Evidence of Structural Anomaly Beneath Saginaw Bay
Analysis of modern and Pleistocene hydrologic exchange between Saginaw Bay (Lake Huron) and the Saginaw Lowlands area
John R. Hoaglund III, Jonathan J. Kolak, David T. Long and Grahame J. Larson
Geological Society of America Bulletin 2004;116;3-15
Given the observations of Westjohn and Weaver (1996c), the presence of a northwest trending anticline under Saginaw Bay wouldlikely control the distribution of freshwater and brine in the Marshall aquifer below the bay. The anticlinal reconstruction assumed in the groundwater-flow model is coincident with extensions of anticlinal structures observed on land, as interpreted by Cohee et al. (1951) and Lane and Hubbard (1895). Cvancara and Melik (1961) do not explicitly mention the presence of an anticline under Saginaw Bay; however, one can infer the existence of such a feature from their reconstruction of the bedrock geology of Lake Huron. Other interpretations of Saginaw Bay subsurface geology have been proposed, including a northeast-trending graben (Herman et al., 1991). The graben reconstruction includes Saginaw Bay and extends southwesterly through most of the Saginaw Lowlands area. The graben interpretation is based on geophysical and stratigraphic relations involving horizons below the Coldwater shale, which constitutes the base of our groundwater flow model. However, the possible propagation of growth faulting into younger strata might imply that the edges of the bay are faultbounded, with the Marshall aquifer dropped down in the bay relative to the mainland and ‘‘thumb’’ regions of Michigan..