CHARACTERIZING RELATIONSHIPS BETWEEN CHANNEL, FLOODPLAIN, AND AVULSION DEPOSITS IN THE WASATCH FORMATION (PALEOCENE/EOCENE, COLORADO)
The Atwell Gulch Member contains small, single story channel sandstones that overlie well-developed, clay-rich floodplain paleosols and lacks avulsion deposits. The Molina Member exhibits large, sheet-like channel bodies that are generally preceded by coarsening upward avulsion successions associated with decreased paleosol development. The Shire Member contains large, multi-story channel sandstones sometimes underlain by well-developed floodplain paleosols and other times underlain by avulsion deposits.
The scarcity of avulsion deposits in the Atwell Gulch Member suggests that the primary mechanism for channel relocation was incisional avulsion. In contrast, common avulsion deposits in the Molina Member imply that Molina avulsions were dominantly progradational. Shire Member channel bodies variably overlie avulsion deposits and floodplain deposits, which may indicate a mix of avulsion styles. Shifts in avulsion style through the Wasatch may be linked to changes in floodplain and channel characteristics resulting from climate change at the P-E boundary.