ABSTRACT U.S. Geological Survey (USGS) Monograph 53 by Frank Leverett and Frank Taylor identified more than 20 deltas of late Pleistocene age in the Lower Peninsula of Michigan. To that list, we add many additional deltas discovered during the course of our research. These “relict” deltas are important proxies for paleoenvironmental conditions, particularly wave energies, as well as prevailing wind and longshore drift directions. If dated, they can help to constrain the chronologies of ice retreat and proglacial lake stages. In plan view, relict delta morphologies usually protrude from a paleolake shoreline and are often elongate or cuspate shaped. Most of the deltas identified by Leverett and Taylor have this morphology and are located at the junction of a major present-day river and a relict paleolake shoreline. In this chapter, we map and discuss these deltas, first identified by Leverett and Taylor, while also identifying and describing the other, newly found deltas. All of these deltas formed during the marine isotope stage 2 ice retreat, roughly 28–13 ka. To identify and characterize them, we utilized a variety of data within a geographic information system, mainly a statewide USGS 7.5′ digital raster graphic, a 10 m digital elevation model (DEM), county-level Natural Resources Conservation Service soil data, and schematic lithologic depth profiles interpreted from descriptive water well and oil/gas logs. DEMs were particularly useful, because they can be “flooded” to various elevations of paleolakes. Maps of soil wetness and textural characteristics were also useful in detecting and delineating deltas. In sum, we mapped 61 deltas; 27 had been known from previous works, whereas 34 are newly reported in this study. Most are composed of sandy, well-drained sediments and have smooth, graded longitudinal profiles. Of these, most are perched above a relatively low-relief, poorly drained lake plain. However, unlike several deltas recognized by Leverett and Taylor, we found that many of the newly reported deltas are (1) adjacent to one or more formerly unknown shorelines, (2) not associated with a modern river, (3) complex, and/or (4) broad, coalesced features, deposited by more than one river, with fan-like morphologies. The methods that we used to identify and delineate these deltas can be applied to other regions. Mapping like the kind reported here will aid in a better understanding of the paleocoastal and terrestrial conditions during the late Pleistocene.

ABSTRACT Mapping of glacial deposits in Michigan dates to the very beginnings of the glacial theory in North America and logically divides into three parts: (1) early work (1885–1924) by Frank Leverett, Frank Taylor, and their colleagues, culminating in U.S. Geological Survey Monograph 53 and the publication of the first surficial geology maps for the state; (2) incremental upgrades (1925–1982) of Leverett and Taylor’s work in subsequent, statewide maps by Helen Martin and William Farrand; and (3) the period since 1982, characterized by a relatively small number of detailed, process-oriented studies at various scales, including the STATEMAP and EDMAP projects and investigations led by university researchers. Progress in mapping the surficial geology of Michigan has been challenged by the complexity of glacial deposits and limited state and federal funding. The most recent maps are Farrand’s statewide maps of glacial geology, which are based on the maps of Martin, which, in turn, were based on the original reconnaissance maps by Leverett and Taylor, now more than a century old. Thus, statewide maps of surficial sediments and landforms in Michigan are outmoded, often inaccurate, and in need of revision. Fortunately, new technologies and data sets are revolutionizing traditional mapping methods, creating opportunities for making cost-effective and accurate maps of Michigan’s glacial deposits. Digital soils data, in particular, when viewed within a geographic information system environment, offer an especially promising avenue for improved glacial mapping.