Last interglacial sediments of the Don Valley Brickyard, Toronto, Canada, and their paleoenvironmental significance

Abstract

The Don Valley Brickyard in Toronto is an internationally designated type site in recognition of diverse faunal remains in the Don Beds of last (Sangamonian) interglacial age; pollen in overlying strata record the climatic deterioration marking the onset of the last (Wisconsinan) glacial cycle. New sedimentological descriptions show that the Don Beds, about 8 m thick, were deposited in a lacustrine lower shoreface environment subject to episodic storms. Storm-deposited sand facies are interbedded with peaty muds that are extensively bioturbated. Water depths, derived from wave-formed ripples using linear wave theory, appear to have increased during deposition of the Don Beds from about 2 m to about 18 m (12 -28 m above the modem lake level), a change that is recorded by an overall fining-up sequence. Increasing water depths may have been the result of isostatic recovery of the lake outlet to the east. The Don Beds overlie a thin bouldery deposit, possibly a remnant of older Illinoian glacial sediments (York Till). The interglacial beds pass up into prodelta rhythmites (Scarborough Clays) of a regionally extensive delta body, indicating continued deepening. Deepening was accompanied by steadily decreasing mean annual temperatures; upper deltaic sediments (Scarborough Sands), exposed to the east along lakeshore bluffs, were deposited in a cold-climate setting during the opening phase of the Wisconsin glaciation.La briqueterie Don Valley B Toronto est reconnue intemationalement comrne un site type de faune fossile diversifike incorporee dans les lits Don laissks par le demier stade interglaciaire sangamonien; les pollens inclus dans les strates sus-jacentes documentent le refroidissement du climat qui marque le dCbut du demier cycle glaciaire (wisconsinien). Une Ctude kcente kvkle que les lits Don, d'environ 8 m d'kpaisseur, furent dt5posCs sur les rives inferieures d'un environnement lacustre sujet aux effets des tempCtes Cpisodiques. Les faciks arknacks accumulks lors des tempCtes sont intercalks avec des boues tourbeuses intenskment bioturbkes. L'application de la thkorie des ondes lineaires h I'ktude des rides de vagues indique que 1'6paisseur de la tranche d'eau a augment6 de 2 m h 18 m (12-28 m au-dessus du niveau actuel du lac) durant la pCriode d'accumulation des lits Don, changement qui est reflkte dans la sCquence ~Cdimentaire par un grano-classement normal. L'augmentation de 1'Cpaisseur de la tranche d'eau peut avoir result6 du recouvrement isostatique de 1'Cmissaire est du lac. Les lits Don reposent sur un dkpbt mince riche en blocs, possiblement des ksidus laissks par la glaciation plus ancienne de 1'Illinoien (Till de York). De bas en haut, les lits interglaciaires ckdent la place aux rythmites prodeltaiques (argiles de Scarborough) d'un vaste delta rkgional, tCmoignant d'un accroissement continu de l'kpaisseur de l'eau. Un diminution continue des tempCratures annuelles moyennes accompagnait cette augmentation de 1'Cpaisseur de la tranche d'eau; les sCdiments deltaiques superieurs (sables de Scarboroug...

Geological framework of the Laurentian trough aquifer system, southern Ontario

“…[Colour online. ] Based on primary lacustrine sedimentary features, Sunnybrook "till" has been considered to result from sediment raining from the base of floating ice onto the floor of a lacustrine basin (Eyles and Clark 1988;Eyles et al 2005). This interpretation questions the need for glacial advance and retreat to produce "till" units that appeared to lack evidence for grounded ice.…”

Dung analysis of the East Milford mastodons: dietary and environmental reconstructions from central Nova Scotia at ∼75 ka years BP

“…The faunal and floral assemblages recorded from the mastodon dung represent a unique snapshot of the environmental conditions of Nova Scotia at the transition between MIS 5a and MIS 4. This record is particularly relevant as sites recording this transition that include both floral and faunal components are still very limited in North America (Miller et al 2014); with the Don Formation of Toronto being the only well-known record from eastern Canada (Terasmae 1960;Kerr-Lawson 1985;Eyles and Clark 1988;Hann and Karrow 1993). The dung sample represents a short interval of time, likely the previous two days of feeding based on the food passage time of modern African elephants (Loxodonta spp.)…”

A Proposed Diachronic Revision of Late Quaternary Time-Stratigraphic Classification in the Eastern and Northern Great Lakes Area

“…Named for the Sangamon soil and Sangamon County, Illinois, this is the time of the last interglaciation or the time of a climate as warm as or warmer than the present (Johnson et al, 1997), and the traditional name is retained. It is principally represented in southern Ontario (at Toronto) by the fluviolacustrine Don Formation (Eyles and Clark, 1988;Karrow, 1990) and in the Hudson Bay Lowland of northern Ontario by the fluvio-paludal Missinaibi Formation (Skinner, 1973). Both formations contain fossils indicating a climate as warm as or warmer than the present.…”