TESSELATED PAVEMENTS RELATED TO POST-DEPOSITIONAL STRUCTURES
JORGE HACHIRO
Instituto de Geociências, USP, São Paulo, SP.
Presented by ANTONIO C. ROCHA-CAMPOS
Tesselated pavements are curved or flat surfaces characterized by polyhedral geometric features (rectangular, pentagonal, hexagonal) of centimetric to metric size.
The genetic difference between desiccation cracks and tesselated structures occurs during lithification, when the sediment surface is exposed to weathering producing mosaic structuring. These structures are typically originated from initial cracking of previously lithified rocks. Simultaneous effects of weathering (climatic factors), fracturing and erosion on the denuded surfaces, impart the tesselated pattern.
Although the polygonal pattern is not penetrative, the edges of polygons may reach 20cm below the surface. Penetrative points may determine the spatial development of the tesselation in some cases.
Another characteristic of the tesselated structures is their occurrence on arched surfaces. These features comprise small oval mounds delimited by discontinuities similar to turtle or armadillo shells.
Well-known tesselated pavements occur in Australia (Branagan & Cains 1993). In Brazil the most conspicuous are located in sandstones of the Cabeças Formation in Parnaíba Basin (Sete Cidades National Park - PI). In an embryonic stage, however, they are common in several stratigraphic units from metasediments of the Precambrian Galho do Miguel (MG) and Morro do Chapéu (BA) formations and in sandstones of the late Paleozoic Itararé Group (Vila Velha State Park - PR) and silicificied pelites of the Permian Teresina Formation (SP). (December 10, 1999)
Publication Dates
-
Publication in this collection
05 Jan 2001 -
Date of issue
Dec 2000
