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The survey's own names for the deposits under and beside the city, with their dates
The Elkhart Formation: The 2024 framework gives the Saginaw Lobe's late Wisconsin deposits in this region a new formal name — the Elkhart Formation, the record of that lobe's advance and retreat around the Last Glacial Maximum — with three members, in order Baugo Creek, Newbury and Lagrange. Its ages are optically stimulated luminescence ages, measured on quartz grains in the deposits themselves, and they are printed here with their errors because the errors are part of the dates: a minimum age for the Baugo Creek Member at about 25.8 thousand years, maximum ages for the Newbury Member at about 25.3 thousand and pooled maxima for the Lagrange at about 25.3 thousand — from which the authors conclude that "ice margin retreat was relatively fast overall." Wood taken from the Lagrange Member's sand and gravel in a Lagrange County borehole returned radiocarbon results beyond the method's reach — greater than 46,600 and greater than 48,000 years (laboratory samples OS-165650 and OS-165651) — the frame within which the luminescence ages sit.
The Baugo Creek Member: The formation's lowest member is named for ground at this city's eastern doorstep: it is "composed of diamicton and glaciolacustrine sediments at or around the headwaters of Baugo Creek, in southern Elkhart County," and "named after the Baugo Creek, where its weathered top surface is exposed to erosion" — the creek that runs west through Osceola and enters the St. Joseph at the edge of Mishawaka's ground. Its stratotype is a borehole near Wakarusa, about two and a half miles east of the creek's headwaters. The member is mapped over about 270 square miles (700 square kilometres) across parts of Elkhart, Kosciusko, Lagrange, Marshall, Noble and St. Joseph counties, at observed thicknesses of 55 to 90 feet, its clay-loam and silt-loam diamicton units commonly 25 to 30 feet thick. The boundary is printed as the paper prints it: the distribution takes in part of this county; the paper does not parcel the member township by township, and this section does not parcel it further.
The Mishawaka Fan: The city's other named deposit belongs to the other lobe. When Bleuer and Melhorn re-read the supposed Maxinkuckee Moraine in 1989 as collapsed moraine-and-fan topography derived from the northwest, the fans they named were the Plymouth Fan, the Miami Highway Ridge, and the Mishawaka Fan — a Lake Michigan Lobe outwash fan at this city's ground, kept in usage by the 2024 framework's correlation charts. Sediment lying on top of the fan — an informal glaciolacustrine facies of the Lemont Formation, lake sediment ponded against the dying ice — has been luminescence-dated in the survey's laboratory: at the boundary between the Wakarusa Upland and the Mishawaka Fan, the base of the ice-disintegration features in that cap dates to 25.8 ± 5.7 thousand years (sample IGWS-422, from two metres' depth), a second sample to 23.8 ± 3.8 thousand (IGWS-415), and the top of the sequence — in the authors' words, the horizon "indicating the end of landscape instability" — to 21.7 ± 4.4 thousand years (IGWS-353). The fan's surface, on the survey's own dates, was finished in a ponded, unstable ice-margin landscape between roughly twenty-six and twenty-two thousand years ago.
Sources: Antinao and others (2024), as above — the Elkhart Formation and its members, the Baugo Creek Member's naming, stratotype, distribution and thickness, the OSL age summary and Table 13 (samples IGWS-422, IGWS-415, IGWS-353 and the Elkhart Formation ages), Table 14 (the Lagrange Member radiocarbon results), and the correlation of the Mishawaka Fan and the Lemont Formation glaciolacustrine facies on top of it, after Bleuer & Melhorn (1989) and Gray (1989).