| Summary: | Crinoidal limestones in the Tethyan Jurassic often occur capping reef or carbonate-platform successions, and these bioclastic deposits commonly exhibit a lensoid form. They may also occur in tectonic fissures or as turbidites in basinal sequences. Their age is commonly Liassic, though they may be younger. The crinoidal lenses are here interpreted as sand-waves formed on current-swept pelagic seamounts; and a parallel may be drawn with the Blake Plateau where partly lithified carbonate sand bodies, albeit composed of globigerines and pteropods, have recently been described. The Liassic was a time when many seamounts were formed by block-faulting of reefs and carbonate platforms, and this explains the widespread distribution of crinoidal deposits of this age. "Autochthonous" crinoidal calcarenites may characterise an early "shallow-water" phase of seamount evolution. The presence of kaolinite in many of the west Sicilian examples of this rock type is taken as suggesting the former presence of exposed and lateritised areas, "oceanic islands", which may also have furnished a food supply for the crinoid gardens. The formation of nodular crinoidal limestones, which occur in some Tethyan localities, is attributed to diagenetic segregation of calcium carbonate. © 1971 Ferdinand Enke Verlag Stuttgart.
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