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Figure 1. Stratigraphic section of the Tertiary and younger strata in the northern Gulf of Mexico coastal plain, with the Frio Formation (equivalent to the Catahoula Formation in updip areas) and Anahuac Formation highlighted in blue (modified from Warwick et al., 2007; Salvador and Quezada Muñeton, 1991). L. = Lower; Mid. = Middle; Up. = Upper; Tria. = Triassic; Pal. = Paleocene; Plei. = Pleistocene; Holo. = Holocene; Quat. = Quaternary; vertical lines = unconformity; wavy line = disconformity; jagged line = interfingering; dashed line = uncertain (modified after Salvador and Quezada Muneton, 1991; Nehring, 1991; Palmer and Geissman, 1999; Humble Geochemical Services et al., 2002; and Warwick et al., 2007).