Quaternary geomorphology, glacial history and relative sea level change in outer Nachvak Fiord, northern Labrador

Bell, Trevor J. (1987) Quaternary geomorphology, glacial history and relative sea level change in outer Nachvak Fiord, northern Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Torngat Mountains of northern Labrador portray a complex history of regional and local ice movements during the Wisconsinan. Research undertaken in outer Nachvak Fiord, central Torngat Mountains, provides the basis for a morphostratigraphic and lithostratigraphic framework. The application of relative and absolute dating techniques allows reconstruction of a tentative glacial and relative sea level chronology for the area. -- The Nachvak glacial phase represents the last regional ice advance into the outer Nachvak Fiord area. During this event, tributary valleys were backfilled by fiord ice as far east as the fiord threshold, whereas south of the fiord, ice terminated at the western end of Adams Lake. This ice advance is distinguished from previous glacial events on the basis of its drift properties. The earlier Adams Lake glacial phase is considered to be local m origin. The eastern limit of this advance, as defined by the maximum extent of local lithological and geochemical drift characteristics, was Valley of the Flies terminal moraine. The MI glacial phase represents an extensive, older regional ice advance and is characterized by the upper limit of till and moraine in the study area. -- Acoustic stratigraphy of Nachvak Fiord and Adams Lake sediments supplements the terrestrial glacial geology of the region. Acoustic units are interpreted as representing sedimentary facies related to one or more glacial - deglacial cycles, in both the fiord and lake basins. Tentative models of deposition require a grounded to partially-grounded outlet glacier m the fiord during the last regional ice advance, and a significant ice margin at the western end of Adams Lake. -- Analysis of raised marine evidence reveals eleven shorelines, ranging in elevation from 9 m to 73 m above present sea level. The extent and geometry of the shorelines are the bases of a model of relative sea level change during deglaciation from the Nachvak phase maximum. This permits the identification of the Shoal Water Cove and Tessersoak glacial readvances, and the Kogarsok and Townley Head glacial still-stands which appear consistent w1th the morphological evidence of moraines in the region. Locations of major loading centers which affected the Nachvak Fiord region, are based on the assumption of synchronous shoreline formation in the outer fiord area. Radiocarbon-dated shells from sediments associated with a raised marine shoreline suggest that approximately 30 m of emergence has occurred since 9 ka BP. -- A tentative chronology of glacial events is reconstructed from radiocarbon dates, amino acid ratios, and soil development rates. The Nachvak glacial maximum is tentatively dated at 22 ± 2 ka BP. It is estimated that the Adams Lake glacial phase occurred during the period 29-50 ka BP. The MI glacial phase is tentatively dated at ≥75 ka BP, based on comparisons with similar regional ice advances on Baffin Island. -- Correlations with local chronologies from northern Labrador are proposed, and critically examined in the context of previous models of glaciation. The Early Wisconsinan in northern Labrador was likely characterized by an extensive advance of Laurentide ice which may have extended onto the Labrador Shelf. The Middle Wisconsinan is suggested to have been a period of local cirque glacier expansion, with associated high relative sea levels. The extent of Late Wisconsinan ice may have been topographically controlled in northern Labrador. In the Nachvak Fiord region ice was restricted to the fiord basin, whereas in areas north and south of the Torngat Mountains the ice advance may have been more extensive than during the Early Wisconsinan. The deglacial chronology proposed for Nachvak Fiord suggests that a stepwise recession of Laurentide ice characterized the late-glacial period.

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