James M. Fausnaugh geotech.org Littleton, Colo. Surface geochemical surveys are often dismissed due to the idea that intervening stratigraphy may block or prevent upwardly moving hydrocarbons from passing through them. Many of the published analogs given as examples of seepage alteration phenomena predominantly show the surface effects and little of the geochemical changes that occur between the reservoir and the surface. The types and causes of surface alteration phenomena have been discussed at length.1-4 In 1994 an opportunity arose to run a significant analog using several exploration techniques that would allow the detection of seepage phenomena throughout the stratigraphic column. O...