(in San Rafael Group)
Age: Middle Jurassic
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).
Marginal marine and tidal
One unconformably-bound, transgressive-regressive (T-R) sequence, marine and marginal-marine (Wilcox, 2007).
A major transgression of the Late Jurassic seaway drowned the eolian sand sea of the Entrada Sandstone. Subsequent regressive paleoflow was to the northeast into the Late Jurassic interior seaway (Kocurek & Dott, 1983, Blakey 2008).
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 intensely hot and arid (Kocurek & Dott, 1983).
The Summerville is noted for its thin red beds of rippled sandstones and mud cracks, overprinted with secondary gypsum veins. The Jurassic "J3" unconformity, a regional surface of erosion atop the Entrada Sandstone, 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 represents a highstand systems tract reflected in upward coarsening cycles from marine shelf to tidal channels to shoreface. The upper sequence is tidal flat, reddish-brown mudstones and evaporites of the Summerville Fm 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 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.
A pdf version of this website is available on the Main Page
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
Copyright (c) 2018, Geology and Geophysics Department, The University of Utah