Stratigraphy and Late Pleistocene-Holocene history of Effingham Inlet, B.C., results from MONA core MD02-2494 and GSC freeze cores

Abstract

The sedimentary record of Effingham Inlet, British Columbia, Canada (Appendix 1) is contained in: a 40.9 m giant (Calypso) piston core (MD02-2494; 49° 04.28 N/ 125° 09.55 W) raised from 120 m water depth in the inner basin, in June 2002, during the 2002 MONA (Marges Ouest Nord Américaines) campaign aboard the French ship RV Mariane Dufresne, and in four Geological Survey of Canada freeze cores (TUL99B04,VEC007-FC01, VEC007-FC02 and VEC007-FC03) which contain the surface sediments and were also raised from 120 m water depth in the inner basin in October, 1999, and April, 2005, from the CCGS John P. Tully, and the CCGS Vector . The piston core MD02-2494, spans from 14,000 14C yr BP (16,700 cal yr BP) to about nine centuries before present, and the freeze cores represent from ~ AD 1992 to ~ 850 y BP. These cores archive changes in sedimentation (Table 1)(Appendix 1 and 2) and relative sea-level immediately following deglaciation of the Late Wisconsin Fraser Glaciation, which peaked about 15,000 14C yr BP. The presence of the Mazama Ash in the MD02-2494 piston core, anchors a detailed chronology (Fig. 1) based on forty-nine radiocarbon dates and seven Pleistocene paleo-magnetic secular variation correlations. Diatom assemblages (Table 2) identify a marine-freshwater transition in the basin, which occurred 11,631 14C yr BP (13,503 cal yr BP). At this time a bedrock sill, presently at 46 m depth, was briefly exposed as sea-level fell. The relative sea level rose again during isostatic crustal adjustments, with a brackish-freshwater-full marine transition at 9,851 14C yr BP (11,165 cal yr BP). These data constrain a new sea-level curve for the outer coast of Vancouver Island covering the past 12,000 14C yr BP (14,000 cal y BP) providing new information on the nature of deglaciation along the west coast of Canada, and informing interpretations of regional paleoceanographic records, and mantle viscosity models.