Foraminifera and the Holocene History of the Gulf of St. Lawrence

Abstract

Foraminifera have been utilized to interpret the response of waters in the Gulf of St. Lawrence to climatic changes during the Holocene. Sediment cores (up to 1000 cm long) from the Gulf of St. Lawrence and environs, are characterized throughout by meager foraminiferal faunas. The microfaunas are characteristic of marginal marine environments and are typified by low foraminiferal numbers (less than 300 and generally less than 100 per unit sample), few genera and species, and hyposaline, shallow-water assemblages. The microfaunal information indicates that marine waters were more brackish and much shallower during the latter stages, and immediately following the Wisconsin glaciation. Shallow-water foraminiferal species such as Elphidium incertum clavatum, Islandiella islandica, and I. teretis are commonly the first to inhabit cool temperate to northern environments after glacial retreat. Consequently, because of the absence of deep water marine microfaunas it is believed that many areas in the Gulf of St. Lawrence were at least 100 to 200 m shallower than at present.The Holocene history of the area is one of transition from a rapidly fluctuating brackish water environment, to one which is more consistent with the present environment. The presence of Globigerinoides ruber (pink), a species commonly associated with subtropical waters, intermixed with the eurybathic benthonic fauna, indicates distinctive lateral and vertical water-mass zonation in a restricted geographic area. Warm water incursions into the Gulf of St. Lawrence from the Gulf Stream, which contained the subtropical foraminiferal species Globigerinoides ruber and Globorotalia menardii, were intermittent, whereas a persistent cold-water marine influence from the Arctic via the Labrador Current is indicated by the presence of Globigerina pachyderma. The adjoining Scotian Shelf faunas, alternating from sparse, to prolific and diverse, during the Holocene, suggest that conditions there were not significantly different from those in the Gulf of St. Lawrence.Extremely brackish and/or shallower waters were present in most of the western Laurentian Channel and shelf waters of the Gulf of St. Lawrence until recently (< 6400 ± 130 yr B.P.). The baymouth bars, persistent features restricting circulation with most bays, estuaries, and lagoons adjoining Prince Edward Island and New Brunswick were established between 4540 ± 180 and 2235 ± 155 yr B.P. Sediments containing subtropic and arctic planktonic species, alternating with eurythermal benthonic species, are indicative of environmental extremes throughout the Holocene. It is believed that many of these marine fluctuations were neither recorded nor preserved in adjoining continental sediments of equivalent age.

Champlain Sea Foraminifera and Ostracoda: a systematic and paleoecological synthesis

“…However, since these species were absent during the Transitional and Hiatella phases, they must have migrated into the sea from the Gulf of St. Lawrence, through the lower St. Lawrence River, a region very close to the retreating ice margin. CRONIN (1977) discusses the possibility that warm Gulf Stream water, the presence of which is well documented for the Gulf of St. Lawrence about 11,000 yr BP (BARTLETT and MOLINSKY, 1972), may have entered the Champlain Sea bringing with it a warmer water fauna. Although the cold Labrador Current was the major factor in determining maritime océanographie conditions at this time, the data of Bartlett and Molinsky indicate periodic warm water incursions with temperatures possibly as high as 24° to 30°C.…”

Upper Holocene Paleoceanography of Inner Miramichi Bay

“…Foraminifera assemblages in core 134B hint alternatively that it may not have occurred until as late as 2500 years BP. Both dates are within the time frame of 4500 to 2200 years BP that was postulated by Bartlett and Molinsky (1972) for the formation of barrier bay systems along this part of the New Brunswick coast.…”

“…3, 7). Bartlett and Molinsky (1972) suggest that baymouth bar systems that presently restrict circulation within most bays along the coast of northeastern New Brunswick were probably developed between 4500 and 2200 years BP. Bousfield and Thomas (1975, Fig.…”

Les plates-formes littorales de l’île aux Coudres, moyen estuaire du Saint-Laurent, Québec

“…La nature des mouvements côtiers verticaux en cours est pratiquement inconnue le long des côtes de l'estuaire. Il est possible que des niveaux marins plus bas que ceux d'aujourd'hui aient été enregistrés durant l'Holocène (DlONNE, 1977, p. 66;SILVERGERG, 1978;BARTLETT et MOLINSKY, 1972). On n'a aucune idée précise de l'amplitude de ces éven-tuelles fluctuations.…”