Late Quaternary environmental changes in southernmost South America reflected in marine calcareous macro-and-microfossils

摘要

Late Quaternary environmental changes, especially sea-level fluctuations and glacial advances and retreats, affected the distribution of the benthic marine fauna which inhabited the Beagle Channel in southernmost South America. To evaluate these changes, calcareous macro-and-microfossils obtained from Holocene marine sediments along a sector of the western side of the Beagle Channel have been used for a multi-proxy approach. In total, 119 species were recovered: 65 mollusks (24 bivalves, 35 gastropods and 6 chitons), 33 foraminifera and 21 ostracods. Other preserved calcareous groups, which appeared in minor proportions, were brachiopods and cirripeds. The calcareous fossil assemblages from the early Holocene represent an ecosystem transition which started with vacant niches first occupied by opportunistic species, and/or eurytopic taxa. These were then replaced by more diverse fauna assemblages, associated with the proliferation of habitats which occurred under truly marine conditions during the Mid Holocene. When Holocene calcareous fauna is compared with its Pleistocene counterparts from the same region, some differences in the proportion of taxonomic groups and taxa composition are noted. These partly follow the heterogeneity of habitats in the Beagle Channel and water masses of different origin which have either greater or less influence throughout the Late Quaternary, but they can also be interpreted in association with environmental changes after the Last Glacial Maximum. In conclusion, the data provide insights into both spatial and temporal changes, and show evidence of a gradual transformation from a brackish to a marine environment caused by the Holocene sea transgression. It also documents Late Quaternary faunistic changes associated with topographic and ocean-ographic local conditions in this microbasin.