Palaeozoic co-evolution of rivers and vegetation: a synthesis of current knowledge M.R. Gibling a, *, N.S. Davies b,1 , H.J. Falcon-Lang c , A.R. Bashforth d , W.A. DiMichele d , M.C. Rygel e , A. Ielpi a a Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada b Department of Geology and Soil Science, Ghent University, Krijgslaan 281 s.8, Ghent B-9000, Belgium c Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK d Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC 20560, USA e Department of Geology, State University of New York, College at Potsdam, NY 13676, USA 1. Introduction The term ‘‘evolution’’ has generally been applied to living organisms, following the work of Charles Darwin and the growth of evolutionary biology. In an essay written late in his life and based on a contemporary understanding of biology, the famous fluvial geomorphologist Luna B. Leopold (1915–2006) argued that the behaviour and morphology of rivers have parallels with biological systems (Leopold, 1994). He pointed out that although rivers as a whole show predictable responses to external factors, each river system is unique and its individual reaches have a natural variability. Thus, a river system is analogous to a species composed of a population of reaches, the variability of which reflects current processes and the system’s geological history. The river system might evolve gradually or through abrupt events. The parallel with biological systems as set out by Leopold largely represents the way in which organised systems respond to external stimuli. He envisaged river evolution mainly as a gradual response to changes in factors such as climate. Of course, in the absence of genetic material in fluvial systems, the parallel should not be taken too far. However, Leopold’s essay implies that the term ‘‘evolution’’ may be applied legitimately to landforms and other essentially physical systems, raising some interesting questions. Might radical changes to the Earth system influence virtually all river ‘‘species’’ worldwide, promoting a higher order of river evolution? Individual rivers might presumably become ‘‘extinct’’, but might entire styles of river behaviour and morphology also become extinct? In contrast to the irreversible nature of biological evolution, might ‘‘primitive’’ fluvial styles reappear if radical changes took place in the physical environment and the biosphere? And over what timescales might gradual or sudden river evolution take place? Since the late 1960s, research by numerous authors has established that, as a consequence of the evolution of terrestrial vegetation, river systems as a whole evolved dramatically through the 240 million years of the Palaeozoic Era, especially during the 120 million years of the Devonian and Carboniferous periods (Schumm, 1968; Cotter, 1978; Went, 2005; Corenblit and Steiger, 2009; Davies and Gibling, 2010a,b, 2013; Gibling and Davies, 2012). Among many effects, plants influenced rock and sediment weathering, the grain-size spectrum supplied to rivers, landscape stability, the roughness of sediment surfaces, and the capacity for Proceedings of the Geologists’ Association 125 (2014) 524–533 A R T I C L E I N F O Article history: Received 23 March 2013 Received in revised form 15 November 2013 Accepted 5 December 2013 Available online 30 December 2013 Keywords: Braided Meandering Anabranching Blackwater Riparian Ecospace A B S T R A C T As vegetation evolved during the Palaeozoic Era, terrestrial landscapes were substantially transformed, especially during the 120 million year interval from the Devonian through the Carboniferous. Early Palaeozoic river systems were of sheet-braided style – broad, shallow, sandbed rivers with non-cohesive and readily eroded banks. Under the influence of evolving roots and trees that stabilised banks and added large woody debris to channels, a range of new fluvial planform and architectural styles came to prominence, including channelled- and island-braided systems, meandering and anabranching systems, and stable muddy floodplains. River systems co-evolved with plants and animals, generating new ecospace that we infer would have promoted biological evolution. By the end of the Carboniferous, most landforms characteristic of modern fluvial systems were in existence. ß 2013 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +1 9024942355. E-mail addresses: mgibling@dal.ca, Martin.Gibling@Dal.Ca (M.R. Gibling). 1 Current address: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. Contents lists available at ScienceDirect Proceedings of the Geologists’ Association jo ur n al ho m ep ag e: www .els evier .c om /lo cat e/p g eo la 0016-7878/$ – see front matter ß 2013 The Geologists’ Association. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pgeola.2013.12.003