35 GEODIVERSITAS • 2012 • 34 (1) © Publications Scientiiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com KEY WORDS Dasycladales, Bryopsidales, Halimeda, bioherm, euphotic zone, phylloid, aragonite, calcite, porosity, epigenesis, cementation. Granier B. 2012. — The contribution of calcareous green algae to the production of limestones: a review. Geodiversitas 34 (1): 35-60. http://dx.doi.org/10.5252/g2012n1a3 ABSTRACT Calcareous green algae (CGA) are an artiicially united but highly heterogeneous group of large unicellular benthic algae with one character in common: all have the capability of secreting a calcareous coating on the outer side of the cytoplas- mic envelope. Today, they are a major contributor to carbonate sedimentation at all scales from clay-sized particles (aragonitic needles) to coarser grains (sand and gravel) and even to plurimetric sedimentary structures. here are fossil analogues to the features listed above. Phycologists know best Halimeda, Penicillus, Acetabu- laria and Cymopolia; micropaleontologists and carbonate sedimentologists are most knowledgeable about Acicularia, Clypeina, Neoteutloporella, Salpingoporella, Anthracoporella, Boueina, and Eugonophyllum. he CaCO 3 precipitated to form the coating is generally aragonite (the orthorhombic form) but there are short periods in the geologic record during which its calcite variant (the rhombohedric form) existed contemporaneously in discrete species. Recent studies on Halimeda have shown that some of the Bryopsidales have the capability to calcify strongly in the lower portion of the euphotic zone (where respiration becomes more im- portant than photosynthesis in the process of mineralization) and to produce positive sedimentary reliefs (bioherms) in situ below the fair-weather wave base. Previous models of paleoenvironments considered the presence of Dasycladales or Bryopsidales to indicate shallow-water, that is the upper euphotic zone (from the sea surface down to –25 m), and predominantly low-energy, protected, lagoonal environments. When the algal remains were found in grain-supported facies, they were taken to have been subjected to dynamic transport and therefore indicative of high-energy environments of deposition. he new deeper-water inds have changed interpretations of the environments ascribed fossil algae. A current con- ception is that ancestral inarticulated Bryopsidales could have grown at depths as great as –120 m (near the base of the lower euphotic zone). his preliminary review concludes with suggestions about ields for continuing investigations. Bruno GRANIER Université de Brest, CNRS, IUEM, Domaines océaniques UMR 6538, Département des Sciences de la Terre et de l’Univers, and Université de Bretagne occidentale (UBO), UFR des Sciences et Techniques, 6 avenue Le Gorgeu, CS 93837, F-29238 Brest cedex 3 (France) bgranier@univ-brest.fr The contribution of calcareous green algae to the production of limestones: a review