Eagle Formation, Billings Montana

One of my favorite places to hike in the Billings area is Zimmerman Park, which is mostly atop the Rimrocks, a cliff formed by sandstone of the Cretaceous Eagle Formation. The Eagle Formation is usually interpreted to be either a barrier island deposit, similar to Padre Island in Texas, or a shallow marine sand bar that ran parallel to the shoreline. The sand was deposited in the Western Interior Seaway, a shallow body of water which stretched across North America from the Arctic to Gulf of Mexico. From Billings, sedimentary rocks become increasingly marine-dominated to the east, and terrestrial to the west.

USGS. From http://en.wikipedia.org/wiki/File:Cretaceous_seaway.png
USGS. From http://en.wikipedia.org/wiki/File:Cretaceous_seaway.png

Here are a few pictures from today’s late afternoon hike:

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Sacrifice Cliff (Eagle Formation), east of downtown Billings. The top of the cliff is about 500 feet above the base of the talus slope. Crow Indian legends state that men (the number varies depending on the version of the legend) jumped off the cliff during a smallpox outbreak.
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Eagle Formation from above Zimmerman Trail.
Ponderosa pine saplings growing out of a fracture on top of a bedding plane.
Ponderosa pine saplings growing out of a fracture.
Concretions (iron-
Concretions weathering out of the sandstone.  Concretions are post-depositional features formed when cement (in this case iron oxides) accumulates around some sort of nucleus. The concretions are then more resistant to erosion than the surrounding sandstone. The Earth Science Picture of the Day has featured concretions from the Eagle Formation.
Me standing next to a concretion.
Me standing next to a concretion.
Concretions and weathering.
Concretions and weathering.
Sunset over the Yellowstone River valley.
Sunset over the Yellowstone River valley.

 

Billings Gazette geology videos

The Billings Gazette has three short videos on the geology of the Billings, Montana area featuring Rocky Mountain College geology professor Derek Sjostrom:

Geology of the Beartooths — Montana’s highest mountain range (Granite Peak, 12799 ft, 3902 m) has a core of 3.2 billion year old metamorphic rocks.

Geology of the Pryors — The Pryor Mountains (East Pryor Mountain, 8786 ft, 2678 m) south of Billings are formed mostly of blocks of Paleozoic sedimentary rocks.

Geology of the Rimrocks — The Rimrocks are Cretaceous sandstone cliffs on the north side of Billings. The fossils and structures indicate that the Eagle formation formed in a barrier island setting, much like modern Padre Island in Texas.

These are at a very basic level, but I still enjoyed them, and it looks like there are more to come in the series.

WordPress won’t let me embed these videos.

K-T iridium layer, Raton NM

The first concrete evidence that an asteroid impact ended the Cretaceous Period was the discovery of an iridium-rich layer marking the Cretaceous-Tertiary (K-T) boundary by a team led by Luis Alvarez in the early 1980s. Iridium is very rare in Earth’s crust, but is considerably more abundant in asteroids, leading geologists to conclude that the layer originated from an asteroid impact. One area where this layer is exposed is in several places near Raton, New Mexico. After our trip to Great Sand Dunes National park last week, we took a little side trip so I could see the K-T iridium layer, conveniently marked by a sign west of Raton.

Me with my fingers on the K-T iridium layer
Me with my fingers on the K-T iridium layer

Google map showing the location of the iridium layer exposure:

Grace and Peace

K-T boundary

From NASA’s Earth Observatory: Raven Ridge, Colorado.

ravenridgeco

This ridge, south of Dinosaur, Colorado, apparently has an exposure of the K-T (Cretaceous-Tertiary) boundary, which marks whatever event ended the age of dinosaurs (asteroid? volcanism? the real reason dinosaurs went extinct?). This gives me two places within a day’s drive to visit the K-T boundary, the other being down by Raton, NM. It looks like a good place for a road trip, with the addition of nearby Dinosaur National Monument.

Grace and Peace