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At Basin Head Harbour, P.E.I., several different sediment deposits record post-glacial variations in local sea level. Homogeneous sands constitute the material of a relatively large system of about 31 ridges. A salt marsh and estuarine sediments are found in a lagoon and a harbour protected by the ridge system. The seaward side of the ridge system is bounded by dunes and a beach.

Variations in the diatom flora preserved in the cored estuarine muds (8.4 meters depth) indicate salinity changes in the aquatic environment through time. Three biostratigraphic zones are established which indicate: 1) Zone 1 (836-600 cm.) represents ponded fresh water, 2) Zone 2 (600-280 cm.) records high salinity conditions, and 3) Zone 3 (280-000 cm.) indicates a fresh to slightly brackish environment.

The base of the core, about 11.5 metres below (Higher High Water) Datum, is radiocarbon dated at 4,185 years Before Present. The earliest marine influence is recorded by diatom microfossils at about 9.5 metres below Datum. This influence occurred after deposition of sediments (738-733 cm.) radiocarbon dated at 3,370 B.P. The boundary between biozones 2 and 3 is extremely well defined (by diatom stratigraphy) as an abrupt freshening of the aquatic habitat and is correlated laterally with the construction of the adjacent sand ridge system.

It is known that the ridges were constructed before 1050 B.P. when a spruce tree lived on the ridges and was subsequently covered by the upward-growing salt marsh. The ridge system, probably a Barrier, was rapidly constructed about 2,000-1,000 B.P.

The Basin Head Harbour study is the first to report the use of diatom stratigraphy as a parameter of post-Glacial marine transgression in the Maritimes.

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Supervisor: H. B. S. Cooke