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Conestogo Dam Cut ANSI contains Late Wisconsinan, Nissouri Stadial, Catfish Creek Till overlain by Port Bruce Stadial, Stirton Till, Tavistock Till and Mornington Till. This ANSI is the Type Section for the Mornington Till and the Stirton Till. The section is important for till stratigraphy interpretation.
The site shows a sequence of Late Wisconsinan and Port Bruce Stadial tills, including the Early Wisconsinan-Missouri Stadial Catfish Creek Till. The till section is located in the Conestogo Lake Conservation Area, therefore it is considered protected. [Earth Science Database, 1998]
Surficial Geology (OMNR, 1983):
Major glacial advances and retreats in the Great Lakes region have been assigned to three substages- Early, Middle and Late Wisconsinan (Dreimanis and Karrow, 1972). Early Wisconsinan tills occur at depth throughout southern Ontario representing advances by the Erie, Huron and Georgian Bay ice lobes. Middle Wisconsinan sediments consist of lacustrine silts and sands with minor organic deposits, indicating that glacial activity was not extensive during this substage. Events during the Late Wisconsinan generated the most varied and complex tills in southern Ontario produced by oscillating ice lobes.
The Mornington Till (till D of Karrow, 1971) and the Stirton Till (till B of Karrow, 1971) are Late Wisconsinan- Port Bruce Stadial deposits. The Port Bruce Stadial exhibits cold weather conditions brought about the readvance of the Wisconsinan glacier that covered most of Ontario. Both tills are believed to have been deposited by the Georgian Bay and/or Huron ice lobes (Cowan, and others, 1975).
The Mornington Till is a stony-surfaced, brown silty clay till with obvious desiccation cracks, extends as the surface till from the east edge of the Milverton Moraine eastward, to coincide with the Macton Moraine (Karrow, 1974). It is named after Mornington Township, Perth County, where it is the surface till. According to Karrow (1974), this till overlies the Tavistock Till and is overlapped along its western and northern margins, by the Stratford Till and Elma Till respectively.
The Stirton Till has been recognized only as a subsurface unit showing a thin, silty to clayey, rather stone free brown till out-cropping in the same area as the Mornington Till (Karrow, 1974). This till underlies the Tavistock and Mornington Tills and overlies the Catfish Creek Till.
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Significance (OMNR, 1983):
During the Port Bruce Stadial the ice was unstable, producing numerous local advances and retreats laying down a series of till sheets. The Mornington and Stirton Tills are believed to have been deposited by ice moving from the northwest associated with either the Georgian Bay or Huron Lobes (Karrow, 1974).
At the Type Section, the Conestogo Dam cut, the Mornington Till is the surface till and overlies Tavistock Till that, in turn, overlies Stirton Till (Karrow, 1974). The Catfish Creek is the lowermost till in the Type Section.
These tills are important to the glacial interpretation of the Waterloo area. Until more information becomes available (Karrow, in press), the significance of the tills in this area is not entirely understood.
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