Algal stromatolites from the Late Precambrian of Sweden

Stromatolitic structures from the Late Precambrian Visingö Beds are described. The mode of development of these sedimentary-biogenic structures and the problems related to their characterization in a system of formulas are discussed. The study of the stromatolitic structures and their associated sediments proved that the stromatolitic structures LLH (vertically arranged, lateral-linked hemispher-oids) and SH (discrete, vertically stacked hemispheroids) could develop together on the same stromatolite dome, depending on different degrees of exposure to the action of water currents in an intertidal environment. Superimposed LLH and SH structures in the Visingsö Beds may indicate periodical changes in current activity depending on repeated periodic events such as tidal and/or storm waves.