2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 13
Presentation Time: 1:30 PM-5:30 PM


BENNER, Jacob S. and RIDGE, John C., Department of Geology, Tufts Univ, Lane Hall, Medford, MA 02155, jacob.benner@tufts.edu

A new discovery of trace fossils produced by fish has been made in L. Wisconsinan varved glacial lake sediment at three exposures along the north central Connecticut, Passumpsic, and Wells River Valleys of Vermont.  Traces are in varves that range in age from ~11.7-11.3 14C ka (13.7-13.3 cal ka). Corresponding water depths range from 90 m for very clayey varves (1-10 cm thick) composed of sediment delivered to the lake dominantly by glacial meltwater to 45 m for silty/sandy varves (0.5-3 cm thick) of a tributary embayment where sediment was delivered by a dominantly meteoric runoff system.  The varve sediment is calcareous due to glacially pulverized marble in Vermont and the environment was likely that of a very turbid hardwater lake. While traces made by a variety of invertebrates (insect larvae, crustaceans, and nematodes) have been found in glacial lake sediment no vertebrate traces have previously been reported from the Wisconsinan in N. America.  The piscine traces are of two main types, both found at all sites: I) a continuous, paired median groove bounded laterally by paired, symmetrical impressions that diverge from the median; II) two or more out-of-phase semi-sinusoidal grooves with side levees.  Type I traces are 2 cm wide, up to 50 cm long, and were observed changing into traces composed of 2 sets of paired impressions diverging from the median and one long impression located precisely in the median.  These probably represent the activity of freshwater sculpin (Cottidae). Type II is up to 1 cm in amplitude, 4 cm in wavelength, and observed up to 83 cm long. It conforms to the ichnogenus Undichna and is interpreted to be a trace left by fins of a fish swimming at substrate level.  The new discoveries expand the list of known inhabitants of New England glacial lakes, aid in the interpretation of glacial lake paleoecology, and support hypotheses regarding an Atlantic Coastal refugium and rehabitation of northerly-glaciated latitudes by cottids.