Sediments are laid down in rivers, lakes, oceans, and deserts in layers. And these layers are laid down in sequence. So, for example, the lowest layers are the oldest layers and ones laid on top of them are the younger layers. Now, here in Dinosaur Provincial Park we have lots of good evidence of this Principle of Superposition. Which is what forms the basis of stratigraphy, we have. Three layers of strata here, three different rock formations. The highest one is the Bearpaw Formation. It's about 70 million years old. And the Bearpaw Formation was laid down in an ocean that covered much of North America about 70 million years ago. Most of the rocks we see behind us now, though, are Dinosaur Provincial Park Formation. The Dinosaur Park Formation was laid down basically on lands by rivers and lakes and marshes and swamps and those kinds of things. And the rocks are quite different because they're coarser and they show different structures in them. So the whites represent river channels for example, and the grays represent the over-bank deposits in between the rivers. These were laid down roughly 72 million years ago. Below the Dinosaur Park Formation you can see a ledge of red iron stone and below that are these cliff forming sand stones, which are yellowish in color. And this represents the Oldman Formation. It's a slightly older formation and it formed under a slightly drier environment and the sediment was coming from a different source. And because of that the rocks look a little bit different, and because it represents an older time, about 77 million years old the dinosaurs we find in that formation are very different than the ones we find in the Dinosaur Park Formation. The rocks themselves have their own characteristics, and we can follow them for great distances. And, we an generally, of course, only see them where the rocks are exposed. But the Dinosaur Park formation extends all the way down to the United States border, whereas the Bearpaw Formation extends almost all the way through Western North America. >> Here's a view of the Alberta Badlands. We've labeled the major rock formations for you. Which layer of rock is the youngest? Is it the Bearpaw Formation, the Dinosaur Park Formation, or the Oldman Formation? The Bearpaw Formation is the youngest, as it is the highest formation. The dinosaur park formation is older and the Oldman Formation is the oldest. All of these rock layers were laid down during the Cretaceous period of the Mesozoic era. It's pretty easy to interpret the stratigraphy of an area where the formations are horizontal. Like they were when they were deposited. But in some places, especially mountains, rock formations that were once horizontal get tipped, crunched, and folded. It is much more complicated to interpret the stratigraphy in these areas. Additionally, igneous rocks can cut across the horizontal layers of sedimentary rocks from past eras making interpretations very difficult. And to make things even more interesting, folded rocks and mountains can then be worn down by erosion and then new rocks can be deposited on top. For this course, we want you to understand that younger rocks are deposited on top of older rocks. When geologists and paleontologists talk about geologic formations, we use diagrams like this stratographic column to show the relationships between formations. This diagram shows the three formations visible in Dinosaur Provincial Park. We put the old information at the bottom and read the diagram from the bottom to the top, just like we would if we were looking at a cross section of the Earth. We also use special symbols to tell us what kinds of rocks each formation has. For example, the dots represent sandstone, and the dashes represent shales. Now, let's add some dinosaurs to the mix. Not all of the species of dinosaurs found within Dinosaur Provincial Park are from the same time period. Some dinosaurs are only found in one of the three formations. And some of the dinosaurs are only found in part of the Dinosaur Park Formation. This is easy to see using the horned dinosaurs. No ceratopsian dinosaur skeletons have been found in the marine Bearpaw Formation. Although we do occasionally find dinosaur bones that must have washed out to sea in the cretaceous. In the upper part of the Dinosaur Park Formation we find the ceratopsian Styracosaurus, which has a very spiky frill. In the lower part of the Dinosaur Park Formation, is Centrosaurus, which has forward pointing hooks on the back of its frill. And in the Oldman Formation, is Coronosaurus, which has a cluster of small spikes on the back of the frill. Which of these ceratopsians is the oldest? Is it styracosaurus, centrosaurus, or coronosaurus? Coronosaurus is found lower in the stratigraphic column then centrosaurus or styracosaurus. So, it is the oldest ceratopsian in this diagram. C is the correct answer. The duck-billed dinosaurs, from Dinosaur Provincial Park, show the same sort of pattern as the ceratopsians. Brachylophosaurus is known from the Oldman Formation. Griphosaurus is known from the lower part of the Dinosaur Park Formation. And prosaurolophus is known from the upper part of that same formation. >> Dinosaur Provincial Park is one of the very best areas where we can do this kind of fine-scale analysis. We have so many specimens here that can be identified, and there are so many layers of volcanic ash from which we can get good radiometric dates. What they clearly show us is that even within this relatively small package of rock, we don't find the same dinosaurs all the way through the formation. There are certain dinosaurs that are characteristic of certain levels. When you extend these studies beyond Dinosaur Park, beyond Alberta, to all other parts of the world, we see the same kind of patterns of changes over time and changes in different geographic areas. A lot of dinosaurs picture books and movies mix up dinosaurs from different places and different times. Which of these sets of dinosaurs do you think lived at the same place at the same time? Stegosaurus and tyrannosaurus, triceratops and pachycephalosaurus, or velociraptor and argentinosaurus? The answer is B, triceratops and pachycephalosaurus. Velociraptor and argentinosaurus lived on different continents at different times. Tyrannosaurus and stegosaurus were separated by more time, almost 90 million years, than tyrannosaurus and humans, almost 65 million years.
