title: Spectroscopic analysis and X-ray diffraction of trunk fossils from the Parnaíba Basin, Northeast Brazil.
abstract: The Parnaiba Sedimentary Basin is of the Paleozoic age and is located in Northeast Brazil, covering the states of Piauí, Maranhão and Tocantins and a small part of Ceará and Pará. In this work we applied several chemical analytical techniques to characterize trunk fossils found in the Parnaíba Sedimentary Basin, collected from four different sites, and discuss their fossilization process. We performed a study of the trunk fossils through X-ray diffraction, energy dispersive spectroscopy, infrared and Raman spectroscopy. The analysis allow us to identify the different compositions which are present in the trunk fossils: kaolinite (Al2Si2O5(OH)4), hematite (Fe2O3) and quartz (SiO2). Based in these results we were able to identify that the main fossilization mechanism of the trunk fossil was silicification. Furthermore, through Raman spectroscopy, we have observed the presence of carbonaceous materials in the Permian fossils, as evidenced by the D and G Raman bands. The relative intensities and bandwidths of the D and G bands indicated that the carbon has a low crystallinity. Thus, most of trunk fossils analyzed were permineralized and not petrified, because there is the presence of carbon that characterizes the partial decomposition of the organic matter in some trunks.
authors.affiliation: Universidade Federal do Piauí, CCN, Departamento de Física, Teresina, Piauí, Brazil.
authors.forename: Wemerson J
authors.initials: WJ
authors.lastname: Alencar
authors.affiliation: Universidade Federal do Piauí, CCN, Departamento de Física, Teresina, Piauí, Brazil.
authors.forename: F Eroni P
authors.initials: FE
authors.lastname: Santos
authors.affiliation: Universidade Federal do Piauí, Núcleo de Arqueologia e Paleontologia, Teresina, Piauí, Brazil.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Cisneros
authors.affiliation: Universidade Federal do Cariri, Cidade Universitária, Juazeiro do Norte, Ceará, Brazil.
authors.forename: João H
authors.initials: JH
authors.lastname: da Silva
authors.affiliation: Universidade Federal do Ceará, C.P. 6030, Departamento de Física, Fortaleza, Ceará, Brazil.
authors.forename: Paulo T C
authors.initials: PT
authors.lastname: Freire
authors.affiliation: Universidade Federal do Piauí, CCN, Departamento de Física, Teresina, Piauí, Brazil; Universidade Federal do Piaui, CCN, Pós Graduação em Ciências dos Materiais, Teresina, Piauí, Brazil. Electronic address: bartolomeu@ufpi.edu.br.
authors.forename: Bartolomeu C
authors.initials: BC
authors.lastname: Viana
mesh_terms: D001938:Brazil; D005580:Fossils; D019015:Geologic Sediments; D010944:Plants / Q000033:anatomy & histology*; D013052:Spectrometry, X-Ray Emission; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D014732:Vibration; D014961:X-Ray Diffraction
keywords: Parnaíba Basin; Silicification; Trunk fossils; Vibrational spectroscopies