The molecular preservation of exceptionally preserved conifer needles from middle Miocene and Pliocene deposits on Banks Island, Canada, was investigated using pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS). Solvent-extracted residues from Miocene Larix, Glyptostrobus, and Pinus, Pliocene Picea, and their associated bulk material, yielded abundant polysaccharide pyrolysis products, such as 2-methylfuran, 2-furaldehyde, and levoglucosan, indicating excellent molecular preservation. Comparison of pyrolysates of individual plant taxa and bulk material from the same deposits revealed the dominance of particular plant taxa in these high latitude floras. Comparison with fossil Lagerstätten from Ellesmere Island (late Paleocene) and Axel Heiberg Island (middle Eocene), both in the Canadian Arctic Archipelago, and Clarkia in Idaho, United States (middle Miocene), demonstrated that the quality of molecular preservation of material from Banks Island is similar to that of Axel Heiberg Island and lies between those of Ellesmere Island and the Clarkia deposit. The ranking of molecular preservation was paralleled by scanning electron microscopy (SEM) observations. Analysis of Larix and Glyptostrobus from different geological ages (Eocene–recent) and locations indicated that age does not correlate with molecular preservation in these fossil Lagerstätten. When relative abundance ratios of vinyl phenol (m/z 91 120), guaiacyl (m/z 109 124), and levoglucosan (m/z 60 73) are used as indicators of the preservation of cutin, lignin, and cellulose, our results suggest that variations in the pyrolysates among several genera reflect different original molecular compositions as well as paleoenvironmental conditions for preservation. The data also illuminate the role of labile biomolecules in the taphonomy of three-dimensionally preserved morphological structures in these Arctic plant fossils.

Study of the Burgess Shale-type deposits of the Cambrian has greatly enhanced scientific understanding of early animal evolution, but as the mechanisms by which these deposits formed are still unclear, here we outline and present data from the application of a new analytical approach, Raman spectroscopy, that can be used to characterize fossils from these deposits. Although these deposits present exceptional views into a diverse, nonbiomineralized to lightly biomineralized biota, this taphonomic regime mostly disappears from the fossil record after the Cambrian, with a few notable exceptions. Numerous detailed taphonomic and chemical studies have provided significant insight into modes of fossil preservation in these deposits, although there is still significant debate regarding the preservational and diagenetic mechanisms that may be involved. Compared to previous electron microscopy-based elemental mapping approaches, which have identified the elemental components of similar fossils, Raman spectroscopy allows a determination of the chemical phases and specific mineralogy at the molecular level, as well as the thermal maturity, of these fossils. This approach therefore provides new types of data, such as hematite phase, that may prove helpful for elucidating some of the mechanisms responsible for the exceptional types of preservation found in these deposits, and potentially helps to resolve the existing taphonomic debates.

This study represents a first attempt to observe soft-tissue decay in association with microbial mats, in order to recreate the death-mask model proposed for terminal Neoproterozoic Lagerstätten. This model explains the precipitation of authigenic iron sulfide minerals on, and around, decaying carcasses in association with microbial mats, cementing the sediment as a sole veneer and retaining the external morphology of the organism in relief on the upper and lower surface of coarse-grained sandy event beds. Although this model has been substantiated by the discovery of abundant microbially induced sedimentary structures (MISS) and pyrite veneers in close association with Ediacaran fossils, it has not been tested previously by experimental taphonomic studies under controlled laboratory conditions. Arthropod larvae that decayed on top of a cyanobacterial mat demonstrated higher quality preservation of fine-scale anatomy than larvae that decayed in the absence of a mat. Decay experiments involving bacterial mats and organic-rich sands generated a black ring extending radially from the decaying carcasses. When this precipitate was analyzed using XPS and ESEM-EDS it revealed the presence of likely iron sulfides, or at least spatially associated Fe and S, and localized concentrations of common aluminosilicate elements (Al, K, Fe, and Mg), which is a composition that has been documented in association with Ediacaran fossil preservation.

Study of noncalcareous algal fossils is problematic due to their broadly defined taxonomy and lack of preserved features by which modern algae are classified. Four distinct morphologically simple, enigmatic fossils from the Wheeler Formation were analyzed using Raman spectroscopy, and elemental mapping by electron microbeam techniques. These fossils have been interpreted as dissociated algal fragments, and accordingly, were compared to known algal fossils: Yuknessia simplex (green alga; Spence Shale), Marpolia spissa (cyanobacteria; Burgess Shale), and Margaretia dorus (green alga; Burgess and Wheeler formations). All fossils examined were composed of carbonaceous films, at least in part, but varied with respect to secondary mineral coatings: iron oxides were associated with the surfaces of all three algal species to some degree, and in addition, Margaretia dorus exhibited silicification. Fossils characterized by a thin, wispy, filamentous form (Linear Morphotype 2) display mineralogical and morphological similarities with Marpolia spissa, but lack the characteristic longitudinal striping of this species. Filamentous fossils with a coiled form were the only fossils found to contain chlorite. These fossils are interpreted to be fecal strings. Stubby, linear fossils (Linear Morphotype 1) that commonly have been interpreted as fragmented Yuknessia simplex exhibit neither the mineralogical nor the microtextural features of this algal fossil, making this interpretation unlikely. As with Linear Morphotype 1, fossils of Morania fragmenta lack secondary iron oxides and phyllosilicates. Accordingly, they are interpreted to have been composed of labile material that preserves only under inhospitable conditions such as sustained anoxia.

The recently discovered Fezouata Biota, from the Early Ordovician (late Tremadocian to late Floian) of Morocco, preserves a diverse soft-bodied fauna. While preservation is mostly of Burgess Shale-type, giant anomalocaridids also occur in siliceous concretions. Petrographic and geochemical analyses of these concretions reveal their growth history and the circumstances that led to the fossilization of nonbiomineralized anatomy within them. The large (>1 m) concretions are homogeneous in composition and geochemical characteristics, suggesting rapid, pervasive growth of mineral frameworks during decay of the large animals at, or near, the sediment-water interface. Concretions are comprised of ultrafine-grained (2–20 µm) authigenic quartz, Fe chlorite, and calcite, a composition unlike other described marine concretions. Abundant pyrite, now represented by oxide pseudomorphs, grew adjacent to the anomalocaridid carcasses, but rarely within the matrix of the concretions. This distribution indicates that sulfate reduction around the carcasses was vigorous within otherwise organic-poor sediments resulting in the establishment of prominent chemical gradients around the giant anomalocaridids that led to early precipitation of mineral overgrowth around nonbiomineralized tissues. Rapid precipitation of intergrown silica and Fe chlorite required an abundant source of silica, iron, and aluminum. These ions were likely derived from dissolution of volcanic ash in the sediments. Limited intergrown calcite (δ¹³C avg. −12.2‰, n  =  23) precipitated from bicarbonate that was generated largely by sulfate reduction of organic tissues of the carcasses. Whereas Burgess Shale-type preservation of fossils in the Fezouata biota required suppression of degradation, exceptional preservation of anomalocaridids within the siliceous concretions resulted from extensive microbial decomposition of a large volume of organic tissues. Rapid mineralization was facilitated by localization of microbial activity around the large carcasses and must have required an unusually reactive sediment composition.

Spectacular trilobite Lagerstätten occur in distinctive offshore calcareous mudstone facies through the Late Ordovician to Devonian, and reflect a combination of mass mortality or molting and burial, coupled with early diagenetic enhancement. Evidence indicates two distinct modes of burial, Type I and II assemblages, which show evidence for burial without or with seafloor disturbance, respectively. Type I assemblages suggest rapid (hours to days), but not instantaneous burial, without bottom disruption, enabling preservation of in situ behavior, including mass aggregations and molt ensembles. Most occurrences contain bedding planes in which trilobites exhibit incipient disarticulation. These assemblages were buried by cascades of flocculated sediment from hypopycnal, detached flows. Type II assemblages show well-articulated, enrolled, semi-enrolled, and outstretched trilobites in varied orientations relative to bedding. In such cases, bottom flows and seafloor disruption by storm or seismic disturbances in shallow waters suspended large amounts of flocculated muds as viscous slurries, which developed into hyperpycnal flows that entrained carcasses of trilobites and other organisms. In many cases, both Type I and II obrution was followed by additional sedimentation, geochemical zones moved upward through the sediment column, and there was little tendency to form diagenetic overprints. Alternatively, if burial was followed by an interval of sediment starvation, the sediments were bioturbated and very early diagenetic mineralization was superimposed, first, in rare cases, as mineralized soft parts in entombed carcasses, and later as pyritization of burrow linings. Development of the concretionary layers required more prolonged periods of stability of the sulfate reduction zone. Cementation of sediment shielded organism bodies from most or all effects of compaction. Thus, ironically, the best preservation of delicate remains required rapid burial, associated with mass mortality, and very low rates of background sedimentation following the event.

Insects are diverse and abundant components of most terrestrial ecosystems today and are well represented in the fossil record with first occurrences in the Early Devonian. Fossil deposits that include exceptionally preserved insect assemblages are found in several different types of Lagerstätten, with their preservation in amber and in lake sediments being of greatest importance. Researchers have used a variety of approaches to study the taphonomy of insects preserved in lacustrine environments and have identified several important variables that contribute to the preservation potential of insects. A combination of insect ecology, morphology, and the depositional setting in which an insect specimen rests influence the preservation potential of insects and ultimately affect the spatial, temporal, and compositional resolution of fossil assemblages. In general, lacustrine insect assemblages experience very little spatial and temporal averaging. Compositional fidelity of assemblages tends to be low, with an overabundance of allochthonous taxa from smaller size classes. In addition, the composition of fossil insect assemblages will be biased depending on the specimen's position within a lake, dependent on both water depth and distance from shore. Focus areas for future research are outlined, as are recommendations for improving field collecting methods and statistical approaches. Finally, the benefits of conducting synthetic studies using global databases and the importance of studying unexceptional deposits are discussed.

Shaanxilithes ningqiangensis is an enigmatic ribbon-shaped fossil from the upper Ediacaran Gaojiashan Member of the Dengying Formation, southern Shaanxi Province, South China. This taxon has also been reported from Ediacaran successions in North China and possibly in Siberia, making it a potential index fossil for interregional biostratigraphic correlation of upper Ediacaran successions. At Gaojiashan, Shaanxilithes ningqiangensis is often preserved along bedding planes of phosphate-rich silty and calcareous shale, with no evidence of vertical intrusion into adjacent beds and containing little to no carbonaceous material. Here, through detailed microstructural and microchemical investigation using a combination of analytical techniques, taphonomic details of Shaanxilithes ningqiangensis and potentially related forms are revealed, showing that these enigmatic fossils are preserved as clay molds. Together with other taphonomic features, such as abruptly bent ribbons, overlapping but not crosscutting ribbons, and co-occurring discoidal structures interpreted as disarticulated sections of the original organism, the new data suggest that Shaanxilithes ningqiangensis is a body fossil consisting of serially arranged units that are discoidal, lensoidal, or crescentic in shape. Shaanxilithes ningqiangensis is not a trace fossil as some previous researchers have suggested.