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Pygocephalid pancrustaceans from the late Carboniferous of Nova Scotia, Canada, with comments on the cuticular microstructures of Pygocephalamorpha

Thomas Laville, Antoine Andréo and Jade B. Atkins
Pygocephalomorphs are fossil eumalacostracans with a shrimp to lobster-like morphology, known from the Late Devonian (Famennian) to the early Permian (Cisuralian; Artinskian). In the late Paleozoic, pygocephalamorphs formed an important component of marginal marine, brackish and freshwater communities. Several species, including species of Tealliocaris and Pygocephalus, have been described from the Carboniferous of Canada, in particular from the Pennsylvanian. A revision of Pygocephalus from the Carboniferous of Nova Scotia, Canada, is proposed based on original material described by Copeland and on undescribed material from the Joggins Fossil Cliffs UNESCO World Heritage Site. The presence of three taxa is confirmed: Pygocephalus cooperi, Pygocephalus cf. cooperi and Pygocephalus dubius. The pygocephalomorphs of Joggins Fossil Cliffs, and more generally Nova Scotia, were likely benthic walkers based on their leg morphology and the paleoichnological evidence. A comparison of the studied assemblages with previously known assemblages from the Mississippian of Canada shows a faunal turnover among these assemblages, which could reflect paleoenvironmental changes in Atlantic Canada during the Carboniferous and thus various ecological affinities among taxa. We also observed three types of microstructures on the shield of Pygocephalus dubius: canal-like pores, which are most probably organule canals, setal attachment site, and polygonal reticular ornamentation.

Redescription of the cockroachoid Archimylacris acadica Scudder 1868, key species of the family Archimylacridae, with description of a new specimen from the early Moscovian (Pennsylvanian) of Canada

Joerg W. Schneider, Olivia A. King, Matthew R. Stimson, Olivier Béthoux, Luke F. Allen, Rowan E. Norrad, Bailey C. Malay, Lucy L. Smith, Caleb P.W. Bohus, Steven J. Hinds and Adrian F. Park
The species Archimylacris acadica Scudder, first described from Nova Scotia (Canada), is the type species of the genus Archimylacris and the family Archimylacridae. It is re-described based on historical drawings and a coeval new specimen from the same geographic area, the Maritimes Basin of eastern Canada from Robertson Point (Sunbury Creek Formation) in central New Brunswick. A precise diagnosis of the genus and the species and an emended diagnosis of the family Archimylacridae are given. This new specimen and the type specimen of Archimylacris lubnensis are proposed as reference specimens for the missing holotype of Archimylacris acadica. Paleobiogeographically and stratigraphically, archimylacrids appeared suddenly in the fossil record of the paralic Appalachian Basin with no evolutionary forerunners yet discovered; they became common in the paralic Variscan foreland basins in northern Europe. They are so far unknown from contemporaneous entomofaunas of Cathaysia, from the Angara biotic province, and from Gondwana.

Early Ordovician Connell Mountain porphyry Cu deposit, Woodstock, New Brunswick, Canada: Geochemical, S isotopic, and Re–Os geochronologic constraints on adakitic slab failure magmatism

David R. Lentz, Robert A. Creaser, Kathleen G. Thorne and Fazilat Yousefi
The Early Ordovician subvolcanic Gibson intrusive complex, located near Woodstock, New Brunswick, Canada, is composed of the main Gibson pluton, and mineralized marginal (satellite) stocks at Connell Mountain, Bulls Creek, and the tuffisitic diatreme at Sharp Mountain. The high-level Connell Mountain hornblende-plagioclase porphyritic tonalite stock (~100 MPa) is a small cupola, 1500 m north of the main Gibson pluton, and hosts low-grade porphyry copper mineralization (23 Mt at 0.18% Cu). These intrusions are calc-alkalic, metaluminous, and magnesian, with low TiO2 (0.16 to 0.38 wt.%) and Zr (67 to 92 ppm), and low Nb (4.3–7.7 ppm) and Ta (<0.5 ppm), low Y (5 to <20 ppm) and Yb (1.0 to 2.9 ppm), which are consistent with adakitic slab failure magmatic rocks. Sulphur isotopic compositions of pyrite and chalcopyrite from the porphyry and altered sedimentary rocks range from δ34S = +9.3 to +12.5‰ (n = 8), indicating derivation from carbonaceous sulphidic metasedimentary rocks of the Cambrian–Ordovician Woodstock Group. The crystallization age of the Connell Mountain tonalite (474.5 +1/-4 Ma, U–Pb zircon, previously published) is similar to a previously determined U–Pb zircon age of the Gibson granodiorite, which is coeval with the volcanic-dominated Meductic Group (470–477 Ma) located just to the west. Three Re–Os model ages of 475.6 ± 1.2, 475.8 ± 1.2, and 476.5 ± 1.2 Ma from three textural varieties of molybdenite at Connell Mountain (Re = 333, 642, and 1562 ppm) yield a weighted average model age of 475.9 ± 1.1 Ma indistinguishable from those earlier zircon U–Pb ages, so the porphyry and Cu mineralization at Connell Mountain are related to a hypabyssal phase of the Gibson Granodiorite that is exposed (part of the Gibson Intrusive Complex).

Kinematics of the Cabot Fault Zone: An example of long-lived large-scale orogen-parallel transcurrent movements during the accretionary history of the northern Appalachian orogen, Canada

Arjan Brem, Shoufa Lin and Cees van Staal
The Cabot Fault Zone (CFZ) in the western Newfoundland Appalachian orogen is a long-lived crustal-scale tectonic zone that separates the Corner Brook Lake block (CBLB) of the internal Humber Zone from the Dashwoods block of the western Dunnage Zone. The two blocks comprise different tectonostratigraphic assemblages and had distinct Early Palaeozoic tectonic histories. Using field and microscopic observations, five phases of deformation have been recognized in the CFZ, demonstrating a progressive evolution of the tectonic zone from mid-crustal levels (D1 gneisses and D2 mylonites) to shallow-crustal levels (D5 cataclasites). Integrating available geochronological data, the CFZ has recorded a protracted history of dominant oblique-dextral transcurrent movement, as evidenced by well-developed Late Ordovician–earliest Silurian (post-Taconic) D1 and late Early Silurian to Early Devonian (post-Salinic) D2 fabrics. Large-scale (i.e., 100s of km) of Early Palaeozoic orogen-parallel movement along the CFZ can explain the present-day juxtaposition of the distinct CBLB and the Dashwoods block. Such large-scale orogen-parallel motion implies that presently neighbouring terranes could have been far apart during convergence and ocean closures, which has significant implications for tectonic interpretation of the Early Palaeozoic evolution of the Newfoundland Appalachian orogen.

Atlantic Geoscience Society Abstracts: 52nd Annual Colloquium and General Meeting, February 6 and 7, 2026

The Editors

Discussion of “Tectonic timing of emplacement of the South Mountain Batholith, southwestern Nova Scotia, Canada” with an alternative interpretation

Daniel J. Kontak and Richard J. Horne

Reply to “Discussion of ‘Tectonic timing of emplacement of the South Mountain Batholith, southwestern Nova Scotia, Canada’ with an alternative interpretation”

D. Barrie Clarke, Michael A. MacDonald and Colin B. McKenzie