ABSTRACT: Glacial history of Prince Edward Island

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Investigations building upon the original research of Vic Prest have revealed a complex pattern of glaciation on PEI. At different times during the Quaternary, the island was influenced by glaciation from the northwest (Grenville Province), west (New Brunswick), north (Gulf of St. Lawrence), and south (Nova Scotia), as indicated by the distribution of erratics, diamicton fabric patterns, striations, and ice-thrust features. Locally, differences in orientations between adjacent diamicton fabric patterns, with associated lithologically-distinctive clasts, and striations indicate distinctive ice-flow events. However, differences in fabric orientation commonly convey more information about the mechanisms of till deposition at individual sites than concerning the regional ice flow pattern. All parts of PEI appear to have been glaciated during OIS 2, and multiple directions of ice flow are recorded at numerous locations. Ice-thrust features in eastern PEI suggest that northward flow from Nova Scotia was followed by southward and eastward flow from the Gulf of St. Lawrence. In western PEI, flows from the west, southwest, northwest, and northeast are recorded. The distribution of igneous and metamorphic erratics is of particular interest, as recognized by Vic Prest more than 40 years ago. Recent investigations indicate that granite and granodiorite erratics found in Prince County (western PEI) and in western Queen's County appear to originate from Appalachian (northern NS-southwestern NB) sources, compatible with striae and diamicton fabrics indicating flow from the west and southwest. Gniess and anorthosite erratics are also present in Prince County, and could indicate Laurentide ice influence. The possible Laurentide erratics are restricted to west.central PEI and are not found in mainland Nova Scotia or Cape Breton. A single southeastward-trending Laurentide ice flow event (e.g. Acadian Bay Lobe) would have been unlikely to have deposited erratics only in PEI, unless it was obstructed by Appalachian ice centred over southeastern New Brunswick and Nova Scotia. An additional difficulty is that the possible Laurentide erratics are associated with striae and diamicton fabric patterns indicating southwestward flow, which is incompatible with the southeasterly patterns suggested by recent reconstructions of the Laurentide events during OIS 2. Possible mechanisms for erratic deposition include OIS 4 Laurentide confluent with Appalachian ice buildup; deposition prior to OIS 4; or restriction of Laurentide ice to PEI by Appalachian ice in NB and NS, coupled with diversion of Laurentide flow towards the Laurentide Channel, as first suggested by Vic Prest and Doug Grant. Sedimentological and chronological research, including cosmogenic dating of erratics, is ongoing in an effort to coordinate the glacial history of PEI with that recorded from adjacent NS and NB.

Bibliography of Canadian Geomorphology