True substrates from a Mississippian wetland: windows into the biogeomorphology of Visean tetrapod habitats (Tyne Limestone Formation, UK)

Abstract

Records of Carboniferous biogeomorphology and tetrapod distribution are drawn predominantly from Pennsylvanian strata, with Mississippian counterparts more sparsely known. In this paper we describe trace fossils and vegetation-induced sedimentary structures from a Mississippian (Visean) fluvio-deltaic succession (Yoredale Group, UK). These structures are archived on true substrates and as sampled topography, providing a high-resolution glimpse into an early tetrapod habitat. A diverse ichnoassemblage comprises 18 invertebrate ichnospecies in addition to what are probably Britain's earliest tetrapod trackways. Vegetation-induced sedimentary structures include upturned laminae, scour-and-mound bedding and mudstone-filled hollows, which developed as plants mediated sedimentation and erosion. The distribution of both the trace fossil and the vegetation-induced sedimentary structure record is controlled by the abundance of true substrates. We contend that sedimentary landscapes that were primarily stabilized by vegetation promoted true substrate preservation, such that a complex interplay between biogeomorphology and palaeoenvironmental records exists in lower Carboniferous terrestrial successions. This case study demonstrates that an improved consideration of true substrate distribution within sedimentary successions can strengthen understanding of faunal habitats and biogeomorphic interaction.