Lithostratigraphic Correlation of Saskatchewan Tills: A Mirror Image of Cretaceous Bedrock
Date
1990-04
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Doctoral
Abstract
The Quaternary stratigraphy of Saskatchewan comprising the Sutherland Group, with its Lower, Middle and Upper Tills, and the Saskatoon Group, with the Floral and the Battleford Formations as defined on the basis of standard lithologic criteria is now confirmed by the use of trace elements, V and Zn, in the tills. The statistical analysis of carbonate and trace element content was performed for all formations from test holes selected to provide a real representation of southern Saskatchewan.
Carbonate can be used to identify and distinguish the tills except between the Upper and Lower Tills of the Sutherland Group and between the Upper and Lower Tills of the Floral Formation. The trace element, V and Zn, content can be used to help differentiate between the Upper and Lower Tills of the Sutherland Group and the Floral Formation. Trace elements in conjunction with carbonates and physical characteristics, such as weathering zones, structure, and colour, can be used to identify and correlate tills throughout Saskatchewan except for the southeastern part.
Trace element levels vary over southern Saskatchewan and commonly decrease in the down—ice direction from the source area. However, relative differences are maintained between tills over most of the area.
The Middle Till of the Sutherland Group and the tills of southeast Saskatchewan are high in carbonate content. The trace element content,
particularly V and Zn, differs only slightly between tills and therefore, cannot be used reliably to separate the tills in southeastern Saskatchewan. The total carbonate content together with the ratio of dolomite/calcite appears to be the most useful criterion for distinguishing these tills.
The Cretaceous bedrock units of eastern Saskatchewan and western Manitoba (Pierre Shale, Niobrara Formation, Morden Shale, Favel, Ashville, and Swan River Formations) have trace element concentrations, particularly V and Zn, that differ between units. These trace element levels along with other lithologic characteristics can be used to associate bedrock source units with the derivative tills. The clay—rich, dark coloured Upper Till of the Sutherland Group with its very high trace elements can be related to the Morden Shale as its prime source rock while the other tills can be related to bedrock units below and above the Morden Shale. Thus the Quaternary stratigraphy is reflected as a mirror image of the Cretaceous bedrock sequence.
A model of progressive stripping of bedrock from one source area by successive glacial ice sheets advancing from an ice dome to the north
accounts for most of the glacial till sequence.
The Middle Till of the Sutherland Group was derived from an area where more carbonate rocks were exposed by a glacier advancing from a
more easterly direction. This ice movement may explain the relatively higher carbonate content of all the tills in the southeastern part of Saskatchewan and also may have contributed to the high carbonate tills of the Floral Formation.
The ice moved off the resistant Shield unsaturated with debris, encountered the soft Cretaceous rocks, and became saturated with material
over a short distance. The ice then carried the load out to the terminus of the glacier without eroding or incorporating much of the deposits over which it passed.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Geological Sciences
Program
Geological Sciences