Abstract

Sedimentary facies observed in cores of the Lower Cretaceous Glauconitic member near Drayton Valley. Alberta, are interpreted to be mesotidal estuary deposits. These facies were deposited in associated riverine channel, tidal channel, and outer-estuary environments.

Riverine channel deposits are tidal sand bars and tidally influenced point bars. Crosslaminated sandstones with mud drapes, flasers, shale lenses, and abundant mud clasts comprise channel-floor and sand-bar sediments. Point bar facies consist of inclined bedsets of ripple and crosslaminated sandstone with mud drapes and flasers, and wavy to flat bedded mudstone and sandstone. Tidal channel point bar bedding is muddier, thinner, and more steeply inclined than riverine point bar bedding. Both types of point bar deposits contain rhythmic interbedding. Channel sequences are capped by channel abandonment or channel margin sediments consisting of thickly bedded mudstone and thin, inclined wavy sandstone beds. Bioturbated textures in the channel sediments are rare, but individual Skolithos, Chondrites, Planolites and Teichichnus traces are common. Outer-estuary sediments underly the channel-fill strata, and conformably overlie shoreface deposits. Sedimentary facies of this setting are crosslaminated sandstones, interpreted as shoal deposits; and burrowed muddy sandstones, with diverse ichnospecies assemblages, interpreted as inter-shoal deposits.

Evidence supporting a mesotidal estuary interpretation for these sedimentary facies include: 1) abundant tidally influenced point bar bedding, 2) diversity of sediment textures, 3) frequent facies transitions, 4) brackish to marine biologic components, and 5) confinement of the deposits to paleovalleys. These characteristics reflect the preferred preservation of migrating channel sediments, and the diversity of tidal and riverine channels in an estuarine setting.