(in San Rafael Group)
Figure 1: Paleogeographic map of the Middle Jurassic, Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation. (Blakey, 2008)
Deposited from early to late Oxfordian time (161 - 155 Ma) (Wilcox, 2007).
Deposition was in a retroarc to craton-margin basin as the region drifted north (Kocurek & Dott, 1983).
With paleolatitude range of 5 to 25 degrees north, the paleoclimate was both hot and arid (Kocurek & Dott, 1983).
The Curtis Formation shows a variety of nearshore sedimentary structures (e.g. horizontal bedding -> beach, rhythmites and sigmoidal bundles -> tidal). The Jurassic "J3" unconformity, a regional surface of erosion atop the Entrada Formation, marks the basal bounding surface of the Curtis-Summerville T-R sequence. A thin, lower Curtis transgressive systems tract is the finest grained facies of the Curtis Formation topped by a maximum flooding surface. Thick middle and upper Curtis deposits represent a highstand systems tract reflected in upward coarsening cycles from marine shelf to tidal channels to shoreface envirionments. The upper sequence is tidal flat, reddish-brown mudstones and evaporites of the Summerville Formation topped by the "J5" unconformity, the upper sequence bounding surface and the contact with overlying Morrison Formation (Wilcox, 2007).
Sites Best to See it:
Stop 1-2: View the Curtis-Summerville Formations and bounding unconformities in distant cliffs at Goblin Valley State Park.
Stop 1-3: Summerville gypsiferous mudstones outcrop along Highway 24 west of Hanksville.
Stop 2-1: San Rafael Group overlook
Stop 4-1: For close inspection of Curtis Formation tide-generated sedimentary structures see the East I-70 road cut where the most impressive tidal features, sigmoid-shaped tidal bundles occur.
Figure 2: View of the Morrison Formation, the Summerville Formation, the Curtis Formation, and the Entrada Formation.
For a complete list of references please go to the References page.
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Disclaimer: The information is property of the University of Utah. Unless cited, images and files found on this site have been taken or created by the Geology and Geophysics Department at the University of Utah. Any use of these images should be cited appropriately. The stratigraphic column is from: Mathis, A. C. 2000. Capitol Reef National Park and Vicinity Geologic Road Logs, Utah, in: P.B. Anderson and D.A. Sprinkel (eds.) Geologic Road, Trail, and Lake Guides to Utah’s Parks and Monuments Utah Geological Association Publication 29. http://www.utahgeology.org/uga29Titles.htm
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