The origin of smectite in the soil of the Kruger 2 archaeological site, Brompton (Québec), Canada.

Kruger 2 is unique among Late Paleoindian sites of eastern Canada because of the presence of a potential hearth (feature #1) characterized by a concentration of blackened fire‐cracked rock and burnt bone embedded in a thick Ae horizon. Comparative mineralogical analysis (X‐ray diffraction) of Ae samples collected inside and outside the feature reveal the absence of calcite and apatite, two minerals commonly found in ashes, and the presence of smectite in the Ae inside feature #1. Smectite genesis is attributed to the weathering of mica and chlorite under geochemical conditions (high base cations, Si and pH; low Al) that are unique in time and space. We hypothesize that these conditions were created by the dissolution, 10,000 years ago, of a layer of hearth ashes resting on an incipient soil. Results confirm the intense weathering of mica and chlorite. We also show that ash dissolution could generate the conditions for smectite formation in the presence of altered mica and chlorite, allowing the development of a chronology explaining this finding. The data largely support our hypothesis and constitute a strong basis for future investigations on the links between hearth ash weathering and smectite genesis in acidic soils. [ABSTRACT FROM AUTHOR]