--> --> Abstract: The Carboniferous Sequence Stratigraphy and Paleovalley Fill Facies, Chaco Basin, Bolivia, by David A. Minicucci, Joseph J. Garbee, Robert M. Mitchum, and Rodolfo E. Porta; #90914(2000)

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David A. Minicucci1, Joseph J. Garbee1, Robert M. Mitchum2, Rodolfo E. Porta1
(1) Repsol - YPF, Englewood, CO
(2) Robert M. Mitchum Exploration Inc, Houston, TX

Abstract: The Carboniferous Sequence Stratigraphy and Paleovalley Fill Facies, Chaco Basin, Bolivia

The Repsol-YPF operated Pilcomayo Block is located in southeast Bolivia within the Chaco foreland basin. To date, hydrocarbons have been discovered in structural traps in sandstone reservoirs ranging from Devonian through Tertiary in age in the sub-Andean range. The block represents an effort to conduct frontier-type exploration for Carboniferous-age foreland targets in primarily stratigraphic trap configurations. Carboniferous strata are located in the Chaco basin and the adjacent sub-Andean belt, where thousand meters of fill have been deposited. The onset of glaciation in central and southern South America during this period resulted in the deposition of a complex succession of glacially influenced strata ranging from valley-filling sandstones and shales to glacially derived regional diamictite deposits. Glacial advances and retreats across the region have resulted in the formation of a network of deeply eroded paleovalleys up to several kilometers wide and several hundred meters deep. These paleovalleys have been filled by a series of glacially derived sands, diamictites, and shales in a variety of depositional settings. Detailed sequence stratigraphy has been performed on a seismic grid of approximately 2600 kilometers in order to delineate paleovalley extent, characterize the paleovalley fill and relate it to an overall depositional model. Five stratigraphic sequences have been established for the Carboniferous section. Paleovalleys occur in three of the sequences, including the Devonian-Carboniferous contact as well as in the Upper Carboniferous. Exploration play concepts developed, to date, involve stratigraphic trapping of Lower Carboniferous paleovalley fill against Devonian paleovalley walls and sealed by regional diamictite layers.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana