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U.S. Geological Survey Open-File Report 2009-1137

## Quaternary Geologic Framework of the St. Clair River between Michigan and Ontario, Canada

| Title PageList of Figures and TablesConversion Factors and DatumAbstractIntroductionData Acquisition and ProcessingGeologic FrameworkConclusionsAcknowledgmentsReferences Cited
  | **By David S. Foster and Jane F. Denny**
Abstract
Concern about the effect of geomorphic changes  in the St. Clair River on water levels in the Upper Great Lakes resulted in the  need for information on the geologic framework of the river. A geophysical  survey of the Upper St. Clair River between Port Huron, MI, and Sarnia,  Ontario, Canada, was conducted to determine the Quaternary geologic framework  of the region. Previously available and new sediment samples and photographic and  video data support the interpretation of the seismic stratigraphy and surficial  geology. Three seismic stratigraphic units and two unconformities were  identified. Glacial drift, consisting of interbedded till and glaciolacustrine  deposits, overlies shale. Glaciofluvial and modern fluvial processes have  eroded the glacial drift. Glaciofluvial, glaciolacustrine, fluvial, and  lacustrine deposits overlie this unconformity. Seismic facies were interpreted  to identify areas where these geologic facies exist; however, in the absence of  distinct boundaries between facies, these deposits were mapped as one  undifferentiated unit. This unit is thickest in the northernmost 3 kilometers  of the river, where it consists of relatively coarse-grained fluvial, reworked  glaciofluvial, and possibly glaciofluvial deposits. To the south, this  coarse-grained unit thins or is absent. The undifferentiated unit comprises  most of the surficial deposits in the northernmost river area. Some areas of  glacial drift, predominantly till, are exposed at the lake and riverbed. The  shale is not exposed anywhere in the region. Geophysical surveys at sites  downriver, together with the results of previous studies, indicate that the  geologic framework is similar to that in the northernmost river area except for  the absence or reduced thickness of the coarse-grained fluvial deposits.  Instead, glacial drift is exposed at the riverbed or is covered by a veneer of  sediment. This information on the substrate is important for ongoing sediment  transport studies. |
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