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

a method to retrieve the spectral complex refractive index and single scattering optical properties of dust deposited in mountain snow dust deposition to snow can have regionally important climatic and hydrologic impacts resulting from direct reduction of surface albedo and indirectly from the initiation of snow albedo feedbacks modeling the radiative impacts of dust deposited in snow requires knowledge of the optical properties of both components here we present an inversion technique to retrieve the effective optical properties of dust deposited in mountain snow cover from measurements of hemispherical dust reflectance and particle size distributions using radiative transfer modeling first modeled reflectance is produced from single scattering properties modeled with mie theory for a specified grain size distribution over a range of values for the imaginary part of the complex refractive index k 0 00001 0 1 then a multi step look up table process is employed to retrieve k and single scattering optical properties by matching measured to modeled reflectance across the shortwave and near infrared the real part of the complex refractive index n for dust aerosols ranges between 1 5 and 1 6 and a sensitivity analysis shows the method is relatively insensitive to the choice of n within this range 1 525 was used here using the values retrieved by this method to update dust optical properties in a snow aerosol radiative transfer model reduces errors in springtime albedo modeling by 50 70

southern laurentide ice sheet retreat synchronous with rising boreal summer insolation establishing the precise timing for the onset of ice sheet retreat at the end of the last glacial maximum lgm is critical for delineating mechanisms that drive deglaciations uncertainties in the timing of ice margin retreat and global ice volume change allow a variety of plausible deglaciation triggers using boulder 10 be surface exposure ages we date initial southern laurentide ice sheet lis retreat from lgm moraines in wisconsin usa to 23 0 0 6 ka coincident with retreat elsewhere along the southern lis and synchronous with the initial rise in boreal summer insolation 24 23 ka we show with climate surface mass balance simulations that this small increase in boreal summer insolation alone is potentially sufficient to drive enhanced southern lis surface ablation we also date increased southern lis retreat after ca 20 5 ka likely driven by an acceleration in rising isolation this near instantaneous southern lis response to boreal summer insolation before any rise in atmospheric co 2 supports the milankovic hypothesis of orbital forcing of deglaciations

numeric control on the late glacial chronology of the southern laurentide ice sheet derived from ice proximal lacustrine deposits abstract we used a combination of radiocarbon and osl dating in ice proximal lacustrine silt and clay and outwash sand to estimate when ice of the green bay lobe of the laurentide ice sheet began retreating from its maximum position in south central wisconsin the radiocarbon ages indicate that lakes had formed in the two tributary valleys by 17 2 and 20 1 ka respectively the osl ages indicate that the green bay lobe was at its maximum position from about 26 4 5 1 ka to 21 4 3 3 ka these data provide entirely new chronologic control on late wisconsin marine isotope stage 2 glacial event in the upper midwest as well as the opportunity to directly compare radiocarbon and osl ages in this setting

constraining the late pleistocene history of the laurentide ice sheet by dating the missinaibi formation hudson bay lowlands canada abstract well dated paleorecords from periods prior to the last glacial maximum lgm are important for validating models of ice sheet build up and growth however owing to glacial erosion most late pleistocene records lie outside of the previously glaciated region which limits their ability to inform about the dynamics of paleo ice sheets here we evaluate new and previously published chronology data from the missinaibi formation a pleistocene aged deposit in the hudson bay lowlands hbl canada located near the geographic center of the laurentide ice sheet lis available radiocarbon ams 44 conventional 36 amino acid n 13 uranium thorium u th n 14 thermoluminescence tl n 15 and optically stimulated luminescence osl n 5 data suggest that an ice free hbl may have been possible during parts of marine isotope stage 7 mis 7 ca 243 000 to ca 190 000 yr bp mis 5 ca 130 000 to ca 71 000 yr bp and mis 3 ca 29 000 to ca 57 000 while mis 7 and mis 5 are well documented interglacial periods the development of peat forest bed and fluvial deposits dating to mis 3 n 20 radiocarbon dates 4 tl dates 3 osl dates suggests that the lis retreated and remained beyond or somewhere within the boundaries of the hbl during this interstadial ice sheet models approximate the margin of the lis to southern ontario during this time which is 700 km south of the hbl therefore if correct our data help constrain a significantly different configuration and dynamicity for the lis than previously modelled we can find no chronological basis to discount the mis 3 age assignments however since most data originate from radiocarbon dates lying close to the reliable limit of this geochronometer future work on dating the missinaibi formation using other geochronological methods e g u th osl is necessary in order to confirm the age estimates and strengthen the boundaries of the lis during this period

pattern of southern laurentide ice sheet margin position changes during heinrich stadials 2 and 1 abstract with concerns over rising global temperatures ice sheet stability and implications for sea level rise the responses of former ice sheets to past climate change provide useful insights into linkages between the atmosphere cryosphere and oceans one example is the behavior of the laurentide ice sheet lis during heinrich stadials times of cooler sea surface temperature sst in the north atlantic using existing cosmogenic surface exposure ages varve chronologies radiocarbon ages and optically stimulated luminescence ages from the southern lis margin this report tests the hypothesis that the southern side of the lis advanced during times of surface cooling of the north atlantic this test reconstructs the timing of local glacial maxima and the times immediately pro and preceding them from multiple areas and compares them to the timing of heinrich stadial 2 hs2 26 6 23 6 ka and to the timing of heinrich stadial 1 hs1 19 3 15 3 ka during hs2 southern sector lobes new england region huron erie lobe lake michigan lobe green bay lobe and the chippewa lobe advanced towards their maximum position except for the des moines lobe for which there is no applicable data during hs1 these same lobes experienced substantial retreat but the des moines lobe advanced thus the southern laurentide margin behaved differently during the two heinrich stadials this pattern may be attributed to differing east west temperature gradients across north america and associated changes in atmospheric circulation

quaternary geology and geomorphology of the dinosaur provincial park area and surrounding plains alberta canada the identification of former glacial lobes drainage diversions and meltwater flood tracks abstract the quaternary geology and geomorphology of the lower red deer river drainage basin centred on the dinosaur provincial park badlands provides information on pre late wisconsinan drainage patterns and the dynamics of former lobes of the laurentide ice sheet in western canada patterns of deglaciation proglacial lake evolution and spillway incision are also reconstructed based upon the distribution of surface materials and glacial glaciofluvial landforms the empress group fluvial and glaciolacustrine sediments which could be as young as 27 ka bp infill the precursor red deer river and its tributaries and document the initial advance of glacier ice into southern alberta glaciotectonic disturbance of older sediments and bedrock the production of deformation tills and the construction of a megafluting complex and cupola hills record the advances of a glacier lobe centred over the study area stratified inter and intra till beds record pulses of subglacial meltwater between phases of subsole deformation the thickening of tills towards the margin of the lobe represents a till wedge an expected product of sediment advection by glaciers moving over deformable beds the eastern margin of the glacier lobe is demarcated by the interlobate suffield hummocky moraine belt which contains overprinted thrust ridges which record diachronous oscillations of neighbouring lobes within the ice sheet proglacial and glaciofluvial sediments were deposited in the area in association with proglacial lake bassano patricia which drained eastwards when the suffield moraine was dissected by spillways changes in the size of glacial lake bassano patricia are clearly documented by a sequence of spillway incisions which culminated in the erosion of scabland topography and the initiation of a new course for the red deer river a 15 km southward diversion of the main channel in distinct contrast to the documented incision histories of other small rivers in alberta one tree creek and little sandhill creek did not start major incisions of the quaternary sediments over buried valley positions until the late holocene when environmental conditions were characterized by higher precipitation

optical ages indicate the southwestern margin of the green bay lobe in wisconsin usa was at its maximum extent until about 18 500 years ago abstract samples for optical dating were collected to estimate the time of sediment deposition in small ice marginal lakes in the baraboo hills of wisconsin these lakes formed high in the baraboo hills when drainage was blocked by the green bay lobe when it was at or very near its maximum extent therefore these optical ages provide control for the timing of the thinning and recession of the green bay lobe from its maximum position sediment that accumulated in four small ice marginal lakes was sampled and dated difficulties with field sampling and estimating dose rates made the interpretation of optical ages derived from samples from two of the lake basins problematic samples from the other two lake basins south bluff and feltz basins responded well during laboratory analysis and showed reasonably good agreement between the multiple ages produced at each site these ages averaged 18 2 ka n 6 and 18 6 ka n 6 respectively the optical ages from these two lake basins where we could carefully select sediment samples provide firm evidence that the green bay lobe stood at or very near its maximum extent until about 18 5 ka the persistence of ice marginal lakes in these basins high in the baraboo hills indicates that the ice of the green bay lobe had not experienced significant thinning near its margin prior to about 18 5 ka these ages are the first to directly constrain the timing of the maximum extent of the green bay lobe and the onset of deglaciation in the area for which the wisconsin glaciation was named

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

outburst flood origin of the central kalamazoo river valley michigan usa abstract geomorphic evidence and stratigraphic information from boreholes suggest that the oversized central kalamazoo river valley ckrv in southwest michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the saginaw lobe of the laurentide ice sheet the ckrv occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the lake michigan saginaw and huron erie lobes the course of the ckrv follows an irregular flow path that bisects the kalamazoo moraine of the lake michigan lobe erosional terraces near the mouth of the channel indicate that lake michigan lobe meltwater drained eastward prior to the westward saginaw outburst prior to valley formation the lake michigan lobe had retreated westward to at least the lake border moraine with the lake michigan lobe absent to impede flow drainage from the ckrv proceeded southwesterly until draining into glacial lake chicago near st joseph michigan the outburst originated from a system of saginaw tunnel channels that display convex up flow profiles and contain eskers meltwater drainage transitioned from subglacial to ice marginal and proglacial environments during the interval represented by the outburst the saginaw lobe appears to have been in a relatively stationary position

kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central lower michigan usa abstract in association with an undergraduate honors seminar at michigan state university we studied two small kame deltas in north central lower michigan these recently identified deltas provide clear evidence for a previously unknown proglacial lake glacial lake roscommon in this large basin located in an interlobate upland our first goal was to document and characterize the geomorphology of these deltas because both deltas are tied to ice contact ridges that mark the former position of the retreating ice margin within the lake our second goal was to establish the age of one of the deltas thereby constraining the timing of ice retreat in this part of michigan for which little information currently exists both deltas are composed of well sorted fine and medium sands with little gravel and have broad nearly flat surfaces and comparatively steep fronts samples taken from the upper 1 5 m of the deltas show little spatial variation in texture aside from a general fining toward their outer margins gullies on the outer margins of both deltas probably postdate the formation of the deltas proper we suggest that they formed by runoff during a permafrost period subsequent to lake drawdown we named the ice lobe that once covered this area the mackinac lobe because it had likely advanced into the region across the mackinac straits area five of six optically stimulated luminescence osl ages from one of the deltas had minimal scatter and were within 1000 years of one another with a mean age of 23 1 0 4 ka these ages suggest that the mackinac lobe had started to retreat from the region considerably earlier than previously thought even while ice was near its maximum extent in illinois and indiana and the remainder of michigan was ice covered this early retreat which appears to coincide with a short lived warm period indicated from the greenland ice core formed an opening that was at least occasionally flooded thick and deep fine textured deposits which underlie much of the region probably date to this time our work provides the first evidence of this extremely early ice retreat from central lower michigan occurring almost 4000 years before the southern margin of the ice saginaw lobe had started its retreat from the state

deposition of the late wisconsin johnstown moraine south central wisconsin abstract the johnstown moraine is made up of three different materials the lower part of the sequence consists of closely spaced bodies of boulder gravel which are cylindrical and plunge upglacier several degrees they are interpreted to be esker bodies they grade distally into proglacial outwash fans the esker bodies are overlain by sandy till some of which is uniform and some of which has colour layers the colour layers are a few millimetres to a metre thick drape over the eskers and dip upglacier several degrees both the uniform and layered till have pebbles plunging upglacier several degrees steeper than the dip of the layers both the uniform and layered till are interpreted to have been deposited subglacially probably both by melting out and by lodgement the till is overlain by a thin layer of boulder gravel interpreted to be washed supraglacial sediment

palynological and radiocarbon evidence for deglaciation events in the green bay lobe wisconsin abstract a new and significant site of organic silty sand has been found beneath the valders till at valders quarry in northeastern wisconsin this is now the earliest known late glacial site associated with red till ice advances in the western great lakes area leaves of terrestrial plants washed into a small depression provide a date of 12 965 200 yr b p wis 2293 which is significantly older than the two creeks forest bed ca 11 800 yr b p percentage and concentration pollen diagrams suggest that the site was open and distant from a closed picea forest no wood or picea needles have been found this date is statistically indistinguishable from 12 550 233 yr b p the mean of three dates for the end of inorganic varve sedimentation at devils lake 160 km southwest at the terminus of the green bay lobe assuming that the green bay lobe vacated its outermost moraine in the interval from 13 000 to 12 500 yr b p only a short time was available for retreat of the ice margin over 350 km drainage of red sediment from lake superior into the lake michigan basin readvance of over 250 km retreat of at least 80 km and advance to this site the time for these events appears to have been too short to resolve by current radiocarbon technique this extremely rapid collapse of the green bay lobe has a calibrated age of about 15 000 cal yr b p about that of the dramatic warming seen in the greenland ice cores

towards successful osl sampling strategies in glacial environments deciphering the influence of depositional processes on bleaching of modern glacial sediments from jostedalen southern norway the optically stimulated luminescence osl signals of quartz and k feldspar are known to bleach poorly within some glacial settings and can present a major challenge to dating applications however because the osl signal is extremely sensitive to sunlight exposure history the residual luminescence signals of modern glacial sediments also encode information about transport and depositional processes through examination of the residual luminescence properties equivalent dose de and overdispersion values of a suite of modern glacial sediments from different depositional settings sandar proglacial delta and main meltwater channel this study provides insights not only into which sediments are likely to be fully bleached within glacial settings but also into how osl can be used to trace different depositional processes across sedimentary landforms improved understanding of the processes of sediment bleaching will enable better sample selection and may improve the accuracy and precision of osl dating of glacial sediments the luminescence signals of both coarse grained quartz and k feldspar with similar sediment sources are found to be sensitive to both depositional process and specific depositional setting whereas modern braid bar head deposits from the nigardsdalen ice proximal proglacial delta typically have ages of 3 ka similar depositional features from the fabergstolsgrandane sandur have residual ages of 26 ka exploration of changing residual luminescence signals across individual sandur and proglacial delta braid bar features shows that braid bar head deposits can retain large residual d e values while the partner braid bar tail deposits are almost completely bleached the quartz osl signal and k feldspar irsl50 and post ir irsl250 signals are shown to bleach at the same rate across the same bar feature and the irsl50 k feldspar signal is also shown to be completely bleached for bar tail deposits in nigardsdalen therefore the irsl50 k feldspar signal is suitable for dating some glacial deposits circumventing the challenges associated with dim quartz signals 2014 the authors published by elsevier ltd this is an open access article under the cc by license

glaciofluvial erosional morphology and sediments of the coronation spondin scabland east central alberta spatially discontinuous meltwater channel networks on the canadian prairies are usually interpreted as having formed subaerially in front of the retreating laurentide ice sheet evidence in the coronation spondin scabland east central alberta supports an alternative formation by progressive channelization of a subglacial sheetflow of water the scabland is an integrated channel network with varying degrees of anabranching the channels having highly variable sizes shapes and orientations enhanced scour at some channel confluences reflects contemporaneous channel utilization channels also display convex up concave up and undulatory along channel profiles with some junctions at the same elevations longitudinal grooves in large scale channels are associated with numerous boulder deposits residual hills demarcated by channels display composite and streamlined forms superimposed on residuals are erosional transverse bedforms longitudinal grooves and undulating surfaces that indicate submergence

rapid laurentide ice sheet advance towards southern last glacial maximum limit during marine isotope stage 3 abstract marine isotope stage mis 3 58 28 ka is a period of intermediate global ice volume between mis 4 and the last glacial maximum of mis 2 here we report geologic evidence for southern laurentide ice sheet rapid growth to near its last glacial maximum extent after a period with limited ice in the southernmost hudson bay lowland a14c age on wood in lacustrine sediments interbedded with glacial tills in central eastern wisconsin dates a laurentide ice sheet advance southwards to an extent at least equivalent to at least its 17 ka deglacial limit by 39 1 0 4 ka this advance ended before 30 4 0 9 ka based on another 14c date on wood in lacustrine sediment overlying the till layers this advance is consistent with 14c ages from michigan and iowa and gulf of mexico runoff records that support a concurrent southern laurentide ice sheet advance we infer changes in north american ice volume using ice sheet model simulations from a large ensemble that are consistent with 14c data and gulf of mexico discharge constraints the simulations show the laurentide ice sheet growing from a volume equivalent to 25 30 m of global mean sea level gmsl before 40 ka to 40 45 m of gmsl at 40 ka and reaching 65 70 m gmsl by 30 ka consistent with glacial isostatic adjustment assessments of near to intermediate field sea level data we thus show from our terrestrial field data and ice sheet model simulations that an individual ice sheet can grow rapidly which has only been inferred previously for global ice volume from gsml records

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

global ice volume during mis 3 inferred from a sea level analysis of sedimentary core records in the yellow river delta abstract estimates of global ice volume during the glacial phase of the most recent ice age cycle are characterized by significant uncertainty reflecting the relative paucity of geological constraints on sea level relevant to this time interval for example during the middle stages of marine isotope stage 3 published estimates of peak global mean sea level gmsl relative to the present range from 25 m to 87 m the large uncertainty in gmsl at mis 3 has significant implications for estimates of the rate of ice growth in the period leading to the last glacial maximum 26 ka we refine estimates of global ice volume during mis 3 by employing sediment cores in the bohai and yellow sea that record a migration of the paleoshoreline at 50 37 ka through a transition from marine to brackish conditions in particular we correct relative sea level at these sites for contamination due to glacial isostatic adjustment using a sea level calculation that includes a gravitationally self consistent treatment of sediment redistribution and compaction and estimate a peak global mean sea level of 38 7 m during the interval 50 37 ka with suitable sedimentary core records the approach described herein can be extended to refine existing constraints on global ice volume across the entire glacial period

correlation of late wisconsin glacial phases in the western great lakes area late wisconsin glacial phases of the superior lobe in wisconsin and adjacent minnesota are tentatively correlated across northern wisconsin and adjacent michigan to phases of the green bay and lake michigan lobes spanning the period from about 26 000 yr b p to about 9500 yr b p 7 phases of the late wisconsin laurentide ice sheet are discussed but only 2 of these are precisely dated ice advanced out of the basins of lakes superior and michigan and stabilized during the st croix hancock phase the most extensive late wisconsin phase in most of the area between about 18 000 and 15 000 yr ago following the st croix hancock phase the general wasting of the ice was interrupted by stillstands or readvances of the ice margin during the intermediate and mountain phases the ice then wasted into the superior basin before readvancing over a landscape containing ice masses from earlier phases during the winegar early athelstane phase this phase is believed to have occurred just prior to growth of the two creeks forest in eastern wisconsin the ice then wasted back and advanced three more times during the marenisco late athelstane porcupine about 11 000 yr b p and marquette about 9900 yr b p phases

late wisconsin landform distribution and glacier bed conditions in wisconsin abstract the late wisconsin laurentide ice sheet advanced across permafrost and reached its maximum extent in wisconsin between about 18 000 and 15 000 years ago deep permafrost persisted in southern wisconsin until about 14 000 years ago and in northern wisconsin until about 13 000 years ago we suggest that during maximum glaciation a zone about 5 km wide in the south and 20 km wide in the north along the margin of the late wisconsin glacier was frozen to its bed meltwater from farther behind the margin where the bed was at least locally thawed cut a series of closely spaced tunnel channels through the frozen bed zone these channels most likely formed episodically and they were the source for much of the meltwater stream sediment deposited in broad outwash plains beyond the ice margin frozen bed conditions near the margin also likely contributed to increased upward shearing of sediment and the accumulation of thicl supraglacial sediment in northern areas up ice from the frozen bed zone the glacier bed was at least locally thawed in a zone about 75 km wide extensive drumlin fields formed in the area of the bed that was thawed by about 13 000 years ago permafrost melted in northern wisconsin and thawed bed conditions probably extended to the ice margin throughout wisconsin and adjacent areas after about 13 000 years ago in northern wisconsin the glacier was sliding on its bed and forming drumlins out to the ice margin and thick supraglacial sediment no longer accumulated