Trilobites and strata of the Lower and Middle Cambrian Peyto, Mount Whyte and Naiset Formations, Alberta and British Columbia

Abstract

<p>The uppermost Lower Cambrian Peyto Formation consists mainly of bioclastic, oolitic, and oncolitic limestones and dolostones which contain locally abundant quartz sand; shales are a minor component. Four carbonate facies-associations record shallow subtidal deposition adjacent to shelf-edge oolitic sand shoals. The uppermost Lower Cambrian to lowermost Middle Cambrian Mt. Whyte Formation conformably overlies the Peyto and consists of a lower bioturbated quartz siltstone and shale member, followed by oolitic and bioclastic limestones with locally abundant oncolites and thrombolites. Four facies associations, all of which include a silt- to mud-grade siliciclastic component, are indicative of shallow subtidal to intertidal shelf deposition. The Naiset Formation is correlative with the Mt. Whyte and comprises mainly thinly laminated lime mudstones, quartz siltstones, and shales. Two primarily fine-grain siliciclastic facies-associations are characterized by slumps, slide scars, debris flows and turbidites that indicate continental slope deposition. Twenty-one collections yielded over 1,686 trilobites. Two Lower Cambrian, and four Middle Cambrian trilobite biofacies are defined from generic relative abundance data. Each biofacies is associated with a particular depositional environment on the Cambrian continental shelf and slope. New, species-based trilobite zones, established in the context of biofacies, provide greater biostratigraphic resolution than the genus-based zones which they replace. In ascending order, the zones are: the Olenellus gilberti - puertoblancoensis Zone, the Syspacephalus laticeps Zone, the Syspacephalus perola Zone, and the Alokistocare cleora Zone. Major revisions to the Corynexochida are made at the suprageneric level: Zacanthoididae Swinnerton, and Dolichometopidae Walcott, are both synonymized with the Corynexochidae Angelin, and the superfamily Oryctocephalacea Beecher is revised to include the Dinesidae Lermontova, Oryctocephalidae Beecher and Dorypygidae Kobayashi. Numerous genus-level revisions are made in the Corynexochida and the Ptychopariida, including the following synonymies: Bonnia Walcott with Olenoides Meek; Stephenaspis Rasetti with Fieldaspis Rasetti; Poulsenia Resser, Onchocephalus Resser, Piaziella Lochman, Eoptychoparia Rasetti, Parapoulsenia Rasetti, Spencella Rasetti, Nyella Palmer, and Illtydaspis Fritz with Antagmus Resser; and Amecephalus Walcott with Alokistocare Lorenz. A total of 32 species representing 16 genera are described and illustrated.</p>