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