STRATIGRAPHY AND CHRONOLOGY OF LATE WISCONSIN LAURENTIDE ICE SHEET FLUCTUATIONS OF THE EAST WHITE SUBLOBE, CENTRAL INDIANA
Here, we compile published and unpublished radiocarbon ages (n=81) within Indiana to establish a chronologic framework and to identify spatial and temporal gaps in the existing data set to guide future work. Using this radiocarbon data set, we interpret that the LIS reached ca. 40.5 degrees north latitude (80 km north of Indianapolis) by 26.0 k cal yr BP, based on the youngest maximum ages from cutbank exposures along Wildcat Creek (Carroll County) and boreholes in Tipton and Hamilton Counties north of Indianapolis. The largest concentration of ages occur within 30 km of the late Wisconsin maximum position, and the majority of ages suggest advance to the maximum limit ca. 24–23 k cal yr BP, in agreement with advance to the maximum limit in southwestern Ohio and east-central Illinois. However, two newer sites—Flat Rock and Plainfield—suggest a younger advance (22 k cal yr BP) to the maximum limit, as well as a younger readvance ca. 19.6 k cal yr BP. This potential readvance is not well understood at this time and requires further investigation. One obstacle in the interpretation of this data set is that a majority of the radiocarbon ages are over 30 years old (pre-AMS with large errors) and the accurate location and stratigraphic position of collected organic material is not known at all sites. A reinvestigation of these sites along with additional outcrop and borehole data from central Indiana will help resolve stratigraphic and chronologic questions.