Date of Award

2006

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Daniel F. Belknap

Second Committee Member

Joseph T. Kelley

Third Committee Member

Brian S. Robinson

Abstract

A geophysical and coring survey of Sebasticook Lake, Newport, Maine, provides evidence of past human-landscape interactions associated with construction and use of a Middle Archaic to Middle Woodland period fish weir, located at the lake inlet. Geophysical methods employed included Seismic Reflection Profiling (SRP) and Sidescan Sonar (SSS) survey of the Sebasticook Lake basin, and Ground Penetrating Radar (GPR) survey of the fish weir site and lake inlet. Three cores were collected using a modified, square-rod Wright piston corer in the lake basin. The Sebasticook fish weir complex consists of >630 stone-tool-modified wooden stakes, driven into stiff underlying glacial mud at the lake inlet. The stakes were presumably connected by wattle or fencing to create a barrier to corral migrating anadromous and/or catadromous fish. Radiocarbon dating of the weir stakes suggests four possible periods of construction: 5820 + 60 BP to 4950 + 80 BP, 3990 + 80 BP to 3780 + 70 BP, 2940 + 70 BP to 2590 + 70 BP, and 1780 + 80 BP to 1560 + 60 BP. The range of dates makes the Sebasticook fish weir one of, if not the earliest, dated fish weirs in North America. The present study focused on three research areas: glacial and deglacial history of the lake basin, Holocene geology and lake-level change, and geoarchaeological site-formation processes of the fish weir inlet. Several submerged glacial features were identified by SRP and SSS surveys in the lake basin, including an esker segment, kame and kettle topography, and a moraine. Basin stratigraphy suggests that following deglaciation, Sebasticook Lake transitioned as an isolation basin from a glaciomarine to a glaciolacustrine environment before reaching its present geological and sedimentological configuration by ~10,000 BP. SRP and SSS survey and coring identified submerged erosional features and wetland deposits associated with a lake-level low-stand of ~9 m below present lake level (PLL) from 7860 BP to 6100 BP. During the low stand, Sebasticook Lake lowered below its outlet, forming a closed basin that was bisected by the esker segment. This study attempts to place this event within a context of regional lake-level and climate change and proposes a hypothesis to explain variability of lake-level records across northern New England and adjacent Canadian provinces. A GPR survey combined with a previous vibracoring study and a preliminary SRP survey identified two incised and infilled paleochannels at the lake inlet. Incision of the first, northern paleochannel was most likely related to lowering base level associated with the lake-level low stand. By 6100 BP, lake level had reached near-modern levels, opening the lake to the larger Kennebec River drainage and connecting the Sebasticook Lake and River to anadromous and catadromous fish runs. Construction of the fish weir at the inlet began shortly after this, by 5820 BP, and centered across the incised northern channel. Construction of the weir promoted sedimentation and infilling of the channel with organic detritus, causing the channel to migrate south. At some point between 2590 BP and 1780 BP, the anthropogenically-induced infilling caused the channel to avulse south, incising the identified southern channel. The northern channel was then abandoned, and humans continued weir construction within the newer, southern paleochannel, until the weir was completely abandoned sometime after 1560 BP.

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