Quaternary Foraminiferal Stratigraphy in Sediments of the Eastern Champlain Sea Basin, Québec

Abstract

Sediments of the late-glacial Champlain Sea basin have been sampled at 18 sites in the Trois-Rivières and Québec City regions. Two successions of foraminif-eral ecozones (deep and shallow water) comparable to those previously reported from the western Champlain Sea are recognized. Faunal composition indicates an early phase (pre-A) of hyposaline waters with consistent freshwater evidence only at the southwestern limit of the area. Salinity control in pre-A could be the result of advance or retreat of an ice lobe in the Québec City region. It is followed by zone A (salinity: 25-32%o) which is in part synchronous with the formation of the St-Narcisse Moraine. In the easternmost Champlain Sea, zone A lasted approximately from 11.3 until after 10.6 ka BP, possibly up to near 10.2 ka BP. In the western part of the area, it is progressively replaced by the less saline conditions of zones B (10-25%o) and C (2-10%o). Near major freshwater inlets, thick delta sequences barren of foraminifera substitute for zones B and C. East of Trois-Rivières, zone B is probably discontinuous and does not reach Québec City. Zone C is present at only one site, west of Trois-Rivières. The shallow water zones EH and EA, contemporaneous with zones A and B, record relatively high salinities (annual maximum of up to 30 %o for EH, somewhat less for EA), zone EA suggesting also warmer summers. The paleoecological results concerning salinity do not allow detection of the diversion of Lake Agassiz outflow. The discharge envisaged by some authors may not have been large enough to detectably change salinity in the deep, late Champlain Sea. In shallow waters, the effect could have been significant but would be difficult to date because of error due to recycled old carbonate.Des sédiments tardiglaciaires de la Mer de Champlain ont été échantillonnés à 18 sites dans les régions de Trois-Rivières et de Québec. Deux séquences d'écozones à foraminifères (eau profonde et peu profonde), semblables à celles précédemment décrites dans l'ouest de la Mer de Champlain, sont reconnues. Le contenu faunique indique une première phase hyposaline (pré-A) avec des indices sûrs d'eau douce seulement à la limite sud-ouest de la région étudiée. Durant cette période, la salinité a dû être déterminée par l'avancée et le recul d'un lobe glaciaire dans la région de Québec. Suit la zone A (salinité : 25-32 %o), qui est en partie synchrone avec la formation de la Moraine de St-Narcisse. Cette zone a duré approximativement de 11,3 à 10,6 ka BP, peut-être jusqu'à près de 10,2 ka BP. Elle est suivie des zones B (10-25 %o) et C (2-10 %o) tandis que près des grands affluents d'eau douce, d'épaisses séries deltaïques dépourvues de foraminifères se substituent aux zones B et C. À l'est de Trois-Rivières, il semble que la zone B soit discontinue et ne se rende pas jusqu'à Québec. La zone C n'est observée qu'à un seul site, à l'ouest de Trois-Rivières. Deux zones peu profondes, EH et EA, contemporaines des zones A et B, se caractérisent par des salinités plutôt élevées (maximum annuel ...

The Early Lake Ontario barrier beach: evidence for sea level about 12.8–12.5 cal. ka BP beneath western Lake Ontario in eastern North America

“…). This conclusion is supported by low salinity foraminifera and ostracode assemblages in the upper St. Lawrence River Valley (Rodrigues ) and by the east‐to‐west decline in foraminiferal diversity in the CS that is interpreted as a trend to lower salinity in the western part of the CS (Guilbault , ). Also, the nearest marine macrofossils to ELO have only been found about 100 km downstream in the St. Lawrence River Valley from the lake outlet (Henderson ).…”

“…Steady freshwater flows of this magnitude and less were found capable of freshening the western CS despite possible occurrences of high palaeotides in studies using modelled estuarine circulation dynamics for the St. Lawrence River Valley (Katz et al 2011). This conclusion is supported by low salinity foraminifera and ostracode assemblages in the upper St. Lawrence River Valley (Rodrigues 1992) and by the east-to-west decline in foraminiferal diversity in the CS that is interpreted as a trend to lower salinity in the western part of the CS (Guilbault 1989(Guilbault , 1993. Also, the nearest marine macrofossils to ELO have only been found about 100 km downstream in the St. Lawrence River Valley from the lake outlet (Henderson 1970).…”

Broad climate variability based on seismic stratigraphy and sediment cores in Willsboro Bay, Lake Champlain.

“…The microfossils were photographed in the Backscatter Scanning Electron (BSE) mode using a Zeiss 490A Digital Scanning Electron Microscope (SEM). Species were identified following the taxonomy of Cronin (1979Cronin ( , 1981, Guilbault (1989, 1993), and Rodrigues (1992. For a complete list of microfossils and photomicrographs, see Appendix E.…”