Nesbitt, Ian M.; Campbell, Seth W.; Arcone, Steven; Smith, Sean M.C.
Geological Society of America Abstracts with Programs (2018)doi: 10.1130/abs/2018NE-311370
Estimates of post-glacial sediment transport volume can be useful when investigating watershed-scale denudation in formerly glaciated landscapes. In New England, anthropogenic activities such as forestry, farming, and construction of transportation and water management infrastructure, have further altered the near-surface sediment record. Unfortunately, these surface dynamics are difficult to constrain, both in space and time. Rate analogs used to estimate erosion and deposition in New England have typically been derived from lake bottom sediment cores. Reliance on core records assumes that derived sedimentation rates are representative of rates across the broader lake-bottom, despite being only a single point measurement. Geophysical surveys suggest that this assumption can be highly erroneous and unrepresentative of the entire lacustrine geological record. Herein, we conducted ground-penetrating radar (GPR) and side-scan sonar (SSS) surveys of multiple lakes in Maine, which are representative of different basin types, to estimate sedimentation rates and volumes since Laurentide retreat. Subsequent age constraints from cores on multiple GPR-imaged horizons could be used to refine estimates of sedimentation rate change caused by evolving physical, biological, and chemical processes that control erosion, transport, and re-deposition. This presentation will provide a summary of GPR and SSS data collection methods, assumptions and limitations, structural and surficial interpretations, key findings from multiple lake basins, and the story they tell of upland denudation from the last deglaciation through human alteration of Maine.
Estimates of sediment accumulation volume and structure can be useful when investigating landscape change in formerly-glaciated landscapes. In New England, the landscape has undergone significant alteration since being deglaciated and colonized. One way of investigating this alteration is to use lake-bottom sediment cores. The use of core records to determine alteration relies on an assumption that derived sedimenation rates are representative of sedimentary conditions in a broad area of the sub-lake floor, despite being a single point measurement. Geophysical surveys suggest that this assumption can lead to errors. We conducted ground-penetrating radar (GPR) and side-scan sonar (SSS) surveys of multiple lakes in Maine, which are representative of different basin types, to estimate sediment volumee since the ice sheet left the watershed. Age constraints from cores can be used to make these estimates more precise. This presentation provides a summary of GPR and SSS data collection, plus assumptions, limitations, interpretations, and key findings from multiple lake basins which tell a story of sediment deposition from the time of deglaciation through today.