A brief introduction to biogenic and organo-sedimentary structures

Abstract

Algal-laminated structures, termed stromatolites, are most prolific at the present day in very shallow waters of both marine and non-marine environments. In the marine environment they are characteristic forms in the shallow subtidal to supratidal zones of tropical to subtropical carbonate environments, although colonisation of siliciclastic shorelines has been increasingly recognised in recent years (Schwarz et al. 1975, Gunatilaka 1975). Stromatolite surface micromorphology varies according to the type of algae present and to ecological position in a given area (e.g. Logan et al. 1974, Kinsman amp; Park 1976), but there is no general rule when different areas are compared. Gradations of large-scale growth forms are related to degrees of wetting, frequency of exposure, and intensity of current action. Algal structures include flat, crinkle, cinder, polygonal, dome, blister, pillar and club forms (Figs. 10.1 & 10.2).