Detection and interpretation of cyclic patterns in coals from Los Cuervos Formation, Venezuela

• Manuel Martínez Universidad Central de Venezuela
• Grony Garbán Universidad Central de Venezuela
• Alfonso Benavides Universidad Central de Venezuela
• Marcos Escobar Instituto Zuliano de investigaciones Tecnológicas (INZIT-CICASI)-Venezuela
• Iván Esteves Instituto Zuliano de investigaciones Tecnológicas (INZIT-CICASI)-Venezuela

Palabras clave: coal, cyclicity, lithofacies, sulfur, Venezuela

Resumen

A total of 21 coal samples, belonging to Los Cuervos Formation, were taken in Villa Páez, Táchira State, Venezuela, with the aim of establishing vertical variations in their geochemical parameters. The samples were subject to immediate (moisture, volatile matter, fixed carbon and ash), elemental (C, H, N, S) and petrographic analysis. It was found a significant correlation between sulfur and ash content in coals, with width ofbeds, and their location in each lithofacies (Spearman correlation coefficient > 0.80): those in which coals are sporadic, the beds are thin, high in sulfur and ash. On the contrary, in lithofacies with abundant coal seams, these are of great thickness, clean (S < 0.7%) and ash low ( < 6% ) . Cyclostratigraphic analysis of the sequence allowed the identification of a cycle of 72 m wavelength, and other two cycles of higher frequency but lower power, of wavelength of 11 and 5 m. These values are in agreement with Milankovitch's cycles of short excentricity (123 ky) and orbital precession (18 ky). Lithofacies and geochemical changes in coals match with the main cycle of 72 m.