Fourier Transform Infrared Spectroscopy analysis of organic fossil remains from the Triassic of Cacheuta, Mendoza, Argentina.

D`ANGELO, JOSÉ A; VOLKHEIMER, WOFGANG

Córdoba, Argentina

Congreso; 9 Congreso Argentino de Paleontología y Bioestratigrafía; 2006

Asoc. Pal. Arg., Acad. Nac. de Cienc. ,Univ. Nac. Córdoba

Although there is a number of contributions reporting the co-occurrence of plant and animal remains (especially in the Carboniferous of the Northern hemisphere), information on their chemistry is still very limited (e.g., Stankiewicz et al, 1998). The Dicroidium flora and the conchostracan fauna include well known fossil remains from the Triassic sequences exposed on the southern side of the Cacheuta hill, Mendoza, central western Argentina (e.g., Gallego, 1992; Morel, 1994; Zamuner et al., 2001). The first reports of Dicroidium flora from the Cacheuta hill area date as far back as the 19th century (Zuber, 1887; Szajnocha, 1888). Similarly, pioneer studies on conchostracan fauna in that area have also been known for more than a century (Jones, 1862; Geinitz, 1876). However, only recently the first chemical data of organic fossil plants from the Triassic of Cacheuta have been shown (D`Angelo, 2004; D`Angelo, in press). In the present contribution functional groups and semi-quantitative data (spectroscopic information) of co-occurring remains of animals and plants from the Cacheuta Formation (lower to upper Upper Triassic), Mendoza, Argentina, are reported for the first time. Identifiable organic fossil remains of Dicroidium odontopteroides (Corystospermales, Corystospermaceae) and Cyzicus (Euestheria) forbesi (Conchostraca, Cyzicidae) were analyzed by Fourier transform infrared spectroscopy (FT-IR). Infrared spectra obtained from compressions showed a relatively rich aliphatic structure as well as hydroxyl, carbonyl and some other oxygen-containing functional groups. Semi-quantitative data were obtained from FT-IR spectra using some area-integration methods (e.g., Sobkowiak and Painter, 1992; D`Angelo, 2004; D`Angelo and Marchevsky, 2004). The following regions of FT-IR spectra were employed to obtain semi-quantitative data: (a) 3100-3700 cm-1 (hydroxyl stretching), (b) 3000-3100 cm-1 (aromatic C-H out-of-plane stretching), (c) 2800-3000 cm-1 (aliphatic C-H stretching), (d) 1600-1800 cm-1 (oxygenated and aromatic carbon groups), (e) 1450-1475 cm-1 (alkyl C-H bending mode) and (f) 700-900 cm-1 (aromatic C-H out-of-plane bending). This preliminary FT-IR study reports chemical data of animal and plant contributions to sedimentary organic matter and provides some information on the survival of organic matter in Triassic sediments. Though cuticles have not preserved in the specimens analyzed, chemical differences found in co-occurring animal and plant organic remains suggest that the incorporation of molecular material from the seed fern into conchostracan remnants during diagenesis did not take place. This is in disagreement with the suggestion that some chemical compounds (especially aliphatic components) might have been transferred between plant and animal remains during diagenesis (Baas et al., 1995). Baas, M., Briggs, D.E.G., van Heemst, J.D.H., Kear, A.J. and de Leeuw, J.W. 1995. Selective preservation of chitin during the decay of shrimps. Geochimica et Cosmochimica Acta 59: 945-951.D`Angelo, J. 2004. FT-IR determination of aliphatic and aromatic C-H contents of fossil leaf compressions. Part 2: applications. Anuario Latinoamericano de Educación Química (ALDEQ) 18: 34-38.D`Angelo, J. in press. Analysis by Fourier transform infrared spectroscopy of Johnstonia (Corystospermales, Corystospermaceae) cuticles and compressions from the Triassic of Cacheuta, Mendoza, Argentina. Ameghiniana.D`Angelo, J. and Marchevsky, E. 2004. FT-IR determination of aliphatic and aromatic C-H contents of fossil leaf compressions. Part 1: analysis, curve-resolving and choice of bands. Anuario Latinoamericano de Educación Química (ALDEQ) 17: 37-41.Gallego, O.F. 1992. Conchostracos triásicos de Mendoza y San Juan. Ameghiniana 29 (2): 159-175.Geinitz, H.B. 1876. Ueber rhätische Pflanzen und Thierreste in den Argentinischen Provinzen La Rioja, San Juan und Mendoza. Palaeontographica 3: 1-14.Jones, R.T. 1862. A monograph of the fossil Estheriae, London. Palaeontographical Society, Monographs, vol. 14: 1-134.Morel, E.M. 1994. El Triásico del cerro Cacheuta, Mendoza (Argentina). Parte I: geología, contenido paleoflorístico y cronoestratigrafía. Ameghiniana 31 (2): 161-176.Sobkowiak, M. and Painter, P. 1992. Determination of the aliphatic and aromatic CH contents of coals by FT-i.r.: studies of coals extracts. Fuel 71: 1105-1125.Szajnocha, L. 1888. Über fossile Planzenreste aus Cacheuta in der Argentinischen Republik. Sonderberichte der Akademie der Wissenschaften, Wien. Mathematisch – Naturwissenchaftliche – Klasse 97: 219-245. Stankiewicz, B.A., Scott, A.C., Collinson, M.E., Finch, P., Mösle, B., Briggs, D.E. and Evershed, R.P. 1998. The molecular taphonomy of arthropod and plant cuticles from the Carboniferous of North America. Journal of the Geological Society of London 155: 453-462.Zamuner, A.B., Zavattieri, A.M., Artabe, A.E. and Morel, E.M. 2001. Paleobotánica. In: A.E. Artabe, E. Morel and A.B. Zamuner (eds.), El Sistema Triásico en la Argentina, Fundación Museo de La Plata, La Plata, Argentina, pp: 143-184.Zuber, R. 1887. Estudio geológico del Cerro Cacheuta y sus contornos. Boletín Academia Nacional de Ciencias 10: 448-472.