Oolitic limestone probably formed by microbes, not by grains rolling on the seafloor and accumulating layers of sediment

A cross section of the ooids inside Rogenstein oolite. Photo: ANU

A new study based on mathematical simulation explains how biofilms were mineralized up to 340 million years ago

Oolitic limestone is a popular building material around the world and is almost completely made of millimeter-sized spheres of carbonate called ooids.

A new study led by scientists from the Australian National University (ANU) found these egg-like mini-structures were made of concentric layers of mineralized microbes that lived up to 340 million years ago, predating the dinosaurs. It contradicts the popular ,snowball theory’ that ooids were formed by grains rolling on the seafloor and accumulating layers of sediment.

„Our mathematical model explains the concentric accumulation of layers, and predicts a limiting size of ooids,“ says Professor Murray Batchelor from the ANU.

Details of the mineralization process are described in the online magazine IFL science: The process starts with a biofilm formed by microbes whose components may grow to extreme size under favorable nutrient conditions. When these microorganisms die, they are mineralized. Precipitated calcium carbonat cements the components together to limestone.

Rogenstein oolite from Germany. Photo: Lannon Harley, ANU

„Many oolitic limestones form excellent building stones,“ Dr Burne from the ANU Research School of Earth Sciences says. „Mississippian oolite found in Indiana in the US has been used to build parts of the Pentagon in Virginia and parts of the Empire State Building in New York City.

„Jurassic oolite in England has been used to construct Buckingham Palace and much of the City of Bath, the British Museum and St Paul’s Cathedral.“

And: „Our research also highlights another vital role that microbes play on Earth and in our lives,” Dr Burne concludes.

Other researchers involved in the study were Professor Bruce Henry from the University of New South Wales, Dr Fei Li from Southwest Petroleum University in China and Professor Josef Paul from Geowissenschaftliches Zentrum der Universität Göttingen in Germany.

The study was published in Scientific Reports.

Australian National University

IFL Science

 Dr Bob Burne (sitting) and Professor Murray Batchelor. Photo: Lannon Harley, ANU

(20.02.2018, USA: 02.20.2018)