The postglacial relative sea-level lowstand in Newfoundland

Abstract

Relative sea level in coastal regions of Newfoundland fell from late-glacial maximum levels to postglacial minima in several phases: (i) an early period of high relative sea level, when Late Wisconsinan ice was at the coast and discharging meltwater plumes into the ocean; (ii) a period of rapidly falling relative sea level, during which glaciers retreated inland; and (iii) a period without glacier ice, during which relative sea level continued to fall, but at decreasing rates. Falling relative sea level caused fluvial incision of glacial deposits in some coastal embayments, and culminated with the construction of lowstand marine deltas. These deltas were submerged during the subsequent Holocene transgression. Seismic reflection data from selected deltas show that they comprise wedges of sediment with prograded, seaward-dipping, foreset-style internal reflections. The depth of the relative sea-level lowstand varies spatially, and it was diachronous. It occurred relatively early and deep in peripheral regions (i.e., farther from the centre of the island), but was later and shallower landward, and close to its northern limits. Approximate ages of the lowstand are 9.5 ± 1 ka in the St. George's Bay – Port au Port region, just over 8.6 ka in Hamilton Sound, before 7.0 ka at Swift Current, 8.7 ka at Connoire Bay, just over 8.2 ka in Bay d'Espoir, and ca. 6.5 ka on the Great Northern Peninsula. The relative sea-level minima range down to at least –30 m, and form a concentric pattern around central Newfoundland, similar to the pattern of raised marine limits.