Overview of Capitol Reef NP     Geology of Capitol Reef NP      Stops of Capitol Reef NP


Moenkopi Formation

(Black Dragon Member, Sinbad Limestone, Torrey Member, Moody Canyon Member)

 

 

Age:

Figure 1: Paleogeographic map of the Early Triassic, Moenkopi Formation. (Blakey, 2008)

Lower Triassic to possibly lower Middle Triassic

 

Depositional Environment:

Tidal (also with nearshore, shallow marine, and some floodplain)

 

Paleogeography:

The Moenkopi Formation was deposited along the western portion of the United States (Figure 1).

    

Tectonics:

Very little tectonic activity was occurring during the time of deposition.

 

Climate:

During the initial deposition of the Moenkopi Formation, the climate was rather hot and dry, then during the later members (the Sinbad Limestone through the Moody Canyon Members) the climate progressively got wetter, but it was likely still arid (Blakey, 1973).

 

Features:

The Moenkopi Formation preserves extensive ancient tidal and nearshore deposits. Continental conditions were located to the east, and marine conditions to the west. Four different members of the Moenkopi were deposited in the Capitol Reef region. The lowest Black Dragon Member was deposited under marine conditions preserving a shallowing upwards sequence, capped by beach sands and fluvial (river) deposits. Cyclic alternation of supratidal (above the ocean level) to subtidal (below ocean the level) deposits resulted in interbedded (alternating) mud and sand beds throughout much of the Moenkopi (Blakey, 1973).

Following the Black Dragon Member, the Sinbad Limestone Member was deposited under shallow marine conditions before clastic sedimentation resumed in the overlying Torrey Member. The final member, The Moody Canyon Member, was deposited under widespread, uniform, low-energy marine conditions, producing a generally "structure-less" mudstone (Blakey, 1973).

The Moenkopi Formation typically contains abundant thinly bedded mudstones and sandstones (Figures 2 and 3) with a large variety of ripple marks (Figures 4 and 5), and some trace fossils (impressions from animals in the sediment) (Figures 6 and 7).  Secondary gypsum veins cut through this formation (Figure 8 and 9).

Sites Best to See it:

Stop 2-3 - Navajo Waterfall

Stop 2-4 - Navajo Sandstone Soft Sediment Deformation

Stop 3-3 - Grand Wash Trail

 

Figure 2: Outcrops along the side of Hwy 24 showing the backside of The Castle. Lines have been added to show the contacts between the various formations visible at this stop.

Figure 3: Thinly laminated, alternating sandstone, siltstone and mudstone beds are typical of the Moenkopi Formation.

 

 

 

Figure 4: Current ripples “cast” from a sandstone bed.

Figure 5: Complex ripples from a sandstone bed.

 

 

 

Figure 6: Bioturbation where worms burrowed through the mud leaving U-shaped burrows.

 

Figure 7: Vertebrate "smears". This is where a small reptile swimming through the body of water scraped its claws through the mud on the bottom.

 

 

 

Figure 8: Gypsum veins running throughout the upper Moenkopi Formation directly underlying a Pleistocene Terrace.

 

Figure 9: Close up of the secondary gypsum veins showing the irregularity of the vein pattern.

 

 

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

Copyright (c) 2018, Geology and Geophysics Department, The University of Utah

 

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