QUATERNARY STRATIGRAPHY OF THE DEFIANCE MORAINE NEAR DETROIT, MICHIGAN

Geologic mapping of the surficial geology of the Northville quadrangle northwest of Detroit shows that the stratigraphy of the Defiance moraine is more complex than previously supposed. The moraine is composed of a stratified sequence of interbedded alluvium and diamicton. The alluvium is of braided fluvial origin. Most of the diamicton was deposited as sediment gravity flows; only that in the upper part of the section is till. The Defiance moraine is generally considered to have formed as part of the late Pleistocene Carey ice advance of the Wisconsinan glaciation. However, a buried paleosol (5YR argillic horizon with associated caliche) located within the morainal section indicates that a significant hiatus is present and suggests that multiple glacial episodes are represented. Isotopic ages on sediments below the paleosol at four sites are all beyond the range of radiocarbon dating, but these ages may be influenced by coal reworked from the underlying bedrock. The Defiance moraine is overlain unconformably by alluvium composing the "Defiance channel," i.e. the abandoned course of a braided Pleistocene paleoriver, and locally by Holocene colluvium, alluvium, peat and marl. Southeast of the Defiance moraine is a concentric series of Pleistocene paleolake plains underlain by thin cappings of lacustrine sand overlying Defiance morainal sediments. A soil chronosequence suggests that: 1) paleolake plains increase systematically in age northwestward with increasing elevation, and 2) alluvial deposits composing the Defiance channel, and river terraces locally along the middle Rouge River, formed contemporaneously with some of the earliest episodes of paleolake sedimentation. The Quaternary structure of the map area appears to be a monocline, tilted very gently southeastward, with minor glaciotectonic or soft-sediment deformation.