Adrian F. Park

Late Paleozoic strike-slip faults in Maritime Canada and their role in the reconfiguration of the northern Appalachian orogen

Major late Paleozoic faults, many with documented strike-slip motion, have dissected the Ordovician-Devonian Appalachian orogen in the Maritime Provinces of Atlantic Canada. Activity alternated between east-west faults (Minas trend) and NE-SW faults (Appalachian trend). NW-SE faults (Canso trend) were probably conjugate to Minas-trend faults. Major dextral movement, on faults with Appalachian trend, in total between 200 and 300 km, began in the Late Devonian. This movement initiated the Maritimes Basin in a transtensional environment at a releasing bend formed around a promontory in the Laurentian margin and thinned the crust, accounting for the major subsidence of the basin. Appalachian-trend strike slip continued in the Mississippian but was accompanied by major movement on E-W Minas-trend faults culminating around the Mississippian-Pennsylvanian boundary, juxtaposing the Meguma and Avalon terranes of the Appalachians close to their present-day configuration. However, strike slip continued during the Pennsylvanian-Permian interval resulting in transpressional deformation that reactivated and inverted earlier extensional faults. A final major episode of transtension, mainly sinistral, occurred during the Mesozoic opening of the Atlantic Ocean. Restoration of movements on these faults, amounting to several hundred kilometers of slip, explains anomalies in the present-day distribution of terranes amalgamated during early Paleozoic Appalachian tectonism. In the restored geometry, the Nashoba and Ellsworth terranes of Ganderia are adjacent to one another, and the Meguma terrane lies clearly outboard of Avalonia. A restored post-Acadian paleogeography, not the present-day geometry of the orogen, should be used as a basis for reconstructions of its earlier Paleozoic history.

Discussion on ecology of earliest reptiles inferred from basal Pennsylvanian trackwaysJournal, Vol. 164, 2007, 1113–1118

David Keighley, John Calder, Adrian Park, Ronald Pickerill & John Waldron write: In a recent article, Falcon-Lang et al . (2007, p. 1113) claim ‘trackways representing the earliest evidence for the origin of reptiles (amniotes) are reported from the basal Pennsylvanian Grande Anse Formation, New Brunswick’. We note inaccuracies in the paper and bring attention to various lines of evidence, any one of which casts serious doubt on their claim. ### Age of the Grande Anse Formation. Falcon-Lang et al . (2007, p. 1113) report a location at Shepody Bay, ‘on the eastern side of the Maringouin Peninsula, New Brunswick’ (actually located on the western side, Fig. 1) that preserves interface sedimentary structures that they interpret as amniote trackways. The authors infer an earliest Langsettian (earliest Westphalian), or possibly latest Namurian, age for the Grande Anse ‘Formation’ at this locality (the unit is not formally defined). This interpreted age of the strata was based on two lines of evidence: (1) a palynological age determination from an unpublished report; (2) its reported stratigraphic position equivalent to the Little River Formation of Nova Scotia, conformably overlying the Boss Point Formation. Fig. 1.  Map of the Maringouin peninsula and nearby Joggins area, New Brunswick and Nova Scotia, incorporating elements of Gussow (1953), Ryan et al . (1990), St. Peter & Johnson (1997) and Calder et al . (2005). (1) The report cited by Falcon-Lang et al . (2007) actually states that the spores indicate an age ‘no older than the early middle Langsettian’ (Dolby 1999, p. 43). Therefore, the Grande Anse Formation would not be of identical biostratigraphic age to that reported for the Little River Formation, which is of probable late Namurian to basal Westphalian (basal Langsettian) age (Calder et al . 2005). Regardless, Upper Palaeozoic strata in eastern Canada (Fig. 2) lack many of the stratigraphically diagnostic marine index fossils and European miospores recorded in the literature (Calder 1998; Utting et al . 2005) and so it is not currently possible to unequivocally constrain the age of the Grande Anse strata. In addition, recent recognition of rapid Mississippian stratigraphic inversions in SE New Brunswick (e.g. Park & St. Peter 2005) has supported interpretations that at least some spore assemblages in the region are entirely reworked (e.g. Dolby 2004). Fig. 2.  Summary of mid-upper Carboniferous stratigraphy for the Maritime Provinces. For brevity and clarity, only formation and group names from this discussion have been included. Data are a compromise of numerous sources and so, although the stratigraphic …

Preliminary investigation of a major high-strain zone in the Caledonian Highlands, southern New Brunswick

A major ductile high-strain zone up to 5 km in width can be traced for at least 70 km diagonally across the Avalonian Caledonia terrane of southern New Brunswick. A study of the northeastern part of this zone from the Prosser Mountain area in the northwest to the Point Wolfe River area west of Fundy National Park shows that both the ca. 630—620 Ma Broad River Group and associated plutons and the 560—550 Ma Coldbrook Group contain similar structural elements, related to a largely shared deformational history. Some of this history is apparent also in the 560—550 Ma plutonic rocks. A pervasive foliation (S1) lies parallel to bedding (S0), and although evidently composite (S0-1) in the Broad River Group, this fabric is very heterogeneous in the younger Coldbrook Group, where low strain enclaves are widespread. No folds have been seen of an F1 generation, and no reversals of facing or vergence are apparent. A mineral lineation (L 1 m) is locally prominent, defined by biotite aggregates. The plutonic rocks have fabrics that developed during and soon after crystallization, including a foliation (S1) producing augen-gneiss with a prominent L-tectonite (L 1 m). S1 in the plutonic rocks also includes a schistosity associated with the growth of white mica and breakdown of feldspar. Geometry suggests that S1 in the granites is related to S0-1 in the supracrustal rocks, and the mineral lineation (L 1 m) in both units shares a common orientation. S1 and S0-1 are crenulated by a strong second cleavage (S2) axial planar to folds (F2), the large-scale expression of which is an asymmetric synform containing a belt of Coldbrook Group rocks. Kinematic indicators for F2 structures suggest an overall top-to-the-southeast motion along thrusts that stack units of Broad River Group, Coldbrook Group, and plutonic rocks. Fabric development in the older plutonic rocks implies a history of exhumation beginning under hot, anhydrous conditions during and soon after crystallization at ca. 620 Ma, followed by hydration during retrogression as plutonic rocks were tectonically emplaced into this crustal stack. The age of the later tectonic events is not yet well constrained, but could be as late as Carboniferous.