DIATOM AND SEDIMENTARY RECORD DURING THE HOLOCENE EVOLUTION OF THE DESEADO RIVER ESTUARY, SOUTHERN PATAGONIA, ARGENTINA

FAYÓ ROCÍO; ESPINOSA MARCELA A.; VELEZ AGUDELO CAMILO A.; ISLA, FEDERICO I.

La Plata

Congreso; XVIII Reunión Argentina de Sedimentología : IX Congreso Latinoamericano de Sedimentología; 2023

Asociación Argentina de Sedimentología

Diatoms have been successfully used as proxies for Holocene paleoenvironmental reconstructions in world numerous coastal evolution studies. A recent review analysis of modern and fossil diatom assemblages of the North Patagonian region in Argentina, showed that tidal effect is a very important factor in the species distribution of estuarine environments, being able to recognize characteristic tidal and non-tidal diatom assemblages. Diatom assemblages and coastal sedimentary succession in the macromareal estuary of Deseado River (Patagonia, Argentina) were studied in order to reconstruct the environment conditions in response to Holocene eustatic sea-level changes. 21 Samples were selected from a 200˗cm core (Cñ. La Mina: 47°46’49,4” S, 66°4’59,5” W). Chronology was based on two radiocarbons dating in bulk samples at 55 cm and 164 cm depth in the DIRECT-AMS laboratory (USA). They allowed obtaining a Holocene age of 5,791±30 and 8,145±35 14C yr. BP, respectively. The gray muds were the dominant sediments and different sedimentary structures are identified (laminated and lenticular bedding). Based on the temporal range included in the upper section of the core, the presence of a hiatus was inferred. Preliminary diatom analysis allowed to recognize that a core sediment was dominated by typical tidal diatoms assemblage: tychoplanktonic coastal-marine taxa (i.e., Paralia sulcata, Cymatocira belgica, Rhamphoneis amphiceros, etc.). Accompanying flora included Epithemia sorex, Shionodiscus oestrupii, Dimeregramma minor and scarce allochthonous fluvial fresh-brackish species were observed to the top. The site was significantly affected by the Holocene Sea-level during the last ca. 8,000 14C yr. BP. Ancient tidal channels were flooded in the Holocene postglacial transgression. Tidal flats and marshes have developed in the area during the late Holocene regression phase.