Response to Accommodation Change in Channel Belt Distribution, Floodplains, and Paleosols: Cretaceous Ferron-Notom Delta, Utah

Models of accommodation change in fluvial systems emphasize deposition in channels versus the adjacent floodplain. This outcrop example, from the Turonian Ferron Notom delta, in Central Utah, evaluates accommodation change in a linked channel-floodplain system by examining channel-belt distribution, rate of channel re-occupation, frequency of floodplain deposition, along with vertical and lateral variations in floodplain paleosol development. Previous work suggests that the uppermost fluvial units of the Ferron form as one sequence, passing from an incised compound valley, comprising amalgamated multi-storey channel belt deposits, into more laterally extensive and unconfined amalgamated channel belts and later into a shale prone, late transgressive/early highstand systems tract characterized by isolated channel belts with extensive coal-prone floodplain deposits, and marked increase in crevassing and rate of channel abandonment. Amalgamated channel belts in the uppermost parts of the section may indicate a late highstand. The transition from incised valley and extensive channel belts with low preservation of floodplain deposits into increased floodplain deposition and storage in the middle part of the section suggests a gradual to rapid increase in accommodation followed by a gradual decrease towards the top of the section marked by more amalgamated channel belts.

Floodplain facies consists of multiple cycles of gleyed paleosols with characteristic horizon development, forming pedostratigraphic units. Pedostratigraphic units represent distinct cycles of floodplain deposition and accompanying soil development that are coeval with suspended and bed load deposition in adjacent channels. A total of seven paleosol cycles were recorded from the base of the sequence to its top. These units may represent non-marine equivalents to marine parasequences. Complete pedostratigraphic units are characterized by C, B, A and O horizons, and constituent paleosols show angular to sub-angular blocky ped structures with root traces, slickensides, illuviation cutans and carbonaceous organic materials.. Associated heterolithic lacustrine mudstones, coarsening-upward crevasse-splay sandstones, and fining-upward crevasse-channel sandstones represent times of greater alluvial aggradation.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California