Abstract: In Bolivia, a marked climatic paleogradient (from west northwest to south) is visible in the Carboniferous depositional systems. In the northwest is the Pangean trend, a warm-water Pennsylvanian and Permian succession (preceded by a Late Devonian glacially derived rock assemblage). To the south is the cold climate Gondwanan trend, a succession of Late Devonian and Pennsylvanian cold-water siliciclastics with glacially influenced deposition. Whereas Devonian through (limited) Mississippian strata are comparable in overall character, a sharp climatic gradient in western South America is established by the earliest Pennsylvanian. The Pangean trend in northwestern Bolivia and Peru continues with warm-water Pennsylvanian and Permian carbonates, evaporites, and mixed siliciclastics of a semiarid, open seaway association (Copacabana Formation). This unit was deposited by marine transgression north (northern Bolivian subsurface and Lake Titicaca area), reaching central Bolivia by the Early Permian (Early Cisuralian). Regionally, the warm Pangean pattern continues into the younger and more restricted overlying Cisuralian and younger Permian and Triassic rocks characterized by restricted marine deposits of both humid and arid association (including red beds). To the south, Early Pennsylvanian rocks in the Gondwanan trend record continental and lacustrine glacial deposition as far north as central Bolivia, with glacial influence strongest in southern Bolivia and northern Argentina. By the Late Pennsylvanian, glacial influence has waned and is restricted to southern Bolivia near the Argentine border. The Copacabana Formation is enigmatic because of the following: (1) its autochthonous succession over cold-water, glaciogenic deposits of the Late Devonian and Mississippian and (2) its apparent coeval deposition with Pennsylvanian (and Permian) glacial diamictites. Although the former can be attributed to paleolatitudinal shift, or a clockwise rotation of Gondwana, what is not easily explained (and much discussed) is the autochthonous continuity of northeastern and central Bolivian carbonate deposits of the northern Peru–Bolivia Basin with southern Pennsylvanian and Permian glaciogenic deposits, which accumulated in the Tarija–Chaco Basin. Given that these cold and warm-water deposits were coeval in time, a severe climate gradient must have existed across Bolivia beginning in Pennsylvanian time. Western Gondwana records steady movement from high latitudes (~55°S) in the Late Devonian to midlatitudes (~40°S) by Pennsylvanian time. Glacial deposits seen in the northwest during the Late Devonian become restricted to the southern Tarija–Chaco Basin by the Late Pennsylvanian. By Early Pennsylvanian (Bashkirian) time, carbonates, evaporites, and siliciclastics were deposited in northwest Bolivia. In central Bolivia, Mississippian diamictites, undated Pennsylvanian siliciclastics, Copacabana lithofacies, and carbonates of the Vitiacua Formation are vertically stacked at a few locations.

ABSTRACT The Madre de Dios Basin, located in the northern sub-Andean zone of Bolivia is an underexplored sub-Andean basin. A complete stratigraphic revision, including biostratigraphy, core description, and sismo-stratigraphy, has been carried out; it suggests some changes in the historical sedimentary models and allows the identification of several reservoir and seal pairs. This revision not only integrates the results of previous studies but also provides new and original interpretations of the existing data set. The geochemical study indicates the existence of an Upper Devonian world-class source rock, in which, the Frasnian interval is characterized with a type I-II kerogen and a source potential index (SPI) higher than 6 ton/m 2 ; the Famennian interval has a type II kerogen and its SPI reaches 3 t/m 2 . The Carboniferous and Permian formations have levels with notable content of organic matter but do not classify as source rock in this area because of their low SPI. To evaluate the hydrocarbon potential of the basin, a 3-D dynamic model has been built. The thermal calibration of the temperature and maturity data is only possible taking into account an increase of the heat flow during Triassic–Jurassic time. As a consequence, 90% of the hydrocarbons are expelled before Cretaceous times by the identified kitchen in the center of the basin. The remaining 10% were expelled between the Oligocene and present time. Considering a petroleum system yield of 1%, the yet to find (mean) of the studied area is evaluated at 7 Gbbl of oil equivalent. The main challenge of the basin remains in finding traps.

Western Gondwana underwent a steady drift from mid-latitudes (~50°S, Early Carboniferous) to lower latitudes (<40°S) by Late Carboniferous time, and glacial deposition had ended in Bolivia by the early Pennsylvanian (Morrowan). At this time, carbonates and evaporites were being deposited across the Perú-Bolivia Basin. The Pennsylvanian and Permian Titicaca Group represents an Andean transgressive marine to restricted carbonate and regressive red bed megasequence (Cuevo Super-sequence or Subandean Cycle). The transgressive part of this Pangean first-order sequence records inherited basement controls and ephemeral pericratonic seaways into the interior of a western landmass. The well-dated Copacabana Formation records many high-frequency sequences and meter-scale cycles that form larger, third- and second-order composite sequences in the central Andes. Diverse carbonates, compositionally immature but texturally more mature arkosic and lithic sandstones, shales, tuffs, and evaporites characterize Copacabana Formation lithologies, which have been dated using foraminifera, fusulinids, conodonts, and palynomorphs. Estuarine barrier sands and cross-bedded, fossiliferous marine sandstones with limestone lithoclasts were derived by reworking of semilithified Copacabana rocks during lowstands and transgressive flooding events. Sedimentation rates in Bolivia were relatively low (7–25 m/m.y.) compared with the thicker and shale-rich Copacabana Formation in Perú. Stacked transgressive systems tracts and highstand systems tracts with significant hiatuses formed in open-marine and restricted to semiarid coastal depositional systems. Twelve second- and third-order, 30–100 m composite sequences have incisement or protosol development above marine limestone of the underlying sequence; extensive siliciclastic lowstand and/or transgressive shoreline facies occur above these sequence boundaries. Thick accumulations of progradational carbonate characterize the highstand systems tracts. More distal subtidal ramp sequences (well-developed in the Cochabamba and northern Subandes areas) are shale-cored with fossiliferous packstone-grainstone caps, but they lack evidence of subaerial exposure or disconformity. Small, meter-scale shallowing-upward parasequences and internal autocyclic, icehouse facies mosaics comprise the larger Copacabana composite sequences. Pennsylvanian sequence boundaries (occurring as a result of glacial drawdowns) occurred at ca. 318 Ma, 311 Ma, 309 Ma, 308 Ma, and 306.5 Ma. Permian drawdowns occurred at 299 Ma, 293 Ma, and 283 Ma.