Holocene history of Bedford Basin, Nova Scotia: foraminifera, dinoflagellate, and pollen records

Abstract

Three piston cores from Bedford Basin, a silled coastal inlet, provide the basis for a micropaleontological study of postglacial to recent sediments. Five faunal units (four foraminiferal, one arcellacean) are found in core 79-11: a surface assemblage, followed by deep estuarine, marginal marine, transition, and freshwater (arcellacean) assemblages. The other cores contain only expanded marine sequences. The top of the transition zone in core 79-11 has a C-14 age of 5830 ± 230 years BP, indicating a rise in sea level of at least 20 m (the sill depth) during the Holocene.Four dinoflagellate assemblage zones are found in core 79-11. The first (O. centrocarpum – B. tepikiense) is typical of a silled basin with marine water of near-normal salinity; the second (P. conicoides – Cyst C) indicates a temperate marine environment with strong fluvial influence (marginal marine); the third (P. limbatum) is dominated by freshwater cysts, and the fourth (Dinocyst sp. A) is dominated by subarctic brackish water cysts.Four pollen assemblage zones are found in core 79-11. Zones C1–C3 indicate mixed boreal–deciduous forest vegetation. Zone B indicates early Holocene park–woodland vegetation, the base of which has a C-14 age of 7705 ± 550 BP. The palynozones in the marine sediment core are correlatable with C-14 dated stratigraphies from Nova Scotian lakes.Foraminifera and dinoflagellate assemblages in core 79-11 reflect the response of the microfauna and microflora to changes in water depth, salinity, and temperature, which have accompanied changes in sea level and climate during the past 8000 years. Major changes in the marine biota during the recent period of urban development may be due to increased sediment influx and effluent discharge. The effects of anthropogenic changes are small, however, compared to those accompanying the Holocene marine transgression.