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

FAYÓ ROCÍO; ESPINOSA MARCELA A.; VELEZ AGUDELO CAMILO A.

GEOBIOS

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

Lugar: Paris; Año: 2023

0016-6995

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 4.40m 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 cmequidistant were extracted and oxidized with H2O2 for diatom analysis. 500 valves/slide were counted in order to calculate relative abundances. Diatom zoneswere 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 of freshwater planktonic taxa and the presence of gypsum suggest a shallower environment with increased salinity during the drier periods of the Plio-Pleistocene.http://dx.doi.org/10.2139/ssrn.4656057