ABSTRACT: Implications to glacial history and urban planning in a glaciated estuarine tributary: Fredericton Junction, New Brunswick.

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Abstract

Valleys that were inundated during deglaciation often represent the thickest deposits and greatest stratigraphic complexity due to the previous interaction between glaciers, ponded meltwater and marine incursions. Thus, interpretation of the sedimentary architecture of glaciated estuarine valleys and their tributaries, pose difficulties to those responsible for identifying constraints to urban development. Two common problems are the (1) lack of understanding of the nature of the subsurface water supply aquifer and (2) limited information concerning the occurrence and extent of buried geotechnical hazards such as sensitive clays. The Village of Fredericton Junction is sited along the Oromocto River approximately 30km upstream of its coalescence with the Saint John River. The Oromocto valley is believed to have been flooded with both lacustrine and marine waters during glacial blockage of the Saint John valley. However, previous investigations provide limited information on the extent and nature of the underlying deposits. Field work included a seismic refraction survey and a review of 14 borehole logs drilled during earlier groundwater exploration programs. Three additional holes were drilled to supplement this information, help establish stratigraphic relationships and to facilitate sample collection. Samples were also retrieved from concurrent drilling at Fredericton located approximately 40 km away. These latter samples were used as a datum for comparative analyses because those sediments are reported to have been deposited under both marine and lacustrine conditions. Atterberg limits, particle size analyses, X-Ray diffraction, and the chloride and boron content of clay samples were analyzed for both locations. Relative to the Fredericton samples, the Fredericton Junction samples contained less clay and lower values for activity, plastic limit and liquid limit, and no calcite or chloride content. This lack of evidence for marine deposition suggests that there were limits to the marine incursion into tributaries of the Saint John River and has implications to current concepts of deglaciation of the region. For example it may indicate that this part of the tributary did not undergo marine submergence, or more likely, that melting glaciers remained close enough to maintain lacustrine conditions during deposition of the clay deposits. Stratigraphic profiles for the borehole logs indicate that glacilacustrine clays overly till and bedrock to an elevation of 14m asl, and also underlie the village sewage lagoon. The bedrock aquifer is locally susceptible to recharge at higher elevations where rare outcrops are exposed due to erosion of the surface till cover and at locations along the river bed.

Bibliography of Canadian Geomorphology