Late Palaeozoic red beds elucidate fluvial architectures preserving large woody debris in the seasonal tropics of central Pangaea

Abstract

Fluvial red beds containing anatomically preserved large woody debris shed new light on seasonally dry biomes of the Pennsylvanian-Permian transition and elucidate the concurrence of river depositional systems and vegetation. As a result, the occurrence, distribution and preservation of petrified large woody debris accumulations are considered crucial to understanding the role of arborescent vegetation in shaping fluvial environments. This study reports sizeable silicified trunks and corresponding fluvial architectures from the uppermost Pennsylvanian (upper Gzhelian) Siebigerode Formation (Kyffh€ auser, central Germany). The origin, taphonomy and depositional environment of the fossil woods are elucidated by using a multidisciplinary approach including geological mapping, lithofacies analysis, sediment petrography, wood anatomical studies and microstructure analyses. Results reflect the gradual burial of a gentle basement elevation by sand-bed to gravel-bed braided rivers at the northwestern margin of the perimontane Saale Basin. Facies architectures resulted from a complex interplay of syndepositional tectonics, repeated palaeorelief rejuvenation, high-frequency channel avulsion, seasonally dry climate and woody debris-sediment interactions. The alluvial influx and cut-bank erosion recruited trunks from adjacent semi-riparian slope habitats vegetated by up to 40 m tall cordaitaleans and conifers. High discharge in wide braids facilitated uncongested transport of large woody debris. Trunk entombment and initial preservation resulted from grounding on barforms, anchoring by attached roots and subsequent burial. The post-depositional two-phase silicification was influenced by hydrothermal hematite mineralization and determined a selective wood preservation pattern known as 'pointstone'. Large woody debris-induced sedimentary structures ('LWDISS') are introduced as a class of sediment structures formed by the biogenic impact on terrestrial deposition.

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

“…VISS were first catalogued from Carboniferous-aged strata (Rygel et al, 2004), and have since been reported from almost every subsequent geological period (e.g., Durand, 2008;Neff et al, 2011;Bashforth et al, 2014;Trümper et al, 2020). However, prior to this study, no true VISS have been described from the Devonian (although microscopic structures attesting to the sub-mm-scale movement and deposition of silt particles around comminuted debris have been termed such (Allen and Gastaldo, 2006)).…”

“…These examples st known tree fossils Fairon-Demaret, 1997, 2002;Giesen and Berry, 2013), provide evidence for the origination of wood as a novel sedimentary particle. Woody debris has subsequently persisted as a component of many sedimentary environments throughout the remainder of Earth history (e.g., Davies and Gibling, 2013;Wohl, 2013Wohl, , 2017Gulbranson et al, 2020;Trümper et al, 2020).…”

“…According to Rygel et al (2004), the term VISS excludes sedimentary structures induced by fallen or transported woody debris. However, driftwood can also act as an obstacle that induces sediment deposition, erosion and mounding (Nakayama et al 2002;Reesink et al, 2020), andTrümper et al (2020) h associated with flow deflection by accumulations of large woody debris in ancient strata . In instances where there is no preservation of plant material, but strata contain VISS-like structures (Figure 16), it may be impossible to tell whether they are VISS sensu stricto, whilst being confident that bedform irregularities were induced by plants, either in situ or transported.…”

Interrelatedness of Biota Revealed in Fossil Trees from the Permian Fossil Forest of Northern Tocantins, Central-North Brazil

“…In contrast to the well-studied fossil assemblages and rich data from the Carboniferous paleoequatorial wetlands (Gastaldo et al 1996;Greb et al 2006;Opluštil et al 2009), still, relatively less is known about the more dynamic environments of the Carboniferous-Permian transition in the same region (Trümper et al 2020). The scarcity of adequate information is not only due to an increasingly biased record.…”

An astronomical timescale for the Permian-Triassic mass extinction reveals a two-step, million-year-long terrestrial crisis in South China

“…However, adpressions of plant fossils are commonly found in red beds, so the absence of these in the Dongchuan Formation may well be a function of a lack of flora in the environment at the time of deposition (see e.g. Trümper et al, 2020).…”