Roadside Geology 2

Rick Meyer

Route 62 descending from Guadalupe Mountains

Elevation: 1449 m

31° 57.083 N

104° 41.780 W

Satellite Image

Content:

This journal entry is a log of the sights that we experienced while traveling from the Guadalupe Mountains National Park to Fort Davis. The trip consisted of two stops. Each of the two stops had unique properties providing us evidence of events that happened millions of years ago.

Content Guides: Keith and Diane Brownlee

Our first stop came as we descended the Guadalupe Mountains entering a deep basin of sandstone and limestone. At an elevation of 1449m, we stopped to explore a road cut characterized by distinct bands of dark rock that was crumbling as it eroded. It was explained to us that the dark color was due to the high level of organic material still contained within the rock. The field geologists shared that this rock contained approximately 3% TOC (Total Organic content). This organic content is material within the limestone that is not yet fossilized. While this explained the dark

color, the significance of these properties were made clear when the rocks were freshly broken from the cut. When the rocks had a freshly exposed face, they smelled like petroleum.

Route 62 descending from Guadalupe Mountains

Elevation 1495 meters

31° 55.903 N

104° 43.849 W

Satellite Image

The next stop on our trip was at a road cut that was unlike the many others to which we were beginning to become accustomed. This cut showed large lightly colored boulders interrupting the steady flow of layered sandstone. This odd collection of limestone surrounded in layers of sandstone sedimentation is the result of a catastrophic event.

This event, possibly a hurricane, triggered a massive underwater landslide. Limestone from the top of Capitan Peak were dislodged from the reef and traveled 800 to 1000 feet into the basin face. The rocks were able to travel these great distances due to low friction caused by the buoyant force of the water. Once these pieces of turbidate flow settled, sandstone continued to form and surround the debris. You can see the formation of additional sedimentary layers of sandstone above the limestone in the photo above.

Saturday, June 3, 2006