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The Partridge Island block is a newly identified tectonic element in the Saint John area of southern New Brunswick, located south of and in faulted contact with Proterozoic and Cambrian rocks of the Ganderian Brookville and Avalonian Caledonia terranes. It includes the Lorneville Group and Tiner Point complex. The Lorneville Group consists of interbedded volcanic and sedimentary rocks, subdivided into the Taylors Island Formation west of Saint John Harbour and West Beach Formation east of Saint John Harbour. A sample from thin rhyolite layers interbedded with basaltic flows of the Taylors Island Formation at Sheldon Point yielded a Late Devonian - Early Carboniferous U-Pb (zircon) age of 358.9 +6/-5 Ma. Petrological similarities indicate that all of the basaltic rocks of the Taylors Island and West Beach formations are of similar age and formed in a continental within-plate tectonic setting. West of Saint John Harbour, basaltic and sedimentary rocks of the Taylors Island Formation are increasingly deformed and mylonitic to the south, and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the Tiner Point complex. Based on magnetic signatures, the deformed rocks of the Tiner Point complex can be traced through Partridge Island to the eastern side of Saint John Harbour, where together with the West Beach Formation, they occupy a thrust sheet above a redbed sequence of the mid-Carboniferous Balls Lake Formation. The Tiner Point complex includes leucotonalite and aegirine-bearing alkali-feldspar granite with A-type chemical affinity and Early Carboniferous U-Pb (zircon) ages of 353.6 ± 5.7 and 346.4 ± 0.7 Ma, respectively. Based on similarities in age, petrological characteristics, alteration, iron oxide - copper - gold (IOCG)-type mineralization, and deformation style, the Partridge Island block is correlated with Late Devonian - Early Carboniferous volcanic-sedimentary-plutonic rocks of the Cobequid Highlands in northern mainland Nova Scotia. Deformation was likely a result of dextral transpression along the Cobequid-Chedabucto fault zone during juxtaposition of the Meguma terrane. [ABSTRACT FROM AUTHOR]

To better understand geodynamic processes related to the assembly of various belts of volcanic–sedimentary rocks in the Avalonian Mira terrane of SE Cape Breton Island (protolith ages 680–560 Ma) we investigated metamorphic processes in 20 white-mica-bearing mafic and felsic metavolcanic rocks. The felsic metavolcanic rocks are foliated and partly sheared with blastoporphyritic relict fabric and contain the assemblage phengite–epidote–chlorite–albite–K-feldspar–quartz–titanite ± stilpnomelane ± calcite ± ilmenite. In contrast, many mafic metavolcanic rocks are relatively undeformed and display relict porphyritic and amygdaloidal textures. They contain the assemblages epidote–chlorite–albite–quartz–titanite ± phengite ± pumpellyite ± prehnite ± calcite ± K-feldspar and actinolite–epidote–chlorite–albite–quartz–titanite ± phengite ± calcite ± K-feldspar. Heterogeneous metamorphic overprinting is indicated by local relicts of magmatic clinopyroxene, magnetite and plagioclase. Metamorphic minerals formed by local precipitation in clusters and are due to continuous nucleation of very low-grade phases during pulses of variably pervasive fluids, which were released during intense dehydration at 250–300°C. Nucleaction rate dominated over growth rate at these conditions. Potassic white mica in both mafic and felsic rocks is mostly phengite with a wide compositional range (3·11–3·41 Si a.p.f.u.). Maximum Si contents are typically between 3·30 and 3·41 a.p.f.u. P–T pseudosections were calculated for the range 200–400°C and 1–7 kbar. The peak metamorphic assemblages occupy P–T fields consistent with the position of isopleths for corresponding maximum Si contents in white mica. Peak P–T conditions in the Mira terrane samples lie within a narrow range of 3·5 ± 0·4 kbar and 280 ± 30°C in samples representing all of the assembled volcanic–sedimentary belts. The derived peak metamorphic conditions suggest syn-collisional burial to 11–14 km depth and a low metamorphic geotherm of 20–25°C km–1. Under these conditions subsequent strike-slip deformation is attributed to the final assembly of magmatic arc slices to form the crust of the Mira terrane. [ABSTRACT FROM PUBLISHER]

Abstract: We present here the results of a pilot study on Cambrian acritarchs from Cape Breton Island, Nova Scotia, based on a material from the MacLean Brook Formation in the Mira River Valley. An assemblage from the base of the formation contains 8 species including Eliasum llaniscum, Cristallinium dubium and Symplassosphaeridium cambriense, and correlates with a position close to the Paradoxides davidis–P. forchhammeri Zone boundary. An assemblage from the upper part of the formation contains 16 species, of which 3 are new, including Cristallinium aciculatum, Petaloferidium lacrimiferum n. sp., Pirea orbicularis, Stelliferidium pingiculum, S. magnum n. sp., S. albanii n.sp, and Timofeevia microretis, correlated to the Olenus Zone. The upper assemblage is particularly noteworthy as it provides the first direct evidence for the Olenus Zone in the MacLean Brook Formation. Furthermore, it contains stratigraphically significant taxa known from sections on Baltica, and northern Gondwana but which have not been reported previously on Avalonia. The distinction between Stelliferidium and Timofeevia is discussed in part based on new data on Timofeevia lancarae from its type area in northern Spain. It is suggested that many reports of Furongian Timofeevia phosphoritica and T. lancarae are better referred to Stelliferidium. [Copyright &y& Elsevier]

Detrital zircon ages from the lower part of the Late Proterozoic(?) to Middle Cambrian Goldenville Group in the Meguma terrane of Nova Scotia suggest derivation from local sources in the Avalonian and Pan-African orogens on the margins of Early Cambrian Gondwana. Samples from near the top of the group show a broader distribution, including ages back to Archean. The εNd data show a corresponding trend, from slightly positive in the lower Goldenville Group to highly negative in the upper Goldenville Group and overlying Upper Cambrian to Lower Ordovician Halifax Group. The trends are consistent with deposition of the lower part of the Meguma succession in a rift, in which uplifted rift-flanks were the main source of the early basin fill, whereas subsequent thermal subsidence of rift margins allowed for more widespread sediment sourcing in younger units. The rift was possibly located between Gondwana and Avalonia, and may have been the locus for separation of Avalonia from Gondwana to form part of the Rheic Ocean. [ABSTRACT FROM AUTHOR]

Distinct 18O depletion is characteristic of a large majority of the 620–550 Ma felsic igneous rocks of Avalonia in the northern Appalachian orogen. Neoproterozoic rocks in the Boston Avalon terrane have the lowest δ18OWR values (≥–3.1‰), followed by the Mira terrane in Cape Breton Island and the Caledonia terrane in New Brunswick (≥–1.2‰), the Avalon terrane in Newfoundland (≥+2.8‰), and the Antigonish Highlands in Nova Scotia (≥+5.3‰). In contrast, this depletion of 18O is observed in very few of the Paleozoic felsic igneous rocks from these Avalonian terranes, and also in very few of the Neoproterozoic and Paleozoic felsic igneous rocks from the inboard Ganderian terranes. The low-18O character of the Neoproterozoic igneous rocks is related to regional pervasive, post-magmatic alteration by predominantly meteoric-hydrothermal fluids (δ18OH2O ~–6‰ to –4‰) at 200–450 °C. The alteration likely occurred during late Neoproterozoic transtensional extension of Avalonia. Large-scale fluid infiltration and circulation within the Avalonian crust accompanied this extension with development of pull-apart sedimentary basins and extension-related magmatism that were the prelude to Cambrian submergence of Avalonia. This regional 18O depletion provides a geochemical fingerprint by which Avalonia can be distinguished from other peri-Gondwanan terranes. These data suggest that Avalonia existed as a composite terrane on the Gondwanan margin in the Neoproterozoic, separate from Ganderia. [ABSTRACT FROM AUTHOR]

A prominent positive magnetic anomaly spans the 100 km distance between Prince Edward Island and Cape Breton Island in the southern Gulf of St. Lawrence. The anomaly occurs in an area of complex structure where Appalachian terrane boundaries are poorly resolved because of thick late Paleozoic sedimentary cover. Analysis of the magnetic anomaly led to the interpretation that it is produced by four separate, approximately circular, source bodies aligned along the northwesterly trend of the anomaly. Seismic data, physical property measurements, and magnetic and gravity anomalies were used to further investigate the anomaly sources through forward modeling techniques. The four source bodies have densities and magnetic susceptibilities compatible with dioritic to granitic compositions. Modeling also suggests that basement to the north of the plutons has higher density and susceptibility than basement to the south, and hence the source bodies are interpreted as plutons emplaced along the boundary between Ganderian composite terranes to the north and the Ganderian Brookville – Bras d’Or terrane to the south. This interpretation suggests that the Ganderia–Avalonia boundary is located farther south, and shows the need for re-evaluation of the location and role of the Canso fault in offsetting terranes between Cape Breton Island and southern New Brunswick. [ABSTRACT FROM AUTHOR]

Paleomagnetic results and a U–Pb baddeleyite age from the Silurian Mavillette gabbroic sill in southwest Nova Scotia, Canada, provide new evidence about the Paleozoic tectonic evolution of the Meguma terrane. The Mavillette gabbro sill intruded ca. 440–430 Myr old bimodal rift-related metavolcanic and metasedimentary rocks of the White Rock Formation in the Silurian–Devonian Rockville Notch Group. The 426.4 ± 2.0 Ma Mavillette gabbro age is notably younger than the ca. 440 Ma magmatism, but is part of a geochemically defined suite of within-plate sills and volcanic rocks of the Rockville Notch Group with ages as young as Early Devonian. Paleomagnetic investigation of 13 sites distributed along the Neoacadian (ca. 390 Ma) synclinal limbs of the Mavillette sill reveal magnetization directions that fail a fold test and therefore postdate Silurian emplacement of the gabbro. The post-folding remanence has a mean direction of D = 153.4, I = 17.1°; α95 = 6.5° (n = 12 sites), with corresponding paleopole 31.9 °S, 325.2 E; dp = 3.5°, dm = 6.7° that resembles a pervasive late Carboniferous Kiaman overprint magnetization in North America, but is rotated significantly 22.2° ± 8.1° counter-clockwise (CCW). Mavillette remanence acquisition likely occurred in concert with fluid mobilization related to Alleghanian deformation, recorded locally by ca. 320 Ma muscovite 40Ar–39Ar ages. Previously published paleomagnetic results from the Meguma terrane also have Carboniferous remanence directions with similar ∼24° CCW discordance. The regional CCW rotation of the southwest Meguma terrane post-dates this ca. 320 Ma tectonothermal remanence acquisition event, likely recording the development of an oroclinal bend of the Meguma terrane during the Alleghanian orogeny. [ABSTRACT FROM AUTHOR]

Pre-Mesozoic rocks on Grand Manan Island are divided into two groups; an older Grand Manan Group of early Ediacaran or older age, and a younger Castalia Group, considered to be latest Ediacaran to earliest Cambrian. The Castalia Group as it is currently defined comprises a basal sequence of clastic marine sedimentary rocks assigned to the Great Duck Island and Flagg Cove formations and an upper sequence of mainly mafic volcanic and volcaniclastic rocks assigned to the Ross Island, North Head, Priest Cove and Long Pond Bay formations. A maximum age for the Castalia Group is ca. 600 Ma, based on the presence of volcanic clasts in conglomerate of the Great Duck Island Formation that are derived from the underlying Ingalls Head Formation (ca. 618 Ma). Additional age constraints include a U-Pb age of 539 ± 3 Ma for felsic tuff from the Priest Cove Formation and a minimum age of earliest Cambrian based on an assumed intrusive relationship between the ca. 535 Ma Stanley Brook Granite and the Flagg Cove Formation. However, stratigraphic relationships are generally poorly known due to intense deformation and thrusting, and most contacts are faulted. The Flagg Cove Formation consists of quartzose sandstone and green to dark grey silty shale, previously reported to contain rare trace fossils (Planolites) in strata along Flagg Cove. A sequence of sandstone and silty shale containing abundant morphologically simple trace fossils, including Planolites, at the south end of Stanley Beach in Flagg Cove recently yielded organic walled microfossils (Micrhystridium sp.) of a type also found in the King Square Formation in the Saint John area. This suggests a much younger (Miaolingian) age for the Flagg Cove Formation, indicating that its relationship with the Stanley Brook Granite and inclusion in the Castalia Group need to be re-evaluated. [ABSTRACT FROM AUTHOR]

The ca. 620 Ma Huntington Mountain pluton and East Bay Hills Group, which comprise part of the Avalonian Mira terrane, Cape Breton Island, Nova Scotia, Canada, are characterized by pervasive propylitic alteration (chlorite, epidote, sericite, and Fe-Ti oxides) and low δ18O values (-3.8 to +6.2‰). This alteration is a product of interaction with hydrothermal fluids of meteoric and/or meteoric-seawater mixed origin at -300 °C over a range of water/rock (w/r) ratios. Locally, the propylitic alteration was further overprinted by quartz-calcite-sericite alteration. Such samples have generally higher δ18OWR values (up to +9.5‰), reflecting interaction with evolved meteoric water at lower temperatures (-200 °C) and very low w/r ratios. The hydrothermal fluids responsible for widespread propylitic alteration of the Huntington Mountain-East Bay Hills complex (and regions beyond) likely entered the crust during initial rifting of the Mira terrane from Gondwana at ca. 575-550 Ma. [ABSTRACT FROM AUTHOR]

Unusual black sandstone beds of Cambrian age (~530 to 511 Ma) occur in the upper part of the Glen Falls Formation and the lower part of the overlying Hanford Brook Formation of the Saint John Group in the Saint John area of southern New Brunswick. The dark color of these beds has been attributed to phosphatic minerals and iron chlorite. The ubiquitous presence of phosphorous, an essential nutrient for life, is important as these rocks formed during the time of the "Cambrian Explosion" in the early evolution of life. This project focuses on mineralogy, origin, and depositional environment of the black sandstones, as well as their disputed stratigraphic relationships with overlying and underlying rocks, and the phosphorous cycling that took place during deposition. The study will investigate also the correlation between the evolution of life as recorded in the Saint John Group and the appearance of phosphorite. Phosphorite is defined as a marine sedimentary rock with equal to or greater than 18% P2O5. The sedimentary phosphate mineral is francolite. The origin of phosphorite involves phosphorous in particulate organic matter being transferred to sediment, followed by diagenetic degradation and dissolved inorganic phosphorous being released from the organic matter to sedimentary pore waters, causing the precipitation of francolite. This process produces phosphorite hardgrounds, as well as individual grains or concretions that become reworked, forming concentrated phosphorite beds. The phosphorite that occurs in the Glen Falls and Hanford Brook formations was likely linked to sea-level rise at the Precambrian-Cambrian boundary and iron-redox cycling. These events allowed more phosphorous to be available for life forms. Fifty-two samples were collected from outcrops in and around the Saint John area and stratigraphic sections were logged for each location. The stratigraphic sections have been compared for lateral and stratigraphic variations. Interpretations of seven lithofacies described in these outcrops suggest deposition was in a tidal barrier island environment to mid-to-distal shelf environment. Thin sections of samples have been cut and examined using both petrographic and scanning electron microscopy to aid in determining paragenesis. Results confirm that francolite occurs as firmgrounds, intraclasts, and coated grains. SEM-EDS was used to determine the chemical composition of the phosphorites. Five samples were sent to the Queen's Facility for Isotopic Research where stable isotope compositions for carbon (δ13C) are being determined by ICP-MS; these data will aid in the interpretation of depositional conditions. [ABSTRACT FROM AUTHOR]

Fossiliferous clasts occur in Carboniferous conglomerate in the Horton Group on western Isle Madame and in the Mabou Group on eastern Isle Madame. Most of the clasts (21 of 23 examined) are calcareous siltstone and sandstone that contain Silurian – Lower Devonian faunas comparable to those in the Arisaig area, northern mainland Nova Scotia, although the lithologies are coarser grained and less calcareous than those of the Arisaig section. These middle Paleozoic faunas are well constrained to the Silurian (uppermost Llandovery through Pridoli) and lowest Devonian and are characteristic of those known from shallow siliciclastic-dominated platforms of the Avalon microcontinent in Wales and England. The remaining two clasts have abundant inarticulate brachiopod shells that indicate provenance from Middle Cambrian proximal marine facies on the Avalonian marginal platform. No clasts were found that are likely to have been derived from the Torbrook Formation, and thus from the Meguma terrane in southwestern Nova Scotia, as has been previously reported. The association of relatively large, reworked fossiliferous clasts in Carboniferous conglomerate on Isle Madame suggests local derivation from lower and middle Paleozoic units not presently exposed, although probably present as subcrop under the Carboniferous units, in southwestern Cape Breton Island and adjacent mainland Nova Scotia. [ABSTRACT FROM AUTHOR]

The High Head member is a ~860 m interval of fine-grained metasedimentary rocks, in the middle of the generally sandy Goldenville Group of southwestern Nova Scotia. The stratigraphy is punctuated by only rare coarser sandstone beds, and one interval of mafic intrusions, which appear to have been intruded while the sediments were still wet. Paleocurrents, deduced from flutes and grooves in the immediately underlying sandstone beds, and from rare washed-out ripple marks that are the largest physical sedimentary structures in the mudrocks, show flow towards the south and west, in contrast with paleocurrents recorded from Atlantic coastal outcrops of the Goldenville Group, which are almost all toward the north or east. The High Head member contains spectacular trace fossils. In the lower part of the section, the trace-fossil assemblage comprises Oldhamia radiata, large, sparsely branching Chondrites acutangulus, Curvolithus sp. Gordia sp., Planolites sp. and Taenidium sp. Up-section, large Glockerichnus sp. are also rarely observed. Near the middle of the section Trichophycus pedum (formerly known as Phycodes pedum) is commonly observed. Also present are taphonomic variants of the Trichophycus pedum (i.e. T. pedum truncated and preserved at a different level); they appear as evenly spaced, reamed intrusions that some researchers have referred to as Hormosiroidea, Saerichnites or Neonereites uniserialis. The upper half of the section is bioturbated sporadically, and dominated by Gordia marina, Helminthopsis sp., Taenidium sp., and rather persistent, if rare Phycodes sp. and Trichophycus pedum. Thick sand beds characterize the uppermost part of the High Head section and trace fossils become rare in that area. Of interest in the High-Head ichnology is: (1) the relatively high diversity of trace fossils observed; (2) the presence of Trichophycus pedum; and (3) the occurrence of Gordia marina with Trichophycus. The observed assemblage is very similar to those in late Precambrian to Early Cambrian sequences of southeastern Newfoundland (Chapel Island Formation), which yielded (in common with the Goldenville Group) Curvolithus sp., Gordia sp., Neonereites uniserialis, Phycodes pedum, Planolites sp., and Skolithos sp. In Newfoundland, the diverse ichnofaunas were reported below the oldest trilobite-bearing strata. Trichophycus has been reported almost globally, with its first occurrence in strata with or immediately above Ediacaran fossils. Trichophycus pedum is taken to indicate the presence of the first well-developed, metazoan animals, and thereby indicative of the boundary between Precambrian and Phanerozoic strata. The occurrence of Trichophycus pedum and the similarities of the observed assemblage suggest that the High Head exposures may indeed straddle the Precambrian-Phanerozoic boundary. [ABSTRACT FROM AUTHOR]