highly irregular bedrock surface marked by flame like extensions of sandy bedrock stringers and wedges into the diamict the sequence is interpreted as initial subglacial meltwater incision into a frozen bedrock substrate with subsequent infilling by a highly viscous diamict flowing along the channel the flame like structures appear to reflect subsequent diapiric processes airphotos show that the diamict forms a hummocky moraine fill within a buried channel about a kilometer wide separating ground moraine and bedrock surfaces similar buried channels occur along the margins of hummocky moraines elsewhere in the prairies and may have formed by similar subglacial processes

geologic evidence for a mantle superplume event at 1 9 ga 1 both preserved and restored areal distributions of proterozoic marine intracratonic passive margin and platform sediments show a prominent peak at 1 9 ga indicating that shallow marine sediments were widespread on the continents and that sea level was high at this time the chemical index of alteration in shales deposited at this time was high suggesting warm climates possibly due to enhanced co2 levels in the atmosphere high sea level and warms climate may also explain an abundance of black shale banded iron formations and shallow marine phosphate deposits and an increase in the number of occurrences and diversity of stromatolites in general and microdigitate stromatolites at 1 9 ga all of these observations are consistent with a 1 9 ga superplume event the occurrence of only a minor positive carbon isotope shift in marine carbonates at 1 9 ga indicates that the relative rates of burial of organic and oxidized carbon remained about the same as at present slightly low 87sr 86sr isotopic ratios in seawater at 1 9 ga reflect increased mantle input of sr from the proposed superplume event whereas higher ratios at 1 85 1 75 ga may reflect increased input of continental sr from a growing supercontinent the first massive sulfate evaporites in the geologic record at 1 8 1 6 ga follow the possible 1 9 ga superplume event this may reflect an increase in both oxidation state and carbonate deposition in the oceans as plume related volcanism wanes

constraining the potential temperature of the archaean mantle a review of the evidence from komatiites the maximum potential temperature of the archaean mantle is poorly known and is best constrained by the mgo contents of komatiitic liquids which are directly related to eruptive temperatures however most archaean komatiites are significantly altered and it is difficult to assess the composition of the erupted liquid relatively fresh lavas from the saskmar suite belingwe greenstone belt zimbabwe 2 7 ga include chills of 25 6 wt mgo and olivines ranging to fo93 6 implying eruption at around 1520 c a chill sample from alexo township ontario also 2 7 ga is 28 wt mgo and associated olivines range to fo94 1 implying eruption at 1560 c however inferences of erupted liquids containing 32 33 wt mgo from lavas in the barberton greenstone belt south africa 3 45 ga and from the perseverance complex western australia 2 7 ga may be challenged on the grounds that they contain excess cumulate olivine or were enriched in mg during alteration or metamorphism re interpretation of olivine compositions from these rocks shows that they most likely contained a maximum of 29 wt mgo corresponding to an eruption temperature of 1580 c this composition is the highest liquid mgo content of an erupted lava that can be supported with any confidence the hottest modern magma on gorgona island 0 155 ga contained 18 20 mgo and erupted at circa 1400 c if 1580 c is taken as the temperature of the most magnesian known eruption then the source mantle from which the liquids rose would have been at up to 2200 c at pressures of 18 gpa corresponding to a mantle potential temperature of 1900 c these temperatures are in excess of the mantle temperatures predicted by secular cooling models and thus komatiites can only be formed in hot rising convective jets in the mantle this result requires that archaean mantle jets may have been 300 c hotter than the archaean ambient mantle temperature this temperature difference is similar to the 200 300 c temperature difference between present day jets and ambient mantle temperatures an important subsidiary result of this study is the confirmation that spinifex rocks may be cumulates and do not necessarily represent liquid compositions

winter variability of aeolian sediment transport threshold on a cold climate dune abstract changes in surface conditions on cold climate aeolian dunes are pronounced during winter dunes are wet snow covered and or frozen for extended periods of time it is unknown how the critical wind speed for sediment transport threshold varies and how threshold may influence sediment transport predictions although the impact of surface conditions on threshold has been examined in synthetic experiments wind tunnels complicated feedbacks between threshold sand transport and surface conditions that occur in natural environments suggest that a ground based empirical approach may provide enhanced insight in this study we investigate threshold variability for 73 days during fall winter spring surface conditions from 18 november 2008 to 30 may 2009 in the bigstick sand hills of saskatchewan canada simultaneous measurements of threshold and atmospheric variables air temperature relative humidity solar radiation wind speed and direction were used to examine the extent to which surface erodibility was regulated by meteorology time lapse images of the surface from a co located camera were used for quality control and interpreting changes in the surface affecting threshold results reveal that threshold varied throughout the deployment 25 75 quartiles 6 92 8 28 m s 1 mean 7 79 m s 1 threshold variability was especially evident at two scales i event timescale and ii seasonal timescale event scale variability peaked during mid winter in one event the threshold varied by 6 m s 1 in 2 h with freezing and re freezing of the surface and relatively constant atmospheric conditions the causes of event scale variability are complex though qualitatively related to changes of wind direction antecedent meteorological conditions and vertical variations of grain scale bonding agents such as pore ice and moisture seasonal scale changes manifested as an increase in threshold during fall peaking in mid winter and decreasing in spring increased threshold in mid winter was linked to lower insolation and air temperature suggesting low erodibility due to the presence of pore ice correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations air temperature r 0 322 relative humidity r 0 388 solar radiation r 0 309 that also varied according to wind direction suggesting that the link between atmospheric conditions and surface erodibility on cold climate dunes is complex this contrasts with results from field based studies in warmer climates and controlled wind tunnel experiments which show a more direct link between atmospheric variables temperature and humidity and surface erodibility nevertheless our results do show a seasonal pattern of threshold that could be important for modeling cold climate aeolian sediment transport

extreme southwestern margin of late quaternary glaciation in north america timing and controls well preserved latero frontal moraines in the eastern san bernardino mountains of southern california provide evidence for several glacial advances during the late quaternary and mark the southwesternmost limit of glaciation in the western cordillera using geomorphology and 10be cosmogenic radionuclide dating a succession of moraines from three glaciated valleys is dated to 18 20 ka last glacial maximum 15 16 ka heinrich event 1 12 13 ka younger dryas stade and 5 9 ka early middle holocene these ages substantiate the view that glaciation throughout the american cordilleras was synchronous during the late quaternary furthermore these data show that glacial advances in southern california occur when a significant decrease in summer temperature is coupled with an increase in moisture flux producing high winter snowfall this allows for perennial snow accumulation that may under appropriate conditions persist to form glacial ice

a continuous record of holocene pollen from harris lake southwestern saskatchewan canada abstract holocene vegetation change in the west block of the cypress hills on the northern great plains is interpreted from a continuous 9120 year pollen record this is one of the few continuous pollen records available from the northern great plains which extends to the early holocene the west block rises to a maximum elevation of 1465 m and is a mosaic of grassland populus forest coniferous forests and wetland vegetation because of the ecotones present climatic changes produced vegetation changes discernible from the pollen record the record indicates that a populus forest grassland complex was established by 9000 yr bp very little coniferous forest was present at that time the predominance of grassland and saline tolerant vegetation between 7700 and 5000 yr b p defines the altithermal for this region climatic deterioration followed as indicated by increases in relative amounts of conifer and aquatic taxa pollen the pinus contorta and picea glauca forests characteristics of the cypress hills today only have been prevalent since about 4600 yr b p both species were present in very low numbers throughout the altithermal by 3230 yr b p the modern vegetation was established with little change since then

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

noritic dykes of southern west greenland early proterozoic boninitic magmatism two major swarms of early proterozoic ca 2 1 ga basic dykes occur within the archaean craton of southern west greenland one swarm comprises ophitic and sub ophitic tholeiitic dolerites while the other the bn dyke swarm constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts the close geochemical similarity between a quenched norite and the coarser grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation the bn dykes are geochemically distinctive most having high mgo ca 16 cr and ni contents in conjunction with relatively high sio2 light rare earth ree and large ion lithophile lil element concentrations the texture mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas the bn dykes also correspond to proposed parental liquids of the bushveld complex and other major layered basic igneous intrusions the two dyke swarms are petrogenetically distinct the tholeiitic dolerites were derived from a relatively undepleted primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source the wide spread distribution of similar proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world wide scale at this time