Oncolite

Photographed by Michael P. Klimetz

UTAH

Oncolites are sedimentary structures formed out of oncoids, which are layered spherical growth structures formed principally by cyanobacterial growth. Oncolites are very similar to stromatolites, but instead of forming columns they form approximately spherical structures. Often the oncoids form around a central nucleus, such as a shell particle, and the calcium carbonate structure is precipitated by encrusting microbes. Oncolites are formed in the warm waters in the photic zone, but are also known in contemporary freshwater environments. Oncolites rarely exceed 10 cm in diameter.

Photographed by Michael P. Klimetz

Algal Oncolites

Early Cambrian

Lyndon Limestone

Pioche

NEVADA

Photographed by Michael P. Klimetz

Algal Oncolites

Early Cambrian

Lyndon Limestone

Pioche

NEVADA