Caracterização icnológica das unidades inferior e média da Formação Furnas no flanco norte do Arco de Ponta Grossa: implicações paleoecológicas.

Abstract

Ichnology provides detailed information on the environmental parameters involved during sedimentary deposition, serving as the basis for paleoenvironmental analyses. To this end, the ichnological analyses focus on the behavioral aspects represented by the ichnoassociations, which provide details of the action of living beings that interact with the substrates, contributing significantly to the understanding of the environmental aspects that work in the environment. There have been ichnological studies in the Furnas Formation since the early twentieth century with reference to the presence of "worm tubes." The evolution of Ichnology as a science internationally and the advances in the recognition of the ichnological content of the unit made it possible, in the 1990s, to elucidate aspects of the extensive discussion about its depositional origin. The shallow marine context influenced by the tides was interpreted for most of the unit, made possible mainly by the identification of Skolithos and Cruziana ichnofacies. However, the vast majority of studies in this unit simply report an ichnogenus or mention "ichnofossils", without performing an integrated analysis with Sedimentary Geology that can elucidate the control by paleoecological parameters and colonization processes by infauna in the substrate. Recently, it has been demonstrated that part of the Furnas Formation has been deposited in the Lower Silurian, based on ichnological data. Here, it seeks to demonstrate the usefulness of paleoecological analyses for the understanding of environmental parameters in the interval corresponding to Lower Silurian. The regions studied are in the municipalities of Jaguariaíva and Piraí do Sul in the state of Paraná, on the northern flank of the Ponta Grossa Arc. This region was chosen because it does not have proposed paleoecological analyses, unlike more southern sections of the arch. Nine ichnotaxon were identified between the lower and middle units in the Furnas Formation. The ichnoassociations allowed to identify proximal and archetypal expressions of Cruziana ichnofacies. The set of faciological and ichnological evidence indicates the deposition in coastal environments between the foreshore and the lower shoreface under conditions of moderate to high hydrodynamic energy, as expected for this depositional context, but with significant pauses that allowed the typical colonization of the Cruziana ichnofacies. The paleoecological interpretations obtained showed that the hydrodynamic energy of the medium is the main factor that prevails in the control of variations faciological and in the processes of colonization by infauna in the interval under study