Organic geochemistry and chemostratigraphy of the Los Molles Formation, Neuquén basin, Argentina

Abstract

The present study comprises the sampling carried out in an outcrop of the Los Molles Formation at the Puente Picún Leufú area, Neuquén Province, Argentina. A section of 22.6 m thickness (“M3”) was described and 22 samples were analysed at the Y-TEC laboratories. The main objective was the characterization of the organic petrology and organic geochemistry in terms of different parameters of quantity, quality and maturity of the organic matter to evaluate the potential of hydrocarbon generation along with chemostratigraphy analyses.The study included the determination of Total Organic Carbon content (TOC) by pyrolysis using a ROCK EVAL 6 equipment, and organic petrology by means of an Axio-Imager microscope with a CRAIC coupled spectrometer and XRF fluorometry. Major, minor and trace elements were characterized by X ray fluorescence. The results obtained showed TOC values between 0.69 and 1.84% wt., and a distribution of HI values in the sequence between 5 - 313 mg HC / g TOC. The organic petrology shows that the content of kerogen was strongly continental, dominated mainly by superior plant material, miospores, resins of vegetal origin, fluorescent and non-fluorescent amorphous organic matter with a low contribution of type II kerogen. The values of Tmax obtained from the pyrolysis are between 423 – 447 °C immature and early oil window in concordance with vitrinite reflectance values (0.38% - 0.45%). Paleoredox elements such as V, As, Zn, Mo, and S, were consistent with the reducing setting related to high TOC values and to kerogen quality, proving the occurrence of anoxic and euxinic environments. From the organic geochemical perspective, the Los Molles Formation in this sector of the Neuquén Basin is a regular to good source rock, with predominant type III kerogen, and in a low proportion type II, in an immature state with potential to generate hydrocarbons, mainly gas.