The ‘Orsten’—More than a Cambrian Konservat-Lagerstätte

• In several areas of southern Sweden, limestone nodules, locally called Orsten occur within bituminous alum shales. Theseshales and nodules were deposited under dysoxic conditions at the bottom of what was most likely a shallow sea during the lateMiddle to Upper Cambrian (ca. 500 million years ago). Subsequently, the name ‘Orsten’ has been referred to particular, mainlyarthropod, fossils from such nodules, and, in a wider sense, to the specific type of preservation of minute fossil through secondarilyphosphatization. This preservation is exceptional in yielding uncompacted and diagenetically undeformed three-dimensional fossils.‘Orsten’-type preservation resulted from incrustation of a thin external layer and also by impregnation by calcium phosphate and,therefore, mineralization of the surface of the former animals during early diagenesis. Primarily, this type of preservation seems tohave affected only cuticle-bearing metazoans such as cycloneuralian nemathelminths and arthropods. ‘Orsten’ preservation in thissense seems to be limited by size, in having yielded no partial or complete animals larger than 2 mm. On the other end of the scale,even larvae 100

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‘Orsten’

Exceptional preservation

Evolution

Phylogeny

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