POTTERY SOURCING AND WEATHERING PROCESSES IN THE WET LOWLAND TROPICS: A CASE STUDY FROM PANAMA (CA. 4,500-3,200 B.P.)

Geologists have long discussed the weathering processes of rocks and minerals as well as elements that get depleted over time. In the wet lowland tropics, the processes are known to be pronounced. Archaeologists source pottery to determine production zones and to make inferences about human mobility and exchange. They conduct ceramic circulation studies in a variety of geographical areas and environmental zones. Nevertheless, archaeologists have not done active discussions of how the weathering processes of clays and temper (added inclusions, for example, to avoid drying cracks and to increase thermal shock resistance) in the humid and hot lowland tropics, affect the sourcing result. I conducted pottery sourcing in central Panama, the lowland tropics, analyzing Monagrillo ware (ca. 4,500-3,200 B.P.). I did petrography examining mineral and rock inclusions, obtained bulk composition using portable XRF, and studied clay chemistry using LA-ICP-MS, of ceramics and raw clays, I collected and fired. The result suggested that petrography was useful in distinguishing clays and their inclusions with temper, consisting of fresh and angular minerals derived from porphyritic volcanic rocks, allowing the ceramic classification by paste type and by broad geological origins. The fresh mineral temper helped chemically separate pottery. Overall, raw clays had similar chemical signatures to pottery, indicating that ceramics were made using central Panamanian clays. However, distinguishing raw clays by geological zones was difficult after the normalization of elemental data to Zr, the element that is hypothetically stable, and with a careful selection of immobile elements, for statistical analyses. Clays do not easily give signatures of geological zones, demonstrated through studies of fresh rock samples. This work serves as a case study for the pottery provenancing in the rainy lowland tropics: archaeologists need to take a critical look at the weathering processes.