CORRELATION ACCOMPLISHED! (25 YEARS LATER): RELATIONSHIPS BETWEEN THE AROOSTOOK-MATAPEDIA AND WATERVILLE SECTIONS, NE AND CENTRAL MAINE

Mapping in NE (JH) , E- and E-central Maine (AL) resolves a decades-old debate about relationships between the Aroostook-Matapedia (AM) and Waterville (W) sections. It also poses new questions about correlations among extensive Silurian sandstone units, Ordovician-Devonian basin geometries, Salinic/Acadian accretion, and post-Acadian faulting.

Previously unrecognized variably calcareous sandstones in NE Maine form the top of an expanded, internally conformable AM sequence south of Houlton: sandstoneß dominantly pelitic Smyrna Mills Fm (Ssm)ß dominantly micritic or dolomicritic Carys Mills Fm (SOcm). An identical sequence has been found in the Lincoln area in east-central Maine. Contacts between units in both areas are gradational and that between the sandstone and pelite units is characterized by anomalous oxic conditions: sulfidic horizons in the sandstone and either black and sulfidic or green and red slate-siltstone in the pelitic unit.

The pelitic unit can be traced from Lincoln NE to Ssm south of Houlton and southwestward to the Waterville Fm (Sw), proving their equivalence. Limestone in the Lincoln area is traceable to SOcm south of Houlton. The sandstone unit in Lincoln extends SW to the type locality of the Vassalboro Fm and NE to rocks presently mapped as Madrid.

The Waterville has been considered a distal facies of a west-derived Central Maine suite, although Osberg (1988) showed that the Lake Messalonskee fault separates it from the inferred intermediate facies. A confirmed eastern (Miramichi) source for the AM section suggests that Ssm and equivalent Sw are a distal facies of a west-fining sequence. If Sw also received sediment from the west as previously thought, it would occupy the axis of a two-sided basin, whose east side is (presently) much narrower than the west. Alternatively, faulting may have dramatically narrowed the proximal and intermediate facies adjacent to the Miramichi source, and may have thrust the AM sequence westward over W.