Remote detection of a tonal anomaly in an area of hydrocarbon microseepage, Tucano basin, north-eastern Brazil

Mapping of a tonal anomaly in an area of hydrocarbon microseepage was possi ble using a Landsat-Thematic Mapper false-colour composite consisting of TM 2/3, TM4/3 and of the difference TM2/3-TM4/3, displayed as red, green and b lue, respectively. In this false-colour composite, green and yellow express variations in the vegetation cover, whereas hues of magenta are related to terrain conditions representing bleached materials, which occur close to t he centre of a soil gas anomaly. Simultaneous occurrence of anomalous soil gas values with magnetic and radioactive minerals suggests that a reducing environment associated with the microseepage phenomenon created the bleache d materials, identified as a tonal anomaly in the enhanced TM image.