The Venado Formation is composed of more than 300 m of mudstone, siltstone, sandstone, limestone, volcaniclastics, and coal beds. The coal beds are of unknown lateral extent and mainly occur in the middle part of the formation. Diatoms are a useful microscopic tool for identifying the depositional environments. They indicate that swamp environments were intermixed with lacustrine environments during the formation of the peat deposit or that the coal records environmental changes through time. -from Authors
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Diatoms and tonsteins as paleoenvironmental and paleodepositional indicators in a Miocene coal bed, Costa Rica.