HOLOCENE SHORELINE BEHAVIOR AND SEQUENCE DEVELOPMENT IN THE UPPER GREAT LAKES BASIN

Long-term shoreline behavior is related to both the rate of water-level change and rate of sediment supply, and this behavior distributes sediment into facies with respect to the sediment characteristics and hydrographic regime of the coastline. In the upper Great Lakes, rapid (cm/yr) and extreme (10s of meters) mid- to late Holocene lake-level change and plentiful sediment supply, especially in embayments to the coast and downdrift of headlands, produced many barrier beaches, strandplains of beach ridges, and spits. Cores and ground penetrating radar lines were collected of coastal sequences and landforms along Lakes Superior, Michigan, and Huron to investigate their internal architecture and sedimentology. Barrier beaches contain depositional transgression and aggradation sequences, whereas strandplains and spits contain depositional regression and forced regression sequences. Facies sequences within the barrier beach can be used to understand long-term patterns of lake-level behavior, but strandplains and spits contain facies contacts that can be used to create accurate paleohydrographs of the upper limit of lake level through time. An important factor to be considered in reconstructing past lake-level change is long-term differential shoreline movement related to glacial isostatic rebound. To produce basinwide paleohydrographs for each lake, remove rates of rebound from relative paleohydrographs created at individual sites in each lake basin and combine the relative paleohydrographs.