Lithogeochemical characterization of the Middle–Upper Devonian Road River Group and Canol and Imperial formations on Trail River, east Richardson Mountains, Yukon: age constraints and a depositional model for fine-grained strata in the Lower Paleozoic Richardson trough

Abstract

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).