Article: Sedimentological factors affecting the distribution and growth of Viséan caninioid corals in north-west Ireland
J. A. E. B. Hubbard
The Visean limestone-shale sequences of north-west Ireland contain a characteristic distribution pattern of alternating coraliferous and 'barren strata' (called 'inter-beds'). The varied geniculation in the assemblages of prone solitary caninioids in both types of strata are interpreted from comparison with observations and experiments on modern corals, as showing a close relationship of coral growth to stability, sedimentation, and penecontemporaneous erosion of the soft lime-mud substrate. Two types of lime-mud are found in the axial region of the corals: fine homogeneous micrite flooring the tabulae is regarded as original infill, while extraneous biomicrite, introduced through openings caused by penecontemporaneous erosion and boring sponges and bryozoa is evidently of subsequent origin. Adverse environmental conditions during skeletogenesis are believed to be responsible for the widely spaced tabulae, conspicuously thin skeleton, and suppression of the dissepimentarium, which are irregularly developed and often associated. The effects of compactional loading and diagenesis are outlined. Each bedding-plane strewn with adult caninioids is regarded as a winnowed death assemblage involving many different generations and accumulating during periods of slow deposition. The difficulties for corals living on an unlithifled sea bed are discussed and some wider regional implications considered.