ICNOLOGIA E TAFONOMIA DOS DEPÓSITOS EMSIANOS DA FORMAÇÃO PONTA GROSSA AFLORANTES NA REGIÃO DE TIBAGI E SEU SIGNIFICADO PALEOAMBIENTAL

Abstract

The present study has as main objective to confront the ichnological and taphonomic interpretations aiming to characterize the paleoenvironmental context represented by one section of the Devoanian (Emsian) of the Paraná Basin (Southern Brazil). Six ichnofabrics were diagnosed, namely: Planolites-Palaeophycus, Skolithos, Asterosoma-Teichichnus, Chondrites, Asterosoma-Zoophycos and Asterosoma-Chondrites. Ichnofabrics of Skolithos and Chondrites, respectively, represent changes in hydrodynamic energy and oxygenation. Amendments in these parameters permitted the opening of the "colonization window ", resulting in momentary suppression of resident ichnofauna by an opportunistic ichnofauna. It also identified three taphofacies to the section (TA, TB and TC). TA occurs with the predominance of fossils with bivalves bodies, disarticulated, entire and concordanting to bedding plane in parautoctonous to aloctonous context; The TB is the expression of bivalves bodies, articulated, in apparent life position in context of autochthony; and the TC expressed bivalves bodies, entire, articulated in apparent life position, multielement bodies, entire, disarticulated and concordanting with the bedding plane, and univalves bodies, entire and concordanting to bedding plane, all of them with a predominance of autochthony. The TA is associated with Planolites-Palaeophycus, Chondrites, Asterosoma-Zoophycos and Asterosoma-Chondrites ichnofabrics, suggesting depositional conditions at transitional offshore. The TB is associated with the Skolithos ichnofabric, expressing shoreface conditions. The taphofacies C occurs in beds with BI 0 probably relating with a maximum of anoxia represented in these layers. Was diagnosed three main peaks of hydrodynamic energy in the section, representing oscillations influenced by storm events (the curve of relative paleobathymetry follows this parameter). As regards the oxygenation, occur five moments of dysoxic to anoxic conditions. The salinity rate not changed, featuring normal situation for the marine environment. The sedimentation rate is moderate, but at certain levels becomes high. From the dominance of the conditions expressed by the TA and the Archetypal Cruziana Ichnofacies, it was concluded that the deposition of sediments occurred in the transitional offshore context, influenced by storm. The levels of occurrence of TB associated with Proximal Cruziana Ichnofacies, has identified a depositional context of shoreface, influenced by storm. Finally, the layers when were diagnosed the TC, even though no associated bioturbações, register the maximum of anoxia at the section, under offshore conditions.