Controls on the regional-scale salinization of the Ogallala aquifer, Southern High Plains, Texas, USA

An extensive saline plume (>250 km) within the regionally important uncon®ned aquifer in the Neogene Ogallala Formation overlies the Panhandle oil and gas ®eld in the Southern High Plains, Texas, USA. Relative to upgradient Ogallala water, the plume waters have dO (ÿ6.7 to ÿ8.8-) and dD (ÿ42 to ÿ88-) values that tend to be depleted and have higher Cl (>150 mg/l) and SO4 (>75 mg/l) concentrations. Various end-member-mixing models suggest that the plume composition re ̄ects the presence of paleowaters recharged during Middle to Late Wisconsinan time rather than salinization associated with petroleum production. Paleowaters probably mixed with salt-dissolution zone waters from the underlying Upper Permian formations before discharging upward into the Ogallala Formation. Cross-formational discharge is controlled primarily by the geometry of the underlying units, as in ̄uenced by the Amarillo uplift, pinch-out of the laterally adjoining con®ned aquifer in the Triassic Dockum Group, variations in the saturated thickness of the Ogallala aquifer and the presence of potential pathways related to salt dissolution. # 2000 Elsevier Science Ltd. All rights reserved.