Depositional dynamics of a giant carbonate platform: The Famennian Palliser Formation of western Canada

Carbonate platforms dominated by great thicknesses of ostensibly uniform, thick bedded, poorly fossiliferous and burrow-mottled, subtidal limestones are found throughout the Phanerozoic, yet are poorly understood. Deposited in the aftermath of the Frasnian-Famennian extinction event, the Palliser/Wabamun Formation with a thickness of up to 600 m and an extent of about 600 000 km 2 represents one of the largest of such platforms to have ever existed.; The architecture and palaeoenvironment of the western side of this epeiric platform is reconstructed based on lateral and vertical variations of microfacies properties. It can be divided into inner and outer ramp and shelf belts that remained submerged virtually throughout the life of the platform. A new subdivision of the Palliser Formation is proposed based on long-term vertical facies patterns in sections with differing facies reflecting relative sea-level dynamics.; Limestones of the Palliser Formation record a rather limited benthic community. The soft substrate and abundant bioturbation deterred the settlement of sedentary organisms. Frequent physical disturbance, including storms and bioturbation, augmented water turbidity causing smothering and destruction. For these reasons at least, reef growth was impeded.; Furthermore, within the apparent facies monotony, two thirds of “non-skeletal” grains are generated by obliteration processes. Microendolithic bioerosion and diminution destroyed a substantial proportion of the skeletal particles, mostly crinoids, resulting in small micritized grains. Pervasive bioerosion is linked to excess nutrient flux caused by perturbations to the regional biogeochemical cycle. The Ellesmerian Orogeny and increased colonization of land surfaces by deep-rooting gymnosperms are identified as the cause of mesotrophy. Early seafloor dissolution consumed a vast amount of aragonite skeletons, dasycladalean algae in particular, leaving ample amounts of micritic steinkerns, which in turn broke down into peloids and small intraclasts. These discoveries suggest that large areas of the giant ramp-shelf system were characterized by subtidal dasycladalean and crinoid meadows.; Finally, established carbonate classifications are re-evaluated and a revised classification for allochthonous limestones for both outcrop and laboratory is introduced. Special emphasis is laid on clast-matrix relationships.