New data from Late Ordovician-Early Silurian Mount Kindle Formation measured sections, Franklin Mountains and eastern Mackenzie Mountains, Northwest Territories

Abstract

Four measured sections of the Late Ordovician-Early Silurian Mount Kindle Formation near Norman Wells, Northwest Territories indicate this unit was deposited on a shallowly dipping carbonate ramp that was subsequently dolomitized. The most shoreward facies are tidal flats that pass basinward into skeletal packstone-grainstone deposited on the ramp crest. Basinward of the ramp crest are burrowed skeletal wackestone-packstone passing downramp into skeletal wackestone or mudstone with nodular chert. The abundance of macrofauna (corals, stromatoporoids, brachiopods, bryozoans, sponges, and crinoids) in this unit indicates that it formed in warm water. The majority of the macrofauna was silicified postdepositionally. Preliminary conodont analysis indicates the base of the Mount Kindle Formation is Late Ordovician (Katian). There is a marked faunal change at a lithological break between shallow-water open-marine skeletal packstone and overlying cherty skeletal mudstone interpreted to be the Ordovician-Silurian unconformity that subdivides the Mount Kindle Formation into two separate sequences.

Re-Os systematics and age of pyrite associated with stratiform Zn-Pb mineralization in the Howards Pass district, Yukon and Northwest Territories, Canada

“…The latter scenario is consistent with recent studies that show a predominant seawater-derived source of Os in modern seafloor massive sulphide deposits (Zeng et al 2014). Based on regional geologic constraints and the textural, isotopic, and geochronological data obtained from this study, a genetic model is proposed for the Howards Pass deposits that is consistent with that proposed for CD Zn-Pb deposits worldwide (Leach et al 2005;: (1) ore fluids originated as evolved, oxidised, brines in shallow evaporative basins; silicified evaporate casts and the abundance and diversity of macrofauna in shallow platform carbonate rocks in the Mackenzie Mountains east of Howards Pass are evidence that warm water, arid conditions prevailed in Late Ordovician and early Silurian time (Pope and Leslie 2013); (2) the brines infiltrated and circulated through underlying oxidised clastic rocks or fractured basement to depths of 3 to 5 km; (3) Pb and Zn were extracted and the metalliferous brines ascended into organic-rich rocks that facilitated reduction of seawater or pore water sulphate to H 2 S; and (4) pyrite, sphalerite, and galena were deposited at or near the seafloor during sedimentation and early diagenesis. The Zn-and Pb-bearing hydrothermal fluid may have leached Os from seawater-deposited footwall sedimentary rocks, or Os was sourced directly from seawater and incorporated in pyrite.…”

“…Conodonts from the mineralized Active mudstone member further constrain the age to early to middle Llandovery as defined by Norford and Orchard (1985). Coeval Late Ordovician to early Silurian carbonate rocks east of Howards Pass in the Mackenzie Mountains record deposition in primarily shallow subtidal and evaporitic conditions (Pope and Leslie 2013).…”

Mackenzie–Peel Platform and Ellesmerian Foreland Composite Tectono-Sedimentary Element, northwestern Canada

“…It encompasses strata of Late Ordovician-Early Silurian age and is separated from underlying strata by a regional disconformity. It records an episode of carbonate platform deposition that was characterized regionally by conditions conducive to an abundant and diverse macrofauna (Norford and Macqueen 1975;Pope and Leslie 2013). Widespread post-Mount Kindle erosion created a regional unconformity between the Mount Kindle and overlying Devonian-Cretaceous strata.…”