OOLITIC LIMESTONE
Oolitic limestones are whitish to cream-colored limestones composed of
sand-sized (1/16 to 2 mm in size), well rounded, concentrically-layered calcite
or aragonite grains called oolites (a.ka. ooliths and ooids).
Oolites form by rolling back and forth on a shallow seafloor, or sometimes on a
shallow lakebed, by wave action. Oolites are forming today on the Bahamas
Platform and in Great Salt Lake, Utah. The technical geologic term for
most oolitic limestones is “oolitic grainstone”.
Uncertainty exists about the specifics of the origin
of oolites. Some researchers
conclude that oolites form by completely inorganic chemical precipitation of
CaCO3 from seawater around some nucleus (a tiny shell or skeletal
fragment or sediment grain). Other
researchers conclude that the presence of bacterial films on oolite grain
surfaces play a significant role in the precipitation of CaCO3
layers. However, the undoubted
presence of bacteria does not necessarily indicate a biogenic origin for
oolites - bacteria are everywhere.
Oolitic limestone
Oolitic limestone