7638

• UCREFRP Catalog Number: 7638
• Author: Stevens, L. E.
• Title: Ecological Characterization of the Wetlands of the Colorado Plateau.
• USFW Year: n.d.
• USFW - Doc Type: Flagstaff, Arizona.
• Copyright Material: NO

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Phanerozoic Eon (550 m.y. Ago to the Present)

The Paleozoic era. The Colorado Plateau was a shallow marine
shelf until about 550 m.y. ago when Cambrian sediments began to
accumulate. During the Cambrian period, the re-exposed, low-lying
crystalline hills were inundated by a Cordilleran sea which
transgressed from the west. Numerous invertebrate traces and
trilobites were fossilized in the Tapeats sandstone and Bright
Angel shale beds left by these seas. From the Cambrian through
the Mississippian periods, an interval of 260 m.y., seas advanced
and retreated across the shallow continental shelf, depositing as
much as 1,000 m of limestone, shale and sandstone, in which
numerous marine invertebrate and a few fish fossils are found.
The Grand Canyon region passed across the equator during the
Mississippian period (Bremner 1986).

Coastal environments during the Pennsylvanian period provide
evidence of abundant marine life, economically valuable supplies
of petroleum, and preserved root casts of terrestrial plant life
which are the oldest evidence of riparian vegetation in the
region. Deformation of the continental shelf along the
Uncompaghgre uplift created a series of embayments along the
coastline, with deposition of the massive sandstone/limestone
Supai group in the Grand Canyon (McKee 1982). Transgression/
regression cycles created evaporitic basins which contained
substantial salt deposits in the Canyonlands area (Baars 1987b),
with deposition of erosional outwash from the Uncompaghgre uplift
over evaporitic sequences during regressions. This cycle was
repeated numerous times, depositing as much as 4,300 m of
subsurface salt in the Pennsylvanian Hermosa group in Paradox
basin. Today, these salt deposits contribute to the high salinity
of Colorado River water.

Permian strata record a change from marine deposition in the
west to terrestrial deposition in the east, as the Uncompaghgre
uplift rose above the coastal plain and shed sediments onto the
Plateau basins. Shallow marine limestones were deposited, along
with localized eolian sand deposits. Permian Cedar Mesa Sandstone
and Cutler formations on the Colorado Plateau are comprised of
eolian dune deposits, wet interdune deposits, fluvial channel
deposits and overbank-interdune deposits. These strata reveal
evidence of interactive processes between eolian and fluvial
environments (Langford 1988), similar in complexity to
sedimentation interactions taking place today on the Plateau.

The late Pennsylvanian and Permian deposits consisted of the
Hermit shale (Grand Canyon) - Organ Rock (Canyonlands) shale, the
marine coastal Coconino sandstone formation (Grand Canyon), the
Toroweap limestone (Grand Canyon) - White Rim (Canyonlands)
sandstone formation, the Kaibab limestone formation, and possibly

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