The Devonian landscape factory: plant–sediment interactions in the Old Red Sandstone of Svalbard and the rise of vegetation as a biogeomorphic agent

Abstract

The Devonian Period was a crucial interval in the evolution of plants. During its 60 myr duration, it witnessed the successive evolution of roots, wood, trees and forests, and many of the biogeomorphic phenomena that operate in modern terrestrial environments came online for the first time. The Old Red Sandstone (ORS) of Svalbard consists of a near-continuous Silurian to Late Devonian record of land plant-colonized sedimentary environments and provides a perfect natural laboratory to aid understanding of the facies signatures and evolution of these phenomena. Here we describe and illustrate a catalogue of ORS features that provide evidence for the stepwise appearance of novel plant-sediment interactions, including: preserved plant material and rooting structures, early large woody debris accumulations, cannel coal deposits, and the oldest known vegetation-induced sedimentary structures, in addition to vegetation-influenced motifs of elevated mudrock content and complex alluvial sand bodies. These characteristics are combined to reconstruct changes to non-marine environments in this Devonian ‘landscape factory’. In addition to tectonic and climate influences, plant evolution first served as a control on the construction of the sedimentary record during this period and has persisted as a fundamental influence on Earth surface processes and landforms ever since.

The Anthropocene as an Event, not an Epoch

“…The evolution of forests and their spread across continents during the Devonian produced an even greater transformation. Many biogeomorphic phenomena that operate in modern terrestrial environments appeared for the first time (Davies et al ., 2021), and the dramatic changes in levels of atmospheric oxygen and carbon dioxide became a driver of Late Devonian mass extinction and latterly of Late Devonian–Carboniferous glaciation (Le Hir et al ., 2011; Dahl and Arens, 2020). However, despite their firm basis in the stratigraphical record, (Eriksson and Cheney, 1992; Buick, 2008), neither the GOE nor the GOBE, nor the Devonian continental forestation event, are employed to define time‐unit boundaries within the GTS.…”

Terrestrial surface stabilisation by modern analogues of the earliest land plants: A multi‐dimensional imaging study

“…Additionally small meandering channels had become globally abundant (Gibling & Davies, 2012) likely not only initiated by more widespread land plants but also with an increased number of cohesive muddy substrates. Proto‐soils would probably also have been more organic‐rich (Mitchell et al, 2021a), and more buried organic matter likely changed sediment properties leading to improved cohesiveness (Davies et al, 2021), with multicellular rhizoids able to stabilise and adhere to soil mineral grains, akin to group 4 in this study. With the evolution of vascular plants with ‘true’ root systems there was a marked shift in sedimentary architecture towards channelled sand‐bed rivers, meandering rivers, and muddy floodplains (the average proportion of mudrock in alluvial successions is 29.9% for formations deposited after the Early Devonian evolution of rooting; Gibling & Davies, 2012; McMahon & Davies, 2018).…”

“…Where palaeosols developed under larger vascular plants, weathering effects similar to those in modern soils can be recognised as well as evidence of rooting systems (Driese et al, 2021). For smaller statured plants, one potential way forward is to identify and characterise vegetation‐induced sedimentary structures (VISS) in the rock record, where indirect effects of sediment accumulation and erosion can also be inferred (Davies et al, 2021; Rygel et al, 2004). Another approach is to identify micro‐to‐nanoscale biologically mediated weathering features (BWFs) that are present in potential proto‐soil like substrates (Mitchell et al, 2019).…”

Low tropical diversity during the adaptive radiation of early land plants

“…The collections come from the extensive 3400-3750 m thick Red Bay Group (typical 'Lower Old Red Sandstone' terrestrial-fluviatilelacustrine deposits (Fig. 1c)) [12][13] , which is well age-constrained by fish fossils (including biostratigraphically useful thelodonts) [14][15][16] . Palaeocontinental reconstructions locate the deposition of the Red Bay Group to northern Laurussia; at, or very close to, the palaeoequator in late Silurian-Early Devonian times (Fig.…”

“…Interestingly, the Lochkovian fish biotas of tropical South China are also abundant and diverse 39 . It should also be pointing out that sedimentological evidence for climate extremes in the Spitsbergen sequences is lacking [12][13] with the stratigraphic sequence comprising typical continental 'Lower Old Red Sandstone' sediments similar to those from mid-high southerly palaeolatitudes of Laurussia.…”