Abstract

CRUZ GUEVARA, Luis Enrique et al. PHYSICO CHEMICAL CHARACTERIZATION, TAPHONOMY AND ECOLOGY OF Orthokarstenia ewaldi (FORAMINIFERA: SIPHOGENERINOIDIDAE) LOS PINOS FORMATION (CRETACEOUS: MAASTRICHTIAN) FROM SAMACÁ (BOYACÁ, COLOMBIA). bol.geol. [online]. 2011, vol.33, n.2, pp.95-105. ISSN 0120-0283.

The Orthokarstenia genus is considered a microfossil guide to the ages of the Cretaceous period. The characteristic species of Los Pinos Formation corresponding to Cretaceous Period and Maastrichtian age and fits to the morphological description of Orthokarstenia ewaldi species. From the siliceous matrix several specimens were taken and macerated for Fourier transform infrared spectroscopy (FTIR) testing with KBr base. Specimens were collected from three levels of a rock. Three-dimensional images were taken with a video-microscopes to detail the form and structure of minerals. A fragment of rock was used to perform Laser-induced breakdown spectroscopy (LIBS) tests and to establish the presence of the elements Ca, Fe and Mg. Thin sections were also made and described. FTIR spectra of foraminifera were similar in the three levels where the samples were taken but showed differences with the spectrum of the silica matrix. LIBS analysis confirmed the presence of Ca and Fe in the samples. In thin sections, amorphous silica filling the shell was observed, and also a faint trace of the original shell as a fine sediment. Traces of Ca found with LIBS analysis confirm the replacement of aragonite to magnesian calcite and finally to silica. Using the relationship between the variance and the mean of three sizes of squares was determined the dispersion of the specimens. The values obtained indicated a clustered distribution type. This type of distribution is indicative of the conditions of resources in the habitat, reproduction and dispersal mode. It is possible to infer that the dominant reproductive system of O. ewaldi was megalospheric, being the asexual forms more common.

Keywords : Benthic; Foraminifera; FTIR; LIBS; Upper Cretaceous.

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