Fossil flowerThe exceptional preservation of this Eocene (56-34 million years ago) flower is due to

Fossil flowerThe exceptional preservation of this Eocene (56-34 million years ago) flower is due to the fine grained nature of the limestone in which it was entombed. The specimen comes from the Green River Formation covering parts of the North American Midwest towards the end of the uplift of the Rocky Mountains. The formation was deposited in the intermontane basins between the chains of growing peaks, and includes a mixture of terrestrial swamp and river sediments and deep lake sequences, which were surrounded by swampy areas with a profusion of warm climate plants. The formation is world famous for its fossil freshwater fish and the formation dates from between 53.5 and 48.5 million years ago.Some of these plants turned into coal seams, while the spring algal blooms in the lakes produced oil shales in the anoxic lake bottom oozes. Some of the lake sediments are varved, with fine laminations that record seasonal changes between organic rich dark sediments from the short mountainous growing season and thin layers of light coloured sediment deposited in winter from suspended particles in the lake water. The best preserved fossils are found in these varved oozes, which are made of very fine grained limy mud. The fossils are well dated due to layers of volcanic ash interleaved in the sediments that were erupted from the nearby Yellowstone caldera and San Juan volcanic field. The area is designated as a Lagerstatte, a German word used to denote an area of rock with exceptional or important fossils.LozImage credit: NPShttp://geology.com/articles/green-river-fossils/[__](https://www.facebook.com/TheEarthStory/photos/a.352867368107647/853838988010480/?type=3&theater#) -- source link

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