Marsh foraminifera of Prince Edward Island: Their recent distribution and application for former sea level studies

A detailed survey of all marsh areas of Prince Edward Island, Canada, was undertaken and the Information derived was used to determine four optimal areas (i.e., thickest marsh deposits) for sea level studies. Although extensive studies of marsh foraminifera have been conducted in Nova Scotia, the mixed tidal system in Prince Edward Island necessitated further investigations which suggested different relationships in some foraminiferal distributions, possibly linked to the tidal regime of the Gulf of St. Lawrence. Plant species distributions were markedly different, indicating that plant remains, even if preserved, would not be suitable sea level indicators. Using marsh foraminiferal zonations in subsurface sediments, four sea level curves were determined. These curves encompass the last 3000 years of submergence on Prince Edward Island. Average rates of relative sea level rise in the east (14-19 cm/century) were almost twice that observed in the west (8 cm/century). These contrasts with previous work that suggested the island had been subsiding at a uniform rate for the last 3000 years. The data obtained here helps to calibrate recently derived geophysical models of the earth's response following deglaciation. Taxonomically, a new genus of marsh foraminifera ( Pseudothurammina n. gen. Scott, Medioli and Williamson) has been proposed with the type species being Thuranmina (? ) limnetis , Scott and Medioli described from marsh sediments in Nova Scotia. RESUME Un examen en detail de toutes les surfaces marecageuses de l’ile-du-Prince-Edouard, Canada, a ete entrepris, et l’information recueillie a servi a identifier quatre regions optimales (c.- a.-d., depots de marais les plus epais) dans le cadre d'etudes du niveau de la mer. Bien qu'en Nouvelle-Ecosse les foraminiferes de marais aient ete le sujet d'etudes poussees, le systeme de marees mixtes de l’ile-du-Prince-Edouard a necessite une etude plus approfondie. Cette etude revele qu'il existe peut-etre des differences de rapport entre certaines repartitions de foraminiferes, liees au regime des marees du Golfe du Saint-Laurent. Les repartitions des especes vegetales etaient tres differentes, indiquant que lea debris de plantes, meme si preserves, ne conviendraient pas comme indicateurs de niveau marin. Quatre courbes de niveau marin ont ete determinees en employant la distribution par zones des foraminiferes dans les sediments sous-jacents- Ces courbes embrassent les 3,000 dernieres annees de submersion sur l’ile-du-Prince-Edouard. Les taux moyens d'elevation du niveau de la mer a l'est (14 a 19 cm/siecle) etaient presque le double de ceux observes a l'ouest (8 cm/siecle). Ceci contraste avec des travaux anterieurs qui suggeraient un affaissement uniforme de l'ile depuis 3,000 ans. Ces donnees aident a etalonner de recents modeles geophysiques qui simulent la reaction de la terre suite a la deglactiation. Quant a la taxonomie, on a propose un nouveau genre de foraminifere de marais ( Pseudothurammina n. gen. Scott, Medioli et Williamson) dont l'espece type est Thurammina (? ) limnetia , decrite par Scott et Medioli a partir de sediments tie marais de la Nouvelle-Ecosse, [Traduit par le journal]