Lithogeochemical characterization of the Road River Group and Canol and Imperial formations as exposed at an outcrop on Trail River, eastern Richardson Mountains, documents the evolution of a ...Laurentian-margin basin during the latest Eifelian through middle Frasnian stages. δ13Corg stable isotope data correlated to conodont-constrained global isotopic curves indicates deposition of the section from ≥387.7 to ≤376.7 Ma. The uppermost Road River Group is latest Eifelian and older in age (≥387.7 Ma) and is primarily calcareous and dolomitic shale and mudstone, representing a slope environment below a carbonate platform that experienced cyclical turbidity current deposition. A 2.3 m, metalliferous and concretionary unit lies transitionally between the Road River Group and Canol Formation and is herein designated as an informal, conformable, lithologic unit called the Road River - Canol transition zone (RCTZ), which records 4.5 Ma of condensed sediment deposition during the Givetian stage (387.7-383.2 Ma). The Canol Formation is confined to the latest Givetian to middle Frasnian stages (383.2-376.7 Ma) and consists of rhythmically bedded, biogenically sourced, siliceous shale and chert that was deposited in an anoxic (and likely euxinic) to oxic basin that evolved from moderately to strongly hydrographically restricted over time. The lowermost Imperial Formation is a siliciclastic mudstone, which documents turbidity current deposition in oxic bottom water conditions in the late Frasnian (≤376.7 Ma). Interpretation of lithofacies, whole-rock geochemistry, mineralogy, and total organic content enable the section to be grouped into eight lithochemozones that record a first-order late-stage sea-level transgression (Road River Group and RCTZ), highstand (lower Canol Formation), and early-stage regression (upper Canol Formation) followed by continued falling stage sea-level conditions with strong detrital influence from a continental collision in the high Arctic (Imperial Formation).
It is clear from modern analogue studies that O2-deficient conditions favor preservation of organic matter (OM) in fine-grained sedimentary rocks (black shales). It is also clear that appreciable ...productivity and OM flux to the sediment are required to establish and maintain these conditions. However, debates regarding redox controls on OM accumulation in black shales have mainly focused on oxic versus anoxic conditions, and the implications of different anoxic redox states remain unexplored. Here, we present detailed multi-proxy sedimentary geochemical studies of major Paleozoic and Mesozoic North American black shale units to elucidate their depositional redox conditions. This is the first broad-scale study to use a consistent geochemical methodology and to incorporate data from Fe-speciation – presently the only redox proxy able to clearly distinguish anoxic depositional conditions as ferruginous (H2S-limited) or euxinic (H2S-replete, Fe-limited). These data are coupled with total organic carbon (TOC), programmed pyrolysis, and redox-sensitive trace element proxies, with almost all measurements analyzed using the same geochemical methodology. Consistent with expectations based on previous geochemical and paleontological/ichnological studies, these analyses demonstrate that the study units were almost exclusively deposited under anoxic bottom waters. These analyses also demonstrate that there is wide variance in the prevalence of euxinic versus ferruginous conditions, with many North American black shale units deposited under predominantly ferruginous or oscillatory conditions. TOC is significantly higher under euxinic bottom waters in analyses of both preserved (present day) TOC and reconstructed initial TOC values, although sediments deposited under both redox states do have economically viable TOC content. While this correlation does not reveal the mechanism behind higher organic enrichment in euxinic environments, which may be different in different basins, it does open new research avenues regarding resource exploration and the biogeochemistry of ancient reducing environments.
•Non-sulfidic bottom waters were common during Phanerozoic black shale deposition•Total Organic Carbon contents are higher in shales deposited under sulfidic conditions•Iron speciation refines paleoenvironmental interpretation for source rock reservoirs
Cambrian-Devonian sedimentary rocks of the northern Canadian Cordillera record both the establishment and demise of the Great American Carbonate Bank, a widespread carbonate platform system that ...fringed the ancestral continental margins of North America (Laurentia). Here, we present a new examination of the deep-water Road River Group of the Richardson Mountains, Yukon, Canada, which was deposited in an intra-platformal embayment or seaway within the Great American Carbonate Bank called the Richardson trough. Eleven detailed stratigraphic sections through the Road River Group along the upper canyon of the Peel River are compiled and integrated with geological mapping, facies analysis, carbonate and organic carbon isotope chemostratigraphy, and new biostratigraphic results to formalize four new formations within the type area of the Richardson Mountains (Cronin, Mount Hare, Tetlit, and Vittrekwa). We recognize nine mixed carbonate and siliciclastic deep-water facies associations in the Road River Group and propose these strata were deposited in basin-floor to slope environments. New biostratigraphic data suggest the Road River Group spans the late Cambrian (Furongian) - Middle Devonian (Eifelian), and new chemostratigraphic data record multiple global carbon isotopic events, including the late Cambrian Steptoean positive carbon isotope excursion, the Late Ordovician Guttenberg excursion, the Silurian Aeronian, Valgu, Mulde (mid-Homerian), Ireviken (early Sheinwoodian), and Lau excursions, and the Early Devonian Klonk excursion. Together, these new data not only help clarify nomenclatural debate centered around the Road River Group, but also provide critical new sedimentological, biostratigraphic, and isotopic data for these widely distributed rocks of the northern Canadian Cordillera.
Early Paleozoic bottom waters were mainly ferruginous, like the Neoproterozoic, with a shift to increased euxinia in the Devonian.
The extent to which Paleozoic oceans differed from Neoproterozoic ...oceans and the causal relationship between biological evolution and changing environmental conditions are heavily debated. Here, we report a nearly continuous record of seafloor redox change from the deep-water upper Cambrian to Middle Devonian Road River Group of Yukon, Canada. Bottom waters were largely anoxic in the Richardson trough during the entirety of Road River Group deposition, while independent evidence from iron speciation and Mo/U ratios show that the biogeochemical nature of anoxia changed through time. Both in Yukon and globally, Ordovician through Early Devonian anoxic waters were broadly ferruginous (nonsulfidic), with a transition toward more euxinic (sulfidic) conditions in the mid–Early Devonian (Pragian), coincident with the early diversification of vascular plants and disappearance of graptolites. This ~80-million-year interval of the Paleozoic characterized by widespread ferruginous bottom waters represents a persistence of Neoproterozoic-like marine redox conditions well into the Phanerozoic.
The nature, origin, and geocryological characteristics of muck deposits have been studied in the Klondike District, Yukon Territory. Klondike mucks comprise two units: Pleistocene silt overlain by ...Holocene peat. Both units are perennially frozen and contain bodies of massive ice, namely segregated and intrusive ice and ice wedges. The Silt unit comprises primary and redeposited McConnell-aged loess, which began accumulating between 26,240 and 24,025 $\sp{14}$C years BP, and declined during later stages of the McConnell glaciation. The Organic unit comprises in situ and colluvial material which began to accumulate as early as 9,945 $\sp{14}$C years BP. Permafrost aggraded through the mucks syngenetically. Massive icy bodies in the Silt unit are mostly late-McConnell phenomena, while those in the Organic unit are smaller, Holocene features. The study sheds new light on eolian and slope processes occurring in eastern Beringia during the Late Wisconsinan glaciation.
Whether death occurs in the context of a chronic illness or as the sudden loss of a previously healthy infant, child, or adolescent, the death of a child is a highly stressful and traumatic event. ...Psychosocial support for families after the death of a child embodies core medical values of professional fidelity, compassion, respect for human dignity, and promotion of the best interests of a grieving family. The pediatrician has an important role in supporting the family unit after the death of a child through a family-centered, culturally humble, trauma-informed approach. This clinical report aims to provide the pediatrician with a review of the current evidence on grief, bereavement, and mourning after the loss of a child and with practical guidance to support family caregivers, siblings, and the child's community. Pediatricians have an important role in helping siblings and helping families understand sibling needs during grief. Ways for pediatricians to support family members with cultural sensitivity are suggested and other helpful resources in the community are described.
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