Facies architecture and time stratigraphic relationships of a confined trunk-tributary valley fill and unconfined fluvial system in the backwater of the Turonian Ferron-Notom Delta, Utah, U.S.A.

ABSTRACT This paper documents a tidally incised, mudstone-prone tributary valley fill linked to a trunk valley in the backwater limit of the Turonian Notom Delta of the Ferron Sandstone Member, Utah. High-resolution 3D photogrammetry models were used to correlate a 20-m-deep valley between 32 measured sections over a 1 km2 area. A GPS survey and GIS geostatistical tools were used to restore the morphology of the tributary valley. The restored valley floor is interpreted as a surface of tidal erosion, based on the overlying facies and surface morphology. Morphological similarities exist between this tributary valley and modern analogs observed in northern Australia, the Memramcook tributary in the Bay of Fundy, and Pleistocene sediments in the Gulf of Thailand. 40Ar/39Ar dating of sanidine crystals using multi-collector mass spectrometry allow for a re-evaluation of depositional rates and timing of 32 fluvial aggradation cycles (FACs) and 9 fluvial-aggradation cycle sets (FAC sets) in this sequence. The new dates show that the entire sequence was deposited in 15 ± 5 kyr, and show that Milankovitch cycles cannot account for the internal complexity of this fluvial stratigraphy, indicating likely autogenic control of the FAC sets. The lateral extent of FACs in floodplain deposits mapped in outcrop are correlated over tens to hundreds of meters, and scale to estimated channel widths reflecting the autogenic control. FAC sets can be correlated for up to 10 km along depositional strike, which suggest controls unrelated to the dynamics of individual channels and may show some elements of allogenic climate-driven processes.