Stratigraphic framework and late Holocene history of a lacustrine beach-ridge complex: Paleoclimate archives within migrating strand promontories

Abstract

This paper focuses on the physiography, stratigraphy, and age composition of a migrating strandplain promontory on Lake Michigan, discussing implied changes in alongshore sediment-transport dynamics within context of regional climate data. The Zion Beach-ridge Plain, a mainland-attached system believed to have migrated by >10 km over the past 4.5 kyrs, is partitioned into distinct physiographic zones. Its structural compartmentalization into distinct ridge sets, recognized in LiDAR-based topographic datasets and subsurface reflection geophysical records, reflects a punctuated morphodynamic development that has implications for understanding groundwater-flow patterns, wetland ecology, and coastal morphodynamic evolution. The most recent physiographic boundary within the strand dates to a high-amplitude lake-level rise event (>3 m in magnitude) that coincided with a regional shift in dominant storm-wind direction. The abrupt juxtaposition of young, high-relief dune-ridge terrain against old, low-relief wetland meadow attests to increased rates of littoral sand transport under conditions of heightened wave and current energies. Ongoing work to refine the geochronology of this and similar events is underway and stands to enhance our understanding of late Holocene coastal evolution. Strandplains are studied globally as important coastal paleoclimate archives, yet in the Great Lakes region the emphasis has been on embayed systems. While sheltered environments (e.g., bedrock-confined strandplains) foster high preservation potentials, optimal for paleohydrographic reconstructions from progradational sequences, the complex depositional architectures of strandplain promontories may provide information on open-water processes not contained within the former.