Mya Seaway Research Paper

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INTRODUCTION The Cretaceous Period, spanning 65.5-146 million years ago (Mya), was a world different from what we are familiar with today. Planetary changes during this period included the extinction of dinosaurs and drastic global warming. The breakup of the super continent Pangea had started about 30 Mya, and seaways had begun to form and cover landmass that had once been a part of the super continent (Geologic Time). Today, scientists know that one of these landmasses, the North American continent as we now know it, was at one point covered by a vast inland sea known as the Western Interior Seaway. The Seaway stretched from the Arctic Circle down to the warm waters of the Gulf of Mexico, and spanned most of the continent. This paper will…show more content…
Geologists have found that the oldest exposed rocks in the national park to date back to 75 million years. The formations resulted from sediments that were largely swept into the area due to the rise of the Rocky Mountains. This eventually resulted in a rising of land above sea level. The deposits consisted of different strata of dark shale beds, many containing fossils of marine life from the Seaway (Stoffer 2003). Pierre shale is a formation of marine origin from the Cretaceous period that resulted from the Western Interior Seaway. The formation stretches from New Mexico to North Dakota, is up to 700 feet thick and rests on top of the Niobrara formation. The Niobrara Formation is a geological formation that appeared around 87-82 Mya during the Cretaceous, also a result of the Western Interior Seaway. It is composed of two layers: a chalk and limestone layer. The chalk was formed due to calcium carbonate left behind by decomposed shells of microscopic algae that populated the Seaway. This layer of the Niobrara contains much evidence of life of vertebrates and aquatic life, including birds. The limestone layer is a thick layer of limestone separated from the chalk layer by shale. The limestone layer also contains many fossilized remains, but is best known for having marine reptiles that have been preserved rather well. The currents from the different seas as well as the draining of surface water into the seaway were important in the formations of these layers and the fossilization of marine life (Colorado Parks and

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