Peta J. Mudie
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Ph. D. Thesis
Palynology of Later Quaternary Marine Sediments, Eastern Canada
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Studies of pollen, spores and dinoflagellate cysts in later quaternary marine sediments on the Eastern Canadian continental margin were undertaken in order to assess whether palynology is a useful tool for investigating the paleoecological history of marine sediments in glaciated shelf regions. The area covered by this investigation extends from Nova Scotia to Baffin Bay and encompasses nearshore to upper slope environments in Cool Temperate to Arctic climatic regions. Because no comprehensive Quaternary palynological studies have previously been made, baseline data on present palynomorph distribution patterns, taxonomy, preservation and methods of transport are described in this thesis. These new data were applied in biostratigraphic studies of later Quaternary sediments on the Nova Scotian and Labrador shelves.
The quantities and taxonomic composition of palynomorphs were studied in 160 samples of surface sediments from the continental margin of Eastern Canada. These data show that the Quaternary pollen assemblages reflect regional, climate-controlled terrestrial vegetation zones. Quaternary dinocyst assemblages correspond to major marine phytogeographic provinces (Temperate Northwest Atlantic, Subarctic and Arctic) and to cross-shelf differences in surface water temperature-salinity characteristics.
Detailed studies were made of pollen preservation in organic-rich marine muds. Observed preservation-state changes were correlated with biochemical parameters to derive a model of early diagenesis in basinal marine sediments. It is established that for full recovery of later Quaternary palynomorphs, processing should not include acetolysis or concentrated hydrochloric acid. A satisfactory processing method using Calgon solution, hydrofluoric acid and Schulze solution is described in detail.
A qualitative model of regional pollen transport from terrestrial to deep-sea marine environments is proposed for the Southeastern Canadian region. Some aspects of this model are tested by data obtained from studies of pollen in aerial spore traps and in suspended sediment samples from nearshore and shelf water off Nova Scotia. Comparison of these data with pollen influx data determined for cores of modern sediment dated by Pb-210 or weed pollen markers forms the basis of a box-model analysis of pollen transport pathways to nearshore marine sediments. It is concluded that: aerial influx from local vegetation is the main pathway by which pollen enters the nearshore marine environment in Southeastern Canada; tidal circulation mixes pollen from aerial and fluvial sources prior to permanent deposition and transports about 50% of the annual pollen influx to the continental shelf.
Detailed palynological studies are reported for long radiocarbon-dated cores from the Central Labrador Shelf and the Nova Scotian Shelf. Correlation between the marine pollen zones and lake pollen assemblage zones provides a means of approximately dating Holocene marine sediments. This biostratigraphic correlation also provides a means of calibrating radiocarbon dates obtained from marine organic material which contains recycled older carbon. Dinocyst assemblage zones are recognised in these cores which reflect changes in oceanographic conditions near the ocean-air interface during the later Quaternary period. These marine palynomorphs may provide a more sensitive index of temperature and salinity changes in the surface shelf water than planktonic foraminifera which are often not abundant in neritic environments.
The most significant paleoecological findings are that 1) the glaical-interglacial palynological records in the shelf sediments indicate that the late Wisconsinan ice sheet margin was far less extensive in Eastern Canada than formerly deduced from undated submarine tills; 2) vegetation probably survived in coastal plain refugia on the inner shelf areas during the Late Wisconsinan glacial interval; 3) influx of warm slope water over the Nova Scotian Shelf between 14,000 and 12,000 years B.P. appears to precede the deglaciation of the Southeastern Canadian uplands, and 4) flux of colder water to the continental shelves precedes the later Holocene climatic cooling which is recorded in both Central Labrador and Nova Scotia.
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Supervisor: D. J. W. Piper