Depositional processes in a shale-dominated Devonian succession: Sedimentary facies and trace fossil integrated analysis

• Published in: Sedimentary geology Vol. 470; p. 106716
• Main Authors: Plantz, Josiane Branco, Sedorko, Daniel, Carelli, Thiago Gonçalves, Ramos, Renato Rodriguez Cabral, Borghi, Leonardo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2024
• Subjects: Fine-grained rocks; Paleoenvironmental interpretation; Paraná Basin; Ponta Grossa Formation; Sedimentary processes; Paraná Basin; Sedimentary processes; Fine-grained rocks; Paleoenvironmental interpretation; Ponta Grossa Formation
• ISSN: 0037-0738
• DOI: 10.1016/j.sedgeo.2024.106716

Fine-grained rocks have historically been interpreted as a product of the settling of fine fractions in low-energy environments. However, recent studies have suggested that in these environments, more dynamic and complex processes operate. These processes involve a much more diverse set of sedimentary processes than those previously assumed. The lithological homogeneity of clayey successions, associated with the obliteration of their primary characteristics by diagenetic and/or weathering processes, makes it difficult to interpret depositional processes and understand the paleoenvironment. To contribute to a better comprehension of the mechanisms of transport and deposition of fine-grained rocks in a siliciclastic mud-dominated succession, as well as their depositional site, the present study aims at the detailed analysis of a continuous drill core. This core contains a thick Devonian succession consisting essentially of shale from the Ponta Grossa Formation (Paraná Basin, Brazil). Throughout the analyzed succession, a wide variety of sedimentary structures have been identified, such as parallel laminations, wave-ripple cross-stratification, hummocky cross-stratification, normal grading, and gutter casts. These structures show the constant performance of high-energy flows, which are configured as important deposition and/or rework agents. The integrated analysis of facies and trace fossils has proven to be more efficient for paleoenvironmental characterization than isolated approaches. This is because facies and ichnofacies (e.g., Cruziana, with its proximal, impoverished, archetypal, and distal expressions; Skolithos and Glossifungites) can be easily correlated, facilitating the identification of facies associations. This approach not only allows for the interpretation of a shallow marine platform with a gentle slope (ramp shelf) paleoenvironment of moderate to high energy, subject to storm wave action, but also enables the identification of the particular characteristics of deposits from different sub-environments (proximal to distal offshore, offshore transition, shoreface to offshore transition, and prodelta) and their deposition mechanisms. Furthermore, the facies associations are useful for highlighting the variations formed in response to oscillations of the relative sea level and changes in sedimentary input. •Facies and trace fossil analyses are key tools in understanding fine-grained rocks.•High-energy processes shape the deposition of mud-dominated successions.•Wave-enhanced gravity and hyperpycnal flows often occur below the storm-wave base.•Mudstones with Archetypal Cruziana indicate storm wave influence on the outer shelf.•Gentle-slope shelves are the best analogs for deposition in epicontinental seas.