Organic petrology and geochemistry of the Los Molles Formation (Middle Jurasic) in the Picún Leufú area, Neuquén Basin

FERNANDO LARRIESTRA; ERRA, GEORGINA; COMERIO MARCOS; JUAN AGUSTIN ALVAREZ PINEDA; GOMEZ DACAL ALEJANDRO; GENTA ITURRERIA SANTIAGO; OTTONE GUILLERMO

Sofia

Congreso; 37th The Society for Organic Petrology Annual Meeting; 2021; 2021

The aim of this study is to estimate the quantity, quality and maturity of the organic matter preserved in the Middle Jurassic Los Molles Formation in relation with the hydrocarbon generation potential and its characterization as a source rock-unconventional play. The unit is considered as an effective source rock in the subsurface of the Neuquén Basin (Uliana et al., 1999; Brisson, 2015); nevertheless, there are few studies that integrate organic and inorganic geochemistry as well as organic petrology, particularly in the southernmost part of the basin (García et al., 2006; Martínez et al., 2005, 2008). The analyzed outcrop section (Matuasto II) is 61 m thick, and it is located near to the Puente Picún Leufú locality. This section of the unit is characterized by thick mudstones interbedded with massive to laminated sandstones, calcareous siltstones and ash-fall tuffs. Forty mudstone samples were obtained and processed for organic petrology, geochemistry and handheld X-ray fluorescence (XRF) at the Y-TEC laboratories. The determination of the Total Organic Content (TOC%), maximum temperature (Tmax) and S1, S2, S3, HI, OI and PI parameters was made through the pyrolysis of organic matter using a Rock Eval 6 equipment (Behar et al., 2001). Additionally, major, minor and trace elements percentages were obtained using a handheld XRF after the method described by Muller et al. (2017). Four representative samples were selected to the visual analysis of the organic components in transmitted light and nine for palynofacies analysis. Tyson?s (2005) classification scheme of the dispersed sedimentary organic matter components is followed herein. Transmitted and reflected light as well as blue light fluorescence analysis were carried out with a Zeiss A2m Imager binocular microscope coupled with the CRAIC PV 508 spectrometer and the software CoalPro. Kerogen in the studied section is, in general, terrigenous in origin, with translucid and opaque phytoclasts (mostly tracheophyte fragments), abundant miospores, and subordinated amorphous organic matter. Miospores show strong golden yellow fluorescence and amorphous organic matter show weak dull yellow fluorescence under blue light.