Caracterização deposicional do intervalo Praguiano-Eifeliano da Formação Ponta Grossa na borda Leste da Bacia do Paraná

Abstract

This work addresses the detailed stratigraphic and paleoenvironmental analysis of the sedimentary record from the Lower and Middle Devonian interval (Praguian – Eifelian) of the 250 meters thick section sampled in TBG-1-PR well, drilled in the Paleozoic outcrop section of Paraná Basin eastern edge. The association of sedimentological, petrographic, geochemical (Total Organic Carbon and Rock-Eval pyrolysis) and mineralogical data set up the basis for the depositional events interpretation presented in the Basin, and allowed to subdivide the studied interval into three third-order depositional sequences, hereby called "B", "C" and "D". These sequences record in detail the relative sea-level variations, demonstrated by the oscillations of both trend curves and faciologic data, expressing its depositional systems tract and the main stratigraphic key surfaces (maximum flooding surfaces - MFS, sequence bounding - SB and transgressive surfaces - TS). The systemstract of the TBG-1-PR well record asymmetric regressive and transgressive cycles, represented by the high stand systems tract, in the regressive context and by the transgressive systems tract in the transgressive context. The MFS (MFS-B, MFS-C and MFS-D) represent the main horizons of chronostratigraphic correlation for the studied interval range. For the definitions of these surfaces, mineralogical data was used in addition to geochemical and sedimentological information. Minerals such as pyrite, siderite and grained gypsum have some specific environmental conditions for their formation, usually found in MFS, which is characterized by a predominantly low-energy reducing environment, with low oxygen circulation (anoxic/dysoxic). Therefore, the mineralogical assembly present in the rock, associated with facies and microfacies data enables several paleoenvironmental interpretations during the process of transport, deposition and diagenesis.