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An interval of late-glacial to early Holocene sedimentation, spanning the period 12.9–8.4 ka BP (14C dated by accelerator mass spectrometry), is contained within 15 cm of gyttja in a core from a small lake on southwestern Cumberland Peninsula, Baffin Island. This sediment was subsampled in continuous 2.5 mm increments for diatom analysis. Extremely low sediment accumulation rates (~1.8 cm ka−1) are characteristic of the initial phase of organic sedimentation, but they increase rapidly (to 14.2 cm ka−1) after 9 ka BP. The first 0.5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments. Thereafter, and throughout the late glacial and earliest Holocene, diatom floras were dominated by alkaliphilous and circumneutral species of Fragilaria. Around 9 ka BP, shifts to acidophilous floras dominated by Brachysira brebissonii, and, later, Eunotia rhomboidea and Frustulia rhomboides vars. saxonica and crassinervia, suggest a period of natural lake acidification. High diatom production accompanied the lowered lake-water pH, which reflects, respectively, the paleolimnological response to an early Holocene climatic optimum, and progressive depletion of lake alkalinity sources. There is no evidence of diatom or sediment responses attributable to the Younger Dryas oscillation, implying that deglacial reorganizations of the North Atlantic Ocean did not necessarily affect paleoclimatic conditions in the southern Cumberland Sound region.

Mazama tephra is a widespread mid-Holocene stratigraphic marker, dating to ca. 6845 BP, and is considered useful for the correlation of Holocene events in western North America. We present evidence from Copper Lake, Alberta, for a tephra layer that underlies Mazama tephra and appears to be a discrete tephra layer but that is indistinguishable from the conventional Mazama tephra by microprobe analysis of glass shards. Three alternative hypotheses are considered to explain this tephra underlying Mazama: in situ position of an earlier Mazama-like tephra, recycling of tephras, and settling of tephra slabs through the gyttja. The size distributions of birch pollen grains indicate that the Mazama-like tephra is in primary stratigraphic position in the early Holocene gyttja, and that sediment recycling has not destroyed the integrity of Copper Lake sediment stratigraphy. It is concluded that most probably a Mazama-like tephra was deposited between 9700 and 10 500 BP. If this in situ hypothesis is correct, the identification of a tephra as Mazama by major-element chemistry does not necessarily fix the age of the enclosing strata. Evidence to confirm the existence and plot the distribution of a Late Pleistocene – early Holocene, Mazama-like tephra is needed from other sites in northwestern America. A collateral result of this study is that ablation of valley-bottom ice in the vicinity of Castle Mountain took place prior to 10 500 BP.

The magnitude 6.3 Timiskaming earthquake of 1935 resulted in discoloration in small lakes in the epicentral region. Sonar profiles for Lac Tee have shown that organic-rich gyttja has been removed from the sides and redeposited in the deep parts of the lake. Lake sediment cores from deep basins contain a 2–3 cm uppermost layer, which is interpreted as the normal accumulation of sediment since 1935. This is followed by a 20 cm chaotic zone of black gyttja mixed with partly tabular fragments of a previously formed silt layer, underlain by a dense 1–2 cm thick silt horizon. The latter is interpreted as having formed by rapid settling of the denser silicate portion of the resuspended sediment. This 20 cm zone is insufficient to account for the abnormal thickness of gyttja in the basins, so events of this kind would have had to have occurred repeatedly since deglaciation. The only major prehistoric event revealed by these ~100 cm cores is at a depth equivalent to about 1500 years ago, based on the amount of sediment deposited since 1935. A minor silting event occurred about 400 years ago. On this basis, the recurrence interval of magnitude 6 or greater earthquakes is longer at Témiscaming than at Charlevoix, Quebec (75 years historically), consistent with the present relative frequency of small earthquakes in these two regions.

The modern sediments in the Cataraqui River lagoon and marsh (Kingston, Ontario) consist of mixtures of organic material and clayey silts, the organic content of which increases as water depth decreases; gyttjas are accumulating in the deeper water parts of the lagoon, whereas peat is the dominant sediment in the very shallow water portion of the lagoon (

Ground penetrating radar (GPR) has been applied to the mapping of stratigraphy and peat thickness of a large bog in southwestern Ontario. The GPR survey was undertaken in conjunction with a conventional coring survey and measurement of peat physical properties. The results indicate that GPR responds to peat moisture content and bulk density, which vary with stratigraphic changes. In particular, the acrotelm–catotelm boundary and the basal clay are GPR reflectors. The presence of gyttja above the clay is indicated by complex basal reflections. Ground penetrating radar is a viable alternative to an intensive coring survey for evaluating peat depth and extent.

The sequence of units (from the base up) in the Sixteen Mile Creek lagoon (Lake Ontario) mimics the longitudinal sequence of surficial environments: pink silt—overbank (flood plain – dry marsh); bottom sand—stream channel and beach; orange silt—marsh; gyttja—wet marsh and very shallow (deltaic) lagoon; and brown and grey clay—open-water lagoon. This entire sequence accumulated over the last 4200 years under slowly deepening, transgressive conditions caused by the isostatic rise of the lake outlet. Land clearing by European settlers dramatically increased the supply of clastic sediment and terminated the deposition of the organic-rich silty clays (gyttja) that make up most of the lagoon fill.Because the gyttja and beach sand are interpreted to have accumulated in water depths of less than 0.5 m, the elevation–time plot of 14C dates from these units can be used to reconstruct a very closely constrained lake-level curve. The data indicate that water levels have risen at an average rate of 0.25 cm/a over the last 3300 years as a result of differential, isostatic rebound. Superimposed on this trend are water-level oscillations with amplitudes on the order of 1 m and periods of several hundred years. These oscillations are synchronous and in phase with water-level fluctuations in Lake Michigan, and with a variety of other climatic variations in North America and Europe. We propose, therefore, that the water-level oscillations are a result of long-term, climatically produced variations in precipitation in the Great Lakes drainage basin.

Lake O'Hara (subalpine) and Opabin Lake (alpine) are situated directly adjacent to a high section of the Continental Divide in the central Canadian Rocky Mountains. Core samples recovered from the lakes show a consistent stratigraphy comprising gyttja and underlying inorganic clastic sediments. The gyttja contains Bridge River (2350 years BP) and Mazama (6800 years BP) tephras and is separated from the lower clastic sediments by a sharp, conformable contact. Radiocarbon dates obtained from conifer needles, extracted from directly above the contact, indicate that deglaciation had proceeded upvalley from the O'Hara basin priorto ca. 10 100 years BP. Preliminary palaeobotanical and macrofossil data suggest that a Pinus–Abies forest with lesser Picea was established in the vicinity of Lake O'Hara by this time. Consequently, the minimum age of moraine systems situated downvalley from Lake O'Hara is Late Wisconsinan.Mean annual sedimentation rates were derived from sediment thickness data from 14 Lake O'Hara and 2 Opabin Lake cores. Averaged total sedimentation rate values from the Lake O'Hara cores are 0.13 mm/year (post-Bridge River), 0.13 mm/year (Mazama – Bridge River) and 0.05 mm/year (11 000 years BP – Mazama). Averaged total sedimentation rate values from the Opabin Lake cores are 0.19 mm/year (post-Bridge River), 0.07 mm/year (Mazama – Bridge River), and 0.06 mm/year (8530 years BP – Mazama). Higher total sedimentation rates in post-Bridge River sediments of Opabin Lake are presumably related to climatic conditions associated with more extensive upvalley ice during the last ca. 2300 years. Highly variable sedimentation rate data obtained from the Lake O'Hara cores suggest that the use of sedimentation rate data as a proxy record of upvalley glacial activity is inappropriate in the Lake O'Hara setting where inflowing glacial stream systems are interrupted by upvalley lake basins.Aspartic acid D/L ratios were derived from bulk gyttja samples of known age from seven Lake O'Hara and one Opabin Lake core. In all but two cases, aspartic acid D/L ratios increase consistently with respect to sediment age. The increasing downcore trends in the aspartic acid D/L ratios suggest the possibility of using amino acid data from bulk gyttja samples as a check for reworking in cases where chronostratigraphic markers are absent.

Study of late Wisconsin deposits in a small bog on the crest of Brampton esker (mantled by the Halton Till), about 30 km west of Toronto, Ontario, yielded a radiocarbon date of 12 320 ± 360 years BP (BGS-551) for a sample of white spruce cones that contained fully-developed seeds. This date on cones (in gyttja) provides an estimate of minimum age for the lower boundary of the spruce pollen zone in southern Ontario. Silty clay beneath the gyttja yielded leaves of Dryas integrifolia and pollen assemblages (a herb pollen zone) that indicate presence of a dwarf-shrub tundra (essentially treeless) type of vegetation.This study supports the Port Huron Stadial age (about 13 000 years BP) of the Halton Till that underlies the silty clay, and suggests an age of between 12 500 – 13 000 years BP for glacial Lake Peel in the Brampton area that preceded the glacial Lake Iroquois phase in the Lake Ontario basin.

Differential postglacial uplifting in the Huron basin has long been recognized from the observed deformation of raised shorelines, particularly those associated with the Algonquin series of glacial lakes (12 000–10 500 years B.P.) and the postglacial Nipissing Great Lakes. From Nipissing time, about 5500 years B.P., to the present, lake levels apparently fell in the northern Huron – Georgian Bay region as the basin upwarped and the outlet was downcut.Recent emergence of Manitoulin Island in northern Lake Huron was inferred, independently of raised shoreline data, from sediment sequences in a series of 3 beach sites and 8 small lake basins at various altitudes up to 20 m above Lake Huron. Organic sediment (gyttja) in each lake overlies clastic inorganic sand or silt, with the contact horizon demarcating the isolation of each basin as its threshold emerged from the high-energy littoral environment of Lake Huron. Radiocarbon dates and elevations of the basal gyttja sediments and organic beach sediments suggest uplift at a constant rate of 2.2 mm/year over the past 5000 years. This rate refers to Little Current, Ontario, and is for movement relative to the outlet area of Huron basin at Sarnia, Ontario. The value agrees with basin tilting inferred from lake level gauge observations made during the last 100 years.