INGEIS   05370
INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Paleobiochemistry of fossil remains (Jurassic Cañadón Asfalto Formation, Chubut, Argentina).
Autor/es:
D`ANGELO, J A; MONFERRÁN, M; VOLKHEIMER, W; CABALERI, N
Lugar:
Trelew, Chubut
Reunión:
Congreso; V Simposio Argentino del Jurásico. Trelew, Chubut, Argentina; 2013
Institución organizadora:
Museo Paleontológico Egidio Feruglio, Trelew, Chubut, Patagonia Argentina
Resumen:
Jurassic remains of animals (?conchostracans?) and plants (gymnosperms) from Cañadón Lahuincó locality, middle Chubut River (near Cerro Cóndor village) are studied using scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) and Fourier Transform Infrared (FTIR) spectroscopy analyses. Provenance is the middle section of the Las Chacritas Member (Aalenian-Bathonian) of the Cañadón Asfalto Formation. SEM-EDS spectra of ?conchostracan? carapaces indicate the presence of chemical elements mainly related to silicate and phosphate minerals. Gymnosperms are preserved as coalified remains without cuticle (cuticle-free coalified layers). FTIR spectra reveal a molecular structure which is similar in composition to Type III kerogen, i.e. characterized mainly by hydrocarbon compounds with a dominant aromatic character. This is evidenced by small aliphatic C?H stretching peaks (2800-3000 cm−1 region) and distinct skeletal C=C stretching vibrations (in benzene rings, 1500-1700 cm−1 region). FTIR spectra of associated fusain remains show that only a few functional groups are left. This is in agreement with medium to high reflectance values of ~3.70 % measured in fusain remains, suggesting high temperatures of ~600º C. Alkaline medium prevalence is indicated by both phosphate mineral preservation in conchostracan carapaces and cuticle loss in cuticle-free coalified layers of gymnosperm leaves. Combined evidence points out to harsh post-diagenetic conditions related to volcanic-ash burial of this Jurassic flora and fauna. However, as demonstrated by a well preserved palynoflora in the same locality a few stratigraphic meters above the macrofossils here studied, different thermal alterations are evident due to varying degrees of heating by basaltic dikes.
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