Abstract: Cretaceous-Tertiary Basins of the Bolivian Altiplano Probed by Gravity and Aeromagnetic Data

William C. Pearson

Recently released regional gravity and magnetic surveys from the Bolivian Altiplano reveal sedimentary basins containing large volumes of Paleozoic and Cretaceous marine sediments as well as younger synorogenic lacustrine sediments. Hydrocarbon exploration has been limited due to the remote nature of the area and the younger sediments that obscure much of the surface geology. Hydrocarbon exploration can now be intensified based upon the gravity/magnetic results.

Gravity maps based upon 63,000 stations have been released by YPFB, GEOBOL, Bolivian Ministry of Mines and Metallurgy, the USGS, TDP and DMA These data reveal north-south basins with more than 5 km of fill. Carboniferous and Cretaceous marine shales, carbonates and Tertiary lacustrine beds provide potential source rocks. Evaporitic sequences from Oligocene to Recent provide excellent seals to hydrocarbon traps.

Aeromagnetic surveys totaling 124,000 line kilometers were flown through 1991. Half of the Altiplano is covered with shield volcanoes and pyroclastics, where hydrocarbon exploration will be difficult. East of the volcanic belt the Altiplano is generally devoid of volcanics based on the aeromagnetic data. Due to low magnetic inclination of the earth's magnetic field (6 to 12° total magnetic intensity anomalies are distorted into east-west low closures seemingly unrelated to geology. An effective reduction-to-pole algorithm combined with neural network depth and structure technology unravels the magnetic anomalies and provides a picture of magnetic basement. The strong correlation of magnetic and gravity anomalies highlights areas for hydrocarbon exploration in this wildcat explora ion area.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994