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Glacial Geology of New Brunswick

Glacial Geology of New Brunswick

Surficial Mapping   

New Brunswick was likely glaciated many times during the Pleistocene Ice Age; however, no record of a glaciation prior to the latest stage, the Wisconsinan, exists. The oldest confirmed Pleistocene deposit in the province is a clay that contained a fossilized mastodon. According to research by the Canadian Museum of Nature and the Geological Survey of Canada, the mastodon, which was found in a sinkhole near Hillsborough (southwestern NB) and is now in the New Brunswick Museum at Saint John, lived during the last interglacial stage (the Sangamonian), approximately 100,000 years ago.

New Brunswick's glacial deposits are between 100,000 and 10,000 years old (Sangamonian to Wisconsinan). The dominant glacial unit is a blanket of basal till, underlain by bedrock, and typically on the order of one to a few metres thick; however, within subglacial bedforms and infilled valleys, significantly greater thicknesses are present. The basal till comprises three facies; the lowermost deformation till facies, the overlying lodgement till facies, and the uppermost meltout till facies. Although all three facies are present throughout New Brunswick, it is rare to see them all at one site. The deformation till (also known as local till), was formed by the entrainment and deformation of the underlying bedrock, and is readily recognizable by this characteristic. The most common facies is the lodgement till, which comprises material of both local and foreign origin, that was plastered onto the substrate from the base of the overriding glacier. The meltout till facies, formed from the same types of materials as the lodgement till, was deposited by basal melting as the glacier waned.

The remaining facies of glacial accumulations in New Brunswick - those associated with the melting of the ice sheets - are ablation till, glaciofluvial, glaciolacustrine, and glaciomarine deposits. The granular aggregates of the Province constitute an economically important part of these types of deposit.

Ablation till deposits consist of material carried within and upon a glacier and subsequently deposited during melting. Glaciofluvial deposits are formed by rivers flowing on, in, or sourced from glaciers. In some of the Province's major valleys, glaciofluvial deposits underlie basal till. This geometry likely reflects deposition by outwash streams flowing in front of advancing glaciers.

Typically fine-grained, New Brunswick's glaciolacustrine deposits were formed in the late glacial stages as valleys were dammed by ice or glacial deposits, whereas glaciomarine deposits accumulated in low-lying coastal areas that were submerged by the elevated late glacial sea - up to 90 metres above current sea level.

According to the glacial erosion record, the province endured an intricate sequence of glacial erosion events during the Wisconsinan. Recorded ice-flow directions from around New Brunswick range from 001 to 360 indicating a complex relationship between ice-flow patterns in different parts of the Province. Glacial dispersal trends also vary throughout the Province, and may differ from the local, or dominant, glacial erosion (and/or ice-flow) trend of that area. This may in part be a result of the reactivation and expansion of some glaciers during the Younger Dryas, a millennial-scale cold event that interrupted the general late-glacial warming trend. Hence, dispersal trends cannot always be predicted from the known glacial erosion trends.

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Last modified: 5/15/2008