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


Morrison Formation

(Tidwell Member, Salt Wash Member, Brushy Basin Member)

 

 

Age:

Figure 1: Paleogeographic map of the Middle Jurassic, Page Sandstone, Carmel Formation, Entrada Sandstone, Curtis Formation, and Summerville Formation. (Blakey, 2008)

v   Late Jurassic (Kimmeridgian) 155-148 Ma

 

Depositional Environment:

Alluvial plain, fluvial channels and floodplains with paleosols

 

Tectonics:

Subduction to the west created a back arc rift basin (between Morrison basin and paleo Pacific Ocean).

Mountain ranges (rift shoulder) to the west were source for clastic sediment

Calderas in rift basin provided abundant ash fall during Brushy Basin deposition

 

Climate:

Located ~32° N (modern southern AZ)

Prevailing easterly winds (present day NE due to rotation of plate)

Warm, dry climate with high evaporation

 

Features:

Morrison Formation - 180-200 m thick

    Tidwell Member  (oldest) 

        Alluvial plain – streams, overbank deposits, paleosols; locally (in Capitol Reef area)

        gypsiferous, hyper-saline lagoons

        Varicolored mudstone with interbedded sandstone, limestone, gypsum

    Salt Wash Member (middle)

        Fluvial channel deposits, floodplain deposits, crevasse splays

        Predominately fine/medium sand - coarse sand/ pebble conglomerates; trough stratification,

        fining upward

    Brushy Basin Member (youngest)

        Lacustrine/ wetlands; local fluvial channels

        Varicolored mudstone

        Mostly ground and surface water flowing to the east (present day NE)

        Losing streams with associated riparian environments prograding to the east

Floodplains with paleosols; grassy savannahs

 

Sites Best to See it:

Stop 1-1: Exhumed paleo channels in Salt Wash Member

Stop 2-1: All three members

 

Figure 2: Channel in Salt Wash Member (outlined with dotted line).

 

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) 2010, Geology and Geophysics Department, The University of Utah

 

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