Two kilometers of carbonates formed in the Jurassic, with large amounts of detrital elements during the Aptian and clastic sedimentation between the Aptian and the Lutetian. The Albian through the Turonian are represented by argillite and organic-rich sediments, followed by biochemical precipitation since the Paleocene epoch of the Cenozoic. During the Maastrichtian, an alkali syenite dome near Saint Louis intruded sand deposits.