Abstract: Seismic and Gravity Analysis, Upper Cauca Basin, Colombia

James A. Noel, Thomas Baldwin

The Upper Cauca Basin is the southern portion of the Cauca Basin in western Colombia. It is bounded on the west by the Cordillera Occidental and the Cauca Fault, and on the east by the Cordillera Central and the Romeral Fault. The study area represents 370,000 acres. The basin is a rift valley between the two faults. The rift was probably caused by the westward movement of the South American Plate against the eastward movement of the Caribbean Plate.

The gravity survey was completed in 1964 by United Geophysical for Intercol. The seismic work was done by Western Geophysical in 1979 and 1981 for ECOPETROL. Intercol drilled Candelaria #1 in 1965, which penetrated over 3700 ft of Tertiary sandstone, shale, and coal, and bottomed in 400 ft of igneous rock.

There are five gravity anomalies of interest: two on the west side, the Vijes and Cali, and three on the east side, the Manulita, Palmira, and Candeleria anomalies. Together the first two are 25 km long, bounded on the west by the Cauca Fault and on the east by the Candeleria Fault, and separated by a transverse fault. The last three are bounded on the west by the Palmira-Buga fault and on the east by the Romeral Fault. Cross faults separate the three and shift the trends.

Seismic lines/sections confirm the gravity interpretations. The anomalies are defined and the many faults are obvious. The sections show events arching over the anomalies and pinching out along the flanks and over the crests. The sedimentary section thins over the anomalies and increases to more than twice the thickness in the center of the basin. The seismic sections show that the anomalies are not intrusions but uplifted basement blocks.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela