Facies partitioning of fluvial, wave, and tidal influences across the shoreline-to-shelf architecture in the Western Interior Campanian Seaway, USA

Abstract

Abstract The influence of bottom currents and tectonic activity on shelf sedimentary processes and sand distribution remains poorly constrained. A growing body of research highlights the importance and variability of the shelf sandstone bodies. To explore the roles of fluvial, wave and bottom current-controlled sediment distribution in the Western Interior Seaway, 21 marine sandstone outcrops in Wyoming and Colorado were analysed. Recurring facies associations include: paralic, tide-influenced coastal margins; mainly east and SE prograding, wave-dominated delta-fronts and shorefaces; heavily bioturbated, glauconitic sandstones; and traction current-dominated, tidally influenced, open-marine subaqueous delta and shelf deposits, with southward palaeocurrent directions. Intense reworking by a moderately diverse ichnofauna occurs in wave-dominated and glauconitic facies. Minimal burrowing occurs in cross-stratified subaqueous delta and shelf deposits. Lithofacies associations are interpreted to change basinward with increasing water depth. Ichnoassociations reflect the proximity of river mouths. Widespread, southward palaeocurrent directions, not restricted to a narrow longshore zone, on the shallow-marine shelf indicate the persistence of strong, along-shelf sand-transport which has not been previously documented in detail. Palaeobathymetric complexity caused by uplift of Laramide structures amplified and accelerated bottom and tidal currents and facilitated the erosion, transport and deposition of older sediments.