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| Entrada Sandstone | |
|---|---|
| Name | Entrada Sandstone |
| Type | Sedimentary formation |
| Period | Jurassic |
| Primary lithology | Sandstone |
| Other lithology | Mudstone, siltstone, evaporite |
| Named by | James Gilluly |
| Region | Colorado Plateau |
| Country | United States |
Entrada Sandstone The Entrada Sandstone is a Middle to Late Jurassic sedimentary unit prominent on the Colorado Plateau of the United States, renowned for sculpted arches and hoodoos in national parks and for preserving diverse trace fossils. It crops out across parts of Utah, Arizona, Colorado, and New Mexico and has been the subject of stratigraphic and sedimentologic research by workers associated with institutions such as the United States Geological Survey, University of Utah, and Brigham Young University. Classic exposures in Arches National Park, Goblin Valley State Park, and Canyonlands National Park have made it a target for studies by geologists from Harvard University, Yale University, and the University of California, Berkeley.
The formation consists predominantly of fine- to medium-grained, well-sorted quartzose sandstone with local interbeds of silty mudstone, gypsum, and siltstone, producing the characteristic red, tan, and white bedding seen in Capitol Reef National Park, Monument Valley, and Natural Bridges National Monument. Detrital composition analyses by researchers affiliated with Stanford University, University of Colorado Boulder, and the Smithsonian Institution indicate a high quartz content with subordinate feldspar and lithic fragments; diagenetic features include calcite cement and hematite staining documented in cores held by the U.S. Bureau of Land Management and samples archived at the Natural History Museum of Utah. Sedimentary structures such as large-scale cross-bedding, ripple marks, and caprock-replacement nodules are mapped in detailed surveys conducted by teams from the National Park Service and the Geological Society of America.
The Entrada is usually assigned to the Middle Jurassic to Late Jurassic (Bajocian to Oxfordian) interval in regional chronostratigraphic schemes used by the Geological Society of America and the American Association of Petroleum Geologists. It typically overlies the Curtis Formation and overlain by the Carmel Formation or Todilto Formation in different locales, relationships charted in stratigraphic columns published by the United States Geological Survey and the Utah Geological Survey. Regional correlation efforts linking Entrada equivalents across the Colorado Plateau and into the Morrison Formation-bearing basins have involved paleontologists and stratigraphers from University of Kansas, Field Museum of Natural History, and University of Chicago.
Interpretations by specialists at Brown University, University of Arizona, and the Scripps Institution of Oceanography reconstruct depositional settings ranging from eolian dune fields to shallow marine and tidal sabkha environments, reflecting fluctuating Jurassic sea levels documented in cyclostratigraphic studies. Large-scale trough and planar cross-stratification, rebound surfaces, and interdune mudstones observed at Zion National Park and Capitol Reef National Park support an eolian origin for significant parts of the unit, while evaporite layers and marine fossils in localities near Moab, Utah indicate episodic marine incursions similar to those studied in the Solnhofen Limestone and Sinemurian outcrops of Europe. Sediment provenance work tying detritus to uplifted source areas such as the ancestral Uncompahgre Uplift has involved geochemists from Argonne National Laboratory and University of Michigan.
Prominent exposures occur in Arches National Park, Canyonlands National Park, Goblin Valley State Park, Capitol Reef National Park, and the environs of Monument Valley Navajo Tribal Park. Other notable localities include the San Rafael Swell, the Henry Mountains region near Glen Canyon, and roadside cliffs along U.S. Route 191 and U.S. Route 24, which have been documented by the Utah Geological Association and visiting field parties from Colorado School of Mines and Arizona State University. International comparisons have been drawn with Jurassic sandstone exposures in the Maltese Islands and the Karoo Basin of South Africa by collaborative teams involving the Natural History Museum, London.
The Entrada Sandstone has local economic importance as a source of dimension stone and aggregate used in construction projects in Salt Lake City, Phoenix, and Denver. Quarries operated by companies associated with the National Stone Institute supply building veneer and paving materials; restrictions managed by the National Park Service and tribal authorities limit extraction within protected areas such as Arches National Park and tribal lands administered by the Navajo Nation. Groundwater reservoirs within Entrada sand bodies influence municipal supplies for communities served by the Central Utah Water Conservancy District and the Glen Canyon National Recreation Area; hydrogeologic assessments have been produced by the U.S. Bureau of Reclamation and state water agencies.
While body fossils are relatively scarce, the Entrada-preserved ichnofauna include abundant dinosaur trackways, invertebrate burrows, and vertebrate resting traces documented in detailed ichnological studies by researchers at University of Colorado Museum of Natural History, Dinosaur National Monument, and the Paleontological Society. Notable tracksites containing theropod and ornithopod impressions have been reported near Moab and the San Rafael Reef, drawing comparisons to trace assemblages from Dinosaur Ridge and La Rioja; preliminary microfossil reports by teams from Texas A&M University and the Field Museum have described palynomorphs that aid in regional correlation.
The formation was named in early 20th-century mapping and later refined by geologists including James Gilluly and survey teams from the United States Geological Survey and the Utah Geological Survey. Historical fieldwork by pioneers associated with Brigham Young University, Colorado Plateau scholars, and the American Museum of Natural History established the lithologic framework; subsequent stratigraphic synthesis and modern sedimentologic models were advanced by researchers at University of Utah, Stanford University, and the Geological Society of America through successive decades of mapping, petrographic analysis, and regional synthesis.