Biogeochemistry was applied to the indirect detection of petroleum microseepage in the vicinity of Eagle Springs oil field, Railroad Valley, Nevada, and Cave Canyon field, Paradox basin, Utah. Trace elements were measured in native vegetation over and surrounding areas of production at the test sites. The oxidation of microseepage in the upper part of the soil column is postulated to cause an increase in plant uptake of transition trace elements such as iron, manganese, and vanadium, and a decrease in plant uptake of alkaline earth elements such as calcium, strontium, and barium.

Compared to nonproductive areas, an increase in uptake of transition trace elements and a decrease in alkaline earth elements was observed in Fourwing saltbush over Eagle Springs field. The postulated increase in uptake of transition trace elements and decrease in alkaline earth elements was not as apparent in Big sagebrush nor in Utah juniper over the Cave Canyon field.

The observation of the postulated effects on vegetation at Eagle Springs may be due to the relatively large rates of microseepage independently observed using other methods, and the extensive faulting in Railroad Valley. The weaker response observed at Cave Canyon may reflect the lack of faulting and the retention of light hydrocarbons in the reservoir. Another possible reason for weak response is that the available plant species at Cave Canyon do not exhibit the effect at the lower soil pH measured in the area. At low pH and low Eh, the solubility of transition elements in soil pore waters and plant uptake is increased. Due to the high soil pH of the Railroad Valley area, the uptake of alkaline earth elements should be decreased where microseepage is occurring because of crystallizat on of carbonate minerals.