southern laurentide ice lobes were created by ice streams des moines lobe in minnesota usa abstract regional mapping in southern minnesota has illuminated a suite of landforms developed by the des moines lobe that delimit the position of the lobe at its maximum and at lesser readvances the ice lobe repeatedly advanced discharged its subglacial water and subsequently stagnated recent glaciological research on antarctic ice streams has led some glacial geologists to postulate that ice streams drained parts of the marine based areas of the laurentide ice sheet i postulate that such ice streams may develop in land based areas of an ice sheet as well and that the des moines lobe 200 km wide and 900 km long was an outlet glacier of an ice stream it appears to have been able to advance beyond the laurentide ice sheet as long as adequate water pressure was maintained however the outer part of the lobe stagnated because subglacial water that facilitated the flow was able to drain away through tunnel valleys stagnation of the lobe is not equivalent to stoppage of the ice stream because ice repeatedly advanced into and onto the stagnant margins stacking ice and debris similar landforms are also seen in other lobes of the upper midwestern united states

influence of provenance and transport process on the geochemistry and radiogenic hf nd and sr isotopic composition of pleistocene glacial sediments minnesota usa abstract we develop a broad geochemical dataset from 50 samples of pleistocene glacial till matrix including three lacustrine samples representing four sediment provenances collected from across minnesota usa such a dataset is useful both in the context of regional studies of glaciation and in efforts to understand how provenance and glacial processes impact the geochemistry of sediment archives the principal sediment sources of the four provenances include materials from the archean proterozoic canadian shield the proterozoic midcontinent rift paleozoic carbonates and cenozoic and mesozoic clastic sediments we measured major element geochemistry in all till samples in both

subglacial sediment dispersal and till composition dispersal of subglacial sediment down ice from its bedrock source assumes the form of a negative exponential decay curve dispersal decay curves can be quantified by their decay constants half distances half lives and total transport distances mapped dispersal decay curves associated with pleistocene ice sheets in north america and europe identify several scales of dispersal ranging from local kilometers to continental 100 s to 1000 s km scales till composition reflects the various scales of dispersal local scales short transport distances result in tills that reflect underlying bedrock whereas continental scales long transport distances result in tills derived largely from sources far up ice a number of parameters proposed as influencing subglacial sediment dispersal and transport distances do not explain the range of scales observed although they may explain minor variations kilometers in transport distances topography and basal ice velocity sliding velocity are interpreted as

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

trace element geochemistry of a thick till and clay rich aquitard sequence saskatchewan canada abstract samples collected from a 170 m borehole penetrating till bentonitic clay and sand at the birsay site saskatchewan canada has been studied as a first step for understanding the controls on dissolution and transport of trace elements including rees in porewaters of a clay rich aquitard the ree budgets of the till clay and sand are dominated by apatite and monazite with sporadic zircon and y phosphate apatites contain 0 3 to 1 7 wt ree and monazites 12 to 55 wt all three units are characterized by unusual bulk sample ree patterns with maxima at eu gd convex down patterns from la sm with minima at ce and variably fractionated hree apatites feature maxima at eu gd consequently the complex patterns arise from variable modal proportions of apatite monazite and plagioclase feldspar relative to post archean average shale paas the till is sio2 and cao rich with about half the contents of al2o3 tio2 and fe2o3 these compositional relationship stem from relatively high proportions of quartz and carbonate but low modal abundances of ferromagnesian and ti oxide minerals similarly the till has cs co ni sc v cu pb and zn contents at about half paas the bentonite clay has slightly higher sio2 and cao contents than paas with lower abundances of most other trace elements including ree which plot at 0 7 to 0 9 paas the major and trace element composition is similar to continental arc andesites and the clay is interpreted to have a mixed provenance of arc andesite and eroded underlying sands the composition of the till appears to reflect mixed provenance erosion of the underlying cretaceous clay and sand paleozoic carbonate rocks and the precambrian shield the silicious ardkenneth sand has lower concentrations of ree and most trace elements compared to the clay but the most fractionated ree patterns the clay and till have inherited more subdued ree patterns in part from the underlying sand unit compositional variations between the units are marked by an upturn of nb th u and ree concentrations at the till clay interface 80 2 m and decrease of these elements at the clay sand boundary 156 2 m ce and eu anomalies vary erratically with depth the anomalies appear to reflect the degree of sedimentary sorting which in turn controls the modal abundances of detrital monazite apatite zircon and plagioclase feldspar zr zr hf hf and zr hf ratios are higher in the till than the clay and sand indicating an additional zr hf bearing phase with a distinctively high zr hf ratio the observed small compositional variations in the till and clay are not reflected in variations of geotechnical properties given that the ree budget of the till and clay are dominated by highly insoluble trace minerals it is unlikely that the ree patterns of porewaters will be controlled by bulk sample ree concentrations weathering of the upper 3 m of the till has oxidized fe2 bearing silicates oxides and sulphides and dissolved carbonates relative to the underlying unoxidized till weathering has not disturbed major ree or other trace element compositions

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

geochemical and nd pb isotopic evidence for the provenance of the early proterozoic virginia formation minnesota implications for the tectonic setting of the animikie basin the early proterozoic animikie basin is located at a major crustal boundary between archean crust of the superior craton and penecontemporaneous early proterozoic crust of the wisconsin magmatic terranes the provenance of sedimentary rocks within the animikie basin constrains the tectonic evolution of the early proterozoic margin of the superior craton published geological petrographic and nd pb isotopic data indicate that the pokegama quartzite lower passive margin unit of the animikie group has a late archean provenance in contrast the virginia formation upper deep water turbidite shale unit of the animikie group was derived from dominantly early proterozoic sources with isotopic compositions similar to igneous rocks of the wisconsin magmatic terranes shales of the virginia formation have nd depleted mantle model ages 2 14 to 2 35 ga and mu 1 of 7 81 to 8 09 ashes within the virginia are more evolved geochemically than shales and have younger model ages of 1 86 and 1 99 ga and simila

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

terrestrial record of laurentide ice sheet reorganization during heinrich events the glacial stratigraphy and geomorphology of the western lake superior region record a complex sequence of late wisconsinan ice advances and retreats of the laurentide ice sheet from accumulation centers in quebec and hudson bay geomorphic evidence indicates that three major late wisconsinan events occurred each marked by gradual buildup of ice formation of a prominent moraine and subsequent rapid ice retreat the established radiocarbon chronology indicates that these three events culminated ca 23 21 16 15 5 and 13 14c ka indicating that major glacial advances culminated immediately prior to heinrich events h 2 and h 1 and that ice underwent rapid retreat during heinrich events the possible linkage between western lake superior region ice dynamics and heinrich events is supported by the presence of indicator rock types in drift associated with each major glacial recession these indicators suggest that progressive southward shifts of the laurentide ice sheet ice divide accompanied each rapid glacial recession furthermore lithologic evidence indicates that there were two episodes of ice divide shifts one 400 600 km occurring during h 2 and a smaller shift occurring during h 1

examining the generality of τ0 tke for gravel and cobble beds with sand fill abstractturbulence measurements over rough beds are used for a variety of purposes including studies of habitat diversity for aquatic organisms stream restoration efforts and assessment of drag induced by vegetation turbulent kinetic energy tke has been used to estimate bed shear stress by use of a proportionality constant of 0 19 0 21 the tke method of bed shear stress estimation is less sensitive to flow misalignment relative to reynolds stress or mean velocity measurements but it has not been tested across a broad range of hydraulic conditions in the work reported here tke was compared to bed shear stresses for gravel d50 35 mm and cobble d50 156 mm beds with varying discharges and levels of sand fill d50 0 3 mm the ratio of bed shear stress 0 with tke was not strongly affected by mean velocity for either the gravel or cobble beds but it was affected by bed roughness the mean of the median values of 0 tke across three mean velocities was 0 24 for gravel with no sand in the bed

geological survey of canada s contributions to understanding the composition of glacial sediments drift compositional studies were initiated at the geological survey of canada gsc in the mid 1960 s in projects that drew heavily on the technology and approaches developed in fennoscandia over the previous century as this research progressed and expanded in the 1970 s its fennoscandian character diminished and like the geochemical exploration research program that it closely paralleled drift prospecting began to acquire a distinctly canadian character imposed by the geographical and logistical constraints of climate and asymmetric population distribution gsc research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering because glacial sediments are generated largely by crushing and abrasion their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness this s

provenance of heinrich layers in core v28 82 northeastern atlantic 40ar 39ar ages of ice rafted hornblende pb isotopes in feldspar grains and nd sr pb isotopes in the fine sediment fraction abstract several correlatable layers of sediment rich in ice rafted grains have been documented in the north atlantic the most notable within the last glacial cycle are the heinrich layers layers extremely rich in ice rafted detritus and generally barren of foraminifera within the north atlantic ice rafted detritus ird belt the view of these layers is that they represent events where great armadas of icebergs were launched into the north atlantic the importance of the heinrich layers lies in their connection with abrupt climate change in the north atlantic and perhaps globally there is a growing number of published provenance studies of the heinrich layers in the north atlantic based on a variety of methods however there is little overlap of methods applied to the same samples in this contribution we present a multi component provenance study of heinrich layers h1 h2 h4 and h5 from core v28 82 in the eastern north atlantic our results indicate that virtually the entire inventory of terrigenous clastic detritus in heinrich layers h2 h4 and h5 came from ancient continental sources surrounding the labrador sea although heinrich layer h1 is similar in many respects it appears to have some significant differences relative to the other three

the geology and geochemistry of the palaeoproterozoic makganyene diamictite abstract the palaeoproterozoic earth experienced a global glacial event at 2400 ma that occurred during the transitional period from anoxic to aerobic conditions in the atmosphere and oceans the transvaal supergroup in the griqualand west basin south africa hosts glacial deposits and associated major iron and manganese deposits that are apparently related to these global changes the focus of this study is to assess the stratigraphy and geochemistry of the glaciogenic makganyene formation in order to constrain its palaeoenvironmental settings the makganyene formation forms the base of the postmasburg group and has been regarded as resting on an erosive regional unconformity throughout the northern cape province systematic regional field observations and regional mapping carried out during this study demonstrate that this stratigraphic relationship is not universal the makganyene formation is in fact conformable with underlying formations of the koegas subgroup in the deep southern prieska basin and rests on an unconformity only on the shallow ghaap platform to the north east the makganyene formation displays lateral facies changes that reflect the palaeogeography of the study area and the advance and retreat of ice sheets shelves geochemical investigations of glacial strata of the makganyene formation demonstrate that underlying banded iron formations of the transvaal supergroup acted as the main clastic source for the diamictite detritus geographic variations in bulk composition of the diamictites correlate well with field observations and show that sorting processes were controlled largely by the morphology of the palaeobasin carbon isotope results emphasize the transitional nature of the makganyene formation in terms of the environmental conditions that resulted in widespread global glaciation in the palaeoproterozoic on the basis of the above geological evidence it is proposed that the transvaal supergroup in the northern cape province represents a continuous depositional event that lasted approximately 250 ma and hence provides a unique opportunity for assessing the transitional changes experienced by the palaeoproterozoic earth

south greenland ice sheet collapse during marine isotope stage 11 varying levels of boreal summer insolation and associated earth system feedbacks led to differing climate and ice sheet states during late quaternary interglaciations in particular marine isotope stage mis 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410 000 to 400 000 years ago implying substantial mass loss from the greenland ice sheet gis there are however no model simulations and only limited proxy data to constrain the magnitude of the gis response to climate change during this super interglacial thus confounding efforts to assess climate ice sheet threshold behaviour and associated sea level rise here we show that the south gis was drastically smaller during mis 11 than it is now with only a small residual ice dome over southernmost greenland we use the strontium neodymium lead isotopic composition of proglacial sediment discharged from south greenland to constrain the provenance of terrigenous silt deposited on the eirik drift a sedimentary deposit off the south greenland margin we identify a major reduction in sediment input derived from south greenland s precambrian bedrock terranes probably reflecting the cessation of subglacial erosion and sediment transport as a result of near complete deglaciation of south greenland comparison with ice sheet configurations from numerical models suggests that the gis lost about 4 5 to 6 metres of sea level equivalent volume during mis 11 this is evidence for late quaternary gis collapse after it crossed a climate ice sheet stability threshold that may have been no more than several degrees above pre industrial temperatures

comparative geochemistry of pleistocene and paleoproterozoic huronian glaciogenic laminated deposits relevance to crustal and atmospheric composition in the last 2 3 ga abstract comparison of the major and trace element geochemistry of glaciogenic laminated deposits of pleistocene and paleoproterozoic age from an area north of lake huron ontario has revealed differences and similarities that may provide insight into the erosional history of part of the archean superior province of the canadian shield during the last 2 ga and some aspects of the evolution of the earth s atmosphere both the major element and trace element compositions of the ancient and recent glacial deposits are very similar the paleoproterozoic mudstones are however enriched in fe and u characteristics that may reflect the oxygen content of the archean early paleoproterozoic atmosphere hydrosphere system strong ca depletion is exhibited by the paleoproterozoic glaciogenic argillites but is absent from the pleistocene samples the proterozoic argillites have slightly higher values for a chemical index of alteration than those of pleistocene muds these characteristics may reflect the acid natur

a geochemical investigation into the provenance of the neoproterozoic port askaig tillite dalradian supergroup western scotland abstract the major and trace element geochemistry of matrix materials from glaciogenic diamictites unsorted polymictic conglomerates consisting of clasts scattered throughout a finer grained matrix of the neoproterozoic port askaig tillite of western scotland shows evidence of an upward change in provenance values for a carbonate corrected chemical index of alteration cia are fairly high 70 80 in the lower diamictites suggesting that they were derived mainly from an older sedimentary cover older dalradian formations that had undergone a previous weathering cycle low cia values more typical of unweathered material were obtained from diamictites in the upper part of the formation thus deposition of the port askaig diamictites is thought to involve a change in provenance with unroofing of a cover of older sedimentary rocks and exposure of basement rocks in spite of these inferred differences in provenance diamictite materials throughout the formation have very uniform chondrite normalized rare earth element ree distributions ree distribution patterns from the diamictites closely resemble that of average post archean shales paas with a significant negative eu anomaly and typical enrichment in lree these results together with the presence of uniform la yb n ratios throughout the formation suggest that the sedimentary cover rocks from which the lower diamictites were derived were themselves derived from a similar post archean basement a th sc versus sc plot suggests that siliciclastic matrix material in the lowest diamictite was derived essentially from provenances similar to paas the higher diamictites appear to have been derived from a mixture of granitic material and paas in a ratio of up to ca 4 1 sparse sedimentary structures suggest derivation of the port askaig tillite from the southeast but the exact source remains unknown

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes

sr nd pb isotope evidence for ice sheet presence on southern greenland during the last interglacial to ascertain the response of the southern greenland ice sheet gis to a boreal summer climate warmer than at present we explored whether southern greenland was deglaciated during the last interglacial lig using the sr nd pb isotope ratios of silt sized sediment discharged from southern greenland our isotope data indicate that no single southern greenland geologic terrane was completely deglaciated during the lig similar to the holocene differences in sediment sources during the lig relative to the early holocene denote however greater southern gis retreat during the lig these results allow the evaluation of a suite of gis models and are consistent with a gis contribution of 1 6 to 2 2 meters to the 4 meter lig sea level highstand requiring a significant sea level contribution from the antarctic ice sheet

influence of late glacial climate changes on sediment transport in the river werra thuringia germany abstract several sedimentary records of floodplain sediments in the werra valley and subcatchments have been analysed in order to investigate the influence of climate change on the sediment transport system in the sedimentary records of the subcatchments a marked change from minerogenic to organic sediments is visible about 14 6 ka b p according to palynological analyses this change occurs in a period with a remarkable rise in arboreal pollen percentages in addition a reverse change from organic to clastic sediments takes place shortly after 12 9 ka b p coincident with a decrease in arboreal pollen percentages during this period assuming that changes in vegetation cover are mainly caused by climate the variations in the sedimentary records are also attributed to these climatic oscillations in contrast to the subcatchments comparable changes in the sedimentary record are not detectable in the floodplain of the werra river this points to the conclusion that the influence of late glacial climate fluctuations on the sedimentary regime of a river with a relatively large and a more heterogeneous catchment seems less pronounced