Paleoenvironmental variations indicated by microfossils in the upper paleozoic Konservat-Lagerstätte of the Paraná Basin, Santa Catarina, Brazil

Abstract

The Lontras Shale is a Brazilian Paleozoic Konservat-Lagerstätte that preserves a remarkable diversity of fossils in an exceptional way. In this study, we aimed to refine the paleoenvironment of the Lontras Shale, in the city of Mafra at Santa Catarina State, using microfossils and phytoclasts as proxies. Sampling was conducted in twelve layers of the shale (1A, 1B, 1C, 1D, 2A, 2B, 3A, 3B, 3C, 3D, 4A, 4B) in a 1.2m outcrop. The samples were collected every 10 cm and weighed 1 kg each. The collected material underwent chemical treatment with 15% hydrogen peroxide for 24 h. Samples were then washed and dried, and all the total fractions were observed under a stereomicroscope. A total of 316 bioclasts (entire fossils or fragments) were identified. Thirty-three of the specimens were analyzed in a scanning electron microscope. As a result, we identified Foraminifera classified as Saccammina sp., Psammosphaera irregularis and Ammobaculitessp. The preservation level of the phytoclasts suggests that these fragments were deposited under a proximal environment. The analysis of the microfossils suggests that the Lontras Shale Konservat-Lagerstätte in the city of Mafra experienced significant changes in its paleoenvironment settings during deposition. The high concentration on the layer 3D suggests an increase in the nutrient supply or temperature variation during the Lontras Shale deposition. Finally, the data provided through microfossil analyses combined with preterit information could support that the Lontras Shale Konservat-Lagerstätte was deposited under a proximal environment such as an estuary or a fjord.