Paper No. 16-2
Presentation Time: 9:00 AM-6:30 PM
STRATIGRAPHY AND ICHNOLOGY OF COASTAL PLAIN HETEROLITHIC AND MUDSTONE FACIES OF THE CAMPANIAN DINOSAUR PARK TO BEARPAW TRANSGRESSION, SOUTHERN ALBERTA
This study integrates ichnology, facies analysis (core, measured field sections), X-ray fluorescence, and grain-size analysis of heterolithics and mudstones from the Campanian Dinosaur Park Formation (DPF) in southern Alberta to better understand the stratigraphic packaging of this coastal plain succession. Although the DPF was deposited during the 3rd-order transgression of the Bearpaw Sea, trace fossils signify that brackish water incursions only occurred sporadically throughout most of the formation, preserved in clay-rich point bar deposits. Laterally extensive (km-scale) shale horizons punctuate the channel-dominated succession and may represent 4th- or 5th-order flooding events, but do not contain trace fossil evidence of brackish faunas. These horizons comprise amalgamated dark brown shale beds with coal and erosive lower contacts, and compare well with the Lethbridge Coal Zone (LCZ), which represents the 3rd-order flooding of the coastal plain. Low diversity and low abundance trace fossil assemblages (Planolites) may be associated with the higher-frequency shale horizons, but are typically preserved in silt-dominated heterolithics of active channels below the shales. In contrast, trace fossils associated with silt- and clay-dominated heterolithics both below and above the LCZ more clearly represent brackish water and the widespread flooding of the coastal plain by the transgressing Bearpaw Sea. Facies and trace fossils (e.g., Thalassinoides, Teichichnus, Palaeophycus, cf. Arenicolites) indicate that active channel bodies were the loci for the marine incursion, but that when base level rose across the area freshwater conditions dominated in a similar way to the higher-frequency mudstone horizons below. Sediment (and freshwater) supply was finally outpaced when Bearpaw Formation marine shales were deposited above estuarine deposits with shark teeth and plesiosaur bones, and marginal marine deposits with Ophiomorpha, Macaronichnus, Rosselia, and Asterosoma.