Abstract
The Misoa Formation (Eocene) is characterized by a monotonous succession of sandstones and shales with scarce faunal content. This unit has been divided into several operational bodies based on its lithological, electric and radioactive log character. Its rich oil content, expressed in the wells studied in the area, leads to the need for a better knowledge and understanding of its stratigraphic development, in order to enhance its exploitation. This works is focus on the upper informal units (B1, B2, B3, B4 and B5) where their lithological content of interbedded sandstones and shales, make difficult to generate accurate chronostratigraphic correlations.
Chemical analysis of 298 samples from three wells were developed to establish concentrations of major (wt%) chemical elements expressed in oxide SiO2, TiO2, Al2O3, Fe2O3, MnO, CaO, MgO, Na2O, K2O, P2O5, minor and trace elements (ppm) Ba, Ce, Co, Cu, La, Mo, V, S, Sn, Rb, Sr, Zr, Y, Cr, Ni, Pb and Zn, by using optical emission spectrometry with inductively coupled plasma (ICP-OES). In addition, mutivariate statistical analysis was undertaken to conduct chemical characterization of informal units for each well. The use of inter-elemental ratio (V/Al) and V/(V+Ni) help to define maximum flooding surfaces (MFS) and flooding surfaces (FS), allowing to confirm the MFS-43 previously defined by seismic correlation in the study area.
These results point out those B-informal units have higher geochemical fingerprint that can be chemically correlated and used in other areas of interest at this level of the Misoa Formation. This method probe to be a valuable tool, to be applied reliably statistically in siliciclastic sequences with little or no biostratigraphic control in order to reduce the uncertainty of the stratigraphic model, also this method contributes to the definition of high-frequency stratigraphic surfaces (thirth, fourth, fifth and up to sixth order).
