Postglacial sequence stratigraphy of Lake Melville, Labrador

Abstract

In Lake Melville, Labrador, the Quaternary glacimarine sediments reflect a single retreat phase of the Laurentide Ice Sheet during the early Holocene. Based on extensive airgun and high-resolution seismic surveys, sediment deposits are subdivided into thirteen units that are associated with glacial, paraglacial, and postglacial styles of deposition. Their distribution patterns reflect: paleo-positions of a retreating ice margin during the period between 10,000 and 9000 years before present; formation of paraglacial deltas during the early to mid-Holocene (6-9 ka); and postglacial tidal-influenced deposition during the late Holocene (<6 ka). Discontinuous ice-contact sediments (unit 1) are encountered at the base of the lake&apos;s stratigraphy, overlain by thickly stacked wedges of morainal (ice-proximal) sediments (units 2 through 7) associated with ice-marginal stillstands and minor retreats and readvances of the ice terminus. Subsequent and rapid retreat of the terminus landward resulted in deposition of ice-distal muds (units 8-10). Once the ice sheet retreated on land, rapid ablation led to meltwater-influenced deltaic sequences with common mass-failure deposits (units 11 and 12) and progradation of the coastline. With the ice sheet fully ablated, postglacial, organic-enriched muds (unit 13) were deposited across much of the marine basin. A sequence stratigraphic model for the generally continuous retreat of an ice margin involves three ice-sheet stages: tidewater, ablation on land, and a fully ablated period. The tidewater stage of the ice sheet is divided further into substages: (1) rapid terminus retreat periods yielding ice-distal, fine-grained sediment, and (2) slower retreat periods involving terminus readvances and localized deposition of coarser ice-proximal sediment. Stages of ice-sheet ablation on land and the fully ablated period correspond with the deposition of paraglacial and postglacial sediments, respectively. These last two stages are characterized by basin-wide sedimentation, in contrast to sediment distribution for the tidewater stage that is largely controlled by basin bathymetry. The proposed model provides an aid to interpreting from seismic records the position and relative speed of ice-margin movement in glaciated coastal basins. (C) 1997 Elsevier Science B.V.