Origin of rectangular and aligned lakes in the Beni Basin of Bolivia

Abstract

The origin of aligned, rectangular shaped lakes in the Beni Basin of Bolivia has been investigated utilizing Landsat imagery, Shuttle Imaging Radar and the available scientific literature. The lakes tend to line up in two preferred orientations, northwest and northeast. They occur in Cenozoic sediments of the Beni Basin situated between the Brazilian Shield and the Andean Foredeep. Available evidence suggests that the shapes and orientations of the lakes are primarily controlled by a nearly orthogonal fracture pattern propagated upward from the underlying granitic (Brazilian Shield) basement. These orientations and shapes may reflect a reactivated ancient global fracture pattern or may be the result of an E-W greatest principal compressive stress ( σ 1) and subsequent downwarping and uplifting of the Beni Basin during the Cenozoic Andean orogeny. The lakes themselves may occupy down-dropped basement blocks induced in the gently upwarped basement. While unusual, these lakes are not unique. This suggests that transmission of basement structure through overlying sediments may occur in other regions, but that special conditions such as little or no lateral compression of the sediments, the absence of high trees and vegetation, stability of surface material from drifting, and a high water table are necessary to preserve and enhance such surface features.