Abstract

GOMKES, Celso B; CASTILLO CLERICI, Ana Maria; GADEA, María  and  COMIN-CHIARAMONTI, Piero. Polygonal jointing in sandstones from Eastern Paraguay. Ser. correl. geol. [online]. 2014, vol.30, n.1, pp.13-23. ISSN 1666-9479.

Columnar joints, resembling those in igneous rocks, are present in quarz sandstones of various formations (Mesozoic to Cenozoic) in Eastern Paraguay. New data concerning the feld relationships and the geochemical characteristics constrain the processes responsible for the generation of columnar fracture patterns in sedimentary rocks. The columns are mostly normal to bedding and occur at several different stratigraphic levels. The host rocks are cut by volcanic necks or plugs, acting as heat sources and the development of columnar jointing may be controlled by the presence of magmatic rocks. Alternatively, thermal waters, circulating through fractures and favorable sedimentary layers, are responsible for the remplacement of the sandstones by opal. As a result of the strain originated by the contraction of opal, a system of joints was developed. It is also possible that the local tectonic stresses have been developed and contributed to the fragmentation processes.

Keywords : Polygonal jointing; Sandstones; Paraguay.

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