Abstract Avalonian sections in the Saint John area, southern New Brunswick, have long contributed to global understanding of Cambrian chronostratigraphy. A tuffaceous bed in the Ratcliffe Brook Formation (RBF) in the Somerset Street section dated at c. 531 Ma has traditionally been considered to post-date small shelly fossils attributed to the Watsonella crosbyi Zone in the Hanford Brook section. A fine-grained tuffaceous bed approximately 8 m stratigraphically lower in the Somerset Street section yields a chemical abrasion isotope dilution–thermal ionization mass spectrometry zircon age of 532.3 ± 0.3 Ma; a tuffaceous carbonate unit in the lower RBF in Hanford Brook gives an age of 531.5 ± 0.3 Ma. Crystal and crystal-lithic tuff beds near the top of the RBF yield ages of 520.3 ± 0.3 Ma (in Hanford Brook) and 519.1 ± 0.3 Ma (in Ratcliffe Brook). The new ages confirm the correlation between the Somerset Street and Hanford Brook sections based on acritarchs and make the association of small shelly fossils in the Hanford Brook section younger than 531 Ma. This result is relevant to ongoing discussions on the age of the base of undefined Cambrian Stage 2. The radiometric ages also support a young age for the upper part of the RBF, perhaps extending into Epoch 2.

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Abstract Remnants of a chain of volcanic centers within the early Silurian–Early Devonian marine waters of the northern Appalachian geosyncline now are exposed along the New England coast and in southern New Brunswick. On the northwest the volcanic rocks lie unconformably on peiitic arenaceous and locally volcanic rocks of probably Cambrian-Ordovician age that generally decrease in metamorphic grade northeastward from Penobscot Bay, Maine, to the St. John River, New Brunswick. On the southeast in New Brunswick, the marine volcanic rocks are faulted against Precambrian metamorphic and Cambrian-Ordovician sedimentary rocks in the Kingston and Caledonian uplifts. The coastal volcanic sequence is varied in thickness and lithologic succession. Maximum thickness is about 45,000 ft in the Eastport quadrangle of southeastern Maine. The volcanic rocks are largely frag mental–flow breccia, tuff breccia, and coarse bedded tuff. The rocks were originally of andesitic to rhyolitic composition but now are locally altered hydrothermally to keratophyre and quartz keratophyre. Basaltic flows, rarely pillowed, and coarse tuff are also present. Sedimentary rocks include shale and siltsfone containing an abundant and varied shallow-water benthonic fauna, and poorly fossiliferous chert and fine-grained siliceous bedded tuff. Folding, faulting, and plutonic intrusion of granitic and gabbroic magmas–the Acadian orogeny–occurred during Middle Devonian time and ended the volcanic activity. During Carboniferous and Triassic times, movements in a system of NE-trending faults, probably largely strike-slip, shuffled together blocks of different lithology, structure, and age that originally may have been many miles apart. The lower Silurian–Lower Devonian volcanic belt thus marks the beginning of

Abstract Identified as the ‘Variscan Front’ 40 years ago, the Pennsylvanian tectonic zone of southern New Brunswick has presented structural and stratigraphic challenges for the last century. In 1986, R. Damian Nance presented an integrated tectonostratigraphic analysis which suggested that the zone represented a transpressive flower structure controlling both deposition of Pennsylvanian sedimentary formations and their subsequent deformation, a consequence of Meguma terrane docking and subsequent adjustment. The strength of this model is demonstrated through the integration of recent field studies and more recent geochronology, which refines the details and expands the scale of the flower structures. Current understanding suggests that three large transpressive structures developed diachronously, and the southern tectonic zone is linked with strike-slip faults to the north (especially the Kennebecasis Fault) via the Spruce Lake Shear Zone. The early history of this zone coincides with a change from deposition of locally sourced continental red beds (lower Pennsylvanian or youngest Mississippian Balls Lake Formation) to more distally sourced fluvial deposits (lower Pennsylvanian Lancaster and Tynemouth Creek formations). Rather than being an isolated segment of a late Pennsylvanian ‘Variscan front’, this tectonic zone can be integrated into the overall strike-slip regime that dominated the Carboniferous evolution of this orogen and the successor basins.