Periglacial conditions in microscale

What is it about?

The present contribution examines microstructures on the surface of sand-sized quartz grains (0.8–1.0mm and 0.5–0.8mm) resulting from frost weathering. It addresses two questions: (1) In what kind of environment are quartz grains exposed to the most intense frost weathering? and (2) Do microstructures resulting from frost weathering depend on the sedimentary environment, that is, what is the influence of previous transport conditions and the type of weathering? Accordingly, it seeks features diagnostic of periglacial conditions and former active layers.

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Why is it important?

Microstructures on the surface of sand-sized quartz grains can be grouped into two types: (1) primary microstructures, which are left by processes that are common in the environment from which the grains are collected (e.g. aeolian, fluvial), and (2) secondary microstructures, which are caused by frost weathering and imprinted on or within the primary microstructures. The most characteristic secondary microstructures are breakage blocks (>10μm nd<10μm) and conchoidal fractures. Less common are crescentic gouges, curved grooves and scaling. Grains from every environment may be affected by frost weathering to the same degree, but grains that were previously transported in, for example, aeolian,fluvial or beach environments are probably the most susceptible to frost weathering. Moreover, the better the rounding of the grains, the more susceptible they are to frost weathering. The primary microstructures that are most susceptible to frost weathering are the convex parts of grains (rounded edges), vertical microsteps (microcliffs) connected with crescentic gauges and big conchoidal fractures, and solution crevasses. Pre-existing microfaults, in-grain weak-ness zones and microcracks facilitate frost weathering.