The Austin Chalk is an upper Cretaceous geologic formation in the Gulf Coast region of the United States.

[2][3] The general absence of dinosaurs is a reflection of the Austin limestone being marine in origin, primarily composed of microscopic shell fragments from floating sea organisms known as "coccolithophores" (the same organisms that contributed to the White Cliffs of Dover, on the south coast of England).

[4] Nevertheless, the Austin Chalk will occasionally produce fossils of larger creatures, such as Inoceramus clams, ammonite cephalopods, and large marine vertebrates such as Xiphactinus, a predaceous fish.

These eruptions occurred along a 250-mile long by 50 mile wide belt of submarine volcanoes, which are located in present-day south-central Texas.

Sea level rose for conditions to be right for the deposition of the Austin Chalk, which also coincides with the maximum extent of the Cretaceous Interior Seaway.