Scanning electron microscope (SEM) microtextural analysis as a paleoclimate tool for fluvial deposits: A modem test

Microtextural analyses of sedimentary quartz grains are increasingly being used as a paleoenvironmental proxy, as some microtextures have been proposed to reflect processes unique to a particular environmental or climatic condition. However, little consensus exists regarding which microtextures or microtextural suites may be unique to an environmentally relevant process, along with appropriate quantitative approaches for data analysis. This study documents microtextures on quartz grains from fluvial systems in modern end-member climates, along with quartz grains from moraine samples in two proglacial fluvial settings, to assess whether climate imparts unique microtextures potentially useful for interpreting paleoclimate. To isolate climate as the primary variable, other attributes such as bedrock lithology, transect length, and drainage basin size were controlled to the degree possible in an empirical comparison. The presence of 17 microtextures on first-cycle quartz from fluvial systems in Puerto Rico, Norway, California, and Peru, as well as two moraine samples from Peru and Norway, was documented under double-blind conditions, and results were analyzed using principal component analysis (PCA). Humid climates were found to be statistically distinct from arid climates on the basis of common precipitation features and V-shaped percussion fractures on grains from humid climates. Grains from arid climates exhibited a larger incidence of upturned plates, interpreted to reflect the influence of high-stress eolian saltation on grains that subsequently underwent fluvial entrainment. Grains from proglacial systems exhibited a higher incidence of fracture faces, possibly attributable to the effects of both freeze-thaw weathering and glacial crushing, corroborated by higher occurrences of these textures on grains from the moraine samples as well. However, with the exception of the humid-arid distinction, differences in microtextural suites are subtle. These results suggest that quartz microtextural analysis holds some promise for aiding paleoclimatic interpretations for coarse-grained fluvial strata, but more research is needed to assess whether additional methodological approaches to grain analyses and/or statistical techniques could further strengthen climatic differentiation.