Early cementation and lithification in intertidal cryptalgal structures, boca jewfish, Bonaire, Netherlands Antilles
On the shore of the Boca Jewfish area of the Lac, Bonaire, N.A., blue-green algae perform a sediment-stabilizing and binding function resulting in a wide variety of cryptalgal structures. The morphology and zonadon of these structures is related to variation in desiccation, sediment influx, water agitation and algal "species." The zunation of intertidal structures consists of stromatolites and oncolites, lithifiod nodules, smooth mat and tufted mat. A cryptalgal crust pavement is found in protected supratidal- areas. In the middle intertidal zone, cryptalgal nodules are lithified during intertidal exposure by pervasive pore-reducing, micritic, high-Mg calcite cement, which is pendent in its distribution around sediment grains. Calcium carbonate cement also occurs as rinds on algal filaments. Precipitated calcium carbonate is found in minor amounts on filaments and mucus within tufted and smooth mats. The preservation potential of the nodules is enhanced by rapid and early cementation. The other structures, not lithified by significant amounts of early cement, have lower preservation potentials. The normal marine salinity of the Lac indicates that growth of cryptalgal structures in fresh, brackish, or hypersaline waters is not essential for their early cementation and lithification.