DinoByte Wednesday: Rock Formations of the DIG Field School

Why do paleontologists care about rocks? Rock formations house the secrets of the past! Let’s take a walk through time, starting with the oldest formation preserved at our field site, the Bearpaw Shale, and work our way forward through the Fox Hills Sandstone, to the Hell Creek and Tullock formations, the two formations that are the focus of our DIG research.

A simplified stratigraphic section of the formations visited during the DIG Field School. The lowest (and oldest) formation is the Bearpaw Shale, while the Tullock Formation is the highest in section (and the youngest) in the area. The meters at the left indicate the approximate stratigraphic position relative to the Hell Creek–Tullock formational contact (0 meters), which also coincides in this area with the K/Pg mass extinction. Modified from Johnson et al. (2002).
A simplified stratigraphic section of the formations visited during the DIG Field School. The lowest (and oldest) formation is the Bearpaw Shale, while the Tullock Formation is the highest in section (and the youngest) in the area. The meters at the left indicate the approximate stratigraphic position relative to the Hell Creek–Tullock formational contact (0 meters), which also coincides in this area with the K/Pg mass extinction. Modified from Johnson et al. (2002).

Bearpaw Shale

The lowest (and oldest) formation exposed near the DIG field camp is called the Bearpaw Shale (or Bearpaw Formation). This formation formed ~74-70 mya (million years ago) as a fine-grained layered mudstone (or shale) in a shallow sea, the Western Interior Seaway, that ran through the United States from the Gulf of Mexico to Canada. This formation was deposited just before the sea began to recede near the end of the Cretaceous Period. Can you believe there was once a sea cutting North America in half, and living in this seaway were sharks, giant marine reptiles like the long-necked plesiosaurs, and extinct molluscs called ammonites? All of these creatures (and others!) went extinct with the dinosaurs 66 mya.

A paleoreconstruction map of Late Cretaceous North America 75 mya depicting the Western Interior Seaway that separated North America (left), and a shark and plesiosaur (right) that inhabited this sea. In addition to these giants, other twenty foot long swimming reptiles like mosasaurs lived in the sea and fed on fish and ammonites, relatives of squids and octopi. We often find the remains of the straight-shelled ammonites, called Baculites, in these shale deposits. *Ron Blakey has produced many maps like this of North America and the world through time that can be found online.
A paleoreconstruction map of Late Cretaceous North America 75 mya depicting the Western Interior Seaway that separated North America (left), and a shark and plesiosaur (right) that inhabited this sea. In addition to these giants, other twenty foot long swimming reptiles like mosasaurs lived in the sea and fed on fish and ammonites, relatives of squids and octopi. We often find the remains of the straight-shelled ammonites, called Baculites, in these shale deposits. *Ron Blakey has produced many maps like this of North America and the world through time that can be found online.

Fox Hills Sandstone

As the Western Interior Seaway receded, eastern Montana went from being covered by a shallow sea to being near shore and beach, with the seaway still present but located further to the south and east. The sediments that preserve this ancient beach make up the Fox Hills Sandstone Formation, and were deposited 70-68 mya. These yellow/tan, plain sandstone beds are very thick and contain few fossils in our field area, so we most often use the resistant, ledge-forming sediments at the top of this formation as a “marker bed” to help identify the  overlying Hell Creek Formation. Scientists think the Fox Hills Sandstone would have been home to a community of dinosaurs, mammals, reptiles, and early birds that would have come down to the shores of the shallow sea to drink and feed.

In Reid Coulee (northeastern MT), the Fox Hills Sandstone and Hell Creek Formation are exposed in one stratigraphic section. This sandstone is “concreted” or “well-indurated,” meaning it’s resistant to weathering and forms steep cliffs like the one pictured here. Photo courtesy of Dave DeMar, 2012.
In Reid Coulee (northeastern MT), the Fox Hills Sandstone and Hell Creek Formation are exposed in one stratigraphic section. This sandstone is “concreted” or “well-indurated,” meaning it’s resistant to weathering and forms steep cliffs like the one pictured here. Photo courtesy of Dave DeMar, 2012.

Hell Creek Formation

The Hell Creek Formation overlies the Fox Hills Sandstone, and is one of the two focus formations for the DIG researchers. This is one of the more famous and widely exposed formations from the Mesozoic Era in the state of Montana. This formation was deposited 68-66 mya and is primarily composed of “drab” and “somber” colored beds of tan sandstones, gray siltstones, and purple mudstones, with little to no coal. These sediments were deposited by freshwater and brackish rivers flowing from the proto-Rocky Mountains into the Western Interior Seaway. Paleontologists have used these sediments to infer an environment that looked something like the picture below. During this time, the environment was composed of large rivers that had rocky shores. Fossils from many animals are found here including invertebrates (like clams and snails), fishes, amphibians, mammals, turtles, crocodiles and dinosaurs. In fact, the first T. rex skeleton, discovered in 1902 by Barnum Brown, was found in the exact region of the Hell Creek Formation that the DIG Field School takes place!

The Hell Creek Formation during the late Cretaceous (left), and in 1902 when Barnum Brown, of the American Museum of Natural History, found the first Tyrannosaurus rex skeleton in the Hell Creek area. Note the preferred attire of the earliest paleontologists: a fur coat and bowler hat.
The Hell Creek Formation during the late Cretaceous (left), and in 1902 when Barnum Brown (right), of the American Museum of Natural History, found the first Tyrannosaurus rex skeleton in the Hell Creek area. Note the preferred attire of the earliest paleontologists: a fur coat and bowler hat.

Tullock Formation

The second focus formation, and the highest we find at the DIG Field school preserves the first Paleogene sediments, and was formed just after the K/Pg mass extinction event. This earliest Paleogene formation was deposited 66-64 mya and is known as the Tullock Formation (also known as the Tullock Member of the Fort Union Formation in some areas). This formation consists of thinner, vibrant and colorful beds with yellow, orange, and tan sandstones, siltstones, and mudstones, and lots of large coal seams (low-grade coals known as “lignites”). These beds are so thin, that from far away the different sediments look like stripes on the outcrop, and they have been dubbed “pajama beds” by someone who must have had striped pj’s! During this Era, rivers carried sediment from the mountains to the inland sea causing a swampy vegetative environment. Here, we find remnants of the mammals, reptiles, amphibians, fish, and birds that succeeded the dinosaurs, some of whom survived, and others who immigrated to the area shortly after the mass extinction.

The Tullock Formation of Montana during deposition in the early Paleocene (left), and as the pajama beds seen today (right). The Paleocene environment included sequoia trees, with a dense undergrowth of shrubs such as tea and laurel, with the addition of ferns and horsetails. Pictured above on the ground is Chriacus, a racoon-like omnivore. On the tree is Ptilodus, a surviving member of the multituberculates, primitive mammals often termed the "rodents of the Mesozoic. " Higher up in the tree is Peradectes, an early opossum-like marsupial. Figure and caption revised from The Book of Life: An Illustrated History of the Evolution of Life on Earth, by Stephen Jay Gould.
The Tullock Formation of Montana during deposition in the early Paleocene (left), and as the pajama beds seen today (right). The Paleocene environment included sequoia trees, with a dense undergrowth of shrubs such as tea and laurel, with the addition of ferns and horsetails. Pictured above on the ground is Chriacus, a racoon-like omnivore. On the tree is Ptilodus, a surviving member of the multituberculates, primitive mammals often termed the “rodents of the Mesozoic. ” Higher up in the tree is Peradectes, an early opossum-like marsupial. Figure and caption revised from The Book of Life: An Illustrated History of the Evolution of Life on Earth, by Stephen Jay Gould.

When you compare the deposits of the Hell Creek and Tullock formations, they look totally different, as do the inferred landscapes they represent! Can you differentiate the drab, somber, mudstones of the Hell Creek Formation from the more finely striped beds of the coal-bearing Tullock Formation in the photo below? Knowing where you are in time when you’re standing on the outcrop is a critical paleontological skill.

Actual Hell Creek and Tullock formation rocks that were formed during the Cretaceous and Paleogene Periods, respectively, in the northeastern Montana.
Hell Creek and Tullock formation rocks formed during the Cretaceous and Paleogene Periods, respectively, in the northeastern Montana, at a site the DIG Field School visits for fossil plants.

Next week we DIG into the fossils we will find during the DIG Field School!

Follow us

DinoByte Wednesday: Rock Formations

What is a geologic formation? We can think of a formation as a unit of rock. Each unit is a package of sediments, such as sand, silt, and volcanic ash, that cover an area large enough to be mapped, and contain a particular group of fossils. As time passes, different sediments are packed on top of one another forming different geologic layers of rock. So, the top layer of rock should be the most recent formation and the deeper we dig down vertically, the older the rocks and corresponding fossils, right?

It’s a bit more complicated than that, as sometimes rocks exposed at the surface are older (or younger) than you would expect. Changes in the earth’s landscape are represented in the geology of the different rock layers. Then, movement of deep molten rock pushing upward to form mountains can rearrange different rock layers and can tip originally flat layers. Similarly, changes in the movement of different bodies of water like streams, lakes, and oceans cut through the rock layers, erasing younger sediments on the surface, and exposing older sediments in stream and road cuts. The Grand Canyon is a picturesque example of geologic change, with billions of years of exposed rock, tilted layers, and river channels cutting through layers.

The Grand Canyon has many formations exposed (top) that differ in rock composition and appearance. These formations illustrate uplift and tilting events, as well as more than two billion years of rock deposition (bottom).
The Grand Canyon has many formations exposed (top) that differ in rock composition and appearance. These formations illustrate uplift and tilting events, as well as more than two billion years of rock deposition (bottom).

Having trouble visualizing how this works? Watch this short video of paleontologist Kirk Johnson as he explains how rocks can change over time, using pancakes!

In Montana, many of the formations are from the Mesozoic Era, but the site of the DIG Field School contains formations from both the Mesozoic and Cenozoic Eras (remember last week’s post?). By looking at the different rock formations we are actually trying to piece together clues about how the environments differed during each of these geologic time periods. We use the rock formations to guide our interpretation of the landscape and environments experienced by the dinosaurs, mammals, crocodiles, turtles, amphibians, and fish when they were alive here, 68-65 mya (million years ago).

An artistic rendition of a paleontologist as she uses exposed rock to infer past environments.
An artistic rendition of a paleontologist as she uses exposed rock to infer past environments.

So what packages of rocks do we encounter during the DIG Field School? Next week we’ll discuss the specific formations found at our field site, namely the Hell Creek and Tullock formations.

Follow us

DinoByte Wednesday: Geologic Time

Welcome to the first DinoByte Wednesday! In preparation for the upcoming 2014 DIG Field School, we’ll be publishing a series of blog posts on our DIG team, research, and fieldwork in the Hell Creek area of northeastern Montana. Today, we’ll discuss the geologic time scale as it relates to our field site.

The Earth is 4.6 BILLION years old, and the geologic time scale breaks this long amount of time into smaller units. These units, arranged from longest to shortest, are eons, eras, periods, epochs, and stages. The divisions between units are based upon major geological and paleontological events. At our field site in Hell Creek, Montana, the fossils indicate dinosaurs lived there during the Phanerozoic Eon, of the Mesozoic Era, during the Maastrichtian Stage of the Cretaceous Period.

Geologic Time Scale
Geologic Time Scale, modified from the Geological Society of America

The Mesozoic Era is the “Age of Dinosaurs,” and the dinosaur fossils we find in the field are 68 million to 66 million years old! We will find dinosaurs during the DIG Field School (as well as turtles, crocodiles, fish, mammals), but one of the things that makes our field site so special is that in this area there are rocks that preserve the last two million years that non-avian dinosaurs inhabited the earth, the layer that shows dinosaur extinction, AND the first one million years of the Paleogene Period.

The Paleogene Period (and the Paleocene Epoch) marks the start of the Cenozoic Era, the “Age of Mammals.” At our field site, in addition to Cretaceous dinosaurs, we find fossils of the mammals and other animals that survived the Cretaceous-Paleogene Mass Extinction that killed the dinosaurs (except birds). That makes this area one of the best places in the world to study dinosaur extinction AND the subsequent recovery of mammals.

Cretaceous-Paleogene rocks in the Hell Creek area of northeastern Montana
Cretaceous-Paleogene rocks in the Hell Creek area of northeastern Montana.

Most of the geologic layers in Montana that contain dinosaurs lay at the surface. Next week, we’ll DIG further into rock formations and uncover why these fossils sit at the surface when they are up to 60+ million years old.

Strata Column by artist Ray Troll, http://www.earth-time.org/trollart.html
Strata Column by artist Ray Troll

P.S. Are you wondering how we can determine the age of the fossils found in the Hell Creek area? These are much too old to use carbon dating, so we can use nearby rocks as clues, particularly layers of ash and coal. Stay tuned for more on dating fossils in a future DinoByte post!

(Most of this information came from the excellent book Dinosaurs Under the Big Sky by Jack Horner)

Follow us

2013 Field School in Pictures

Another Amazing Field School!

Last week, we returned from another amazing Field School. This year we had twice as many teachers! 19 K-12 teachers from Washington and Montana joined us in the Hell Creek badlands of eastern Montana to participate in on-going research into the extinction of dinosaurs and the rise of mammals.

Teachers arrived on the evening of the 26th, and we settled into camp. UW PhD candidate Dave DeMar had been keeping camp set up throughout the summer – 5 weeks already!

DSC01164Day One: an introduction to reading rocks and finding fossils. Teachers learned how to identify rock and rock layers, and how to prospect for small fossils by crawling fossil-rich areas.

Have you ever heard that geologists lick rocks? It’s true! It’s a great way to determine the size of grains in rocks, which helps you identify them. (Just be careful what you lick!)

 

 

 

DIG 2013 crawlingNo big dinosaur bones today ! The first day focused on “looking small” and crawling the site for the tiny fossils of mammals, fish and turtles that lived alongside the dinosaurs.

DSC01155

 

 

 

 

 

Hiking out to the dino sites!Day Two was our big dino dig! A morning rainstorm threatened to wash our plans away, but luckily it dried up early enough. We headed out a rugged road, then hiked the last mile to the dinosaur bone sites.

 

DSC01369Excavating the bones and protecting them with burlap and plaster stole the show.

The dinosaur dig was a success – several hundred pounds of everyone’s favorites, including Triceratops and duck-billed hadrosaurs, were excavated and hauled back to the Burke Museum of Natural History and Culture.

DSCN8074
Teachers and PhD candidate Jonathan Calede celebrate finishing the excavation of a dinosaur rib.

DSCN8083
Taking turns hauling out a several-hundred-pound dinosaur bone by hand.

DSCN8066
Jenny, elementary teacher from Monroe, hefts a jacketed dinosaur bone.

DSCN8068
Teachers load a jacketed dinosaur bone onto a hand cart. The weight eventually proved to be too much for the hand cart wheels.

 

To be continued…

Follow us

Back home – with bones!

Thank you, everyone, for another great Field School!

Group photo 2013 small croppedThe DIG Team is back in Seattle, more or less awake. We all took the weekend to relax and catch up on sleep, and hope you all got the chance to, too! Most of our gear is still in a huge pile in the lab, all the bones you all helped find, excavate, and haul out are tucked away in the Burke Museum. For the jackets, the next step is up to Bruce and his prep lab – he’ll open the jackets one by one and begin to prepare them (use tools to remove the rock matrix from around the bone). For the sediment, Greg’s lab will begin screening and picking some of the matrix – and a lot of it will end up in the DIG Boxes for you and your students to pick!

We’ve started a Flickr group to share photos and videos. We’ll have a nice recap of the Field School with lots of photos later this week!

Hiking out to the dino sites!
Hiking out to the dino sites!

 

Follow us

It’s ALIVE in Montana!

Here at DIG HQ in Seattle, the team is getting ready for a 2-day drive to Hell Creek! We’ve been busy putting together a few new resources for this year, including diagrams of the stratigraphy as well as a “cheat sheet” of living animals you might see wandering around Montana. That’s right, folks – not all of Montana’s inhabitants are millions-of-years-dead! In fact, what looks like a barren wasteland from far away is actually home to an amazing variety of animals, especially birds that feast on all the insects.

Ferruginous hawk
The ferruginous hawk’s name gives you a hint to identifying it in the field! (Photo from the USFWS.)

Among the birds you might see are bald eagles, golden eagles, red-tailed hawks, ferruginous hawks, and Swainson’s hawks. Ferruginous hawks (from the Latin Ferrugo meaning rust) hunt everything from amphibians and other birds to jackrabbits and ground squirrels by flying fast and low, or by swooping down from a hovering position or a perch. Like other raptors (the bird kind ;), they kill using the talons on their feet.

Common Nighthawk
The common nighthawk likes to perch branch-like during the day.

One bird you might hear but not see is the common nighthawk (Chordeiles minor). Like their name suggests, nighthawks are most active at dawn and dusk, when they scoops up insects from as many as 50 different species. Their owl-like eyes help them see better in low light, and their bat-like erratic flight is easy to recognize. Bark-like feather coloring makes the nighthawk difficult to see during the daytime, especially since they like to perch horizontal on tree branches. Click here to listen to a common nighthawk. Read more about them at Animal Diversity Web.

Killdeer
(cc) Dick Daniels, http://carolinabirds.org/

One bird you might be surprised to find hanging out in eastern Montana is the killdeer (Charadrius vociferus). These shorebirds actually have huge ranges. Killdeer live year-round in diverse habitats from the Gulf of Alaska to the Andes Mountains, migrating only if temperatures get below 50F (10C). Their name comes from their extremely loud and piercing “kill-dee” call. They eat a variety of aquatic and terrestrial invertebrates. Scroll to the bottom of this page to listen to their call and watch a video of a killdeer performing a “wounded bird” routine to distract a predator (with a videocamera) from its nest.

Follow us

We’re gearing up for summer!

We’re gearing up for this summer’s DIG Field School! We’ve ordered new hammers, and a few fun surprises. This afternoon’s task: compiling a list of Things That Bite or Sting! (Montana has surprisingly few, so they’re really not much to worry about.)

Follow us