Bay Lobe Research Articles

Modeling the deglaciation of the Green Bay Lobe of the southern Laurentide Ice Sheet

We use a time‐dependent two‐dimensional ice‐flow model to explore the development of the Green Bay Lobe, an outlet glacier of the southern Laurentide Ice Sheet, leading up to the time of maximum ice extent and during subsequent deglaciation (c. 30 to 8 cal. ka BP). We focus on conditions at the ice‐bed interface in order to evaluate their possible impact on glacial landscape evolution. Air temperatures for model input have been reconstructed using the GRIP δ8O record calibrated to speleothem records from Missouri that cover the time periods of c. 65 to 30 cal. ka BP and 13.25 to 12.4 cal. ka BP. Using that input, the known ice extents during maximum glaciation and early deglaciation can be reproduced reasonably well. The model fails, however, to reproduce short‐term ice margin retreat and readvance events during later stages of deglaciation. Model results indicate that the area exposed after the retreat of the Green Bay Lobe was characterized by permafrost until at least 14 cal. ka BP. The extensive drumlin zones that formed behind the ice margins of the outermost Johnstown phase and the later Green Lake phase are associated with modeled ice margins that were stable for at least 1000 years, high basal shear stresses (c. 100 kPa) and permafrost depths of 80–200 m. During deglaciation, basal meltwater and sliding became more important.

A numerical investigation of ice-lobe–permafrost interaction around the southern Laurentide ice sheet

AbstractPermafrost existed around and under marginal parts of the southern Laurentide ice sheet during the Last Glacial Maximum. The presence of permafrost was important in determining the extent, form and dynamics of ice lobes and the landforms they produced because of influences on resistance to basal motion and subglacial hydrology. We develop a two-dimensional time-dependent model of permafrost and glacier-ice dynamics along a flowline to examine: (i) the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology, and (ii) the influence of permafrost on ice motion and surface profile. The model is applied to the Green Bay lobe, which terminated near Madison, Wisconsin, during the Last Glacial Maximum. Simulations of ice advance over permafrost indicate that the bed upstream of the ice-sheet margin was frozen for 60–200 km at the glacial maximum. Permafrost remained for centuries to a few thousand years under advancing ice, and penetrated sufficiently deep (tens of meters) into the underlying aquifer that drainage of basal meltwater became inefficient, likely resulting in water storage beneath the glacier. Our results highlight the influence of permafrost on subglacial conditions, even though uncertainties in boundary conditions such as climate exist.

Paleobiology of the Sand Beneath the Valders Diamicton at Valders, Wisconsin

Previously undescribed pollen, plant macrofossils, molluscs, and ostracodes were recovered from a 2.5-m-thick glaciolacustrine unit of silty sand and clay at Valders, Wisconsin. The interstadial sediment was deposited about 12,20014C yr B.P. after retreat of the Green Bay lobe that deposited diamicton of the Horicon Formation, and before advance of the Lake Michigan lobe that deposited the red-brown diamicton of the Valders Member of the Kewaunee Formation. Fluctuations of abundance ofCandona subtriangulata, Cytherissa lacustris,and three other species define four ostracode biozones in the lower 1.7 m, suggesting an open lake environment that oscillated in depth and proximity to glacial ice. Pollen is dominated byPiceaandArtemisia,but the low percentages of many other types of long-distance origin suggest that the terrestrial vegetation was open and far from the forest border. The upper part of the sediment, a massive sand deposited in either a shallow pond or a sluggish stream, contains a local concentration of plant macrofossils. The interpretation of a cold open environment is supported by the plant macrofossils of more than 20 species, dominated by those of open mineral soils (Arenaria rubella, Cerastium alpinumtype,Silene acaulis, Sibbaldia procumbens, Dryas integrifolia, Vaccinium uliginosumvar.alpinum, Armeria maritima,etc.) that in North America occur largely in the tundra and open tundra–forest ecotone of northern Canada. Ice-wedge casts occur in the sand.

Genesis of streamlined landforms and flow history of the Green Bay Lobe, Wisconsin, USA

The distribution of streamlined landforms in southeastern Wisconsin suggests that drumlins and flutes formed during several phases of the Green Bay Lobe between 18 and 14,000 BP. The largest group of drumlins formed during a still-stand of the ice margin during the Johnstown phase, presumably about 18–16,000 BP Flutes and smaller drumlins are superimposed on larger forms, and larger drumlins are remolded. This indicates that drumlin modification continued during retreat. Three fields containing smaller drumlins formed after ice re-advanced a short distance or stabilized during the Green Lake, Rush Lake, and St. Anna phases about 16–14,000 BP The drumlin-forming process included erosion and deformation of pre-existing ice-marginal and proglacial sediments. Drumlins associated with the Johnstown phase show an increase in length up glacier. This is probably the result of variations in flow velocity, length of time of drumlin formation, and sediment availability. Flutes and small drumlins are associated with retreat moraines and formed near a thin, retreating ice margin. Ice surface profile reconstructions suggest that margins were relatively steep during the Johnstown, Milton, Green Lake, and early Rush Lake phases. During the Lake Mills and late Rush Lake phases, when flutes were forming, the ice surface slopes were lower and margins were retreating. During retreat minor sublobes developed, some perhaps resulting from surges into small proglacial lake basins. Thus, steep ice margins and driving stresses on the order of 15–25 kPa were typical during drumlin formation. The formation of flutes, and the remolding of larger drumlins into smaller forms, took place beneath gently sloping ice of retreating margins associated with lower driving stresses (< 10 kPa).

Palynological and Radiocarbon Evidence for Deglaciation Events in the Green Bay Lobe, Wisconsin

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 closedPiceaforest. No wood orPiceaneedles 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.

Using Hydrogeochemical Methods To Evaluate Complex Quaternary Subsurface Stratigraphy Block Island, Rhode Island, USA

One of the major problems in hydrogeologic investigations of glaciated regions is the determination of complex stratigraphic relationships in the subsurface where insufficient information is available from drilling and geophysical records. In this paper, chemical characteristics of groundwater were used to identify stratigraphic changes in glacial deposits that were previously inferred on Block Island, Rhode Island, USA, an emergent remnant of the late Wisconsinan terminal moraine, located approximately 16 km south of the Rhode Island mainland. Two chemically distinct water types are recognized on the island: 1) high-iron, characterized by dissolved silica levels in excess of 20 mg/L, bicarbonate greater than 30 mg/L and dissolved iron ranging from 1–20 mg/L; and 2) low-iron, characterized by dissolved silica levels below 16 mg/L, bicarbonate less than 30 mg/L, and less than 0.3 mg/L dissolved iron. The spatial distribution of iron-bearing minerals and organic matter and the resulting redox conditions are believed to control the occurrence of high-iron groundwater. The high-iron waters occur almost exclusively in the eastern half of the island and appear to coincidence with the presence of allochthonous blocks of Cretaceous-age coastal-plain sediments that were incorporated into Pleistocene-age deposits derived from the Narragansett Bay-Buzzard's Bay lobe of the Late Wisconsinan Laurentide ice sheet. The low-iron waters occur in the western half of the island, where the occurrence of these Cretaceous-age blocks is rare and the sediments are attributed to a sublobe of the Hudson-Champlain lobe of the Late Wisconsinan ice-sheet.

Tracking the sources of icebergs with lead isotopes: The provenance of ice‐rafted debris in Heinrich layer 2

The provenance of ice‐rafted debris (IRD) deposited in the North Atlantic before, during, and after Heinrich event 2 has been determined through measuring the lead isotopic composition of single feldspar grains and multiple‐grain composites from the larger than 150‐µm size fraction, from cores from the eastern and western North Atlantic and from the Labrador Sea. Single‐grain analyses are used to identify the specific continental sources of the IRD, whereas composite samples are used to assess the relative IRD contributions from different sources. All single grains from Heinrich layer 2 (H 2) as well as H 2 composites plot along a correlation line on a 207Pb/204Pb versus 206Pb/204Pb diagram characteristic of the Churchill province of the Canadian shield. This is yet another strong piece of evidence that this Heinrich event was dominated by a massive iceberg discharge of the Laurentide ice sheet lobe located over Hudson Bay. In contrast, single grains from the ambient glacial sediment (above and below H 2) have multiple sources: many of them also lie along the correlation line with H 2 grains, but many others have Pb signatures consistent with derivation from the Grenville province and the Appalachian range in North America and possibly from Scandinavia and Greenland. Composites from the ambient sediment generally lie well to the right of the H 2 reference line in agreement with the results of the single‐grain analyses. The evidence provided by lead isotopes regarding the dominant role played by the Hudson Bay lobe of the Laurentide ice sheet in the development of the Heinrich events lends support to the binge/purge model advanced by MacAyeal [1993a, b] that invokes trapping of geothermal heat by the base of the icecap and subsequent basal melting as the mechanism that triggered the Heinrich events.

Lobal interactions and rheologic superposition in subglacial till near Bradtville, Ontario, Canada

Structural, stratigraphic, and lithologic data from a section 69 m long of Catfish Creek drift (north shore of Lake Erie) tell a complex story of two competing glacial lobes. Stone surface features and orientations indicate that stones rotated in viscously deforming, fine‐medium textured subglacial till prior to final emplacement. Fractures, shears, and attenuated sediment lenses in tills reveal that they experienced some brittle shear superposed on ductile shear during till dewatering and stiffening. The Huron‐Georgian Bay lobe advanced first from the northwest, deforming interstadial sediments and depositing subglacial till. Next, southward confluent flow of the Huron, Georgian Bay, and Erie lobes carved subglacial troughs into sediments and deposited (then deformed) bouldery deformation till by squeeze flow. The northwest flowing Erie lobe then prevailed, depositing deformation till, subglacial aquatic sediments, and mudflows. Finally, a pavement‐bearing, hybrid deformation‐lodgement till covered the section. Till formation was mainly by subglacial viscous flow with minor lodgement superposed as water content decreased and some fines were probably winnowed. This implies that till deformation probably accounted for much of the glacier movement. Therefore, rapid ice flow could have occurred over the section, along the southern margin of the Laurentide Ice Sheet.

Surface form of the southern Laurentide Ice Sheet and its implications to ice-sheet dynamics

Reconstructions of the ice-surface morphology of several lobes of the southern Laurentide Ice Sheet reinforce previous arguments that this sector of the ice sheet was thin and low sloping. Driving stresses, estimated from the geometry of the reconstructed ice surfaces, are 0.7-4.3 kPa for the 14 ka Des Moines Lobe, 0.9-1.2 kPa for the 14 ka James Lobe, 0.9-1.7 kPa for the 18-20 ka Lake Michigan Lobe, 1.8-2.9 kPa for the 15-18 ka Chippewa Sublobe, and 17-22 kPa for the 15-18 ka Green Bay Lobe. Previous estimates of rates of ice-margin advance (450-2,000 m/yr) indicate moderate-to-fast ice velocities for the ice lobes. Reconstructed driving stresses and velocity estimates of the Des Moines, James, and Lake Michigan Lobes are analogous to the distal ends (ice Plains) of low-sloping (0.4 X 10 -3 ) but fast moving (500 m/yr) West Antarctic ice streams, whose dynamics have been attributed to sliding and/or subglacial sediment deformation by pervasive shear. These reconstructions support recent models of the Laurentide Ice Sheet which include movement by sliding or by subglacial sediment deformation along its southern, western, and northwestern sectors; evidence for either mechanism should be represented in the sedimentologic and geomorphic records. Thin ice in these regions indicates that the Laurentide Ice Sheet contained less ice volume and represented less of an orographic obstacle to atmospheric circulation than has been considered in models of the ice sheet on a rigid bed with steep profiles.

Correlation of glacial deposits of the Huron, Lake Michigan and Green Bay Lobes in Michigan and Wisconsin

Michigan and eastern Wisconsin were glaciated several times during the Pleistocene. Ice erosion overdeepened river valleys in the weaker units of the sequence of sedimentary rocks now exposed as a result of structural basining. Glacial erosion led to development of the three relatively deep bedrock basins, now occupied by Lakes Huron, Michigan, and Superior. As a result, whenever an ice margin crossed the area it had a lobate form, with ice tongues extending relatively far south in the bedrock basins while much of the area between the lobes was ice-free. Lobe margins within the basins terminated in proglacial lakes. The ice lobes of importance in the area are (a) the Huron lobe and its Saginaw sublobe, (b) the Lake Michigan lobe, and (c) the Green Bay lobe (Fig. 1). The granulometry and mineralogy of the drift related to each lobe reflect the nature of both the bedrock and older surficial units upice. In much of the area, the glacially-related deposits are over 30 m thick, and in some places the thickness is more than 300 m. The surface deposits nearly everywhere are late Wisconsin in age, and relatively little is known of the glacial history of the area prior to that time, Formal names have not been established for lithostratigraphic units in Michigan, and most units in Wisconsin have only recently been formally defined (Mickelson et al., 1984).

Discussion on a tectonic model for the emplacement of the Main Donegal Granite, NW Ireland

P rofessor W. S. P itcher remarked: Dr Hutton has enthusiastically addressed himself to the main problem highlighted by the previous work: the reason for the wide variety of emplacement mechanisms within coeval and contiguous plutons at the same level in the crust, central to which is the relationship in time between the Main Donegal Granite and the localized but intense deformation. This new structural analysis clearly establishes the presence of an important sinistral shear component, and my reservations concern only the timing and the magnitude of the calculated displacements. Concerning the latter, the evidence is that where the ductile shear zone leaves the Main Donegal Granite pluton it seems not to displace the contact zone, and where it runs off SSW it barely displaces an earlier dislocation known as the Knockateen slide. I am equally in doubt of the extension of the postulated shear zone far into northern Fanad, unless it has been conveniently cut out by movement on the post-shear Cashelmore Fault. Within the granite outcrop itself, where the shear zone runs along the apparent boundary between the Trawenagh Bay lobe and the Main Granite, to the S of Meenderryherk, a train of xenoliths straddles the zone of deformation, by which it is distorted but not dislocated. I conclude that whilst sinistral rotational strain has been proved, the displacements suggested seem excessive. I am much attracted to the proposed model whereby magma was emplaced into space created by a curvature in an active shear zone, particularly so as the early

Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin: Discussion and reply

Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin: Discussion and reply

Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin: Discussion and reply

Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin: Discussion and reply

Till stratigraphy and late glacial events in the Lake Michigan Lobe of eastern Wisconsin

Four late Wisconsinan reddish-brown tills are present along the Lake Michigan shoreline in eastern Wisconsin. These tills are distinguished by differences in grain-size distribution, clay mineral content, and stratigraphic position. The Ozaukee and Haven tills underlie the Two Creeks Forest Bed. The younger Valders Till, although not present at a forest bed locality, is also pre-Twocreekan age based on several arguments including correlation with tills of the adjoining Green Bay Lobe. One Greatlakean age till, the Two Rivers Till, has been recognized, and this clearly overlies the Two Creeks Forest Bed. As previously reported, we conclude that the Valders Till is most likely of pre-Twocreekan age and that “Valderan” is an inappropriate term as a substage name for post-Twocreekan time and that the use of the term “Greatlakean” is justified by stratigraphic studies.

Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin

Advances of the Green Bay Lobe deposited at least three till sheets that are late Woodfordian age and younger. In the western part of the lowland, the tills are distinguished on the basis of stratigraphic position, texture, color, and depth of leaching. In the central part of the lowland, tills are covered by lacustrine sediment; on the east side, however, a similar sequence of tills is present. Here till units are distinguished on the basis of stratigraphic position, magnetic susceptibility, and depth of leaching. The Chilton till, which is overlain by Two-creekan wood at one locality, is correlative with the Valders Till of the Lake Michigan lowland, as is the age-equivalent Kirby Lake till. One Greatlakean till, correlative with the Two Rivers Till of the Lake Michigan lowland, overlies forest beds at several localities.

Heavy mineral assemblages in tills and their use in distinguishing glacial lobes in the Great Lakes region

Two main source areas of heavy minerals in tills have been defined in the Great Lakes region: a source in the Superior and Southern Provinces and another in the Grenville Province. The Superior–Southern source is typified by low heavy mineral content and high epidote percentage in contrast to the Grenville source which has a high content of heavy minerals of which garnet, tremolite, and to a lesser extent sphene and orthopyroxene are characteristic. The Huron lobe tills have a mineral suite characteristic of the Superior–Southern source. Two subsources can be distinguished in the Superior–Southern area; however, they are too limited in extent to be characteristic of major glacial lobes. Two other subsources have been identified in the Grenville provenance area: a western Grenville subsource containing abundant garnet and having a low purple–red garnet ratio; and an eastern Grenville subsource distinguished by high garnet and tremolite content and a garnet ratio generally greater than one. The western and eastern Grenville subsources are the provenance areas for the tills of the Georgian Bay lobe and the Ontario–Erie lobe respectively. A possible third Grenville subsource in the Adirondack Mountains is distinguished from other Grenville sources by a lower heavy mineral content and more abundant orthopyroxene and magnetic minerals. This assemblage may be characteristic of the southern portion of the Ontario–Erie lobe.

La función morfogenética de las Islas del Cabo de Hornos en el Wurm Superior

In the southern end of Chile and South America (55 to 56 S.) there are forms wich allow to formulate the following by pothesis:In the southern end, the action and movement field of the ice field during the last glaciation must be reconstructed as it follows: The mountain range Peninsula Hardy (Hoste Island) Wollaston Islands, wich is proposed to appeal Cape Horn (Hoste Island) Wollaston Islands, wich is proposed to appeal Cape Horn Cordillera in the paleogeographic sense, was the break up center of the ice field toward the North as well as the South. Consequently, Nassau Bay acted as glacigenic piedmont during an alaskian type glaciation.The morainic system of the southern coast of Navarino and Lennox islands is related to the genesis of the Windhond Bay lobe in an area of piedmont lakes, showing the push of the ice mantle from the South on the platform wich-paleogeographically can be called Nassau- Windhond glacigenic piedmont.This hypothesis is different to that of KRANCK and CALDENIUS, whose theory assumes that the ice push was from the N W (Darwin Range). The new hypothesis is proved with the use of morphological stratigraphical, sedimentological and geochronological methods.The results show that during the Dryas (Gotiglacial and Finiglacial) the ice advanced fragging eroded materials from the Cape Horn mountains range. This involucres new criteria to establish the age of the glacigenic and coastal forms in the area, with reference to Upper Wurm's stadia.

Pre-Twocreekan age of the type Valders till, Wisconsin

Red tills deposited by post-Twocreekan (Valderan) ice advances of the Green Bay and Lake Michigan Lobes in eastern Wisconsin do not extend to the type locality of the Valders till. The post-Twocreekan ice of the Lake Michigan Lobe terminated at the Two Rivers Moraine, 30 km northeast of Valders. Likewise, geomorphic criteria and depth of carbonate leaching indicate that post-Twocreekan ice of the Green Bay Lobe did not reach Valders from the west.

Till Stratigraphy in Parts of Southwestern Ontario

Late Wisconsinan fluctuations of the Huron, Georgian Bay, Ontario, and Erie glacial lobes gave rise to a complex sequence of interfingering till sheets in the area between Stratford and Toronto, Ontario. Tills are the basis of establishing the stratigraphy of the area because of their distinctive and consistent characteristics. New names (Tavistock Till, Stratford Till, Stirton Till, Mornington Till, Elma Till, Maryhill Till, Pottery Road Formation) are proposed to replace previous informal names. The extent of Wentworth Till and Halton Till is revised. Subdivision of the Thorncliffe Formation into three members and dropping of the name Leaside Till are proposed. While a small area of older till is exposed between Woodstock and Waterloo, most tills are of Port Bruce Stadial age, and some are of Port Huron Stadial age. Probable Middle Wisconsinan interstadial deposits are now known from the interior of southwestern Ontario, as well as from previously described sites near Lake Erie and Toronto. Although over 16,600 sq km of mapping has been carried out in the region in the last 15 yr, only the deposits of the Erie and Ontario glacial lobes are relatively well known; sequences of Huron and Georgian Bay lobe deposits remain inadequately known or poorly understood.

PLEISTOCENE GEOLOGY OF THE DOOR PENINSULA, WISCONSIN

Research Article| July 01, 1957 PLEISTOCENE GEOLOGY OF THE DOOR PENINSULA, WISCONSIN F. T THWAITES; F. T THWAITES WISCONSIN GEOLOGICAL SURVEY, UNIVERSITY OF WISCONSIN, MADISON 6, WIS.; DEPARTMENT OF GEOGRAPHY, THE CATHOLIC UNIVERSITY OF AMERICA, WASHINGTON 17, D. C. Search for other works by this author on: GSW Google Scholar KENNETH BERTRAND KENNETH BERTRAND WISCONSIN GEOLOGICAL SURVEY, UNIVERSITY OF WISCONSIN, MADISON 6, WIS.; DEPARTMENT OF GEOGRAPHY, THE CATHOLIC UNIVERSITY OF AMERICA, WASHINGTON 17, D. C. Search for other works by this author on: GSW Google Scholar Author and Article Information F. T THWAITES WISCONSIN GEOLOGICAL SURVEY, UNIVERSITY OF WISCONSIN, MADISON 6, WIS.; DEPARTMENT OF GEOGRAPHY, THE CATHOLIC UNIVERSITY OF AMERICA, WASHINGTON 17, D. C. KENNETH BERTRAND WISCONSIN GEOLOGICAL SURVEY, UNIVERSITY OF WISCONSIN, MADISON 6, WIS.; DEPARTMENT OF GEOGRAPHY, THE CATHOLIC UNIVERSITY OF AMERICA, WASHINGTON 17, D. C. Publisher: Geological Society of America Received: 02 Mar 1955 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1957, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1957) 68 (7): 831–880. https://doi.org/10.1130/0016-7606(1957)68[831:PGOTDP]2.0.CO;2 Article history Received: 02 Mar 1955 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation F. T THWAITES, KENNETH BERTRAND; PLEISTOCENE GEOLOGY OF THE DOOR PENINSULA, WISCONSIN. GSA Bulletin 1957;; 68 (7): 831–880. doi: https://doi.org/10.1130/0016-7606(1957)68[831:PGOTDP]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The area described completes the detailed mapping of the glacial geology of the Green Bay lobe. The drift belongs to two substages of the Wisconsin stage of glaciation. The major topographic features due to glaciation are the result of the Cary substage. Above this drift lies the till of a later substage, tentatively named Valders because its relation to the Mankato drift of Minnesota is unknown. Separating the two drifts is the Forest Bed which indicates a retreat of the ice margin far enough to free from ice both the Straits of Mackinac and the entire St. Lawrence valley. The advance of the Valders ice buried the two creeks Forest Bed with lake deposits formed in front of the ice. The age of this deposit by radiocarbon dating is about 11,400 years. The Valders till is red and is high in clay and silt because the ice readvanced over red lake clays formed during the Two Creeks interval of recession. Valders till smoothed and almost obliterated Cary land forms but was so thin over wide areas that it is no longer identifiable. These areas were not nunatacks. When the Valders ice receded, lakes were again formed in front of it. Four outlets of Lake Oshkosh in the Green Bay lowland across the Niagara cuesta to Lake Chicago in the Lake Michigan basin are described. Opening of the last outlet caused the two lakes to merge into Lake Algonquin. Ice was not far away then since varved clays accumulated in this lake. Further recession of the ice margin uncovered an outlet to the northeast which caused the water level to fall about 350 feet below that of the present. Evidence of this low level, now named Lake Chippewa, is described from this area. Rise of the land to the northeast caused the water to rise to the level of Lake Nipissing about 20 feet above the present. Erosion of the modern outlet of lake Huron caused the fall to present conditions. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.