Silica biomineralizations in Holocene peatlands and fossil peat layers from Tierra del Fuego, Argentina

Abstract

Phytolith analyses are practically absent from peatlands, except for studies developed on tropical mires and peat profiles. In Tierra del Fuego, Argentina, peatlands represent the largest surface coverage in the South American continent. Because of their continuous sedimentation pattern, they represent relevant palaeoenvironmental records from which the econstruction of the latest Pleistocene-Holocene history of this region can be obtained. The aim of the study was to analyze the presence of phytoliths in selected mires and fossil peat layers from Tierra del Fuego, Argentina, and to compare these records with present vegetation. Phytoliths from the most abundant and representative plant species, a minerotrophic mire and an alluvial sequence with fossil peat layers were analyzed and described. Nine of the ten plant families analyzed produced phytoliths. The morphotypes described coincided with previous studies carried on species from other regions. Phytolith assemblages from top soil of both sites mostly coincided with the phytolith assemblages of the plants developed over them, except for tabular and cone sedge phytoliths, which were hardly found in soil samples. A lower silicification level and/or fragmentation processes could account for this absence. Profile analyses showed a low diversity of phytolith morphologies, either due to low plant diversity, a poor phytolith production of the species or to dissolution/fragmentation processes. Besides this low diversity, the phytolith assemblages described reflect the presence of grass communities during the development of these environments, being the Pooideae subfamily the dominant component of these communities. This study is the first to present results of phytolith analyses from cold-temperate, subantarctic peatlands, showing the importance of this proxy as a complement of others, such as pollen or charcoal particles in the palaeoenvironmental interpretation of the region.