Integrating ichnology and paleopedology in the analysis of Albian alluvial plains of the Parnaíba Basin, Brazil

Abstract

Studies integrating ichnology and paleopedology in paleoenvironmental interpretations are uncommon in Brazilian continental sedimentary successions. Nevertheless, they are crucial for understanding the interactions between sediments, organisms and soil-forming processes. The Albian sediments of the Parnaíba Basin were deposited in continental environments. These are constituted of very fine-to fine-grained sandstones, interbedded with mudstones and composite and compound paleosol profiles with preserved invertebrate and vertebrate trace fossils and rhizoliths. In this study, ichnological, sedimentological and paleopedological data are integrated in order to define the paleoenvironmental conditions of the Albian deposits of the Parnaíba Basin. The depositional environment is interpreted as alluvial with floodplain and crevasse splay deposition. In the paleosol profiles five invertebrate ichnogenera, one vertebrate ichnogenus and two types of rhizoliths were recognized and attributed to Scoyenia ichnofacies. The water saturation level of paleosols evidenced by the distribution of redoximorphic features and the variation of ichnofossil types suggests that the profiles were developed under moderately well drained conditions with short periods of water retention and that the paleoclimate was seasonal and characterized by alternating wet and dry seasons. The alluvial paleoenvironment was characterized by periods of landscape stability in which the pedogenesis exceeded the sedimentation rates and resulted in formation of soil profiles.