WHERE IN MAINE IS THE DOG BAY LINE?

An Acadian suture has been difficult to pin-point in the Northern Appalachian orogen. Recognized in 1992, the Dog Bay Line is a significant boundary within the Newfoundland Exploits subzone that separates a Silurian sequence linked to Laurentia from a contrasting Silurian sequence to the southeast (Williams et al., 1993). Northwest of the line, Ordovician through Lower Silurian turbidites and marine conglomerates (Badger Group) underlie terrestrial volcanic rocks and sandstones (Botwood Group); to the southeast, shallow marine shales and limestones underlie red sandstones (Indian Islands Group). Structures along the line indicate that the sequences were juxtaposed via dextral transpression prior to ~420 Ma, and the Dog Bay Line may mark the site of final closure of the Iapetan seaway.

In New England, van Staal et al. (1998) suggested that the Dog Bay Line occupies a medial position within the Central Maine basin. The northwesterly Rangeley sequence, which may extend as far southeast as Skowhegan, has been tied to Silurian Laurentia, and volcanic and sedimentary rocks (The Forks Formation) are comparable to the Botwood Group. To the southeast, Silurian strata (Sangerville and Waterville Formations) include ribbon limestones, shales, turbidites, and polymictic conglomerates that at best loosely correlate with the Indian Islands Group. In Farmington, centrally located and close to the proposed trace of the Dog Bay Line, highly disrupted shales contain isolated boulder-sized sandstone blocks; in Athens, on strike to the northeast, an isolated small body of volcanic rocks is also a candidate for a block in Silurian mélange. The ribbon limestone-shale-turbidite-conglomerate-mélange assemblage may record pre-Late Silurian accretion, and all strata in the region display evidence of dextral transpression. 1:24 000 scale mapping, supplemented by comparative volcanic geochemical and sediment provenance studies across and along strike, are planned to test the hypothesis that the Farmington-Athens "line" correlates with the type Dog Bay Line in Newfoundland and represents the Acadian suture in Maine.