Carbonate Cementation in Coralline Algal Nodules in the Skagerrak, North Sea: Biochemical Precipitation in Undersaturated Waters

摘要: North Sea sublittoral carbonate sediments in the Skagerrak are affected by submarine dissolution which attacks skeletal grains of aragonite, Mg-calcite, and low-Mg calcite, coarse detrital calcite limestone clasts. All post-mortem changes destructive intragranular space hollow microborings remains empty secondary after disappearance cavity-forming organisms. As a consequence, boring--filling micritization mechanism does not operate these waters. Evidently, marine environment is undersaturated with calcium carbonate. Yet, this environment, cement forming various kinds openings within living coralline algal nodules (rhodoliths) consisting mostly Lithothamnium . The internal composed aragonite needle cement, spherulitic Mg-calcite fringe micrite, intraskeletal micro-druses, latter exclusively skeleton proper. Cement growth related to metabolic activities carbonate-secreting red algae. After death algae, rhodoliths their undergo dissolution. Theoretically, precipitation may take place several steps, involving accessory organisms rhodoliths, for example, unicellular green or bacteria. However, all observations indicate that primary cause cementation lies life processes frame-building thin films encrusting algae exceptionally well suited as instruments microenvironmental control. Few passages lead interior except through sieve filaments. Furthermore, secrete much 30-40% total photosynthetic product form extracellular metabolites. data suggest biochemical influence be an important reefs crusts environment.