Paleogene Sedimentary Basin Development in the Bolivian Altiplano and Implications for Initial Mountain Building in the Central Andes

Louisiana State University, Baton Rouge LA

Investigators

Abstract

9908003 Brian K. Horton The Altiplano plateau of the central Andes contains up to 10 km of Tertiary sedimentary rocks and is arguably the type example of a sedimentary basin in the center of a contractional orogenic belt. Despite numerous hypotheses regarding the history of the Altiplano's surface, particularly the timing and mechanism(s) of surface uplift, there has been no systematic analysis of the exposed Tertiary sedimentary rocks which ultimately contain the most complete record of surface processes. This project aims to evaluate the Paleogene succession of the north-central Altiplano in order to provide an understanding of the early-middle Tertiary tectonic-sedimentary evolution of the region and a detailed assessment of local stratigraphic geometries (including thickening trends, facies transitions, and unconfonnities) and regional correlations that will aid syntheses of the tectonic-sedimentary development of the central Andes. The project will evaluate four hypotheses regarding Paleogene basin development in the Altiplano. First, that it was a single integrated foreland basin receiving sediment from an early fold-thrust belt to the west. Second, that it was composed of a number of sub-basins, probably related to strike-slip deformation, that received sediment from localized source areas. Third, that it was a rift system flanked by sediment sources to the east and west. Or fourth, that it represents simple ponding (or "trapping") of sediment in a closed topographic basin. The hypotheses are distinguishable on the basis of the age of the deposits, sediment dispersal patterns, location and composition of sediment source areas, and subsidence histories-unknowns that will be determined by stratigraphic, sedimentologic, and 4OAr/39Ar geochronologic research. This study will place constraints on the early-middle Tertiary history of the plateau, thus improving modeling efforts aimed at understanding Altiplano uplift, and would provide a conceptual basis (and possibly new hypotheses) for the origin of sedimentary basins in the cores of mountain belts.