Paleoenvironmental Analysis of Halifax Harbour: Sedimentology, Paleoclimatology, and Holocene Sea Level
Edgecombe, Roger B.
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Three cores (numbered 2,9,10) collected from Halifax Harbour using new submersible vibracoring equipment permits a reinterpretation of an acoustically distinct seismostratigraphic unit. This unit, never previously sampled, occurs in the base of Core 2. The benthic foraminiferal assemblages in the cores enable a determination of the paleoecology and paleoenvironment for the post-glacial history of Halifax Harbour. Foraminiferal species abundance and diversity permit an interpretation of the effects of organic and nutrient loading in the upper 30-70 cm, caused by an increased sediment flux and effluent discharge from anthropogenic sources on the marine benthic community. The presence of foraminifera within the distinct seismic unit requires a reinterpretation of the distinct seismic unit previously interpreted as lacustrine. The foraminiferal assemblages, in combination with the lithology, indicates an estuarine depositional environment. Peat and foraminiferal samples yielded three carbon-14 dates: (i) The peat sample from Core 9 (261-262 cm) is not in situ, but provides a date of 1,065 +/-80ybp. Erroneous peat dates may provide insight into previously unexplainable sea-level points. (ii) The peat sample from Core 10 (459-463 cm) is in situ and yielded a date of 7,770 +/-260 ybp. (iii) The date yielded from a foraminifera sample (474-489 cm, 8,480 +/-60 ybp) corresponds to a time when glaciers were no longer present in Nova Scotia. Therefore, the age suggests that a paleoenvironmental interpretation of estuarine deposition is realistic. Carbon-14 dating permits the construction of an extended Holocene relative sea-level curve by plotting carbon-14 dates against corresponding sample depths (sample depth in core plus water depth). The new sea-level curve in this study indicates that the inner continental shelf experienced initial emergence, followed by a prolonged period of submergence from 7500 ybp to the present. The theoretical model of glacio-isostatic rebound, resulting in the migration of the peripheral forebulge following deglaciation, can explain the various sea-level curves observed in Atlantic Canada, but may not be able to explain short term fluctuations in relative sea level. Keywords: foraminifera, Halifax Harbour, seismostratigraphy, estuarine, Holocene, sea level, peripheral forebulge, eustatic Pages: 128 Supervisor: David Scott