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). Inte-grating 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 Palaeo-zoic 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.
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 (similar to 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 delta S-34 = +9.3 to +12.5 parts per thousand (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).
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.
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.
The Eight Mile Brook Plutonic Suite (EMBPS) consists of co-mingled gabbroic, syenitic, and granitic rocks that intruded Tonian rocks of the Mount Thom Formation and Mount Ephraim Plutonic Suite at the southeastern edge of the Mount Ephraim block in the Cobequid Highlands. It is unconformably overlain by or in faulted contact with Carboniferous sedimentary rocks. In situ dating of zircon in three samples by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) yielded Early Ordovician concordia and weighted mean 207Pb/238U ages of about 480 Ma. Age and chemical similarities among the EMBPS, West Barneys River Plutonic Suite in the Antigonish Highlands, and the Cape Porcupine Complex near the Strait of Canso suggest that all are closely related and formed by magma fractionation processes during an event that occurred between ca. 481 and 466 Ma based on previously published U-Pb zircon ages from thermal ionization mass spectrometry. The magmatism may be a far-field effect of subduction, a localized area of extension, or a hot spot. Chemical and age differences between these plutonic suites and the bimodal volcanic Dunn Point and McGillivray Brook formations in the northwestern Antigonish Highlands suggest that the magmatism in these units may not be directly related. Minor gabbroic and syenitic intrusions in the northern Antigonish Highlands are undated but show chemical differences from the dated magmatic rocks and hence may not be related.
