FOSSIL DIATOM STUDY REVEALS SIGNIFICANT FRESHWATER INPUT IN MIOCENE COASTAL MARINE ENVIRONMENTS OF THE SOUTHWESTERN ATLANTIC (PATAGONIA, ARGENTINA)

ALLENDE-MOSQUERA, AYLÉN; CUITIÑO, JOSÉ; ESPINOSA, MARCELA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2023

0002-7014

A 209 m-thick sedimentary succession exposed a 24 t Estancia Redonda Chicalocality (northeastern Patagonia, Argentina) includes both the Gaiman Formation (EarlyMiocene) and the Puerto Madryn Formation (Late Miocene). Based on thesedimentologic analysis, the Gaiman Formation is interpreted as accumulated in amarine inner shelf to shoreline environment, whereas an estuarine to terrestrialenvironment is interpreted for the Puerto Madryn Formation. Fifteen samples wereprocessed and analyzed for diatoms, providing for the first time a micropaleontologicalrecord for these units, allowing us to go deeper into the paleoenvironmentalinterpretations. Fourteen diatom species, two diatom genera, and chrysophytestomatocysts were identified. The dominant diatom elements among the samples areParalia sulcata, Lemnicola hungarica, Cocconeis placentula, and Pseudopodosira sp.,together with chrysophyte stomatocysts. Paleoecological information drawn fromdiatom assemblages is consistent with paleoenvironmental interpretations based onsedimentological analysis for both units. However, diatom analysis for the GaimanFormation suggests a strong freshwater influence in an inner shelf environment, whichwent unnoticed by utilizing other proxies. We suggest a high productivity marine zonemay have developed as consequence of nutrients supply from rivers favoring diatomgrowth. This could explain the unique great abundance of macroinvertebrates andmarine vertebrates preserved in the sedimentary succession.