Organic petrology and geochemistry of the Santa Clara Abajo Formation, Triassic, Cuyana Basin, Argentina

SIDERAC FEDERICO; ERRA GEORGINA; CECILIA A. BENAVENTE

Congreso; 4th Palaeontological Virtual Congress; 2023

We present the results of visual analyses of organic matter(OM) recovered from outcrop samples of the Santa Clara AbajoFormation (SCAb) and geochemical studies of the sedimentobtained. The unit belongs to the Peñasco Group, and is locatedin the northern Mendoza province, which form part of theTriassic infill of the Santa Clara sub-basin (Cuyana Basin). The unitis approximately 500 m thick, and corresponds to fluvio-deltaicand lacustrine deposits. Five mudstone samples representing thecentral areas of the lacustrine area were obtained and analyzed toprovide data about the depositional environment and to evaluatetheir potential for hydrocarbon generation. The study included thedetermination of total organic carbon (TOC) content by pyrolysis,Rock Eval and OM analysis by transmitted light microscopy.Pyrolysis results showed TOC values between 1.03 and 1.84wt%, maximum temperature of S2 peak (Pyrolysis of kerogen)between 439°-445°C, Hydrogen Index between 332 to 626 mgHC/g rock, and kerogen type defined as KI-KIII. The OM contentis mainly terrestrial in origin, including palynomorphs such aspollen grains and spores (Inaperturopollenites, Klausipollenites,Neoraistrichia, Platysaccus, Leptolepidites and indet. striatedpollen), together with biostructured, opaque and translucentphytoclasts, and abundant amorphous OM components. Thecombination of the visual analysis and the geochemical resultssuggest a dominant terrestrial contribution of MO inputs towater bodies of low stability or reduced extension, with episodicrecharge, resulting in unfavorable conditions for the developmentof plants with higher moisture requirements. These rocks presentan early thermal maturation with good generation potential.