Inferring Vegetation and Climate from Playa Phytolith Assemblages

The calibration of paleoclimate and paleovegetation proxies must rest on actualism: observation of contemporary processes in settings analogous to the fossil record being studied. In this study we test the decay-in-place assumption invoked by some grassland phytolith researchers. If correct, variability in grass phytolith assemblages should be correlated with local vegetation differences. Alternatively, we argue that grass short-cell phytolith assemblages are regionally homogenized so that assemblages reflect extralocal or regional vegetation. This paper examines the phytolith variability in the Texas High Plains for the purpose of better interpreting playa fossil records. Twenty-three samples were analyzed from two separate transects. Each transect extended to capture the full range of local edaphic and vegetation variability within and adjacent to playas. Phytoliths were extracted from these surface samples using ZnBr2 heavy liquid separation and analyzed using standard light microscopy techniques. While a few rare non-grass phytolith morphtypes could indicate a decay-in-place process, grass short-cell assemblages do not record the local vegetation variability but reflect a homogenization of dominate regional grasslands. This finding supports our assertion that playa phytolith records can be used to infer change in regional climate and vegetation.