Pastel Study Of The Triassic Stratigraphy Of Ghost Ranch - Rio Chama Valley Abiquiu New Mexico

Title

Pastel Study Of The Triassic Stratigraphy Of Ghost Ranch - Rio Chama Valley Abiquiu New Mexico

Artist

Silvio Ligutti

Medium

Pastel - Pastel

Description

Geologic History of Ghost Ranch, https://geoinfo.nmt.edu/tour/landmarks/ghost_ranch/home.html

The Mesozoic rocks in the breathtaking red, white, and yellow 1300-foot escarpment surrounding Ghost Ranch contain a rich, but fragmentary, geologic record spanning approximately 130 million years of Earth's history. Portions of river systems, vast deserts, saline lakes, broad mudflats, and ocean shorelines are preserved at Ghost Ranch.

Triassic Rocks
The oldest rocks exposed at Ghost Ranch belong to the Late Triassic Chinle Group, a thick package of brick-red to red siltstone and mudstone and white to tan sandstone that consist of six distinct rocks units that can be traced around the Chama Basin (Lucas et al., 2005). These rocks were deposited by rivers between 205 and 228 million years ago, when the Ghost Ranch area was located about 10° north of the equator. The basal Shinarump Formation (formerly called Agua Sarca Sandstone) is a white to yellow to green, coarse-grained quartz sandstone that locally contains abundant well-rounded quartzite cobbles; this sandstone is overlain the maroon shales of the Salitral Formation. The Shinarump and Salitral Formations are exposed south of the main Ghost Ranch headquarters along the Rio Chama. On top of the Salitral Formation is a second conglomeratic sandstone – mudstone sequence composed of the Poleo Formation, a medium-bedded, yellowish-gray micaceous sandstone with conglomeratic lenses of siltstone and calcrete clasts, overlain by a thick red to reddish brown mudstone, the Painted Desert Member of the Petrified Forest Formation. In many places, a transitional, thinly-bedded sandstone unit, the Mesa Montosa Member of the Petrified Forest Formation, is present between the Poleo Formation and the Painted Desert Member. The Poleo Formation and Mesa Montosa Member sandstones can be seen along Highway 84 southeast and south of the Ghost Ranch Headquarters. Both of these sandstone-mudstone packages were deposited by large Mississippi River-scale river systems flowing from central Texas toward the northwest to Nevada.


Stratigraphic column for the Ghost Ranch area modified from the diagram inside the back cover of the 2005 New Mexico Geological Society guidebook. Thanks to Kate Zeigler for providing this diagram.
The uppermost part of the late Triassic Chinle Group is exposed in the vicinity of the Ghost Ranch headquarters. Most of the facilities at Ghost Ranch are built on the mudstones of the Painted Desert Member of the Petrified Forest Formation. Several of the notable fossil quarries at Ghost Ranch, the Snyder Quarry, Orphan Mesa site, Hayden quarry and the Canjilon phytosaur quarry, are located in this unit at about the same stratigraphic level. The youngest Chinle Group unit, the Rock Point Formation of Lucas et al. (2005), is locally exposed in the escarpment north and east of the ranch just below the conspicuous red and yellow Entrada Sandstone cliffs. The uppermost unit is a thin-bedded red-brown to gray brown siltstone to sandstone. The world-renowned Whitaker quarry, which contains hundreds of skeletons of an early Triassic dinosaur, Coelophysis bauri, is located in this interval (Colbert, 1995).

Uploaded

April 30th, 2020

Statistics

Viewed 425 Times  -  Last Visitor from San Francisco, CA on 04/19/2024 at 1:02 PM

Colors

Embed

Sales Sheet