Biotic-abiotic environmental characterization of the Cerro Pampa Paleolake (Chiquimil Formation, Upper Miocene) in Catamarca, Argentina

The Villavil-Quillay Basin (Catamarca Province, Argentina) preserves a well-documented Late Miocene to Pliocene sequence, offering insights into Southamerican shifts during a period of global climate changes. The Chiquimil Formation (Late Miocene) at the Cerro Pampa locality contains lacustrine sediments rich in fossil diversity and of unique sedimentological features. Here we analyze the paleoflora, paleofauna, stratigraphy and geochemistry of the Cerro Pampa Paleolake, to reconstruct its environmental conditions. Fossil-bearing pelites exhibit a tabular disposition intercalated with sandstones, siltstones and claystones. Clay mineralogy comprises illite-smectite, chlorite and quartz. The Chemical Index of Alterations analysis yielded values ranging from 55 to 76, indicating moderate degrees of alteration. Furthermore, we identified 34 morphotypes of leaves and the physiognomic analysis revealed values of Mean Annual Temperature = 23.95° ± 4.8° and Mean Annual Precipitation = 118 mm². Concerning the paleofauna, fish remains were identified as the anablepid Jenynsia Günther, 1866 and additionally, the bivalves Cyanocyclas anzoteguiae (Morton, 2003 in Morton and Herbst, 2003) and C. herbsti (Morton, 2003 in Morton and Herbst, 2003) and the gastropods Heleobia sp. Stimpson, 1865, Gastrocopta sp. Wollaston 1878 and Biomphalaria sp. Preston, 1910 were recorded. Microfossils correspond mainly to Cyprideis calchaquiensis Zamudio and Carignano, 2023 and to a lesser extent to Limnocythere sp. Brady, 1867 and Ilyocypris sp. Brady and Norman, 1889 (ostracods). Integrated data suggest that paleolake sediments were firstly deposited under relatively humid and warm conditions, then transitioning to drier conditions primarily driven by Andean uplift. This interpretation is supported by fossil plants, which point to arid conditions, similar to the contemporary Monte phytogeographical region. Additionally, the macro and microfossils indicate a primarily freshwater system with periods of desiccation and episodic increases in salinity transitioning the system to oligo and meso-haline waters.