Lake Erie Holocene Coastal Evolution near the Portage River-Catawba Island, Ohio
Abstract (Summary)Previous studies on the sedimentology and coastal geomorphology of the Great Lakes have recognized individual features (spits, barrier islands, beaches, coastal wetlands, estuaries) but have compartmentalized the information rather than recognizing that these features are all components in wave-influenced deltas. Wave-influenced deltas form where discharge from a river is sufficient to impose a groin-effect on longshore drift. Such deltas tend to be asymmetric in plain view, with the updrift side of the delta characterized by accreting beach ridges (cheniers or strandplains) and the downdrift side of the delta characterized by coastal wetlands and occasional accreted bars. An asymmetry index > 200 (Bhattacharya and Giosan, 2003) defines wave-influenced deltas. The Portage River delta (north-central Ohio coast of Lake Erie) has an asymmetry index of about 296, meaning it is a wave-influenced delta. Historical aerial photography from the 1930s-1940s, pre-land development, show a chenier plain updrift (east) of the Portage River delta, while downdrift (west) of the Portage River delta are extensive coastal wetlands and rare beach ridges in the Ottawa National Wildlife Refuge. The Portage River delta, then, appears to be a wave-influenced delta. This study used 28 vibracores up to 4.5-m in length, sediment analyses, and 14C geochronology to confirm the classification of this delta and evaluate the implications for understanding the coastal features of the Great Lakes. Sediment cores updrift of the delta consisted of sandy deposits about 4.5-m thick overlying glacial-lacustrine sediment. These sandy deposits are interpreted as a relatively continuous, overall shallowing-upward sequence (shoreface overlain by foreshore overlain by backbeach and dune), with a coarsening-upward, storm-dominated shoreface succession influenced more by wave-driven currents in the shallower upper shoreface. Sediment cores from downdrift of the Portage River also represent an overall shallowing-upward sequence with a coarsening-upward, storm-dominated shoreface succession. However, these sandy deposits are only 1.5-m thick and overlie thick wetland (peaty) deposits. In this succession, coarser horizons in the upper shoreface are associated with sediment transport within rip channels during storm intervals. In downdrift areas, the vertical facies succession of sediment cores is very irregular suggesting more input from the fluvial system. The 14C analysis in this study determined three 14C age dates from vibracore 07-PC-14 in a thick peat interval overlying glacial lacustrine sediment. The 14C age dates ranged in age from 1616-2025 cal BP representing a much younger age than the underlying glacial lacustrine sediment. The cal BP age determinations followed a linear trend (R2 = 0.9931) when plotted with depth, indicating a constant sedimentation rate of 0.86 mm/yr throughout the peat sequence. The 14C age dates indicate the formation of a coastal wetland from about 1700-2070 YBP. The top 39-cm of vibracore 07-PC-14 showed a sedimentation rate of 2.05 cm/yr while the siliciclastic interval just below indicated a sedimentation rate of 0.58 mm/yr. After the formation of wetlands, the multiple coarsening-upward successions are present resulting from the accretion of beach ridges along the shoreline. The deposition of the shoreface sequence begins at about 1513 cal BP and multiple shoreface sequences coarsen upward to about 19 cal BP.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:wave influenced deltas asymmetry longshore drift
Date of Publication:01/01/2008