Gravitational Constraints on the Burial of Chengjiang Fossils

Zhang, Xiguang; Hou, Xianguang

doi:10.2110/palo.2006.p06-085r

Cited by 23 publications

(21 citation statements)

References 55 publications

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“…Mass asphyxiation events owing to a fluctuating oxycline, which would have also affected parts of the water column, may also explain the abundance of free-swimming taxa within the EBS mudstones, especially Isoxys communis, the most common soft-bodied species in the EBS. Such forms are frequently preserved in either dorso-ventral or lateral aspect (with the largest and flattest surface area oriented parallel to bedding), suggestive of gravitational settling (see Zhang & Hou 2007), as opposed to turbid burial, which can result in oblique orientations (Caron & Jackson 2006;Gabbott et al 2008;Gaines 2014). In the case of the free-swimming arthropods, the abundance and orientation of their remains may also be a consequence of moulting, as indicated by the common occurrence of 'bivalved' carapaces without trunks, and isolated elements (especially frontal appendages and body flaps) of Anomalocaris.…”

Section: Preservation Of Emu Bay Shale Fossilsmentioning

confidence: 99%

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

Paterson

García‐Bellido

Jago

et al. 2015

JGS

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Recent fossil discoveries from the lower Cambrian Emu Bay Shale (EBS) on Kangaroo Island, South Australia, have provided critical insights into the tempo of the Cambrian explosion of animals, such as the origin and seemingly rapid evolution of arthropod compound eyes, as well as extending the geographical ranges of several groups to the East Gondwanan margin, supporting close faunal affinities with South China. The EBS also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in Cambrian Konservat-Lagerstätten. EBS fossils display a range of taphonomic modes for a variety of soft tissues, especially phosphatization and pyritization, in some cases recording a level of anatomical detail that is absent from most Cambrian Konservat-Lagerstätten.

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Section: Preservation Of Emu Bay Shale Fossilsmentioning

confidence: 99%

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

Paterson

García‐Bellido

Jago

et al. 2015

JGS

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“…2A and SI Appendix, Fig. S2) and by the chaotic orientations of soft-bodied fossils within individual claystone beds (20,21). In most BST deposits, eventdeposited claystone beds range from approximately 1 to 15 mm in thickness, but in the Chengjiang and Burgess Shale, event beds up to 8-cm thick are present (17,18).…”

Section: Entombmentmentioning

confidence: 99%

Mechanism for Burgess Shale-type preservation

Gaines

Hammarlund

Hou

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

180

147

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Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft-bodied fossil assemblages has remained enigmatic since Walcott’s initial discovery in 1909. Here, we demonstrate the mechanism of Burgess Shale-type preservation using sedimentologic and geochemical data from the Chengjiang, Burgess Shale, and five other principal Burgess Shale-type deposits. Sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation. Low sulfate concentrations in the global ocean and low-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier, provided by bed-capping cements that were emplaced at the seafloor, is a feature that is shared among Burgess Shale-type deposits, and resulted from the unusually high alkalinity of Cambrian oceans. Thus, Burgess Shale-type preservation of soft-bodied fossil assemblages worldwide was promoted by unique aspects of early Paleozoic seawater chemistry that strongly impacted sediment diagenesis, providing a fundamentally unique record of the immediate aftermath of the “Cambrian explosion.”

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“…(2007) found examples of trace fossils in direct contact with soft‐bodied fossils in the Yu’anshan Formation, demonstrating that it is possible for BST preservation to occur in close association with sediments deposited under bottom water with oxygen high enough to support a benthic fauna, at least periodically. The orientations of Chengjiang fossils indicate transport of most assemblages; only rarely fossils appear to have been preserved in situ (Zhang & Hou 2007), which again would have required preservation in close temporal and spatial association with at least marginally oxygenated bottom waters.…”

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confidence: 99%

Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah

Garson

Gaines

Droser

et al. 2012

LET

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Garson, D.E., Gaines, R.R., Droser, M.L., Liddell, W.D. & Sappenfield, A. 2011: Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah. Lethaia, Vol. 45, pp. 164–177. Burgess Shale‐type faunas provide a unique glimpse into the diversification of metazoan life during the Cambrian. Although anoxia has long been thought to be a pre‐requisite for this particular type of soft‐bodied preservation, the palaeoenvironmental conditions that regulated extraordinary preservation have not been fully constrained. In particular, the necessity of bottom water anoxia, long considered a pre‐requisite, has been the subject of recent debate. In this study, we apply a micro‐stratigraphical, ichnological approach to determine bottom water oxygen conditions under, which Burgess Shale‐type biotas were preserved in the Middle Cambrian Spence Shale of Utah. Mudstones of the Spence Shale are characterized by fine scale (mm‐cm) alternation between laminated and bioturbated intervals, suggesting high‐frequency fluctuations in bottom water oxygenation. Whilst background oxygen levels were not high enough to support continuous infaunal activity, brief intervals of improved bottom water oxygen conditions punctuate the succession. A diverse skeletonized benthic fauna, including various polymerid trilobites, hyolithids, brachiopods and ctenocystoids suggests that complex dysoxic benthic community was established during times when bottom water oxygen conditions were permissive. Burgess Shale‐type preservation within the Spence Shale is largely confined to non‐bioturbated horizons, suggesting that benthic anoxia prevailed in intervals, where these fossils were preserved. However, some soft‐bodied fossils are found within weakly to moderately bioturbated intervals (Ichnofabric Index 2 and 3). This suggests that Burgess Shale‐type preservation is strongly favoured by bottom water anoxia, but may not require it in all cases. □Anoxia, Burgess Shale, Burgess Shale type‐preservation, Langston Formation, Spence Shale Member, Utah.

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Gravitational Constraints on the Burial of Chengjiang Fossils

Cited by 23 publications

References 55 publications

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

Mechanism for Burgess Shale-type preservation

Dynamic palaeoredox and exceptional preservation in the Cambrian Spence Shale of Utah

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