Date of Award

2007

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Daniel F. Belknap

Second Committee Member

Joseph T. Kelley

Third Committee Member

Stephen M. Dickson

Abstract

The stratigraphic record of paraglacial lakes provides detailed information on paleohydrologic changes and their potential mechanisms during and since deglaciation. Lakes are ideal for paleohydrologic and paleoecologic analyses because their sediments are generally undisturbed and contain continuous stratigraphy with proxies such as fossils that record syndepositional climate conditions. Determining rates and intensity of global climatic changes due to natural and recent human influences requires widespread analysis of these and other proxy records. In addition, characterization of the lake floor is of use to fisheries biologists interested in lake management. Stratigraphic and geomorphologic investigations at Rangeley Lake, western Maine aim to elucidate a past lake-level change timeline and to isolate potential mechanisms driving these climate changes. Digital sidescan sonar was used to image the morphology and composition of the lake bottom, showing deep basins, bedrock outcrop, extensive till and wave-washed bottoms, and sandy coves. High-resolution boomer seismic reflection profiles reveal stratigraphy of the lake from patches of till, ubiquitous glaciolacustrine draping deposits, basin muds, and sandy shallow-water deposits. Geophysical results show submerged former shorelines, possibly indicating a drier period during the Holocene. Complementing the geophysical data are four sediment cores. Radiocarbon dating of the four cores yields timing of shoreline emplacement and sediment accumulation rates. Preliminary results indicate ages of 10,450 ± 80 14C yr BP (12,381 ± 298) cal. yr. BP) immediately above the glacial lacustine surface. Cores into the submerged shoreline bracket the Holocene lowstand to between 9,540 ± 40 14C yr BP and 7,440 ± 35 14C yr BP (10,895 ± 192 cal. yr. BP and 8,265 ± 80 cal. yr. BP). Climate change is the likely mechanism behind this lowstand, as lake-level tilt was even across the lake basin; glacioisostatic response may be limited by a bedrock sill at the lake outlet. Thus lakes of this size (4.28 km2) and depth (44.8 m maximum) are large enough to be relatively hydrologically stable yet small enough to respond to significant climatic shifts.

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