ABSTRACT: Glacial Lake Gayhurst: Insights into the MidWisconsinan history of the southeastern sector of the Laurentide Ice Sheet.

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Abstract

Complex sequences of ice marginal and frontal deposits have been mapped and documented in the Saint-François and Chaudière river valleys, north of the international border. In most cases, these sediments and landforms, as well as other geomorphological features, are significant indicators of the extent of former ice-dammed lakes primarily because their elevation is intimately linked to well-documented outlets. Their stratigraphic architecture is, however, complex, and their subsurface extent poorly documented. The Quaternary geology of South Eastern Québec is unique in several aspects. The Pleistocene stratigraphy is characterized by a three-till sequence, each till being underlain and overlain by glaciolacustrine sediments deposited in ice-dammed lakes during advance or retreat phases. Occurrences of sub-till glacial lake sediments in the region are commonly regrouped under the Gayhurst Formation, which stratigraphic position between the Chaudière and Lennoxville glacial deposits suggests a mid-wisconsinan age (MIS 3?). Interpretations of Gayhurst Formation derived mainly from many stratigraphic sections that provide elevation estimates of some possible outlets that controlled the lake evolution. Sediments deposited by retreating glaciers are generally thick and irregularly bedded in couplets of variable thickness. In contrast, fine-grained sediments deposited in lakes dammed by advancing glaciers consist of thin and evenly laminated sediments. These glacial lake deposits are widely exposed in stratigraphic sections and have been documented in numerous boreholes. The objectives of this study are 1) to define the physical lateral extension of the Gayhurst Formation; 2) to bring additional precisions on the paleogeographic reconstructions through the evaluation of different meltwater routing scenarios in New-Brunswick, Maine and Vermont, and; 3) to determine the age of this glaciolacustrine sequence using IRSL dating. Here will present recent field and stratigraphic data that were acquired in the course of a groundwater/Quaternary geology mapping project in the Chaudière and Saint-François valleys.

Bibliography of Canadian Geomorphology