Glacial geomorphology and chronology in the Selamiut Range – Nachvak Fiord area, Torngat Mountains, Labrador

Abstract

The Selamiut Range of the Torngat Mountains, northern Labrador, rises to over 1700 m above sea level and constituted a barrier to eastward-flowing Laurentide ice during former glaciations. Local and regional ice has left an assemblage of landforms exhibiting cross-cutting relationships. Three glacial phases are recognized in the area. The oldest and most extensive (the Ivitak phase) is marked by high-elevation till deposited when regional and local ice coalesced. At this time regional ice flowed eastward down Nachvak Fiord while interfiord highlands extended above the ice as nunataks. During a late Ivitak phase a large proglacial lake was dammed in the lower McComick Valley at 80 m above sea level when regional and local ice in Nachvak Fiord blocked the local drainage. During the subsequent Nachvak phase, lakes were dammed in the lower McCornick Valley at 67 and 53 m above sea level for ca. 3000 years by Laurentide ice alone. The Superguksoak had three subphases when local cirque glaciers expanded up to 5 km beyond their present limits. The Holocene marine limit around 33 m reflects the small ice load influencing Nachvak Fiord, or very late deglaciation of the Ivitak Cove area.The chronology of these glacial and proglacial deposits is based on their spatial relationships as well as pedology and lichenometry. Seventy-nine soil pits excavated to the base of the Cox horizon indicate the relative duration of weathering since deglaciation. Absolute ages for the soils are estimated to be > 40–40 ka BP for the Ivitak phase, 23–17 ka BP for the Nachvak phase, and 12–5 ka BP for Superguksoak I. Measurements of Rhizocarpon geographicum indicate that prominent Superguksoak-phase moraines bordering the present-day cirques were abandoned approximately > 4000, 3000, and 1500 years BP. Collectively these data are compared with earlier fieldwork in northern Labrador, and some discrepancies are discussed.