Salinity Variations and Chemical Compositions of Waters in the Frio Formation, Texas Gulf Coast

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Morton, Robert A.
Garrett, C. M., Jr.
Posey, J. S.

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Waters produced from sandstone reservoirs of the deep Frio Formation exhibit spatial variations in chemical composition that roughly coincide with the major tectonic elements (Houston and Rio Grande Embayments, San Marcos Arch) and corresponding depositional systems (Houston and Norias deltas, Greta-Carancahua barrier/strandplain system) that were respectively active along the upper, lower, and middle Texas Coast during Frio deposition. Waters of the upper coast typically have relatively high salinities (maximum total dissolved solids >80,000 mg/L), high calcium (200 to 9,000 mg/L), high sodium (>15,000 µg/L), relatively high potassium (>150 mg/L), low to moderate Cl/Na ratios (1.4 to 1.9), and high Cl/Br ratios (>400). When compared with adjacent areas of Frio production, waters of the middle coast have lower salinities (maximum total dissolved solids <80,000 mg/L), low calcium (27 to 2,900 mg/L), low sodium (<15,000 mg/L), low potassium (<150 mg/L), low to moderate Cl/Na ratios (1.2 to 1.8), and low to intermediate Cl/Br ratios (55 to 400). Deep South Texas waters from the lower coast (Kenedy and Kleberg Counties) also have high salinities (maximum total dissolved solids >80,000 mg/L, extremely high calcium (1,800 to 34,000 mg/L), high sodium (>15,000 mg/L), high potassium (>150), extremely high Cl/Na ratios (>2), and low Cl/Br ratios (<250). Calcium concentrations actually exceed sodium concentrations in some South Texas waters.


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