On the Îles de la Madeleine, a rock platform as much as 20 m asl, locally with clam borings, is correlated to the regional interglacial surface at 2–8 m; its anomalous height may be a consequence of salt tectonics. Overlying lagoonal and paludal organic beds, one with Th/U ages of 89–101 ka, record the Sangamonian climatic optimum (substage 5e), which culminated in forest more thermophilous than that of the Holocene optimum. Overlying littoral gravel and sand, considered analogous to sediments in present-day tombolos, and organic beds with less temperate pollen types were deposited during the marine transgressive climax of substage 5e and thus indicate that sea level remained high after the thermal optimum, as in Holocene time. Cold-based Early Wisconsinan ice, probably centred on the Magdalen Shelf, tectonized bedrock and interglacial beds and deposited till upon them. Periglacial features indicate a subsequent long cold period. An organic bed dating from 11.3 to 10.6 ka records a warm interval followed by cooling. Buried peat, a submerged fossil sea cliff, and barrier beaches record a marine transgression during the late Holocene.
Quaternary deposits in northeastern Manitoba are related to pre-Wisconsin and Wisconsin glaciations, the Sangamon Interglaciation ,and postglaciallakes and seas. During the Wisconsin Glaciation, the map area was continually glaciated by Laurentide ice from two centres of outflow. Keewatin ice flowed southward and deposited a sandy to bouldery granitic till sheet, the surface of which is divided into belts of rib moraine and crevasse fillings. A second ice mass, centred over Hudson Bay, flowed westwards and deposited several silty calcareous till sheets, the uppermost of which is gently ridged by grounding-line moraines. The position of convergence of the two ice masses varied during the course of glaciation. A major segmented interlobate kame moraine, which was deposited largely during de glaciation, marks the final confluence. Lake Agassiz covered the area vacated by the receding glaciers and persisted as long as ice sheets blocked drainage into Hudson Bay. Turbidite sands and varved or massive clays deposited into this water body cover the southern part of the region. Hudson ice disintegrated suddenly about 7800 (or 8000) BP, and the glacioisostatic Tyrrell Sea flooded areas below 180 m elevation; the land continues to emerge at a rate of 40 cm per century. A major raised beach, formed about 7200 BP, constitutes a major aggregate deposit. Icy muskeg forms the terrain south of Seal River. Frost-riving of bedrock and aggradation or degradation of ground ice are current periglacial processes. Areas east of the Great Beach lie within the zone of continuous permafrost; those to the west lie in discontinuous permafrost. Because ground temperatures are near 0 C, the region is extremely sensitive to climatic or man-induced changes in thermal regime: a small change in ground temperature can produce major terrain disturbances. Permafrost has also limited the buffering capacity of the soils to counteract the effects of acid rain. The surface till sheet has anomalously high concentrations of uranium north of Seal River and interesting gold associations near Great Island.
Surficial mapping and geologic information on the nature and evolution of surficial materials in the Slave geologic province indicate that the geotechnical properties and potential ground ice contents associated with these materials depend largely upon their provenance, depositional conditions, and the postglacial climatic history. This information may be used to provide a regional-scale view of the distribution of ground ice conditions and terrain sensitivities associated with various surficial materials. In till veneers and blankets, ground ice content is generally low, as suggested by lack of thermokarst and other permafrost features. However, distinctive surface relief in hummocky till including kettle depressions, rim-ridges, and shallow thaw flowslides may be attributed to massive ice, resulting in sensitive till terrain. Although many outwash sediments have low ice contents near the surface, massive ice ranging from 5 to 10 m thick is present in some eskers and ice-contact outwash sediments. These are associated with thermokarst, slope movement, and collapse features, indicative of meltout or creep of large bodies of massive ice. The terrain sensitivity associated with these deposits is typically low to moderate, due to the coarse-grained nature of the sediments. In contrast, terrain sensitivity is high, and active-layer detachment slides are common along the Coronation Gulf coast where frozen silty clay marine sediments contain a wide range of ice contents. Results from this study may be applied to a much more extensive area of the glaciated western Arctic mainland and adjacent Arctic coastal plain in which materials with a similar glacial history are found.
This report presents the field database and analytical results from the Geological Survey of Canada's 2010 to 2012 surficial geology mapping and till sampling campaign in the north Wager Bay project area, mainland Nunavut. An overview of the Quaternary geology of this area is provided together with an interpretation of till provenance, as well as a discussion on the implications for mineral exploration. Field observations and surficial geological mapping indicate the region is key for the glacial history reconstruction of the northeastern part of the Keewatin Sector of the Laurentide Ice Sheet. Most of the study area was located within an extensive onset zone of a large ice stream flowing north into Committee Bay during the last glaciation and early deglaciation, from an ice divide located over and/or south of Wager Bay. Major ice-flow reversals into Repulse Bay and Wager Bay, as a result of drawdown into the opening marine waters in Hudson Bay, are indicated for the latest deglaciation phases. Coldbased ice remnant masses over the uplands north of Wager Bay preserved relict, weathered and fresh glacial landscapes at the end of deglaciation. Although there is evidence of multiple ice-flow directions in the study area, the main ice-flow phase, which converges north (NNE to NNW) towards Committee Bay, is the predominant direction of glacial transport and shaped most prominent streamlined landforms. The carbonate clast content and Al2O3 concentrations in surface till indicates relatively long glacial transport distances linked to glacial dispersal by the ice stream. Mg-rich olivine, many having >Fo90 and high NiO contents, are abundant in till in the center of the study area where a frost-shattered ultramafic lamprophyre boulder was found at the surface. Location of the boulder, its distinctive composition, and the olivine in till distribution in conjunction with the glacial transport history, suggest an ultramafic bedrock source other than kimberlite fields known in the region. In the western part of the study area south of Walker Lake, forsteritic olivine and chromite grains in till, locally coincident with ultramafic boulders, form a 35 km-long NNE dispersal train. This dispersal plume points to olivine-rich crustal rocks within undifferentiated Archean supracrustal rocks, and suggests these rocks have potential to host Ni-Cu-PGE mineralization. In addition to known Penhryn Group rocks and extensions of this belt to the southwest, there are suspected but poorly mapped strands of supracrustal rocks between Beach Pt and Wager Bay which show potential for base- and/or preciousmetal mineralization. More detailed till sampling, prospecting and bedrock mapping is required to better assess mineral potential in these areas.
Evidence for Middle Wisconsinan ice limits and climates comes from sites scattered around the periphery of the Laurentide Ice domain and from the Hudson Bay Lowlands. Interpretations are based on dated wood, peat, shell and sediment; biological climate indicators (chiefly cool-climate indicators); and stratigraphie sequences of both glacial and nonglacial units. The best evidence comes from the prairie provinces and the Great Lakes areas, both of which indicate substantial ice retreat from earlier southern glacial limits, and cool, boreal-tundra climates. The western arctic may have experienced an early warm period but both the western arctic — northwestern plains and eastern maritime areas may later have become ice accumulation areas. Three maps portray various possible ice limits. The first shows substantial ice cover in the arctic, but reduced ice cover in the prairies and Great Lakes, and expanded maritime ice caps (rather than Laurentide Ice) in the southeast and on Baffin Island. This ice mass distribution may reflect Middle Wisconsinan shifts in air masses and ocean currents. Ice volumes generated by this model are in accord with the marine oxygen isotope record and perceived global sea level changes. A modification to this model, which resolves some of the controversy in the Hudson Bay Lowlands, shows a calving bay penetrating into the heart of the ice sheet, induced by dynamic instability of the marine-based ice mass in Hudson Bay during relatively high glacial isostatic and eustatic seas. A third reconstruction portrays extensive climatically induced déglaciation and retains Laurentide ice only in parts of the northwest and Labrador-Ungava, with local ice in the Appalachian-Atlantic region. This model is based on alternative genetic interpretations of lithologic units and reassessment of age assignments.
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