A geochemical model for the preservation of insects in the Crato Formation (Lower Cretaceous) of Brazil

Barling, Nathan; Martill, David M.; Heads, Sam W.

doi:10.1016/j.cretres.2020.104608

Cited by 15 publications

(7 citation statements)

References 53 publications

(143 reference statements)

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“…The formation of pyrite replacements and their direct involvement in the replication of insect morphology are intrinsically associated with the time the fossils spent in the bacterial sulfate reduction zone of the sediment (Schiffbauer et al 2014). The taphonomic pathways of pyritized insects during the early diagenesis of the Crato Formation have been well documented in previous studies (Barling et al 2015(Barling et al , 2020Osés et al 2016;Bezerra et al 2020;Dias & Carvalho, 2020.…”

Section: A Micro-structure Preservation Of Weathered Insects From The...mentioning

confidence: 78%

“…The presence of microcracks in the insect cuticles of the Crato Formation has been frequently reported (Delgado et al 2014;Barling et al 2015Barling et al , 2020Osés et al 2016;Bezerra et al 2020Bezerra et al , 2021Dias & Carvalho, 2020Prado et al 2021). Crato insects with iron-oxide overgrowths show intricate zones of microcracks associated with compact cuticular surfaces without individualized 914 FI Bezerra et al…”

Section: B Scanning Electron Micrograph Analysismentioning

confidence: 94%

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Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

Bezerra

Silva²,

Agressot³

et al. 2023

Geol. Mag.

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Many studies have improved our understanding of the mode of preservation at the Crato fossil Lagerstätte. The high degree of preservation of the Crato mineralized insects is thought to be a consequence of the diffusion of ions through carcasses and envelopment by bacteria that, in turn, created microenvironmental conditions that led to mineralization, mainly pyritization. Pyritized insects have been oxidized by in situ weathering to more stable oxide/hydroxy minerals during Quaternary time. This transformation is essential to maintain the palaeontological information acquired during microbially induced pyritization in an oxidizing atmosphere. However, intense weathering can diminish or obscure the morphological fidelity, and little attention has been paid to the post-diagenetic processes experienced by these fossils. Here, we aim to determine the degree of alteration undergone by Crato pyritized insects using the following combination of analytical tools: scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared and Raman spectroscopy. Our results show that well-preserved insects are preferentially replaced by haematite and poorly preserved fossils are replaced by goethite. In addition, we recorded three types of post-diagenetic alteration: insects with iron-oxide overgrowths; insects associated with black coatings, sometimes with the formation of dendrites; and insects preserved as an impression, where only the outline of the body remains. All of these alterations have the potential to distort or tarnish palaeontological information. Here, we measured the effects of such telodiagenetic alterations at macro and micro scales. Therefore, this taphonomic approach has wide applicability wherever fine-grained deposits bearing mineralized insects are found.

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Section: A Micro-structure Preservation Of Weathered Insects From The...mentioning

confidence: 78%

Section: B Scanning Electron Micrograph Analysismentioning

confidence: 94%

Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

Bezerra

Silva²,

Agressot³

et al. 2023

Geol. Mag.

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“…The fossils were preserved with the cuticle being replaced by dark brown iron hydroxide (goethite) (Barling et al, 2015(Barling et al, , 2020. The holotype of Cratoaeschnidium martinsnetoi gen. et Remark: The coloration on wings or bodies of fossil insects from the Crato Formation is often well preserved (Nel and Jouault, 2021) allowing species delineation in some cases.…”

Section: Methodsmentioning

confidence: 99%

The third aeschnidiid dragonfly genus and species from the Lower Cretaceous Crato Formation (Odonata, Anisoptera)

2022

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Cratoaeschnidium martinsnetoi gen. et sp. nov., third genus and species of Aeschnidiidae from the Crato Formation (Brazil), is described and illustrated based on one well-preserved forewing.It can be differentiated from the other genera in the family, inter alia, because of its discoidal triangle very narrow with only one row of cells; three rows of cells between Mspl and MAa, and between Rspl and IR2; one row of cells between CuAa and MP in basal part; three rows of cells between RP3/4 and MAa. This new genus and species confirms that much can be expected in regard to discovering the Odonata in the Crato Formation.

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“…The Crato Formation is known for its high-fidelity preservation of flattened fossil insects. They are preserved in forms of pyrite and goethite, replacing the original cuticle, and of calcium phosphate, replacing the original internal soft tissues (Barling et al, 2020), as FPDM-I-145 most probably is. These fossilized insects are preserved within finely laminated limestones that tend to split into a form of plates, revealing insect fossils on its surface.…”

Section: Specimensmentioning

confidence: 99%

High-energy X-ray micro-laminography to visualize microstructures in dense planar objects

Hoshino¹,

Uesugi²,

Imai³

2023

J Synchrotron Radiat

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High-energy X-ray micro-laminography has been developed to observe inner- and near-surface structures in dense planar objects that are not suitable for observation by X-ray micro-tomography. A multilayer-monochromator-based high-intensity X-ray beam with energy of 110 keV was used for high-energy and high-resolution laminographic observations. As a demonstration of high-energy X-ray micro-laminography for observing dense planar objects, a compressed fossil cockroach on a planar matrix surface was analyzed with effective pixel sizes of 12.4 µm and 4.22 µm for wide field of view and high-resolution observations, respectively. In this analysis, the near-surface structure was clearly observed without undesired X-ray refraction-based artifacts from outside of the region of interest, a problem typical in tomographic observations. Another demonstration visualized fossil inclusions in a planar matrix. Micro-scale features of a gastropod shell and micro-fossil inclusions in the surrounding matrix were clearly visualized. When observing local structures in the dense planar object with X-ray micro-laminography, the penetrating path length in the surrounding matrix can be shortened. This is a significant advantage of X-ray micro-laminography where desired signals generated at the region of interest including optimal X-ray refraction effectively contribute to image formation without being disturbed by undesired interactions in the thick and dense surrounding matrix. Therefore, X-ray micro-laminography allows recognition of the local fine structures and slight difference in the image contrast of planar objects undetectable in a tomographic observation.

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A geochemical model for the preservation of insects in the Crato Formation (Lower Cretaceous) of Brazil

Cited by 15 publications

References 53 publications

Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

Effects of chemical weathering on the exceptional preservation of mineralized insects from the Crato Formation, Cretaceous of Brazil: implications for late diagenesis of fine-grained Lagerstätten deposits

The third aeschnidiid dragonfly genus and species from the Lower Cretaceous Crato Formation (Odonata, Anisoptera)

High-energy X-ray micro-laminography to visualize microstructures in dense planar objects

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