Chemical data for soils over and around the Velma oil field, Stephens County, Oklahoma

Abstract

The Velma structure is a faulted, asymetrical anticline whose axis runs northwest-southeast. Oil production is centered over the anticlinal axis. Seeping hydrocarbons and/or associated compounds may produce a locally reducing environment resulting in reduction, mobilization, and redistribution of iron and manganese within near-surface rocks and soils. The most extreme alteration in rocks is seen over the crest of the anticline where carbonate cements have been replaced by hematite cements. Alteration of soil chemistry is seen following a DTPA soil test, wherein the amounts of chelate-extractable iron and manganese fall into two distinct populations: 1) higher concentrations over the oil field, and 2) lower concentrations constituting the background, which is presumably unaffected by hydrocarbon microseepage.