POSTGLACIAL SEQUENCE STRATIGRAPHY OF LAKE MELVILLE, LABRADOR

In Lake Melville, Labrador, the Quaternary glacimarine sediments refle ct a single retreat phase of the Laurentide Ice Sheet during the early Holocene. Based on extensive airgun and high-resolution seismic surve ys, sediment deposits are subdivided into thirteen units that are asso ciated 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 pre sent; 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 en countered at the base of the lake'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 read vances of the ice terminus. Subsequent and rapid retreat of the termin us landward resulted in deposition of ice-distal muds (units 8-10). On ce the ice sheet retreated on land, rapid ablation led to meltwater-in fluenced deltaic sequences with common mass-failure deposits (units 11 and 12) and progradation of the coastline. With the ice sheet fully a blated, postglacial, organic-enriched muds (unit 13) were deposited ac ross 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 sed iment, and (2) slower retreat periods involving terminus readvances an d localized deposition of coarser ice-proximal sediment. Stages of ice -sheet ablation on land and the fully ablated period correspond with t he deposition of paraglacial and postglacial sediments, respectively. These last two stages are characterized by basin-wide sedimentation, i n contrast to sediment distribution for the tidewater stage that is la rgely controlled by basin bathymetry. The proposed model provides an a id to interpreting from seismic records the position and relative spee d of ice-margin movement in glaciated coastal basins. (C) 1997 Elsevie r Science B.V.