|Oligocene, Gulf Coast, Gulf of Mexico
The Anahuac Formation is the top seal on the Frio Formation. It is a thick, shale-rich unit deposited during widespread transgression. Surprisingly, we failed to find an isopach of the Anahuac, perhaps because of stratigraphic uncertainty. Seal quality is an issue; the Anahuac pinches out updip. Many shale beds within the Frio serve as traps for hydrocarbons and would most likely similarly trap CO2; these units must be mapped at a more local scale than we used.