Quaternary deposits and soils in and around Spanish Valley, Utah

Examination of Quaternary deposits in Spanish Valley near Moab, Utah, revealed a complex pattern of soil development and distribution on alluvial fans and terraces previously correlated by Richmond (1962) with glacial deposits in the La Sal Mountains. Longitudinal profiles show downstream convergence of terraces and burial of older surfaces in the middle portion of the valley. In this area, buried soils at two localities have carbonate accumulations similar to those on Placer Creek terraces considered to be of Bull Lake age. The reappearance of inset terraces in lower Spanish Valley suggests that the depositional history has been complex or that the middle part of the valley has subsided since Placer Creek time. Progressive changes in the morphology and content of pedogenic carbonate were used to correlate deposits. Soils developed on gravel of the latest Pleistocene Beaver Basin Formation (Pinedale age) have thin carbonate coats on clasts, display Stages I and II carbonate morphology, and contain 7 to 9 gm/cm 2of pedogenic CaCO 3. Placer Creek deposits have up to 75 cm of continuous CaCO 3; three sampled profiles contain about 36 to 38 gm/cm 2. Carbonate contents of soils on the middle Pleistocene Middle Member of the Harpole Mesa Formation are similar to those of Placer Creek soils; however, a buried argillic horizon preserved at one locality suggests that the Harpole Mesa deposit is older. The Stage IV K horizon on older Harpole Mesa alluvium has a strong platy structure and a well-developed laminar horizon; about 182 gm/cm 2of pedogenic CaCO 3is present in one profile. Sandy alluvium in the Lower Member of the Harpole Mesa Formation has reversed magnetic polarity. A similar pedogenic calcrete containing 98 to 130 gm/cm 2of accumulated CaCO 3overlies magnetically reversed deposits on an erosion surface southwest of Green River, Utah. Using a minimum age of 700,000 years for the magnetically reversed sediments, maximum carbonate accumulation rates for this portion of Utah range from 0.14 to 0.26 gm/cm 2/1,000 years.