80-11 Revisiting the Lake Michigan Lobe Stratigraphy in Southwest Michigan, USA; Observations from New and Historic Cores at the Michigan Geological Survey

Session: Recent Advances in Glacial Geology, Geomorphology, and Chronology

Presenting Author:

Authors:

Abstract:

Analysis of new cores from across southwest Michigan is helping shed light on the complex story of the Lake Michigan Lobe (LML) stratigraphy. Ongoing and recently completed surficial geological mapping by the Michigan Geological Survey (MGS) in southwest Michigan provides insight into the sediment, landforms, and stratigraphy of the LML terrain. MGS collected a total of 53 cores across Allegan, Ottawa, Muskegon, and Kent counties over the past 3 years and has access to over 118 archived cores in the LML terrain at the MGS.  

The LML terrain is marked by a series of moraine uplands and ridges extending across southwest Michigan in a roughly NE-SW orientation. They are, in order from east-to-west, the Kalamazoo, Valparaiso, Lake Border, and Montague moraines. These uplands and ridges are often capped with Saugatuck till (ST) but can be capped with thin glaciolacustrine sediments or sand and gravel from ice-contact collapse. Notably the Valparaiso upland is drumlinized in places indicating that it is an over-ridden upland.  The Montague moraine is capped with the Montague till (MT) and glaciolacustrine fines. Moraine ridges are separated by areas of ground moraine, outwash (channels and fans), and glaciolacustrine sediments.  

The stratigraphy observed in cores from the LML terrain in southwest Michigan is becoming clearer and matches observations from previous research. The oldest glacial sediments above Paleozoic bedrock are commonly diamicton either the Glen Shores till (likely predating MIS-2) or the Ganges till (MIS-2 till). Overlying the Ganges are glaciolacustrine sediments associated with Glacial Lake Milwaukee (GLM). Overlying GLM is the ST, a fine-grained surface diamicton capping moraine uplands and ridges across the LML terrain. West of the Valparaiso and Lake Border moraines, Glacial Lake Chicago sediments are present at the surface above the ST. In Northwest Muskegon County a Port Huron Phase diamicton, the MT is present in the Montague moraine ridges. Coastal and inland eolian dunes, organic sediment, and alluvium are common as the surface most deposits.  

The LML terrain is a story of ice advancing and retreating from the Lake Michigan basin. This action produced a series of complex ice marginal deposits separated by pro-glacial lake and outwash deposits. The stratigraphic picture of the LML is becoming clearer as additional cores and samples continue to be analyzed. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10411

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.