Glacial Geology of New Brunswick
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
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 001º to
360º 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.