| 1. |
- Almqvist, Bjarne, et al.
(författare)
-
Magnetic characterisation of magnetite and hematite from the Blötberget apatite-iron-oxide deposits (Bergslagen), south-central Sweden
- 2019
-
Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 56:9, s. 948-957
-
Tidskriftsartikel (refereegranskat)abstract
- Rock magnetic measurements were carried out on drill core material and hand specimens from the Blötberget apatite-iron oxide deposit in the Bergslagen ore province, south-central Sweden, to characterise their magnetic properties. Measurements included several kinds of magnetic susceptibility and hysteresis parameters. Petrographic and scanning electron microscopy (SEM) were used to independently identify and quantify the amount and type of magnetite and hematite. Two hematite-rich samples were studied with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to quantify the trace element chemistry in hematite and investigate the potential influence of trace elements on magnetic properties. Three aspects of this study are noteworthy. 1) Hematite-rich samples display strong anisotropy of magnetic susceptibility, which is likely to affect the appearance and modelling of magnetic anomalies. 2) The magnitude-drop in susceptibility across Curie and Néel temperature transitions show significant correlation with the respective weight percent (wt%) of magnetite and hematite. Temperature dependent magnetic susceptibility measurements can therefore be used to infer the amounts of both magnetite and hematite. 3) observations of a strongly depressed Morin transition at ca -60 to -70 C (200 to 210 K) are made during low-temperature susceptibility measurements. This anomalous Morin transition is most likely related to trace amounts of V and Ti that substitute for Fe in the hematite. When taken together, these magnetic observations improve the understanding of the magnetic anomaly signature of the Blötberget apatite-iron oxide deposits and may potentially be utilised in a broader context when assessing similar (Paleoproterozoic) apatite-iron oxide systems.
|
|
| 2. |
- Bazarnik, Jakub, et al.
(författare)
-
Reinterpretation of a major terrane boundary in the northern Svalbard Caledonides based on metamorphic fingerprinting of rocks in northern Spitsbergen
- 2023
-
Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 60:8, s. 1188-1205
-
Tidskriftsartikel (refereegranskat)abstract
- Tectonic models for development of the Svalbard Caledonides depend on reliable assessment of the metamorphic evolution of the various basement provinces involved. The Mosselhalvoya Group (MG) and the Atomfjella Complex (AC) have previously been assigned to the Nordaustlandet andWest Ny-Friesland terranes, respectively. New analytical data and petrographic observations indicate that both units experienced two-stage metamorphism under similar pressure-temperature (P-T) conditions. Two stages of amphibolite facies metamorphism (M1 and M2) are clearly recorded by garnet and staurolite porphyroblast textures. The results of thermodynamic phase equilibrium modeling indicate that peak M2 metamorphism occurred at similar to 7-7.5 kbar and 590-600 degrees C in both units. Zirconium-in-rutile trace element thermometry confirms the temperature estimates for M1 and M2 stages of metamorphism. Monazite chemical Th-U-Pb dates from the MG resolve a two-stage garnet growth at 444 +/- 7 Ma (M1) and 423 +/- 6 Ma (M2). In contrast, monazite dated in the AC defines a single age of 420 +/- 4 Ma interpreted as M2 growth. We suggest M2 was coeval with early strike-slip motion along the Billefjorden Fault Zone, whereas M1 reflects initial tectonic burial of the studied units. The similarity in metamorphic history between the both units suggests that the boundary between them is a subordinate thrust fault within the Atomfjella thrust stack rather than a major boundary separating the Nordaustlandet and West Ny-Friesland terranes. The MG should be included within the West Ny-Friesland terrane and the tectonic boundary with the Nordaustlandet terrane is likely the Eolussletta Shear Zone.
|
|
| 3. |
- Bell, Phil R., et al.
(författare)
-
Taphonomy of the Danek Bonebed : a monodominant Edmontosaurus (Hadrosauridae) bonebed from the Horseshoe Canyon Formation, Alberta
- 2014
-
Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 51:11
-
Tidskriftsartikel (refereegranskat)abstract
- The Danek Bonebed (Horsethief Member, Horseshoe Canyon Formation, Late Campanian) is dominated by the remains of at least 12 Edmontosaurus regalis. Skeletal remains of a tyrannosaurid and ceratopsid are also known. The predominantly disarticulated remains were interred on a periodically inundated floodplain and, although the cause of death is unknown, a sudden, catastrophic death explains the demographic spread, faunal diversity, rare greenstick fractures, and homogeneous weathering/abrasion categories of the assemblage. The Danek Bonebed shares a similar taphonomic signature to the Liscomb Bonebed (Prince Creek Formation, Alaska), but it is unique among all other described hadrosaurid bonebeds in the unusually high proportion of bite-marked bones (similar to 30%), suggesting scavenging played a major role in the reworking of the assemblage. The highest frequency of bite marks is found on small, often unidentifiable (and commonly ignored) bone fragments, underscoring the role that such fragments can play in taphonomic interpretation. Finally, the recognition of E. regalis from central Alberta is an important datum linking contemporaneous occurrences in southern Alberta with slightly older records of this species from the Wapiti Formation in northwestern Alberta.
|
|
| 4. |
- Bellefleur, Gilles, et al.
(författare)
-
Reprocessing legacy three-dimensional seismic data from the Halfmile Lake and Brunswick No. 6 volcanogenic massive sulphide deposits, New Brunswick, Canada
- 2019
-
Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 56:5, s. 569-583
-
Tidskriftsartikel (refereegranskat)abstract
- We reprocessed legacy three-dimensional (3D) seismic data from the Halfmile Lake and Brunswick areas, both of which were acquired for mineral exploration in the Bathurst Mining Camp, New Brunswick. Each 3D seismic survey was acquired over known volcanogenic massive sulphide deposits and covered areas with strong mineral potential. Most improvements resulted from a reduction of coherent and random noise on prestack gathers and from an improved velocity model, combined with re-imaging with dip moveout corrections and poststack migration or prestack time migration. At Halfmile Lake, the new imaging results show the Deep zone and a possible extension of the sulphide mineralization at greater depth. True amplitude processing has shown that this anomaly has strong amplitudes and is offset from the Deep zone by a shallowly dipping fault (<15 degrees). With the clearer geological context provided by our results, this anomaly, which appears as a stand-alone anomaly on an original image obtained by Noranda Exploration Ltd., becomes a defendable exploration target. Nonorthogonal acquisition geometry and receiver patches of the Brunswick No. 6 3D seismic survey generated artefacts after dip moveout processing that reduced the overall quality of the seismic volumes. By using a filtering approach based on the application of a weighted Laplacian-Gaussian filter in the Kx-Ky domain, we reduced the noise and improved the continuity of reflections. We also imaged the short and flat reflections observed previously only in the shallow part of prestack time migrated data. These short reflections appear as diffractions on the filtered stacked section with dip moveout corrections, indicating that they originate from small geological bodies or discontinuities in the subsurface.
|
|
| 5. |
- Beranek, Luke P., et al.
(författare)
-
Detrital zircon geochronology of Ediacaran to Cambrian deep-water strata of the Franklinian basin, northern Ellesmere Island, Nunavut : implications for regional stratigraphic correlations
- 2013
-
Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 50:10, s. 1007-1018
-
Tidskriftsartikel (refereegranskat)abstract
- Enigmatic successions of deep-water strata referred to as the Nesmith beds and Grant Land Formation comprise the exposed base of the Franklinian passive margin sequence in northern Ellesmere Island, Nunavut. To test stratigraphic correlations with Ediacaran to Cambrian shallow-water strata of the Franklinian platform that are inferred by regional basin models, >500 detrital zircons from the Nesmith beds and Grant Land Formation were analyzed for sediment provenance analysis using laser ablation (LA-ICP-MS) and ion-microprobe (SIMS) methods. Samples of the Nesmith beds and Grant Land Formation are characterized by 1000-1300, 1600-2000, and 2500-2800 Ma detrital zircon age distributions and indicate provenance from rock assemblages of the Laurentian craton. In combination with regional stratigraphic constraints, these data support an Ediacaran to Cambrian paleodrainage model that features the Nesmith beds and Grant Land Formation as the offshore marine parts of a north-to northeast-directed depositional network. Proposed stratigraphic correlations between the Nesmith beds and Ediacaran platformal units of northern Greenland are consistent with the new detrital zircon results. Cambrian stratigraphic correlations within northern Ellesmere Island are permissive, but require further investigation because the Grant Land Formation provenance signatures agree with a third-order sedimentary system that has been homogenized by longshore current or gravity-flow processes, whereas coeval shallow-water strata yield a restricted range of detrital zircon ages and imply sources from local drainage areas or underlying rock units. The detrital zircon signatures of the Franklinian passive margin resemble those for the Cordilleran and Appalachian passive margins of Laurentia, which demonstrates the widespread recycling of North American rock assemblages after late Neoproterozoic continental rifting and breakup of supercontinent Rodinia.
|
|
| 6. |
- Bergstrom, Stig M., et al.
(författare)
-
Revision of the position of the Ordovician-Silurian boundary in southern Ontario: regional chronostratigraphic implications of delta C-13 chemostratigraphy of the Manitoulin Formation and associated strata
- 2011
-
Ingår i: Canadian Journal of Earth Sciences. - 0008-4077. ; 48:11, s. 1447-1470
-
Tidskriftsartikel (refereegranskat)abstract
- delta C-13 values of 142 samples from the Manitoulin Formation and subjacent strata collected from 14 exposures and two drill-cores on Manitoulin Island, Bruce Peninsula, and the region south of Georgian Bay suggest that the Manitoulin Formation is latest Ordovician (Hirnantian) rather than earliest Silurian in age. A delta C-13 excursion identified as the Hirnantian isotope carbon excursion (HICE), which has a magnitude of nearly 2.5 parts per thousand above baseline values, is present in an interval from the upper Queenston Formation to the lower to middle part of the Manitoulin Formation in most of Bruce Peninsula and in the area south of Georgian Bay, whereas on Manitoulin Island the RICE appears to be absent. This indicates that a significant part of the Manitoulin Formation is older on the Bruce Peninsula and in its adjacent region than on Manitoulin Island. The chemostratigraphically based conclusions are consistent with biostratigraphic data from conodonts and brachiopods. The Hirnantian delta C-13 curve from Anticosti Island, Quebec is closely similar to those of southern Ontario. Traditionally, the Ordovician-Silurian boundary has been placed at the base of the Manitoulin Formation, but the new results suggest that it is more likely to be at, or near, the base of the overlying Cabot Head Formation. These new results have major implications For the interpretation of the geologic history and marine depositional patterns of the latest Ordovician of a large part of the North American Midcontinent.
|
|
| 7. |
- Castiello, Marco, et al.
(författare)
-
Endocranial morphology of the petalichthyid placoderm Ellopetalichthys scheii from the Middle Devonian of Arctic Canada, with remarks on the inner ear and neck joint morphology of placoderms
- 2021
-
Ingår i: Canadian journal of earth sciences (Print). - : CANADIAN SCIENCE PUBLISHING. - 0008-4077 .- 1480-3313. ; 58:1, s. 93-104
-
Tidskriftsartikel (refereegranskat)abstract
- Petalichthyid and "acanthothoracid" placoderms have taken pivotal positions in the debate on placoderm- and, by extension, jawed vertebrate - relationships owing to perceived similarities with certain jawless vertebrates. Neurocranial characters are integral to current hypotheses of early gnathostome relationships. Here, we describe the three-dimensionally preserved neurocranial anatomy of the petalichthyid placoderm Ellopetalichthys scheii (Kiaer, 1915), from the Middle Devonian (early Eifelian) of Ellesmere Island, Canada. Using X-ray computed microtomography, we generated three-dimensional reconstructions of the endocranial surfaces, orbital walls, and cranial endocavity. These reconstructions verify the absence of a crus commune of the skeletal labyrinth and the complex shape of the petalichthyid endolympathic duct. Details of the craniothoracic joint and occipital musculature fossae help resolve the problematic comparative anatomy of the occipital surface of petalichthyids. These new data highlight similarities with arthrodire placoderms, consistent with older hypotheses of a sister-group relationship between petalichthyids and that clade.
|
|
| 8. |
- Cuthbertson, Robin S., et al.
(författare)
-
A new species of mosasaur (Squamata: Mosasauridae) from the Pierre Shale (lower Campanian) of Manitoba
- 2007
-
Ingår i: Canadian journal of earth sciences (Print). - : NRC Research Press. - 0008-4077 .- 1480-3313. ; 44:5, s. 593-606
-
Tidskriftsartikel (refereegranskat)abstract
- Plioplatecarpus nichollsae, sp. nov., from the lower Campanian (Pembina Member, Pierre Shale Formation) is diagnosed by the following: a thickened ventral rim of the external naris, a short supratemporal fenestra, a frontal shield with well-developed posterolateral lappets that overlap the parietal dorsally, proximal rib shafts with an approximately circular (but not inflated) cross section, a scapula shaped as in other Plioplatecarpus species but approximately the same size (not larger) than the coracoid, and a moderately large parietal foramen that reaches the frontoparietal suture but does not invade the frontal. The last two characters require that the diagnosis of the genus Plioplatecarpus be emended. With other Plioplatecarpus species, P. nichollsae shares a robust humerus with a distal expansion at least as great as the total length of the bone, a rectangular preorbital frontal shield, a "peg and socket" postorbitofrontal-jugal articulation, a transversely directed ectopterygoid process of the pterygoid, a large, robust quadrate with a distinct eminence on the posterior surface of its shaft, an unossified gap in the ventral wall of the basioccipital, and at least 11 pygal vertebrae. P. nichollsae also shares primitive features with Platecarpus, as well as features apparently intermediate betweenPlatecarpus and Plioplatecarpus. Revision of the genus Platecarpus, currently hypothesized to be both paraphyletic and polyphyletic, as well as a better understanding of the early Campanian mosasaur fauna from the Morden area, are necessary before the phylogenetic significance of some of these characters, and therefore the relationships of Plioplatecarpus nichollsae, can be fully resolved.
|
|
| 9. |
- Daley, Allison C.
(författare)
-
Statistical analysis of mixed-motive shell borings in Ordovician, Silurian, and Devonian brachiopods from northern and eastern Canada
- 2008
-
Ingår i: Canadian journal of earth sciences (Print). - 0008-4077 .- 1480-3313. ; 45:2, s. 213-229
-
Tidskriftsartikel (refereegranskat)abstract
- Hundreds of shell borings of different origin and displaying variable patterns were found in strophomenide, pentameride, and orthide brachiopods of five Paleozoic localities in northern and eastern Canada. The borings were analyzed using simple statistics as well as cluster and nonmetric multidimensional scaling analyses. At the Ordovician Anticosti Island locality, all borings are parasitic or post-mortem in origin, while at the Wenlock-Ludlow Baillie-Hamilton Island, almost all borings are predatory. At the remaining three localities, borings represent a mix of predatory, parasitic, and post-mortem domichnial borings in all three brachiopod taxa, the proportions of which were controlled largely by brachiopod shell morphology and paleoecology. For the strophomenides, predatory borings can be segregated from parasitic and post-mortem domichnial using simple and multivariate statistical analyses. Sowerbyella-type strophomenides have a higher proportion of predatory borings at the Lochkovian localities than at the Ordovician localities, while the reverse is true for the Strophomena-type strophomenides. In pentamerides and orthides, very few predatory borings are identified; most borings were emplaced by parasitic or post-mortem domichnial borers. In pentamerides, this is due to the internal structure of the shells, which elevated the muscles of the organism above the shell floor, rendering them inaccessible to boring predators. In orthides, more deliberate defense mechanisms such as toxins or external ornamentation may have deterred predation. This study indicates that throughout the Paleozoic interactions between borers and brachiopods were complex but can be elucidated using a large sample size and statistical analyses.
|
|
| 10. |
- Ebbestad, Jan Ove R., et al.
(författare)
-
Failed predation in Late Ordovician gastropods (Mollusca) from Manitoulin Island, Ontario, Canada
- 2008
-
Ingår i: Canadian journal of earth sciences (Print). - 0008-4077 .- 1480-3313. ; 45:2, s. 231-241
-
Tidskriftsartikel (refereegranskat)abstract
- Shell repairs resulting from presumed failed predation are documented in gastropods from the Late Ordovician (Cincinnatian; Richmondian) mid-to-upper Kagawong Submember of the Georgian Bay Formation on Manitoulin Island, Ontario, Canada. The bryozoan-mollusc biota and associated sediments generally suggest nearshore, shallow (<10m), low energy (lagoonal), and perhaps mesotrophic to eutrophic conditions. Two sample sets from this unit have been studied for shell repair. One of the more commonly applied estimates of shell repair frequencies involves division of the number of individuals with at least one scar by the total number of individuals in the sample (the Individuals with scars method). Using this calculation, 207 specimens ofLophospira trilineata Ulrich and Scofield yielded a shell repair frequency of 4.8%; in 28specimens of Trochonemella sp. the shell repair frequency was 35.7%. Repairs in Trochonemella occur primarily in the larger size class, suggesting that a size refuge was achieved by this species. Low repair frequencies in L. trilineata suggest predation with a higher success rate or fewer encounters. This study demonstrates that the paradigm of a standardized low level of shell repair in Ordovician and Silurian gastropods is oversimplistic and a range of frequency rates can be expected.
|
|
