Fig. 2. Secondary salts and mineral nodules in the micromorphology samples.

(A) Photomicrograph of the contact between a layer of intact dung and the underlying sediment. The dung layer contains thin, undulating lenses of calcareous spherulites (S) interbedded with siliceous phytoliths (p). The sediment beneath contains fragments of volcanic glass (v), degraded organic material (om), and secondary nodules of apatite (a) in a matrix rich in wood ashes and clay minerals. A concentration of secondary mineral crystals—unidentified but likely soluble salts—formed within a void is indicated with an arrow. Plane-polarized light. (B) Same view as (A), cross-polarized light. Area scanned using micro–x-ray fluorescence indicated with the red box. (C) Elemental distribution map showing enrichment of sodium in the secondary mineral crystals, as well as phosphorus in the apatite and organic material, potassium in the volcanic glass, and aluminum in the clay-rich matrix. Note that although concentrations of suspected soluble salts (as well as other secondary minerals such as apatite and gypsum) have been observed in the micromorphology samples, further identification is limited because of highly variable crystal morphologies (58).