Physical volcanology, stratigraphy, and depositional setting of the Middle Paleozoic volcanic and sedimentary rocks of Passamaquoddy Bay, southwestern New Brunswick

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The Lower Paleozoic volcanic and sedimentary belt of Passamaquoddy Bay, southwestern New Brunswick comprises a 4 km thick sequence of intercalated bimodal volcanic and sedimentary rocks deposited in a tidal flat to subaerial environment. The belt preserves four cycles of volcanism. Basaltic volcanism accompanied rhyolitic volcanism in each of the four cycles, with rhyolitic units being the most voluminous in the first three. In the final cycle, sedimentary rocks predominate and mafic flows dominate over felsic rocks, suggesting waning volcanism. Rhyolitic volcanic rocks are welded and unwelded pyroclastic deposits, domes, and lava flows. Basaltic volcanic rocks are predominantly lava flows with rare pyroclastic deposits. Proximal and distal vent facies are represented. Reworked volcanic rocks are rare. A spectrum of eruptive styles is present. The basaltic scoria and flows are typical of Hawaiian and Strombolian volcanism. Bedded rhyolitic tuffs and densely welded tuffs indicate Plinian- or sub-Plinian volcanism. Rhyolitic and basaltic lapilli-tuffs and tuff breccias containing accretionary lapilli and blocky and bubble-wall shards, suggest phreatomagmatic (Vulcanian) volcanism. Flow directions of rhyolitic pyroclastic and lava flows are complex, suggesting several small eruptive centres. Basaltic flows exhibit consistently southward flow directions, suggesting eruption from a localized vent system. Sedimentary rocks typically have sedimentary structures and a faunal assemblage typical of peritidal conditions with a microtidal range. All sedimentary units contain well preserved shards indicating deposition in a low energy environment with rapid sedimentation rates. The sequence remained at or near sea level for its entire depositional history.