CONICET | Buscador de Institutos y Recursos Humanos

Los Monos Formation (Devonian), Tarija basin: geochemical and mineralogical approach of the potential as shale gas and shale oil. The object of this study is to analyze the sedimentology and mineralogy of Los Monos Formationat Balapuca, in southern Bolivia, immediately north of the limit with Argentina, and in wells of the subandean region of Argentina. To this end, a sedimentological profile was taken from this unit and a total of 48 samples of outcrop and 50 samples of well cuttings were analyzed by X-ray diffraction on total rock and clays. It is possible to observe, through he X-ray diffraction mineralogical analysis that Los Monos Formation presents marked vertical and lateral lithological and mineralogical variability. Unrelated to whether they are psammites or shales, at least six stretches of low clay content (10%) are present along the whole length of the column; some of these are kaolinite enriched (40%) to the detriment of illite, and three contain intermediate clay content (20%). While in the middle to upper section there are two levels with 40% clay content. Los Monos Fm presents average total rock mineralogy principally composed of quartz (70%), plagioclase (10%) and clays (20%). Mineralogy of the clay fraction is characterized by the average presence of illite (45%), illite/smectite (20%), chlorite (25%) and kaolinite (10%). Three samples of outcrop with good crystallinity in IS showing 20% of expansive layers for the lower section of Los Monos Formation. These values would indicate the diagenesis of a deeply buried (Telodiagenesis) window of gas generation. In cutting samples, the IS component includes 30%-50% of expansive layers, indicating a diagenesis (late Mesodiagenesis) equivalent to end oil ? early gas hydrocarbon generation.