Stratigraphy, sedimentology and structure of the Oak Bay and Waweig formations, Mascarene Basin: Implications for the paleotectonic evolution of southwestern New Brunswick

Abstract

The northwestern margin of the Mascarene Basin is preserved within a southeasterly dipping homocline in the Oak Bay area of southwestern New Brunswick. The Mascarene Group in this area comprises up to 600 m of massive, resedimented conglomerate of the Oak Bay Formation and approximately 4200 m of volcanic and resedimented volcaniclastic and siliciclastic sandstone and mudstone of the conformably overlying Waweig Formation. The Waweig Formation is formally subdivided into three members: a lower volcaniclastic- and felsic volcanic-dominated Campbell Point Member (~600 m thick), a medial grey to black shale- and mafic volcanic-dominated Sawyer Brook Member (~300 to 600 m thick), and an upper siliciclastic-dominated Simpson Corner Member with minor associated volcanic rocks (~3000 m thick). Five lithofacies recognized in the well-exposed Campbell Point Member include: (i) bedded tuffaceous sandstone facies, (ii) chaotic tuffaceous sandstone facies, (iii) waterlain pyroclastic facies, (iv) medium- to thick-bedded sandstone facies, and (v) thin-bedded mudstone facies, all of which are products of sediment gravity flows. The massive conglomerates of the Oak Bay Formation were deposited as debris flows contemporaneous with faulting along the margin of the basin. Strata within the homocline possess a pervasive S1 cleavage oriented approximately 35°oblique to bedding and a locally developed S2 cleavage; minor folds are rare and folds related to S1 are absent. Correlation with a more complete Siluro-Devonian sequence in an adjacent fault block in Maine suggests that the Oak Bay and Waweig formations are Late Silurian (Ludlovian-Pridolian). The volcanic centres in Maine were potential sources of much of the epiclastic and pyroclastic detritus in the Waweig Formation. Distinctive stratigraphic sections in more highly deformed fault blocks farther to the southeast attest to the composite architecture of the Mascarene Basin. Existing paleontological evidence may indicate that subsidence of these blocks occured progressively later to the northwest as a result of sequential downfaulting. Consideration of the regional relationships between the Mascarene Basin with respect to the St. Croix Terrane and Fredericton Trough to the northwest and the New River Terrane to the southeast suggests that the basin developed by back-arc rifting from the Silurian to Early Devonian and was flanked by a Late Ordovician to Silurian volcanic arc (Kingston Arc) to the southeast.