Abstract:Sponges are one of the major faunistic components of the Burgess Shale-type fossil Lagerstätte of Chengjiang (Cambrian Stage 3, South China). Although pyritization is often invoked as a key process linked to the early diagenetic preservation in the Chengjiang Fauna, the unweathered specimens analyzed lack evidence of pyrite. Energy dispersive X-ray (EDX) analyses of these specimens show a robust and continuous film of organic carbon. Most of the Chengjiang sponges underwent extensive weathering and diagenetic … Show more
“…A comprehensive analysis of the effects of weathering on the Chengjiang fossils was undertaken by Forchielli et al (2014), who characterized the elemental composition of fossils and the mineralogic and chemical composition of the host mudstones across a weathering gradient. The results of this study confirmed earlier suggestions (Hu, 2005;Forchielli et al, 2012) that pyritization in Chengjiang fossils was limited to discrete anatomical aspects, and verified the dominance of carbonaceous preservation in unweathered specimens. With weathering, Chengjiang fossils were shown to progressively lose carbon and to acquire coatings of Fe-oxides derived from the oxidation of pyrite in the enclosing mudstones (as evidenced by the loss of S) and resulting from the redistribution of Fe along voids and cracks, including those associated with Burgess Shaletype fossils (Forchielli et al, 2014).…”
Section: ! Auxiliary Mineralization Of Selected Soft Tissuessupporting
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.
“…A comprehensive analysis of the effects of weathering on the Chengjiang fossils was undertaken by Forchielli et al (2014), who characterized the elemental composition of fossils and the mineralogic and chemical composition of the host mudstones across a weathering gradient. The results of this study confirmed earlier suggestions (Hu, 2005;Forchielli et al, 2012) that pyritization in Chengjiang fossils was limited to discrete anatomical aspects, and verified the dominance of carbonaceous preservation in unweathered specimens. With weathering, Chengjiang fossils were shown to progressively lose carbon and to acquire coatings of Fe-oxides derived from the oxidation of pyrite in the enclosing mudstones (as evidenced by the loss of S) and resulting from the redistribution of Fe along voids and cracks, including those associated with Burgess Shaletype fossils (Forchielli et al, 2014).…”
Section: ! Auxiliary Mineralization Of Selected Soft Tissuessupporting
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.
“…Although it is impossible to confirm the original compositions based on the current material, the impressions were probably produced by mineralized tissues. Silica and carbonates, both commonly utilized in sponge skeletal construction, are often diagenetically dissolved in Chengjiang fossils (e.g., Forchielli et al, 2012). Figure 4.Raman spectra measured from Vauxia leioia n.…”
Non-spicular sponges constitute >8% of the extant sponge biodiversity at the species level, yet their evolutionary history is poorly known due to a sparse fossil record. The genus Vauxia, previously only known from middle Cambrian (Miaolingian, Wuliuan) Lagerstätten, was regarded as the earliest fossil record of non-spicular demosponges. Here we describe the first vauxiid sponge, Vauxia leioia new species, from the early Cambrian Chengjiang Biota (Series 2, Stage 3). This sponge exhibits a double-layered fibrous skeleton: the mesh and fiber thickness of the endosomal layer are irregular while the dermal layer, which directly connects with the endosomal skeleton without intermediate supporting fibers, is regular in both aspects. Measurements using scanning electron microscope and Raman spectroscopy revealed that the endosomal fibers are composed of carbonaceous material, but are tomographically indiscernible from the host rock, while the dermal fibers are preserved as impressions without obvious accumulation of carbonaceous material. Although the original composition of the dermal skeleton is now hard to establish, we cannot rule out that it was siliceous. The morphological characters of V. leioia n. sp. represent an intermediate state between other Vauxia species and the recently established vauxiid genus Angulosuspongia. However, more data are required to reconstruct the phylogenetic relationship among these taxa.UUID: http://zoobank.org/0ebb91b8-5dad-420f-bb2c-dc203d37bebd
“…The oxidation of early-formed iron pyrite would produce a low pH environment and small amounts of H 2 SO 4 on and perhaps around the carcass. Thus, original biominerals have been dissolved 28 (but see 31 , who report un-weathered sponge spicules showing a robust carbon film and no pyrite), and it is not possible to determine the original composition of the spines.…”
Nidelric pugio gen. et sp. nov. from the Cambrian Series 2 Heilinpu Formation, Chengjiang Lagerstätte, Yunnan Province, China, is an ovoid, sac-like metazoan that bears single-element spines on its surface. N. pugio shows no trace of a gut, coelom, anterior differentiation, appendages, or internal organs that would suggest a bilateral body plan. Instead, the sac-like morphology invites comparison with the radially symmetrical chancelloriids. However, the single-element spines of N. pugio are atypical of the complex multi-element spine rosettes borne by most chancelloriids and N. pugio may signal the ancestral chancelloriid state, in which the spines had not yet fused. Alternatively, N. pugio may represent a group of radial metazoans that are discrete from chancelloriids. Whatever its precise phylogenetic position, N. pugio expands the known disparity of Cambrian scleritome-bearing animals, and provides a new model for reconstructing scleritomes from isolated microfossils.
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