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Show WINTER 2013 UHQ pp 4-90_UHQ Stories/pp.4-68 12/5/12 9:38 AM Page 47 SANPETE OOLITE LIMESTONE Park City and Heber City, granite from Little Cottonwood Canyon near Salt Lake City, and volcanic rock from St. George and Beaver.1 The oolite limestone exposed in the isolated Sanpete Valley one hundred miles south of Salt Lake City was the most widely used. The widespread use of the Sanpete oolite limestone was due to its cream color, ease of quarrying and carving, durability, and its exposure in easily accessible sites near the valley floor. Stone craftsmen among early Mormon immigrant settlers recognized the value of the stone and opened quarries soon after settlement. Architects inspired by the Beaux-Arts and Neoclassical styles found the stone suited their artistic talents, and the arrival of railroad transportation, made possible the use of the stone for structures beyond Sanpete County. The attractive physical properties of the Sanpete oolite limestone were due to the geological conditions of formation and exposure in Sanpete Valley. Sanpete Valley is surrounded by great slabs of inclined sedimentary rock layers that rise from the valley floor and flatten on the crest of the Wasatch Plateau on the east, and the cliffs of the San Pitch Mountains on the west. Oolite limestone beds occur at the base of the Wasatch Plateau near the valley floor. The oolite limestone is a part of the Green River Formation, which was formed in a large prehistoric lake named Lake Uinta that extended from Sanpete Valley into the Uinta Basin. The age of the lake and the limestone is 43.1 to 46.4 million years.2 The formation of oolites in a lake environment required some special conditions. First, the water must be supersaturated with the carbonate minerals. Next a suitable nucleus must be present around which the carbonate mineral may precipitate. Wave action agitates the grains to permit precipitation to completely surround the nucleus. Oolites are restricted to water that is less than a few meters in depth and agitated by wave action near a shoreline.3 The properties of the stone reflect its texture, mineralogy, and chemical composition. Oolites 1.5 to 2 millimeters in diameter are the most striking textural feature. They are either hollow or partially filled with granular material cemented by medium gray silica and calcite. Composition includes both calcium and magnesium carbonate. The carbonate minerals are relatively soft and easily carved. The limestone contains small amounts of iron and aluminum oxides that contribute to the pleasing color of the quarried stone.4 Exposure of the stone at the surface made quarrying Sanpete oolite 1 Bryce Tripp, Utah Stone (Salt Lake City: Utah Geological Survey Public Information Series No. 17, 1993), 1-17. 2 Malcolm P. Weiss and Douglas A. Sprinkel, Geologic Map of the Manti 7.5-minute Quadrangle, Sanpete County, Utah (Salt Lake City: Utah Geological Survey Map 188, 2002), 10. 3 B. W. Sellwood, “Shallow-water carbonate environments,” in H. G. Reading ed. Sedimentary Environments and facies (New York: Elsevier, 1978), 268; R. C. Selly, Ancient Sedimentary Environments and Their Subsurface Recognition, 4th ed.(London: Chapman and Hall, 1996), 213. 4 A. R. Pratt and Eugene Callaghan, Land and Mineral Resources of Sanpete County, Utah, Utah Geological and Mineralogical Survey, Bulletin 85 (Salt Lake City: Utah Geological and Mineralogical Survey, 1970), 38. 47 |
