Microfacies analysis of mudstone in a freshwater to marine transect: Upper Cretaceous Dunvegan and Kaskapau formations, Western Canada Foreland Basin
Abstract
In the Cenomanian-Turonian Dunvegan and Kaskapau formations in Alberta and British Columbia, terrestrial, and nearshore to offshore environments can be related temporally and spatially using a well-established allostratigraphic framework. In these varied environments, ten mudstone microfacies were identified, using optical and scanning electron microscopy. Microfacies 1 through 3 were deposited in a freshwater lacustrine environment by hyperpycnal flows, and consist of rippled, structureless, and inverse-to-normally graded thin beds that record turbulent, laminar, and waxing and waning flow. Microfacies 4 and 5 were deposited from turbulent flow in a fluvial environment. Microfacies 6 represents a paleosol that underlies a maximum flooding surface above the base of Dunvegan allomember E. Marine prodelta mudstones contain microfacies 7 to 9 that comprise bioturbated mudstone characterised by a randomly oriented clay fabric, and storm-generated interlaminated siltstone and mudstone. Microfacies 10 is the most distal offshore facies and includes organo-mineralic aggregates and re-worked intraclastic aggregates.