Paleoenvironmental reconstruction of a Neogene diatomite deposit from La Pampa Province (Argentina)

• Published in: Geobios 2024-08
• Main Authors: Fayó, Rocío, Espinosa, Marcela Alcira, Vélez-Agudelo, Camilo Andrés
• Format: Article
• Language: English
• Subjects: Diatomite; Diatoms; Neogene; Northern Patagonia; Paleoenvironmental changes; Paleolakes
• ISSN: 0016-6995
• DOI: 10.1016/j.geobios.2024.02.009

•The diatom evidence confirms that the CP diatomite deposit has a continental origin.•A shallow and alkaline paleolake was established during Plio-Pleistocene in La Pampa.•Volcanic ash provides Si and P for the diatom blooms and diatomite deposition.•Small fragilarioids are ubiquitous in Northern Patagonia from the Plio/Pleistocene.•CP Diatomite results from regional drying trend in the Patagonian Argentina. Diatomite deposits constitute siliceous biogenic sedimentary rocks primarily composed of diatoms. In Argentina, there is a scarcity of paleoenvironmental reconstructions for these deposits. This study focuses on the analysis of the diatom content in a Plio-Pleistocene diatomite from La Pampa Province. The aim is to identify diatom diversity and reconstruct the evolution of paleoenvironments. The studied section of 4.40 m is located at the CP site (38°08′40.5′’S; 67°09′23.2′’W, El Sauzal Formation). The profile is a laminated white diatomite with three levels of volcanic ash. Seven samples 50 cm-equidistant were extracted and oxidized with H2O2 for diatom analysis. 500 valves/slide were counted in order to calculate relative abundances. Diatom zones were defined using CONISS. The analysis revealed 72 morphospecies, with 28 of them exhibiting abundances > 4%. The diatom flora is predominantly composed of small fragilarioid diatoms accompanied by Discostella, Aulacoseira, Epithemia, Rhopalodia, and Cymbella species, indicating a lacustrine origin. At the base, a paleolake with a relatively alkaline pH, low nitrogen concentrations and high phosphates (volcanic ash) favored the growth of a diverse diatom community. Towards the top, the dominance of fragilarioids, the decrease in freshwater planktonic taxa and the presence of gypsum suggest a shallower environment with increased salinity during the drier periods of the Plio-Pleistocene.