Hydrocarbon generation in relation to thrusting in the Sub Andean zone from 18 to 22 degrees S, Bolivia

Formation of the Bolivian eastern cordillera started at the end of the Oligocene and continues to the present day with thrusting affecting the Sub Andean Zone since late Miocene. The 'classical' source rock is the Devonian, but the Silurian interval has some potential. Their initial original potential is not high but they are thick (700 m, Los Monos Fm) and may be thicker still due to stacking in thrust duplexes. The three phases of sedimentation during the Tertiary each start with conglomeratic deposits and are discordant over the previous one. Seismic data allow us to correlate these steps with three periods of tectonic accretion: Late Miocene (Tariquia Fm), Pliocene (Guandacay Fm) and Plio-Quaternary (Emborozu Fm). Modelling demonstrates two phases of hydrocarbon generation. A first phase from Devonian to Carboniferous is due to the deepening of the Palaeozoic basin. The second phase of maturation is due to the Tertiary deposits in the foreland and under the piggyback basins. The central area (Santa Cruz) has never been more deeply buried than during the Palaeozoic and has been a high during the Tertiary.