Subsurface Geophysical Investigations of Oneida Lake Ny: Insights Into Ice Sheet Processes and Deglaciation At Termination I

Reconstructing the retreat of the Laurentide Ice Sheet (LIS) provides insight into understanding end-Pleistocene climate, a critical set of boundary conditions prior to the onset of Holocene climates that were optimal for human dispersal and societal growth. Constraining ice sheet dynamics, glacier retreat rates, and the timing of still-stands and readvances requires identifying glacial landforms such as moraines, drumlins, and mega-scale glacial lineations (MSGLs). Drumlins and MSGLs indicate ice sheet flow directions and provide the location of paleo-ice streams, which were accelerated and localized pathways for ice discharge. Ice streams control ice sheet mass balance; therefore, identifying the location of paleo-ice streams aids in reconstructing ice sheets. Topographic lows focus ice flow and encourage ice stream development. In addition, proglacial lakes also form in topographic lows, and enhance calving processes and can accelerate deglaciation or serve as corridors of easy ice sheet readvance. The deepest section of a basin likely contains the most complete and highest resolution proglacial lake sequence. High-resolution proglacial lake records can be used to reconstruct ice sheet retreats and readvances on annual timescales. Comparing proglacial lake records to other paleoclimate data provides insight into regional climate and ice sheet processes. Therefore, the investigation of a previously glaciated basin may provide information on ice streaming processes, the locations of calving margins, and paleoclimate within the basin. Modern Oneida Lake occupies the Oneida Basin in Central New York. Previous studies indicate the Oneida Ice Stream of the LIS was present in the area adjacent to the Oneida Basin. The southeast section of Glacial Lake Iroquois, a large proglacial lake that covered the Lake Ontario watershed during the end-Pleistocene, occupied the Oneida Basin. The floor of Oneida Lake preserves sedimentary deposits from Glacial Lake Iroquois. This dissertation presents the first subsurface investigation of Glacial Lake Iroquois deposits and the underlying glacial bedforms of the Oneida Lake basin. Subsurface investigations of the glacial deposits in the Oneida Basin provide insights into LIS recession and ice stream activity in the basin and contribute to establishing the extent of the sedimentary materials available for paleoclimate reconstructions contained within the lake. In this dissertation, multiple geophysical methods are used to image the subsurface geology of Oneida Lake; the data provide new information on the retreat of the ice sheet from the basin, and provide site survey information for sampling sediments for paleoclimate reconstruction. In Chapter 2, Compressed High Intensity Radiated Pulse (CHIRP) seismic reflection data were used to image the Holocene and Proglacial Lake deposits within the lake. These high-fidelity data identify Holocene and proglacial lake deposits, and the top of the till and subglacial bedforms. The CHIRP data provide excellent images of the proglacial deposits and critical information relevant for ongoing paleoclimate efforts, but failed to image the thicker proglacial sections of the basin and cannot image beneath the till surface. Multichannel seismic (MCS) reflection data, presented in Chapter 3, were collected to image the entire Quaternary section of the basin. MCS data image the internal structures in the till and the top of the sub-till boundary, which here is the heavily-scoured Paleozoic bedrock surface. In the deeper sections of the basin, biogenic gas attenuates the MCS signal. Seismic profiles in some locations are ambiguous because of the interruption of underlying reflectors by point reflections, probably from cobbles and boulders. Therefore, the depth to top of the Paleozoic strata cannot be identified with the reflection data especially in the eastern part of the basin. However, this information is essential for understanding the duration of the paleoclimate record within the basin and for estimating the depth of proglacial lakes within the basin. A first arrival seismic tomography analysis using refractions in the MCS data is presented in Chapter 4, and was used to estimate the depth to the Paleozoic strata where reflection imaging failed. The first arrival seismic tomography data provide a more refined understanding of the basin geometry and validates the overall MCS reflection results. This dissertation provides a more complete understanding of the deglaciation of the region. The deep topographic/bedrock low in the eastern end of the basin likely affected Oneida Ice Stream evolution. The presence of drumlins and megagrooves incised into Paleozoic bedrock supports the interpretation that an ice stream was present in the basin. These results expand the Oneida Ice Stream's known extent into the Oneida Basin. The presence of a deep proglacial lake and De Geer moraines support the interpretation that there was a systematically retreating calving margin in the basin. A thick proglacial lake sequence imaged by the geophysical data provides a framework for future coring expeditions that can acquire a very complete and detailed paleoclimate record.

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