Reply to Butterfield: Low-sulfate and early cements inhibit decay and promote Burgess Shale-type preservation

Gaines, Robert R.; Hammarlund, Emma U.; Hou, Xianguang; Qi, Changshi; Gabbott, Sarah E.; Zhao, Yuanlong; Jin, Peng; Canfield, Donald E.

doi:10.1073/pnas.1207451109

Cited by 2 publications

(2 citation statements)

References 6 publications

(5 reference statements)

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“…Tissue loss occurred via limited sulfate reduction, as well as by the far less efficient pathways of methanogenesis and fermentation. Although Burgess Shale-type fossils have lost >99% of their volume to decay (Gaines et al, 2012d), decay was sufficiently restricted that it did not reach completion, and macrofossils were conserved as organic films. The remarkable anatomical detail captured in Burgess Shale-type fossils resulted from the firm and fine-grained nature of sediments, which aided in the retention of fine anatomical features-including those of labile tissues (Gaines et al, 2012c)-after organic tissues lost structural integrity and collapsed into two dimensions as they underwent degradation (Briggs and Kear, 1994 Carbonate cements at bed tops appear bright, clay-rich bed bases appear gray.…”

Section: ! Preservation Of Organic Fossils By Sealing Of the Early Bumentioning

confidence: 99%

Burgess Shale-type Preservation and its Distribution in Space and Time

Gaines

2014

Paleontol. Soc. pap.

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107

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Burgess Shale-type fossil assemblages provide a unique record of animal life in the immediate aftermath of the so-called “Cambrian explosion.” While most soft-bodied faunas in the rock record were conserved by mineral replication of soft tissues, Burgess Shale-type preservation involved the conservation of whole assemblages of soft-bodied animals as primary carbonaceous remains, often preserved in extraordinary anatomical detail. Burgess Shale-type preservation resulted from a combination of influences operating at both local and global scales that acted to drastically slow microbial degradation in the early burial environment, resulting in incomplete decomposition and the conservation of soft-bodied animals, many of which are otherwise unknown from the fossil record. While Burgess Shale-type fossil assemblages are primarily restricted to early and middle Cambrian strata (Series 2–3), their anomalous preservation is a pervasive phenomenon that occurs widely in mudstone successions deposited on multiple paleocontinents. Herein, circumstances that led to the preservation of Burgess Shale-type fossils in Cambrian strata worldwide are reviewed. A three-tiered rank classification of the more than 50 Burgess Shale-type deposits now known is proposed and is used to consider the hierarchy of controls that regulated the operation of Burgess Shale-type preservation in space and time, ultimately determining the total number of preserved taxa and the fidelity of preservation in each deposit. While Burgess Shale-type preservation is a unique taphonomic mode that ultimately was regulated by the influence of global seawater chemistry upon the early diagenetic environment, physical depositional (biostratinomic) controls are shown to have been critical in determining the total number of taxa preserved in fossil assemblages, and hence, in regulating many of the important differences among Burgess Shale-type deposits.

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Section: ! Preservation Of Organic Fossils By Sealing Of the Early Bumentioning

confidence: 99%

Burgess Shale-type Preservation and its Distribution in Space and Time

Gaines

2014

Paleontol. Soc. pap.

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107

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“…Though not fossil-associated calcite, such extensive bed-top calcite cementation could serve to restrict the diffusion of oxygen and sulfate to the site of decay (Gaines et al, 2012a). Weathering results in the dissolution of the bed tops, necessitating unweathered material for their identification (Gaines et al, 2012b). Under experimental conditions, pure carbonate sediment is not advantageous for the inhibition of decay (Wilson and Butterfield, 2014), but BST preservation has occurred in carbonate settings without aluminosilicates (Anderson, 2010).…”

Section: Calcificationmentioning

confidence: 99%

Taphonomic characteristics of fossils on the burgessshale-type spectrum

Broce¹

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"Study of exceptional fossil preservation tends to yield exciting results. Since soft-bodied organisms and the soft tissues of biomineralizing organisms are usually not preserved in the fossil record, instances of soft-tissue preservation are of immense value to paleontology and biology. Anatomical details of soft tissues are invaluable for understanding the phylogenetic relationships between organisms, as well as interpreting their life modes. Soft-bodied organisms are not only valuable phylogenetically, but they also are important members of ecological community structure. Without soft-tissue preservation, the interpretation of past environments, ecologies, and evolutionary lineages becomes extremely limited. That soft-tissue preservation is relatively rare is an unfortunate phenomenon that not only decreases the amount of available information, but also imposes biases on our understanding of the past. Soft-bodied organisms represent the vast majority of diversity, but are the minority of diversity in the fossil record. In fact, only about 30% of modern marine benthic macroorganisms contain hard parts suitable for easy preservation (Johnson, 1964) and in the Phyllopod Bed of the Cambrian Burgess Shale, only about 14% of species or 2% of individuals have hard parts (Morris, 1986), and consequently would not be preserved in most fossiliferous deposits." -- Introduction

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Reply to Butterfield: Low-sulfate and early cements inhibit decay and promote Burgess Shale-type preservation

Cited by 2 publications

References 6 publications

Burgess Shale-type Preservation and its Distribution in Space and Time

Burgess Shale-type Preservation and its Distribution in Space and Time

Taphonomic characteristics of fossils on the burgessshale-type spectrum

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