Baking Geophytes and Tracking Microfossils: Taphonomic Implications for Earth-Oven and Paleodietary Research

Abstract

Archaeologically oriented starch-granule and other plant-food microfossil research contribute to human subsistence studies primarily through analysis of residue adhering to plant processing tools. Little is known about whether or how plant-food microfossils may be present in remains of ancient earth ovens and other cooking facilities. Earth ovens with rock heating elements are found worldwide, especially in savannah and fuel-poor regions; they date to about 30,000 and 9,000 years old in the Old and New Worlds, respectively. Earth-oven baking is a cooking technology that effectively increases the availability of food in a given area by affording nutritional access to difficult-to-cook or toxic plant foods that would otherwise be indigestible. It effectively increases a landscape’s capacity to support population growth. Conventional-oven and lab-oven baking experiments assess the potential of ancient earth ovens to yield identifiable microfossils of underground storage organs (USOs) baked therein. During 15 min to 12 h of baking at 135–150 °C, identifiable and degraded USO microfossils accumulated as part of baking residue on cloth coverings, leafy packing materials, the inside of the containers, and on suspended microscope slides. Results of these taphonomic experiments indicate that an abundance of microfossils, including starch granules, phytoliths, raphides, and plant tissue, are emitted from USOs during the baking process. As hypothesized, these microfossils should be mobilized and dispersed in earth ovens per se during baking, primarily via liquid and vapor forms of water. Illuviation and other transformation processes are expected to redeposit baked, yet still identifiable, plant-food microfossils on heating-element rocks.