Crinoid lime

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Trochitic limestone from Arkansas , USA

Crinoid limestone is a biogenic limestone ( biogenic sediment ) formed on the sea ​​floor , which consists of the fossilized remains of sea ​​lilies and starfish (Crinoidea).

Sea lilies and hair stars

This class of echinoderms (Echinodermata) , which still exists today, is divided into the freely moving ( vagile ) forms, which are referred to as "hair stars", and in contrast to the ( sessile ) "sea lilies" attached to the seabed with a multi-limbed stem . A crinoid limestone, which mainly consists of these petrified stalk limbs, the trochites , is called trochitic limestone.

Rock formation

The calcareous hard parts of the crinoids sank to the ground after their death and over time they formed increasingly thick deposits . During the rock formation , the loose material gradually compacted and solidified into limestone. Due to plate tectonic movements , rocks such as crinoid limestone can be transported over great distances and unfolded in the course of mountain formation . Examples of this are the Dolomites and the Northern Limestone Alps, where the fossil crinoid remains, which have solidified to form a rock, spread out again on the surface.

Together with deposits formed by shellfish and especially by tiny calcareous algae and similar plankton , crinoid limestone - z. B. in the formations of the Werfener layers and the main dolomite - can reach a thickness of up to 2000 meters.