title: Deciphering the preservation of fossil insects: a case study from the Crato Member, Early Cretaceous of Brazil.
abstract: Exceptionally well-preserved three-dimensional insects with fine details and even labile tissues are ubiquitous in the Crato Member Konservat Lagerstätte (northeastern Brazil). Here we investigate the preservational pathways which yielded such specimens. We employed high resolution techniques (EDXRF, SR-SXS, SEM, EDS, micro Raman, and PIXE) to understand their fossilisation on mineralogical and geochemical grounds. Pseudomorphs of framboidal pyrite, the dominant fossil microfabric, display size variation when comparing cuticle with inner areas or soft tissues, which we interpret as the result of the balance between ion diffusion rates and nucleation rates of pyrite through the originally decaying carcasses. Furthermore, the mineral fabrics are associated with structures that can be the remains of extracellular polymeric substances (EPS). Geochemical data also point to a concentration of Fe, Zn, and Cu in the fossils in comparison to the embedding rock. Therefore, we consider that biofilms of sulphate reducing bacteria (SRB) had a central role in insect decay and mineralisation. Therefore, we shed light on exceptional preservation of fossils by pyritisation in a Cretaceous limestone lacustrine palaeoenvironment.
authors.affiliation: Programa de Pós-graduação em Geoquímica e Geotectônica, Institute of Geosciences, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Gabriel Ladeira
authors.initials: GL
authors.lastname: Osés
authors.affiliation: Institute of Geosciences, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Setembrino
authors.initials: S
authors.lastname: Petri
authors.affiliation: Programa de Pós-Graduação em Ecologia e Recursos Naturais, Universidade Federal de São Carlos , São Carlos , São Paulo , Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Becker-Kerber
authors.affiliation: Institute of Geosciences, Universidade Federal do Pará , Belém , Brazil.
authors.forename: Guilherme Raffaeli
authors.initials: GR
authors.lastname: Romero
authors.affiliation: Institute of Physics, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Marcia de Almeida
authors.initials: MA
authors.lastname: Rizzutto
authors.affiliation: Department of Fundamental Chemistry/Institute of Chemistry, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Fabio
authors.initials: F
authors.lastname: Rodrigues
authors.affiliation: Brazilian Synchrotron Light Laboratory , Campinas , Brazil.
authors.forename: Douglas
authors.initials: D
authors.lastname: Galante
authors.affiliation: Institute of Physics, Universidade de São Paulo , São Paulo , Brazil.
authors.forename: Tiago Fiorini
authors.initials: TF
authors.lastname: da Silva
authors.affiliation: Department of Physics, Centro Universitário FEI , São Bernardo do Campo , Brazil.
authors.forename: Jessica F
authors.initials: JF
authors.lastname: Curado
authors.affiliation: Laboratory of Technological Plasmas, Universidade Estadual Paulista , Sorocaba , Brazil.
authors.forename: Elidiane Cipriano
authors.initials: EC
authors.lastname: Rangel
authors.affiliation: Laboratory of Technological Plasmas, Universidade Estadual Paulista , Sorocaba , Brazil.
authors.forename: Rafael Parra
authors.initials: RP
authors.lastname: Ribeiro
authors.affiliation: Department of Biology, Universidade Federal de São Carlos , Sorocaba , Brazil.
authors.forename: Mírian Liza Alves Forancelli
authors.initials: ML
authors.lastname: Pacheco
keywords: Araripe Basin; Crato Member; Early Cretaceous; Exceptional preservation; Insects; Paleometry; Pyrite; Taphonomy