arizona, volcanology

San Francisco Volcanic Field

Located just north of Flagstaff, Arizona, the San Francisco volcanic field comprises an area of 1,800 sq miles and contains around 600 volcanoes. These volcanoes range in age from 6 million years old to less than 1,000 years old. Given their location on the Colorado Plateau, many volcanoes have experienced little erosion (like SP Crater… Continue reading San Francisco Volcanic Field

paleobiology

Trilobite trace fossils

If you ever happen to find yourself at the Clinch Mountain Lookout Restaurant in Thorn Hill, Tennessee, be sure to 1) try a piece of their vinegar pie and 2) ask to check out the spectacular outcrop featuring trilobite trace fossils directly behind the restaurant. Trace fossils are not remains of the organism itself (i.e. a… Continue reading Trilobite trace fossils

geomorphology

The Badlands in Chicago?

Just by quickly looking at this harshly eroded landscape, you might think you were at Badlands National Park in South Dakota. In reality, this image is actually from Thornton Quarry just south of Chicago, Illinois; hardly a place where you would expect to see badlands-like formations. Badlands landscapes are predominantly erosional terrains. The rocks in… Continue reading The Badlands in Chicago?

sedimentary

Ooids • Sedimentary Spheres

While these dark gray spherical clasts could be mistaken for some type of fossil, they’re actually ooids, which are chemically precipitated sedimentary grains. Ooids form around a nucleus of a mineral grain or shell fragment. Concentric layers composed of calcium carbonate precipitate out and progressively coat the nucleus, forming a pattern almost like tree rings.… Continue reading Ooids • Sedimentary Spheres

Glacial, sedimentary, structure, wisconsin

Glaciated breccia: A three-part rock story

This piece of glaciated breccia from the Brussels Hill meteorite impact structure in Brussels, Wisconsin is probably one of my favorites in my collection. It’s not the oldest, nor is it necessarily the prettiest, but it holds one of the best stories. This rock began its life ~440 million years ago during the Silurian Period.… Continue reading Glaciated breccia: A three-part rock story

petrology

Rocks of Art

Under the cross-polar light from an optical microscope, this thin section of a rock almost looks like it could be stained glass. The grains of olivine and pyroxene in this peridotite sample display vibrant birefringence interference colors. Not all minerals have such vivid hues under a microscope, though. A mineral’s birefringence depends on its refractive… Continue reading Rocks of Art

geomorphology, wisconsin

Wave-cut Platforms and Coastal Geomorphology

While Wisconsin more so conjures images of snow and cold (and cheese) than it does the ocean, it actually has a spectacular coastline along Lake Michigan that undergoes traditional coastal geomorphology processes. Cave Point County Park in Door County, Wisconsin features great examples of wave-cut platforms (shown in the above photos). Wave-cut platforms are the… Continue reading Wave-cut Platforms and Coastal Geomorphology

structure, volcanology

Meteorite Impact or Maar?

Looking at the two images above, they appear quite similar: both are of very large (~1 mile wide), nearly perfectly circular craters in the ground. However, one was formed by a meteorite impact and the other is a maar formed by an explosive volcanic eruption. Think you can figure out which one is which? From just… Continue reading Meteorite Impact or Maar?

structure, tectonics

Which way is up?

No, your eyes aren’t deceiving you, these rock layers are nearly vertical! Although they were once horizontal, these Paleozoic sedimentary units have been tilted so that they now dip nearly 90 degrees. These rocks are located in northeast Tennessee and are part of the Appalachian foreland fold-thrust belt. Though built by multiple orogenies, the Alleghenian… Continue reading Which way is up?