Petroleum exploration in eastern Panama and northwestern Colombia has gained impetus from recent side-looking radar mapping. Radar-derived geologic information is now available for approximately 40,000 sq km where previous reconnaissance investigations have been extremely limited because of inaccessibility and perpetual cloud cover.

With radar imagery as the sole source of remote sensing data, the distribution, continuity, and structural grain of key strata provide evidence that the eastern Panamanian Isthmus can be divided into 3 main physiographic-structural parts. Two composite coastal mountain ranges are separated by the Medial Basin which trends southeastward from the mouth of the Bayano River to the Atrato River valley of northwestern Colombia. Within the Medial Basin, the most obvious site for petroleum exploration, the majority of clearly exposed surface structures are not particularly attractive prospects because prime reservoir strata have been stripped from their crests. However, several large geomorphic anomalies which have been mapped in the Medial Basin may be reflections of subsurface structures ha ing a complete stratigraphic section. The possibilities of gravity-type entrapment in fractured organic shales, siltstones, and carbonates have been suggested along the southern synclinal trends of the Medial Basin. The southwestward extension of the Medial Basin trend, coincident with unique beach ridges from a possible granitic source, provides an attractive petroleum prospect in the western part of the Gulf of Panama. The occurrence of active shell bars in the Bay of San Miguel and present reef trends on the northern Caribbean coast suggest possible offshore sites for geophysical surveying.

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