CGRG Bibliography of Canadian Geomorphology
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Author : Clet, M.; and Occhietti, S.
Date : 1996
Title : The upper Pleistocene sub-sequence of St. Pierre Sediments - St. Maurice Rhythmites - Vieilles-Forges Sands, St. Lawrence Valley, Quebec
Publication : Geographie physique et Quaternaire
Issue : 50(3):
Page(s) : 287-310
Abstract
The Quaternary of the valley and middle estuary of the St. Lawrence is characterized by sedimentary sequences inset into each other. The most common is the upper sequence, which is composed of the St. Pierre Sediments (Les Becquets Interstade), Saint-Maurice Rhythmites, Vieilles-Forges Sands, Gentilly Till (Wisconsinan) and sediments of the Champlain and Goldthwait seas. The bottom of this sequence is encased into La Perade Clay related to the late Sangamonian Cartier Sea invasion. The pollen content of this clay indicates that the deglaciated land was progressively recolonised by vegetation, and that a brief warming phase occurred before the establishment of a stable boreal forest. Above the erosional disconformity, the fluvial St. Pierre Sediments contain pollen which corresponds to a boreal forest and remains consistent throughout the various lithozones. Above the fluvial sediments, the Saint-Maurice Rhythmites were sedimented during more than 1000 years in the La V rendrye Lake. The pollen content and plant debris of the lower zone show that a boreal forest was progressively flooded in the valley lowlands. In the upper zone, the pollen content shows both a decline in the percentage of thermophilous trees and in the arboreal/non arboreal ratio. The overlying Vieilles-Forges Sands extend throughout the central valley. They contain three lithozones : lacustrine fine sand, deltaic sand and proglacial sand and gravel. The pollen content of the lowest zone changes progressively to a tundra. The upper zones are apparently sterile. This palynostratigraphy enables the correlation of units and sequences from different sites distributed over more than 400 km along the valley and the differentiation of units which seem similar.
Bibliography of Canadian Geomorphology