[B-PT02_1PO1] Biocalcification and the Geochemistry of Proxies

[BPT02-P01] New evidence for halite co-precipitation during coral calcification

*Satoko MOTAI¹, Takaya NAGAI¹, Jun KAWANO², Tsuyoshi WATANABE¹ (1.Hokkaido University Faculty of Science, 2.Creative Reseach Institution, Hokkaido University)

Keywords:reef-building coral, calcification, biomineral, aragonite

In the last JpGU Meeting, we reported halite grains in coral skeleton through the observation of massive coral skeleton of Porites lobata by Analysis Transmission Electron Microscope (ATEM). Each halite grain typically shows a square shape and its grain size is around 80 nm. The spatial distribution of halite grains is inhomogeneous and seems to be independent on the arrangement of growth lines.We observed new evidence that the halite grains in coral skeleton could precipitate during coral calcification. The electron diffraction patterns from some selected areas including both an aragonite and a halite grain show that there are special crystallographic orientation relationships between them. In consideration of misfit ratios between some selective bond lengths of halite and those of aragonite, crystallographic orientations of halite and aragonite seem to be a kind of hetero-epitaxial relationship.This is the first observation for a primary precipitated mineral phase other than aragonite in coral skeletons. The halite phase in coral skeleton will provide a new perception for understanding the process of coral calcification.