Biogeomorphology of Ireland's oldest fossil forest: Plant-sediment and plant-animal interactions recorded in the Late Devonian Harrylock Formation, Co. Wexford

Abstract

The mid-Palaeozoic was a significant interval in the evolution of plants, during which their biogeomorphic influence on terrestrial landscapes increased dramatically. The products of plant-sediment interactions are well known from Carboniferous strata, but earlier evidence dating to the initial rise of arborescent trees in the Devonian is less common. We present new evidence for early plant-sediment interactions from the Late Devonian (Famennian) Harrylock Formation (County Wexford, Ireland), which hosts standing trees that represent Ireland's earliest known fossil forest. The formation records deposition in fluvial and lacustrine environments, the former of which is here shown to have hosted Earth's earliest known log jam as well as early examples of vegetation-induced sedimentary structures (VISS) and a vegetation-stabilized chute channel. Fossilized driftwood preserved in the lacustrine facies contains the earliest evidence for arthropod(?) borings in large vascular plant debris. Together these early examples show that plant-sediment and plant-animal interactions, frequently recorded in Carboniferous strata, were already in existence by the Devonian and may have been previously underreported in other successions of the same age. The sparse Devonian record of plant-related sedimentary phenomena could be explained by a lesser abundance and/or longevity of such features in landscapes prior to subsequent evolutionary innovations in large vascular plants.