The ichnological expression of marine and marginal marine conglomerates and conglomeratic intervals, Cretaceous Western Interior Seaway, Alberta and northeastern British Columbia

摘要

Although uncommon, conglomeratic successions and their associated interbeds do contain trace fossils that attest to their marine or marginal marine origins. Intervals within the Cretaceous of the Western Interior Seaway of Alberta and northeastern British Columbia contain ichnological assemblages consistent with open bay, estuarine incised valley, shoreface, and transgressive ravinement settings. Conglomerates and conglomeratic sandstones of open bays are largely confined to bay margins, and are markedly heterolithic, commonly trough cross-stratified, and moderately bioturbated with Diplocraterion, Skolithos, Palaeophycus, Conichnus and Ophiornorpha. Interbedded sandstones and mudstones contain Teichichnus, Planolites, Terebellina, Arenicolites, Bergaueria, Rosselia, Asterosoma, Cylindrichnus, Thalassinoides, and fugichnia. Burrowed incised valley conglomerates and pebbly sandstones mainly record channel fills of tidal inlets or flood-tidal deltas at wave-dominated estuary mouths. Trace fossil suites comprise Teichichnus, Ophiornorpha, Skolithos, Diplocraterion, Arenicolites, Rosselia, Cylindrichnus, and fugichnia. Intercalated sandstone and mudstone beds are moderately burrowed with Planolites, Teichichnus, Terebellina (sensu laid), Ophiornorpha, Palaeophycus, Asterosoma, Chondrites, Conichnus and fugichnia. Upper shoreface and foreshore conglomerates are well sorted, clast supported, and display good clast segregation. Bioturbation is uncommon, comprising Palaeophycus, Ophiornorpha, Cylindrichnus, Rosselia and fugichnia. Interbedded sandstones and pebbly sandstones may contain Macaronichnus and Palaeophycus. The Cardium Formation locally contains conglomeratic intervals interpreted to reflect the entire shoreface succession. These conglomeratic intervals are unburrowed, though they overlie Glossifungites ichnofacies-demarcated discontinuities, and grade upward into burrowed shelf mudstones. Conglomeratic transgressive lags and pebbly sandstones mantle wave or tidal scour ravinement surfaces, and commonly infill palimpsest Diplocraterion, Skolithos, Arenicolites, Thalassinoides, and Rhizocorallium of the Glossifungites ichnofacies, which demarcate these discontinuities. Transgressive lags may be variably burrowed with virtually any softground suite, depending on the depositional setting.%Bien que peu communes, les successions conglomérées et leurs lits interstratifiés associés contiennent des traces de fossiles qui attestent leurs origines marines ou marines marginales. Les intervalles de la route maritime intérieure ouest du Crétacé située dans l'Alberta et au nord-est de la Colombie Britannique contiennent des assemblages ichnologiques compatibles avec les baies ouvertes, les vallées estuariennes incisées, les avant-côtes, et les milieux de ravinement transgressifs. Les conglomérats et les grès conglomérés des baies ouvertes sont largement confinés aux lisières des baies, et sont nettement hétérolitiques, généralement à travers des stratifications entrecroisées, et modérément bioturbatées par des Diplocraterion, des Skolithos, des Palaeophycus, des Conichnus et des Ophiomorpha. Les grès intercalés et les tnudstones contiennent, des Teichichnus, des Planolites, des Terebeflina, des Arenicolites, des Bergaweria, des Rosselia, des Asterosoma, des Cylindrichnus, des Thalassinoides, et des traces de fuites.