Geological heritage of the Três Barras Farm section, Ordovician-Silurian record in the Paraná Basin, Brazil

Abstract

The Três Barras Farm section is an outcrop located at the northern edge of the Paraná Basin, in Midwest Brazil. Rocks from the Ordovician-Silurian period are found in this section, represented by the Iapó and Vila Maria formations of the Rio Ivaí Group, which lie directly on the crystalline basement. Devonian rocks of the Furnas Formation are also visible at the top of the section. Although the first fieldwork was conducted there in 1985, the site has been visited by multiple generations of researchers, often for paleontological studies. The fossil record in this section includes invertebrates such as mollusks and brachiopods, mineralized microfossils like ostracods, and palynomorphs such as acritarchs and cryptospores. Analyses conducted up until the 2000s suggested a Lower Silurian age for the complete strata of the Vila Maria Formation, with no invertebrate fossils reported. However, since then, knowledge about the Rio Ivaí Group and the Três Barras Farm section has advanced. Recent studies have challenged the previously assigned Silurian age, with fossil ostracods and brachiopods indicating a Hirnantian age for the upper Iapó and lower Vila Maria formations. Recent palynological research has also reported the presence of palynomorphs in the Iapó Formation for the first time, supporting interpretations of a post-glacial paleoenvironment. Despite these advances, significant knowledge gaps remain regarding the palaeobiodiversity of the Iapó and Vila Maria formations, particularly considering recent discoveries at the Três Barras Farm. This site, located in a remote area, preserves the transition of Late Ordovician strata to Early Silurian ones, enabling studies on Lower Paleozoic speciation and on the impact of a major glaciation on the biota. Preservation measures include sharing directions and mapping routes to the section, as well as raising awareness among the non-scientific community about its importance.