The Late Quaternary Stratigraphy and Paleogeographic Evolution of the New Meadows Embayment, Northeastern Casco Bay, Gulf of Maine

The New Meadows River in northeastern Casco Bay, Maine is a deeply indented embayment and deeply incised paleovalley with no modern fluvial connection. A deltaic deposit (Belknap et al., 1986; Shipp et al., 1991; Barnhardt et al., 1997) at the mouth of the embayment has led other authors to suggest that the Androscoggin River flowed into the Gulf of Maine through the New Meadows paleovalley (Kelley and Hay, 1986; Belknap et al., 1989; Buynevich et al., 1999). This investigation primarily utilized seismic stratigraphy constrained by archival vibracore ground-truth data to reconstruct the paleogeography, post glacial evolution of the embayment, and determine the connection between the Androscoggin River, New Meadows River, and this deltaic deposit in Casco Bay. This interpretation of seismic stratigraphy suggests that the New Meadows was never a large fluvial system. The channel is filled largely with glaciomarine Presumpscot Formation (Bloom, 1960, 1963) that shows a discemable basal unconformity, and is capped primarily by estuarine mud. At the time of sea-level slowstand, (between 11,500- 7,500 cal. years BP, Kelley et al., 2013) when the deltaic deposit at the mouth of the New Meadows was deposited, the valley was either dry or contained a small stream and a salt marsh in the mid-estuary near Winnegance Bay. When subsequent rapid sea-level rise occurred after the slowstand period, the salt marsh deposits were drowned and did not appear in the system during this transgression until reaching the Thomas Bay area. The sand and gravel deposits present in the upper part of the New Meadows can be correlated to the tidal channel incision and migration in the Thomas Bay area, with the Brunswick sand plain being the obvious source of sediment. This sand and gravel is held in the upper part of the system by a greater flood-to-ebb ratio in tidal processes, and is at the top of the stratigraphic sequence. The hypothesis that the Androscoggin River flowed through the New Meadows, or deposited the deltaic deposit at the mouth of the embayment is implausible and is therefore rejected