EduR43 Oolitic Limestone

3D Model

60×60×51mm

Jurassic (201-145Ma)

Dorset, England

Limestone is a sedimentary rock formed of grains of calcium carbonate, which in this rock are almost perfect spheres called ooids, because they look like tiny eggs. They form in warm, shallow tropical waters with small, gentle waves like in the Bahamas today. Sand grains and other particles are rolled gently around the ocean floor, so when calcium carbonate deposits onto them, they form perfectly spherical layers, kind of like how you can roll a ball of dough between your hands. If you break an ooid apart, you will see the concentric layers around a central nucleus.

That this oolitic limestone can be found in the British Isles today, with weather nothing like what is needed to form them, suggests that during the Jurassic, the British Isles were closer to the equator, then were moved North afterwards, further giving evidence for plate tectonics. This oolite in Dorset contains many important Jurassic fossils!