INTRODUCING GLACIAL LAKE ROSCOMMON, CENTRAL LOWER MICHIGAN, USA

In 2017, an article in the journal Geomorphology described a large, previously undocumented, paleolake that formed atop the interlobate uplands of central lower Michigan. This Pleistocene lake, named Glacial Lake Roscommon, was at times surrounded - partially or wholly - by ice of the Saginaw, Lake Michigan and Mackinac Lobes. The 2017 study of Glacial Lake Roscommon focused on a kame delta that had formed in the lake 23.1 ka ago, confirming that this part of Michigan was “open water” at about the time of the LGM. The five dates reported from this study were the first to confirm the very early existence of the lake, hundreds of kilometers north of the main ice margin to the south. Since then, an unpublished luminescence date on beach sands from a lower shoreline of the lake established that the lake was still present, but in a restricted part of the basin, at 16.8 + 0.8 ka ago. A second unpublished date on a higher shoreline (20.1 + 1.9 ka ago) further confirmed the longevity and persistence of the lake. Together, these early dates establish that Glacial Lake Roscommon existed from about the time of the LGM until at least 16 ka ago – a span exceeding 7000 years.

In this poster, we provide maps and graphics depicting the current state of knowledge about Glacial Lake Roscommon. Outflows of water from the lake formed large spillway channels, many of which end in paleodeltas in nearby paleolakes, and/or in subaerial fans. Glacial meltwater flowing into the lake from subaqueously grounded ice margins formed kame deltas, kame moraines, and fans - some of which demonstrate textbook-like stratigraphy. Shorelines and beach ridges suggest that Glacial Lake Roscommon had at least four or five different lake level stages. Recent work has confirmed that, subsequent to final lake drainage, a major dune-forming event occurred in the basin between 13 and 10 ka ago.