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

origin of placer gold nuggets and history of formation of glacial gold placers gold creek granite county montana placer gold along the upper portions of gold creek near deer lodge montana occurs in pliocene fossil alluvial placers pleistocene till and alluvium the upper gold creek placers yielded an estimated 175 to 200 kg gold during 1890 to 1990 the gold probably originated in veins skarn or replacement deposits in paleozoic and mesozoic sedimentary units near the contact with late cretaceous granodiorite of the royal stock gold was initially concentrated in alluvial placers along the ancestral gold creek valley during late tertiary pliocene time pleistocene glaciers scoured the pliocene placers from most parts of the valley although the fossil placers were locally buried beneath till and gold was also incorporated into till that was deposited farther down valley gold from pliocene and pleistocene placers has locally been reconcentrated into alluvium as a result of postglacial stream incision the placer gold occurs as coarse sized oval to elongate grains characterized by rounded protuberances and inclusions of quartz and sulfide minerals in polished section the grains have alternating convex and concave borders interrupted by pits and embayments grain borders and interiors of embayments display supergene gold rims averaging 98 8 percent au microprobe analysis of cores indicate average compositions of 83 6 percent au and 16 5 percent ag and spectrographic data indicate a trace element signature enriched in cu pb and sb which is compatible with derivation from mesothermal plutonic lode deposits associated with the royal stock

crystal features of supergene gold at hannan south western australia deep weathering of basalt hosted sulphidic gold mineralisation has resulted in remobilisation of the gold and the formation of a supergene deposit the deposit occurs beneath an ephemeral lake system and is at least partially saturated by highly saline groundwater a general downward movement of an iron redox front associated with the weathering has controlled the distribution of the gold and its morphology it is unusual in that the high fineness gold crystals formed are coarse and well preserved small octahedra up to 50 m are the most abundant form of gold crystals but large up to 3 mm octahedral plates are common crystal morphology variations described here suggest that the gold is initially precipitated as euhedral octahedra and plates subsequent dissolution and recrystallisation associated with fluctuations in the chemical environment above the redox front has led to the development of the more common irregular dendritic or wire gold forms observed in other supergene deposits

using a multiple variogram approach to improve the accuracy of subsurface geological models subsurface geological models are often used to visualize and analyze the nature geometry and variability of geologic and hydrogeologic units in the context of groundwater resource studies the de

late quaternary temporal and event classifications great lakes region north america abstract several temporal and event classifications are used for the quaternary glacial and interglacial record in the great lakes region of north america although based on contrasting principles the classifications as practiced are similar to one another in most respects and they differ little from the classification proposed by chamberlin a century ago all are based on stratigraphic units having time transgressive boundaries thus the associated time spans and events are diachronous where application of geochronologic classification based on isochronous boundaries is not practical or useful we advocate the use of diachronic principles to establish local and regional temporal and event classifications diachronic and event classifications based on such principles are proposed herein for the great lakes region well established names including wisconsin sangamon and illinois are used at the episode or glaciation interglaciation rank without significant redefinition the hudson episode interglaciation is introduced for postglacial time the current interglacial interval the wisconsin episode is divided into the ontario elgin and michigan subepisodes in the eastern and northern parts of the great lakes region and into the athens and michigan subepisodes in the southern and western parts of the great lakes region

preservation of local high resolution data in a regional low resolution dataset a nested 3d modeling approach using an example from a quaternary glacial stratigraphy ontario canada abstract regional scale 3d models provide insight into general unit geometries and stratigraphic relationships however potentially significant local scale data and unit geometries are rarely preserved accurate modeling of local scale unit geometries and stratigraphic relationships is important for understanding aquifer aquitard connectivity estimation of aquifer volume and prediction of contaminant migration pathways this is particularly important in previously glaciated areas because of the high degree of lithological heterogeneity and stratigraphic variation in glaciogenic deposits this study presents a case study ontario canada that explores the impacts of an optimized model in which high resolution data are preserved in local scale models as golden blocks and non optimized regional scale 3d models on the predicted geometries and stratigraphic relationships of coarse and fine grained units lithofacies associations within a quaternary stratigraphy each of the regional scale models include high quality data outcrop and cored borehole logs and low quality data water well lithology logs however the optimized model was constructed by seamlessly integrating the golden blocks into the regional scale model using an algorithm producing a nested model whereas the non optimized model was built using a global modeling approach by way of comparison to unit geometries previously delineated in outcrops and surficial geology maps and hydraulic responses from pumping tests the results of this study indicate that coarse grained units which host significant municipal aquifers and fine grained units were more realistically and accurately represented in the optimized model as a result of the nested 3d modeling approach this case study demonstrates a relatively simple and effective method for preserving high quality data in a regional scale 3d model without sacrificing model accuracy in key areas of interest e g aquifer well fields

a proposed diachronic revision of late quaternary time stratigraphic classification in the eastern and northern great lakes area abstract a succession of stratigraphic codes 1933 1961 1983 has guided attempts to refine classifications and naming of stratigraphic units for quaternary deposits of the great lakes region the most recent classifications for the late quaternary of the lake michigan lobe 1968 and the eastern great lakes 1972 have been widely used but later work has created the need for revision an attempt has been made to integrate the two previous classifications following the diachronic system of the 1983 code of stratigraphic nomenclature a new nomenclature for the higher more broadly recognized units was presented in 1997 we here present the diachronic nomenclature for finer subdivisions recognized in the eastern and northern great lakes following the interglacial sangamon episode the three parts of the wisconsin episode are further subdivided as follows the ontario subepisode former early wisconsinan comprises the greenwood willowvale and guildwood phases the elgin subepisode former middle wisconsinan comprises the port talbot brimley and farmdale phases and the michigan subepisode former late wisconsinan consists of nissouri erie port bruce mackinaw port huron two creeks onaway gribben marquette abitibi and driftwood phases succeeding interglacial time to the present is the hudson episode

last interglacial sediments of the don valley brickyard toronto canada and their paleoenvironmental significance the don valley brickyard in toronto is an internationally designated type site in recognition of diverse faunal remains in the don beds of last sangamonian interglacial age pollen in overlying strata record the climatic deterioration marking the onset of the last wisconsinan glacial cycle new sedimentological descriptions show that the don beds about 8 m thick were deposited in a lacustrine lower shoreface environment subject to episodic storms storm deposited sand facies are interbedded with peaty muds that are extensively bioturbated water depths derived from wave formed ripples using linear wave theory appear to have increased during deposition of the don beds from about 2 m to about 18 m 12 28 m above the modern lake level a change that is recorded by an overall fining up sequence increasing water depths may have been the result of isostatic recovery of the lake outlet to the east the don beds overlie a thin bouldery deposit possibly a remnant of older illinoian glacial sediments yo

morphology and gpr stratigraphy of a frontal part of an end moraine of the laurentide ice sheet paris moraine near guelph on canada abstract during deglaciation the laurentide ice sheet developed lobate ice termini in the great lakes area where the lobes remained quasi stationary for considerable time and sediment was supplied by the glacier end moraines fronted by outwash plains were formed one of the best examples in southern ontario is the paris moraine formed by the lake ontario lobe this study is a detailed examination of the morphology transverse and longitudinal of part of the paris moraine near guelph ontario and an analysis of the stratigraphy as derived from borehole information and ground penetrating radar gpr surveys parts of the northwestern frontal zone of the moraine are characterized by c 30 m high semi isolated hills composed in great part by aprons fans of debris flow and waterlaid sediments to the southeast these hills are backed by moat like depressions similar to those formed by ice push generating hill hole morphology the ice push effect is corroborated by evidence of folding and dislocation in the gpr profiles farther southeastward still the main body of the end moraine is characterized by hummocky topography typical of differential melting of sediment charged stagnant ice

optical image and microchemical analysis of gold grains from a weathered profile of the minvoul greenstone belt northern gabongold grain analysis minvoul greenstone beltm iglesias martinez et al morphological characterization and quantification of gold particles by optical image analysis oia and by compositional analysis of microprobes using scanning electron microscope and electron microprobe analysis techniques were carried out on gold grains from the minvoul area archean greenstone belt in gabon large grains of almost pure gold were found throughout a weathering profile which consisted of saprolite mottled clay zone iron duricrust pisolitic gravels and yellow latosol in the deeper horizons gold was dissolved as shown by corrosion features on the surface of particles with average sizes of 2 6 and 2 35 in the saprolite and mottled clay zones respectively the occurrence of secondary gold in the duricrust was indicated by the larger size of the nuggets average 1 8 the high fineness 995 in average and the close textural relationship between gold and neoformed iron oxyhydroxides the uppermost horizons composed of yellow latosol and pisolitic gravels were interpreted as transported materials based on their size distribution average 0 85 and 1 34 sorting and shape parameters the best morphological parameter to describe the whole weathering profile was found to be the perimeter area ratio the highest ratios were recorded in the saprolite average 0 192 m 1 and decreased towards the surface average 0 057 m 1 the combination of the oia technique and the microchemical analysis of gold grains allowed us to define specific morphological and compositional characteristics of the gold particles for each horizon both methods proved to be of great utility to understand gold concentration dissolution and dispersion processes in supergene environments

geophysical geological and hydrogeological characterization of a tributary buried bedrock valley in southern ontario buried bedrock valleys infilled with quaternary aged sediment have the potential to become productive aquifers owing to prevalent sand and gravel deposits often associated with these topographic lo

subsurface heterogeneity in the geological and hydraulic properties of the hummocky paris moraine guelph ontario the advance and retreat of ice lobe margins of the laurentide ice sheet formed moraines that are a prevalent feature throughout southwestern ontario in contrast to the well studied stratified moraine complexes recessional and end moraines have largely been ignored in the context of hydrogeological studies recent urban growth has led to development pressures on these moraines and a need to better understand their hydrogeology this study presents data sets from the paris moraine near guelph ontario to examine its geomorphology internal composition and the corresponding hydraulic properties of these ice marginal features the moraine s geomorphic elements were mapped using high resolution global positioning system transects aerial photograph analysis and ground truthing nine continuous sediment cores were recovered to determine the nature and distribution of subsurface sedimentary units and their relation to the regional stratigraphic framework cores were described in detail using standard sedime

concentration of gold in in situ laterites from mato grosso the gold concentration studied is located in lateritic soils overlying precambrian schists of the cuiaba group in mato grosso brazil the following five horizons may be recognized from bottom to top 1 a gray blue altered schist horizon 2 a red argillaceous alterite 3 a horizon characterized by iron oxihydroxide rich pebbles and quartz fragments in an iron oxihydroxide rich matrix and clays 4 an iron crust and 5 the present soil the most significant gold content is found in the third horizon just below the iron crust according to geological study and morphological observations of the gold particles the gold ore mined today is the result of two combined processes i e the ferrallitic alteration of quartz lodes enclosed in schists and the effect of the red argillaceous alterite which acts as an impervious structure preventing the largest gold grains from migrating downward during their mechanical concentration

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

morphology and chemistry of placer gold from attappadi valley southern india we report the morphological textural and chemical characteristics of gold grains in stream gravels from the siruvani river in attappadi valley southern india the placer gold deposits contain both primary grains with jagged grain contours and secondary grains with smooth grain margins the primary and secondary gold grains are also distinguished by marked contrast in microtextures with the latter displaying a range of corrosion textures including striations etch pits and chemical corrosion cavities that coalesce to form honey comb patterns some of these cavities are filled with fine clay derived from lateritic weathering front while the primary grains are characterized by high silver content up to 35 77 wt with marginal overgrowths of high purity gold the secondary grains show exceedingly high fineness 1000 au au ag levels up to 984 with no marked compositional variation indicating selective extraction of ag and or reprecipitation of au from morphological and chemical characteristics we propose that the high purity gold grains were not derived directly from primary sources but underwent chemical refinement in the weathering front before they were transferred to the fluvial systems our findings have important implications for gold exploration in the attappadi valley

dissolution features of gold particles in a lateritic profile at dondo mobi gabon abstract this paper describes the morphological evolution of gold particles in a lateritic weathering profile under rain forest inherited from primary quartz veins associated with amphibolite the gold particles can be recognized from the weathering front up through the saprolite and overlying regolith to the land surface in the central part of the supergene gold dispersion halo gold particles undergo some changes in the uppermost 10 m voids and corrosion pits appear on particle surfaces their numbers and sizes increase toward the land surface edges of particles become progressively more blunt from the bottom to the top of the section the morphological changes are attributed to dissolution of gold over time possible causes for such dissolution are discussed occurrence of gold particles in the soil could be helpful for gold explorations in the humid tropics

removal of terrain effects from sar satellite imagery of arctic tundra synthetic aperture radar sar images of the earth s terrestrial surface contain geometric and radiometric image effects which are caused by varying terrain elevation and slope the radiometric effects tend to mask signal variations caused by other physical variables such as soil moisture and surface vegetation type which are known to influence sar backscatter signals as a result raw sar images are of limited use in classifying surface vegetation type or quantifying the spatial distribution of soil moisture in regions of terrain relief the authors present a technique for removing radiometric terrain effects from sar images image correction was carried out in two steps first an existing modeling package was used in combination with digital elevation data in order to map the raw image pixels onto a geodetic coordinate system thereby removing the geometric portion of the image distortion radiometric effects were then removed with the aid of a backscatter model which treats the reflected radiation as a combination of diffuse lambertian and specular components parameters in the backscatter model were determined by comparing two c band sar images of a test area in a region of arctic tundra which were taken from ascending and descending orbit tracks of the ers 1 satellite the ascending and descending images displayed reductions in pixel value variance of 30 and 13 respectively after processing direct comparison of the two test area images reveals a dramatic improvement in image similarity after processing

summary of quaternary stratigraphy and history eastern canada deposits of three wisconsinan substages sangamonian stage and older quaternary stratigraphic units are recognized in eastern canada the age assignment of these units is based on radiocarbon dating and correlation of events quaternary deposits older than sangamonian are recognized locally in eastern canada in southern ontario glacial deposits directly underlie sangamonian sediments and are referred to as illinoian in age in other areas the ages of older sediments are largely unknown offshore core stratigraphy suggests that a major glaciation took place about 436 ka and that the illinoian oxygen isotope stage 6 was also a time of extensive glaciation in this report sangamonian is used as the name for the chronostratigraphic stage that includes all of deep sea oxygen isotope stage 5 and consequently on a regional basis it includes warm interglacial deposits glacial deposits and cool interglacial deposits in southern ontario the warm interglacial deposits are represented by the don formation the stadial deposits by the scarborough formation and the cool interglacial deposits by the pottery road formation warm interglacial deposits have not been recognized in quebec unless they are part of the pre johnville sediments the becancour till is included as glacial sangamonian sediments and the st pierre sediments are recognized as cool interglacial sediments the early wisconsinan appears to have been the time of maximum wisconsinan glaciation in eastern canada with ice moving south of the international boundary and well out onto the continental shelf the middle wisconsinan was primarily a nonglacial period in southern ontario and a glacial stade elsewhere in eastern canada in southern ontario the middle wisconsinan record has been subdivided into two interstades port talbot and plum point separated by a stade cherrytree the port talbot interstade began before the limit of radiocarbon dating before 48 ka and ended about 40 ka glacial or near glacial conditions of the cherrytree stage lasted from about 40 to 35 ka ago and the plum point interstade was from about 35 to 23 ka ago central st lawrence lowland was occupied by ice throughout the middle wisconsinan but southeastern quebec and the montreal area were briefly deglaciated scattered evidence in atlantic canada suggests local deglaciation of coastal areas during middle wisconsinan but extensive ice remained on the continental shelf and ice from centres located on the shelf flowed onto land in at least two areas glacial conditions predominated throughout eastern canada during the late wisconsinan at the late wisconsinan maximum through moving ice deposited the catfish creek drift in southern ontario but ice lobes which developed in the basins of the great lakes after 15 5 ka controlled ice flow during a period of ice margin oscillation and retreat a calving bay developed in lower st lawrence valley after the late wisconsinan maximum causing a reversal of flow on the south shore of the st lawrence and replacing ice in the valley with the champlain sea about 12 ka late wisconsinan glaciers were largely limited to land areas in atlantic canada local ice caps dominated with complicated patterns of flow and retreat developing as centres of accumulation shifted and competing ice centres achieved dominance the period of late wisconsinan retreat in atlantic canada appears to have lasted from about 14 to 10 ka

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

the application of microchemical analysis of alluvial gold grains to the understanding of complex local and regional gold mineralization a case study in the irish and scottish caledonides terranes of the appalachian caledonian orogen north of the iapetus suture host gold mineralization in north america scotland and ireland to date commercial exploitation has been confined to the appalachian terrane of canada in scotland and ireland regional analysis of the types of gold mineralization has been handicapped by the relatively small number of bedrock gold occurrences available for study however there are a large number of alluvial gold localities a technique of microchemical characterization of gold grains has been applied to facilitate the classification of alluvial gold localities in terms of the style or styles of source mineralization thereby permitting a more complete interpretation of regional gold mineralization the technique of microchemical characterization used in this study classifies populations of gold grains from each locality in terms of the assemblage of opaque mineral inclusions enclosed within the gold grains and the concentration of minor alloying elements in the gold a total of 2 400 gold grains collected from 44 sites in ireland and scotland have been studied the microchemical signatures of populations of gold grains extracted from bedrock samples correlate closely with those from adjacent alluvial populations and furthermore our data are compatible with the descriptions of the vein mineralogy of bedrock mineralization reported by other workers this result has facilitated informed speculation on the type of source mineralization of other alluvial occurrences where the bedrock source remains undiscovered populations of alluvial gold from individual localities have been grouped into larger regional data sets on the basis of similarities in microchemical signature the signatures of these data sets were analyzed using the same criteria and 10 classes of gold were identified regional analysis of the distribution of the gold classes showed that the occurrence of the four major classes correlates strongly with host terrane irrespective of geographical location gold from the southern uplands terrane is characterized by inclusions of base metal sulfides and sulfarsenides with the silver content of the gold being less than 15 percent in contrast populations of alluvial gold from the grampian and highland terranes commonly exhibit median silver contents of over 20 percent and frequently contain silver telluride and bismuth telluride inclusions which are extremely rare in gold from the southern uplands terrane however in other cases the style of mineralization is controlled by specific host or source rocks and is independent of the terrane two examples are gold mineralization within porphyry systems and gold associated with red bed sediments the study has confirmed the value of the technique of gold grain characterization using information from both concentrations of alloying elements and inclusion assemblages as a powerful tool in interpreting complex local and regional gold mineralization

evidence for the two creeks interstade in the lake huron basin new radiocarbon age dates for the cheboygan bryophyte bed in northern lower michigan indicate that the bed was not deposited during the mackinaw interstade as was previously proposed but is correlative to the two creeks forest bed deposited during the two creeks interstade approximately 11 850 bp furthermore the till overlying the bryophyte bed does not represent continuous deposition by ice throughout the two creeks interstade as proposed by others but represents deposition during the greatlakean stade a major implication resulting from the reassignment of the age of the cheboygan bryophyte bed is that the straits of mackinac could have been ice free during the two creeks interstade and that during that time the kirkfield phase of glacial lake algonquin may have extended into the lake michigan basin

polarimetric sar data compensation for terrain azimuth slope variation this paper addresses the problem of polarimetric sar polsar data correction for changes in radar cross sections which are caused by azimuth slopes most radiometric slope corrections remove slope effects to account for the effective scattering pixel area however few studies address the slope effect on the radar cross section as a function of polarization states the authors propose two approaches to compensate for this azimuth slope effect for polsar data in the first approach the digital elevation model dem obtained from interferometric sar or from other means is used to estimate orientation angles and in the second approach orientation angles are derived directly from the polsar data they have developed three new methods to implement this second approach one is based on the right right and left left circular polarizations and the other two are based on cloude s and huynelt s decompositions the results are compared with the original polarization signature method using the dem generated orientation angles as the reference polsar data is then compensated using the derived orientation angles significant changes were observed in many elements of the coherency matrix the compensated polsar data should improve the accuracy of geophysical parameter estimation techniques nasa jpl airsar data for an area in central california is used for illustration

alteration lateritique du gite aurifere d ovala gabon et formation d une anomalie superficielle de dispersion les sols de la region d ovala sud gabon presentent une anomalie superficielle en or a l aplomb d une mineralisation de la roche mere lateritisee sur 50 m d epaisseur de bas en haut le profil d alteration comprend trois horizons principaux saprolitique nodulaire et sablo argileux cette alteration est developpee in situ a partir de gneiss archeens et de roches metamorphiques proterozoiques du facies schiste vert dans la roche fraiche l or est associe avec du quartz de la pyrite de la tourmaline et de la muscovite lorsque l alteration progresse les particules auriferes sont liberees et chimiquement arrondies depuis la mineralisation primaire jusqu a la surface les mecanismes de dissolution amenuisent de plus les particules d or et les appauvrissent en argent une dispersion mecanique laterale vers l aval des versants se superpose a l evolution verticale ce mecanisme fournit les particules de plus petite taille dans l horizon superficiel des mecanismes a la fois chimiques et physiques sont a l origine de la formation du halo supergene

correction of sar imagery for variation in pixel scattering area caused by topography the radiometric correction of synthetic aperture radar sar imagery for topographically induced changes in the pixel scattering area is examined the relative significance of ground slope in the range and azimuth directions is compared and a widely used correction factor based on the sin of the local radar incidence angle is shown to be sufficiently accurate the importance of performing this correction in slant range rather than ground range is demonstrated

thermoluminescence chronology of toronto area quaternary sediments and implications for the extent of the midcontinent ice sheet s we report direct dating by thermoluminescence tl methods of key quaternary stratigraphic horizons in the toronto area tl ages indicate that 1 most of the exposed sediments of the don formation at the sampled site were probably deposited during the closing phase of the sangamon interglacial 80 ka oxygen isotope stage 5a not the climatic optimum substage 5e 120 130 ka as generally supposed 2 overlying deltaic strata of the scarborough formation which accumulated in an ice dammed ancestral lake ontario were deposited between 60 and 50 ka early wisconsin oxygen isotope stage 4 3 the sunnybrook diamict overlying the scarborough formation was deposited in the middle wisconsin at 40 45 ka oxygen isotope stage 3 likely by glaciolacustrine processes rather than before 65 ka as previously supposed 4 sediments of the upper thorncliffe formation lying stratigraphically just beneath the last glacial maximum hallton till were deposited at 23 ka consistent with reliable 14 c dating thus the earliest wisconsin incursion of the proto laurentide ice sheet into the lake ontario basin as recorded by the scarborough formation probably did not take place until at least 60 ka and did not extend south and southwest of the toronto area until after 25 ka ice free conditions probably persisted over large areas of midcontinent north america from the end of the illinoian glaciation at 130 ka to the late wisconsin glacial maximum at 20 ka

quaternary continental stratigraphy and neocatastrophism abstract recent papers on pre quaternary stratigraphy have emphasized that the rock record represents only a small portion of geologic time with the gaps representing the majority of elapsed time quaternary continental stratigraphy also yields such evidence in abundance time between dated organic sites in glaciated areas is commonly depicted as filled by glacial ice yet there is much evidence of rapid sedimentation and most deposits could be laid down in short time spans non glaciated areas yield similar evidence because of gaps over which depositional rates are averaged calculated rates are often lower than they really are continental stratigraphy requires attention from many workers supported by much improved dating methods to establish time spans and gaps for the rock record

silver and mercury in single gold grains from the witwatersrand and barberton south africa the contents of silver and mercury in 323 spots on gold grains from seven localities of the witwatersrand palaeo placer and archaean vein deposits from barberton were measured using an electron microprobe the objective was to obtain information on the extent of gold alteration during fluvial transport and post depositional geological processes the results however show that ag and hg are distributed homogeneously in the gold grains studied no indications were found that the gold was transported in solution nor that leaching took place in an oxidizing fluvial environment this strongly suggests that the ag and hg contents in witwatersrand gold grains represent geochemical fingerprints inherited from their eroded primary sources combined analysis for ag and hg in witwatersrand gold grains by electron microprobe can therefore be a valuable tool in establishing the types of primary sources for the gold

testing the application and limitation of stochastic simulations to predict the lithology of glacial and fluvial deposits in central glasgow uk abstract glacigenic and fluvial deposits of variable lithological composition underlie many major cities in europe and north america traditional geological mapping and 3d modelling techniques rarely capture this complexity as they use lithostratigraphic designations which are commonly based on genesis and age rather than lithological compositions in urban areas thousands of boreholes have been and continue to be drilled to facilitate the planning design and construction of buildings and infrastructure while these data may provide the basis for geological maps and 3d models based on lithological interpretation they are too numerous for manual correlation to be undertaken efficiently in this paper we explore the application of largely automated stochastic modelling techniques to develop predictive lithology models for glacial and fluvial deposits in the city of glasgow uk these techniques are commonly used to assess facies variation in oilfield models and are applied here in an urban setting using over 4000 borehole records predictions derived from these methods have been evaluated by removing control data and re running the simulations we demonstrate a moderate improvement in the prediction of lithology when using a lithologically derived stochastic model compared with a conventionally interpolated lithostratigraphic model it is possible to report uncertainty within the resulting models either with probability maps or through a suite of plausible simulations of the lithologies across the study region

evidence for an aeolian origin of the holocene lateritic surface cover of gabon central africa abstract field granulometric and geochemical data are reported for a set of twenty one samples collected at six sites spread over gabon in the extensive lateritic clayey to sandy layer cover horizon which constitutes the upper part of the profiles of surficial formations granulometric analyses show that this material of homogeneous aspect is a mixture of two fractions a clay fraction and a medium to coarse grained sandy fraction relative proportions of these two constituents show strong variations from one site to another but are almost constant from the bottom to the top of a given profile the coarse grained fraction includes lithic elements of local provenance irrespective of their underlying basement the samples display many common geochemical features including a lack of ca na and mg their major element compositions may be accounted by the combination of a discrete number of mineralogical phases namely quartz kaolinite gibbsite fe oxides hydroxides and subordinate k minerals micas the normative contents of aluminous and ferrous phases regularly increase with the weight percent of clays conversely the quartz regularly decreases this inverse relationship is consistent with mixing between an al and fe bearing clay fraction and a coarse grained fraction dominated by quartz correlations between most immobile trace elements and the weight percent of clays indicate a control of those elements by al and fe bearing phases the main exception is for zr and hf as those elements are probably associated with zircons in the coarse fraction because of the control of the trace element distribution by secondary phases the geochemical signatures of all samples are clearly distinct from those of the upper continental crust and any basement rocks thus the trace element characteristics of the cover horizon carry no sign of any source material being the sole consequence of mineralogical sorting prior to deposit from field granulometric and geochemical data an aeolian origin appears as the most probable for the cover horizon geochronological constraints including archaeological data and 14 c dating indicate that this aeolian event took place during the holocene and probably occurred in less than 3000 y additional works will be necessary to assess the global context which made possible this very fast and extended event over large areas of central africa

compensation of terrain azimuthal slope effects in geophysical parameter studies using polarimetric sar data abstract the existence of significant terrain relief reduces the accuracy of algorithms intended to extract geophysical parameters from polarimetric synthetic aperture radar sar images for this reason most inversion studies attempting to estimate biomass crop type snow cover surface roughness or soil moisture from sar data are best done in areas of flat earth in areas which require compensation for topography limited corrections have been made in the past for range slopes using a coregistered digital elevation model dem no corrections have been made however for terrain slope induced polarimetric effects in the azimuthal or along track direction recent methods using polarimetric sar data of measuring terrain slopes in the azimuthal direction have been developed this article presents an algorithm to use these slope estimates to compensate for the effects of azimuthal terrain slopes the algorithm involves rotation of the polarimetric covariance matrix to achieve maximum azimuthal symmetry evidence is given to substantiate the degree to which azimuthal slope effects have been removed from the data nasa airsar p l and c band data obtained for open terrain in death valley national park california 1994 are used to evaluate the compensation algorithm

reply to the discussion by n eyles and a mohajer on analysis and reinterpretation of deformation features in the rouge river valley scarborough ontario eyles and mohajer 2003 begin their discussion by stating that any new information regarding the geology of the rouge river area is to be welcomed but then dismiss the new information contained in our paper godin et al 2002 as bearing the hallmarks of having been completed by outside workers we share eyles and mohajer s view that the deformational features of the rouge river valley are both interesting and important we believe it is valuable and appropriate to have them documented and interpreted by more than one group of researchers thus presenting diverse perspectives it is for this reason that we assembled a multidisciplinary team including structural geologists experienced in neotectonics godin and brown a quaternary geologist with half a century of experience in interpreting glacial features in ontario dreimanis a seismologist specializing in earthquake hazard atkinson and geologists familiar with the stratigraphy of southern ontario dreimanis and armstrong it is interesting to note that although our paper focussed on a structural analysis of deformation features in relation to local ice flow directions 80 of our paper the main criticisms raised by eyles and mohajer 2003 concern our use of literature our understanding of the quaternary stratigraphic framework of southern ontario and interpretation of drumilinoid features and our documentation of subsurface information the following reply addresses these points

evidence for the intra glenwood mackinaw low water phase of glacial lake chicago a 14c age estimate of 13 470 130 bp isgs 1378 from organic material at the base of transgressive lake deposits exposed in a southern lake michigan shore bluff near riverside michigan confirms

pleistocene glacio lacustrine deltaic deposits of the scarborough formation ontario canada abstract the late pleistocene scarborough formation of the lake ontario basin represents a lacustrine deltaic sequence strongly affected by a nearby glacier it shows gradual upward coarsening and thickening of layers from varve like clay rich rhythmites at the base to channelized cross bedded sands at the top thick lensing massive layers cm of silty sand are found interstratified with thin layers of silt and clay in the lower and middle parts of the sequence these massive layers were probably formed by subaqueous gravity flows of material in part derived directly from a glacier absence of pebbles and of other features such as glacial silt pellets suggests dispersal away from the foot of the glacier rather than deposition under floating ice varve like rhythmites pollen and insect fauna indicate subarctic to arctic climatic conditions at the time of sediment deposition the large amount of sand in the upper part of the formation is best explained as derived from active outwash fans similar fans were formed during the last deglaciation in southern ontario and can be observed on the landscape

the effect of topography on sar calibration during normal synthetic aperture radar sar processing a flat earth is assumed when performing radiometric corrections such as antenna pattern and scattering area removal the authors examine the effects of topographic variations on these corrections local slopes will cause the actual scattering area to be different from that calculated using the flat earth assumption it is shown that this effect may easily cause calibration errors larger than a decibel ignoring the topography during antenna pattern removal may also introduce errors of several decibels in the case of airborne systems the effect of topography on antenna pattern removal is expected to be negligible for spaceborne sars the authors show how these effects can be taken into account if a digital elevation model is available for the imaged area the errors are quantified for two different types of terrain a moderate relief area near tombstone az and a high relief area near oetztal in the austrian alps the authors show errors for two well known radar systems the c band ers 1 spaceborne radar system and the three frequency nasa jpl airborne sar system airsar

geological and geochemical controls on the silver content fineness of gold in gold silver deposits abstract a compilation of microprobe fineness data and a re evaluation of bullion production fineness data suggest that the gold fineness model of fisher 1945 can be updated and applied to a wide range of gold mineralised environments the major deposit classes are characterised by the overall average or range of deposits averages and total range of gold fineness values as follows archaean 940 780 1000 slate belt 920 800 1000 plutonic 825 650 970 porphyry 700 1000 650 1000 volcanogenic 650 850 520 870 epithermal 440 1000 0 1000 the archaean including witwatersrand slate belt and plutonic classes are characterised by a high and consistent average fineness and a narrow fineness range there is no clear subdivision within these classes according to deposit style or inferred genesis the porphyry volcanogenic and epithermal classes have a variable average deposit fineness and a wide total range of fineness values within these three classes higher fineness is typical of deposits in andesitic rather than rhyolitic volcanic settings deposits with cu au rather than cu mo or pb zn element associations and deposits with telluride or selenide minerals solubility calculations indicate that in all these environments gold and silver form the same aqueous species with agcl 2 dominating for silver and au hs 2 dominating for gold in all the environments the fluids transport an equal amount of gold and silver in the form of their bisulphide complexes therefore the observed gold fineness values can not be explained by the transporting mechanism only low silver in the ores and higher gold fineness values observed in the archaean plutonic and slate belt environments can be attributed to sulphidation as the dominant mechanism of ore deposition sulphidation of wall rocks destabilises only the bisulphide complexes of gold and silver in contrast epithermal volcanogenic and porphyry environments are characterised by a diversity of ore depositing mechanisms cooling boiling mixing which act alone or in combination and destabilise chloro and bisulphide complexes of gold and silver the high silver concentration in the ores low fineness values and large variation in the fineness values in these environments can be attributed to the complexities in the ore depositing mechanisms

the quaternary stratigraphic record of british columbia evidence for episodic sedimentation and erosion controlled by glaciation the terrestrial quaternary stratigraphic record of british columbia is largely a product of brief depositional events separated by long periods of nondeposition and erosion thick stratified quaternary sediments are present mainly in valleys and coastal lowlands and accumulated during periods of growth and decay of the cordilleran ice sheet at glacial maxima till was deposited over large areas of low and moderate relief however at the same time much of the landscape was eroded by glaciers sedimentation has been more restricted and has occurred at lower rates during nonglacial periods than during glaciations on land the only important sediment accumulation sites during nonglacials have been lakes floodplains and fans however large amounts of sediment have accumulated offshore especially in fjords and basins such as the strait of georgia because of the restricted aspect of sedimentation during nonglacials the stratigraphic record of these periods is meagre in most places true nonglacial uni

mobility of gold and silver in lateritic weathering profiles some observations from western australia experimental evidence suggests that very acid chloride solutions generated in lateritic profiles by ferrolysis oxidation and hydrolysis of iron are responsible for the dissolution of gold and silver au is subsequently reprecipitated by reduction of the aucl 4 super ion with fe super 2 reduction of the agcl complex does not similarly occur because of the relative redox potentials of fe super 2 fe super 3 and ag agcl thus chemical refinement of gold occurs during lateritization the development of low ph and the redistribution of gold and silver in lateritic weathering profiles appear to be more common over granitic and gneissic basement and may be inhibited by the presence of carbonate in the weathering zone of basic rock sequences modified journal abstract