The climatic and vegetational history of the postglacial in Central Saskatchewan
Abstract
Pollen and diatom samples from three lakes in the La Ronge area
of central Saskatchewan provide information on the vegetation and climate
for a period of time from 9,000 years ago to the present. Pollen stratigraphy
can be presented in percentage form and as absolute influx data.
Both methods were employed and fanned the basis of a numerical stratigraphic
zonation and a description of vegetational sequences.
From approximately 9,000 to 8,100 years ago the level of Glacial
Lake Agassiz dropped from its Campbell Phase level of 423 m to below
370m above sea level. At this time most presently existing water-bodies
became in outline and area much as they are today. The ice retreated
from the Cree Lake Moraine close to 9,000 years ago, allowing Glacial
Lake Agassiz to drain to the east. It is suggested that before 9,000
years ago the Polar Air Mass dominated the region. This resulted in
stagnation of the glacier and stabilization of a zone of treeless
vegetation close to the ice front. It also explains why tree pollen
are absent from the lake sediments. After 9,000 years ago, the Pacific
Air Mass became dominant, causing rapid ice retreat and permitting the
northward expansion of spruce forest. Approximately 8,500 years ago,
or even earlier, tree pollen became an important component of the pollen
assemblage.
From approximately 8,000 to 6,700 years ago, first alder and
then pine migrated into the La Ronge area. This resulted in a true
boreal forest much like the one now growing there. Between approximately
3,500 to 3,000 years ago, the conditions became slightly cooler and/or
moister, rather like today's climate.
Diatoms, several of which have not been previously recorded
from Saskatchewan, reveal little additional information. Lake waters
remained relatively unaltered since organic or calcareous sedimentation
began 8,000 years ago. Only the southernmost of the three lakes studied,
Marl Pond, displays a brief change from its normally slightly basic
waters to slightly acidic, approximately 3,500 years ago. A more recent
fluctuation to acid conditions is not yet clearly reflected in the
diatom flora.
***Omissions***
Page 110, Para.2, Line 8, Ritchie (1968, p.325) should read:
Lichti-Federovich and Ritchie (1968, p.325).
Page 136, the omission of:
Mott, R.J., 1975, Palynological studies of lake sediment profiles from southwestern New Brunswick: Canadian Journal of Earth Sciences. 12,pp. 273-288