2020

Permanent URI for this collectionhttps://hdl.handle.net/1807/98911

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Cryostratigraphical studies of ground ice formation and distribution in a High Arctic polar desert landscape, Resolute Bay, Nunavut
(Canadian Science Publishing, 2020-10-11) Paquette, Michel; Fortier, Daniel; Lamoureux, Scott F
Ground ice distribution and abundance have wide-ranging effects on periglacial environments, and possible impacts on climate change scenarios. In contrast, very few studies measure ground ice in the High Arctic, especially in polar deserts and where coarse surficial material complicates coring operations. Ground ice volumes and cryostructures were determined for eight sites in a Polar desert, near Resolute Bay, Nunavut, chosen from their hydrogeomorphic classification. Dry, unvegetated polar desert sites exhibited ice content close to soil porosity, with a
Magmatic activity and hydrocarbon potential revealed by Paleozoic collapse structures in the Hangjinqi area, northern Ordos Basin, China
(Canadian Science Publishing, 2020-09-30) Ji, Tianyu; Wang, Donghui; Gui, Pingjun; Pu, Renhai; Wu, Xiaochuan; Wu, Xueqiong
Collapsed reflections of lower Ordovician carbonates and upper Carboniferous-lower Permian coal-bearing strata occur below the middle Permian lower Shihezi Formation in the Hangjinqi area, northern Ordos Basin. This study takes advantage of three-dimensional seismic data, logging data, core data and well-testing data to investigate the genesis of the collapsed reflections and their implications for hydrocarbon potential. These collapse structures have a subcircular appearance in map view. The columnar reflections in the basement and the volcanic tuff in the lower Shihezi Formation around collapse structures indicate that the formation of these structures are related to magmatic activity. Most of the collapse structures terminate upward in the H1 member of the lower Shihezi Formation, which explains its greater thickness and supports the hypothesis that magmatic activity occurred during the depositional stage of the lower Shihezi Formation in the early middle Permian. The collapse structures can increase the thickness and space of the reservoirs, and the collapse of magma conduit can also increase the thickness of the regional sedimentary cap rock above the collapse structures and improve the sealing capacity of the cap rock. These results provide insights into the magmatic activity and hydrocarbon potential of Paleozoic rocks in the Ordos Basin.
Geochemistry and U/Pb geochronology of the Williams Brook area, Tobique-Chaleur zone, New Brunswick: stratigraphic and geotectonic setting of gold mineralization
(Canadian Science Publishing, 2020-12-04) Snchez-Mora, Dennis; McFarlane, Christopher R.M.; Walker, James A; Lentz, David R.
Gold mineralization at Williams Brook in northern New Brunswick is hosted within the Siluro-Devonian, bimodal, volcano-sedimentary rocks of the Tobique-Chaleur Zone (Wapske Formation). Gold mineralization occurs in two styles: 1) as disseminations (refractory gold) in rhyolite, and 2) in cross-cutting quartz veins (free gold). Dating of the felsic volcanic host rocks by in situ LA-ICP-MS zircon U-Pb geochronology returned ages of 422 3, 409 2, 408 3, 405 2, 401 9 Ma. Zr/Y of subvolcanic felsic intrusion (
A systematic reappraisal and quantitative study of the non-marine teleost fishes from the late Maastrichtian of the Western Interior of North America – evidence from vertebrate microfossil localities
(Canadian Science Publishing, 2020-11-28) Brinkman, Donald B.; Divay, Julien; DeMar, David Gerard; Wilson Mantilla, Gregory P.
The diversity and distribution of non-marine teleost fishes in the Western Interior of North America during the late Maastrichtian is documented based on isolated elements from vertebrate microfossil localities in the Hell Creek Formation of Montana, the Lance Formation of Wyoming, and the Scollard Formation of Alberta. A minimum of 20 taxa are recognized based on >1900 abdominal centra and tooth-bearing elements. These include two elopomorphs, six osteoglossomorphs, three ostariophysans, one esocid, six acanthomorphs, and two taxa of unknown relationships. These assemblages differ from late Campanian assemblages in the absence of the Clupeomorpha and the presence of the Perciformes. Within the Hell Creek Formation, we record patterns in the relative abundances of the most abundant taxa leading up to the Cretaceous/Paleogene (K/Pg) boundary. Most notably, acanthomorphs increased in abundance up-section whereas a group of osteoglossomorphs represented by Coriops and/or Lopadichthys concurrently decreased in abundance. Conversely, some teleosts exhibited more stable or slightly fluctuating relative abundances through the formation (Wilsonichthyidae, Esocidae). These late Maastrichtian teleost assemblages are of higher diversity than an early Eocene assemblage from Wyoming that is preserved under similar taphonomic conditions. This pattern either suggests that lower Cenozoic deposits in the Western Interior are insufficiently sampled or that the K/Pg mass extinction event adversely affected non-marine teleosts.
Redescription of Lophorhothon atopus (Ornithopoda: Dinosauria) from the Late Cretaceous of Alabama based on new material
(Canadian Science Publishing, 2020-12-18) Gates, Terry A; Lamb, James
Diagnostic dinosaur fossils of the southeastern United States are rare discoveries, and even more precious are those fossils that preserve a large portion of a skeleton. Sixty years ago, the dinosaur Lophorhothon atopus was described from Upper Cretaceous sediments of Alabama. It then represented the oldest, most complete, dinosaur in the southeast United States. Based on a reexamination of the holotype material and a new specimen collected from the same beds, we provide a new diagnosis of this taxon. In particular, the solid nasal crest has several autapomorphies including caudally projecting frontal processes that are oval in cross-section, meaning that they did not coalesce at the midline. Other autapomorphies are found on the prefrontal and squamosal. Combining the two Lophorhothon specimens provides nearly the entire skeleton for phylogenetic analysis, which we find as a hadrosauromorph just outside of Hadrosauridae. The original diagnosis of this taxon included the frontonasal fontanelle as a distinguishing character, but comparing the many examples of frontonasal openings across hadrosauromorph taxa shows that in at least a few species, such as Lophorhothon, the structures should be considered a frontonasal fenestra instead of a fontanelle. Additionally, the notion that dinosaurs from the East Coast of the United States represent primitive relicts is an idea that originated before many of the European and Asian hadrosauromorphs known today had been discovered. With new dating and phylogenetic information, it appears that Appalachian dinosaurs are on par evolutionarily with most of the global community and the term ‘relict fauna’ should be abandoned.
Nd isotope mapping of the Frontenac Terrane in the SW Grenville Province
(Canadian Science Publishing, 2020-07-24) Dickin, Alan; Strong, Jacob
Nd isotope analyses are presented for granitoid rocks from the western part of Frontenac Terrane in the Grenville Province of Ontario. TDM ages show no correlation with the silica content of the rocks, but instead correlate with geographical location, suggesting that the TDM ages are indicative of regional crustal formation age, and do not result from mixing between sources with different provenance ages. Based on these observations, we identify a new crustal age boundary that follows the Desert Lake – Canoe Lake fault and the Rideau Lake fault, and hence a new juvenile crustal block (Westport domain). This domain is identified as part of the ensimatic back-arc rift zone that formed the juvenile segment of the Central Metasedimentary Belt in Ontario. However, additional sampling along the Ottawa River suggests that the juvenile Westport domain does not extend into Quebec. Instead, a narrower ensialic rift zone is represented by the Marble domain in Quebec. Based on comparison with the Taupo volcanic zone and the northern Red Sea as modern analogues, we suggest that the transition from a wide ensimatic rift zone in Ontario to a narrow ensialic rift in Quebec was accommodated by transtensional motion along a zone of diffuse shear east of Ottawa.
The mid-Cretaceous Peninsular Ranges orogeny: a new slant on Cordilleran tectonics? I: Mexico to Nevada
(Canadian Science Publishing, 2020-12-07) Hildebrand, Robert S.; Whalen, Joseph B.
Dear Author: Please reduce the abstract length down below 250 words both in the manuscript text file and pasted here.
Anatomical, morphometric, and stratigraphic analyses of theropod biodiversity in the Upper Cretaceous (Campanian) Dinosaur Park Formation
(Canadian Science Publishing, 2020-12-18) Cullen, Thomas Michael; Zanno, Lindsay; Larson, Derek W; Todd, Erinn; Currie, Philip J.; Evans, David C
The Dinosaur Park Formation (DPF) of Alberta, Canada has produced one of the most diverse dinosaur faunas, with the record favouring large-bodied taxa, in terms of number and completeness of skeletons. Although small theropods are well documented in the assemblage, taxonomic assessments are frequently based on isolated, fragmentary skeletal elements. Here we reassess DPF theropod biodiversity using morphological comparisons, high-resolution biostratigraphy, and morphometric analyses, with a focus on specimens/taxa originally described from isolated material. In addition to clarifying taxic diversity, we test if DPF theropods preserve faunal zonation/turnover patterns similar to those previously documented for megaherbivores. Frontal bones referred to a therizinosaur (cf. Erlikosaurus), representing among the only skeletal record of the group from the Campanian-Maastrichtian (83-66 Ma) fossil record of North America, plot most closely to troodontids in morphospace, distinct from non-DPF therizinosaurs, a placement supported by a suite of troodontid anatomical frontal characters. Postcranial material referred to cf. Erlikosaurus in North America is also reviewed and found most similar in morphology to caenagnathids, rather than therizinosaurs. Among troodontids, we document considerable morphospace and biostratigraphic overlap between Stenonychosaurus and the recently described Latenivenatrix, as well as a variable distribution of putatively autapomorphic characters, calling the validity of the latter taxon into question. Biostratigraphically, there are no broad-scale patterns of faunal zonation similar to those previously documented in ornithischians from the DPF, with many theropods ranging throughout much of the formation and overlapping extensively, possibly reflecting a lack of sensitivity to environmental changes, or other cryptic ecological or evolutionary factors.
LITHOBIOTOPES OF THE NEMEGT GOBI BASIN
(Canadian Science Publishing, 2020-11-25) Jerzykiewicz, Tomasz; Currie, Philip J.; Fanti, Federico; Lefeld, Jerzy
Three distinct but overlapping dinosaur-dominated faunas characterize the Upper Cretaceous Djadokhta, Baruungoyot and Nemegt formations of the Nemegt Basin of Mongolia. Documented faunal differences cannot be explained easily by temporal succession, but can be understood in the light of physical processes controlling life, death, and burial of taxa. The stratigraphy of the Gobi Desert region records tectonically driven geometries, clearly documenting preservational processes different than those acting in most other dinosaur-dominated beds worldwide. Small, asymmetric tectonic grabens were filled with Upper Cretaceous, dinosaur bearing deposits showing asymmetric distributions of facies, here termed Lithobiotopes. The water-lain fluvial and alluvial plain facies of the Nemegt Lithobiotope supported and preserved a fauna dominated by gigantic dinosaurs, but had a preservational bias against smaller animals. The Nemegt passed laterally into interdune facies of the Baruungoyot Lithobiotope, which represented a hostile environment for large species, but preserved smaller animals. This in turn passed laterally into the aeolianite facies of the Djadokhta Lithobiotope, which is characterized by remains of small dinosaurs and a rich fauna of other animals. The Nemegt Gobi Basin can be visualized as an oasis with a central pond supplied with water from ephemeral channels and surrounded by a semi-arid alluvial plain and dune fields.
Dale Alan Russell (1937-2019): Voyageur of a Vanished World
(Canadian Science Publishing, 2020-11-26) Cumbaa, Stephen L.; Currie, Philip J.; Dodson, Peter; Mallon, Jordan
We review the distinguished and varied career of our friend and colleague, palaeontologist Dr. Dale A. Russell, following the recent news of his death. Dale relished his work, and approached his research—whether it be on mosasaur systematics, dinosaur extinction, or the evolution of animal intelligence—with great gusto. A deep and contextual thinker, Dale had a penchant for metanarrative rarely equaled in these times of increased research specialization. This quality, combined with his outgoing and collaborative nature, allowed Dale to make friends and colleagues with highly varied research interests throughout the world. We remember Dale fondly, and cherish the opportunity to share the stories of his adventures (and misadventures) across the globe.
A reinterpretation of the Snow Lake gold camp, Trans-Hudson Orogen, Canada: The use of cleavages as markers to correlate structures across deformed terranes
(Canadian Science Publishing, 2020-10-18) Rubingh, Kate Elizabeth; Lafrance, Bruno; Gibson, Harold L.
The Snow Lake gold camp is located within amphibolite facies volcanic rocks of the ca. 1.88 – 1.87 Ga Flin Flon-Glennie Complex (FFGC) in the Trans-Hudson Orogen, Manitoba. During thrusting and collision with the Archean Sask craton, volcanic rocks were interleaved with turbidites of the ca. 1.855 - 1.84 Ga Burntwood Group and sandstone and conglomerate of the ca. 1.845 - 1.835 Ga Missi Group. The main cleavage in the turbidites was previously attributed to thrusting and used as a marker for correlating structures across the camp. A re-examination of this cleavage suggests that it overprints the thrust faults and formed during later collision between the FFGC and the Archean Superior craton. This has important implications as it further suggests that (1) previously unrecognized, early brittle thrust faults repeat volcanic stratigraphy and may have created the boundary conditions that enabled the formation of ductile thrust faults, fold nappes, and mega sheath folds; (2) shear sense indicators along ductile thrust faults formed during their reactivation as sinistral shear zones rather than during thrusting; and (3) peak metamorphic conditions were caused by thrusting and stacking during collision with the Sask craton but were attained later during collision with the Superior craton due to the time lag between orogenesis and the re-equilibration of regional isotherms. Results from this study may be applicable to other complexly deformed terranes where the dominant regional cleavage differs in expression in mixed volcanic and sedimentary successions and has been used as a marker for correlating structures.
Structural analysis and metamorphism of the Barlow Fault Zone, Chibougamau area, Neoarchean Abitibi Subprovince: implications for gold mineralization
(Canadian Science Publishing, 2020-10-24) Bedeaux, Pierre; Brochu, Antoine; Mathieu, Lucie; Gaboury, Damien; Daigneault, Ral
Faults and deformation zones are important features of Archean terranes because of their significance for structural evolution and the formation of large gold districts. In the Chibougamau area, northeastern portion of the Abitibi Subprovince, an Apogee Metal Earth seismic reflection survey identified an association between an exceptional shallow-dipping subsurface reflector zone and the Barlow Fault Zone visible at the surface. This study aimed to reconstruct the kinematic evolution of the Barlow Fault Zone, determine its position within the structural setting of this section of the Abitibi Subprovince, and evaluate its importance for gold potential in the northern part of the Chibougamau area. Structural reconstruction and field observations are compatible with a reverse south-over-north movement related to a ductile north–south shortening event, which culminated with amphibolite metamorphism. Geothermobarometers indicate peak metamorphism conditions of 550 50 C and 6 1.2 kbar. Results from this study suggest that amphibolite facies metamorphism covers a much wider area within the Chibougamau region than previously documented. The Barlow Fault Zone shares similar geometric characteristics and evolutionary history with other gold-bearing structures in the Abitibi Subprovince, but ultimately it was unable to provide optimal conditions for channelling fluid and precipitating gold. The Barlow Fault Zone is interpreted as a back-thrust fault that belongs to a more extensive south-dipping fault system encasing juxtaposed tectonic slivers. This system, with amphibolite facies metamorphism, is a defining feature of the northern portion of the Chibougamau area and developed during the accretion between the Opatica and Abitibi subprovinces.
Petrogenesis and economic potential of the Obatogamau Formation, Chibougamau area, Abitibi greenstone belt
(Canadian Science Publishing, 2020-11-24) Boucher, Adrien; Mathieu, Lucie; Hamilton, Michael A.; Bedeaux, Pierre; Daigneault, Réal
Unravelling the petrogenesis and stratigraphy of Archean mafic lava flows is essential to our comprehension of the early geodynamic evolution and economic potential of greenstone belts. This study focuses on one of the oldest and thickest sequences of lava flows observed in the Neoarchean Abitibi Subprovince (greenstone belt), that is, the Obatogamau Formation. The undated formation extends for more than 100 km in an E–W direction and consists mostly of aphyric and feldspar megacryst-bearing basaltic-andesite lava flows. These lava flows are tholeiitic, mostly Fe-rich, and have nearly homogeneous chemistry. Petrogenetic modelling carried out using MELTS software points to limited magmatic differentiation as most samples of mafic lava flows did not reach Fe-Ti-oxide saturation. Zircon U-Pb dating establishes a crystallization age of 2726.2 ± 1.6 Ma for a felsic unit located at an intermediate stratigraphic position in the sequence of lava flows. Constraints from stratigraphically overlying volcanic units suggest that the Obatogamau Formation was likely emplaced rapidly, possibly within a few million years and as a consequence of frequent replenishment of shallow magma accumulations. High eruption rates are consistent with short episodes of volcanic quiescence deduced from field observations, indicating non-optimal conditions for volcanogenic massive sulfide systems. The pressure and temperature of peak metamorphism deduced from amphibole chemistry, however, points to favorable conditions for the release of metamorphic fluids. The study area may thus be prospective for orogenic gold mineralization, provided that fluids had access to a source of gold and that structural conduits allowed for the channeling of hydrothermal fluids.
Late Devonian magmatism and clastic deposition in the upper Earn Group (central Yukon) mark the transition from passive to active margin along western Laurentia
(Canadian Science Publishing, 2020-10-07) Cobbett, Rose Natalie; Colpron, Maurice; Crowley, James J.L.; Cordey, Fabrice; Blodgett, Robert B.; Orchard, Micheal J.
The Earn Group of central Yukon records the transition from a passive to an active margin along western Laurentia in the Late Devonian. Fine-grained clastic rocks and chert of the lower Earn Group contain late Early to Middle Devonian fossils and were deposited in an offshelf environment. The upper Earn Group comprises a mixture of sandstone and conglomerate, fine-grained siliciclastic rocks, and widespread crystal lithic tuff. Zircon from this succession are precisely dated using CA-ID-TIMS methods on igneous (ca. 363 Ma) and detrital (ca. 378-363 Ma) grains and confirmed by Frasnian to Famennian fossils. Abrupt, along-strike facies changes within the upper Earn Group of the Glenlyon–Tay River area occur across mapped faults that are inferred to have originated as syn-depositional extension faults in the Late Devonian. Occurrences of ca. 363 Ma tuff horizons within all facies of the upper Earn Group provide a temporal correlation across the area. Diorite plutons intrude lower Paleozoic rocks in the area and have U-Pb zircon crystallization dates of ca. 364 Ma. The diorite has calc-alkaline composition consistent with arc magmatism or crustal contamination. The Late Devonian magmatism in the Earn Group is coincident with onset of arc magmatism in the allochthonous Yukon-Tanana terrane, and extension related to rifting and opening of the Slide Mountain ocean in a back-arc setting. Magmatic rocks in the Earn Group of central Yukon thus represent part of a remnant continental arc and back-arc stranded behind the Slide Mountain ocean in the Mississippian.
Long-lived deformation history recorded along the Precambrian Thelon and Judge Sissons faults, northeast Thelon Basin, Nunavut
(Canadian Science Publishing, 2020-11-16) Hunter, Rebecca Corrine; Lafrance, Bruno; Heaman, Larry M; Thomas, David
The ENE-striking Thelon and Judge Sissons faults of south-central Nunavut are well-preserved, and record long-lived dextral transcurrent movement with complex reactivation and fluid flow histories. The faults cut across Archean gneisses, Paleoproterozoic plutons, and a Mesoproterozoic sedimentary basin in the Rae domain of the western Churchill Province. They formed and were reactivated during multiple deformation events beginning with an initial faulting event at 1830-1760 Ma, followed by an epithermal faulting event at 1760-1750 Ma and late reactivation events at 1600-1300 Ma. The initial faulting event produced the core-damage zone architecture of the faults. Damage zones are characterized by multiple fracture sets, quartz veins and hydrothermal crackle breccias, surrounding core zones defined by multiple mosaic to chaotic breccias and cataclasites with dextral slip indicators. The epithermal faulting event is expressed by the presence of crosscutting comb, crustiform-cockade and lattice-bladed quartz hematite carbonate veins, and is likely associated with a magmatic event of similar age. The late reactivation events resulted in the formation of irregular, non-cohesive crackle to mosaic breccias and gouges, which became the primary pathways for uranium-bearing hydrothermal fluids and the formation of unconformity-type uranium deposits. The Thelon and Judge Sissons faults are similar to other major continental faults in the Rae domain (e.g. McDonald fault, Wager Bay shear zone), which formed during the Paleoproterozoic Taltson-Thelon and Trans-Hudson orogenies, and to modern analogues, such as the Karakorum, Altyn Tagh, and Hunan-Jaingxi faults, which formed during the Himalayan-Tibetan orogeny and experienced prolonged hydrothermal and even hot spring activity.
Crustal thickening and uplift of the Qiangtang Terrane, Tibetan Plateau during the Late Cretaceous to Early Palaeocene: geochronology and geochemistry of the Saiduopugangri granite
(Canadian Science Publishing, 2020-10-05) li, xue; Sun, Guo-Sheng; Liu, Gen-Yi; Zhou, Huan; Shan, Zi-Ling; Sun, Jiu-Da; Wang, Guang-Wei
There continues to be debate regarding the timing of the collision between the Indian and Eurasian plates and the uplift of the Tibetan Plateau. This study presents zircon U–Pb geochronology, whole-rock geochemistry, and Lu–Hf isotopic data for the Saiduopugangri granite of the Qiangtang Terrane, located within the core of the Tibetan Plateau. These data provide the basis for the geodynamic setting, petrogenesis, and characteristics of its magma source. Zircons from the Saiduopugangri granite yield a weighted-mean 206Pb/238U age of 62.72 0.06 Ma, indicating that these rocks formed during the early Palaeocene. The rocks are members of the highly calc-alkaline to shoshonitic series, with weak peraluminous characteristics. Trace elements are characterised by high Sr (483–616ppm), and low Y (6–10ppm) and Yb (1ppm) content, typical of a high Sr and low Yb granite. The εHf(t) of zircon range from −2.14 to 2.35, with two-stage Hf model ages (TDM2) ranging from 1182 to 895Ma. These data suggest that the Saiduopugangri granite magma was derived from the melting of lower-crustal clastic meta-sedimentary rocks and mantle-derived basalts. The high Sr and low Yb granite characteristics and experimental results indicate that melting occurred at >1.2 GPa and >750 C, consistent with a crustal thickness greater than 50km. Magmatism occurred from the Late Cretaceous to the early Palaeogene and is broadly synchronous with the collision timing between the Indian and Eurasian plates. The Saiduopugangri granite provides evidence of crustal thickening of the Tibetan Plateau and its age and petrogenesis constrain the timing of the initial uplift.
Age and tectonic setting of Neoproterozoic granitoid rocks, Antigonish Highlands, Nova Scotia, Canada: Implications for Avalonia in the northern Appalachian orogen
(Canadian Science Publishing, 2020-10-23) White, Chris E; Barr, Sandra M.; Hamilton, Michael A.; Murphy, J. Brendan
The oldest rocks in the Avalonian Antigonish Highlands of northern mainland Nova Scotia, Canada, are Late Neoproterozoic (> 618 Ma) volcanic and sedimentary rocks of the Georgeville Group intruded by gabbroic/dioritic to granitic plutons. New U-Pb zircon ages presented here for 5 samples from plutons intruded into the James River and/or Keppoch formations of the Georgeville Group have ages ranging from ca. 615 to 604 Ma. They have petrological characteristics of expanded calc-alkalic "Andean-type" suites but are compositionally biased toward evolved high-silica compositions and are interpreted as evolved I-type granites. They were emplaced at shallow depths and some were likely comagmatic with felsic volcanic components of their host rocks. These plutons are younger and show less varied Sm-Nd isotopic compositions than most plutonic rocks formed in the early Ediacaran "main arc phase" elsewhere in Avalonian terranes in the northern Appalachian orogen, although they are similar in age to plutons in southeastern New England and in the Bass River and Jeffers blocks of the Cobequid Highlands, Nova Scotia. The Jeffers block of the Cobequid Highlands appears to be most similar to the Antigonish Highlands but both areas record a Neoproterozoic history less protracted than in other parts of Avalonia.
Late Neoproterozoic – early Paleozoic basin evolution in the Coal Creek inlier of Yukon, Canada: Implications for the tectonic evolution of northwestern Laurentia
(Canadian Science Publishing, 2020-10-14) Busch, James Francis; Rooney, Alan D.; Meyer, Edward E.; Town, Caleb F.; Moynihan, David; Strauss, Justin V.
The age and nature of the Neoproterozoic–early Paleozoic rift-drift transition has been interpreted differently along the length of the North American Cordillera. The Ediacaran “upper” group (herein elevated to the Rackla Group) of the Coal Creek inlier, Yukon, Canada, represents a key succession to reconstruct the sedimentation history of northwestern Laurentia across the Precambrian-Cambrian boundary and elucidate the timing of active tectonism during the protracted break-up of the supercontinent Rodinia. These previously undifferentiated late Neoproterozoic-early Paleozoic map units in the Coal Creek inlier are here formally defined as the Lone, Cliff Creek, Mount Ina, Last Chance, Shade, and Shell Creek formations. New sedimentological and stratigraphic data from these units is used to reconstruct the depositional setting. In the Last Chance Formation, chemostratigraphic observations indicate a ca. 5‰ δ
Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America
(Canadian Science Publishing, 2020-11-17) Funston, Gregory F.; Powers, Mark James; Whitebone, S. Amber; Brusatte, Stephen; Scannella, John B.; Horner, John R.; Currie, Philip J.
Tyrannosaurids were the apex predators of Late Cretaceous Laurasia and their status as dominant carnivores has garnered considerable interest since their discovery, both in the popular and scientific realms. As a result, they are well studied and much is known of their anatomy, diversity, growth, and evolution. In contrast, little is known of the earliest stages of tyrannosaurid development. Tyrannosaurid eggs and embryos remain elusive, and juvenile specimens — although known — are rare. Perinatal tyrannosaurid bones and teeth from the Campanian–Maastrichtian of western North America provide the first window into this critical period of the life of a tyrannosaurid. An embryonic dentary (cf. Daspletosaurus) from the Two Medicine Formation of Montana, measuring just 3 cm long, already exhibits distinctive tyrannosaurine characters like a “chin” and a deep Meckelian groove, and reveals the earliest stages of tooth development. When considered together with a remarkably large embryonic ungual from the Horseshoe Canyon Formation of Alberta, minimum hatchling size of tyrannosaurids can be roughly estimated. A perinatal premaxillary tooth from the Horseshoe Canyon Formation likely pertains to Albertosaurus sarcophagus and it shows small denticles on the carinae. This tooth shows that the hallmark characters that distinguish tyrannosaurids from other theropods were present early in life and raises questions about the ontogenetic variability of serrations in premaxillary teeth. Sedimentary and taphonomic similarities in the sites that produced the embryonic bones provide clues to the nesting habits of tyrannosaurids and may help to refine the prospecting search image in the continued quest to discover baby tyrannosaurids.
Volcanic reconstruction and geochemistry of the Powderhouse formation in the Paleoproterozoic VMS-hosting Chisel sequence, Snow Lake, Manitoba, Canada
(Canadian Science Publishing, 2020-03-24) Friesen, Vanessa Christine; DeWolfe, Yvonne Michelle; Gibson, Harold L.
The Powderhouse formation of the Paleoproterozoic Snow Lake arc assemblage comprises the stratigraphic footwall to six volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada. It is interpreted to be a product of voluminous pyroclastic eruptions and concomitant subsidence followed by a period of relative volcanic quiescence that was dominated by suspension sedimentation, the reworking of previously deposited pyroclastic units by debris flows and bottom currents, and localized emplacement of rhyolite domes. The rhyolite domes are spatially associated with the Chisel, Chisel North, Lost, Ghost, Photo, and Lalor deposits. The Chisel, Lalor, and Lost members compose the Powderhouse formation and are subdivided into 13 lithologically distinct lithofacies, which allows, for the first time, correlation of stratigraphy between the South Chisel basin and Lalor areas, critical in predicting the location of largely stratiform VMS deposits. The Chisel and Lalor members contain lithofacies and bedforms that are characteristic of emplacement by subaqueous pyroclastic mass flows and concomitant subsidence. The Chisel member also contains coarse volcaniclastic breccias emplaced by mass debris flows derived from movement along fault scarps following early pyroclastic eruptions, and during continued subsidence. The Lost member consists of lithofacies deposited by mass flows generated from faults scraps during continued subsidence, but also contains lithofacies reworked by bottom currents, those deposited by suspension sedimentation, and, locally, coherent rhyolite. The Lost member represents a time stratigraphic interval, the “ore interval”, that marks contemporaneous rhyolite dome emplacement, VMS formation, and a hiatus in explosive volcanism.

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