Note about linear structures in the Napost Formation, Sierra de la Ventana, Buenos Aires Province (Argentina)

Abstract

Note about linear structures in the Napost Formation, Sierra de la Ventana, Buenos Aires Province (Argentina)?. Different microstructures located in the Napostá Formation quartzites (Devonian) of Sierra de la Ventana are described. The authors recognize three different types of structures: (a) pseudo-cilinders of quartz with elliptic contours and their consequent casts; (b) ?Step-like? structures; and (c) tight microfolds. Even though they are different elements, there is a common and distinctive feature, which is their spatial onentation, referred to their host rocks and the major structures of this ones.

The authors discuss for the (a) type, three possible origins: one merely organic, another which involves simple shear affecting fossil traces, and the third one which is merely tectonic; for the (b) type, a simple shear origin due to microliths displacement along cleavage planes is proposed; and for the (c) type, an analogous origin to that of the ?fold mulions? of Wilson (1953) is proposed, that is, due to simple shear according to ?in this particular case? vertical planes.