Hi I’m Ali Sealander with UTD Geonews and today we’re quite a
ways from Dallas in South Dakota’s very own Badlands National Park.
This place is wonderful. Layer cake geology spectacularly displayed by the powerful effects
of erosion. The rock here show 75 million years of Earth's history and the tectonic movements along the
way. There are marine, near shore, and terrestrial deposits … and the fossils to prove it.
The hot summers, dry winters, intense rainfalls, and lack of vegetation all combine to create the
badlands topography that was first typified here in the Badlands of South Dakota!
On this area the American novelist John Steinbeck had this to say,
“The Badlands deserve this name. They are like the work of an evil
child. Such a place the Fallen Angels might have built as a spite to heaven.”
So join us as we check out the spiteful hellscape with all its spires, pinnacles, caprocks,
mesas, buttes, castles, yardangs, and sod tables, at Badlands National Park.
Let’s start with where we are. Badlands National Park sits in southwestern South
Dakota within the larger Great Plains ecoregion. It’s just off interstate 90
a little over 50 miles from Mt. Rushmore in the Black Hills and about 50 miles from Rapid City.
What are Badlands? Badlands are areas with rough topography due to erosion of soft sediments.
The area is usually dry with bouts of heavy rain that erode the soft rock.
The park gets about 16 inches of rain a year
mostly in the late spring and summer.
Badlands can be found all over the world.
In just the U.S. there are badlands in Montana, North Dakota, Arizona,
Utah, Nebraska, Colorado, Wyoming, and California.
Badlands National Park is where we get the name for this type of terrain.
For hundreds of years the Lakota people called it mako sica or “bad land.”
It was also the Lakota people who
first noticed fossils in these sedimentary rocks and suggested that this place was once underwater.
But it wasn’t until the 1840s when geoscientists got interested in these fossils. One of the first
fossils studied from this area was a jaw fragment from a Titanothere, an 8-foot tall, 16-foot long,
rhino-looking mammal that existed in the late Eocene epoch around 35 million years ago.
And it was fossils like these that are responsible for this badland becoming a national park.
In fact, this is the world’s best site for vertebrate fossils from the Oligocene,
20-30 million years ago. Fears of fossil hunters depleting the badlands of important specimens
was the basis for creating Badlands National Monument in 1939 and then a national park in 1978.
But the history here goes back way further than that. We are talking 75 million years
of history preserved in a handful of rock formations found in the park.
They tell the story of change over geologic time, of shifting seas,
uplift, erosion, climate change, and the types of creatures that are seen with these changes.
From oldest to youngest the rocks are separated into the following units: the Pierre Shale and
Fox Hills Formations, the Yellow Mounds paleosol, and then the Chamberlain Pass,
Chadron, and Brule Formations. Topping these off are the Rockyford Ash and the Sharps Formation.
Let’s go through each of these to see how geologists figured out the
environments they were deposited in. Let’s start at the beginning
The oldest rocks exposed at Badlands National Park are the Pierre Shale Formation.
These rocks were deposited in Late Cretaceous time, about 75-69 million years ago.
The area was then under a broad, shallow inland sea known as the Western Interior Seaway.
At the bottom of this shallow sea, silt and clay particles were deposited, compacted,
and cemented to form the Pierre Shale that we see today.
Giant clam and ammonite fossils found in the Pierre Shale show that it was a marine environment.
From about 69 to 66 million years ago - the end of the Cretaceous - the rocks of
the Fox Hills Formation were deposited. At this time, the Western Interior Seaway
was disappearing. Eroding mountains to the west were depositing their sediments into the basin,
and the basin itself was also being uplifted. The Fox Hills formation represents this big change.
Within the park, the Fox Hills formation contains rocks and fossils from marine and
nearshore environments. Fossils of ammonites, belemnites, fish remains, plant material, clams,
and oyster fragments can be found. There are also trace fossils that show the presence of life,
like tracks, trails, or burrows. The trace fossils here are known to belong to creatures
that spent their time in the intertidal or shallow subtidal zone, where the sea meets the shore.
Just around the end of the Cretaceous the rocks in the park become distinctly
terrestrial and no longer marine. These rocks make up the White River Group. By this time the
Western Interior Seaway had disappeared and we start to see fossils from land animals.
The Yellow Mounds paleosol is the first indicator of this change.
This lovely addition to the Badland’s landscape is a fossil soil. For this soil to form,
sea levels would have to have fallen so that rocks were exposed to the weathering effects of wind,
rain, and plant growth. Root casts indicate the presence of a forest. You might also see in
the park bands of red, these are also paleosols some of which contain fossilized termite nests!
Younger formations were deposited in lakes, stream channels and floodplains. Floodplains are broad,
flat areas around a river or stream that flood when the adjacent stream gets full.
Sediments settling out of stream or flood waters get compacted and cemented together to make
up rocks of the White River Group. Around 37 to 34 million years ago,
during the Eocene epoch, the region was a forested floodplain. The sandy clay deposits of the Chadron
formation were once called the Titanotherium beds, due to the Titanotherium fossils found within it.
Over the next few million years this forested region dried out, becoming
dryer and more savannah-like. During this time, from around 34 to 30 million years ago, the Brule
Formation was deposited. The Brule Formation is home to the Big Pig Dig site where over
19,000 fossils have been found. Some of these. are the “Big Pig” Archaeotherium,
the Subhyracodon, Mesohippus, and the Leptomeryx. Between the Brule and the underlying Chadron
formation there are fossils of aquatic turtles, semi-aquatic rhinoceros, cursorial rhinoceros,
horses, creodont carnivores, oreodonts, pig-like entelodont, and fossils of
alligators, birds, opossums, small insectivores, saber-tooth cats,
tapiroids, camels, and squirrel-like, rabbit-like, and fox-like animals.”
30 to 26 million years ago the conditions here transitioned from desert-like to a semi-arid,
treeless grassland. In the Great Basin Region, an area that makes up significant
parts of Nevada and Utah, volcanic eruptions spread ash as far as the Badlands area.
This ash mixed with various sediments and washed into the Badlands to form the Rockyford Ash,
a 10–23-foot layer that marks the base of the sandy stream channel and floodplain
deposits of the Sharps Formation, the youngest formation in the park.
From this time until today, erosion, rather than deposition, dominated the area.
This plateau of layer cake geology, with all the fossils hidden inside,
continues to be carved by the Cheyenne River, the White River, and the Bad River.
Episodes of heavy rain also contribute to this erosion. Because the layers are made
up of different types of rocks, what results is called differential weathering and erosion. The
softer rocks erode more quickly than the harder, more resistant rocks. This is one of the reasons
that the Badlands landscape is so unique.
An attentive tourist might also spot some unusual features crosscutting the horizontal layers.
These are called clastic dikes and are one of my favorite parts of the park.
But how they got here is kind of a mystery. There’s a couple of explanations to how they
have formed, but nobody is 100% certain at this point. there are still some unresolved issues
that require more research. If you find yourself equally fascinated or curious by these features,
then check out our references at the end of the video to learn more about them.
The badlands are a fantastic display of geology and deep time. In the cross cut rocks we can see
millions of years of Earth's history. The types of rocks and the fossils within them allow geologists to
piece together the story of each formation
Sea creatures from the Western Interior Seaway to land roaming mammals like the
Titanotheres are all represented here and are all on display due to the powerful
effects of erosion. And one day ths place will no longer be here. Steinbeck’s spiteful
landscape will be undone by the most spiteful thing there is… erosion, the effects of time.
Erosion, the very thing that has drawn us to the Badlands in the first place,
will take over and the Badlands will no longer be here…..
but we’ll leave the dramatic prose to Steinbeck because that process will take like 500,000 years.
I'm Ali Sealander with UTD GeoNews and I’ll see you next time!