Microfósseis de parede orgânica do “Carbonato Salto Magessi”, proterozoico da Bacia dos Parecis, Mato Grosso (Brasil)

Abstract

Salto Magessi Limestone, or Lower Carbonate Sequence, is an informal unit found in subsurface in the cores 2-SM-1-MT and 2-ANP-6-MT drilled by ANP-Petrobrás in the Parecis Basin, Mato Grosso, western Brazil. Available information on this unit indicates deposition prior to the Marinoan glaciation. However, no biostratigraphical framework has been developed for the unit, hampering a better understanding of its geological history. In this study, we report well preserved organic microfossils in core 2-ANP-6-MT, which are typical of the Proterozoic, forming an assemblage marked by the high abundance of sphaeromorph acritarchs, followed by acanthomorphs, filaments and subordinate vase-shaped microfossils (VSM). Seven palynomorph species were identified, including Bavlinella faveolata, Germinosphaera bispinosa, Jacutianema solubila, Leiosphaeridia minutissima, L. tenuissima, Tappania tubata and Limeta lageniformis. Although most taxa have a wide stratigraphical range, comparisons with assemblages worldwide suggests a Tonian age for the Salto Magessi Limestone.