Re-examination of a supposed 'archaeocyath' specimen from the Hyangsanni Formation, Okcheon Basin, Korea

Abstract

A supposed 'archaeocyath' specimen from the Hyangsanni Formation of the Okcheon Basin (Okcheon Metamorphic Belt), Korea, reported about 50 years ago, has previously been used to constrain the depositional age of the metasedimentary succession in the basin. However, a re-examination of the specimen reveals that it lacks the typical morphology of archaeocyaths. A detailed petrographic and microfabric analysis of the specimen, combined with a review of outcrop structures and microstructures of the dolomitic marble in the Hyangsanni Formation indicates that the supposed archaeocyath- like shape of the specimen was caused by deformations and metamorphic reactions. The Cambrian age of the Hyangsanni Formation should therefore be re-examined on the basis of unequivocal palaeontological evidence and/or radiometric dating.