WAGGING THE DOG: TALES OF THE DEGLACIATION OF THE WABASH VALLEY FROM ITS MOUTH

Leverett and Taylor (1915) recognized interfingering deglacial deposits and landforms along the southern margin of the Great Lakes, including several proglacial lake deposits and the geomorphic effects of potentially catastrophic flows from those lakes. Research has since confirmed that spillover from meltwater sourced in the interlobate area of Michigan and Indiana flowed catastrophically across the Tippecanoe (Indiana) Lowland to the Wabash Valley at ~19 ka. Leverett and Taylor also described three phases of Glacial Lake Maumee (Huron-Erie Lobe), two of which flowed episodically down the Wabash Valley. A fourth phase was later recognized and the duration of the four phases was constrained to ~17.4 – 14.2 ka on the basis of three ¹⁴C dates.

Outwash, slackwater lake, and eolian deposits in the lowest reach of the Wabash Valley, about 100-150 km downstream of the Wisconsin Episode terminal moraine, constitute integrated archives of meltwater flow from the Huron-Erie, Saginaw, and Lake Michigan lobes in the headwaters, and thus may inform interpretations of growth and decay of those lobes. Calibrated ¹⁴C dates from slackwater deposits and OSL dates from outwash indicate that aggradation was underway by 45-38 ka. OSL dates on outwash and overlying loess show that highest aggradation occurred by 23-22 ka, consistent with other data that constrain a minimum age for the Last Glacial Maximum to that period. The subsequent ~19 ka jökulhlaup was largely erosional in the lower Wabash, downcutting ~10 m into the valley fill. Re-aggradation or reworking of the upper ~2m of valley train ensued until one or more erosional episodes associated with Glacial Lake Maumee occurred between 17.6-13.5 ka. An outwash terrace ~8 m below the upper terrace has been correlated to a jökulhlaup from the first phase of Glacial Lake Maumee. Additional OSL and ¹⁴C dates support that correlation, so later flows may have been non-catastrophic or relatively small. Valley morphology, relict braid bar dimensions, and the dominantly coarse sand sediment caliber may constrain decades-old discharge estimates. Eolian dunes formed on the highest (slackwater lake) surface and on lower outwash terraces at ~12-10 ka. Early post-glacial alluviation partly eroded the outwash plains, but incised meander belts were well established by 9-8.5 ka.