QEMSCAN® analysis of clay-rich stratigraphy associated with early agricultural contexts at Kuk Swamp, Papua New Guinea

Abstract

Quantitative Evaluation of Minerals by Scanning Electron Microscope (QEMSCAN®) provides a diagnostic analytical tool to investigate clay-rich stratigraphy in early agricultural contexts at Kuk Swamp, Papua New Guinea. Previous in situ microstratigraphic analyses at Kuk, comprising thin section description and X-radiography, have been unable to differentiate and characterise clay mineralogy in the archaeological stratigraphy. Although prior X-ray diffraction provided compositional information on clay mineralogy for bulk samples, QEMSCAN® elemental and mineral analyses enable in situ identification and mapping of clay mineral occurrences and relationships. The results of the QEMSCAN® analyses permit reconstruction of the origin and post-depositional transformation of geogenic and biogenic sediments in clay-rich feature fills associated with former plant exploitation and cultivation. QEMSCAN® mineral analyses identify a positive association between smectite-rich contexts and biogenic silica (diatoms and phytoliths) and a negative association between kaolinite-rich contexts and biogenic silica. QEMSCAN® elemental analyses provide valuable information on neoformed minerals, which can be difficult to characterise optically within stratigraphy. These results show the value of QEMSCAN®, especially in combination with thin section micromorphology, to understand the origin and post-depositional formation of clay minerals at archaeological sites in the wet tropics, as well as in other environmental contexts.