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

The northwestern margin of the Mascarene Basin is preserved within a southe asterly dipping homocline in the Oak Bay area of southwestern New Brunswick . The Mascarene Group in this area comprises up to 600 m of massive, resedi mented conglomerate of the Oak Bay Formation and approximately 4200 m of vo lcanic and resedimented volcaniclastic and siliciclastic sandstone and muds tone 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 (similar to 600 m thick), a media l grey to black shale- and mafic volcanic-dominated Sawyer Brook Member (si milar to 300 to 600 m thick), and an upper siliciclastic-dominated Simpson Corner Member with minor associated volcanic rocks (similar to 3000 m thick ). Five lithofacies recognized in the well-exposed Campbell Point Member in clude: (i) bedded tuffaceous sandstone facies, (ii) chaotic tuffaceous sand stone facies, (iii) waterlain pyroclastic facies, (iv) medium- to thick-bed ded sandstone facies, and (v) thin-bedded mudstone facies, all of which are products of sediment gravity flows. The massive conglomerates of the Oak B ay Formation were deposited as debris flows contemporaneous with faulting a long the margin of the basin. Strata within the homocline possess a pervasi ve S-1 cleavage oriented approximately 35 degrees oblique to bedding and a locally developed S-2 cleavage; minor folds are rare and folds related to S -1 are absent. Correlation with a more complete Siluro-Devonian sequence in an adjacent fa ult block in Maine suggests that the Oak Bay and Waweig formations are Late Silurian (Ludlovian-Pridolian). The volcanic centres in Maine were potenti al sources of much of the epiclastic and pyroclastic detritus in the Waweig Formation. Distinctive stratigraphic sections in more highly deformed faul t blocks farther to the southeast attest to the composite architecture of t he Mascarene Basin. Existing paleontological evidence may indicate that sub sidence of these blocks occurred progressively later to the northwest as a result of sequential downfaulting. Consideration of the regional relationships between the Mascarene Basin wit h respect to the St. Croix Terrane and Fredericton Trough to the northwest and the New River Terrane to the southeast suggests that the basin develope d by backarc rifting from the Silurian to Early Devonian and was flanked by a Late Ordovician to Silurian volcanic are (Kingston Arc) to the southeast .