Fluvial to tidal transition in proximal, mixed tide‐influenced and wave‐influenced deltaic deposits: Cretaceous lower Sego Sandstone, Utah, USA

摘要: Facies models for regressive, tide-influenced deltaic systems are under-represented in the literature compared with their fluvial-dominated and wave-dominated counterparts. Here, a facies model is presented of mixed, wave-influenced strata Sego Sandstone, which was deposited Western Interior Seaway North America during Late Cretaceous. Previous work on Sandstone has focused medial to distal parts outcrop belt where tides waves interact. This study focuses proximal belt, fluvial tidal processes Five associations recognized. Bioturbated mudstones (Facies Association 1) were an offshore environment gradationally overlain by hummocky cross-stratified sandstones 2) lower shoreface environment. These erosionally tide-dominated cross-bedded 4) interbedded ripple cross-laminated heterolithic 3) channelized 5). Palaeocurrent directions derived from cross-bedding indicate bidirectional currents flood-dominated part studied interval become increasingly ebb-directed/fluvial-directed upward. At top succession, ebb-dominated/fluvial-dominated, high relief, narrow channel forms present, interpreted as distributary channels. When channels abandoned they effectively estuaries landward sediment transport fining trends. have 4 at mouth fine through 3 5. Therefore, complex distribution relatively mud-rich sand-rich deposits attributed avulsion history active distributaries, response subtly expressed allogenic change supply relative sea-level controls autocyclic delta lobe abandonment.