Chaco Foreland Basin, Bolivia: An Archive of the Propagation Sequence of the Andean Deformation

Cornelius Eji Uba and Manfred Strecker
University of Potsdam, Potsdam, Germany

Eastward Andean orogenic growth since Late Cenozoic led to variable crustal loading, flexural subsidence, and foreland sedimentation in the Chaco basin. To understand the interaction between Andean tectonics, contemporaneous foreland development, and the timing of hydrocarbon reservoirs and plays in the central Andean, we analysed stratigraphic, sedimentologic, and seismic data.

The Neogene Chaco foreland basin consists of five stratigraphic successions controlled by Andean orogenic and climate: The foreland sedimentation commenced between 27 and 14 Ma with widespread fluvial Petaca Fm. It represents a time interval of low sediment accumulation in a forebulge-backbulge depocenter and the onset of deformation in the Eastern Cordillera. The overlying marine-continental 14-7 Ma Yecua Fm. represents distal foredeep and increased subsidence as a result of thrust-belt loading outpacing sedimentation rates. It marks the onset of active tectonics in the Subandean Zone. The overlying, 7-6 Ma-old, Tariquia Fm. indicates high accommodation and sediment supply rates concomitant with the onset of deposition of Andean-derived sediment in the medial-foredeep depocenter. Progradation of syntectonic, thickening- and coarsening-upward clastics of the 6-3.3 Ma-old Guandacay and 3.3 Ma-to-Recent Emborozú Fms. indicate the arrival of the deformation front in the present Subandean Zone. It represents the proximal foredeep and wedge-top depocenters, respectively.

The basin records the easterly propagation of basement-involved thrusting, depocenters, and variation in accommodation space. The hydrocarbon generation and migration is contemporaneous with the onset of deformation, and enhance a better understading of the possibilities of hydrocarbon entrapment and petroleum system risks in and underlying the foreland strata.