Paleontologists use the German term Lagerstätte [storage place] for fossil sites with exceptional preservation and abundant fossils. Such deposits are rare worldwide. Stonerose in Washington state is considered an example of a Lagerstätte for plant fossils. Now a new Lagerstätte for marine animals (invertebrates and vertebrates) has been found at Ya Ha Tinda in Alberta, Canada, and dates from the same time period as similar marine fossil sites in Italy, Germany, and Great Britain. The special preservation (including soft tissues) may be the result of low oxygen levels in the water at the time, preventing decay before the animals were buried in sediment.
Rowan C. Martindale, Theodore R. Them II, Benjamin C. Gill, Selva M. Marroquín, and Andrew H. Knoll (2017) A new Early Jurassic (ca. 183 Ma) fossil Lagerstätte from Ya Ha Tinda, Alberta, Canada. Geology 45:. 255-258, doi:10.1130/G38808.1 http://geology.gsapubs.org/content/45/3/255.abstract