THE MEANDERING MORRISON: THE CAINEVILLE, UTAH, “FOSSIL” MEANDERBELT EXPOSURES

Much of the current literature on the Salt Wash Member of the Morrison Formation in southeastern Utah interprets the fluvial morphology as braided; however, exposures located northwest of Caineville, Utah, clearly show that the Salt Wash Member in this area consisted of amalgamated meanderbelts. Extensive, lateral (plan view) exposures that cover an approximately 20 km² area show clear scroll bar topography produced by channels that were approximately 30-40 m wide. Aerial photographs and field surveys were used to develop a preliminary map of meanderbelt form and channel distribution. This preliminary work indicates that large (up to 2m wide) trough crossbeds dominate the in-channel lithofacies. Paleoflow measurements from these well-exposed crossbeds confirm that these are meander bends, with general flow direction to the northeast but widely ranging from the northwest to the south, following apparent plan view meanders. Rare lateral accretion surfaces are present in the sandstone; however these are difficult to interpret in cross section without the benefit of the plan view exposures since they appear to be broadly spaced and are relatively subtle features that could easily be confused with broad scours. This outcrop is located in a medial position on the Salt Wash DFS (based on maps by Craig et al. 1955; Mullens and Freeman 1957; and Tyler and Ethridge 1983). Further detailed evaluation of this deposit is currently underway to (1) determine whether other Morrison Formation exposures show evidence of deposition on large meanderbelts and (2) how the sediments at this location fit into the overall context of the Salt Wash DFS.