Paper No. 1
Presentation Time: 8:10 AM
NEW STUDIES ON THE INTERGLACIAL TO EARLY STADIAL DON AND SCARBOROUGH FORMATIONS OF THE TORONTO AREA, CANADA
The continental series of interglacial and transitional units of the Toronto area is one of the most complete in North America. The Don Formation exposures, described since the 19th century, give a partial view of a large sedimentary body accumulated by the ancestral Laurentian River at the margin of Lake Coleman. From a renewed stratigraphic analysis and 42 additional pollen spectra, the formation is subdivided into 6 allo- and pollen zones: - the lowermost clayey zone D1, exposed until the 1950's, contains a cladoceran fauna found today in glacial lakes; it corresponds to the Illinoian-Sangamonian transition;- zones D2 (Terasmae 1960) and D3 record the Sangamonian climatic optimum (as warm as today and warmer parts of MIS 5e); - the incised decimetric gravelly zone D4 marks an erosional disconformity and a lowered lake level; - zone D5 indicates a transition from a southern to a northern boreal forest; the lake level rose by about 18 m; - the uppermost zone D6 comprises beds of shale cobbles and weathered sand, deposited in hemiarctic conditions and very shallow waters; long discontinuities are usually inferred in this unit. The overlying Scarborough Formation represents prodelta and delta sediments deposited in an ice-dammed lake, in continuous subarctic conditions. Deep channels are incised into this formation, filled with the composite Pottery Road Formation. A new fading-corrected TL age of 129 ± 10 ka places the deposition of zone D3 of the Don Formation during MIS 5e substage. This age is consistent with the age of circa 120 ka estimated from the pollen zone Don3b. A new TL age of 100 ± 10 ka for the lower beds of the Scarborough Formation dates the first evidence of continental ice in the St. Lawrence River Valley, namely the Deschaillons Varves-Lévrard Till episode, during MIS5 stage. Due to fading uncertainties, the age difference between the two formations and the consequent hiatus may be real but remains to be confirmed.