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How did Jurassic rock layers preserve fossils in the Morrison Formation?

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Jurassic paleogeography — Jurassic Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Jurassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The Morrison Formation preserved fossils through the rapid burial of organisms within a variety of terrestrial environments, including rivers, streams, lakes, mudflats, swamps, and alluvial plains.1

During the Late Jurassic, these areas covered the western interior of North America, receiving sediments derived from newly uplifted western mountains. The formation consists of mudstones, sandstones, and conglomerates that effectively entombed plant and animal remains.12

Many dinosaur fossils are found as jumbled, partially disarticulated skeletons, suggesting that carcasses were transported by streams and subsequently buried on sandbars. In addition to these sedimentary processes, the presence of volcanic ash beds within the formation has provided scientists with a means to date these deposits using radiometric techniques.13