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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 56 (1972)

Issue: 3. (March)

First Page: 604

Last Page: 604

Title: Stratigraphy and Depositional Environments of Moenkopi Formation in Southeastern Utah: ABSTRACT

Author(s): R. C. Blakey

Article Type: Meeting abstract


In southeastern Utah the Triassic Moenkopi Formation is composed mainly of red and yellowish-gray siltstone, sandstone, mudstone, and limestone. Continuity of individual units in this formation provides a basis for regional correlation. Five members are recognized here: Hoskinnini Member, "lower slope-forming member," Sinbad Limestone Member, "ledge-forming member," and "upper slope-forming member."

The Moenkopi Formation was deposited on a fairly uniform and gentle west slope that was bordered and at times covered by an epicontinental sea. Prominently stratified mudstone and fine siltstone were deposited when the rate of subsidence slightly exceeded the rate of deposition. Mudstone or massive sandy siltstone was deposited from a suspension load or by gravity flow. Ripple-marked and platy siltstone was deposited when subsidence and deposition were nearly equal and currents distributed thin layers of sediment over tidal flats, floodplains, and sea bottom. Horizontally stratified or low-angle cross-stratified sandstone is indicative of beach, bar, or shallow-marine environment. Prominently cross-stratified sandstone was deposited by restrictive currents such as those found in fluvi l and tidal channels and some offshore bars. Fossiliferous carbonate was deposited in shallow marine waters.

Using these data, the following conclusions can be drawn. The Hoskinnini Member was deposited in a quiet body of water but was disturbed after deposition. The "lower slope-forming member" was deposited on a large tidal and in shallow marine waters; the sea transgressed farther east and deposited the Sinbad Limestone Member. As the sea retreated, a large delta spread across much of the basin of deposition and the complex "ledge-forming member" was deposited. Lithology of the "upper slope-forming member" indicates a widespread low-energy tidal, sabkha, and shallow marine environment.

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