Oncoids: Comment to Recent Developments

Abstract

Oncoids are a group of algally (red algae excepted), cyanobacterially and bacteri-ally coated grains which originate(d) in marine and freshwater phreatic zones, although some workers prefer to use the term oncoids for all coated grains which are not ooids. Recent oncoids have been described from the lacustrine, fluvial and marine environments. The marine oncoids, occurring in the intertidal and shallow subtidal environments, are non-lithified, as opposed to hard freshwater oncoids. As noticed by Monty (1972), recent freshwater forms are closely similar to the ancient marine oncoids (see Flügel 1978, Tables 15 and 16). This in turn may be related to the replacement of porostromate oncoids by spongiostromate oncoids in marine settings in the Jurassic (see Peryt 1981, with discussion). At that time, porostromate oncoids (and mainly Girvanella oncoids — see Peryt 1981, Tables 1 and 2, and papers by Biddle, Bowman, Catalov, Poncet, and Tichy, this vol.) and spongiostromate oncoids existed in different environmental settings.