Stop #7 - Niobrara formation, Smoky Hills member. Limestone shales, also deep in the Western Interior Seaway with abundant marine fossils. This image shows cracking, slipping and recementing with calcite that occurred much later in time. Light color indicates more carbonate ( > 50%) than mud.
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Niobrara formation, Smoky Hills member. Darker shales indicates more mud ( > 50%) than carbonates.
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Niobrara formation showing darker shales (foreground) and lighter shales (top of hill).
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Niobrara formation, Smoky Hills member. Clams, forams (single-celled organisms that construct shells) and oysters are abundant here. Note: After death, the abundance of forams in sediment samples can reach tens of thousands of individuals per cubic centimeter!
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Niobrara formation, Smoky Hills member. This is a side view of a giant clam called "Platyceramus", sometimes referred to as "Dinner on the half platter" because of their size - often over 2 feet in diameter. Many specimens of Platyceramus have been found with fossil fishes (see arromw in image) inside. Scientists believe the fish found shelter within the clam. These giant clams also serve as a home to clusters of barnacles and oysters which are often found attached to the clam shell (source: Natural History Museum of Los Angeles County)
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Giant clam "Platyceramus" in Niobrara formation, Smoky Hills member.
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Oysters in Niobrara formation, Smoky Hills member.
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More oysters in Niobrara formation, Smoky Hills member.
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Close up of Platyceramus showing prism crystal structure of fossil. Niobrara formation, Smoky Hills member.
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Close up of Platyceramus showing prism crystal structure of fossil. Niobrara formation, Smoky Hills member.
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Tan/yellow line is a layer of volcanic ash. The ash came fell on the surface of the ocean and settled to the bottom. Volcanic ash is a great time marker because it can be accurately dated using radiometric techniques. Niobrara formation, Smoky Hills member.
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Summarizing the geological concepts seen during the day. Sitting on the Niobrara formation, Smoky Hills member and looking out over the vast expance of the Pierre Shale. Haystack Butte off in the distance at left.
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