STRATIGRAPHIC DETAILS AND GRAIN SIZE CHARACTERISTICS OF QUATERNARY SEDIMENTS EXPOSED AT ERIE BLUFFS STATE PARK, ERIE COUNTY, PENNSYLVANIA

Along Lake Erie’s southern shoreline, powerful waves contribute to significant erosion, gradually stripping away bluffs and threatening nearby beaches. Bluffs and beaches are connected via a cause-and-effect relationship, where sediment eroded from the bluffs is transported down-drift to the beaches. Eroded bluff sediments such as sand are not being produced at a sustainable rate to maintain the current shoreline, and this can be seen at beaches such as nearby Presque Isle State Park. A detailed understanding of bluff stratigraphy is required to create realistic sediment budgets that accurately describe sources and sinks of the shoreline system. Sediment budgets for the Lake Erie shoreline are based upon the types of eroding sediments and their rate of retreat. If either the stratigraphy or grain size characteristics are misinterpreted, inaccurate sediment budgets will result.

This study presents a detailed analysis of the stratigraphy and grain size characteristics of Quaternary sedimentary units exposed at Erie Bluffs State Park (EBSP). Results are compared with previous regional studies in order to better understand the sediment contribution of EBSP to the down-current littoral system that supplies sediment to popular beaches, such as those at Presque Isle State Park. Five stratigraphic units comprise the bulk of the bluffs at EBSP, including two glacial tills, and lacustrine basin, near-shore, and beach deposits. Measured sections show that the lacustrine basin unit is more wide-spread and stratigraphically thicker than previously recognized. In addition, laser diffraction derived sediment grain size distributions from all units show that much less sand (up to 55% less) is available from natural bluff erosion than previous studies suggest. Future sediment budgets used to quantify sediment flux along the Lake Erie shoreline may need to re-evaluate available grain sizes across smaller stretches of shoreline, as beaches that are dependent on sand from bluff erosion may require more beach nourishment.