Paleolimnological interpretations from organic matter data for the Santa Clara Abajo paleolake, Triassic, Cuyana Basin, Argentina

SIDERAC FEDERICO; BENAVENTE CECILIA; ERRA GEORGINA

San Carlos de Bariloche

Congreso; International Association of Limnogeology- International Paleolimnology Association; 2022

The Santa Clara Abajo Formation (Peñasco Group) outcrops at the north of Mendoza province, as part of the Triassic infill of the Santa Clara subbasin, Cuyana Basin. It is composed of siltstones, fossiliferous shales, sandstone and subordinated conglomerates, corresponding to fluvial, deltaic and lacustrine deposits. The organic matter content was analyzed stratigraphically from five samples representing two facies association: a marginal lake facies association (samples M1 and M2 in lower section); and a lake center facies association (samples M3, M4, M5 in the middle and upper section). Organic matter (OM) extraction was carried out according to conventional techniques with hydrochloric (HCl) and hydrofluoric (HF) acids to obtain kerogen that was filtered through 10 and 150 um meshes. The retained material was mounted on glass slides and observed under a transmitted light optical microscope. All the samples were fertile and allowed the recognition of organic elements such as phytoclasts, palynomorphs and amorphous organic matter. The OM identified is mixed presenting both terrigenous and algal content in similar quantities, without variations in the proportions of the elements throughout the sequence. The recognized terrestrial components correspond to well preserved brown biostructured plants debris of woody particles, tracheids, cuticles and translucent plant tissues and various terrestrial palynomorphs (pollen and spores). Fluvio-lacustrine elements appeared as granular or spongy aggregates without defined structure, translucent, yellow to pale brown in color, corresponding to debris of algae in association with Botryococcus sp. The similarity in the composition of the OM both for the marginal subenvironment and for the center of the lake would indicate a shallow lacustrine body of reduced extension. This is coherent with previous findings of the overlying and more extensive Santa Clara Arriba paleolake with well differentiated palynofacies for the lake center facies association.