Root trace fossils as indicators of biogeomorphological stages in a Cretaceous fluvial system: Insights from the Sanfranciscana basin

Abstract

Rhizoliths, or root traces, are key indicators of subaerial exposure and vegetation colonization in ancient continental settings, yet they remain underexplored compared to invertebrate trace fossils. This study investigates rhizolith and invertebrate ichnofabrics within the Capacete Formation (Campanian, Sanfranciscana Basin, SE Brazil), aiming to reconstruct aspects of fluvial biogeomorphological succession and paleoenvironmental dynamics. Detailed sedimentological and ichnological analyses were conducted across a succession of channel, lateral accretion, crevasse splay, and floodplain deposits. Rhizoliths, including root casts and rhizohaloes, were most abundant in paleosols developed on floodplain fines, whereas invertebrate trace fossils such as Scoyenia, Taenidium, and Macanopsis occur in association with both overbank and sandy bar deposits. The ichnofabrics record a range of colonization phases, reflecting variable hydrogeomorphic regimes and vegetation stabilization states. The data suggests a close correspondence with the fluvial biogeomorphological succession model (FBS), with ichnofossils representing different stages of fluvial bar stabilization and floodplain forest maturation. These results provide high-resolution insight into ancient riparian ecosystem dynamics, sedimentary cyclicity, and landscape evolution in a meandering fluvial system.