Relative sea‐level history and isostatic rebound in Newfoundland, Canada

Abstract

The island of Newfoundland, Canada, is situated close to the former margins of the Laurentide ice sheet. The post‐glacial sea‐level history is complex, dominated by the effects of an ice‐marginal crustal forebulge produced by isostatic deformation of the lithosphere. Marine fossils found above present sea‐level can be 14C dated, and examination of the temporal and geographical distribution of these 14C dates in combination with geomorphological indicators of past sea‐levels indicates regional trends of relative sea‐level change. For most of the island (apart from the Northern Peninsula) no samples have been recovered that date younger than 8000 BP. suggesting that sea‐level lay below the present one in these areas for the last 8000 years. The same areas commonly show geomorphological evidence for stands of sea‐level both above and below present sea‐level. This evidence is interpreted as showing that over most of Newfoundland, following deglaciation, sea‐level fell to below present levels, and subsequently rose to the modern level. Exceptions to this pattern are the north of the Northern Peninsula, which shows a history of continuous emergence, or a more complex pattern of sea‐levels falling below present, subsequently rising above present, and currently falling; and the northeast Avalon Peninsula, which may have had sea‐levels below present throughout post glacial times. This pattern of relative sea‐level change is interpreted as being mostly due to isostatic recovery, with the main factor being northerly migration of the forebulge. Mapping the time at which sea‐level fell below the present level allows estimation of the rate of northerly migration and collapse of the forebulge at between 4.5 and 11 km/100 years; this is considerably faster than previous estimates.

Late Quaternary Relative Sea-Level Change on the West Coast of Newfoundland*

“…This rate compares favourably with other estimates for the west coast of Newfoundland based on salt-marsh and tidegauge data (50 km per ka; Daly, 2002) and the raised marine shell record (45 km per ka; Liverman, 1994), although the latter was predicated on forebulge migration between 13 000 and 7000 14 C BP (Liverman, 1994). This rate is also consistent with the rate of forebulge migration calculated between Moosehead Lake (Maine) and Québec City (Balco et al, 1998), but is somewhat lower than the 70-110 km per ka rate estimated for the Gulf of Maine (Barnhardt et al, 1995).…”

“…Existing RSL data broadly confirm the modelled pattern, although the data mostly consist of emergent features that date to initial establishment of higher sea levels in the late Wisconsinan and early Holocene (~17 000-8500 cal BP), with much less coverage spanning the mid to late Holocene (~8000-2000 cal BP) when sea levels were lower than present (Liverman, 1994;Shaw and Forbes, 1995;Shaw et al, 2002). The west coast of Newfoundland has been the focus of several RSL studies over the last decade or so (Clark and Fitzhugh, 1992;Grant, 1992Grant, , 1994Batterson and Catto, 2001;Daly, 2002;Bell et al, 2003;Smith et al, 2005) such that there is now a sufficient database with which to critically examine the proposed migration of a marginal forebulge.…”

“…Although the apparent absence of raised marine deposits postdating 9000 cal BP between Hawke's Bay and Daniel's Harbour (Fig. 2), may be interpreted to reflect a period of RSL lower than present (Liverman, 1994), it may also simply reflect a lack of exposure and research effort. For instance, contrast the amount of RSL data for Port au Choix (Fig.…”

“…1A-B), based on new and published data. This region is of particular interest from the standpoint of sealevel studies and geodynamical modelling because it is here that the transition from rising to falling sea level, known as the glacioisostatic hinge, apparently intersects the west coast of the island (Liverman, 1994). In addition, the almost perpendicular orientation of the west coast of Newfoundland to the regional isobase pattern (Fig.…”

Insight into the late Holocene sea-level changes in the NW Atlantic from a paraglacial beach-ridge plain south of Newfoundland

“…These include eustacy, isostacy, glacio-isostacy and hydro-isostacy as well as local to regional subsidence or tectonic uplift, changes in meteorological or oceanographic patterns, among others (Milne et al, 2009). The primary driver of RSL changes in northeast Atlantic since the end of the last glacial period has been glacio-isostatic adjustments caused by retreat of the Laurentide Ice Sheet and collapse of the associated forebulge (e.g., Shaw and Forbes, 1990;Forbes and Syvitski, 1994;Liverman, 1994;Gehrels et al, 2004;Daly et al, 2007;Cazenave and Llovel, 2010). Regional differences in maximum ice-sheet thickness, timing of deglaciation, and the size and retreat/collapse rate of the glacial forebulge largely explain the variability in RSL over millennial timescales (type A and B; Fig.…”