Abstract A foraminiferal faunal study was carried out in a Holocene marine section from Arroyo Baliza, located on the northwest coast of the Beagle Channel, to contribute to the knowledge of the palaeoenvironmental conditions during the marine Holocene event. Foraminiferal assemblage was represented by 32 species distributed among 21 genera. The assemblage was dominated by Elphidium macellum (Fichtel & Moll) Elphidium alvarezianum (d’Orbigny), Cribroelphidium excavatum (Terquem) and Buccella peruviana (d’Orbigny), accompanied by Cibicides fletcheri Galloway & Wissler and Cibicidoides dispars (d’Orbigny) in low proportion. The predominance of Peridiniales dinocysts in the marine palynomorphs assemblage, suggested inner neritic conditions with cooler and more nutrient-rich waters. The distribution of the foraminiferal species was variable throughout the section indicating palaeoenvironmental changes in Arroyo Baliza between 3499–2595 cal yr BP. A gradual passage from high energy, cold and well-oxygenated marine waters towards a shallower environment with low energy and low to moderate salinity of the waters were linked to the regressive phase. This study complements and supports the previous palynological data from this section, which reflects an increase in number and diversity of dinocyst species indicating marine environmental conditions during the late Holocene as it exists today in the Beagle Channel.

The Aserradero Lapataia 1 and 2 sites present clayey silty sediments including mollusk shell; Mulinia edulis, Mytilus chilensis, Aulacomya atra and Yoldia sp. Besides, dinoflagelate cysts, covers of benthonic foraminifera and copepod eggs are dominant. The microflora is represented by sporomorphs and fresh to salty water microplancton. Radiocarbon dates on Mulinia edulis shells yielded ages of 8094 ± 43 (AA74047) and 8167 ± 43 (AA74048) yr B.P. At Arroyo Baliza, clayey silts were found including Venus antiqua, Aulacomya atra, Mytilus chilensis, among others, accompanied by acritarchs and remnants of copepods. This association suggests marginal marine environments, with low to moderate salinity, and high nutrient concentration in the surface waters. Radiocarbon dating on Venus antiqua shells yielded 2844 ± 34 yr B.P. (AA74046). Marine deposits of the Aserradero Lapataia sites confirm the oldest ages known for the estuarine phase of the Holocene transgression in the Beagle Channel. Arroyo Baliza provide new evidence for the Late Holocene regressive phase in the Beagle Channel.

Los sitios Aserradero Lapataia 1 y 2 presentan depósitos limo-arcillosos portadores de valvas de moluscos: Mulinia edulis, Mytilus chilensis, Aulacomya atra y Yoldia sp. Además predominan los quistes de dinoflagelados, revestimientos de foraminíferos bentónicos y huevos de copépodos. Valvas de Mulinia edulis fueron datadas radiocarbónicamente en 8.094 ± 43 (AA74047) y 8.167 ± 43 (AA74048) a A.P. En Arroyo Baliza depósitos limo-arcillosos son portadores de Venus antiqua, Aulacomya atra, Mytilus chilensis, entre otros. La microflora está dominada por dinoquistes protoperidinioideos, acritarcos y restos de copépodos. Se sugiere ambientes marino-marginales, con baja a moderada salinidad, y altas concentraciones de nutrientes en las aguas superficiales. La datación radiocarbónica sobre Venus antiqua en Arroyo Baliza indica 2.844 ± 34 a A.P. (AA74046). Aserradero Lapataia confirma las edades más antiguas conocidas para la fase estuárica de la transgresión holocena en el canal Beagle. Arroyo Baliza aporta nueva evidencia de la fase regresiva en este canal durante el Holoceno tardío.