LATE HOLOCENE COASTAL DEVELOPMENT ALONG THE SOUTHERN SHORE OF LAKE MICHIGAN DETERMINED FROM EOLIAN AND PALUSTRINE DEPOSITS OF THE TOLLESTON BEACH

Coastal features and deposits of Northwest Indiana that are associated with the Nipissing Phase and post-Nipissing lake-level variability in Lake Michigan are part of the Tolleston Beach, a barrier beach of complex parabolic dunes toward the east that fans out to an arcuate system of over 100 beach ridges to the west near Gary, Indiana. The Tolleston Beach is thought to have begun forming ~6000 years ago as lake level rose from the low water levels of the Chippewa Phase. While the timing of beach-ridge development constrains the timing of shoreline development near the Gary area of the shoreline, the detailed chronology of dunes associated with Nipissing and post-Nipissing coastal development along the southern shore of Lake Michigan remains largely unconstrained. This study targets samples collected from dunes and wetlands in the oldest (landward) portion of the Tolleston Beach where large, stabilized, well-developed individual parabolic dunes record a predominant westerly wind orientation during the early development of the Tolleston Beach. Optical ages from stabilized parabolic dunes are considered with subsurface sedimentology and associated radiocarbon ages from wetlands in the oldest portion of the Tolleston Beach to refine the understanding of shoreline evolution associated with Nipissing and post Nipissing water levels. Stratigraphic data from wetlands indicates that dune development on the Tolleston Beach began from 4400 to 4200 years ago concomitant with an increased sediment supply initiated by the rapid ~4m decline in lake level from the Nipissing phase peak ~4500 cal BP. Optical ages determine that the dunes became stabilized by ~3500 years ago. In the western study site these newly formed dunes migrated along the shoreline and across nearshore sediments and wetlands formed shortly after dune stabilization. In the east where the shoreline is more oriented to the north, the dunes migrated obliquely landward into the Great Marsh that developed during the lake-level fall from the Nipissing peak as the back barrier lacustrine area was transitioning from marl ponds to a peatland.