CLAST & BEDROCK MINERALOGY OF THE POKROVNIK SITE, DALMATIA, CROATIA: EVIDENCE FROM XRD ANALYSIS AND COMPARISON WITH SOIL MINERALOGY

We analyzed x-ray diffraction spectra of soil, gravel, and bedrock samples from the Neolithic Pokrovnik site as part of the Early Farming in Dalmatia Project, an interdisciplinary effort toward understanding the origins of European agriculture. Pokrovnik is an open lowland site in a polje-karst region. The area has carbonate bedrock, but the overlying soil fines in much of the valley are homogenous with no apparent relation to the bedrock. Such a composition is unexpected in a well-developed karst region and may explain the choice by early farmers to utilize this location.

Soil samples we analyzed previously were from the profiles of both on-site excavation trenches and off-site test pits. As the test pits are in locations presumably unaffected by human influence, we hoped they would function as a control to help distinguish human influences on soil form and development. Our data support the hypothesis that the non-carbonate input to the soil fines could be volcanic ash. The presence of quartz and montomorillonite in particular supports the possibility of an altered ash deposit.

Given the lack of calcite observed in portions of the soil profiles, we analyzed the mineralogy of both large clasts within the soil column and the bedrock directly underlying the soils to elucidate any possible chemical exchange from the limestone rock in contact with the soil fines. We also aimed to learn more about the relationship between the clasts and the underlying bedrock.

Clast and bedrock spectra from soil profiles of three on-site excavation trenches and three test pits suggest these materials do function as a chemical input to the soil via localized dissolution and reprecipitation; however, they do not serve as a soil parent. It is likely that the fine silicate-rich subsoil chemically isolates the bedrock, locally inhibiting karstic processes. Further investigation of the pH and ion content of the soil and soil pore water could provide further perspective on the chemical exchange between the soil fines and local limestones. Understanding these relationships at Pokrovnik will further our understanding of Neolithic settlement strategy and the role of poljes and volcanic ejecta deposits in the prehistory of Central Dalmatia.