Métodos de análisis del contenido en carbonatos de series hemipelágicasestudio comparado en la Formación Represa (Albiense superior, Prebético)

Resumo

In this work a comparative analysis among four different methods for determining the percentage of carbonates in sedimentary rocks of mixed carbonate-siliciclastic composition is carried out: 1) X-ray diffraction, 2) total organic carbon (TOC), 3) loss in ignition (LOI) and 4) calcimetry. With this purpose, these techniques are applied to the Represa Formation (upper Albian) in the Serra dels Almaens in the Prebetic of Alicante. This unit is 450 m thick and consists of rhythmic hemipelagic facies (limestones and marls). The evolution of carbonate content throughout the series, obtained by the four techniques, shows similar patterns, indicating that all of them are adequate for the analyses. However, LOI is most inaccurate and imprecise, as it has a strong dependence on the mineralogy of the sample. By contrast, XRD appears as the most appropriate technique, not only because its good precision and accuracy, but because it yields a complete information about the mineralogy of the sample. The calcimetry technique has the advantage of simplicity and speed, at the expense of a more incomplete and imprecise information. Finally, the TOC technique has the advantage of needing smaller sample sizes and also it gives the most accurate results. But the good results are conditioned to the absence of other carbonates rather than calcium carbonate.