The Tumblagooda Sandstone revisited: exceptionally abundant trace fossils and geological outcrop provide a window onto Palaeozoic littoral habitats before invertebrate terrestrialization

Abstract

The establishment of permanent animal communities on land was a defining event in the history of evolution, and one for which the ichnofauna and facies of the Tumblagooda Sandstone of Western Australia have been considered an archetypal case study. However, terrestrialization can only be understood from the rock record with conclusive sedimentological evidence for non-marine deposition, and original fieldwork on the formation shows that a marine influence was pervasive throughout all trace fossil-bearing strata. Four distinct facies associations are described, deposited in fluvial, tidal and estuarine settings. Here we explain the controversies surrounding the age and depositional environment of the Tumblagooda Sandstone, many of which have arisen due to the challenges in distinguishing marine from non-marine depositional settings in lower Palaeozoic successions. We clarify the terminological inconsistency that has hindered such determination, and demonstrate how palaeoenvironmental explanations can be expanded out from unambiguously indicative sedimentary structures. The Tumblagooda Sandstone provides a unique insight into an early Palaeozoic ichnofauna that was strongly partitioned by patchy resource distribution in a littoral setting. The influence of outcrop style and quality is accounted for to contextualize this ichnofauna, revealing six distinct low-disparity groups of trace fossil associations, each related to a different sub-environment within the high-ichnodisparity broad depositional setting. The formation is compared with contemporaneous ichnofaunas to examine its continued significance to understanding the terrestrialization process. Despite not recording permanent non-marine communities, the Tumblagooda Sandstone provides a detailed picture of the realm left behind by the first invertebrate pioneers of terrestrialization.

The Silurian inception of inland desert ecosystems: trace fossil evidence from the Mereenie Sandstone, Northern Territory, Australia

“…The palaeogeographic and tectonic context of the Mereenie Sandstone thus favour that it was deposited some distance from any marine influence, with a high perched water table due to local groundwater flow, which rose further as the basin centre continued to subside (Shaw et al, 1991). In light of this assessment, the ichnofauna of the succession may have global significance in comparison with known Silurian-Devonian continental ichnofaunas from settings that retained some marine connectivity (Draganits et al, 2001;Krapovickas et al, 2016;Shillito & Davies, 2020).…”

“…Palaeomagnetic studies have suggested that it was most likely deposited between the early Silurian and the Early Devonian (with the caveat that signals may have been overprinted) (Li et al, 1991). Gouramanis and McLoughlin (2016) favoured a late Silurian to Early Devonian age for the unit, based on comparison with other trace fossil-bearing strata across Australia: although ichnostratigraphic age estimates must be treated with caution (Egenhoff et al, 2007;Buatois & Mángano, 2011;Davies et al, 2011;Mángano et al, 2012), especially as the units with which it was compared (Tumblagooda Sandstone, Major Mitchell Sandstone, Mount Daubeny Formation, Ravendale Formation) are themselves not directly dated (Cayley & Taylor, 1997;Neef & Bottrill, 2001;Neef, 2004;McNamara, 2014;Shillito & Davies, 2020).…”

“…Despite these new perspectives, almost all ichnological insights into early terrestrialization come from sedimentary successions that were deposited in environments with periodic marine influence, typically occurring in close proximity to emergent tidal facies (Draganits et al, 2001;MacNaughton et al 2002;Shillito & Davies, 2020). There is thus a knowledge gap concerning the establishment of trace fossil communities in inland regions, with little published evidence for colonization until the latest Silurian and early Devonian (Morrissey et al, 2012a;Minter et al, 2016b;.…”

Ediacaran life close to land: Coastal and shoreface habitats of the Ediacaran macrobiota, the Central Flinders Ranges, South Australia

“…Facies 8 bedding planes, which archive intricately preserved sedimentary surface textures that formed at the time of deposition, can be defined as ''true substrates'' (Davies and Shillito 2018). Recent work attests that the preservation of such high-resolution original morphology requires no unusual circumstances, with the occasional preservation of true substrates an inevitability of the interplay between the ordinariness, sedimentary stasis, and spatial variation that sculpt the siliciclastic record (e.g., Miall 2015;Tipper 2015;Davies et al 2017Davies et al , 2019Shillito and Davies 2020). Notions that delicate sedimentary surface textures (e.g., adhesion marks, ripple marks) require the aid of microbial cohesion of sediment for preservation (in the Rawnsley Quartzite and elsewhere) (e.g., Gehling 2000;Seilacher 2008;Sarkar et al 2011;Sappenfield et al 2017;Bradley et al 2018;MacNaughton et al 2019) are unnecessary.…”

Cold feet: Trackways and burrows in ice-marginal strata of the end-Ordovician glaciation (Table Mountain Group, South Africa)

“…to be an environmental stress that resulted in low diversity or diminutive ichnofaunas in late Paleozoic strata (Buatois et al, 2006;Jackson et al, 2016). However, the Matjiesgoedkloof ichnofauna differs from expectations as it is similar to non-glacial shallow marine strata elsewhere in the Table Mountain Group (Rust, 1967;Braddy and Almond, 1999), and some of its most prominent ichnotaxa are archetypal constituents of other lower Paleozoic Gondwanan sandy littoral environments in non-glacial settings (e.g., Heimdallia and Diplichnites : Shillito and Davies, 2020). The similarities between the glacial Matjiesgoedkloof ichnofauna and its nonglacial contemporaries resembles trends observed in modern settings, where comparable ichnofauna occur in both arctic and temperate littoral settings and it is position on the high-low tidewater transect that chiefly controls specific ichnoassemblages (Aitken et al, 1988).…”