SPRING AND SHOUT: A COMPARISON OF EARLY CRETACEOUS CEDAR MOUNTAIN FORMATION CARBONATE TEXTURES TO MODERN SPRING DEPOSITS

Lithologic and textural comparison of Early Cretaceous Cedar Mountain Formation (CMF) to subrecent cold-spring deposits suggests paleospring deposition at the Jurassic-Cretaceous unconformity. Subrecent travertine deposits near Crystal Geyser, Utah, display five distinctive calcium carbonate textures typical of spring deposits. At Crystal Geyser, mounded deposits exhibit a boxwork of calcite sheets 1.0-4.0 mm thick cementing poorly lithified purple and green mottled mudstone, fluvial sandstone, and micrite. Dense tufa and mm-scale banded travertine occur throughout the deposits. Sheets of fibrous calcite up to 50 cm thick formed on both subaerial surfaces and within fractures. Centimeter scale fractures contain drusy spar veins.

Near Elk Springs, Colorado, the CMF exhibits similar spring textures, and a sequence of formation can be developed. Following formation of meter-scale, bioturbated calcrete in semi-lithified mudstone, groundwater below the calcrete deposited a boxwork of calcite veins, laterally continuous for at least a kilometer. Pipes (avg. 0.5 m diameter) of tufa extend through the earlier boxwork and the overlying calcrete. In cross-section, the pipes are composed of four concentric layers: 1st, a central core of micrite with spar-filled fractures, 2nd, a surrounding tufa, 3rd, meshy boxwork, and 4th, a capping fibrous calcite. Fibrous calcite is also found in bands up to 10 cm thick surrounding and within tufa pipes and layers, and also surrounding subround Fe-rich micrite nodules (avg. 20 cm diameter) in the mudstone above the calcrete. Fibrous calcite bands may also have coated exposed sections of the calcrete. Drusy spar veins are also common in the micrite and tufa.

Similar calcitic boxwork in the basal bioturbated calcrete of the CMF near Green River, Utah, occurs in decimeter-scale patches. CMF outcrops near Vernal, Utah contain calcitic boxwork in centimeter to decimeter discontinuous patches within a layer of brown micrite approximately 30 cm thick. Within this layer, small zones of 5 cm thick isopachous radial calcite form around brown micrite nodules, but not on boxy meshwork.

Further study will include petrographic microscopy, XRD, and oxygen isotope analysis.