Morphology and development of some microbialites on coastal cliffs in central Norway

Microbialites from coastal cliffs on the west coast of central Norway are described and categorised according to their morphology and mineral composition.Five morphotypes are described (botryoid, columnar, bush-, club-and mushroom-shaped) and categorised according to their dominant mineral content, with amounts of calcite and gypsum as opposing endpoints.More detailed analyses of the most common type, the botryoid morphotype, suggested that certain stages of establishment and development are likely connected to biomineralisation.Analyses using light microscopy and scanning electron microscopy (SEM) indicated that microbes were involved in the calcification and development of the botryoid microbialites and their laminated structure.Analyses also demonstrate the possible development of different morphotypes from the botryoid type.All morphotypes examined display laminated internal structures which could potentially be used as environmental proxies in studies of cyclic growth variations.Radiocarbon dating, as well as observations of the establishment of microbialites on an artificial surface after two years, indicate recent formations.The morphotypes described represent examples of microbialites similar to speleothems.Knowledge gained from this study of recent microbialites might be of relevance as analogues for studies of the fossil record.(2020).Dupraz et al. (2011) have classified microbialites according to their macrostructure using the following categories: club-shaped, columnar, dome, knob, flat and 'mini' conoform.Having a global distribution, microbialites are most common in marine and freshwater environments, cf., White (2020).There are very few investigations of recent microbialites from northern, terrestrial, coastal environments (e.g., Cooper et al., 2022) as most are from marine, saline or aquatic temperate