Sunday, May 17, 2015

Basal Triassic Conglomerate

The Permian-Triassic boundary in central and southern Utah is marked with Conglomerates.  Some are probably Permian, those deep in paleo channels, and some are earliest Triassic, those mixed in with the sand and silt at the base of the Black Dragon Formation red beds.

In the East, there is a nice outcrop in Black Dragon Canyon coming off the San Rafael Swell.
Close-up of conglomerate in Black Dragon Canyon.
Outcrop of conglomerate (~1 meter thick here) in Black Dragon Canyon.  Above the yellowish Permian Black Box Dolomite "Kaibab Limestone", and below the yellowish Black Dragon Formation, the gray Sinbad Formation.  The Torrey, Moody Cyn., Chinle, and Wingate Formations continue the section.

At Minersville, the beds are much like those in Black Dragon Canyon.  The chert gravel is a little more rounded.

Close-up of conglomerate at the Minersville section.

Conglomerate, lower left, under the "Black Dragon" red beds in Minersville Canyon.

In the Confusion Range, three forms of the conglomerate are present; A chert pebble, a breccia, and a boulder.
Chert pebble conglomerate under "Woodside/Black Dragon" red beds on the eastern exposures at Disappointment Hills and Cowboy Pass.

Breccia in karstic crevices under "Reef limestones (Sinbad?)" on the west side exposures in the Disappointment Hills.

Boulder conglomerate under "Reef limestones (Sinbad?)" in the SW corner of the Cowboy Pass exposure.
Down in southern Utah, the only place where the conglomerate has an official name, the Rock Canyon Conglomerate crops out between the Sinbad and Permian rocks from Cedar City down into Arizona.

Close-up of the Rock Canyon Conglomerate in Spring Creek Canyon.