Not all rhodoliths need a bed–depositional mechanisms in shallow water Sporolithon nodosum rhodoliths from the Whangaparaoa peninsula (North Island, New Zealand)

Résumé fourni par la source

ABSTRACT Rhodoliths, formed by crustose coralline algae (CCA), are prominent components in carbonate platform deposits, contributing to the characteristic rhodalgal facies. Their formation is influenced by both biological and physical factors, and under specific conditions, they can accumulate, forming extensive rhodolith beds. This study examines the depositional mechanisms underlying the formation of monospecific ( Sporolithon nodosum ) shallow‐water rhodoliths from the Whangaparaoa Peninsula, North Island, New Zealand. The findings suggest that these rhodoliths originate in subtidal rocky channels at approximately 5 m depth, by the encrustation of nuclei derived from surrounding geological strata. Following their formation, these rhodoliths are transported into intertidal channel systems and eventually deposited in supratidal beach areas. Notably, the structure, morphology and composition of rhodoliths across these three depositional settings exhibit minimal variation, suggesting that the rhodoliths belong to a strongly interconnected coastal system with only brief intervals between translocation events. In this context, the study provides a sedimentological model for the development of rhodoliths in a coastal setting. Furthermore, it challenges the presence of a significant rhodolith bed sensu stricto in deeper offshore waters, as exploratory diving surveys revealed extensive sand deposits that hinder rhodolith development in these areas.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.