One of the most famous formations is the Niobrara Chalk. This formation is exposed in northwest Kansas and southern Nebraska. Formations are sometimes divided into members, subsections of the formation based upon its rock type. The Niobrara Chalk has two members: the lower Fort Hays Limestone and the upper Smoky Hill Chalk. It is the Smoky Hill Chalk which is best known for its fossils.
The sediments that comprise the Niobrara Chalk were deposited in the Western Interior basin during the Late Cretaceous. At that time sea levels rose and the interior of North America was inundated by a shallow sea, the Western Interior Sea. The sea cut North America in half by spreading from the Gulf of Mexico to the Canadian Arctic. Volcanoes to the west, in what is now Utah and Nevada, spewed ash into the sea and sediments eroded from mountains along the western coast were washed into the sea by rivers. What is today Kansas was much closer to the eastern shore of the sea, a low alluvial plain, also gently washing sediment into the sea basin.
Image from Hattin, 1982.
The upper member, the Smoky Hill, was deposited from 87 to 82 million years ago, so it preserves a five million year window into the past. Elsewhere we discussed that the Cretaceous sea had a wealth of planktonic organisms. Many of those organisms had calcium carbonate-based shells and body parts, which furnished a steady supply of material to sink to the sea floor. The consistent supply of sediment, both from land and sea, and conditions at the sea floor allowed for the excellent preservation of animals. Those that died and sank to the bottom were rapidly covered by the rain of sediment and entombed until today.
And the diversity of organisms preserved is amazing. In almost every museum with fossils that I have been in, I recognize fossils from Kansas. Giant marine reptiles (mosasaurs and plesiosaurs), flying reptiles (pterosaurs), great toothy fishes, large turtles, and toothed diving birds have all been found. Each of these groups has a very interesting story to share, and we will explore many of them here. An extensive website on fossils from the Niobrara Chalk can be found at OceansofKansas.com.
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April 2nd, 2010 on 8:01 AM
[...] WERE REQUIRED TO HARVEST ENOUGH PLANKTONIC (CULTURABLE) ORGANISMS TO YIELD POSITIVE RESULTS. …Niobrara Chalk | Boneblogger: Fossils, natural science, and …The Niobrara Chalk is one of the best known geologic formations, and is especially known for its [...]
June 9th, 2010 on 11:24 AM
[...] A geologic formation is a formal unit, technically called a lithostratographic unit. That fancy word simply means that rocks are grouped by similar lithology, or rock type. For example, during the Late Cretaceous the last inland sea across the mid-continent of North America (a specific environment) deposited thick accumulations of chalk and shale. Today, we can lump specific sections of that collection of rock (lithology) into a single formation and call it the Niobrara Formation. [...]
June 10th, 2010 on 8:47 AM
[...] years by George F. Sternberg, famed fossil collector. He spent his free time out in the chalk, the Niobrara Formation of western Kansas, collecting the fish and swimming and flying reptiles that left their remains [...]
June 24th, 2010 on 5:44 PM
[...] Posts: Formations Niobrara Chalk My National Geographic moment Anurognathus, Hatzegopteryx, Kansas, Mesozoic, O. C. Marsh, [...]
September 8th, 2010 on 7:13 PM
[...] Plains, and numerous specimens have been preserved in museums all over the world (see posts on the chalk formation and on rock formations in general). Yet despite the great numbers of specimens collected, we still [...]