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.

An early-middle Holocene section in Bahía Lapataia (54º 50' S, 68º 34' W), Beagle Channel, Tierra del Fuego, Argentina has been examined taking into account its sporomorphs and organic-walled microplankton. The palynological assemblage suggests nearshore environments. Two relatively higher sea levels were identified by the increased abundance of organic-walled dinoflagellate cysts (Brigantedinium spp., Selenopemphix sp., Operculodinium centrocarpum sensu Wall and Dale, Spiniferites spp.), the acritarch Halodinium sp. and zoomorph remains (test linings of foraminifera and copepod egg-envelopes). The littoral vegetation at the time of the marine incursion was mainly arboreal, as can be seen in the pollen records by significant increase in Nothofagus dombeyi type frequencies, while a forest-steppe vegetational pattern developed regionally. After comparison with another nearby fossil marine terrace, the palynological analysis has demonstrated that these terraces represent the same transgressive-regressive event. The relative altitudinal differences between these terraces in the area may be the result of seismotectonic activity during the Holocene.

Se estudia una sección del Holoceno temprano-medio en Bahía Lapataia (54º 50' S, 68º 34' O), Canal Beagle, Tierra del Fuego teniendo en cuenta los esporomorfos y el microplancton. La asociación de microplancton sugiere ambientes cercanos a la costa. Son identificados dos niveles relativos de mar alto con las mayores abundancias de quistes de dinoflagelados (Brigantedinium spp., Selenopemphix sp., Operculodinium centrocarpum sensu Wall y Dale, Spiniferites spp.), del acritarco Halodinium sp. y restos de zoomorfos (caparazón de foraminíferos y huevos de copépodos). La vegetación del litoral durante la incursión marina fue principalmente arbórea, como puede observarse en los registros polínicos con un incremento significante de Nothofagus tipo dombeyi, mientras patrones vegetacionales de bosque-estepa se extendían regionalmente. Por comparación con una terraza marina cercana, el análisis palinológico ha demostrado que las dos terrazas representan el mismo evento transgresivo- regresivo. Las diferencias relativas altitudinales entre las terrazas podrían ser el resultado de la actividad sismotectónica durante el Holoceno.