Palaeozoic landscapes shaped by plant evolution

Journal name:
Nature Geoscience
Volume:
5,
Pages:
99–105
Year published:
DOI:
doi:10.1038/ngeo1376
Published online

Abstract

Fluvial landscapes diversified markedly over the 250 million years between the Cambrian and Pennsylvanian periods. The diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover. In the absence of widespread vegetation, landscapes during the Cambrian and Ordovican periods were dominated by rivers with wide sand-beds and aeolian tracts. During the late Silurian and Devonian periods, the appearance of vascular plants with root systems was associated with the development of channelled sand-bed rivers, meandering rivers and muddy floodplains. The widespread expansion of trees by the Early Pennsylvanian marks the appearance of narrow fixed channels, some representing anabranching systems, and braided rivers with vegetated islands. We conclude that the development of roots stabilized the banks of rivers and streams. The subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels. Our contention is supported by studies of modern fluvial systems and laboratory experiments. In turn, fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems. We suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms.

At a glance

Figures

  1. Palaeozoic events of fluvial and landscape development, in relation to plant evolution and atmospheric change.
    Figure 1: Palaeozoic events of fluvial and landscape development, in relation to plant evolution and atmospheric change.

    Data sources: atmospheric CO2 and O2 curves11, employing volcanic weathering factor in CO2 curve, and carbon burial curve12 (curves have wide error bars); fluvial styles and vascular-plant events14, 18, 37, 55; numbers of plant families in time intervals and their origination rates96, 97; plant nutritional traits29; events of rapid vegetation expansion, inferred from isotopic excursions at the Siluro–Devonian boundary34 and at the Famennian–Frasnian boundary (Late Devonian)41; key events in animal evolution88, 90, 93, 94, 98, 99; geological timescale100. Protero., Proterozoic; Miss., Mississippian; Penn., Pennsylvanian; Serp., Serpukhovian; Vis., Visean; Tour., Tournaisian; Prid., Pridolian; Lud., Ludfordian; Wen., Wenlockian; Llan., Llandovery.

  2. Plants and fluvial systems in ancient and modern settings.
    Figure 2: Plants and fluvial systems in ancient and modern settings.

    a, Braided-fluvial sheets, Alderney Sandstone, Cambrian, Channel Islands. b, Rhynia (R) and Aglaophyton (A) in growth position in hotspring silica, Rhynie Chert, Pragian, Scotland. Pound coin is 2.3 cm in diameter (See Fig. 6a,b of ref. 31 for more detail). Image courtesy of N. Trewin. c, Lycopsid trees, arrowed, rooted in former peat (coal seam), Sydney Mines Formation, Middle Pennsylvanian, Canada. Hammer (centre, right) is 30 cm long. d, Fixed-channel body of sandstone and mudstone, possibly deposited by an anastomosing river, with red mudstone and crevasse-splay sandstone, Joggins Formation, Canada. e, Anastomosing Diamantina River, Queensland, Australia, with eucalyptus trees (Eucalyptus microtheca) along riparian zones. f, Extensive eucalyptus roots exposed by bank erosion, Thomson River, Queensland, Australia.

  3. Palaeozoic diversification of fluvial style.
    Figure 3: Palaeozoic diversification of fluvial style.

    Proportions of rock units with braided, meandering and fixed-channel styles based on assessment of 330 rock units14, 55. Meandering rivers were identified by heterolithic lateral-accretion sets, and fixed channels by ribbons to narrow sheets with vertically aggraded fill. The proportion of channelled-braided and island-braided styles is estimated, as few literature descriptions provide sufficient detail for assessment. Penn., Pennsylvanian; Miss., Mississipian; Dev., Devonian; Sil., Silurian; Ord., Ordovician; Camb., Cambrian; Protero.; Proterozoic.

  4. Experimental study of effects of vegetation on channels.
    Figure 4: Experimental study of effects of vegetation on channels.

    Meandering channel created in flume at St Anthony Falls Laboratory, Minneapolis. Following initial set-up of a braided channel, seeding with alfalfa (green) during low-discharge periods stabilized the banks and resulted in restriction of flow to a self-maintaining single-thread channel, shown with red dye. The channel migrated systematically, and was bordered by a stable floodplain80. A flume length of 10 m is shown, viewed during low flow. Image courtesy of M. Tal.

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Affiliations

  1. Department of Earth Sciences, Dalhousie University, PO Box 15000, Halifax, Nova Scotia, Canada B3H 4R2

    • Martin R. Gibling &
    • Neil S. Davies
  2. Present address: Department of Geology and Soil Sciences, Krijgslaan 281, S8, University of Ghent, 9000 Ghent, Belgium

    • Neil S. Davies

Contributions

M.R.G. and N.S.D. jointly conceived and undertook the study and fieldwork involved. Both authors contributed to the writing of the manuscript and figure construction.

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