Early Cambrian metazoans in fluvial environments, evidence of the non-marine Cambrian radiation: COMMENT

Davies, Neil S.; Gibling, Martin R.

doi:10.1130/g32737c.1

Cited by 15 publications

(5 citation statements)

References 10 publications

(13 reference statements)

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“…After extensive and detailed examination of bedding tops and cross‐sections in the southern Marble Mountains, this study identified no evidence of fossil traces in the distal fluvial environment. Such a conclusion reinforces the hypothesis that the reported trace fossils represent marine organisms that burrowed older fluvial sediments during periods of marine flooding (Davies & Gibling, ; McIlroy, ) and emphasizes the importance of gathering detailed architectural analysis and palaeoenvironmental constraints when assessing the habitability of distal terrestrial environments. Near the coastline, braid deltas (McPherson et al ., ) form tidally influenced areas of stagnant water that interfinger with the fluvial system and may harbour life (e.g.…”

Section: Discussion: Depositional System Synthesissupporting

confidence: 83%

Architecture of a distal pre‐vegetation braidplain: Cambrian middle member of the Wood Canyon Formation, southern Marble Mountains, California, USA

2019

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Architectural element analysis and detailed mapping of a 300 m along-strike exposure of the middle member Wood Canyon Formation, southern Marble Mountains, California, USA, provides new evidence for extensive braidedfluvial channel-belt deposits with adjacent overbank environments. Threedimensional models constructed using 'Structure from Motion' techniques, combined with field-based observations, allowed interpretation of outcropscale trends, barforms, channel fills and fine-scale features. The ca 80 m thick member is divisible into five distinct units, including units M1 to M3 that form the bulk of the stratigraphy. Units are defined by stacking patterns of three facies associations (Facies Association 1 to Facies Association 3), each representing the product of a subenvironment within the fluvial system. In Facies Association 1, stacked cosets, interpreted as low-relief fluvial bars and channel fills, preserve vertical-accretion and downstream-accretion elements under unimodal north-north-west palaeoflow, with minor lateral accretion near bar edges. Deposits of Facies Association 2 to Facies Association 3, linked to overbank environments, are found only in unit M2, in the middle 27 m of the middle member. Floodplains, represented by Facies Association 2, include crumbly red-orange intervals of fine to mediumgrained sandstone and thinner sets of cross-bedding than Facies Association 1, interbedded with thicker cross-stratification indicative of overbank splay or overland flow aggradation from adjacent channel belts during flood stage. Possible aeolian beds of Facies Association 3 preserve broad festooned trough cross-strata that average 23 cm in thickness; their small size, medium-grained sandstone and iron oxide cement suggest a high water table. The diverse assemblage of interpreted subenvironments, paired with bedform and facies patterns, implies a perennial fluvial system that gradually built large sand bars as the channel belt migrated and avulsed across an unconfined braided-fluvial reach, leaving the overbank area on its flanks subject to weathering and aeolian transport. Despite the occurrence of strata deposited in low-energy and ponded settings, and a marine influence proposed for nearby sections of middle member, no ichnofossils were encountered.

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Section: Discussion: Depositional System Synthesissupporting

confidence: 83%

Architecture of a distal pre‐vegetation braidplain: Cambrian middle member of the Wood Canyon Formation, southern Marble Mountains, California, USA

2019

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“…Our current understanding of the ichnological record reveals that arthropods were the earliest pioneer animals to make forays onto land. Evidence for sporadic excursions onto subaerially exposed substrates by marine-dwelling arthropods can be witnessed in Cambrian and Ordovician successions worldwide, where sedimentological evidence proves that trackwayhosting strata were deposited in littoral environments, often demonstrably within metres of the marine shoreline (MacNaughton et al 2002;Collette et al 2010;Davies et al 2011a;Davies & Gibling, 2012;McIlroy, 2012;Minter et al 2016a;MacNaughton et al 2019;Shillito & Davies, 2019a, b). In younger strata, deposited around the Silurian-Devonian boundary, unequivocal instances of fully non-marine trace fossil communities occur (Minter et al 2016b(Minter et al , 2017Buatois & Mángano, 2018); their environmental preferences demonstrated by close association with diagnostic non-marine sedimentary phenomena including palaeosols, certain fluvial architectural styles, and in situ plant or root fossils (e.g.…”

Section: Terrestrialization and The Tumblagooda Sandstonementioning

confidence: 99%

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

Shillito

Davies

2020

Geol. Mag.

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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.

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“…Notwithstanding, the absence of rooted vegetation on the Earth's surface during the Meso-and Neoproterozoic should have exerted a marked influence on the development of continental depositional systems (Davies and Gibling, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…On the current Earth's surface, the stabilising influence of vegetation controls the intensity and the rate of weathering, and rates of sediment erosion, transport and deposition. The absence of the stabilising influence of vegetation during the Precambrian might suggest the development of continental sedimentary systems that differed considerably to those that post-dated the evolution of land plants (Davies and Gibling, 2012). Thus, it seems reasonable to believe that in the Precambrian, a bare land surface might have encouraged the mobilisation of sand-grade sediment by the wind and the construction and accumulation of large aeolian systems, which might be expected to develop in more widespread environments and climates than in postvegetation landscapes.…”

Section: Introductionmentioning

confidence: 99%

Microbial influence on the accumulation of Precambrian aeolian deposits (Neoproterozoic, Venkatpur Sandstone Formation, Southern India)

Basílici

Soares

Mountney

et al. 2020

Precambrian Research

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Early Cambrian metazoans in fluvial environments, evidence of the non-marine Cambrian radiation: COMMENT

Abstract: Early Cambrian metazoans in fl uvial environments, evidence of the non-marine Cambrian radiation

Cited by 15 publications

References 10 publications

Architecture of a distal pre‐vegetation braidplain: Cambrian middle member of the Wood Canyon Formation, southern Marble Mountains, California, USA

Architecture of a distal pre‐vegetation braidplain: Cambrian middle member of the Wood Canyon Formation, southern Marble Mountains, California, USA

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

Microbial influence on the accumulation of Precambrian aeolian deposits (Neoproterozoic, Venkatpur Sandstone Formation, Southern India)

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