ABSTRACT This field guide provides an updated synthesis of the stratigraphy and chronology of glacial deposits in central Indiana near the southern limit of glaciation in the midcontinent. Central Indiana contains evidence of multiple glaciations—deposits from the last two glaciations (Oxygen Isotope Stages [OIS] 2 [Wisconsin Episode] and 6 [Illinois Episode]) have been the focus of recent stratigraphic and chronologic investigation. New radiocarbon and optically stimulated luminescence (OSL) dating from outcrop and core has refined the timing of OIS 2 and OIS 6 ice sheet advances, outwash/slackwater aggradation, glacial lake formation, and eolian activity. Radiocarbon ages within or below late Wisconsin till from three sites within 5 km (3 mi) of the late Wisconsin maximum limit indicate an age of 24.0 k cal yr B.P. for maximum OIS 2 ice sheet extent in central Indiana, consistent with chronology from Illinois and Ohio. A subsequent >50 km (31 mi) readvance (21.6 k cal yr B.P.) across central Indiana came within 10 km (6 mi) of the maximum limit and in the western part of the field-trip area, terminated in glacial Lake Eminence. The start of outwash aggradation and associated slackwater sedimentation in the West Fork White River valley and tributaries began ca. 27 k cal yr B.P. and continued until ca. 20.5 k cal yr B.P., representing the timing of ice sheet advance into and out of the paleo–White River drainage basin. Ice sheet advance and retreat rates average ~40 m/yr before and after the global Last Glacial Maximum (ca. 26−21 k cal yr B.P.) when ice was within ~50 km of the late Wisconsin maximum. OSL dating of pre-Wisconsin outwash and glacio-lacustrine sediment return ages between ca. 218 and 127 ka, confirming deposition during OIS 6. These ages document spatially complex sedimentation in bedrock valleys beyond the Wisconsin limit.

ABSTRACT Recent mapping in southwestern Michigan conducted through U.S. Geological Survey STATEMAP, EDMAP, and Great Lakes Geologic Mapping Coalition projects has produced new interpretations of the origin of the landforms and sediments of the Lake Michigan and Saginaw lobes of the Laurentide Ice Sheet and the dynamics of these lobes. The Lake Michigan lobe advanced southeastward into a proglacial lake at least as far east as the Kalamazoo moraine. During its advance, the lobe extensively deformed the lacustrine sediments it overrode. These structures will be discussed in several pits. When ice backed away from the Kalamazoo moraine, it formed a series of proglacial lakes, several of which were described for the first time in the studies upon which this guidebook is based. As the ice retreated, lowland areas between morainal uplands were utilized by meltwater drainage events, some of them probably catastrophic in nature. The Saginaw lobe stagnated over a broad marginal area as it retreated northeastward toward Saginaw Bay. The resulting stagnant marginal zone is coincident with the subcrop of the Marshall Sandstone. Enhanced basal drainage into the underlying sandstone may have played a role in the dynamics of the lobe. High-relief, supraglacial landforms such as hummocky topography and ice-walled lake plains overprint subglacial landforms in this region, which include large tunnel valleys with inset eskers. Better understanding of the glacial geology of this region is critical to economic development, management of water resources, and exploration for aggregates and other resources.