Fine Material in Rock Fractures: Aeolian Dust or Weathering?

Abstract

Fine material in rock crevices from the deserts of southwestern North America and Hawaii, studied by light and electron microscopy, derive from both in situ weathering of the adjacent rock and the accumulation of aeolian dust. In some cases, such as quartz found in Hawaiian rock crevices, we see evidence for an aeolian origin. In other cases, the texture and chemistry of the fine material indicates a weathering origin. Fines in rock fractures are analogous to soils, and a general model for development of “fissuresols” is presented. Where rocks are friable and weathering is rapid, a residual fissuresol develops. Where dust storms are common and rocks are resistant to weathering, a cumulic fissuresol forms. A continuum likely exists between these two extremes in space today, from drier to wetter climates. Fissuresols can be tens of thousands of years old and experience drastically different climates. Therefore, the relative importance of weathering and aeolian input can shift over time.