Cyanobacteria fix and bind sediments and generate versicolored, laminated patterns in quartz sand flats. They are developed in the lower supratidal zone (between mean high water and mean high water springs). The cyanobacteria mats protect the sediments from erosion and desiccation and provide food for marine and terrestrial invertebrates. Burrowing and grazing polychaetes, amphipods, and gastropods are present as well as a diverse meiofauna. The bioturbation structures are described. At some places the population density of the macrofauna averages 20,000 individuals per m 2 . Typical are smooth surfaces and erosional pockets with rippled sand. The deposits consist of laminated sand in which organic-rich mat generations are intercalated. The sediment is medium to fine-grained sand. The development of versicolored systems by interaction of migrating cyanobacteria and episodic low-rate sedimentation was studied in the laboratory. The depositional record reveals characteristics from both, the terrestrial and the marine surrounding. There are bioturbation structures from marine and terrestrial burrowing animals, hard skeletal parts from shelled marine organisms and plant roots of halophytes. Fenestrae produced by burrowing beetles are observed. The described mats characterize the type of quartz sandy potential stromatolites.

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