Editing Finger Lakes (section)

== Quaternary geology ==
[[File:S. Main Bench.jpg|thumb|right|Seneca Lake, from South Main Street in [[Geneva, New York]].]]
These glacial [[finger lake]]s originated as a series of northward-flowing streams. Around two million years ago, the area was glaciated by first of many continental glaciers of the [[Laurentide Ice Sheet]] moved southward from the [[Hudson Bay]] area. During the glacial maximums, [[Subglacial stream|subglacial]] [[meltwater]] and glacial ice widened, deepened, and accentuated the existing river valleys to form subglacial [[tunnel valley]]s.<ref name="MullinsOthers1989a">Mullins, H.T. and Hinchey, E.J., 1989. ''Erosion and infill of New York Finger Lakes: Implications for Laurentide ice sheet deglaciation''. ''Geology'', 17(7), pp.622-625.</ref> Glacial debris, possibly [[terminal moraine]] left behind by the receding ice, acted as dams, allowing lakes to form. Despite the deep erosion of the valleys, the surrounding uplands show little evidence of glaciation, suggesting the ice was thin, or at least unable to cause much erosion at higher elevations. The deep cutting by glacial erosion left some [[Valley#Hanging valleys|tributaries hanging]] high above the lakes—both Seneca and Cayuga have tributaries hanging as much as {{cvt |120 |m}} above the valley floors.<ref name="MullinsOthers1996a"/><ref name="MullinsOthers1989a"/> Based upon sediments cores, seismic stratigraphy, and radiocarbon dates, the finger lakes became ice-free about 14,400 [[Before Present|BP]] [[Radiocarbon dating#Calibration|calendar]]. At this time scouring by ice and meltwater ceased and these lakes filled initially with [[proglacial lake]] [[rhythmite]]s. The deposition of proglacial lake rhythmites occurred between 14,400 and 13,900 BP calendar. After the magins of the Laurentide Ice Sheet retreated into the Ontario lowlands after 13,900 BP calendar, The accumulation, at first, of massive gray clays followed by dark gray to black, laminated, organic-rich muds, accumulated without interruption until present within the Finger Lakes.<ref name="MullinsOthers1996a"/><ref name="EllisOthers2004a">Ellis, K.G., Mullins, H.T. and Patterson, W.P., 2004. ''Deglacial to middle Holocene (16,600 to 6000 calendar years BP) climate change in the northeastern United States inferred from multi-proxy stable isotope data, Seneca Lake, New York''. ''Journal of Paleolimnology'', 31(3), pp.343-361.</ref>

Detailed studies of [[Marine Isotope Stage]] 3 and 4 age [[sediment]]s exposed at a locality called the ''Great Gully'' on the eastern flank of the Cayuga Lake, near [[Union Springs, New York]], record the presence of a [[paleolake]] that existed prior to Cayuga Lake. This paleolake, which is called '''Glacial Lake Nanette''', was a [[proglacial lake]] that filled the bedrock valley currently occupied by Cayuga Lake from about 50,000 [[Before Present|BP]] [[Radiocarbon dating#Calibration|calibrated]] until it was overridden by a glacial readvance that occurred prior to 30,000 [[Before Present|BP]] [[Radiocarbon dating#Calibration|calendar]] and buried it beneath younger glacial [[till]]. This research shows that bedrock valleys, in which the Finger lakes lie, existed prior to the Last Glacial Maximum and developed over multiple glaciations.<ref name="KozlowskiOthers2014a"/><ref name="KozlowskiOthers2018">Kozlowski, A.L., Bird, B., Mahan, Shannon, F., Robert, Teal, C., and Leone, J., 2018, ''Glacial Lake Nanette–a middle Wisconsin (MIS 4 – 3) proglacial lake in the Cayuga Basin'', in Thorleifson, L. H., ed., ''Geologic Mapping Forum 2018 abstracts:'' ''Minnesota Geological Survey Open-File Report,'' 18-1, p. 41.</ref>

Finally, although sub-glacial scour during the Last Glacial Maximum removed the majority of pre-existing sediment down to the [[bedrock]] bottoms of the Finger Lakes, patches of [[interglacial]] deposits are likely preserved locally within or near hanging valleys on the margins of their valleys. For example, the principal site that has been well-studied is the ''Fembank'' exposure of interglacial deposits on the west margin of Cayuga. This deposit provides direct evidence that some version of Cayuga Lake and its bedrock valley existed prior to Last Glacial Maximum.<ref name="KnuepferOthers2000a">Knuepfer, P.L.K., Hensler, S.M., 2000. ''A5: Proglacial Lakes, Southern Cayuga and Seneca Valleys.'' In ''Guide Book to Field Trips [of The] 72nd Annual Meeting New York Geological Association. September 29 - October 1, 2000.'' pp. 75-90.</ref><ref name="KarrowOthers2014a">Karrow, P.F., Bloom, A.L., Haas, J.N., Heiss, A.G., McAndrews, J.H., Miller, B.B., Morgan, A.V. and Seymour, K.L., 2009. ''The Fernbank interglacial site near Ithaca, New York, USA.'' ''Quaternary Research'', 72(1), pp.132-142.</ref>