FOSSIL PHYTOLITH ASSEMBLAGES FROM SOUTHERN PATAGONIA INDICATE CHANGING HABITATS DURING THE MIDDLE MIOCENE CLIMATIC OPTIMUM
Here, we present preliminary results from analysis of phytolith assemblage composition (% plant functional types) from the main stratigraphic section of coastal SCF, documenting vegetation change during the early part of the MMCO, and interpreting it in light of current climatic reconstructions based on isotopic and faunal data. With the exception of the oldest assemblage, most phytolith assemblages analyzed so far are more or less dominated by forest indicators, including palms. Although there is no clear pattern of variation in overall assemblage composition (e.g., forest indicator: open habitat indicator ratio) through time, different forest indicators dominate different assemblages, which could be explained by vegetation shifts through time, spatial heterogeneity, or both. Grass phytolith assemblages consist mainly of morphotypes from C3 pooid grasses throughout the section, but are characterized by a substantial decrease in morphotype size from older to younger levels, which may reflect decreased water availability. These results are consistent with isotopic data indicating dominantly C3 vegetation and a shift toward a more arid climate characterized by decreased MAP as well as increased MAT during the onset of the MMCO, but suggest that this drying did not result in an expansion of open-habitat grasses.