Northwestern Manitoba constitutes a gently rolling pre-Quaternary peneplain which was subsequently modified by Quaternary processes. The surface deposits and landforms are a product of two confluent ice masses that occupied the region during the last glaciation,
and of the glacial lakes which succeeded the receding glaciers. Keewatin ice flowed southwards across the region and deposited a sandy to bouldery till sheet whose surface is divided into belts of transverse and longitudinal bedforms. The radial moraines and long, massive, regularly spaced eskers
which interrupt the till blanket attest to the importance of meltwater within the Keewatin ice domain. The orientation of glacial features systematically changed as the Keewatin ice divide migrated eastwards; one limb of this divide stagnated near Caribou Lake. A second major ice mass, from an ice
divide over Hudson Bay, flowed westwards across the southern part of the area and deposited several calcareous, silty till sheets, the uppermost of which is gently ridged with grounding line moraines. The zone of convergence of Keewatin and Hudsonian ice shifted over time, but the location of final
convergence is marked by the Knife River Interlobate Moraine. During deglaciation, Lake Agassiz covered the area vacated by the receding ice sheets and persisted as long as glacier ice blocked natural drainage into Hudson Bay. Blanket sands, esker deltas, and De Geer moraines formed where debris
from the Keewatin glacier entered the lake. More extensive deposits of substratified diamicton or massive and varved clay were left by Hudsonian ice. Beach ridges and wave cut notches mark lake levels, which fell from 442 m to less than 155 m as new outlets opened in eastern Manitoba and Ontario.
Between 8000 BP and 7800 BP the ice mass occupying Hudson Bay disintegrated, and Tyrrell Sea flooded areas below 180 m elevation. Thick deposits of peat with large amounts of ground ice accumulated over the silty substrates during postglacial time. Frost riving of bedrock, frost churning of soils,
and aggradation or degradation of ground ice are current periglacial processes. The surface till sheet has anomalously high uranium concentrations over some of the pelitic gneisses, and high arsenic or iron-zinc-chromium concentrations south of the Great Island volcanic and metasedimentary
rocks.
North Kaipara Barrier is formed by sediments, mainly estuarine and dune sands of the Kaihu Group, deposited in a major cyc1e of transgression (subsidence) and regression (uplift) during the Quatemary. Hautawan, Okehuan and younger lignites along with terrace surfaces at 105 m, 67 m, 40 m, 24 m, 8 m and 4-2 m a.s.l., which can be correlated with dated surfaces elsewhere in the North Island, provide chronologie contro!. Five units, the Hautawan DargaviIle Formation, Nukumaruan-Castlec1iffian Rototuna Formation, Castlec1iffian-Hawera Pareotaunga Formation, Hawera South Head Formation, and the Hawera Shelly Beach Formation, are present. The barrier has changed littie since the end ofOkehuan time when the major existing valleys were cut in Rototuna sediments. Upper Pleistocene terrace surfaces are locally preserved within these valleys. Undifferentiated Hawera and Holocene deposits are also present on the barrier.
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